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Recent discovery of nuclear retinoid receptors revealed that a variety of retinoid (vitamin A) action is exerted by the nuclear receptors-mediated gene expression. Nuclear retinoid receptors are classified into two classes, all-trans-retinoic acid receptors (RARα, β and γ) and retinoid-X-receptors (RXRα,β and γ). Ho- mo- and hetro-dimers of RAR and RXR bind to specific retinoid response elements (RARE and RXRE) located in the target gene promoters. These response elements are composed of two direct repeated AGGTCA motifs (or related motif) spaced by 1,2 and 5bp (DR 1,2 and 5). Based upon these observations, the molecular mechanisms of retinoid actions were considered from different experimental approaches. By extending our previous findings in unusual estrogen response elements, other classes of retinoid response elements have been identified from systematic studies. Using animal models of various status of retinoid, vitamin D and thyroid hormone, we found that the gene expression of RARβ our of three RARs is positively regulated at transcriptional level by retinoid, but not vitamin D and thyroid hormone. In the contrast, the gene expression of RXRβ (positive) and RXRγ (negative) is regulated transcriptionally and post-transcriptionally by only thyroid hormone. Furthermore, the effects of these three ligands on the gene expression of cellular retinoid binding proteins are under investigation. In addition, isomerization of active form of retinoic acids and the functional domain of RAR and RXR with special attention to phosphorylation are also studied. Thus, taken together, these studies may clarify a part of the molecular mechanisms of retinoid actions.

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Capillary basement membrane thickening is a characteristic of diabetic microangiopathy. Type IV collagen is the major component of basement membrane. To elucidate the pathogenesis of diabetic nephropathy, we investigated serum type IV collagen and serum ascorbic acid in non-insulin-dependent diabetes mellitus (NIDDM) (n=37) and in normal subject s (n=14). Serum ascorbic acid level was lower in NIDDM than in normal subjects. Serum type IV collagen level was higher in NIDDM than in normal subjects. There was a significant positive correlation between serum type IV collagen and HbA_<IC> in poorly controlled diabetes (HbA_<IC>>8%) (p<0.05). A significant negative correlation was found between serum type IV collagen and serum ascorbic acid (p<0.05). A significant positive correlation was found between serum type IV collagen and urinary albumin excretion in patients with microalbuminuria (U-alb>30 mg/g・Cr) in NIDDM. In conclusion, serum type IV collagen is helpful as a early indicator of nephropathy.

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藤田らのTLC法を応用したHPLC法について検討し,以下の結果を得た。1)内部標準としてDNPH試薬を用いることを検討した結果,AsA濃度を100〜1000μg/mlの間で変化させても,オサゾン生成後に残存するDNPH(検液2ml,0.1M DNPH溶液0.5ml使用の場合)のピーク面積は,ほぼ一定値を示した(図1)。2)DAsAオサゾンの酢酸エチル抽出,HPLC測定において,DAsAオサゾンのピーク面積(200μg/ml AsA標準液使用)は,0.08M DNPHを添加した場合に上限に達した。したがって,内部標準を兼ねるDNPH試薬の濃度は0.1Mとした。3)酢酸エチル添加後の振とう抽出時間を検討した結果,5分間でDAsAオサゾンの抽出量は上限に達した。4)本HPLC法とTLC法およびDNPH法により食品中の総C量を測定した結果,HPLC法による総C量はDNPH法と同等,あるいはそれより低値を示すものが多く,TLC法の結果に近似していた。5)HPLC法によるCの添加回収率は95〜106%の範囲であり,本法はTLC法に代わり食品中Cの真値定量法として使用できる。

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