Onion peel extract increases hepatic low-density lipoprotein receptor and ATP-binding cassette transporter A1 messenger RNA expressions in Sprague-Dawley rats fed a high-fat diet

Phytochemical Characterization and Antioxidant Activity Evaluation for Some Plant Extracts in Conjunction with Pharmacological Mechanism Prediction: Insights into Potential Therapeutic Applications in Dyslipidemia and Obesity

Lipid metabolism dysregulation can lead to dyslipidemia and obesity, which are major causes of cardiovascular disease and associated mortality worldwide. The purpose of the study was to obtain and characterize six plant extracts (ACE-Allii cepae extractum; RSE-Rosmarini extractum; CHE-Cichorii extractum; CE-Cynarae extractum; AGE-Apii graveolentis extractum; CGE-Crataegi extractum) as promising adjuvant therapies for the prevention and treatment of dyslipidemia and its related metabolic diseases. Phytochemical screening revealed that RSE was the richest extract in total polyphenols (39.62 ± 13.16 g tannic acid/100 g dry extract) and phenolcarboxylic acids (22.05 ± 1.31 g chlorogenic acid/100 g dry extract). Moreover, the spectrophotometric chemical profile highlighted a significant concentration of flavones for CGE (5.32 ± 0.26 g rutoside/100 g dry extract), in contrast to the other extracts. UHPLC-MS quantification detected considerable amounts of phenolic constituents, especially chlorogenic acid in CGE (187.435 ± 1.96 mg/g extract) and rosmarinic acid in RSE (317.100 ± 2.70 mg/g extract). Rosemary and hawthorn extracts showed significantly stronger free radical scavenging activity compared to the other plant extracts (p < 0.05). Pearson correlation analysis and the heatmap correlation matrix indicated significant correlations between phytochemical contents and in vitro antioxidant activities. Computational studies were performed to investigate the potential anti-obesity mechanism of the studied extracts using target prediction, homology modeling, molecular docking, and molecular dynamics approaches. Our study revealed that rosmarinic acid (RA) and chlorogenic acid (CGA) can form stable complexes with the active site of carbonic anhydrase 5A by either interacting with the zinc-bound catalytic water molecule or by directly binding Zn2+. Further studies are warranted to experimentally validate the predicted CA5A inhibitory activities of RA and CGA and to investigate the hypolipidemic and antioxidant activities of the proposed plant extracts in animal models of dyslipidemia and obesity.

Potential Role of Quercetin Glycosides as Anti-Atherosclerotic Food-Derived Factors for Human Health

Quercetin is a monomeric polyphenol of plant origin that belongs to the flavonol-type flavonoid subclass. Extensive studies using cultured cells and experimental model animals have demonstrated the anti-atherosclerotic effects of dietary quercetin in relation to the prevention of cardiovascular disease (CVD). As quercetin is exclusively present in plant-based foods in the form of glycosides, this review focuses on the bioavailability and bioefficacy of quercetin glycosides in relation to vascular health effects. Some glucose-bound glycosides are absorbed from the small intestine after glucuronide/sulfate conjugation. Both conjugated metabolites and deconjugated quercetin aglycones formed by plasma β-glucuronidase activity act as food-derived anti-atherogenic factors by exerting antioxidant, anti-inflammatory, and plasma low-density lipoprotein cholesterol-lowering effects. However, most quercetin glycosides reach the large intestine, where they are subject to gut microbiota-dependent catabolism resulting in deglycosylated aglycone and chain-scission products. These catabolites also affect vascular health after transfer into the circulation. Furthermore, quercetin glycosides may improve gut microbiota profiles. A variety of human cohort studies and intervention studies support the idea that the intake of quercetin glycoside-rich plant foods such as onion helps to prevent CVD. Thus, quercetin glycoside-rich foods offer potential benefits in terms of cardiovascular health and possible clinical applications.

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.

Rojo Duro Red Onion Extract Loaded Spray Thermogel as a Sustainable Platform for the Treatment of Oral Mucosa Lesions

The urgent need for new green and sustainable models is ground for the current demand of innovative renewable resource based pharmaceutical products. We propose a Rojo Duro skin onion extract loaded poloxamer/chitosan spray mucoadhesive thermogel aimed at solving current limitations in oral mucosits treatment. Being among the main side effects of radio- and chemotherapy, effective treatment of buccal lesions still represents an unmet medical need. The obtained thermogel combined optimal gelling capacity, release behavior, sprayability, mucoadhesion properties, while maintaining the extract antioxidant and antimicrobial properties. The product preserved all properties when stored for 1 month as a freeze-dried powder at 4 °C. This potential new product is highly translational, as it combines a recognized safety to administration/application advantages, as well as simplicity and sustainability.

Anti-obesity and Hypolipidemic effects of garlic oil and onion oil in rats fed a high-fat diet

Background

Until now, little research concerning the lipid-lowering and anti-obesity functions of garlic oil and onion oil has been performed. The objective of this study was to explore the effects of garlic oil and onion oil on serum lipid levels in hyperlipidemia model rats, to provide a scientific basis for the prevention of hyperlipidemia through a dietary approach, and to explore the potential health benefits of garlic and onion.

Method

Ninety-six male Sprague-Dawley rats were randomly allocated into eight groups based on their body weight and serum levels of triglycerides (TG) and total cholesterol (TC). The rats received repeated oral administration of volatile oils extracted from garlic and onion for 60 days. Serum lipids and parameters of obesity were examined.

Results

The volatile oils suppressed the HFD-induced body weight gain and tended to decrease adipose tissue weight. The oils decreased the levels of TG, TC and LDL-C and increased the serum level of HDL-C compared with the rats in the hyperlipidemia model groups (P < 0.05). The oils were also effective at improving the lipid profile and alleviating hepatic steatosis.

Conclusion

Our results implied that garlic oil and onion oil have anti-obesity properties that can counteract the effects of an HFD on body weight, adipose tissue weight, and serum lipid profiles.

Electronic supplementary material

The online version of this article (10.1186/s12986-018-0275-x) contains supplementary material, which is available to authorized users.

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.

Vitamin E and caloric restriction promote hepatic homeostasis through expression of connexin 26, N-cad, E-cad and cholesterol metabolism genes

Connexins (Cx) and cadherins are responsible for cell homeostasis. The Cx activity is directly related to cholesterol. The present work investigates whether vitamin E, with or without caloric restriction (CR), alters the mRNA expression of Cx26, Cx32, Cx43, N-cadherins (N-cads), E-cadherins (E-cads) and alpha-smooth muscle actin (α-SMA), and evaluates their relation to cholesterol metabolism in rat liver. Animals were divided into different groups: control with ad libitum diet (C), control+vitamin E (CV), aloric restriction with intake to 60% of group C (CR), and the intake of group CR+vitamin E (RV). There were increases of manganese superoxide dismutase (Mn-SOD) and glutathione S-transferase mu 1, indicating antioxidant effects of CR and vitamin E. An increase of nitric oxide in the CR group was in agreement with the Mn-SOD data. Supplementation with vitamin E, with or without CR, upregulated the expression of Cx26 mRNA and increased low-density lipoprotein cholesterol (LDL-c) in the CV group. Reductions of Cx32 and Cx43 were associated with lower LDL-c. Increases in Hmgcr and low-density lipoprotein receptor (LDLr) in the CV and RV groups could be explained by the effect of vitamin E. A reduction of LDLr in the CR group was due to the reduced dietary intake. Increases in cadherins in the CV, CR and RV groups were indicative of tissue maintenance, which was also supported by increases of α-SMA in groups CV and RV. Finally, vitamin E, with or without CR, increased Cx26, probably modulated by expression of the Hmgcr and LDLr genes. This suggests important relationship of Cxs and cholesterol metabolism genes.

Effects of gangliosides from deer bone extract on the gene expressions of matrix metalloproteinases and collagen type II in interleukin-1β-induced osteoarthritic chondrocytes

BACKGROUND/OBJECTIVES

We investigated the anti-osteoarthritic effects of deer bone extract on the gene expressions of matrix metalloproteinases (MMPs) and collagen type II (COL2) in interleukin-1β-induced osteoarthritis (OA) chondrocytes.

MATERIALS/METHODS

Primary rabbit chondrocytes were treated as follows: CON (PBS treatment), NC (IL-1β treatment), PC (IL-1β + 100 µg/mL glucosamine sulphate/chondroitin sulphate mixture), and DB (IL-1β + 100 µg/mL deer bone extract).

RESULTS

The results of the cell viability assay indicated that deer bone extract at doses ranging from 100 to 500 µg/mL inhibits cell death in chondrocytes induced by IL-1β. Deer bone extract was able to significantly recover the mRNA expression of COL2 that was down-regulated by IL-1β (NC: 0.79 vs. DB: 0.87, P < 0.05) and significantly decrease the mRNA expression of MMP-3 (NC: 2.24 vs. DB: 1.75) and -13 (NC: 1.28 vs. DB: 0.89) in OA chondrocytes (P < 0.05).

CONCLUSIONS

We concluded that deer bone extract induces accumulation of COL2 through the down-regulation of MMPs in IL-1β-induced OA chondrocytes. Our results suggest that deer bone extract, which contains various components related to OA, including chondroitin sulphate, may possess anti-osteoarthritic properties and be of value in inhibiting the pathogenesis of OA.

Hypocholesterolemic effect of quercetin-rich onion peel extract in C57BL/6J mice fed with high cholesterol diet

Onion peel (OP) extract is known as a rich source of flavonoids, mainly quercetin. We hypothesized that OP has hypocholesterolemic effects. To investigate the effect of OP, C57BL/6J mice were divided into 4 dietary groups (n=10); normal diet (ND); high cholesterol diet (HC); and high cholesterol diet with 100 or 200 mg OP extract (OP-100 or OP-200, respectively) per kg of body weight. After 12 weeks, lower values of liver weight, serum total cholesterol levels, LDL cholesterol, atherogenic index, cardiac risk factor, hepatic triacylglycerol, and total cholesterol, and higher fecal cholesterol levels were observed in the OP-200 than in the HC group. The hepatic mRNA expression levels of low-density lipoprotein receptors (LDL-R) and cholesterol 7-alpha-monooxygenase (CYP7A1) were high in the OP-200 compared to the HC group. These observations suggest that OP promoted lowering of serum and hepatic cholesterol in mice primarily via fecal excretion.

Antioxidant activity of phenolic extracts from different cultivars of Italian onion (Allium cepa) and relative human immune cell proliferative induction

CONTEXT

The total antioxidant activity (TAC) may vary considerably between onion cultivars. Immunological effects of onion phenolic compounds are still underestimated.

OBJECTIVE

The objective of this study is to determine the total phenol content (TPC) and the relative TAC of three Allium cepa L. (Liliaceae) onion cultivars cultivated in Cannara (Italy): Rossa di Toscana, Borettana di Rovato, and Dorata di Parma, and to evaluate the phenol extracts ability to induce human immune cell proliferation.

MATERIALS AND METHODS

TPC was determined by the Folin-Ciocalteu method, TAC with FRAP, TEAC/ABTS, and DPPH methods. Peripheral blood mononuclear cells from healthy human donors were incubated for 24 h at 37 °C with 1 ng/mL of phenolic extract in PBS, immunostained, and then analyzed by 4-color flow cytometry for the phenotypic characterization of T helper cells (CD4+ cells), cytotoxic T lymphocytes (CD8+ cells), T regulatory cells (CD25high CD4+ cells), and natural killer cells/monocytes (CD16+ cells).

RESULTS

Rossa di Toscana displayed the highest TPC (6.61 ± 0.87 mg GA equivalents/g onion bulb DW) and the highest TAC with the experienced methods: FRAP, 9.19 ± 2.54 μmol Trolox equivalents/g onion bulb DW; TEAC/ABTS, 21.31 ± 0.41 μmol Trolox equivalents/g onion bulb DW; DPPH, 22.90 ± 0.01 μmol Trolox equivalents/g onion bulb DW. Incubation with Rossa di Toscana extract determined an increase in the frequency of the antitumor/anti-infection NK CD16+ immune cells (23.0 ± 0.4%).

DISCUSSION AND CONCLUSIONS

Content of health-promoting phenols and the deriving antioxidant and immunostimulating activity vary considerably among the investigated cultivars. Rossa di Toscana can be considered as a potential functional food.

Recovery effect of onion peel extract against H2 O2 -induced inhibition of gap-junctional intercellular communication is mediated through quercetin

Cellular oxidative damage mediated by reactive oxygen species has been reported to inhibit gap-junctional intercellular communication (GJIC). In turn, the inhibition of GJIC can be attenuated by functional food compounds with antioxidant properties. In this study, we compared the protective effects of onion peel extract (OPE) and onion flesh extract (OFE) on oxidative stress-mediated GJIC inhibition, and investigated the mechanisms of action responsible. OPE restored H2 O2 -induced GJIC inhibition to a higher degree than OFE in WB-F344 rat liver epithelial cells. OPE was found to inhibit H2 O2 -induced phosphorylation of ERK1/2 and Cx43. A radical scavenging assay demonstrated superiority of OPE over OFE, suggesting that the observed effects might be mediated via an antioxidant mechanism. Quercetin is the major compound that is likely to be responsible for the protective effect against H2 O2 -mediated GJIC inhibition. This study suggests that OPE, a material often discarded, may be of value for the future development of functional food products.

PRACTICAL APPLICATION

This study demonstrates that onion peel extract (OPE) exhibits a protective effect against the inhibition of gap-junctional intercellular communication (GJIC) mediated by H2 O2 , which is likely to occur via its antioxidant activity. OPE contains significant concentrations of bioactive phenolic compounds. Reductions in oxidative stress can lead to recovery of GJIC, which has been reported to be implicated in the prevention and treatment of cancers. These findings suggest that onion peel, a common waste product, could be used as potential resources for functional food development. Onion peel could be processed into a quercetin-rich powder or a pill for the prevention of cancer and other oxidative stress-related diseases.

Onion peel tea ameliorates obesity and affects blood parameters in a mouse model of high-fat-diet-induced obesity

The present study examined the effects of onion peel tea (OPT) in a mouse model of high-fat-diet-induced obesity. BALB/c mice were fed a high-fat diet for three weeks, followed by a normal diet with or without OPT for 28 days. OPT suppressed the increases in body weight and level of epididymal fat tissue; it also significantly reduced the serum concentrations of total cholesterol on day 14 and those of glucose and leptin on day 28. The results indicate that OPT has anti-obesity effects in an experimental mouse model of high-fat-diet-induced obesity.

Hypocholesterolemic effect of daily fisetin supplementation in high fat fed Sprague-Dawley rats

We aimed to test whether fisetin could modulate cholesterol homeostasis in rats with diet-induced hypercholesterolemia, and further investigated the underlying mechanisms by which fisetin exerts its cholesterol lowering effect. Blood lipid profile, hepatic cholesterol content, as well as gene expressions in cholesterol metabolism were examined. Elevated levels of total cholesterol and LDL-cholesterol, along with hepatic cholesterol content in a high fat group were found to be significantly reduced by fisetin. The high fat diet significantly decreased hepatic mRNA levels of LDLR, SREBP2, HMGCR and PCSK9 in comparison to the control diet, however, fisetin did not further elicit any changes in mRNA levels of the same genes. The high fat diet dramatically increased the transcript levels of CYP7A1, which was subsequently reversed by the fisetin. In HepG2 cells, fisetin was found to increase the levels of a nuclear form of SREBP2 and LDLR. In conclusion, fisetin supplementation displayed hypocholesterolemic effects by modulating the expression of genes associated with cholesterol and bile acid metabolism.