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Background:  HIV-1 protease inhibitors (PI) are widely used for the therapeutic intervention of HIV infection. However, some PI produce elevations in serum triglycerides, cholesterol, and low-density lipoproteins (LDL) that may be associated with long-term cardiovascular disease. Identifying new PI that are not associated with dyslipidemia has been hindered by the lack of mechanistic information and the unavailability of relevant animal models. The present study evaluated the potential use of gene expression changes in rat liver in the development of an exploratory hyperlipidemia model.

Methods:  Male Sprague-Dawley rats were dosed orally for 1 or 3 days with vehicle or PI, either alone or boosted with low-dose ritonavir. RNA from livers was harvested, amplified and analyzed using Affymetrix U34A rat microarray chips. Results were analyzed using Rosetta Resolver software. Plasma exposure was estimated by 12-hour pharmacokinetic analysis in parallel experiments.

Results:  At ≥5 0 mg/kg/day, treatment with ritonavir induced the expression of nearly all of the 33 genes encoding eukaryotic proteasomal subunits comprising the 20S and PA700 activator regions in a dose-dependent fashion. Other PI that elevate lipids in humans (lopinavir, amprenavir, indinavir, and nelfinavir) demonstrated up-regulation of many of the proteasomal genes at plasma levels approximating human exposures. In contrast, these genes were not substantially regulated by atazanavir, either alone or in combination with low-dose ritonavir. A link between proteasomal regulation and cholesterol elevation was supported by an observed correlation between the elevation of cholesterol in rats and activation of proteasomal subunits in a 2-week investigational toxicology study of rats treated with ritonavir and a novel protease inhibitor. This model was used to identify a novel PI, A-681799, with potential lipid-neutral characteristics.

Conclusions:  These results suggest that in vivo regulation of the eukaryotic proteasome by HIV PI may be related to the development of hyperlipidemia. The correlation with clinical observations suggests that proteasome gene regulation may be useful as a practical model for identification of new inhibitors with lower hyperlipidemic potential.

Keywords: Protease Inhibitor; Hyperlipidemia; Proteasome