Regulation of inflammation and redox signaling by dietary polyphenols
Section snippets
Polyphenols: an overview
A wide variety of dietary plants including grains, legumes, fruits, vegetables, tea, wine, etc. contain polyphenols [1]. The disease preventive abilities of fruit and vegetables have been attributed to the antioxidants/polyphenols present in these dietary sources [2]. It is noteworthy that most reports on the beneficial effects of polyphenols have been obtained from in vitro studies and more detailed investigations are required to extrapolate these results to in vivo situations. This is
Chemistry of polyphenols
Polyphenols, with over 8000 structural variants, are secondary metabolites of plants and denote a huge gamut of substances having aromatic ring(s) bearing one or more hydroxyl moieties. The structure of natural polyphenols varies from simple molecules, such as phenolic acids, to highly polymerized compounds, such as condensed tannins [3]. Polyphenols are effective free radical scavengers and metal chelators which are mediated by the presence of para-hydroxyl group. The most widely distributed
Absorption, pharmacokinetics, tissue distribution and metabolism of polyphenols
In view of polyphenols having complex absorption, biotransformation and bioavailability characteristics, it is important to probe these aspects before we embark on the investigation of the molecular mechanisms and therapeutic applications of these versatile compounds. A proper understanding of how polyphenols are absorbed and transformed pre- and post-absorption is helpful in understanding how in vitro observations can be translated into the in vivo context.
Bioavailability of polyphenols
Although the knowledge of absorption, bioavailability, biodistribution and metabolism of polyphenols is not entirely known, in general it appears that some polyphenols are bioactive and are absorbed through the intestine in their native or modified form. The absorbed forms are then metabolized and the end products may be detected in plasma in nanomolar ranges. The plasma forms of polyphenols may retain at least part of their antioxidant capacity before being excreted [16]. In general, the
Polyphenols as antioxidants
In recent years there has been a remarkable increment in scientific knowledge dealing with the beneficial role of polyphenols during oxidative stress. This is due to the identification of flavonoids and other dietary polyphenol antioxidants present in plant foods as bioactive molecules. Data supports the idea that the health benefits associated with fruits, vegetables and red wine in the diet are probably linked to the polyphenol antioxidants they contain. Indeed, the high content of polyphenol
Cellular signaling, NF-κB and polyphenols
Much of the earlier studies on polyphenols have viewed these compounds from the perspective of antioxidants. The antioxidant property of these molecules was later explained on the basis of the availability of –OH and the system of conjugated double bonds present in these molecules. However, many other effects of polyphenols such as anti-inflammatory, anti-tumor, anti-atherogenic abilities could not be explained solely on the basis of their antioxidant properties. Investigations into the
Polyphenols and cellular redox system
Since a variety of oxidants, free radicals and aldehydes are implicated in the pathogenesis of chronic inflammatory diseases, therapeutic intervention with a variety of polyphenolic antioxidants may therefore be an effective alternative for the treatment of chronic inflammatory diseases. An alternative mechanism may be that polyphenolic components of dietary plants may increase the endogenous antioxidant defense potential and thus modulate cellular redox state. It is therefore apt to consider
Polyphenols and glucocorticoid signaling
Although corticosteroids are highly effective in the control of asthma and other chronic inflammatory and immune diseases, a small proportion of patients with asthma fail to respond even to high doses of oral corticosteroids. Resistance to the therapeutic effects of corticosteroids is also recognized in other inflammatory and immune diseases, including rheumatoid arthritis and inflammatory bowel disease. Patients with corticosteroid-resistant asthma, although uncommon, present considerable
Challenges for research on polyphenols
Hundreds of polyphenols with antioxidant activity are potential contributors to the antioxidant mechanisms present in humans and animals. Although these compounds are excellent candidates to explain the health benefits of diets rich in fruits and vegetables, there is still not enough information on food composition data, bioavailability, interaction with other food components and their biological effects. There is evidence that polyphenols are metabolized by intestinal flora and that they and
Conclusions
Polyphenols and flavonoids seem to be important metabolic modulators by virtue of their ability to moderate and influence several cellular processes such as signaling, proliferation, apoptosis, redox balance, differentiation, etc. (Fig. 3). Although abundant in most dietary sources such as fruits, vegetables, tea and wine, more detailed studies are still required to determine their true absorption and bioavailability. It would serve well to remember that most studies and results on the effects
Acknowledgement
This work was supported by the Environmental Health Sciences Center Support #ES01247.
References (98)
Overview of dietary flavonoids: nomenclature, occurrence and intake
J Nutr
(2003)- et al.
Distribution of [14C]-trans-resveratrol, a cancer chemopreventive polyphenol, in mouse tissues after oral administration
Life Sci
(2003) - et al.
In vitro studies on the intestinal absorption of curcumin in rats
Toxicology
(1981) - et al.
Stability of curcumin in buffer solution and characterization of its degradation products
J Pharm Biomed Anal
(1997) - et al.
Flavonoids: antioxidants or signalling molecules?
Free Radic Biol Med
(2004) - et al.
Structures of (−)-epicatechin glucuronide identified from plasma and urine after oral ingestion of (−)-epicatechin: differences between human and rat
Free Radic Biol Med
(2003) Antioxidant activity of curcumin and related compounds
Biochem Pharmacol
(1976)- et al.
Role of capsaicin, curcumin and dietary n − 3 fatty acids in lowering the generation of reactive oxygen species in rat peritoneal macrophages
Biochim Biophys Acta
(1994) - et al.
Disparate effects of similar phenolic phytochemicals as inhibitors of oxidative damage to cellular DNA
Mutat Res
(2001) - et al.
Prooxidant activity and cellular effects of the phenoxyl radicals of dietary flavonoids and other polyphenolics
Toxicology
(2002)