Effect of tamoxifen and raloxifene on the conjugation of bile acids with taurine and glycine in ovariectomized rats

The selective estrogen receptor modulators tamoxifen and raloxifene represent a major therapeutic advance for clinical practice. Unlike estrogens, which are uniformly agonists, tamoxifen and raloxifene exert selective agonistic or antagonistic effects on various estrogen target tissues. The aim of the study was to evaluate the influence of tamoxifen and raloxifene on the conversion of cholesterol to bile acids in estrogen deficiency in rats. The study included 40 female Wistar rats. The animals were divided into four groups: sham operated control, ovariectomized control, ovariectomized rats treated with tamoxifen ovariectomized rats treated with raloxifene. After 42 days of drug administration, bile was collected under anesthesia after administration of radioactive 4-(14)C cholesterol. Bile was assayed for concentration of (14)C bile acids conjugated with taurine and glycine after thin-layer chromatography separation by the use of isotopic technique. In rats treated with tamoxifen and raloxifene, the statistically significant increase in concentration of bile acids conjugated with glycine was observed as compared to ovariectomized animals from control group. Moreover, in rats treated with tamoxifen the concentration of bile acids conjugated with taurine significantly increased. The results of the present study suggest that tamoxifen and raloxifene increase the concentrations of conjugated bile acids in bile.     

Comparative evaluation of the hypolipidemic effects of coconut water and lovastatin in rats fed fat–cholesterol enriched diet

The coconut water presents a series of nutritional and therapeutic properties, being a natural, acid and sterile solution, which contains several biologically active components, l-arginine, ascorbic acid, minerals such as calcium, magnesium and potassium, which have beneficial effects on lipid levels. Recent studies in our laboratory showed that both tender and mature coconut water feeding significantly (P < 0.05) reduced hyperlipidemia in cholesterol fed rats [Sandhya, V.G., Rajamohan, T., 2006. Beneficial effects of coconut water feeding on lipid metabolism in cholesterol fed rats. J. Med. Food 9, 400–407]. The current study evaluated the hypolipidemic effect of coconut water (4 ml/100 g body weight) with a lipid lowering drug, lovastatin (0.1/100 g diet) in rats fed fat–cholesterol enriched diet ad libitum for 45 days. Coconut water or lovastatin supplementation lowered the levels of serum total cholesterol, VLDL + LDL cholesterol, triglycerides and increased HDL cholesterol in experimental rats (P < 0.05). Coconut water feeding decreased activities of hepatic lipogenic enzymes and increased HMG CoA reductase and lipoprotein lipase activity (P < 0.05). Incorporation of radioactive acetate into free and ester cholesterol in the liver were higher in coconut water treated rats. Coconut water supplementation increased hepatic bile acid and fecal bile acids and neutral sterols (P < 0.05). Coconut water has lipid lowering effect similar to the drug lovastatin in rats fed fat–cholesterol enriched diet.     

Taurine prevents high‐fat diet‐induced‐hepatic steatosis in rats by direct inhibition of hepatic sterol regulatory element‐binding proteins and activation of AMPK

This study investigated if the protective effect of taurine against high fat diet‐induced hepatic steatosis involves modulating the hepatic activity of 5' AMP‐activated protein kinase (AMPK) and levels/activity of the sterol regulatory element‐binding proteins‐1/2 (SREBP1/2). Rats were divided into four groups (n = 12/group) as (a) STD, fed standard diet (3.85 kcal/g); (b) STD + taurine (500 mg/kg); (c) HFD, fed HFD (4.73 kcal/g); and (d) HFD + taurine. All treatments were conducted for 12 weeks. Independent of food intake or modulating glucose or insulin levels, taurine administration to STD and HFD‐fed rats significantly lowered weekly weight gain and the accumulation of the retroperitoneal, visceral and subcutaneous fats. In both groups, taurine also reduced serum and hepatic levels of triglycerides and cholesterol and reduced hepatic mRNA and protein levels of fatty acid synthase (FAS), acetyl CoA carboxylase‐1 (ACC‐1), HMG‐CoA‐reductase and HMG‐CoA synthetase. In control rats only, taurine reduced hepatic levels of mature forms of sterol regulatory element‐binding proteins (SREBP)‐1/2. In HFD‐fed rats, taurine reduced SREBP‐1/2 precursor and mature forms in the livers of HFD‐fed rats. Besides, taurine significantly increased levels of glutathione (GSH), the activity of superoxide dismutase (SOD), and the activity of AMPK and its downstream β‐oxidation genes including peroxisome proliferator‐activated receptor‐α (PPAR‐α) and carnitine palmitoyltransferase (CPT‐1) in the livers of both the control and HFD‐fed rats. In conclusion, taurine protects against HFD‐induced hepatic steatosis stimulating antioxidant levels, and concomitant stimulating hepatic β‐oxidation and suppressing lipid synthesis, mediated by activation of AMPK and suppression of SREBP‐1.     

Ebselen Protects against the Reduction in Levels of Drug‐Metabolizing Enzymes in Livers of Rats with Deoxycholic Acid‐Induced Liver Injury

Abstract: Ebselen is a seleno‐organic compound that inhibits oxidative stress by lipid peroxidation through a glutathione peroxidase‐like activity. We studied the effect of ebselen on the expression of hepatic drug‐metabolizing enzymes in rats with deoxycholic acid‐induced liver injury. Hydrophobic bile acids, such as deoxycholic acid, are known to cause cholestatic liver injury, and it was reported that expression of hepatic cytochrome P‐450 (CYP) was reduced by deoxycholic acid administration in rats. Hydrophobic bile acids induce lipid peroxidation in the liver, and this may be one mechanism of the development of liver injury. In the present study, we investigated the effect of ebselen (30 mg/kg/day for 10 days) on rats ingesting deoxycholic acid (1% of diet for 10 days). Deoxycholic acid decreased levels of CYP1A1, 2B1, 2E1 and 3A2 to 34, 58, 62 and 37% of control values, respectively, and increased serum alkaline phosphatase (ALP) and alanine aminotransferase (ALT) activities to 1.8 and 8.6 times the levels of controls, respectively. Administration of ebselen with deoxycholic acid prevented the decreases in levels of CYP1A1 and 3A2 (86 and 65% of control, respectively) and the increases in serum ALP and ALT activities (1.4 and 1.9 times of control, respectively) caused by deoxycholic acid. These results indicate that ebselen may have a protective effect against hydrophobic bile acid‐induced liver injury.     

Polysaccharide-rich red algae (Gelidium amansii) hot-water extracts ameliorate the altered plasma cholesterol and hepatic lipid homeostasis in high-fat diet-fed rats

We have demonstrated that red algae Gelidium amansii (GA) hot-water extract (GHE) is a polysaccharide-rich fraction, containing 68.54% water-soluble indigestible carbohydrate polymers; the molecular weight of major polysaccharide is 892. Here, we investigated the mechanisms of GHE on plasma and hepatic lipid metabolisms in high-fat (HF) diet-fed rats. Rats were divided into: normal diet group, HF-diet group, HF-diet+5% GHE group, and HF-diet+1% cholestyramine group. GHE supplementation for 8 weeks significantly decreased plasma cholesterol, LDL-C, and VLDL-C levels and increased the fecal triglyceride and bile acid excretion in HF diet-fed rats. GHE group has lower lipid contents in the liver and adipose tissues. GHE supplementation decreased the activities of acetyl-CoA carboxylase, fatty acid synthase, and HMG-CoA reductase in the livers. The levels of increased phosphorylated AMP-activated protein kinase (AMPK), peroxisome proliferator activated receptor (PPAR)-α, farnesoid-X receptor (FXR), low density lipoprotein receptor (LDLR), and cytochrome P450-7A1 (CYP7A1) protein expression, and the decreased PPAR-γ protein expression in the livers were observed in GHE group. These results suggest that GHE supplementation is capable of interfering in cholesterol metabolism and increasing hepatic LDLR and CYP7A1 expression to decrease blood cholesterol, and activating FXR and AMPK to inhibit lipogenic enzyme activities and reduce the hepatic lipid accumulation.     

Gender, but not CYP7A1 or SLCO1B1 polymorphism, affects the fasting plasma concentrations of bile acids in human beings

Abstract: Cholesterol 7α‐hydroxylase (CYP7A1) is the rate‐limiting enzyme of bile acid production in human beings, and organic anion‐transporting polypeptide 1B1 (OATP1B1) may influence bile acid hepatic uptake and cholesterol and bile acid synthesis rate. Our purpose was to investigate the effects of gender and CYP7A1 and SLCO1B1 polymorphisms on the fasting plasma concentrations of bile acids, bile acid synthesis marker and total cholesterol in a Finnish population. Fasting plasma concentrations of 16 endogenous bile acids, their synthesis marker (7α‐hydroxy‐4‐cholesten‐3‐one) and total cholesterol were measured in 243 samples from 143 healthy volunteers. The volunteers were genotyped for 6 haplotype‐tagging single‐nucleotide polymorphisms (SNPs) of CYP7A1 and two functionally relevant SNPs in SLCO1B1. The mean plasma concentrations of chenodeoxycholic acid, glycochenodeoxycholic acid, ursodeoxycholic acid and glycoursodeoxycholic acid were 61–111% higher in men than in women (P ≤ 0.001). Accordingly, the mean concentration of total bile acids was 51% higher in men than in women (P = 0.001). The CYP7A1 rs8192879 and rs1023652 SNPs were associated with deoxycholic acid and hyodeoxycholic acid concentrations, respectively, but the associations were not significant after correction for multiple testing. None of the six CYP7A1 SNPs was associated with the plasma concentrations of cholesterol or 7α‐hydroxy‐4‐cholesten‐3‐one. SLCO1B1 genotype was associated with total plasma cholesterol concentration only, but the association was not significant after correction for multiple testing. In general, the gender contributes substantially more to variation in fasting plasma bile acid concentrations than CYP7A1 or SLCO1B1 polymorphism do. Common genetic variability in CYP7A1 is unlikely to play a significant role in cholesterol metabolism and bile acid homeostasis under normal physiological conditions.     

Pharmacokinetics of ursodeoxycholic acid in rat

The pharmacokinetic behaviour and metabolism of ursodeoxycholic acid (UDCA) have been studied in the rat. After oral administration of both 3H-labelled (4 muCi/kg body wt) and unlabelled (20 mg) UDCA, UDCA appeared in serum almost entirely in conjugated form (taurine conjugated); UDCA was present in bile mostly as taurine conjugated; the more relevant metabolite is 3 alpha,6 alpha, 7 beta-trihydroxycholanoic acid which represents 10% of the total bile acid pool. UDCA increased bile flow and selectively decreased biliary cholesterol secretion, while phospholipid secretion was unaffected. Faecal UDCA excretion was 15-20% while the urinary extraction was 1.5% during 24 h. The data show that UDCA, when administered in high dose, is promptly secreted into bile almost entirely metabolized to tauroursodeoxycholic acid, where it (1) desaturates the cholesterol in bile, (2) exerts choleretic properties.     

Roles of endogenous and exogenous taurine and glycine in the formation of conjugated bile acids: analyses using freshly isolated and primary cultured rat hepatocytes

The regulatory roles of intracellular taurine and glycine, transported and biosynthesized in hepatocytes, on the formation of conjugated bile acids were studied using freshly isolated hepatocytes (fresh hepatocytes) and hepatocytes in primary culture (cultured hepatocytes). Transported taurine significantly increased the rate of taurocholic acid formation both in fresh hepatocytes and cultured hepatocytes. Similarly, the addition of cysteine and hypotaurine, which were metabolically converted to taurine in hepatocytes, facilitated the formation of taurocholic acid in these cells. On the other hand, exogenous glycine into the incubation medium had no effect on the formation of glycocholic acid both in fresh and cultured hepatocytes. In contrast, the addition of serine and threonine, which are metabolically converted to glycine in hepatocytes, significantly increased the formation of glycocholic acid in fresh hepatocytes, although little effect of the additions of serine and threonine on the formation of glycocholic acid was noted in the case of cultured hepatocytes. The present results indicate that the formation of taurine-conjugated bile acids in hepatocytes is maintained by both transported and intracellularly formed taurine in hepatocytes, while that of glycine-conjugated bile acids is regulated by glycine formed within hepatocytes, but not by transported glycine.     

2,3,7,8‐Tetrachlorodibenzo‐p‐dioxin (TCDD) Increases Bilirubin Formation but Hampers Quantitative Hepatic Conversion of Biliverdin to Bilirubin in Rats with Wild‐Type AH Receptor

In haem degradation, haem oxygenase‐1 (HO‐1) first cleaves haem to biliverdin, which is reduced to bilirubin by biliverdin IXα reductase (BVR‐A). The environmental pollutant 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) causes hepatic accumulation of biliverdin in moderately TCDD‐resistant line B (Kuopio) rats. Using line B and two TCDD‐sensitive rat strains, the present study set out to probe the dose–response and biochemical mechanisms of this accumulation. At 28 days after exposure to 3–300 μg/kg TCDD in line B rats, already the lowest dose of TCDD tested, 3 μg/kg, affected serum bilirubin conjugates, and after doses ≥100 μg/kg, the liver content of bilirubin, biliverdin and their conjugates (collectively ‘bile pigments’) as well as HO‐1 was elevated. BVR‐A activity and serum bile acids were increased only by the doses of 100 and 300 μg/kg TCDD, respectively. Biliverdin conjugates correlated best with biliverdin suggesting it to be their immediate precursor. TCDD (100 μg/kg, 10 days) increased hepatic bilirubin and biliverdin levels also in TCDD‐sensitive Long‐Evans (Turku/AB; L‐E) rats. Hepatic bilirubin and bile acids, but not biliverdin, were increased in feed‐restricted L‐E control rats. In TCDD‐sensitive line C (Kuopio) rats, 10 μg/kg of TCDD increased the body‐weight‐normalized biliary excretion of bilirubin. Altogether, the results suggest that at acutely toxic doses, TCDD induces the formation of bilirubin in rats. However, concurrently, TCDD seems to hamper the quantitative conversion of biliverdin to bilirubin in line B and L‐E rats' liver. Biliverdin conjugates are most likely formed as secondary products of biliverdin.     

Hypocholesterolemic effect of bile acid sulfonate analogs in hamsters

We studied the effects of bile acid sulfonate analogs, namely, 3alpha,7alpha,12alpha-trihydroxy-5beta-cholane-24-sulfonate (C-sul), 3alpha,7alpha-dihydroxy-5beta-cholane-24-sulfonate (CDC-sul), and 3alpha,7beta-dihydroxy-5beta-cholane-24-sulfonate (UDC-sul), on serum and liver cholesterol levels, cholesterol 7alpha-hydroxylase activity, and biliary bile acid composition in hamsters fed cholesterol. Of the three analogs studied, UDC-sul slightly but significantly decreased free, esterified, and total cholesterol concentrations in the serum. UDC-sul and CDC-sul reduced liver total cholesterol levels by 25% and 18%, respectively, particularly in the esterified cholesterol fraction. Analysis of biliary bile acids showed the presence of the administered analogs, indicating that sulfonate analogs efficiently participate in enterohepatic cycling. The proportion of cholic acid was increased in all groups fed sulfonate analogs, but the ratio of glycine to taurine conjugated bile acids (G/T) was elevated only in UDC-sul feeding hamsters. There was no significant change in cholesterol 7alpha-hydroxylase activity in hamsters fed C-sul or CDC-sul, while UDC-sul slightly stimulated the enzyme activity compared to the control. The UDC-sul induced decrease in serum and liver cholesterol concentrations may be secondary to enhanced bile acid synthesis. This is supported by the increased cholesterol 7alpha-hydroxylase activity and elevated G/T ratio in biliary bile acids observed following UDC-sul administration.     

Mechanisms responsible for the altered pharmacokinetics of Bosentan: analysis utilizing rats with bile duct ligation‐induced liver dysfunction

The purpose of this study was to evaluate the mechanisms responsible for the pharmacokinetic variability of bosentan utilizing rats with liver dysfunction induced by 7‐day bile duct ligation (BDL). Bosentan was administered intravenously at a constant infusion rate (I) of 24, 40 or 60 µg/min/kg. The blood bosentan concentration (BBC) following infusion was measured by HPLC, and apparent clearance (CL) of the drug was estimated as I/BBC. The CL values in normal rats were 30.5 and 19.3 ml/min/kg at infusion rates of 24 and 60 µg/min/kg, respectively, suggesting non‐linear pharmacokinetics of bosentan. The BBC in BDL rats was much higher than that in normal rats, and the CL values in BDL rats were 3.80 and 3.08 ml/min/kg at infusion rates of 24 and 60 µg/min/kg, respectively. The CL value of bosentan at an infusion rate of 40 µg/min/kg in normal rats was decreased significantly by the coadministration of taurocholic acid or bilirubin. In addition, the hepatic mRNA expression of CYP2C6, CYP3A2, Oatp1a1, Oatp1a4 and Oatp1b2 in BDL rats decreased to 77.6%, 34.0%, 65.4%, 84.8% and 44.2% of that in normal rats, respectively. These results suggested that bile acids and/or bilirubin accumulated in BDL rat plasma inhibited the hepatic uptake of bosentan, and that the decreased bosentan clearance in BDL rats was caused at least partly by the impaired expression of hepatic drug‐metabolizing enzymes and uptake transporters. Moreover, because the pharmacokinetics of bosentan was non‐linear at the tested doses, the increased BBC in BDL rats might further induce the saturation of hepatic uptake and/or metabolism of bosentan. Copyright © 2009 John Wiley & Sons, Ltd.     

Long-term feeding of red algae (Gelidium amansii) ameliorates glucose and lipid metabolism in a high fructose diet-impaired glucose tolerance rat model

This study was designed to investigate the effect of Gelidium amansii (GA) on carbohydrate and lipid metabolism in rats with high fructose (HF) diet (57.1% w/w). Five-week-old male Sprague-Dawley rats were fed a HF diet to induce glucose intolerance and hyperlipidemia. The experiment was divided into three groups: (1) control diet group (Con); (2) HF diet group (HF); and (3) HF with GA diet group (HF + 5% GA). The rats were fed the experimental diets and drinking water ad libitum for 23 weeks. The results showed that GA significantly decreased retroperitoneal fat mass weight of HF diet-fed rats. Supplementation of GA caused a decrease in plasma glucose, insulin, tumor necrosis factor-α, and leptin. HF diet increased hepatic lipid content. However, intake of GA reduced the accumulation of hepatic lipids including total cholesterol (TC) and triglyceride contents. GA elevated the excretion of fecal lipids and bile acid in HF diet-fed rats. Furthermore, GA significantly decreased plasma TC, triglyceride, low density lipoprotein plus very low density lipoprotein cholesterol, and TC/high density lipoprotein cholesterol ratio in HF diet-fed rats. HF diet induced an in plasma glucose and an impaired glucose tolerance, but GA supplementation decreased homeostasis model assessment equation-insulin resistance and improved impairment of glucose tolerance. Taken together, these results indicate that supplementation of GA can improve the impairment of glucose and lipid metabolism in an HF diet-fed rat model.     

Studies on the metabolism of arylacetic acids. 7. The influence of varying dose size upon the conjugation pattern of 2-naphthylacetic acid in the guinea pig,mouse and hamster

1. The influence of dose size upon the metabolic conjugation of 2-naphthylacetic acid with various amino acids and glucuronic acid has been studied in the guinea pig, mouse and hamster.

2. Guinea pigs conjugated 2-naphthylacetic acid with glycine and glucuronic acid.

3. Mice conjugated 2-naphthylacetic acid with glycine, taurine and glucuronic acid. Taurine conjugation had the highest capacity, and both this and the glycine mechanism were saturated at doses above 100 mg/kg.

4. Hamsters utilized glutamine, glycine, taurine and glucuronic acid for the conjugation of 2-naphthylacetic acid. No conjugation pathway was saturated by doses up to 200 mg/kg.

5. The thus-far unique ability of 2-naphthylacetic acid to evoke multiple amino acid conjugations, using the taurine and glutamine mechanisms hitherto unknown in these species, appears to be due to its affinity for previously unrecognized enzyme systems, rather than to saturation of ‘normal’ pathways revealing novel routes at high doses.     

Altered bile acid metabolism in alloxan diabetic rats

Changes of cholesterol, phospholipid, triglyceride or bile acid levels in serum liver, bile and feces after the treatment with alloxan were examined in Wistar strain male rats. Serum cholesterol, phospholipid and triglyceride levels and liver cholesterol level markedly increased but liver phospholipid and triglyceride levels remained unchanged. The lipid levels in serum very low density and low density lipoproteins were elevated but those in high density lipoprotein were not. Bile flow was not changed but biliary secretion of cholesterol, phospholipid and bile acids markedly increased. Among the biliary bile acid components, cholic acid markedly increased but the amount of chenodeoxycholic acid was similar to that of normal rats. Fecal excretion of deoxycholic acid increased but that of lithocholic and hyodeoxycholic acids decreased, and alpha, beta- and omega-muricholic acids did not change, thus, the total amount of fecal bile acids remained unchanged. Hepatic cholesterol synthesis was markedly depressed, while cholesterol 7 alpha-hydroxylase activity did not change and cytochrome P-450 content was elevated by about 40%. From such evidence, it was apparent that synthesis of cholic acid increased while that of chenodeoxycholic acid decreased and the total amount of bile acids synthesized did not change in the diabetic rats. Furthermore, marked increase of the pool size of cholic acid and hepatic secretion of cholic acid stimulated the absorption of lipids and produced a hyperlipidemia in the diabetic rats.     

Modulation of bile acids induced by paraquat in rabbits

Rabbit bile was examined for changes in composition induced by paraquat. Paraquat was administered intraperitoneally and changes in bile components were monitored by high performance liquid chromatography. Alterations in the ratios of total glycine/taurine conjugated bile acids (TGC/TTC), cholic acid/deoxycholic acid (CA/DC), cholic acid/chenodeoxycholic acid (CA/CDC) and cholic acid/cholesterol (CA/CH) were measured as an index of paraquat toxicity. A statistically significant increase in the ratio of TGC/TTC was observed, while CA/DC, CA/CDC and CA/CH showed a decrease. Phospholipids, protein, sugar, bilirubin, beta-carotene, vitamin A and vitamin E in the bile and serum of the experimental animals were also monitored. In bile, the levels of cholesterol, phospholipids, protein, sugar, and total bile acids increased while the levels of the antioxidants beta-carotene, vitamin A and vitamin E decreased. A decrease in the bilirubin content of the bile was also observed. These modifications may be useful clinically for assessment of paraquat toxicity.     

Comparison of the choleretic properties of bile acids

The choleretic properties of cholic, chenodeoxycholic, and deoxycholic acid and their taurine and glycine conjugates were compared to their ability to form micelles. It has previously been concluded that deoxycholate has the lowest critical micellar concentration; chenodeoxycholate is slightly higher and cholic is much higher. Conjugation with glycine and taurine has little or no effect on the critical micelle concentration. Since the choleretic properties of bile salts are thought to be directly proportional to their osmotic activities, one might suspect that deoxycholic acid would be the least choleretic, chenodeoxycholic slightly more choleretic and cholic much more choleretic, with little difference between the conjugated and unconjugated forms. However, in the present study, cholic, chenodeoxycholic and taurocholic acid produced similar increases in bile flow (450–700 μl/kg) after an equimolar dose (55 μM/kg). Except for the conjugation of deoxycholic acid with taurine, conjugation of these bile acids with glycine or taurine always decreased the choleretic properties of the bile acids. Therefore, it has been concluded that there is not a good correlation between the in vitro osmotic properties of bile acids and their ability to increase bile flow.     

Curcumin Attenuates Diet‐Induced Hepatic Steatosis by Activating AMP‐Activated Protein Kinase

Curcumin is a well‐known component of traditional turmeric (Curcuma longa), which has been reported to prevent obesity and diabetes. However, the effect of curcumin on hepatic lipid metabolism remains unclear. The aim of this study was to examine the effects of curcumin on hepatic steatosis in high‐fat/cholesterol diet (HFD)‐induced obese mice. Male C57BL/6J mice were fed a normal diet (ND), HFD or HFD with 0.15% curcumin (HFD+C) for 11 weeks. We found that curcumin significantly lowered the body‐weight and adipose tissue weight of mice in the HFD+C group compared with the findings for the HFD group (p < 0.05). The levels of total cholesterol, fasting glucose and insulin in serum were decreased, and HFD‐induced impairment of insulin sensitivity was improved by curcumin supplementation (p < 0.05). Curcumin protected against the development of hepatic steatosis by reducing hepatic fat accumulation. Moreover, curcumin activated AMP‐activated protein kinase (AMPK) and elevated the gene expression of peroxisome proliferator‐activated receptor alpha. By contrast, curcumin suppressed the HFD‐mediated increases in sterol regulatory element‐binding protein‐1, acetyl‐CoA carboxylase 1, fatty acid synthase and cluster of differentiation 36 expression. Taken together, these findings indicate that curcumin attenuates HFD‐induced hepatic steatosis by regulating hepatic lipid metabolism via AMPK activation, suggesting its use as a therapeutic for hepatic steatosis.     

Studies on the metabolism of arylacetic acids. 7. The influence of varying dose size upon the conjugation pattern of 2-naphthylacetic acid in the guinea pig, mouse and hamster

1. The influence of dose size upon the metabolic conjugation of 2-naphthylacetic acid with various amino acids and glucuronic acid has been studied in the guinea pig, mouse and hamster. 2. Guinea pigs conjugated 2-naphthylacetic acid with glycine and glucuronic acid. 3. Mice conjugated 2-naphthylacetic acid with glycine, taurine and glucuronic acid. Taurine conjugation had the highest capacity, and both this and the glycine mechanism were saturated at doses above 100 mg/kg. 4. Hamsters utilized glutamine, glycine, taurine and glucuronic acid for the conjugation of 2-naphthylacetic acid. No conjugation pathway was saturated by doses up to 200 mg/kg. 5. The thus-far unique ability of 2-naphthylacetic acid to evoke multiple amino acid conjugations, using the taurine and glutamine mechanisms hitherto unknown in these species, appears to be due to its affinity for previously unrecognized enzyme systems, rather than to saturation of 'normal' pathways revealing novel routes at high doses.     

Effect of taurine supplementation on cytochrome P450 2E1 and oxidative stress in the liver and kidneys of rats with streptozotocin-induced diabetes

To investigate whether diabetes-induced alterations of CYP2E1 and oxidative stress can be modulated by dietary taurine supplementation, male Wistar rats were divided into non-diabetic, diabetic, and diabetic taurine-supplemented groups (administered at 2% in the drinking water). Increased levels of CYP2E1-catalyzed p-nitrophenol hydroxylation were found in liver and kidney microsomes of rats with STZ-induced diabetes compared to those of non-diabetic control rats. Immunoblot and RT-PCR analyses of CYP2E1 protein and mRNA levels in the liver and kidneys showed the same trend as with enzyme activities. Taurine supplementation significantly decreased the enzyme activity and expression (protein and mRNA) of CYP2E1 in diabetic rat kidneys. Plasma β-hydroxybutyrate concentration was significantly reduced in taurine-treated diabetic rats. The induction of heme oxygenase-1 mRNA was suppressed by taurine treatment in diabetic rat kidneys. An increase in reduced glutathione (GSH) and a higher ratio of reduced to oxidized glutathione (GSH/GSSG) together with lower values of thiobarbituric acid-reactive substances (TBARS) were observed in the kidneys of taurine-treated diabetic rats. However, taurine supplementation caused only a slight or insignificant effect on these alternations in the liver of diabetic rats. Our results show dietary taurine may reduce CYP2E1 expression and activity, and oxidative stress in kidneys of diabetic rats.     

2-Fluoro-beta-alanine, a previously unrecognized substrate for bile acid coenzyme A:amino acid:N-acyltransferase from human liver

Our laboratory has demonstrated recently that conjugates of 2-fluoro-beta-alanine (FBAL) and bile acids are the major biliary metabolites of 5-fluorouracil (FUra) in cancer patients. Bile acids are normally conjugated with glycine or taurine, and therefore the identification of the FBAL-bile acid conjugates suggested that FBAL may also be a substrate for the bile acid conjugating enzyme, bile acid CoA:amino acid:N-acyltransferase. Enzyme activity detected using glycine and taurine as substrates was purified 8-fold from human liver cytosol using a DEAE-cellulose column. This preparation when tested for its activity towards beta-alanine and FBAL using cholyl CoA as the bile acid substrate only catalyzed the formation of FBAL-cholate. beta-Alanine was not a substrate. Confirmation of FBAL-cholate as the enzymatic product was demonstrated by (1) coelution of the product of this reaction on HPLC with authentic FBAL-cholate, (2) specific hydrolysis of this product by cholylglycine hydrolase, and (3) molecular weight of the product (497) being identical to that of the authentic FBAL-cholate. Kinetic experiments demonstrated that the enzyme had an affinity for FBAL (Km 1.45 mM) comparable to taurine (Km 1.32 mM), but greater than glycine (Km 6.45 mM). Formation of FBAL-cholate was inhibited competitively by taurine (Ki 1.27 mM) and glycine (Ki 4.47 mM), suggesting that a single enzyme is responsible for conjugation of glycine, taurine and FBAL with bile acids. These data indicate that the formation of the FBAL-bile acid conjugates in patients receiving FUra results from high affinity of the bile acid conjugating enzyme for FBAL.