Publications by authors named "Clarisa Bozzini"

34 Publications

Mandibular biomechanical behavior of rats submitted to chronic intermittent or continuous hypoxia and periodontitis.

Sleep Breath 2021 Mar 6;25(1):519-527. Epub 2020 Aug 6.

Cátedra de Fisiología, Facultad de Odontología, Universidad de Buenos Aires, M.T. de Alvear 2142, 3rd floor "A", Buenos Aires, Argentina.

Background: The aim of this study was to investigate the effects of exposure to continuous (CH) and intermittent (IH) hypoxia on biomechanical properties of the mandible and periodontal tissue of animals submitted to experimental periodontitis (EP) when applying loads in a hypoxic environment.

Methods: Adult female Wistar rats were exposed during 90 days to IH or CH (simulated high altitude of 4200 m above sea level). Fourteen days prior to the euthanasia, EP was induced to half of the animals of each group.

Results: Only in the rats with EP, IH decreased the maximum capacity of the mandible to withstand load and the limit of elastic load. Indicators of intrinsic properties of the bone material were significantly reduced by both types of hypoxia in rats with EP. Hypoxia enhanced the alveolar bone loss induced by EP in the buccal side of the mandible, without showing additional effects in lingual or interradicular bone. Hypoxia increased prostaglandin E content in gingival tissue of healthy animals and further elevated the E levels increased by EP.

Conclusions: When periodontitis is present, hypoxic stress induces a decrease in mineral properties that ultimately affects the ability of the mandible to resist load, mainly during intermittent exposure to hypoxia. These effects on bone may be related to the higher levels of prostaglandin E reached in the surrounding gingival tissue. The findings of this study may stimulate strategies to prevent unwanted effects of hypoxia on periodontal tissues.
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http://dx.doi.org/10.1007/s11325-020-02158-2DOI Listing
March 2021

A new target to ameliorate the damage of periodontal disease: The role of transient receptor potential vanilloid type-1 in contrast to that of specific cannabinoid receptors in rats.

J Periodontol 2019 11 6;90(11):1325-1335. Epub 2019 Jun 6.

Department of Physiology, Faculty of Dentistry, University of Buenos Aires, Buenos Aires, Argentina.

Background: Transient receptor potential vanilloid type-1 (TRPV1) is expressed in oral tissues cells and its activity can be regulated by inflammation products and anandamide. The aim of the present study was to evaluate the effects of blocking TRPV1 or specific cannabinoid receptors 1 (CB1r) and 2 (CB2r) on periodontal status of rats subjected to experimental periodontitis (EP).

Methods: Male rats were distributed in groups 1) control, 2) lipopolysaccharide-induced EP (LPS), and 3) LPS plus capsazepine (Capz, TRPV1 antagonist) application (LPS+Capz). EP was induced by injections of LPS (1 mg/mL) around first molars and treatment was performed with Capz (2 µg/mL) applied locally during 6 weeks. Additional experiment was performed by applying CB1r and CB2r antagonists (AM251 and AM630) to rats with EP.

Results: Capz prevented alveolar bone loss (ABL) on the external crests and in the interradicular bone of the first molars (periodontal space height: LPS, 270.7 ± 33.5µm versus LPS+Capz, 216.4 ± 19.9 µm; P <0.01). Inflammatory mediators, like tumor necrosis factor-alpha and prostaglandin E , increased by LPS-induced EP, were diminished in gingival tissue of rats treated with Capz. In contrast, application of AM251 and AM630 exacerbated ABL and gingival inflammatory mediators, increased by LPS, altering also biomechanical properties.

Conclusions: TRPV1 blockade attenuates periodontal impairment in EP rats, since it reduces local inflammation, unlike CB1r and CB2r blockade. This work lays the foundation for developing therapeutics in humans based on the pharmacological manipulation of these receptors to treat periodontal disease.
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http://dx.doi.org/10.1002/JPER.18-0766DOI Listing
November 2019

Changes in PGE2 signaling after submandibulectomy alter post-tooth extraction socket healing.

Wound Repair Regen 2018 03 19;26(2):153-162. Epub 2018 May 19.

Department of Physiology, School of Dentistry, University of Buenos Aires, Buenos Aires, Argentina.

Saliva is very important to oral health, and a salivary deficit has been shown to bring serious problems to oral health. There is scant information about the mechanisms through which salivary glands participate in post-tooth extraction socket healing. Therefore, the aim of the present study was to investigate the effect of submandibulectomy (SMx), consisting of the ablation of submandibular and sublingual glands (SMG and SLG, respectively), on PGE signaling and other bone regulatory molecules, such as OPG and RANKL, involved in tooth extraction socket healing. Male Wistar rats, 70 g body weight, were assigned to an experimental (subjected to SMx) or a control group (sham operated). One week later, the animals in both groups underwent bilateral extraction of the first mandibular molars. The effect of SMx on different stages of socket healing after tooth extraction (7, 14, and 30 days) was studied by evaluating some parameters of inflammation, including PGE and its receptors, and of bone metabolism, as well as by performing bone biomechanical studies. SMx increased TNFα and PGE content as well as cyclooxygenase-II (COX-II) expression in tooth socket tissue at almost all the studied time points. SMx also had an effect on mRNA expression of PGE receptors at the different time points, but did not significantly alter osteoprotegerin (OPG) and RANKL mRNA expression at any of the studied time points. In addition, an increase in bone mass density was observed in SMx rats compared with matched controls, and the structural and mechanical bone properties of the mandibular socket bone were also affected by SMx. Our results suggest that the SMG/SLG complex regulates cellular activation and differentiation by modulating the production of molecules intervening in tooth extraction socket repair, including the PGE signaling system, which would therefore account for the higher density and resistance of the newly formed bone in SMx rat.
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http://dx.doi.org/10.1111/wrr.12625DOI Listing
March 2018

Increased intrinsic stiffness and mineralization in femurs of adult rats after high intensity treadmill running training.

Biomed Mater Eng 2017 ;28(4):431-441

Cátedra de Fisiología, Facultad de Odontología, Universidad de Buenos Aires, Argentina.

Background: Physical activity plays a tremendous role in determining bone mechanical behavior, which is superimposed to gravidity.

Objective: Compare the geometric and material responses of the rat femur to a high intensity treadmill running training of a relatively short duration, as assessed by 3-point mechanical test.

Methods: Mature male rats (180.0 ± 30 g) were assigned (7 rats/group) to no exercise (NE) or treadmill exercise (EX). After a preconditioning period, the running speed was set at 45 cm.seg-1 during 2 wks, frequency 5 d/wk, 2-hour sessions/day. Body weight and weight of the crural quadriceps were registered at euthanasia. The right femur was mechanically tested through 3-point bending. The left femur was ashed to estimate bone mineral content. Geometric and material bone properties were estimated directly or calculated by appropriate equations.

Results: 1) Final body weight was 14% reduced in EX rats, while the crural quadriceps was 47% increased. Yield and fracture loads, and structural stiffness were significantly higher in the EX rats, as were the apparent elastic modulus, the bone mineral content and the degree of mineralization. Geometric properties were not affected.

Conclusions: High intensity treadmill running training increases bone strength and stiffness by increasing material stiffness and mineralization, without affecting geometric bone parameters.
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http://dx.doi.org/10.3233/BME-171684DOI Listing
December 2017

Mechanical mandible competence in rats with nutritional growth retardation.

Arch Oral Biol 2017 Aug 16;80:10-17. Epub 2017 Mar 16.

Department of Physiology, School of Dentistry, University of Buenos Aires, Buenos Aires, Argentina. Electronic address:

Objective: In order to provide a better understanding of the sympathetic nervous system as a negative regulator of bone status, the aim of the study was to establish the biomechanical mandible response to different doses of a β-adrenergic antagonist such as propranolol (P) in a stress-induced food restriction model of growth retardation.

Methods: Rats were assigned to eight groups: Control (C), C+P3.5 (CP3.5), C+P7 (CP7), C+P14 (CP14), NGR, NGR+P3.5 (NGRP3.5), NGR+P7 (NGRP7) and NGR+P14 (NGRP14). C, CP3.5, CP7 and CP14 rats were freely fed with the standard diet. NGR, NGRP3.5, NGRP7 and NGRP14 rats received, for 4 weeks (W4), 80% of the amount of controls food consumed. Propranolol 3.5, 7 and 14mg/kg/day was injected ip 5days per week in CP3.5 and NGRP3.5, CP7 and NGRP7, CP14 and NGRP14, respectively. At W4, zoometry, mandible morphometry, static histomorphometric and biomechanical competence were performed.

Results: A dose of Propranolol 7mg/kg/day induced interradicular bone volume accretion reaching a mandible stiffness according to chronological age.

Conclusion: These findings evidenced that sympathetic nervous system activity is a negative regulator of mandible mechanical competence in the nutritional growth retardation model. Propranolol 7mg/kg/day, under the regimen usage, seems to be appropriate to blockade SNS activity on mandible mechanical performance in NGR rats, probably associated to an effect on bone mechanostat system ability to detect disuse mode as an error.
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http://dx.doi.org/10.1016/j.archoralbio.2017.03.009DOI Listing
August 2017

Sequential administration of alendronate and strontium ranelate: histomorphometry and bone biomechanics in ovariectomized animals.

Acta Odontol Latinoam 2016 Sep;29(2):168-177

Histology and Embryology Department, School of Dentistry, University of Buenos Aires.

Bisphosphonates are the first choice therapy for the pharmaco logical treatment of osteoporosis. Following reports of cases of bisphosphonaterelated osteonecrosis of the jaw and atypical femur fracture, the safety of longterm use of bisphosphonates has been evaluated, resulting in the proposal of strontium as an alternative drug. No experimental study using a sequential administration design has been reported to date. Hence, the aim of this study was to evaluate the effect on bone tissue of ovariectomized rats of administration of alendronate followed by strontium ranelate. Fortyeight female Wistar rats were ovariectomized on day 1 of the experiment. Beginning on day 30, they were administered 0.3 mg/kg/week of alendronate (ALN) or vehicle (VEH) for 8 weeks. Two groups (ALN and corresponding control) were euthanized at this time, and the remaining animals were divided into 4 groups and given 290 mg/kg/day of strontium ranelate (SR) in their drinking water (TW) or only water for 4 months. Experimental groups were: ALN+SR, ALN+TW, VEH+SR, VEH+TW, ALN and VEH. The tibiae and hemimandibles were resected for histomorphometric evaluation, and the right femur was used to perform biomechanical studies. ANOVA and Bonferroni test were applied. Diaphyseal stiffness, maximum elastic load and fracture load increased in animals that received alendronate, regardless of whether or not they received subsequent SR treatment. Fracture load also increased in VEH+ SR versus control (VEH+TW). Subchondral and interradicular bone volumes were significantly higher in animals that received ALN than in those that received vehicle. No difference was observed in cortical area or thickness of the tibia among treatments. The results obtained with the model presented here, evaluating tibial and mandibular interradicular bone, showed that the combination of ALN and SR and administration of ALN alone are equally effective in preventing bone loss associated with ovariectomyinduced estrogen depletion.
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September 2016

Efficacy of phytosterols and fish-oil supplemented high-oleic-sunflower oil rich diets in hypercholesterolemic growing rats.

Int J Food Sci Nutr 2016 Jun 17;67(4):441-53. Epub 2016 Mar 17.

d Department of General and Oral Biochemistry, School of Dentistry , University of Buenos Aires , Buenos Aires , Argentina.

Phytosterols (P) and fish-oil (F) efficacy on high-oleic-sunflower oil (HOSO) diets were assessed in hypercholesterolemic growing rats. Controls (C) received a standard diet for 8 weeks; experimental rats were fed an atherogenic diet (AT) for 3 weeks, thereafter were divided into four groups fed for 5 weeks a monounsaturated fatty acid diet (MUFA) containing either: extra virgin olive oil (OO), HOSO or HOSO supplemented with P or F. The diets did not alter body weight or growth. HOSO-P and HOSO-F rats showed reduced total cholesterol (T-chol), non-high-density lipoprotein-cholesterol (non-HDL-chol) and triglycerides and increased HDL-chol levels, comparably to the OO rats. Total body fat (%) was similar among all rats; but HOSO-F showed the lowest intestinal, epididymal and perirenal fat. However, bone mineral content and density, and bone yield stress and modulus of elasticity were unchanged. Growing hypercholesterolemic rats fed HOSO with P or F improved serum lipids and fat distribution, but did not influence material bone quality.
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http://dx.doi.org/10.3109/09637486.2016.1161010DOI Listing
June 2016

Effect of chronic undernutrition on body mass and mechanical bone quality under normoxic and altitude hypoxic conditions.

Br J Nutr 2016 05 10;115(9):1687-95. Epub 2016 Mar 10.

Department of Physiology, Faculty of Odontology,University of Buenos Aires,Buenos Aires C1122 AAH,Argentina.

Both undernutrition and hypoxia exert a negative influence on both growth pattern and bone mechanical properties in developing rats. The present study explored the effects of chronic food restriction on both variables in growing rats exposed to simulated high-altitude hypoxia. Male rats (n 80) aged 28 d were divided into normoxic (Nx) and hypoxic (Hx) groups. Hx rats were exposed to hypobaric air (380 mmHg) in decompression chambers. At T0, Nx and Hx rats were subdivided into four equal subgroups: normoxic control and hypoxic controls, and normoxic growth-restricted and hypoxic growth-restricted received 80 % of the amount of food consumed freely by their respective controls for a 4-week period. Half of these animals were studied at the end of this period (T4). The remaining rats in each group continued under the same environmental conditions, but food was offered ad libitum to explore the type of catch-up growth during 8 weeks. Structural bone properties (strength and stiffness) were evaluated in the right femur midshaft by the mechanical three-point bending test; geometric properties (length, cross-sectional area, cortical mass, bending cross-sectional moment of inertia) and intrinsic properties of the bone tissue (elastic modulus) were measured or derived from appropriate equations. Bone mineralisation was assessed by ash measurement of the left femur. These data indicate that the growth-retarded effects of diminished food intake, induced either by food restriction or hypoxia-related inhibition of appetite, generated the formation of corresponding smaller bones in which subnormal structural and geometric properties were observed. However, they seemed to be appropriate to the body mass of the animals and suggest, therefore, that the bones were not osteopenic. When food restriction was imposed in Hx rats, the combined effects of both variables were additive, inducing a further reduction of bone mass and bone load-carrying capacity. In all cases, the mechanical properties of the mineralised tissue were unaffected. This and the capacity of the treated bones to undergone complete catch-up growth with full restoration of the biomechanical properties suggest that undernutrition, under either Nx or Hx conditions, does not affect bone behaviour because it remains appropriate to its mechanical functions.
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http://dx.doi.org/10.1017/S000711451600060XDOI Listing
May 2016

Structural and Material Mechanical Quality of Femoral Shafts in Rats Exposed to Simulated High Altitude from Infancy to Adulthood.

High Alt Med Biol 2016 Mar 7;17(1):50-3. Epub 2016 Mar 7.

1 Department of Physiology, Faculty of Odontology, University of Buenos Aires , Buenos Aires, Argentina .

The growth of the body and bone mass and the mechanical properties of appendicular bone are impaired in immature rats exposed to different simulated high altitudes (SHA) (1850-5450 m) between the 32nd and the 74th days of postnatal life. Now, we report the effects of exposure to 4100 m on the above cited variables in female rats from infancy (age: 1 month) to adulthood (age: 8 months) to define the occurrence of catch up and to establish whether the effects of altitude are transient or permanent. The ex vivo right femur was mechanically tested in three-point bending. Body weight and length, and structural (loads at yielding and fracture, and stiffness) and architectural (diaphyseal cross-sectional area, cortical area, and cross-sectional moment of inertia) properties were measured at 2, 4, 6, and 8 months of exposure to SHA. The negative influence of hypoxia on all variables was similar at different ages or, in other words, the difference among ages was maintained at any extent of hypoxia. Hypoxia did not affect the elastic modulus, thus suggesting that the mechanical properties of the bone tissue were maintained. Catch up did not occur. The resulting osteopenic bone remained appropriate to its mechanical function during the entire exposure to SHA.
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http://dx.doi.org/10.1089/ham.2015.0105DOI Listing
March 2016

Chronic lead poisoning magnifies bone detrimental effects in an ovariectomized rat model of postmenopausal osteoporosis.

Exp Toxicol Pathol 2016 Jan 28;68(1):47-53. Epub 2015 Sep 28.

Department of Physiology, Faculty of Dentistry, University of Buenos Aires, Argentina. Electronic address:

Lead (Pb) is a persistent environmental contaminant that is mainly stored in bones being an important source of endogenous lead exposure during periods of increased bone resorption as occurs in menopause. As no evidence exists of which bone biomechanical properties are impaired in those elderly women who had been exposed to Pb during their lifetime, the aim of the present study is to discern whether chronic lead poisoning magnifies the deterioration of bone biology that occurs in later stages of life. We investigated the effect of Pb in the femora of ovariectomized (OVX) female Wistar rats who had been intoxicated with 1000 ppm of Pb acetate in drinking water for 8 months. Structural properties were determined using a three-point bending mechanical test, and geometrical and material properties were evaluated after obtaining the load/deformation curve. Areal Bone Mineral Density (BMD) was estimated using a bone densitometer. Femoral histomorphometry was carried out on slices dyed with H&E (Hematoxylin and Eosin). Pb and OVX decreased all structural properties with a higher effect when both treatments were applied together. Medullar and cortical area of femurs under OVX increased, allowing the bone to accommodate its architecture, which was not observed under Pb intoxication. Pb and OVX significantly decreased BMD, showing lead treated ovariectomized rats (PbOVX) animals the lowest BMD levels. Trabecular bone volume per total volume (BV/TV%) was decreased in OVX and PbOVX animals in 54% compared to the control animals (p<0.001). Pb femurs also showed 28% less trabeculae than the control (p<0.05). We demonstrated that Pb intoxication magnifies the impairment in bone biomechanics of OVX rats with a consequent enhancement of the risk of fracture. These results enable the discussion of the detrimental effects of lead intoxication in bone biology in elderly women.
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http://dx.doi.org/10.1016/j.etp.2015.09.007DOI Listing
January 2016

Effect of physical consistency of food on the biomechanical behaviour of the mandible in the growing rat.

Eur J Oral Sci 2015 Oct 4;123(5):350-355. Epub 2015 Sep 4.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires, Argentina.

This study investigated the effect of a soft diet, given to growing rats, on the biomechanical behaviour of the mandible. Female rats, 30 d of age, received an ordinary diet in the form of pellets (i.e. hard-diet group), and another group of female rats received the same diet, but ground and mixed with water, forming a paste (i.e. soft-diet group). The experiment lasted 8 wk. Body-weight and body-length gains were not affected by the consistency of the diet. No significant differences were found between groups concerning the length, height, and area of the right hemimandible. Mechanical properties of the right hemimandibles were determined using a three-point bending test, in which bones were stressed on a perpendicular line immediately posterior to the posterior face of the third molar. Structural properties (load at yielding, load at fracture, structural stiffness, and elastic energy absorption) and geometric properties of the fracture section (cross-sectional area, cortical area, and moment of inertia) were significantly lower in hemimandibles of rats of the soft-diet group than in those of rats of the hard-diet group. Material properties of the mandibular bone tissue (elastic modulus and maximal elastic stress), which were estimated through appropriate equations, did not differ between groups. It was concluded that the reduced physical consistency of the diet, possibly associated with a reduced masticatory load, diminished the skeletal load-bearing capacity of the mandible in growing rats. This observed reduction in the bone structural behaviour was attributed to changes occurring at the level of bone mass and its geometrical properties because intrinsic properties of the bone material tissue were unaffected.
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http://dx.doi.org/10.1111/eos.12209DOI Listing
October 2015

Effect of dexamethasone on mandibular bone biomechanics in rats during the growth phase as assessed by bending test and peripheral quantitative computerized tomography.

Acta Odontol Latinoam 2015 Apr;28(1):83-8

Department of Physiology, School of Dentistry, University of Buenos Aires.

Long-term glucocorticoid administration to growing rats induces osteopenia and alterations in the biomechanical behavior of the bone. This study was performed to estimate the effects of dexamethasone (DTX), a synthetic steroid with predominant glucocorticoid activity, on the biomechanical properties of the mandible of rats during the growth phase, as assessed by bending test and peripheral quantitative computed tomographic (pQCT) analysis. The data obtained by the two methods will provide more precise information when analyzed together than separately. Female rats aged 23 d (n=7) received 500μg.kg-1 per day of DXT for 4 weeks. At the end of the treatment period, their body weight and body length were 51.3% and 20.6% lower, respectively, than controls. Hemimandible weight and area (an index of mandibular size) were 27.3% and 9.7% lower, respectively. The right hemimandible of each animal was subjected to a mechanical 3-point bending test. Significant weakening of the bone, as shown by a correlative impairment of strength and stiffness, was observed in experimental rats. Bone density and cross-sectional area were measured by pQCT. Cross-sectional, cortical and trabecular areas were reduced by 20% to 30% in the DTX group, as were other cortical parameters, including the bone density, mineral content and cross-sectional moment of inertia. The "bone strength index" (BSI, the product of the pQCT-assessed xCSMI and vCtBMD) was 56% lower in treated rats, which compares well with the 54% and 52% reduction observed in mandibular strength and stiffness determined through the bending test. Data suggest that the corticosteroid exerts a combined, negative action on bone geometry (mass and architecture) and volumetric bone mineral density of cortical bone, which would express independent effects on both cellular (material quality) and tissue (cross-sectional design) levels of biological organization of the skeleton in the species.
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http://dx.doi.org/10.1590/S1852-48342015000100012DOI Listing
April 2015

Gestational and early postnatal exposure to simulated high altitude does not modify postnatal body mass growth trajectory in the rat.

High Alt Med Biol 2014 Sep 3;15(3):418-21. Epub 2014 Sep 3.

Department of Physiology, Faculty of Odontology, University of Buenos Aires , Argentina .

Postnatal hypoxia blunts body mass growth. It is also known that the quality of the fetal environment can influence the subsequent adult phenotype. The main purpose of the study was to determine whether gestational hypoxia and early postnatal hypoxia are able to blunt growth when the offspring is raised under normoxia. Hypobaric hypoxia was induced in simulated high altitude (SHA) chambers in which air was maintained at 380 mmHg (5450 m). Mature Sprague-Dawley rats of both sexes were divided in normoxic (NX) and hypoxic (HX) groups and, in the case of the HX group, maintained for 1 month at 5450 m. Mating was then allowed under NX or HX conditions. Offspring were NX-NX, NX-HX, HX-HX, or HX-NX: the first term indicates NX or HX during both gestation and the first 30 days of life; the second term indicates NX or HX during postnatal life between days 30 and 133. Body mass (g) was measured periodically and body mass growth rate (BMGR, g/d) was estimated between days 33 and 65 of postnatal life. Results can be summarized as follows: 1) BM was significantly higher in NX than in HX rats at weaning; 2) BMGR was not significantly different between NX-NX and HX-NX rats, and between HX-HX and NX-HX animals; and 3) BMGR was significantly higher in rats living under NX conditions than in those living under HX conditions during postnatal life. Data suggest that that hypobaric hypoxia during gestational and early postnatal development of rats does not alter the regulation of body mass growth in rats when compared to that seen under sea-level conditions.
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http://dx.doi.org/10.1089/ham.2014.1022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4175034PMC
September 2014

Static biomechanics in bone from growing rats exposed chronically to simulated high altitudes.

High Alt Med Biol 2013 Dec;14(4):367-74

Department of Physiology, Faculty of Odontology, University of Buenos Aires , Argentina .

Biomechanical behavior of bone is related to the amount (bone mass) and its architectural distribution, as well as the mechanical quality of bone material. This investigation reports the effects of exposure to different simulated high altitudes (SHA) (1850, 2900, 4100, and 5450 m) on femur biomechanical properties in female growing rats exposed to SHA (22-23 h/d) between the 32° and the 74° days of life. The ex vivo right femur was mechanically tested in three-point bending. The left femur was ashed at 600°C and the ash weight obtained. Final body weight and structural (loads at yielding and fracture, stiffness, and elastic energy absorption) and architectural (diaphyseal cross-sectional area, cortical area, and cross-sectional moment of inertia) were negatively affected in the animals exposed to the two highest SHA. Material properties of the mineralized tissue (Young's modulus and limit elastic stress) and the degree of mineralization were unaffected. In conclusion, hypoxic bone is weaker than normoxic one because of its smaller bone mass, which appear to have been negatively influenced by SHA in relation to its effects on overall body mass.
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http://dx.doi.org/10.1089/ham.2013.1038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880101PMC
December 2013

Growth inhibition in rats fed inadequate and incomplete proteins: repercussion on mandibular biomechanics.

Acta Odontol Latinoam 2013 ;26(1):43-53

Department of Physiology, University of Buenos Aires School of Dentistry, Buenos Aires, Argentina.

This study describes the effects of feeding growing rats with a diet containing inadequate and incomplete proteins on both the morphological and the biomechanical properties of the mandible. Female rats aged 30 d were fed freely with one of two diets, control (CD, 301 Cal/100g) and experimental (ED, 359 Cal/100g). CD was a standard laboratory diet, while ED was a synthetic diet containing cornflower supplemented with vitamins and minerals. Both diets had the same physical characteristics. Control (C) and experimental (E) animals were divided into 4 groups of 10 animals each. C40 and E40 rats were fed CD and ED, respectively, for 40 d; C105 were fed the CD for 105 d; and E105 were fed the ED for 40 d and then the CD for the remainder of the experimental period (65 d). Mandibular growth was estimated directly on excised and cleaned bones by taking measurements between anatomical points. Mechanical properties of the right hemimandible were estimated by using a 3-point bending test to estimate the structural properties of the bone. Geometric properties of both the entire bone and the cross-section were determined. Bone material properties were calculated from structural and geometric properties. The left hemimandibles were ashed and the ash weight obtained. Rats fed the ED failed to achieve normal body weight gain. Complete catch-up was observed at the end of nutritional rehabilitation. Mandibular weight and length were negatively affected by the ED, as were the cross-sectional area, the mineralized cortical area, and the cross-sectional moment of inertia. All of these parameters showed incomplete catch-up. The structural bone mechanical properties indicative of strength and stiffness were negatively affected. Intrinsic material properties, as assessed by the modulus of elasticity and maximal elastic stress, were within normal values. In summary, the experimental bone was weaker than the control and structurally incompetent. The bone considered was smaller than the control bone, showing a significant reduction in the cross-sectional area and the moment of inertia. However, material properties as well as the ash fraction and degree of mineralization were similar in E and C bones. Therefore, the E bone was weaker than the C bone because of its smaller bone mass, which appears to have been negatively influenced by the ED in relation to its effects on overall body mass.
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February 2014

Mechanical testing at the whole-bone level of the femur in immature rats stunted by cornstarch consumption.

Food Funct 2013 Oct;4(10):1543-51

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Marcelo T. de Alvear 2142, Buenos Aires 1122, Argentina.

Both body weight and somatic muscle forces are the main "mechanical factors" in the determination of bone strength in the "weight-bearing bones". However, other "non-mechanical factors", such as dietary proteins, also exist, which modulate bone physiology. This study was designed to explore the mechanical behavior of the femur in post-weaning female rats stunted by feeding on cornstarch. Forty female rats aged 30 days were fed freely with one of the two diets: control (CD) and experimental (ED). CD was the standard rat laboratory diet, whereas ED was cornstarch supplemented with vitamins and minerals. Control (C) and experimental (E) animals were divided into 4 groups: C40 and E40 rats were given CD and ED, respectively, for 40 days; C105 were fed the CD for 105 days; and E40-105 were given the ED for 40 days and then the CD for the remaining experimental period (65 days). Growth of rats was assessed following Parks' model. The biomechanical structural properties of the right femur middiaphysis were estimated using a 3-point bending test. The geometric properties of both the entire bone and the cross-section were determined. The left femur was ashed and both the Ca mass and the Ca concentration were determined. Rats fed the ED failed to achieve normal weight gain. Complete catch-up was observed at the end of a 65 day period of nutritional rehabilitation. The femoral weight and length were negatively affected by the ED, as were the mid-diaphyseal cross-sectional area, the mineralized cortical area, and the cross-sectional moment of inertia. All of these parameters showed incomplete catch-up. The structural bone mechanical properties indicative of strength and stiffness were seriously negatively affected. Intrinsic material bone properties, as assessed by the modulus of elasticity and the maximal elastic stress, were within normal values. In summary, the experimental bone was weaker than the control and structurally incompetent. The considered bone was smaller than the control one, showing a significant reduction in the cross-sectional area and the moment of inertia. However, material properties as well as the ash fraction and Ca concentration were similar in E and C bones. Therefore, E bone is weaker than the C one because of its smaller bone mass, which appears to have been negatively influenced by the ED in relation to its effects on overall body mass.
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http://dx.doi.org/10.1039/c3fo30346bDOI Listing
October 2013

Alveolar bone loss associated to periodontal disease in lead intoxicated rats under environmental hypoxia.

Arch Oral Biol 2013 Oct 9;58(10):1407-14. Epub 2013 Jul 9.

Department of Physiology, Faculty of Dentistry, University of Buenos Aires, Argentina.

Previously reported studies from this laboratory revealed that rats chronically intoxicated with lead (Pb) under hypoxic conditions (HX) impaired growth parameters and induced damages on femoral and mandibular bones predisposing to fractures. We also described periodontal inflammatory processes under such experimental conditions. Periodontitis is characterised by inflammation of supporting tissues of the teeth that result in alveolar bone loss. The existence of populations living at high altitudes and exposed to lead contamination aimed us to establish the macroscopic, biochemical and histological parameters consistent with a periodontal disease in the same rat model with or without experimental periodontitis (EP). Sixty female rats were divided into: Control; Pb (1000ppm of lead acetate in drinking water); HX (506mbar) and PbHX (both treatments simultaneously). EP was induced by placing ligatures around the molars of half of the rats during the 14 days previous to the autopsy. Hemi-mandibles were extracted to evaluate bone loss by histomorphometrical techniques. TNFα plasmatic concentration was greater (p<0.01) in Pb and HX animals. TBA-RS content was significantly higher in gums of rats with or without EP only by means of Pb. The SMG PGE2 content increased by Pb or HX was higher in PbHX rats (p<0.01). Pb and HX increased EP induced alveolar bone loss, while Pb showed spontaneous bone loss also. In conclusion, these results show that lead intoxication under hypoxic environment enhanced not only alveolar bone loss but also systemic and oral tissues inflammatory parameters, which could aggravate the physiopathological alterations produced by periodontal disease.
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http://dx.doi.org/10.1016/j.archoralbio.2013.06.010DOI Listing
October 2013

[Operational mechanism modification of bone mechanostat in an animal model of nutritional stress: effect of propranolol].

Rev Invest Clin 2013 Jan-Feb;65(1):39-51

Citedra de Fisiología, Universidad de Buenos Aires, Argentina.

Introduction: Propranolol (P) treatment exerts a preventive effect against the detrimental consequences to bone status in mildly chronically food-restricted growing rats (NGR) by an increment in cortical bone and by improving its spatial distribution.

Objective: To study the effect of beta-blocker on operational mechanism of bone mechanostat in an animal model of nutritional stress.

Material And Methods: Weanling male Wistar rats were randomly assigned to four groups: control (C), C + P (CP), NGR and NGR + P (NGRP). C and CP rats were fed freely with the standard diet. NGR and NGRP rats received, for 4 weeks, 80% of the amount of food consumed by C and CP respectively, the previous day, corrected by body weight. Propranolol (7 mg/kg/day) was injected ip 5 days per week, for four weeks in CP and NGRP rats. C and NGR received saline injections at an identical dosage regimen. Body weight and length were determined during the experimental period. Dietary intake was registered daily. Animals were sacrificed after 4 weeks of food restriction. Immediately, cuadriceps, femur and tibiae from each animal were dissected and weighed, and histomorphometric and mechanical studies were performed. Serum a-CTX, osteocalcin, intact PTH, calcium and phosphorous were determined. Body protein (% prot) was measured in all groups.

Results: Food restriction induced detrimental effects on body and femoral growth, load-bearing capacity (Wf), % prot and cuadriceps weight in NGR us. C (p < 0.01). beta-blocker did not modify anthropometric and bone morphometric parameters in NGRP and CP us. NGR and C, respectively (p > 0.05). However, Wf NGRP vs. NGR was significantly higher (p < 0.01). alpha-CTX was significantly higher in NGR vs. C (p < 0.01). No significant differences were observed in alpha-CTX levels between CP, NGRP and C (p > 0.05). Serum osteocalcin, intact PTH, calcium and phospho- rous showed no significant difference between groups (p > 0.05).

Conclusion: These results suggest that modeling increase in bone mass and strength in NGRP rats could be due to an anticatabolic interaction of the beta-blocker propranolol on operational mechanism of bone mechanostat in an animal model of nutritional stress.
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June 2013

Biomechanical properties of the mandible, as assessed by bending test, in rats fed a low-quality protein.

Arch Oral Biol 2013 Apr 28;58(4):427-34. Epub 2012 Sep 28.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Marcelo T. de Alvear 2142, Buenos Aires, Argentina.

Objective: The present study describes the effects of feeding growing rats with diets containing increasing concentrations of wheat gluten (a low quality protein, G) on both the morphometrical and the biomechanical properties of the mandible.

Design: Female rats were fed one of six diets containing different concentrations (5-30%) of G between the 30th and 90th days of life. Control rats were fed a diet containing 20% casein (C), which allows a normal growth and development of the bone. Mandibular growth was estimated directly on excised and cleaned bones by taking measurements between anatomical points. Mechanical properties of the right hemimandibles were determined by using a three-point bending mechanical test to obtain a load/deformation curve and estimate the structural properties of the bone. Bone material properties were calculated from structural and geometric properties. The left hemimandibles were ashed and the ash weight obtained. Calcium content was determined by atomic energy absorption. Results were summarised as means±SEM. Comparisons between parameters were performed by ANOVA and post-test.

Results: None of the G-fed groups could achieve a normal growth performance as compared to the C-fed control group. Like body size, age-related increments in mandibular weight, length, height and area (index of mandibular size) were negatively affected by the G diets, as was the posterior part of the bone (posterior to molar III). The cross-sectional geometry of the mandible (cross-sectional area and rectangular moment of inertia) as well as its structural properties (yielding load, fracture load, and stiffness) were also severely affected by the G diets. However, material properties (Young's modulus and maximum elastic stress) and calcium concentration in ashes and the degree of mineralisation were unaffected.

Conclusions: The differences in strength and stiffness between treated and control rats seemed to be the result of an induced loss of gain in bone growth and mass, in the absence of changes in the quality of the bone mineralised material.
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http://dx.doi.org/10.1016/j.archoralbio.2012.08.007DOI Listing
April 2013

Lead bone toxicity in growing rats exposed to chronic intermittent hypoxia.

Bull Environ Contam Toxicol 2012 Oct 31;89(4):693-8. Epub 2012 Jul 31.

Department of Physiology, University of Buenos Aires, MT Alvear 2142, 3rd. floor A, Buenos Aires, Argentina.

Lead chronic intoxication under hypoxic conditions revealed growth retardation in growing rats and damages on femoral and mandibular bones that predispose to fractures. These findings aimed us to investigate if bone material and geometric properties, bone mass in terms of histomorphometry or antioxidant capacity are also impaired in such experimental model. Combined treatments significantly reduced hemimandible cross sectional geometry and intrinsic stiffness (-16% and -34%); tibia and hemimandible bone volume (-45% and -40%) and growth plate cartilage thickness (-19%). These results show a previously unreported toxic effect of lead on mandible however, longer studies should be necessary to evaluate if an adaptation of bone architecture to maintain structural properties may occur and if the oxidative stress can be identified as the primary contributory agent in the pathogenesis of lead poisoning.
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http://dx.doi.org/10.1007/s00128-012-0753-1DOI Listing
October 2012

Effects of lead exposure on growth and bone biology in growing rats exposed to simulated high altitude.

Bull Environ Contam Toxicol 2012 Jun 29;88(6):1033-7. Epub 2012 Mar 29.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, MT Alvear 2142, Buenos Aires, Argentina.

The existence of children living at high altitude suffering from lead (Pb) poisoning prompted us to investigate the long term effects of this pollutant on growth and bone biology in growing rats maintained at simulated high altitude (SHA). Pb and hypoxia (HX) significantly reduced body weight (-9.4 % and -24 %; p < 0.01) and length (-3 % and -8 %; p < 0.01); decreased femoral ultimate load (-16 % and -40 %; p < 0.01) and femoral energy absorption capacity (-18 % and -74 %; p < 0.01). Oral pathologic alterations were observed in experimental groups. Our findings revealed growth retardation and damages on femoral and mandibular bones that predispose to fractures.
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http://dx.doi.org/10.1007/s00128-012-0602-2DOI Listing
June 2012

Biomechanical properties of the mid-shaft femur in middle-aged hypophysectomized rats as assessed by bending test.

Endocrine 2012 Oct;42(2):411-8

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires, Argentina.

Both stiffness and strength of bones are thought to be controlled by the "bone mechanostat". Its natural stimuli would be the strains of bone tissue (sensed by osteocytes) that are induced by both gravitational forces (body weight) and contraction of regional muscles. Body weight and muscle mass increase with age. Biomechanical performance of load-bearing bones must adapt to these growth-induced changes. Hypophysectomy in the rat slows the rate of body growth. With time, a great difference in body size is established between a hypophysectomized rat and its age-matched control, which makes it difficult to establish the real effect of pituitary ablation on bone biomechanics. The purpose of the present investigation was to compare mid-shaft femoral mechanical properties between hypophysectomized and weight-matched normal rats, which will show similar sizes and thus will be exposed to similar habitual loads. Two groups of 10 female rats each (H and C) were established. H rats were 12-month-old that had been hypophysectomized 11 months before. C rats were 2.5-month-old normals. Right femur mechanical properties were tested in 3-point bending. Structural (load-bearing capacity and stiffness), geometric (cross-sectional area, cortical sectional area, and moment of inertia), and material (modulus of elasticity and maximum elastic stress) properties were evaluated. The left femur was ashed for calcium content. Comparisons between parameters were performed by the Student's t test. Average body weight, body length, femur weight, femur length, and gastrocnemius weight were not significantly different between H and C rats. Calcium content in ashes was significantly higher in H than in C rats. Cross-sectional area, medullary area, and cross-sectional moment of inertia were higher in C rats, whereas cortical area did not differ between groups. Structural properties (diaphyseal stiffness, elastic limit, and load at fracture) were about four times higher in hypophysectomized rats, as were the bone material stiffness or Young's modulus and the maximal elastic stress (about 7×). The femur obtained from a middle-aged H rat was stronger and stiffer than the femur obtained from a young-adult C rat, both specimens showing similar size and bone mass and almost equal geometric properties. The higher than normal structural properties shown by the hypophysectomized femur were entirely due to changes in the intrinsic properties of the bone; it was thus stronger at the tissue level. The change of the femoral bone tissue was associated with a high mineral content and an unusual high modulus of elasticity and was probably due to a diminished bone and collagen turnover.
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http://dx.doi.org/10.1007/s12020-012-9616-0DOI Listing
October 2012

Growth-dependent effects of dietary protein concentration and quality on the biomechanical properties of the diaphyseal rat femur.

Endocrinol Nutr 2012 Jan 3;59(1):35-43. Epub 2011 Dec 3.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires 1122, Argentina.

Objectives: This study compares the effects of feeding growing rats with increasing concentrations of casein (C) and wheat gluten (G), proteins that show different biological qualities, on the morphometrical and biomechanical properties of the femoral diaphysis.

Materials And Methods: Female rats were fed with one of ten diets containing different concentrations (5-30%) of C and G between the 30th and 90th days of life (Control=C-20%). Biomechanical structural properties of the right femur middiaphysis were estimated using a 3-point bending mechanical test with calculation of some indicators of bone material properties.

Results: Body weight and length were affected by treatments, values being highest in rats fed the C-20% diet. G diets affected negatively both parameters. Changes in cross-sectional geometry (mid-diaphyseal cross-sectional and cortical areas, femoral volume, and rectangular moment of inertia) were positively related to the C content of the diet, while they were severely and negatively affected by G diets. Similar behaviors were observed in the bone structural properties (fracture load, yielding load, diaphyseal stiffness and elastic energy absorption). When values of strength and stiffness were normalized for body weight, the differences disappeared. The bone material quality indicators (elastic modulus, yielding stress, elastic energy absorption/volume) did not differ significantly among all studied groups. Femoral calcium concentration in ashes was not significantly different among groups.

Conclusion: The clear differences in strength and stiffness of bone beams induced by dietary protein concentration and quality seemed to be the result of an induced subnormal gain in bone structural properties as a consequence of a correlative subnormal gain in bone growth and mass, yet not in bone material properties.
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http://dx.doi.org/10.1016/j.endonu.2011.09.005DOI Listing
January 2012

[Effect of different propranolol doses on skeletal structural and mechanic efficiency in an animal model of growth retardation].

Endocrinol Nutr 2012 Jan 16;59(1):9-20. Epub 2011 Nov 16.

Cátedra de Fisiología, Facultad de Odontología, Universidad de Buenos Aires, Argentina.

Objective: To assess in a growth retardation (GR) model the impact of different propranolol (P) doses on anthropomorphometric and biomechanical variables of the appendicular skeleton.

Materials And Methods: Twenty-one day-old male Wistar rats were divided into the following groups: control (C), C+P3.5 (CP3.5); C+P7 (CP7); C+P10.5 (CP10.5); C+P14 (CP14); ED, ED+P3.5 (EDP3.5); ED+P7 (EDP7); ED+P10.5 (EDP10.5), and ED+P14 (EDP14). Control animals with/without P were fed a rodent diet ad libitum. GR rats with/without P were given 80% of the same diet per 100g body weight for 4 weeks (T4). Propranolol 3.5, 7, 10.5, and 14 mg/kg/day was intraperitoneally injected 5 days/week for 4 weeks to the CP3.5 and EDP3.5; CP7 and EDP7; CP10.5 and EDP10.5, and CP14 and EDP14 groups respectively.

Results: At T4, energy restriction had negative effects upon overall growth, femur, and its mechanical competence. Propranolol improved bone rigidity in GR animals at doses of 7 and 10.5mg/kg/day, with a maximum response at 7 mg/kg/day.

Conclusions: Propranolol 7 mg/kg/day would be the most effective dose for modeling incorporation of bone, as shown by the increased skeletal structural and mechanic efficiency in this animal model of growth retardation. Such effect may result from maintenance of mechanosensor viability, changes in its sensitivity, the biomechanical reference point and/or effector response in GR rats.
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http://dx.doi.org/10.1016/j.endonu.2011.09.006DOI Listing
January 2012

Aluminum bone toxicity in immature rats exposed to simulated high altitude.

J Bone Miner Metab 2011 Sep 17;29(5):526-34. Epub 2011 Feb 17.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires, Argentina.

Aluminum (Al) is an element to which humans are widely exposed. Chronic administration induces a negative effect on bone tissue, affecting collagen synthesis and matrix mineralization. Its toxic effects are cumulative. Hypobaric hypoxia induces stress erythropoiesis, leading to hypertrophy of the erythropoietic marrow affecting the bone. This study was designed to evaluate the risk of Al bone toxicity among immature rats maintained at simulated high altitude (SHA) by mechanical assessment of stiffness and strength, calculation of some indicators of bone material and geometrical properties, as well as blood determinations. Forty growing rats were divided into control and experimental groups whether injected with vehicle or Al, as Al(OH)(3), three times a week for 3 months. Half of each group was exposed to hypobaric conditions (HX) by placing the animals in a SHA chamber. Both treatments negatively affected structural properties of bones, decreasing the maximum capacity to withstand load, the limit elastic load and the capacity of absorbing energy in elastic conditions. Al administration significantly depressed mandible structural stiffness, although diaphyseal stiffness was not modified. Indicators of bone material intrinsic properties, elastic modulus and stress, were significantly reduced by Al or HX. Treatments increased the diaphyseal sectional bending moment of inertia, suggesting that femur, but not mandible, compensates for the decline in the material properties with an adaptation of its architecture to maintain structural properties. The different biomechanical behaviors between the two kinds of bone are probably due to their different embryological origin and specific functions, as mandible is a bone that adjusts its strength to biting forces, whereas femur is designed to support load.
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http://dx.doi.org/10.1007/s00774-010-0254-4DOI Listing
September 2011

Bone mineral density and bone strength from the mandible of chronically protein restricted rats.

Acta Odontol Latinoam 2011 ;24(3):223-8

Department of Physiology, Faculty of Dentistry, University of Buenos Aires Buenos Aires, Argentina.

Unlabelled: The present investigation was performed to assess the biomechanical repercussion of protein malnutrition imposed on rats between the 26th and 135th days of postnatal life on the mandible, which is not a weight-bearing bone but supports the loads related to the masticatory activity. Female Wistar rats aged 26 d (n = 14) were placed on either a 4%-protein diet (ICN 960254, P4 group) or a 20%-protein diet (ICN 960260, P20 group) and killed 111 d later. Both body weight and length were recorded regularly. The mandibles were dissected and cleaned of adhering soft tissue. Mandibular growth was estimated directly by taking measurements between anatomical points. Areal Bone Mineral Density (BMD) was estimated using a bone densitometer (LUNAR DPX-L). Mechanical properties of the right hemimandible were determined using a three-point bending mechanical test to obtain the load/deformation curve and estimate the structural properties of the bone. Results were summarized as means +/- SD. Comparisons between parameters were performed by Student's t test. A 75% reduction in body weight and a 32% reduction in body length were observed in P4 rats. Like body size, mandibular weight, length, height and area (index of mandibular size) were negatively affected by P4 diet, as was the posterior part of the bone (posterior to molar III). The anterior part (alveolar and incisor alveolar process) was not affected by age or diet. The "load capacity" extrinsic properties of the mandible (load fracture, stiffness, yielding point) were between 43% and 64% of control value in protein restricted rats. BMD was similar in both groups of animals.

Conclusion: 1) Chronic protein malnutrition imposed on rats from infancy to early adulthood reduces the growth of the posterior part of the mandible without inducing changes in the anterior part, which produces some deformation of the bone in relation to age-matched rats; and 2) the significant reduction of strength and stiffness of the mandible seem to be the result of an induced loss of gain in bone structural properties as a consequence of a correlative loss of gain in both growth and mass, yet not in bone material properties.
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July 2012

Biomechanical performance of diaphyseal shafts and bone tissue of femurs from hypothyroid rats.

Endocrine 2009 Oct 11;36(2):291-8. Epub 2009 Aug 11.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires, Argentina.

The bone changes in hypothyroidism are characterized by a low bone turnover with a reduced osteoid apposition and bone mineralization rate, and a decreased osteoclastic resorption in cortical bone. These changes could affect the mechanical performance of bone. The evaluation of such changes was the object of the present investigation. Hypothyroidism was induced in female rats aged 21 days through administration of propylthiouracil in the drinking water for 70 days (HT group). Controls were untreated rats (C group). Right femur mechanical properties were tested in 3-point bending. Structural (load bearing capacity and stiffness), geometric (cross-sectional area and moment of inertia) and material (modulus of elasticity) properties were evaluated. The left femur was ashed for calcium content determination. Plasma T(4) concentration was significantly decreased in HT rats. Body and femur weight and length in HT rats were also reduced. Femoral calcium concentration in ash was higher in HT than in C rats. However, the femoral calcium mass was significantly lower in HT than in C rats because of the reduced femoral size seen in the former. The stiffness of bone material was higher in HT than in C rats, while the bone geometric properties were significantly lower. The "load capacity" was between 30 and 50% reduced in the HT group, although, the differences disappeared when the values were normalized per 100-g body weight. The lowered biomechanical ability observed in the femoral shafts of HT rats seems to be the expression of a diminished rate of growth. Qualitative alterations in the intrinsic mechanical properties of bone tissue were observed in HT rats, probably because the mineral content and the modulus of elasticity were positively affected. The cortical bone of the HT rat thus appears as a bone with a higher than normal strength and stiffness relative to body weight, probably due to improvement of bone material quality due to an increased matrix calcification.
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http://dx.doi.org/10.1007/s12020-009-9212-0DOI Listing
October 2009

Improved bone status by the beta-blocker propranolol in an animal model of nutritional growth retardation.

Br J Nutr 2009 Jun;101(11):1616-20

Department of Physiology, School of Dentistry, University of Buenos Aires, Buenos Aires, Argentina.

The aim of the present research was to study if the beta-blocker propranolol, which is known to increase bone mass, could reverse the adverse skeletal effects of mild chronic food restriction in weanling rats. Male Wistar rats were divided into four groups: control, control+propranolol (CP), nutritional growth retardation (NGR) and nutritional growth retardation+propranolol (NGRP). Control and CP rats were fed freely with the standard diet. NGR and NGRP rats received, for 4 weeks, 80 % of the amount of food consumed by the control and CP rats, respectively. Results were expressed as mean values and sem. Food restriction induced detrimental effects on body and femur weight and length (P < 0.05) and bone structural and geometrical properties (P < 0.001), confirming results previously shown in our laboratory. However, the beta-blocker overcame the deleterious effect of nutritional stress on load-bearing capacity, yielding load, bone stiffness, cross-sectional cortical bone area and second moment of inertia of the cross-section in relation to the horizontal axis without affecting anthropometric, histomorphometric and bone morphometric parameters. The results suggest that propranolol administration to mildly chronically undernourished rats markedly attenuates the impaired bone status in this animal model of growth retardation.
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http://dx.doi.org/10.1017/s000711450811145xDOI Listing
June 2009

Long-term exposure to hypobaric hypoxia in rat affects femur cross-sectional geometry and bone tissue material properties.

Ann Anat 2009 Apr 20;191(2):212-7. Epub 2009 Jan 20.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, M.T. de Alvear 2142, Buenos Aires 1122, Argentina.

Hypoxia leads to an increase in erythropoiesis, which induces hypertrophy of the erythropoietic marrow and may induce bone resorption. This study investigates the effect of chronic hypobaric hypoxia (simulated high altitude, SHA) on the biomechanics of rat femurs by mechanical tests of diaphyseal stiffness and strength and calculation of some indicators of bone material properties. Adult female rats were exposed to SHA (5500 m, 23.5h/d for 60 d =HX rats; NX=normoxic). This treatment induced reticulocytosis and polycythemia. Bone mineral content did not differ between NX and HX rats at the end of the study. To determine cortical bone mechanical properties, the right femur was assessed using a 3-point bending test. Endosteum and periosteum moved away from the central axis in HX rats as deduced by an increase in the cross-sectional moment of inertia. The two indicators of bone material properties, the elastic modulus and stress at the yielding point, were significantly reduced. However, the strength of the femur as an intact organ ("load capacity" parameters) was not compromised by exposure to SHA. It is thus proposed that the negative effect of SHA on bone material quality was completely offset by an improvement in diaphyseal cross-sectional design, thus allowing a normal biomechanical response to bending of the femur as a whole.
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http://dx.doi.org/10.1016/j.aanat.2008.11.002DOI Listing
April 2009

Permanent reduction of mandibular size and bone stiffness induced in post-weaning rats by cyclophosphamide.

Arch Oral Biol 2009 Jan 24;54(1):6-11. Epub 2008 Sep 24.

Department of Physiology, Faculty of Odontology, University of Buenos Aires, Buenos Aires, Argentina.

It has been previously reported that several doses of cyclophosphamide (CPA) reduce body weight gain, diaphyseal torsional strength and longitudinal femoral growth in the growing rat. The present study was thus designed to estimate both the initial and the possible long-term effects of CPA treatment, by analyzing mandibular dimensions and biomechanical performance of the bone in adulthood in rats treated with the drug around weaning. Female Sprague-Dawley rats (N=20), 26 d of age, received 100mg/kg of CPA by the intraperitoneal route during days 0, 7 and 21 of the experimental period. Controls (C) received saline. Groups of rats were sacrificed at day 28 to estimate initial changes induced by the drug and on day 126 in order to determine long-term effects. The dimensions of the excised mandibles were measured directly between anatomical points; the geometry and material biomechanical quality of mandibular bone were assessed using a three-point bending mechanical test in an Instron Universal Testing Machine model 4442. CPA reduced body weight, body length and mandibular size (posterior part of the bone) significantly, when the parameters were measured at day 28. They did not recover with time, which means that catch-up growth did not occur and that the overall growth of the body was permanently affected by the drug. CPA treatment was also associated with a marked depression of the natural increase in the mandibular bone mass (cross-sectional area). The bending cross-sectional moment of inertia of the fracture sections (xCSMI) was also negatively affected by treatment. Significant decreases of both ultimate load and stiffness were also observed. The above structural parameters did not recover enough with time to attain control values at the end of the study. The intrinsic stiffness (E) of the mandibular bone was not affected by treatment. These findings suggest that CPA treatment during early postnatal life causes permanent changes in mandibular morphology and affects the adaptation of mandibular bone architecture to body growth, thus not allowing complete compensation at the end of the study because of an inadequate distribution of the resistive material through its cross-section rather than a qualitative impairment of cortical bone.
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http://dx.doi.org/10.1016/j.archoralbio.2008.08.004DOI Listing
January 2009
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