Neutral glycosphingolipids of murine lymphoma EL-4

Neutral glycosphingolipids of murine T-lymphoma EL-4 were studied. The major glycolipid components were identified as GlcCer, LacCer, GgOse3Cer and GgOse4Cer. It has been shown for the first time that not only gangliosides but also neutral glycolipids are shed from the cell surface into the outer medium.     

Investigation of the lipid dependence of pyrophosphatase activity from rat liver microsomes and hepatoma by phospholipase C

The lipid dependence of pyrophosphatase activity was studied by treatment of liver and hepatoma microsomes with phospholipase C from Cl. perfringens and B. cereus and a subsequent incorporation of various classes of phospholipids into the delipidated microsomes. Phospholipase C hydrolysis sharply lowers the pyrophosphatase activity of liver and hepatoma microsomes. The enzyme activity is restored after introduction of phospholipids into delipidated liver microsomes, the maximal effect being achieved on incorporation of phosphatidylcholine. All the phospholipids tested exerted the same reactivation effects on the delipidated microsomes of hepatoma. However, a more complete delipidation of hepatoma microsomes by phospholipase C hydrolysis and a subsequent organic solvent extraction revealed a specific dependence of the enzyme activity on phosphatidylserine.     

Effect of gangliosides on the cytotoxic activity of natural killers from Syrian hamsters

The ability of various gangliosides to inhibit the cytotoxic activity of natural killers (NK-cells) from Syrian hamsters towards human lymphoma MOLT-4 cells was studied. The inhibitory effect was found to depend on the structure and concentration of the gangliosides. At concentrations corresponding to those in the blood of tumour-bearing hosts, SiaLacCer and Sia2LacCer inhibited the NK-activity. A significant inhibition was also found for (NeuAc)2GgOse3Cer, whereas NeuGcGgOse3Cer and NeuAcGgOse4Cer were practically inactive. Previously it was shown that Sia2LacCer which is either absent or very low in normal blood, is produced by a number of tumours and that tumour cells "shed" considerable amounts of gangliosides. On this ground, it was proposed that elevated concentrations of SiaLacCer and Sia2LacCer in the blood of tumour-bearing animals may inhibit the NK-activity and thus contribute to the "escape" of tumour cells from host immune surveillance.     

Bioeffector sphingolipids as stimulators of cell growth and survival

The effects of various bioactive sphingolipids (sphingosine 1-phosphate, sphingosine 1-phosphocholine, ceramide 1-phosphate, ceramide beta-glucoside and beta-lactoside, and gangliosides) on cell proliferation and apoptosis are reviewed. It is concluded that the balance between the bioeffector sphingolipids determines their overall effect on cell. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 3; see also http://www.maik.ru.     

The changes in the sphingenine/sphinganine ratio in sphingolipids of transplantable rat tumors depends on a transplantation organ

The content of sphingenine (sphingosine) and sphinganine was determined in the total pool of sphingomyelin and ceramide in the rat tumors transplanted subcutaneously and intrahepatically. The sphingenine/sphinganine ratio in the subcutaneously transplanted sarcoma M1 and cholangiocellular carcinoma RS1 was lower than that in the sphingolipids of the intrahepatically transplanted tumors. However, the sphingenine/sphinganine ratio in the subcutaneously transplanted rat hepatoma 27 was higher than in the intrahepatically transplanted hepatoma. These observations indicate that the sphingenine/sphinganine ratio in sphingolipids of tumors depends on the tumor type and its cellular microenvironment.     

Composition of fatty acids and sphingosine bases of placental gangliosides

The fatty acids and sphingosine bases from major placenta gangliosides (NeuAcLacCer, IV3NeuAc-nLc4Cer, VI3NeuAc-nLc6Cer, (NeuAc)2LacCer, II3IV3(NeuAc)2Gg4Cer and VI3NeuAc, IV6(II3NeuAc-nLcNAc)-nLc6Cer) were studied. The C18-sphingenine was shown to be present in all ganglioside fractions; fraction GD1a contained, in addition, C20-sphingenine. Saturated fatty acids were identified as major fatty acid fragments. The content of long-chain acids (22-25 C-atoms) in the monosialogangliosides was much higher than that in disialogangliosides.     

Lipid dependence of mitochondrial monoamine oxidase from rat hepatoma 27 with the use of rat liver lipid exchange proteins]

The ability of liver lipid exchange proteins to introduce foreign phospholipids into intact mitochondria was used for a study of the lipid dependence of monoamine oxidase. Introduction of exogenous phosphatidylcholine into rat hepatoma mitochondria, in which both the monoamine oxidase activity and the phosphatidylcholine content are comparatively low, leads to considerable activation of the enzyme. The introduction of exogeneous phosphatidylserine, phosphatidylethanolamine and cardiolipin has no activating effect. This indicates that the decreased activity of monoamine oxidase in the hepatoma may be due to a low amount of phosphatidylcholine. The method described allows the study in situ of the lipid dependence of non-solubilized membrane-bound enzymes.     

New method of lysophospholipid incorporation into biological membranes. Effect of lysophosphatidylcholine on the activity of membrane-bound enzymes

The incorporation of lysophosphatidylcholine into biological membranes and its effect on some membrane-bound enzymes of mitochondria and microsomes from rat liver and hepatoma were studied. It was shown that in the presence of lipid-exchange proteins of the liver a far greater amount of lysophosphatidylcholine is incorporated into the membranes than in the-iv absence. The increase of the lysophosphatidylcholine content in the membranes has no effect on the activity of mitochondrial monoamine oxidase, inhibits the activity of microsomal cytochrome P-450 and activates glucose-6-phosphatase.