have many potential targets in the inflammatory cascade, such
as Bax, Bcl-2, caspases, c-Fos, IĸB kinase, PI3-kinase, and NF-ĸB
to name a few.22 The antioxidant capacity of phenolics varies depending
on the chemical ring structure, particularly the number
and arrangement of hydroxyl group and ring substituents, and
the ionization state and stability of resulting phenoxy radicals.23
One common method of classification is to divide polyphenols
into flavinoid and nonflavinoid phenolics (Figure 3). All flavinoids
consist of two benzene rings linked by a heterocyclic pyrone C
ring in contrast to non-flavinoids, which include a heterogenous
range of compounds. Flavinoids are the most common polyphenol
found in the human diet, with over 4000 identified, and have
thus attracted the most attention.17,24 To provide a better understanding
of the mechanism of action of natural ingredients, the
available data on several commonly used polyphenols will be
reviewed and their applications for dermatologic disease, particularly
protection from UV damage, will be explored.
Soy
Soy beans are a rich source of isoflavones and contain high
concentrations of genistein, daidzein and glycitein. Isoflavones
are a type of phytoestrogen, which due to the structural similarity
to estradiol can bind to both ER-β and ER-α receptors.25
As an estrogen analog, soy isoflavones have been utilized to
treat post-menopausal symptoms, including hot flashes, bone
loss and skin ageing. It has been hypothesized that genistein
reduces skin damage particularly through estrogen receptor
binding, and has been considered as an alternative to hormone
replacement therapy (HRT) as a means of avoiding the
adverse effects of HRT. In addition to its estrogenic activity, the
role of isoflavones in skin ageing is likely due to its antioxidant
properties. Genistein is a potent antioxidant and has been
shown to reduce 8-hydroxy-2’-deoxyguanosine (8-OHdG)
formation (a product of DNA oxidation), scavenge hydrogen
peroxide and superoxide anion26 and induce increased activity
of antioxidant enxymes, such as SOD, catalase and glutathione
reductase.27 In an in vivo study, pretreatment with genistein
resulted in inhibition of cjun, the heterodimer of AP-1, which
stimulates the breakdown of collagen via enhanced MMP expression.
This resulted from genistein’s antioxidant activity,
particularly its inhibition of the ERK and JNK MAP kinases that
activate AP-1.10 Soybeans have also been shown to reduce the
clinical signs of aging by inducing elastin promoter activity
