Influence of intestinal bacterial desulfation on the enterohepatic circulation of dehydroepiandrosterone sulfate

Selective association of germ-free (GF) rats with dehydroepiandrosterone sulfate (DHEAS) desulfating bacteria allowed us to assess the exact impact of intestinal bacterial desulfation on the excretion and enterohepatic circulation of orally administered DHEAS. Germ-free rats selectively associated with the DHEAS-desulfating strain Peptococcus niger H4 (H4 rats) excreted 50% of the total label recovered within 17 h vs 21 h in GF rats and 13 h 23 min in conventional (CV) rats. Germ-free rats excreted 30% of the total label recovered via their urine. However, association of GF rats with the desulfating microorganism increased urinary excretion to 46%, comparable to the 45.5% found in CV rats. Fractionation of fecal label yielded 70% sulfoconjugated DHEAS and 2% unconjugated dehydroepiandrosterone in GF rats vs 5 and 77% in CV rats, and 55 and 14% in H4 rats, respectively. Our results demonstrate that the intestinal bacterial desulfation of DHEAS stimulated the enterohepatic circulation of DHEAS. This in turn increased the urinary excretion of label resulting in an accelerated elimination of labeled DHEAS from the body.     

Absorption and enterohepatic circulation of baicalin in rats

Pharmacokinetics of baicalin, in form of its parent drug (BG) and conjugated metabolites (BGM), were studied following intravenous and oral administration of baicalin to intact rats. The enterohepatic circulation of BG and BGM was also assessed in a linked-rat model. Multiple plasma and urine samples were collected, and concentrations of BG and BGM were determined using a liquid chromatography/tandem mass spectrometry method. The concentration of BGM was assayed in the form of baicalein after treatment with beta-glucuronidase/sulfatase. After i.v. administration, plasma concentration of BG rapidly declined with the elimination half-life (T1/2) of 0.1 till 4 h post dose, followed by slight increase from 4-8 h in plasma concentrations after drug administration. These plasma concentrations resulted in a significant prolongation of the terminal elimination half-life of BG (T1/2 TER, 9.7 h). BG also displayed slight increase in plasma concentrations (12-24 h) after oral administration, with T1/2 TER of 12.1 h. Based on the AUC of BG and BGM, the absolute bioavailability of baicalin was 2.2+/-0.2% and 27.8+/-5.6%, respectively. The exposure of baicalin to the systemic circulation was approximately 118-fold lower than that of BGM after oral administration (AUC0-t, 4.43 versus 523.97 nmol.h/mL). The high extent of glucuronidation suggested the possible presence of enterohepatic circulation, which was confirmed in the linked-rat model since plasma concentrations of BG and BGM were observed in bile-recipient rats at 4 to 36 h. The extent of enterohepatic circulation after intravenous administration of baicalin was 4.8% and 13.3% for BG and BGM, respectively. It was determined that 18.7% and 19.3% of the administered baicalin were subjected to enterohepatic circulation for BG and BGM, respectively, after oral administration. These results confirm that BG undergoes extensive first-pass glucuronidation and that enterohepatic circulation contributes significantly to the exposure of BG and BGM in rats.     

Generation of thioarsenicals is dependent on the enterohepatic circulation in rats

Three minor sulfur-containing arsenic metabolites: monomethylmonothioarsonic acid (MMMTA(V)), dimethylmonothioarsinic acid (DMMTA(V)), and dimethyldithioarsinic acid (DMDTA(V)) were recently found in human and animal urine after exposure to inorganic arsenic. However, it remains unclear how the thioarsenicals are formed in the body and then excreted into the urine. It is hypothesized that the generation of thioarsenicals occurs during enterohepatic circulation. To address this hypothesis, male Sprague Dawley (SD) rats and Eisai hyperbilirubinuric (EHB) rats (with deficiency of multidrug resistance-associated protein 2) were orally administered a single dose of inorganic arsenite (iAs(III)) at 3.0 mg kg(-1) of body weight. Five hours after dosing, less than 1.0% of the dose was recovered in the bile of EHB rats, while more than 27% of the dose was recovered in the bile of SD rats, with the majority being monomethylarsinodiglutathione [MMA(SG)(2)] with a small amount of arsenic triglutathione [iAs(SG)(3)]. During the early time periods (3 h and 6 h) the arsenic levels in the liver, red blood cells (RBCs) and plasma of EHB rats were higher than those of SD rats, and approximately 76% and 87% of the dose was recovered in the RBCs of SD and EHB rats, respectively, at day 5 after dosing. However, there were no significant differences in arsenic concentration in urine between the two types of animal. Regarding the arsenic species in the urine of both types of rat, significant levels of thiolated arsenicals MMMTA(V) and DMMTA(V) were detected in SD rat urine, however in EHB rat urine only low levels of DMMTA(V) were detected. The present result of the metabolic balance and speciation study suggests that the formation of MMMTA(V) and DMMTA(V) in rats is dependent on enterohepatic circulation. In addition, in vitro experiments indicated that arsenicals excreted from bile may be transformed by gastrointestinal microbiota into MMMTA(V) and DMMTA(V), which are then absorbed into the bloodstream and finally excreted into the urine.     

Prebiotic oligosaccharides and the enterohepatic circulation of bile salts in rats

Human milk contains prebiotic oligosaccharides, which stimulate the growth of intestinal bifidobacteria and lactobacilli. It is unclear whether the prebiotic capacity of human milk contributes to the larger bile salt pool size and the more efficient fat absorption in infants fed human milk compared with formula. We determined the effect of prebiotic oligosaccharides on bile salt metabolism in rats. Rats were fed a control diet or an isocaloric diet containing a mixture of galactooligosaccharides (GOS), long-chain fructooligosaccharides (lcFOS), and acidified oligosaccharides (AOS) for 3 wk. We determined synthesis rate, pool size, and fractional turnover rate (FTR) of the primary bile salt cholate by using stable isotope dilution methodology. We quantified bile flow and biliary bile salt secretion rates through bile cannulation. Prebiotic intervention resulted in significant changes in fecal and colonic flora: the proportion of lactobacilli increased 344% (P < 0.01) in colon content and 139% (P < 0.01) in feces compared with the control group. The number of bifidobacteria also increased 366% (P < 0.01) in colon content and 282% in feces after the prebiotic treatment. Furthermore, pH in both colon and feces decreased significantly with 1.0 and 0.5 pH point, respectively. However, despite this alteration of intestinal bacterial flora, no significant effect on relevant parameters of bile salt metabolism and cholate kinetics was found. The present data in rats do not support the hypothesis that prebiotics naturally present in human milk contribute to a larger bile salt pool size or altered bile salt pool kinetics.     

Regulation of bile acid synthesis under reconstructed enterohepatic circulation in rats

Cholesterol 7alpha-hydroxylase (CYP7A1) is regulated by bile acids through the farnesoid X receptor (FXR) mechanism in a negative feedback fashion. However, the fact that CYP7A1 is down-regulated by intraduodenal administration of bile acid, but not by intravenous administration may not be explained only by this mechanism. The aim of this study was to establish a new rat model with reconstructed or simulated enterohepatic circulation to examine if intravenous or portal administration of bile acid can regulate CYP7A1. Under biliary drainage, taurocholate (0 or 6 micromol/h/100g body weight) was administered continuously for 48h into the duodenum (ID-0/ID-6), femoral vein (IV-0/IV-6), or portal vein (IP-0/IP-6) to create a condition in which biliary bile acids were continuously lost, and a similar dose of taurocholate was supplied to the liver simultaneously. CYP7A1 activity and mRNA expression of the ID-0 group were significantly increased compared with the no treatment (NT) group. CYP7A1 activity and mRNA expression of the ID-6 group were suppressed significantly to 41 and 46% of those of the ID-0 group, respectively. In the IV-6 and IP-6 groups, however, enzyme activity and mRNA expression were decreased slightly, but the suppression was not statistically significant. The results suggested that portal as well as intravenous administration of bile acids cannot suppress bile acid synthesis as effectively as intraduodenal administration. It was concluded that an unidentified regulatory factor other than the nuclear receptors may be involved in bile acid synthesis in vivo.     

On the enterohepatic cycle of triiodothyronine in rats; importance of the intestinal microflora

Until 70 h after a single iv injection of 10 uCi [125I]triiodothyronine (T3), normal rats excreted 15.8 +/- 2.8% of the radioactivity with the feces and 17.5 +/- 2.7% with the urine, while in intestine-decontaminated rats fecal and urinary excretion over this period amounted to 25.1 +/- 7.2% and 23.6 +/- 4.0% of administered radioactivity, respectively (mean +/- SD, n = 4). In fecal extracts of decontaminated rats 11.5 +/- 6.8% of the excreted radioactivity consisted of T3 glucuronide (T3G) and 10.9 +/- 2.8% of T3 sulfate (T3S), whereas no conjugates were detected in feces from normal rats. Until 26 h after ig administration of 10 uCi [125I]T3, integrated radioactivity in blood of decontaminated rats was 1.5 times higher than that in normal rats. However, after ig administration of 10 uCi [125I]T3G or [125I]T3S, radioactivity in blood of decontaminated rats was 4.9- and 2.8-fold lower, respectively, than in normal rats. The radioactivity in the serum of control animals was composed of T3 and iodide in proportions independent of the tracer injected, while T3 conjugates represented less than 10% of serum radioactivity. These results suggest an important role of the intestinal microflora in the enterohepatic circulation of T3 in rats.     

内毒素血症对新生鼠肠道菌群的影响

利用高通量测序技术分析内毒素血症新生鼠肠道菌群的变化, 探究肠道菌群与内毒素血症的关系, 为临床诊治提供思路。

复制新生大鼠内毒素损伤模型, 注射LPS后第24小时、第3天、第7天分别处死新生大鼠, 留取粪便并将对照组(C1组6只、C3组5只、C7组7只)和LPS组(L1组5只、L3组5只、L7组5只)按处死天数各分为3组。高通量测序分析各组间菌群多样性及相对丰度差异。

(1) Alpha多样性分析提示对照组和LPS组菌群多样性及丰度有显著差异, C3组较L3组Shannon指数均值小(t=-3.386 8, P=0.009 5), Simpson指数均值大(t=3.102 4, P=0.014 6);C7组较L7组Shannon指数均值大(t=2.459 4, P=0.033 7), Simpson指数均值小(t=-2.475 6, P=0.032 8)。(2)物种组成分析表明LPS组的菌群结构发生改变, 在门水平LPS组较对照组变形菌门相对丰度高, 厚壁菌门相对丰度低; 在属水平上LPS组较对照组埃希菌-志贺菌属相对丰度高, 乳杆菌属相对丰度低; 且随着天数的递增LPS组埃希菌-志贺菌属呈递增趋势, 红球菌属呈递减趋势。

内毒素血症可以改变新生鼠肠道菌群的组成, 并与肠道菌群失调有一定的关系。

     

青春双歧杆菌对2型糖尿病模型大鼠肠道菌群和脂质代谢的影响

目的通过观察青春双歧杆菌对2型糖尿病模型大鼠肠道菌群的变化,和血清中总胆固醇（TC）、甘油三酯（TG）、高密度脂蛋白（HDL-C）、超氧化物歧化酶（SOD）和丙二醛（MDA）的水平,探讨青春双歧杆菌对2型糖尿病模型大鼠肠道功能和脂质代谢的影响。方法采用青春双歧杆菌灌胃2型糖尿病模型大鼠,取粪便检查正常菌群,取血和脏器检测TC、TG、HDL-C、SOD和MDA含量。结果青春双歧杆菌导致肠道内双歧杆菌、乳杆菌的数量增加,而肠杆菌、肠球菌数量下降;TC、TG和MDA水平下降,而HDL-C和SOD水平升高。结论青春双歧杆菌具有改善2型糖尿病模型大鼠肠道功能和降血脂作用,与二甲双胍联合应用效果更佳。     

大鼠失血性休克后肠道微生态的改变

本研究对无特殊致病菌大鼠失血性休克后肠道微生态的改变及肠道细菌易位进行了动态观察。结果表明,失血性休克复苏后5小时,肠道微生态即发生改变,表现为回肠内肠杆菌菌量增多,肠道内类杆菌与肠杆菌菌量比值下降,而后这一改变随时间推移逐渐恢复;肠道细菌易位率也有类似变化,易位细菌以肠杆菌为主。结果提示,大鼠失血性休克后肠道细菌易位与肠道微生态的改变有密切关系。     

活性乳酸菌饮料对人体肠道菌群影响的研究

目的 探讨一种活性乳酸菌饮料对人体肠道菌群的影响作用.方法 采用卫生部《保健食品检验与评价技术规范》调节肠道菌群功能检验方法进行检验.结果 试食组试验前后自身比较：肠道内双歧杆菌、乳杆菌数量明显增加（P＜0.01）,肠球菌数量增加（P＜0.05）,产气荚膜梭菌数量明显减少（P＜0.01）,肠杆菌和拟杆菌无明显变化;试验后对照组与试食组组间比较：双歧杆菌数量明显增加（P＜0.01）,乳杆菌的数量增加（P＜0.05）,肠杆菌、肠球菌、产气荚膜梭菌和拟杆菌无明显变化.结论 活性乳酸菌饮料具有调节人体肠道菌群、改善肠道内环境的作用.     

Effects of sphincterectomy on bile acid enterohepatic circulation in dogs

Relative rates of bile enterohepatic circulation (EHC) and bile acid pool distribution were compared in intact and sphincterectomized dogs with portacaval shunt. There was no significant difference in the rates of EHC or in the bile acid pool distribution in the groups of animals. Feeding and cholecystokinin administration caused similar increases in bile acid EHC rates in sphincterectomized and intact animals. It was concluded that the sphincter of Oddi has little or no effect on these aspects of bile acid metabolism in dogs.     

25-Hydroxyvitamin D3: evidence of an enterohepatic circulation in man.

Within 24 hr after intravenous administration of isotopic 25-hydroxyvitamin D3 to three normal adults for kinetic studies, one-third of the radioactivity was secreted into the lumen of the duodenum, probably with the bile. The subsequent intestinal reabsorption of over 85% of secreted radioactivity suggests that this major metabolite of vitamin D has a hitherto unrecognized enterohepatic circulation. Our observation of a dynamic hepatic secretion and intestinal reabsorption of radioactivity administered as 3H-labeled 25-hydroxyvitamin D3 to vitamin D-replete man is indicative of an enterohepatic circulation that may be of physiologic importance. It is conceivable that interruption in the recycling of 25-OH-D3 may be an important mechanism of acquired deficiency of vitamin D in gastrointestinal disease.     

Formation and enterohepatic circulation of metabolites of retinol and retinoic acid in bile duct-cannulated rats

Four hours after intraportal injection of retinoic acid-(14)C into bile duct-cannulated rats, less than 10% of the radioactivity was recovered in the liver, intestine, and kidneys. Within 6 hr, 40% of the radioactivity had appeared in bile. When suspensions of retinol-(14)C or retinal were similarly injected, 25-35% of the dose was excreted in bile within 24 hr and equivalent amounts were deposited in the liver as retinol ester. The isolated perfused liver also produced these bile metabolites and is probably the major site of their formation in vivo. The intestine may metabolize retinoic acid, however, since some metabolites were found in the intestinal wall and lumen, even in bile duct-cannulated rats. The bile metabolites of retinol-(14)C and retinoic acid-(14)C undergo extensive enterohepatic circulation. The bile radioactivity was not volatilized on boiling at acid pH, was not present in digitonin-precipitated sterols, and did not migrate with bile salts on reversed-phase paper chromatography. Anion-exchange chromatography resolved the metabolites of bile into three fractions containing nonionic compounds, acidic substances like retinoic acid, and more polar acidic derivatives.