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Biomedical subjects

R Singh

Publications and source records attributed to R Singh.

At least 181 records · Page 10Linked to original sources
PubMed2001

High glucose decreases matrix metalloproteinase-2 activity in rat mesangial cells via transforming growth factor-beta1.

Diabetic nephropathy is characterized by accumulation of mesangial matrix. Glucose-induced inhibition of matrix-degrading enzymes such as collagenases is believed to contribute to matrix accumulation. We have previously demonstrated that 72 kDa type IV collagenase activity is decreased in the rat mesangial cells cultured in high glucose media [Diabetes 1995;44:929-935]. The present studies were designed to investigate if the cytokine transforming growth factor-beta1 (TGF-beta1) mediates this effect of glucose. Type IV collagenases degrade type IV collagen as well as gelatin (denatured collagen) and are thus also called gelatinases. They belong to the family of matrix metalloproteinases (MMPs); MMP activity is controlled by tissue inhibitors of metalloproteinases (TIMPs). The activity of 72 kDa type IV collagenase, also known as matrix metalloproteinase-2 (MMP-2), was assessed using three methods: (1) fluoresceinated gelatin degradation assay to detect free enzyme activity (activity which is present in excess of TIMP-inhibited activity); (2) zymography to measure total (free + TIMP-bound) enzyme activity; (3) ELISA using specific antibodies to measure MMP-2 levels. TGF-beta1 and TIMP-2 levels were also determined by ELISA. Incubation of primary cultures of rat mesangial cells for 5 days in 30 vs. 5 mM glucose resulted in a 3-fold increase in production of total TGF-beta1, a significant decrease in MMP-2 activity and immunoreactive MMP-2 levels, and an increase in TIMP-2 levels. Addition of exogenous TGF-beta1 to mesangial cells incubated in 5 mM glucose replicated the high glucose effect by producing a significant decrease in MMP-2 levels with a concurrent increase in TIMP-2 levels. Furthermore, glucose-induced inhibition of MMP-2 activity was completely blocked by neutralization of TGF-beta1 with anti-TGF-beta1 antibody. We conclude that the decrease in MMP-2 activity induced by glucose loading is mediated via TGF-beta1.

Animals↗
PubMed2001

Receptors for the carboxyl-terminal region of pth(1-84) are highly expressed in osteocytic cells.

PTH is a potent systemic regulator of cellular differentiation and function in bone. It acts upon cells of the osteoblastic lineage via the G protein-coupled type-1 PTH/PTH-related peptide receptor (PTH1R). Carboxyl fragments of intact PTH(1-84) (C-PTH fragments) are cosecreted with it by the parathyroid glands in a calcium-dependent manner and also are generated via proteolysis of the hormone in peripheral tissues. Receptors that recognize C-PTH fragments (CPTHRs) have been described previously in osteoblastic and chondrocytic cells. To directly study CPTHRs in bone cells, we isolated clonal, conditionally transformed cell lines from fetal calvarial bone of mice that are homozygous for targeted ablation of the PTH1R gene and transgenically express a temperature-sensitive mutant SV40 T antigen. Cells with the highest specific binding of the CPTHR radioligand (125)I-[Tyr(34)]hPTH(19-84) exhibited a stellate, dendritic appearance suggestive of an osteocytic phenotype and expressed 6- to 10-fold more CPTHR sites/cell than did osteoblastic cells previously isolated from the same bones. In these osteocytic (OC) cells, expression of mRNAs for CD44, connexin 43, and osteocalcin was high, whereas that for alkaline phosphatase and cbfa-1/osf-2 was negligible. The CPTHR radioligand was displaced completely by hPTH(1-84), hPTH(19-84) and hPTH(24-84) (IC(50)s = 20-50 nM) and by hPTH(39-84) (IC(50) = 500 nM) but only minimally (24%) by 10,000 nM hPTH(1-34). CPTHR binding was down-regulated dose dependently by hPTH(1-84), an effect mimicked by ionomycin and active phorbol ester. Human PTH(1-84) and hPTH(39-84) altered connexin 43 expression and increased apoptosis in OC cells. Apoptosis induced by PTH(1-84) was blocked by the caspase inhibitor DEVD. We conclude that osteocytes, the most abundant cells in bone, may be principal target cells for unique actions of intact PTH(1-84) and circulating PTH C-fragments that are mediated by CPTHRs.

Animals↗
PubMed2001

Depot-specific variation in protein-tyrosine phosphatase activities in human omental and subcutaneous adipose tissue: a potential contribution to differential insulin sensitivity.

Compared with the sc depot, omental (om) adipose tissue is relatively resistant to the metabolic actions of insulin. Protein-tyrosine phosphatases (PTPases) modulate receptor kinase activation and signal transduction in insulin-sensitive tissues, and their activity is dependent on the reduced state of the cysteine thiol required for catalysis. Using a novel anaerobic technique to avoid air oxidation, we found that the mean endogenous PTPase activity was 2.1-fold higher in om compared with paired samples of sc adipose tissue (P < 0.003). The specific activity of PTP1B isolated under anaerobic conditions was also 41% higher in om adipose tissue (P < 0.001). Interestingly, the total PTPase activity from both adipose depots and the specific activity of PTP1B was increased by 42-71% after reduction in vitro with dithiothreitol, indicating that a major fraction of the cellular PTPase activity can be reactivated by sulfhydryl reduction. The mass of the insulin receptor beta-subunit and the PTPases PTP1B and leukocyte antigen related was not significantly different between the two adipose depots. These studies provide the first demonstration that endogenous PTPase activity, including PTP1B, is increased in om adipose tissue and may contribute to the relative insulin resistance of this fat depot. The finding that a substantial fraction of PTPase activity in human adipose tissue is present in a latent, oxidized form also suggests a potential means of in vivo regulation of these important cellular enzymes that modulate the insulin signaling cascade.

Adipose Tissue↗
PubMed2001

Redundant function of Runt Domain binding partners, Big brother and Brother, during Drosophila development.

The Core Binding Factor is a heterodimeric transcription factor complex in vertebrates that is composed of a DNA binding alpha-subunit and a non-DNA binding beta-subunit. The alpha-subunit is encoded by members of the Runt Domain family of proteins and the beta-subunit is encoded by the CBF beta gene. In Drosophila, two genes encoding alpha-subunits, runt and lozenge, and two genes encoding beta-subunits, Big brother and Brother, have been previously identified. Here, a sensitized genetic screen was used to isolate mutant alleles of the Big brother gene. Expression studies show that Big brother is a nuclear protein that co-localizes with both Lozenge and Runt in the eye imaginal disc. The nuclear localization and stability of Big brother protein is mediated through the formation of heterodimeric complexes between Big brother and either Lozenge or Runt. Big brother functions with Lozenge during cell fate specification in the eye, and is also required for the development of the embryonic PNS. ds-RNA-mediated genetic interference experiments show that Brother and Big brother are redundant and function together with Runt during segmentation of the embryo. These studies highlight a mechanism for transcriptional control by a Runt Domain protein and a redundant pair of partners in the specification of cell fate during development.

Animals↗
PubMed2001

Identification of persons with cardiorespiratory conditions who are at risk of dying from the acute effects of ambient air particles.

This study was undertaken to identify subgroups of the population susceptible to the effects of ambient air particles. Fixed-site air pollution monitors in Montreal, Quebec, Canada, provided daily mean levels of various measures of particulates and gaseous pollutants. Total sulfates were also measured daily (1986-1993) at a monitoring station 150 km southeast of the city (Sutton, Quebec, Canada). We used coefficient of haze (COH), extinction coefficient, and Sutton sulfates to predict fine particles and sulfates from a fine particles model for days that were missing. We used the universal Quebec medicare system to obtain billings and prescriptions for each Montreal resident who died in the city from 1984 to 1993. These data were then used to define cardiovascular and respiratory conditions that subjects had before death. Using standard Poisson regression time-series analyses, we estimated the association between daily nonaccidental mortality and daily concentrations of particles in the ambient air among persons with cardiovascular and respiratory conditions diagnosed before death. We found no persuasive evidence that daily mortality increased when ambient air particles were elevated for subgroups of persons with chronic upper respiratory diseases, airways disease, cerebrovascular diseases, acute coronary artery disease, and hypertension. However, we found that daily mortality increased linearly as concentrations of particles increased for persons who had acute lower respiratory diseases, chronic coronary artery diseases (especially in the elderly), and congestive heart failure. For this latter set of conditions, the mean percent increase in daily mortality (MPC) for an increase in the COH across its interquartile range (18.5 COH units per 327.8 linear meters), averaged over the day of death and the 2 preceding days, was MPC = 5.09% [95% confidence interval (CI) 2.47-7.79%], MPC = 2.62 (95% CI 0.53-4.75%), and MPC = 4.99 (95% CI 2.44-7.60%), respectively. Adjustments for gaseous pollutants generally attenuated these associations, although the general pattern of increased daily mortality remained. In addition, there appeared to be a stronger association in the summer season. The positive associations found for persons who had acute lower respiratory diseases and congestive heart failure are consistent with some prevailing hypotheses and may also be consistent with recent toxicologic data implicating endothelins. Further epidemiologic studies are required to confirm these findings.

Aged↗
PubMed2001

Enzyme kinetics of cytochrome P450-mediated reactions.

The most common drug-drug interactions may be understood in terms of alterations of metabolism, associated primarily with changes in the activity of cytochrome P450 (CYP) enzymes. Kinetic parameters such as Km, Vmax, Ki and Ka, which describe metabolism-based drug interactions, are usually determined by appropriate kinetic models and may be used to predict the pharmacokinetic consequences of exposure to one or multiple drugs. According to classic Michaelis-Menten (M-M) kinetics, one binding site models can be employed to simply interpret inhibition (pure competitive, non-competitive and uncompetitive) or activation of the enzyme. However, some cytochromes P450, in particular CYP3A4, exhibit unusual kinetic characteristics. In this instance, the changes in apparent kinetic constants in the presence of inhibitor or activator or second substrate do not obey the rules of M-M kinetics, and the resulting kinetics are not straightforward and hamper mechanistic interpretation of the interaction in question. These unusual kinetics include substrate activation (autoactivation), substrate inhibition, partial inhibition, activation, differential kinetics and others. To address this problem, several kinetic models can be proposed, based upon the assumption that multiple substrate binding sites exist at the active site of a particular P450, and the resulting kinetic constants are, therefore, solved to adequately describe the observed interaction between multiple drugs. The following is an overview of some cytochrome P450-mediated classic and atypical enzyme kinetics, and the associated kinetic models. Applications of these kinetic models can provide some new insights into the mechanism of P450-mediated drug-drug interactions.

Algorithms↗
PubMed2001

Levels of malondialdehyde-deoxyguanosine in the gastric mucosa: relationship with lipid peroxidation, ascorbic acid, and Helicobacter pylori.

Helicobacter pylori infection is associated with elevated gastric mucosal concentrations of the lipid peroxidation product malondialdehyde and reduced gastric juice vitamin C concentrations. Malondialdehyde can react with DNA bases to form the mutagenic adduct malondialdehyde-deoxyguanosine (M(1)-dG). We aimed to determine gastric mucosal levels of M(1)-dG in relation to H. pylori infection and malondialdehyde and vitamin C concentrations. Patients (n = 124) attending for endoscopy were studied. Levels of antral mucosal M(1)-dG were determined using a sensitive immunoslot-blot technique; antral mucosal malondialdehyde was determined by thiobarbituric acid extraction, and gastric juice and antral mucosal ascorbic acid and total vitamin C were determined by high-performance liquid chromatography. Sixty-four H. pylori-positive patients received eradication therapy, and endoscopy was repeated at 6 and 12 months. Levels of M(1)-dG did not differ between subjects with H. pylori gastritis (n = 85) and those with normal mucosa without H. pylori infection (n = 39; 56.6 versus 60.1 adducts/10(8) bases) and were unaffected by age or smoking habits. Malondialdehyde levels were higher (123.7 versus 82.5 pmol/g; P < 0.001), gastric juice ascorbic acid was lower (5.7 versus 15.0 micromol/ml; P < 0.001), and antral mucosal ascorbic acid was unchanged (48.0 versus 42.7 micromol/g) in H. pylori gastritis compared with normal mucosa. Multiple regression analysis revealed that M(1)-dG increased significantly with increasing levels of malondialdehyde, antral ascorbic acid, and total antral vitamin C. M(1)-dG levels were unchanged 6 months (63.3 versus 87.0 adducts/10(8) bases; P = 0.24; n = 38) and 12 months (66.7 versus 77.5 adducts/10(8) bases; P = 0.8; n = 13) after successful eradication of H. pylori. M(1)-dG thus is detectable in gastric mucosa, but is not affected directly by H. pylori.

Adult↗
PubMed2001

Comparative functional characterization of mouse bone marrow-derived mast cells and peritoneal mast cells in response to non-immunological stimuli.

The cultured mouse mast cells that are dependent on spleen-derived factor for their proliferation and maintenance and have been shown to be similar to mucosal mast cells in terms of their T-cell dependence and histochemical staining characteristics. Mast cell heterogeneity has been confirmed by functional characterization of mouse bone marrow-derived mast cells (MBMMC) and mouse peritoneal mast cells (MPMCs). MPMCs released around 30% of histamine when stimulated with compound 48/80 whereas MBMMC were almost unresponsive to the same stimulus. Calcium Ionophore A23187 on the other hand, released histamine in dose-dependent manner from MBMMC. The study was undertaken to investigate the effect of antiallergic drug, disodium cromoglycate (DSCG), a synthetic cromone and quercetin, a plant-derived flavonoid on Ca ionophore A23187 induced histamine release from MBMMC. MBMMCs were almost unresponsive to DSCG whereas Ca Ionophore induced histamine release was blocked by Quercetin. The results indicate that response of mast cells at one anatomic site to a given stimulus does not necessarily predict the response of mast cells at a different anatomic location to the same stimulus. It shows functional heterogeneity within a single species. So, it cannot be assumed that antiallergic compounds stabilizing mast cells in one tissue site or organ will be equally efficacious against mast cells in other sites.

Animals↗
PubMed2001

Leiomyosarcoma of the gallbladder: a case report.

Primary sarcoma of the gallbladder is a rare disease. The tumor occurs more frequently in women. Usually gallstones are present. Symptoms resemble those of cholelithiasis or cholecystitis. The diagnosis is rarely made preoperatively. The patient was a 51-year-old woman with a 2-month history of right upper quadrant pain, nausea, vomiting, and a 10-pound weight loss. Ultrasound showed cholelithiasis and cholecystitis. Laparoscopic cholecystectomy was converted to open as a result of dense tissue in the middle to distal gallbladder. Exploration by a right subcostal incision revealed multiple implants on the surface of the liver and the peritoneum of the upper abdomen. The wall of the gallbladder was very thick and inflamed. Cholecystectomy with liver biopsy was performed. Pathology revealed poorly differentiated epithelioid leiomyosarcoma of the gallbladder with extension to the liver. The disease followed a very aggressive course and the patient died 3 weeks after the procedure. Recommended treatment is extensive surgical resection that can be followed by radiotherapy or chemotherapy. The tumor follows a very aggressive course, which often lasts a few weeks. Prognosis is poor with rare reported 5-year survivals.

Diagnosis, Differential↗
PubMed2001

Reversible neurologic manifestations after glycerol: a short report.

A 46 year old male inadvertently consumed 500 ml of glycerol and presented with altered sensorium, focal neurologic signs and generalised seizures. He was managed conservatively and recovered fully within 48 hours. The case highlights the rare presentations of overdosage and neurologic effects with glycerol, an otherwise safe drug used in neurology.

Basal Ganglia Diseases↗
PubMed2001

Impact of gender on diabetes mellitus and its associated cardiovascular risk factors.

Diabetes mellitus is a common disorder associated with devastating chronic complications involving end-organ damage and cardiovascular disease. In addition, diabetes imposes a heavy burden due to medical costs, hospitalization, and time lost from work. Women who suffer from the condition have a high risk of developing the complications that stem from it, and, therefore, there must be unknown factors contributing to high mortality and morbidity among women with diabetes. There is a great need for future research to address the issues regarding women and diabetes to help clinicians develop preventive and management strategies that target this population.

Age Factors↗
PubMed2001

Potential for cytokine and product manipulation to improve the results of autologous stem cell transplantation for rheumatoid arthritis.

The eradication of autoreactive T cells by high dose therapy and stem cell transplantation and the resultant alterations in the immunologic network, thymic reeducation, and peripheral tolerance provide treatment mechanisms for autoimmune and inflammatory diseases. One outcome of autologous stem cell transplantation is a significant decrease in the CD4:CD8 ratio due to a loss in CD4+ cells and a depression in T cell function. Mechanistically, the loss of T cell function is associated with an increased frequency of circulating monocytes, their expression of Fas ligand (FasL), and a high frequency of apoptotic CD4+ T cells. This suggests that activated Fas+ CD4+ lymphocytes interact with FasL+ monocytes. resulting in apoptosis, preferential deletion of CD4+ T cells, an inversion in the CD4:CD8 ratio, and depressed T cell function. These observations suggest the potential for immune regulation using stem cell manipulation or posttransplant cytokine administration as therapeutic strategies for autoimmune/inflammatory diseases.

Apoptosis↗
PubMed2001

Pharmacokinetics and metabolism of a RAS farnesyl transferase inhibitor in rats and dogs: in vitro-in vivo correlation.

Compound I (1-(3-chlorophenyl)-4-[(1-(4-cyanobenzyl)-1H-imidazol-5-yl)methyl]piperazin-2-one) is a potent and selective inhibitor of farnesyl-protein transferase (FPTase). The pharmacokinetics and metabolism of compound I displayed species differences in rats and dogs. After oral administration, the drug was well absorbed in dogs but less so in rats. Following i.v. administration, compound I was cleared rapidly in rats in a polyphasic manner with a terminal t(1/2) of 41 min. The plasma clearance (CL(p)) and volume of distribution (V(dss)) were 41.2 ml/min/kg and 1.2 l/kg, respectively. About 1% of the dose was excreted in rat bile and urine as unchanged drug over a period of 24 h, suggesting that biotransformation is the major route of elimination of compound I. Using liquid chromatography (LC)-tandem mass spectometry, nineteen metabolites of compound I were identified in urine and bile from dogs and rats. Structures of two major metabolites were confirmed by LC-NMR. N-Dealkylation and phase II metabolism were the major metabolic pathways. Animal and human liver microsomal intrinsic clearance values were scaled to predict hepatic clearance and half-life in humans, and the predicted values were in good agreement to the in vivo data.

Algorithms↗
PubMed2001

Dermatoglyphic analysis in Malay subjects with bipolar mood disorder.

Dermatoglyphic is the study of the epidermal ridges and the pattern formed by them. It may be pointed out that genetic factors have a large share in determining the variations in dermatoglyphics. It is however, suggested by evidence that bipolar mood disorder factors are determined more by genetic factors than by the environmental factors. The experiment has been undertaken to look for the effects of the bipolar mood disorder on dermatoglyphics. The dermatoglyphic characteristics of subjects with bipolar mood disorder when compared with control group revealed significant differences. The radial loop were increased in bipolar mood disorder, but there were little changes in 'atd' angles between normal and bipolar mood disorder.

Bipolar Disorder↗
PubMed2001

Video game epilepsy.

Reflex epilepsy is the commonest form of epilepsy in which seizures are provoked by specific external stimulus. Photosensitive reflex epilepsy is provoked by environmental flicker stimuli. Video game epilepsy is considered to be its variant or a pattern sensitive epilepsy. The mean age of onset is around puberty and boys suffer more commonly as they are more inclined to play video games. Television set or computer screen is the commonest precipitants. The treatment remains the removal of the offending stimulus along with drug therapy. Long term prognosis in these patients is better as photosensitivity gradually declines with increasing age. We present two such case of epilepsy induced by video game.

Adolescent↗