Long-term use of
HIV-1 protease inhibitors (PIs) is associated with a
lipodystrophy syndrome. To delineate the associated mechanisms, adipogenesis was determined in 3T3-L1 cells in the presence or absence of either
indinavir (2-50 microg/ml) or
ritonavir (0.4-10 microg/ml). A concentration-dependent decrease in both
lipid (4-59%) and
triglyceride (11-49%) levels was seen after 10 days of exposure. Simultaneous treatment with
TNF-alpha showed a synergistic suppression in
lipid levels by 45-95%
at 10 U/ml and almost complete suppression at 100 U/ml. The effect of PIs on
insulin-induced lipogenesis was monitored by [(14)C)]
glucose incorporation into
lipids, which was suppressed by 21-86% in a concentration-dependent manner.
Insulin-sensitizing agent,
troglitazone (80 and 400 nM), effectively blocked the PI-mediated adipogenic suppression. Preadipocyte factor 1 gene (pref-1) expression, as monitored by RT-PCR, was downregulated (4- to 6-fold) within 48 hr after
insulin stimulation; however, a smaller decrease (1.2- to 1.8-fold) was observed in PI-exposed cells. The decrease in proteolytic activity of matrix
metalloproteases (
MMP-2 and
MMP-9) during adipogenesis was reversed on exposure to the PIs. Similarly, the plasminolytic activity was increased and
plasminogen activator inhibitor (PAI) activity was decreased in supernatants from PI-treated cells. The
insulin-mediated induction (3- to 4-fold) of PAI-1 and PAI-2 message was suppressed on exposure to PIs, which was reversed by
troglitazone treatment. Thus, the HIV-1 PIs may suppress adipogenesis by disrupting the concerted actions of host
proteases that regulate ECM integrity required for initiation of differentiation.