Abstract: BACKGROUND: There is a growing recognition that the adipose tissue is an endocrine organ that secretes signaling molecules such as adiponectin and resistin.The peroxisome proliferator activated receptor γ (PPARγ)is expressed in high levels in the adipose tissue.Thiazolidinediones are selective PPARγagonists with insulin-sensitizing properties.It has been postulated that thiazolidinediones such as rosiglitazone exert their pharmacodynamic effects in part through modulation of resistin (implicated in insulin resistance)and adiponectin (an insulin- sensitizing molecule)expression subsequent to activation of PPARγ.There are conflicting data, however, on the biological direction in which resistin expression is modulated by PPARγagonists and whether an increase in adiponectin expression can occur in the face of an upregulation of resistin. METHODS: Using the murine 3T3-L1 adipocytes as a model, we evaluated the changes in resistin and adiponectin gene expression after vehicle, rosiglitazone (10 μmol/L, a PPARγagonist), GW9662 (5 μmol/L, a selective PPARγantagonist)or GW662 and rosiglitazone co-treatment. RESULTS: In comparison to vehicle treatment, rosiglitazone increased the average adiponectin and resistin mRNA expression by 1.66- and 1.55-fold, respectively (P<0.05).Importantly, GW9662 also upregulated adiponectin expression (by 1.57-fold, P<0.05)but did not influence resistin expression (P> 0.05).Co-treatment with rosiglitazone and GW9662 maintained the adiponectin upregulation (1.87-fold increase from vehicle, P<0.05)while attenuating resistin upregulation (1.31-fold increase from vehicle, P<0.05)induced by rosiglitazone alone (1.55-fold increase from vehicle, P<0.05). CONCLUSION: This study presents new evidence that adiponectin transcript is upregulated with both a PPARγagonist (rosiglitazone)and antagonist (GW9662), while GW9662 co-treatment does not block rosiglitazone-induced adiponectin upregulation.These data collectively suggest that biological mechanisms independent from PPARγmay underlie thiazolidinedione pharmacodynamics on adiponectin expression.Moreover, increased adiponectin expression by GW9662, in the absence of an upregulation of resistin expression, lends further support on the emerging clinical potential of PPARγ antagonists in treatment of insulin resistance.Decreased resistin expression may not be crucial for the insulin-sensitizing effect of rosiglitazone.These findings may serve as a foundation for future dose-ranging and time-course studies of thiazolidinedione pharmacodynamics on adipocytokine expression in human adipocytes.

Key words: PPARγ, obesity, diabetes, insulin resistance, GW9662, thiazolidinediones, rosiglitazone, adipocytokine, 3T3-L1 adipocytes, gene expression