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Item Development of Therapies to Treat Polycystic Kidney Disease(2013-03-06) Flaig, Stephanie Marge; Blazer-Yost, Bonnie; Gattone II, Vincent H.; Belecky-Adams, TeriPolycystic kidney diseases (PKD) are genetic disorders characterized by fluid filled cysts in the kidney tubules and liver bile ducts. There are two forms of PKD, autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD). The focus of the studies in this thesis has been on ADPKD. The disease progresses slowly and the fluid-filled cysts grow in size due to increased rates of cell proliferation and fluid secretion into the cyst lumen. The expanding cysts compromise the normal kidney function and result in a decrease of renal function to the point of end-stage renal failure in midlife. Cyst enlargement is due, at least in part, to chloride secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. Currently therapy is limited to renal cyst aspiration, dialysis, and eventually renal transplantation after organ failure, thus it has critical to determine possible drug therapies for the treatment of PKD. Previous studies showed that cyst fluid caused a secretory response in cells lining the cysts. We hypothesized that once the cyst have expanded and become so large that they burst or leak, which could also occur due to renal injury or aging, the cyst fluid may stimulate additional cyst growth. Lysophosphatidic Acid (LPA) was determined to be the active component of human cyst fluid, and we investigated the LPA stimulated signaling pathway. Our data suggest that the LPA stimulates chloride and fluid secretion by a combination of CFTR and Calcium-Activated chloride channels (CaCC) and that the two channels may functionally be linked to each other. The secretion is not occurring through a cAMP stimulated pathway, and it is possible that TMEM16A, a CaCC, plays a larger role than previously expected. Previous studies demonstrated that PPARγ agonists, insulin sensitizing drugs used to treat diabetes, inhibit chloride secretion by the collecting duct principal cells by decreasing CFTR synthesis. It was logical therefore to considered PPARγ agonists as long-term treatment for PKD. The first preclinical studied showed that high (20 mg/kg BW) dose pioglitazone, a PPARγ agonist, inhibited cyst growth in the PCK rat model, a slow progressing model, of PKD. To continue to look at the effects of the PPARγ agonists another preclinical study was completed, which tested if there was a class action of PPARγ agonists and if a lower dose was effective in treating the cystic burden. Using the PCK rat model, and another PPARγ agonist, rosiglitazone, a 24 week study was completed using 3 doses (4, 0.4, and 0.04 mg/kg BW). 4 mg/kg BW rosiglitazone is analogous to 20 mg/kg BW pioglitazone. The data indicated that the rosiglitazone is effective in lowering the cystic burden, and importantly the low dose proved to be effective. An additional rat model, the W-WPK rapidly progressing model was used to determine efficacy across multiple models, and to determine if there was a way to track the progress of the disease in a manner analogous to that used in human patients. The animals were treated with pioglitazone using 2 doses (2 and 20 mg/kg BW), and were imaged using CT scans to track the progress of the disease. The data suggest that pioglitazone was not as effective in the W-WPK rat model as it was the PCK rat model. There was a trend however, that low dose PPARγ agonist was as effective ad high dose. Even more important, the CT scans proved to be an effective way to track the progress of the disease in animal models.Item Inhibition of cyst growth in PCK and Wpk rat models of polycystic kidney disease with low doses of peroxisome proliferator-activated receptor γ agonists(De Gruyter Open, 2016-09) Flaig, Stephanie M.; Gattone, Vincent H.; Blazer-Yost, Bonnie L.; Department of Biology, School of ScienceBackground and Objectives The studies were designed to test the efficacy of two peroxisome proliferator-activated receptor γ (PPARγ) 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 PPARγ 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 PPARγ agonists effectively inhibit cyst growth; 2) there is a class action of the drugs with both commercially available PPARγ 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 PPARγ agonists below the human equivalent diabetic doses are effective in slowing cyst growth in two rodent models of PKD.Item Kidney stone formation in a novel murine model of polycystic kidney disease(American Physiological Society, 2022) Riddle, Heather A. L.; Zhang, Shiqin; Qian, Feng; Williams, James C., Jr.; Stubbs, Jason R.; Rowe, Peter Stanley N.; Parnell, Stephen C.; Anatomy, Cell Biology and Physiology, School of MedicineIndividuals with autosomal dominant polycystic kidney disease have a higher incidence of stone formation than the general population. However, there are no cystic animal models known to develop stones. Cystic mice compound heterozygous for hypomorphic Pkd1V and Pkd1RC alleles develop cystic kidneys within a few weeks of birth but live beyond 20 wk of age, allowing for the study of cystic comorbidities including stone formation. Cystic Pkd1V/RC mice were euthanized at 3, 13, or 26 wk of age, and their kidneys were analyzed by microcomputed tomography (µCT) for stone formation. Mice had occasional mineral aggregates that could be detected by µCT analysis at 3 wk of age. At 13 or 26 wk of age, numerous white masses were visible beneath the kidney surface. µCT analysis confirmed the masses to be large mineral stone deposits throughout the renal cortex, with mineral content increasing with age. Staining of histological sections with alizarin red and von Kossa suggested that the stone deposits were composed primarily of calcium and phosphate. Microdissection confirmed stones localized within cyst lumens. Analysis of individual stones by µCT and infrared spectroscopy confirmed apatite mineral composition. Urinalysis revealed elevated levels of phosphate and citrate at 3 wk of age and lower pH and elevated levels of calcium and citrate at 13 wk of age, suggesting altered phosphate and calcium homeostasis as a potential cause of mineralization and renal stone formation. This is the first animal model exhibiting overt kidney stone formation in the context of cystic kidney disease. NEW & NOTEWORTHY: Compound heterozygous Pkd1V/RC mice were found to form calcium phosphate-containing stones within cysts of the renal cortex by 13 wk of age. This is the first polycystic kidney disease animal model exhibiting spontaneous stone formation. A growing body of evidence suggests a link between renal stone formation and cystic kidney disease. This mouse model may be useful for studying the interplay between stone and cyst formation and the functional role of polycystins in mineral homeostasis.Item Pioglitazone, an Insulin Sensitizing Drug, Attenuates the Development of Kidney and Liver Disease in the PCK Rodent Model of Polycystic Kidney Disease(Office of the Vice Chancellor for Research, 2010-04-09) Blazer-Yost, Bonnie L.; Haydon, Julie; Eggelston, Tracy; Chen, Jey-Hsin; Torres, Vicente E.; Gattone, VincentPolycystic kidney disease is a genetic disorder characterized by growth of fluid-filled cysts predominately in kidney and liver. The only treatment currently available is the removal/aspiration of the largest cysts or organ transplantation. Promising pharmaceutical agents in clinical trials interfere with the action of hormones that increase cAMP thereby inhibiting secretion of Cl-, and compensatory fluid flux, into the cysts. Other treatments proposed include chemotherapeutic and immunosuppressive drugs that interfere with cellular proliferation as well as with signaling pathways for Cl- secretion. Long-term use of these agents will have multiple side effects. Based on a recent observation that peroxisome proliferator activated receptor γ agonists such as Actos (pioglitazone) and Avandia (rosiglitazone) decrease mRNA levels of a Cl- transport protein and the Cl- secretory response to vasopressin stimulation in cultured renal cells, it is hypothesized that PPARγ agonists will inhibit cyst growth. The current studies show that a 7 or 14 week feeding regimen of 20 mg/Kg BW pioglitazone inhibits renal and hepatic bile duct cyst growth in a rodent model orthologous to human PKD. In addition, the degree of renal cortical fibrosis was diminished in the pioglitazone-treated animals after 14 weeks. These results suggest that PPARγ agonists may be effective in controlling both renal and hepatic cyst growth and renal fibrotic development in polycystic kidney disease.