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Biomedical subjects

K A Chandrabose

Publications and source records attributed to K A Chandrabose.

16 recordsLinked to original sources
PubMed1992

Stimulated release of arachidonate and prostaglandins is vectorial in MDCK epithelial cells.

The receptor mediated activation of phospholipase A2 by appropriate ligands results in the synthesis and release of eicosanoids, a class of potent bioregulatory molecules. Madin-Darby canine kidney cells (MDCK) are polarized epithelial cells, with structurally and functionally distinct plasma membrane domains separated by tight junctions. Using MDCK cells grown in dual sided chambers, we show in this report, that a) the receptor mediated release of prostaglandins and arachidonate into the extracellular medium is predominantly unidirectional, b) the direction of release is agonist specific, and c) the magnitude of the response due to a given agonist is cell-domain specific. These characteristics, if operative in vivo, would contribute towards the optimal function of trans-cellular metabolism of eicosanoids already demonstrated.

Adenosine Triphosphate↗
PubMed1985

Role of cell membrane composition in receptor-mediated internalization of vesicular stomatitis virus in human HEp-2 cells.

The role of essential fatty acids in membrane functions related to receptor-mediated endocytosis of vesicular stomatitis virus (VSV) was investigated using a human laryngeal carcinoma cell line (HEp-2) grown in chemically defined serum-free medium (DM) to deplete their essential fatty acid contents. VSV replicated much less effectively in HEp-2 cells grown in DM as compared to serum containing complete medium (CM). Observed reduction in the rate of virus multiplication was, at least in part, due to reduced virus penetration which was monitored using VSV labeled with nitroxyl free radicals as electron spin probe. Surface proteins of VSV were labeled with maleimide spin-label, and succinimide spin-label. Ni2+ was used as a broadening agent to identify the spin-label signals from viruses inside the cell. HEp-2 cells and mouse leukemia cell line L1210 treated with 5-dimethylaminonaphthalene-1-sulfonyl (dansyl) cadaverine, an agent previously shown to inhibit the uptake of VSV in vitro, was used as a positive control in some experiments. VSV penetrated less effectively in both DM-grown cells and in CM-grown cells in the presence of dansylcadaverine. Similar results were obtained by monitoring the uptake of 125I-labeled VSV. When HEp-2 cells grown for several generations in DM were incubated with 10% fetal calf serum for 16 h, the cells supported virus replication to a similar extent as the cells grown in CM. In contrast, addition of arachidonic acid restored VSV growth only partially. Continued growth of HEp-2 cells in DM resulted in a shift in fatty acyl chain composition of phospholipids. The results indicate a finite role for essential fatty acids in receptor-mediated internalization of virus particles.

Animals↗
PubMed1985

Essential fatty acids in diabetes and systemic lupus erythematosus (SLE) patients.

Sera obtained from normal subjects and juvenile-onset diabetes (JD) and systemic lupus erythromatus (SLE) patients were examined for free fatty acid composition and 6-keto-PGF1 alpha content. In addition, prostaglandins in urine samples from normal and diabetic individuals were separated by HPLC, and 6-keto-PGF1 alpha levels were monitored by RIA. Arachidonate (20:4) content in diabetic and SLE individuals were significantly lower than that of controls. Urine from diabetic individuals showed decreased levels of 6-keto-PG F1 alpha. The study also indicated that RIA measurements on crude biological samples may yield erroneous data due to immune cross reactivity with other compounds.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

Interferon-resistant cell line lacks fatty acid cyclooxygenase activity.

A clone of L1210 mouse leukemia cells selected for resistance to both the antiviral and anticellular properties of mouse interferon were essentially devoid of fatty acid cyclooxygenase activity. Experiments in which broken cell preparations were mixed or the two cell types were cultivated together failed to indicate the presence of a diffusible enzyme inhibitor. Fatty acid lipoxygenase activity of similar magnitude was detectable in both cell types. A selective impairment of fatty acid cyclooxygenase in interferon-resistant cells is consistent with recently described data suggesting that this enzyme may play a crucial role in mediating the antiviral and anticellular effects of interferon.

Animals↗
PubMed1981

Establishment of the interferon-mediated antiviral state: possible role of superoxide dismutase.

Superoxide dismutase (SOD; superoxide: superoxide oxidoreductase, EC 1.15.1.1) catalyzes the dismutation of O2- free radicals formed during various enzymatic reactions or by ionizing radiation. Genes coding for SOD and sensitivity to exogenous interferon (IF) are syntenic in both mouse and man. Diethyldithiocarbamate (DDC) has been shown to inhibit SOD activity by chelating Cu2+, the metal ion essential for the catalytic activity of the enzyme. Mouse cell lines L, L929, L1210 S6, and L1210 R3 and a human cell line (WISH) pretreated with homologous IF and different concentrations of DDC for various periods of time were tested for their ability to support virus multiplication. Treatment of cells with DDC resulted in dose- and time-dependent inhibition of SOD activity and, simultaneously, in the reduction of antiviral protection by exogenous IF. Cells pretreated for 4 hr with DDC and then washed thoroughly were also resistant to IF, but DDC was without effect if the IF effect was first "established" by a 4-hr exposure to IF before addition of DDC. Under the conditions employed, DDC treatment did not result in any detectable inhibition of DNA, RNA, or protein synthesis in these cells. The data suggest that SOD or a related Cu2+-requiring enzyme may be necessary for the establishment of the IF-induced antiviral state in both human and murine cells.

Animals↗
PubMed1980

Establishment of the interferon-mediated antiviral state: role of fatty acid cyclooxygenase.

Inhibitors of fatty acid cyclooxygenase 8,11,14-icosatrienoate, hydrogen donor:oxygen oxidoreductase, EC 1.14.99.1) were found to suppress the establishment of the interferon-mediated antiviral state. The prevention, by these compounds, of the development of interferon protection correlated with the degree as well as the duration of cyclooxygenase inhibition. Anti-inflammatory substances lacking cyclooxygenase inhibitory activity did not interfere with the establishment of interferon protection. The addition of exogenous prostaglandins was not found to replace the need for a functional cyclooxygenase and, in some instances, could be shown to diminish the establishment of interferon protection. It is proposed that fatty acid cyclooxygenase is an essential component in the optimal induction of the interferon antiviral state.

Animals↗
PubMed1980

Thrombin and bradykinin modulate prostaglandin synthetase independently of phospholipase.

Thrombin and bardykinin stimulate prostaglandin production from exogenous arachidonic acid in 3T3 cells. The increase in PG production cannot be explained simply by the contribution from endogenous AA metabolism. The rates of stimulated PG production from exogenous and endogenous AA both remain linear fro 3 min, then fall rapidly. It is suggested that BK and Th may act by directly stimulating cyclooxygenase independently of phospholipase.

Animals↗
PubMed1980

Role of extracellular arachidonate in regulation of prostaglandin biosynthesis in cultured 3T3 fibroblasts.

The stimuli that activate phospholipase releasing substrate fatty acids for PG biosynthesis also activates the reuptake of liberated fatty acids by the cell. The substrate released by these stimuli is accessible to albumin in 3T3 cells, and it is therefore presumably released into the extracellular space before it undergoes enzymatic conversion. Added exogenous arachidonate competes freely with endogenous arachidonate released by a stimulus, suggesting no apparent coupling mechanism between phospholipase and cyclooxygenase enzyme systems.

Animals↗
PubMed1978

Action of corticosteroids in regulation of prostaglandin biosynthesis in cultured fibroblasts.

Various vasoactive agents (e.g., thrombin and bradykinin) and serum stimulate arachidonate production and thus prostaglandin biosynthesis in cultured fibroblasts. Treatment of 3T3 cells with the anti-inflammatory steroid, dexamethasone, inhibits this stimulation but has no inhibitory effect on the basal activity of phospholipase (or on prostaglandin content) in resting, confluent fibroblasts. In intact cells, the proportion of released arachidonic acid converted into prostaglandins is increased by steroid treatment, in quiescent, dense cells and in serum-treated cells, the total incorporation into prostaglandins is increased. Furthermore, the cyclo-oxygenase activity of homogenates from steroid-treated cells is increased very substantially. Thus, although steroids may affect phospholipase (EC 3.1.1.1.4) activities it is possible that these effects may be secondary to a more important stimulatory effect on cyclo-oxygenase activity which leads to selective alterations in prostaglandin biosynthesis. The steroid-induced increase in cyclo-oxygenase activity is not observed in a transformed variant of the same cell line. Fatty acid lipoxygenase (EC 1.13.11.12) activity exists in the particulate rather than the cytosolic fraction of 3T3 cells.

Cell Division↗
PubMed1978

Ionophore A-23187- and thrombin-induced platelet aggregation: independence from cycloxygenase products.

Stimulation of platelets labeled with [14C]-arachidonate by ionophore A23187 or thrombin produces rapid degradation of specific membrane phospholipids. This is also reflected by the release of [14C]archidonate, which is immediately transformed into products of the cycloxygenase and lipoxygenase enzyme systems, and by increased labeling of phosphatidic acid. Arachidonate metabolism can be effectively prevented by preincubation with indomethacin and eicosatetraynoic acid, but platelet aggregation induced by ionophore A23187 or trombin is not blocked under these conditions. Nevertheless, in the virtually total absence of metabolism of arachidonate, platelet aggregation still occurs concomitantly with phospholipid breakdown and with increased labeling of phosphatidic acid. Increased levels of cyclic AMP block both phospholipase activation and aggregation induced by ionophore A23187 and trombin. These data suggest that some early consequence of phospholipase activation, independent of a metabolic product of arachidonate but possibly related to the production of phosphatidic acid, may play a central, causative role in mediating platelet aggregation.

Animals↗
PubMed1976

Glycolipid glycosyl transferases of a hamster cell line in culture. I. Kinetic constants, substrate and donor nucleotide sugar specificities.

The properties of enzymes catalysing the transfer of a galactose from UDP-galactose to exogenous ceramide monohexoside and ceramide di-hexoside derived from the Syrian hamster cell line NIL 2 were studied. The products of these enzymes were characterized by chemical and enzymatic methods. Kinetic analyses showed that the enzymes are susceptible to inhibition and activation by a number of substrate analogues. The kinetic and inhibition constants, glycolipid substrate specificity and nucleotide sugar donor specificity have been studied.

Cell Line↗
PubMed1976

Glycolipid glycosyl transferases of a hamster cell line in culture. II. Subcellular distribution and the effect of culture age and density.

The activities of two galactosyl transferases catalysing the formation of di- and tri-glycosyl ceramides in NIL-2 hamster cells have been studied with respect to culture age and density, subcellular distribution, and transformation of cells by virus. The activity of the transferases was found to increase considerably as culture density increased, although maximal activities were found before appreciable cell contact occurred. The highest transferase activities were found in the endoplasmic reticulum. Virus transformation reduces the activity of the transferase catalysing triglycosyl ceramide synthesis, while the transferase catalysing diglycosyl ceramide synthesis is slightly increased. There is no evidence that the transformed cells produce a dialysable soluble inhibitor of transferase activities.

Adenosine Triphosphatases↗