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K Singh

Publications and source records attributed to K Singh.

At least 163 records · Page 9Linked to original sources
PubMed1999

Analysis of the role of glutamine 190 in the catalytic mechanism of murine leukemia virus reverse transcriptase.

To determine the catalytic role of Gln(190), a member of the highly conserved LPQG motif in Moloney murine leukemia virus reverse transcriptase, we carried out site-directed mutagenesis of this residue to generate Q190N and Q190A. Both mutant proteins exhibited a significant loss in their polymerase and pyrophosphorolysis activities with a more pronounced effect noted with the Gln --> Asn substitution. The catalytic efficiencies of the mutants exhibited a 40-70-fold reduction with poly(rC) and poly(dC) templates in the presence of Mg(2+) and a 10-20-fold reduction with poly(rA) template in the presence of Mn(2+). Interestingly, the K(m) for NTP exhibited only a moderate 3-10-fold increase irrespective of the template-primer and the metal ion. Photoaffinity labeling of both the mutant and the WT enzymes exhibited an identical affinity for RNA.DNA and DNA.DNA template-primers. However, unlike the WT enzyme, the mutant enzymes exhibited a significantly reduced ability to catalyze the nucleotidyltransferase reaction on the covalently immobilized template-primer. An examination of the rate constants for the first and the second nucleotide for the mutant enzymes indicated dissimilar rates, indicating that Gln(190) may be involved in a rate-limiting, conformational change step both before and after the phosphodiester bond formation. Furthermore, the processivity of DNA synthesis by the mutant enzymes was decreased severely, which may result from the lower catalytic efficiency as well as translocation defect.

Animals↗
PubMed1999

Inhibition of copper-zinc superoxide dismutase induces cell growth, hypertrophic phenotype, and apoptosis in neonatal rat cardiac myocytes in vitro.

Oxidative stress has been implicated in the pathophysiology of myocardial failure. We tested the hypothesis that inhibition of endogenous antioxidant enzymes can regulate the phenotype of cardiac myocytes. Neonatal rat ventricular myocytes in vitro were exposed to diethyldithiocarbamic acid (DDC), an inhibitor of cytosolic (Cu, Zn) and extracellular superoxide dismutase (SOD). DDC inhibited SOD activity and increased intracellular superoxide in a concentration-dependent manner. A low concentration (1 micromol/L) of DDC stimulated myocyte growth, as demonstrated by increases in protein synthesis, cellular protein, prepro-atrial natriuretic peptide, and c-fos mRNAs and decreased sarcoplasmic reticulum Ca(2+)ATPase mRNA. These actions were all inhibited by the superoxide scavenger Tiron (4,5-dihydroxy-1,3-benzene disulfonic acid). Higher concentrations of DDC (100 micromol/L) stimulated myocyte apoptosis, as evidenced by DNA laddering, characteristic nuclear morphology, in situ terminal deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL), and increased bax mRNA expression. DDC-stimulated apoptosis was inhibited by the SOD/catalase mimetic EUK-8. The growth and apoptotic effects of DDC were mimicked by superoxide generation with xanthine plus xanthine oxidase. Thus, increased intracellular superoxide resulting from inhibition of SOD causes activation of a growth program and apoptosis in cardiac myocytes. These findings support a role for oxidative stress in the pathogenesis of myocardial remodeling and failure.

Animals↗
PubMed1999

Species differences in cis-elements of the proalpha1(I) procollagen promoter and their binding proteins.

Previous studies suggest that there may be species differences in the utilization of cis-elements of the type I collagen genes. The present study was designed to examine this possibility by focusing on two regions of the proalpha1(I) collagen promoter. One is the GC-rich A1 region (-194/168) that modulates transcriptional activity of the mouse promoter. The other contains a glucocorticoid response element (GRE) implicated in negative glucocorticoid regulation of the rat promoter. Unlike mouse A1 probes, probes representing the analogous human (-195/-168) and rat (-193/-179) regions failed to bind nuclear proteins in gel shift assays. Binding assays with mouse A1 probes containing base substitutions indicated that this behavior could be ascribed to five bases in the human, and two in the rat sequences. In addition, the pattern of expression of c-Krox, a protein that alters transcriptional activity via the mouse A1 element, differed in mouse and human tissues. Computer analysis revealed differences in the arrangement of GRE half-sites in human and rat proalpha1(I) collagen promoters. In a region of the human promoter (-700/673) analogous to the rat (-672/-633), there are three half-sites, each separated by two nucleotides, that cooperate in binding of glucocorticoid receptor. There also is a proximal half-site at position -335 of the human promoter that binds glucocorticoid receptor, but it is not present in the rat promoter. This study has defined several species-specific differences in the sequences and nuclear protein binding activity of regions involved in transcriptional activity of the proalpha1(I) collagen promoter. The results suggest that the A1 regions of the human and rat promoters examined here are unlikely to function as regulatory cis-elements, and they provide a framework for investigating the role of GREs in transcriptional regulation. They also suggest that species differences in cis-elements and transcription factors should be taken into consideration when using heterologous systems to study collagen gene regulation.

3T3 Cells↗
PubMed1999

Tyrosine 222, a member of the YXDD motif of MuLV RT, is catalytically essential and is a major component of the fidelity center.

Tyrosine 222 of MuLV RT is an invariant residue of the highly conserved YXDD motif in the reverse transcriptase class of enzymes. The residue X is Met 184 in HIV-1 RT and Val 223 in MuLV RT. This residue has been implicated in the fidelity of DNA synthesis, whereas the role of the preceding tyrosine in this aspect, as well as in the catalytic mechanism of MuLV RT, remains to be elucidated. We have substituted Tyr 222 with Phe, Ser, and Ala by site-directed mutagenesis and have characterized the properties of the individual mutant enzymes. The results show that Tyr-->Phe substitution did not affect the polymerase activity of the enzyme, while Tyr-->Ser and Tyr-->Ala substitutions significantly reduced the polymerase activity. The pyrophosphorolysis activities of these mutants showed the same trend as the polymerase activities, suggesting an essential role for Y222 in the catalytic mechanism of MuLV RT. One of the most interesting observations of Y-->F substitution was the significantly increased fidelity of DNA synthesis on RNA templates. In addition, a limited extent of ribonucleotide incorporation on RNA template that was consistently noted with the wild-type enzyme was reduced with the Y222F mutant. The resistance to all four ddNTPs, however, persisted in the wild type and Y222 mutants on the RNA template. A ternary complex model of MuLV RT shows that (a) the aromatic ring of Tyr/Phe is positioned between the terminal and penultimate primer bases and (b) the phenolic OH group is seen within hydrogen bonding distance with the base moieties of two template and penultimate primer nucleotides. We propose that the base stacking interaction of Tyr 222 stabilizes the primer terminus position which is essential for the catalytic reaction. However, the weaker stacking interaction of Y compared to F, due to polarization of the pi-charge toward the phenoxyl-OH as well as the resonating character of its H-bond center, may provide slight flexibility to the position of the template base which may be responsible for the error-proneness of MuLV RT.

Base Pair Mismatch↗
PubMed1999

Studies on the Electrochemical Characterization of Cellulose Acetate and Dowex-50 Membranes for Uni-Univalent Electrolytes in Aqueous Solutions.

Membrane potential and bi-ionic potential studies using cellulose acetate and Dowex-50 membranes and sodium chloride and potassium chloride aqueous solutions have been carried out. The results have been used to estimate solute permeability, ionic transport numbers, fixed charge density, and surface charge density of both the membranes. Both membrane potential and bi-ionic potential are affected by adsorption of ions. Adsorbed ions affect the surface potential as well as solute retention capacity of the membranes. Solute retention expressed in terms of the "maximal retention" of membranes could thus be estimated. Furthermore, a correlation between permselectivity of the membrane and effective concentration with the dielectric constant of the membrane has also been established. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Fine-needle aspiration biopsy of orbital meningioma.

Fine-needle aspiration was performed on an orbital mass in a 53-yr-old woman. The cytologic diagnosis was meningioma, which was later confirmed by histologic study of biopsy material. The cytologic features of the aspirated material (nuclear pseudoinclusions, psammoma bodies, and cells arranged in syncytial sheets and whorls) allowed a rapid, reliable, outpatient diagnosis to be formulated. The cytologic features are discussed and the literature is reviewed. Diagn. Cytopathol. 1999;21:402-404.

Biopsy, Needle↗
PubMed1999

Marked non-uniformity of fiber-type composition in the primate suboccipital muscle obliquus capitis inferior.

Obliquus capitis inferior (OCI) is a monoarticular suboccipital muscle linking the transverse process of the atlas (C1) to the spinous process of the axis (C2). Histochemical analysis of fiber-type composition showed that the muscle has a marked gradient of fiber-type distribution in which type I fibers comprise 95-100% of fibers in the deepest region but less than 10% of fibers in the superficial layer. Step-like changes in fiber-type proportions occurred between groups of fascicles. In most instances the boundaries between these fascicles did not exhibit different perimysial features from those fascicles with similar fiber-type proportions. OCI contained large numbers of muscle spindles, which were concentrated in deep regions rich in type I fibers. The degree of nonuniformity in fiber-type distribution seen in OCI is unusually large when compared with patterns described in other primate muscles, and has implications for the way that the muscle is studied anatomically and physiologically.

Adenosine Triphosphatases↗
PubMed1999

Effects of carteolol and timolol on plasma lipid profiles in older women with ocular hypertension or primary open-angle glaucoma.

PURPOSE: To determine the effect on serum lipid levels of carteolol hydrochloride 1.0% or timolol maleate 0.5% given twice a day to women age 60 years and older with primary open-angle glaucoma or ocular hypertension. METHOD: We included 112 patients in this double-masked, randomized, multicenter trial. Fasting clinical laboratory studies were evaluated at baseline and at 12 weeks. Patients were instructed not to change their dietary, alcohol consumption, or exercise habits during the study. RESULTS: For the carteolol group, the high-density lipoprotein (HDL) and total cholesterol/high-density lipoprotein (TC/HDL) ratio at baseline of 50.1 +/- 1.5 mg/dl and 4.7 +/- 0.2 changed by the 12-week visit to 51.3 +/- 1.9 mg/dl (P = .25) and 4.6 +/- .02 (P = .47), respectively. For the timolol maleate group, the baseline HDL and TC/HDL ratio of 53.6 +/- 2.2 mg/dl and 4.4 +/- 0.2 changed to 50.2 +/- 1.9 mg/dl (P < .001) and 4.7 +/- 0.2 (P = .001), respectively, at the 12-week visit. Carteolol patients showed no significant change from baseline, whereas the HDL (P < .001) and TC/HDL ratio decreased (P = .001) significantly in the timolol maleate group. There also was a significant difference in the change from baseline at 12 weeks between carteolol and timolol maleate groups for the HDL and TC/HDL ratio (P = .01 and .012, respectively). No differences in TC, low-density lipoprotein (LDL), or triglycerides (TG) or in changes from baseline were observed between groups at 12 weeks (P > .05). At 12 weeks, no differences were observed between carteolol and timolol maleate groups in intraocular pressure or safety (P > .05), except that patients given carteolol demonstrated fewer solicited ocular symptoms (P = .007). CONCLUSIONS: Carteolol appears to be neutral in its effect on serum lipid levels, whereas timolol maleate adversely affects the HDL and TC/HDL ratio in women age 60 years and older with ocular hypertension or primary open-angle glaucoma.

Adrenergic beta-Antagonists↗
PubMed1999

Effect of the levonorgestrel-releasing intrauterine system on uterine myomas in a renal transplant patient.

The levonorgestrel-releasing intrauterine system (LNG-IUS) has been used in the treatment of both idiopathic menorrhagia and adenomyosis. An electronic search of the on-line medical literature revealed no reports of its use for menorrhagia secondary to uterine myomas. Presented here is the successful treatment of uterine myomas with menorrhagia in a woman with a renal transplant. There was a significant reduction in menorrhagia, dysmenorrhea, and uterine and myoma size with the use of the LNG-IUS. We believe that this system provides an alternative to conventional hysterectomy and gonadotrophin-releasing hormonal analog medical treatment for uterine myomas, with a possibly inhibitory effect on myoma growth.

Adult↗
PubMed1999

Medical treatment of a grossly enlarged adenomyotic uterus with the levonorgestrel-releasing intrauterine system.

Adenomyosis is an important cause of menorrhagia. Besides hysterectomy, the treatment options for adenomyosis have been limited. Presented here is the successful treatment of adenomyosis in a woman presenting with menorrhagia, dysmenorrhea, and an enlarging uterus, for whom conservative therapy initiated with mefenamic acid was unsatisfactory. The patient had insertion of the levonorgestrel-releasing intrauterine system (LNG-IUS). A marked decrease in uterine size occurred within 12 months of insertion accompanied by resolution of the menorrhagia and dysmenorrhea. Thus, the LNG-IUS is a viable option and represents a real advance in the treatment of adenomyosis.

Adult↗
PubMed1999

Intralesional steroids augment the effects of endoscopic dilation in corrosive esophageal strictures.

BACKGROUND: Intralesional corticosteroid injection has been shown to be effective in refractory esophageal strictures of various etiologies. The present study was conducted to determine the efficacy of intralesional triamcinolone in augmenting results of endoscopic dilation in corrosive esophageal strictures. METHODS: Seventeen patients with corrosive esophageal strictures were treated with endoscopic dilation together with injection of triamcinolone acetonide into the stricture. Fourteen patients were already undergoing dilation; 3 patients were newly recruited. The interval between dilations and frequency of dilation were calculated before and after corticosteroid injections, and periodic dilation index was calculated as number of dilations/number of months. RESULTS: The mean age of the 17 patients (8 men and 9 women) was 30+/-9.21 (range 13 to 52). Thirteen had strictures due to acid ingestion, four to alkali ingestion. There were 18 strictures in total, involving the upper (n = 2), middle (n = 10), and lower (n = 6) thirds of esophagus. Fourteen patients already on a dilation program had undergone 27.92+/-28.63 (range 6 to 92) dilations over a period of 22.92+/-30.73 months (range 2 to 96) before corticosteroid injections. Nine patients received a single injection of triamcinolone, whereas four each had two and three sessions. The dilation requirement after injections in these 14 patients was reduced to 3.57+/-2.90 (range 0 to 10) dilations over a period of 10.5+/-5.58 (range 4 to 21) months. The median total periodic dilation index irrespective of corticosteroid therapy was 0.33 (range 0.55 to 1.8). In 12 of the 14 patients, periodic dilation index before injections (range 0.91 to 3.0, median 1.67) was higher than the median total periodic dilation index and in all the 14 patients periodic dilation index after corticosteroid therapy (range 0 to 0.83, median 0.32) was less than the median of total periodic dilation index (p < 0.01). In addition three patients received intralesional corticosteroid injections at the time of first dilation. These three patients could be effectively dilated with 5, 3, and 3 dilations. CONCLUSIONS: Intralesional triamcinolone injections augment the effects of endoscopic dilation in patients with corrosive esophageal strictures.

Adult↗
PubMed1999

Evacuation interval after vaginal misoprostol for preabortion cervical priming: a randomized trial.

OBJECTIVE: To determine the optimal interval for evacuation after preabortion cervical priming with vaginal misoprostol. METHODS: One hundred eighty healthy nulliparas requesting legal termination of pregnancy between 6 and 11 weeks' gestation were assigned randomly to receive 400, 600, or 800 microg of intravaginal misoprostol. Vacuum aspiration was done after 3 hours in the 400-microg group and after 2 hours in the 600- and 800-microg groups. The degree of cervical dilatation before operation was measured with a Hegar dilator. Preoperative and intraoperative blood loss and associated side effects were also assessed. RESULTS: Eleven (18.3%) and 15 (25.0%) women in the 600-and 800-microg groups, respectively, had cervical dilatation of at least 8 mm after an interval of 2 hours; 55 (91.7%) women who received 400 microg for a 3-hour interval had similar cervical dilatation. Using 400 microg as a baseline, the odds ratio (OR) was 0.02; 95% confidence interval (CI) was 0.01, 0.06 for 600 microg and OR 0.03; 95% CI 0.01, 0.09 for 800 microg for achieving successful preabortion cervical dilatation of at least 8 mm. The mean cervical dilatation of 6.7 mm and 6.8 mm for the higher doses was also significantly less than that of 8.1 for the 400-microg dose (P<.001). The mean preoperative and intraoperative blood loss was only statistically different when the 400- and 800-microg groups were compared (P = .03). There were also significantly more side effects, namely abdominal pain and fever above 38.0 C, in the 600- and 800-microg groups (P<.001), compared with the 400-microg group. When the 600- and 800-microg groups were compared, there were still significantly more women complaining of abdominal pain (P<.001). None of the women in the study required analgesics for pain or antipyretics for fever. CONCLUSION: The minimal evacuation interval should be at least 3 hours for successful preabortion cervical priming.

Abortifacient Agents, Nonsteroidal↗
PubMed1999

Characterization of SiO2-Na2O-Fe2O3-CaO-P2O5-B2O3 glass ceramics.

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO2-Na2O-Fe2O3-CaO-P2O5-B2O3 system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na3CaSi3O8 and Na3-XFeXPO4 phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.

Journal Article↗
PubMed1999

Pregnancy and its outcome in patients with noncirrhotic portal hypertension.

There is paucity of data in the literature on the occurrence of pregnancy and its outcome in patients with noncirrhotic portal hypertension. The present study was undertaken to assess the fertility pattern, fetal loss, and consequences of variceal bleeding during pregnancy in these patients. Fifty-five women of child-bearing age with a diagnosis of noncirrhotic portal hypertension (including 32 with noncirrhotic portal fibrosis and 23 with extrahepatic portal venous obstruction) and 44 age-matched controls were studied. A detailed history of obstetric events and bleeding episodes was recorded in all patients. Any complication of portal hypertension was managed accordingly. Patients were classified into three groups for analysis: group 1-obstetric events after the diagnosis of portal hypertension in patients; group II-obstetric events before the diagnosis of portal hypertension in patients; and group III-obstetric events in controls. A total of 116 pregnancies took place in 44 patients. Of these, 36 occurred after and 80 before the diagnosis of portal hypertension was made. In the 44 controls, 118 pregnancies took place. The mean fertility rates of groups I, II and III were 0.20+/-0.24, 0.18+/-0.21, and 0.22+/-0.12 pregnancies per year, respectively, which were not statistically different (P>0.05). The numbers of fetal losses in groups I, II and III were 3/36 (8.3%), 6/80 (7.5%), and 12/118 (10.17%) pregnancies, respectively. Menstrual irregularities were found in 7/55 (12.72%) patients and 6/44 (13.6%) controls (P>0.05). Five episodes of variceal bleeding occurred in 36 pregnancies after the diagnosis of portal hypertension (13.88%). All five were successfully managed with endoscopic sclerotherapy. In conclusion, noncirrhotic portal hypertensive patients have normal fertility and outcome of pregnancy. Variceal bleeding episodes are not common and endoscopic sclerotherapy is safe and effective in pregnancy.

Adult↗
PubMed1999

A lack of evidence for down-modulation of CD3 zeta expression in colorectal carcinoma and pregnancy using multiple detection methods.

Loss of the T cell receptor-associated CD3 zeta chain has been proposed as a possible mechanism of the acquired immunosuppression in both tumour-bearing hosts, and in symptomatic patients with HIV infection. However, other reports suggest that the zeta-chain loss may in part be caused by protease activity of contaminating phagocytes ex vivo. Using flow cytometry and Western blot analysis on highly purified T cells, and ensuring adequate addition of protease inhibitors, we have studied the expression of CD3zeta on peripheral blood T cells from patients with colorectal carcinoma, and compared these with normal controls, and pregnant donors, as a further example of an immunocompromised state. Immunohistochemistry was performed on tumour sections from patients with colorectal carcinoma to measure CD3zeta expression in tumour infiltrating T cells, and compared with normal mucosa and tonsil. Using these three approaches, our data provide no evidence for downregulation of CD3zeta chain expression either in colorectal carcinoma or pregnancy and suggest that this explanation is unlikely to fully account for the reduced T cell function associated with these conditions in all patients.

Adenocarcinoma↗
PubMed1999

[14C]-urea breath test to confirm eradication of Helicobacter pylori.

BACKGROUND: Treatment for Helicobacter pylori reduces ulcer recurrence. Eradication rates of the organism vary with different drug regimens from 30% to 90%. There is a need to identify patients who have failed treatment. [14C]-Urea breath test (UBT) is non-invasive, sensitive, safe and highly reliable test for diagnosis of H. pylori infection. As there is a paucity of reports on the utility of [14C]-UBT in confirming H. pylori eradication, this study was undertaken. METHODS: Thirty-eight patients (age 34 +/- 17 years, range 16-84 years, 27 men) with upper gastrointestinal symptoms underwent upper gastrointestinal endoscopy. Baseline H. pylori infection was diagnosed by identification of the organism on antral biopsies and positive rapid urease test (RUT). After 1 month of completion of treatment, repeat RUT and histological examination of antral endoscopic biopsies were performed. Eradication of H. pylori was defined as absence of the organism on histology, and negative RUT. The [14C]-UBT was performed using 185 kBq [14C]-urea dissolved in 300 mL water. Breath samples were collected once before ingestion of [14C]-urea, and subsequently at 5 and 15 min. Results were expressed as 14CO2/mmol CO2 exhaled as per cent of administered urea. RESULTS: Endoscopy revealed antral gastritis (n = 14), duodenal ulcer (n = 8), duodenitis (n = 2), oesophagitis (n = 1), antral gastritis and duodenal ulcer (n = 3), antral gastritis and duodenitis (n = 7) and normal upper gastrointestinal endoscopy (n = 3). All the 20 patients who were negative for H. pylori on RUT and histology, tested negative for H. pylori on [14C]-UBT. However, of 18 patients shown to have H. pylori infection on RUT and histology, 16 were positive for H. pylori on [14C]-UBT. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of [14C]-UBT were 100, 89, 91, 100 and 95% respectively. CONCLUSIONS: The [14C]-UBT is a reliable indicator of H. pylori eradication after treatment. It can obviate the need for antral biopsies to confirm eradication of H. pylori after completion of treatment.

Adult↗