Korean Diabetes J KDJ Korean Diabetes Journal 1976-9180 Korean Diabetes Association 10.4093/kdj.2008.32.1.21 Original Article The Effect of α-Lipoic Acid on Proteinuria and Renal TGFβ Expression in Obese Type 2 Diabetic Rat Model Kang Seok Woo Lee Seong Jin 1 Kim Dong-Sun 2 Kim Tae Wha 2 Department of Internal Medicine, Seoul Red Cross Hospital, Korea. Department of Internal Medicine College of Medicine, Hallym University, Korea. Department of Internal Medicine College of Medicine, Hanyang University, Korea. 02 2008 29 02 2008 32 1 21 29 08 10 2007 11 01 2008 Copyright © 2008 Korean Diabetes Association 2008 Background

It is well known that renal TGFβ expression is related to the development of diabetic nephropathy. Alpha-lipoic acid (ALA), a potent antioxidant and cofactor of mitochondrial respiratory enzymes, can improve the insulin resistance and the vascular endothelial dysfunction, and suppresses the development of diabetic vascular complications. This study was undertaken to investigate whether ALA could reduce urinary protein excretion and renal TGFβ protein expression in obese type 2 diabetes mellitus animal model, Otsuka Long-Evans Tokushima Fatty (OLETF) rat.

 Methods

Obese 30 male OLETF rats were randomly divided to 3 groups at the age of 30 weeks. The rats in the Control group fed normal rat chow while the rats in the ALA group were fed with rat chow containing ALA (0.5% of food weight). Ten rats in the Pair-fed group were fed with normal rat chow, but were given the same amount of food as consumed by the ALA group. During 5 weeks of ALA feeding, food intake and body weight were checked in metabolic chamber. Blood glucose levels, HbA1c and urinary protein excretion were measured at 30 weeks and 35 weeks of age, and renal TGFβ protein expression at 35 weeks of age was measured by Western blot and represented by relative unit (RU). Immunohistochemical staining for TGFβ protein in renal tissue was also examined at 35 weeks of age.

 Results

Food intake, body weight, blood glucose levels, HbA1c and urinary protein excretion among the Control, ALA and Pair-fed groups at 30 weeks of age were not different. At 35 weeks of age, food intake was significantly decreased in the ALA group than the Control group (Control group vs. ALA group, 27.7 ± 1.1 g/day vs. 22.4 ± 1.4 g/day, P < 0.001), and body weight was significantly decreased in the ALA group than the Control and Pair-fed groups (Control group: 694.4 ± 10.3 g, ALA group: 600.4 ± 7.4 g, Pair-fed group: 685.4 ± 11.6 g, P < 0.001). Blood glucose levels were significantly decreased in the ALA group than the Control and Pair-fed groups (Control group: 157.7 ± 4.6 mg/dL, ALA group: 130.7 ± 4.8 mg/dL, Pair-fed group: 153.7 ± 3.3 mg/dL, P < 0.001) although blood glucose levels from 30 weeks to 34 weeks of age and HbA1c at 35 weeks of age were not different among the groups. Urinary protein excretion and renal TGFβ protein expression were significantly decreased in the ALA group than the Control and Pair-fed groups (urinary protein excretion, Control group: 5.033 ± 0.254 mg/mgCr, ALA group: 3.633 ± 0.303 mg/mgCr, Pair-fed group: 4.977 ± 0.339 mg/mgCr, P < 0.001; renal TGFβ protein expression, Control group: 7.09 ± 0.17 RU, ALA group: 4.14 ± 0.26 RU, Pair-fed group: 7.00 ± 0.29 RU, P < 0.001). In the ALA group at 35 weeks of age, urinary protein excretion and renal TGFβ protein expression were positively related in the Control, ALA and Pair-fed groups (Control group, r = 0.847, P = 0.002; ALA group, r = 0.954, P < 0.001; Pair-fed group, r = 0.858, P = 0.002). TGFβ staining in glomeruli was observed in all groups but was decreased in the ALA group at 35 weeks of age.

 Conclusion

These results suggest that ALA may prevent the increase of food intake, body weight, blood glucose, urinary protein excretion and renal TGFβ protein expression in obese type 2 diabetic rat model. The effect of ALA on diabetic nephropathy presented as proteinuria and renal TGFβ expression in diabetic patients needs to be further clarified.

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The body weight was significantly decreased in the ALA group than the Control and Pair-fed groups after ALA (0.5% wt/wt) administration. *P < 0.001 vs. the Control and Pair-fed groups.

The blood glucose levels were significantly decreased in the ALA group than the Control and Pair-fed groups at 35 week after ALA (0.5% wt/wt) administration. *P < 0.001 vs. the Control and Pair-fed groups.

The renal TGFβ protein expression was significantly decreased in the ALA group than the Control and Pair-fed groups at 35 week after ALA (0.5% wt/wt) administration. RU, relative unit. *P < 0.001 vs. the Control and Pair-fed groups.

The renal tissue at 35 weeks of age was stained with periodic acid Schiff (PAS). The glomerular hypertrophy and mesangial matrix expansion are shown in the Control (A), ALA (B) and Pair-fed groups (C) (H&E stain, ×400).

The TGFβ immunostaining of glomeruli at 35 weeks of age is observed in all groups but decreases in the ALA group (brown color, ×400). Immunoperoxidase TGFβ, hematoxylin counterstaining.

Food intake, body weight, blood glucose level, urinary protein excretion and renal TGFβ protein expression of the Control, ALA and Pair-fed groups

ALA, α-lipoic acid. *P < 0.001 vs. 35 week of the Control group. **P < 0.001 vs. 30 week of the ALA group. †P < 0.001 vs. 35 week of the Control and Pair-fed groups.