Effective activation of antioxidant system by immune-relevant factors reversely correlates with apoptosis of Eisenia andrei coelomocytes.

Oxidative stress is harmful to the microbes but also to the host, and may result in bystander damage or death. Because of this, respiratory burst triggered in phagocytes by pathogens is counteracted by production of antioxidative factors. The aim of this work was to examine effectiveness of the latter system in earthworms Eisenia andrei by induction of reactive oxygen species, lipofuscin and phenoloxidase by natural (LPS, zymosan, Micrococus luteus) and synthetic (phorbol ester, PMA) stimulants. The compounds impaired numbers, viability (increased apoptosis) and composition of coelomocytes, and triggered the antioxidant activity of catalase and selenium-dependent glutathione peroxidase. The natural pathogenic compounds, unlike PMA, strongly activated antioxidative responses that diminished cell apoptosis. Moreover, repeated exposure to the same or different pathogenic compounds did not induce respiratory burst exhausted phenotype showing that coelomocytes are constantly at bay to withstand numerous infections. The current study reveals importance and efficiency of the oxidative-antioxidative systems in annelids but also confirms its evolutionary conservatism and complexity even in lower taxa of the animal kingdom.

Metabolism of phospholipids and lysophospholipids by Trypanosoma brucei.

African trypanosomes (Trypanosoma brucei brucei) rapidly metabolize exogenous 1-acyl-lysophospholipids by at least two routes: (1) hydrolysis by a phospholipase A1; (2) acylation by an acyl-CoA-dependent acyltransferase. In contrast to lysophospholipids, exogenous phospholipids are not rapidly metabolized by T. brucei. The acyltransferase (EC 2.3.1.23) converts exogenous 1-acyl lysophosphatidylcholine and exogenous acyl-CoA to phosphatidylcholine and CoA-SH. It is a membrane-bound enzyme and shows maximal activity within the first 2 min of exposure of trypanosomes to the exogenous substrates. The acyltransferase specificity for lysophospholipids is lysophosphatidylcholine greater than lysophosphatidylinositol greater than lysophosphatidylethanolamine greater than lysophosphatidate. Phosphatidylcholine enhances the enzyme activity towards lysophosphatidylethanolamine and lysophosphatidic acid. The preference for CoA acyl thioesters is oleoyl greater than palmitoyl greater than myristoyl greater than stearoyl greater than arachidonoyl, and this specificity distinguishes the protozoan enzyme from those of cells of mammalian hosts, which are specific for arachidonoyl-CoA. When the acyltransferase converts exogenous lysophosphatidylethanolamine to phosphatidylethanolamine, the latter is rapidly methylated to form dimethylphosphatidylethanolamine. There is also rapid hydrolysis of exogenous oleoyl-CoA by a thioester hydrolase in living trypanosomes, to yield free oleate and CoA-SH.

Co-mitogenic tumor promoters suppress the phosphatidylinositol response in lymphocytes during early mitogenesis.

The tumor-promoting agents 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and phorbol-12,13-dibenzoate inhibited the increased accumulation of [32P]phosphatidylinositol (PI) induced in mouse spleen lymphocytes by mitogenic lectins in the presence of [32P]orthophosphate. Similar inhibition of [32P]PI levels by TPA was seen in human tonsil T-lymphocytes stimulated with phytohemagglutinin. Only co-mitogenic phorbol esters prevented the [32P]PI accumulation during early mitogenesis. No increased 32P-labelling due to mitogen or decreases due to TPA was observed when cells were equilibrated with [32P]orthophosphate for 24 h prior to stimulation with mitogen, from which it is concluded that the total concentrations of phosphatidylcholine (PC) and PI are unaffected by mitogen or co-mitogen. The [32P]PI elevation but not the [32P]PC elevation was proportional to T-cell mitogenic potency for the lectins concanavalin A, divalent succinyl concanavalin A and phytohemagglutinin, and was prevented in each case by 5 X 10(-8) M TPA. Escherichia coli lipopolysaccharide did not give increased 32P incorporation into PI or PC, and TPA had no effect on 32P labelled phospholipid levels in the presence of this B-cell mitogen. The results indicate that the phosphatidylinositol response is not an invariable correlate of T-cell mitogenesis by polyclonal mitogens.

Two proline porters in Escherichia coli K-12.

Escherichia coli mutants defective at putP and putA lack proline transport via proline porter I and proline dehydrogenase activity, respectively. They retain a proline uptake system (proline porter II) that is induced during tryptophan-limited growth and are sensitive to the toxic L-proline analog, 3,4-dehydroproline. 3,4-Dehydroproline-resistant mutants derived from a putP putA mutant lack proline porter II. Auxotrophic derivatives derived from putP+ or putP bacteria can grow if provided with proline at low concentration (25 microM); those derived from the 3,4-dehydroproline-resistant mutants require high proline for growth (2.5 mM). We conclude that E. coli, like Salmonella typhimurium, possesses a second proline porter that is inactivated by mutations at the proP locus.

The microsomal metabolism of the organometallic derivatives of the group-IV elements, germanium, tin and lead.

The NADPH- and oxygen-dependent microsomal metabolism of the di-, tri- and tetra-ethyl-substituted derivatives of germanium, tin and lead was shown to give rise to ethylene as a major product and ethane as a minor product. These reactions were shown to be catalysed by the liver microsomal cytochrome P-450-dependent mono-oxygenase. Since formation of ethane and ethylene was differentially inhibited by anaerobiosis, the results suggest that at least a large portion of the ethane produced may be derived by a reductive mechanism. Triethyltin bromide in both the absence and presence of NADPH was shown to convert cytochrome P-450 into cytochrome P-420 and to affect the function of the mono-oxygenase in vitro. Tetraethyltin caused the NADPH- and time-dependent formation of cytochrome P-420, suggesting that tetraethyltin is converted into triethyltin salts in significant concentrations. The order of potency in formation of cytochrome P-420 was closely paralleled by the ability of the tin derivatives to induce microsomal lipid peroxidation in vitro.

Plasma lipoprotein regulation of progesterone biosynthesis by human corpus luteum tissue in organ culture.

The role of plasma lipoproteins in supplying cholesterol for progesterone biosynthesis by human corpus luteum tissue in culture was investigated. Progesterone secretion by tissue fragments maintained in organ culture reached a maximum rate by the third day and subsequently declined. Maximal secretion of progesterone was dependent on the presence of both low density lipoprotein (LDL) and hCG in the culture medium, whereas high density lipoprotein (HDL) was ineffective in supporting progesterone biosynthesis. Human corpus luteum tissue degraded [125I]iodo-LDL by a mechanism which was saturable, and degradation of [125I]iodo-LDL was stimulated by hCG. Although 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was present in microsomes prepared from fresh human corpus luteum tissue, the activity of this enzyme in microsomes prepared from tissue maintained in culture for 3 days was virtually undetectable. Fresh human corpus luteum tissue contained 3 times more unesterified cholesterol than esterified cholesterol. It is concluded that LDL, but not HDL, is the major source of cholesterol used by the human corpus luteum for progesterone biosynthesis.