Publications by authors named "Hakan Erdogan"

38 Publications

Cation-based approach to morphological diversity of diphenylalanine dipeptide structures.

Authors:
Hakan Erdoğan

Soft Matter 2021 May 4. Epub 2021 May 4.

University of Health Sciences Turkey, Gülhane Faculty of Pharmacy, Department of Pharmaceutical Chemistry, 06018 Ankara, Turkey.

Different approaches are taken in order to examine the spontaneous arrangement processes of dipeptide structures. One of these approaches is to examine the effects of common cations on dipeptide structures' self-assembly processes. In this study, the effects of Al3+, Cu2+, Pb2+, Hg2+, Mg2+, Zn2+, Cd2+, Fe2+ and Ni2+ cations on the self-assembly processes of diphenylalanine (FF) dipeptide molecules were investigated. A detailed examination was made of the self-assembly of FF dipeptides in the presence of Hg2+, and a spherical architecture structure was shown. The morphological diversity resulting from the effects of Hg2+ cations at different concentrations on FF dipeptides was explained using Scanning Electron Microscopy (SEM), X-ray Diffraction, (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) techniques. It is thought that this work will contribute to the indexing of the effects of toxic species such as Hg2+ on dipeptides, which are the smallest peptide units obtained. We think that the examination of FF dipeptides in the structures of amyloid plaques, which are thought to affect neurological disorders such as Alzheimer's and Parkinson's, will prompt further studies.
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http://dx.doi.org/10.1039/d1sm00083gDOI Listing
May 2021

Serum indoxyl sulfate concentrations associate with progression of chronic kidney disease in children.

PLoS One 2020 27;15(10):e0240446. Epub 2020 Oct 27.

Division of Pediatric Nephrology, Center of Pediatric and Adolescent Medicine, University Hospital Heidelberg, Heidelberg, Germany.

The uremic toxins indoxyl sulfate (IS) and p-cresyl sulfate (pCS) accumulate in patients with chronic kidney disease (CKD) as a consequence of altered gut microbiota metabolism and a decline in renal excretion. Despite of solid experimental evidence for nephrotoxic effects, the impact of uremic toxins on the progression of CKD has not been investigated in representative patient cohorts. In this analysis, IS and pCS serum concentrations were measured in 604 pediatric participants (mean eGFR of 27 ± 11 ml/min/1.73m2) at enrolment into the prospective Cardiovascular Comorbidity in Children with CKD study. Associations with progression of CKD were analyzed by Kaplan-Meier analyses and Cox proportional hazard models. During a median follow up time of 2.2 years (IQR 4.3-0.8 years), the composite renal survival endpoint, defined as 50% loss of eGFR, or eGFR <10ml/min/1.73m2 or start of renal replacement therapy, was reached by 360 patients (60%). Median survival time was shorter in patients with IS and pCS levels in the highest versus lowest quartile for both IS (1.5 years, 95%CI [1.1,2.0] versus 6.0 years, 95%CI [5.0,8.4]) and pCS (1.8 years, 95%CI [1.5,2.8] versus 4.4 years, 95%CI [3.4,6.0]). Multivariable Cox regression disclosed a significant association of IS, but not pCS, with renal survival, which was independent of other risk factors including baseline eGFR, proteinuria and blood pressure. In this exploratory analysis we provide the first data showing a significant association of IS, but not pCS serum concentrations with the progression of CKD in children, independent of other known risk factors. In the absence of comorbidities, which interfere with serum levels of uremic toxins, such as diabetes, obesity and metabolic syndrome, these results highlight the important role of uremic toxins and accentuate the unmet need of effective elimination strategies to lower the uremic toxin burden and abate progression of CKD.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0240446PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7591021PMC
December 2020

Microalbuminuria and Serum Cystatin C in Prediction of Early-Renal Insufficiency in Children with Obesity.

Indian J Pediatr 2020 Dec 8;87(12):1009-1013. Epub 2020 May 8.

Department of Pediatric Nephrology, Bursa Yuksek Ihtisas Training and Research Hospital, Bursa, Turkey.

Objective: Serum cystatin-C (SCysC) and microalbuminuria are well-recognized early markers of renal damage. This study aims to assess whether these early markers are elevated in children with obesity and normal serum creatinine (SCr).

Methods: Pediatric patients diagnosed with obesity were included (n = 105, ages 4-18 y) in this study. The patients were divided into three groups as follows: solely obese, metabolic syndrome and type 2 diabetes. Serum cystatin-C, 24-h microalbuminuria, SCr and glomerular filtration rate (GFR) were evaluated in all patients. All patients were examined with history, physical examination, laboratory analysis and ultrasonography evaluation.

Results: The findings showed that renal function, GFR and SCr levels were normal in all patients. There was microalbuminuria in six patients and SCysC was elevated in eight patients. There were also both elevated SCysC and microalbuminuria in eight patients. Significant elevations of both microalbuminuria and SCysC were detected in cases with type 2 diabetes (p < 0.05).

Conclusions: The findings suggest that SCysC may have a diagnostic value in early-renal insufficiency. Although there was not any statistically significant difference between groups in GFR, significant elevations for both microalbuminuria and SCysC in patients with type 2 diabetes were detected. This suggests that the risk factors of diabetes may have a direct relation with renal damage. Regarding renal function in type 2 diabetic and obese pediatric patients, microalbuminuria and SCysC may be screened to observe early-renal damage, even in cases with normal GFR and SCr levels.
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http://dx.doi.org/10.1007/s12098-020-03294-zDOI Listing
December 2020

Discontinuation of RAAS Inhibition in Children with Advanced CKD.

Clin J Am Soc Nephrol 2020 05 6;15(5):625-632. Epub 2020 Apr 6.

Division of Pediatric Nephrology, University Hospital Heidelberg, Heidelberg, Germany.

Background And Objectives: Although renin-angiotensin-aldosterone system inhibition (RAASi) is a cornerstone in the treatment of children with CKD, it is sometimes discontinued when kidney function declines. We studied the reasons of RAASi discontinuation and associations between RAASi discontinuation and important risk markers of CKD progression and on eGFR decline in the Cardiovascular Comorbidity in Children with CKD study.

Design, Setting, Participants, & Measurements: In this study, 69 children with CKD (67% male, mean age 13.7 years, mean eGFR 27 ml/min per 1.73 m) who discontinued RAASi during prospective follow-up were included. Initial change in BP, albuminuria, and potassium after discontinuation were assessed (median time 6 months). Rate of eGFR decline (eGFR slope) during a median of 1.9 years before and 1.2 years after discontinuation were estimated using linear mixed effects modeling.

Results: Physician-reported reasons for RAASi discontinuation were increase in serum creatinine, hyperkalemia, and symptomatic hypotension. After discontinuation of RAASi, BP and albuminuria increased, whereas potassium decreased. eGFR declined more rapidly after discontinuation of RAASi (-3.9 ml/min per 1.73 m per year; 95% confidence interval, -5.1 to -2.6) compared with the slope during RAASi treatment (-1.5 ml/min per 1.73 m per year; 95% confidence interval, -2.4 to -0.6; =0.005). In contrast, no change in eGFR slope was observed in a matched control cohort of patients in whom RAASi was continued.

Conclusions: Discontinuation of RAASi in children with CKD is associated with an acceleration of kidney function decline, even in advanced CKD.
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http://dx.doi.org/10.2215/CJN.09750819DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7269205PMC
May 2020

The Number of Patients Diagnosed with Brain Death and Organ Donation Rates at the Başkent University Konya Hospital: 6-Year Experience.

Exp Clin Transplant 2020 01;18(Suppl 1):60-63

From the Department of General Surgery, Division of Transplantation, Başkent University, Ankara, Turkey.

Objectives: Kidney transplant started at Başkent University Konya Hospital in July 2016. In this study, we compared the causes of brain death and the organ donation rates in our center between 2013 and 2016 versus between 2016 and 2019.

Materials And Methods: Patient files and records were analyzed retrospectively. Age, biologic sex, cause of brain death, and organ donation rates of patients diagnosed with brain death were examined and compared.

Results: The number of patients who were diagnosed with brain death and became deceased donors at our center increased 4-fold during the period from 2016 to 2019 compared with that shown from 2013 to 2016. In addition, organ donation rates increased to 71.4%, which is much higher than the average in Turkey (24%-28%). Between 2013 and 2016, trauma was the leading cause of brain death (42.8%), whereas between 2016 and 2019 cerebral hemorrhages rose to first place with a rate of 89.3%. In 2018 and 2019, there were 199 and 62 brain deaths, respectively, reported in our organ donation coordination region with an approximate organ donation rate of 25%. In our center, 12 patients were diagnosed with brain death in 2018 and 8 of these patients (66.7%) became donors; 6 brain deaths were diagnosed in 2019, and 4 patients (66.7%) became donors. Since we started kidney transplant at our center in 2016, the number of patients diagnosed with brain death has increased significantly.

Conclusions: Establishing a healthy communication with relatives of patients and having a dedicated organ transplant center are important reasons for our much higher organ donation rates compared with the general rate in Turkey. A healthy communication is the most effective way to establish trust with next-of-kin and the general public.
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http://dx.doi.org/10.6002/ect.TOND-TDTD2019.P1DOI Listing
January 2020

Low levels of urinary epidermal growth factor predict chronic kidney disease progression in children.

Kidney Int 2019 07 20;96(1):214-221. Epub 2019 Mar 20.

Department of Internal Medicine/Nephrology, University of Michigan, Ann Arbor, Michigan, USA; Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, Michigan, USA.

Urinary epidermal growth factor (uEGF) has recently been identified as a promising biomarker of chronic kidney disease (CKD) progression in adults with glomerular disease. Low levels of uEGF predict CKD progression and appear to reflect the extent of tubulointerstitial damage. We investigated the relevance of uEGF in pediatric CKD. We performed a post hoc analysis of the Cardiovascular Comorbidity in Children with CKD (4C) study, which prospectively follows children aged 6-17 years with baseline estimated glomerular filtration rate (eGFR) of 10-60 ml/min/1.73 m. uEGF levels were measured in archived urine collected within 6 months of enrollment. Congenital abnormalities of the kidney and urinary tract were the most common cause of CKD, with glomerular diseases accounting for <10% of cases. Median eGFR at baseline was 28 ml/min/1.73 m, and 288 of 623 participants (46.3%) reached the composite endpoint of CKD progression (50% eGFR loss, eGFR < 10 ml/min/1.73 m, or initiation of renal replacement therapy). In a Cox proportional hazards model, higher uEGF/Cr was associated with a decreased risk of CKD progression (HR 0.76; 95% CI 0.69-0.84) independent of age, sex, baseline eGFR, primary kidney disease, proteinuria, and systolic blood pressure. The addition of uEGF/Cr to a model containing these variables resulted in a significant improvement in C-statistics, indicating better prediction of the 1-, 2- and 3-year risk of CKD progression. External validation in a prospective cohort of 222 children with CKD demonstrated comparable results. Thus, uEGF may be a useful biomarker to predict CKD progression in children with CKD.
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http://dx.doi.org/10.1016/j.kint.2019.01.035DOI Listing
July 2019

Difficulties of Distal Catheter Insertion of Ventriculoatrial Shunting in Infants and Little Children.

Turk Neurosurg 2017 Sep 26. Epub 2017 Sep 26.

Adatıp Hospital, Neurosurgery Clinic, Istanbul, Turkey.

Aim: Ventriculoatrial (VA) shunting is a well-described cerebrospinal fluid diversion method for the treatment of hydrocephalus. However, it may be very challenging in infants and little children because of atrial catheter placement difficulties. This study aimed to create an algorithm to solve problems faced during open surgical procedures based on the present authors' experience.

Material And Methods: We conducted a retrospective analysis on 18 infants and children who underwent VA shunt insertion at the Department of Neurosurgery, Ondokuz Mayıs University School of Medicine Hospital between 2005 and 2012. Complications, clinical outcomes, revisions, and solutions for overcoming distal catheter placement difficulties were evaluated.

Results: Twenty-six VA shunt operations were performed in 18 patients. Six patients required eight VA shunt revisions. VA shunting was primarily performed from the internal jugular, facial, cephalic, and subclavian veins to the right atrium. In revision procedures, the internal jugular, cephalic, and subclavian veins were used.

Conclusion: VA shunting in infants and little children requires careful surgical techniques. Neurosurgeons should necessarily have an appropriate strategy for VA shunting considering the complications and revisions. Our results suggest open surgical solutions to overcome distal catheter placement difficulties in this age group.
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http://dx.doi.org/10.5137/1019-5149.JTN.21304-17.2DOI Listing
September 2017

Metabolic acidosis is common and associates with disease progression in children with chronic kidney disease.

Kidney Int 2017 12 18;92(6):1507-1514. Epub 2017 Jul 18.

Division of Pediatric Nephrology, Center for Pediatrics and Adolescent Medicine, Heidelberg University Hospital, Heidelberg, Germany. Electronic address:

Recent studies in adult chronic kidney disease (CKD) suggest that metabolic acidosis is associated with faster decline in estimated glomerular filtration rate (eGFR). Alkali therapies improve the course of kidney disease. Here we investigated the prevalence and determinants of abnormal serum bicarbonate values and whether metabolic acidosis may be deleterious to children with CKD. Associations between follow-up serum bicarbonate levels categorized as under 18, 18 to under 22, and 22 or more mmol/l and CKD outcomes in 704 children in the Cardiovascular Comorbidity in Children with CKD Study, a prospective cohort of pediatric patients with CKD stages 3-5, were studied. The eGFR and serum bicarbonate were measured every six months. At baseline, the median eGFR was 27 ml/min/1.73m and median serum bicarbonate level 21 mmol/l. During a median follow-up of 3.3 years, the prevalence of metabolic acidosis (serum bicarbonate under 22 mmol/l) was 43%, 60%, and 45% in CKD stages 3, 4, and 5, respectively. In multivariable analysis, the presence of metabolic acidosis as a time-varying covariate was significantly associated with log serum parathyroid hormone through the entire follow-up, but no association with longitudinal growth was found. A total of 211 patients reached the composite endpoint (ESRD or 50% decline in eGFR). In a multivariable Cox model, children with time-varying serum bicarbonate under 18 mmol/l had a significantly higher risk of CKD progression compared to those with a serum bicarbonate of 22 or more mmol/l (adjusted hazard ratio 2.44; 95% confidence interval 1.43-4.15). Thus, metabolic acidosis is a common complication in pediatric patients with CKD and may be a risk factor for secondary hyperparathyroidism and kidney disease progression.
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http://dx.doi.org/10.1016/j.kint.2017.05.006DOI Listing
December 2017

Hemostasis vs. epidural fibrosis?: A comparative study on an experimental rat model of laminectomy.

Neurol Neurochir Pol 2016;50(5):323-30. Epub 2016 May 25.

Faculty of Medicine, Department of Neurosurgery, Maltepe University, Istanbul, Turkey.

Aim: The aim of this study was to evaluate the histopathological and biochemical impact and effectiveness of two hemostatic agents, Ankaferd blood stopper (ABS) and Microporous Polysaccharide Hemospheres (MPH), on epidural fibrosis in an experimental rat laminectomy model.

Material And Methods: Twenty adult Wistar albino rats were divided into MPH-treated (n=6), ABS-treated (n=6) and control (n=8) groups. Laminectomy of the lumbar spine was performed in all animals and treatment groups were exposed to MPH and ABS while closure was applied in control group as per usual. Epidural fibrosis was evaluated in all groups macroscopically, histopathologically, biochemically and with electron microscopy four weeks later.

Results: Statistically, it was found that MPH-treated group had significantly less epidural fibrosis compared to ABS-treated and control groups.

Conclusion: We compared two hemostatic agents for their propensity to cause adhesions in the present study. Our results show that MPH significantly reduces epidural scar formation and dural adhesion in a rat model of laminectomy while ABS increases postoperative fibrosis.
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http://dx.doi.org/10.1016/j.pjnns.2016.05.002DOI Listing
January 2017

Searching Evidences of Stroke in Animal Models: A Review of Discrepancies A Review of Discrepancies.

Turk Neurosurg 2017 ;27(2):167-173

Anadolu Medical Center, Department of Neurological Sciences, Istanbul, Turkey.

So far, animal models have helped us better understand the pathophysiology of the ischemic brain damage but they could not contribute so much to clinical practice. The discrepancies in results regarding neuroprotective agents in animal experiments compared to clinical trials have not been solved. Various animal models of ischemic stroke have proven efficacy of many neuroprotective agents without any considerable result in phase III clinical trials. As is well known, stroke-related focal cerebral ischemia or cardiac arrest related global cerebral ischemia are major causes of disability and death among human subjects. Animal models are essential to evaluate the therapeutic approaches for humans. In this review, we will try to answer two important questions: 1) Which factors endanger the reliability of experimental studies of stroke on animal models? 2) How can we design our experiments to reflect the neurorestoration and/or neuroprotection mechanisms following ischemic injury, when it comes to human disease?
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http://dx.doi.org/10.5137/1019-5149.JTN.15373-15.2DOI Listing
April 2017

Secondary Hemophagocytic Lymphohistiocytosis in an Infant with Wolman Disease.

Turk J Haematol 2017 08 18;34(3):264-265. Epub 2016 Apr 18.

Şevket Yılmaz Training and Research Hospital, Clinic of Pediatric Metabolism, Bursa, Turkey.

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http://dx.doi.org/10.4274/tjh.2015.0454DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5544048PMC
August 2017

Fabrication of Plasmonic Nanorod-Embedded Dipeptide Microspheres via the Freeze-Quenching Method for Near-Infrared Laser-Triggered Drug-Delivery Applications.

Biomacromolecules 2016 05 18;17(5):1788-94. Epub 2016 Apr 18.

Bio-inspired Materials Research Laboratory (BIMREL), Department of Chemistry, Gazi University , 06500 Ankara, Turkey.

Control of drug release by an external stimulus may provide remote controllability, low toxicity, and reduced side effects. In this context, varying physical external stimuli, including magnetic and electric fields, ultrasound, light, and pharmacological stimuli, have been employed to control the release rate of drug molecules in a diseased region. However, the design and development of alternative on-demand drug-delivery systems that permit control of the dosage of drug released via an external stimulus are still required. Here, we developed near-infrared laser-activatable microspheres based on Fmoc-diphenylalanine (Phe-Phe) dipeptides and plasmonic gold nanorods (AuNRs) via a simple freeze-quenching approach. These plasmonic nanoparticle-embedded microspheres were then employed as a smart drug-delivery platform for native, continuous, and pulsatile doxorubicin (DOX) release. Remarkable sustained, burst, and on-demand DOX release from the fabricated microspheres were achieved by manipulating the laser exposure time. Our results demonstrate that AuNR-embedded dipeptide microspheres have great potential for controlled drug-delivery systems.
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http://dx.doi.org/10.1021/acs.biomac.6b00214DOI Listing
May 2016

Pentoxifylline Inhibits Epidural Fibrosis in Post-Laminectomy Rats.

Med Sci Monit 2016 Mar 14;22:840-7. Epub 2016 Mar 14.

Department of Anesthesia, Kartal Kosuyolu Research and Training Hospital, Istanbul, Turkey.

Background: The aim of this experimental study was to investigate the effectiveness of intramuscular pentoxifylline in the prevention of postoperative fibrosis.

Material/methods: We divided 16 adult Wistar albino rats into 2 equal groups: treatment and control. Both groups underwent L1 vertebral total laminectomy to expose the dura. The intramuscular treatment group received pentoxifylline. Four weeks later, epidural fibrosis was studied in both groups using electron microscopy, light microscopy, histology, biochemistry, and macroscopy.

Results: The evaluation of epidural fibrosis in the 2 groups according to macroscopic (p<0.01) assessment and light microscopy revealed that epidural scar tissue formation was lower in the treatment group compared to the control group (p<0.001) and the number of fibroblasts was also decreased significantly in the pentoxifylline-treated group (p<0.05). More immature fibers were demonstrated in the treatment group by electron microscopy in comparison with the control group. In biochemical analysis, a statistically significant decrease was detected in hydroxyproline, which indicates fibrosis and myeloperoxidase activity, and shows an inflammatory response (P<0.001).

Conclusions: Systemic pentoxifylline application prevents postoperative epidural fibrosis and adhesions with various mechanisms. Our study is the first to present evidence of experimental epidural fibrosis prevention with pentoxifylline.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4793638PMC
http://dx.doi.org/10.12659/msm.897668DOI Listing
March 2016

Assessment of the neuroprotective effects of the acetylcholinesterase inhibitor huperzine A in an experimental spinal cord trauma model.

J Neurosurg Sci 2018 Apr 16;62(2):128-139. Epub 2015 Oct 16.

Private Consultant, Istanbul, Turkey.

Background: Spinal cord injury is nowadays still a challenging disease, and a treatment option aimed at the primary site of injury does not currently exist. Therefore, the management of acute spinal cord injury has recently focused on the reasons behind the aggravation of the initial insult through secondary mechanisms, and the search for pharmacological treatment protocols is generally aimed at reducing and minimizing the neural injury and neurological sequela. The secondary spinal cord injury usually develops following a primary lesion induced by spinal cord contusion and the emergence of apoptotic cells has been found to play an important role in the development of secondary injury. We propose that huperzine A may induce a significant reduction in the number of apoptotic cells because it possesses the ability to protect cells against glutamate, ischemia and staurosporine-induced cytotocity and apoptosis.

Methods: Huperzine A was administered intraperitoneally to male Wistar Albino rats (220-340 g of body weight) after moderate static clip compression (70 g for 60 s) of the spinal cord at T7 level. Neurological functions were assessed using the Basso-Beattle-Breshanan (BBB) motor rating scale until 3th and 7th days before perfusion, following which the spinal cord was harvested for histopathological examinations and apoptotic cell counts.

Results: Histopathological evaluations of the spinal cord of the control, trauma and huperzine A treated groups were evaluated. Control group showed normal neuronal and vascular structures of the spinal cord. However, in both trauma groups 3rd- and 7th-day perfusion showed extensive cavitation and hemorrhage, areas of necrosis and edema in gray matter, and degeneration in motor neurons along with patchy areas of necrotic and apoptotic cells. In the group treated with huperzine A, an increased number of normal cells was observed, along with a lower number of necrotic cells, with a significant reduction in the apoptotic cells (P<0.01). The administration of huperzine A improved post-trauma motor performance. Furthermore, BBB scores of all groups showed that there was an improvement of locomotor abilities in the treatment group as compared with the control.

Conclusions: When compared with controls, huperzine A treatment demonstrates a significant reduction in the number of apoptotic cells. In addition, the group treated with huperzine A showed significant and appreciable neurological improvement in rats.
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http://dx.doi.org/10.23736/S0390-5616.16.03428-7DOI Listing
April 2018

The Effects of Difumarate Salt S-15176 after Spinal Cord Injury in Rats.

J Korean Neurosurg Soc 2015 Jun 30;57(6):445-54. Epub 2015 Jun 30.

Istanbul ME-DI ENT Surgery Center, Istanbul, Turkey.

Objective: In the present study we analyzed neuroprotective and antiapoptotic effect of the difumarate salt S-15176, as an anti-ischemic, an antioxidant and a stabilizer of mitochondrial membrane in secondary damage following spinal cord injury (SCI) in a rat model.

Methods: Three groups were performed with 30 Wistar rats; control (1), trauma (2), and a trauma+S-15176 (10 mg/kg i.p., dimethyl sulfoxide) treatment (3). SCI was performed at the thoracic level using the weight-drop technique. Spinal cord tissues were collected following intracardiac perfusion in 3rd and 7th days of posttrauma. Hematoxylin and eosin staining for histopatology, terminal deoxynucleotidyl transferase dUTP nick end labeling assay for apoptotic cells and immunohistochemistry for proapoptotic cytochrome-c, Bax and caspase 9 were performed to all groups. Functional recovery test were applied to each group in 3rd and 7th days following SCI.

Results: In trauma group, edematous regions, diffuse hemorrhage, necrosis, leukocyte infiltration and severe degeneration in motor neurons were observed prominently in gray matter. The number of apoptotic cells was significantly higher (p<0.05) than control group. In the S-15176-treated groups, apoptotic cell number in 3rd and 7th days (p<0.001), also cytochrome-c (p<0.001), Bax (p<0.001) and caspase 9 immunoreactive cells (p<0.001) were significantly decreased in number compared to trauma groups. Hemorrhage and edema in the focal areas were also noticed in gray matter of treatment groups. Results of the locomotor test were significantly increased in treatment group (p<0.05) when compared to trauma groups.

Conclusion: We suggest that difumarate salt S-15176 prevents mitochondrial pathways of apoptosis and protects spinal cord from secondary injury and helps to preserve motor function following SCI in rats.
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http://dx.doi.org/10.3340/jkns.2015.57.6.445DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4502243PMC
June 2015

Morphological Versatility in the Self-Assembly of Val-Ala and Ala-Val Dipeptides.

Langmuir 2015 Jul 25;31(26):7337-45. Epub 2015 Jun 25.

†Bio-inspired Materials Research Laboratory (BIMREL), Department of Chemistry, Gazi University, 06500 Ankara, Turkey.

Since the discovery of dipeptide self-assembly, diphenylalanine (Phe-Phe)-based dipeptides have been widely investigated in a variety of fields. Although various supramolecular Phe-Phe-based structures including tubes, vesicles, fibrils, sheets, necklaces, flakes, ribbons, and wires have been demonstrated by manipulating the external physical or chemical conditions applied, studies of the morphological diversity of dipeptides other than Phe-Phe are still required to understand both how these small molecules respond to external conditions such as the type of solvent and how the peptide sequence affects self-assembly and the corresponding molecular structures. In this work, we investigated the self-assembly of valine-alanine (Val-Ala) and alanine-valine (Ala-Val) dipeptides by varying the solvent medium. It was observed that Val-Ala dipeptide molecules may generate unique self-assembly-based morphologies in response to the solvent medium used. Interestingly, when Ala-Val dipeptides were utilized as a peptide source instead of Val-Ala, we observed distinct differences in the final dipeptide structures. We believe that such manipulation may not only provide us with a better understanding of the fundamentals of the dipeptide self-assembly process but also may enable us to generate novel peptide-based materials for various applications.
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http://dx.doi.org/10.1021/acs.langmuir.5b01406DOI Listing
July 2015

Large area uniform deposition of silver nanoparticles through bio-inspired polydopamine coating on silicon nanowire arrays for practical SERS applications.

J Mater Chem B 2014 Aug 26;2(30):4894-4900. Epub 2014 Jun 26.

Bio-Inspired Materials Research Laboratory (BIMREL), Department of Chemistry, Gazi University, 06500 Ankara, Turkey.

Despite the significant progress, the controlled deposition of nanoparticles onto the support materials having 3-D nano-morphologies is still facing challenges due to the limited diffusion of metal ions into the nanostructures and uncontrolled aggregation of nanoparticles. In this study, a simple yet versatile alternative is demonstrated to control the silver nanoparticle (AgNP) density and morphology onto the 3-D silicon nanowire (SiNW) arrays based on bio-inspired polydopamine (PDOP) coating and electroless plating approaches for practical Surface-Enhanced Raman Spectroscopy (SERS) applications. In order to control silver deposition and its morphology and to optimize the SERS performance of AgNP decorated SiNW arrays, the effect of some key experimental parameters including SiNW length and morphology, silver reduction time and PDOP thickness are investigated in detail. The optimized samples demonstrate remarkable surface-enhancement ability in Raman signals with high reproducibility (lower than ∼10% spot-to-spot and sample-to-sample). Interestingly, it is found that PDOP coating not only serves as a reducing agent for the deposition of AgNPs on SiNW arrays in a controlled manner, but also contributes to the observed SERS enhancements in terms of improving photon scattering and promoting electron transfer processes due to its organic semiconductor nature.
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http://dx.doi.org/10.1039/c4tb00616jDOI Listing
August 2014

Tumor-to-tumor metastasis of the central nervous system.

Turk Neurosurg 2014 ;24(2):151-62

Maltepe University, Faculty of Medicine, Department of Neurosurgery, Istanbul, Turkey.

Tumor-to-tumor metastasis is a well recognized phenomenon. Although any tumor may be potential recipient of metastasis, renal cell carcinoma and meningioma are the most common malignant and benign recipients, respectively, whereas the lung and breast are the most common metastatic donors respectively, in both settings. Patients with hereditary cancer syndromes may be at higher risk for the development of tumor-to-tumor metastases. The most common pattern of tumor-to-tumor metastasis for intracranial neoplasms is the type in which an aggressive high-grade malignancy serves as the source of tumor and a more indolent neoplasm serves as the recipient tumor. The development of tumor metastasis from a second primary malignancy is uncommon and remains biologically puzzling. Its low incidence has made its full biological characterization evasive. Although rare, neurosurgeons should be aware of the entity of tumor-to-tumor metastasis.
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http://dx.doi.org/10.5137/1019-5149.JTN.8317-13.1DOI Listing
February 2015

A single-center experience on percutaneously performed partial omentectomy in pediatric peritoneal dialysis patients.

Ren Fail 2014 Jun 3;36(5):755-9. Epub 2014 Mar 3.

Department of Pediatric Nephrology, Izmir Tepecik Training and Research Hospital , Izmir , Turkey .

Objective: This study describes a single-center experience on percutaneously performed partial omentectomy procedure in pediatric peritoneal dialysis (PD) patients who showed early catheter dysfunction and required catheter replacement due to catheter flow obstruction.

Materials And Methods: We performed a retrospective review of clinical outcomes from pediatric PD patients who underwent percutaneous catheter replacement by pediatric nephrologists between November 1995 and December 2012. Partial omentectomy was performed in those patients in whom omental or adhesion trapping to the catheter tip was seen.

Results: During the study period, catheter dysfunction that eventually required percutaneous catheter replacement occurred in 32 (23.7%) children. Of these, 9 patients were performed partial omentectomy. Mean age at initiation of PD and time of omentectomy was 97.48 ± 46.06 and 98.53 ± 45.55 months, respectively. Catheter dysfunction appeared after a mean 1.20 ± 1.0 months. The causes of catheter dysfunction were omental wrapping and malposition. No peritonitis occurred before omentectomy. Mean total operation time was 60 ± 8.83 min. No complications were encountered during the procedure. After omentectomy, mean catheter survival period was 5.92 ± 6.88 months. A total of five peritonitis episodes occurred. Three patients were transferred to hemodialysis. Six patients were on PD treatment without any problem at the end of the first year of their follow-up. Two patients underwent kidney transplantation. Four patients were still on chronic PD treatment at the end of the study period.

Conclusion: When performed by an experienced nephrologist, the performance of partial omentectomy by percutaneous route, when required, is an easy, safe and efficient therapeutic procedure in children on chronic PD treatment.
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http://dx.doi.org/10.3109/0886022X.2014.890860DOI Listing
June 2014

H1N1 Infection-Related Hemophagocytic Lymphohistiocytosis in a Child.

Turk J Haematol 2013 Dec 5;30(4):426-8. Epub 2013 Dec 5.

Medical Faculty, Abant İzzet Baysal University, Department of Pediatrics, Bolu, Turkey.

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http://dx.doi.org/10.4274/Tjh.2013.0022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3874979PMC
December 2013

One-dimensional surface-imprinted polymeric nanotubes for specific biorecognition by initiated chemical vapor deposition (iCVD).

ACS Appl Mater Interfaces 2013 Jul 1;5(14):6447-52. Epub 2013 Jul 1.

Faculty of Engineering and Natural Sciences, Sabanci University, 34956 Istanbul, Turkey.

Molecular imprinting is a powerful, generic, and cost-effective technique; however, challenges still remain related to the fabrication and development of these systems involving nonhomogeneous binding sites, insufficient template removing, incompatibility with aqueous media, low rebinding capacity, and slow mass transfer. The vapor-phase deposition of polymers is a unique technique because of the conformal nature of coating and offers new possibilities in a number of applications including sensors, microfluidics, coating, and bioaffinity platforms. Herein, we demonstrated a simple but versatile concept to generate one-dimensional surface-imprinted polymeric nanotubes within anodic aluminum oxide (AAO) membranes based on initiated chemical vapor deposition (iCVD) technique for biorecognition of immunoglobulin G (IgG). It is reported that the fabricated surface-imprinted nanotubes showed high binding capacity and significant specific recognition ability toward target molecules compared with the nonimprinted forms. Given its simplicity and universality, the iCVD method can offer new possibilities in the field of molecular imprinting.
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http://dx.doi.org/10.1021/am401769rDOI Listing
July 2013

Laser-triggered degelation control of gold nanoparticle embedded peptide organogels.

Langmuir 2013 Jun 24;29(23):6975-82. Epub 2013 May 24.

Bio-inspired Materials Research Laboratory (BIMREL), Department of Chemistry, Gazi University, 06500 Ankara, Turkey.

Further understanding of the interactions between nanoparticles (NPs) and biological molecules offers new possibilities in the applications of nanomedicine and nanodiagnostics. The properties of NPs, including size, shape, and surface functionality, play a decisive role in these interactions. Herein, we evaluated the influences of gold NPs (AuNPs) with different sizes (5-60 nm) and shapes (i.e., spherical, rod, and cage) on the self-assembly of diphenylalanine (Phe-Phe) dipeptides. We found that the size of AuNPs smaller than 10 nm did not affect the self-assembly process of Phe-Phe, while bigger AuNPs (>10 nm) caused the formation of starlike peptide morphologies connected to one center. In the case of shape differences, nanorod and nanocage morphologies acted differently than spherical ones and caused the formation of densely packed, networklike dipeptide morphologies. In addition to these experiments, by combining photothermal properties of AuNPs with a Phe-Phe-based organogel having a thermo-responsive property, we demonstrated that the degelation process of AuNPs embedded organogels may be controlled by laser illumination. Complete degelation was achieved in about 10 min. We believe that such control may open the door to new opportunities for a number of applications, such as controlled release of drugs and tissue engineering.
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http://dx.doi.org/10.1021/la401300uDOI Listing
June 2013

May we use communication as an instrument? A simple neuromonitoring method peripheral nerve tumour resection.

J Perioper Pract 2013 Mar;23(3):53-5

Department of Neurosurgery, Kafkas University, Faculty of Medicine, Kars, Turkey, 36100-TR.

We performed a procedure called awake simple peripheral nerve monitoring of the distal lower extremity. In this procedure we aimed to protect the patient's peroneal nerve during the successful removal of a tumour arising from this nerve. This is the first report that explores the use of communication with the patient during peripheral nerve tumour resection.
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http://dx.doi.org/10.1177/175045891302300303DOI Listing
March 2013

Alpha-lipoic acid reduces peridural fibrosis after laminectomy of lumbar vertebrae in rabbits.

Acta Neurochir (Wien) 2012 Jul 19;154(7):1241-5. Epub 2012 May 19.

Department of Neurosurgery, Faculty of Medicine, Kafkas University, Kars, Turkey, 36100.

Background: Peridural fibrosis is an inevitable healing process causing failed back surgery syndrome after lumbar spinal operations. In this study, alpha-lipoic acid (ALA), reported to reduce fibrosis in liver, oral mucosa, and peritoneum, investigated as a potential candidate for prevention of peridural fibrosis.

Method: Twelve adult New Zealand white male rabbits were divided into control (n = 5) and ALA groups (n = 7). Laminectomy of lumbar spine was performed and ALA was applied on the exposed dura mater topically in ALA group.

Results: According to histological peridural grading, the ALA group (median grade 1) showed significantly less peridural fibrosis than the control group (median grade 3, p = 0.005).

Conclusions: ALA is a promising substance in the prevention of peridural fibrosis, especially in early preoperative and postoperative period.
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http://dx.doi.org/10.1007/s00701-012-1382-5DOI Listing
July 2012

Renal scarring and osteopontin gene C/T polymorphism in children with primary vesicoureteral reflux.

Indian Pediatr 2012 Apr 1;49(4):311-3. Epub 2011 Nov 1.

Department of Pediatric Nephrology, Dortcelik Children Hospital, Bursa, Turkey.

We examined for osteopontin (OPN) gene C/T polymorphism in 78 patients (53 girls) with vesicoureteric reflux, with or without renal scarring. The T allele frequency was associated with a significantly increased risk (26.4 fold) of renal scarring.
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http://dx.doi.org/10.1007/s13312-012-0038-0DOI Listing
April 2012

Bayesian models and algorithms for protein β-sheet prediction.

IEEE/ACM Trans Comput Biol Bioinform 2011 Mar-Apr;8(2):395-409

Department of Genome Sciences, University of Washington, Genome Sciences, Box 357456, 1705 NE Pacific St., Seattle, WA 98195-5065, USA.

Prediction of the 3D structure greatly benefits from the information related to secondary structure, solvent accessibility, and nonlocal contacts that stabilize a protein's structure. We address the problem of \beta-sheet prediction defined as the prediction of \beta--strand pairings, interaction types (parallel or antiparallel), and \beta-residue interactions (or contact maps). We introduce a Bayesian approach for proteins with six or less \beta-strands in which we model the conformational features in a probabilistic framework by combining the amino acid pairing potentials with a priori knowledge of \beta-strand organizations. To select the optimum \beta-sheet architecture, we significantly reduce the search space by heuristics that enforce the amino acid pairs with strong interaction potentials. In addition, we find the optimum pairwise alignment between \beta-strands using dynamic programming in which we allow any number of gaps in an alignment to model \beta-bulges more effectively. For proteins with more than six \beta-strands, we first compute \beta-strand pairings using the BetaPro method. Then, we compute gapped alignments of the paired \beta-strands and choose the interaction types and \beta--residue pairings with maximum alignment scores. We performed a 10-fold cross-validation experiment on the BetaSheet916 set and obtained significant improvements in the prediction accuracy.
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http://dx.doi.org/10.1109/TCBB.2008.140DOI Listing
June 2011

A rare emergency condition in neurosurgery: foot drop due to Paget's disease.

Turk Neurosurg 2009 Apr;19(2):208-10

Maltepe University School of Medicine, Neurosurgery Department, Istanbul, Turkey.

Paget's disease is a chronic, focal skeletal disorder that usually affects the pelvis and spine. Spinal cases are generally asymptomatic; in the symptomatic cases, the neurological dysfunctions are related to non-compressive vascular defects, hemorrhage, sarcomatoid degeneration, spinal stenosis, or pathological fractures, primarily in the lumbar region. The Neurosurgeon should have a fundamental understanding of the complications of Paget's disease and should be familiar with the indications for treatment, as well as available medical and surgical therapies. In the present paper, we report a case of Paget's disease that presented with an isolated foot drop due to a pathological fracture of L5 vertebra, and then discuss the therapeutic strategies presented in the literature.
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April 2009

Training set reduction methods for protein secondary structure prediction in single-sequence condition.

Annu Int Conf IEEE Eng Med Biol Soc 2007 ;2007:5025-8

School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA.

Orphan proteins are characterized by the lack of significant sequence similarity to database proteins. To infer the functional properties of the orphans, more elaborate techniques that utilize structural information are required. In this regard, the protein structure prediction gains considerable importance. Secondary structure prediction algorithms designed for orphan proteins (also known as single-sequence algorithms) cannot utilize multiple alignments or alignment profiles, which are derived from similar proteins. This is a limiting factor for the prediction accuracy. One way to improve the performance of a single-sequence algorithm is to perform re-training. In this approach, first, the models used by the algorithm are trained by a representative set of proteins and a secondary structure prediction is computed. Then, using a distance measure, the original training set is refined by removing proteins that are dissimilar to the given protein. This step is followed by the re-estimation of the model parameters and the prediction of the secondary structure. In this paper, we compare training set reduction methods that are used to re-train the hidden semi-Markov models employed by the IPSSP algorithm [1]. We found that the composition based reduction method has the highest performance compared to the alignment based and the Chou-Fasman based reduction methods. In addition, threshold-based reduction performed better than the reduction technique that selects the first 80% of the dataset proteins.
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http://dx.doi.org/10.1109/IEMBS.2007.4353469DOI Listing
April 2008

A male infant with bilateral upper urinary tract dilatation and recurrent infection: answer.

Pediatr Nephrol 2007 Sep 17;22(9):1269-71. Epub 2007 May 17.

Department of Pediatric Nephrology, Ministry of Health Cekirge Children's Hospital, Bursa, Turkey.

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http://dx.doi.org/10.1007/s00467-007-0506-2DOI Listing
September 2007

A male infant with bilateral upper urinary tract dilatation and recurrent infection: question.

Pediatr Nephrol 2007 Sep 17;22(9):1267-8. Epub 2007 May 17.

Department of Pediatric Nephrology, Ministry of Health Cekirge Children's Hospital, Bursa, Turkey.

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http://dx.doi.org/10.1007/s00467-007-0511-5DOI Listing
September 2007