Therapeutic dose of HIV-1 protease inhibitor saquinavir does not permanently influence Early insulin signaling

The introduction of HIV-1 protease inhibitor therapy has significantly improved the expectancy and quality of life for HIV-infected patients. Recent reports have highlighted the development of metabolic complications in patients taking protease inhibitors, including abnormalities in glucose metabolism such as impaired glucose tolerance and type 2 diabetes. The mechanisms by which protease inhibitors induce these metabolic syndromes are not well understood. The aim of this study was to determine whether treatment with the HIV-1 protease inhibitor, saquinavir, influences the early insulin signaling cascade in insulin-sensitive cell lines. Methods: Insulin-stimulated phosphorylation of insulin receptor (IR-β), insulin receptor substrates (IRS-1 and IRS-2), association of phosphatidylinositol 3-kinase (PI 3-kinase), Ser 473 -phosphorylation of Akt and Thr 202 /Tyr 204 -phosphorylated p44/42 MAP kinase in 3T3L1 adipocytes and FAO hepatoma cells incubated with increasing concentrations of saquinavir for 24, 36 hours, 2, 3 and 6 days were measured. Results: Phosphorylation of IR-β, IRS-1 and IRS-2 was not permanently affected by incubation with therapeutic doses (2.5 μM) of saquinavir for 36 hours. After 24 hours we observed an increase of IR-β and IRS-1 phosphorylation. However, this initial stimulation of IR-β and IRS-1 phosphorylation was not permanent and did not result in an increased PI 3-kinase association. Phosphorylation of IRS-2 and MAP kinase as well as glucose transport activity was not altered by therapeutic doses. Doses of 10, 25 and 50 μM of saquinavir altered the early insulin signaling events in a dose-dependent manner. However, this effect was primarily due to the cytotoxic effect of higher saquinavir doses. Glucose transport activity was not significantly reduced in 3T3L1 cells treated with 2.5 μM saquinavir in comparison to the control cells stimulated with insulin. Conclusion: Early insulin signaling cascade, essential for normal glucose metabolism, is not affected by therapeutic doses of saquinavir. The reduction of insulin-induced phosphorylation in higher concentrations is primarily related to cytotoxic effects. Other mechanisms than early insulin signaling must be primarily responsible for the metabolic alterations during saquinavir therapy.