Ether lipid synthesis from enantiomeric medium-chain and long-chain O-alkyl-sn-glycerols in Leishmania donovani promastigotes

Localization of the initial steps in alkoxyphospholipid biosynthesis in glycosomes (microbodies) of Trypanosoma brucei

Cell fractionation of Trypanosoma brucei cultured procyclic stages showed that the key enzyme of glycerol-ether lipid synthesis, dihydroxyacetone-phosphate acyltransferase (EC 2.3.1.42) was exclusively associated with the microbody fraction. These organelles contained in addition 1-acyl glycerol-3-phosphate: NADP+ oxidoreductase (EC 1.1.1.101) and acyl-CoA reductase and were capable of utilizing DHAP, but not G-3-P, as substrate for lysophosphatidic acid formation. It is concluded that in T. brucei the glycosomes are the exclusive site of the synthesis of precursors for glycerol-ether lipid synthesis and that they contain the entire pathway to form alkoxylipids from glycerol and acyl-CoA.

Proton NMR lipid profile of Leishmania donovani promastigotes

The proton nuclear magnetic resonance (NMR) lipid profile of Leishmania donovani was obtained in the one-dimensional and two-dimensional modes. Partial assignments of lipid classes and individual lipids were obtained purely from the proton NMR spectrum of the mixture. A more complete assignment and quantitative analysis was achieved by prior separation of the lipids by high pressure liquid chromatography (HPLC) followed by proton NMR analysis of the fractions. This work showed that proton NMR spectroscopy could facilitate lipid analysis and classification of various parasitic protozoa and serve as a basis for rapid studies of comparative lipid metabolism in parasites.

Cytotoxicity of ester and ether lysophospholipids on Leishmania donovani promastigotes

The cytotoxic activity of four ester lysophospholipids, three ether lysophospholipids, and two radylglycerols on Leishmania donovani promastigotes was determined by measuring the inhibition of cell growth. The 1-acyl lysophospholipids reduced cell growth to 50% of controls at concentrations of 6.4-10.9 microM. In contrast, 1-O-alkenyl-sn-glycero-3-phosphoethanolamine, 1-O-hexadecyl-sn-glycero-3-phosphocholine, and 1-O-hexadecyl-sn-glycerol already showed a 50% inhibition of growth at concentrations between 2.1 and 2.8 microM. Moreover, the unnatural alkyl lysophospholipid analogue 1-O-octadecyl-2-methoxy-sn-glycero-3-phosphocholine was even 10-fold more toxic. Incubations of L. donovani promastigotes with radioactively labelled ether lysophospholipids revealed a rapid uptake of these compounds and their incorporation into cellular lipids at a non-toxic concentration of 1.0 microM. An accumulation of the lysophospholipids in the cell due to insufficient metabolism may be the cause of its cytotoxic effect. The sensitivity of L. donovani cells towards ether lysophospholipids was found to be similar to that reported for tumor cells.

Metabolism of 1-0-[1'-14C]octadecyl-sn-glycerol in Leishmania donovani promastigotes. Ether lipid synthesis and degradation of the ether bond

A long-chain 0-alkylglycerol, 1-0-[1'-14C]octadecyl-sn-glycerol, was taken up and metabolized extensively in Leishmania donovani promastigotes grown on a lipid-free, semi-defined medium as well as on a lipid-free, synthetic medium in nearly identical ways. Cleavage of the ether bond was the main event even after short incubation times (1 h) and low precursor concentration (2 microM), as judged from the appearance of radioactive acyl moieties residing mainly in phosphatidylcholine. In addition, labeled plasmanyl inositol and plasmenyl ethanolamine were formed to a considerable extent. However, when administered in higher concentrations (25 microM), 1-0-alkyl-sn-glycerols as well as their enantiomers inhibited lipid metabolism dramatically, accompanied by rounding of the cells and appearance of cellular debris in the medium. This effect was not dependent on the aliphatic side chain (12:0, 16:0, 18:0, 18:1) of the 0-alkylglycerols. It is suggested that, by incorporation into cellular membranes, 0-alklglycerols affect factors responsible for the interaction of membranes and the cytoskeleton as well as enzymes of lipid metabolism.

Incorporation of [1-14C]acetate into fatty acids and aliphatic moieties of glycerolipids in Leishmania donov ani promastigotes

1. Short-time incubations (20-300 sec) of Leishmania donovani with [1-14C] acetate showed lauric, myristic and palmitic acid to be labeled first, whereas from 150 sec on the radioactivity was mainly found in stearic and oleic acid. 2. After an incubation period of 7 days the distribution of radioactivity in fatty acids was similar to the mass distribution of fatty acids. 3. Up to 300 sec 14C-activity was present mainly in acyl moieties of lipids (94%). 4. Ether moieties of radylglycerols, diradylglycerophosphoethanolamine and -inositol slowly incorporated radioactivity in pulse-chase experiments from 1 to 24 hr. 5. Pulse-chase experiments revealed significant differences in plasmanylethanolamine, acylglycerol and sterol metabolism of cells in the logarithmic or stationary phase of growth.