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Biomedical subjects

M Das

Publications and source records attributed to M Das.

At least 73 records · Page 4Linked to original sources
PubMed1999

Mutagenic and genotoxic effects of theophylline and theobromine in Salmonella assay and in vivo sister chromatid exchanges in bone marrow cells of mice.

The mutagenic and genotoxic effects of two methylxanthines, theophylline (TH) and theobromine (TB), were assessed in the Ames mutagenicity assay (in strains TA97a, TA100, TA102 and TA104) and in vivo sister chromatid exchanges (SCEs) in bone marrow cells of mice. These are the two most commonly used nervous system stimulators throughout the world. TH is used in the long-term treatment of asthma. Bacterial mutagenicity assay showed very weak mutagenic effects of both drugs in Salmonella strains TA102 and TA104 only in certain concentrations when S9 was added to it. No mutagenic effects were observed in any other strains used in this assay either with or without metabolic activation. But results of in vivo SCE assay indicate that these two drugs can induce significant SCE in bone marrow cells of mice.

Animals↗
PubMed1999

Proconvulsive effect of tea (Camellia sinensis) in mice.

Investigations were carried out to evaluate the effect of acute and chronic administration of both black and green tea on three models of experimentally induced convulsions in mice. Tea extract (both black and green) significantly accelerated the onset of convulsion, increased the duration of convulsion and mortality in mice. Since both the extracts failed to alter the GABA level in brain, based on the earlier report that both black and green tea might act on Ca(2+) channels, it can be suggested that the observed proconvulsive effect of tea is not mediated through GABA but through Ca(2+) channels.

Animals↗
PubMed1999

Hypoxia induces cell-specific changes in gene expression in vascular wall cells: implications for pulmonary hypertension.

Mammals respond to reduced oxygen concentrations (hypoxia) in many different ways at the systemic, local, cellular and molecular levels. Within the pulmonary circulation, exposure to chronic hypoxia has been demonstrated to illicit increases in pulmonary artery pressure as well as dramatic structural changes in both large and small vessels. It has become increasingly clear that the response to hypoxia in vivo is differentially regulated at the level of specific cell types within the vessel wall. For instance, in large pulmonary blood vessels there is now convincing evidence to suggest that the medial layer is made up of many different subpopulations of smooth muscle cells. In response to hypoxia there are remarkable differences in the proliferative and matrix producing responses of these cells to the hypoxic environment. Some cell populations proliferate and increase matrix protein synthesis, while in other cell populations no apparent change in the proliferative or differentiation state of the cell takes place. In more peripheral vessels, the predominant proliferative changes in response to hypoxia in the pulmonary circulation occur in the adventitial layer rather than in the medial layer. Here again, specific increases in proliferation and matrix protein synthesis take place. Accumulating evidence suggests that the unique responses exhibited by specific cell types of hypoxia in vivo can be modeled in vitro. We have isolated, in culture, specific medial cell populations which demonstrate significant increases in proliferation in response to hypoxia, and others which exhibit no change or, in fact, a decrease in proliferation under hypoxic conditions. We have also isolated and cloned several unique populations of adventitial fibroblasts. There is good evidence that only certain fibroblast populations are capable of responding to hypoxia with an increase in proliferation. We have begun to elucidate the signaling pathways which are activated in those cell populations that exhibit proliferative responses to hypoxia. We show that hypoxia, in the absence of serum or mitogens, specifically activates select members of the protein kinase C isozyme family, as well as members of the mitogen-activated protein kinase (MAPK) family of proteins. This selective activation appears to take place in response to hypoxia only in those cells exhibiting a proliferative response, and antagonists of this pathway inhibit the response. Thus, there appear to be cells within each organ that demonstrate unique responses to hypoxia. A better understanding of why these cells exist and how they specifically transduce hypoxia-mediated signals will lead to a better understanding of how the changes in the pulmonary circulation take place under conditions of chronic hypoxia.

Animals↗
PubMed1999

The neural mechanism of rectal motility response induced by the epicardial application of lactic acid.

The epicardial application of lactic acid induced a biphasic rectal motility response in lightly anaesthetised, open-chested and artificially ventilated cats. This rectal biphasic response is reflexogenic in nature as epicardial lignocaine abolished such response. This rectal biphasic response is abolished by cardiac sympathectomy and reprecipitated by left inferior cardiac afferent nerve stimulation. Such response is also abolished by sacral ventral rhizotomy and reproduced by stimulation of the peripheral cut end of split sacral ventral roots. This indicates that the afferent and efferent pathways for such reflex are lying in the cardiac sympathetic and sacral pelvic nerves, respectively. The higher centers involved for such reflex are lying above the mid-collicular level of the brain as decerebration at the mid-collicular level completely abolished such type of rectal response. Furthermore, the relaxation phase and contraction phase of such rectal response are mediated through nitric oxide release and cholinergic neurones, respectively, as NG-nitro-L-arginine and atropine abolished relaxation and contraction phase of the rectal response, respectively.

Animals↗
PubMed1999

Negligible male gene flow across ethnic boundaries in India, revealed by analysis of Y-chromosomal DNA polymorphisms.

From the historically prevalent social structure of Indian populations it may be predicted that there has been very little male gene flow across ethnic boundaries. To test this finding, we have analyzed DNA samples of individuals belonging to 10 ethnic groups, speaking Indo-European or Austroasiatic languages and inhabiting the eastern and northern regions of India. Eight Y-chromosomal markers, two biallelic and six microsatellite, were studied. All populations were monomorphic for the deletion allele at the YAP (DYS287) locus and for the 119-bp allele at the DYS288 locus. Y-chromosomal haplotypes were constructed on the basis of one RFLP locus and five microsatellite loci. The haplotype distribution among the groups showed that different ethnic groups harbor nearly disjoint sets of haplotypes. This indicates that there has been virtually no male gene flow among ethnic groups. Analysis of molecular variance revealed that there was significant haplotypic variation between castes and tribes, but nonsignificant variation among ranked caste clusters. Haplotypic variation attributable to differences in geographical regions of habitat was also nonsignificant.

DNA↗
PubMed1999

Toxicological impact of benzenehexachloride on the behaviour and neuropathology of Heteropneustes fossilis.

Toxicological Impact of Benzenehexachloride on the behaviour and Neuropathology of Heteropneustes fossilis. Organochlorine pesticides are widely used in the vast agricultural fields of Assam, India. Run-offs from treated fields contaminates nearby bodies of water with organochlorine compounds, which are neurotoxic to the ichthyofouna. The present work was designed to study the effect of bezenehexachloride on the behaviour and histopathology of Heteropneustes fossilis, as an experimental model. The experimental fish were exposed to different concentrations of the pesticide for 72 hours. After exposure, the fish exhibited various behavioural changes. Histopathological examination of brain tissue revealed cytopathic and gross histopathological alterations, including necrosis and infractional changes. These results are consistent with the finding that organochlorides cause neurotoxic effects.

Animals↗
PubMed1998

Antigenicity of fullerenes: antibodies specific for fullerenes and their characteristics.

The recent interest in using Buckminsterfullerene (fullerene) derivatives in biological systems raises the possibility of their assay by immunological procedures. This, in turn, leads to the question of the ability of these unprecedented polygonal structures, made up solely of carbon atoms, to induce the production of specific antibodies. Immunization of mice with a C60 fullerene derivative conjugated to bovine thyroglobulin yielded a population of fullerene-specific antibodies of the IgG isotype, showing that the immune repertoire was diverse enough to recognize and process fullerenes as protein conjugates. The population of antibodies included a subpopulation that crossreacted with a C70 fullerene as determined by immune precipitation and ELISA procedures. These assays were made possible by the synthesis of water-soluble fullerene derivatives, including bovine and rabbit serum albumin conjugates and derivatives of trilysine and pentalysine, all of which were characterized as to the extent of substitution and their UV-Vis spectra. Possible interactions of fullerenes with the combining sites of IgG are discussed based on the physical chemistry of fullerenes and previously described protein-fullerene interactions. They remain to be confirmed by the isolation of mAbs for x-ray crystallographic studies.

Animals↗
PubMed1998

Cloning, sequencing and expression of the flagellin core protein and other genes encoding structural proteins of the Vibrio cholerae flagellum.

Vibrio cholerae is a Gram-negative bacterium with a single polar flagellum. Motility is an important virulence factor for this non-invasive pathogen. We cloned and sequenced a locus in V. cholerae V86 (El Tor, Inaba) that contained five different structural genes of the flagellum. The cloned genes and their products were assigned names and functions based on homology with sequences of similar genes and their products from other related bacteria. All of these genes of V. cholerae V86, namely, flgI, J, M, L and flaA, were transcribed in the same direction. These genes respectively encoded the P- and L-ring proteins, the hook-associated proteins 1 and 3 and the flagellin core protein of the flagellum. Our data indicated the presence of more than one flagellar locus in V. cholerae which could provide a means of immunoavoidance during infection. When compared with homologs in other bacteria, the flagellin core protein of V. cholerae exhibited conservation in the N- and C-termini, but had diverged in the central region.

Amino Acid Sequence↗
PubMed1998

Enhancement of transcriptional activity of T7 RNA polymerase by guanidine hydrochloride.

T7 RNA polymerase shows an increase in processive transcription in the presence of low concentrations of guanidine hydrochloride (GdnCl) upto 60 mM, which is not observed when the enzyme is treated with urea. Higher concentrations of the denaturant lead to a progressive loss in the processive transcriptional activity of the enzyme. We have attempted to explain the above phenomenon in terms of the structural change in the enzyme. Fluorescence and CD studies suggest that the tertiary structure of the native enzyme undergoes an alteration upon addition of low concentration of guanidine hydrochloride. This is also indicated from the decreased susceptibility of the enzyme to limited proteolysis by trypsin.

Bacteriophage T7↗
PubMed1998

Characterization of an abundant short interspersed nuclear element (SINE) present in Canis familiaris.

A short interspersed nuclear element (Can SINE) of approximately 130-150 bp was cloned and characterized from Canis familiaris. We demonstrate that this element is interspersed, present approximately every 5-8.3 kbp, and many are sufficiently close to allow IRS (interspersed repetitive DNA sequences) PCR. Sequence analysis of > 20 Can SINEs from the dog has identified a conserved region that was used to design oligonucleotides for IRS PCR. Since Can SINEs are not present in human or rodent genomes, IRS PCR using oligonucleotides directed to the conserved region of Can SINEs can be used to simplify analysis of canid DNA in somatic cell hybrids, as well as in large insert cloning vectors. We demonstrate that the canid IRS products are polymorphic and could be developed as genetic markers for filter-based genotyping in this organism.

Animals↗
PubMed1998

Role of cytochrome P-450 in quinalphos toxicity: effect on hepatic and brain antioxidant enzymes in rats.

Quinalphos (QP), an organophosphate pesticide, is used in controlling the pests of a variety of crops. To understand the mechanism of the metabolic basis of the toxicity of QP it was thought pertinent to study the role of cytochrome P-450 (P450) and antioxidant enzyme systems. Albino rats treated orally with QP (0.52 and 1.04 mg/kg body weight) for 60 days showed a significant decrease in body, brain and liver weights. Hepatic P450 content and its dependent monooxygenases, namely aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin-O-deethylase (ERD), were induced to 1.8-2.5-fold, while neuronal AHH was induced to 1.8-fold following QP treatment (1.04 mg/kg) to animals. The hepatic antioxidant defence system, comprising catalase, glutathione (GSH) reductase, superoxide dismutase (SOD) and GSH peroxidase, was also significantly increased in QP-treated animals, while in the brain only catalase was increased and GSH reductase decreased. There was no significant change in hepatic GSH content and lipid peroxide levels in QP treated animals at any dose group in comparison with the control group. Pretreatment of rats with phenobarbitone (PB) or 3-methylcholanthrene (MC) (P450 inducers) prevented mortality caused by the LD50 dose of QP, whereas pretreatment with cobalt chloride (a P450 inhibitor) enhanced the mortality rate to 100% within 3 days. From the above study it can be inferred that the toxicity of QP may be due to the parent compound or its metabolite(s) produced prior to P450 oxidation and that the induction of P450 system by QP may be a defence mechanism.

Acetylcholinesterase↗
PubMed1998

The views of senior students and young doctors of their training in a skills laboratory.

The study was carried out in the Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates (UAE) University, UAE, where a skills laboratory was set up in 1988 to train medical students in clinical skills before they use such skills on patients. The students learn clinical skills using simulated patients, models and mannequins. The training starts in the first year of the 6-year undergraduate curriculum and continues until the end of the fourth year, after which students rotate through the clinical specialties. This study sought to identify: (1) the views of senior clerks (sixth year) and interns (first postgraduate year) regarding the clinical skills training in the skills laboratory (SKL) during the early years of the medical curriculum; (2) the differences in views between senior clerks and interns; (3) the differences in views between women and men students. Students' views about communication, interviewing, physical examination, therapeutic, diagnostic and laboratory skills were investigated. The results indicated that prior training in clinical skills was helpful to the senior clerks and the interns. Statistically significant differences in opinion were noted between the senior clerks and the interns, the interns being more positive about the usefulness of the SKL training compared with learning clinical skills directly on patients. There was no difference between men and women students except that women students were not comfortable with allowing their peers to examine any part of their bodies. The findings of the study have direct implications for the SKL programme.

Clinical Clerkship↗
PubMed1998

Self and tutor evaluations in problem-based learning tutorials: is there a relationship?

It is now recognized that acquiring specific skills in self-evaluation helps students in a more general appraisal of their overall performance. Self- and peer-evaluation skills are essential prerequisites for the success of every doctor in maintaining professional competence. In the Faculty of Medicine and Health Sciences (FMHS) of the United Arab Emirates, problem-based learning (PBL) is instituted in the first year. Self-evaluation by students and tutor rating of students' performances are an integral part of the PBL tutorials. This has provided the opportunity to conduct a systematic study of the role of self-evaluation by students as distinct from the tutor evaluation of students in the PBL tutorials for five themes. The study sample included all preparatory year (first-year) students who joined the FMHS in 1994 and 1995. A total number of 64 students participated, of whom 17 (26%) were male and 47 (74%) female. Mean self-evaluation scores were high throughout the module and did not follow any trend from theme one to theme five. While self and tutor scores were similar, male student self-evaluation scores were higher than for female students on overall scores. The sharing of assessment reports between students and tutors has been perceived to be a useful tool for the students' development of the skills of analysis, differentiation and critical appraisal.

Adult↗
PubMed1998

Facility with the English language and problem-based learning group interaction: findings from an Arabic setting.

The Faculty of Medicine and Health Sciences (FMHS), United Arab Emirates (UAE) University is in a unique position to explore issues related to English language proficiency and medical student performance. All students entering the FMHS have English as a second language. This study focused on the issues of students' proficiency in English as measured by the TOEFL test, student background factors and interaction in problem-based learning (PBL) groups. Using a modification of Bales Interaction Process Analysis, four problem-based learning groups were observed over four thematic units, to measure the degree of student interaction within PBL groups and to compare this to individual TOEFL scores and key background variables. The students' contributions correlated highly with TOEFL test results in the giving of information (range r = 0.67-0.74). The female students adhered to interacting in English during group sessions, whereas the male students were more likely to revert to using Arabic in elaborating unclear phenomena (p < 0.01). The educational level of the student's mother was highly predictive of TOEFL scores for the male students, but not for female students. Multivariate analysis was undertaken to analyse the relative contribution of the TOEFL, parental education and years of studying in English. The best predictor of students' contributions in PBL groups was identified as TOEFL scores. The study demonstrates the importance of facilitating a locally acceptable level of English proficiency prior to admission to the FMHS. However, it also highlights the importance of not focusing only on English proficiency but paying attention to additional factors in facilitating medical students in maximizing benefits from interactions in PBL settings.

Clinical Competence↗
PubMed1998

Pseudo-affinity column chromatography based rapid purification procedure for T7 RNA polymerase.

Based on the observation that T7 RNAP binds reversibly to the polyaromatic sulphonated triazine dye, cibacron blue, we have developed a rapid purification procedure for T7 RNAP. It employs chromatography of the ammonium sulfate fraction through a blue sepharose column, which has the dye coupled to the solid sepharose support. The enzyme can be eluted by 2M NaCl or 1M NaCl together with 1 mM UTP. These methods are compared with another purification procedure using ion-exchange column chromatography. All of them yield essentially pure T7 RNAP with high specific activity.

Chromatography, Affinity↗
PubMed1998

Antisera to selected outer membrane proteins of Vibrio cholerae protect against challenge with homologous and heterologous strains of V. cholerae.

Each year cholera epidemics occur in various places around the world. Though there is no effective vaccine against cholera, people who recover from an infection usually have prolonged immunity to the disease. Sera from convalescent patients contain antibodies to a number of outer membrane proteins (OMPs) of V. cholerae. We isolated several OMPs (43, 42, 30, and 22 kDa) from V. cholerae V86 E1 Tor Inaba, sequenced their amino-termini, and generated hyperimmune sera against them in rabbits. Antisera to the 43-, 42-, and 22-kDa OMPs, but not the preimmune sera, significantly reduced V. cholerae-induced fluid secretion seen in rabbit intestinal loops challenged with the homologous strain. In addition, a combination of antisera to the different OMPs reduced the fluid secretion induced by challenge with heterologous V. cholerae Ogawa and O139 strains. These results have significance in the development of vaccines to V. cholerae, as the hyperexpression of these OMP encoding genes in vaccine strains may improve the efficacy of cholera vaccines.

Adhesins, Bacterial↗
PubMed1998

Respiratory symptoms and lung function in garage workers and taxi drivers.

The aim of this study was to determine the prevalence of some respiratory symptoms and possible diseases among occupationally-exposed garage workers and taxi drivers. This study involved 158 garage workers and 165 taxi drivers, matched for age, sex, nationality and duration of employment. The mean age of 158 Indian subcontinent garage workers was 34.4 +/- 10.4 years; their mean height and weight were 167.7 +/- 6.6 cm and 72.0 +/- 12.3 kg respectively, and the mean duration of employment garage workers was 8.8 +/- 7.6 years. The mean age of 165 Indian subcontinent male taxi drivers was 34.5 +/- 7.7 years; their mean height and weight were 168.7 +/- 6.1 cm and 71.3 +/- 12.6 kg respectively; and the mean duration of employment was 7.5 +/- 5.4 years. The data on chronic respiratory symptoms showed that garage workers had higher prevalence of symptoms than taxi drivers being significantly greater for chronic phlegm, (p < 0.007); dyspneoa (p < 0.001); and sinusitis (p < 0.03). A higher prevalence of all acute symptoms was recorded in garage workers than in taxi drivers, although the differences were significant only for throat (p < 0.02), hearing problems (p < 0.002); nose (dryness, bleeding and secretion) (p < 0.008); and low back pain (p < 0.05). Almost all forced spirometric tests in the exposed garage workers were lower than in taxi drivers. The results of stepwise multiple regression analysis showed that only phlegm, sinusitis, hearing problems, nasal catarrh, throat, low back pain, smoking and FEF25-75, variables were statistically significant predictors as risk factors. In conclusion, the present study suggests that a high prevalence of respiratory symptoms is associated with exposure to motor vehicle exhaust emission in garage working places. Long-term working as garage workers in the United Arab Emirates (UAE), may be associated with the development of chronic respiratory symptoms and have effects on their daily life and health.

Adult↗