Background: Rosiglitazone is an agonist of the peroxisome proliferator-activated receptor (PPAR) gamma that may modify HDL metabolism in humans, but this effect has not been completely elucidated. Therefore, we determined the effect of rosiglitazone on apo AI turnover, HDL structure, and PON1 plasma activity.
Methods: Kinetic studies of HDL-apo AI radiolabeled with (125)I were performed in 7 chow-fed, male, New Zealand white rabbits after 6 weeks of 0.32 mg/kg/d rosiglitazone-treatment vs. vehicle-treated rabbits (n=11). HDL size distribution was determined by polyacrylamide gradient electrophoresis and paraoxonase-1 (PON1); plasma activity was assessed spectrophotometrically using phenylacetate as substrate.
Results: Fractional catabolic rate (FCR) of HDL apo AI was higher in the rosiglitazone-treated group than in the control group (0.031+/-0.004 vs. 0.025+/-0.006 pools/h, respectively, p<0.05). The mean apo AI production rate (PR) was 62% higher in the rosiglitazone group as compared to controls (0.918+/-0.238 vs. 0.564+/-0.160 mg/kg/h, p<0.01). Accordingly, apo AI plasma levels in rosiglitazone-treated animals were about 37% higher than in the control group. Rosiglitazone-induced changes in apo AI turnover appeared concomitantly with a significant increase of phospholipids and a decrease in colesteryl esters content of the HDL. Compositional changes resulted in a relative increase of the HDL3b and HDL3c subfractions and a significant enhancement of the plasma PON1 activity (488.5+/-138.2 vs. 595.2+/-179.4 micromol/min/ml, p<0.05).
Conclusions: Rosiglitazone increased apo AI plasma concentrations, resulting from an enhancement of apo AI synthesis, and induced the synthesis of smaller HDL particles with a concomitant increase of plasma PON1 activity. These modifications may contribute to the anti-atherogenic potential of rosiglitazone.