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Biomedical subjects

I Mahmud

Publications and source records attributed to I Mahmud.

At least 19 recordsLinked to original sources
PubMed1997

Prostaglandin D synthase in human megakaryoblastic cells.

The cytosol fraction of human platelets did not convert prostaglandin (PG) H2 to PGD2. However, a homogenate of human megakaryoblastic CMK cells (precursor cells of platelets) produced PGD2 from PGH2. The PGD synthase activity was localized in the cytosol of CMK cells, and absolutely required glutathione. The catalytic properties and Western and Northern blottings indicated that the enzyme was PGD synthase of the hematopoietic type rather than the lipocalin type. When CMK cells were differentiated to megakaryocytes with phorbol ester along with induction of cyclooxygenase-1, the PGD synthase activity increased about 2-fold for 2 days and then decreased. In another human megakaryoblastic cell line, Dami, the PGD synthase increased about 10-fold by the addition of phorbol ester. Thus, the PGD synthase, which was undetectable in platelets, appeared during differentiation of megakaryoblasts to megakaryocytes.

Chromatography, Affinity↗
PubMed1993

Induction of cyclooxygenase and suppression of 12-lipoxygenase in human erythroleukemia cells upon phorbol ester-induced differentiation.

When human erythroleukemia (HEL) cells were incubated with arachidonic acid, both fatty acid cyclooxygenase and arachidonate 12-lipoxygenase activities were exhibited. Subcellular localization of these enzymes were examined by differential centrifugation, and both the cyclooxygenase and the 12-lipoxygenase were present predominantly in the microsomes rather than the cytosol of the cells. The cyclooxygenase activity was stimulated by 12-O-tetradecanoylphorbol 13-acetate (TPA) in a dose-dependent and time-dependent manner. Actual increase in the cyclooxygenase protein by TPA was demonstrated by immunoprecipitation and Western blot analysis of the enzyme with the aid of an anti-cyclooxygenase antibody. Furthermore, the cyclooxygenase mRNA level increased as assessed by RNA blot analysis using a cDNA probe for the enzyme. In contrast, the TPA treatment reduced the activity of 12-lipoxygenase. By RNA blot analysis using a cDNA probe of HEL cell 12-lipoxygenase, the mRNA level of the enzyme was shown to decline by the TPA treatment. Taken together, the TPA treatment of HEL cells brought about the induction of cyclooxygenase and the suppression of 12-lipoxygenase.

Arachidonate 12-Lipoxygenase↗
PubMed1984

On the identification and biological properties of prostaglandin J2.

Prostaglandin D2 spontaneously decomposes at physiological pH and temperature to 9-deoxy-delta 9-PGD2 (designated PGJ2). We developed a TLC procedure for the isolation of PGJ2 which was identified by both proton-NMR and mass spectrometry. Freshly prepared PGJ2 was active in inhibiting aggregation induced by ADP in citrated human platelet rich plasma. As reported by Fukushima et al. (1). PGJ2 was less active (x 0.1-0.25) than PGD2 as an inhibitor. Concentrations of PGJ2 that markedly inhibited aggregation of human platelets were generally incapable of inhibiting aggregation of rat or guinea pig platelets. Using a heterologous system of human platelets mixed with guinea pig plasma samples (2), it was shown that the ability of PGJ2 to inhibit platelet aggregation was lost immediately following intravenous injection in anesthetized guinea pigs. This apparent rapid uptake and/or degradation of PGJ2 might also explain why PGJ2 had no effect on blood pressure of anesthetized guinea pigs. PGJ2 was potent in inhibiting proliferation of cultured vascular smooth muscle cells, mouse melanoma cells and mouse fibroblasts. Less potent anti-proliferative effects were seen with two other degradation products of PGD2, one of which was the delta 12 metabolite reported (3,4) to be formed from PGJ2 in a reaction catalyzed by serum albumin.

Adenosine Diphosphate↗
PubMed1984

Eicosanoid effects on cell proliferation in vitro: relevance to atherosclerosis.

Several eicosanoids were tested for ability to inhibit proliferation of cells in culture. In rabbit aortic smooth muscle cells and mouse B16BL6 melanoma cells, order of potency was: 12-HETE greater than PGJ2 greater than PGA1 greater than or equal to PGE1 greater than PGE2 greater than or equal to PGD2 greater than or equal to PGA2. PGB1 was active in smooth muscle cells (greater than PGD2) but not in B16 cells. 5-HETE and Leukotriene B4 were weakly active in smooth muscle cells, and PGB2, PGF2 alpha and TXB2 were inactive in both cells types. In Swiss albino mouse 3T3 fibroblasts, PGJ2 and PGE1 showed much lower relative potency than in the other two cell lines, although the profile was otherwise similar. These findings may be relevant to the anti-atherosclerotic (and perhaps anti-tumor activity) of some eicosanoids.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1984

Thromboxane synthesizing system in rat liver.

Thromboxane B2 (TXB2), along with other primary prostaglandins, was synthesized when rat liver microsomes were incubated with radioactive arachidonic acid. TXB2 was identified directly by chemical ionization mass spectrometry and indirectly by using specific inhibitors of TX synthetase, viz., imidazole and OKY-1555 ((E)-3(4-(3-pyridyl-methyl) phenyl)-2 methyl acrylic acid HCl). The supernatant fraction obtained after centrifugation at 105,000 X g for 60 min contained a possible regulatory component that suppressed thromboxane synthesis. The regulatory influence is lost after partial hepatectomy.

Animals↗
PubMed1982

Mechanism of stimulation by human interferon of prostaglandin synthesis in human cell lines.

Human interferon beta (IFN-beta) stimulated the synthesis of prostaglandin E (PGE) and prostaglandin F2 alpha in IFN-sensitive RSa and GM258 cell lines, but not in IFN-resistant HEC-1 cells. IFN-beta at a concentration of 1000 units/ml elicited 2- to 3-fold increases in PGE production in these cell lines. In the presence of exogenous arachidonic acid (1 microgram/ml), IFN-pretreated cells produced 5-fold more PGE compared to the cell cultures in the absence of arachidonic acid. Prednisolone, an inhibitor of phospholipase A2, at a concentration of 2 micrograms/ml inhibited the enhanced synthesis of PGE by IFN-pretreated cells. Indomethacin (4 micrograms/ml), a potent fatty acid cyclooxygenase inhibitor, also inhibited the increased synthesis of PGE. IFN stimulated the release of [14C]arachidonic acid from phospholipids but did not stimulate the activity of fatty acid cyclooxygenase. These data suggest that IFN stimulates prostaglandin synthesis by promoting the release of arachidonic acid from phospholipids. Since cycloheximide and actinomycin D inhibited the stimulation of PGE synthesis, the stimulation of prostaglandin synthesis by IFN seemed to be due to de novo enzyme synthesis which catalyzes the release of fatty acid. Addition of exogenous PGE suppressed the growth of RSa and GM258 cells. Prednisolone and iodomethacin partially inhibited anti-cell growth activity of IFN, suggesting a possibility that IFN-inhibited cell growth was partly mediated by prostaglandin.

Arachidonic Acid↗
PubMed1977

Protein in the food prolongs DNA synthesis in the liver of rats after starvation.

After a period on protein-free diet and then starvation, high protein diet induces DNA synthesis in rat liver for a longer period than diet containing an equivalent amount of amino acids. The requirement for high protein diet is limited to an early part of the prereplicative period and administration of the high protein diet later did not prolong DNA synthesis.

Amino Acids↗
PubMed1976

Purification and some properties of NADP+ -specific isocitrate dehydrogenase from an extreme thermophile, Thermus flavus AT-62.

Thermostable NADP+ -specific isocitrate dehydrogenase (EC 1.1.1.42) was purified from crude extract of an extremely thermophilic bacterium Thermus flavus AT-62 through DEAE-cellulose column, acetone fractionation, DEAE-Sephadex A-50 column and isoelectric focussing. The enzyme was purified about 500-folds in its specific activity and purity was found to be about 96%. The enzyme was not inactivated after 60 min at 70 degrees C, but 20 and 80% of the activity were lost after 60 min at 80 degrees and 90 degrees C, respectively. Oxalacetate plus glyoxylate (each 1 nM) demonstrated 75% inhibition of the activity in concerted manner. The degree of the inhibition and the affinity of the enzyme for isocitrate and NADP+ decreased with the rise of temperature, especially above 60 degrees C. The activation energy below and above 60 degrees C were 14,500 and 8,000 cal per mole respectively. In CD spectra negative bands at 210 and 220nm were observed and alpha-helix content was calculated to be about 26%. In the course of heating up to 60 degrees practically no change in CD bands are observed, but above 60 degrees the depth of CD bands decreased gradually and remarkably above 80 degrees C. The effect of temperature on kinetic parameters and secondary structures of the enzyme was discussed in relation to the temperature adaptation of the organism.

Circular Dichroism↗