Ritonavir exhibits anti-atherogenic properties on vascular smooth muscle cells

Objectives: HIV protease inhibitors (PI) such as ritonavir have dramatically decreased HIV-related morbidity and mortality. However they exhibit significant side-effects such as hyperlipidemia, hyperglycemia with or without lipodystrophy, which may increase patients' risk for atherosclerosis. Direct effects of PI on the vascular wall have not been investigated. Platelet-derived growth factor (PDGF) is a major contributor to atherogenesis. Design: in the present study the effects of ritonavir on PDGF-BB-induced responses of vascular smooth muscle cells (VSMCs) were evaluated. Methods: PDGF-induced proliferation of VSMCs was measured by BrdU-incorporation, and chemotaxis was assessed by utilizing modified Boyden chambers. Cytotoxicity and apoptosis were quantified using LDH-release- and apoptosis-kits. Immunoprecipitation and Western blot analyses were performed to evaluate betaPDGF receptor (betaPDGFR) expression and phosphorylation, and to monitor intracellular signaling. Results: Pretreatment of VSMCs with ritonavir resulted in a significant concentration-dependent inhibition of PDGF-BB-induced cellular responses. At a therapeutic concentration (10 mug/ml), ritonavir significantly reduced PDGF-induced DNA synthesis and chemotaxis by 46.8 +/- 5.5% and 37.2 +/- 3.3%, respectively (P < 0.05 each). In addition it significantly inhibited PDGF-dependent downstream signaling, such as Erk activation. These inhibitory effects were not due to cytotoxicity or apoptosis. Instead, ritonavir inhibited the ligand-induced tyrosine phosphorylation of the betaPDGFR, whereas it did not alter betaPDGFR expression. Conclusions: Ritonavir has direct effects on VSMCs at clinically relevant concentrations in vitro, as it inhibits betaPDGFR activation and PDGF-clepenclent proliferation and migration of VSMCs. Although ritonavir may increase the risk of vascular disease by its metabolic side effects, it may exhibit anti-atherogenic properties on the cellular level. (C) 2004 Lippincott Williams Wilkins.