The Vancouver Prostate Centre at Vancouver General Hospital, 2660 Oak Street, Vancouver, BC, Canada V6H 3Z6.
The Vancouver Prostate Centre at Vancouver General Hospital, 2660 Oak Street, Vancouver, BC, Canada V6H 3Z6.
J Steroid Biochem Mol Biol. 2014 May;141:94-103. doi: 10.1016/j.jsbmb.2014.01.007. Epub 2014 Jan 30.
The beneficial effects of vitamin D3 are exerted through 1α,25-dihydroxyvitamin D3 [1α,25(OH)2D3], the dihydroxy metabolite of vitamin D3. Hepatic and intestinal biotransformation of 1α,25(OH)2D3 and modifiers of metabolic capacity could be important determinants of bioavailability in serum and tissues. Ginsenosides and their aglycones, mainly 20(S)-protopanaxadiol (aPPD) and 20(S)-protopanaxatriol (aPPT), are routinely ingested as health supplements. The purpose of the present study was to investigate the potential of ginsenosides and their aglycones to block hepatic and intestinal inactivation of 1α,25(OH)2D3, which is the most potent ligand of vitamin D receptor. In vitro biotransformation reactions were initiated with NADPH regenerating solutions following initial preincubation of pooled human hepatic or intestinal microsomal protein or human recombinant CYP3A4 supersomes with 1α,25(OH)2D3 or midazolam. Formation of hydroxylated metabolites of 1α,25(OH)2D3 or midazolam was analyzed using liquid chromatography-mass spectrometry. Co-incubation of 1α,25(OH)2D3 with various ginsenosides (Rg1, Rh2, aPPD, aPPT and total ginsenosides) led to differential inhibition (30-100%) of its hydroxylation. Results suggest that aPPD, aPPT and Rh2 strongly attenuated the hydroxylation of 1α,25(OH)2D3. Follow up inhibition studies with aPPD and aPPT at varying concentrations (0.5-100μM) led to up to 91-100% inhibition of formation of hydroxylated metabolites of 1α,25(OH)2D3 thus preventing inactivation of active vitamin D3. The IC50 values of aPPD or aPPT for the most abundant hydroxylated metabolites of 1α,25(OH)2D3 ranged from 3.3 to 9.0μM in human microsomes. The inhibitory mechanism of aPPD or aPPT for CYP3A4-mediated biotransformation of 1α,25(OH)2D3 was competitive in nature (apparent Ki: 1.7-2.9μM). Similar inhibitory effects were also observed upon addition of aPPD or aPPT into midazolam hydroxylation assay. In summary, our results suggest that ginsenosides, specifically aPPD and aPPT, inhibit the CYP3A4-mediated catabolism of active vitamin D3 in human liver and intestine, potentially providing additional vitamin D-related benefits to patients with cancer, neurodegenerative and metabolic diseases.
维生素 D3 的有益作用是通过 1α,25-二羟维生素 D3 [1α,25(OH)2D3]发挥的，1α,25-二羟维生素 D3 是维生素 D3 的二羟代谢产物。1α,25(OH)2D3 的肝和肠生物转化以及代谢能力的调节剂可能是血清和组织中生物利用度的重要决定因素。人参皂苷及其苷元，主要是 20(S)-原人参二醇 (aPPD) 和 20(S)-原人参三醇 (aPPT)，通常作为保健品摄入。本研究的目的是研究人参皂苷及其苷元是否具有阻断 1α,25(OH)2D3 肝和肠失活的潜力，1α,25(OH)2D3 是维生素 D 受体最有效的配体。在初始预孵育后，通过 NADPH 再生溶液启动体外生物转化反应，将人肝或肠微粒体蛋白或人重组 CYP3A4 超分子与 1α,25(OH)2D3 或咪达唑仑一起孵育。使用液相色谱-质谱法分析 1α,25(OH)2D3 或咪达唑仑的羟基化代谢物的形成。1α,25(OH)2D3 与各种人参皂苷 (Rg1、Rh2、aPPD、aPPT 和总人参皂苷) 共孵育导致其羟基化的差异抑制 (30-100%)。结果表明，aPPD、aPPT 和 Rh2 强烈抑制 1α,25(OH)2D3 的羟基化。在不同浓度 (0.5-100μM) 下用 aPPD 和 aPPT 进行后续抑制研究，导致 1α,25(OH)2D3 的羟基化代谢物形成高达 91-100% 的抑制，从而防止活性维生素 D3 的失活。aPPD 或 aPPT 对 1α,25(OH)2D3 的最丰富的羟基化代谢物的 IC50 值在人微粒体中为 3.3-9.0μM。aPPD 或 aPPT 对 CYP3A4 介导的 1α,25(OH)2D3 生物转化的抑制机制本质上是竞争性的 (表观 Ki：1.7-2.9μM)。在咪达唑仑羟基化测定中加入 aPPD 或 aPPT 也观察到类似的抑制作用。总之，我们的结果表明，人参皂苷，特别是 aPPD 和 aPPT，抑制人肝和肠中活性维生素 D3 的 CYP3A4 介导的分解代谢，这可能为癌症、神经退行性和代谢性疾病患者提供额外的维生素 D 相关益处。
