Beneficial effects of thiazolidinediones on diabetic nephropathy in OLETF rats

PPARγ agonists regulate tobacco smoke-induced Toll like receptor 4 expression in alveolar macrophages

Background

Peroxisome proliferator-activated receptor-gamma (PPARγ) is a ligand-activated transcription factor that exerts multiple biological effects. Growing evidence suggests that PPARγ plays an important role in inflammation; however, the effects of this transcription factor on the inflammation caused by smoking are unclear.

Methods

We measured the expression of inflammatory cytokines (leukotriene B4, LTB4 and interleukin 8, IL-8), PPARγ and toll-like receptors (TLR2 and TLR4) in alveolar macrophages (AMs) harvested from rats exposed to cigarette smoke (CS) for 3 months in vivo. Some of the rats were pre-treated with rosiglitazone (PPARγ agonist, 3 mg/kg/day, ip), rosiglitazone (3 mg/kg/day, ip) + BADGE (bisphenol A diglycidyl ether, a PPARγ antagonist, 30 mg/kg/day, ig), or BADGE alone (30 mg/kg/day, ig). We also measured the expression of PPARγ, TLR2, TLR4 and nuclear factor-kappaB (NF-κB) in AMs gained from normal rats, which exposed to 5% CSE (cigarette smoke extract) for 12hrs, respectively pretreated with PBS, rosiglitazone (30 uM), rosiglitazone (30 uM) + BADGE (100 uM), 15d-PGJ2 (PPARγ agonist, 5 uM), 15d-PGJ2 (5 uM) + BADGE (100 uM), or BADGE (100 uM) alone for 30 min in vitro.

Results

In vivo, rosiglitazone counteracted CS-induced LTB4 and IL-8 release and PPARγ downregulation, markedly lowering the expression of TLR4 and TLR2. In vitro, both rosiglitazone and 15d-PGJ2 inhibited CS-induced inflammation through the TLR4 signaling pathway.

Conclusions

These results suggest that PPARγ agonists regulate inflammation in alveolar macrophages and may play a role in inflammatory diseases such as COPD.

Thiazolidinediones improve hepatic fibrosis in rats with non-alcoholic steatohepatitis by activating the adenosine monophosphate-activated protein kinase signalling pathway

Thiazolidinediones (TZDs) markedly reduce hepatic steatosis in both rodents and humans. However, the effects and mechanisms of action of TZDs on hepatic fibrosis remain unclear. The aim of the present study was to determine the effects of TZDs on histological changes in the liver and on the modulation by adiponectin via the AMP-activated protein kinase (AMPK) signalling pathway in rats with non-alcoholic steatohepatitis (NASH). Forty rats were divided into normal control, high-fat diet (HFD), pioglitazone control and pioglitazone intervention groups. After 24 weeks treatment with pioglitazone (10 mg/kg per day by gavage), changes in liver histology, serum aminotransaminase, triglyceride (TG), free fatty acid (FFA), glucose, insulin, adiponectin and transforming growth factor (TGF)-β1 concentrations and hepatic adiponectin, AMPK, α-smooth muscle actin (α-SMA) and collagen I expression were evaluated. The degree of hepatic steatosis and fibrosis was significantly higher in HFD-induced NASH rats compared with normal controls, as were serum concentrations of aminotransaminase, TG, FFA, glucose, insulin and TGF-β1 and hepatic expression of α-SMA and collagen I protein. Serum adiponectin concentrations and hepatic expression of adiponectin mRNA and AMPK protein were significantly lower in the HFD-induced NASH rats compared with the normal control. Pioglitazone significantly reduced the degree of hepatic steatosis and fibrosis, as well as serum concentrations of aminotransaminase, TG, FFA, glucose, insulin and TGF-β1 and hepatic expression of α-SMA and collagen I protein. In addition, pioglitazone significantly increased serum adiponectin concentrations and hepatic expression of adiponectin mRNA and AMPK protein. In conclusion, the TZD pioglitazone improved hepatic fibrosis in rats with NASH by upregulating adiponectin expression and activating AMPK, thus subsequently inhibiting the activation of hepatic stellate cells and the overproduction of extracellular matrix.

Pioglitazone upregulates angiotensin converting enzyme 2 expression in insulin-sensitive tissues in rats with high-fat diet-induced nonalcoholic steatohepatitis

Background and Aim. Thiazolidinediones (TZDs) can improve hepatic steatosis in nonalcoholic steatohepatitis (NASH). Angiotensin (Ang) II, the primary effector of renin-angiotensin system (RAS), plays vital roles in the development and progression of NASH. And some AngII-mediated effects can be regulated by TZDs. Angiotensin-converting enzyme (ACE) 2, a new component of RAS, can degrade Ang II to attenuate its subsequent physiological actions. We aimed to evaluate the effects of TZDs on ACE2 expression in insulin-sensitive tissues in NASH rats. Methods. Forty rats were divided into the normal control, high-fat diet (HFD), pioglitazone control, and HFD plus pioglitazone groups. After 24 weeks of treatment, we evaluated changes in liver histology and tissue-specific ACE2 expression. Results. ACE2 gene and protein expression was significantly greater in liver and adipose tissue in the HFD group compared with normal control group, while was significantly reduced in skeletal muscle. Pioglitazone significantly reduced the degree of hepatic steatosis compared with the HFD group. Pioglitazone significantly increased ACE2 protein expression in liver, adipose tissue, and skeletal muscle compared with the HFD group. Conclusions. Pioglitazone improves hepatic steatosis in the rats with HFD-induced NASH and upregulates ACE2 expression in insulin-sensitive tissues.

The effect of hydrochloride pioglitazone on urinary 8-hydroxy -deoxyguanosine excretion in type 2 diabetics

OBJECTIVE

To observe the effects of hydrochloride pioglitazone on urinary 8-hydroxy-deoxyguanosine (8OHdG) excretion in type 2 diabetics and explore its possible reno-protective mechanisms.

METHODS

Ninety-eight uncontrolled type 2 diabetics were assigned randomly into group DP (pioglitazone add-on) and group DS (sulfonylureas add-on). At the basal and after 12 weeks treatment, FBG, HbA1c, urinary 8-OHdG, urinary albumin(ALB) and urinary creatinine (Cr) were determined, respectively.

RESULTS

Compared with pre-treatment, FBG, HbA1c and urinary 8-OHdG /Cr ratio(U8CR) were all obviously decreased in both therapy groups; urinary albumin/urinary creatinine ratio(UACR) markedly decreased in group DP (P<0.01), while slightly decreased in group DS (P>0.05) after twelve weeks of observation. After 12-week treatment, UACR and U8CR in group DP were significantly lower than those in group DS (both P<0.05) without no marked difference in FBG and HbA1c between group DP and group DS. Meanwhile, U8CR had positive correlation with UACR (r=0.755, P<0.01).

CONCLUSION

Pioglitazone can decrease urinary 8-OHdG excretion and lighten oxidative stress in vivo in type 2 diabetics, which may play a protective role for the kidney damage.

Losartan and pioglitazone ameliorate nephropathy in experimental metabolic syndrome rats

It is well known that metabolic syndrome (MS) is a risk factor for proteinuria and chronic kidney disease. Losartan (angiotensin II receptor blocker, ARB) and pioglitazone (peroxisome proliferator-activated receptor-γ, PPARγ agonist) have been shown to confer renoprotection. However, to date, whether or not an ARB and a PPARγ agonist have synergistic renoprotective effects remains controversial. Thus, the present study was designed to evaluate a combined treatment with losartan and pioglitazone in Sprague-Dawley rats fed with a high-fat, high-salt (HFS) diet and 20% sucrose solution for 16 weeks, an animal model of MS accompanying with renal lesions. Losartan, pioglitazone, and their combination were orally administered in the MS rats from 8 weeks to the end of this study. At 16 weeks, the MS rats showed the elevation in systolic blood pressure (SBP), urinary albumin excretion (UAE), and glomerulosclerosis (GS) score, but creatinine clearance, urinary protein excretion, and score of tubulointerstitial damage were not affected. Renal vascular endothelial growth factor (VEGF) protein level, mRNA and protein expression, which were respectively measured by enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis, were obviously decreased in the MS rats. Treatment with the combination of losartan and pioglitazone provided synergistic effects in reducing the SBP, UAE, and GS score when compared with monotherapy. These effects were not associated with ameliorated the downregulation of renal VEGF expression. Our data suggest that combined treatment with losartan and pioglitazone may offer additional advantages in treating MS nephropathy.

Effect of pioglitazone on diabetic nephropathy and expression of HIF-1α and VEGF in the renal tissues of type 2 diabetic rats

OBJECTIVE

To investigate the effect of pioglitazone on the progression of diabetic nephropathy and the expression of hypoxia inducible factor-1α (HIF-1a) and vascular endothelial growth factor (VEGF) in a rat model of type-2 diabetes.

METHODS

Streptozotocin-induced type-2 diabetes mellitus (DM) model was set up in male Sprague Dawley rats. DM rats were treated with or without pioglitazone (4 mg/kg/day for 8 weeks) and/or cobalt chloride. Normal rats were used as controls. The blood chemistry, urine albumin, kidney histology, and expression of HIF-1α and VEGF of the different groups were compared.

RESULTS

The kidney weights and kidney weight indexes of DM rats were significantly higher than in NC rats (P<0.01) and the kidney weights and kidney weight indexes of rats in pioglitazone and/or cobalt chloride treatment group were significantly less than in DM group. Relative to rats in the NC group, rats in the DM group had significantly disrupted serum chemistry, urinary albumin, and kidney histology, and significantly enhanced expression of HIF-1a and VEGF. Rats in the pioglitazone and/or cobalt chloride treatment group experienced significant amelioration of these effects.

CONCLUSION

In a rat model, pioglitazone ameliorated many of the physiological, cellular, and molecular processes associated with diabetic nephropathy.

Hydrochloride pioglitazone decreases urinary cytokines excretion in type 2 diabetes

OBJECTIVE

To observe the effects of hydrochloride pioglitazone on urinary cytokine excretion in type 2 diabetes and to explore its possible reno-protective mechanisms.

DESIGN

Subjects and Methods. Ninety-eight patients with type 2 diabetes and a fasting blood glucose (FBG) levels between 7.0 and 13.0 mm and glycated haemoglobin A1c (HbA1c) ≥ 7.0% were assigned randomly to receive either the pioglitazone (DP group) or a sulphonylurea (DS group). Another 49 healthy individuals were chosen as normal controls (group NC). At the start of the study and after 12 weeks of treatment, urinary cytokines including monocyte chemoattractant protein-1 (MCP-1), transforming growth factor-β1 (TGF-β1) and vascular endothelial growth factor were measured and were expressed as a ratio of urinary creatinine excretion. Urinary albumin/creatinine ratio, FBG and HbA1c were determined at the same time.

RESULTS

The excretion of each urinary cytokine, corrected for urinary creatinine, was significantly increased in both groups of patients with diabetes, compared with normal controls, and after a 12-week treatment were significantly decreased by both therapies but the effect of pioglitazone was statistically greater than with sulphonylureas. Urinary albumin/UCr and both systolic and diastolic blood pressure were decreased significantly by pioglitazone (P < 0.01 or P < 0.05) but not by sulphonylurea treatment (P < 0.05), while there was no significant difference in FBG or HbA1c between two groups. There was a positive correlation between the excretion of cytokines and urinary albumin /UCr (all P < 0.01).

CONCLUSIONS

This study indicates that pioglitazone reduces urinary albumin excretion by a mechanism that is at least partly independent of blood sugar control. The correlation of urinary albumin excretion with improvement in urinary cytokines suggests that this reno-protective effect of piogliazone in diabetes may be related to local reduction in cytokine activity within the kidney.

Hydrochloride pioglitazone decreases urinary TGF-beta1 excretion in type 2 diabetics

BACKGROUND

Thiazolidinediones (TZDs) exert a number of direct reno-protection beyond its hypoglycaemic effect in type 2 diabetics, which may be partly related to its anti-fibrosis and anti- inflammatory action.

MATERIALS AND METHODS

A total of 98 type 2 diabetics with fasting blood glucose (FBG) between 7.0 and 13.0 mmol L(-1) and glycated haemoglobin A1c (HbA1c) > or = 7.0% were randomly assigned to add pioglitazone (group DP) or sulfonylurea (group DS) for 12 weeks. FBG, HbA1c, serum creatinine (SCr) and blood urea nitrogen (BUN), and urinary TGF-beta1, albumin (UALB) and creatinine (UCr) were determined at the basal and the 12th week.

RESULTS

Fasting blood glucose, HbA1c and urinary TGF-beta1/UCr ratio (UTCR) were obviously decreased in both groups after 12 weeks treatment; UALB/UCr ratio (UACR) decreased obviously in group DP (P < 0.01), while slightly in group DS. UACR and UTCR in group DP were significantly lower than those in group DS after treatment, while FBG and HbA1c had no statistical differences between the two groups. In addition, UTCR had positive correlation with UACR (r = 0.367, P < 0.01).

CONCLUSIONS

Pioglitazone decreases urinary TGF-beta1 excretion in type 2 diabetics, which may be partly contributed to its direct reno-protection.

Podocyte-specific overexpression of GLUT1 surprisingly reduces mesangial matrix expansion in diabetic nephropathy in mice

Increased expression of the facilitative glucose transporter, GLUT1, leads to glomerulopathy that resembles diabetic nephropathy, whereas prevention of enhanced GLUT1 expression retards nephropathy. While many of the GLUT1-mediated effects are likely due to mesangial cell effects, we hypothesized that increased GLUT1 expression in podocytes also contributes to the progression of diabetic nephropathy. Therefore, we generated two podocyte-specific GLUT1 transgenic mouse lines (driven by a podocin promoter) on a db/m C57BLKS background. Progeny of the two founders were used to generate diabetic db/db and control db/m littermate mice. Immunoblots of glomerular lysates showed that transgenic mice had a 3.5-fold (line 1) and 2.1-fold (line 2) increase in GLUT1 content compared with wild-type mice. Both lines showed similar increases in fasting blood glucose and body weights at 24 wk of age compared with wild-type mice. Mesangial index (percent PAS-positive material in the mesangial tuft) increased 88% (line 1) and 75% (line 2) in the wild-type diabetic mice but only 48% (line 1) and 39% (line 2) in the diabetic transgenic mice (P < 0.05, transgenic vs. wild-type mice). This reduction in mesangial expansion was accompanied by a reduction in fibronectin accumulation, and vascular endothelial growth factor (VEGF) levels increased only half as much in the transgenic diabetic mice as in wild-type diabetic mice. Levels of nephrin, neph1, CD2AP, podocin, and GLUT4 were not significantly different in transgenic compared with wild-type mice. Taken together, increased podocyte GLUT1 expression in diabetic mice does not contribute to early diabetic nephropathy; surprisingly, it protects against mesangial expansion and fibronectin accumulation possibly by blunting podocyte VEGF increases.

Effects of NADPH oxidase inhibitor on diabetic nephropathy in OLETF rats: the role of reducing oxidative stress in its protective property

Diabetic nephropathy is the most serious complication in diabetes mellitus. Oxidative stress via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and vascular endothelial growth factor (VEGF) pathway play critical roles in the development of diabetic nephropathy. We evaluated the effects of apocynin, NADPH oxidase inhibitor on diabetic nephropathy in a type 2 diabetic rat model. Sixteen Otsuka Long Evans Tokushima Fatty (OLETF) rats and 9 Long Evans Tokushima Otsuka (LETO) were divided into the following three groups: LETO rats (n=9), control OLETF rats (n=7) and apocynin-treated OLETF rats (n=9). We examined body weights, plasma glucose levels, urinary albumin-creatinine ratio (ACR) and protein-creatinine ratio (PCR). At 50 weeks, experimental rats were sacrificed and their kidneys were extracted for hematoxylin eosin stain, immunohistochemical VEGF stain and VEGF mRNA real-time RT-PCR. To examine oxidative stress, we checked 24h urinary 8-OHdG (8-hydroxy-2'-deoxyguanosine) and MDA (malondialdehyde). Urinary protein and albumin excretions were reduced after apocynin treatment, though apocynin could not significantly decrease serum glucose levels. There were improvements of glomerular and mesangial expansion in the apocynin-treated OLETF rats. Apocynin significantly decreased optical density of glomerular VEGF expression in immunohistochemical stain and reduced the concentration of 24h urinary 8-OHdG and MDA. From these results, it was suggested that apocynin may have the potential to protect against diabetic nephropathy via amelioration of oxidative stress.