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Biomedical subjects

S Biswas

Publications and source records attributed to S Biswas.

At least 127 records · Page 7Linked to original sources
PubMed1997

Conformational changes in plant Ins(1,4,5)P3 receptor on interaction with different myo-inositol trisphosphates and its effect on Ca2+ release from microsomal fraction and liposomes.

The interaction of the only reported plant inositol trisphosphate receptor with different myo-inositol trisphosphates (InsP3 species), namely Ins(1,4,5)P3, Ins(1,3,4)P3, Ins(1,5,6)P3, and Ins(2,4,5)P3, were studied to assess the extent of Ca2+ mobilization from microsomes/vacuoles as well as liposomes in vitro. Ins(1,4,5)P3 and Ins(2,4,5)P3 bind with the receptor with comparable affinities, as evidenced from their dissociation constants (Kd approx. 100 nM at 5 degrees C), whereas the interaction between Ins(1,3,4)P3/Ins(1,5,6)P3 and the receptor was not detected even with these ligands at 5 microM. Ins(1,3,4)P3/Ins(1,5,6)P3 isomers also do not elicit Ca2+ release from liposomes or microsomes/ vacuoles. The ability of any InsP3 to bind the receptor for Ins(1,4,5)P3 is a prime requirement for Ca2+ release. However, the comparison of binding affinities at a single temperature does not help to correlate it directly with the extent of Ca2+ release from the intracellular stores because the concentration of Ca2+ released by Ins(1,4,5)P3 as estimated over a period of 20 s is 3500 +/- 200 nM/mg of protein and is about 4-fold higher than that by Ins(2,4,5)P3 under identical conditions. To understand the role of the receptor conformation in Ca2+ release by different isomers, we have probed the conformational change of the receptor when the different isomers bind to it. Accessibility of the tryptophan residues in the free and Ins(1,4,5)P3/Ins(2,4,5)P3-bound receptor was monitored by a neutral fluorescence quencher, acrylamide. The resulting Stern-Volmer-type quenching plots of the internal fluorescence indicate a change in the conformation of the receptor on binding to Ins(1,4,5)P3 and Ins(2,4,5)P3. It is also detected when far-UV CD spectra (205-250 nm) of the free and ligand [Ins(1,4,5)P3/Ins(2,4,5)P3]-bound receptor are compared. The results from CD spectroscopic studies further indicate that the conformational changes induced by the two isomers are different in nature. When thermodynamic parameters, such as enthalpy (delta H), entropy (delta S) and free energy (delta G), for the formation of the two InsP3-receptor complexes are compared, a major difference in the extent of changes in enthalpy and entropy is noted. All these findings taken together support the proposition that it is the overall interaction leading to the requisite conformational change in the receptor that determines the potency of the InsP3 isomers in their abilities of Ca2+ mobilization from the intracellular stores or reconstituted liposomes.

Acrylamide↗
PubMed1997

Stimulation of IL-2 production and CD2R expression by splenopentin analogs.

Splenopentin (SP-5), is a pentapeptide corresponding to the amino acid sequence 32-36 (Arg-Lys-Glu-Val-Tyr) of the splenic hormone splenin. Its synthetic analogs: Lys-Lys-Glu-Val-Tyr(1) and D-Lys-Lys-Glu-Val-Tyr (2) have been evaluated for active T-cell rosette (CD2R), total T-cell rosette (CD2), interleukin-2 (IL-2) stimulation and effect on antibody production. SP-5 as well as both the analogs stimulated CD2R. Analogs (1) and (2) were also found to stimulate IL-2 production. These observations suggest that in vitro human NK cell augmentation with analogs (1) and (2) reported earlier may be due to enhanced IL-2 production.

Adjuvants, Immunologic↗
PubMed1997

Similar nature of inhibition of mitochondrial respiration of heart tissue and malignant cells by methylglyoxal. A vital clue to understand the biochemical basis of malignancy.

The effect of methylglyoxal on the oxygen consumption of mitochondria of heart and of several other organs of normal animals of different species has been tested. The results indicate that methylglyoxal (3.5 mM) strongly inhibits ADP-stimulated alpha-oxoglutarate and malate plus pyruvate-dependent respiration of exclusively heart mitochondria of normal animals of different species. Whereas, with the same substrates, but at a higher concentration of methylglyoxal (7.5 mM), the respiration of mitochondria of other organs of normal animals is not inhibited. Methylglyoxal also inhibits the respiration of slices of rat and toad hearts. But this inhibition is less pronounced. However, methylglyoxal (15 mM) fails to have any effect on perfused toad heart. Using rat heart mitochondria as a model, the effect of methylglyoxal on the oxygen consumption was also tested with different respiratory substrates, electron donors at different segments of the mitochondrial respiratory chain and site-specific inhibitors to identify the specific respiratory complex which might be involved in the inhibitory effect of methylglyoxal. The results strongly suggest that methylglyoxal inhibits the electron flow through complex I of rat heart mitochondrial respiratory chain. Moreover, lactaldehyde (0.6 mM), a catabolite of methylglyoxal, can exert a protective effect on the inhibition of rat heart mitochondrial respiration by methylglyoxal (2.5 mM). The effect of methylglyoxal on heart mitochondria as described in the present paper is strikingly similar to the results of our previous work with mitochondria of Ehrlich ascites carcinoma cells and leukemic leukocytes. We have recently proposed a new hypothesis on cancer which suggests that excessive ATP formation in cells may lead to malignancy. The above mentioned similarity apparently provides a solid experimental foundation for the proposed hypothesis which has been discussed.

Animals↗
PubMed1997

Entomological and rodent surveillance of suspected plague foci in agro-environmental and feral biotopes of a few districts in Maharashtra and Gujarat states of India.

Studies carried out on entomological and rodent surveillance in agroclimatic and feral biotopes of five districts of Maharashtra and two districts of Gujarat revealed that the terrain features of the seven districts surveyed were conducive to wild rodent species, Tatera indica, a natural reservoir of plague and vector flea species, Xenopsylla cheopis. A total of 214 Tatera indica and three Bandicoota bengalensis were collected from burrows by the digging method and 89 rat fleas were retrieved. The flea index calculated ranged from 0.26 to 1.0 in different districts. The examination of blood serum samples, contact tissue impression smears and tissue organs (heart, lung, liver and spleen) of these wild rodents did not reveal any evidence of plague activity. The natural harbourages of Tatera indica were found to be elevated land or raised margins of agricultural fields or barren land with thorny bushes/xerophytic plants and parthenium grass. Agricultural fields having wet soil were found to be the preferred harbourages of Bandicoota bengalensis. Movement of wild rodents toward human settlement was observed to be the common phenomenon during the harvesting season which may lead to the creation of favorable conditions for plague outbreaks.

Animals↗
PubMed1997

Exaggerated lithotomy position-related rhabdomyolysis.

A case report and review of the exaggerated lithotomy position, in particular, and other position-related rhabdomyolysis is presented. The objective is to emphasize that the exaggerated lithotomy position, although providing good exposure for urethral and prostatic surgery, is associated with a low but definite risk of rhabdomyolysis and acute renal failure. Certain risk factors for the complication have been outlined. Close perioperative monitoring, including the use of pulmonary artery pressure and lower-extremity compartment pressure measurements in high-risk cases, is suggested for the prevention and the early detection of these cases. Prompt volume replacement and diuresis is the cornerstone of therapy in preventing acute renal failure in patients who develop rhabdomyolysis and myoglobinuria.

Acute Kidney Injury↗
PubMed1997

Efficacy of alpha,beta-arteether in acute uncomplicated P. falciparum malaria.

A phase-III clinical trial was conducted in 50 patients (42M + 8F) with acute uncomplicated falciparum malaria from Delhi during the period of September to November 1995. Their mean age was 27.2 years, and the mean parasitaemia on day 0 was 0.65%. Patients were hospitalized and treated with a new ethyl derivative of artemisinin developed at CDRI called alpha, beta-arteether, at the dosage of 150 mg l/M for three consecutive days. Peripheral smears were examined every day for 4 days and then weekly up to 28 days. The results of the study showed that the mean parasite and fever clearance times were respectively 19.94 +/- 6.87 and 37.81 +/- 21.67 hours. Within 48 h, 70% of the cases became afebrile and the peripheral smear was negative in 100% of the cases. The drug was well tolerated. Three cases (6%) had recrudescence within 28 days. It is concluded that alpha, beta-arteether is a safe, effective and rapidly acting antimalarial.

Adolescent↗
PubMed1996

High prevalence of chloroquine resistant Plasmodium falciparum infection in Rajasthan epidemic.

Plasmodium falciparum is the main killer among all human malaria parasites. In 1994, there was a falciparum malaria epidemic in Rajasthan, India, with many deaths. We have investigated active falciparum malaria cases from this epidemic and found that most of the parasite isolates (95%) were resistant to chloroquine. Nevertheless, all the tested isolates from the epidemic, were sensitive to mefloquine and quinine and ninety percent were also susceptible to sulfadoxine/pyrimethamine. Most individuals had moderate levels of TNF-alpha (20-220 pg/ml) and anti-parasite IgM antibodies compared to IgG levels which were relatively lower. In conclusion, the high transmission rate of the chloroquine resistant P. falciparum parasite could be the probable cause of the disease epidemic in Rajasthan. The timely drug sensitivity test and availability of appropriate antimalarial drugs are, therefore, warranted.

Animals↗
PubMed1996

Insulin- and mitogen-activated protein kinase-mediated phosphorylation and activation of peroxisome proliferator-activated receptor gamma.

Peroxisome proliferator-activated receptor (PPAR) gamma plays an important role in adipocyte differentiation and the regulation of adipocyte gene expression. Insulin also serves to promote adipogenesis. We report that insulin and a PPARgamma ligand (thiazolidinedione (TZD)) stimulate in a synergistic manner the expression of an adipocyte-specific gene (aP2) in rat adipocytes and 3T3-L1 cells. Potential cross-talk between insulin signaling and PPARgamma was studied in Chinese hamster ovary cells expressing insulin receptors (CHO.T), PPARgamma, and reporter genes. Both TZD and insulin independently stimulated PPARgamma-mediated transactivation of aP2 promoter-luciferase reporter genes; both agents combined resulted in a synergistic effect. Co-transfection of CHO.T cells with dominant-negative mitogen-activated protein (MAP) kinase-kinase (MKK1) abrogated both insulin- and TZD-mediated activation of PPARgamma; transactivation was markedly increased in cells co-transfected with constitutively active MKK1. Both insulin and constitutively active MKK1 also stimulated 32P incorporation into PPARgamma in vivo. The conclusions are: 1) Insulin synergizes with a PPARgamma ligand and can activate the receptor in a ligand-independent fashion. 2) PPARgamma is phosphorylated in vivo by insulin stimulation or activation of the MAP kinase pathway. 3) MAP kinase is an important mediator of cross-talk between insulin signal transduction pathways and PPARgamma function.

3T3 Cells↗
PubMed1996

Guanylyl cyclase C is a selective marker for metastatic colorectal tumors in human extraintestinal tissues.

Guanylyl cyclase C (GCC) has been detected only in intestinal mucosa and colon carcinoma cells of placental mammals. However, this receptor has been identified in several tissues in marsupials, and its expression has been suggested in tissues other than intestine in placental mammals. Selective expression of GCC by colorectal tumor cells in extraintestinal tissues would permit this receptor to be employed as a selective marker for metastatic disease. Thus, expression of GCC was examined in human tissues and tumors, correlating receptor function with detection by PCR. GCC was detected by ligand binding and catalytic activation in normal intestine and primary and metastatic colorectal tumors, but not in extraintestinal tissues or tumors. Similarly, PCR yielded GCC-specific amplification products with specimens from normal intestine and primary and metastatic colorectal tumors, but not from extraintestinal tissues or tumors. Northern blot analysis employing GCC-specific probes revealed an approximately 4-kb transcript, corresponding to recombinant GCC, in normal intestine and primary and metastatic colorectal tumors, but not in extraintestinal tissues. Thus, GCC is selectively expressed in intestine and colorectal tumors in humans and appears to be a relatively specific marker for metastatic cancer cells in normal tissues. Indeed, PCR of GCC detected tumor cells in blood from some patients with Dukes B colorectal cancer and all patients examined with Dukes C and D colorectal cancer, but not in that from normal subjects or patients with Dukes A colon carcinoma or other nonmalignant intestinal pathologies.

Biomarkers, Tumor↗
PubMed1996

Interaction of aldehydes with glyoxalase I and the status of several aldehyde metabolizing enzymes of Ehrlich ascites carcinoma cells.

The possible effect of several physiologically important aldehydes has been tested on partially purified glyoxalase I of Ehrlich ascites carcinoma (EAC) cells. The results indicate that D, and L-lactaldehyde are strong non-competitive inhibitors of glyoxalase I and the effect with the D-isomer is more pronounced, whereas both D,L-glyceraldehyde and acetaldehyde are moderately inhibitory and the nature of inhibition is strictly competitive. Moreover, D,L-glyceraldehyde strongly inhibits the utilization of methylglyoxal by intact EAC cells. A search for the presence of several aldehyde metabolizing enzymes in EAC cells indicates that non-specific aldehyde reductase, methylglyoxal reductase, aldehyde dehydrogenase and alcohol dehydrogenase are apparently absent in this rapidly growing, highly de-differentiated malignant cell.

Acetaldehyde↗
PubMed1996

Relative importance of inositol (1,4,5)trisphosphate and inositol (1,3,4,5)tetrakisphosphate in Entamoeba histolytica.

[3H]Inositol tetrakisphosphate (Ins(1,3,4,5)P4) binding sites which were poorly displaced by unlabelled inositol (1,4,5)-trisphosphate (Ins(1,4,5)P3) were detected in membrane fractions of Entamoeba histolytica. Similarly, unlabelled Ins(1,3,4,5)P4 was 30-fold less efficient in displacing [3H]Ins(1,4,5)P3 binding. pH sensitivities of binding of the two isomers were markedly different. Scatchard analysis of the data revealed single binding sites and similar receptor densities for each of the two isomers. Formation of both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 in E. histolytica was also demonstrated. Calcium release studies showed that after treatment with a saturating dose of either Ins(1,4,5)P3 or Ins(1,3,4,5)P4 the other inositol polyphosphate could partially revive the response to a subsequent addition of the first inducer. Our data clearly demonstrate that Ins(1,4,5)P3 and Ins(1,3,4,5)P4 are two equally important but independent second messengers in E. histolytica.

Animals↗
PubMed1996

Interaction of myoinositoltrisphosphate-phytase complex with the receptor for intercellular Ca2+ mobilization in plants.

One of the myoinositol trisphosphates produced by the phytase-myoinositol hexakisphosphate (InsP6) reaction is Ins(2,4,5)P3. That Ins(2,4,5)P3 can elicit Ca2+ mobilization from intracellular stores in plants [Samanta, S., Dalal, B., Biswas, S., & Biswas, B.B.(1993) Biochem. Biophys. Res. Commun. 191,427] prompted us to elucidate the mechanism. The InsP3 [Ins(1,4,5)P3/Ins(2,4,5)P3]-phytase complex has been found to interact with the receptor for InsP3 in vitro forming a ternary complex, and a nanomolar concentration of InsP3 is required. For enzymatic cleavage of InsP3 by phytase, micromolar concentrations are needed, and the affinities of the phytase for different myoinositol phosphates have been found to depend upon the number of phosphate groups present in the substrate. Fraction accessibility of tryptophan residues to a neutral fluorescence quencher, acrylamide in free and myoinositol phosphates bound phytase, as determined by Stern-Volmer plot, records a progressive decrease starting from InsP6 to InsP with the notable exceptions of both Ins (1,4,5)P3 and Ins(2,4,5)P3. This deviation from the trend of change in the accessibility of tryptophan residues in myoinositol phosphate bound phytase is recorded from the fact that there is a high affinity (dissociation constant of the nanomolar order) and noncatalytic binding site in phytase for the two isomers of InsP3. In the nanomolar range of concentrations, both isomers of InsP3 bind to a second site of phytase having about 40-fold higher affinity than the normal substrate binding site. InsP3, when bound to noncatalytic site in phytase is not hydrolyzed but induces a significant change in the conformation of phytase as assayed from the relative accessibility of tryptophan residues. This conformational change in phytase is recognized by the receptor for InsP3, because in absence of InsP3 no interaction between the receptor and phytase is detected. However, InsP3-phytase complex is a better elicitor of Ca2+ efflux from microsomal/vacuolar fractions than free InsP3. This is further confirmed by the fact that when Ins(1,3,4)P3-phytase complex can elicit Ca2+ efflux from intracellular stores, Ins(1,3,4)P3 per se is minimally effective.

6-Phytase↗
PubMed1996

Effect of elevated temperature on cytotoxic effector cells.

Several studies have shown a direct correlation between temperature and immune response. The effect of elevated temperature on cytotoxic effector functions is not well known. In the present study we have investigated the effect of elevated temperatures (38.5 and 40 degrees C) on cytotoxicity of lymphokine-activated killer cells (LAK), monocyte cytotoxicity, cytotoxic T lymphocytes (CTL) and tumor necrosis factor (TNF)-mediated cytotoxicity, and compared them with results at 37 degrees C. LAK cell cytotoxicity was inhibited significantly at 40 degrees C (p < 0.01) and there was no marked difference at 38.5 degrees C (p = 0.17) as compared to 37 degrees C when natural killer (NK)-sensitive K562 cells were used as target. When NK-resistant Raji cells were used as a target, cytotoxicity was inhibited at 40 degrees C (p = 0.33). Monocyte cytotoxicity was enhanced at 40 degrees C (p = 0.19) as well as at 38.5 degrees C (p = 0.38) as compared to 37 degrees C but differences were not statistically significant. Lipopolysaccharide (LPS) enhanced monocyte cytotoxicity. LPS-stimulated enhancement was further enhanced significantly at 40 degrees C (P < 0.05) and 38.5 degrees C (p < 0.05). Cytotoxicity of CTL was significantly inhibited at 38.5 compared to 37 degrees C (p < 0.0002). TNF-mediated cytotoxicity was significantly enhanced at 40 degrees C (p < 0.0004) and 38.5 degrees C (p < 0.001).

Animals↗
PubMed1996

Application of peptide ELISA in tribal malaria of Madhya Pradesh.

A recently developed peptide ELISA method was used for monitoring the efficacy of malaria control programme in the tribal areas of Madhya Pradesh. Both crude Pf antigen and synthetic nonapeptide were used in ELISA for seroepidemiological studies. Both antigen responded equally well but the synthetic peptide had advantages of purity, defined characteristic and easy availability. Population of Mandla protected by vector control measures showed lower antibody titre and lower percentage positivity compared to the unprotected population of Jabalpur. A 0-5 yrs sentinel population from Haldwani almost seronegative has been taken as control.

Animals↗
PubMed1996

Bromo-deoxyuridine based assay for detection of parasite and drug sensitivity in Plasmodium falciparum in vitro.

A non-radioactive, thymidine analogue-bromodeoxyuridine (Brdu), derivative of uridine has been used for incorporation in DNA in culture of P. falciparum at various dosages and at different time period. Parasite growth rate and effect of chloroquine in culture were monitored by microscopic observation of stained smears and incorporation of Brdu molecules were visualized by immunofluorescence and measured by enzyme immuno assay using anti-Brdu. Uptaking of Brdu in parasite is slower unlike tumour cells. A positive correlation between parasite growth and Brdu uptake measurement by ELISA has been observed.

Animals↗