Publications by authors named "Victor Contreras"

17 Publications

  • Page 1 of 1

Adjusting single-axis acoustic levitators in real time using rainbow schlieren deflectometry.

Rev Sci Instrum 2021 Jan;92(1):015107

Computer Science, Public University of Navarre, Pamplona 31006, Navarre, Spain.

Acoustic levitation uses focused high-intensity airborne ultrasound to hold particles in mid-air. It is becoming an important tool for experiments in spectrometry, lab-on-a-droplet, and display technologies. Nowadays, arrays of multiple small transducers can be used to build acoustic levitators; however, their performance depends on the optimal alignment. This work describes a simple method capable of visualizing a 2D projection of the acoustic field in real time using rainbow schlieren deflectometry. Good agreement was found between the images obtained with this technique and simulations of the acoustic pressure. It was also found that the maximum amplitudes of the field were obtained with the levitator aligned so that the power consumption was minimum, showing another simple and affordable way to adjust the levitators. As a result of the alignment optimization, it was possible for the first time to levitate steel and mercury in a levitator constructed with off-the-shelf components. The schlieren technique was applied to the TinyLev acoustic levitation system, but it can be applied to visualize the acoustic potential produced by different types of levitation systems.
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http://dx.doi.org/10.1063/5.0013347DOI Listing
January 2021

Sequential Collinear Photofragmentation and Atomic Absorption Spectroscopy for Online Laser Monitoring of Triatomic Metal Species.

Sensors (Basel) 2020 Jan 18;20(2). Epub 2020 Jan 18.

Photonics Laboratory, Physics Unit, Tampere University, Post Office Box 692, FI-33101 Tampere, Finland.

Industrial chemical processes are struggling with adverse effects, such as corrosion and deposition, caused by gaseous alkali and heavy metal species. Mitigation of these problems requires novel monitoring concepts that provide information on gas-phase chemistry. However, selective optical online monitoring of the most problematic diatomic and triatomic species is challenging due to overlapping spectral features. In this work, a selective, all-optical, in situ gas-phase monitoring technique for triatomic molecules containing metallic atoms was developed and demonstrated with detection of PbCl. Sequential collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) enables determination of the triatomic PbCl concentration through detection of released Pb atoms after two consecutive photofragmentation processes. Absorption cross-sections of PbCl, PbCl, and Pb were determined experimentally in a laboratory-scale reactor to enable calibration-free quantitative determination of the precursor molecule concentration in an arbitrary environment. Limit of detection for PbCl in the laboratory reactor was determined to be 0.25 ppm. Furthermore, the method was introduced for in situ monitoring of PbCl concentration in a 120 MW power plant using demolition wood as its main fuel. In addition to industrial applications, the method can provide information on chemical reaction kinetics of the intermediate species that can be utilized in reaction simulations.
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http://dx.doi.org/10.3390/s20020533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7014508PMC
January 2020

Incorporating the Patient Voice Into Practice Improvement: A Role for Medical Trainees.

Fam Med 2019 04;51(4):348-352

Division of Primary Care and Population Health, Department of Medicine, Stanford University School of Medicine.

Background And Objectives: Many primary care clinics rely on providers and staff to generate quality improvement (QI) ideas without explicitly including patients. However, without understanding patient perspectives, clinics may miss areas for improvement. We identified practice improvement opportunities using a medical student-driven pilot of QI design that incorporates the patient voice and explored provider/staff perceptions of patient perspectives.

Methods: One medical student interviewed eight patients for their perspectives on QI opportunities at a university-based primary care practice. Two trainees independently coded interview transcripts using directed content analysis (final codebook: 11 themes) and determined frequency of mentions for each theme. We surveyed 11 providers/staff by asking them to select 5 of the 11 themes and place them in rank order based on their perceptions of patient concerns; their surveys were aggregated into one ranked list.

Results: Patients most frequently identified the following themes as QI opportunities: relationship (ie, feeling of personal connection with providers/staff), specialty care, convenience, sustainability, and goal follow-up. While patients frequently identified relationship (rank=1) and goal follow-up (rank=3) as QI opportunities, the provider/staff top five list did not include relationship (rank=10) or goal follow-up (rank=7).

Conclusions: Our study demonstrates two things: (1) there are areas of discordance between provider/staff perceptions and patient perspectives regarding practice improvement opportunities; and (2) medical students can participate meaningfully in the QI process. By harnessing patient perspectives with the help of medical trainees, clinics may better understand patient concerns and avoid potential QI blind spots.
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http://dx.doi.org/10.22454/FamMed.2019.386631DOI Listing
April 2019

Propofol pharmacokinetic and pharmacodynamic profile and its electroencephalographic interaction with remifentanil in children.

Paediatr Anaesth 2018 12 11;28(12):1078-1086. Epub 2018 Oct 11.

Department of Anesthesiology, University of Auckland, Auckland, New Zealand.

Background: Propofol and remifentanil are commonly combined during total intravenous anesthesia. The impact of remifentanil in this relationship is poorly quantified in children. Derivation of an integrated pharmacokinetic and pharmacodynamic propofol model, containing remifentanil pharmacodynamic interaction information, enables propofol effect-site target-controlled infusion in children with a better prediction of its hypnotic effect when both drugs are combined.

Aims: We designed this study to derive an integrated propofol pharmacokinetic-pharmacodynamic model in children and to describe the pharmacodynamic interaction between propofol and remifentanil on the electroencephalographic bispectral index effect.

Methods: Thirty children (mean age: 5.45 years, range 1.3-11.9; mean weight: 23.5 kg, range 8.5-61) scheduled for elective surgery with general anesthesia were studied. After sevoflurane induction, maintenance of anesthesia was based on propofol and remifentanil. Blood samples to measure propofol concentration were collected during anesthesia maintenance and up to 6 hours in the postoperative period. Bispectral index data were continuously recorded throughout the study. A pharmacokinetic-pharmacodynamic model was developed using population modeling. The Greco model was used to examine the pharmacokinetic-pharmacodynamic interaction between propofol and remifentanil for BIS response RESULTS: Propofol pharmacokinetic data from a previous study in 53 children were pooled with current data and simultaneously analyzed. Propofol pharmacokinetics were adequately described by a three-compartment distribution model with first-order elimination. Theory-based allometric relationships based on TBW improved the model fit. The Greco model supported an additive interaction between propofol and remifentanil. Remifentanil showed only a minor effect in BIS response.

Conclusion: We have developed an integrated propofol pharmacokinetic-pharmacodynamic model that can describe the pharmacodynamic interaction between propofol and remifentanil for BIS response. An additive interaction was supported by our modeling analysis.
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http://dx.doi.org/10.1111/pan.13486DOI Listing
December 2018

Chemical elemental analysis of single acoustic-levitated water droplets by laser-induced breakdown spectroscopy.

Opt Lett 2018 May;43(10):2260-2263

Laser-induced breakdown spectroscopy is presented for trace element detection of liquid samples by analyzing a single droplet levitated by ultrasonic waves. A single liquid droplet is placed in the node of a standing acoustic wave produced by a uniaxial levitator for further chemical analysis. The acoustic levitator consists of a commercial Langevin-type transducer, attached to a concave mechanical amplifier, and a concave reflector. A micro-syringe was used to manually place individual liquid droplet samples in the acoustic levitation system. For chemical analysis, a laser-induced plasma is produced by focusing a single laser pulse on the levitated water droplet after it partially dries. The performance of the acoustic levitator on micron-sized droplets is discussed, and the detection of Ba, Cd, Hg, and Pb at parts per million (milligrams/liter) and sub-parts per million levels is reported. The process, starting from placing the sample in the acoustic levitator and ending on the chemical identification of the traces, takes a few minutes. The approach is particularly interesting in applications demanding limited volumes of liquid samples and relative simple and inexpensive techniques.
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http://dx.doi.org/10.1364/OL.43.002260DOI Listing
May 2018

[Thrombotic and haemorrhagic complications in patients with cerebral aneurysms treated by endovascular approach and their association with the use of antiplatelet agents: Descriptive evaluation].

Neurocirugia (Astur : Engl Ed) 2018 Jan - Feb;29(1):18-24. Epub 2017 Nov 27.

Pontificia Universidad Javeriana, Bogotá, Colombia.

Objective: The protocol for optimal antiplatelet therapy to prevent thrombotic complications following brain aneurysm embolisation is not clear. Our objective is to describe the characteristics of patients presenting with thrombotic or haemorrhagic complications secondary to endovascular treatment.

Methods: A cross sectional descriptive study was performed, which included all patients that required endovascular treatment for brain aneurysm at San Ignacio University Hospital from November 2007 to January 2016. Thrombotic and haemorrhagic complications over six months of follow-up were assessed, considering the premedication regimen with antiplatelet agents, location, size of the aneurysm and embolisation technique performed.

Results: 122 patients were evaluated, on whom 130 procedures were performed for endovascular treatment of brain aneurysms. Thrombotic complications were more frequent in patients who did not receive premedication (25%) compared to those who did receive an antiplatelet treatment regimen (standard dose 3.87% or loading dose 8.70%), and this difference was statistically significant (P=.043).

Conclusions: Thromboembolic events are the most common complication of brain aneurysm embolisation. Both our study and the literature suggest that the use of dual antiplatelet therapy with aspirin and clopidogrel lowers the rate of symptomatic thromboembolic complications, regardless of the administration protocol.
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http://dx.doi.org/10.1016/j.neucir.2017.08.002DOI Listing
September 2018

Growth arrest and morphological changes triggered by emodin on Trypanosoma cruzi epimastigotes cultivated in axenic medium.

Biochimie 2017 Nov 10;142:31-40. Epub 2017 Aug 10.

Departamento de Biología Celular, Universidad Simón Bolívar, Caracas, Venezuela. Electronic address:

Emodin is an anthraquinone obtained from Rheum palmatum rootstocks. Here we tested the cytotoxic effects of emodin on Trypanosoma cruzi epimastigotes, as well as the morphological changes that were induced by this compound in the parasite. Emodin was permeable and blocked in vitro cell division of T. cruzi epimastigotes in axenic medium, causing growth arrest in a dose-dependent but reversible manner. Emodin-exposed epimastigotes underwent duplication of organelles, such as the nucleus, kinetoplast and flagellum, but were incapable of completing cytokinesis. Neither elongation of the parasite body nor appearance of the regular longitudinal cleavage furrow was displayed, suggesting that emodin is most likely affecting components of the parasite cytoskeleton. Moreover, drug-treated parasites acquired alterations such as protuberances, folds and indentations on their membrane surface. Since emodin has been shown to be a potent protein kinase CK2 inhibitor, and we have previously described an association between tubulin and CK2 in T. cruzi epimastigotes (De Lima et al. Parasitology132, 511-523, 2006), we also measured the indirect effect of the drug on tubulin. Incubation of epimastigotes with axenic medium containing emodin hindered the endogenous phosphorylation of tubulin in whole-cell parasite extracts. All our results suggested that the parasite CK2 may be important for the maintenance of the morphology and for the regulation of mitosis-cytokinesis transition in T. cruzi epimastigotes.
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http://dx.doi.org/10.1016/j.biochi.2017.08.005DOI Listing
November 2017

Enhanced self-mixing interferometry based on volume Bragg gratings and laser diodes emitting at 405-nm wavelengths.

Opt Lett 2017 Jun;42(11):2221-2223

Self-mixing interferometry (SMI) represents a robust, self-aligned technique for metrology applications. Recently, it has been shown that the detection of the frequency-modulated (FM) signal enhances the conventional SMI signal based on the amplitude modulation. Here, an all-optical, simple and effective alternative approach to detect the FM self-mixing signal is presented. We demonstrate the enhanced self-mixing approach using a laser diode emitting at 405 nm and a volume Bragg grating (VBG) to map frequency to intensity modulations for further optical detection. Our approach overcomes the spectral range limitation of the edge filtering approach based on molecular absorption filters, since the VBGs can be fabricated at any spectral range.
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http://dx.doi.org/10.1364/OL.42.002221DOI Listing
June 2017

Recently differentiated epimastigotes from Trypanosoma cruzi are infective to the mammalian host.

Mol Microbiol 2017 Jun 9;104(5):712-736. Epub 2017 May 9.

Instituto Carlos Chagas, FIOCRUZ, Curitiba, PR, Brazil.

Trypanosoma cruzi, the etiologic agent of Chagas disease, has a complex life cycle in which four distinct developmental forms alternate between the insect vector and the mammalian host. It is assumed that replicating epimastigotes present in the insect gut are not infective to mammalian host, a paradigm corroborated by the widely acknowledged fact that only this stage is susceptible to the complement system. In the present work, we establish a T. cruzi in vitro and in vivo epimastigogenesis model to analyze the biological aspects of recently differentiated epimastigotes (rdEpi). We show that both trypomastigote stages of T. cruzi (cell-derived and metacyclic) are able to transform into epimastigotes (processes termed primary and secondary epimastigogenesis, respectively) and that rdEpi have striking properties in comparison to long-term cultured epimastigotes: resistance to complement-mediated lysis and both in vitro (cell culture) and in vivo (mouse) infectivity. Proteomics analysis of all T. cruzi stages reveled a cluster of proteins that were up-regulated only in rdEpi (including ABC transporters and ERO1), suggesting a role for them in rdEpi virulence. The present work introduces a new experimental model for the study of host-parasite interactions, showing that rdEpi can be infective to the mammalian host.
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http://dx.doi.org/10.1111/mmi.13653DOI Listing
June 2017

Detection of single microparticles in airflows by edge-filter enhanced self-mixing interferometry.

Opt Express 2016 Apr;24(8):8886-94

A laser Doppler velocimetry (LDV) sensor using the edge-filter enhanced self-mixing interferometry (ESMI) is presented based on speed measurements of single microparticles. The ESMI detection utilizes an acetylene edge-filter that maps the frequency modulation of a semiconductor laser into an intensity modulation as the laser wavelength is tuned to the steep edge of the absorption profile. In this work, the ESMI signal was analyzed for aerosol particles of different sizes from 1 μm to 10 μm at a distance of 2.5 m. At this operation range, the signal from single particles of all sizes was successfully acquired enabling particle velocity measurements through the Doppler shifted frequency along the beam axis. For the particular case of 10 μm particles, single aerosol particles were still detected at an unprecedented range of 10 m. A theoretical treatment describing the relation between Mie scattering theory and the self-mixing phenomenon on single-particle detection is presented supporting the experimental results. The results show that the edge-filter enhanced self-mixing technique opens new possibilities for self-mixing detection where longer ranges, lower backscattering laser powers and higher velocities are involved. For example, it can be used as a robust and inexpensive anemometer for LDV applications for airflows with low-number density of microparticles.
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http://dx.doi.org/10.1364/OE.24.008886DOI Listing
April 2016

Edge filter enhanced self-mixing interferometry.

Opt Lett 2015 Jun;40(12):2814-7

Self-mixing interferometry (SMI) represents a simple, robust, and self-aligned technique for metrology applications. Still, its applicability on diffuse targets is limited to distances up to few meters. We present an enhanced approach based on the detection of the frequency-modulated (FM) self-mixing signal. The FM signal detection is achieved using an acetylene edge filter that maps laser frequency variations into intensity variations as the laser wavelength is tuned to the edge of the steep absorption profile. An experimental comparison between the enhanced and the conventional SMI approach is presented. The new approach yields to about two orders of magnitude larger signal-to-noise ratio and extends the applicability of SMI into new fields allowing longer detection ranges and lower backscattering signals.
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http://dx.doi.org/10.1364/OL.40.002814DOI Listing
June 2015

Synthesis and Pharmacological Characterization of Two Novel, Brain Penetrating P2X7 Antagonists.

ACS Med Chem Lett 2013 Apr 12;4(4):419-22. Epub 2013 Mar 12.

Janssen Research and Development, LLC , 3210 Merryfield Row, San Diego, California 92121-1126, United States.

The synthesis and preclinical characterization of two novel, brain penetrating P2X7 compounds will be described. Both compounds are shown to be high potency P2X7 antagonists in human, rat, and mouse cell lines and both were shown to have high brain concentrations and robust receptor occupancy in rat. Compound 7 is of particular interest as a probe compound for the preclinical assessment of P2X7 blockade in animal models of neuro-inflammation.
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http://dx.doi.org/10.1021/ml400040vDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4027403PMC
April 2013

Fast and environmentally friendly quantitative analysis of active agents in anti-diabetic tablets by an alternative laser-induced breakdown spectroscopy (LIBS) method and comparison to a validated reversed-phase high-performance liquid chromatography (RP-HPLC) method.

Appl Spectrosc 2012 Nov;66(11):1294-301

Centro de Investigaciones en Óptica, León, Gto., México.

Laser-induced breakdown spectroscopy (LIBS) is evaluated as a potential analytic technique for rapid screening and quality control of anti-diabetic tablets. This paper proposes a simple LIBS-based method for the quantitative analysis of two active pharmaceutical ingredients (APIs): metformin (Met) and glybenclamide (Gly). In order to quantify both APIs, chlorine (Cl) concentration was estimated by employing the Cl/Br optical emission ratio, where Br was introduced as internal standard. Calibration curves were prepared, achieving linearity higher than 99%. On the other hand, for comparison to the proposed method, an isocratic reversed-phase high-performance liquid chromatography (RP-HPLC) method was also developed for quantitative determination of the same analytes by ultraviolet (UV) detection. The chromatographic separation was achieved on a Phenomenex Hypersil C18, 250 mm × 4.6 mm, 5 μm column. The mobile phase was K(2)HPO(4)/H(3)PO(4)-CH(3)OH and flow rate was 1.0 mL min(-1). The method is linear over a range of 10-60 μg mL(-1) for Gly and 5-30 μg mL(-1) for Met and the correlation coefficients were ≥0.99. Recoveries were found to be in the range of 95-101%. Furthermore, four different commercial brands of each active agent were evaluated by both proposed LIBS and chromatographic methods and results were compared with each other. The comparison was satisfactorily validated by analysis of variance (ANOVA).
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http://dx.doi.org/10.1366/12-06724DOI Listing
November 2012

Cultivation of Trypanosoma cruzi epimastigotes in low glucose axenic media shifts its competence to differentiate at metacyclic trypomastigotes.

Exp Parasitol 2008 Jul 15;119(3):336-42. Epub 2008 Mar 15.

Laboratorio de Protozoología, Centro BioMolP, Universidad de Carabobo, Bárbula, Valencia, Estado Carabobo, Venezuela.

This study offers an insight into why Trypanosoma cruzi epimastigotes lose their capacity to differentiate into metacyclic forms, if maintained in culture media long-term through serial passages. The biological and metabolic behaviour of two T. cruzi strains isolated from various origins (human, opossum), and maintained under two schedules (alternate triatomine/mouse passages and serial culture media) were compared. To determine the effect of the environment on the parasites, the epimastigotes were grown under extreme conditions (high and low glucose concentrations), and the glucose consumption, ammonia production and changes in pH, either in one compartment (along the growth curve) or two compartments (induced metacyclogenesis) were compared. The glucose effect on the stages involved in metacyclogenesis at antigenic level was also evaluated. The results indicate that T. cruzi adapts to various environmental conditions and also that the ability of epimastigotes to undergo metacyclogenesis are influenced by the maintenance schedule. Antigenic profile analysis supports the idea that epimastigotes adapted to culture media do not complete their molecular differentiation into the trypomastigote metacyclic stage. These transition forms conserve some degree of gene expression of the epimastigote stage.
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http://dx.doi.org/10.1016/j.exppara.2008.03.003DOI Listing
July 2008

Morphological comparison of axenic amastigogenesis of trypomastigotes and metacyclic forms of Trypanosoma cruzi.

Mem Inst Oswaldo Cruz 2003 Jan 9;98(1):83-91. Epub 2003 Apr 9.

Laboratorio de Protozoolog a, Centro BioMolP, Facultad de Ciencias de la Salud, Universidad de Carabobo, Valencia, Estado Carabobo, Venezuela.

Amastigogenesis occurs first when metacyclic trypomastigotes from triatomine urine differentiate into amastigotes inside mammalian host cells and a secondary process when tissue-derived trypomastigotes invade new cells and differentiate newly to amastigotes. Using scanning electron microscopy, we compared the morphological patterns manifested by trypomastigotes and metacyclic forms of Trypanosoma cruzi during their axenic-transformation to amastigotes in acidic medium at 37 C. We show here that in culture MEMTAU medium, secondary and primary axenic amastigogenesis display different morphologies. As already described, we also observed a high differentiation rate of trypomastigotes into amastigotes. Conversely, the transformation rate of in vitro-induced-metacyclic trypomastigotes to amastigotes was significantly slower and displayed distinct patterns of transformation that seem environment-dependent. Morphological comparisons of extracelullar and intracellular amastigotes showed marked similarities, albeit some differences were also detected. SDS-PAGE analyses of protein and glycoprotein from primary and axenic extracelullar amastigotes showed similarities in glycopeptide profiles, but variations between their proteins demonstrated differences in their respective macromolecular constitutions. The data indicate that primary and axenic secondary amastigogenesis of T. cruzi may be the result of different developmental processes and suggest that the respective intracellular mechanisms driving amastigogenesis may not be the same.
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http://dx.doi.org/10.1590/s0074-02762003000100012DOI Listing
January 2003

Production of amastigotes from metacyclic trypomastigotes of Trypanosoma cruzi.

Mem Inst Oswaldo Cruz 2002 Dec 20;97(8):1213-20. Epub 2003 Jan 20.

Laboratorio de Protozoolog a, Centro BioMolP, Facultad de Ciencias de la Salud, Universidad de Carabobo, Valencia, Carabobo, Venezuela.

Attempts to recreate all the developmental stages of Trypanosoma cruzi in vitro have thus far been met with partial success. It is possible, for instance, to produce trypomastigotes in tissue culture and to obtain metacyclic trypomastigotes in axenic conditions. Even though T. cruzi amastigotes are known to differentiate from trypomastigotes and metacyclic trypomastigotes, it has only been possible to generate amastigotes in vitro from the tissue-culture-derived trypomastigotes. The factors and culture conditions required to trigger the transformation of metacyclic trypomastigotes into amastigotes are as yet undetermined. We show here that pre-incubation of metacyclic trypomastigotes in culture (MEMTAU) medium at 37 degrees C for 48 h is sufficient to commit the parasites to the transformation process. After 72 h of incubation in fresh MEMTAU medium, 90% of the metacyclic parasites differentiate into forms that are morphologically indistinguishable from normal amastigotes. SDS-PAGE, Western blot and PAABS analyses indicate that the transformation of axenic metacyclic trypomastigotes to amastigotes is associated with protein, glycoprotein and antigenic modifications. These data suggest that (a) T. cruzi amastigotes can be obtained axenically in large amounts from metacyclic trypomastigotes, and (b) the amastigotes thus obtained are morphological, biological and antigenically similar to intracellular amastigotes. Consequently, this experimental system may facilitate a direct, in vitro assessment of the mechanisms that enable T. cruzi metacyclic trypomastigotes to transform into amastigotes in the cells of mammalian hosts.
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http://dx.doi.org/10.1590/s0074-02762002000800025DOI Listing
December 2002

Early and late molecular and morphologic changes that occur during the in vitro transformation of Trypanosoma cruzi metacyclic trypomastigotes to amastigotes.

Biol Res 2002 ;35(1):47-58

Laboratorio de Protozoología, Centro BioMolP, Facultad de Ciencias de la Salud, Universidad de Carabobo, Bárbula, Valencia, Estado Carabobo, Venezuela.

The amastigogenesis primary of T. cruzi occurs naturally when metacyclic trypomastigotes transform into amastigotes within the cells of the mammalian host. The in vitro study of the macromolecular changes that occur over several days during the transformation process should provide significant indications of how the parasite adapts to the mammalian host environment. We show here that metacyclic trypomastigotes pre-incubated at 37 degrees C in a protein-rich medium reach a high degree of transformation to amastigotes when re-incubated in the fresh medium. Giemsa-stained smears show that during the pre-incubation phase, the metacyclic trypomastigotes undergo lengthening at the posterior end and a thinning out of the entire body. SDS-PAGE analysis of polypeptides and glycopeptides or Western blot with stage-specific antisera analyses indicate that the in vitro primary amastigogenesis is associated with abrupt changes in protein, glycoprotein, and stage-specific antigens that occur simultaneously during the first 24 hours of pre-incubation. Since the differentiating system consists of a rich media at 37 degrees C, temperature and medium constitution must trigger a macromolecular differentiation to amastigotes that precedes the morphological transformation by several days. This transformation is associated with the rearrangement of stage-specific antigens and takes place when the culture medium is changed.
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http://dx.doi.org/10.4067/s0716-97602002000100008DOI Listing
September 2002