Inhibition of cyst growth in PCK and Wpk rat models of polycystic kidney disease with low doses of peroxisome proliferator-activated receptor gamma agonists

Background and Objectives: The studies were designed to test the efficacy of two peroxisome proliferator-activated receptor gamma (PPAR gamma) agonists in two rodent models of polycystic kidney disease (PKD). Materials and Methods: The PCK rat is a slowly progressing cystic model while the Wpk(-/-) rat is a rapidly progressing model. PCK rats were fed with a pharmacological (0.4 mg/kg body weight [BW]) and a sub-pharmacological (0.04 mg/kg BW) dose of rosiglitazone (week 4-28). Wpk(-/-) rats were fed with pharmacological (2.0 mg/kg BW) and sub-pharmacologic (0.2 mg/kg BW) doses of pioglitazone from day 5 to 18. At termination, kidney weights of treated versus untreated cystic animals were used to determine efficacy. The current studies were also compared with previous studies containing higher doses of PPAR gamma agonists. The concentrations used in the animals were calculated with reference to equivalent human doses for both drugs. Results: The current studies demonstrate: 1) that low, pharmacologically relevant, doses of the PPAR gamma agonists effectively inhibit cyst growth; 2) there is a class action of the drugs with both commercially available PPAR gamma agonists, rosiglitazone, and pioglitazone, inhibiting cyst growth; 3) the drugs showed efficacy in two different preclinical cystic models. In the PCK rat, animals fed with a sub-pharmacological dose of rosiglitazone for 24 weeks had significantly lower kidney weights than untreated animals (3.68 +/- 0.13 g vs. 4.17 +/- 0. 11 g, respectively, P < 0.01) while treatment with a pharmacologic dose had no significant effect on kidney weight. The rapidly progressing Wpk(-/-) rats were fed with pharmacological and sub-pharmacologic doses of pioglitazone from day 5 to 18 and the kidneys were compared with non-treated, cystic animals. Kidney weights on the pharmacologic dose were not statistically lower than the untreated animals while rats fed a sub- pharmacologic dose showed a significant decrease compared with untreated animals (3.35 +/- 0.15 g vs. 4.55 +/- 0.46 g, respectively, P = 0.045). Conclusion: Concentrations of PPAR gamma agonists below the human equivalent diabetic doses are effective in slowing cyst growth in two rodent models of PKD.