Reduction of paraquat-induced oxidative stress in rats by dietary soy peptide

MyD88 deficiency ameliorates weight loss caused by intestinal oxidative injury in an autophagy-dependent mechanism

BACKGROUND

Gut health plays a vital role in the overall health and disease control of human and animals. Intestinal oxidative stress is a critical player in the induction and progression of cachexia which is conventionally diagnosed and classified by weight loss. Therefore, reduction of intestinal oxidative injury is a common and highly effective strategy for the maintenance of human and animal health. Here we identify intestinal myeloid differentiation primary response gene 88 (MyD88) as a novel target for intestinal oxidative stress using canonical oxidative stress model induced by paraquat (PQ) in vitro and in vivo.

METHODS

Intestinal oxidative stress was induced by administration of PQ in intestinal epithelial cells (IECs) and mouse model. Cell proliferation, apoptosis, DNA damage, mitochondrial function, oxidative status, and autophagy process were measured in wild-type and MyD88-deficient IECs during PQ exposure. Autophagy inhibitor (3-methyladenine) and activator (rapamycin) were employed to assess the role of autophagy in MyD88-deficient IECs during PQ exposure. MyD88 specific inhibitor, ST2825, was used to verify function of MyD88 during PQ exposure in mouse model.

RESULTS

MyD88 protein levels and apoptotic rate of IECs are increased in response to PQ exposure (P < 0.001). Intestinal deletion of MyD88 blocks PQ-induced apoptosis (~42% reduction) and DNA damage (~86% reduction), and improves mitochondrial fission (~37% reduction) and function including mitochondrial membrane potential (~23% increment) and respiratory metabolism capacity (~26% increment) (P < 0.01). Notably, there is a marked decrease in reactive oxygen species in MyD88-deficient IECs during PQ exposure (~70% reduction), which are consistent with high activity of antioxidative enzymes (~83% increment) (P < 0.001). Intestinal ablation of MyD88 inhibits mTOR signalling, and further phosphorylates p53 proteins during PQ exposure, which eventually promotes intestinal autophagy (~74% increment) (P < 0.01). Activation of autophagy (rapamycin) promotes IECs growth as compared with 3-methyladenine-treatment during PQ exposure (~173% increment), while inhibition of autophagy (3-methyladenine) exacerbates oxidative stress in MyD88-deficient IECs (P < 0.001). In mouse model, inhibition of MyD88 using specific inhibitor ST2825 followed by PQ treatment effectively ameliorates weight loss (~4% increment), decreased food intake (~92% increment), gastrocnemius and soleus loss (~24% and ~20% increment, respectively), and intestinal oxidative stress in an autophagy dependent manner (P < 0.01).

CONCLUSIONS

MyD88 modulates intestinal oxidative stress in an autophagy-dependent mechanism, which suggests that reducing MyD88 level may constitute a putative therapeutic target for intestinal oxidative injury-induced weight loss.

Protective effect of genistein pre-treatment on paraquat hepatotoxicity in rats

Paraquat (PQ), an herbicide widely used in agriculture, is considered a highly toxic compound. In hepatocytes, P-glycoprotein (P-gp/Abcb1) is a canalicular transporter involved in PQ extrusion from the cell. Previously, we demonstrated that genistein (GNT) induces P-gp in rat liver. In this study, the protective role of GNT pretreatment towards hepatic damage in a model of acute intoxication with PQ in rats, was investigated. Wistar rats were randomized in 4 groups: Control, GNT (5 mg/kg/day sc, 4 days), PQ (50 mg/kg/day ip, last day) and GNT+ PQ. Hepatic lipoperoxidation (LPO) was evaluated by the thiobarbituric acid reactive substances method. Hepatic levels of 4-hydroxynonenal protein adducts (4-HNEp-add) and glutathione-S-transferase alpha (GSTα) protein expression were evaluated by Western blotting. Hepatic glutathione levels and plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST) were also measured. Biliary excretion of PQ was studied in vivo and in isolated perfused liver. PQ was quantified by HPLC. PQ significantly increased AST and ALT activities, malondialdehyde and 4-HNEp-add levels, whereby pretreatment with GNT ameliorated this effect. PQ biliary excretion remained unchanged after treatments in both experimental models. Hepatic GSTα expression was augmented in GNT group. GNT pretreatment increased hepatic glutathione levels in PQ + GNT group. These results agree with the lower content of 4-HNEp-adds in GNT + PQ group respect to PQ group. Unexpectedly, increased activity of P-gp did not enhance PQ biliary excretion. Thus, GNT protective mechanism is likely through the induction of GSTα which results in increased 4-HNE metabolism before formation of protein adducts.

Ameliorative effect of flaxseed (Linum usitatissimum) and its protein on ethanol-induced hepatotoxicity in Wistar rats

Hepatoprotective effect of flaxseed and its protein on ethanol-induced hepatotoxicity in adult Wistar rats was investigated. The rats were divided into eight groups of which two served as control (group I: Control for AIN-93M diet groups and group II: Control for cereal-pulse diet groups) and six groups received ethanol orally every day. After 10 days along with ethanol, the rats received AIN-93M diet (group III); AIN-93M diet and commercial hepatoprotective formulation (CHF) (group IV); casein replaced by flaxseed protein in AIN-93M diet (group V); cereal-pulse diet (group VI); cereal-pulse diet and CHF (group VII); cereal-pulse diet containing flaxseed (group VIII) for four weeks. The flaxseed and its protein significantly prevented the elevation of plasma markers of hepatic damage, lowered lipid peroxidation, mitigated changes in antioxidant enzymes, and suppressed histopathological signs of hepatic damage. The hepatoprotective effect of flaxseed and its protein was comparable to CHF. These findings implicate the ameliorative effect of flaxseed and its protein on ethanol-induced hepatotoxicity. PRACTICAL APPLICATIONS: Owing to globalization and an increase in earning capacity, alcohol consumption is becoming a part of social life and gradually transforming to addiction. Binge drinking is highly prevalent among low socioeconomic status population, which poses severe risks to health. Alcohol abuse is a public health problem causing three million deaths annually worldwide. Alcohol consumption is known to be a major cause of liver damage worldwide and has contributed to 44% of deaths from liver disease. As abstaining from alcohol is a challenging task, there is an escalating need to formulate potential hepatoprotective agents to prevent alcohol-induced hepatic damage. This study investigates the efficacy of flaxseed and its protein in conferring protection to the liver against ethanol-induced hepatotoxicity. This study also explores the benefits of incorporating flaxseed in the staple cereal-pulse diet. Findings of this study suggest that incorporation of flaxseed or its protein in food formulations can prevent hepatotoxicity and improve the overall quality of life among alcoholics.

Evaluation of the antirheumatic effects of isoflavone-free soy protein isolate and etanercept in rats with adjuvant-induced arthritis

IMPACT STATEMENT

In view of the partial clinical benefit and significant toxicity of traditional rheumatoid arthritis (RA) treatments, there is a growing trend to use complementary therapy. The antiarthritic activity of soy is related to the effect of soy isoflavones. However, little is known about the antiarthritic activity of soy protein itself. This study demonstrates that soy protein isolate (SPI) and etanercept (ETN), a tumor necrosis factor-α (TNF-α) inhibitor, protect rats against the effects of adjuvant-induced arthritis (AIA) by reducing inflammation (TNF-α and matrix metalloproteinase-3), autoantibody production (anticyclic citrullinated peptide), and lipid peroxidation (malondialdehyde). Only SPI improved dyslipidemia accompanied by RA, giving it the advantage of reducing cardiovascular risk. Additionally, the severity of arthritis-induced pathology, including inflammatory infiltrates, synovial hyperplasia, pannus formation, synovial vascularity, and cartilage erosions, was reduced by both SPI and ETN. This research ascertains the possible antiarthritic effect of SPI, making it a recommended alternative therapy for RA.

Bioactive food derived peptides: a review on correlation between structure of bioactive peptides and their functional properties

The presence of bioactive peptides has already been reported in many foods such as milk, fermented products, plant and marine proteins. Bioactive peptides are sequences between 2 and 20 amino acids that can inhibit chronic diseases by modulating and improving physiological functions, so these peptides contribute in holding the consumer health. Also, bioactive peptides can affect pro-health or functional properties of food products. Fractionation of the protein hydrolysate revealed a direct relationship between their structure and functional activity. So, this review focuses on different factors effecting on bioactive peptide structures, biological and functional properties such as antihypertensive, antioxidative, hypocholesterolemic, water-holding capacity, foaming capacity, emulsifying properties and solubility. Also, this review looks at the identified bioactive peptides from food protein sources as potential ingredients of health promoting functional foods.

Health Implications of Bioactive Peptides: A Review

Abstract. Today, due to immobility, improper food habits, and changes in lifestyle, communities are faced with an increase in health problems such as blood pressure, cholesterol, diabetes, and thrombosis. Bioactive peptides are considered as being the main products of protein hydrolysis which exert high effects on the nervous, immune, and gastrointestinal systems. Unlike synthetic drugs, bioactive peptides have no side effects and this advantage has qualified them as an alternative to such drugs. Due to the above-mentioned properties, this paper focuses on the study of health-improving attributes of bioactive peptides such as anti-oxidative, anti-hypertensive, immunomodulatory, anti-microbial, anti-allergenic, opioid, anti-thrombotic, mineral-binding, anti-inflammatory, hypocholesterolemic, and anti-cancer effects. We also discuss the formation of bioactive peptides during fermentation, the main restrictions on the use of bioactive peptides and their applications in the field of functional foods. In general, food-derived biologically active peptides play an important role in human health and may be used in the development of novel foods with certain health claims.

Can the indicators of chronic ethanol consumption be minimized by a continuous flaxseed intake?

The aim of this study was to evaluate the use of flaxseed in animals subjected to ethanol-induced hepatotoxicity. Twenty-four male rats were divided into four groups (n = 6): control group (CG) which received a control diet and water ad libitum; flaxseed group (FG) which received control diet with an addition of 25% flaxseed flour and water ad libitum; ethanol control group (ECG) which received control diet and a solution of 10% ethanol (v/v) as the only liquid source; and ethanol flaxseed group (EFG) which received control diet with an addition of 25% flaxseed flour and a solution of 10% ethanol (v/v) as the only liquid source. The animals were euthanized at 60 days, when blood was collected for biochemical analysis and liver was collected for histomorphometric analysis. Rats fed with diets containing flaxseed showed lower values of alkaline phosphatase (P = 0.020) and lower concentration of total bilirubin (P = 0.006), direct bilirubin (P = 0.013) and indirect bilirubin (P = 0.018) compared to ECG and EFG. The groups receiving flaxseed diets demonstrated higher expression of superoxide dismutase (SOD) enzyme (P < 0.001) than CG and ECG but did not affect thiobarbituric acid (TBARS) expression (P = 0.055). Regarding liver analysis, the ECG and EFG showed larger hepatocyte nuclei and paler cytoplasm than the groups who had not received ethanol, and less in fluid accumulation (oedema) in the cytoplasm than was seen in the FG and EFG livers. These latter two groups showed fewer fatty cells than was seen in the groups that had not been given flaxseed, so that the diagnosis of hepatic steatosis was not justified. In conclusion, therefore, this study showed that the indicators of ethanol chronic consumption can be reduced by the introduction of continuous flaxseed dietary intake.

Effects of melatonin in rats in the initial third stage of pregnancy exposed to sub-lethal doses of herbicides

Exposure to the herbicides Paraquat (PQ) and Roundup® may cause cell lesions due to an increase in oxidative stress levels in different biological systems, even in the reproductive system.

OBJECTIVE

Evaluate the possible changes in reproductive parameters and hepatic, as well as its prevention by simultaneous application of melatonin.

METHODS

Thirty-five female rats at the age of 3 months were divided into seven groups: three groups exposed to sub-lethal doses of the herbicides PQ (50mg/kg) and Roundup® (500mg/kg) (n=5, G2, G3 and G4); three groups exposed to herbicides and simultaneous treatment with 10mg/kg of Melatonin (n=5, G5, G6 and G7) and control group (n=5, G1) from the first to the seventh day of pregnancy. On the seventh day of pregnancy, the rats were anesthetized and euthanized, followed by laparotomy to remove their reproductive tissues and liver. Body and ovary weights were taken and the number of implantation sites, corpora lutea, preimplantation losses, implantation rates were counted and histopathology of the implantation sites, morphometry of the surface and glandular epithelia of endometrium and hepatic oxidative stress were undertaken.

RESULTS

The present study shows the decrease in body and ovary weight, decrease in the number of implantation sites, implantation rate, in the total number of corpora lutea and increase of preimplantation percentages were observed when compared to the G1: Fig. 1 and Table 1, (p>0.001 ANOVA/Tukey). The histopathological analysis of the implantation sites showed a disorder of the cytotrophoblast and cell degeneration within the blastocyst cavity in Fig. 4. Morphometry revealed a reduction in surface and glandular epithelia and in the diameter of the endometrial glands (Table 2; p>0.05 ANOVA/Tukey), whereas in liver, serum levels of thiobarbituric acid reactive substances (TBARS) were found to be significantly elevated (Fig. 2; p>0.001; p>0.05 ANOVA/Tukey), and serum level of reduced glutathione (GSH) was significantly lower (Fig. 3; p>0.001 ANOVA/Tukey). However, treatments with melatonin exhibited improvements in reproductive parameters, as well as reduced lesions in the implantation sites (Fig. 4.) and in serum levels TBARS (Fig. 2; p>0.001 ANOVA/Tukey), serum levels GSH (Fig. 3; p>0.001; p>0.05 ANOVA/Tukey).

CONCLUSIONS

These results reveal that melatonin is a protective agent against experimentally induced maternal/embryo toxicity with herbicides and favoring normalization of reproductive parameters and hepatic.

Inflammaging and Skeletal Muscle: Can Protein Intake Make a Difference?

Inflammaging is the chronic low-grade inflammatory state present in the elderly, characterized by increased systemic concentrations of proinflammatory cytokines. It has been shown that inflammaging increases the risk of pathologic conditions and age-related diseases, and that it also has been associated with increased skeletal muscle wasting, strength loss, and functional impairments. Experimental evidence suggests that the increased concentrations of proinflammatory cytokines and primary tumor necrosis factor α observed in chronic inflammation lead to protein degradation through proteasome activation and reduced skeletal muscle protein synthesis (MPS) via protein kinase B/Akt downregulation. Dairy and soy proteins contain all the essential amino acids, demonstrate sufficient absorption kinetics, and include other bioactive peptides that may offer nutritional benefits, in addition to those of stimulating MPS. Whey protein has antioxidative effects, primarily because of its ability to enhance the availability of reduced glutathione and the activity of the endogenous antioxidative enzyme system. Soy protein and isoflavone-enriched soy protein, meanwhile, may counteract chronic inflammation through regulation of the nuclear transcription factor κB signaling pathway and cytokine production. Although evidence suggests that whey protein, soy protein, and isoflavone-enriched soy proteins may be promising nutritional interventions against the oxidative stress and chronic inflammation present in pathologic conditions and aging (inflammaging), there is a lack of information about the anabolic potential of dietary protein intake and protein supplementation in elderly people with increased systemic inflammation. The antioxidative and anti-inflammatory effects, as well as the anabolic potential of protein supplementation, should be further investigated in the future with well-designed clinical trials focusing on inflammaging and its associated skeletal muscle loss.

In vitro antioxidant activity and in vivo antifatigue effect of layered double hydroxide nanoparticles as delivery vehicles for folic acid

Folic acid antioxidants were successfully intercalated into layered double hydroxides (LDH) nanoparticles according to a previous method with minor modification. The resultant folic acid-LDH constructs were then characterized by X-ray powder diffraction and transmission electron microscopy. The in vitro antioxidant activities, cytotoxicity effect, and in vivo antifatigue were examined by a series of assays. The results showed that folic acid-LDH antioxidant system can scavenge 1,1-diphenyl-2-picrylhydrazyl and hydroxyl free radicals and chelate pro-oxidative Cu²⁺. The in vitro cytotoxicity assays indicated that folic acid-LDH antioxidant system had no significant cytotoxic effect or obvious toxicity to normal cells. It also prolonged the forced swimming time of the mice by 32% and 51% compared to folic acid and control groups, respectively. It had an obvious effect on decreasing the blood urea nitrogen and blood lactic acid, while increasing muscle and hepatic glycogen levels. Therefore, folic acid-LDH might be used as a novel antioxidant and antifatigue nutritional supplement.

Effects of soy protein hydrolysates on the growth and fermentation performances of brewer's yeast

Soy protein isolate was hydrolysed with Alcalase, Papain, Flavorzyme and Protemax, respectively, and further fractioned by ultrafiltration. The resulting soy protein hydrolysates (SPH) and their ultrafiltration fractions were used to examine their effects on the growth and fermentation performances of brewer's yeast. Results showed that degree of hydrolysis, molecular weight distribution and amino acid composition of SPH significantly affected the growth, viability and fermentation performance of brewer's yeast. The SPH prepared from different proteolytic enzymes exhibited distinct growth‐ and fermentation‐promoting activity for brewer's yeast. The SPH treated with Protemax for 9 h and with the molecular weight below 3 kDa showed the highest growth‐promoting activity and induced more rapidly reducing sugar consumption and higher ethanol production. The relatively lower molecular weight and the hydrophilic and electropositive amino acid residues (Lys, His, Arg and Ile) in SPH might be responsible for its functionality, promoting the growth and fermentation of brewer's yeast.

Functional implications and ubiquitin-dependent degradation of the peptide transporter Ptr2 in Saccharomyces cerevisiae

The peptide transporter Ptr2 plays a central role in di- or tripeptide import in Saccharomyces cerevisiae. Although PTR2 transcription has been extensively analyzed in terms of upregulation by the Ubr1-Cup9 circuit, the structural and functional information for this transporter is limited. Here we identified 14 amino acid residues required for peptide import through Ptr2 based on the crystallographic information of Streptococcus thermophilus peptide transporter PepTst and based on the conservation of primary sequences among the proton-dependent oligopeptide transporters (POTs). Expression of Ptr2 carrying one of the 14 mutations of which the corresponding residues of PepTst are involved in peptide recognition, salt bridge interaction, or peptide translocation failed to enable ptr2Δtrp1 cell growth in alanyl-tryptophan (Ala-Trp) medium. We observed that Ptr2 underwent rapid degradation after cycloheximide treatment (half-life, approximately 1 h), and this degradation depended on Rsp5 ubiquitin ligase. The ubiquitination of Ptr2 most likely occurs at the N-terminal lysines 16, 27, and 34. Simultaneous substitution of arginine for the three lysines fully prevented Ptr2 degradation. Ptr2 mutants of the presumed peptide-binding site (E92Q, R93K, K205R, W362L, and E480D) exhibited severe defects in peptide import and were subjected to Rsp5-dependent degradation when cells were moved to Ala-Trp medium, whereas, similar to what occurs in the wild-type Ptr2, mutant proteins of the intracellular gate were upregulated. These results suggest that Ptr2 undergoes quality control and the defects in peptide binding and the concomitant conformational change render Ptr2 subject to efficient ubiquitination and subsequent degradation.

Effect of whey protein hydrolysates with different molecular weight on fatigue induced by swimming exercise in mice

BACKGROUND

In order to improve the antioxidant and anti-fatigue capacities of whey protein for wider utilization, it was hydrolyzed by chymotrypsin (EC 3.4.21.1) to produce whey protein hydrolysate (WPH). Fractions of WPH with different molecular weight (MW) were separated by ultrafiltration. Kunming mice in various treatment groups were orally administered (1.5 g kg(-1) body weight) whey protein isolate (WPI), WPH or WPHs with different MW (<5, 5-10, 10-30 or >30 kDa) for 6 weeks to explore whether different MW fractions of WPH affected mice fatigue.

RESULTS

Compared with the control group (orally administered 9 g kg(-1) saline) or the WPI group, low-MW (<10 kDa) WPH groups showed prolonged swimming time (P < 0.05) and had higher concentrations (P < 0.05) of glucose, non-esterfied fatty acid, liver glycogen, superoxide dismutase and glutathione peroxidase and lower concentration of lactate. Low-MW (<10 kDa) WPHs had higher hydroxyl- and α,α-diphenyl-β-picrylhydrazyl-scavenging abilities and ferrous-chelating capacity than WPI.

CONCLUSION

The results proved that low-MW (<10 kDa) WPHs with higher anti-fatigue capacity showed higher free radical-scavenging and ferrous-chelating activities.

Effects of soya oligosaccharides and soya oligopeptides on lipid metabolism in hyperlipidaemic rats

In the present study, we aimed to examine the effects of soya oligosaccharides (SOS) and soya oligopeptides (SOP) on blood lipid levels, release of vasoactive substances, antioxidant activity and faecal bile acid (FBA) excretion in rats fed a high-fat diet (HFD). Male Sprague-Dawley rats were evenly divided into five groups according to diets as follows: regular diet (control), HFD, HFD enriched with 2 % of SOS (SOS), HFD enriched with 3 % of SOP (SOP) and HFD enriched with 2 % SOS and 3 % SOP (SOSP). The results showed that SOS and SOP significantly reduced plasma total cholesterol, LDL-cholesterol and TAG, whereas HDL-cholesterol concentration was significantly increased. Furthermore, SOS and SOP reduced plasma apoB, apoE and the apoB:apoAI ratio, whereas apoAI was significantly increased. Moreover, SOS and SOP also reduced plasma thromboxane A₂ (TXA₂) and the TXA₂:prostacyclin (PGI₂) ratio, whereas plasma PGI₂ and nitric oxide were significantly increased. In addition, SOS and SOP significantly reduced serum and liver malondialdehyde concentrations and increased FBA excretion. However, we did not observe obvious influences of SOS and SOP on superoxide dismutase activities in the liver of HFD-fed rats. The combination of 2 % SOS and 3 % SOP showed a more marked effect than SOS or SOP alone in improving the lipid profile, release of vasoactive substances and increasing FBA excretion (P < 0.05). In summary, SOS and SOP might help prevent atherosclerosis through improving abnormal blood lipid levels, regulating vasoactive substances and protecting against oxidative stress.

Soy peptides enhance heterologous membrane protein productivity during the exponential growth phase of Saccharomyces cerevisiae

In this study, the production of eight G protein-coupled receptors by Saccharomyces cerevisiae was compared using two types of media, one of which contained soy peptides and the other free amino acids. Yeast cell growth improved in the medium with soy peptides, and the expression levels of six of the receptors increased during the exponential phase by an average of 2.3-fold as against the free amino acid-based medium. The enhancement of protein expression by soy peptides can be explained by alleviation of metabolite stress due to amino acid source depletion caused by heterologous protein expression.

Possible role of milk-derived bioactive peptides in the treatment and prevention of metabolic syndrome

The growing prevalence of metabolic syndrome as well as its impact on public health has garnered increased attention in recent years. As a result, metabolic syndrome is now considered one of the world's leading public health problems. Bioactive peptides deriving from milk proteins may play an important role in the prevention and treatment of metabolic syndrome and its complications via several mechanisms, such as the satiety response, the regulation of insulinemia levels and blood pressure, the uptake of free radicals, and alteration of the lipid profile. These peptides can be incorporated into functional foods or administered via nutraceuticals to decrease the risk of obesity, atherogenesis, arterial hypertension, and type 2 diabetes. Recent findings have generated considerable scientific and commercial interest in milk-derived bioactive peptides, leading to numerous publications on the effectiveness of these substances. This review summarizes the current knowledge on bioactive peptides derived from milk proteins and examines the potential value of these peptides in the treatment and prevention of metabolic syndrome and its complications.

Soy protein retards the progression of non-alcoholic steatohepatitis via improvement of insulin resistance and steatosis

OBJECTIVE

Non-alcoholic steatohepatitis (NASH) is a common cause of liver disease, and it may progress to fibrosis or cirrhosis. The aim of this study was to investigate the effects of soy protein on hepatic steatosis and insulin resistance in NASH.

METHODS

Forty male Sprague-Dawley rats were fed a high-fat diet for 4 wk to induce NASH and then were allocated to one of four diets: a NASH-inducing diet, a standard diet, a NASH-inducing diet plus soy protein, and a standard diet plus soy protein.

RESULTS

After the 10-wk experimental period, the results showed that soy protein significantly lowered plasma cholesterol concentrations and body fat accumulation. Soy protein intake also decreased the hepatic lipid depots of triacylglycerols and cholesterol and decreased the concentrations of lipid peroxides. In an analysis of antioxidative status, rats fed the soy protein diet showed improved antioxidative potential due to increases in superoxide dismutase and catalase activities and a decrease in the protein expression of cytochrome P450 2E1.

CONCLUSION

Soy protein may improve the liver function in patients with NASH by lowering lipid levels in the blood and liver, increasing the antioxidative capacity, and improving insulin resistance.

Antioxidative peptides from food proteins: a review

Bioactive peptides, as products of hydrolysis of diverse food proteins, are the focus of current research. They exert various biological roles, one of the most crucial of which is the antioxidant activity. Reverse relationship between antioxidant intake and diseases has been approved through plenty of studies. Antioxidant activity of bioactive peptides can be attributed to their radical scavenging, inhibition of lipid peroxidation and metal ion chelation properties of peptides. It also has been proposed that peptide structure and its amino acid sequence can affect its antioxidative properties. This paper reviews bioactive peptides from food sources concerning their antioxidant activities. Additionally, specific characteristics of antioxidative bioactive peptides, enzymatic production, methods to evaluate antioxidant capacity, bioavailability, and safety concerns of peptides are reviewed.

Soy constituents: modes of action in low-density lipoprotein management

Reviewed here are the modes of action of soy components used as ingredients in foods, which can lower plasma levels of low-density lipoprotein (LDL) and cholesterol, which are markers for the risk for atherosclerosis. Soy ingredients act via more than one mode of action including the following: LDL absorption suppression, cholesterol efflux stimulation, LDL resorption stimulation, LDL oxidation prevention, LDL particle size increase, cholesterol synthesis reduction, and bile secretion increase. Individual genetics, lifestyle, and nutrition habits alter LDL management and a better understanding of the various modes of actions of soy ingredients may facilitate the composition of effective ingredient cocktails. The optimization of food components offers further alternatives to LDL management to augment drug therapy for patients who are unable to reach their target LDL cholesterol levels or who are suffering from side effects or drug insensitivity.

Improvement of tolerance to freeze–thaw stress of baker’s yeast by cultivation with soy peptides

The tolerance to freeze-thaw stress of yeast cells is critical for frozen-dough technology in the baking industry. In this study, we examined the effects of soy peptides on the freeze-thaw stress tolerance of yeast cells. We found that the cells cultured with soy peptides acquired improved tolerance to freeze-thaw stress and retained high leavening ability in dough after frozen storage for 7 days. The final quality of bread regarding its volume and texture was also improved by using yeast cells cultured with soy peptides. These findings promote the utilization of soy peptides as ingredients of culture media to improve the quality of baker's yeast.

Soybean Foods and Their Benefits: Potential Mechanisms of Action

Isoflavones have been proposed to be the active component responsible for the beneficial effects of soybean foods, and appear to work in conjunction with the proteins to protect against cancer, cardiovascular disease, and osteoporosis. Most of the research activities on the benefits of soybean foods have focused on the role these isoflavones play in disease prevention or treatment; however, there is also some evidence that the benefits are attributable to certain peptides or protein fractions from soybeans. This review will focus on some of the potential mechanisms whereby soybeans exert their protective effects against heart disease, cancer, and osteoporosis.

Plasma antioxidant capacity in response to diets high in soy or animal protein with or without isoflavones

BACKGROUND

Several clinical trials have suggested that soy intake decreases oxidative stress. Soy isoflavones have antioxidant properties in vitro, but results of supplementation in clinical trials are inconclusive.

OBJECTIVE

The objective was to evaluate the independent effects of soy protein and soy-derived isoflavones on plasma antioxidant capacity and biomarkers of oxidative stress.

DESIGN

Forty-two hypercholesterolemic (LDL cholesterol > 3.36 mmol/L) subjects aged >50 y were provided with each of 4 diets in random order in a crossover design. Diets varied in protein source (10% of energy, soy or animal) and isoflavone content (trace or 50 mg/1000 kcal) and were consumed for 42 d each. Plasma antioxidants, protein carbonyls, malondialdehyde, total antioxidant performance, LDL oxidizability, and urinary F(2)-isoprostanes were measured at the end of each dietary phase.

RESULTS

Plasma antioxidant concentrations were not significantly different, regardless of dietary treatment, except for isoflavones, which were higher after isoflavone supplementation (P = 0.0001). Although plasma total antioxidant performance was 10% higher with soy protein intake, regardless of dietary isoflavones (P = 0.0003), soy protein did not significantly affect most individual markers of oxidative stress (LDL oxidizability, urinary F(2)-isoprostanes, malondialdehyde, or protein carbonyls in native plasma). However, soy protein was associated with modestly lower concentrations of protein carbonyls in oxidized plasma. There was no significant effect of isoflavones on LDL oxidation, urinary F(2)-isoprostanes, or protein carbonyl groups, although, paradoxically, the plasma malondialdehyde concentration was significantly higher after the isoflavone-rich diets (P = 0.04).

CONCLUSIONS

Diets relatively high in soy protein or soy-derived isoflavones have little effect on plasma antioxidant capacity and biomarkers of oxidative stress.