Chain-melting transition temperatures of phospholipids with acylated or alkylated headgroups (N-acyl phosphatidylethanolamines and O-alkyl phosphatidic acids), or with alpha-branched chains

Covalent modification of lipids and proteins in rat hepatocytes and in vitro by thioacetamide metabolites

Thioacetamide (TA) is a well-known hepatotoxin in rats. Acute doses cause centrilobular necrosis and hyperbilirubinemia while chronic administration leads to biliary hyperplasia and cholangiocarcinoma. Its acute toxicity requires its oxidation to a stable S-oxide (TASO) that is oxidized further to a highly reactive S,S-dioxide (TASO(2)). To explore possible parallels among the metabolism, covalent binding, and toxicity of TA and thiobenzamide (TB), we exposed freshly isolated rat hepatocytes to [(14)C]-TASO or [(13)C(2)D(3)]-TASO. TLC analysis of the cellular lipids showed a single major spot of radioactivity that mass spectral analysis showed to consist of N-acetimidoyl PE lipids having the same side chain composition as the PE fraction from untreated cells; no carbons or hydrogens from TASO were incorporated into the fatty acyl chains. Many cellular proteins contained N-acetyl- or N-acetimidoyl lysine residues in a 3:1 ratio (details to be reported separately). We also oxidized TASO with hydrogen peroxide in the presence of dipalmitoyl phosphatidylenthanolamine (DPPE) or lysozyme. Lysozyme was covalently modified at five of its six lysine side chains; only acetamide-type adducts were formed. DPPE in liposomes also gave only amide-type adducts, even when the reaction was carried out in tetrahydrofuran with only 10% water added. The exclusive formation of N-acetimidoyl PE in hepatocytes means that the concentration or activity of water must be extremely low in the region where TASO(2) is formed, whereas at least some of the TASO(2) can hydrolyze to acetylsulfinic acid before it reacts with cellular proteins. The requirement for two sequential oxidations to produce a reactive metabolite is unusual, but it is even more unusual that a reactive metabolite would react with water to form a new compound that retains a high degree of chemical reactivity toward biological nucleophiles. The possible contribution of lipid modification to the hepatotoxicity of TA/TASO remains to be determined.

Molecular interactions between DPPC and morphine derivatives: a DSC and EPR study

The interaction between different morphine derivatives (morphine, codeine, N-methyl-morphine, N-methyl-codeine) and alpha-L-dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied with differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. Small unilamellar DPPC-liposomes with the given morphine-derivative were prepared by sonication. The size distribution of liposomes was checked by dynamic light scattering (DLS). The amount of entrapped morphine was determined spectrophotometrically. Our results indicate that the morphine and its derivatives principally interact with the lipid head groups, and this interaction leads to a decrease in the mobility of the polar head groups, especially in case of codeine and N-methyl-codeine.

Derivatised lipids in membranes. Physico-chemical aspects of N-biotinyl phosphatidylethanolamines, N-acyl phosphatidylethanolamines and N-acyl ethanolamines

The physical properties of N-biotinyl phosphatidylethanolamines, N-acyl phosphatidylethanolamines and of N-acyl ethanolamines, in aqueous dispersions, are reviewed. Emphasis is placed on the calorimetric (i.e. chain melting) properties, the thermotropic phase behaviour, certain aspects of the structure and dynamics, and the miscibility with other membrane lipids. In the case of N-biotinyl phosphatidylethanolamines, the specific binding of avidin, and in the case of N-acyl ethanolamines, the function of the third chain, is also considered. All of these properties are relevant to the role of these rather unusual lipids in membranes.