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 βPDGF receptor (βPDGFR) 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 μg/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 βPDGFR, whereas it did not alter βPDGFR expression.
Conclusions: Ritonavir has direct effects on VSMCs at clinically relevant concentrations in vitro, as it inhibits βPDGFR activation and PDGF-dependent 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.
From the aKlinik III für Innere Medizin, the bAbteilung für Herzchirurgie der Universität zu Köln, Joseph-Stelzmann-Str. 9, 50924 Köln, cKlinik I für Innere Medizin, Germany.
Correspondence to Dr. med. Stephan Rosenkranz, Klinik III für Innere Medizin der Universität zu Köln, Joseph-Stelzmann-Str. 9, 50924 Köln, Germany.
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Received: 24 April 2003; revised: 20 August 2003; accepted: 8 September 2003.