Dietary taurine alters ascorbic acid metabolism in rats fed diets containing polychlorinated biphenyls

The effect of dietary taurine on ascorbic acid metabolism and hepatic drug-metabolizing enzymes was investigated in rats fed diets containing polychlorinated biphenyls (PCB) to determine whether taurine has an adaptive and protective function in xenobiotic-treated animals. Young male Wistar rats (60 g) were fed diets containing 0 or 0.2 g/kg diet PCB with or without 30 g/kg diet of taurine for 14 d. The rats fed the PCB-containing diets had greater liver weight, higher ascorbic acid concentrations in the liver and spleen and greater hepatic cytochrome P-450 contents than control rats that were not treated with PCB (P < 0.01). In PCB-fed rats, urinary ascorbic acid excretion was enhanced, and serum cholesterol concentration (especially HDL-cholesterol) was significantly elevated compared with those in control rats. Dietary taurine significantly potentiated the increases in the urinary excretion of ascorbic acid and the rise in the levels of cytochrome P-450 which were caused by PCB treatment. On the other hand, the supplementation of taurine to control diet did not alter these variables. Taurine may enhance the hepatic drug-metabolizing systems, leading to the stimulation of the ascorbic acid metabolism in rats fed diets containing PCB.     

Influence of maternal cholestyramine treatment on cholesterol and bile acid metabolism in adult offspring

To reduce ileal reabsorption of bile acids and to deplete hepatic cholesterol pools, female rats were fed a diet containing 5% (wt/wt) cholestyramine from 4 days prior to mating. Control rats were fed the same diet without cholestyramine. In one group on day 20 of gestation diet-fed dams and their fetuses were investigated. Additional pups were raised in litters of eight and nursed by their mothers for 30 days at which time they were weaned to the control diet. All dams were given the control diet from day 14 of lactation; at no time did neonates have access to cholestyramine. Offspring were raised until 3 months of age then fed the control, cholestyramine or a high fat, high cholesterol diet for 5 days. Maternal cholestyramine produced significant elevation of fetal hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase; fetal 7 alpha-hydroxylase (7 alpha-OH) activity, plasma cholesterol and triglyceride levels, however, were not significantly altered. The elevated HMG-CoA reductase activity persisted in liver and in addition was present in jejunum of 3-month-old male offspring challenged with the control or cholestyramine diet for 5 days. When challenged with the high fat, high cholesterol diet, male offspring from cholestyramine-treated dams had significantly higher plasma cholesterol levels but HMG-CoA reductase and 7 alpha-OH activity similar to controls. Maternal treatment had no apparent effect on plasma triglyceride or hepatic 7 alpha-OH in 3-month-old male offspring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of methyl-group acceptors on the regulation of plasma cholesterol level in rats fed high cholesterol diets

The effects of methyl-group acceptors such as glycine, guanidinoacetic acid, and nicotinamide on cholesterol metabolism and phosphatidylcholine(PC) biosynthesis were investigated with rats fed a 25% casein diet containing cholesterol with or without methionine supplement. The effect of ethanolamine, an indirect methyl-group acceptor via phosphatidylethanolamine(PE) formation, was also compared with those of methyl-group acceptors. The methyl-group acceptors and ethanolamine decreased or tended to decrease plasma total cholesterol level when added to the 25% casein diet. These compounds also significantly depressed the methionine-induced enhancement of plasma cholesterol level. The activity of PE N-methyltransferase was decreased by the addition of glycine, guanidinoacetic acid, and nicotinamide, but not ethanolamine, to the reaction mixture when assayed using the postmitochondrial fraction of liver homogenate, suggesting that PE N-methyltransferase activity can be depressed by glycine N-methyltransferase, guanidinoacetic acid N-methyltransferase, and nicotinamide N-methyltransferase systems. The PE N-methyltransferase activity in liver microsomes, however, did not decrease in response to the dietary addition of methyl-group acceptors. The in vitro incorporation of [CH3-14C]methionine into PC of liver slices was also significantly inhibited by the addition of glycine and nicotinamide, but not guanidinoacetic acid and ethanolamine, to the incubation medium. It is suggested that methyl-group acceptors can decrease plasma cholesterol level at least in part through the depression of PC biosynthesis via PE N-methylation pathway, and that the mechanism for the plasma cholesterol-lowering effect of ethanolamine is different from that of methyl-group acceptors.     

Comparative gastrointestinal and plasma cholesterol responses of rats fed on cholesterol-free diets supplemented with guar gum and sodium alginate

The present study investigated the digestion and cholesterol-lowering effects of the water-soluble NSP guar gum (GG) and sodium alginate (SA) in laboratory animals. Groups of five male Wistar strain rats were fed semi-purified cholesterol-free diets containing 0, 50 or 100 g NSP source/kg for 21 d which comprised a 14-d adaptation period followed by a 7-d balance period. Weight gain over the balance period and food conversion ratio decreased linearly with increasing NSP intake ( and respectively). DM digestibility decreased with increasing NSP intake and this effect was greater for SA-containing diets compared with GG-containing diets At the lower inclusion rate, 0.9-1.0 of the additional NSP was digested, but this value fell to 0.8 for both NSP sources at the 100 g/kg inclusion rate, implying that the capacity for near complete digestion of the test NSP had been exceeded. Intestinal tissue mass was increased in response to inclusion of both NSP sources. Caecal digesta pH decreased linearly with additional GG, but increased slightly with consumption of SA. Total caecal short-chain fatty acid concentrations (micromol/g caecal contents) increased markedly with 50 g GG/kg but did not increase further with 100 g GG/kg, and were slightly lower than control values in rats consuming SA. Plasma cholesterol concentration fell linearly with increasing NSP in the diet and the effect was similar for both GG and SA. Total output of faecal bile acids rose in rats fed 50 g GG/kg and 50 g SA/kg (59 micromol/7 d v. 24 micromol/7 d for control rats) with no further increase at the higher inclusion rate. These results show that SA has a strong hypocholesterolaemic effect in rats which is similar to that of GG, and that this effect is most likely to be mediated through an interruption in the entero-hepatic circulation of bile acids and not through increased hepatic supply of propionate from fermentation of the NSP in the large bowel.     

The effect of dietary fibre on bile acid metabolism in rats

1. Forty-eight male rats were fed sequentially for 14 d periods on diets containing different fibre contents. 2. One of the high-fibre diets was a commercial pelleted diet. The other was a low-fibre diet supplemented with 200 g wheat bran/kg. 3. At the end of each feeding period eight rats were killed. Liver microsomal cholesterol 7 alpha-hydroxylase (EC 1.14.1.-) activity and bile acid content of small intestine and colon were determined. 4. The different diets did not significantly alter the total intestinal bile acids, but affected the distribution and qualitative pattern in the colon and small intestine. 5. On the high-fibre diets deoxycholate, and hyodeoxycholate tended to be increased. 6. On the low-fibre diets the alpha, beta- and omega-muricholic acids tended to be increased. 7. Liver microsomal cholesterol 7 alpha-hydroxylase activity was lower in rats on the low-fibre and bran-supplemented low-fibre diets compared with that in rats fed on the commercial pelleted diet.     

Fish protein hydrolysates affect cholesterol metabolism in rats fed non-cholesterol and high-cholesterol diets

Fish consumption is well known to provide health benefits in both experimental animals and human subjects. Numerous studies have demonstrated the beneficial effects of various protein hydrolysates on lipid metabolism. In this context, this study examined the effect of fish protein hydrolysates (FPH) on cholesterol metabolism compared with the effect of casein. FPHs were prepared from Alaska pollock meat using papain as a protease. Male Wistar rats were divided into the following four dietary groups of seven rats each: either casein (20%) or FPH (10%)?+?casein (10%), with or without 0.5% cholesterol and 0.1% sodium cholate. Serum and liver lipid levels, fecal cholesterol and bile acid excretions, and the hepatic expression of genes encoding proteins involved in cholesterol homeostasis were examined. In rats fed the FPH diets compared with casein diets with or without cholesterol and sodium cholate, the indexes of cholesterol metabolism-namely, serum cholesterol, triglyceride, and low-density lipoprotein-cholesterol levels-were significantly lower, whereas fecal cholesterol and bile acid excretions were higher. Rats fed the FPH diets compared with casein with cholesterol exhibited a lower liver cholesterol level via an increased liver cholesterol 7α-hydroxylase (CYP7A1) expression level. This study demonstrates that the intake of FPH has hypocholesterolemic effects through the enhancement of fecal cholesterol and bile acid excretions and CYP7A1 expression levels. Therefore, fish peptides prepared by papain digestion might provide health benefits by decreasing the cholesterol content in the blood, which would contribute to the prevention of circulatory system diseases such as arteriosclerosis.     

Water maze performance is unaffected in artificially reared rats fed diets supplemented with arachidonic acid and docosahexaenoic acid

Four groups of male Long-Evans rats were reared artificially from postnatal d 5 to 18 by being fed through a gastrostomy tube with rat milk substitutes containing oils providing 10% linoleic acid and 1% alpha-linolenic acid (g/100 g fat); with the use of a 2 x 2 design, they were fed one of two levels of arachidonic acid (AA) and docosahexaenoic acid (DHA) (0.0 and 2.5 g/100 g of fatty acids). A fifth artificially reared group was fed a diet high in saturated fat, and a sixth group was reared by dams fed a standard AIN-93M diet. The pups were weaned onto modified AIN-93G diets, with a fat composition similar to that fed during the artificial rearing period. Behavioral testing was conducted between 6 and 9 wk of age; brain lipid composition was then assessed. Relative to the unsupplemented group (0.0 g/100 g AA and DHA), dietary supplementation resulted in a wide range of AA (84-103%) and particularly DHA (86-119%) levels in forebrain membrane phospholipids. AA supplementation increased AA levels and decreased DHA levels, and DHA supplementation increased DHA levels and decreased AA levels, with the magnitude of these effects dependent on the level of the other fatty acid. DHA levels were very low in the saturated fat group. The groups did not differ on the place or cued version of the Morris water-maze, but on a test of working memory, the saturated fat group was impaired relative to the suckled control group. Further correlational analyses in the artificially reared animals did not support a relationship between the wide range of DHA and AA levels in the forebrain and working-memory performance.     

High temperature- and high pressure-processed garlic improves lipid profiles in rats fed high cholesterol diets

Garlic protects against degenerative diseases such as hyperlipidemia and cardiovascular diseases. However, raw garlic has a strong pungency, which is unpleasant. In this study, we examined the effect of high temperature/high pressure-processed garlic on plasma lipid profiles in rats. Sprague-Dawley rats were fed a normal control diet, a high cholesterol (0.5% cholesterol) diet (HCD) only, or a high cholesterol diet supplemented with 0.5% high temperature/high pressure-processed garlic (HCP) or raw garlic (HCR) for 10 weeks. The body weights of the rats fed the garlic-supplemented diets decreased, mostly because of reduced fat pad weights. Plasma levels of total cholesterol (TC), low-density lipoprotein cholesterol, and triglyceride (TG) in the HCP and HCR groups decreased significantly compared with those in the HCD group. Additionally, fecal TC and TG increased significantly in the HCP and HCR groups. It is notable that no significant differences in plasma or fecal lipid profiles were observed between the HCP and HCR groups. High temperature/high pressure-processed garlic contained a higher amount of S-allyl cysteine than raw garlic (P<.05). The results suggest that high temperature/high pressure-processed garlic may be useful as a functional food to improve lipid profiles.     

Effect of exercise on lipid metabolism of rats fed high carbohydrate diets.

Two experiments were conducted to determine whether high carbohydrate diets or exercise would have a greater influence on certain parameters of lipid metabolism. Male Fischer rats were used in both experiments, separated into exercise and sedentary groups, and fed either a high sucrose (63%) or a high starch (63%) diet. There were no differences in body weight or food consumption between the two diets. Exercise resulted in a highly significant increase in food consumption in both experiments. Rats fed sucrose had a higher serum cholesterol value than rats fed starch. Diet did not influence serum triglycerides but the rats on excercise had significantly lower serum triglycerides than the sedentary rats. Liver weight was significantly larger in rats fed sucrose. Sucrose caused an increase in the activity of both glucose-6-phosphate dehydrogenase and malic enzyme activities in liver tissue, whereas exercise caused an increase in the activity of these enzymes in adipose tissue.     

Energy balances of eight volunteers fed on diets supplemented with either lactitol or saccharose

1. Complete 24 h energy and nitrogen balances were measured for eight subjects both while consuming a basal diet supplemented with 49 g saccharose/d (diet S) and while consuming the same basal diet but supplemented with 50 g lactitol monohydrate/d (diet L). 2. The subjects ate the two diets for 8 d. Faeces and urine were collected for the final 4 d. Exchange of respiratory gases (oxygen, carbon dioxide, hydrogen and methane) was measured during the final 72 h while the subjects stayed in an open-circuit respiration chamber, 11 m3, and simulated office work. Before eating diet L, subjects ate 50 g lactitol daily for 10 d. 3. On diets L and S, faecal moisture content averaged 0.787 and 0.753 g/g respectively, the difference being significant (P less than 0.05). On diet L, energy and nitrogen digestibilities and energy metabolizability averaged 0.922, 0.836 and 0.881 respectively, and on diet S 0.935, 0.869 and 0.896 respectively; the differences were also significant (P less than 0.05). Urinary energy losses and N balances were not significantly different for the two diets. 4. In all subjects only traces of methane were produced but hydrogen production differed significantly (P less than 0.05) for diets L and S, being 2.3 and 0.4 litres (normal temperature and pressure)/d respectively. 5. Intakes of metabolizable energy (ME) were corrected, within subjects, to energy equilibrium and equal metabolic body-weight. The corrected ME intakes did not show differences between diets. However, when on diet L the subjects were probably less active than when on diet S because differences within subjects of ankle actometer counts between diets showed a high correlation with the corresponding differences in corrected ME intakes (r 0.92). Further correction of ME intake toward equal actometer activity showed a significant (P less than 0.05) difference between diets: for maintaining energy equilibrium 5.6 (SE 0.8; P less than 0.05)% more ME from diet L was needed than from diet S. The reliability of this 5.6% difference depends on whether or not one ankle actometer gives an accurate picture of the subject's physical activity. 6. The energy contribution to the body is clearly smaller from lactitol than from saccharose, certainly due to the effect of lactitol on digestion, and probably also due to the effect on the utilization of ME.     

Investigation of gene expressions related to cholesterol metabolism in rats fed diets enriched in n-6 or n-3 fatty acid with a cholesterol after long-term feeding using quantitative-competitive RT-PCR analysis

We have developed a method to quantitate hepatic apolipoprotein (apo) B, LDL receptor, 3-hydroxy-3-methylglutary coenzyme A reductase (HMG-CoA reductase) and cholesterol 7alpha-hydroxylase mRNA expression in rats fed a cholesterol-enriched diet after long-term feeding using competitive RT-RCR. Rats (8 wk of age) fed a conventional diet were shifted to diets containing 10% perilla oil (PEO, oleic acid+linoleic acid+alpha-linolenic acid), borage oil (BRO, oleic acid+linoleic acid+gamma-linolenic acid), evening primrose oil (EPO, linoleic acid+gamma-linolenic acid), mixed oil (MIO, oleic acid+linoleic acid+gamma-linolenic acid+alpha-linolenic acid), or palm oil (PLO, palmitic acid+oleic acid+linoleic acid) with 0.5% cholesterol for 15 wk. There were no significant differences in the food intake and body weight gain among the groups. The liver weight in the PEO and PLO groups was significantly higher than other groups. The serum total cholesterol and very low density lipoprotein (VLDL)+intermediate density lipoprotein (IDL)+low density lipoprotein (LDL)-cholesterol concentrations were consistently higher in PLO group than in the other groups. The serum high density lipoprotein cholesterol concentration was significantly lower in the PEO group than in the other groups. The liver cholesterol concentration group was significantly higher in the PEO than in the other groups. There were no significant differences in the hepatic LDL receptor mRNA level among the groups. Hepatic apo B, HMG-CoA reductase and cholesterol 7alpha-hydroxylase mRNA levels were not affected by the experimental conditions. However, hepatic cholesterol 7alpha-hydroxylase mRNA level in the PEO and MIO groups tended to be higher than in the other groups. The fecal cholesterol extraction was significantly higher in the MIO and PLO groups than in the PEO and EPO groups and the total bile acid extraction was significantly higher in the PEO and MIO groups than in the PLO group. The results of this study demonstrated that both n-6 fatty acid and n-3 fatty acids such as gamma-linolenic acid and alpha-linolenic acid lowered serum total cholesterol and VLDL+IDL+LDL-cholesterol concentrations of rats in the presence of excess cholesterol in the diet compared with dietary saturated fatty acid.     

Apparent fat digestibility in rats fed different diets is negatively correlated with faecal bile acid excretion

Seventy-two rats were fed one out of 9 diets differing as to protein source and calcium concentration. For the individual rats apparent fat digestibility and faecal bile acid excretion were negatively correlated. It is suggested that a high solubility of bile acids in the small intestinal digesta, which is associated with little loss of bile acids with faeces, stimulates the process of fat digestion.     

Changes in plasma cholesterol density distribution of young adult male rats fed a high fat and cholesterol diet following maternal cholestyramine treatment

The effects of feeding cholestyramine to pregnant rats, which has been shown to increase the fetal hepatic rate-limiting enzyme in cholesterol synthesis, HMG CoA reductase, on the plasma cholesterol density distribution was studied in the young adult male rat offspring before and after feeding a diet high in fat and cholesterol. As in previous studies, offspring of rats fed cholestyramine during pregnancy had a plasma total cholesterol level similar to controls when fed a low fat and cholesterol diet, but higher than controls when fed a 20% (wt/wt) fat plus 5% (wt/wt) cholesterol diet. Analyses of the plasma cholesterol density distribution by continuous gradient ultracentrifugation showed that, compared to control rats, rats born to dams fed cholestyramine had more cholesterol in the higher density regions of plasma before and after a 7-d high fat and cholesterol diet challenge. After a 4- or 7-d diet challenge, rats fed cholestyramine had 2-3 times more cholesterol in the d less than or equal to 1.006 g/ml range of plasma compared to the control offspring. The results suggest that long term changes in cholesterol metabolism due to early nutrition in the rat may include altered plasma or intestinal lipoprotein metabolism, rather than an effect specific to hepatic cholesterol synthesis.     

Plasma, tissue and fecal cholesterol of young pigs fed restricted or liberal amounts of beef, soy or conventional diets

Cholesterol disposition (tissue deposition + fecal excretion) was determined in young pigs fed restricted (trial 1) or liberal (trial 2) amounts of beef-based, soy-based or conventional swine diets. Cholesterol content of diet is greater than average United States consumption per kilogram body weight but is very similar on a per-kilocalorie intake basis. Both beef and soy diets contained more cholesterol (0.09% by weight vs. 0%) and fat (40-50% of calories vs. 8-9%) than did conventional diets. Dried egg yolk was the source of cholesterol in the soy diets. Beef- and soy-fed pigs had greater plasma, HDL and LDL cholesterol concentrations than did conventionally fed pigs; beef-fed pigs had greater plasma, HDL and LDL cholesterol concentrations than did soy-fed pigs in trial 2 only. Final HDL-to-LDL cholesterol ratios did not differ. Neutral steroid and bile acid excretion was twofold greater in soy-fed than in conventionally or beef-fed pigs in trial 2 only. Differences in cholesterol concentrations were found in liver (soy, beef greater than conventional) and heart (soy greater than beef, conventional) in trial 1 and in liver (soy, beef greater than conventional), adipose tissue (soy greater than conventional greater than beef) and aorta and other viscera (conventional greater than soy, beef) in trial 2. In both trials, soy-fed pigs had greatest whole-body cholesterol concentrations. Thus, in both trials, disposition of cholesterol was similar in conventionally fed and beef-fed pigs, despite greater cholesterol intake in the latter, but was greater soy-fed pigs.     

Trans fatty acids and cholesterol metabolism: mechanistic studies in rats and rabbits fed semipurified diets

Studies were conducted in rabbits and rats to investigate the effects of diets rich in oleic (CIS diet), palmitic (SAT diet) and trans fatty acids (TRANS diet) on plasma lipids and lipoprotein metabolism. An important difference between these species is that rabbits possess plasma cholesteryl ester transfer protein (CETP) activity while rats are devoid of transfer activity. In the presence of dietary cholesterol (0.2% w/w) the change in plasma low density lipoprotein-cholesterol (LDL-C) concentration from baseline was significantly higher in rabbits fed the TRANS diet compared with those fed the CIS diet (P < 0.01). Despite this difference, the hepatic LDL-receptor activity was similar in all groups. Also, the fatty acid composition of hepatic phospholipids was affected by diet with lower proportion of palmitic (11%) and higher (19%) linoleic acid despite a similar content in the diet. These effects may represent the maintenance of membrane fluidity within narrow limits to ensure optimal function. The studies in rats showed that the plasma total cholesterol concentration was 20% lower (P < 0.01) in TRANS-fed rats compared with those fed the CIS diet. The results of an in vivo assay of reverse cholesterol transport (RCT) suggested that the three diets gave rise to high density lipoprotein (HDL) particles with similar capacity to accept cellular cholesterol. The differential effects of dietary trans fatty acids in these animal models provide another line of evidence that reinforces the significant role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.