GI262570, a peroxisome proliferator-activated receptor {gamma} agonist, changes electrolytes and water reabsorption from the distal nephron in rats.

Department of Molecular Pharmacology, GlaxoSmithKline, Inc., Five Moore Drive, Research Triangle Park, NC 27709, USA.
Journal of Pharmacology and Experimental Therapeutics (Impact Factor: 3.89). 03/2005; 312(2):718-25. DOI: 10.1124/jpet.104.074088
Source: PubMed

ABSTRACT Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists have been shown to have significant therapeutic benefits such as desirable glycemic control in type 2 diabetic patients; however, these agents may cause fluid retention in susceptible individuals. Since PPARgamma is expressed selectively in distal nephron epithelium, we studied the mechanism of PPARgamma agonist-induced fluid retention using male Sprague-Dawley rats treated with either vehicle or GI262570 (farglitazar), a potent PPARgamma agonist. GI262570 (20 mg/kg/day) induced a plasma volume expansion. The plasma volume expansion was accompanied by a small but significant decrease in plasma potassium concentration. Small but significant increases in plasma sodium and chloride concentrations were also observed. These changes in serum electrolytes suggested an activation of the renal mineralocorticoid response system; however, GI262570-treated rats had lower plasma levels of aldosterone compared with vehicle-treated controls. mRNA levels for a group of genes involved in distal nephron sodium and water absorption are changed in the kidney medulla with GI262570 treatment. In addition, due to a possible rebound effect on epithelial sodium channel (ENaC) activity, a low dose of amiloride did not prevent GI262570-induced fluid retention. On the contrary, the rebound effect after amiloride treatment potentiated GI262570-induced plasma volume expansion. This is at least partially due to a synergistic effect of GI262570 and the rebound from amiloride treatment on ENaCalpha expression. In summary, our current data suggest that GI262570 can increase water and sodium reabsorption in distal nephron by stimulating the ENaC and Na,K-ATPase system. This may be an important mechanism for PPARgamma agonist-induced fluid retention.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The efficacy of diuretics in the management of rosiglitazone (RSG)-induced fluid retention was evaluated in a multicenter, randomized, open-label, parallel-group, proof-of-concept study. Of 381 patients who had type 2 diabetes and were on treatment with sulfonylurea or sulfonylurea plus metformin, 260 (63% male, 37% female) showed evidence of volume expansion as defined by an absolute reduction in hematocrit (Hct) of > or =0.5% after 12 wk of rosiglitazone 4 mg twice daily. They were randomly assigned to five treatments for 7 d: (1) Continuation of RSG (RSG-C), (2) RSG + furosemide (RSG+FRUS), (3) RSG + hydrochlorothiazide (RSG+HCTZ), (4) RSG + spironolactone (RSG+SPIRO), and (5) discontinuation of RSG. The primary end point was change in Hct at day 7 of diuretic treatment phase, powered to compare each diuretic group and the RSG discontinuation with the control group of RSG-C, with adjustments for multiple testing. After 12 wk on RSG, Hct fell by mean of 2.92% (95% confidence interval [CI] -3.10 to -2.63%; P < 0.001) and extracellular fluid volume increased by 0.62 L/1.73 m(2) (95% CI 0.26 to 0.90 L/1.73 m(2); P < 0.001). After treatment, the RSG+SPIRO group only showed a mean increase in Hct of 0.24%. The estimated mean difference in Hct reduction was significant: 1.14% (95% CI 0.29 to 1.98%) for RSG+SPIRO (P = 0.004) and 0.87% (95% CI 0.03 to 1.71%) for RSG+HCTZ (P = 0.041) only. In additional analyses of between-diuretic treatment effects SPIRO induced a greater Hct rescue at 0.88% (95% CI -0.12 to 1.87%; P = 0.095) and extracellular fluid volume reduction of -0.75 L/1.73 m(2) (95% CI -1.52 to 0.03 L/1.73 m(2); P = 0.06) compared with FRUS, suggesting superiority in the management of RSG-associated fluid retention. There were no significant differences between SPIRO and HCTZ. These findings are consistent with peroxisome proliferator-activated receptor-gamma agonist activation of the epithelial sodium channel in the distal collecting duct, a site of action of SPIRO and a potential target for thiazide diuretics.
    Journal of the American Society of Nephrology 01/2007; 17(12):3482-90. · 8.99 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Increased renal expression of the angiotensin II, type-1 receptor (AT1R) has been associated with increased blood pressure (BP) and progression of renal disease. We tested whether common medications used to treat hypertension and the metabolic syndrome alter renal AT1R; and whether urine AT1R can be used as a reasonable noninvasive marker of renal levels in the obese Zucker rat, a model for human metabolic syndrome. Immunoblotting revealed that renal and urinary levels of AT1R were significantly higher in obese versus lean rats and correlated (R = 0.62, p < 0.05). Chronic treatment with BP lowering, candesartan, an AT1R antagonist, increased renal levels of AT1R in both lean (282% of lean controls) and obese (178% of obese controls) rats, but decreased urine AT1R levels in obese rats (72% of obese controls). Similarly, chronic treatment with rosiglitazone (RGZ), a peroxisome proliferator activated receptor (subtype gamma) agonist, significantly decreased urine (43% of obese controls) but not renal AT1R (105%) in obese rats. Blood pressure, measured by radiotelemetry, was significantly correlated in untreated and RGZ-treated rats to renal AT1R (R = 0.57, p = 0.0035). Finally, high- (4%) and medium- (0.4%) NaCl diets increased excretion of AT1R in obese rats to approximately 400% of low- (0.04%) NaCl diet. This effect was markedly blunted in lean rats. Overall, we demonstrate increased renal AT1R levels in obese rats. Urine AT1R correlated with renal levels only in the untreated state. Relative salt-sensitivity of AT1R excretion in obese, relative to lean rats, may have implications for both BP and renal disease in the metabolic syndrome.
    Clinical and Experimental Hypertension 03/2009; 31(1):49-63. · 1.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Much concern has arisen regarding critical adverse effects of thiazolidinediones (TZDs), including rosiglitazone and pioglitazone, on cardiac tissue. Although TZD-induced cardiac hypertrophy (CH) has been attributed to an increase in plasma volume or a change in cardiac nutrient preference, causative roles have not been established. To test the hypothesis that volume expansion directly mediates rosiglitazone-induced CH, mice were fed a high-fat diet with rosiglitazone, and cardiac and metabolic consequences were examined. Rosiglitazone treatment induced volume expansion and CH in wild-type and PPARγ heterozygous knockout (Pparg(+/-)) mice, but not in mice defective for ligand binding (Pparg(P465L/+)). Cotreatment with the diuretic furosemide in wild-type mice attenuated rosiglitazone-induced CH, hypertrophic gene reprogramming, cardiomyocyte apoptosis, hypertrophy-related signal activation, and left ventricular dysfunction. Similar changes were observed in mice treated with pioglitazone. The diuretics spironolactone and trichlormethiazide, but not amiloride, attenuated rosiglitazone effects on volume expansion and CH. Interestingly, expression of glucose and lipid metabolism genes in the heart was altered by rosiglitazone, but these changes were not attenuated by furosemide cotreatment. Importantly, rosiglitazone-mediated whole-body metabolic improvements were not affected by furosemide cotreatment. We conclude that releasing plasma volume reduces adverse effects of TZD-induced volume expansion and cardiac events without compromising TZD actions in metabolic switch in the heart and whole-body insulin sensitivity.
    American Journal Of Pathology 11/2013; · 4.60 Impact Factor