Dipeptidyl peptidase (DPP) IV inhibitors are probably beneficial for preventing diabetic complication and modulating glucagonlike peptide-1 receptor (GLP-1R) expression. The aim of this study was to determine whether the DPP IV inhibitor LAF237 (vildagliptin) has renoprotective qualities in streptozotocin-induced diabetic rats. Diabetic and nondiabetic rats were treated with an oral dose of 4 or 8 mg/kg/day LAF237 or placebo for 24 weeks, and renal injury was observed by light and electron microscopy. We also assessed DPP IV activity, active GLP-1 level, cAMP and 8-hydroxy-deoxyguanosine excretion, and GLP-1R, cleaved caspase 3, and transforming growth factor-␤1 (TGF-␤1) expression. LAF237 significantly decreased proteinuria, albuminuria, and urinary albumin/creatinine ratio, improved creatinine clearance, and dose-dependently inhibited interstitial expansion, glomerulosclerosis, and the thickening of the glomerular basement membrane in diabetic rats. It is noteworthy that LAF237 markedly down-regulated DPP IV activity and increased active GLP-1 levels, which probably prevented oxidative DNA damage and renal cell apoptosis by activating the GLP-1R and modulating cAMP. Renoprotection was also associated with a reduction in TGF-␤1 overexpression. Our study suggests that DPP IV inhibitors may ameliorate diabetic nephropathy as well as reduce the overproduction of TGF-␤1. The observed renoprotection is probably attributable to inhibition of DPP IV activity, mimicking of incretin action, and activation of the GLP-1R.

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BACKGROUND AND PURPOSEGlucagon-like peptide-1 (GLP-1) receptors are widely expressed in neural tissues and diminish neuronal degeneration or induce neuronal differentiation. The aim of this study was to investigate the effect of the GLP-1 pathway on peripheral nerves in streptozotocin-induced diabetic rats. EXPERIMENTAL APPROACHDiabetic and nondiabetic rats were treated with the GLP-1 receptor agonist, synthetic exendin-4 (i.p., 1 nmol·kg) or placebo for 24 weeks, and current perception threshold values, cAMP levels and nerve fibre size in the sciatic nerve were measured. We also investigated GLP-1 receptor expression, quantitative changes in PGP9.5-positive intraepidermal nerve fibres and cleaved caspase 3-stained Schwann cells by immunohistochemistry. KEY RESULTSGLP-1 receptor expression was detected in the sciatic nerve and skin. After exendin-4 treatment, the increase seen in current perception threshold values at 2000 and 250 Hz in diabetic rats was reduced. Also, the decrease in myelinated fibre size or axon/fibre area ratio in the sciatic nerve and the loss of intraepidermal nerve fibre in the skin of diabetic rats were ameliorated. These responses were closely associated with the attenuation of Schwann cell apoptosis and improvement in the cAMP level in exendin-4-treated diabetic rats, compared with placebo-treated animals. CONCLUSION AND IMPLICATIONSSynthetic exendin-4 may prevent peripheral nerve degeneration induced by diabetes in an animal model, supporting the hypothesis that GLP-1 may be useful in peripheral neuropathy. The neuroprotection is probably attributable to GLP-1 receptor activation, antiapoptotic effects and restoration of cAMP content.

Despite the rapidly increasing prevalence of non-alcoholic fatty liver disease (NAFLD) in type 2 diabetes (T2D), few treatment modalities are currently available. We investigated the hepatic effects of the novel thiazolidinedione (TZDs), lobeglitazone (Duvie) in T2D patients with NAFLD. We recruited drug-naïve or metformin-treated T2D patients with NAFLD to conduct a multicenter, prospective, open-label, exploratory clinical trial. Transient liver elastography (Fibroscan®; Echosens, Paris, France) with controlled attenuation parameter (CAP) was used to non-invasively quantify hepatic fat contents. Fifty patients with CAP values above 250 dB/m were treated once daily with 0.5 mg lobeglitazone for 24 weeks. The primary endpoint was a decline in CAP values, and secondary endpoints included changes in components of glycemic, lipid, and liver profiles. Lobeglitazone-treated patients showed significantly decreased CAP values (313.4 dB/m at baseline vs. 297.8 dB/m at 24 weeks; P = 0.016), regardless of glycemic control. Lobeglitazone improved HbA1C values (7.41% [57.5 mM] vs. 6.56% [48.2 mM]; P < 0.001), as well as the lipid and liver profiles of the treated patients. Moreover, multivariable linear regression analysis showed that hepatic fat reduction by lobeglitazone was independently associated with baseline values of CAP, liver stiffness, and liver enzymes, and metformin use. Lobeglitazone treatment reduced intrahepatic fat content, as assessed by transient liver elastography, and improved glycemic, liver, and lipid profiles in T2D patients with NAFLD. Further randomized controlled trials using liver histology as an end point are necessary to evaluate the efficacy of lobeglitazone for NAFLD treatment (Clinical trial No. NCT02285205).

Inflammatory pathway from hyperglycemia to diabetic peripheral neuropathy is very important in diagnosis and management. Inflammatory cytokine can be used for prediction and progression of diabetic peripheral neuropathy.