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Biomedical subjects

I Singh

Publications and source records attributed to I Singh.

At least 91 records · Page 5Linked to original sources
PubMed2000

Kidney ischemia-reperfusion: modulation of antioxidant defenses.

Reactive oxygen species (ROS; O2-, H2O2, and OH), normal by-products of cellular metabolic processes, are kept in control by antioxidant enzymes, such as catalase, glutathione peroxidase (GPX) and superoxide dismutases (SODs). To understand the role of antioxidant enzymatic defenses against ROS injury following ischemia-reperfusion, we examined the effect on kidney exposed to varying periods (30, 60 or 90 min) of ischemia followed by different periods of reperfusion. The enzymatic activities and protein levels of catalase, GPX, CuZnSOD and MnSOD were relatively unaffected at 30 min of ischemia followed by 0, 2 or 24 h reperfusion. However, 60 or 90 min of ischemia followed by 0, 2 or 24 h of reperfusion resulted in a decrease in activities and protein levels which paralleled the duration of ischemic injury. MnSOD activity tended to recover towards normal during reperfusion. Examination of the mRNA levels of these antioxidant enzymes demonstrated a severe decrease in mRNA levels of catalase and GPX at a time point of minimal ischemic injury (30 min of ischemia followed by reperfusion) suggesting that loss of mRNA of catalase and GPX may be the first markers of alterations in cellular redox in ischemia-reperfusion injury. Greater loss of mRNA for catalase, GPX and CuZnSOD was observed following longer periods (60 or 90 min) of ischemia. The mRNA for MnSOD was upregulated at all time points of ischemia-reperfusion injury. Actually, the greater decrease in mRNAs for catalase, GPX and CuZnSOD in the acute phase (within 24 h) subsequently showed a further decrease in these enzyme activities in the subacute phase (72 or 120 h after ischemia). These enzyme activities in the 30 min ischemia group, (but not in the 90 min group), already showed tendencies for normalization at 120 h after ischemia. To understand the molecular basis of the loss of mRNA of these antioxidant enzymes during ischemia-reperfusion injury, we examined the rate of transcription by nuclear run-on assays. The similar rates of transcription in control and kidney exposed to ischemia-reperfusion indicates that the loss of mRNA for catalase, GPX and CuZnSOD is possibly due to the increased rate of turnover of their mRNAs. These studies suggest that expression of antioxidant genes during ischemia-reperfusion are not coordinately expressed and that the differential loss of antioxidant enzymes may be the contributing factor(s) towards the heterogeneous renal tissue damage as a result of ischemia-reperfusion induced oxidative stress.

Animals↗
PubMed2000

Isolation and biochemical characterization of peroxisomes from cultured rat glial cells.

Peroxisomes are now recognized to play important cellular functions and its dysfunction leads to a group of neurological disorders. This study reports peroxisomal enzyme activities in cultured glial cells and peroxisomes isolated from cultured oligodendrocytes and C6 glial cells. Peroxisomal enzyme activities were found to be higher in oligodendroglial cells than in astrocytes or mixed glial cells. We also developed a method for the isolation of peroxisomes from glial cells by a combination of differential and density gradient centrifugation techniques. Peroxisomes from oligodendrocytes in nycodenz gradient were isolated at a density of 1.165 g/ml +/- 0.011. Activities of dihydroxyacetone phosphate acyl transferase, beta-oxidation of lignoceric acid and alpha-oxidation of phytanic acid were almost exclusively associated with the distribution of catalase activity (a marker enzyme for peroxisomes) in the gradient. This protocol should be a resource for studies designed to investigate the structure and function of peroxisomes in brain cells.

Animals↗
PubMed2000

The role of tear physiology in ocular surface temperature.

PURPOSE: To determine whether the more rapid cooling of the tear film in dry eyes is related to other tear film parameters, a battery of tear physiology tests was performed on dry eye patients and control subjects. METHODS: Tear evaporation rate was measured with a modified Servomed (vapour pressure) evaporimeter and ocular temperature with an NEC San-ei 6T62 Thermo Tracer in 9 patients diagnosed as having dry eye and in 13 healthy control subjects. Variability in temperature across the ocular surface was described by the temperature variation factor (TVF). Lipid layer structure and tear film stability were assessed with the Keeler Tearscope and tear osmolality was measured by freezing point depression nanolitre osmometry. RESULTS: The data were explored by principal component analysis. The subjects with and without dry eye could be separated into two distinct groups entirely on the basis of their tear physiology. Dry eye patients exhibited higher tear evaporation rates, osmolalities and TVF, lower tear film stabilities and poorer-quality lipid layers than the control subjects. A significant linear relationship was found to exist between tear evaporation rate and TVF for all subjects (R2 = 0.242, p = 0.024). CONCLUSIONS: Rapid cooling of the tear film in dry eyes appears to be related to the reduced stability of the tears and the increased rate of evaporation. The higher latent heat of vaporisation, associated with the increased evaporation in dry eyes, may account for the increased rate of cooling of the tear film in this condition.

Adult↗
PubMed2000

Interleukin-10 and interleukin-13 inhibit proinflammatory cytokine-induced ceramide production through the activation of phosphatidylinositol 3-kinase.

Ceramide produced by hydrolysis of plasma membrane sphingomyelin (SM) in different cells including brain cells in response to proinflammatory cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta)] plays an important role in coordinating cellular responses to stress, growth suppression, and apoptosis. The present study underlines the importance of IL-10 and IL-13, cytokines with potent antiinflammatory properties, in inhibiting the proinflammatory cytokine (TNF-alpha and IL-1beta)-mediated degradation of SM to ceramide in rat primary astrocytes. Treatment of rat primary astrocytes with TNF-alpha or IL-1beta led to rapid degradation of SM to ceramide, whereas IL-10 and IL-13 by themselves were unable to induce the degradation of SM to ceramide. Interestingly, both IL-10 and IL-13 prevented proinflammatory cytokine-induced degradation of SM to ceramide. Both IL-10 and IL-13 caused rapid activation of phosphatidylinositol (PI) 3-kinase, and inhibition of that kinase activity by wortmannin and LY294002 potently blocked the inhibitory effect of IL-10 and IL-13 on proinflammatory cytokine-mediated induction of ceramide production. This study suggests that the inhibition of proinflammatory cytokine-mediated degradation of SM to ceramide by IL-10 and IL-13 is mediated through the activation of PI 3-kinase. As ceramide induces apoptosis and IL-10 and IL-13 inhibit the induction of ceramide production, we examined the effect of IL-10 and IL-13 on proinflammatory cytokine-mediated apoptosis. Inhibition of TNF-alpha-induced apoptosis by IL-10 and IL-13 suggests that the antiapoptotic nature of IL-10 and IL-13 is probably due to the inhibition of ceramide production.

Androstadienes↗
PubMed2000

Inducible nitric oxide synthase in the central nervous system of patients with X-adrenoleukodystrophy.

X-Adrenoleukodystrophy (X-ALD) is an inherited peroxisomal disorder of deficient catabolism of very long-chain (VLC) fatty acids with resulting neuroinflammatory demyelinating disease. Our recent documentation of nitric oxide (NO)-mediated increase in VLC fatty acid levels in glial cells and demonstration of greater increase of VLC fatty acids levels in the inflammatory region (plaque) of X-ALD brain as compared to the normal-looking region away from the plaque prompted us to investigate the possible involvement of NO in the pathophysiology of X-ALD. Herein we provide evidence of the expression of inducible nitric oxide synthase (iNOS) in the CNS of X-ALD patients. In situ hybridization demonstrated that iNOS mRNA was present in brain tissues from X-ALD patients but not in normal controls. Double-labeling immunofluorescence studies using cell-specific markers confirmed that iNOS-expressing cells in the CNS of X-ALD were astrocytes and microglia/macrophages. Finally, antibodies against nitrotyrosine strongly immunoreacted with tissues from the center of the plaque region of X-ALD brains suggesting the presence of the NO reaction product nitrotyrosine in the CNS of X-ALD. Taken together, these results demonstrate that iNOS is expressed in the brains of patients with X-ALD and may contribute to the pathogenesis of the disease.

Adrenoleukodystrophy↗
PubMed2000

Renal cell carcinoma in cases of adult polycystic kidney disease: changing diagnostic and therapeutic implications.

Renal cell carcinoma in adult polycystic kidney disease is of rare occurrence and poses a diagnostic and therapeutic challenge. We have treated three such patients in our department. One was male and two were females ranging in age from 20 to 60 years. All were diagnosed preoperatively with ultrasonography or contrast-enhanced CT. Radical nephrectomy was performed in all patients. During the follow-up no patient had recurrence in the contralateral kidney. One patient had local recurrence in the renal fossa and was treated with local radiotherapy and immunotherapy. In the past due to difficulty in diagnosis, invasive investigations like angiography were recommended and prophylactic contralateral nephrectomy was often undertaken. With the availability of reliable noninvasive investigations these patients can be diagnosed accurately and the contralateral kidney saved in most cases.

Adult↗
PubMed2000

Increased vascular adrenergic vasoconstriction and decreased vasodilation in blacks. Additive mechanisms leading to enhanced vascular reactivity.

Blood pressure reactivity is enhanced in young black subjects through mechanisms that are poorly understood. We compared alpha-adrenergic-mediated vasoconstrictor and ss-adrenergic vasodilator sensitivity and their relation to sympathetic activity in blacks and whites. Ten healthy black (age, 29.9+/-2.4 years) and 10 white (age, 28.3+/-1.9 years) men were studied. Forearm blood flow was measured with strain-gauge plethysmography after the intrabrachial artery administration of phenylephrine (1.25 to 20 microgram/min) and isoproterenol (60 and 400 ng/min) after application of lower-body negative pressure and after a cold pressor test. Forearm and systemic norepinephrine spillover were measured with a radioisotope dilution technique. alpha-Adrenergic vasoconstriction was markedly increased (ANOVA P=0.008) and ss-adrenergic vasodilation decreased (ANOVA P=0.02) in blacks. Phenylephrine (10 microgram/min) decreased forearm blood flow by 58.0+/-2.5% in blacks but only by 26.6+/-6.0% in whites (P<0.001). Vasoconstrictor response to endogenous norepinephrine, stimulated by a cold pressor test, resulted in a higher forearm vascular resistance in blacks than in whites (107.3+/-13 versus 64.8+/-13 mm Hg. mL(-)(1). 100 mL(-)(1), P=0.03). There were no significant ethnic differences in basal or stimulated forearm or systemic norepinephrine spillover. Increased vasoconstrictor and decreased vasodilator responses in blacks were not correlated. Increased sympathetically mediated vascular tone caused by enhanced vasoconstriction and attenuated vasodilation, effects that would be additive, and not increased sympathetic activity could enhance vascular reactivity and may play a role in the pathogenesis of hypertension in blacks.

Adrenergic alpha-Agonists↗
PubMed2000

Endotoxin-induced alterations of lipid and fatty acid compositions in rat liver peroxisomes.

The structure/function of peroxisomal lipids in rat liver treated with a sublethal dose of endotoxin, a lipopolysaccharide (LPS), was investigated. Peroxisomes isolated from LPS-treated rat liver had remarkable alterations in lipid content compared with saline treated control liver peroxisomes. Cholesterol and phospholipids (PL) decreased significantly by 28.7% and 50.8%, respectively, leading to the change in the ratio of cholesterol/phospholipids (control 0.081 versus LPS 0.118, P < 0.001). A quantitative analysis from LPS-treated rat liver peroxisomes showed a general decrease in all classes of PL. No such alterations were observed in lipid content of other subcellular organelles. The peroxisomal fatty acid composition in LPS-treated animals was also altered. An analysis of fatty acid composition in PL and phosphatidylcholine from LPS-treated peroxisomes showed an increase in arachidonic acid (C20:4) and docosahexaenoic acid (C22:6). Very long chain (VLC) fatty acids (> C22:0) were also found increased in all classes of lipids in LPS-treated peroxisomes. Gadolinium chloride (GAD) mediated inactivation of Kupffer cells (KC) normalized cholesterol/PL ratio in LPS-treated peroxisomes. Collectively, the results indicate that the peroxisome metabolism of lipids and fatty acids is specifically altered in endotoxin-treated rat liver and at least part of the alterations may be mediated by factors released by KC.

Animals↗
PubMed2000

Bioequivalence of rifampicin when administered as a fixed-dose combined formulation of four drugs versus separate formulations.

A bioequivalence study of the antitubercular drug rifampicin in a four-drug combination (rifampicin, isoniazid, pyrazinamide and ethambutol) and separate formulations of the drugs at the same dose levels was carried out in a group of 22 healthy male volunteers. The investigation was designed as an open crossover study. The drugs were administered once in individual formulations and once in a fixed-dose combination. The WHO-approved protocol was followed according to which six blood samples were collected over a period of 8 h for each volunteer and each experimental session. Pooled urine samples were also collected during the study. Rifampicin and desacetyl rifampicin concentrations in both plasma and urine samples were assessed. Various pharmacokinetic parameters such as AUC0-8 h, Cmax and Tmax were calculated for both rifampicin and desacetyl rifampicin. The results indicated that combined (the four-drug combination) and separate formulations are bioequivalent for rifampicin.

Adult↗
PubMed2000

Evaluation of rifampicin bioequivalence in fixed-dose combinations using the WHO/IUATLD recommended protocol.

For an accurate assessment of rifampicin bioequivalence from fixed-dose combinations (FDCs), and to reduce the time and cost constraints associated with bioequivalence studies, the World Health Organization and the International Union Against Tuberculosis and Lung Disease have developed a simplified screening protocol. This study was undertaken with the objective of testing the applicability of this protocol for all types of FDCs. Data were obtained for volunteers common to three studies, and pharmacokinetic parameters were evaluated by different statistical tests. From the results, it has been demonstrated that the simplified screening protocol is suitable for evaluating the bioequivalence of rifampicin in all the types of FDCs available on the market.

Adult↗
PubMed1999

Hemangiopericytoma in a child: a case report.

Hemangiopericytoma (HPC) is a rare vascular tumour seen infrequently in the paediatric age group. It has an incidence of about 10% in children. The difficulty in assessing the malignant potential of this tumour may cause confusion to the clinician in deciding the proper line of management.

Adolescent↗
PubMed1999

Plasma urokinase antigen and plasminogen activator inhibitor-1 antigen levels predict angiographic coronary restenosis.

BACKGROUND: The fibrinolytic system is intimately involved in several processes that contribute to restenosis, including clot dissolution, cell migration, and tissue remodeling. However, the role of the individual activators (urokinase [uPA] and tissue plasminogen [tPA] activators) and inhibitors (plasminogen activator inhibitor [PAI-1]) of the fibrinolytic system in maintaining patency after coronary artery angioplasty and stenting is unclear. METHODS AND RESULTS: We prospectively studied 159 patients with stable angina who underwent successful elective angioplasty (n=110) or stenting (n=49) of de novo native coronary artery lesions. Plasma samples were drawn at baseline (before angioplasty) and serially after angioplasty (immediately afterward and 6 hours, 24 hours, 3 days, 7 days, 1 month, 3 months, and 6 months afterward). Antigen and activity assays were performed for uPA, tPA, and PAI-1. Follow-up quantitative coronary angiography was performed in 92% of eligible patients. The overall angiographic restenosis rate (diameter stenosis >50%) was 31% (37% in PTCA patients, 17% in stented patients). At all time periods, including baseline, uPA antigen levels were significantly higher and PAI-1 antigen levels were significantly lower in patients with restenosis. Restenosis rates for patients in the upper tertile of baseline uPA antigen levels were 2-fold higher than for those in the lower 2 tertiles (46% versus 24% and 22%, respectively; P<0.004). In a stepwise regression multivariate analysis, obstruction diameter after the procedure and uPA antigen were significant predictors of follow-up diameter stenosis. CONCLUSIONS: Plasma uPA antigen levels and PAI-1 antigen levels identify patients at increased risk for restenosis after percutaneous coronary revascularization.

Aged↗
PubMed1999

Structural organization of mammalian lipid phosphate phosphatases: implications for signal transduction.

This article describes the regulation of cell signaling by lipid phosphate phosphatases (LPPs) that control the conversion of bioactive lipid phosphates to their dephosphorylated counterparts. A structural model of the LPPs, that were previously called Type 2 phosphatidate phosphatases, is described. LPPs are characterized by having no Mg(2+) requirement and their insensitivity to inhibition by N-ethylmaleimide. The LPPs have six putative transmembrane domains and three highly conserved domains that define a phosphatase superfamily. The conserved domains are juxtaposed to the proposed membrane spanning domains such that they probably form the active sites of the phosphatases. It is predicted that the active sites of the LPPs are exposed at the cell surface or on the luminal surface of intracellular organelles, such as Golgi or the endoplasmic reticulum, depending where various LPPs are expressed. LPPs could attenuate cell activation by dephosphorylating bioactive lipid phosphate esters such as phosphatidate, lysophosphatidate, sphingosine 1-phosphate and ceramide 1-phosphate. In so doing, the LPPs could generate alternative signals from diacylglycerol, sphingosine and ceramide. The LPPs might help to modulate cell signaling by the phospholipase D pathway. For example, phosphatidate generated within the cell by phospholipase D could be converted by an LPP to diacylglycerol. This should change the relative balance of signaling by these two lipids. Another possible function of the LPPs relates to the secretion of lysophosphatidate and sphingosine 1-phosphate by activated platelets and other cells. These exogenous lipids activate phospholipid growth factor receptors on the surface of cells. LPP activities could attenuate cell activation by lysophosphatidate and sphingosine 1-phosphate through their respective receptors.

Amino Acid Sequence↗
PubMed1999

Amelioration of experimental allergic encephalomyelitis in Lewis rats by lovastatin.

Proinflammatory cytokines and inducible nitric oxide synthase (iNOS) are involved in the pathogenesis of experimental allergic encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). We have previously reported that lovastatin (Pahan, K., Sheikh., F.G., Namboodiri, A. and Singh, I., Lovastatin and Phenylacetate inhibit the induction of nitric oxide synthase and cytokines in rat primary astrocytes, microglia and macrophages. J. Clin. Invest., 100 (1997) 2671-2679.), an inhibitor of the mevalonate pathway, inhibits the expression of iNOS and proinflammatory cytokines in rat primary glial cells (astroglia and microglia) and macrophages. The present study underlines the therapeutic importance of lovastatin in ameliorating the neuroinflammatory disease process in the central nervous system of EAE rats. Immunohistochemical results show a higher degree of expression of iNOS, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in brains of rats with acute monophasic EAE relative to the control animals. Administration of lovastatin inhibited the expression of iNOS, TNF-alpha and IFN-gamma in the CNS of EAE rats and improved the clinical signs of EAE suggesting that this compound may have therapeutic potential in the treatment of neuroinflammatory diseases like MS.

Animals↗
PubMed1999

Lipid phosphate phosphohydrolase-1 degrades exogenous glycerolipid and sphingolipid phosphate esters.

Lipid phosphate phosphohydrolase (LPP)-1 cDNA was cloned from a rat liver cDNA library. It codes for a 32-kDa protein that shares 87 and 82% amino acid sequence identities with putative products of murine and human LPP-1 cDNAs, respectively. Membrane fractions of rat2 fibroblasts that stably expressed mouse or rat LPP-1 exhibited 3.1-3. 6-fold higher specific activities for phosphatidate dephosphorylation compared with vector controls. Increases in the dephosphorylation of lysophosphatidate, ceramide 1-phosphate, sphingosine 1-phosphate and diacylglycerol pyrophosphate were similar to those for phosphatidate. Rat2 fibroblasts expressing mouse LPP-1 cDNA showed 1.6-2.3-fold increases in the hydrolysis of exogenous lysophosphatidate, phosphatidate and ceramide 1-phosphate compared with vector control cells. Recombinant LPP-1 was located partially in plasma membranes with its C-terminus on the cytosolic surface. Lysophosphatidate dephosphorylation was inhibited by extracellular Ca2+ and this inhibition was diminished by extracellular Mg2+. Changing intracellular Ca2+ concentrations did not alter exogenous lysophosphatidate dephosphorylation significantly. Permeabilized fibroblasts showed relatively little latency for the dephosphorylation of exogenous lysophosphatidate. LPP-1 expression decreased the activation of mitogen-activated protein kinase and DNA synthesis by exogenous lysophosphatidate. The product of LPP-1 cDNA is concluded to act partly to degrade exogenous lysophosphatidate and thereby regulate its effects on cell signalling.

Animals↗
PubMed1999

Inhibition of phosphatidylinositol 3-kinase induces nitric-oxide synthase in lipopolysaccharide- or cytokine-stimulated C6 glial cells.

Nitric oxide (NO) produced by inducible nitric-oxide synthase (iNOS) in different cells including brain cells in response to proinflammatory cytokines plays an important role in the pathophysiology of demyelinating and neurodegenerative diseases. The present study underlines the importance of phosphatidylinositol 3-kinase (PI 3-kinase) in the expression of iNOS in C6 glial cells and rat primary astrocytes. Bacterial lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) was unable to induce the expression of iNOS and the production of NO in rat C6 glial cells. Similarly, wortmannin and LY294002, compounds that inhibit PI 3-kinase, were also unable to induce the expression of iNOS and the production of NO. However, a combination of wortmannin or LY294002 with LPS or IL-1beta induced the expression of iNOS and the production of NO in C6 glial cells. Consistent with the induction of iNOS, wortmannin also induced iNOS promoter-derived chloramphenicol acetyltransferase activity in LPS- or IL-1beta-treated C6 glial cells. The expression of iNOS by LPS in C6 glial cells expressing a dominant-negative mutant of p85alpha, the regulatory subunit of PI 3-kinase, further supports the conclusion that inhibition of PI 3-kinase provides a necessary signal for the induction of iNOS. Next we examined the effect of wortmannin on the activation of mitogen-activated protein (MAP) kinase and nuclear factor NF-kappaB in LPS- or IL-1beta-stimulated C6 glial cells. In contrast to the inability of LPS and IL-1beta alone to induce the expression of iNOS, both LPS and IL-1beta individually stimulated MAP kinase activity and induced DNA binding and transcriptional activity of NF-kappaB. Wortmannin alone was unable to activate MAP kinase and NF-kappaB. Moreover, wortmannin had no effect on LPS- or IL-1beta-mediated activation of MAP kinase and NF-kappaB, suggesting that wortmannin induced the expression of iNOS in LPS- or IL-1beta-stimulated C6 glial cells without modulating the activation of MAP kinase and NF-kappaB. Similar to C6 glial cells, wortmannin also stimulated LPS-mediated expression of iNOS and production of NO in astrocytes without affecting the LPS-mediated activation of NF-kappaB. Taken together, the results from specific chemical inhibitors and dominant-negative mutant expression studies demonstrate that apart from the activation of NF-kappaB, inhibition of PI 3-kinase is also necessary for the expression of iNOS and production of NO.

Androstadienes↗
PubMed1999

The role of oxidative stress in rhinovirus induced elaboration of IL-8 by respiratory epithelial cells.

A direct correlation has been reported between the severity of symptoms associated with rhinovirus infection and the concentration of interleukin-8 in nasal secretions. The purpose of these studies was to examine the mechanism of rhinovirus-induced IL-8 elaboration. Rhinovirus infection induced oxidative stress in Beas-2b cells and the concentration of H2O2 in supernatant media from rhinovirus challenged cells was 12.5 +/- 6.1 microM 1 h after challenge compared to 0.7 +/- 0.3 microM in supernatant from control cells. N-acetyl cysteine inhibited RV-induced NF-kappaB activation and IL-8 elaboration. IL-8 concentrations were 36 +/- 2 pg/ml and 10 +/- 1 pg/ml 6 h after virus challenge in untreated and NAC-treated (30 mM NAC) cells, respectively. Despite the effects of NAC on IL-8 elaboration and NF-kappaB activation, RV stimulated increases in supernatant H2O2 were not altered by NAC. These data suggest that RV stimulation of IL-8 in respiratory epithelium is mediated through production of oxidative species and the subsequent activation of NF-kappaB.

Acetylcysteine↗