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At least 1,531 records · Page 85Linked to original sources
PubMed1990

CD2 triggering stimulates a phospholipase A2 activity beside the phospholipase C pathway in human T lymphocytes.

In previous studies we demonstrated the triggering of the phospholipase C (PLC) pathway during the activation of an Ag-specific human CD4+ T lymphocyte clone by a mitogenic pair of CD2 (X11,D66) mAb. Similar conditions were applied to investigate a possible involvement of a phospholipase A2 (PLA2) acting as an additional alternative pathway during human T cell activation. Our results show that arachidonic acid or its derivatives are released after CD2 triggering. This release is largely independent of PLC activation and is mediated by a PLA2 because: 1) phosphatidylcholine is the preferential source of [3H]arachidonate release; 2) [3H]arachidonic acid release and phosphatidylcholine hydrolysis are blocked by two inhibitors of solubilized PLA2, mepacrine, and 4-p-bromophenacylbromide; and 3) we evidenced a PLA2 activity in cell homogenates. Extracellular calcium appears to play a critical role because the effects of CD2 mAb were inhibited in a Ca2(+)-depleted medium. In contrast, protein kinase C is not implicated since PMA, a protein kinase C activator, neither stimulated arachidonic acid release nor modulated CD2-induced arachidonic acid release. Cyclic AMP which has been proved to regulate the activity of the PLC in T lymphocytes does not appear to play an important role in the regulation of PLA2 activity since PGE2 has only a minimal effect on [3H]-arachidonate release. Altogether, these findings suggest that CD2 triggering stimulates a PLA2 activity in T lymphocytes via an extracellular Ca2(+)-dependent PLC protein kinase C independent mechanism.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1990

Enhancing effect of piperidone derivatives on the percutaneous absorption of indomethacin.

Following our previous demonstration that Azone and 2-n-alkylcyclohexanones enhanced the percutaneous absorption of indomethacin, six 1-n-alkylpiperidones were prepared and examined as potential transdermal absorption enhancers. In vitro skin experiments showed that indomethacin absorption enhancement was related to the lipophilicity of the enhancer, and that 1-n-dodecyl piperidone caused the greatest enhancement. The structure of this piperidone is similar to that of Azone, and both compounds had similar lipophilicity and drug absorption enhancement activity. We suggest that they act in the same way by decreasing diffusional resistance in the stratum corneum, and so modifying the hard barrier of the stratum corneum.

Animals↗
PubMed1990

Crosslinked fibrous collagen for use as a dermal implant: control of the cytotoxic effects of glutaraldehyde and dimethylsuberimidate.

Collagen intended for use as a dermal implant may be crosslinked to increase its strength and persistence in vivo. Sheets of rat fibrous dermal collagen were crosslinked with either glutaraldehyde or dimethylsuberimidate and the cytotoxicity to human dermal fibroblasts resulting from these treatments was measured by following the inhibition of [3H]leucine incorporation into protein. Both agents were cytotoxic at the concentrations required to effect adequate crosslinking (0.005% and 25 mM, respectively). This cytotoxicity could be limited by extensive washing and by incubation with 5 mM L-lysine, with 66 mM (0.25% w/v) sodium borohydride, or with 71.3 mM (1% w/v) dimedone. However, cytotoxicity was most efficiently controlled by treatment with a combination of 66 mM sodium borohydride and 5 mM L-lysine or 66 mM sodium borohydride and 71.3 mM dimedone. [3H]Leucine incorporation by cells exposed to crosslinked collagen treated with these combinations approached 100% of the values recorded with cells exposed to uncrosslinked collagen.

Aldehydes↗
PubMed1979

Receptor-mediated low density lipoprotein catabolism in man.

Binding of human low density lipoproteins (LDL) to their specific receptor on cultured cells can be inhibited by treatment with 1,2-cyclohexanedione which blocks a number of functionally significant arginyl residues on the apolipoprotein. We have used this observation to examine the role of the receptor pathway in LDL catabolism in man. The plasma clearance rates of 125I-LDL and 131I-cyclohexanedione-treated LDL were measured in four normal and four heterozygous familial hypercholesterolemic subjects. Chemical modification of the lipoprotein significantly reduced its fractional clearance rate and permitted calculation of receptor-mediated and receptor independent catabolism in both groups. The normal subjects cleared 11% of their plasma LDL pool (corresponding to 3.0 mg/kg per day) by a receptor-independent path. In tared daily by these pathways, respectively. Because the mean apoLDL pool size in the group was increased 3-fold over normal, this gave absolute clearance rates for the apoprotein of 2.5 mg/kg per day via the receptors and 12.8 mg/kg per day by the nonreceptor pathway. We conclude that the specific LDL receptor mechanism operates in vivo and probably accounts for 33% and 16% of overall LDL catabolism in normal and heterozygous familial hypercholesterolemic subjects, respectively.

Adult↗
PubMed1990

Phospholipase A2 is a differentiation-dependent enzymatic activity for adipogenic cell line and adipocyte precursors in primary culture.

Phospholipase A2 enzymatic activity was measured in the teratoma-derived adipogenic cell line 1246 and in adipocyte precursors in primary cultures. It was shown that enzymatic activity was low while the cells were undifferentiated and increased by 20-24-fold after the cells had undergone adipocyte differentiation. The increase of phospholipase A2 activity follows the same time course as that observed for glycerol-3-phosphate dehydrogenase activity used as a marker of differentiation. In contrast, the differentiation-deficient, insulin-independent cell line 1246-3A always contained very low levels of phospholipase A2 activity. Phospholipase A2 activity measured in the 1246 cells was inhibited in a dose-dependent fashion by incubation with ONO-RS-082 and quinacrine which are inhibitors of phospholipase A2 activity. Measurements of arachidonate metabolites in 1246 cells showed that production of prostaglandin F2 alpha by the 1246 cells followed the same time course as the increase of phospholipase A2 activity during differentiation. Similar results were obtained with primary cultures of adipocyte precursors. These results indicate that phospholipase A2 is a differentiation-dependent enzymatic activity for the adipogenic cell line 1246 and for adipocyte precursors in primary culture. These data suggest that metabolic pathways controlled by phospholipase A2 activity could play an important physiological role in adipose tissue differentiation.

Adipose Tissue↗
PubMed1990

Compound I formation is a partially rate-limiting process in chloroperoxidase-catalyzed bromination reactions.

The kinetics of chloroperoxidase-catalyzed bromination and chlorination reactions were studied at various halide and hydrogen peroxide concentrations. At very high concentrations, both chloride (KI = 370 mM) and bromide (KI = 150 mM) are competitive substrate inhibitors versus hydrogen peroxide. Results at subinhibitory halide concentrations for bromination reactions (kcat = 4 ms-1, kcat/KPeroxide = 1.6 microM-1 x s-1 and kcat/KBr = 4.0 microM-1 x s-1) and chlorination reactions (kcat = 1.5 ms-1, kcat/Kperoxide = 2.3 microM-1 x s-1, and kcat/KBr = 0.32 microM-1 x s-1) indicate that halide oxidation is rate-limiting in chlorination reactions. However, in bromination reactions, both compound I formation and bromide oxidation are partially rate-limiting. This is the first documented case where compound I formation participates in determining the overall rate of a peroxidase reaction.

Binding, Competitive↗
PubMed1985

Chemical reactivities of bleomycin.

Ferric bleomycin was tested for its ability to catalyze a set of six oxidative reactions characteristic of the heme-containing proteins, cytochrome P-450 and chloroperoxidase. These reactions included peroxyacid decarboxylation and aliphatic hydroxylation as typical cytochrome P-450 chemistries. Peroxyacid-supported oxygen evolution and hydrogen peroxide-mediated chlorination were utilized as characteristic chloroperoxidase reactivities. A typical peroxidative reaction and heteroatom dealkylation, common to both O2 activating enzymes, were also studied. Bleomycin was found to catalyze peroxidation of o-dianisidine. The ferric drug complex was found competent in carrying out N-demethylation of N,N-dimethylaniline when peroxides or peroxyacids or iodosobenzene were used as the oxidants. N-Demethylation was not achieved when N,N-dimethylaniline-N-oxide was substituted as the oxidant under similar conditions. Hydroxylation of cumene and decarboxylation of phenylperacetic acid were not found to be catalyzed by bleomycin. Oxygen evolution from m-chloroperbenzoic acid and chlorination of monochlorodimedone from chloride ion and hydrogen peroxide were found to be catalyzed by bleomycin. Cytochrome P-450cam was also evaluated for O2 evolution, and halogenation activity and was found not to demonstrate such reactivities. The results of this initial survey, along with those of previous studies, appear to indicate that the chemical reactivity of bleomycin can be more closely aligned with the reactivities demonstrated by chloroperoxidase than those of cytochrome P-450.

Aniline Compounds↗
PubMed1988

Insulin antagonism of catecholamine stimulation of fatty acid transport in the adipocyte. Studies on its mechanism of action.

Insulin at physiological concentrations can suppress catecholamine activation of the membrane transport of long chain fatty acids in the adipocyte. We have previously shown that the stimulatory effect of catecholamines was mediated by a beta-receptor interaction and cAMP (Abumrad, N.A., Park, C.R., and Whitesell, R. R. (1986) J. Biol. Chem. 261, 13082-13086). In this study we have investigated the mechanism of insulin action to antagonize transport activation. Fatty acid transport was stimulated using different cAMP derivatives with varying susceptibilities to hydrolysis by the cAMP-degrading enzyme phosphodiesterase. Insulin was effective in antagonizing the effect of cAMP analogs which were good substrates for the phosphodiesterase and failed to suppress the effect of those which were poorly hydrolyzed by the enzyme. Addition of increasing concentrations (1-100 microM) of the phosphodiesterase inhibitor methylisobutylxanthine (MIX) to norepinephrine (0.1 microgram/ml) gradually abolished insulin's antagonism. Insulin was completely ineffective in inhibiting stimulation by norepinephrine and 20 microM methylisobutylxanthine. Also consistent with involvement of cAMP lowering in insulin action was the finding that adenosine removal greatly diminished insulin's responsiveness. Treatment of cells with adenosine deaminase (1 unit/ml) enhanced the effect of norepinephrine by about 30%. A 10-fold higher range of insulin concentrations was then required to produce inhibition of fatty acid transport. The effect of adenosine removal was reversed by addition of phenylisopropyladenosine (500 nM), which is resistant to hydrolysis by the deaminase. Finally, exposure of insulin-treated cells (1 nM for 5 min) to dinitrophenol (1 mM for 5 min) reversed insulin action, consistent with reports of reversal of insulin's activation of the phosphodiesterase. In conclusion, our studies support the involvement of cAMP lowering in insulin's antagonism of fatty acid transport stimulation in the adipocyte.

1-Methyl-3-isobutylxanthine↗
PubMed1989

[Probable side effects caused by plethoryl. Common acute hepatitis, anicteric hepatitis, cirrhosis due to hypervitaminosis A, inflammatory arthralgias].

Plethoryl is a combination of triatricol, cyclovalone and vitamin A normally prescribed in the treatment of hypercholesterolaemia. Four cases of side-effects most probably caused by this product are reported. They include: 1) a case of common acute hepatitis, 23 cases of which have already been published, with aggravation and reduced time-lapse after reintroduction; 2) a case of clinically silent but biochemically classical hepatitis; 3) a case of cirrhosis due to vitamin A toxicity; 4) a case of inflammatory arthralgias recurring after the same time-lag when the drug was reintroduced despite double doses and without clinical evidence of hepatitis. The last three side-effects have never been previously reported. The adverse reactions to Plethoryl almost always occur in the unofficial indications of the product, notably in the "treatment" of obesity.

Acute Disease↗
PubMed1989

Arginine residues at the active site of avian liver phosphoenolpyruvate carboxykinase.

The presence of arginine at the active site of avian liver phosphoenolpyruvate carboxykinase was studied by chemical modification followed by a characterization of the modified enzyme. The arginine-specific reagents phenylglyoxal, 2,3-butanedione, and 1,2-cyclohexanedione all irreversibly inhibit the enzyme with second-order rate constants of 3.42 M-1 min-1, 3.13 M-1 min-1 and 0.313 M-1 min-1, respectively. The substrates phosphoenolpyruvate, IDP, and the activator Mn2+ offer little to modest protection from inhibition. Either CO2 or CO2 in the presence of any of the other substrates elicited potent protection against modification. Protection by CO2 against modification by phenylglyoxal or 1,2-cyclohexanedione gave a biphasic pattern. Rapid loss in activity to 40-60% occurred, followed by a very slow loss. Kinetics of inhibition suggest that the modification of arginine is specific and leads to loss of enzymatic activity. Substrate protection studies indicate an arginine residue(s) at the CO2 site of phosphoenolpyruvate carboxykinase. Apparently no arginine residues are at the binding site of the phosphate-containing substrates. Partially inactive (40-60% activity) enzyme, formed in the presence of CO2, has a slight change of its kinetic constants, and no alteration of its binding parameters or secondary structure as demonstrated by kinetic, proton relaxation rate, and circular dichroism studies. Labeling of enzyme with [(7-)14C]phenylglyoxal in the presence of CO2 (40-60% activity) showed 2 mol of phenylglyoxal/enzyme or 1 arginine or cysteine residue modified. Labeling of phosphoenolpyruvate carboxykinase in the absence of CO2 yielded 6 mol of label/enzyme. Labeling results indicate that avian phosphoenolpyruvate carboxykinase has 2 or 3 reactive arginine residues out of a total of 52 and only 1 or 2 are located at the active site and are involved in CO2 binding and activation.

Animals↗
PubMed1989

Study of the role of tryptophanyl and arginyl residues in the specific binding of 3,5,3'-triiodothyronine to rat liver nuclear receptors.

The role of tryptophane and arginine residues of rat liver receptors for the specific binding of 3,5,3'-triiodothyronine (T3) was studied by chemically modifying the receptor molecule. Soluble T3 receptor fraction was prepared from purified rat liver nuclei and the kinetics of the modification of a tryptophane indol ring of nuclear receptor by N-bromsuccinimide (NBS) in the presence of excess -SH protecting agent was examined. Moreover the kinetics of the formation of N5-(4-oxo-1,3-diazospiro[4,4]non-2-ylidene)-I-ornithine or N7,N8-(1,2-dihydroxycyclohexyl-1,2-ylene)-L-arginine from arginine residue(s) of nuclear receptor by 1,2-cyclohexanedione was investigated. The efficiency of the reactions were followed spectrophotometrically and the modified nuclear receptor fraction separated from chemical modifiers on a Sephadex G-25 column was assayed at pH 8.0 for T3 specific binding. The T3 specific binding was tested by Scatchard plot analysis. No changes in nuclear receptor Ka or MBC were observed after 1,2-cyclohexanedione treatment. Tryptophanyl residue(s) of the receptor molecule may play an effective role in the maintaining the nuclear receptor in a conformation optimal for T3 binding.

Animals↗
PubMed1989

Inactivation of Escherichia coli L-threonine dehydrogenase by 2,3-butanedione. Evidence for a catalytically essential arginine residue.

Incubation of homogeneous preparations of L-threonine dehydrogenase from Escherichia coli with 2,3-butanedione, 2,3-pentanedione, phenylglyoxal, or 1,2-cyclohexanedione causes a time- and concentration-dependent loss of enzymatic activity; plots of log percent activity remaining versus time are linear to greater than 90% inactivation, indicative of pseudo-first order inactivation kinetics. The reaction order with respect to the concentration of modifying reagent is approximately 1.0 in each case suggesting that the loss of catalytic activity is due to one molecule of modifier reacting with each active unit of enzyme. Controls establish that this inactivation is not due to modifier-induced dissociation or photoinduced nonspecific alteration of the dehydrogenase. Essentially the same Km but decreased Vmax values are obtained when partially inactivated enzyme is compared with native. NADH (25 mM) and NAD+ (70 mM) give full protection against inactivation whereas much higher concentrations (i.e. 150 mM) of L-threonine or L-threonine amide provide a maximum of 80-85% protection. Amino acid analyses coupled with quantitative sulfhydryl group determinations show that enzyme inactivated 95% by 2,3-butanedione loses 7.5 arginine residues (out of 16 total)/enzyme subunit with no significant change in other amino acid residues. In contrast, only 2.4 arginine residues/subunit are modified in the presence of 80 mM NAD+. Analysis of the course of modification and inactivation by the statistical method of Tsou (Tsou, C.-L. (1962) Sci. Sin. 11, 1535-1558) demonstrates that inactivation of threonine dehydrogenase correlates with the loss of 1 "essential" arginine residue/subunit which quite likely is located in the NAD+/NADH binding site.

Alcohol Oxidoreductases↗
PubMed1989

Identification of essential arginine residue(s) for Mg-ATP binding of human argininosuccinate synthetase.

Human argininosuccinate synthetase (ASS) activity was found to be inactivated by alpha-dicarbonyls such as 1,2-cyclohexanedione and phenylglyoxal in accordance with pseudo first-order kinetics. The enzyme was almost completely protected from this inactivation by Mg-ATP and partially by its analogues. The strongest protective effect against inactivation was found with Mg-ATP, followed by Mg-ADP, AMP, adenosine and Mg-inorganic pyrophosphate. These results suggest the importance of arginine residue(s) for Mg-ATP binding. We determined the amino acid sequence of the peptide with the highest specific radioactivity derived from ASS which had been labeled with [14C]phenylglyoxal and then cleaved by cyanogen bromide treatment. The sequence obtained, PEFYNRFKGRNDLM, corresponds to residues 148-161 of the amino acid sequence deduced from the cDNA nucleotide sequence determined by Bock et al. [Nucleic Acids Res 11:6505-6512, 1983], and has a high homology with the sequences of ATP-binding sites proposed for several ATP-requiring enzymes.

Adenosine Triphosphate↗
PubMed1986

Inhibition of cell-mediated cytotoxicity by 2-cyclohexene-1-one: evidence for a role for glutathione and/or glutathione-protein interactions in cytolysis.

In order to explore the role of glutathione in cell-mediated cytotoxicity, we have examined the effect of the sulphydryl-reactive and glutathione-depleting agent 2-cyclohexene-1-one on antibody-dependent cellular cytotoxicity, spontaneous cell-mediated cytotoxicity, and cell-mediated lympholysis by human peripheral blood mononuclear cells. 2-Cyclohexene-1-one significantly inhibited (P less than 0.001) both antibody-dependent and spontaneous cell-mediated cytotoxicity using three different cell-line targets, at three different killer:target cell ratios (10:1, 25:1 and 50:1). Using K-562 cell-line targets, spontaneous cell-mediated cytotoxicity was inhibited by 2-cyclohexene-1-one with an ID50 of 0.71 X 10(-4) M-1.48 X 10(-4) M, while antibody-dependent cellular cytotoxicity was less sensitive to inhibition, and required slightly higher concentrations of 1.48 X 10(-4) M-3.98 X 10(-4) M to achieve 50% inhibition. Similar results were seen with human colon tumour cell-line and Chang liver cell-line cells as targets. Maximal inhibition occurred when 2-cyclohexene-1-one was added to the cytotoxicity assay 60 min prior to, at the start of, or within the first 60 min of a 4-hr assay; inhibition of cytotoxicity occurred with pretreatment of effector cells; and no inhibition of cytotoxicity was observed with pretreatment of target cells. Both the allogeneic mixed leucocyte reaction and cell-mediated lympholysis were also significantly inhibited (P less than 0.001) by 2-cyclohexene-1-one. These studies demonstrate that 2-cyclohexene-1-one is an effective inhibitor of cell-mediated cytotoxicity and suggest that glutathione, specific glutathione-protein interactions, or protein-bound sulphydryl groups are involved in allowing cells to carry out cytolysis.

Antibody-Dependent Cell Cytotoxicity↗