Objective: Current understanding of adipogenesis derives mainly from studies with in vitro cell culture systems with divergent experimental requirements. We aimed to investigate the discrepancy between the anti-adipogenic effects of the HIV protease-inhibitor indinavir (IDV) in vitro and the lack of evidence that IDV inhibits adipogenesis in humans.
Design and methods: We studied cell viability and adipogenesis in murine 3T3-F442A, 3T3-L1 and primary human subcutaneous preadipocytes (phsPA). Differentiation was studied after activation of the established four signalling pathways in different combinations. We analyzed CCAAT/enhancer-binding protein (C/EBP) alpha and peroxisome proliferator-activated receptor (PPAR) gamma expression and triacylglyceride accumulation. Cells were exposed to IDV at concentrations around therapeutic C(max) levels and higher (10 muM and 20 muM) for up to 30 days.
Results: Under insulin and fetal calf serum (FCS) input, IDV inhibited 3T3-F442A differentiation, an effect that was partially rescued by the addition of 3-isobutyl-1-methylxanthine (IBMX) stimulation. Combined stimulation with FCS, insulin, dexamethasone (DEX) and IBMX led to normal 3T3-L1 differentiation even in the presence of IDV. However, omission of IBMX rendered this cell line sensitive to IDV's anti-adipogenic effects. Differentiation of phsPA requiring complete adipogenic stimulation was not affected by IDV presence.
Conclusions: Our data suggest that the potency of IDV to impair differentiation under partial stimulation disappears when all of the differentiation pathways are activated. Such compensatory mechanisms might be responsible for the inability of the drug to affect adipogenesis in vivo.