Effects of barley variety,dietary fiber and β-glucan content on bile acid composition in cecum of rats fed low- and high-fat diets

Diet-induced obesity and insulin resistance have been linked to changes in bile acid (BA) profiles, which in turn are highly dependent on the dietary composition and activity of the gut microbiota. The objective of the present study was to investigate whether the type and level of fiber had an effect on cecal BA composition when included in low- and high-fat diets. Groups of rats were fed two barley varieties, which resulted in three test diets containing three levels of β-glucans and two levels of dietary fiber. BAs were preconcentrated using hollow fiber liquid-phase microextraction and quantified by gas chromatography. The amount of the secondary BAs, lithocholic-, deoxycholic- and hyodexycholic acids was generally higher in groups fed high-fat diets compared with corresponding acids in groups fed low-fat diets (P<.05). In contrast, most of the primary and the secondary BAs, ursodeoxycholic acid and β- and ω-muricholic acids, were two to five times higher (P<.05) in groups fed low-fat diets than in groups fed high-fat diets. This was particularly true for groups fed the highest level of β-glucans and in some cases also the medium level. The BA profile in the gut was strongly dependent on the amount and type of dietary fiber in the diet, which may be useful in the prevention/treatment of diseases associated with changes in BA profiles.     

Physiological effects of chicory root preparations with various levels of fructan and polyphenolic fractions in diets for rats

The experiment was aimed at studying the effects of easily fermentable oligosaccharides and phenolic compounds from chicory root meal (CRM) on the fermentative processes in the caecum, the antioxidative status and the lipoprotein profile of rats. Five different diets were fed ad libitum to 40 Wistar rats (eight animals per group, individually housed): a control group (C); group PCM (10% processed CRM, deprived of polyphenolic fraction); group PCMO (8% processed CRM and 1.6% oligofructose); group UCM (10% unprocessed CRM); and group FP (8.3% fructan-polyphenol concentrate from CRM). Diets PCM, PCMO, UCM and FP induced favourable metabolic changes in the caecum, blood lipid profile and the antioxidative status of the body. In the caecum, the experimental diets increased the production of volatile fatty acids (VFA) and acidification of digesta as well as a decrease in the ammonia concentration and bacterial beta-glucuronidase activity. In blood serum, the total cholesterol concentration was reduced and, simultaneously, the proportion of HDL in the total cholesterol concentration was increased. The presence of the polyphenolic fraction in the unprocessed meal (diets UCM and FP) evoked a significant increase in the total antioxidative status in blood serum. Dietary fibre and the polyphenolic fraction present in diet UCM and the FOS-polyphenol concentrate in diet FP did not exhibit an antagonistic activity regarding the physiological parameters analysed, except for in the intensity of caecal fermentation. The results of the experiment point to the benefits of dietary supplementation with chicory preparations containing both prebiotic saccharides and polyphenolic compounds, which enable us to take advantage of the physiological traits of both components.     

Dietary fiber-rich colloids from apple pomace extraction juices do not affect food intake and blood serum lipid levels, but enhance fecal excretion of steroids in rats

The aim of this study was to investigate the effects of colloids isolated from apple pomace extraction juices (so-called B-juices) produced by enzymatic liquefaction on food intake, levels of blood serum lipids, and fecal excretion of bile acids (BA) and neutral sterols (NS) in vivo. Ten male Wistar rats per group were fed diets containing either no apple dietary fiber (DF) (control), a 5% supplementation with juice colloids, or an alcohol-insoluble substance (AIS) from apples for 6 weeks. Apple DF in diets led to lower weight gain in rats fed with B-juice colloids (P< 0.05). For these rats, food intake was not affected but was highest with feeding AIS (10% more than control) to cover energy requirements. The supplementation of diet with apple DF from extraction juices or AIS had minor effects on blood serum lipids. In rats fed either juice colloids or AIS, up to 30% (5.31 micromol/g dry weight) and 88% (7.69 micromol/g dry weight) more primary BA were excreted in feces, respectively, as compared to that in the control group (4.10 micromol/g dry weight) (P < 0.05). In cecal contents, a 15% (juice colloids) to 37% (AIS) increase in primary BA was found. In contrast, concentrations of secondary BA were lower in feces of test groups (P < 0.05). Excretion of total BA and NS was higher in rats fed apple DF (P < 0.05). Our study is the first to prove that there are beneficial physiologic effects of apple DF isolated from pomace extraction juices produced by enzymatic liquefaction. These results may help to develop such innovative juice products that are rich in DF of fruit origin for diminishing the lack of DF intake.     

Physiological effects of chicory root preparations with various levels of fructan and polyphenolic fractions in diets for rats

The experiment was aimed at studying the effects of easily fermentable oligosaccharides and phenolic compounds from chicory root meal (CRM) on the fermentative processes in the caecum, the antioxidative status and the lipoprotein profile of rats. Five different diets were fed ad libitum to 40 Wistar rats (eight animals per group, individually housed): a control group (C); group PCM (10% processed CRM, deprived of polyphenolic fraction); group PCMO (8% processed CRM and 1.6% oligofructose); group UCM (10% unprocessed CRM); and group FP (8.3% fructan-polyphenol concentrate from CRM). Diets PCM, PCMO, UCM and FP induced favourable metabolic changes in the caecum, blood lipid profile and the antioxidative status of the body. In the caecum, the experimental diets increased the production of volatile fatty acids (VFA) and acidification of digesta as well as a decrease in the ammonia concentration and bacterial β-glucuronidase activity. In blood serum, the total cholesterol concentration was reduced and, simultaneously, the proportion of HDL in the total cholesterol concentration was increased. The presence of the polyphenolic fraction in the unprocessed meal (diets UCM and FP) evoked a significant increase in the total antioxidative status in blood serum. Dietary fibre and the polyphenolic fraction present in diet UCM and the FOS-polyphenol concentrate in diet FP did not exhibit an antagonistic activity regarding the physiological parameters analysed, except for in the intensity of caecal fermentation. The results of the experiment point to the benefits of dietary supplementation with chicory preparations containing both prebiotic saccharides and polyphenolic compounds, which enable us to take advantage of the physiological traits of both components.     

Effects of chronic modification of dietary fat and carbohydrate in rats.

1. Rats were fed on diets enriched with starch, sucrose, corn oil or beef tallow for 3 weeks and the activities of various enzymes in the liver were measured. 2. The mitochondrial glycerol phosphate acyltransferase activity was lower in rats fed on the starch diet than on the two high-fat diets. 3. The non-microsomal (presumably peroxisomal) dihydroxyacetone phosphate acyltransferase activity was higher in rats fed on the starch diet and corn-oil diets than in those fed on the sucrose and beef-tallow diets. Urate oxidase activity was higher in rats fed on the starch diet than in the three other groups. There were no significant differences in the activity of acyl-CoA oxidase among the groups. 4. The activity of soluble phosphatidate phosphohydrolase was not significantly different among the dietary groups. There were increases of 3.3--4.3-fold in this activity in the dietary groups 6h after injection of corticotropin. The equivalent increases for the mitochondrial glycerol phosphate acyltransferase were 1.4--1.6 fold. 5. The corticosterone responses to the corticotropin injection were not significantly different between dietary groups. However, the corticosterone response of the rats fed on the two high-fat diets was prolonged when the rats were given an acute load of fructose [Brindley, Cooling, Glenny, Burditt & McKechnie (1981) Biochem. J. 200. 275--283]. 6. Rats fed on the high-fat diets had higher concentrations of circulating cholesterol than those fed on the starch and sucrose diets. Serum triacylglycerol concentrations were lower in the rats fed on the starch diet than in the three other groups. 7. The results are discussed in terms of the relationship between diet, hormonal balance and hepatic glycerolipid metabolism.     

Beneficial influence of dietary curcumin, capsaicin and garlic on erythrocyte integrity in high-fat fed rats

In rats rendered hyperlipidemic by maintaining them on a high-fat diet (30%) for 8 weeks, inclusion of spice principles [curcumin (0.2%) or capsaicin (0.015%)] or garlic (2.0%) in the diet produced significant hypotriglyceridemic effect. Plasma cholesterol remained unaffected in high-fat treatment. Hepatic triglyceride content was significantly higher in high-fat fed rats, and this increase was effectively countered by inclusion of the hypolipidemic spice agents -- curcumin, capsaicin or garlic in the diet. The lipid profile of erythrocyte membranes of hyperlipidemic rats was similar to basal controls. An examination of the osmotic fragility of erythrocytes in various groups indicated that the red blood cells of hyperlipidemic rats display a slight resistance to osmotic lysis. Inclusion of spice principles [curcumin (0.2%) or capsaicin (0.015%)] or garlic (2.0%) in the diet, which produced the hypotriglyceridemic effect, appeared to beneficially correct this altered osmotic fragility of erythrocytes. Activities of ouabain-sensitive Na(+),K(+)-ATPase as well as acetylcholinesterase of erythrocyte membranes in high-fat fed rats remained unaltered. Activity of Ca(2+),Mg(2+)-ATPase in erythrocyte membrane was significantly decreased in high-fat fed animals, whereas dietary spice principles and garlic countered this reduction in enzyme activity. In the absence of any change in the cholesterol/phospholipid molar ratio in the erythrocyte membrane, a decreased activity of membrane-bound Ca(2+),Mg(2+)-ATPase could have probably contributed to the accumulation of intracellular calcium leading to the diminished deformability of the erythrocytes in high-fat fed rats.     

Fish protein hydrolysate elevates plasma bile acids and reduces visceral adipose tissue mass in rats

Conjugation of bile acids (BAs) to the amino acids taurine or glycine increases their solubility and promotes liver BA secretion. Supplementing diets with taurine or glycine modulates BA metabolism and enhances fecal BA excretion in rats. However, it is still unclear whether dietary proteins varying in taurine and glycine contents alter BA metabolism, and thereby modulate the recently discovered systemic effects of BAs. Here we show that rats fed a diet containing saithe fish protein hydrolysate (saithe FPH), rich in taurine and glycine, for 26 days had markedly elevated fasting plasma BA levels relative to rats fed soy protein or casein. Concomitantly, the saithe FPH fed rats had reduced liver lipids and fasting plasma TAG levels. Furthermore, visceral adipose tissue mass was reduced and expression of genes involved in fatty acid oxidation and energy expenditure was induced in perirenal/retroperitoneal adipose tissues of rats fed saithe FPH. Our results provide the first evidence that dietary protein sources with different amino acid compositions can modulate the level of plasma bile acids and our data suggest potential novel mechanisms by which dietary protein sources can affect energy metabolism.     

Improvement in cholesterol metabolism in mice given chronic treatment of taurine and fed a high-fat diet

The effects of chronic treatment of taurine on hypercholesterolemia and atherosclerosis were examined in C57BL/6J mice fed a high-fat diet containing 15% fat and 1.25% cholesterol. Taurine was dissolved in drinking water at 1% (w/v) and was given to mice ad libitum during 6 months-feeding of a high-fat diet. Hypercholesterolemia occurred and lipid accumulation on the aortic valve was evident. Taurine treatment lowered serum LDL + VLDL cholesterol by 44% in mice fed a high-fat diet, while it elevated serum HDL cholesterol by 25%. As a result, the atherogenic index, the ratio of HDL to LDL + VLDL was markedly improved. Cholesterol content in the liver also decreased by 19% with taurine. Similar tendencies were seen in mice fed regular chow, but the changes were not significant. The area of aortic lipid accumulation, which served as an index of atherosclerosis, was reduced by 20% with taurine. In the liver, taurine doubled the activity of cholesterol 7alpha-hydroxylase. These observations, together with prior findings, suggest that the cholesterol-lowering action of taurine may relate to the increased conversion of cholesterol to bile acids via stimulation of cholesterol 7a-hydroxylase activity. Thus, chronic treatment of high-fat mice with taurine improves the abnormal profile of the serum lipoproteins, and thereby retards the progression of atherosclerosis.     

Increased hepatic activity of inducible nitric oxide synthase in rats fed on a high-fat diet

The effects were examined of the dietary level of fat on the activity of inducible nitric oxide synthase (iNOS) in the liver of rats. In experiment 1, rats were fed on a diet containing 5% or 20% beef tallow or safflower oil for 32 d. The animals were given a subcutaneous injection of the carcinogen, 1,2-dimethylhydrazine (DMH), on d 4. The activity of hepatic iNOS was significantly elevated by the high-fat diet, but was unaffected by the dietary source of the fat examined. In experiment 2, rats were fed on a 5% or 20% beef tallow diet for 11 d or 32 d with or without the DMH treatment. Feeding the high-fat diet and DMH treatment caused higher activity of hepatic iNOS. In experiment 3, the high-fat diet elevated hepatic iNOS activity and the amount of its protein in the lipopolysaccharide-treated rats. The results suggest that hepatic NO production is enhanced by a high-fat diet.     

Plasma cholesterol-lowering effect on rats of dietary fiber extracted from immature plants

Crude dietary fiber samples were prepared from beet, cabbage, Japanese radish, onion and mung bean sprouts (BF, CF, RF, OF and MF, respectively). These samples contained total dietary fiber at the levels of 814, 699, 760, 693 and 666 g/kg, respectively. To examine the effect of these dietary fiber sources on the plasma cholesterol concentration, male Sprague-Dawley rats were fed on a fiber-free (FF) diet or on an FF diet supplemented with 5% or 10% dietary fiber. Dietary fiber extracted from vegetables, wood cellulose (CL), pectin (PE) and guar gum (GG) were used as the fiber sources. Compared with the rats fed on the FF diet, a significant reduction in the plasma cholesterol concentration was observed in the rats fed on BF, CF, RF, MF, PE or GG after a 21-d feeding period. Cecal acetate, n-butyrate and total short-chain fatty acids were significantly higher in the rats fed on these dietary fibers, except for CF, than in those fed on the FF diet. A negative correlation was apparent between the total dietary fiber content, hemicellulose content and pectin content of each dietary fiber source and the plasma cholesterol concentration. These results suggest that some vegetable fibers exert a plasma cholesterol-lowering effect through cecal fermentation of these fibers.     

Metabolic alterations of the gut–liver axis induced by cholic acid contribute to hepatic steatosis in rats

12α-Hydroxylated (12αOH) bile acids (BAs) selectively increase with high-fat diet intake. Dietary supplementation with cholic acid (CA) in rats is a possible strategy to reveal the causal link between 12αOH BAs and hepatic steatosis. The present study aimed to investigate the metabolic mechanism underlying the effect of 12αOH BAs on hepatic steatosis. Male WKAH rats were fed either a control (Ct) or CA-supplemented diet (0.5 g/kg). After the 12-week intervention, the CA diet elevated the 12αOH BA levels in the gut–liver axis. CA-fed rats showed greater hepatic lipid accumulation than in the Ct group, regardless of the dietary energy balance. Untargeted metabolomics suggested marked differences in the fecal metabolome of rats subjected to the CA diet compared with that of Ct, characterized by the depletion of fatty acids and enrichment of amino acids and amines. Moreover, the liver metabolome differed in the CA group, characterized by an alteration in redox-related pathways. The CA diet elevated nicotinamide adenine dinucleotide consumption owing to the activation of poly(ADP-ribose) polymerase 1, resulting in impaired peroxisome proliferator-activated receptor α signaling in the liver. The CA diet increased sedoheptulose 7-phosphate, and enhanced glucose-6-phosphate dehydrogenase activity, suggesting promotion of the pentose phosphate pathway that generates reducing equivalents. Integrated analysis of the gut–liver metabolomic data revealed the role of deoxycholic acid and its liver counterpart in mediating these metabolic alterations. These observations suggest that alterations in metabolites induced by 12αOH BAs in the gut–liver axis contribute to the enhancement of liver lipid accumulation.     

The Physico-Chemical Properties of Dietary Fibre Determine Metabolic Responses,Short-Chain Fatty Acid Profiles and Gut Microbiota Composition in Rats Fed Low- and High-Fat Diets

The aim of this study was to investigate how physico-chemical properties of two dietary fibres, guar gum and pectin, affected weight gain, adiposity, lipid metabolism, short-chain fatty acid (SCFA) profiles and the gut microbiota in male Wistar rats fed either low- or high-fat diets for three weeks. Both pectin and guar gum reduced weight gain, adiposity, liver fat and blood glucose levels in rats fed a high-fat diet. Methoxylation degree of pectin (low, LM and high (HM)) and viscosity of guar gum (low, medium or high) resulted in different effects in the rats, where total blood and caecal amounts of SCFA were increased with guar gum (all viscosities) and with high methoxylated (HM) pectin. However, only guar gum with medium and high viscosity increased the levels of butyric acid in caecum and blood. Both pectin and guar gum reduced cholesterol, liver steatosis and blood glucose levels, but to varying extent depending on the degree of methoxylation and viscosity of the fibres. The medium viscosity guar gum was the most effective preparation for prevention of diet-induced hyperlipidaemia and liver steatosis. Caecal abundance of Akkermansia was increased with high-fat feeding and with HM pectin and guar gum of all viscosities tested. Moreover, guar gum had distinct bifidogenic effects independent of viscosity, increasing the caecal abundance of Bifidobacterium ten-fold. In conclusion, by tailoring the viscosity and possibly also the degree of methoxylation of dietary fibre, metabolic effects may be optimized, through a targeted modulation of the gut microbiota and its metabolites.     

Effect of pectin and amidated pectin on cholesterol homeostasis and cecal metabolism in rats fed a high-cholesterol diet

Two experiments were performed to compare the effect of pectin and its hydrophobic derivatives on homeostasis of cholesterol and cecal metabolism in male young rats. Control rats were fed a diet supplemented with palm fat and cholesterol (50 and 10 g/kg, respectively). Rats of other groups were fed the same diet containing citrus pectin or octadecylpectinamide (60 g/kg). Diets were fed for 4 weeks. In experiment I, pectinamide of lower degree of amidation (30 %) increased serum HDL cholesterol from 1.20 to 1.43 micromol/ml (p>0.05) at the expense of other cholesterol fractions. In experiment II, pectinamide of a higher degree of amidation (53 %) significantly decreased total serum cholesterol from 2.08 to 1.67 micromol/ml. Amidated pectins at both levels of substitution significantly decreased hepatic concentrations of cholesterol and fat. In both experiments the relative weight of cecum in the pectinamide group was significantly lower than in pectin group. The highest cecal concentrations of short-chain fatty acids (SCFA) were found in rats fed a diet with pectin (133.2 and 129.3 micromol/g in experiment I and II, respectively). In other groups, cecal SCFA was significantly (pectinamide groups) or non-significantly (controls) lower. In wet feces, SCFA concentrations were higher and butyrate molar proportions lower than in corresponding cecal contents. Pectinamide of a lower or higher degree of substitution significantly increased fecal content of cholesterol from 18.5 and 17.3 micromol/g in controls to 31.8 and 28.0 micromol/g, respectively. Corresponding concentrations of coprostanol were decreased. Effects of pectin on cholesterol homeostasis were absent or marginal. Histological examination revealed that hepatic tissue of control and pectin-fed rats was infiltrated with lipids. The Sudan black-positive material was absent in the liver of rats fed pectinamides. No pathological changes of liver tissue were apparent. In summary, hydrophobic amidated pectins significantly altered cholesterol homeostasis in rats and might be considered as a clinically effective hypocholesterolemic agent. Low cecal SCFA concentrations in rats fed pectinamides suggest that amidation of pectin had decreased its fermentability.     

A krill oil supplemented diet suppresses hepatic steatosis in high-fat fed rats

Krill oil (KO) is a dietary source of n-3 polyunsaturated fatty acids, mainly represented by eicosapentaenoic acid and docosahexaenoic acid bound to phospholipids. The supplementation of a high-fat diet with 2.5% KO efficiently prevented triglyceride and cholesterol accumulation in liver of treated rats. This effect was accompanied by a parallel reduction of the plasma levels of triglycerides and glucose and by the prevention of a plasma insulin increase. The investigation of the molecular mechanisms of KO action in high-fat fed animals revealed a strong decrease in the activities of the mitochondrial citrate carrier and of the cytosolic acetyl-CoA carboxylase and fatty acid synthetase, which are both involved in hepatic de novo lipogenesis. In these animals a significant increase in the activity of carnitine palmitoyl-transferase I and in the levels of carnitine was also observed, suggesting a concomitant stimulation of hepatic fatty acid oxidation. The KO supplemented animals also retained an efficient mitochondrial oxidative phosphorylation, most probably as a consequence of a KO-induced arrest of the uncoupling effects of a high-fat diet. Lastly, the KO supplementation prevented an increase in body weight, as well as oxidative damage of lipids and proteins, which is often found in high-fat fed animals.     

A diet-induced Sprague–Dawley rat model of nonalcoholic steatohepatitis-related cirrhosis

Certain modified diets containing saturated fatty acids, cholesterol or fructose lead to the development of nonalcoholic steatohepatitis (NASH)-related fibrosis in rodents; however, progression to cirrhosis is rare. Experimental liver cirrhosis models have relied on genetic manipulation or administration of hepatotoxins. This study aimed to establish a reliable dietary model of NASH-related cirrhosis in a relatively short period. Male Sprague–Dawley rats (9 weeks of age) were randomly assigned to normal, high-fat (HF), or two types (1.25% or 2.5% cholesterol) of high-fat and high-cholesterol (HFC) diets for 18 weeks. All HFC diets contained 2% cholic acid by weight. Histopathological analysis revealed that the HFC diets induced obvious hepatic steatosis, inflammation with hepatocyte ballooning and advanced fibrosis (stage 3–4) in all 12 rats at 27 weeks of age. In contrast, all five rats given the HF diet developed mild steatosis and inflammation without fibrosis. The amount of cholesterol in the liver and hepatocellular mitochondrial and microsomal fractions was significantly higher in rats fed the HFC diets than the normal or HF diets. The HFC diets significantly suppressed mRNA levels of microsomal triglyceride transfer protein, adenosine triphosphate binding cassette transporter G5, bile acid CoA: amino acid N-acyltransferase and bile salt export pump, as well as the enzymatic activity of carnitine palmitoyltransferase in the liver. In conclusion, the HFC diets induced liver cirrhosis in conjunction with hepatic features of NASH in Sprague–Dawley rats within 18 weeks, and altered gene expression and enzyme activity to accumulate lipid and bile acid in the liver.     

Increase of bile acids synthesis and excretion caused by taurine administration prevents the ovariectomy-induced increase in cholesterol concentrations in the serum low-density lipoprotein fraction of Wistar rats

We examined the effect of dietary taurine on the concentrations of serum cholesterol and apolipoprotein in lipoprotein fractions of Six-month-old ovariectomized, which were used as a model of hypercholesterolemia in postmenopausal woman, or sham operated rats. Taurine significantly reduced the serum total and low-density lipoprotein cholesterol concentrations only in the ovariectomized rats. In contrast, taurine significantly lowered the serum apolipoprotein B concentration and serum very low-density lipoprotein-apolipoprotein E concentration only in the sham operated rats. The serum total and high density lipoprotein-apolipoprotein E concentrations were significantly lower in the rats fed taurine than in those fed the control diet regardless of whether they had undergone ovariectomy. The esterified cholesterol level in the liver was significantly lower and the level of hepatic cholesterol 7 alpha-hydroxylase activity was significantly higher in the rats fed taurine than in those fed the control diet. The total bile acids concentration in the feces and intestinal contents of rats fed taurine were significantly higher than those in rats fed the control diet regardless of whether they had undergone ovariectomy. In the sham-rats, taurine accelerated bile acid synthesis and excretion, thereby increasing cholesterol consumption. The increased cholesterol consumption might be compensated by accelerating cholesterol synthesis and/or reducing the synthesis and release of very low-density lipoprotein from the liver. But in the ovariectomized rats, although taurine also accelerated bile acid synthesis and excretion, cholesterol demand might be compensated by excess cholesterol in the blood.     

Consumption of Sericin Reduces Serum Lipids,Ameliorates Glucose Tolerance and Elevates Serum Adiponectin in Rats Fed a High-Fat Diet

The effect was examined of dietary sericin on the lipid and carbohydrate metabolism in rats fed with a high-fat diet. The rats were fed with a 20% beef tallow diet with or without sericin at the level of 4% for 5 weeks. The final body weight and white adipose tissue weight were unaffected by dietary manipulation. The consumption of sericin significantly reduced the serum levels of triglyceride, cholesterol, phospholipids and free fatty acids. Serum very-low-density lipoprotein (VLDL)-triglyceride, VLDL-cholesterol, low-density lipoprotein (LDL)-cholesterol and LDL-phospholipids were also significantly reduced by the sericin intake. Liver triglyceride and the activities of glucose 6-phosphate dehydrogenase and malic enzyme, the lipogenic enzymes, were also reduced by the sericin intake. Dietary sericin caused a marked elevation in serum adiponectin. The consumption of sericin suppressed the increases in plasma glucose and insulin levels after an intraperitoneal glucose injection. These results imply the usefulness of sericin for improving the lipid and carbohydrate metabolism in rats fed on a high-fat diet.     

Effect of taurine on cholesterol metabolism in hamsters: up-regulation of low density lipoprotein (LDL) receptor by taurine

The effects of taurine on hepatic cholesterol metabolism were investigated in hamsters fed a high-fat diet or normal chow. Two weeks-treatment of taurine at 1% in drinking water prevented high-fat diet-induced increase in cholesterol levels of serum and liver. The decrease in serum cholesterol by taurine was due to decrease in non-HDL cholesterols. A similar tendency was noted in serum and liver cholesterol levels of hamsters fed a normal diet. In hamsters fed a high-fat diet, taurine prevented elevation in hepatic activity of acyl-CoA:cholesterol acyltransferase (ACAT) and increased the activity of cholesterol 7alpha-hydroxylase. Taurine also increased cholesterol 7alpha-hydroxylase activity in hamsters fed normal chow. Studies on liver membranes revealed that taurine increased 125I-labeled LDL binding by 52% and 58% in hamsters fed either a normal chow or high-fat diet, respectively. Furthermore, LDL kinetic analysis showed that taurine intake resulted in significant faster plasma LDL fractional catabolic rates (FCR). These results suggest that taurine elevates hepatic LDL receptor and thereby decreases serum cholesterol levels, an event which may be the result of hepatic cholesterol depletion as a consequence of increased bile acid synthesis via enhancement of cholesterol 7alpha-hydroxylase activity. Thus, up-regulation of the LDL receptor and subsequent increase in receptor- mediated LDL turnover may be a key event in the cholesterol-lowering effects of taurine in hamsters.     

Supplementation of orotic acid to the casein, but not to egg protein, soy protein, or wheat gluten diets, increases serum ornithine carbamoyltransferase activity

Effects of dietary supplementation of orotic acid to a diet containing the casein protein were compared with diets containing egg protein, soy protein, or wheat gluten on lipid levels in the liver and serum and activities of ornithine carbamoyltransferase (OCT) and alanine aminotransferase in the serum of rats. We found that supplementation of orotic acid to each diet increased the contents of the liver total lipids, triacylglycerol, and phospholipids compared with those not supplemented. The contents of liver total lipids, triacylglycerol, cholesterol, and phospholipids in rats fed the casein diet were significantly higher than those of rats fed the other three diets when orotic acid was supplemented. The levels of triacylglycerol, cholesterol, and phospholipids in the serum of rats fed the casein diet were markedly decreased by addition of orotic acid. The supplementation of orotic acid significantly increased the activities of both serum OCT and alanine aminotransferase in rats fed the casein diet, but not in rats fed the other diets. In conclusion, liver lipid accumulation induced by dietary orotic acid depends on the type of dietary protein. The enhancement of serum OCT activity may result from liver lipid accumulation in rats fed the casein diet supplemented with orotic acid, demonstrating hepatic damage.