Antioxidative Activity of Onion Peel Extract in Obese Women: A Randomized, Double-blind, Placebo Controlled Study

Natural H2S-donors: A new pharmacological opportunity for the management of overweight and obesity

The prevalence of overweight and obesity has progressively increased in the last few years, becoming a real threat to healthcare systems. To date, the clinical management of body weight gain is an unmet medical need, as there are few approved anti-obesity drugs and most require an extensive monitoring and vigilance due to risk of adverse effects and poor patient adherence/persistence. Growing evidence has shown that the gasotransmitter hydrogen sulfide (H2S) and, therefore, H2S-donors could have a central role in the prevention and treatment of overweight/obesity. The main natural sources of H2S-donors are plants from the Alliaceae (garlic and onion), Brassicaceae (e.g., broccoli, cabbage, and wasabi), and Moringaceae botanical families. In particular, polysulfides and isothiocyanates, which slowly release H2S, derive from the hydrolysis of alliin from Alliaceae and glucosinolates from Brassicaceae/Moringaceae, respectively. In this review, we describe the emerging role of endogenous H2S in regulating adipose tissue function and the potential efficacy of natural H2S-donors in animal models of overweight/obesity, with a final focus on the preliminary results from clinical trials. We conclude that organosulfur-containing plants and their extracts could be used before or in combination with conventional anti-obesity agents to improve treatment efficacy and reduce inflammation in obesogenic conditions. However, further high-quality studies are needed to firmly establish their clinical efficacy.

An ethnopharmacological, phytochemical, and pharmacological overview of onion (Allium cepa L.)

ETHNOPHARMACOLOGICAL RELEVANCE

Onion (Allium cepa L.) is one of the most widely distributed species within the Allium genus of family Amaryllidaceae. Onion has been esteemed for its medicinal properties since antiquity. It has been consumed for centuries in various indigenous cultures for the management of several ailments including microbial infections, respiratory, gastrointestinal, skin and cardio-vascular disorders, diabetes, renal colic, rheumatism, sexual impotence, menstrual pain, and headache. However, so far, there is a scarcity of recent data that compiles the plant chemistry, traditional practices, biological features, and toxicity.

AIM OF THE WORK

The aim of this review is to provide a comprehensive and analytical overview of ethnopharmacological uses, phytochemistry, pharmacology, industrial applications, quality control, and toxicology of onion, to offer new perspectives and broad scopes for future studies.

MATERIALS AND METHODS

The information gathered in this review was obtained from various sources including books, scientific databases such as Science Direct, Wiley, PubMed, Google Scholar, and other domestic and foreign literature.

RESULTS

Onion has a long history of use as a traditional medicine for management of various conditions including infectious, inflammatory, respiratory, cardiovascular diseases, diabetes, and erectile dysfunction. More than 400 compounds have been identified in onion including flavonoids, phenolic acids, amino acids, peptides, saponins and fatty acids. The plant extracts and compounds showed various pharmacological activities such as antimicrobial, antidiabetic, anti-inflammatory, anti-hyperlipidemic, anticancer, aphrodisiac, cardioprotective, and neuroprotective activities. In addition to its predominant medicinal uses, onion has found various applications in the functional food industry.

CONCLUSION

Extensive literature analysis reveals that onion extracts and bioactive constituents possess diverse pharmacological activities that can be beneficial for treating various diseases. However, the current research primarily revolves around the documentation of ethnic pharmacology and predominantly consists of in vitro studies, with relatively limited in vivo and clinical studies. Consequently, it is imperative for future investigations to prioritize and expand the scope of in vivo and clinical research. Additionally, it is strongly recommended to direct further research efforts towards toxicity studies and quality control of the plant. These studies will help bridge the current knowledge gaps and establish a solid basis for exploring the plant's potential uses in a clinical setting.

Healthy Aging in Times of Extreme Temperatures: Biomedical Approaches

Climate extremes and rising energy prices present interconnected global health risks. Technical solutions can be supplemented with biomedical approaches to promote healthy longevity in hot and cold conditions. In summer, reducing basal metabolic rate through mild caloric restriction or CR mimetics, such as resveratrol, can potentially be used to lower body temperature. In winter, activating brown adipose tissue (BAT) for non-shivering thermogenesis and improved metabolic health can help adaptation to colder environments. Catechins found in green tea and in other food could be alternatives to drugs for these purposes. This review examines and discusses the biomedical evidence supporting the use of CR mimetics and BAT activators for health benefits amid increasingly extreme temperatures.

Onion supplementation and health metabolic parameters: A systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

Functional foods, such as onions, have been the center of many recent investigations. In this systematic-review and meta-analysis, we aimed to gather up the existing information with regard to the impact of onion supplementation on anthropometric measurements/indices, lipid profile, indices of glycemic control and hepatic health, systolic and diastolic blood pressures (SBP and DBP), and adiponectin and leptin.

METHODS

All major online datasets (PubMed, Web of Science, Cochrane, and Scopus) were thoroughly searched from inception up to October 2022. Relevant randomized controlled trials (RCTs) were obtained using the eligibility criteria. Weighted mean differences (WMDs) were calculated and reported. Statistical significance was set as p-values <0.05.

RESULTS

Among all the retrieved data, 14 RCTs were eligible to be included. The results of the crude analysis showed that onion supplementation significantly improved body fat percentage (BFP), low-density lipoprotein-cholesterol (LDL-c), total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-c), systolic blood pressure, adiponectin, and aspartate aminotransferase (AST). Subgroup analysis revealed that interventions lasting more than 12 weeks can significantly alter weight, waist circumference (WC), body mass index (BMI), BFP, LDL-c, TC, SBP, and DBP. Moreover, the intake of dosages of >300 mg/day of onion supplementation could significantly improve weight, WC, BMI, BFP, LDL-c, HDL-C, TC, AST, ALT, SBP and DBP.

CONCLUSION

It seems that the intake of onion supplementation can improve health metabolic parameters. We observed that with either longer follow-up periods or higher dosages of onion supplementation, improvements in cardio-metabolic parameters could be expected.

Protective effect of onion peel extract on ageing mouse oocytes

Mammalian oocytes not fertilized immediately after ovulation can undergo ageing and a rapid decline in quality. The addition of antioxidants can be an efficient approach to delaying the oocyte ageing process. Onion peel extract (OPE) contains quercetin and other flavonoids with natural antioxidant activities. In this study, we investigated the effect of OPE on mouse oocyte ageing and its mechanism of action. The oocytes were aged in vitro in M16 medium for 16 h after adding OPE at different concentrations (0, 50, 100, 200, and 500 μg/ml). The addition of 100 μg/ml OPE reduced the oocyte fragmentation rate, decreased the reactive oxygen species (ROS) level, increased the glutathione (GSH) level, and improved the mitochondrial membrane potential compared with the control group. The addition of OPE also increased the expression of SOD1, CAT, and GPX3 genes, and the caspase-3 activity in OPE-treated aged oocytes was significantly lower than that in untreated aged oocytes and similar to that in fresh oocytes. These results indicated that OPE delayed mouse oocyte ageing by reducing oxidative stress and apoptosis and enhancing mitochondrial function.

Antiobesity effects of onion (Allium cepa) in subjects with obesity: Systematic review and meta-analysis

Onions are rich in bioactive compounds and have been found to prevent various chronic diseases, including obesity. We performed a systematic review and meta-analysis to investigate the antiobesity effect of onions. Studies were identified in PubMed/MEDLINE, Embase, Web of Science, and CENTRAL focusing on clinical trials evaluating the antiobesity effects of onion in obese subjects. The risk of bias in the studies was evaluated using Cochrane's Risk of Bias tool. The effect of onions was analyzed using data from the selected studies, and the results were indicated by weighted mean difference with 95% CI. The I 2 static test was used to examine heterogeneity between the studies. A total of 38 studies were reviewed, of which five clinical trials meeting the criteria were selected. As investigational products, onion peels were used in four studies and onions were used in one study. Following systematic review, it was determined that the risk of bias was generally low, and body weight, BMI, waist circumference, and triglyceride levels were significantly reduced in the onion groups compared to the placebo. In conclusion, onion intake had an antiobesity effect by reducing body weight and body fat, and this effect was particularly pronounced with onion peel.

The role of ageing and oxidative stress in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the primary cause of intervertebral disc (IVD) disease. With the increased ageing of society, an increasing number of patients are plagued by intervertebral disc disease. Ageing not only accelerates the decreased vitality and functional loss of intervertebral disc cells but also increases intracellular oxidative stress. Moreover, the speed of intervertebral disc ageing is also linked to high levels of reactive oxygen species (ROS) production. Not only is the production of ROS increased in ageing intervertebral disc cells, but antioxidant levels in degenerative intervertebral discs also decrease. In addition to the intervertebral disc, the structural components of the intervertebral disc matrix are vulnerable to oxidative damage. After chronic mitochondrial dysfunction, ROS can be produced in large quantities, while autophagy can eliminate these impaired mitochondria to reduce the production of ROS. Oxidative stress has a marked impact on the occurrence of IDD. In the future, IDD treatment is aiming to improve oxidative stress by regulating the redox balance in intervertebral disc cells. In summary, ageing and oxidative stress promote the degeneration of IVD, but further basic and clinical trials are needed to determine how to treat oxidative stress. At present, although there are many in-depth studies on the relationship between oxidative stress and degeneration of intervertebral disc cells, the specific mechanism has not been elucidated. In this paper, the main causes of intervertebral disc diseases are studied and summarized, and the impact of oxidative stress on intervertebral disc degeneration is studied.

Targeting Oxidative Stress and Inflammation in Intervertebral Disc Degeneration: Therapeutic Perspectives of Phytochemicals

Low back pain is a major cause of disability worldwide that declines the quality of life; it poses a substantial economic burden for the patient and society. Intervertebral disc (IVD) degeneration (IDD) is the main cause of low back pain, and it is also the pathological basis of several spinal degenerative diseases, such as intervertebral disc herniation and spinal stenosis. The current clinical drug treatment of IDD focuses on the symptoms and not their pathogenesis, which results in frequent recurrence and gradual aggravation. Moreover, the side effects associated with the long-term use of these drugs further limit their use. The pathological mechanism of IDD is complex, and oxidative stress and inflammation play an important role in promoting IDD. They induce the destruction of the extracellular matrix in IVD and reduce the number of living cells and functional cells, thereby destroying the function of IVD and promoting the occurrence and development of IDD. Phytochemicals from fruits, vegetables, grains, and other herbs play a protective role in the treatment of IDD as they have anti-inflammatory and antioxidant properties. This article reviews the protective effects of phytochemicals on IDD and their regulatory effects on different molecular pathways related to the pathogenesis of IDD. Moreover, the therapeutic limitations and future prospects of IDD treatment have also been reviewed. Phytochemicals are promising candidates for further development and research on IDD treatment.

The Role of Oxidative Stress in Intervertebral Disc Degeneration

Intervertebral disc degeneration is a very common type of degenerative disease causing severe socioeconomic impact, as well as a major cause of discogenic low back pain and herniated discs, placing a heavy burden on patients and the clinicians who treat them. IDD is known to be associating with a complex process involving in extracellular matrix and cellular damage, and in recent years, there is increasing evidence that oxidative stress is an important activation mechanism of IDD and that reactive oxygen and reactive nitrogen species regulate matrix metabolism, proinflammatory phenotype, autophagy and senescence in intervertebral disc cells, apoptosis, autophagy, and senescence. Despite the tremendous efforts of researchers within the field of IDD pathogenesis, the proven strategies to prevent and treat this disease are still very limited. Up to now, several antioxidants have been proved to be effective for alleviating IDD. In this article, we discussed that oxidative stress accelerates disc degeneration by influencing aging, inflammation, autophagy, and DNA methylation, and summarize some antioxidant therapeutic measures for IDD, indicating that antioxidant therapy for disc degeneration holds excellent promise.

Onion (Allium cepa L.) peels: A review on bioactive compounds and biomedical activities

Huge quantities of byproducts/wastes generated in onion processing are usually discarded, but they are excellent sources of bioactive compounds and phytochemicals. However, with growing interest in the sustainable use of resources and the circular economy to reduce adverse impacts on the environment, food processing wastes such as onion peel/skin can be extracted and employed as inputs in developing or reformulating nutrient supplements, and pharmacological drugs. This review highlights major bioactive components, especially total phenolics, total flavonoid, quercetin and its derivatives present in onion peel/skin and their therapeutic applications as cardioprotective, neuroprotective, antiobesity, antidiabetic, anticancer and antimicrobial agents. The present review emphasized that onion peel is one of the important agricultural by-products which is rich in bioactive compounds and can be utilized as health promoting ingredient especially in pharmacological and biomedical fields. Thus, with increasing burden of life style disorders/non-communicable diseases, finding suitable natural alternative for their treatment is one major concern of the researchers and onion peel and its extract can be exploited as a prime ingredient.

Quercetin as an antiviral agent inhibits the Pseudorabies virus in vitro and in vivo

Pseudorabies virus (PRV) accounts for a critical swine disease incurring economic losses worldwide. Several PRV vaccines are commercially available but these vaccines are effective against only certain prevalent PRV strains in China. To prevent PRV-induced latent infection and decrease the pathogenicity, novel anti-PRV drugs are required to prevent PRV infection. Natural products show exceptional structural diversity representing an important source for developing novel therapeutic agents. Quercetin is a flavonoid with anti-oxidant, anti-cancer, anti-bacterial and anti-viral activities. This study involved quercetin for studying the anti-PRV function in vitro and in vivo. Quercetin was found to significantly decrease the PRV virulent strain HNX at a half-maximal inhibitory concentration (IC₅₀) of 2.618 μM and selectivity index 229. This anti-PRV activity of quercetin was found to be dose-dependent. Furthermore, quercetin also inhibited a wide the infections by a spectrum of PRV strains like HNX, Ea, Bartha and Fa strain. These virucidal effects of quercetin suggest the interaction between these molecules and viral particles, and quercetin is responsible for inhibiting the adsorption of PRV infections. The silico assays suggesting that quercetin might interact with the gD-protein on the surface of the PRV important for viral infection. Additional, the quercetin plantar injection protected the mice from the lethal challenge, decreasing the PRV-infected mice's brain viral loads and mortality. These results provides a anti-PRV strategy and contribute to drug discovery and development.

Effect of onion on blood lipid profile: A meta-analysis of randomized controlled trials

BACKGROUND

Studies indicate that onion supplementation may be effective in the treatment of dyslipidemia; however, the results remain controversial. This meta-analysis was conducted to evaluate potential benefits of onion on lipid profile.

METHODS

Up to 12 October 2020, PubMed, Cochrane Library, Web of Science, and Scopus were searched for randomized controlled trials evaluating the effects of onion on lipid profile. Mean differences (MD) and 95% confidence intervals (CI) were calculated. Meta-analysis was conducted using the fixed-effects model.

RESULTS

Ten trials with 446 participants in total were included in the meta-analysis. The pooled findings of 10 studies suggested that onion supplementation significantly improved high-density lipoprotein cholesterol (HDL) (MD: 2.29 mg/dl; 95% CI: 0.87, 3.72; I 2 = 0%) and low-density lipoprotein cholesterol (LDL) (MD: -6.64 mg/dl; 95% CI: -10.91, -2.36; I 2 = 32%),while onion supplementation did not significantly lower triglycerides (TG) (MD: -6.55 mg/dl; 95% CI: -15.64, 2.53; I 2 = 45%). Analysis of nine trials showed a significant reduction in total cholesterol (TC) (MD: -5.39 mg/dl; 95% CI: -10.68, -0.09; I 2 = 49%) in patients with onion supplementation compared to the control group.

CONCLUSION

In summary, supplementation of onion was beneficial to control dyslipidemia, including improving levels of HDL, LDL, and TC, but could not reduce TG level. The therapeutic benefits of onion for dyslipidemia need to be treated with caution considering that some of the results are not robust.

Protocatechuic acid and quercetin glucosides in onions attenuate changes induced by high fat diet in rats

Yellow onion waste from industrial peeling was used to obtain three pure preparations: protocatechuic acid (PA), quercetin diglycosides (QD) and quercetin monoglycosides (QM). PA contained 61% protocatechuic acid, QD contained 35% quercetin diglucosides, mainly quercetin-3,4'-diglucoside, and QM contained 41% monoglucosides, mainly quercetin-4'-glucoside. The highest antioxidant activity was shown by PA. The effects of preparations on the digestive functions of the gastrointestinal tract of rats as well as the biochemical parameters and antioxidant capacity of the blood in model research on Wistar rats sustained by a high-fat diet were assessed (5 groups per 8 animals). The results of the present experiment showed that different onion phenolic preparations differently modulated the enzymatic activity of faecal (P < 0.001) and caecal (P < 0.001) microbiota. For instance, the QD preparation but not QM efficiently reduced the faecal and caecal bacterial β-glucuronidase activity. Both protocatechuic acid and quercetin monoglycosides showed a beneficial effect by regulating blood lipids (reduction of TC (P < 0.001) and TG (P < 0.001), non-HDL increase in HDL (P < 0.001)), thereby lowering the risk factors for atherosclerotic lesions AI (P = 0.038) and AII (P = 0.013). In addition, onion phenols showed a strong antioxidant effect, however, with a different mechanism: protocatechuic acid via serum ACL (P = 0.033) increase and hepatic GSSG (P = 0.070) decrease, QM via ACW (P < 0.001) increase and hepatic TBARS (P = 0.002) decrease, and QD via serum ACW increase and hepatic GSSG decrease. It can be concluded that onion polyphenols with a lower molar weight, i.e. QM more preferably affect the blood lipid profile than QD. However QD more efficiently reduced the faecal and caecal bacterial β-glucuronidase activity.

Effect of quercetin supplementation on plasma lipid profiles, blood pressure, and glucose levels: a systematic review and meta-analysis

CONTEXT

Clinical trials examining the cardiovascular protective effects of quercetin in humans have reported conflicting results.

OBJECTIVE

The aim of this systematic review was to summarize evidence of the effects of quercetin supplementation on plasma lipid profiles, blood pressure (BP), and glucose levels in humans by performing a meta-analysis of randomized controlled trials.

DATA SOURCES

MEDLINE, Embase, and Scopus databases were searched electronically from their inception to July 2018 to identify randomized controlled trials that assessed the impact of quercetin on lipid profiles, BP, and glucose levels.

STUDY SELECTION

Randomized controlled trials assessing the effects of quercetin or a standardized quercetin-enriched extract on plasma lipid profiles, BP, and glucose levels in humans were eligible for inclusion.

DATA EXTRACTION

A random-effects model was used for data analysis. Continuous variables were expressed as weighted mean differences (WMDs) and 95%CIs. Subgroup analyses were conducted to explore possible influences of study characteristics. Sensitivity analyses were also performed, as were analyses of publication bias.

RESULTS

Seventeen trials (n = 896 participants total) were included in the overall analysis. Pooled results showed that quercetin significantly lowered both systolic BP (WMD, -3.09 mmHg; 95%CI, -4.59 to -1.59; P = 0.0001) and diastolic BP (WMD, -2.86 mmHg; 95%CI, -5.09 to -0.63; P = 0.01). Neither lipid profiles nor glucose concentrations changed significantly. In subgroup analyses, significant changes in high-density lipoprotein cholesterol and triglycerides were observed in trials with a parallel design and in which participants consumed quercetin for 8 weeks or more.

CONCLUSION

Quercetin intake resulted in significantly decreased BP in humans. Moreover, participants who consumed quercetin for 8 weeks or more showed significantly changed levels of high-density lipoprotein cholesterol and triglycerides in trials with a parallel design.

Allium Flavonols: Health Benefits, Molecular Targets, and Bioavailability

Allium species are revered worldwide as vegetables, condiments, and spices as well as the therapeutic agents in traditional medicine. The bioactive compounds in alliums mainly include organosulfur compounds, polyphenols, dietary fibers, and saponins. Flavonoids, particularly flavonols from alliums, have been demonstrated to have the antioxidant, anticancer, hypolipidemic, anti-diabetic, cardioprotective, neuroprotective, and antimicrobial activities. However, flavonols are mostly characterized from onions and have not been comprehensively reviewed across different species. This article therefore focuses on flavonol profiles from different Allium species, their health effects, underlying molecular mechanisms, and bioavailability. Intriguingly, the functional health effects of flavonols were mainly ascribed to their antioxidant and anti-inflammatory activities involving a cascade of multiple signaling pathways. Although the Allium-derived flavonols offer tremendous potential in preventing chronic disease risks, in-depth studies are needed to translate their clinical application.

The Effects of Quercetin Supplementation on Blood Pressures and Endothelial Function Among Patients with Metabolic Syndrome and Related Disorders: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

This systematic review and meta-analysis of randomized controlled trials (RCTs) were performed to determine the effect of quercetin administration on blood pressures and endothelial function among patients with metabolic syndrome (MetS) and related disorders.

METHODS

We searched systematically online databases including Cochrane Library, EMBASE, MEDLINE, and Web of Science to identify the relevant RCTs until December 2018. Q-test and I2 statistics were applied to assess heterogeneity among the included studies. Data were pooled using a random-effects model and weighted mean difference (WMD) was considered as the overall effect size.

RESULTS

Out of 284 citations, 8 RCTs were included in the meta-analysis. We found a significant reduction in systolic blood pressure (SBP) (WMD: -1.69; 95% CI: -3.22, -0.17) following the intake of quercetin supplements. However, quercetin supplementation did not significantly affect diastolic blood pressure (DBP) (WMD: -3.14; 95% CI: -8.24, 1.95), vascular cell adhesion molecule 1 (VCAM-1) (WMD: -24.49; 95% CI: -53.74, 4.77) and intercellular adhesion molecule 1 (ICAM-1) (WMD: -5.78; 95% CI: -12.93, 1.38).

CONCLUSION

In summary, the current meta-analysis demonstrated that quercetin supplementation significantly reduced SBP, yet did not affect DBP, VCAM-1 and ICAM-1 among patients with MetS and related disorders.

Bioadhesive Polymeric Films Based on Red Onion Skins Extract for Wound Treatment: An Innovative and Eco-Friendly Formulation

The onion non-edible outside layers represent a widely available waste material deriving from its processing and consumption. As onion is a vegetable showing many beneficial properties for human health, a study aiming to evaluate the use of extract deriving from the non-edible outside layers was planned. An eco-friendly extraction method was optimized using a hydroalcoholic solution as solvent. The obtained extract was deeply characterized by in vitro methods and then formulated in autoadhesive, biocompatible and pain-free hydrogel polymeric films. The extract, very soluble in water, showed antioxidant, radical scavenging, antibacterial and anti-inflammatory activities, suggesting a potential dermal application for wounds treatment. In vitro studies showed a sustained release of the extract from the hydrogel polymeric film suitable to reach concentrations necessary for both antibacterial and anti-inflammatory activities. Test performed on human keratinocytes showed that the formulation is safe suggesting that the projected formulation could be a valuable tool for wound treatment.

Efficiency of newly formulated functional instant soup mixtures as dietary supplements for elderly

Healthy diet for elderly not only provides them with their needs from macro and micronutrients but also help preventing and treating age-related disorders including non-communicable diseases. So, the present study established to evaluate physical, sensory, chemical and biological characteristics of newly formulated functional instant soup mixtures as dietary supplements for elderly. Lyophilized chickpea, some vegetables and some by-products (at 5% and 10%) were incorporated in the preparation of two instant soup mixtures. The biological effects of the mixtures were studied using a geriatric animal model. The results revealed a reasonable acceptance of the two mixtures even after storage period (4 months) in addition to their contents from protein, fat, crude fiber and carbohydrates (16.62, 6.20, 6.60 and 65.89%, respectively in mixture I; 16.89, 6.30, 6.30 and 54.16%, respectively in mixture II). Mixture II was more promised in flavonoids content and scavenging radical activity than mixture I. Feeding the geriatric rats on the two mixtures did not produce any change in either liver or kidney functions and suggested the ability of these mixtures to prevent the hyperglycemia and hyperlipidemia and improve bone health. A slight decrease in brain lipid peroxidation, although not statistically significant, of rats has been observed upon feeding on these mixtures. Also, the two mixtures increased feces weight of rats which indicates to the beneficial effects of these mixtures in prevention of constipation. In conclusion the formulated instant soup mixtures with high acceptability and antioxidant activity can provide elderly people with high percent of their requirements from macro and micronutrients.

Flavonoids as inducers of white adipose tissue browning and thermogenesis: signalling pathways and molecular triggers

Background

Flavonoids are a class of plant and fungus secondary metabolites and are the most common group of polyphenolic compounds in the human diet. In recent studies, flavonoids have been shown to induce browning of white adipocytes, increase energy consumption, inhibit high-fat diet (HFD)-induced obesity and improve metabolic status. Promoting the activity of brown adipose tissue (BAT) and inducing white adipose tissue (WAT) browning are promising means to increase energy expenditure and improve glucose and lipid metabolism. This review summarizes recent advances in the knowledge of flavonoid compounds and their metabolites.

Methods

We searched the following databases for all research related to flavonoids and WAT browning published through March 2019: PubMed, MEDLINE, EMBASE, and the Web of Science. All included studies are summarized and listed in Table 1.

Result

We summarized the effects of flavonoids on fat metabolism and the specific underlying mechanisms in sub-categories. Flavonoids activated the sympathetic nervous system (SNS), promoted the release of adrenaline and thyroid hormones to increase thermogenesis and induced WAT browning through the AMPK-PGC-1α/Sirt1 and PPAR signalling pathways. Flavonoids may also promote brown preadipocyte differentiation, inhibit apoptosis and produce inflammatory factors in BAT.

Conclusion

Flavonoids induced WAT browning and activated BAT to increase energy consumption and non-shivering thermogenesis, thus inhibiting weight gain and preventing metabolic diseases.

Effects of quercetin supplementation on glycemic control among patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized controlled trials

This systematic review and meta-analysis of randomized controlled trials was performed to determine the effect of quercetin supplementation on glycemic control among patients with metabolic syndrome and related disorders. Databases including PubMed, MEDLINE, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials were searched until August 30, 2018. Nine studies with 10 effect sizes out of 357 selected reports were identified eligible to be included in current meta-analysis. The pooled findings indicated that quercetin supplementation did not affect fasting plasma glucose (FPG), homeostasis model of assessment-estimated insulin resistance, and hemoglobin A1c levels. In subgroup analysis, quercetin supplementation significantly reduced FPG in studies with a duration of ≥8 weeks (weighted mean difference [WMD]: -0.94; 95% confidence interval [CI; -1.81, -0.07]) and used quercetin in dosages of ≥500 mg/day (WMD: -1.08; 95% CI [-2.08, -0.07]). In addition, subgroup analysis revealed a significant reduction in insulin concentrations following supplementation with quercetin in studies that enrolled individuals aged <45 years (WMD: -1.36; 95% CI [-1.76, -0.97]) and that used quercetin in dosages of ≥500 mg/day (WMD: -1.57; 95% CI [-1.98, -1.16]). In summary, subgroup analysis based on duration of ≥8 weeks and used quercetin in dosages of ≥500 mg/day significantly reduced FPG levels.

Clinical effectiveness of quercetin supplementation in the management of weight loss: a pooled analysis of randomized controlled trials

Purpose: The previous investigations which considered the possible effect of the quercetin supplementation for overweight and obesity have led to inconsistent results. Here, we aimed to evaluate the effects of quercetin on weight loss using a meta-analysis of randomized controlled clinical trials (RCTs). Methods: Relevant studies were systematically searched from the MEDLINE, EMBASE, Google Scholar, and Scopus databases. RCTs that investigated the effects of quercetin on weight loss in humans were included for quality assessment, meta-analyses, sensitivity analysis, subgroup analyses, and publication bias assessment. Effect size was expressed as weighted mean difference (WMD) and 95% CI by using a random-effects model. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology was used to rate the level of evidence. Results: Nine RCTs (11 treatment arms) with 525 participants were finally included for data pooling. Our meta-analysis revealed that daily quercetin supplementation did not significantly affect the body weight (WMD: -0.35 kg, 95% CI: -2.03, 1.33; P=0.68), body mass index (WMD: -0.04 kg/m², 95% CI: -0.54, 0.45; P=0.87), waist circumference (WMD: -0.37 cm, 95% CI: -1.81, 1.06; P=0.61), and waist to hip ratio (WMD: -0.01, 95% CI: -0.03, 0.01; P=0.48). Subgroup analysis could not identify factors significantly influencing these parameters. These results were robust in sensitivity analysis, and no significant publication bias was found. Conclusion: The current evidence suggests that quercetin intake did not show a notably favorable effect on weight loss. Future well-designed and long-term clinical trials are required to confirm these results.

Effect of a functional food (vegetable soup) on blood rheology in patients with polycythemia

OBJECTIVE

Key hemorheological variables are associated with several life-threatening diseases including cardio-cerebro-vascular diseases. A diet can influence the blood rheological variables. To compare the effectiveness of a vegetable soup on blood viscosity (BV), hematocrit (Hct), plasma fibrinogen, lipid profile, fasting blood sugar (FBS), and blood osmolarity in patients with polycythemia in comparison to a control group.

MATERIALS AND METHODS

This randomized controlled trial study was conducted at Isar health clinics in Mashhad, Iran, during a 7-month period. Forty male participants (35 to 60 years old) with polycythemia, but without underlying diseases, were included. They randomly assigned to two groups and either received diet/phlebotomy or phlebotomy alone, for 6 weeks. The data were analyzed by SPSS version 16 using parametric tests.

RESULTS

A significant reduction in BV at 30s (p ≤ 0.001), BV at 40s (p ≤ 0.001), BV at 50s (p ≤ 0.001), Hct (p ≤ 0.001), plasma fibrinogen (p ≤ 0.001), total cholesterol (p<0.01), LDL-cholesterol (p<0.01), VLDL-cholesterol (p ≤ 0.001), HDL-cholesterol (p ≤ 0.01), osmolarity (p ≤ 0.001), and FBS (p ≤ 0.001) was observed in diet recipients. Following the intervention, there was a significant decrease in triglyceride (intervention group, p<0.05; control group, p<0.05), in both groups.

CONCLUSION

This trial showed that the plant-based food used in this study could improve blood rheology.

Effect of diet on blood viscosity in healthy humans: a systematic review

Background

Increased whole blood viscosity is associated with increased risk of morbidity and mortality of several life-threatening diseases, including cardiovascular and cerebrovascular disease. The effect of diet on human health has been indicated in many studies, and a health dietary pattern can reduce the incidence of several chronic diseases.

Objective

The aim of this systematic review was to assess the effect of diet on blood viscosity and related parameters such as haematocrit (HCT).

Methods

This systematic review was carried out in 2017. MEDLINE, Embase, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials were searched from inception to 2 May 2017. We selected and included randomized clinical trials (RCTs) in the study. The inclusion criteria were articles that describe the effect of any types of local and traditional diet on blood viscosity in apparently healthy individuals.

Results

Three randomized controlled trials were included in this systematic review. Different diets were used in the included trials. In one study, ingested dried–bonito broth (DBB) for four weeks, significantly reduced the blood passage time in the intervention group from 55.4±3.4 to 47.6±2.0 sec (mean ± SEM, p<0.05) compared with no significant change in the placebo group. Another study has shown significantly increased blood fluidity score in a vegetarian group in contrast to the control group after six weeks. In the last study, plasma viscosity was significantly decreased in a group which used onion–olive-oil capsules compared to the placebo group, with a highly significant difference between the two groups (p=0.0015).

Conclusions

Our components of food diets may decrease blood viscosity in health status. Better and expanded methodology may improve our results.

Translational Aspects of Brown Fat Activation by Food-Derived Stimulants

Since the rediscovery of brown adipose tissue (BAT) in humans, its energy-dissipating ability has been well-recognized. The negative correlations of BAT activity with adiposity and insulin sensitivity provided an obvious rationale for discerning reliable and practical strategies for stimulating BAT. Though cold exposure or use of pharmacological adrenomimetics can activate BAT, they may have adverse effects. Therefore, determining alternative stimulants of BAT with lower risks such as commonly used food ingredients is highly desirable. Recent observations revealed that chemical activation of temperature-sensitive transient receptor potential (TRP) channels by food ingredients can recruit BAT in humans. Furthermore, animal studies have identified several food-derived stimulants of BAT acting through multiple mechanisms distinct from a TRP-mediated process. Dietary compounds acting as an activator of Sirtuin 1, a critical regulator of mitochondrial biogenesis and brown adipocyte differentiation, are one such class of promising food-derived BAT activators in humans. While the individual effects of various dietary factors are increasingly established in a laboratory setting, the potential synergistic effects of multiple stimulants on BAT remain to be tested in a clinical environment. These investigations may support the development of efficient, flexible dietary regimens capable of boosting BAT thermogenesis.

Onion (Allium cepa L.) peel extract (OPE) regulates human sperm motility via protein kinase C-mediated activation of the human voltage-gated proton channel

Onion (Allium cepa L.) and quercetin protect against oxidative damage and have positive effects on multiple functional parameters of spermatozoa, including viability and motility. However, the associated underlying mechanisms of action have not yet been identified. The aim of this study was to investigate the effect of onion peel extract (OPE) on voltage-gated proton (Hv1) channels, which play a critical role in rapid proton extrusion. This process underlies a wide range of physiological processes, particularly male fertility. The whole-cell patch-clamp technique was used to record the changes in Hv1 currents in HEK293 cells transiently transfected with human Hv1 (HVCN1). The effects of OPE on human sperm motility were also analyzed. OPE significantly activated the outward-rectifying proton currents in a concentration-dependent manner, with an EC₅₀ value of 30 μg/mL. This effect was largely reversible upon washout. Moreover, OPE induced an increase in the proton current amplitude and decreased the time constant of activation at 0 mV from 4.9 ± 1.7 to 0.6 ± 0.1 sec (n = 6). In the presence of OPE, the half-activation voltage (V_1/2 ) shifted in the negative direction, from 20.1 ± 5.8 to 5.2 ± 8.7 mV (n = 6), but the slope was not significantly altered. The OPE-induced current was profoundly inhibited by 10 μm Zn²⁺ , the most potent Hv1 channel inhibitor, and was also inhibited by treatment with GF109203X, a specific protein kinase C (PKC) inhibitor. Furthermore, sperm motility was significantly increased in the OPE-treated groups. OPE exhibits protective effects on sperm motility, at least partially via regulation of the proton channel. Moreover, similar effects were exerted by quercetin, the major flavonoid in OPE. These results suggest OPE, which is rich in the potent Hv1 channel activator quercetin, as a possible new candidate treatment for human infertility.

Impact of Flavonols on Cardiometabolic Biomarkers: A Meta-Analysis of Randomized Controlled Human Trials to Explore the Role of Inter-Individual Variability

Several  epidemiological  studies  have  linked  flavonols  with  decreased  risk  of  cardiovascular  disease  (CVD).  However,  some  heterogeneity  in  the  individual  physiological  responses to the consumption of these compounds has been identified. This meta-analysis aimed to  study the effect of flavonol supplementation on biomarkers of CVD risk such as, blood lipids, blood  pressure and plasma glucose, as well as factors affecting their inter-individual variability. Data from  18 human randomized controlled trials were pooled and the effect was estimated using fixed or  random effects meta-analysis model and reported as difference in means (DM). Variability in the  response of blood lipids to supplementation with flavonols was assessed by stratifying various  population subgroups: age, sex, country, and health status. Results showed significant reductions  in total cholesterol (DM = -0.10 mmol/L; 95% CI: -0.20, -0.01), LDL cholesterol (DM = -0.14 mmol/L;  Nutrients 2017, 9, 117  2 of 21  95% CI: -0.21, 0.07), and triacylglycerol (DM = -0.10 mmol/L; 95% CI: -0.18, 0.03), and a significant  increase in HDL cholesterol (DM = 0.05 mmol/L; 95% CI: 0.02, 0.07). A significant reduction was also  observed in fasting plasma glucose (DM = -0.18 mmol/L; 95%CI: -0.29, -0.08), and in blood pressure  (SBP: DM = -4.84 mmHg; 95% CI: -5.64, -4.04; DBP: DM = -3.32 mmHg; 95% CI: -4.09, -2.55).  Subgroup analysis showed a more pronounced effect of flavonol intake in participants from Asian  countries and in participants with diagnosed disease or dyslipidemia, compared to healthy and  normal baseline values. In conclusion, flavonol consumption improved biomarkers of CVD risk,  however, country of origin and health status may influence the effect of flavonol intake on blood  lipid levels.

The Effect of Onion Peel Extract on Inflammatory Mediators in Korean Overweight and Obese Women

Quercetin, found abundantly in onion peel, has been known to have antioxidant and anti-obesity effects and improves endothelial function. The purpose of this study was to evaluate the effects of a quercetin-rich onion peel extract (OPE) on the inflammatory mediators in overweight and obese women. This study was a randomized double-blind, placebo-controlled study. Thirty-seven healthy overweight and obese women were randomly assigned to two groups, and one group was given a soft capsuled OPE (100 mg quercetin/day, n = 18) and the other group a same capsuled placebo (n = 19) for 12 weeks. Fat mass was measured by bioimpendance method at baseline and after 12 weeks of intervention. The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured with colorimetric assay kits. The concentrations of leptin, adiponectin, visfatin, tumor necrosis factor (TNF)-α and interleukin (IL)-4 in plasma were determined by using enzyme-linked immunosorbent assay kits. Baseline characteristics of anthropometric indicators and blood metabolic profiles were not significantly different between placebo and OPE groups. Compared with baseline value, both placebo and OPE supplementation significantly decreased the percent of body fat mass and induced plasma adiponectin levels while ALT and AST activities as well as leptin, visfatin, TNF-α, and IL-4 levels in plasma were not significantly different between two groups after 12 weeks of the supplementation. These findings suggest that 12-week supplementation of OPE do not affect modulators of systemic inflammation in overweight and obese women.