Basic biochemical mechanisms behind the health benefits of polyphenols

Olive oil polyphenols decrease blood pressure and improve endothelial function in young women with mild hypertension

BACKGROUND

Olive oil polyphenols have been associated with several cardiovascular health benefits. This study aims to examine the influence of a polyphenol-rich olive oil on blood pressure (BP) and endothelial function in 24 young women with high-normal BP or stage 1 essential hypertension.

METHODS

We conducted a double-blind, randomized, crossover dietary-intervention study. After a run-in period of 4 months (baseline values), two diets were used, one with polyphenol-rich olive oil (∼30 mg/day), the other with polyphenol-free olive oil. Each dietary period lasted 2 months with a 4-week washout between diets. Systolic and diastolic BP, serum or plasma biomarkers of endothelial function, oxidative stress, and inflammation, and ischemia-induced hyperemia in the forearm were measured.

RESULTS

When compared to baseline values, only the polyphenol-rich olive oil diet led to a significant (P < 0.01) decrease of 7.91 mm Hg in systolic and 6.65 mm Hg of diastolic BP. A similar finding was found for serum asymmetric dimethylarginine (ADMA) (-0.09 ± 0.01 µmol/l, P < 0.01), oxidized low-density lipoprotein (ox-LDL) (-28.2 ± 28.5 µg/l, P < 0.01), and plasma C-reactive protein (CRP) (-1.9 ± 1.3 mg/l, P < 0.001). The polyphenol-rich olive oil diet also elicited an increase in plasma nitrites/nitrates (+4.7 ± 6.6 µmol/l, P < 0.001) and hyperemic area after ischemia (+345 ± 386 perfusion units (PU)/sec, P < 0.001).

CONCLUSIONS

We concluded that the consumption of a diet containing polyphenol-rich olive oil can decrease BP and improve endothelial function in young women with high-normal BP or stage 1 essential hypertension.

Inhibition of angiotensin-converting enzyme activity by flavonoids: structure-activity relationship studies

Previous studies have demonstrated that certain flavonoids can have an inhibitory effect on angiotensin-converting enzyme (ACE) activity, which plays a key role in the regulation of arterial blood pressure. In the present study, 17 flavonoids belonging to five structural subtypes were evaluated in vitro for their ability to inhibit ACE in order to establish the structural basis of their bioactivity. The ACE inhibitory (ACEI) activity of these 17 flavonoids was determined by fluorimetric method at two concentrations (500 µM and 100 µM). Their inhibitory potencies ranged from 17 to 95% at 500 µM and from 0 to 57% at 100 µM. In both cases, the highest ACEI activity was obtained for luteolin. Following the determination of ACEI activity, the flavonoids with higher ACEI activity (i.e., ACEI >60% at 500 µM) were selected for further IC₅₀ determination. The IC₅₀ values for luteolin, quercetin, rutin, kaempferol, rhoifolin and apigenin K were 23, 43, 64, 178, 183 and 196 µM, respectively. Our results suggest that flavonoids are an excellent source of functional antihypertensive products. Furthermore, our structure-activity relationship studies show that the combination of sub-structures on the flavonoid skeleton that increase ACEI activity is made up of the following elements: (a) the catechol group in the B-ring, (b) the double bond between C2 and C3 at the C-ring, and (c) the cetone group in C4 at the C-ring. Protein-ligand docking studies are used to understand the molecular basis for these results.

Blood pressure-lowering effect of dietary (-)-epicatechin administration in L-NAME-treated rats is associated with restored nitric oxide levels

Epidemiological and intervention studies have shown that the intake of certain chocolates or cocoa products decreases blood pressure (BP) in humans. (-)-Epicatechin is the most abundant flavanol present in cocoa seeds and its derived foods. This work investigates the effects of dietary (-)-epicatechin on BP in rats that received N(ω)-nitro-l-arginine methyl ester (L-NAME) for 4 days. (-)-Epicatechin administration prevented the 42mm Hg increase in BP associated with the inhibition of NO production in a dose-dependent manner (0.2-4.0g/kg diet). This BP effect was associated with a reduction in L-NAME-mediated increase in the indexes of oxidative stress (plasma TBARS and GSSG/GSH(2) ratio) and with a restoration of the NO concentration. At the vascular level, none of the treatments modified NOS expression, but (-)-epicatechin administration avoided the L-NAME-mediated decrease in eNOS activity and increase in both superoxide anion production and NOX subunit p47(phox) expression. In summary, (-)-epicatechin was able to prevent the increase in BP and in oxidative stress and restored NO bioavailability. The fact that (-)-epicatechin is present in several plants usually consumed by humans gives the possibility of developing diets rich in those plants or pharmacological strategies using that flavonoid to diminish BP in hypertensive subjects.

(-)-Epicatechin prevents TNFα-induced activation of signaling cascades involved in inflammation and insulin sensitivity in 3T3-L1 adipocytes

Obesity is major public health concern worldwide and obese individuals exhibit a higher risk of chronic diseases such as type 2 diabetes. Inflammation plays a significant role in metabolic regulation and mounting evidence highlight the contribution of adipose tissue to systemic inflammatory state. Food extracts with a high content of (-)-epicatechin have been found to exert systemic anti-inflammatory actions, however the anti-inflammatory actions of (-)-epicatechin on adipose tissue remain to be determined. The aim of this study was to investigate the capacity of (-)-epicatechin to prevent tumor necrosis alpha (TNFα)-induced activation of cell signals involved in inflammation and insulin resistance (NF-κB, mitogen-activated protein kinases (MAPKs), AP-1, and peroxisome proliferator activated receptor γ (PPARγ)) in differentiated white adipocytes (3T3-L1). TNFα triggered the activation of transcription factors NF-κB and AP-1, and MAPKs ERK1/2, JNK, and p38. (-)-Epicatechin caused a dose (0.5-10 μM)-dependent decrease in TNFα-mediated JNK, ERK1/2, and p-38 phosphorylation, and nuclear AP-1-DNA binding. (-)-Epicatechin also inhibited TNFα-triggered activation of the NF-κB signaling cascade, preventing TNFα-mediated p65 nuclear transport and nuclear NF-κB-DNA binding. (-)-Epicatechin also attenuated the TNFα-mediated downregulation of PPARγ expression and decreased nuclear DNA binding. Accordingly, (-)-epicatechin inhibited TNFα-mediated altered transcription of genes (MCP-1, interleukin-6, TNFα, resistin, and protein-tyrosine phosphatase 1B) involved in inflammation and insulin signaling. In conclusion, (-)-epicatechin can attenuate TNFα-mediated triggering of signaling cascades involved in inflammation and insulin resistance. These findings could be of relevance in the dietary management of obesity and metabolic syndrome.

Polyphenol derivatives - potential regulators of neutrophil activity

The study provides new information on the effect of natural polyphenols (derivatives of stilbene - resveratrol, pterostilbene, pinosylvin and piceatannol and derivatives of ferulic acid - curcumin, N-feruloylserotonin) on the activity of human neutrophils in influencing oxidative burst. All the polyphenols tested were found to reduce markedly the production of reactive oxygen species released by human neutrophils on extra-and intracellular levels as well as in cell free system. Moreover, pinosylvin, curcumin, N-feruloylserotonin and resveratrol decreased protein kinase C activity involved in neutrophil signalling and reactive oxygen species production. Our results suggest that due to their anti-neutrophil activity, the polyphenols tested might be attractive candidates in therapeutic development.

Recent developments on polyphenol–protein interactions: effects on tea and coffee taste, antioxidant properties and the digestive system

Tea and coffee are widely consumed beverages across the world and they are rich sources of various polyphenols. Polyphenols are responsible for the bitterness and astringency of beverages and are also well known to impart antioxidant properties which is beneficial against several oxidative stress related diseases like cancer, cardiovascular diseases, and aging. On the other hand, proteins are also known to display many important roles in several physiological activities. Polyphenols can interact with proteins through hydrophobic or hydrophilic interactions, leading to the formation of soluble or insoluble complexes. According to recent studies, this complex formation can affect the bioavailability and beneficiary properties of both the individual components, in either way. For example, polyphenol-protein complex formation can reduce or enhance the antioxidant activity of polyphenols; similarly it can also affect the digestion ability of several digestive enzymes present in our body. Surprisingly, no review article has been published recently which has focused on the progress in this area, despite numerous articles having appeared in this field. This review summarizes the recent trends and patterns (2005 onwards) in polyphenol-protein interaction studies focusing on the characterization of the complex, the effect of this complex formation on tea and coffee taste, antioxidant properties and the digestive system.

Toxicological aspects of the use of phenolic compounds in disease prevention

The consumption of a diet low in fat and enhanced by fruits and vegetables, especially rich in phenolic compounds, may reduce risks of many civilization diseases. The use of traditional medicines, mainly derived from plant sources, has become an attractive segment in the management of many lifestyle diseases. Concerning the application of dietary supplements (based on phenolic compounds) in common practice, the ongoing debate over possible adverse effects of certain nutrients and dosage levels is of great importance. Since dietary supplements are not classified as drugs, their potential toxicities and interactions have not been thoroughly evaluated. First, this review will introduce phenolic compounds as natural substances beneficial for human health. Second, the potential dual mode of action of flavonoids will be outlined. Third, potential deleterious impacts of phenolic compounds utilization will be discussed: pro-oxidant and estrogenic activities, cancerogenic potential, cytotoxic effects, apoptosis induction and flavonoid-drug interaction. Finally, future trends within the research field will be indicated.

Flavonoids and metabolic syndrome

Increasing evidence indicates that several mechanisms, associated or not with antioxidant actions, are involved in the effects of flavonoids on health. Flavonoid-rich beverages, foods, and extracts, as well as pure flavonoids are studied for the prevention and/or amelioration of metabolic syndrome (MS) and MS-associated diseases. We summarize evidence linking flavonoid consumption with the risk factors defining MS: obesity, hypertriglyceridemia, hypercholesterolemia, hypertension, and insulin resistance. Nevertheless, a number of molecular mechanisms have been identified; the effects of flavonoids modifying major endpoints of MS are still inconclusive. These difficulties are explained by the complex relationships among the risk factors defining MS, the multiple biological targets controlling these risk factors, and the high number of flavonoids (including their metabolites) present in the diet and potentially responsible for the in vivo effects. Consequently, extensive basic and clinical research is warranted to assess the final relevance of flavonoids for MS.

Phytochemical profile and nutraceutical value of old and modern common wheat cultivars

Among health-promoting phytochemicals in whole grains, phenolic compounds have gained attention as they have strong antioxidant properties and can protect against many degenerative diseases. Aim of this study was to profile grain phenolic extracts of one modern and five old common wheat (Triticum aestivum L.) varieties and to evaluate their potential antiproliferative or cytoprotective effect in different cell culture systems.Wheat extracts were characterized in terms of antioxidant activity and phenolic composition (HPLC/ESI-TOF-MS profile, polyphenol and flavonoid contents). Results showed that antioxidant activity (FRAP and DPPH) is mostly influenced by flavonoid (both bound and free) content and by the ratio flavonoids/polyphenols. Using a leukemic cell line, HL60, and primary cultures of neonatal rat cardiomyocytes, the potential antiproliferative or cytoprotective effects of different wheat genotypes were evaluated in terms of intracellular reactive oxygen species levels and cell viability. All tested wheat phenolic extracts exerted dose-dependent cytoprotective and antiproliferative effects on cardiomyocytes and HL60 cells, respectively. Due to the peculiar phenolic pattern of each wheat variety, a significant genotype effect was highlighted. On the whole, the most relevant scavenging effect was found for the old variety Verna. No significant differences in terms of anti-proliferative activities among wheat genotypes was observed.Results reported in this study evidenced a correspondence between the in vitro antioxidant activity and potential healthy properties of different extracts. This suggests that an increased intake of wheat grain derived products could represent an effective strategy to achieve both chemoprevention and protection against oxidative stress related diseases.

A versatile targeted metabolomics method for the rapid quantification of multiple classes of phenolics in fruits and beverages

Compelling evidence of the health benefits of phenolic compounds and their impact on food quality have stimulated the development of analytical methods for the identification and quantification of these compounds in different matrices in recent years. A targeted metabolomics method has been developed for the quantification of 135 phenolics, such as benzoates, phenylpropanoids, coumarins, stilbenes, dihydrochalcones, and flavonoids, in fruit and tea extracts and wine using UPLC/QqQ-MS/MS. Chromatography was optimized to achieve separation of the compounds over a period of 15 min, and MRM transitions were selected for accurate quantification. The method was validated by studying the detection and quantification limits, the linearity ranges, and the intraday and interday repeatability of the analysis. The validated method was applied to the analysis of apples, berries, green tea, and red wine, providing a valuable tool for food quality evaluation and breeding studies.

Evolution of phenolic compounds from color and flavor problems to health benefits

Early studies focused on the negative effects on color and flavor of foods, followed by exploration of the antioxidant properties and the associated health benefits. The growing body of evidence suggests that plant-based polyphenols may help prevent or delay the onset of a multiplicity of diseases. Newer work suggests that a variety of polyphenols can alter the expression of genes in the inflammatory pathway. Data also show that the absorption of the polyphenols is very limited. Insulin resistance and endothelial and mitochondrial dysfunction are hallmarks of the metabolic syndrome and aging and occur at the early stages of the disease. There is limited clinical evidence that certain polyphenolic metabolites by virtue of their anti-inflammatory activities can improve insulin sensitivity and endothelial and mitochondrial function, suggesting that polyphenols are good for disease prevention. The goal of this review is to summarize the evolution and emphasize the potential benefits of polyphenols.

Xanthohumol-supplemented beer modulates angiogenesis and inflammation in a skin wound healing model. Involvement of local adipocytes

Angiogenesis and inflammation are two intermingled processes that play a role in wound healing. Nevertheless, whenever exacerbated, these processes result in nonhealing wounds. Xanthohumol (XN), a beer-derived polyphenol, inhibits these processes in many physiopathological situations. This study aimed at examining whether XN ingestion affects wound healing. Wistar rats drinking water, 5% ethanol, stout beer (SB) or stout beer supplemented with 10 mg/L XN (Suppl SB) for 4 weeks, were subjected to a 1.5 cm full skin-thickness longitudinal incision, and further maintained under the same beverage conditions for another week. No differences in beverage consumption or body weight were found throughout the study but food intake decreased in every group relative to controls. Consumption of Suppl SB resulted in decreased serum VEGF levels (18.42%), N-acetylglucosaminidase activity (27.77%), IL1β concentration (9.07%), and NO released (77.06%), accompanied by a reduced redox state as observed by increased GSH/GSSG ratio (to 198.80%). Also, the number of blood vessels within the wound granulation tissue seems to reduce in animals drinking Suppl SB (23.08%). Interestingly, SB and primarily Suppl SB showed a tendency to increase adipocyte number (to 194.26% and 156.68%, respectively) and reduce adipocyte size (4.60% and 24.64%, respectively) within the granuloma. Liver function and metabolism did not change among the animal groups as analyzed by plasma biochemical parameters, indicating no beverage toxicity. This study shows that XN intake in its natural beer context reduced inflammation, oxidative stress, and angiogenesis, ameliorating the wound healing process, suggesting that this polyphenol may exert beneficial effect as a nutritional supplement.

Identification of microbial metabolites derived from in vitro fecal fermentation of different polyphenolic food sources

OBJECTIVE

The biological effects of dietary polyphenols are linked to their bioavailability and catabolism in humans. The colon, with its symbiotic microbiota, is an active site where complex polyphenolic compounds are possibly modified to smaller and more absorbable molecules. The aim of this study was to identify the major metabolites derived from microbial colonic fermentation of some common polyphenol-rich foods.

METHODS

An in vitro fecal fermentation model was applied to 16 polyphenol-rich foods and polyphenolic precursors. Phenolic metabolites were identified by high-performance liquid chromatography coupled with tandem mass spectrometric detection.

RESULTS

Twenty-four phenolic fermentation metabolites were characterized. Some metabolites were common to several polyphenol-rich foods, whereas others were characteristic of specific sources.

CONCLUSION

The metabolites identified in vitro likely are generated in the human colon after consumption of polyphenol-rich foods. Their occurrence in plasma and/or urine should be considered when evaluating the bioavailability of polyphenols from specific food groups in humans and in the definition of markers of exposure to specific foods or food groups in epidemiologic studies. However, the search for these and other microbial metabolites after a feeding study in vivo should consider their possible further conjugation at the level of the liver.

Quercetin and epigallocatechin gallate induce in vitro a dose-dependent stiffening and hyperpolarizing effect on the cell membrane of human mononuclear blood cells

The bioactivity of polyphenols is closely linked to their ability to interact with biological membranes. The study evaluates the in vitro effect of quercetin and epigallocatechin on the membrane anisotropy and transmembrane potential of peripheral blood mononuclear cells (PBMCs) isolated from 26 type 2 diabetes mellitus patients compared to 25 age matched controls. The in vitro assays were analyzed in correlation with the biochemical and inflammatory profile of the subjects and with insulin resistance parameters (HOMA-IR, plasma resistin) as well. For type 2 diabetes patients, the increase of HOMA-IR and resistin concentration was associated with a significant decrease of the PBMCs membrane anisotropy. The two tested polyphenols induced a dose-dependent hyperpolarizing effect and stiffening of the cell membranes for all tested subjects. Physiological levels of quercetin and epigallocatechin gallate had the tendency to normalize the PBMCs membrane anisotropy of the cells isolated from diabetes patients, bringing it to the level of cells isolated from normoglycemic ones. Epigallocatechin gallate induced higher effects compared to quercetin on the membranes isolated from subjects with higher cardiovascular risk. The decrease of membrane fluidity and the hyperpolarizing effect could explain the cardiovascular protective action of the tested compounds.

PM6 and DFT study of free radical scavenging activity of morin

Flavonoids have long been recognised for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work, we have studied the properties of flavonoid morin using semiempirical and density functional theory (DFT) methods in order to validate the application of the recently developed parametric method 6 (PM6). Reaction enthalpies related to mechanisms of free radical scavenging by flavonoid morin were calculated by DFT and PM6 methods in gas-phase, water, DMSO and benzene. It has been shown that fast semiempirical PM6 method can mimic results obtained by means of more accurate time consuming DFT calculations. Thermodynamically favoured mechanism depends on reaction medium: SPLET (sequential proton loss electron transfer) is preferred in water and DMSO, and HAT (hydrogen atom transfer) is predominant in gas-phase. In benzene these two mechanisms are competitive.

Antagonistic effect of the Ainu-selected traditional beneficial plants on the transformation of an aryl hydrocarbon receptor

Transformation of an aryl hydrocarbon receptor (AhR) is the initial step to express the multiple toxicity of halogenated and polycyclic aromatic hydrocarbons (HAHs and PAHs) including dioxins. Therefore, it has been suggested that suppression of the transformation induced by HAHs and PAHs leads to reduce their toxicological effects. In this study, the antagonistic effect of 110 indigenous plants (192 plant parts) used as medicine and/or food by the Ainu on the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced AhR transformation was investigated. Of these, a stalk of Aralia elata (Miq.) Seemann and a bark of Fraxinus mandshurica Rupr. var. japonica Maxim. exhibited the strong antagonistic effect in a dose-dependent manner. An antioxidative activity and polyphenol content were also measured, and the strong correlation (r= 0.96) between these two parameters could be confirmed. However, correlation coefficients of the antagonistic effect of 192 extracts compared to their antioxidative activity and polyphenol content were 0.17 and 0.20, respectively. These results suggest that the Ainu-selected traditional beneficial plants are useful source for findings of novel AhR antagonists, and the antagonistic activity of these plants may be independent on their antioxidative activity and polyphenol content.

PRACTICAL APPLICATION

Our findings lead to discovery of the valuable plants used by the Ainu and the novel active compounds useful for human's life, and furthermore, may contribute to the development of new medicines and functional foods.

Effect of consumption of dark chocolate on oxidative stress in lipoproteins and platelets in women and in men

The goal of this research was to investigate the effects of 3 weeks consumption of 50 g flavonoid-rich dark chocolate on lipoprotein oxidative stress in vitro and in vivo in 25 women compared to 25 men. Levels of thiobarbituric acid-reactive substances, conjugated dienes and hydroperoxide levels in HDL and LDL before and after consumption of dark chocolate were determined. Moreover in platelets of the same subjects NO and peroxynitrite levels were studied. TBARs concentration in women's HDL decreased by 26.7% while in men's HDL 23.4%; lipid hydroperoxides decreased in women's HDL by 62.8% while in men's HDL they decreased by 21.1%. Conjugate diene formation decreased in women's HDL by 55.9%, while in men's HDL it decreased by 49.2%. Moreover TBARs concentration decreased in women's LDL by 26.7% after supplementation and in men's LDL by 21.6%; lipid hydroperoxides decreased in women's LDL by 83.6% while in men's LDL they decreased by 64.7%. Moreover conjugate diene formation decreased in women's LDL by 48.2%, while in men's LDL it decreased by 21.6%. After supplementation peroxynitrite values decreased in women by 24% and in men by 18.6% while NO increased after supplementation by 15.7% compared to basal determination in women, and by 32.2% in men. This study showed that a short-term intake of dark chocolate might improve the lipoprotein profile in healthy humans, more so in women than in men, and this might exert a protective effect on the cardiovascular system.

Large procyanidins prevent bile-acid-induced oxidant production and membrane-initiated ERK1/2, p38, and Akt activation in Caco-2 cells

Procyanidins are oligomers of flavanol subunits present in large amounts in fruits and vegetables. Their consumption is associated with health benefits against colonic inflammation and colorectal cancer (CRC). Large procyanidins (with more than three subunits) are not absorbed by intestinal epithelial cells but could exert biological actions through their interactions with the cell membrane. This study investigated the capacity of hexameric procyanidins (Hex) to prevent oncogenic events initiated by deoxycholic acid (DCA), a secondary bile acid linked to the promotion of CRC. Hex interacted with Caco-2 cell membranes preferentially at the water-lipid interface. Hex (2.5-20 μM) inhibited DCA-triggered increase in cellular calcium, NADPH oxidase activation, and oxidant production. DCA promoted the activation of protein kinase B (Akt), of the mitogen-activated protein kinases ERK1/2 and p38, and of the downstream transcription factor AP-1. This activation was not triggered by calcium or oxidant increases. Hex caused a dose-dependent inhibition of DCA-mediated activation of all these signals. DCA also triggered alterations in the cell monolayer morphology and apoptotic cell death, events that were delayed by Hex. The capacity of large procyanidins to interact with the cell membrane and prevent those cell membrane-associated events can in part explain the beneficial effects of procyanidins on CRC.

Flavonoids, cognition, and dementia: actions, mechanisms, and potential therapeutic utility for Alzheimer disease

There is increasing evidence that the consumption of flavonoid-rich foods can beneficially influence normal cognitive function. In addition, a growing number of flavonoids have been shown to inhibit the development of Alzheimer disease (AD)-like pathology and to reverse deficits in cognition in rodent models, suggestive of potential therapeutic utility in dementia. The actions of flavonoid-rich foods (e.g., green tea, blueberry, and cocoa) seem to be mediated by the direct interactions of absorbed flavonoids and their metabolites with a number of cellular and molecular targets. For example, their specific interactions within the ERK and PI3-kinase/Akt signaling pathways, at the level of receptors or kinases, have been shown to increase the expression of neuroprotective and neuromodulatory proteins and increase the number of, and strength of, connections between neurons. Concurrently, their effects on the vascular system may also lead to enhancements in cognitive performance through increased brain blood flow and an ability to initiate neurogenesis in the hippocampus. Additional mechanisms have been suggested for the ability of flavonoids to delay the initiation of and/or slow the progression of AD-like pathology and related neurodegenerative disorders, including a potential to inhibit neuronal apoptosis triggered by neurotoxic species (e.g., oxidative stress and neuroinflammation) or disrupt amyloid β aggregation and effects on amyloid precursor protein processing through the inhibition of β-secretase (BACE-1) and/or activation of α-secretase (ADAM10). Together, these processes act to maintain the number and quality of synaptic connections in key brain regions and thus flavonoids have the potential to prevent the progression of neurodegenerative pathologies and to promote cognitive performance.

Natural polyphenols in cancer therapy

Natural polyphenols are secondary metabolites of plants involved in defense against different types of stress. Extracts containing these compounds have been used for thousands of years in traditional eastern medicine. Polyphenols act on multiple targets in pathways and mechanisms related to carcinogenesis, tumor cell proliferation and death, inflammation, metastatic spread, angiogenesis, or drug and radiation resistance. Nevertheless, reported effects claimed for polyphenols are controversial, since correlations between in vitro effects and in vivo evidence are poorly established. The main discrepancy between health claims versus clinical observations is the frequent use of nonphysiologically relevant concentrations of these compounds and their metabolites in efficacy and mechanistic studies. The present review will discuss how in vivo administration correlates with polyphenol metabolism, toxicity, and bioavailability. Analysis of the general application of polyphenols in cancer therapy will be complemented by potential applications in the therapy of specific tumors, including melanoma, colorectal and lung cancers. Possible pharmaceutical formulations, structural modifications, combinations, and delivery systems aimed to increase bioavailability and/or biological effects will be discussed. Final remarks will include recommendations for future research and developments.

Lemon verbena infusion consumption attenuates oxidative stress in dextran sulfate sodium-induced colitis in the rat

BACKGROUND

Inflammatory bowel diseases (IBD) consist of an uncontrolled intestinal inflammation leading to mucosal disruption. This inflammation is accompanied by an excessive production of reactive oxygen species (ROS). Polyphenols are micronutrients with antioxidative and anti-inflammatory properties, and may play an interesting role in the prevention of intestinal inflammation. Lemon verbena (Aloysia triphylla) infusion is a popular herbal infusion rich in polyphenols (flavones and verbascoside).

AIMS

This study evaluated the preventive effects of lemon verbena infusion consumption against mild-to-moderate dextran sulfate sodium (DSS)-induced colitis in rats.

METHODS

Wistar rats drank water or lemon verbena infusion for 14 days. On day 15, half of the rats received DSS (4%) in their drink for 7 days. At the end of the experimental period, the colon was taken for histopathological examination and determination of myeloperoxidase (MPO) activity, antioxidant enzyme activities (superoxide dismutase [SOD], glutathione peroxidase [GPx], glutathione reductase [GR], catalase [CAT]), glutathione and lipid peroxidation. Lymphocyte populations were determined in blood, mesenteric nodes and Peyer's patches.

RESULTS

Rats ingested daily 5.6 μmol of polyphenols. DSS reduced food intake and induced colitis, as reflected by histological lesions and increased MPO activity. Although these alterations were not significantly counteracted by lemon verbena consumption, the herbal infusion increased colonic SOD activity and decreased lipid peroxidation (malondialdehyde). Other oxidative stress markers (GPx, GR, CAT, glutathione) were not significantly modified.

CONCLUSION

Our study shows that the preventive consumption of lemon verbena infusion offered some antioxidative protection during experimental colitis by stimulating SOD activity and decreasing lipid peroxidation.

The natural antioxidant rosmarinic acid spontaneously penetrates membranes to inhibit lipid peroxidation in situ

Exogenous molecules from dietary sources such as polyphenols are very efficient in preventing the alteration of lipid membranes by oxidative stress. Among the polyphenols, we have chosen to study rosmarinic acid (RA). We investigated the efficiency of RA in preventing lipid peroxidation and in interacting with lipids. We used liposomes of 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC) to show that RA was an efficient antioxidant. By HPLC, we determined that the maximum amount of RA associated with the lipids was ~1 mol%. Moreover, by using Langmuir monolayers, we evidenced that cholesterol decreases the penetration of RA. The investigation of transferred lipid/RA monolayers by atomic force microscopy revealed that 1 mol% of RA in the membrane was not sufficient to alter the membrane structure at the nanoscale. By fluorescence, we observed no significant modification of membrane permeability and fluidity caused by the interaction with RA. We also deduced that RA molecules were mainly located among the polar headgroups of the lipids. Finally, we prepared DLPC/RA vesicles to evidence for the first time that up to 1 mol% of RA inserts spontaneously in the membrane, which is high enough to fully prevent lipid peroxidation without any noticeable alteration of the membrane structure due to RA insertion.

Protective role of puerarin on lead-induced alterations of the hepatic glutathione antioxidant system and hyperlipidemia in rats

Puerarin (PU), a natural flavonoid, has been reported to have many benefits and medicinal properties. The aim of the present study was to investigate the effects of puerarin on hepatic oxidative stress and hyperlipidemia in rats exposed to lead. Our data showed that puerarin significantly prevented lead-induced hepatotoxicity, indicated by both diagnostic indicators of liver damage (serum aminotransferase levels) and histopathological analysis. Moreover, lead-induced profound elevation of ROS production and oxidative stress, as evidenced by increasing of lipid peroxidation level, reducing of GPx, GST, GR and GCL activities and depleting of intracellular reduced GSH level in liver, were suppressed by treatment with puerarin. Furthermore, the increase of serum cholesterol, triglycerides and LDL induced by lead was effectively suppressed by puerarin. The HDL level in the lead treatment rats was also increased by puerarin. Western blot analysis showed that puerarin remarkably inhibited hyperlipidemia by regulating the expression of cholesterol 7a-hydroxylase (CYP7A1), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) and low-density lipoprotein receptor (LDL-R) in liver of lead treated rats. Altogether, these results suggest that puerarin could protect the lead-induced liver injury and hyperlipidemia by reducing ROS production, renewing the activities of antioxidant enzymes and influencing expression of hepatic lipid biosynthesis and metabolism genes.

Dietary flavonoids: Role of (-)-epicatechin and related procyanidins in cell signaling

Plant polyphenols are among the most abundant phytochemicals present in human diets. Increasing evidence supports the health-promoting effects of certain polyphenols, including flavonoids. This review discusses current knowledge of the capacity of monomeric flavanols, i.e., (-)-epicatechin and (+)-catechin, and their derived procyanidins to modulate cell signaling and the associations of these actions with better health. Flavanols and procyanidins can regulate cell signaling through different mechanisms of action. Monomers and dimeric procyanidins can be transported inside cells and directly interact and modulate the activity of signaling proteins and/or prevent oxidation. Larger and nonabsorbable procyanidins can regulate cell signaling by interacting with cell membrane proteins and lipids, inducing changes in membrane biophysics, and by modulating oxidant production. All these actions would be limited by the bioavailability of flavanols at the target tissue. The protection from cardiac and vascular disease and from cancer that is associated with a high consumption of fruit and vegetables could be in part explained by the capacity of flavanols and related procyanidins to modulate proinflammatory and oncogenic signals.

Protective effect of apple polyphenols against stress-provoked influenza viral infection in restraint mice

This study was conducted to investigate the effects of apple polyphenol extract (APE) against influenza virus in mice loaded with restraint stress. The high-performance liquid chromatography (HPLC) fingerprint of APE was recorded, and the percentage composition of polyphenols was determined as 81.7%. Our results showed that restraint stress significantly promoted the mortality and duration of complications of mice infected with the H1N1 virus. However, oral administration of APE (100 and 200 mg/kg) improved the survival rates and prolonged living time of stressed mice infected with influenza virus in a dose-dependent manner. APE was further found to significantly improve the number of immunocytes, ratio of CD4 helper cells, secretion of IL-2, and capabilities of natural killer (NK) cytotoxicity (LU10/spleen) in spleens of restraint-stressed mice. In addition, APE also significantly decreased the level of lipid peroxidation and increased oxygen radical absorbance capacity (ORAC) in splenocytes. These results indicated that the protective effects of APE on mice infected with influenza virus were related to the alleviation of stress-induced impairment of immune functions and its antioxidant property might contribute to the immune recovery.