Antihypertensive and vasculo- and renoprotective effects of pioglitazone in genetically obese diabetic rats

A Real-World Study of Long-Term Safety and Efficacy of Lobeglitazone in Korean Patients with Type 2 Diabetes Mellitus

BACKGROUND

Thiazolidinediones (TZDs) have been associated with various safety concerns including weight gain, bladder cancer, and congestive heart failure (CHF). This study evaluated the efficacy and safety of lobeglitazone, a novel TZD in patients with type 2 diabetes mellitus (T2DM) in real practice.

METHODS

In this non-interventional, multi-center, retrospective, and observational study conducted at 15 tertiary or secondary referral hospitals in Korea, a total of 2,228 patients with T2DM who received lobeglitazone 0.5 mg for more than 1 year were enrolled.

RESULTS

Overall adverse events (AEs) occurred in 381 patients (17.10%) including edema in 1.97% (n=44). Cerebrovascular and cardiovascular diseases were identified in 0.81% (n=18) and 0.81% (n=18), respectively. One case of CHF was reported as an AE. Edema occurred in 1.97% (n=44) of patients. Hypoglycemia occurred in 2.47% (n=55) of patients. Fracture occurred in 1.17% (n=26) of all patients. Lobeglitazone significantly decreased HbA1c level, resulting in a mean treatment difference of -1.05%± 1.35% (P<0.001), and decreased total cholesterol, triglyceride, and low-density lipoprotein cholesterol. However, it increased high-density lipoprotein cholesterol, regardless of statin administration. The patients who received lobeglitazone 0.5 mg showed an apparent reduction in glycosylated hemoglobin (HbA1c) from baseline during the first 6 months of treatment. The HbA1c levels remained stable between months 6 and 42.

CONCLUSION

Lobeglitazone has long-term safety profile, good glycemic-lowering effect and long-term durability of glycemic control in real-world clinical settings.

Drug Therapies Affecting Renal Function: An Overview

Undesirable side effects of medication are inevitable. Due to the role of the kidneys in clearance and filtration, the renal system faces a unique situation when it comes to the side effects of drugs. It has an important role for different classes of drugs to be excreted, and drugs are a key factor for this system to be at risk. Medications in articles were divided into classes using the standard set by the Saudi Pharmaceutical Journal. Many drug classes cause renal insults. The top six classes were pain killers, antibiotics, proton pump inhibitors, antidiabetics, antihyperlipidemics, and agents for erectile dysfunction. Renal insults caused by these agents could vary in severity. Some drugs could cause nephrotoxicity from one dose, while others may only need continuous monitoring. Different populations also operate under different rules, as some people need dose adjustments while others who are medically free of major illnesses do not. A variety of unfavorable outcomes for the kidney could take place, such as acute kidney injury, chronic kidney disease, and end-stage renal disease, and unfortunately, some of these issues could lead to the need for renal replacement therapies. The outcome of this review paper will help multidisciplinary physicians to understand the renal side effects of the most used drug classes in the Kingdom of Saudi Arabia, their destructive mechanisms, and most importantly, the clinical presentations of renal dysfunction in relation to each class. Emphasizing these adverse effects will prevent future unfavorable outcomes, especially in commonly used drugs that are frequently prescribed for different age groups. Moreover, some of these drugs are considered to be over-the-counter medications, which makes them a serious problem that needs to be handled cautiously.

Role of Fatty Acid Binding Protein 4 (FABP4) in Kidney Disease

Accumulating evidences indicated that obesity and metabolic syndrome were independent risk factors for the development and progression of kidney diseases. Apart from inflammation, lipotoxicity, and hemodynamic factors, adipokines have been proposed to play crucial roles in the relationship between kidney diseases and metabolic disorders. As one of the key adipokines, fatty acid binding protein 4 (FABP4), which is mainly expressed in adipocytes and macrophages, has recently been shown to be associated with renal dysfunction and kidney damage. Both clinical and experimental studies have proposed circulating FABP4 as a novel predictor for renal injuries, and it might also be a predictor for cardiovascular events in patients with end stage renal disease (ESRD). FABP4 has also been detected in the glomerular cells and epithelial tubular cells in mouse and human kidneys, and the expression of FABP4 in these cells has been involved in the pathogenesis of kidney diseases. In addition, experimental studies suggested that inhibition of FABP4 had protective effects on renal damage. Here, we reviewed current knowledge regarding the role of FABP4 in pathophysiological insights as well as its potential function as a predictor and therapeutic target for kidney diseases.

Peroxisome Proliferator-Activated Receptors and the Heart: Lessons from the Past and Future Directions

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear family of ligand activated transcriptional factors and comprise three different isoforms, PPAR-α, PPAR-β/δ, and PPAR-γ. The main role of PPARs is to regulate the expression of genes involved in lipid and glucose metabolism. Several studies have demonstrated that PPAR agonists improve dyslipidemia and glucose control in animals, supporting their potential as a promising therapeutic option to treat diabetes and dyslipidemia. However, substantial differences exist in the therapeutic or adverse effects of specific drug candidates, and clinical studies have yielded inconsistent data on their cardioprotective effects. This review summarizes the current knowledge regarding the molecular function of PPARs and the mechanisms of the PPAR regulation by posttranslational modification in the heart. We also describe the results and lessons learned from important clinical trials on PPAR agonists and discuss the potential future directions for this class of drugs.

Nephroprotection by Hypoglycemic Agents: Do We Have Supporting Data?

Current therapy directed at delaying the progression of diabetic nephropathy includes intensive glycemic and optimal blood pressure control, renin angiotensin-aldosterone system blockade and multifactorial intervention. However, the renal protection provided by these therapeutic modalities is incomplete. There is a scarcity of studies analysing the nephroprotective effect of antihyperglycaemic drugs beyond their glucose lowering effect and improved glycaemic control on the prevention and progression of diabetic nephropathy. This article analyzes the exisiting data about older and newer drugs as well as the mechanisms associated with hypoglycemic drugs, apart from their well known blood glucose lowering effect, in the prevention and progression of diabetic nephropathy. Most of them have been tested in humans, but with varying degrees of success. Although experimental data about most of antihyperglycemic drugs has shown a beneficial effect in kidney parameters, there is a lack of clinical trials that clearly prove these beneficial effects. The key question, however, is whether antihyperglycemic drugs are able to improve renal end-points beyond their antihyperglycemic effect. Existing experimental data are post hoc studies from clinical trials, and supportive of the potential renal-protective role of some of them, especially in the cases of dipeptidyl peptidase-4 inhibitors, glucagon-like peptide-1 receptor agonists and sodium-glucose cotransporter 2 inhibitors. Dedicated and adequately powered renal trials with renal outcomes are neccessary to assess the nephrotection of antihyperglycaemic drugs beyond the control of hyperglycaemia.

Thiazolidinediones and Edema: Recent Advances in the Pathogenesis of Thiazolidinediones-Induced Renal Sodium Retention

Thiazolidinediones (TZDs) are one of the major classes of antidiabetic drugs that are used widely. TZDs improve insulin resistance by activating peroxisome proliferator-activated receptor gamma (PPARγ) and ameliorate diabetic and other nephropathies, at least, in experimental animals. However, TZDs have side effects, such as edema, congestive heart failure, and bone fracture, and may increase bladder cancer risk. Edema and heart failure, which both probably originate from renal sodium retention, are of great importance because these side effects make it difficult to continue the use of TZDs. However, the pathogenesis of edema remains a matter of controversy. Initially, upregulation of the epithelial sodium channel (ENaC) in the collecting ducts by TZDs was thought to be the primary cause of edema. However, the results of other studies do not support this view. Recent data suggest the involvement of transporters in the proximal tubule, such as sodium-bicarbonate cotransporter and sodium-proton exchanger. Other studies have suggested that sodium-potassium-chloride cotransporter 2 in the thick ascending limb of Henle and aquaporins are also possible targets for TZDs. This paper will discuss the recent advances in the pathogenesis of TZD-induced sodium reabsorption in the renal tubules and edema.

Immune and inflammatory role in renal disease

Chronic and acute renal diseases, irrespective of the initiating cause, have inflammation and immune system activation as a common underlying mechanism. The purpose of this review is to provide a broad overview of immune cells and inflammatory proteins that contribute to the pathogenesis of renal disease, and to discuss some of the physiological changes that occur in the kidney as a result of immune system activation. An overview of common forms of acute and chronic renal disease is provided, followed by a discussion of common therapies that have anti-inflammatory or immunosuppressive effects in the treatment of renal disease.

Short-Term Therapy with Rosiglitazone, a PPAR-γ Agonist, Improves Metabolic Profile and Vascular Function in Nonobese Lean Wistar Rats

A number of preclinical and clinical studies have reported blood-pressure-lowering benefits of thiazolidinediones in diabetic subjects and animal models of diabetes. This study was designed to further elucidate vascular effects of rosiglitazone, on healthy nonobese, lean animals. Adult male Wistar rats were randomized and assigned to control and rosiglitazone-treated groups and were dosed daily with either vehicle or rosiglitazone (10 mg kg(-1) day(-1)) by oral gavage for 5 days. Compared with control group, rosiglitazone treatment significantly reduced plasma levels of triglycerides (>240%) and nonesterified free fatty acids (>268%) (both, P < 0.001). There were no changes in vascular contractility to KCl or noradrenaline between two groups. However, rosiglitazone therapy improved carbamylcholine-induced vasorelaxation (93 ± 3 % versus control 78 ± 2, P < 0.01) an effect which was abolished by L-NAME. There was no difference in sodium nitroprusside-induced vasorelaxation between the control and rosiglitazone-treated animals. These results indicate that short-term rosiglitazone therapy improves both metabolic profile and vascular function in lean rats. The vascular effect of rosiglitazone appears to be mediated by alteration in NO production possibly by activation of endothelial PPARγ. This increased NO production together with improved lipid profile may explain mechanism(s) of blood-pressure-lowering effects of thiazolidinediones on both human and experimental animals.

Therapeutic modalities in diabetic nephropathy: standard and emerging approaches

Diabetes mellitus is the leading cause of end stage renal disease and is responsible for more than 40% of all cases in the United States. Current therapy directed at delaying the progression of diabetic nephropathy includes intensive glycemic and optimal blood pressure control, proteinuria/albuminuria reduction, interruption of the renin-angiotensin-aldosterone system through the use of angiotensin converting enzyme inhibitors and angiotensin type-1 receptor blockers, along with dietary modification and cholesterol lowering agents. However, the renal protection provided by these therapeutic modalities is incomplete. More effective approaches are urgently needed. This review highlights the available standard therapeutic approaches to manage progressive diabetic nephropathy, including markers for early diagnosis of diabetic nephropathy. Furthermore, we will discuss emerging strategies such as PPAR-gamma agonists, Endothelin blockers, vitamin D activation and inflammation modulation. Finally, we will summarize the recommendations of these interventions for the primary care practitioner.

Evaluation of blood pressure in Spontaneously Diabetic Torii-Lepr(fa) rats

The Spontaneously Diabetic Torii-Lepr(fa) (SDT-fa/fa) rat, a new model of obese type 2 diabetes, shows obesity, hyperglycemia, and hyperlipidemia from 6 weeks of age. Diabetic complications such as nephropathy and cataract are observed with aging; however, blood pressure change with age has not previously been examined. In this study, blood pressure was periodically measured and the change was investigated. Blood pressure in male SDT-fa/fa rats was elevated at 8, 16, and 24 weeks of age, whereas the heart rate was not changed. In addition to hyperglycemia, hyperlipidemia, and proteinuria, hyperleptinemia and increased urine angiotensinogen were observed in SDT-fa/fa rats. Blood pressure and heart rate in the male original SDT (SDT-+/+) rat did not significantly change. In conclusion, the SDT-fa/fa rat is a promising model, showing significant hypertension with diabetes mellitus.

Hepatic inflammation and insulin resistance in pre-diabetes - further evidence for the beneficial actions of PPAR-gamma agonists and a role for SOCS-3 modulation

Pre-diabetes is a condition affecting increasing numbers of the population who find themselves caught in the grey area between normal glucose regulation and diabetes mellitus and who experience impaired glucose tolerance or fasting glucose. The ability of thiozolidinediones (TZDs) to ameliorate the clinical signs of diabetes mellitus is well-known but there is also emerging evidence for the benefits of PPAR-gamma agonists in pre-diabetes. In this issue of the British Journal of Pharmacology, Collino and colleagues report that pioglitazone can reduce hepatic inflammation and insulin resistance in rats administered a high cholesterol and fructose diet. Furthermore, pioglitazone reduced the expression of suppressor of cytokine signalling (SOCS)-3 - considered to be a key link between inflammation and insulin resistance. Although much work remains to be performed in fully understanding how TZDs modulate the cellular mechanisms which underlie pre-diabetes, these findings provide preliminary evidence that administration of TZDs to pre-diabetics could be beneficial.

Pioglitazone improves lipid and insulin levels in overweight rats on a high cholesterol and fructose diet by decreasing hepatic inflammation

BACKGROUND AND PURPOSE

Nutrient overload leads to obesity and insulin resistance. Pioglitazone, a selective peroxisome proliferator-activated receptor (PPAR)gamma agonist, is currently used to manage insulin resistance, but the specific molecular mechanisms activated by PPARgamma are not yet fully understood. Recent studies suggest the involvement of suppressor of cytokine signalling (SOCS)-3 in the pathogenesis of insulin resistance. This study aimed to investigate the hepatic signalling pathway activated by PPARgamma activation in a non-genetic insulin-resistant animal model.

EXPERIMENTAL APPROACH

Male Wistar rats were maintained on a high-cholesterol fructose (HCF) diet for 15 weeks. Pioglitazone (3 mg x kg(-1)) was administered orally for the last 4 weeks of this diet. At the end of the treatment, serum was collected for biochemical analysis. Levels of PPARgamma, SOCS-3, pro-inflammatory markers, insulin receptor substrate-2 and Akt/glycogen synthase kinase-3beta phosphorylation were assessed in rat liver.

KEY RESULTS

Rats fed the HCF diet exhibited hyperlipidemia, hyperinsulinemia, impaired glucose tolerance and insulin resistance. Pioglitazone administration evoked a significant improvement in lipid metabolism and insulin responsiveness. This was accompanied by reduced hepatic expression of SOCS-3, interleukin-6, tumour necrosis factor-alpha and markers of neutrophil infiltration. Diet-induced PPARgamma expression was unaffected by the pioglitazone treatment.

CONCLUSION AND IMPLICATIONS

Chronic pioglitazone administration reduced hepatic inflammatory responses in rats fed a HCF diet. These effects were associated with changes in hepatic expression of SOCS-3, which may be a crucial link between the reduced local inflammation and the improved insulin signalling.

Peroxisome proliferator-activated receptors in diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease, which is increasing in incidence worldwide, despite intensive treatment approaches such as glycemic and blood pressure control in patients with diabetes mellitus. New therapeutic strategies are needed to prevent the onset of diabetic nephropathy. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear transcription factors that play important roles in lipid and glucose homeostases. These agents might prevent the progression of diabetic nephropathy, since PPAR agonists improve dyslipidemia and insulin resistance. Furthermore, data from murine models suggest that PPAR agonists also have independent renoprotective effects by suppressing inflammation, oxidative stress, lipotoxicity, and activation of the renin-angiotensin system. This review summarizes data from clinical and experimental studies regarding the relationship between PPARs and diabetic nephropathy. The therapeutic potential of PPAR agonists in the treatment of diabetic nephropathy is also discussed.

Diabetes-associated complications in Spontaneously Diabetic Torii fatty rats

The Spontaneously Diabetic Torii (SDT) fatty rat, established by introducing the fa allele of the Zucker fatty rat into the SDT rat genome, is a new model of obese type 2 diabetes. The SDT-fa/fa (SDT fatty) rat shows overt obesity, and hyperglycemia and hyperlipidemia are observed at a young age as compared with the SDT-+/+ (SDT normal) rat. However, the features of the diabetic complications in the SDT fatty rat have not been reported. In the present study, the incidence and the progression of diabetic complications in the SDT fatty rat were examined, and compared with those of the SDT normal rat. Renal function parameters, such as blood urea nitrogen, urine volume and urinary protein, increased from 4 weeks of age in the SDT fatty rat, and pathological findings in the renal tubule were observed from 8 weeks. Furthermore, cataract was observed in the SDT fatty rat from 8 weeks of age, and prolongation of peak latencies on electroretinograms was observed at 16 and 24 weeks of age. On the other hand, in the SDT normal rat, renal or ocular changes were observed from 24 weeks of age. With early incidence of diabetes mellitus, diabetes-associated complications in the SDT fatty rat were seen at younger ages than those in the SDT normal rat. In conclusion, the SDT fatty rat is expected to be a useful model for the analysis of diabetic complications and the evaluation of drugs related to metabolic diseases.

PPARs and the kidney in metabolic syndrome

The metabolic syndrome (MetS) is defined by a set of metabolic risk factors, including insulin resistance, central obesity, dyslipidemia, hyperglycemia, and hypertension for type 2 diabetes and cardiovascular disease. Although both retrospective and prospective clinical studies have revealed that MetS is associated with chronic renal disease, even with a nondiabetic cause, the cellular and molecular mechanisms in this association remain largely uncharacterized. Recently, increasing evidence suggests that peroxisome proliferator-activated receptors (PPARs), a subgroup of the nuclear hormone receptor superfamily of ligand-activated transcription factors, may play an important role in the pathogenesis of MetS. All three members of the PPAR nuclear receptor subfamily, PPARalpha, -beta/delta, and -gamma, are critical in regulating insulin sensitivity, adipogenesis, lipid metabolism, inflammation, and blood pressure. PPARs have also been implicated in many renal pathophysiological conditions, including diabetic nephropathy and glomerulosclerosis. Ligands for PPARs such as hypolipidemic PPARalpha activators, and antidiabetic thiazolidinedione PPARgamma agonists affect not only diverse aspects of MetS but also renal disease progression. Emerging data suggest that PPARs may be potential therapeutic targets for MetS and its related renal complications. This review focuses on current knowledge of the role of PPARs in MetS and discusses the potential therapeutic utility of PPAR modulators in the treatment of kidney diseases associated with MetS.

Anti-inflammatory effect of antidiabetic thiazolidinediones prevents bone resorption rather than cartilage changes in experimental polyarthritis

Background

Rosiglitazone and pioglitazone are high-affinity peroxisome proliferator-activated receptor (PPAR)-γ agonists with potent anti-diabetic properties and potential anti-inflammatory effects. We compared the ability of a range of oral doses of these thiazolidinediones, including those sufficient to restore insulin sensitization, to inhibit the pathogenesis of adjuvant-induced arthritis (AIA).

Methods

AIA was induced in Lewis rats by a subcutaneous injection of 1 mg of complete Freund's adjuvant. Rats were treated orally for 21 days with pioglitazone 3, 10 or 30 mg/kg/day, rosiglitazone 3 or 10 mg/kg/day, or with vehicle only. The time course of AIA was evaluated by biotelemetry to monitor body temperature and locomotor activity, by clinical score and plethysmographic measurement of hindpaw oedema. At necropsy, RT-PCR analysis was performed on synovium, liver and subcutaneous fat. Changes in cartilage were evaluated by histological examination of ankle joints, radiolabelled sulphate incorporation (proteoglycan synthesis), glycosaminoglycan content (proteoglycan turnover) and aggrecan expression in patellar cartilage. Whole-body bone mineral content was measured by dual-energy X-ray absorptiometry.

Results

The highest doses of rosiglitazone (10 mg/kg/day) or pioglitazone (30 mg/kg/day) were required to reduce fever peaks associated with acute or chronic inflammation, respectively, and to decrease arthritis severity. At these doses, thiazolidinediones reduced synovitis and synovial expression of TNF-α, IL-1β and basic fibroblast growth factor without affecting neovascularization or the expression of vascular endothelial growth factor. Thiazolidinediones failed to prevent cartilage lesions and arthritis-induced inhibition of proteoglycan synthesis, aggrecan mRNA level or glycosaminoglycan content in patellar cartilage, but reduced bone erosions and inflammatory bone loss. A trend towards lower urinary levels of deoxipyridinolin was also noted in arthritic rats treated with thiazolidinediones. Rosiglitazone 10 mg/kg/day or pioglitazone 30 mg/kg/day increased the expression of PPAR-γ and adiponectin in adipose tissue, confirming that they were activating PPAR-γ in inflammatory conditions, although an increase in fat mass percentage was observed for the most anti-arthritic dose.

Conclusion

These data emphasize that higher dosages of thiazolidinediones are required for the treatment of arthritis than for restoring insulin sensitivity but that thiazolidinediones prevent inflammatory bone loss despite exposing animals to increased fatness possibly resulting from excessive activation of PPAR-γ.

Lack of the serum and glucocorticoid-inducible kinase SGK1 attenuates the volume retention after treatment with the PPARgamma agonist pioglitazone

PPARgamma-agonists enhance insulin sensitivity and improve glucose utilization in diabetic patients. Adverse effects of PPARgamma-agonists include volume retention and edema formation. Recent observations pointed to the ability of PPARgamma agonists to enhance transcription of the serum and glucocorticoid-inducible kinase SGK1, a kinase that is genomically upregulated by mineralocorticoids and stimulates various renal channels and transporters including the renal epithelial Na+ channel ENaC. SGK1 has been proposed to mediate the volume retention after treatment with PPARgamma agonists. To test this hypothesis, food containing the PPARgamma agonist pioglitazone (0.02%, i.e., approximately 25 mg/kg bw/day) was administered to gene-targeted mice lacking SGK1 (sgk1-/-, n=12) and their wild-type littermates (sgk1+/+), n=12). According to in situ hybridization, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence, treatment with pioglitazone significantly increased renal SGK1 mRNA and protein expression in sgk1+/+ mice. The treatment increased body weight significantly in both, sgk1+/+ mice (+2.2+/-0.3 g) and sgk-/- mice (+1.3+/-0.2 g), and decreased hematocrit significantly in sgk1+/+ mice (-6.5+/-1.0%) and sgk1-/- mice (-3.1+/-0.6%). Both effects were significantly (p<0.05) more pronounced in sgk1+/+ mice. According to Evans Blue distribution, pioglitazone increased plasma volume only in sgk1+/+ mice (from 50.9+/-3.9 to 63.7+/-2.5 microl/g bw) but not in sgk-/- mice (from 46.8+/-3.8 to 48.3+/-5.2 microl/g bw). Pioglitazone decreased aldosterone plasma levels and blood pressure and increased leptin plasma levels in both genotypes. We conclude that SGK1 contributes to but does not fully account for the volume retention during treatment with the PPARgamma agonist pioglitazone.

Beneficial effects of thiazolidinediones on diabetic nephropathy in OLETF rats

PURPOSE

Diabetic nephropathy is the most serious of complications in diabetes mellitus. Thiazolidinedione (TZD) is thought to ameliorate diabetic nephropathy; however, the mechanism underlying this effect has not been elucidated. We hypothesized that the vascular endothelial growth factor (VEGF) participates in the pathogenesis of diabetic nephropathy and that TZD may be beneficial for the treatment of diabetic nephropathy because of the effect it has on VEGF.

MATERIALS AND METHODS

23 Otsuka- Long-Evans-Tokushima-Fatty (OLETF) rats and eight control Long-Evans-Tokushima-Otsuka (LETO) rats were divided into the following four groups: LETO group, control OLETF group, pioglitazone treated group (10mg/ kg/day), and rosiglitazone treated group (3mg/kg/day).

RESULTS

A progressive increase in urinary protein excretion was observed in the diabetic rats. Glomerular VEGF expression in the control OLETF rats was significantly higher than in the control LETO rats. However, there was a significant reduction in both the glomerular VEGF expression and the VEGF mRNA levels after treatment with pioglitazone and rosiglitazone. The twenty-four hour urine protein levels were significantly decreased in both groups of the treated OLETF rats.

CONCLUSION

These results suggest that TZD may have beneficial effects on diabetic nephropathy by reducing the VEGF expression.

PPAR-gamma agonists and diabetic nephropathy

Diabetic nephropathy is a clinical syndrome of albuminuria, declining glomerular filtration rate, and increased risk of cardiovascular disease. Multiple mechanisms have been implicated in its pathogenesis. Although current therapies appear to be effective, treatment of diabetic nephropathy remains suboptimal. This review summarizes the recently emerging evidence suggesting that peroxisome proliferator-activated receptor-gamma agonists may prove to be effective therapeutic agents in the treatment of diabetic renal complications.

Collecting duct-specific deletion of peroxisome proliferator-activated receptor gamma blocks thiazolidinedione-induced fluid retention

The peroxisome proliferator-activated receptor subtype gamma (PPARgamma) ligands, namely the synthetic insulin-sensitizing thiazolidinedione (TZD) compounds, have demonstrated great potential in the treatment of type II diabetes. However, their clinical applicability is limited by a common and serious side effect of edema. To address the mechanism of TZD-induced edema, we generated mice with collecting duct (CD)-specific disruption of the PPARgamma gene. We found that mice with CD knockout of this receptor were resistant to the rosiglitazone- (RGZ) induced increases in body weight and plasma volume expansion found in control mice expressing PPARgamma in the CD. RGZ reduced urinary sodium excretion in control and not in conditional knockout mice. Furthermore, RGZ stimulated sodium transport in primary cultures of CD cells expressing PPARgamma and not in cells lacking this receptor. These findings demonstrate a PPARgamma-dependent pathway in regulation of sodium transport in the CD that underlies TZD-induced fluid retention.

Peroxisome proliferator-activated receptor-gamma activity is associated with renal microvasculature

Peroxisome proliferator-activated receptor-gamma (PPAR gamma) is a nuclear transcription factor and the pharmacological target for antidiabetic thiazolidinediones (TZDs). TZDs ameliorate diabetic nephropathy and have direct effects on cultured mesangial cells (MCs); however, in situ hybridization failed to detect expression of PPAR gamma in glomeruli in vivo. The purpose of this study was to determine whether PPAR gamma is expressed in renal glomeruli. Two rabbit PPAR gamma isoforms were cloned. Nuclease protection assays demonstrate that both PPAR gamma isoforms are expressed in freshly isolated glomeruli. Treatment of rabbits with the TZD troglitazone selectively induced expression of an endogenous PPAR gamma target gene, adipocyte fatty acid-binding protein (A-FABP), in renal glomerular cells and renal medullary microvascular endothelial cells, demonstrated by both in situ hybridization and immunostain. Troglitazone also dramatically increased A-FABP expression in cultured MCs. Constitutive PPAR gamma expression was detected in cultured rabbit MCs. Endogenous MC PPAR gamma can also drive PPAR gamma reporter. Troglitazone and 15-deoxy-Delta 12,14 prostaglandin J(2) at low concentrations reduced mesangial cell [(3)H]thymidine incorporation without affecting viability. These data suggest that constitutive PPAR gamma activity exists in renal glomeruli in vivo and could provide a pharmacological target to directly modulate glomerular injury.