Oxidized high-density lipoproteins modulate endothelin secretion by adult bovine aortic endothelial cells.

BACKGROUND: High-density lipoprotein (HDL) cholesterol levels are well established as an inverse risk factor for atherosclerosis. This fact is probably related to the ability of HDL to induce cholesterol efflux from the vascular cell. It is also possible that HDL affects the production of different mediators implicated in the development of atheroslerosis. Endothelin is a vasconstricting mitogenic peptide involved in the development of atherosclerosis. We studied whether native HDL, oxidized HDL and tetranitromethane HDL modulate the endothelin secretion of cultured adult bovine aortic endothelial cells. METHODS: We determined the effect of native HDL and modified HDLs (oxidized HDL and tetranitromethane HDL) on the secretion of endothelin by cultured adult bovine aortic endothelial cells. An endothelin radioimmunoassay system was used to quantify levels of immunoreactive endothelin in the cultured media. RESULTS: Native HDL, tetranitromethane HDL and oxidized HDL produced a highly significant stimulation of endothelin secretion (maximum 294% of control), even at low concentrations (10 and 20 micrograms/ml). Oxidized HDL2 and oxidized HDL3 produced a biphasic effect, with maximum secretion occurring with 100 micrograms/ml oxidized HDL3 (294% of control) and 50 micrograms/ml oxidized HDL2 (252% of control). The secretion of the peptide decreased with higher concentrations of oxidized HDL2 and oxidized HDL3. CONCLUSION: Because modified HDLs (oxidized HDL and tetranitromethane HDL) do not bind to the 'HDL receptor' to stimulate endothelin secretion, we propose that the stimulation of secretion is mediated by unspecific binding of the lipoprotein to the cell membrane. Nevertheless, oxidized HDL and tetranitromethane HDL may stimulate endothelin secretion via the scavenger-receptor pathway. Our results suggest that HDL and modified HDL participate in the regulation of vascular tone.

Preparation of anti-HIV-low-density lipoprotein complexes for delivery of anti-HIV drugs via the low-density lipoprotein pathways.

Lipophilic prodrugs of 3'-azido-3'-deoxythymidine (AZT) and of 2',3'-didehydro-3'-deoxythymidine (D4T) have been synthesized. 3 beta-(2'-carboxymethoxy)-cholest-5-ene acid, palmitic acid, linolenic acid, linoleic acid, and cholanic acid have been covalently bound to AZT and D4T. In some experiments the fluorescent molecule NBD was simultaneously linked. These prodrugs were incorporated into LDL or acetylated LDL. The best incorporation was obtained with drugs presenting a steroid moiety (cholesterol derivative or cholanic acid) in their structure. The incorporation of prodrugs into LDL was estimated as approximately 200 molecules of prodrug per LDL particle. Cytofluorimetric studies clearly show that the NBD-steroid LDL or NBD-steroid acetylated LDL are bound and then internalized by the B-E receptor (U937) or the scavenger receptor (mouse peritoneal macrophage), respectively. The antiretroviral activity of palmitate-D4T, cholanic-AZT, and cholanic-AZT-LDL complex was similar to the activity of free D4T and free AZT, respectively. Development of lipid nucleoside-LDL complexes to attach specifically to cells involved in HIV infection might have a direct clinical relevance.

Oxidized low density lipoproteins exert arrhythmogenic effects in rabbit Purkinje fibers.

The electrophysiological effects of oxidized low density lipoproteins (ox-LDLs) have been studied in rabbit Purkinje fibers using standard microelectrode techniques, in comparison with native LDLs (n-LDLs) and lysophosphatidylcholine (LPC). At the concentration of 100 micrograms protein/ml, ox-LDL but never n-LDL induced the abrupt occurrence of abnormal electrical activities during the basic stimulation of 1 Hz (6/13 fibers) and the development of either early afterdepolarizations (6/13 fibers) or abnormal automaticity (4/13 fibers) at low frequencies (0.1 and 0.03 Hz). Short trains of rapid stimulation (2, 3, 4 and 5 Hz) did not trigger delayed afterdepolarizations. However, early afterhyperpolarizations were commonly seen after each action potential. 30 microM LPC caused quite similar electrophysiological derangements. The results suggest that ox-LDLs may exert arrhythmogenic effects partly explained by their LPC content.