北アメリカ原産のイネ科マコモ属の単子葉植物, ワイルドライス (Zizania palustris) は, その独特の風味が好まれている。我々はその特異なテクスチャーに関連する成分としてデンプンおよび細胞壁多糖に着目し, ワイルドライス製品の多糖成分の分画を行い, 特にデンプンの性状を調べた。
1) ワイルドライス粉末からアルカリ浸漬法によりデンプンを分離し, この上清からエタノール沈澱により水溶性多糖を分離した。ふるい上の残渣を脱脂・除タンパク後再度デンプンを分別し, 不溶性残渣から細胞壁標品を得た。
2) ワイルドライスからのデンプンの収量は30.5%であり, ウルチ米の半分以下であった。ワイルドライスの細胞壁標品の収量 (3.54%) は, ウルチ米 (0.12%), モチ米 (0.3%) と比較すると, 細胞壁の含量が著しく高いことを示唆している。
3) デンプン画分の走査電子顕微鏡写真から, ワイルドライスのデンプン粒の形はウルチ米と類似の多面体で, サイズはやや小さく, 1.5-6μm程度の粒径であった。細胞壁標品の走査電子顕微鏡像から, ワイルドライスの細胞壁はウルチ米に比し相当厚く強固な様子が観察された。
4) デンプンをイソアミラーゼおよびプルラナーゼで完全に分枝切断し, ゲルろ過により鎖長分布を調べた結果, ワイルドライスのFr. I (アミロース) の比率は23.8%で, ウルチ米よりかなり高かつた。一方, Fr. III (アミロペクチンの短鎖長, DP 10-30) とFr. II (長鎖長, DP 30-60) の比は3.5で, ウルチ米 (2.6) よりも大きかった。
5) 上記の枝切りデンプンの精密鎖長分布を, 陰イオン交換高速液体クロマトグラフィーにより解析した結果, 短鎖部分の鎖長分布はワイルドライスでは11糖が最多で, またウルチ米, モチ米と比べて10-14糖部分の含量 (モル%) が高く, アミロペクチンの微細構造も米とは異なることが示唆された。

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Nutrients ingested orally are important physiological insulin secretagogues: a much greater inslin response is observed after oral glucose loading than after intravenous injection of the same amount of glucose. Gastroz inhibitory polypeptide (GIP) is the primary hormonal messenger relaying information from the gut to pancreatic β cells. To investigate the role of GIP as an incretin, we have generated mice with a targeted mutation of the GIP receptor gene. GIPR-/-mice have higher blood glucose levels with an impaired insulin response after an oral glucose load, suggesting that the early insulin secretion mediated by GIP determines glucose tolerance after oral glucose loading in vivo. In the Goto-Kakizaki rat, a new genetic model of type 2 diabetes, the insulin response to glucose is selectively impaired. We exanined the properties of ATP-sensitive K⁺ channels, whose inhibition is a key step in insulin secretion induced by fuel substrates, using the patch-clamp technique. The sensitivity of the K_ATP channels to glucose is considerably reduced in GK rats. It appears that the impaired insulinotropic action of glucose in the β cells of GK rats is insufficient closure of the K_ATP channels, probably because of deficient ATP production due to impaired glucose metabolism. In order to elucidate which step in ATP production by the metabolic pathway is responsible in diabetic β cells, we tested glyceraldehyde and KIC (ketoisocaproate, which can be metabolized in mitochondria via acetyl-CoA). K_ATP-channel activities in both control and diabetic β cells were equally suppressed by glyceraldehyde and 2-ketoisocaproate. We also investigated the insulin-secretory capacity of β cells by stimulation with dihydroxyacetone (DHA), which is known to be directly converted to DHA-phosphate and preferentially enter the glycerol phosphate shuttle. The DHA sensitivity of the K_ATP channels was found to be reduced in the β cells of GK rats. These results suggest that the intracellular sites responsible for the impaired glucose metabolism in pancreatic β cells of GK rats are located both in the glycolytic pathway proximal to glyceraldehyde and in the glycerol phosphate shuttle.

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Potent therapeutic actions of dietary manipulations and food factors on nephritis and cancer were evaluated using in vivo and in vitro disease models. In rats with glomerulonephritis, dietary manipulations of amino acids-fortified low-protein diets reduced proteinuria, hypoalbuminemia and hyperlipidemia without severe protein malnutrition. A cysteine derivative from cabbage, S-methyl-L-cysteine sulfoxide, suppressed hypercholesterolemia in response to hepatoma (AH109A) growth by upregulating cholesterol catabolism. Fish oil suppressed hyperlipidemia secondary to glomerulone-phritis and presence of hepatoma. Screening of food factors with the potential to suppress the proliferation and invasion of cancer cells was conducted using in vitro assay systems in which AH109A cells were employed as model cancer cells. Food factors such as catechins from teas, curcumin in turmeric, and astaxanthin in crustaceans were effective in suppressing hepatoma proliferation and/or invasion. The antioxidative properties of these food factors were suggested to be involved in their anti-invasive activities. Both advantageous and disadvantageous aspects of in vivo and in vitro disease models were discussed in evaluating the therapeutic actions of food factors.

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