Defective catabolism of oxidized LDL by J774 murine macrophages.

In J774 murine macrophages, chemically oxidized LDL (OxLDL) and biologically oxidized LDL (BioOxLDL) have similar metabolic fates, characterized by a relatively poor degradation when compared with acetylated LDL (AcLDL), and a modest ability to activate acyl-CoA:cholesterol acyltransferase (ACAT) (850 and 754 pmol [14C]oleate/mg cell protein in OxLDL- and BioOxLDL-incubated cells, versus 425 and 7070 pmol [14C]cholesteryl oleate/mg cell protein in control and AcLDL-incubated cells) with a massive increase of cellular free cholesterol. Therefore, OxLDL were used to investigate the cellular processing of oxidatively modified LDL. Binding and fluorescence microscopy studies demonstrated that OxLDL are effectively bound and internalized by macrophages and accumulate in organelles with density properties similar to those of endo/lysosomes. Although the overall metabolism of OxLDL is modestly affected by 100 microM chloroquine, owing to the poor cellular degradation of the substrate, the drug can further depress OxLDL degradation, indicating that this process takes place in an acidic compartment. Failure to detect products of extensive degradation of OxLDL in the medium is due to their relative resistance to enzymatic hydrolysis, as demonstrated also by in vitro experiments with partially purified lysosomal enzymes, rather than to the intracellular accumulation of degradation products (degraded intracellular protein is, at most, 8.5% of total). This sluggish degradation process is not due to a cytotoxic effect since OxLDL do not affect the intracellular processing of other ligands like AcLDL or IgG. The accumulation of OxLDL-derived products within macrophages may elicit cellular responses, the relevance of which in the atherosclerotic process remains to be addressed

The new calcium antagonist lercanidipine and its enantiomers affect major processes of atherogenesis in vitro: is calcium entry involved?

Atherosclerosis results from multiple factors and involves several mechanisms, including endothelial monocyte and smooth muscle cell (SMC) changes, cholesterol accumulation, plaque rupture and thromboembolism. Calcium ions play a role in the initial and chronic development of atherosclerotic lesions. Several studies in experimental animal models have demonstrated the potential direct antiatherosclerotic effects of calcium antagonists. In this study the antiatherogenic activity of lercanidipine, a new lipophilic, second-generation calcium antagonist, was investigated. Lercanidipine and its enantiomers inhibited the replication and migration of arterial myocytes in concentrations ranging from 10 to 50 microM. The antiproliferative effect of lercanidipine was dose dependent, with a potency similar to that of lacidipine and nifedipine, and was unrelated to the stereoselectivity of enantiomers to bind L-type calcium channels. Lercanidipine and its enantiomers (25 microM) decreased the serum-induced elevation of [Ca2+]i in SMC, with the (S)-enantiomer (69% inhibition) being 2.4-fold more active than the (R)-counterpart (29% inhibition). The studies performed with enantiomers of lercanidipine suggest that the observed effects are not related to the blockade of voltage-dependent Ca2+ channels and confirm, at least in vitro, the pharmacological potential of the compound to influence negatively the process of atherogenesis

Monoclonal antibodies to human low density lipoprotein identify distinct areas on apolipoprotein B-100 relevant to the low density lipoprotein-receptor interaction.

We have characterized the epitopes for ten murine monoclonal antibodies (Mabs) to human low density lipoprotein (LDL) and studied their ability to interfere with the LDL-receptor interaction. The epitopes for the antibodies were defined by using the following approaches: 1) interaction with apoB-48; 2) interaction with apoB-100 thrombolytic fragments; and 3) interaction with beta-galactosidase-apoB fusion proteins spanning different areas of the apoB-100 sequence. The results obtained are consistent with the following map of epitopes: Mab 6E, amino acids (aa) 1-1297, Mabs 5A and 6B, aa 1480-1693, Mabs 2A, 7A, 3B, and 4B, aa 2152-2377, Mabs 8A and 9A, aa 2657-3248 and 3H, aa 4082-4306. Four Mabs (2A, 5A, 7A, and 9A) whose epitopes are located in three different areas of apoB, dramatically reduced (up to 95%) the LDL-receptor interaction on cultured human fibroblasts; Fab fragments were as effective as the whole antibodies. Mab 3H, on the other hand, increased LDL binding up to threefold. These findings are consistent with the hypothesis that several areas of apoB-100 are involved independently or in concert in modulating the apoprotein B conformation required for interaction with the LDL receptor