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Biomedical subjects

S Sen

Publications and source records attributed to S Sen.

At least 253 records · Page 14Linked to original sources
PubMed1994

Characterization of the mitochondrial DNA polymerase from Saccharomyces cerevisiae.

The mitochondrial DNA (mtDNA) polymerase was isolated from a protease-deficient yeast strain (PY2), and purified about 3000 fold by a column chromatography on phosphocellulose, heparin-agarose, and single-stranded DNA cellulose. The purified polymerase was characterized with respect to optimal nucleotide concentrations, template-primer specificity and sensitivity to some inhibitors. These results were compared with the nuclear DNA polymerase I activity. Both polymerases showed similar requirement of deoxynucleotide concentrations (Km < 1 microM), and highest activity with poly(dA-dT) template. However, the mtDNA polymerase was more sensitive to ddTTP, EtBr and Mn2+ inhibition in comparison to the nuclear DNA polymerase I. The mtDNA polymerase did not need ATP as an energy source for in vitro DNA synthesis. This mtDNA polymerase preparation also showed 3'-->5' exonuclease activity.

DNA Primers↗
PubMed1994

Clinical evaluation of a herbal antidiabetic product.

Sixty-seven diabetic patients and 12 normal subjects were selected for a clinical study with an indigenous herbal product. The study consisted of 2 phases. In phase 1 study out of 25 diabetics (both insulin dependent and non-insulin dependent) only those in the age group of 41-50 years ie, 11 cases showed lowering of mean high blood sugar level in all samples from 1/2 an-hour to 2 hours with the test drug containing guar gum, methi, tundika and mesha shringi. But in phase 2 study there was lowering of blood sugar level with the test drug and with 2 of its constituents ie, guar gum and methi when used separately in 42 non-insulin dependent diabetics. While there was some blood sugar level lowering effect with guar gum and methi when used separately in 12 normal subjects in phase 2 study, but that was not the same observed with the test drug. The results of this study indicate the efficacy of the product as an adjuvant.

Adult↗
PubMed1993

Oxypurinol attenuates hydroxyl radical production during ischemia/reperfusion injury of the rat cerebral cortex: an ESR study.

Free radical generation and release from the cerebral hemispheres of rats subjected to four vessel occlusion followed by reperfusion was monitored using a cortical cup technique in conjunction with the spin-trapping agent alpha(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN). Electron spin resonance (ESR) was used to detect the presence of free radical adducts of POBN in the cortical superfusates. 30 min of ischemia plus reperfusion resulted in the release of .OH radical adducts during the period of ischemia and, especially, during the initial phases of reperfusion. No radical adducts were detectable 90 min after the onset of reperfusion. Pretreatment with the xanthine oxidase inhibitor, oxypurinol (40 mg/kg i.p.), virtually abolished free radical formation and release. The results of this study are consistent with earlier evidence of free radical formation during ischemia/reperfusion and suggest that the cerebroprotective actions of oxypurinol may be related to its ability to prevent the cascade of free radical generation.

Animals↗
PubMed1993

Oxypurinol inhibits free radical release from the cerebral cortex of closed head injured rats.

Traumatic brain injury (TBI) is a significant cause of mortality and morbidity. Although the sequence of events underlying the resultant neuronal loss is still poorly understood, there are indications that oxygen-free radical generation is critically involved. Free radical generation in the cerebral cortex of closed head injury rats was monitored by measuring free radical release into cortical superfusates containing the spin trap agent 4-pyridyl-1-oxide-N-tert-butylnitrone (POBN, 100 mM). ESR analysis of the superfusates revealed six line spectra (alpha N = 15.4 G and alpha H beta = 2.5 G) characteristic of POBN-OH adducts. Administration of oxypurinol (40 mg/kg) 15 min prior to TBI prevented the formation of these radical adducts.

Animals↗
PubMed1993

Alteration of cardiac collagen phenotypes in hypertensive hypertrophy: role of blood pressure.

The myocardium contains a fibrillar collagen matrix that consists primarily of type I and type III collagens. There is a marked alteration in the ratio and amount of collagen phenotypes in myocardial hypertrophy due to pressure overload. The purpose of the present study is (1) to study the effect of antihypertensive therapy on collagen phenotypes, if instituted before development of hypertension in spontaneously hypertensive rat (SHR), and continued into adult life and (2) to study the effects of dissociation of hypertension from hypertrophy, on collagen phenotypes in SHRs. The present study shows the effect of two antihypertensive drugs, hydralazine and captopril, on collagen phenotypes in SHRs. Both hydralazine and captopril effectively controlled blood pressure in SHRs, but only captopril regressed hypertrophy and corrected the altered distribution of myocardial collagen phenotypes I and III. Untreated SHRs had a collagen type I:III ratio of 10.19 +/- 0.27, compared with that of 6.41 +/- 0.30 in normotensive WKY (P < 0.001). Captopril-treated SHRs had a collagen type I:III ratio of 6.75 +/- 0.37, which did not differ significantly from that in normotensive WKY. Hydralazine-treated SHRs had a collagen I:III ratio of 10.07 +/- 0.39, which is similar to the ratio in untreated SHRs. In normotensive rats, neither captopril nor hydralazine significantly altered collagen content or the ratio of type I:III collagen. Thus captopril, an angiotensin converting enzyme inhibitor, not only regressed hypertrophy but also reversed the altered distribution of type I and type III collagen whereas hydralazine which effectively controlled blood pressure, did not regress hypertrophy and did not correct the altered distribution in collagen phenotypes. These studies suggest that alteration of collagen phenotypes during hypertensive hypertrophy is independent of blood pressure control and myocardial mass.

Animals↗
PubMed1993

Expression of differentially phosphorylated Rb and mutant p53 proteins in myeloid leukemia cell lines.

We studied the structure and expression of Rb and p53 genes in six myeloid leukemia cell lines (HL-60, KBM3, K562, KBM5, EM2, KBM7) in the light of the published reports that structural abnormalities of these genes are rarely seen in leukemic cells and also a recent finding that Rb gene expression can be regulated by the p53 protein. Except for HL-60 cells which have a truncated p53 gene, none of the other cell lines revealed any gross structural abnormalities in the Rb and p53 genes. KBM3, KBM5 and EM-2 expressed lower levels of Rb mRNA than HL-60, K562 and KBM7. The amount of Rb protein was lowest in KBM3 cells and in this and two other cell lines (KBM5, KBM7) Rb was markedly hypophosphorylated compared to the other three cell lines. HL-60 and K562 did not express p53 m-RNA, while the other four cell lines all expressed high levels of mutant p53 protein. Thus even in the absence of gross structural alterations, subtle abnormalities in the expression pattern of Rb and p53 genes occur in myeloid leukemia cells.

Base Sequence↗
PubMed1993

Ciprofloxacin: mammalian DNA topoisomerase type II poison in vivo.

Ciprofloxacin (CF), a fluoroquinolone widely used as a potent antimicrobial drug, was evaluated in vivo in mouse bone marrow cells for its ability to induce clastogenicity and DNA damage in terms of increased sister-chromatid exchange (SCE) frequencies. Doses of 0.6, 6 and 20 mg/kg body weight of CF given intraperitoneally induced a positive dose-dependent significant clastogenicity (trend test alpha < or = 0.05), though the effects were not specific for specific phases of the cell cycle. The DNA-damaging effect observed as increased SCE frequencies using doses of 0.15, 0.30, 0.60, 1.2 and 6 mg/kg body weight showed a significant dose-dependent increase (trend test alpha < or = 0.05; lowest effective concentration 1.2 mg/kg of body weight). Compared to a potent eukaryotic DNA topoisomerase type II poison, etoposide (VP-16, 0.5, 1 and 5 mg/kg body weight, given intraperitoneally), ciprofloxacin produced comparable dose-dependent SCE frequency increases. Ciprofloxacin was postulated to be specific for the target DNA gyrase, the prokaryotic homologue of DNA topoisomerase type II enzyme. The present paper along with the existing earlier data strongly suggest that topoisomerase type II and DNA gyrase are physiological targets for the drug action. In view of the present significant in vivo mammalian DNA topoisomerase type II-mediated genotoxicity and clastogenicity data, ciprofloxacin should be administered with caution.

Analysis of Variance↗
PubMed1993

Oxygen cost of stress development in hypertrophied and failing hearts from the spontaneously hypertensive rat.

Left ventricular isovolumic stress development and metabolic parameters were studied in 18-24-month-old spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rat controls using the isolated, isovolumic (balloon in left ventricle) buffer-perfused rat heart preparation. After WKY rats and all SHRs were compared, SHRs were divided into two groups: those animals with (SHR-F) and without (SHR-NF) evidence of heart failure. Hearts were perfused at 100 mm Hg using a constant pressure system at a temperature of 37 degrees C. In the baseline state, peak systolic pressure was greatest in the SHR-NF group and lowest in the SHR-F group. Peak midwall stress was greatest in the WKY group and, again, lowest in the SHR-F group. Oxygen consumption was lowest in the SHR-F group. When the oxygen cost of stress development was estimated by normalizing myocardial oxygen consumption by peak developed midwall stress, values were lowest in the WKY, greater in the SHR-NF, and greatest in the SHR-F group. Lactate production did not occur in the baseline state in any of the groups. Functional and metabolic responses to graded hypoxia, induced by changing the gas mixture of the perfusate from 95% to 50%, 25%, and 0% oxygen at perfusion pressures of 100 and 130 mm Hg, were studied. Increasing perfusion pressure generally resulted in small increases in peak systolic pressure and myocardial oxygen consumption but did not substantially reverse the contractile or metabolic deficit present in the SHR-F group.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Myotrophin induces early response genes and enhances cardiac gene expression.

We have identified and partially sequenced a soluble factor, myotrophin, from spontaneously hypertensive rat hearts and hypertrophic human hearts that enhances myocyte protein synthesis and stimulates myocardial cell growth. Our studies suggest that myotrophin may be a biochemical link between hemodynamic stress and myocardial cellular hypertrophy. When rat neonatal cardiac myocytes maintained in culture were incubated with myotrophin for 30 minutes, they showed a marked increase in c-myc, c-fos, and c-jun messenger RNA levels. Cardiac myocytes treated for 24 hours with myotrophin showed a fourfold increase in connexin 43 (gap junction protein), a sixfold increase in atrial natriuretic factor, a threefold increase in skeletal alpha-actin, and a threefold increase in total myosin transcript levels. Studies on myosin isoforms showed a selective increase in the beta-myosin heavy chain transcript levels but no reciprocal decrease in alpha-myosin heavy chain transcript levels. Our data suggested that myotrophin appears to be a primary modulator for myocardial cell growth and differentiation and may play an important role in the pathogenesis of cardiac hypertrophy. Myotrophin may be involved in the upregulation of myofibrillar protein and the activation of cardiac gene transcription during growth and hypertrophy of the myocardium, and the induction of early response gene expression may be linked to this response.

Actins↗
PubMed1993

Myotrophin in human cardiomyopathic heart.

Earlier, myotrophin, a factor, has been isolated, purified, and partially sequenced from spontaneously hypertensive rat hearts that stimulated myocyte growth. To evaluate the role of myotrophin in the initiation of the human dilated cardiomyopathic heart, we have isolated and purified myotrophin to homogeneity (approximately 50,000-fold) as defined by reverse-phase high-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). During purification, we used a bioassay system in which adult myocardial cells maintained in culture were used to evaluate protein synthesis by the incorporation of [3H]leucine into myocyte protein. Myotrophin purified from human dilated cardiomyopathic hearts is composed of a single polypeptide chain having an apparent molecular mass of 12 kD, determined by SDS-PAGE. The partial internal amino acid sequence of human myotrophin is very similar to that of rat myotrophin peptide T9. Using a rat myotrophin peptide (T26) antibody, we identified human myotrophin on an immunoblot. These results showed that human myotrophin possesses the T9 and T26 regions of rat myotrophin. Human myotrophin stimulated myocardial protein synthesis and cell growth, similar to the way in which rat myotrophin stimulated these factors. Western blot analysis showed the presence of myotrophin in both dilated cardiomyopathic and normal human hearts. In addition, we observed significantly elevated levels of myotrophin in dilated cardiomyopathic human hearts when compared with age- and sex-matched normal control hearts. From these observations, we conclude that myotrophin is present in normal human hearts, is found at higher levels in dilated cardiomyopathic human hearts, and may play a role in the initiation of cardiac hypertrophy as well as in normal growth of cardiac myocytes in humans.

Adult↗
PubMed1993

Human chorionic gonadotropin binding sites in the human endometrium.

The existence of high-affinity and low-capacity specific binding sites for luteinizing hormone (LH)/human chorionic gonadotropin (hCG) has been reported in porcine, rabbit and rat uteri. We have identified hCG binding sites in the human endometrium collected from 35-42-year-old ovulatory and anovulatory women. The binding characteristics of hCG to endometrial tissue preparations from ovulatory and anovulatory women showed saturability with high affinity and low capacity. Scatchard plot analysis showed the dissociation constant of specific binding sites in the ovulatory women to be 3.5 x 10(-10) mol/l and in anovulatory women to be 3.1 x 10(-10) mol/l. The maximum binding capacity varied considerably between ovulatory (3.85 nmol/kg protein) and anovulatory (6.12 nmol/kg protein) endometrium. Among the divalent metal ions tested (Zn2+, Mg2+, Mn2+, Ca(2+)--4 mol/l), Zn2+ effected a remarkable increase in [125I]hCG binding to the endometrium (p < 0.005) whereas Mn2+ showed a marginal increase and other metal ions did not have any effect. Data obtained with human endometrium indicate an influence of the functional state of the ovary on [125I]hCG binding to endometrium.

Adult↗
PubMed1993

alpha-Phenyl-tert-butyl-nitrone (PBN) attenuates hydroxyl radical production during ischemia-reperfusion injury of rat brain: an EPR study.

Alpha-phenyl-tert-butyl-nitrone (PBN) a spin adduct forming agent is believed to have a protective action in ischemia-reperfusion injury of brain by forming adducts of oxygen free radicals including .OH radical. Electron paramagnetic resonance (EPR) has been used to both detect and monitor the time course of oxygen free radical formation in the in vivo rat cerebral cortex. Cortical cups were placed over both cerebral hemispheres of methoxyflurane anesthetized rats prepared for four vessel occlusion-evoked cerebral ischemia. Prior to the onset of sample collection, both cups were perfused with artificial cerebrospinal fluid (aCSF) containing the spin trap agent alpha-(4-pyridyl-1-oxide)-N-tert butylnitrone (POBN 100 mM) for 20 min. In addition 50 mg/kg BW of POBN was administered intraperitoneally (IP) 20 min prior to ischemia in order to improve our ability to detect free radical adducts. Cup fluid was subsequently replaced every 15 min during ischemia and every 10 min during reperfusion with fresh POBN containing CSF and the collected cortical superfusates were analyzed for radical adducts by EPR spectroscopy. After a basal 10 min collection, cerebral ischemia was induced for 15 or 30 min (confirmed by EEG flattening) followed by a 90 min reperfusion. .OH radical adducts (characterized by six line EPR spectra) were detected during ischemia and 90 min reperfusion. No adduct was detected in the basal sample or after 90 min of reperfusion. Similar results were obtained when diethylenetriaminepenta-acetic acid (100 microM; DETAPAC) a chelating agent was included in the artificial CSF. Systemic administration of PBN (100 mg/kg BW) produced a significant attenuation of radical adduct during reperfusion. A combination of systemic and topical PBN (100 mM) was required to suppress .OH radical adduct formation during ischemia as well as reperfusion. PBN free radical adducts were detected in EPR spectra of the lipid extracts of PBN treated rat brains subjected to ischemia/reperfusion. Thus this study suggests that PBN's protective action in cerebral ischemia/reperfusion injury is related to its ability to prevent a cascade of free radical generation by forming spin adducts.

Animals↗
PubMed1993

Effects of triiodothyronine (T3) supplementation upon ozone-induced lung injury.

Ozone exposure results in an acute decrease in the serum levels of thyroid hormones; the physiologic sequelae of this are unclear. Whereas thyroid hormone supplementation appears to benefit pulmonary function in septic, oxyradical models of injury, thyroid hormone increases ozone toxicity. We demonstrated an increase in metabolic rate and pulmonary injury in lungs from ozone exposed, T3 treated animals. This was evidenced by an increase in pulmonary weight gain, vascular perfusion pressure, and decrease in compliance in the supplemented animals. However, an increase in alkane generation, as an index of lipid peroxidation, was not seen in the ozone exposed, hormonally treated animals. This suggests that although thyroid hormone supplementation increases metabolic rate and ozone toxicity, an increased rate of lipid peroxidation plays a minimal role.

Animals↗