Inhibition Of Lipid Metabolism Research Articles

Staphylococcal alpha-toxin: repair of a calcium-impermeable pore in the target cell membrane.

Staphylococcal alpha-toxin forms heptameric pores that render membranes permeable for monovalent cations. The pore is formed by an amphipathic beta-barrel encompassing amino acid residues 118-140 of each subunit of the oligomer. Human fibroblasts are susceptible to alpha-toxin but are able to repair the membrane lesions. Thereby, toxin oligomers remain embedded in the plasma membrane and exposed to the extracellular medium. In this study, we sought to detect structural changes occurring in the pore-forming sequence during lesion repair. Single cysteine substitution mutants were labelled with the environmentally sensitive fluorochrome acrylodan and, after mixing with wild-type toxin, incorporated into hybrid heptamers on fibroblast membranes. Formation of the lipid-inserted beta-barrel was accompanied by characteristic fluorescence emission shifts. After lesion repair, the environment of the residues at the outer surface of the beta-barrel remained unchanged, indicating continued contact with lipids. However, the labelled residues oriented towards the channel lumen underwent a green to blue shift in fluorescence, indicating reduced exposure to water. Pore closure proceeded in the presence of calmodulin inhibitors and of microtubule disruptors; however, it was prevented by cytochalasin D and by inhibitors of lipid metabolism. Our findings reveal the existence of a novel mechanism of membrane repair that may consist in constriction of the inserted proteinaceous pore within the lipid bilayer.

Eclosion hormone-stimulated cGMP levels in the central nervous system of Manduca sexta: inhibition by lipid metabolism blockers, increase in inositol(1,4,5)trisphosphate and further evidence against the involvement of nitric oxide.

Previous studies have shown that the neuropeptide, eclosion hormone, stimulates a nitric oxide-independent increase in the levels of cGMP in the nervous system of Manduca sexta. By contrast, recent results in Bombyx mori suggest that eclosion hormone increases cGMP via the production of nitric oxide. In view of these conflicting results we have carried out additional studies to test whether nitric oxide is involved in this process in Manduca. Evidence presented here supports our earlier observations that in Manduca the eclosion hormone-stimulated increase in cGMP is nitric oxide- and carbon monoxide-independent. In addition, we show that a wide variety of inhibitors of lipid metabolism block the eclosion hormone-stimulated cGMP increase. This supports the hypothesis that the activation of the guanylate cyclase is mediated by a lipid messenger. We also show that eclosion hormone stimulates an increase in the levels of inositol(1,4,5)trisphosphate. The time-course of this increase is consistent with the hypothesis that eclosion hormone stimulation of a phospholipase C is an early event in the cascade that results in an increase in cGMP. Receptor-mediated lipid hydrolysis is often mediated by G protein-coupled receptors. Experiments using pertussis toxin show that the eclosion hormone-stimulated increase in cGMP is not mediated by a pertussis toxin-sensitive G protein.

The Unmodified (Apo) Form of Escherichia coli Acyl Carrier Protein Is a Potent Inhibitor of Cell Growth

Acyl carrier protein (ACP) is the carrier of fatty acids during their synthesis and utilization. ACPs (or ACP-like protein domains) have been found throughout biology and share significant amino acid sequence similarities. All ACPs undergo a post-translational modification in which 4'-phosphopantetheine is transferred from CoA to a specific serine of apo-ACP. This modification is essential for activity because fatty acids are bound in thioester linkage to the sulfhydryl of the prosthetic group. Overproduction of Escherichia coli ACP from multicopy plasmids strongly inhibits growth of E. coli. We report that upon overexpression of ACP in E. coli post-translational modification is inefficient and the apo protein accumulates and blocks cell growth by inhibition of lipid metabolism. Moreover, a mutant form of ACP that is unable to undergo post-translational modification is a potent inhibitor of growth. Finally, we observed that an increase in the efficiency of modification of overexpressed ACP results in decreased toxicity. The accumulated apo-ACP acts as a potent in vitro inhibitor of the sn-glycerol-3-phosphate acyltransferase resulting in an inability to transfer the completed fatty acid to sn-glycerol 3-phosphate. The degree of inhibition depended upon the species of donor acyl chain. Utilization of cis-vaccenoyl-ACP by the sn-glycerol-3-phosphate acyltransferase was inhibited to a much greater extent by apo-ACP than was utilization of palmitoyl-ACP. 1-Acyl glycerol-3-phosphate acyltransferase was also inhibited in vitro by apo-ACP, although not at physiologically relevant concentrations. These in vitro data are supported by in vivo labeling data, which showed a large decrease in cis-vaccenate incorporation into phospholipid during overproduction of ACP, but no decrease in the rate of synthesis of long chain acyl-ACPs. These data indicate that acylation of sn-glycerol 3-phosphate is the major site of inhibition by apo-ACP.

Protein sparing in skeletal muscle during prolonged starvation. Dependence on lipid fuel availability.

Previous studies indicated that protein sparing in skeletal muscle during prolonged starvation depends on the availability of lipid fuels. To test this relationship further, fasted rats conserving protein were treated in vivo for 6-8 h with the antilipolytic agent nicotinic acid (NA) or with tetradecylglycidate (TDGD), an inhibitor of long-chain fatty acid oxidation. After treatment, protein synthesis and degradation in skeletal muscle were evaluated with the perfused rat hindquarter. NA treatment decreased plasma 3-hydroxybutyrate and free fatty acids and increased plasma urea and urine urea excretion, indicating increased breakdown of body protein. TDGD produced similar metabolic effects, except that plasma free fatty acids were markedly increased as a result of inhibition of fatty acid oxidation. NA and TDGD also decreased plasma insulin and increased plasma corticosteroid. Inhibition of lipid metabolism in vivo resulted in accelerated loss of protein from skeletal muscle due to decreased protein synthesis and increased protein breakdown. NA increased both total (i.e., tyrosine release) and myofibrillar (i.e., 3-methylhistidine release) protein breakdown, whereas TDGD increased the breakdown of only nonmyofibrillar proteins (i.e., 3-methylhistidine release by perfused hindquarter was not altered). These data indicate that lipid fuels may directly modulate protein metabolism in muscle during prolonged starvation and may prevent a rise in catabolic hormones. They also indicate that free fatty acids may directly attenuate the breakdown of myofibrillar proteins in muscle during prolonged starvation and that this may be unrelated to their oxidation.

Effects of inhibitors of carbohydrate absorption of lipid metabolism on meal patterns of Zucker rats

Peripherally active anorectic agents represent a new approach to the pharmacological management of obesity. Two inhibitors of carbohydrate absorption: an alpha-glucosidase inhibitor, acarbose (Bay g 5421) and an alpha-amylase inhibitor, Ro 12-2272, were compared with two novel inhibitors of lipid metabolism: an inhibitor of human pancreatic lipase (Ro 20-0083) and of hepatic fatty acid synthesis (Ro 22-0654). All drugs were presented as diet admixtures over 3 or 4 consecutive days. Total food and water intakes, the temporal pattern of feeding, and the average meal frequency and meal size were measured using computerized data collection procedures. Inhibitors of carbohydrate absorption failed to suppress food intake in either obese or lean Zucker rats and had no effect on the parameters of feeding. In contrast, inhibitors of lipid metabolism reduced food intake by 56–77% by reducing both meal frequency and meal size. Direct inhibition of lipid metabolism may be a viable mechanism for anti-obesity agents.

Study of the cellular action of drugs with protozoa. II. Comparative study of the inhibitions induced by hypocholesteremic agents on Ochromonas danica multiplication; annulment by oleic acid.

SYNOPSIS. Several hypocholesteremic agents inhibit multiplication of Ochromonas danica, Euglena grucilis, and Tetrahy‐menu pyriformis. Inhibiting O. danica are benzmalecene, triparanol, diazacholestanol. 3‐β‐(2‐diethylaminoethoxy) androst‐5‐en‐17‐one, α‐phenylbutyric acid, β‐diethylaminoethyldiphenyl‐n‐propylacetate (SKF‐525A) 2,2‐diphenyl‐1‐ (β‐dimethylaminoethoxy)pentane (SKF‐3301A), trans‐3‐(p‐chlorophenyl)‐2‐[p‐(2‐diethylaminoethoxy)phenyll‐2‐pentenenitrile (P‐3429), frans‐3‐[p‐(2‐diethylaminoethoxy) phenyll‐2‐pentenenitrile (P‐3013), vanadyl SO† and L‐thyroxine but not nicotinic acid, 3‐pyridylacetic acid, 3‐pyridylacetamide, nicotinuric acid, p‐aminosalicylic acid. tris‐(2‐dimethylaminoethyl) phosphate (SKF‐7732‐A3), tris‐ (2‐diethylaminoethyl) phosphate (SKF‐7997‐A3), 2,3‐bis[p‐(2‐diethylaminoethoxy) phenyl] acrylonitrile bis (P‐2681).Inhibition of Ochromonas multiplication by benzmalecene, triparanol, diazacholestanol, SKF‐525A. SKF‐3301A, P‐3013, and P‐3429 was annulled by lecithin, TEM, and specifiically by oleic acid. The following compounds equimolar with oleic acid were ineffective: stearic, palmitic, myristic, and lauric acids; cholesterol, stigmasterol, ergosterol, lanosterol, and β‐sitosterol; mevalonic acid lactone, geranyl acetate, farnesol, and squalene.Evidence is presented for the usefulness of protozoa as detectors of toxicity and possible harmful side effects of inhibitors of lipid metabolism in mammals.