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.     

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.     

Effect of proteins from beef, pork, and turkey meat on plasma and liver lipids of rats compared with casein and soy protein

OBJECTIVE: We assessed the effect of dietary proteins isolated from beef, pork, and turkey meat on concentrations of cholesterol and triacylglycerols in plasma, lipoproteins, and liver and the composition of the microsomal membrane (fatty acids, phosphatidylcholine/phosphatidylethanolamine ratio) compared with that of casein and soy protein in rats. METHODS: Five groups of 12 rats each were fed semisynthetic diets for 20 d that contained 200 g/kg of proteins isolated from beef, pork, or turkey meat or, as controls, casein or soy protein. RESULTS: Rats fed beef, pork, or turkey proteins did not differ in cholesterol concentrations of plasma, lipoproteins, and liver and in composition of microsomal membrane from rats fed the casein diet. All groups fed a protein from an animal source had higher very low-density lipoprotein (VLDL) and liver cholesterol concentrations than did rats fed soy protein. However, rats fed pork protein had lower concentrations of triacylglycerols in liver, plasma, and VLDL and lower mRNA concentrations of sterol regulatory element binding protein-1 and glucose-6-phosphate dehydrogenase than did rats fed casein. However, concentrations of plasma and VLDL triacylglycerols in rats fed pork protein were not as low as those observed in rats fed soy protein. CONCLUSION: Proteins isolated from beef, pork, or turkey meat do not differ from casein in their effects on cholesterol metabolism. Pork protein decreases plasma triacylglycerol concentrations compared with casein but not compared with soy protein. The triacylglycerol-lowering effect of pork protein compared with casein is suggested to be caused by decreased hepatic fatty acid synthesis.     

A soy protein diet alters hepatic lipid metabolism gene expression and reduces serum lipids and renal fibrogenic cytokines in rats with chronic nephrotic syndrome

Nephrotic syndrome (NS) is characterized by the presence of proteinuria and hyperlipidemia. However, ingestion of soy protein has a hypolipidemic effect. The present study was designed to determine whether the ingestion of a 20% soy protein diet regulates the expression of hepatic sterol regulatory element binding protein (SREBP)-1, fatty acid synthase (FAS), malic enzyme, beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA) reductase (r) and synthase (s), and LDL receptor (r), and to assess whether soy protein improves lipid and renal abnormalities in rats with chronic NS. Male Wistar rats were injected with vehicle or with puromycin aminonucleoside to induce NS and were fed either 20% casein or soy protein diets for 64 d. NS rats fed 20% soy protein had improved creatinine clearance and reduced proteinuria, hypercholesterolemia, hypertriglyceridemia, as well as VLDL-triglycerides and LDL cholesterol compared with NS rats fed the 20% casein diet. In addition, the soy protein diet decreased the incidence of glomerular sclerosis, and proinflammatory cytokines in kidney. Ingestion of the soy protein diet by control rats reduced the gene expression of SREBP-1, malic enzyme, FAS and increased HMG-CoAr, HMG-CoAs and LDLr. However, NS rats fed either casein or soy protein diets had low insulin concentrations with reductions in SREBP-1, FAS and malic enzyme expression compared with control rats fed the casein diet. NS rats fed the soy diet also had lower HMG-CoAr and LDLr mRNA levels than NS rats fed casein. In conclusion, the beneficial effects of soy protein on lipid metabolism are modulated in part by SREBP-1. However, in NS rats, the benefit may be through a direct effect of this protein on kidney rather than mediated by changes in expression of hepatic lipid metabolism genes.     

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.     

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.     

Soy protein peptic hydrolysate with bound phospholipids decreases micellar solubility and cholesterol absorption in rats and caco-2 cells.

This experiment was designed to evaluate the effects of casein, soy protein, soy protein with bound phospholipids (SP), soy protein peptic hydrolysate (SPH) or soy protein peptic hydrolysate with bound phospholipids (SPHP) on the micellar solubility of cholesterol and the taurocholate binding capacity in vitro. We also evaluated the effects of various proteins on cholesterol metabolism in rats and Caco-2 cells. SPHP had a significantly greater bile acid-binding capacity than that of SPH in vitro. Micellar cholesterol solubility in vitro was significantly lower in the presence of SPHP compared to casein tryptic hydrolysate (CTH). The cholesterol micelles containing SPHP and SPH significantly suppressed cholesterol uptake by Caco-2 cells compared to the cholesterol micelles containing CTH. Consistent with these findings in the in vivo cholesterol absorption study using radioisotopes, fecal excretion of total steroids was significantly greater in rats fed the SPHP diet compared with those fed the casein, soy protein, SP and SPH diets. Serum total cholesterol was significantly lower in rats fed SPHP than in those fed casein. The concentrations of total lipids and cholesterol in liver were significantly lower in the SPHP-fed group compared with all other groups. These results suggest that the suppression of cholesterol absorption by direct interaction between cholesterol-mixed micelles and SPHP in the jejunal epithelia is part of the mechanism underlying the hypocholesterolemic action of SPHP. SPHP may also inhibit the reabsorption of bile acids in the ileum, thus lowering the serum cholesterol level.     

Cod protein lowers the hepatic triglyceride secretion rate in rats

The objective of the present study was to determine the combined effects of cod protein and fish oil on the modulation of triglyceride metabolism in rats, and to evaluate their potential mechanisms of action. Plasma and hepatic lipid concentrations, triglyceride (TG) secretion rates and postheparin plasma lipoprotein lipase (LPL) activity were determined in rats fed for 28 d diets varying in both protein (200 g/kg) and lipid (140 g/kg) sources: 1) casein-menhaden oil, 2) casein-beef tallow, 3) cod protein-menhaden oil or 4) cod protein-beef tallow. Menhaden oil feeding diminished hepatic TG concentrations (P = 0.02), hepatic TG secretion rates (P = 0.003) and triglyceridemia (P = 0.02) compared with beef tallow. Hepatic TG concentrations (P = 0.05) and TG secretion rates (P = 0.04) were reduced in rats fed cod protein compared with those fed casein. The protein source did not exert an independent effect on triglyceridemia, whereas the combination of cod protein and menhaden oil resulted in 50% lower plasma TG compared with the casein-beef tallow mixture, whereas the combination of menhaden oil and casein did not significantly decrease triglyceridemia compared with casein-beef tallow. Menhaden oil (P = 0.005) and cod protein (P = 0.03) also lowered plasma cholesterol concentrations in comparison with beef tallow and casein, respectively. This was associated with a reduction in hepatic cholesterol concentrations when rats fed cod protein were compared with those fed casein (P = 0.006). No diet effect was observed on postheparin plasma LPL activity, but the activity of hepatic triglyceride lipase was reduced in rats fed menhaden oil compared with those fed beef tallow. These findings show that both cod protein and menhaden oil exert independent and beneficial effects on lipid metabolism in rats.     

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.     

Effect of soy protein and casein intake on intestinal absorption and lymphatic transport of cholesterol and oleic acid

Rats were fed for 4 wk on defined diets containing either casein or soy as the protein source, or diets in which the lysine/arginine ratios were modified by addition of arginine to casein, and lysine to the soy diet. During this period, weight gains and food intakes were comparable in the four dietary groups. Animals were subjected to cannulation of the left thoracic lymphatic duct, and after an overnight fast, were given a single intragastric dose of a lipid emulsion containing oleic acid and cholesterol. The overall 24-h recoveries of cholesterol and fatty acid in lymph were similar in the four groups, as were the distribution of lipids among the major lipid fractions and lipoprotein classes of thoracic duct lymph. However, analysis of timed lymph collections indicated that absorption of lipids was more rapid in casein-fed rats than in those fed soy protein. Furthermore, addition of arginine to the casein diet resulted in a slowed rate of lipid absorption, and addition of lysine to the soy diet markedly increased the rate of lipid absorption.     

Soy protein affects serum insulin and hepatic SREBP-1 mRNA and reduces fatty liver in rats

The consumption of soy protein was shown to reduce blood lipids in humans and other animal species. Furthermore, it was shown that the ingestion of soy protein maintains normal insulinemia. Thus, the purpose of the present study was to determine whether soy protein affects the synthesis of lipids in the liver through sterol-regulatory element binding protein-1 (SREBP-1) due to modulation of insulin levels. We first conducted a short-term study in which rats were fed a diet containing 18 g/100 g soy protein or casein for 10 d. Rats fed soy protein had significantly lower serum insulin concentrations than rats fed casein, and this response was accompanied by an elevation in hepatic SREBP-1 mRNA that was 53% lower than that in rats fed casein at d 10. The increase in SREBP-1 mRNA occurred 30 min after consumption of the casein mean, and increased steadily for the next 2 h. We then conducted a second study to assess the long-term effect of soy protein consumption for 150 d on hepatic SREBP-1 expression. Long-term consumption of soy protein maintained normal insulin concentrations compared with rats fed casein, which were hyperinsulinemic. Thus, rats fed the soy protein diet had significantly lower expression of SREBP-1 mRNA than rats fed the casein diet. Soy protein intake also reduced the expression of fatty acid synthase (FAS) and malic enzyme, leading to low hepatic lipid depots of triglycerides and cholesterol, whereas rats fed the casein diet developed fatty liver. These data suggest that soy protein regulates SREBP-1 expression by modulating serum insulin concentration, thus preventing the development of fatty liver.     

Long-term effect of feeding a new fiber fraction from soybean to zucker fatty rats

Feeding for a 14-week period, of a diet containing soybean dietary fiber to Zucker fatty (fa/fa) rats decreased plasma glucose and insulin levels, while plasma triglyceride and cholesterol levels remained unchanged. The triglyceride and cholesterol levels in liver and epididymal fat-pads were lower in fiber-fed rats compared to those fed without fiber. Fecal weight was higher and transit time was also shorter in these rats. Soybean dietary fiber decreased the protein fecal excretion.     

Effects of feeding oyster,Crassostrea gigas,on serum and liver lipid levels in rats

The effects of feeding dietary and defatted oyster meat on lipid metabolism were investigated in rats by comparing measurements with those of casein and soybean protein. In the first experiment, male rats were fed 0.1% and 1% cholesterol-supplemented diets containing casein, oyster or soybean protein under the same dietary level of protein (20%). The concentrations of serum and liver cholesterol in the oyster group were significantly lower than those in the casein group for both the 0.1% and 1% cholesterol-supplemented diets. The cholesterol-lowering effect of oyster meat was more predominant than that of soybean protein. Feeding oyster meat significantly decreased the serum triglyceride concentration as compared to feeding casein for the 0.1% cholesterol-supplemented diets, and it reduced hepatic triglyceride concentration in both groups fed the 0.1% and 1% cholesterol-supplemented diets. The excretion of fecal total steroids was higher in the rats fed oyster meat than those fed casein or soybean protein for both the 0.1% and 1% cholesterol-supplemented diets. In the second experiment, the effects of defatted oyster on lipid metabolism were compared with casein and soybean protein in diets supplemented with cholesterol. The serum cholesterol concentration in the defatted oyster group was comparable to that in the other two groups, but the ratio of high-density lipoprotein-cholesterol to total cholesterol was higher in the defatted oyster group. The feeding of defatted oyster induced a lower liver cholesterol concentration as compared to casein and soybean protein. Serum and liver triglyceride levels were lower in the defatted oyster group than in the casein group. Defatted oyster accelerated the fecal excretion of both neutral and acidic steroids as compared to casein. Our results suggest that the feeding of oysters exerts a more potent hypolipidemic activity than soybean protein, and the effect may be ascribed to both lipid and non-lipid fractions in oyster.     

Relationship between amino acid composition of diet and plasma cholesterol level in growing rats fed a high cholesterol diet

The effects of dietary sulfur-containing amino acids and glycine on plasma cholesterol level were studied in rats fed amino acid mixture diets containing cholesterol. The relationship between the amino acid composition of dietary proteins and plasma cholesterol levels was also investigated in rats fed diets containing various kinds of protein such as casein, egg albumin, pork protein, fish protein, corn gluten, wheat gluten and soy protein. Feeding the amino acid mixture corresponding to casein led to an approximately two-fold level of plasma total cholesterol as compared with feeding the amino acid mixture corresponding to wheat gluten. It was possible to reduce the plasma cholesterol of rats fed the amino acid mixture of the casein type by increasing the proportion of cystine in the total sulfur amino acids. Inversely, the deprivation of cystine resulted in an enhancement of the plasma cholesterol of rats fed the gluten type amino acid mixture. Glycine had a tendency to resist increases in the plasma cholesterol level. A significant negative correlation was noted between plasma cholesterol levels and the content of cystine in intact dietary proteins. The results suggest that the differential effect of dietary proteins on plasma cholesterol level is mainly associated with sulfur-containing amino acids included in the protein, regardless of whether it is of animal or plant origin.     

Dietary flaxseed meal is more protective than soy protein concentrate against hypertriglyceridemia and steatosis of the liver in an animal model of obesity

OBJECTIVE: Soy protein and flaxseed meal have been reported to have beneficial effects on many chronic diseases in humans and animals. The primary objective of the study was to evaluate the beneficial effects of soy protein and flaxseed meal on hypertriglyceridemia and liver steatosis associated with obesity and diabetes. We compared the effects of dietary soy protein and flaxseed meal with that of casein on plasma and liver lipids in a genetic model of obesity, type II diabetes and insulin resistance, namely the SHR/N-cp rat. METHODS: Lean and obese phenotypes of SHR/-cp rats were fed AIN 93 diets containing 20% of energy from casein (control), soy protein concentrate or flaxseed meal for six months. Plasma was analyzed for total cholesterol, LDL cholesterol, triglyceride and total protein. Liver was analyzed for steatosis by light microscopy after staining samples with Hematoxylin-Eosin and Oil-Red-O. RESULTS: In lean rats soy protein and flaxseed meal significantly decreased plasma total cholesterol (26.0% and 20.3% respectively) compared to casein. In obese rats flaxseed meal had significant cholesterol lowering effect compared to control rats (41%). Soy protein significantly lowered both plasma LDL-cholesterol and HDL-cholesterol in lean phenotypes while in obese phenotypes flaxseed meal significantly lowered LDL-cholesterol and HDL-cholesterol compared to casein-fed rats. Flaxseed meal also significantly lowered plasma triglyceride in both lean and obese rats compared to casein fed rats (33.7% and 37% respectively). There was significantly greater fat accumulation in livers of obese rats than lean rats (200%) regardless of dietary protein type. Flaxseed meal significantly lowered fat deposition in livers of both lean and obese rats compared to rats fed casein or soy protein. Dietary component(s) present in flaxseed meal or soy protein responsible for hypolipidemic effects is not clear. CONCLUSIONS: The marked hypotriglyceridemic and hypocholesterolemic effects of flaxseed meal may have important therapeutic implications in patients with hypertriglyceridemia and hypercholesterolemia and deserve further study in humans with these disorders. Flaxseed meal supplementation may provide a new therapeutic strategy to reduce hypertriglyceridemia and fatty liver.     

Effect of soy protein, casein and trypsin inhibitor on cholesterol, bile acids and pancreatic enzymes in mice

Dietary vegetable proteins may lower plasma cholesterol compared to animal proteins. We considered the possibility that lower digestibility and the trypsin inhibitor (TI) content of plant proteins could lead to alterations in bile acid metabolism and exocrine pancreatic function mediating some of this change. Mice were fed cholesterolemic diets of different protein source and TI content: casein, soy protein isolate, or casein plus TI for 4 weeks. Plasma and liver cholesterol were measured; pancreata, intestinal contents and mucosal scrapes were collected for bile acid, trypsin, chymotrypsin, amylase, and lipase assays. The soy group had lower plasma cholesterol levels. Intestinal bile acids in this group were higher, suggesting a causal relationship (increased bile acid secretion leading to increased cholesterol catabolism). Conversely, liver cholesterol in this group was raised, reflecting a possible shift in body cholesterol pools. TI addition did not affect lipid metabolism, though it did affect pancreatic function: it led to increased pancreatic weight and depressed intestinal trypsin activity, but elevated chymotrypsin and amylase levels in pancreas and intestine and increased trypsin levels in the pancreas. Therefore, soybean TI does not seem to affect cholesterol metabolism, though it greatly affects pancreatic secretion. On the other hand, soy protein has a marked effect on the bile acid and cholesterol metabolism, which may be a function of protein quality.     

Effects of sources of dietary fat and protein on tissue cholesterol

Dietary variables were soy oil, beef tallow, soy protein, and casein. Dietary combinations were soy oil-soy protein, soy-oil casein, beef tallow-soy protein, and beef tallow-casein, and 96 rats were allotted randomly to the four isocaloric diets. [Crystalline cholesterol was added to standardize each diet at 0.2%.] Two randomly selected rats from each dietary group were killed at 0, 7, 9, 11, 13, 15, 18, 22, 30, 36, 42, and 48 days on experiment to determine the effects of sources (plant versus animal) of dietary fat and protein on tissue cholesterol concentrations and on cholesterogenesis in liver and small intestine. Feeding soy oil, a polyunsaturated fat, resulted in lower blood cholesterol concentrations, higher liver cholesterol concentrations, and lower intestinal cholesterogenesis than did feeding beef tallow, a saturated fat. Feeding soy protein, a plant protein, resulted in lower blood and liver cholesterol concentrations and less intestinal cholesterogenesis than did feeding casein, an animal protein. Hepatic cholesterogenesis and intestinal tissue cholesterol levels were not affected significantly by diet. Eight rats killed at day 0 had, on the average, lesser plasma cholesterol concentrations and greater rates of intestinal cholesterogenesis than rats fed experimental diets. Our results demonstrate that the hypocholesterolemic action of soy oil and soy protein fed to rats may be related to decreased intestinal cholesterogenesis. In addition, soy oil, a polyunsaturated fat caused a redistribution of cholesterol from plasma to liver.     

Soy protein and fish oil independently decrease serum lipid concentrations but interactively reduce hepatic enzymatic activity and gene expression involved in fatty acid synthesis in rats

The degree of interaction between dietary protein and fat sources to modulate hepatic lipid metabolism was investigated. Male rats were fed diets containing either casein or soy protein isolate as the protein source and either palm or soy oil as the fat source. After 3 wk, the activity and mRNA expression of enzymes involved in hepatic fatty acid synthesis were significantly lower with soy protein than casein when palm oil was the fat source. The same values for the same enzymes were greatly lowered regardless of the protein source when fish oil was the fat source. Both enzymatic activity and mRNA expression for fatty acid oxidation were significantly stimulated by fish oil, but only the former was increased by soy protein. Although both soy protein and fish oil reduced serum lipid concentrations, they worked independently. In soy protein-fed rats, mRNA levels of key enzymes related to cholesterol and bile acid synthesis were decreased and increased, respectively, compared with levels in casein-fed animals. Instead, fish oil strongly induced the mRNA expression of biliary cholesterol transporters, ATP-binding cassette sub-family G, member 5 (ABCG5) and ATP-binding cassette sub-family G, member 8 (ABCG8). Therefore, dietary soy protein and fish oil generally exerted independent hypolipidemic actions in rats. However, the reduction of hepatic fatty acid synthesis caused by the simultaneous ingestion of soy protein and fish oil was smaller than their expected additive reduction, because fish oil strongly decreased the synthesis.     

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