Effects of dietary polyphenols on metabolic syndrome features in humans: a systematic review.

Dietary polyphenols constitute a large family of bioactive substances potential beneficial effect on metabolic syndrome (MetS). This review summarizes the results of clinical studies on patients with MetS involving the chronic supplementation of a polyphenol-rich diet, foods, extracts or with single phenolics on the features of MetS (obesity, dyslipidemia, blood pressure and glycaemia) and associated complications (oxidative stress and inflammation). Polyphenols were shown to be efficient, especially at higher doses, and there were no specific foods or extracts able to alleviate all the features of MetS. Green tea, however, significantly reduced body mass index and waist circumference and improved lipid metabolism. Cocoa supplementation reduced blood pressure and blood glucose. Soy isoflavones, citrus products, hesperidin and quercetin improved lipid metabolism, whereas cinnamon reduced blood glucose. In numerous clinical studies, antioxidative and anti-inflammatory effects were not significant after polyphenol supplementation in patients with MetS. However, some trials pointed towards an improvement of endothelial function in patients supplemented with cocoa, anthocyanin-rich berries, hesperidin or resveratrol. Therefore, diets rich in polyphenols, such as the Mediterranean diet, which promote the consumption of diverse polyphenol-rich products could be an effective nutritional strategy to improve the health of patients with MetS. © 2016 The Authors. Obesity Reviews published by John Wiley & Sons Ltd on behalf of World Obesity.

Lycopene inhibits proinflammatory cytokine and chemokine expression in adipose tissue.

Obesity is associated with a low-grade inflammation which is correlated with an increased secretion of pro-inflammatory cytokines and chemokines by adipose tissue, suspected to contribute to the development of insulin resistance. Because lycopene is mostly stored in adipose tissue and possesses anti-inflammatory properties, we hypothesize that lycopene could reduce the production of proinflammatory markers in adipose tissue. In agreement with this hypothesis, we observed a decrease of inflammatory markers such as IL-6, MCP-1 and IL-1ß at both the mRNA and protein level when explants of epididymal adipose tissue from mice fed with a high-fat diet were incubated with lycopene ex vivo. The same effect was reproduced with explants of adipose tissue preincubated in lycopene and then subjected to TNFα stimulation. The contribution of adipocytes and preadipocytes was evaluated. In both preadipocytes and differentiated 3T3-L1 adipocytes, lycopene preincubation for 24 h decreased the TNFα-mediated induction of IL-6 and MCP-1. Finally, the same results were reproduced with human adipocyte primary cultures. The molecular mechanism was also studied. In transient transfections, a decrease of the luciferase gene reporter under control of NF-κB responsive element was observed for cells incubated in the presence of lycopene and TNFα compared to TNFα alone. The involvement of the NF-κB pathway was confirmed by the modulation of IKKα/ß phosphorylation by lycopene. Altogether, these results showed for the first time a limiting effect of lycopene on adipose tissue proinflammatory cytokine and chemokine production. Such an effect could prevent or limit the prevalence of obesity-associated pathologies, such as insulin resistance.

Effect of the main dietary antioxidants (carotenoids, gamma-tocopherol, polyphenols, and vitamin C) on alpha-tocopherol absorption.

OBJECTIVE: (R,R,R)-alpha-tocopherol is a fat-soluble antioxidant vitamin generally ingested with other dietary antioxidants. The objective of this study was to assess whether the main dietary antioxidant classes, that is carotenoids, polyphenols, vitamin C and gamma-tocopherol, affect the intestinal absorption of alpha-tocopherol. METHODS, DESIGN AND SUBJECTS: We evaluated first the effect of different combinations of antioxidants on (R,R,R)-alpha-tocopherol absorption by a human intestinal cell line (Caco-2 clone TC7). Then we compared the effect of two doses of a dietary antioxidant (lutein) on the postprandial chylomicron alpha-tocopherol responses to an alpha-tocopherol-rich meal. Eight healthy men ate two similar meals in a random order at a 1 month interval. The meals contained 24 mg alpha-tocopherol in sunflower oil plus either 18 or 36 mg lutein. Blood samples were collected during the postprandial periods to compare chylomicron alpha-tocopherol responses. RESULTS: A mixture of polyphenols (gallic acid, caffeic acid, (+)-catechin and naringenin) and a mixture of carotenoids (lycopene, beta-carotene and lutein) significantly impaired alpha-tocopherol absorption in Caco-2 cells (P<0.001 and P<0.0001, respectively). The inhibitory effect of gamma-tocopherol was close to significance (P=0.055). In contrast, vitamin C had no significant effect (P=0.158). Naringenin was the only polyphenol that significantly impaired alpha-tocopherol absorption. Postprandial alpha-tocopherol response was weakest at the highest dose of lutein (616+/-280 nmol/l h vs 1001+/-287 nmol/l h). The observed extent of reduction (-38%, P=0.069) supported the inhibitory effect of carotenoids observed in the Caco-2 experiments. CONCLUSION: Naringenin, carotenoids and probably gamma-tocopherol can impair alpha-tocopherol absorption whereas vitamin C and phenolic acids have no effect.

Effect of onion consumption by rats on hepatic drug-metabolizing enzymes.

Fruits and vegetables or their natural constituents which increase detoxication enzymes and/or reduce activating enzymes are considered as good candidates to prevent chemically-induced carcinogenesis. In this study, rats were fed a diet supplemented with 20% onion powder for 9 days. Several cytochrome P450 (CYP)s enzymes (CYP 1A, 2B, 2E1, 3A), which are involved in carcinogen activation, were determined by measuring their enzyme activities using specific substrates. In addition, phase II enzymes activities such as UDP-glucuronosyltransferase (UGT) and glutathione S-transferase (GST), involved in detoxication of carcinogens, were measured. Protein levels of CYPs and GST A1/A2, A3/A5, Ml, M2 and P1 were measured using antibodies in Western blots. Consumption of onion induced CYP 1A and CYP 2B activities while it decreased CYP 2E1 activity. This later modification was accompanied by a decrease of CYP 2E1 levels. The same dietary treatment caused a slight increase of the total GST activity. The relative proportions of GST subunits were modified. GST Al/A2 subunits were increased while GST A3/A5 and GST M2 subunits were decreased and GST M1 and P1 were not modified. Onion consumption also increased p-nitrophenol UGT activity. Taken together, these results suggest that the decrease of CYP 2E1 and the increase of phase II enzymes by onion can afford protection against some carcinogens, while the decrease of some GST subunits could increase the genotoxic effects of other chemicals. The modulating effect of onion could be ascribed to alk(en)yl polysulphides and/or glycosides of flavonols, which were identified in the onion powder.

Induction of cytochrome P450 and/or detoxication enzymes by various extracts of rosemary: description of specific patterns.

The ability of rosemary to modulate cytochrome P450 (CYP) and detoxication enzymes in rat liver was evaluated by comparing the effects of dried leaves and leaf extracts with different chemical compositions: essential oil (EO) containing monoterpenes, a dichloromethane extract (DCME) containing phenolic diterpenes and a water-soluble extract (WSE) containing phenolic compounds such as rosmarinic acid and flavonoids. Chemical analyses were done in order to characterize the composition of extracts. Male Wistar rats received the leaves or extracts of rosemary in their diet at 0.5% (w/w) for 2 weeks. The effects of such treatments were evaluated for CYP (1A, 2B, 2E1), glutathione S-transferase (GST), NAD(P)H: quinone reductase (QR) and UDP-glucuronosyltransferase (UGT) activities and on protein levels (immunoblot analyses). Expression of specific UGT isoforms (mRNA semi-quantification by RT-PCR) was measured. Our study reports that EO selectively induced CYP, particularly CYP2B. WSE enhanced both CYP and detoxication enzymes. DCME acted as a monofunctional inducer, inducing GST, QR and UGT, in particular UGT1A6. Considering the specific pattern of induction obtained with DCME and WSE treatment, it should be relevant to evaluate the chemopreventive potency of these extracts on carcinogenesis in animal models.

Flavonoids in food and natural antioxidants in wine.

Plant foodstuffs are an important source of a wide variety of flavonoids with protective properties on low-density lipoprotein oxidation as shown in vitro and in some human and animal experiments. Increasing information is available concerning the absorption and pharmacokinetics of these molecules, but their long-term protective effect on coronary heart disease still needs further investigation.

Enzymatic browning reactions in apple and apple products.

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.