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Biomedical subjects

S Sinha

Publications and source records attributed to S Sinha.

At least 271 records · Page 15Linked to original sources
PubMed1997

In vitro activation of the human Harvey-ras proto-oncogene by aflatoxin B1.

Activation of ras proto-oncogenes occurs frequently in vivo in chemically induced rodent tumours, including rat hepatomas induced by aflatoxin B1. This study examines the in vitro activation of a human ras gene by this mycotoxin. A plasmid containing the human Ha-ras proto-oncogene, together with a neomycin resistance gene (pECneo), was incubated in vitro with a microsomal system generating aflatoxin B1 8,9-epoxide. Subsequent transfection of the plasmid into mouse NIH 3T3 fibroblasts, followed by G418 selection and s.c. injection of surviving cells into immunodeficient mice demonstrated that the proto-oncogene had acquired transforming capacity. Although a single tumour resulted from similar treatment of incubated unconjugated plasmid, no tumours were produced by a secondary round of transfections using DNA from this tumour. Selective PCR amplification of the human Ha-ras gene in extracted tumour DNA followed by sequencing demonstrated the presence of G-->T transversions either at the first or middle base of codon 12 in tumours resulting from transfection with the aflatoxin-B1-modified pECneo plasmid, but this was not detected in the single tumour resulting from transfection with the unmodified plasmid. Thus, although a mutation in the Ha-ras gene has not been reported for human primary hepatomas occurring in aflatoxin-exposed populations, metabolically activated aflatoxin B1 is capable of mutating this proto-oncogene to its oncogenic form in vitro. No mutations were observed in codon 61. It appears that, in contrast to the frequently reported G-->T transversions in codon 249 of the p53 gene in primary hepatomas in aflatoxin-exposed humans, the failure to detect Ha-ras mutations in these tumours is not due to an inability of aflatoxin B1 to activate this proto-oncogene. The G-->T transversions observed in this study contrast with the most frequent aflatoxin B1 in vivo induced mutations, G-->A transitions in the rat Ki-ras gene. Possible mechanisms for these differences are discussed.

3T3 Cells↗
PubMed1997

Biopsy of hepatic dome lesions: semi-real-time coronal MR guidance technique.

OBJECTIVE: MR imaging, with its coronal imaging capability, may be ideally suited for biopsies of hepatic dome lesions. We are reporting on the successful semi-real-time biopsy of such lesions using a 0.2-T open-configuration MR scanner in five patients. CONCLUSION: MR guidance holds promise for facilitating biopsies of hepatic dome masses.

Adult↗
PubMed1997

Estimation of the left ventricular ejection fraction using a novel multiphase, dark-blood, breath-hold MR imaging technique.

OBJECTIVE: In this paper, we evaluate a recently proposed dual-phase dark-blood MR sequence for estimating the left ventricular ejection fraction, compare Simpson's method of estimation of ejection fraction with a model based on the biplane method, assess the reproducibility of both methods, and finally, test a semiautomated method for contouring the endocardial border. SUBJECTS AND METHODS: An MR pulse sequence was implemented to acquire cardiac images in both diastolic and systolic phases within a single breath-hold. A special magnetization preparation scheme rendered blood dark while a segmented acquisition allowed breath-hold scan times. Five healthy volunteers and five patients with cardiac disease were imaged. Ejection fractions were estimated using (1) long-axis and four-chamber biplane views with an ellipsoid model and (2) a series of short-axis views in combination with Simpson's model. These values of ejection fractions were then compared with values obtained from echocardiography. RESULTS: Estimates of ejection fractions obtained using biplane ellipsoid volume and Simpson's rule methods varied by 14% in healthy volunteers. However, for patients with severe cardiomyopathy, differences between the values of ejection fraction obtained with the two methods varied by as much as 150%. Ejection fraction estimates obtained from MR images with the biplane ellipsoid method and from echocardiography varied by approximately 14% for all subjects. Ejection fraction estimates obtained with the semiautomated algorithm agreed well with estimates obtained with manual contours made by experienced radiologists. Intraobserver variability was low for both the short-axis (3%) and biplane (4%) methods. However, interobserver variability of the biplane method (12%) exceeded that of the short-axis method (4%). Interexamination variability (9%) was the largest factor in determining the reproducibility of the ejection fraction estimates. CONCLUSION: Breath-hold dark-blood MR imaging technique with simultaneous acquisition of a series of short-axis views during systolic and diastolic phases permits rapid and accurate estimates of ejection fractions in healthy subjects and in patients. Model based biplane MR imaging methods are less reliable in patients with global cardiomyopathy. The estimation of ejection fractions can be automated using the proposed contouring algorithm and the dark-blood short-axis views.

Adult↗
PubMed1997

Genotype-phenotype correlation in Duchenne/Becker muscular dystrophy patients seen at Lucknow.

The molecular basis of two allelic forms of muscular dystrophy, Duchenne (DMD) and Becker (BMD), has been explained by frame shift hypothesis. In order to test this hypothesis, deletional mutations in 59 patients confirmed to have DMD and 11 BMD patients were analysed using multiplex polymerase chain reaction and Southern hybridization with dystrophin cDNA probes. Translational reading frame of the dystrophin gene was derived from 'Border type' analysis of exons flanking the intragenic deletions. The correlation between genotype (reading frame) and phenotype (clinical severity) showed higher number of DMD patients (approximately 20%) deviating from the frame shift hypothesis. The patients who deviated had deletions at the central hot spot region of the dystrophin gene. The presence of these deviations in a large number of DMD patients highlights the difficulties in predicting the clinical progression of the disease based only on DNA profile.

Gene Deletion↗
PubMed1997

Study of myopathies by histological and histochemical methods with special reference to staining for desmin expression.

An attempt was made to study the histological and histochemical changes as well as immunohistochemical changes in desmin expression occurring in four types of clinical myopathies e.g. Chronic ischaemic myopathy due to Buerger's disease (Group I), Carcinomatous myopathy (Group II), Metabolic myopathy (Group III) and Muscular dystrophy (Group IV). The number of cases studied were 16 cases, 15 cases, 4 cases and 5 cases respectively. The study revealed: (i) a combination of normal, degenerated, necrotic and regenerating fibres in different proportions in all the four groups having maximum number of degenerated fibres in Group I and Group IV, relatively more number of regenerating fibres in groups III and absence of necrotic fibres in Group I. (ii) Altered tinctorial property in most of the fibres indicating degenerated and regenerating fibres in all the groups with Masson's trichrome staining against inconstant staining with PTAH appear to be a good indicator for myopathy. (iii) The Desmin expression was week and irregular in most of the cases with most of the fibres probably due to reduction of desmin content probably indicating degenerated fibres, appear to be a good indicator for myopathy. (iv) Chronic ischaemic myopathy showed close resemblance with muscular dystrophy though no typical or distinct distinguishing feature could be identified in these four groups.

Desmin↗
PubMed1996

Beta-secretase processing of the beta-amyloid precursor protein in transgenic mice is efficient in neurons but inefficient in astrocytes.

Alzheimer's disease is characterized by the extracellular deposition of beta-amyloid peptide (Abeta) in cerebral plaques and evidence is accumulating that amyloid is neurotoxic. Abeta is derived from the beta-amyloid precursor protein (APP). Proteolytic processing of APP by the enzyme, beta-secretase, produces the N terminus of Abeta, and releases a secreted ectodomain of APP (beta-s-APP). To develop animal models for measuring beta-secretase activity in specific brain cells in vivo, we have targeted the expression of the full-length human APP to either neurons or astrocytes in transgenic mice using the neuron- specific enolase (NSE) promoter or a modified glial fibrillary acidic protein (GFAP) gene, respectively. The APP cDNAs expressed were mutated (KM to NL at 670/671) to encode amino acid substitutions that enhance amyloidogenic processing in vitro. Western analyses revealed abundant production of beta-s-APP in the brains of NSE-APP mice and enzyme-linked immunosorbent assay analyses showed production of Abeta in fetal primary mixed brain cultures and brain homogenates from these transgenic animals. Because the NSE promoter drives expression primarily in neurons, this provides in vivo evidence that the beta-secretase cleavage necessary for generation of beta-s-APP and Abeta is efficiently performed in neurons. In contrast, only little beta-s-APP was detected in brain homogenates of GFAP-APP mice, indicating that astrocytes show very little beta-secretase activity in vivo. This provides strong in vivo evidence that the major source of Abeta in brain is from neurons and not from astrocytes.

Amyloid Precursor Protein Secretases↗
PubMed1996

Chromosomal assignment and tissue expression of CBF-C/NFY-C, the third subunit of the mammalian CCAAT-binding factor.

The mammalian CCAAT-binding factor CBF (NFY) consists of three subunits, CBF-A, CBF-B, and CBF-C. All three subunits are evolutionarily conserved and are essential for DNA binding of CBF. In this study we report the identification of human and plant homologs of CBF-C. Northern analysis revealed that, like the other two subunits, CBF-C was produced at equal levels in all rat tissues that were examined. We assigned the mouse CBF-C gene (designated Nfyc) to chromosome 4 with tight linkage to Lmyc. Our mouse linkage data suggest that the human NFYC homolog will map to 1p32.

Amino Acid Sequence↗
PubMed1996

Microheterogeneity of C-reactive protein in the sera of fish Labeo rohita induced by metal pollutants.

A group of C-reactive proteins (CRPs) have been purified to apparent homogeneity by calcium (Ca++) dependent affinity chromatography on phosphoryl choline sepharose column from the sera of L. rohita confined in normal and nonlethal doses of cadmium (Cd++) and mercury (Hg++) polluted water. The CRPs levels are elevated in the serum of both Cd++ and Hg++ polluted fishes. All three CRPs are glycoproteins having identical subunits of Mr 33,000. The total content of carbohydrate are 21.4%, 16.4% and 14.2% and that of sialic acid are 3.5%, 2.4% and 1.5% in CRPHg++, CRPCd++ and CRPN respectively. In native gel electrophoresis all three CRPs show differences in mobility. However they move to identical position after desialylation and deglycosylation. These CRPs react differentially with different lectins which indicates a variation in the carbohydrate moieties resulting their microheterogeneity.

Animals↗
PubMed1996

Cloning of the sodium-dependent, broad-scope, neutral amino acid transporter Bo from a human placental choriocarcinoma cell line.

We have isolated a cDNA from a human placental choriocarcinoma cell cDNA library which, when expressed in HeLa cells, induces a Na+-dependent amino acid transport system with preference for zwitterionic amino acids. Anionic amino acids, cationic amino acids, imino acids, and N-methylated amino acids are excluded by this system. These characteristics are identical to those described for the amino acid transporter Bo. When expressed in Xenopus laevis oocytes that do not have detectable endogenous activity of the amino acid transporter Bo, the cloned transporter increases alanine transport in the oocytes severalfold and induces alanine-evoked inward currents in the presence of Na+. The cDNA codes for a polypeptide containing 541 amino acids with 10 putative transmembrane domains. Amino acid sequence homology predicts this transporter (hATBo) to be a member of a superfamily consisting of the glutamate transporters, the neutral amino acid transport system ASCT, and the insulin-activable neutral/anionic amino acid transporter. Chromosomal assignment studies with somatic cell hybrid analysis and fluorescent in situ hybridization have located the ATBo gene to human chromosome 19q13.3.

Alanine↗
PubMed1996

The transcriptional activity of the CCAAT-binding factor CBF is mediated by two distinct activation domains, one in the CBF-B subunit and the other in the CBF-C subunit.

CBF-A, CBF-B, and CBF-C together form the heterotrimeric mammalian CCAAT-binding factor, CBF, which binds to DNA to form a CBF-DNA complex. Here we examined the transcription activation function of CBF in an in vitro reconstituted system using the three purified recombinant CBF subunits expressed in Escherichia coli. Two of the subunits, CBF-A and CBF-C, were coexpressed and purified as a CBF-A/CBF-C complex. Addition of the three wild-type recombinant CBF subunits to EL4 cell nuclear extracts depleted of CBF stimulated transcription 5-20-fold from proalpha2(1) collagen promoters and 10-fold from the Rous sarcoma virus long terminal repeat. Two CBF deletion mutants, one containing full-length CBF-A and CBF-C and a CBF-B lacking the NH2-terminal residues 1-224, and the other containing full- length CBF-A and CBF-B and a CBF-C lacking the COOH-terminal residues 114-309, also stimulated transcription from these promoters, but the level of activation was reduced to half that obtained with the full-length CBF subunits. In contrast, a CBF deletion mutant protein containing full-length CBF-A and deleted forms of both CBF-B and CBF-C showed very little transcription activation from these promoters. Hence, this study demonstrates that the heterotrimeric CBF protein consists of two transcription activation domains, one present in CBF-B and the other in CBF-C, and that the two domains act additively in the in vitro assay. The activation domains of both CBF-B and CBF-C, which are rich in glutamine and hydrophobic residues, showed amino acid sequence similarities with each other and with the glutamine-rich activation domain of transcription factor Sp1.

Animals↗
PubMed1996

c-myc oncogene expression and cell proliferation in mixed oligo-astrocytoma.

Mixed gliomas (oligo-astrocytomas) are brain tumours with an admixture of 2 different cell populations: astrocytes and oligodendroglia. On the basis of histological features and behaviour, these tumours are classified as low-grade mixed gliomas (MG) and malignant mixed gliomas (MMG). We have studied the relationship between c-myc protein expression and cellular proliferation in this class of tumours. Using antibody c-33 for c-myc and PC-10 for the proliferating cell nuclear antigen (PCNA), immunohistochemistry was performed on 14 MG and 9 MMG. PCNA was increased in MMG as compared to MG in both astrocytic and oligodendroglial areas. However, more c-myc-positive cells were seen only in the astrocyte areas of MMG. Analysis of the relationship of c-myc and PCNA suggests that the correlation of c-myc with cellular proliferation is dependent on tissue type and differentiation status.

Antibodies, Monoclonal↗
PubMed1996

Unusual dynamics of extinction in a simple ecological model.

Studies on natural populations and harvesting biological resources have led to the view, commonly held, that (i) populations exhibiting chaotic oscillations run a high risk of extinction; and (ii) a decrease in emigration/exploitation may reduce the risk of extinction. Here we describe a simple ecological model with emigration/depletion that shows behavior in contrast to this. This model displays unusual dynamics of extinction and survival, where populations growing beyond a critical rate can persist within a band of high depletion rates, whereas extinction occurs for lower depletion rates. Though prior to extinction at lower depletion rates the population exhibits chaotic dynamics with large amplitudes of variation and very low minima, at higher depletion rates the population persists at chaos but with reduced variation and increased minima. For still higher values, within the band of persistence, the dynamics show period reversal leading to stability. These results illustrate that chaos does not necessarily lead to population extinction. In addition, the persistence of populations at high depletion rates has important implications in the considerations of strategies for the management of biological resources.

Animals↗
PubMed1996

Evaluation of lymphatic drainage in free flaps by lymphoscintigraphy: a preliminary study.

Lymphatic drainage from free flaps was studied by lymphoscintigraphy in 14 patients in whom free vascularised flaps were used to cover defects caused by trauma or tumour ablation. Lymphoscintigrams were done after intradermal injection of Technetium-99m-Dextran in the flap and in the corresponding contralateral normal area. The retention of radioactivity at the injection sites after 1 h was computed and expressed as percentages of baseline activity at the time of injection. 25 studies were done in 14 patients at intervals varying from 9 days to 6 years postoperatively. In all cases, radioactivity was detected beyond the flaps in the lymphatic channels and draining lymph nodes. There was no significant difference (P = 0.27) between the retention of activity in the flaps (mean 88.68%; s.e.m. 1.25) and that in the corresponding contralateral control area (mean 86.88%; s.e.m. 1.35). This study shows that lymphatic drainage in a free flap is established early after surgery.

Adolescent↗
PubMed1996

Pediatric kidney: functional outcome after extracorporeal shock wave lithotripsy.

PURPOSE: We studied the efficacy, functional outcome and morphological changes following extracorporeal shock wave lithotripsy (ESWL*) of renal calculi in a pediatric population. MATERIALS AND METHODS: We prospectively evaluated 50 patients 2 to 12 years old (mean age 7.64) undergoing ESWL with the Siemens Lithostar Plus. Functional outcome was assessed by comparing total and ipsilateral glomerular filtration rates before and after ESWL. Glomerular filtration rate was measured using Gates' method on a 99mtechnetium-pentetic acid radionuclide renal scan corrected to body surface area times 1.73 m.2. Ultrasound was performed to assess morphological changes after ESWL. RESULTS: The immediate fragmentation rate was 86% and the clearance rate was 82%. At the end of the study 40 patients were evaluable. Immediately after ESWL ultrasonography showed perirenal hematoma in 3 patients, intrarenal hematoma in 2 and subcapsular hematoma in 1. These changes resolved spontaneously at followup. There was no change in total or ipsilateral glomerular filtration rate at a mean followup of 31.7 months. Before and after ESWL total glomerular filtration rates were 86.58 +/- 12.43 and 86.27 +/- 12.82 ml. per minute per 1.73 m.2, respectively. Treated kidney glomerular filtration rate decreased insignificantly from 40.58 +/- 12.61 to 40.41 +/- 12.61 ml. per minute per 1.73 m.2 at 3 months. At the last followup the change in glomerular filtration rate was insignificant. CONCLUSIONS: ESWL is effective in the pediatric population, and it can be safely performed without long-term bio-effects on the function or morphology of the growing kidney.

Child↗
PubMed1996

Effect of immune globulin on the prevention of experimental hepatitis C virus infection.

The efficacy of postexposure prophylaxis for the prevention of hepatitis C virus (HCV) infection was studied in experimentally infected chimpanzees. Three chimpanzees were inoculated with HCV: Two were treated 1 h later with anti-HCV--negative intravenous immune globulin (IGIV) or hepatitis C immune globulin (HCIG), and a third animal was not treated. HCV infection was detected in all 3 animals within a few days of inoculation. Once passively transferred anti-HCV declined in the HCIG-treated animal, there was an increase of HCV antigen (Ag)--positive hepatocytes followed by reappearance of anti-HCV; HCV Ag disappeared concordant with the development of acute hepatitis. Acute hepatitis C developed in both the IGIV-treated and untreated chimpanzees, with peak liver enzyme activity on day 59, but was delayed in the HCIG-treated animal until day 146. Postexposure HCIG treatment markedly prolonged the incubation period of acute hepatitis C but did not prevent or delay HCV infection. IGIV had no effect on the course of HCV infection.

Animals↗