每一天,高达1克的胆固醇,由未吸收的膳食胆固醇组成,胆汁胆固醇分泌,和从肠上皮细胞脱落的胆固醇,进入结肠。到达大肠的所有胆固醇都可以被结肠细菌代谢。胆固醇主要转化为共前列腺素,排泄物中的一种不可吸收的甾醇。有趣的是,人群中胆固醇向共前列腺素的转化是可变的,大多数高转换器和少数低或低效转换器。已经提出了两种主要途径,一种涉及直接立体定向还原Δ5双键,而间接途径涉及4-cholelesten-3-one和coprostanone的中间形成。尽管肠胆固醇转化在一个多世纪前被发现,只有少数胆固醇转化为共前列腺素的细菌菌株被分离和表征。此外,负责的基因直到最近才主要未知。有趣的是,胆固醇向共前列腺素的转化受到饮食的高度调节。最后,这种肠道细菌代谢与健康和疾病有关,最近的证据表明,它可能有助于降低血液胆固醇和心血管风险。
Every day, up to 1 g of cholesterol, composed of the unabsorbed dietary cholesterol, the biliary cholesterol secretion, and cholesterol of cells sloughed from the intestinal epithelium, enters the colon. All cholesterol arriving in the large intestine can be metabolized by the colonic bacteria. Cholesterol is mainly converted into
coprostanol, a non-absorbable sterol that is excreted in the feces. Interestingly, cholesterol-to-
coprostanol conversion in human populations is variable, with a majority of high converters and a minority of low or inefficient converters. Two major pathways have been proposed, one involving the direct stereospecific reduction of the Δ5 double bond direct while the indirect pathway involves the intermediate formation of 4-cholelesten-3-one and coprostanone. Despite the fact that intestinal cholesterol conversion was discovered more than a century ago, only a few cholesterol-to-
coprostanol-converting bacterial strains have been isolated and characterized. Moreover, the responsible genes were mainly unknown until recently. Interestingly, cholesterol-to-
coprostanol conversion is highly regulated by the diet. Finally, this gut bacterial metabolism has been linked to health and disease, and recent evidence suggests it could contribute to lower blood cholesterol and cardiovascular risks.