Membrane-phorbol ester interactions monitored by circular dichroism

Catalytic radical cascade cyclization of alkene-tethered enones to fused bicyclic cyclopropanols

Fused bicyclic cyclopropanols were achieved via an unprecedented HAT-triggered radical cascade reaction of alkene-tethered enones in the presence of an iron catalyst.

Alteration of epithelial cell lipid synthesis by N-nitrosonornicotine

Changes in the lipid composition of a cell membrane due to the binding of one cell modulator may affect binding of a second modulator, whether that binding is receptor-mediated (specific) or non-receptor-mediated (nonspecific). Such altered binding interactions have been demonstrated in oral epithelial cells, wherein N-nitrosonornicotine (NNN), a nonspecific ligand, enhances phorbol ester binding. To characterize membrane changes that may be responsible for such an effect, the current study examined lipid changes in hamster oral epithelial (HCP) cells associated with NNN binding. HCP cultures at two cell densities, 5 x 10(6) cells/100 mm plate (subconfluent cultures) or 10 x 10(6) cells/100 mm plate (confluent cultures) were incubated in Keratinocyte-Serum-Free Medium and exposed to 10 microM NNN or DMSO (solvent control) for 48 h. Lipids were labeled with 14C-acetate, then extracted, separated by thin layer chromatography, and the 14C-lipids located by autoradiography and counted. Exposure of subconfluent cultures to NNN for 48 h, with 14C-acetate present during the final 24 h, resulted in altered phospholipid and fatty acid labeling. Phospholipid labeling increased slightly in the presence of NNN compared to controls, while fatty acid labeling showed a modest but significant decrease in the presence of NNN. Similar changes occurred in the confluent cultures. Prelabeling of lipids in subconfluent cultures, followed by exposure to NNN in the absence of radiolabel, resulted in significantly (P < 0.05) greater phospholipid labeling in the presence of NNN compared to control cultures. At the same time, fatty acid labeling decreased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

On the interaction of the liposomal membrane with blood components

Liposome-encapsulated hemoglobin (LEH) has been shown to be a viable candidate as a blood replacement. However, few data have been presented as to how LEH interacts with normal blood components. Liposomes were prepared from egg lecithin, cholesterol, and dicetyl phosphate or phosphatidic acid, and mixed with fresh blood plasma or whole blood. Erythrocyte osmotic fragility, prothrombin time (extrinsic coagulation efficiency), activated partial thromboplastin time (intrinsic coagulation efficiency), plasma clot stability in urea (fibrin stabilizing factor), and clot retraction (platelet activation) were measured. Although liposomes were found to bind extensively to erythrocytes, all tests indicated that the liposomes had no significant adverse effects, provided that normal levels of plasma Ca++ were maintained. The ability of liposomes to absorb Ca++ from the plasma was related directly to the amount of dicetyl phosphate or phosphatidic acid present and thus, presumably, to the presence of negatively charged species in the membrane. The mechanics of deformation of the LEH membrane were investigated by encapsulating Hemoglobin S in liposomes. Liposomes containing Hemoglobin S were found to sickle when deoxygenated, but not liposomes containing normal hemoglobin. Shape analysis of sickled liposomes yielded a deforming stress of 10(6) dynes/cm2, about 50 times greater than the reported limit for shear elasticity of the erythrocyte membrane.

Binding and uptake of N-nitrosonornicotine by oral epithelial cells

N-nitrosonornicotine (NNN), a significant nitrosamine component of tobacco binds to and is taken up by cells prior to its activation by intracellular enzymes. A variety of factors may affect the binding of substances to a cell including the cell type, medium composition and the cell membrane lipid composition. This study examines the binding and uptake of NNN to various cell types and relates these to the cells' lipid composition. Hamster buccal pouch keratinocytes were exposed to NNN and the amount of bound NNN determined. This was compared with cells pretreated with 12-0-tetradecanoylphorbol-13-acetate (TPA). While the keratinocytes bound significant amounts of NNN, this binding was not specific. Pretreatment of the cells with TPA significantly increased the amount of NNN bound. Cultures of human gingival fibroblasts and a human liver cell line also bound NNN, in quantities greater than that bound to the keratinocytes. The TPA caused changes in long chain unsaturated fatty acids although major changes in lipid metabolism were not detected. The fatty acid composition of the liver cells more closely resembled that of the TPA treated keratinocytes than the untreated ones. The data suggest that NNN binds to the cells non-specifically and the binding may be related to the amount of long-chain, unsaturated fatty acids present.