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Biomedical subjects

I Singh

Publications and source records attributed to I Singh.

At least 163 records · Page 9Linked to original sources
PubMed1996

Epoxide hydrolase in human and rat peroxisomes: implication for disorders of peroxisomal biogenesis.

To understand the basis of excretion of excessive amounts of epoxydicarboxylic fatty acids (EDFA) in urine of patients with disorders of peroxisomal biogenesis (Pitt, J. J., and A. Poulos. 1993. Clin. Chim. Acta. 223: 23-29), the activity of epoxide hydrolase (EH) was measured in cultured skin fibroblasts from control subjects and patients with peroxisomal disorders. EH activity was approximately 40% lower in fibroblasts that lack intact peroxisomes (Zellweger syndrome), whereas the activity in other peroxisomal disorders (X-adrenoleukodystrophy and rhizomelic chondrodysplasia punctata) with intact peroxisomes was similar to control. To identify the specific enzyme/organelle that represents the decrease in EH activity in Zellweger cells, we have analyzed this activity in different subcellular organelles from control and Zellweger skin fibroblasts. EH activity was enriched in peroxisomes from control fibroblast. EH activity in isolated mitochondria, microsomes, or cytosol from Zellweger fibroblast was similar to that of control fibroblast. These observations indicate that deficient activity of EH in cells from Zellweger patients is due to lack of peroxisomal EH activity. The peroxisomal EH is differentially induced to a higher degree by ciprofibrate, a hypolipidemic agent and peroxisome proliferator, than EH activity in other organelles and cytoplasm. The high specific activity of EH in peroxisomes and differential induction of EH activity in peroxisomes as compared to other organelles, and the excretion of EDFA in patients who lack peroxisomes suggests that peroxisomal EH may be responsible for the detoxification of EDFA, and that this enzyme in peroxisomes may be a different protein than the EH found in other organelles.

Animals↗
PubMed1996

Evaluation of HBsAg carrier rate in acute viral hepatitis and high risk individuals using RPHA and ELISA.

A total of 600 individuals including 500 cases of hepatitis and 100 individuals at high risk for developing hepatitis were screened for hepatitis B surface antigen (HBsAg) using reverse passive haemagglutination (RPHA) and enzyme linked immunosorbent assay (ELISA). HBsAg carrier rate in clinically diagnosed cases of hepatitis was 38% and 32.4% by RPHA and ELISA respectively. In high risk individuals, the carrier rate was 14% by RPHA and 11% by ELISA. Taking ELISA as gold standard, RPHA showed 5.33% false positivity and 0.33% false negativity. The over all correlation between RPHA and ELISA was to the tune of 82.66%.

Acute Disease↗
PubMed1995

Ketoconazole and other imidazole derivatives are potent inhibitors of peroxisomal phytanic acid alpha-oxidation.

The imidazole antimycotics like ketoconazole, clotrimazole, bifonazole, miconazole and CO, known as powerful inhibitors of cytochrome P-450, are potent inhibitors of peroxisomal phytanic acid alpha-oxidation to pristanic acid suggesting the possible involvement of the cytochrome P-450 mono-oxygenase system in this oxidation. In contrast to the inhibition of the oxidation of [1-14C]phytanic acid, [1-14C]phytanoyl-CoA and [(2,3)-3H]phytanic acid, these drugs and CO have no effect on the oxidation of [1-14C]alpha-hydroxy phytanic acid indicating that these drugs and CO inhibit only the alpha-hydroxylation of phytanic acid. These studies using purified peroxisomes from liver and cultured human skin fibroblasts and Hep G2 cells clearly demonstrate that alpha-hydroxylation, an intermediate step in the alpha-oxidation of phytanic acid found to be impaired in Refsum Disease, is mediated by cytochrome P-450 containing enzyme.

Carbon Monoxide↗
PubMed1995

Molecular cloning and sequencing of human palmitoyl-CoA ligase and its tissue specific expression.

A complimentary DNA clone encoding the entire human palmitoyl-CoA ligase has been isolated from a liver cDNA library and sequenced in it's entirety. The predicted product is a 699 amino acid protein. Southern analysis utilizing the human palmitoyl-CoA ligase gene as a probe revealed varying degrees of similarity amongst various mammalian species. The palmitoyl-CoA ligase gene is highly expressed in liver, heart, skeletal muscle and kidney, and to a lesser extent in brain, lung, placenta and pancreas. The expression of palmitoyl-CoA ligase in various tissue parallels the function of this enzyme in the metabolism of fatty acids in these tissues.

Amino Acid Sequence↗
PubMed1995

Kinetic characteristics of rat liver peroxisomal nafenopin-CoA ligase.

In this study we have demonstrated that rat hepatic peroxisomes catalyse the formation of nafenopin-CoA. The process is mediated by apparent high affinity (Km 6.7 microM), low capacity (Vmax 0.31 nmol/mg/min) and low affinity, high capacity isoforms. Palmitic acid (Ki 1.1 microM), R(-) ibuprofen (Ki 7.9 microM), ciprofibrate (Ki 60.2 microM) and clofibric acid (Ki 86.8 microM) competitively inhibited nafenopin-CoA formation catalysed by the apparent high affinity isoform. An antibody raised against the microsomal palmitoyl-CoA ligase inhibited the equivalent peroxisomal enzyme significantly (P < 0.001) but did not inhibit peroxisomal nafenopin-CoA ligase activity. These data suggest that nafenopin-CoA formation is catalysed by a peroxisomal CoA ligase which differs from the peroxisomal long chain fatty acid-CoA ligase in relation to its xenobiotic/antibody inhibitor profile and kinetic characteristics.

Animals↗
PubMed1995

A major role of class I Fc gamma receptors in immunoglobulin G anti-D-mediated red blood cell destruction by fetal mononuclear phagocytes.

OBJECTIVE: To examine Fc gamma receptor (Fc gamma R) classes that direct immunoglobulin (Ig) G anti-D-mediated red blood cell interaction with fetal mononuclear phagocytes. METHODS: Mononuclear phagocytes isolated from fetal blood and spleen at 20-35 and 12-15 weeks' gestation, respectively, were tested in a modified mononuclear phagocytosis assay against IgG anti-D-coated red blood cells in the absence and presence of Fc gamma R class-specific monoclonal antibodies as inhibitors. Monocytes from cord and adult blood served as controls. RESULTS: In the absence of any inhibitor, attachment and phagocytosis indices of fetal monocytes were similar to those of their newborn and adult counterparts but markedly less than those of mononuclear phagocytes from fetal spleen. Blockade of the high-affinity Fc gamma RI caused a profound (more than 93%) reduction in red blood cell attachment and phagocytosis indices of fetal as well as newborn and adult monocytes. It also brought about a marked decrease in the attachment and phagocytosis indices of mononuclear phagocytes from fetal spleens (64 and 81%, respectively). With fetal spleen mononuclear phagocytes, anti-Fc gamma RII lacked any significant effect on their interaction with red blood cells, whereas anti-Fc gamma RIII caused a significant (43%) inhibition of their phagocytosis. CONCLUSION: Immunoglobulin G anti-D-mediated attachment to and phagocytosis by fetal mononuclear phagocytes of red blood cells is well developed early during the second trimester. High-affinity Fc gamma RI plays a major role in the effector function of circulating monocytes and splenic mononuclear phagocytes, whereas Fc gamma RIII, expressed strongly on the latter effectors, participates in target ingestion.

Antibodies, Monoclonal↗
PubMed1995

Mortality in a hospitalized mentally handicapped population: a 10-year survey.

The mortality experiences of a hospitalized mentally handicapped population between 1981 and 1990 (inclusive) were examined. A continued trend for increasing longevity in both males and females was found, with mean ages at death now approaching those in the general population. The commonest cause of death was non-tubercular respiratory infection, from which patients were particularly at risk during the months of December to February (inclusive). Patients diagnosed as suffering from psychoses other than schizophrenia and mood disorder had an increased mortality and should be thoroughly investigated for the presence of organic pathology. Epilepsy and Down's syndrome were associated with increased risk of earlier death, although in the case of Down's syndrome there has been a marked increase in longevity.

Adult↗
PubMed1995

Nitric oxide regulates peroxisomal enzyme activities.

We have previously shown that peroxisomes are involved in the production and detoxification of reactive oxygen species and that peroxisomal functions are damaged by such oxygen species. Since nitric oxide is not only a cellular messenger, but also a free radical, it would be interesting to detect a connection between nitric oxide levels and peroxisomal enzyme activities. To determine if nitric oxide has an effect on the activities of peroxisomal functions and whether this effect is based solely on its chemical properties as reactive oxygen species or its action as a second messenger, effectors of the cellular nitric oxide level were applied to a cell model (human skin fibroblasts in culture) or directly to the enzymatic assays or both. If applied to the monolayer at non-cytotoxic concentrations, N-nitro-L-arginine methyl ester hydrochloride, an inhibitor of nitric oxide synthase (EC 1.14.13.39), increased catalase (EC 1.11.1.6) activity by more than 10% and decreased the activity of the peroxisomal fatty acid oxidation system by more than 10%. The effect was concentration-dependent. L-Arginine had the contrary effect. Combinations of L-arginine and N-nitro-L-arginine methyl ester hydrochloride compensated one another. If applied directly to the assays, S-nitroso-N-acetylpenicillamine and sodium nitroprusside inhibited catalase activity in a concentration-dependent manner. Sodium nitro-prusside had no effect on the peroxisomal beta-oxidation system unless cells were pretreated with N-nitro-L-arginine methyl ester overnight (50% inhibition). The results show a differential effect for the application of nitric oxide-effectors on fibroblast monolayers, cell suspensions and under assay conditions. Depending on the conditions of the incubation, nitric oxide applied to the cell monolayer at low doses acts as a second messenger in cells rather than as reactive oxygen species. Under assay conditions the effect of nitric oxide is more likely that of a reactive oxygen species because it inhibits all measured enzyme activities.

Arginine↗
PubMed1995

Cholesterol emboli presenting as acute allograft dysfunction after renal transplantation.

Cholesterol emboli are a common complication of atherosclerotic vascular disease. A 40-yr-old renal transplant recipient who developed acute allograft dysfunction 1 day after the initiation of cyclosporine therapy and 6 days after transplantation is described. A renal allograft biopsy revealed cholesterol emboli in interlobular arteries and in glomeruli. Four previously reported cases of cholesterol emboli in renal allografts are described, and the cause and pathogenesis of atheroembolic disease are reviewed. Atheroemboli causing injury to the renal allograft may arise from either donor or recipient vessels. Vigilance for the occurrence of these emboli needs to be maintained when donor or recipient vessels demonstrate evidence of significant atherosclerotic vascular disease.

Acute Disease↗
PubMed1995

Effect of hypoxia-reoxygenation on peroxisomal functions in cultured human skin fibroblasts from control and Zellweger syndrome patients.

To delineate the role of peroxisomes in the pathophysiology of hypoxia-reoxygenation we examined the functions of peroxisomes and mitochondria in cultured skin fibroblasts from controls and from patients with cells lacking peroxisomes (Zellweger cells). The loss of peroxisomal functions (lignoceric acid oxidation and dihydroxyacetonephosphate acyltransferase [DHAP-AT] activities) in control cells following hypoxia and hypoxia followed by reoxygenation, suggests that peroxisomes are sensitive to oxidative injury. The sensitivity of peroxisomes to oxidative stress was compared to that of mitochondria by examining the oxidation of palmitic acid (a function of both mitochondria and peroxisomes) in control and Zellweger cell lines, following hypoxia-reoxygenation. The greater loss of activity of palmitic acid oxidation observed in control cells as compared to that seen in Zellweger cells suggests that the peroxisomal beta-oxidation system is relatively more labile to hypoxia-reoxygenation induced oxidative stress. This data clearly demonstrates the difference in the response of mitochondria and peroxisomes to oxidative stress.

Cell Hypoxia↗
PubMed1995

Phytanic acid oxidation: topographical localization of phytanoyl-CoA ligase and transport of phytanic acid into human peroxisomes.

To understand the possible role of phytanoyl-CoA ligase, present in the membrane, in the oxidation of phytanic acid in the matrix of peroxisomes (Pahan, K. and I. Singh. 1993. FEBS Lett. 333: 154-158) we examined the transport of phytanic acid/phytanoyl-CoA into peroxisomes and the topology of the active site of phytanoyl-CoA ligase in the peroxisomal membrane. The increase in lignoceroyl-CoA ligase as compared to no change in the activities of palmitoyl-CoA and phytanoyl-CoA ligases when peroxisomes were disrupted with detergent or sonication and inhibition of the activities of both palmitoyl-CoA and phytanoyl-CoA ligase by impermeable inhibitor of acyl-CoA ligases (mercury-dextran) and trypsin treatment in the intact peroxisomes. On the other hand, the lignoceroyl-CoA ligase activity was inhibited by mercury-dextran and trypsin only in the disrupted peroxisomes. Taken together, these studies support the conclusion that the enzymatic site of phytanoyl-CoA ligase is on the cytoplasmic surface of peroxisomal membrane. This implies that phytanoyl-CoA is synthesized on the cytoplasmic surface of peroxisomal membrane and is translocated through the membrane for its alpha-oxidation to pristanic acid in the matrix of peroxisomes. To delineate the transport for phytanic acid through the peroxisomal membrane, we examined cofactors and energy requirements for its transport into peroxisomes. The similar rates of transport of phytanoyl-CoA and phytanic acid under conditions favorable for fatty acid activation (presence of ATP, CoASH, and MgCl2) and the lack of transport of phytanic acid when ATP and/or CoASH were removed or replaced with their inactive analogues (ATP and/or CoASH) from assay medium clearly demonstrates that the transport of phytanic acid requires prior synthesis of phytanoyl-CoA by phytanoyl-CoA ligase. The prerequisite activation of phytanic acid to phytanoyl-CoA for its alpha-oxidation only in intact peroxisomes, and oxidation of free phytanic acid in digitonin-permealized peroxisomes or isolated matrix, suggests that phytanoyl-CoA ligase (in peroxisomal membrane) regulates the oxidation of phytanic acid in peroxisomes by providing phytanoyl-CoA for its transport into peroxisomes.

Binding Sites↗
PubMed1995

Diabetes mellitus in the elderly.

Diabetes mellitus is prevalent among the elderly. Although the principles of management of diabetes are fundamentally the same in both the young and elderly, many aspects of the disease and its manifestations are unique to the elderly. Older patients may have atypical presentations of diabetes. Numerous factors may impair adequate nutrition and dietary and exercise compliance in the elderly. Pharmacologic therapy, with either sulfonylureas or insulin, entails a particular risk for hypoglycemia among the elderly, who are more susceptible to hypoglycemia and are more likely to have neuroglycopenic symptoms. Diabetic hyperosmolar coma occurs predominantly in the older type II diabetic population. It requires aggressive hydration and insulin therapy, but most patients can ultimately be managed without insulin. The macrovascular complications (coronary and peripheral vascular disease) are the major source of morbidity and mortality among elderly diabetics, but microvascular complications (nephropathy, retinopathy, neuropathy) also occur and often respond to a variety of therapeutic interventions.

Adult↗
PubMed1995

Aeromonas species and Plesiomonas shigelloides in diarrhoea in Goa.

Sixty six strains (1.9%) of Aeromonas species and 7 strains (0.2%) of Plesiomonas shigelloides were isolated from 3484 stool/rectal swabs from cases of diarrhoea during the study period of four years from August 1986 to July 1990 in Goa. Although the selective medium (Ampicillin sheep blood agar) was not used for the isolation of Aeromonas, an increase in the rate of isolation of Aeromonas from 0.2% in the year 1986 to 6.0% in 1990 was observed. Stool samples from 100 controls (patients without diarrhoea) examined in the year 1989 did not yield either of the pathogens.

Adult↗
PubMed1994

Phytanic acid alpha-oxidation in rat liver mitochondria.

The alpha-oxidation of phytanic acid in rat liver is a mitochondrial function. The inhibition of phytanic acid oxidation activity by inhibitors of acyl-CoA ligases (Naproxen and Triacsin C) and that of carnitine acyltransferase I (2-(5-(4-chlorophenyl)pentyl)oxirane-2 carboxylic acid (POCA) and 2-bromopalmitate) and increase in phytanic acid oxidation activity by the addition of exogenous carnitine and CoA to purified mitochondria suggests that phytanoyl-CoA ligase and carnitine acyltransferase I are essential for the activation and transport of phytanic acid across the mitochondrial membrane. This was further supported by the fact that activation of phytanic acid to phytanoyl-CoA was required only in intact mitochondria but not in mitochondria permealized with digitonin. DesulfoCoA, Naproxen and POCA treatment resulted in a significant decrease in phytanic acid oxidation in intact mitochondria but not in digitonin permealized mitochondria. These results show that alpha-oxidation of phytanic acid to pristanic acid, in contrast to beta-oxidation of fatty acids, requires free fatty acid as substrate. The inhibition of alpha-oxidation (approximately 90%) of phytanic acid by different cytochrome P-450 enzyme inhibitors indicated that alpha-oxidation of phytanic acid is mediated through cytochrome P-450 containing enzyme system. Similar to the omega-hydroxylation system in endoplasmic reticulum, alpha-hydroxylation and the subsequent alpha-oxidation of phytanic acid in mitochondria is induced by ciprofibrate, a hypolipidemic drug.

Animals↗
PubMed1994

Impairment of peroxisomal beta-oxidation system by endotoxin treatment.

It is now clear that peroxisomes play a crucial role in many cellular processes, including the beta-oxidation of very long chain fatty acids. Recently, mammalian peroxisomes have been shown to contain the antioxidant enzymes, superoxide dismutase and glutathione peroxidase, in addition to catalase. The presence of these enzymes in peroxisomes suggests that peroxisomes undergo oxidative stress in normal and disease states. As an indicator of the potential impact of an oxidative stress on peroxisomal functions, we evaluated the effect of endotoxin exposure on the beta-oxidation enzyme system in rat liver. Peroxisomes were isolated from liver homogenates by differential and density gradient centrifugations. Endotoxin treatment decreased the beta-oxidation of lignoceric acid to 56% of control values (p < 0.01). The specific activity of the rate limiting enzyme in the system, acyl-CoA oxidase, was decreased to 73% of control values (p < 0.05). Immunoblot analysis revealed a 25% decrease in the 21KD subunit of the acyl-CoA oxidase protein. In contrast, the protein levels of the other enzymes in the pathway, trifunctional protein and 3-ketoacyl-CoA thiolase, were increased by 10 and 15%, respectively. These findings suggest that impairment of beta-oxidation of lignoceric acid by endotoxin treatment is due primarily to a reduction in the activity and protein level of the key enzyme, acyl-CoA oxidase. Oxidative stresses such as endotoxin exposure may have deleterious effects on important peroxisomal functions, such as beta-oxidation of very long chain fatty acids.

3-Hydroxyacyl CoA Dehydrogenases↗