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

<p>Abstract</p> <p>Background</p> <p>To study the effects of a pre-germinated brown rice diet (PR) on diabetic neuropathy in streptozotocin (STZ)-induced diabetic rats.</p> <p>Methods</p> <p>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.</p> <p>Results</p> <p>Compared with diabetic rats fed BR or WR diets, those fed a PR diet demonstrated significantly lower blood-glucose levels (<it>p </it>< 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, <it>p </it>< 0.001). The <it>in vitro </it>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) <it>in vitro </it>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).</p> <p>Conclusion</p> <p>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.</p

Postprandial blood glucose and insulin responses to pre-germinated brown rice in healthy subjects

Effects of pre-germinated brown rice (PGBR) on postprandial blood glucose and insulin concentrations were compared with brown rice (BR)and white rice (WR) in two studies. In the first study, we investigated the time course of postprandial blood glucose and insulin concentrations after ingesting 25% (W/V) glucose solution, PGBR, BR or WR in 19 healthy young subjects. In the second study, dose-dependent effect of PGBR on the time course of postprandial blood glucose concentrations was compared among 4 different mixtures of PGBR and WR in 13 healthy young subjects. They were solely PGBR, 2/3 PGBR(PGBR:WR= 2 : 1), 1/3 PGBR (PGBR : WR=1 : 2) and solely WR. Each sample was studied on a different day. The samples were selected randomly by the subjects. All the rice samples contained 50g of available carbohydrates. The previous day the subjects ate the assigned dinner by 9 : 00 pm and then were allowed only water until the examination. The next morning, they ingested each test rice sample with 150ml of water in 5-10min.Blood was collected into capillary tubes from finger at 0, 30, 60, 90 and 120 min after the ingestion. The incremental areas under the curve (IAUC) of blood glucose concentrations (IAUC-Glc) for 120min after the administration of PGBR and BR were lower than those after WR. In contrast the IAUC-Glc of BR and PGBR were not different (Study 1). The higher the ratio of PGBR/WR, the lower the glycemic index became (Study 2). These results suggest that intake of PGBR instead of WR is effective for the control of postprandial blood glucose concentration without increasing the insulin secretion

IGF-1 Induction by Acylated Steryl β-Glucosides Found in a Pre-Germinated Brown Rice Diet Reduces Oxidative Stress in Streptozotocin-Induced Diabetes

BACKGROUND: The pathology of diabetic neuropathy involves oxidative stress on pancreatic β-cells, and is related to decreased levels of Insulin-like growth factor 1 (IGF-1). Acylated steryl β-glucoside (PR-ASG) found in pre-germiated brown rice is a bioactive substance exhibiting properties that enhance activity of homocysteine-thiolactonase (HTase), reducing oxidative stress in diabetic neuropathy. The biological importance of PR-ASG in pancreatic β-cells remains unknown. Here we examined the effects of PR-ASG on IGF-1 and glucose metabolism in β-cells exposed to oxidative stress. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, a pre-germinated brown rice (PR)-diet was tested in streptozotocin (STZ)-induced diabetic rats. Compared with diabetic rats fed control diets, the PR-diet fed rats showed an improvement of serum metabolic and neurophysiological parameters. In addition, IGF-1 levels were found to be increased in the serum, liver, and pancreas of diabetic rats fed the PR-diet. The increased IGF-1 level in the pancreas led us to hypothesize that PR-ASG is protective for islet β-cells against the extensive injury of advanced or severe diabetes. Thus we examined PR-ASG to determine whether it showed anti-apoptotic, pro-proliferative effects on the insulin-secreting β-cells line, INS-1; and additionally, whether PR-ASG stimulated IGF-1 autocrine secretion/IGF-1-dependent glucose metabolism. We have demonstrated for the first time that PR-ASG increases IGF-1 production and secretion from pancreatic β-cells. CONCLUSION/SIGNIFICANCE: These findings suggest that PR-ASG may affect pancreatic β-cells through the activation of an IGF-1-dependent mechanism in the diabetic condition. Thus, intake of pre-germinated brown rice may have a beneficial effect in the treatment of diabetes, in particular diabetic neuropathy

Effects of Pre-Germinated Brown Rice on Blood Glucose and Lipid Levels in Free-Living Patients with Impaired Fasting Glucose or Type 2 Diabetes

White rice (WR) is made by polishing brown rice (BR) and has lost various nutrients; however, most people prefer it to BR, maybe because of the hardness of BR. Pre-germinated brown rice (PGBR) improves the problem of BR. It is made by soaking BR kernels in water to germinate and becomes softer than BR. In this study we compared the effects of WR and PGBR on blood glucose and lipid concentrations in the impaired fasting glucose (IFG) or type 2 diabetes patients. Six men and 5 women with impaired fasting glucose (IFG) or type 2 diabetes were randomly allocated to 6wk on WR or PGBR diet separated by a 2wk washout interval in a crossover design. Each subject was instructed to consume 3 packs of cooked WR or PGBR (180g/pack) daily in each intervention phase. Blood samples were collected 4 times (in study weeks 0, 6, 8 and 14) for biochemical examination. Blood concentrations of fasting blood glucose, fructosamine, serum total cholesterol and triacylglycerol levels were favorably improved on the PGBR diet (p<0.01), but not on the WR diet. The present results suggest that diets including PGBR may be useful to control bl ood glucose level

Final body weights, blood glucose concentrations, and serum parameters in non-diabetic and diabetic rats (3 weeks).

<p>One-way ANOVA was performed to analyze the variation between 3 groups of non-diabetic or diabetic treatment. The data were then analyzed using Tukey's multiples comparison test (if parametric). Values were expressed as means±SEM. Differences between the PR-treated group and other diet groups were analyzed by Dunnet's multiple comparison test (*p<0.05, **p<0.01, ***p<0.001).</p

Effect of PR-ASG treatment on cellular ROS level and HTase activity in STZ-exposed cells.

<p>A) Initially, cells were incubated under one of these sets of experimental parameters: STZ-negative, PR-ASG-negative (control); 1 mM STZ (STZ group); or 1 mM STZ supplemented with 4 µg/mL of PR-ASG (STZ+PR-ASG). After 1 hr of incubation, the cells were pre-washed with fresh medium, stained with DCF-DA (1.0 µM), and incubated in darkness for 10 min. DCF-DA green fluorescence was viewed under a fluorescence microscope. B) DCF-DA green fluorescing cells were also quantitated by a Perkin-Elmer Victor V multilabel plate reader with excitation/emission filters set at 490 and 535 nm, and expressed as the percent of the total number of cells that exhibit DCA-DA green fluorescence. C) Cells (2.5×10⁵ in 1 mL of 10% serum- containing RPMI 1640 medium well) were cultured in12-well plates. One day later, the cells were divided into 3 groups fro 1 hour of exposure to one of the following in RPMI medium containing 1.0 µg/mL rat LDL; no STZ with no PR-ASG (control); 1 mM STZ (STZ); or 1 mM STZ with 4 µg/mL of PR-ASG (STZ+PR-ASG). Subsequently, cells were pre-washed; cultured for 24 hours in serum-free RPMI-1640 medium with 0 or 4 µg/mL of PR-ASG; harvested; and eventually used for enzyme preparation. The cellular supernatant produced during enzyme preparation was assessed for activity using an Alfresa auto HTLase assay kit (Alfresa Pharma Corp., Osaka, Japan). One unit of HTase activity is defined as 1 nmol of HT hydrolyzed in 1 min by 1 mg of protein. In B) and C), values were expressed as means ± SEM, n = 6 individual experiments, and analyzed by one-way ANOVA followed by Tukey's multiples comparison test and then Dunnet's test. The single asterisk denotes a statistically significant difference between STZ and STZ+PR-ASG (*p<0.01).</p

Suggested mechanism for PR-ASG's protective action against oxidative stress in INS-1 cells.

<p>Reactive oxgen species (ROS) generated from STZ exposure are metabolized and inactivated by SOD, to produce H₂O₂. It has been shown that an imbalance in the coordinated expression/activity of glutathione peroxidase (GSHPx) and glutathione reductase (GR) can cause excessive generation of ROS, leading to oxidative stress. GSHPx converts H₂O₂ to water using glutathione (GSH). Maintenance of the redox state in cells' redox state is controlled by intracellular regulators such as reduced glutathione (GSH) and NADPH. Both GR and glucose-6-phosphate dehydrogenase (G6PD) are enzymes suspected to have protective activity against conditions of oxidative stress. On the other hand, 2-deoxy-glucose (2-DG, an inhibitor of glycolytic pathway) and 6-aminonicotinamide (6-AN, an inhibitor of pentose phosphate pathway) both decrease the cellular levels of pyruvate and NADPH. This leads to an accumulation of H₂O₂, the building of which acts to induce apoptosis. PR-ASG's defensive action is exerted via an increase in two targets: increasing homocysteine-thiolactonase (HTase) enhances homocysteine (Hcy) metabolism; and increasing pyruvate enhances protection against cell via IGF-1-related glucose metabolism.</p