Effect of pre-germinated brown rice intake on diabetic neuropathy in streptozotocin-induced diabetic rats

Background. To study the effects of a pre-germinated brown rice diet (PR) on diabetic neuropathy in streptozotocin (STZ)-induced diabetic rats. Methods. The effects of a PR diet on diabetic neuropathy in STZ-induced diabetic rats were evaluated and compared with those fed brown rice (BR) or white rice (WR) diets with respect to the following parameters: blood-glucose level, motor-nerve conduction velocity (NCV), sciatic-nerve Na⁺/K⁺-ATPase activity, and serum homocysteine-thiolactonase (HTase) activity. Results. Compared with diabetic rats fed BR or WR diets, those fed a PR diet demonstrated significantly lower blood-glucose levels (p < 0.001), improved NCV (1.2- and 1.3-fold higher, respectively), and increased Na⁺/K ⁺-ATPase activity (1.6- and 1.7-fold higher, respectively). The PR diet was also able to normalize decreased serum homocysteine levels normally seen in diabetic rats. The increased Na⁺/K⁺-ATPase activity observed in rats fed PR diets was associated with elevations in HTase activity (r = 0.913, p < 0.001). The in vitro effect of the total lipid extract from PR bran (TLp) on the Na⁺/K⁺-ATPase and HTase activity was also examined. Incubation of homocysteine thiolactone (HT) with low-density lipoprotein (LDL) in vitro resulted in generation of HT-modified LDL, which possessed high potency to inhibit Na⁺/K⁺-ATPase activity in the sciatic nerve membrane. The inhibitory effect of HT-modified LDL on Na⁺/K⁺-ATPase activity disappeared when TLp was added to the incubation mixture. Furthermore, TLp directly activated the HTase associated with high-density lipoprotein (HDL). Conclusion. PR treatment shows efficacy for protecting diabetic deterioration and for improving physiological parameters of diabetic neuropathy in rats, as compared with a BR or WR diet. This effect may be induced by a mechanism whereby PR intake mitigates diabetic neuropathy by one or more factors in the total lipid fraction. The active lipid fraction is able to protect the Na⁺/K⁺-ATPase of the sciatic-nerve membrane from the toxicity of HT-modified LDL and to directly activate the HTase of HDL.