Search PubMed⌕ Search

Biomedical subjects

S K Ghosh

Publications and source records attributed to S K Ghosh.

At least 73 records · Page 4Linked to original sources
PubMed1997

Kinetic analysis of the cis-diamminedichloroplatinum(II)--cysteine reaction: implications to the extent of platinum--DNA binding.

The reaction between cis-diamminedichloroplatinum(II) (cis-DDP) and L-cysteine was examined at neutral pH at 37 degrees C. The reaction proceeds through a Pt(NH3)2 (cys)Cl intermediate which undergoes parallel reactions with a second molecule of cysteine to form a bis(cysteine) complex, Pt(NH3)2(cys)2 and with the starting platinum complex to form a cysteine-bridged dinuclear complex. In the presence of excess cysteine, the product is predominantly the bis(cysteine) complex. The intermediate is formed by the direct reaction of the platinum complex with cysteine with a bimolecular rate constant 2.2 +/- 0.2 x 10(-2) M-1.s-1 at 37 degrees C as well as through a rapid reaction with the mono aqua-platinum complex. The rate constant for the formation of the dimer was evaluated to be 0.24 +/- 0.4 M-1.s-1, an order of magnitude higher than that for the mononuclear complex formation. The intermediate reacts with a second cysteine molecule with a bimolecular rate constant, 5.6 +/- 0.4 x 10(-2) M-1.s-1. The rate constant for the equation of Pt(NH3)2(cys)Cl was evaluated to be 1.8 +/- 0.2 10(-4) s-1. The Pt-195 chemical shifts for the mono(cysteine), bis(cysteine), and cysteine bridged dimer were found to be -3308, -3705, and -3104 ppm. The bis(cysteine) complex at neutral pH undergoes slow reaction (t1/2 approximately equal to four days) to form a secondary product, presumably Pt(NH3)(cys)2, in which one cysteine acts a bidentate chelating agent. In acidic solution, with equimolar concentrations of cysteine and diaqua-platinum complex, the reaction predominantly yielded a cysteine bridged dimeric complex. When cysteine concentration was increased fourfold over the platinum complex, the bis(cysteine) chelate with complete removal of coordinated ammonia appeared as the dominant product. The platinum-195 chemical shift for this chelate was found to be -3290 ppm. Considering the abundance of thiols in amino acids/peptides and replication enzymes in the cellular milieu, it remains to be seen how platinum complexes react with DNA. Direct platination to replication enzymes as a possible mechanism for antineoplactic activity is yet to be ruled out.

Antineoplastic Agents↗
PubMed1997

Interleukin-4 is effective in restoring cytotoxic T cell activity that declines during in vivo progression of a murine B lymphoma.

We previously reported [Chakrabarti et al. (1992) Cell Immunol 142:54; 144:455] that, in a murine B lymphoma model 2C3, idiotype (Id)-specific CD8+ cytotoxic T lymphocytes (CTL) are generated in mice following hyperimmunization with irradiated tumor cells, and that they are effective in tumor rejection. The present study reveals that 2C3-specific CTL are also induced in spleens during tumor progression, but are not sustained. At the early stage of tumor growth, the splenic T cells following a 5-day incubation in vitro with killed 2C3 tumor targets, produce high levels of cytokines, namely interleukin-4 (IL-4), IL-10 and interferon gamma (IFN gamma). Their cytotoxic T lymphocyte (CTL) activity and cytokine levels, except IL-2, sharply decline at the late stage when the mice are increasingly moribund. Although the decline in cytokine level is also evident with CD4+ T cells, a precipitous and concurrent decrease occurs primarily in the IL-4 level with both CD4+ and CD8+ T cells of late-tumor-bearing animals (TBA). Study with the unseparated splenocytes also reveals that sevenfold less IL-4 is produced at the late stage. Furthermore, the cytotoxicity of CTL from late TBA can be effectively restored by addition of supernatants from the splenocyte culture of early TBA, or by IL-4, but not by IFN gamma and IL-10. In addition, only IL-4-activated CD8+ T cells from the late TBA are found, by Winn assay, to be protective in vivo. Thus it appears that IL-4, required to sustain antitumor CTL activity, is consumed by T and possibly other cells at the late stage of tumor growth, thereby compromising host immunity against the tumor. We contend that induction or maintenance of protective immunity depends not only on the tumor antigen but also on the specific cytokine milieu in a tumor-bearing host.

Animals↗
PubMed1997

Promoter/leader deletion analysis and plant expression vectors with the figwort mosaic virus (FMV) full length transcript (FLt) promoter containing single or double enhancer domains.

The boundaries required for maximal expression from the promoter/leader region of the full length transcript of figwort mosaic virus (FLt promoter) coupled to reporter genes were defined by 5' and 3' deletion analyses. In transient expression assays using protoplasts of Nicotiana edwardsonii, a 314 bp FLt promoter fragment sequence (-249 to +65 from the transcription start site) was sufficient for strong expression activity. Plant expression vectors developed with modified FLt promoters were tested with GUS or CAT as reporter genes in transgenic plants. The FLt promoter is a strong constitutive promoter, with strength comparable to or greater than that of the CaMV 35S promoter. The FLt promoter with its double enhancer domain linked to GUS or CAT reporter genes provides an average 4-fold greater activity than the FLt promoter with a single enhancer domain (-55 to -249 bp upstream fragment) in tests with transgenic plants and in protoplast transient expression assays.

Base Sequence↗
PubMed1997

Airborne aflatoxin in the grain processing industries in India.

Airborne aflatoxin generated in rice and maize processing plants was assayed by an indirect competitive enzyme-linked immunosorbent assay. In the rice mill, levels of airborne aflatoxin were always higher in the respirable dust samples (< 7 microns) compared with the total dust samples (< 7 microns). The concentrations of total airborne aflatoxin in the respirable dusts were 26 picogram/m3 and 19 pg/m3, respectively, for the workplace and the storage area of the rice mill, while the concentrations of total dust were 12 pg/m3 for the workplace and 11 pg/m3 for the storage area. Airborne aflatoxin was not detected in control sites of either of the grain processing plants or from the total dust samples obtained from the maize plant. Three sites in the maize processing plant-the elevator (18 pg/m3), the loading/unloading area (800 pg/m3), and the oil mill (816 pg/m3)-showed the presence of airborne aflatoxin only in the respirable dust samples.

Aflatoxins↗
PubMed1997

Involvement of p21racA, phosphoinositide 3-kinase, and vacuolar ATPase in phagocytosis of bacteria and erythrocytes by Entamoeba histolytica: suggestive evidence for coincidental evolution of amebic invasiveness.

Trophozoites of Entamoeba histolytica, the protozoan parasite that causes amebic dysentery, phagocytose bacteria in the colonic lumen and erythrocytes (RBC) in host tissues. Because tissue invasion is an evolutionary dead end, it is likely that amebic pathogenicity is coincidentally selected, i.e., the same methods used to kill bacteria in the colonic lumen are used by parasites to damage host cells and cause disease. In support of this idea, the amebic lectin and pore-forming peptide are involved in binding and killing, respectively, bacteria and host epithelial cells. Here amebic phagocytosis of bacteria, RBC, and mucin-coated beads was disrupted by overexpression of E. histolytica p21(racA-V12), a ras-family protein involved in selection of sites of actin polymerization, which had been mutated to eliminate its GTPase activity. p21(racA-V12) transformants were also defective in capping and cytokinesis, while pinocytosis of fluorescent dextrans was not affected. Wortmannin, a fungal inhibitor of phosphoinositide 3-kinase, markedly inhibited phagocytosis of bacteria, RBC, and mucin-coated beads by wild-type amebae. In contrast to p21(racA-V12) overexpression, wortmannin abolished amebic pinocytosis of dextrans but had no inhibitory effects on capping. Inhibition of amebic vacuolar acidification by bafilomycin also decreased bacterial and RBC uptake. These results, which demonstrate similarities between mechanisms of phagocytosis of bacteria and RBC by amebae and macrophages, support the idea of coincidental selection of amebic genes encoding proteins that mediate destruction of host cells.

Ammonium Chloride↗
PubMed1997

Seasonality of indoor resting anophelines in stone quarry area of District Allahabad, U.P.

Alongitudinal study was conducted in four indicator villages of PHC Shankargarh, District Allahabad, U.P. from July 1991 to June 1992 to have information on seasonality of indoor resting anopheline species in silica sand/hard stone quarry area. Fourteen anopheline species namely, An. aconitus (0.35%), An. annularis (17.03%), An. barbirostris (0.09%), An. culicifacies (36.74%), An. fluviatilis (0.13%), An. nigerrimus (0.01%), An. pallidus (4.40%), An. splendidus (0.02%), An. stephensi (0.01%), An. subpictus (40.84%), An. tessellatus (0.15%), An. turkhudi (0.004%), An. vagus (0.20%) and An. varuna (0.02%) were collected. An. culicifacies, An. subpictus and An. annularis were found throughout the year. An. fluviatilis, An. pallidus, An. vagus and An. aconitus were also observed in all the seasons except extreme summer. However, An. barbirostris and An. splendidus were collected only in monsoon/post-monsoon and winter seasons. An. tessellatus and An. stephensi were recorded in winter and spring seasons. An. nigerrimus and An. varuna were recorded in winter, while An. turkhudi in spring. Prolonged high vector density may be attributed to the extended malaria transmission in this area.

Animals↗
PubMed1997

Chemical modifications and dissociation characteristics of tyrosine and tryptophan residues in alpha-crystallin.

A quantitative estimation of surface accessibility of aromatic residues in alpha-crystallin from goat lens has been accomplished by chemical modifications using different specific reagents having varying sizes. Results of modification of tyrosine residues with N-acetylimidazole and tetranitromethane when combined with those of ionization studies carried out with hydroxyl ions having the smallest size reveal different classes of tyrosine residues in the native protein: 78 +/- 2 residues have been found to be easily available for modification; among the rest, 94 +/- 2 residues appear to be comparatively less exposed to the reagents while 28 +/- 2 residues are found to be completely unavailable for modification in the native protein and are modified only when the protein is denatured. Modification of tryptophan residues with H2O2 also indicates different classes of these residues available for oxidation at different concentrations of the oxidant. 34 +/- 2 residues of tryptophan are found to be easily oxidized at a lower concentration of H2O2 during the first phase of the reaction. The remaining tryptophan residues appear to be less exposed to the reagent. This is also corroborated from the studies of reactivities of these residues towards another specific but bulkier reagent, 2-hydroxy-5-nitrobenzyl bromide. These surface exposed aromatic residues in alpha-crystallin may be considered to be vulnerable to in vivo oxidative modifications forming insoluble aggregates which may finally contribute to the formation of cataract.

Crystallins↗
PubMed1996

Role of an aprotinin-sensitive protease in the activation of Ca(2+)-ATPase by superoxide radical (O2-.) in microsomes of pulmonary vascular smooth muscle.

We have investigated the role of an aprotinin-sensitive protease in regulating Ca(2+)-ATPase activity and Ca2+ uptake (ATP-dependent and Na(+)-dependent) in microsomes of bovine pulmonary vascular smooth muscle during treatment with the O2(-.)-generating system hypoxanthine plus xanthine oxidase. Treatment of the smooth muscle microsomes with the O2(-.)-generating system produced a protease in a gelatin-containing zymogram with an apparent molecular mass of 16 kDa. This 16 kDa proteolytic protein was found to be inhibited by superoxide dismutase (SOD) and aprotinin but not by PMSF. Using polyclonal antiserum to aprotinin, we found that it is an ambient antiprotease of the smooth muscle microsomes. Treatment of the microsomes with the O2(-.)-generating system stimulated protease activity tested with a synthetic substrate N-benzoyl-DL-arginine p-nitroanilide and also enhanced Ca(2+)-ATPase activity. It also stimulated ATP-dependent Ca2+ uptake. In contrast, Na(+)-dependent Ca2+ uptake was found to be inhibited by the O2(-.)-generating system. Pretreatment of the microsomes with SOD and aprotinin preserved the increase in protease activity, Ca(2+)-ATPase activity and ATP-dependent Ca2+ uptake. In addition, O2(-.)-caused inhibition of the Na(+)-dependent Ca2+ uptake which was reversed by SOD and aprotinin. Pretreatment with PMSF did not cause any discernible alteration in the protease activity, Ca(2+)-ATPase activity. ATP-dependent Ca2+ uptake and Na(+)-dependent Ca2+ uptake in the microsomes caused by the O2(-.)-generating system. These results suggest that an aprotinin-sensitive protease plays a pivotal role in regulating Ca(2+)-ATPase and Ca(2+)-uptake activities in microsomes of pulmonary vascular smooth muscle under oxidant O2(-.)-triggered conditions.

Animals↗
PubMed1996

Role of hydroxyl radical in the oxidant H2O2-mediated Ca2+ release from pulmonary smooth muscle mitochondria.

We sought to investigate the mechanism(s) by which the oxidant H2O2 stimulates Ca2+ release from mitochondria of bovine pulmonary vascular smooth muscle tissue and to test the hypothesis that hydroxyl radical is involved in this phenomenon. Treatment of the smooth muscle tissue with 1 mM H2O2 dramatically stimulated hydroxyl radical generation as measured by methane (CH4) production by GLC using dimethylsulfoxide (DMSO) as the substrate. Pretreatment of the mitochondria with the hydroxyl radical scavanger dimethylthiourea (DMTU) prevented the increase in CH4 production caused by H2O2. In the absence of EGTA, H2O2 caused stimulation of Ca2+ release from mitochondria occurred with a lag time of about 4 min. Addition of EGTA to Ca2+ loaded mitochondria resulted an immediate loss of Ca2+ and that has been found to be augmented by H2O2. The release of Ca2+ by H2O2 did not appear to occur with concommitant increase in sucrose entry into, K+ release from, and swelling of mitochondria when the Ca2+ cycling was prevented by EGTA. These observations suggested that H2O2-mediated Ca2+ release from bovine pulmonary vascular smooth muscle tissue mitochondria occurred (i) through the involvement of hydroxyl radical; (ii) via specific pathway(s); and (iii) did not appear to happen primarily via nonspecific "pore' formation.

Animals↗
PubMed1996

Oxidant-mediated proteolytic activation of Ca(+)-ATPase in microsomes of pulmonary smooth muscle.

Treatment of bovine pulmonary artery smooth muscle tissue microsomes with H2O2 (1 mM) markedly stimulated protease activity tested with a synthetic substrate N-benzoyl-DL-arginine p-nitroanilide (BAPNA), and also enhanced Ca(2+)-ATPase activity. ATP-dependent Ca(2+) uptake was found to be stimulated upon treatment of the microsomes with H2O2. Pretreatment of the microsomes with vitamin E and aprotinin prevented the H2O2-induced stimulation of Ca(2+)-ATPase activity and also ATP-dependent Ca(2+) uptake. In contrast, H2O2-induced inhibition of Na(+)-dependent Ca(2+) uptake was reversed by vitamin E and aprotinin.

5'-Nucleotidase↗
PubMed1996

Histidine residues in alpha-crystallin are not all available for chemical modification and acid-base titration.

We have determined the number of histidine residues available for chemical modification with the specific reagent diethylpyrocarbonate in both bovine and goat alpha-crystallins. Results indicate that there are two distinctly different classes of histidine residues in the native protein. Out of 300 total histidine residues in the protein (on the basis of 800-kDa protein molecular weight) about 170 +/- 2 residues have been found to be modified by the reagent. The remaining 130 +/- 2 residues are modified when the protein is partially denatured in 1.5 M guanidine hydrochloride. The H(+)-titration behavior of the histidine residues in the protein corroborates this result. The observed differential accessibility of histidine residues may be important in maintaining the surface hydrophobicity of the aggregate as well as in stabilizing its quaternary structure.

Animals↗
PubMed1996

Protective role of anion channel blocker in lipid peroxidation caused by H2O2 in microsomes of bovine pulmonary arterial smooth muscle tissue.

The role of hydroxyl radical (OH.) in H2O2-mediated stimulation of lipid peroxidation in microsomes of bovine pulmonary arterial smooth muscle tissue and the protective effects of DIDS, the anion channel blocker have been studied. Treatment of microsomes with H2O2 (1 mM) stimulate iron release, OH. production and lipid peroxidation. Pretreatment with DFO (an iron chelator) or DMTU (a hydroxyl radical scavenger) prevents OH. production and thereby reduces lipid peroxidation without any appreciable reduction of iron release. Simultaneous treatment of either DFO or DMTU with H2O2 significantly reduces lipid peroxidation and prevents OH. production without any significant reduction of iron release. However, addition of DFO or DMTU 2 min after treatment of the microsome with H2O2 does not produce any significant reduction of lipid peroxidation, OH production and iron release. Pretreatment of microsomes with DIDS markedly reduces the stimulation of lipid peroxidation without appreciably altering the increase in OH. production and iron release caused by H2O2.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1996

Redox state of pyridine nucleotides, but not glutathione, regulate Ca2+ release by H2O2 from mitochondria of pulmonary smooth muscle.

Treatment of bovine pulmonary artery smooth muscle mitochondria with H2O2 stimulated oxidation of GSH and NAD(P)H along with an increase in Ca2+ release. Addition of oxaloacetate to mitochondrial suspension stimulated Ca2+ release and oxidation of NAD(P)H while GSH level remained unchanged. Subsequently, addition of beta-hydroxybutyrate which reduced mitochondrial pyridine nucleotides caused reuptake of the released Ca2+ without causing appreciable alteration of GSH level. Treatment of the mitochondria with 1,3-bis(2-dichloroethyl)-1-nitrosourea (BCNU), an inhibitor of glutathione reductase, significantly decreased GSH level without producing discernible change in Ca2+ release and NAD(P)H oxidation.

Animals↗
PubMed1996

Involvement of a protease in tert-butylhydroperoxide-mediated activation of Ca2+ ATPase in microsomes of pulmonary smooth muscle.

Microsomes isolated from bovine pulmonary artery smooth muscle tissue treated with the oxidant t-buOOH stimulated Ca2+ ATPase activity dose-dependently as also protease activity when tested with a synthetic substrate N-benzoyl-DL-arginine p-nitroanilide. At 300 microM, t-buOOH optimally stimulated these activities. Treatment of the microsomes with t-buOOH stimulated ATP dependent Ca2+ uptake while Na+ dependent Ca2+ uptake was inhibited by t-buOOH. Pretreatment of the microsomes with vitamin E (1 mM) and aprotinin (1 mg/ml) prevented t-buOOH caused stimulation of protease activity and Ca2+ ATPase activity, and also stimulation of ATP dependent Ca2+ uptake while t-buOOH caused inhibition of Na+ dependent Ca2+ uptake was reversed by vitamin E and aprotinin. Treatment of the microsomes with trypsin (1 microgram/ml) stimulated Ca2+ ATPase and ATP dependent Ca2+ uptake while Na+ dependent Ca2+ uptake was inhibited. Pretreatment of the microsomes with aprotinin prevented trypsin caused stimulation of Ca2+ ATPase and ATP dependent Ca2+ uptake, while trypsin caused inhibition of Na+ dependent Ca2+ uptake was reversed by aprotinin.

Animals↗
PubMed1996

H2O2-induced lipid peroxidation in mitochondria of pulmonary vascular smooth muscle tissue and its modification by DFO, DMTU and DIDS.

Treatment of bovine pulmonary artery smooth muscle tissue mitochondria with H2O2 stimulated iron release, hydroxyl radical (OH) production and lipid peroxidation. Pretreatment of mitochondria with deferoxamine (DFO) and dimethyl thiourea (DMTU) prevented OH production and markedly reduced lipid peroxidation without appreciably altering iron release caused by H2O2. Simultaneous treatment of either DFO or DMTU with H2O2 significantly reduced lipid peroxidation and also prevented OH production without causing marked decrease in iron release. In contrast, addition of DFO or DMTU even 2 min after treatment of the mitochondria with H2O2 did not significantly altered iron release, OH production and lipid peroxidation. Pretreatment of the mitochondria with 4,4'-dithiocyano-2,2'-disulfonic acid stilbene (DIDS) markedly reduced lipid peroxidation without appreciably altering the increase in OH production and iron release caused by H2O2.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗