Background:  Although protease inhibitors (PI) are widely used to treat HIV, little is know concerning the effects of PI on blood pressure.

Methods:  To determine whether PI alter blood pressure, C57BL/6 mice were treated with amprenavir, indinavir, and ritonavir (25 mg/animal/day) for various times. To determine whether the PI altered the amount of endothelial nitric oxide synthase, acetylcholine receptors or bradykinin receptors, femoral arteries were isolated and analyzed. To determine if PI-induced increases in caveolin were responsible for the inhibition of endothelial nitric oxide synthase activity, we used a human microvascular endothelial cell line (HME). To ensure that the increase in caveolin was responsible for the decrease in endothelial nitric oxide synthase activity we used caveolin morpholinos to eliminate the expression of caveolin.

Results:  The resting blood pressure of animals treated with PI (87±3 mmHg) was similar to control animals (88±3 mm Hg). The infusion of acetylcholine or bradykinin into control animals induced a transient decrease in blood pressure (61±5 mm Hg). In contrast, infusion into animals treated with PI (3 days or 6 weeks) did not promote a decrease in blood pressure (85±5 mm Hg). Removal of PI for 5 days restored the ability of acetylcholine and bradykinin to induce a decrease in blood pressure. All of the effects with acetylcholine and bradykinin were inhibited by L-NNA which indicates the involvement of nitric oxide. PI did not alter the levels of endothelial nitric oxide synthase, or acetylcholine or bradykinin receptors, however, caveolin, an endogenous inhibitor of endothelial nitric oxide synthase, was greatly increased.  In unstimulated HME cells, inactive endothelial nitric oxide synthase associated with caveolin and the addition of acetylcholine or bradykinin promoted the dissociation and stimulation of endothelial nitric oxide synthase. The addition of 50 ng/mL of PI for 24 hours promoted a 12-fold increase in caveolin. Importantly, the addition of acetylcholine or bradykinin failed to dissociate endothelial nitric oxide synthase from caveolin or to increase endothelial nitric oxide synthase activity. The removal of the PI correlated with a decrease in caveolin and agonist-mediated endothelial nitric oxide synthase activation. The morpholinos eliminated caveolin and prevented the PI from inhibiting agonist stimulation of endothelial nitric oxide synthase.

Conclusions:  We conclude that HIV PI promote the up-regulation of caveolin in endothelial cells which subsequently inhibits endothelial nitric oxide synthase activity and contributes to endothelial-mediated dysfunction of blood pressure.

Keywords: hypertension; caveolin; lipid rafts