Medicinal Plants Classification Biosynthesis and ... - Index of

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Rosa Martha Perez Gutierrez, Adriana Maria Neira Gonzalez et al.
isothiocyanates (sulforaphane), offer exciting platforms for the development of such
protective strategies. These phytochemicals have been consumed by humans for many
centuries as part of plant-rich diets and are presumed to be of low toxicity, an essential
requirement for a chemoprotective agent. Mechanistically, they affect multiple signalling
pathways and protect against UV radiation-inflicted damage by their ability to act as direct
and indirect antioxidants, as well as anti-inflammatory and immunomodulatory agents
(Dinkova-Kostova, 2008).
Skin cancer is a major public health issue in white-skinned populations in the United
States, Europe, and Australia, and the incidence continues to rise (Staples et al., 1998). Solar
keratoses (SKs) are among the strongest determinants of skin cancer risk. The risks of the
main types of skin cancer-basal cell carcinoma and squamous cell carcinoma (BCC and SCC)
are increased 3- to 12-fold in the presence of SKs (Marks et al., 1988). Indeed, a high
proportion of SCCs are believed to arise in SKs, although the actual rate of transformation is
small (Frost et al., 2000). Despite the possibility that controlling SK development may
effectively reduce skin cancer.
The effect of sunscreen (application of a high-protection sunscreen to their head, neck,
arms, and hands every morning) or application of sunscreen at their usual discretionary rate
was determinate in an randomized controlled trial conducted between 1621 adults aged 25 to
74 years. They were also randomly assigned to take either one 30-mg tablet of beta carotene
or one placebo tablet each day.
The results showed a reduction in the rate of change of SK prevalence was also seen in
the sunscreen intervention group relative to the discretionary sunscreen group between 1994
and 1996, but it was not significant. No effect on the rate of change of prevalent SK counts
was seen among those taking beta carotene supplements relative to those taking placebo
tablets. Daily application of sunscreen retarded the rate of SK acquisition among adults in a
subtropical environment, while a beta carotene supplementation of 30 mg/day had no
influence on the occurrence of SKs (Darlington et al., 2003).
β -Carotene has been extensively investigated as a chemopreventive agent that may
protect against skin photodamage (Mathews-Roth, 1990). Recently, β-carotene has been used
as a component of some cosmetics (Harang, 2000.) However, inconsistent findings exist in
various studies (Garmyn et al.,1995). For example, Black (Black, 1998.) found that βcarotene-supplemented
semidefined diets, in contrast to commercial closed formulas, not
only fail to protect against UV-induced carcinogenesis but also lead to significant
exacerbation in mice. Black et al. (2000) pointed out that the inconsistency in the
photoprotective effect of β-carotene in animal studies may have been due to the interaction
between β-carotene and other dietary antioxidants including phytochemicals. Similarly, an in
vitro study showed that preincubation of skin fibroblasts with either β-carotene or lycopene
(0.1–1.0 µM) increases ultraviolet A (UVA)-induced expression of metalloproteinase 1
(MMP-1) (Offord et al., 2002), a collagenase associated with skin aging, while concurrent
addition of vitamin E or vitamin C during preincubation suppresses the increase in MMP-1
mRNA. However, limited data exist regarding the interaction of β-carotene with other
phytochemicals on UVA-induced oxidative damage.
Flavonoids are a major type of phytochemicals that are ubiquitously present in fruits and
vegetables. Growing evidence demonstrate an inverse relation between the dietary intake of