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We studied the effect of troglitazone on cellular acid-base balance and alanine formation in isolated rat mesangial cells. Mesangial cells were grown to confluency in RPMI 1640 media on 30-mm chambers used to monitor both cellular pH using the pH-sensitive dye 2'7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein and metabolic acid production as well as glutamine metabolism. Troglitazone (10 [micro]M) induced a spontaneous cellular acidosis (6.95 [+ or -] 0.02 vs. 7.47 [+ or -] 0.04, respectively; P < 0.0001) but without an increase in lactic acid production. Alanine production was reduced 64% (P < 0.01) consistent with inhibition of the glutamate transamination. These findings pointed to a decrease in acid extrusion rather than an increase in acid production as the underlying mechanism leading to the cellular acidosis. To test their acid extrusion capabilities, mesangial cells were acid loaded with N[H.sup.+.sub.4] and then allowed to recover in Krebs-Henseleit media or in Krebs-Henseleit media minus bicarbonate (HEPES substituted), and the recovery response ([DELTA]p[H.sub.i]/min) was monitored. In the presence of 10 [micro]M troglitazone, the recovery response to the N[H.sup.+.sub.4] acid load was virtually eliminated in the bicarbonate-buffered media (0.00 [+ or -] 0.001 vs. 0.06 [+ or -] 0.02 p[H.sub.i]/min, P < 0.0001 vs. control) and reduced 75% in HEPES-buffered media (0.01 [+ or -] 0.01 vs. 0.04 [+ or -] 0.02 p[H.sub.i]min, P < 0.002 vs. control). These results show that troglitazone induces a spontaneous cellular acidosis resulting from a reduction in cellular acid extrusion. 2'7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein; lactic acid; sodium/hydrogen exchange; bicarbonate-activated acid extrusion; glutamine metabolism

Troglitazone inhibits glutamine metabolism in rat mesangial cells. Am J Physiol Endocrinol Metab 282: E231-E238, 2002.--Troglitazone is a peroxisome proliferator-activated receptor-[gamma] agonist that has been shown to halt mesangium expansion in experimental models of type 2 diabetes mellitus and to act directly on rat mesangial cells. Because glutamine serves as the precursor for cellular biosynthetic processes, we asked whether troglitazone would inhibit mesangial cell glutamine metabolism under these conditions. Confluent monolayers of rat mesangial cells were incubated in RPMI medium in the presence of troglitazone or vehicle (DMSO). Troglitazone effected a dose-dependent reduction in glutamine utilization and in alanine formation, associated with a decrease in monolayer collagen-glycosaminoglycan content. Despite the reduced glutamine uptake, ammonium formation did not decrease, consistent with increased glutamate flux through the deamination pathway. Assayable activity of the alanine aminotransferase decreased by 63%, whereas assayable glutamate dehydrogenase remained unchanged. In control monolayers, the sum of ammonium plus alanine plus glutamate nitrogen released accounted for peroxisome proliferator-activated receptor-[gamma]; alanine aminotransferase; matrix proteins; intracellular pH

Troglitazone halts diabetic glomerulosclerosis by blockade of mesangial expansion. Background. Renal complications of long-term, poorly controlled type 2 diabetes mellitus include glomerulosclerosis and interstitial fibrosis. The onset and progression of these complications are influenced by underlying pathophysiologies such as hyperglycemia, hypertriglyceridemia, and hypercholesterolemia. Troglitazone, a thiazolidinedione, has been shown to ameliorate these metabolic defects. However, it was not known whether therapeutic intervention with troglitazone would prevent the onset and progression of glomerulosclerosis. Methods. Sixty male ZDF/Gmi™ rats and 30 age-matched Zucker lean rats were in the study. The ZDF/Gmi™ rats were divided into two groups, one in which blood glucose levels were uncontrolled (30 animals) and another (30) in which blood glucose was controlled via dietary administration of troglitazone. Ten animals from each group were sacrificed at one, three, and six months into the study. The kidneys were harvested and processed for immunostaining with BM-CSPG, a marker for mesangial matrix. Images of 200 glomeruli per animal were captured using digital imaging microscopy, and the index of mesangial expansion (total area mesangium/total area of tuft) per glomerular section was measured. Results. The administration of troglitazone ameliorated the metabolic defects associated with type 2 diabetes mellitus. Moreover, the glomeruli from tissue sections of animals given troglitazone showed no mesangial expansion when compared with normoglycemic control animals, whereas the uncontrolled diabetic animals showed significant mesangial expansion at all time intervals. Conclusions. Therapeutic intervention with the thiazolidinedione troglitazone halts the early onset and progression of mesangial expansion in the ZDF/Gmi™ rat, preventing the development of glomerulosclerosis in this animal model of type 2 diabetes mellitus. [ABSTRACT FROM AUTHOR]