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Biomedical subjects

S Sen

Publications and source records attributed to S Sen.

At least 289 records · Page 16Linked to original sources
PubMed1992

Detection of extrachromosomal circular DNA sequences from tumor cells by an alkaline lysis, Alu-polymerase chain reaction technique.

Extrachromosomal circular DNAs ranging in size from submicroscopic molecules of approximately 100 kb to cytogenetically resolvable structures of 1000+ kb called minute and double-minute chromosomes have been shown to harbor amplified genes in primary tumor cells, tumor cell lines, and drug-resistant cells grown in vitro. The presence of these molecules in transformed and malignant cells trends to reflect genetic instability and also suggests that role in tumor progression. Using a colon carcinoma cell line, we developed a technique to detect extrachromosomal circular DNA-specific sequences by Alu-polymerase chain reaction. Circular DNA was enriched by selective alkaline denaturation of genomic DNA. We have successfully performed this procedure with a minimum of 5 x 10(5) cells. The technique does not require any prior knowledge of the sequences located on the covalent circular DNA molecules for their detection. The procedure should be useful as a routine screen of primary tumor cells for the presence of extrachromosomal circular DNA and should permit the preparation of specific probes ot aid in their detailed characterizations.

Base Sequence↗
PubMed1992

O6-Alkylguanine-DNA alkyltransferase content in synchronised human cancer cells.

The DNA repair enzyme O6-alkylguanine-DNA alkyltransferase (AT) was analysed in the human ovarian-cancer SW626 cell line and in the human promonocytic leukemia U937 cell line following their synchronisation with low non-toxic concentrations of methotrexate. In SW626, AT increased in the early S phase of the cell cycle and then declined during progression of the S phase to levels found in the G1 phase of unsynchronised cells. In contrast, at the G1/S-phase boundary and in the S phase, U937 cells showed a lower AT content than did exponentially growing unsynchronised cells. In addition, AT activity was greatly reduced in resting U937 cells but was not reduced appreciably in resting SW937 cells but was not reduced appreciably in resting SW626 cells. The results of these studies indicate that AT fluctuations do not follow a constant pattern during the cell cycle of different cell lines.

Cell Cycle↗
PubMed1992

Flavonol glycosides from Calotropis gigantea.

Besides isolation and characterization of isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucopyranoside and taraxasteryl acetate, a new flavonol trisaccharide was isolated from the aerial parts of Calotropis gigantea, and its structure was established as isorhamnetin-3-O-[2-O-beta-D-galactopyranosyl-6-O-alpha-L-rhamnopy ranosyl]- beta-D-glucopyranoside by a combination of fast atom bombardment mass spectroscopy, 1H and 13C NMR spectra and some chemical degradations.

Carbohydrate Sequence↗
PubMed1992

Melting characteristics of highly supercoiled DNA.

The effect of high supercoil densities on the melting characteristics of a supercoiled DNA has been studied. It is found that although the melting temperature increases abruptly on converting a linear DNA merely into the relaxed circular form, it falls back substantially at high supercoil densities. It is further predicted, in such cases, that the number of melted base pairs should be significantly enhanced even at the physiological temperature, which may facilitate the binding of other molecules to the highly supercoiled DNA.

Journal Article↗
PubMed1992

Potentiation of etoposide cytotoxicity against a human ovarian cancer cell line by pretreatment with non-toxic concentrations of methotrexate or aphidicolin.

Exposure of human ovarian cancer SW626 cell line to 0.08 mumol/l methotrexate or 25 mumol/l aphidicolin for 24 h caused no cytotoxicity but enhanced etoposide cytotoxicity. Methotrexate or aphidicolin treatment induced a reversible blockade at the beginning of S phase which was reversed upon drug removal with a consequent wave of synchronisation. The enhancement of etoposide cytotoxicity was not due to higher etoposide intracellular uptake in the methotrexate or aphidicolin-pretreated cells. The topoisomerase II content in methotrexate or aphidicolin pretreated SW626 cells was higher than in control cells assessed by western blotting or flow cytometry. The higher etoposide cytotoxicity observed after synchronization with methotrexate or aphidicolin was apparently unrelated to the number of drug-induced DNA-topoisomerase II complexes evaluated as DNA double strand breaks or DNA-protein crosslinks. These data support the view that etoposide-induced DNA-topoisomerase II complexes are more cytotoxic in cells which are in S-phase.

Aphidicolin↗
PubMed1992

Extraordinary stability of enzymes dried in trehalose: simplified molecular biology.

We show that extremely fragile biomolecules such as DNA restriction and modifying enzymes can be dried in vitro in the presence of trehalose with no loss of activity, even after prolonged storage. A remarkable and unexpected property of the dried enzyme preparations is their ability to withstand prolonged exposure to temperatures as high as +70 degrees C. This stability is unique to trehalose and is not found with other sugars irrespective of their physical or chemical properties. The immediate significance of these observations is the ability to convert enzymes used in molecular biology into stable reagents. The indefinite stability and high temperature tolerance of these dried enzymes should permit the design of convenient formats that may be of particular significance in the automation of genome mapping and sequencing projects. The stabilization of a wide range of biomolecules by trehalose also has practical implications for a number of areas ranging from basic science, through healthcare and agriculture, to bio-electronics.

Bacteriophage lambda↗
PubMed1992

Programmed cell death: concept, mechanism and control.

Programmed cell death or apoptosis occurs under physiological conditions as a result of physiological effectors. It is a relatively slower process and requires active participation of the cell in the suicidal mechanism. Apoptosis is controlled by precise intrinsic genetic programme and may be induced by almost all those stimuli causing necrosis. The role played by the intensity in determining the death process and the underlying mechanism is imperfectly understood. Morphologically apoptotic cells appear as small condensed body. The chromatin is dense and fragmented, packed into compact membrane-bound bodies together with randomly distributed cell organelles. The plasma membrane loses its characteristic architecture and shows extensive blebbing. It buds off projections so that the whole cell may split into several membrane-bound apoptotic bodies. Significant chemical changes take place in the plasma membrane. This helps in recognition of the apoptotic bodies by phagocytes. At this moment it is unclear if all cells can undergo apoptosis or it is a characteristic of only some tissues which are predisposed to apoptotic death being directly under the control of hormones or growth factors. Experimental studies aimed at comparison of induction of apoptosis in cells of different origin are warranted to elucidate this point. Biochemically a pre-commitment step for induction of death programmation through macromolecular synthesis is essential for most systems. The double-stranded linker DNA between nucleosomes is cleaved at regular inter-nucleosomal sites through the action of a Ca2+, Mg(2+)-sensitive neutral endonuclease. Zinc is a potent inhibitor of the enzyme. Calcium probably plays a key controlling role in activation of the enzyme since prevention of Ca2+ increase prevents endonuclease activation. It is becoming evident that signal transduction through appropriate receptors control the Ca2+ flux in the cells. Most apoptotic cells require synthesis of RNA and proteins. Delay or abrogation of apoptosis by inhibition of macromolecular synthesis is well known. The dying cells show high mRNA levels for several enzymes. Several degradative enzymes become active. Regulatory proteins maintain control over the apoptotic cascade. At the molecular level, search has been initiated for the mammalian equivalents of the cell death (ced) gene. Activation of several specific genes is indicated. Specific expression of cell death-associated gene products (e.g. TRPM-2/SGP-2) has been reported in several unrelated apoptotic cell systems. Sequential induction of c-fos, c-myc and 70 kDa heat shock protein is reported. Studies demonstrate that certain genes must remain in a transcriptionally active demethylated state during programmed cell death. Recent evidences clearly indicate that apoptosis may be positively or negatively modulated by certain genes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Hypertension and insulin resistance.

Insulin resistance and hyperinsulinemia is now recognized in non-insulin-dependent diabetes, essential hypertension, obesity, atherosclerotic heart disease, dyslipidemia, heart failure, and in heavy smokers. Several mechanisms have been proposed to explain hyperinsulinemia, insulin resistance and its relationship to hypertension; reduced sodium excretion, activation of the sympathetic nervous system, increased activity of the sodium/hydrogen pump, and stimulation of cellular growth. Some of the nonpharmacological methods to control hyperinsulinemia are of benefit in the management of hypertension, most notably weight loss, exercise program, and reduced salt intake. High-fiber and reduced-protein diets also reduce hyperinsulinemia. Thiazide diuretics can result in insulin resistance, and insulin secretion may be inhibited, possibly associated with concomitant hypokalemia. beta-Blockers result in some reduction of glucose tolerance and mask some of the features of hypoglycemia. Angiotensin-converting enzyme (ACE) inhibitors and alpha-receptor blockers do not effect insulin resistance; probably the same is true for calcium antagonists. Although the effect on risk factors should not be discounted, it is the effect of treatment on hard end points, cerebrovascular accidents, myocardial infarction, or death that is most important. Evidence in hypertension is at present restricted to diuretics and beta-blocking drugs.

Animals↗
PubMed1992

Binding of radiolabelled luteinizing hormone to intact and ovariectomised rat uterus.

Binding of ovine LH to uterine tissue preparation from intact and ovariectomised rat clearly indicates that uterus possesses specific binding sites for LH. Binding characteristics of LH to uterine tissue preparation from intact rat showed saturability with high affinity and low capacity. Scatchard plot analysis showed dissociation constant of the specific binding site to be 0.12 x 10(-9) mol/l and the number of binding sites was 2.31 +/- 0.05 f mol/mg protein. Ovariectomy did not change the binding affinity but effected a decrease in the number of binding sites (1.7 +/- 0.08 f mol/mg protein). LH treatment of ovariectomized (ovx) rat had no effect on binding affinity but significantly increased the number of binding sites (3.23 +/- 0.1 f mol/mg protein). Reduction of uterine weight due to ovariectomy and marked increase of ovx rat uterine weight by LH administration indicate a source of estrogen in ovx rat. An in vitro uterine tissue slice (from intact and ovx rat) incubation showed depletion of 17 beta-estradiol (E2) content in ovx rat which significantly elevated on LH addition. Data suggest that LH binding to rat uterine tissue has biological relevance.

Animals↗
PubMed1992

Effect of antihypertensive therapy upon myosin isozyme distribution in spontaneously hypertensive rats.

INTRODUCTION: Myosin isozymes have been known to become altered during the development and regression of myocardial hypertrophy, but the mechanism by which the shifting takes place is not known. The present paper describes the effects of antihypertensive drugs, with a known mechanism of action, upon myocardial mass, blood pressure and myosin isoforms in spontaneously hypertensive rats (SHR). METHODS: SHR were treated with antihypertensive drugs and their blood pressure, myocardial mass and myosin isoforms determined. RESULTS: A shift of myosin isoform from the V3 to the V1 type and normalization of myocardial hypertrophy were seen in rats treated with captopril but not in those treated with diuretics. Clonidine and guanethidine increased the V3 form in association with moderate control of blood pressure and no change in myocardial mass. Treatment with a beta-blocker regressed hypertrophy, controlled hypertension but increased the V3 form. Treatment with minoxidil normalized blood pressure, increased cardiac mass and increased the V3 type. CONCLUSIONS: Treatment with different antihypertensive drugs does not cause similar types of shifts in myosin isoform and has divergent effects upon blood pressure and heart weight. Furthermore, there is no correlation between myocardial mass, blood pressure and myosin isozyme shifts. We conclude that factors other than blood pressure, myocardial mass and catecholamines modulate the shifting of myosin isoforms. Since captopril had a greater remedial effect upon myosin isoforms in our study than the more commonly used agents, we recommend that the current criteria for selection of antihypertensive drugs and the relation between those drugs and cardiac function be re-evaluated.

Animals↗
PubMed1992

[Apoptosis or programmed cell death: concepts, mechanisms and contribution in oncology].

Programmed cell death, or apoptosis, corresponds to a sequence of intracellular events that lead to cell death. It has been shown that apoptosis is necessary in some physiological conditions such as embryogenesis, homeostasis of the immune system, erythropoiesis, etc. Some xenobiotics can induce apoptosis at lower doses and necrosis at higher doses. When a cell dies, it is either by apoptosis or by necrosis, and there are many differences between these two deaths. Apoptosis begins by a pre-commitment phase, which is reversible; during this phase the cell has a high level of second messengers. The commitment phase then follows and is irreversible, even when the xenobiotic that triggered the induction is removed. Most often, apoptotic cell death requires synthesis of macromolecules, the inhibition of their synthesis can prevent it. The cell undergoes important morphological changes during apoptosis, its volume decreases when its density increases. Then chromatin becomes granular, intensively osmiophilic, it condenses along the nuclear membrane. Later, chromatin disintegrates into small granules which will be phagocytized. One of the most important characteristics of the programmed cell death is the activation of an endonuclease, that gives rise to DNA fragments of 180-200 base pairs or multiples of these numbers; then after electrophoresis, the DNA gives the appearance of a ladder. Apoptotic cells can be characterized after classic staining, and flow cytometry; they can be separated from other cells by centrifugation on a gradient of density. It has been hypothesized that cell transformation could be due to a sudden resistance to apoptosis. However, the most interesting aspect in oncology recently demonstrated is that well-known anticancer drugs are able to induce apoptosis. One can hope that the discovery of new targets for anticancer drugs could lead to discovering new drugs that could be more active.

Animals↗
PubMed1992

KBM-3, an in vitro model of human acute myelomonocytic leukemia.

A human acute myelomonocytic leukemia cell line, KBM-3, was developed to study the pathophysiology of human acute myeloid leukemia. This cell line was characterized by morphology, immunophenotype, Giemsa-banding pattern, in vitro proliferation capacity, and tumorigenicity in nude mice. The KBM-3 cell line was established in the presence of exogenous lymphokines (human placenta-conditioned medium, HPCM), but medium for later passages did not contain HPCM. We found high cellular expression of the mRNA message for granulocyte-macrophage colony-stimulating factor (GM-CSF), which we suggest may be important for the immortalization of the cell line. KBM-3 cells have an immature myelomonocytic phenotype. Cytogenetic analysis revealed a pseudodiploid karyotype with five characteristic marker chromosomes and ranging in total number from 45 to 49. In suspension cultures, the cells had a doubling time of 23 h and a cloning efficiency of about 30% in soft agar independent of exogenous lymphokines. Two-thirds of nude mice injected with 1 x 10(4) KBM-3 cells and all animals injected with 1 x 10(5) cells developed S.C. granulocytic sarcomas within 6-8 weeks. These tumors were locally invasive but did not give rise to distant metastases. When transplanted to a new set of nude mice, all tumors formed secondary sarcomas at the site of implant. We conclude that the KBM-3 cell line may have value for studying the molecular events that underlie the neoplastic transformation in human myeloid leukemia.

Adult↗
PubMed1992

Renal involvement in kala-azar.

Fifty one patients in a series of 1000 parasitologically confirmed patients of kala-azar showing proteinuria were studied from the point of view of renal involvement. Forty two out of these patients showed blood urea above 40 mg/dl and 12 had decreased glomerular filtration rate as well. Serum creatinine level was normal in all patients including those with blood urea of more than 100 mg/dl. It is therefore suggested that although there may be glomerular involvement in some patients of kala-azar, the changes are reversible.

Animals↗
PubMed1991

Treatment of unstable angina pectoris (European experience).

Unstable angina pectoris is used to describe accelerated angina, new onset of angina, or prolonged angina. The natural history of the angina varies according to clinical presentation. The 1-year mortality rate ranges from 2% to nearly 40%. Specific therapy includes nitrates, beta-adrenergic blockers, and/or calcium antagonists as well as antithrombotic therapy in the form of aspirin. Patients with severe angina at rest and ST- and T-wave changes should be admitted to a coronary care unit where full-dose heparin is administered. Coronary angiography should be performed in individuals who fail to respond to the conventional therapy in order to evaluate other therapeutic options, including percutaneous transluminal coronary angioplasty (PTCA) and coronary bypass surgery. In some cases, especially in patients with intracoronary thrombus, thrombolytic therapy may be beneficial.

Angina, Unstable↗