Immobilized enzymes for assaying bile acids

Guar gum improves growth performance, intestinal microbiota homeostasis, and hepatic lipid metabolism in juvenile largemouth bass (Micropterus salmoides) fed high-fat diets

The study aimed to investigate the effects of guar gum on the growth performance, gut microbiota composition, and hepatic lipid metabolism of largemouth bass (Micropterus salmoides) fed high-fat diets. Experimental fish were fed a normal-fat diet (Control), high-fat diet (HF), or HF diets supplemented with 0.3 %, 1 %, and 3 % guar gum (GG0.3, GG1, and GG3, respectively) for eight weeks. The results showed that HF significantly decreased fish growth performance, increased hepatic lipid accumulation, upregulated the expression of sterol regulatory element binding proteins 1 (SREBP1), and downregulated the expression of liver X receptor alpha (LXRα), cytochrome P450 7A1 (CYP7A1), and CYP8B1, compared to Control. However, these problems of high-fat diets were significantly alleviated by GG 0.3. The intestinal microbial communities of the GG0.3 and Control were similar but distinctly different from that of the HF group. Compared to HF, GG0.3 significantly increased the relative abundances of Firmicutes and Lactococcus and decreased the relative abundance of Tenericutes, Mesomycoplasma, and Phenylobacterium. In addition, the GG0.3 and GG1 treatments significantly enhanced the bile salt hydrolase (BSH) activity in the digesta compared to HF. In conclusion, 0.3 % guar gum supplementation can improve growth performance, intestinal health, and hepatic lipid metabolism in fish fed high-fat diets.

Repetitive short-term bile duct obstruction and relief causes reproducible and reversible bile acid regurgitation

BACKGROUND

Long-term bile duct obstruction causes sinusoidal regurgitation of bile acids, a shift in bile acid metabolism, and alterations of liver histology. In this study we investigated the regurgitation of bile acids during short-term bile duct obstruction and its reversibility and reproducibility. In addition, the biotransformation of taurodeoxycholate and its appearance in bile and perfusate effluent were studied as well as liver histology.

METHODS

Rat livers (n = 5) were perfused in vitro with 32 nmol/min/g liver taurodeoxycholate over 85 min with the bile duct being intermittently closed for 30 and 20 min, respectively.

RESULTS

Within the first 5 min after bile duct obstruction bile acids started to regurgitate to the perfusate effluent amounting to approximately 15% of hepatic uptake until the end of the perfusion period. After relief of obstruction, bile flow and biliary bile acid excretion showed an overshoot phenomenon and were almost doubled compared to preobstruction. In contrast, sinusoidal bile acid regurgitation declined. The same phenomenon was observed during the second closure/opening cycle of the bile duct. Regurgitated bile acids consisted of significantly more taurodeoxycholate metabolites (approximately 70%) than did biliary bile acids (approximately 30%). Histology of liver parenchyma was preserved.

CONCLUSIONS

During repetitive short-term bile duct obstruction bile acid regurgitation is reversible and reproducible. The absence of altered mechanical barriers suggests that specific pathways are involved in the regurgitation process of bile acids.

Effects of bile duct ligation on hepatic expression of female-specific CYP2C12 in male and female rats

Gender differences in hepatic sex steroid and drug metabolism result from hormonal regulation of specific cytochrome P450 genes (CYP). In male rats, bile duct ligation (BDL) is associated with down-regulation of the male-specific genes, CYP2C11 and CYP3A2, together with a decrease in serum testosterone levels and a two- to three-fold increase in serum estradiol concentrations. We anticipated that if estrogen is responsible for down-regulation of male-specific CYPs in BDL male rats, the female-specific CYP2C12, which is not normally present in adult male rat liver, should be up-regulated. We examined this proposal by determining the profile of hepatic cytochrome P450 enzymes in female rats subjected to BDL, and by seeking evidence for expression of CYP2C12 in male rats that do not normally express this gene. In female rats killed 5 days after BDL, total cytochrome P450 content and NADPH-cytochrome P450-reductase (P450-reductase) were decreased to 74% and 58% of control, respectively. Microsomal enzyme activities attributable to CYP2A1, CYP2C6, and CYP2E1 were 50% to 60% of control, but ethylmorphine N-demethylase, which in female liver is catalyzed by CYP2C12 and to a lesser extent CYP2C6, was significantly less affected (81% of control). Likewise, levels of CYP2C6 and P450-reductase proteins were decreased in proportion to the corresponding enzyme activities (50% to 60%), while CYP2C12 protein (and mRNA levels) were not altered in BDL female rat liver. In sham-operated male rats, transcripts for CYP2C12 were rarely detected, but mRNA levels rose to appreciable levels within 24 hours of BDL, and CYP2C12 protein was expressed in hepatic microsomes of BDL male rats. Administration of estradiol to male rats produced a similar elevation of CYP2C12 mRNA, to values approximately 40% of female rats. It is concluded that CYP2C12 is up-regulated in male rats with cholestasis caused by BDL, while CYP2C12 protein is preserved in female rats when other microsomal proteins are decreased. These changes may be related to the increase in serum estradiol levels that result from altered hepatic steroid metabolism. The results demonstrate that activities of individual drug-metabolizing enzymes in liver disease can be determined by dysregulation of the constitutive expression of hepatic CYP genes.

Different protective effects of tauroursodeoxycholate, ursodeoxycholate, and 23-methyl-ursodeoxycholate against taurolithocholate-induced cholestasis

The coinfusion of tauroursodeoxycholate (TUDC) prevents taurolithocholate (TLC) -induced cholestasis. 23-Methyl-ursodeoxycholate (MUDC) is a side-chain derivative of ursodeoxycholate (UDC). If conjugation with taurine is important for the protective effect of UDC, the MUDC may not be as able as TUDC to prevent TLC-induced cholestasis since it is poorly amidated by the liver. To answer this question, isolated livers of adult Sprague-Dawley rats were coinfused with MUDC (UDC, TUDC) and TLC. After 15 min, inflow rates of the bile acids were doubled. In further experiments taurine in excess was added to the coinfused bile acids. The uptake of bile acids was >90% in all groups, irrespective of whether they were perfused alone or in combination. Single perfusion of TLC caused a rapid decrease in bile flow. UDC and MUDC were hypercholeretic; TUDC moderately choleretic. During coinfusion experiments, TUDC not only completely abolished cholestasis but in addition increased bile flow and biliary bile acid secretion. UDC did prevent TLC cholestasis at the lower inflow rates. At high inflow rates, bile flow decreased significantly. Addition of taurine to this bile acid combination did not significantly improve the anticholestatic effect of UDC. At low and high infusion rates of MUDC, cholestasis induced by TLC was reduced very little. Cumulative bile flow over 30 min fell by approximately 70% as compared to that of singly perfused MUDC. Addition of taurine to the coinfused MUDC/TLC slightly, but less significantly, improved the anticholestatic effect of MUDC. Since MUDC is by far less protective than UDC (and TUDC) despite similar physiochemical properties, it is concluded that taurine conjugation of UDC seems to be a prerequisite to prevent TLC-induced cholestasis. The results imply that treatment of cholestatic liver diseases with taurine-conjugated UDC might be more appropriate than with unconjugated UDC in cases where taurine conjugation is defective or where taurine depletion has occurred.

Change of zonal bile acid processing after partial hepatectomy in the rat

The aim of this study was to analyze whether partial hepatectomy alters functional liver heterogeneity with respect to bile acid processing. One, 5 and 21 days after liver resection (approximately 80% of liver mass) in male Sprague-Dawley rats (300-400 g), isolated livers were perfused in either the antegrade or the retrograde direction, respectively, with 32 nmol cholate/min per g liver. Uptake, metabolism and biliary secretion kinetics were determined by bolus injection of 14C-cholate. Uptake and biliary recovery (within 30 min) of cholate were > 90% in all groups. One day postresection, liver mass had already doubled and it regenerated to over 80% 5 days after resection. Serum bile acid concentration increased rapidly, peaking 6 h after resection (176.7 +/- 28.5 mumol/l) (mean +/- SEM). Twenty-one days after resection it fell to control values (23.2 +/- 3.8 mumol/l). T25 (T50), the time (min) necessary to excrete 25% (50) of the bile acid load into bile, was strikingly different between periportal and pericentral cells of controls (1.8 vs 5.7 and 3.4 vs 8.1). Five days after resection this difference became smaller (1.4 vs 2.9 and 2.8 vs 5.5) due to accelerated biliary cholate secretion in pericentral cells. Pericentral cells of controls metabolized cholate more extensively to taurocholate (approximately 83%) and glycocholate (approximately 13%) than periportal cells of controls (65%, 10%), leading to a 5-fold higher proportion of unmetabolized cholate in periportal than pericentral cells (25% vs 5%). Five days after resection the percentage of taurocholate decreased significantly at the expense of an increased formation of glycocholate.(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern of bile acid regurgitation and metabolism during perfusion of the bile duct obstructed rat liver

Bile acid processing in the long-term, bile duct obstructed rat liver was studied ex vivo. Twenty four and 72 h, respectively, after bile duct obstruction the isolated liver was perfused with taurodeoxycholate (16 nmol/min per g liver) the bile duct still being closed. Uptake, metabolism and regurgitation profile were traced by bolus injection of tritium-labeled bile acid; in addition, concurrent histological changes were examined by light- and electron microscopy. Ligation caused dilatation of the intrahepatic ductular branches and increased the serum bile acid concentration to 740 +/- 75 microM (controls: 16 +/- 2.12), reaching its maximum within 24 h. At 16 nmol/min per g liver uptake rate was > 96% in controls and in bile duct obstructed rats. Maximal uptake rates (assessed separately) differed between controls and bile duct obstructed rats (700 nmol/min per g liver vs. 460). Controls excreted more than 80% of labeled bile acid in bile within 10 min after bolus injection. Biliary recovery of label was virtually completed after 30 min. In bile duct obstructed rats excretion of label back to the perfusate effluent (regurgitation) started quantitatively 5 min after bolus application and peaked between 10 and 40 min; after 80 min, effluent recovery was incomplete (about 60% of bolus injected). Biliary bile acids of controls consisted of about 20% taurodeoxycholate-metabolites; bile acids in the perfusate effluent of bile duct obstructed rats of about 55%. The major metabolite in all animal groups was taurocholate; minor metabolites were tauroursocholate, tauro-3 alpha,7 = 0,12 alpha-cholanoic acid and 3-sulfo-taurodeoxycholate. Histologically, inflammation and periportal edema were present after 1 day of bile duct obstruction. After 3 days, marked proliferation of bile ductules was the dominant histological feature. It is concluded that during initial bile duct obstruction, bile acid processing is not altered, although ultrastructural alterations occur early.

Flow injection determination of glucose, bile acid and ATP using immobilized enzyme reactor and chemiluminescent assay of NAD(P)H

We have developed a chemiluminescent flow injection method for analysis of bile acid, glucose and ATP using the chemiluminescent assay of NADH using 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS)/isoluminol(IL)/microperoxidase (m-POD) system and immobilized enzyme reactors such as 3 alpha-hydroxysteroid dehydrogenase, glucose-dehydrogenase, hexokinase and glucose-6-phosphate dehydrogenase. The standard curves were obtained in the range of 5-100 pmol for bile acid, 0.5-5.0 nmol for glucose and 10(-7)-10(-5) mol/L for ATP. The coefficient of variation for each assay was not more than 4.1% for bile acid, 2.3% for glucose and 5.3% for ATP, respectively.

Cholestasis, metabolism and biliary lipid secretion during perfusion of rat liver with different bile salts

The biological effects of bile acids depend largely upon their molecular structure. When bile acid uptake exceeds the maximal biliary secretory rate (SRm) cholestasis occurs. In order to characterize the influence of bile acid structure on its cholestatic potency we systematically studied SRm, maximal bile flow, maximal and cumulative phospholipid and cholesterol secretion with different taurine-conjugated tri-, di- and keto bile acids (Table I) in the isolated perfused rat liver. Bile acids with a high critical micellar concentration (CMC) promoted the greatest bile flow; a positive non-linear correlation between CMC and maximal bile flow was found. 3 alpha-Hydroxylated bile acids with a hydroxyl group in 6 alpha and/or 7 beta position and lacking a 12 alpha hydroxy group had a high SRm. SRm was not related to CMC or maximal bile flow, respectively. Phospholipids and cholesterol were secreted in a nearly fixed ratio of 12:1; a strong linear relationship could be observed. Cumulative phospholipid secretion over 48 min was significantly lower for non and poor micelle forming bile acids (TDHC and TUC) than for those with comparatively low CMC values (TUDC, TC, THC, THDC, TCDC) (70-140 vs. 210-450 nmol/g liver). At SRm all bile acids with good micelle forming properties showed a similar cumulative biliary lipid output. However, when biliary lipid output was related to 1 mumol bile acid secreted bile acids with a low SRm induced the highest lipid secretion (TCDC, TC). These data (1) demonstrate that a 6 alpha and/or a 7 beta hydroxy group on the steroid nucleus reduce cholestatic potency if the 12 alpha hydroxy group is absent, (2) suggest that in the case of micelle forming bile acids the total amount of phospholipids secreted in bile (depletion of cellular phospholipids) is associated with the occurrence of cholestasis whereby bile acids with a low SRm deplete the cellular phospholipid content at much lower bile acid concentrations than those with a higher SRm and (3) imply that bile acids with non and poor micelle forming properties (TDHC, TUC) presumably do not cause cholestasis (solely) by depletion of cellular phospholipids.

Loss of zonal heterogeneity and cell polarity in rat liver with respect to bile acid secretion after bile drainage

Functional liver heterogeneity depends on the current perihepatic environment. The effect of chronic bile drainage on hepatic secretion of bile acids in periportal and pericentral rat liver cells was studied. After 4 days of biliary drainage, rat livers were perfused in vitro in either forward (through the portal vein) or backward direction (through the vena cava) in single-pass arrangement with taurodeoxycholate (32 nmol.min-1.g liver-1). Tritium-labeled taurodeoxycholate (0.5 muCi) was injected as a pulse to determine uptake, biotransformation, and hepatic secretion. During bile drainage, bile flow fell from 1.8 microL.min-1.g liver-1 to approximately 0.6 microL.min-1.g liver-1. Bile acid secretion rate dropped from initially 50 nmol.min-1.g liver-1 to approximately 5 nmol.min-1.g liver-1 within 24 hours and remained at this level for the next 3 days. After bile drainage, liver histology was well preserved and was indistinguishable from controls. During liver perfusion of controls in both directions, bile flow exceeded 1 microL.min-1.g liver-1, whereas bile-drained animals demonstrated a bile flow between 0.4 and 0.6 microL.min-1.g liver-1. In contrast to controls, the drained-animal liver did not excrete label exclusively in bile but simultaneously excreted about one third back to the perfusate medium (regurgitation). Biliary bile acid recovery within the first 10 minutes after 3H-taurodeoxycholate bolus injection was 90% (of label taken up) in forward-perfused controls but only 40% in forward-perfused drained animals. Backward-perfused control and drained animals. Backward-perfused control and drained animals excreted about 20% in this time interval and did not differ significantly. T50, the time to excrete 50% of label taken up in bile or both bile and effluent, increased from 4.3 +/- 0.36 minutes (SD) in forward-perfused controls to 13.2 +/- 2.28 minutes in forward-perfused, drained animals. T50 of backward-perfused controls and backward-perfused drained animals did not differ significantly (17.8 +/- 1.75 minutes vs. 21.0 +/- 3.95 minutes). In conclusion, chronic bile drainage reduces liver heterogeneity with respect to velocity of bile acid excretion and cell polarity is lost with respect to hepatocellular translocation of bile acids.

Hepatic passage of bile acids increases oxygen uptake by perfused rat liver

It has been claimed that the hepatic passage of conjugated bile acids does not increase oxygen uptake by the isolated perfused rat liver. We studied a variety of bile acids in the single-pass perfused rat liver. All bile acids studied except taurocholate and tauro-beta-muricholate induced an increase in oxygen uptake of 2.1%-11.2% (baseline 2.54 +/- 0.57 mumoles/min per g liver). Raised values for oxygen uptake were not specifically associated with the critical micellar concentration of the bile acid, with bile acid uptake, or with bile acid secretion. It is postulated that bile acid toxicity may have an intracellular effect on hepatic oxygen uptake.

Taurohyocholate, taurocholate, and tauroursodeoxycholate but not tauroursocholate and taurodehydrocholate counteract effects of taurolithocholate in rat liver

The infusion of taurolithocholate (TLC) in vivo or in the isolated perfused liver of the rat causes cholestasis and cellular necrosis. In order to analyze the protective effect of bile salts differing in number and steric position of their hydroxy groups against TLC-induced cholestasis, isolated rat livers were perfused with taurocholate (TC), taurohyocholate (THC), tauroursocholate (TUC), taurodehydrocholate (TDHC), and tauroursodeoxycholate (TUDC) (16 and 32 mumol/l) with or without TLC (8 and 16 mumol/l). Bile flow, bile salt secretion, and the hydroxylation pattern of the bile salts secreted were analyzed. TLC caused complete cholestasis after 15 min of perfusion. All bile salts studied had a protective effect. THC, TC, and TUDC completely abolished the cholestasis induced by TLC while TUC did so only for the first 10 min. TDHC was protective only as long as it was biotransformed into hydroxyoxo bile salts. Coinfusion of bile salts did not influence uptake of TLC (greater than or equal to 93% of dose). Differences were found regarding the amount of TLC biotransformed (% of uptake): TC 50%; THC 32%; TUDC 36%; TUC 20%. Light microscopy revealed cellular necrosis, and dilated canaliculi were found in livers perfused with TLC only or in combination with TUC or TDHC, while the other bile salts prevented these changes. We conclude that bile salts with low micelle-forming capacity have little protective effect against TLC-induced cholestasis. These bile salts induce less biotransformation of TLC than TC, THC, and TUDC. The protective effect is not dependent on the hydrocholeretic effect of the added bile salt and is not due to an uptake inhibition.

Tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and toxicity in rat liver

Ursodeoxycholate has been advocated for the treatment of cholestatic liver diseases. The coinfusion of tauroursodeoxycholate with taurolithocholate in the perfused rat liver completely prevented the decrease of bile flow and the increase of oxygen uptake found with taurolithocholate only. Bile flow and bile salt secretion were increased with the coinfusion of both bile acids as compared with the infusion of tauroursodeoxycholate only (+4.30 microliters/g liver per 30 min) with 16 and 32 mumol/l tauroursodeoxycholate (+1.55 microliters/g liver per 30 min with 80 and 160 mumol/l). Morphological examination revealed a 50% decrease of the number of necrotic cells in the periportal area. Tauroursodeoxycholate did not inhibit the uptake of taurolithocholate, but increased its transcellular passage and biotransformation. Thus, tauroursodeoxycholate prevents taurolithocholate-induced cholestasis and liver cell toxicity probably by an intracellular mechanism.