Effect of Benfotiamine on the Expression of Phosphodiesterase Type 5 and Its Isoforms in Type 2 Diabetic Rat Kidneys

Shim, Jong Baek; Yang, Dae Yul; Han, Young Kook; Lee, Sun Ju; Kim, Hyo Jong; Jung, Hyun Chul; Kim, Sung Yong; Kim, Ha Young; Lee, Young Jae

Abstract

PURPOSE
The phosphodiesterases (PDEs) are critical components in the cyclic AMP/protein kinase A and the cyclic GMP/phosphokinase G signaling pathways. The cAMP and cGMP pathways are regulated by activation and dissolution of PDEs. Benfotiamine, a lipophilic derivation of thiamine is known an activator of transketolase, is reported to prevent diabetic nephropathy by decreasing proteinuria and reducing oxidative stress. We did this study to investigate the effect of benfotiamine in type 2 diabetic rat kidneys.
MATERIALS AND METHODS
We prepared 10 male Long-Evans Tokushima Fatty (LETO: control) and 20 male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which developed non-insulin-dependent diabetes mellitus (NIDDM) naturally. An oral glucose tolerance test confirmed diabetic development in the OLETF rats at 26 weeks. We classified 10 of the OLETF rats into Group I, the no treatment group and the other 10 into Group II, the treatment group. Group II received 100 mg/kg benfotiamine after developing DM. At 44 weeks, we checked kidney weight, serum glucose, free testosterone, insulin, total cholesterol, and triglyceride before sacrifice. We designed the primers for rat PDE5, PDE5A1, and PDE5A2 genes were carried out semiquantitive multiplex RT-PCR. Immunohistochemical staining was performed for monoclonal mouse anti-cGB-PDE5 and mouse monoclonal anti-smooth muscle alpha-actin.
RESULTS
For the Control Group, Group I, and Group II, kidney weight was 2.13+/-0.23, 2.08+/-0.22, and 1.94+/-0.44 g; serum glucose was 279.50+/-56.79, 338.00+/-55.00, and 314.71+/-139.1 mg/dl; free testosterone was 1.46+/-1.08, 1.05+/- 0.42, and 0.72+/-0.56 pg/dl; insulin was 1.03+/-0.43, 1.09+/-0.83, and 1.15+/-1.08 ng/ml; total cholesterol was 86.83+/-4.79, 132.00+/-7.69, and 118.14+/-30.93 mg/dl; and triglyceride was 78.83+/-16.47, 177.83+/-75.62, and 194.57+/-92.57 mg/dl, respectively. All three groups expressed PDE5, PDE5A1, PDE5A2 mRNA, but Group I PDE5 mRNA expression was lower than that of Group C, II. However, the expression of PDE5A1 and PDE5A2 mRNA was not significantly different among the three groups.
CONCLUSIONS
Serum cholesterol, triglyceride, and glucose were significantly higher in OLETF than in LETO rats. The PDEs were lower in diabetic rat (OLETF) kidneys and PDEs may play a significant role in the development of diabetic renal complications. Benfotiamine is suggested to increase expression of PDE5 mRNA in the type 2 diabetes rat kidney, but the difference in expression levels between PDE5A1 and PDE5A2 was not significant. These findings suggest that benfotiamine may play a specific role in diabetic changes of the rat kidney via a PDE5-related pathway, but it is not clear whether subtype PDE5A1 and PDE5A2 genes play a specific role.