Abstract
BackgroundThe 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 FindingsIn 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/SignificanceThese 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.
Highlights
Dietary intake of pre-germinated brown rice (PR) (Hatsuga genmai) [1] has widely been found useful for alleviating symptoms of both diabetes and pre-diabetes
We revealed that germination of brown rice led to de novo production of a special lipid ingredient, PR-derived Acylated steryl b-glucoside (ASG) (PR-ASG), as purified from the bran of PR [5]
PR-ASG is a unique ingredient found in the bran of pregerminated brown rice that can be purified from the glycolipid fractions, as previously reported [5]
Summary
Dietary intake of pre-germinated brown rice (PR) (Hatsuga genmai) [1] has widely been found useful for alleviating symptoms of both diabetes and pre-diabetes. Later it was demonstrated that the beneficial effects of the PR-diet were due to the germination process, which was considered contributory to development of the intrinsic potential to elevate the activities of protective enzymes that respond to oxidative stress in diabetic neuropathy [3]. One such known stress is an increase in homocysteine (Hcy), which is elevated in diabetes [3], and undergoes intra-molecular thiolactone formation. Acylated steryl b-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. We examined the effects of PR-ASG on IGF-1 and glucose metabolism in b-cells exposed to oxidative stress
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