Influence of fish protein as compared to casein and soy protein on serum and liver lipids, and serum lipoprotein cholesterol levels in the rabbit

Regulation of Macronutrients in Insulin Resistance and Glucose Homeostasis during Type 2 Diabetes Mellitus

Insulin resistance is an important feature of metabolic syndrome and a precursor of type 2 diabetes mellitus (T2DM). Overnutrition-induced obesity is a major risk factor for the development of insulin resistance and T2DM. The intake of macronutrients plays a key role in maintaining energy balance. The components of macronutrients distinctly regulate insulin sensitivity and glucose homeostasis. Precisely adjusting the beneficial food compound intake is important for the prevention of insulin resistance and T2DM. Here, we reviewed the effects of different components of macronutrients on insulin sensitivity and their underlying mechanisms, including fructose, dietary fiber, saturated and unsaturated fatty acids, and amino acids. Understanding the diet-gene interaction will help us to better uncover the molecular mechanisms of T2DM and promote the application of precision nutrition in practice by integrating multi-omics analysis.

Three differently generated salmon protein hydrolysates reveal opposite effects on hepatic lipid metabolism in mice fed a high-fat diet

This study investigates the effects of salmon peptide fractions, generated using different enzymatic hydrolyzation methods, on hepatic lipid metabolism. Four groups of mice were fed a high-fat diet with 20% casein (control group) or 15% casein and 5% of peptide fractions (treatment groups E1, E2 and E4) for 6weeks. Weight gain was reduced in mice fed E1 and E4-diets compared to control, despite a similar feed intake. Reduced plasma and liver triacylglycerol levels in E1 and E4-mice were linked to reduced fatty acid synthase (FAS) activity and hepatic expression of lipogenic genes. By contrast, plasma and liver lipids increased in the E2 group, concomitant with increased hepatic FAS activity and Δ9 desaturase gene expression. Shotgun lipidomics showed that MUFAs were significantly reduced in the E1 and E4 groups, whereas PUFAs were increased, and the opposite was observed in the E2 group. In conclusion, bioactive peptides with distinctive properties could potentially be isolated from salmon hydrolysates.

Recent advances in dietary proteins and lipid metabolism

PURPOSE OF REVIEW

There is growing interest in defining the dietary approaches for the management of lipid disorders. This review focuses on dietary proteins.

RECENT FINDINGS

Increasing protein intake was coupled with improved lipid profiles in humans and animals. However, most studies increased the protein content by reducing that of fat or carbohydrate or both, making unclear the role of protein alone. Mechanisms of action differ with the sources of proteins, because of amino acid composition and bioactive peptides encrypted in their sequences. Soy protein was investigated the most, and many studies show that its consumption reduces blood cholesterol. The role of other constituents including isoflavones is debated. Short-term studies are consistent in showing lipid-lowering properties of whey proteins, attributed to their relative high content in branched chain amino acids. A limited number of studies, the majority being on animals, have shown hypocholesterolemic activities of fish proteins.

SUMMARY

Dietary proteins regulate lipid metabolism in a manner dependent on their quantity and composition. There is a general consensus that proteins slow lipid absorption and synthesis, and promote lipid excretion. The benefits of dietary proteins remain to be confirmed in individuals with lipid abnormalities, for formulation of optimal dietary alternatives for the management of lipid disturbances.

Effects of antinutritional factors on plasma lipoprotein levels in Japanese flounder Paralichthys olivaceus

This study examined the effects of four types of antinutritional factor (phytic acid, stachyose, soy saponins and soy isoflavones) on lipoprotein levels in plasma of Japanese flounder Paralichthys olivaceus. A basal diet was prepared with fish meal as primary protein source, the other diets were supplemented with 0·2, 0·4 or 0·8% phytic acid, 0·4, 0·8 or 1·5% stachyose, 0·1, 0·35 or 0·7% soy saponins and 0·10, 0·35 or 0·70% soy isoflavones, by dry mass, in place of white flour in the basal diet. Total cholesterol (TC) and triglyceride (TG) levels in plasma of P. olivaceus were not affected by phytic acid or stachyose. In general, addition of 0·2-0·8% phytic acid or 0·4-1·5% stachyose decreased plasma high-density lipoprotein cholesterol (HDL-C) levels, increased plasma low-density lipoprotein cholesterol (LDL-C) levels, thereby increasing the LDL-C:HDL-C ratio. By contrast, supplementation with 0·35-0·7% soy saponins generally depressed plasma TC levels and the LDL-C:HDL-C ratio. Supplementation with 0·35-0·7% soy isoflavones, however, increased plasma TC and TG levels. These results indicate that soy saponins may be partly responsible for the cholesterol-lowering effects of soybean meal.

Effects of a supplementation of n-3 polyunsaturated fatty acids with or without fish gelatin on gene expression in peripheral blood mononuclear cells in obese, insulin-resistant subjects

AIM

To investigate gene expression changes in peripheral blood mononuclear cells (PBMCs) following an n-3 polyunsaturated fatty acid (PUFA) and n-3 PUFA plus fish gelatin (+FG) supplementation.

METHODS

A transcriptome comparison of 8-week supplementation with n-3 PUFA and n-3 PUFA+FG was carried out in PBMCs of 16 obese insulin-resistant subjects.

RESULTS

Erythrocyte n-3 PUFA concentration increased and plasma triglycerides decreased significantly without altering inflammatory parameters after both supplementations. n-3 PUFA supplementation changed the expression of 805 genes, whereas n-3 PUFA+FG supplementation altered the expression of 184 genes. Three genes were commonly changed: fatty acid desaturase 1, free fatty acid receptor 3, and ectodysplasin. Pathway analyses indicate changes in gene expression via the nuclear receptor peroxisome proliferator-activated receptor α pathway after both supplementations. Further, the extent of modifications in the expression of genes implicated in the inflammatory pathways - the oxidative stress response mediated by nuclear factor (erythroid-derived 2)-like 2, nuclear transcription factor κB, oxidative stress, and hypoxia-inducible factor signaling - was different after each supplementation.

CONCLUSION

Although n-3 PUFA and n-3 PUFA+FG supplementations have a distinct impact on gene expression levels, the consequences on biochemical parameters and metabolic pathways were comparable after both supplementations.

Fish nutrients decrease expression levels of tumor necrosis factor-α in cultured human macrophages

Numerous studies have demonstrated the beneficial effects of fish consumption on inflammatory markers. Until now, these beneficial effects of fish consumption have been mostly linked to the omega-3 fatty acids (FA). The objective of the present study was to examine, in vitro, whether expression levels of genes involved in the inflammatory response differ in human macrophages incubated with casein hydrolysates (CH) or fish protein hydrolysates (FPH) in the presence or absence of omega-3 FA compared with omega-3 FA alone. Peripheral blood monocytes differentiated into macrophages from 10 men were incubated in the presence of omega-3 FA (10 μM eicosapentaenoic acid and 5 μM docosahexaenoic acid) or CH or FPH (10, 100, 1,000 μg) with or without omega-3 FA for 48 h. Results demonstrate that expression levels of tumor necrosis factorα ( TNFα) had a tendency to be lower after the addition of FPH alone or CH with omega-3 FA compared with omega-3 FA treatment. Furthermore, the combination of FPH and omega-3 FA synergistically decreased expression levels of TNFα compared to treatment with omega-3 FA or FPH alone. No difference on gene expression levels of interleukin-6 was observed between treatments. In conclusion, these preliminary results suggest that the anti-inflammatory effects of fish consumption can be explained by a synergistic effect of the omega-3 FA with the protein components of fish on TNFα expression and therefore contribute to the beneficial effects of fish consumption. Hence, follow-up studies should be performed to confirm the effects of a diet rich in FPH and omega-3 FA on serum proinflammatory cytokine concentrations.

The mechanism of the cholesterol-lowering effect of water-insoluble fish protein in ovariectomised rats

The purpose of the present study was to investigate whether water-insoluble fish protein (IFP) from Alaska pollock (Theragra chalcogramma) prevents hypercholesterolaemia induced by ovarian hormone deficiency. Wistar female rats, aged 6 months, were subjected to sham-operation or ovariectomy, and fed a cholesterol-free diet containing casein or IPF as a protein source for 28 d. Body-weight gain and food intake increased in the ovariectomised rats as compared with the sham-operated rats. Plasma total cholesterol concentration was decreased and faecal bile acid excretion was increased by IFP in the ovariectomised rats, but not in the sham-operated rats. Plasma homocysteine concentration was decreased by IFP in the ovariectomised rats, but not in the sham-operated rats. Liver lipids and liver cholesterol concentrations were increased and cholesterol 7alpha-hydroxylase (CYP7A1) activity was decreased by ovariectomy, but not by diet. Bile acid content and the ratio of cholic acid groups to chenodeoxycholic acid groups in bile were increased by ovariectomy, but decreased by IFP. Bile acid content in the small intestine was increased by IFP in the ovariectomised rats, but not in the sham-operated rats. 3-Hydroxy-3-methylglutaryl-CoA reductase and microsomal TAG transfer protein mRNA levels were decreased by ovariectomy and IFP, whereas LDL-receptor mRNA level was decreased by ovariectomy but unaffected by diet. Thus, the preventive effect of IFP on the ovarian hormone deficiency-associated increase in plasma cholesterol concentration seems to be mediated by accelerated faecal excretion of bile acids, coupled with an increase in the intestinal pool of bile acids.

Effect of dietary protein level and origin on the redox status in the digestive tract of mice

The present study was undertaken to evaluate the effects of high protein (soybean protein or casein) on the balance between production of free radicals and antioxidant level in digestive organs of mice. For this purpose, male (C57BL/6J) mice were adapted to experimental diets containing soybean protein or casein with 20% (normal protein diets, NPDs) or 60% (high protein diets, HPDs), and HPDs supplemented with 0.06g/kg cysteamine. After two weeks of feeding, oxidative and antioxidative parameters in duodenum, liver and pancreas were measured. The results show that ingestion of high protein markedly increased contents of superoxide anion and malondialdehyde (MDA), decreased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and Na⁺ K⁺-ATPase, and content of reduced glutathione (GSH) in digestive organs of mice (P<0.05). Levels of oxidative parameters were lower and antioxidant capacity of both enzyme and non-enzyme was higher in mice fed with soybean protein than those fed with casein. In groups fed HPDs supplemented with cysteamine, oxidative stress was mitigated. However, oxidative parameter levels were still higher than those of NPD-fed groups. The present study indicates that ingestion of high protein diets could result in an imbalance between oxidant and antioxidant, and thus induce oxidative stress in digestive organs of mice. The oxidative damage was smaller in mice fed with high level of soy protein in comparison with casein.

Hypocholesterolemic effect of katsuobushi, smoke-dried bonito, prevents ovarian hormone deficiency-induced hypercholesterolemia

The purpose of this study was to examine whether katsuobushi, smoked-dried bonito (KB), which is a traditional Japanese food, prevents ovarian hormone deficiency-induced hypercholesterolemia. In experiment 1, ovariectomized rats (OVX-rats) were fed a purified diet containing casein or KB. Compared with the casein diet, the KB diet reduced the plasma cholesterol concentration and apparent protein digestibility, and increased the fecal dry weight and fecal bile acid excretion. In experiment 2, OVX-rats were fed one of the following four diets: casein diet containing corn oil or fish oil (CA/CO or CA/FO), or a diet containing the digested or undigested fraction of KB after treatment with microbial protease (KBE or KBR). KBR contains mainly two components: oil and protease-undigested protein of KB origin. In comparison with the CA/CO diet, the KBE diet did not affect the plasma and liver lipids concentrations, apparent protein digestibility nor fecal bile acid excretion. However, the KBR and CA/FO diets reduced the plasma cholesterol and triacylglycerol (TAG) concentrations and the liver total lipid and TAG concentrations, but increased the liver total and esterified cholesterol concentrations. The KBR diet increased fecal bile acid excretion and fecal dry weight, whereas the CA/FO diet did not. Thus, the preventive effect of KB on the ovarian hormone deficiency-associated increase in plasma cholesterol concentration appears to be mediated by an increase in bile acid excretion through a promoted secretion of bile acids by the binding of bile acids to resistant proteins.

Role of Dietary Proteins and Amino Acids in the Pathogenesis of Insulin Resistance

Dietary proteins and amino acids are important modulators of glucose metabolism and insulin sensitivity. Although high intake of dietary proteins has positive effects on energy homeostasis by inducing satiety and possibly increasing energy expenditure, it has detrimental effects on glucose homeostasis by promoting insulin resistance and increasing gluconeogenesis. Varying the quality rather than the quantity of proteins has been shown to modulate insulin resistance induced by Western diets and has revealed that proteins derived from fish might have the most desirable effects on insulin sensitivity. In vitro and in vivo data also support an important role of amino acids in glucose homeostasis through modulation of insulin action on muscle glucose transport and hepatic glucose production, secretion of insulin and glucagon, as well as gene and protein expression in various tissues. Moreover, amino acid signaling is integrated by mammalian target of rapamycin, a nutrient sensor that operates a negative feedback loop toward insulin receptor substrate 1 signaling, promoting insulin resistance for glucose metabolism. This integration suggests that modulating dietary proteins and the flux of circulating amino acids generated by their consumption and digestion might underlie powerful new approaches to treat various metabolic diseases such as obesity and diabetes.

Fish protein hydrolysate reduces plasma total cholesterol, increases the proportion of HDL cholesterol, and lowers acyl-CoA:cholesterol acyltransferase activity in liver of Zucker rats

There is growing evidence that soy protein improves the blood lipid profiles of animals and humans. We compared the effects of fish protein hydrolysate (FPH), soy protein, and casein (control) on lipid metabolism in Wistar rats and genetically obese Zucker (fa/fa) rats. In Zucker rats, FPH treatment affected the fatty acid composition in liver, plasma, and triacylglycerol-rich lipoproteins. The mRNA levels of Delta 5 and Delta 6 desaturases were reduced by FPH and soy protein feeding compared with casein feeding. In Zucker rats both FPH and soy protein treatment reduced the plasma cholesterol level. Furthermore, the HDL cholesterol:total cholesterol ratio was greater in these rats and in the Wistar rats fed FPH and soy protein compared with those fed casein. Although fecal total bile acids were greater in soy protein-fed Zucker rats than in casein-fed controls, those fed FPH did not differ from the controls. However, the acyl-CoA:cholesterol acyltransferase activity was reduced in Zucker rats fed FPH and tended to be lower (P = 0.13) in those fed soy protein compared with those fed casein. Low ratios of methionine to glycine and lysine to arginine in the FPH and soy protein diets, compared with the casein diet, may be involved in lowering the plasma cholesterol concentration. Our results indicate that the effects of FPH and soy protein on fatty acid metabolism are similar in many respects, but the hypocholesterolemic effects of FPH and soy protein appear to be due to different mechanisms. FPH may have a role as a cardioprotective nutrient.

Tissue antioxidant status differs in spontaneously hypertensive rats fed fish protein or casein

The present study was designed to determine whether changes in dietary protein source are related to changes in antioxidant status determined by enzyme activities of catalase, superoxide dismutase (SOD), gluthatione peroxidase (GSH-Px) and gluthatione reductase (GSSG-Red) and lipid peroxidation levels in various tissues. Spontaneously hypertensive rats (SHR; 5 wk old) were fed diets containing 20% casein or fish protein for 2 mo. Feeding the fish protein diet lowered blood pressure and reduced plasma total cholesterol levels and SOD activity in all tissues except muscle compared with the casein diet. Feeding fish protein also enhanced GSH level and GSH-Px activity in liver and heart, accompanied by lower lipid peroxidation. In kidney, however, the lower catalase activity in rats fed fish protein was associated with an enhancement in lipid peroxidation. Plasma and VLDL + LDL lipid peroxidation was unaffected by dietary proteins. In conclusion, the fish protein diet did not play a relevant role in plasma antioxidative defense status but increased it in liver and heart compared with the casein diet. Fish protein attenuated the development of hypertension and also decreased plasma total cholesterol concentration. Thus, it enhances protection against cardiovascular diseases.

Dietary proteins modulate the effects of fish oil on triglyceridemia in the rat

Sprague-Dawley rats were fed purified diets varying in both protein (20%) and lipid (11%) content for 28 d to verify the independent and interactive effects of dietary proteins and lipids on serum and hepatic lipids, and on tissue lipoprotein lipase (LPL) activity in both fasted and postprandial states. These diets consisted of either casein-menhaden oil, casein-coconut oil, soy protein-menhaden oil (SPMO), soy protein-coconut oil, cod protein-menhaden oil, or cod protein-coconut oil. A randomized 3 x 2 factorial design was used. A significant protein-lipid interaction was seen on serum triglyceride levels: menhaden oil, compared with coconut oil, induced a decrease in serum triglyceride levels when combined with soy protein but not when combined with cod protein and casein. The lower serum triglyceride concentrations observed in the SPMO-fed rats could be the result of decreased hepatic triglycerides when soy protein was compared with casein and when menhaden oil was compared with coconut oil. Total LPL activity in the heart was higher in menhaden oil-fed rats than in coconut oil-fed rats in the postprandial state. The higher LPL activity in the heart could, however, explain only 10% of the reduction of serum triglycerides, contributing slightly to the lowering effects of SPMO diet on serum triglycerides. Therefore, the present results indicate that dietary proteins can modulate the effects of fish oil on triglyceridemia in the rat, and that could be mainly related to specific alterations in hepatic lipid concentrations.

Influence of dietary fish proteins on plasma and liver cholesterol concentrations in rats

The effects of amount and type of dietary fish proteins on plasma and liver cholesterol concentrations were evaluated in female rats. The isonitrogenous diets used contained 10 g cholesterol/kg and were carefully balanced for residual fat, cholesterol, Ca, Mg and P in the protein preparations. Cod meal, soya-bean protein or casein was incorporated into the diets as the only source of dietary protein at three levels: either 24, 48 or 72 g N/kg diet. Extra protein was added to the diet at the expense of the glucose component. In a second experiment soya-bean protein, casein, cod meal, whiting meal or plaice meal was added to the diet at a level of 24 g N/kg. When compared with casein, cod meal and soya-bean protein decreased plasma and liver cholesterol concentrations. A further cholesterol-lowering effect was achieved by increasing the proportion of either soya-bean protein or cod meal in the diet. Substitution of casein for glucose did not influence plasma and liver cholesterol concentrations. Plaice meal in the diet produced lower group mean plasma cholesterol concentrations than did whiting meal. In rats fed on the diet containing plaice meal, liver cholesterol concentrations were significantly lower than those in their counterparts fed on either cod meal or whiting meal. The present study demonstrates that different fish proteins in the diet have different effects on cholesterol metabolism and that the cholesterol-influencing properties of cod meal can be enhanced by the incorporation of higher proportions of this protein in the diet.

Interaction between dietary proteins and lipids in the regulation of serum and liver lipids in the rabbit. Effect of fish protein

Purified diets varying in dietary protein, namely casein (CA), soy protein (SP), fish protein (FP), and lipid origin (corn oil (CN), coconut oil (CO)) were fed to rabbits to evaluate the effects of protein and fat source, as well as protein-lipid interactions, on serum total, lipoprotein and hepatic lipid levels. Dietary proteins and lipids exerted a separate effect on serum total cholesterol (C), very low-density lipoprotein cholesterol (VLDL-C), and low-density lipoprotein cholesterol to high density lipoprotein cholesterol (LDL-C/HDL-C) ratio. Hence, CA increased serum cholesterol compared to SP, while coconut oil enhanced serum and VLDL-C, and decreased LDL-C/HDL-C compared to corn oil. Dietary proteins interacted with dietary lipids to modulate HDL-C levels. Thus, FP maintained a high level of HDL-C regardless of lipid origin, compared to CA and SP whose HDL-C levels were decreased by corn oil, compared to coconut oil. A dietary protein-lipid interaction was also observed in the regulation of liver cholesterol levels. Coconut oil, compared to corn oil, decreased liver cholesterol in rabbits fed FP, whereas hepatic cholesterol concentration was unaltered by dietary lipid source in CA- and SP-fed rabbits. These results demonstrate that dietary proteins act synergistically with dietary lipids to regulate cholesterol metabolism in the rabbit.

Effects of a soy-protein beverage on plasma lipoproteins in children with familial hypercholesterolemia

The effects of soy protein (35% of protein energy) given as a beverage and those of cow-milk proteins were investigated on plasma lipoprotein concentrations in children with familial hypercholesterolemia (FH). Subjects were randomly assigned to either the soy-protein or cow-milk-protein experimental period, with subsequent crossover after a washout period, each period lasting 4 wk. Diets were planned to provide 20% energy as protein, 28% as fat (polyunsaturated:monounsaturated:saturated fatty acids, 1:3:3) and less than 200 mg cholesterol/d. No changes were observed in either plasma cholesterol, low-density-lipoprotein cholesterol, or apolipoprotein concentrations. However, the soy beverage significantly reduced the concentrations of triglyceride and very-low-density-lipoprotein cholesterol (P less than 0.05) and significantly increased the concentrations of high-density-lipoprotein cholesterol (HDL-C) and HDL3-C (P less than 0.04 and P less than 0.03, respectively). These results indicate that the administration of soy protein may induce clinically beneficial effects in children with FH.