A casein diet added isoflavone-enriched soy protein favorably affects biomarkers of steatohepatitis in obese Zucker rats

ObjectiveDietary supplementation of a soy protein enriched with isoflavones (HDI) has been shown to improve fatty liver in obese rats. The main objective of this study was to investigate whether HDI would influence the inflammatory status in livers of obese rats with fatty liver.MethodsMale obese Zucker fa/fa rats were fed casein (controls) or casein supplemented with HDI (containing 4.00 g of genistein and 4.50 g of daidzein per kilogram of diet) for 6 wk.ResultsThe HDI-fed rats had a markedly lower hepatic concentration of triacylglycerol when compared with controls. The decreased aspartate transaminase/alanine transaminase ratio in plasma, together with lower circulating levels of alkaline phosphatase and bile acids after HDI feeding, implied an improved hepatitis. This was supported by decreased plasma and hepatic mRNA levels of tumor necrosis factor-α, lower plasma levels of interleukin-1β and monocyte chemoattractant protein-1, and an increased anti-inflammatory fatty acid index in plasma. HDI also seemed to protect the rats from oxidative damage, because the level of lipid peroxides in triacylglycerol-rich lipoproteins after in vitro copper oxidation was lower for HDI-fed rats when compared with controls.ConclusionThese results show that isoflavone-enriched soy protein favorably affects biomarkers of hepatic inflammation in obese Zucker fa/fa rats with fatty liver. Thus, dietary soy proteins enriched in isoflavones may be a promising agent to improve steatohepatitis in patients.     

A cooperative interaction between soy protein and its isoflavone-enriched fraction lowers hepatic lipids in male obese Zucker rats and reduces blood platelet sensitivity in male Sprague-Dawley rats

Soy protein diets lower plasma cholesterol in hyperlipoproteinemic human subjects, as well as in animal models. We fed 7-wk-old male obese (fa/fa) and lean Zucker rats a modified AIN-76 diet (20 g protein/kg diet) containing casein (C), low isoflavone soy protein (38 mg isoflavones/kg diet; LI), or high isoflavone soy protein (578 mg isoflavones/kg diet; HI) for 70 d. In obese rats, plasma total cholesterol was 21 and 29% lower in the LI and HI groups, respectively, than in the C group (P: 相似文献   

Effects of the whole seed and a protein isolate of faba bean (Vicia faba) on the cholesterol metabolism of hypercholesterolaemic rats

The aim of the present work was to analyse the hypocholesterolaemic efficiency of a Vicia faba-protein isolate in relation to the intact legume. In addition, the mechanisms underlying the effects of this isolate were investigated. Hypercholesterolaemic rats were divided into three groups and fed high-fat diets rich in cholesterol-containing casein, whole seeds of Vicia faba or the protein isolate of faba beans as protein source, for 2 weeks ad libitum. The protein isolate was prepared by isoelectric precipitation and spray dried. Analyses of serum, liver and faeces, as well as of the activity of hepatic 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, were assessed by enzymatic methods. The rats fed on Vicia faba diets showed significantly lower body weights and energy intakes than rats fed on casein diets. The whole-seed diet induced a significant reduction in plasma triacylglycerol. Feeding rats on diets containing faba bean seeds, or the protein isolate, induced a significant decrease in plasma (LDL+VLDL)-cholesterol but not in HDL-cholesterol. Hepatic cholesterol and triacylglycerol were also reduced. The hypocholesterolaemic effects of Vicia faba were not the result of a reduction in cholesterol synthesis as assessed from HMG-CoA reductase activity, but the result of an increase in steroid faecal excretion. The faba bean-protein isolate obtained under our experimental conditions was useful in improving the metabolic alterations induced by feeding with a hypercholesterolaemic diet compared with casein. The effectiveness of the whole seeds was higher than that of the protein isolate.     

Hepatic steatosis and serum very low density lipoproteins during two types of protein malnutrition followed by balanced refeeding

The relation of serum very low density lipoproteins (VLDL) to hepatic steatosis was studied during protein malnutrition followed by refeeding of a balanced diet in growing rats. A control group was fed a balanced diet containing 15% casein for 42 days. Two depleted groups were fed low protein diets containing 2% casein (group C) or 5% gluten (group GI) (protein malnutrition phase) for 28 days and then were fed the balanced diet for 14 days (refeeding phase). The concentrations of phospholipids and proteins in both liver and serum VLDL were decreased during protein malnutrition, whereas triacylglycerols, unesterified cholesterol, and cholesteryl esters were higher in the liver and lower in the serum VLDL in the C and GI groups compared with the control group. There was a significant inverse relation between serum VLDL apolipoproteins and liver triacylglycerols on the one hand and between serum VLDL triacylglycerols and liver triacylglycerols on the other hand, in both depleted groups, although this relation was less important in the GI group. The major fatty acid levels of liver triacylglycerols were negatively correlated with those of serum VLDL during protein malnutrition. Our results show that in spite of a similar fatty acid intake, protein malnutrition involved an important decrease in essential fatty acids in VLDL triacylglycerols and phospholipids. Moreover, triacylglycerol accumulation was accompanied by increases in unesterfied cholesterol and cholesteryl esters in the liver of rats fed low protein diets, especially with 5% gluten. Hence, the hepatic steatosis was not entirely attributable to impaired transport of triacylglycerols by VLDL.     

Dietary soya protein concentrate enriched with isoflavones reduced fatty liver, increased hepatic fatty acid oxidation and decreased the hepatic mRNA level of VLDL receptor in obese Zucker rats

Casein-based diets containing a low (LDI) or high (HDI) dose of soya protein concentrate enriched with isoflavones were fed to obese Zucker rats for 6 weeks. HDI feeding, but not LDI feeding, reduced the fatty liver and decreased the plasma levels of alanine transaminase and aspartate transaminase. This was accompanied by increased activities of mitochondrial and peroxisomal beta-oxidation, acetyl-CoA carboxylase, fatty acid synthase and glycerol-3-phosphate acyltransferase in liver and increased triacylglycerol level in plasma. The decreased fatty liver and the increased plasma triacylglycerol level appeared not to be caused by an increased secretion of VLDL, as HDI decreased the hepatic mRNA levels of apo B and arylacetamide deacetylase. However, the gene expression of VLDL receptor was markedly decreased in liver, but unchanged in epididymal white adipose tissue and skeletal muscle of rats fed HDI, indicating that the liver may be the key organ for the reduced clearance of triacylglycerol-rich lipoproteins from plasma after HDI feeding. The n-3/n-6, 20:4n-6/18:2n-6 and (20:5n-3+22:6n-3)/18:3n-3 ratios were increased in liver triacylglycerol by HDI. The phospholipids in liver of rats fed HDI contained a low level of 20:4n-6 and a high level of 20:5n-3, favouring the production of anti-inflammatory eicosanoids. When obese Zucker rats were fed soya protein, this also resulted in reduced fatty liver, possibly through reduced clearance of VLDL by the liver. We conclude that the isoflavone-enriched soya concentrate as well as soya protein may be promising dietary supplements for treatment of non-alcoholic fatty liver.     

Effect of cholesterol supplementation on plasma and liver cholesteryl ester fatty acids in rats fed casein or soy protein

The effect of supplementation with cholesterol on plasma and liver cholesteryl ester fatty acids was examined in rats fed diets containing different protein sources. Weanling male rats were fed a semi-purified diet containing 20% casein or 20% soy protein for seven weeks and then 1% (by weight) of cholesterol was added for three more weeks. Rats fed soy protein grew consistently slower than those fed casein. The plasma and liver cholesterol contents were not significantly different between the two protein groups in the unsupplemented rats; however, they were significantly increased in cholesterol-fed animals, particularly in casein-fed rats. Analysis of the cholesteryl ester fatty acid composition in plasma and liver demonstrated that cholesterol-feeding significantly increased the levels of saturated fatty acids, monounsaturated fatty acids and linoleic acid in casein-fed rats as compared to those fed soy protein. The level of cholesteryl arachidonate in liver, which was low initially, increased slightly in the liver of casein-fed rats but did not significantly change in the plasma of either protein group.     

Factors contributing to the resistivity of a higher casein diet against choline deficiency-induced hyperhomocysteinemia in rats

The mechanism by which feeding a higher casein diet results in resistance to choline deprivation-induced hyperhomocysteinemia was investigated in rats. Plasma homocysteine concentration was significantly lower in rats fed a 30% casein diet (30C) than in rats fed a 10% casein diet (10C). Choline deprivation did not enhance plasma homocysteine concentration in rats fed 30C, while it significantly enhanced plasma homocysteine concentration in rats fed 10C. The choline deprivation-induced enhancement of plasma homocysteine concentration in rats fed 10C was significantly suppressed by methionine supplementation in a dose-dependent manner in the range of 0.1 to 0.3%, but the suppressive effect of methionine became smaller with an increase in supplementation level in the range of 0.3 to 0.5%. At a 0.5% supplementation level, methionine did not exhibit any suppressive effect on choline deprivation-induced hyperhomocysteinemia. The higher plasma homocysteine concentration in rats fed choline-deprived 10C+0.5% methionine was significantly decreased by concurrent supplementation with 0.32% glycine+0.94% serine to the level of rats fed 10C. Raising dietary total amino acid level by adding 3.61% branched-chain amino acids (BCAA)+4.5% acidic amino acids (AAA) to choline-deprived 10C+0.5% methionine+0.32% glycine+0.94% serine resulted in a further decrease in plasma homocysteine concentration to a level lower than the level in rats fed 10C. Choline deprivation-induced increases in hepatic S-adenosylhomocysteine and homocysteine concentrations were significantly suppressed by supplementation with glycine+serine and further suppressed by BCAA+AAA. Hepatic cystathionine β-synthase activity and its gene expression were significantly increased by BCAA+AAA. Hepatic triglyceride concentration changed in a manner similar to that of plasma homocysteine concentration. The results indicate that there are at least three factors contributing to the resistivity of rats fed a higher casein diet (30C) to choline deprivation-induced hyperhomocysteinemia, i.e., higher intake of methionine, higher intake of glycine and serine, and higher intake of other amino acids such as BCAA and AAA.     

Combination of fish oil and fish protein hydrolysate reduces the plasma cholesterol level with a concurrent increase in hepatic cholesterol level in high-fat-fed Wistar rats

ObjectiveThis study investigated the potential additive or synergistic effect of fish oil (FO) and fish protein hydrolysate (FPH) on cholesterol concentration in plasma and the liver.MethodsMale Wistar rats were fed high-fat diets (30% fat, 20% protein, wt/wt) containing FO (5%), FPH (10%), a combination of FO and FPH, or a high-fat control diet. After 7 wk of feeding, the rats were fasted for 12 h before lipid levels in plasma and the liver and hepatic activities of acyl-coenzyme A:cholesterol acyltransferase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and fatty acid synthase were measured.ResultsThe combination of FO and FPH in the diet profoundly reduced the plasma cholesterol level, mainly due to lowering of high-density lipoprotein cholesterol, whereas the hepatic total cholesterol concentration was elevated compared with control rats and rats fed diets containing FPH or FO alone. The elevated cholesterol concentration in the liver was caused by an increased amount of cholesteryl esters and was in correlation to an increased activity of acyl-coenzyme A:cholesterol acyltransferase. There was a reduced fatty acid synthase activity that could lead to a reduced lipogenesis in the rats fed a combination of FO and FPH.ConclusionA dietary combination of FO and FPH resulted in lower levels of plasma cholesterol and higher levels of hepatic cholesterol compared with dietary FO or FPH alone. Further studies are warranted to confirm whether the hypocholesterolemic effect was due to a reduced secretion of very low-density lipoprotein from the liver.     

Dietary soy protein isolate and isoflavones modulate hepatic thyroid hormone receptors in rats

Thyroid hormone receptors (TRs) are regulators of many genes involved in cholesterol and lipid metabolism. The purpose of this study was to examine the effect of soy protein isolate (SPI) and isoflavones on hepatic TRs in rats. In Expt. 1, Sprague-Dawley rats were fed diets containing either casein or alcohol-washed SPI with or without isoflavone supplementation (5-1250 mg/kg diet) for 70, 190, and 310 d. The offspring (F1) were fed the same diets as their parents (F0). In Expt. 2, Sprague-Dawley rats were fed diets containing casein or casein plus isoflavones (50-400 mg/kg diet) for 120 d. The mRNA and protein contents of the hepatic TRs were measured by semiquantitative RT-PCR and Western blot, respectively. TRalpha1, TRalpha2, and TRbeta2 contents were not affected by SPI. However, the content of the 52-kDa TRbeta1 protein, the major isoform present in the liver, was markedly increased by dietary SPI in both sexes of F0 and F1 compared with casein. The supplemental isoflavones had no effect on TRbeta1, whereas the high doses of isoflavones (250 and 1250 mg/kg diet) reduced the hepatic TRalpha1 protein content in F1 male rats on d 28. SPI had no effect on total T3 and T4 levels. However, higher dose of supplemental isoflavones markedly increased T4 level in female rats. Overall, this study demonstrates for the first time that SPI upregulates hepatic TRbeta1 expression, and that isoflavones reduce the hepatic TRalpha1 level in young male rats. The SPI-induced TRbeta1 may play a role in mediating the hypocholesterolemic and lipid-lowering actions of soy protein.     

Dietary fish protein alters blood lipid concentrations and hepatic genes involved in cholesterol homeostasis in the rat model

It is known that various dietary plant proteins are capable of influencing the lipid metabolism of human subjects and animals when compared with casein. Less, however, is known about the effects of fish protein on the cholesterol and triacylglycerol metabolism. Therefore, two experiments were conducted in which rats were fed diets containing 200 g of either fish protein, prepared from Alaska pollack fillets, or casein, which served as control, per kilogram, over 20 and 22 d, respectively. As parameters of lipid metabolism, the concentrations of cholesterol and triacylglycerols in the plasma and liver, the faecal excretion of bile acids and the hepatic expression of genes encoding proteins involved in lipid homeostasis were determined. In both experiments, rats fed fish protein had higher concentrations of cholesteryl esters in the liver, a lower concentration of cholesterol in the HDL fraction (rho > 1.063 kg/l) and lower plasma triacylglycerol concentrations than rats fed casein (P < 0.05). The gene expression analysis performed in experiment 2 showed that rats fed fish protein had higher relative mRNA concentrations of sterol regulatory element-binding protein (SREBP)-2, 3-hydroxy-3-methylglutaryl coenzyme A reductase, LDL receptor, apo AI, scavenger receptor B1 and lecithin-cholesterol-acyltransferase in their liver than did rats fed casein (P < 0.05). The faecal excretion of bile acids and the mRNA concentrations of cholesterol 7alpha-hydroxylase, SREBP-1c and corresponding target genes were not altered. These findings show that fish protein had multiple effects on plasma and liver lipids that were at least in part caused by an altered expression of the hepatic genes involved in lipid homeostasis.     

Hypocholesterolaemic effect of water-insoluble fish protein from Alaska pollock in ovariectomised rats is not abolished by methionine addition

The present study investigated whether the hypocholesterolaemic effect of water-insoluble fish protein (IFP) from Alaska pollock in ovariectomised (OVX) rats was affected by methionine (Met) addition. OVX rats (6 months old) were fed a cholesterol-free diet containing casein, IFP or IFP+Met as a protein source for 28?d. The ratio of Met:glycine was lower in the IFP and IFP+Met diets compared with the casein diet. Body-weight gain, food intake and liver lipids were not affected by the diet. Plasma total cholesterol concentration was lower in OVX rats fed the IFP diet compared with those fed the casein diet. The hypocholesterolaemic effect of the IFP diet was not abolished by Met addition. Amount of bile acids in the small-intestinal content and faecal excretion of bile acids were higher in OVX rats fed the IFP and IFP+Met diets compared with those fed the casein diet. Ileal bile acid transporter (IBAT) mRNA level and faecal excretion of bile acids were significantly lower and higher, respectively, in OVX rats fed the IFP diet compared with those fed the casein diet, but not in those fed the IFP+Met diet. Thus, the hypocholesterolaemic effect of the IFP diet seems to be mediated by increased faecal excretion of bile acids coupled with decreased reabsorption of bile acids from the ileum through a decrease in IBAT and the change in cholesterol metabolism linked to the amino acid profile.     

Supplementation of difructose anhydride III enhanced elevation of plasma equol concentrations and lowered plasma total cholesterol in isoflavone-fed rats

Equol, a derivative of daidzein produced by enterobacteria, has greater activity as a phyto-oestrogen compared with daidzein. Difructose anhydride III (DFAIII) is a newly manufactured non-digestible disaccharide with unique fermentation properties. The present study evaluated the prebiotic effects of DFAIII on equol production and on plasma cholesterol concentrations related to the changes in equol production. We compared plasma equol concentrations at 10.00 and 18.00 hours and faecal isoflavone excretion in three groups of seven rats (male Wistar-ST strain, 6 weeks old) fed a basal diet or a DFAIII or fructooligosaccharide (15 g/kg diet) diet containing 1 g soya isoflavones/kg diet for 20 d. Equol concentrations in the DFAIII group were higher than in the control and fructooligosaccharides groups, especially in the later phase of the light period (18.00 hours) throughout the experiment. Daizein and genistein concentrations did not change between the diet groups. The faecal ratios of equol:daidzein were very high in all groups, but the ratios were higher in the DFAIII group than the control and fructooligosaccharide groups on day 3, and this tendency continued throughout the experiment. On day 20, the plasma total cholesterol concentration was lowest in the DFAIII group. Additionally, the cholesterol concentrations were inversely correlated to plasma equol concentration in all the rats. In conclusion, DFAIII efficiently enhanced plasma equol concentrations, which may be associated with an increase in equol production and a decrease in equol degradation by enterobacteria. Higher plasma equol concentrations may contribute to the hypocholesterolaemic effect of DFAIII feeding.     

Dietary rhubarb (Rheum rhaponticum) stalk fibre stimulates cholesterol 7 alpha-hydroxylase gene expression and bile acid excretion in cholesterol-fed C57BL/6J mice.

Both experimental and clinical studies have indicated that a novel source of dietary fibre, produced from rhubarb (Rheum rhaponticum) stalks, is potentially hypolipidaemic. The present study, using C57BL/6J mice, was undertaken to examine if this fibre source affects cholesterol degradation. Mice were maintained on semi-purified diets containing 50 g rhubarb fibre or cellulose/kg with or without 5 g cholesterol/kg for 4 weeks. In cholesterol-supplemented mice, rhubarb fibre caused significant lowering of plasma cholesterol (-13%) and the hepatic concentrations of total cholesterol (-34%) and cholesteryl esters (-34%). In parallel to the reduction of hepatic cholesteryl ester content, animals fed on rhubarb fibre had significantly lower activity of acyl CoA: cholesterol acyltransferase (EC 2.3.1.26) than the mice maintained on a diet containing cellulose and cholesterol. Rhubarb-fibre feeding accelerated the faecal bile-acid loss and diminished the gall-bladder bile-acid pool in both the normal and the cholesterol-fed mice. The increase in the bile-acid excretion was positively correlated with an increased activity as well as mRNA abundance of cholesterol 7 alpha-hydroxylase (EC 1.14.13.17). The increased excretion of bile acids and induction of cholesterol 7 alpha-hydroxylase activity may account for the hypocholesterolaemic effect of rhubarb fibre.     

Plasma lipoprotein cholesterol in rats fed a diet enriched in chitosan and cholesterol

To investigate the effect of dietary chitosan on plasma lipoprotein cholesterol metabolism, male Sprague-Dawley (SD) rats fed a cholesterol-enriched diet containing cellulose (CE) or chitosan (CS) were studied for 2 wk. Lower plasma total cholesterol, low-density lipoprotein (LDL) cholesterol and very-low-density lipoprotein (VLDL) cholesterol were observed in rats fed a diet containing chitosan. In addition, significantly higher high-density lipoprotein (HDL) cholesterol and HDL2 cholesterol were observed in rats after 2 wk of chitosan feeding. Rats fed the chitosan diet had increased triacylglycerol percentages and decreased free cholesterol, cholesteryl ester and phospholipid percentages in VLDL lipid composition. Chitosan significantly decreased the surface lipid proportions and increased the core lipid proportions in VLDL particles. In addition, the ratios of surface lipids to core lipids of the VLDL particles in rats fed a diet containing chitosan were significantly decreased. A significantly lower plasma apolipoprotein B (Apo B) concentration was observed in rats fed the chitosan diet as compared to those fed the cellulose diet. No significant difference in plasma triacylglycerols or glucose levels was observed between the two dietary groups. Results from this study suggest that chitosan may alter the VLDL particle size and also play an important role in the regulation of lipoprotein metabolism in rats.     

Soy protein enhances the cholesterol-lowering effect of plant sterol esters in cholesterol-fed hamsters

This study aimed to investigate whether the combination of plant sterol esters (PSE) with soy protein or soy isoflavones may have extra cholesterol-lowering effects. Male hamsters (n=20/group) were fed diets containing (g/100 g diet) (A) 20 casein (control), (B) 0.24 PSE, (C) 20 intact soy protein (replacing casein), (D) 0.02 soy isoflavones, (E) 0.24 PSE plus 20 soy protein (replacing casein), or (F) 0.24 PSE plus 0.02 soy isoflavones, for 5 wk. All diets contained 0.08 g cholesterol/100 g diet. Compared with the control diet, the PSE and soy protein diets significantly lowered the plasma total cholesterol concentration by 13% (P<0.05) and 9% (P<0.05), respectively, whereas the isoflavone diet (D) had no effect. The combination of PSE and soy protein (diet E) decreased plasma total cholesterol by 26% (P<0.05). The decrease in plasma cholesterol concentration was mainly in the non-HDL fraction. In addition, the combination of PSE and soy protein significantly decreased plasma triacylglycerol concentration (37%, P<0.05) and reduced cholesterol accumulation in the liver. The abundance of hepatic LDL-receptors was not influenced by any of the test diets. PSE selectively increased fecal excretion of neutral sterols by 190% (P<0.05), whereas soy protein increased fecal excretion of neutral sterols and bile acids by 66% (P<0.05) and 130% (P<0.05), respectively. The combination of PSE and soy protein increased the fecal excretion of neutral sterols and bile acids compared with PSE and soy protein alone. In conclusion, the combination of PSE and soy protein more dramatically lowers plasma lipids than the individual ingredients.     

Effects of betaine supplementation and choline deficiency on folate deficiency-induced hyperhomocysteinemia in rats

The effect of betaine status on folate deficiency-induced hyperhomocysteinemia was investigated to determine whether folate deficiency impairs homocysteine removal not only by the methionine synthase (MS) pathway but also by the betaine-homocysteine S-methyltransferase (BHMT) pathway. For this purpose, we investigated the effect of dietary supplementation with betaine at a high level (1%) in rats fed a folate-deprived 10% casein diet (10C) and 20% casein diet (20C). We also investigated the effect of choline deprivation on folate deficiency-induced hyperhomocysteinemia in rats fed 20C. Supplementation of folate-deprived 10C and 20C with 1% betaine significantly suppressed folate deprivation-induced hyperhomocysteinemia, but the extent of suppression was partial or limited, especially in rats fed 10C, the suppression of plasma homocysteine increment being 48.5% in rats fed 10C and 69.7% in rats fed 20C. Although betaine supplementation greatly increased hepatic betaine concentration and BHMT activity, these increases did not fully explain why the effect of betaine supplementation was partial or limited. Folate deprivation markedly increased the hepatic concentration of N,N-dimethylglycine (DMG), a known inhibitor of BHMT, and there was a significant positive correlation between hepatic DMG concentration and plasma homocysteine concentration, suggesting that folate deficiency increases hepatic DMG concentration and thereby depresses BHMT reaction, leading to interference with the effect of betaine supplementation. Choline deprivation did not increase plasma homocysteine concentration in rats fed 20C, but it markedly enhanced plasma homocysteine concentration when rats were fed folate-deprived 20C. This indicates that choline deprivation reinforced folate deprivation-induced hyperhomocysteinemia. Increased hepatic DMG concentration was also associated with such an effect. These results support the concept that folate deficiency impairs homocysteine metabolism not only by the MS pathway but also by the BHMT pathway.     

Effects of dietary animal and plant proteins on the cholesterol metabolism in immature and mature rats

Three- and 9-mo-old rats were fed purified diets that contained either casein, cottonseed or soybean protein for 28 d, and plasma total and high density lipoprotein (HDL) cholesterol, lecithin cholesterol acyltransferase (LCAT) activity and excretion of fecal neutral sterols were measured. These analyses were performed in order to examine how various dietary proteins from animal and plant sources fed in a purified diet influence the changes in the cholesterol metabolism of the young and old rats. Both immature (3-mo-old) and mature (9-mo-old) rats fed purified diet containing casein maintained significantly higher plasma total and HDL cholesterol levels than their counterparts fed the same diets but containing plant proteins (soybean and cottonseed). The fractional rate of esterification (FR) of plasma free cholesterol in mature casein-fed rats was lower than that in immature rats. The FR was also lower in immature rats fed casein than in those fed plant protein. The net turnover rate (NR) of plasma cholesteryl esters (CE) tended to be higher in mature rats and in general was not affected by the dietary protein source. The rate of fecal excretion of neutral sterols was significantly higher in immature rats than in mature rats and in animals fed plant proteins at both ages than in those fed casein.     

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.     

Hepatic cytochrome p450-2A and phosphoribosylpyrophosphate synthetase-associated protein mRNA are induced in gerbils after consumption of isoflavone-containing protein

Soy intake reduces cholesterol levels, but neither the exact component in soy causing this reduction nor the mechanism by which cholesterol is reduced is known with certainty. In this study, a genetic screen was performed to identify hepatic mRNA in gerbils regulated by soy or soy isoflavones. Gerbils were fed casein, an alcohol-washed soy-based diet (containing low levels of isoflavones), and the soy-based diet supplemented with an isoflavone-containing soy extract. After feeding for 28 d, gerbils were killed, hepatic RNA was isolated, and genes that were differentially expressed in any of the three dietary conditions were identified. Fifteen different mRNA were originally selected, including two mRNA that were studied further and shown to be highly regulated. Messenger RNA levels for both cytochrome P450-2A and phosphoribosylpyrophosphate synthetase-associated protein were up-regulated in a dose-dependent manner when soy replaced casein in the diet at 0, 33, 67 and 100% of original casein levels. A subsequent experiment used purified amino acid mixtures resembling the percentage amino acid composition of soy and casein to ensure that isoflavone-free protein sources could be tested. Using these mixtures, a 2 x 2 x 2 design tested: natural vs. synthetic protein sources, casein- vs. soy-based diets, and isoflavone extract-supplemented or supplement-free diets. This design demonstrated that these two mRNA were again significantly up-regulated more than twofold (P < 0.05) in gerbils fed all diets containing isoflavones. Induction of these two mRNA by soy may be due to the aryl hydrocarbon receptor element in the promoter region of both genes.     

Excessive cholesterolemic response in analbuminemic rats fed a cholesterol-rich diet containing casein.

Female Nagase analbuminemic rats and Sprague-Dawley rats were fed purified diets with or without 1% cholesterol and containing either soybean protein or casein. After consuming the cholesterol-free diets, the analbuminemic rats had significantly higher plasma cholesterol and triglyceride concentrations than the Sprague-Dawley rats. The higher plasma cholesterol levels were essentially in the low density and high density lipoproteins. Based on the fact that the analbuminemic rats excreted more bile acids in feces it is possible that the higher baseline plasma cholesterol concentrations in Nagase analbuminemic rats were partly caused by overproduction of cholesterol. The Nagase analbuminemic rats displayed a greater cholesterolemic response to cholesterol feeding than Sprague-Dawley rats, but only if casein was the protein source in the diet. Casein vs. soybean protein in either cholesterol-free or high cholesterol diets reduced bile acid excretion in Sprague-Dawley but not in Nagase analbuminemic rats. The increased sensitivity to casein plus cholesterol feeding in Nagase analbuminemic rats may be caused by a lack of inhibition of de novo cholesterol synthesis.