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Biomedical subjects

Y Singh

Publications and source records attributed to Y Singh.

At least 91 records · Page 5Linked to original sources
PubMed1991

Experimental pathogenicity of mollicutes from bovines with reproductive disorders in rabbit fallopian tube organ culture.

Mollicutes (10) belonging to Mycoplasma and Acholeplasma isolated from various reproductive disorders were tested in rabbit fallopian tube (FT) organ culture. Parameter for describing pathogenic status of Mollicutes in rabbit FT organ culture included multiplication of organisms, and its effect on ciliary activity along with histopathological changes in FT explants. M. mycoides (LC, Y-Goat), M. bovoculi, M. bovigenitalium, Mycoplasma sp. and A. oculi were categorized as pathogenic; A. axanthum and A. laidlawii as mildly pathogenic; and M. bovis, M. arginini. and A. granularum, as nonpathogenic to rabbit FT organ culture. Thus, rabbit FT organ culture is recommended for use as a suitable and economical in vitro model to assess the pathogenicity of Mollicutes of reproductive tract origin.

Animals↗
PubMed1991

Congenital factor XIII deficiency. A family report.

Four sisters born to consanguineous muslim parents with a bleeding disorder since birth are presented. They also had prolonged umbilical cord bleeding and history of delayed wound healing. Since childhood, they have been developing spontaneous ecchymotic spots. Three out of four sisters had Factor XIII deficiency. Their mother's sisters, who have been developing ecchymotic spots were found to have normal clot stability and Factor XIII levels. Family study indicates autosomal recessive mode of inheritance of the congenital Factor XIII deficiency.

Adolescent↗
PubMed1990

Circadian variation of serum urea concentration in north Indian subjects.

Circadian rhythm of serum urea concentration was studied in 25 clinically healthy, diurnally active, nocturnally resting young male Indians. The mean urea concentration was observed to be 22.32 mg/dl at 0800 h which increased gradually reaching maximum at 0000 h with a mean of 31.00 mg/dl. A marked circadian variation in serum urea was recorded with a statistically significant amplitude and acrophase at 2232 h (Cosinor analysis). The observation that serum urea concentration oscillates physiologically in the peripheral blood according to a circadian rhythm may prove to be of importance in the clinical interpretation of values at different times along the 24 h light-dark period.

Adolescent↗
PubMed1989

A deleted variant of Bacillus anthracis protective antigen is non-toxic and blocks anthrax toxin action in vivo.

Anthrax toxin is the only protein secreted by Bacillus anthracis that contributes to the virulence of this bacterium. An obligatory step in the action of anthrax toxin on eukaryotic cells is cleavage of the receptor-bound protective antigen (PA) protein (83 kilodaltons) to produce a 63-kilodalton, receptor-bound COOH-terminal fragment. A similar fragment can be obtained by limited treatment with trypsin. This proteolytic processing event exposes a site with high affinity for the other two anthrax toxin proteins, lethal factor and edema factor. Terminal sequencing of the purified fragment showed that the activating cleavage occurred in the sequence Arg164-Lys165-Lys166-Arg167. The gene encoding PA was mutagenized to delete residues 163-168, and the deleted PA was purified from a Bacillus subtilis host. The deleted PA was not cleaved by either trypsin or the cell-surface protease, and was non-toxic when administered with lethal factor. Purified, deleted PA protected rats when administered 90 min before injection of 20 minimum lethal doses of toxin. This mutant PA may be useful as a replacement for the PA that is the major active ingredient in the current human anthrax vaccine, because deleted PA is expected to have normal immunogenicity, but would not combine with trace amounts of LF and EF to cause toxicity.

Amino Acid Sequence↗
PubMed1989

Internalization and processing of Bacillus anthracis lethal toxin by toxin-sensitive and -resistant cells.

Anthrax lethal toxin consists of two separate proteins, protective antigen and lethal factor (LF). Certain macrophages and a mouse macrophage-like cell line, J774A.1, are lysed by low concentrations of lethal toxin. In contrast, another macrophage cell line, IC-21, and all other cell types tested were resistant to this toxin. To discover the basis for this difference, each step in the intoxication process was examined. No differences between sensitive and resistant cells were found in receptor binding or proteolytic activation of protective antigen, steps that are required prior to LF binding. To determine whether resistance results from a defect in translocation to the cytosol, we introduced LF into J774A.1 and IC-21 cells and a nonmacrophage cell line (L6 myoblast) by osmotic lysis of pinocytic vesicles. Only J774A.1 cells were lysed; no effect was observed in IC-21 and L6 cells. These results suggest that resistant cells either lack the intracellular target of LF or fail to process LF to an active form. The relatively low potency of LF introduced into J774A.1 cells by osmotic lysis suggests that protective antigen may also be required at a stage subsequent to endocytosis.

Animals↗
PubMed1989

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine inhibits proton motive force in energized liver mitochondria.

It is known that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like disease in primates and humans, depletes hepatocytes of ATP and subsequently causes cell death. Incubation of rat liver mitochondria with MPTP and 1-methyl-4-phenyl pyridinium ion (MPP+) significantly inhibited incorporation of 32Pi into ATP.MPTP and MPP+ inhibited the development of membrane potential and pH gradient in energized rat liver mitochondria, suggesting that reduction of the proton motive force may have reduced ATP synthesis. Since deprenyl, an inhibitor of monoamine oxidase, prevented the formation of MPP+ and inhibited the decrease in membrane potential caused by MPTP, but not that caused by MPP+, these effects of MPTP, as well as cell death, probably were mediated by MPP+. This mechanism may play a role in the specific loss of dopaminergic neurons resulting in MPTP-induced Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1989

Structural requirements for anthracycline-induced cardiotoxicity and antitumor effects.

By employing rat cardiac myocytes in culture and mouse L-1210 leukemia cells, we have compared different anthracycline analogs with respect to their ability to kill cardiac myocytes and tumor cells. Anthracyclines induced a decrease in cellular ATP and glutathione from both cardiac myocytes and L-1210 cells in a time- and concentration-dependent fashion. Moreover, the decrease in ATP in cardiac myocytes was followed by release of the cytoplasmic enzyme lactic acid dehydrogenase and of adenine nucleotides after anthracycline treatment. At very low concentrations of anthracyclines, at which ATP and glutathione were not affected, the drugs induced complete cessation of the growth of L-1210 cells. Some structural alterations in the anthracycline molecule resulted in parallel changes in antitumor activity and in cardiotoxicity. But other structural alterations resulted in dissimilar changes in antitumor activity and cardiotoxicity. Although the results indicate that the structural requirements for inducing cardiotoxicity and antitumor activity may be different, they also indicate that the mechanisms by which anthracycline causes cell death in tumor cells and cardiac myocytes may be the same.

Animals↗
PubMed1989

Maitotoxin-induced liver cell death involving loss of cell ATP following influx of calcium.

Maitotoxin, one of the most potent marine toxins known, produced cell death in cultures of rat hepatocytes with a TD50 of 80 pM at 24 hr. The cell death, as indicated by a dose- and time-dependent leakage of lactate dehydrogenase (LDH), was also associated with the leakage of [14C]adenine nucleotides from hepatocytes prelabeled with [14C]-adenine. The toxic effect of maitotoxin was completely abolished by the omission of calcium from the culture medium. The cell death induced by maitotoxin increased with increasing concentrations of calcium in the medium. Treatment of hepatocytes with low concentrations of the toxin (less than 0.5 ng/ml) resulted in increases in 45Ca influx into the cells. At higher concentrations of maitotoxin (greater than 1ng/ml), the initial increase in 45Ca influx was followed by the release of the 45Ca from the cells into the medium. Since the 45Ca release paralleled the LDH leakage, the release of calcium was due to cell death. The 45Ca influx, [14C]adenine nucleotide leakage, and LDH leakage were effectively inhibited by verapamil, a calcium channel blocker. Maitotoxin also induced a time- and dose-dependent loss of ATP from hepatocytes, which preceded the [14C]adenine nucleotide and LDH leakage. Thus, it appears that the cell death resulting from maitotoxin treatment is caused by the elevated intracellular calcium, which in turn inhibits mitochondrial oxidative phosphorylation causing depletion of cell ATP. Loss of cell ATP may be the causative event in the maitotoxin-induced cell death.

Adenosine Triphosphate↗
PubMed1989

Calcium is required for the expression of anthrax lethal toxin activity in the macrophagelike cell line J774A.1.

Anthrax lethal toxin, which consists of two separate proteins, protective antigen (Mr, 82,700) and lethal factor (Mr, approximately 83,000), is cytotoxic to the macrophagelike cell line J774A.1. Removal of calcium from the culture medium protected cells against the action of lethal toxin. Calcium depletion during the binding phase of intoxication afforded only partial protection. Further analysis showed that calcium removal caused some inhibition of protective antigen binding but that it had minimal effect on proteolytic conversion of protective antigen to the active 63-kilodalton fragment and that it had no effect on lethal factor binding. Cells to which lethal toxin had bound in the presence of calcium were protected when transferred to calcium-depleted culture medium, indicating a role for calcium at a postbinding stage. When ammonium chloride is present with lethal toxin, toxin accumulates in intracellular vesicles. Calcium-free medium protected these cells upon removal of the amine block, suggesting that calcium is also required at a step after internalization of lethal toxin. Calcium channel blockers inhibited 45Ca2+ uptake and protected cells against cytotoxicity. Calmodulin inhibitors also protected against the action of lethal toxin, suggesting involvement of calmodulin at a step during intoxication. We conclude that calcium is required at several steps in the intoxication of cells by anthrax lethal toxin.

Animals↗
PubMed1989

Effects on intestinal nutrient uptake and brush border membrane enzymes in response to atherogenic diet in rhesus monkeys.

Transport of nutrients and kinetic parameters (Vmax and Km) of brush border membrane (BBM) enzymes were studied in duodenum, jejunum, and ileum from atherogenic diet-fed monkeys. The Km remained unaltered while feeding of atherogenic diet resulted in higher Vmax of sucrase, maltase, and alkaline phosphatase and lower Vmax of gamma-glutamyltranspeptidase and leucine-aminopeptidase compared to controls. Na+-dependent D-glucose transport was higher in duodenum and jejunum and unaltered in ileum. In contrast to D-glucose transport, the transport of amino acids was decreased in all three intestinal segments from atherogenic diet-fed monkeys.

Alkaline Phosphatase↗
PubMed1988

Hepatic phosphatidylcholine synthesis in deficiency of lysine and threonine: effect of malathion.

Rats fed on a rice diet deficient in lysine and threonine showed increased activities of CDP-Choline pathway enzymes and incorporation of (methyl-3H)-choline into hepatic microsomal phosphatidylcholine, compared to rats fed on the same diet supplemented with lysine and threonine. However, the amount of microsomal phosphatidylcholine was significantly decreased in rats fed a deficient rice diet. These results suggest an enhanced phosphatidylcholine catabolism in rats fed on a rice diet deficient in lysine and threonine. Malathion administration reduced the amount of phosphatidylcholine in all the groups.

Animals↗
PubMed1988

MPTP and MPTP analogs induced cell death in cultured rat hepatocytes involving the formation of pyridinium metabolites.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) which has been shown to produce a Parkinson-like syndrome in humans and monkeys also causes cell death in cultures of rat hepatocytes. Treatment of cells with MPTP or its metabolite MPP+ (1-methyl-4-phenyl pyridinium ion), resulted in leakage of lactic acid dehydrogenase and 14C-labeled adenine nucleotides, as well as marked depletion of ATP and glutathione. Deprenyl, a specific inhibitor of monoamine oxidase-B, the enzyme catalyzing the oxidation of MPTP into MPP+, blocked the lethal effect of MPTP, but gave no protection from MPP+-induced cell death. The 4'-fluoro and 4'-chloro analogs of MPTP evoked toxicities similar to that of the parent compound, while N-butyl-PTP, 4'-amino-MPTP, and 2'-methyl-MPTP were relatively less toxic. N-Acetylamino-MPTP was found virtually nontoxic. The cell death produced by these analogs was also associated with leakage of [14C]adenine nucleotides, which is an indicator of loss of ATP from cells. All these compounds except the N-acetylamino analog were converted to corresponding pyridinium metabolites by liver cells when analyzed by high-pressure liquid chromatography and plasma desorption mass spectrometry. MPTP and its analogs also served as substrates for rat liver mitochondrial monoamine oxidase to varying degrees. Toxicity of various analogs, with the noticeable exception of 2'-methyl-MPTP, was inhibited by deprenyl. These findings indicate that the conversion of MPTP and its analogs to corresponding pyridinium metabolites is essential for the expression of toxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1988

A spectrophotometric method for calmodulin assay.

The activity of calmodulin as an activator of cAMP phosphodiesterase was assayed. AMP was hydrolyzed by 5'-nucleotidase, and the adenosine formed was measured by both liquid scintillation counting and spectrophotometry at 265 nm. Calmodulin activities measured by the two methods were equivalent, indicating that spectrophotometric assay of calmodulin can be used in place of the isotopic method.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1988

Mixed function oxidases in response to quality and quantity of dietary protein.

Feeding of rice diet reduced the food consumption and growth of rats. Hepatic Cytochrome P-450, NADPH Cytochrome c reductase and the activity of cytochrome P-450 dependent enzymes (Aniline hydroxylase, aminopyrine N-demethylase, p-nitroanisole O-demethylase) were also decreased by feeding rice diet. Supplementation of lysine and threonine to rice diet improved the activity of these enzymes. NADPH regeneration and microsomal phosphatidylcholine were reduced by feeding rice diet. The phenobarbitone induced sleeping time was decreased by supplementing rice diet with lysine and threonine. The effect of protein is probably partly attributed to changes in membrane phosphatidylcholine content and NADPH regeneration rate.

Animals↗