Photoprotective Activity of some Mexican Plants - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 255

skin cancers comprising BCC and SCC are
the most frequently diagnosed cutaneous
malignancies in the world now and their
incidence is increasing. It is well known
that they are associated with a low mortality
rate, but they have a high cost in the health
system. In addition, they produce a broad
range of disfigurement if the lesions are
located in the head or neck. Melanoma is
related to the frequency of severe sunburn
in childhood. Melanoma can be treated with
surgery if it is detected in time; however,
when it presents metastasis there is no cure
(Stratton et al ., 2000).
The UVR generates reactive oxygen
species (ROS) and induced oxidative stress
in skin cells. Oxidative stress may cause
damage at the cellular level, as well as at the
molecular level, and this can result in cuta-
neous inflammation, lipid and protein
oxidation, DNA damage, and activation or
inactivation of certain enzymes such as cata-
lase (CAT) and superoxide dismutase (SOD),
all of which could potentially contribute to
UVB-induced photodamage of the skin. It has
been estimated that there are approximately
35 DNA adducts in the presence of ROS; one
of the key markers of oxidative DNA damage
is 8-hydroxy-2-deoxy-guanosine (8-OHdG),
which induces the change of guanine to
thymine (T→G) (Ichihashi et al ., 2003). ROS
are intracellular mediators that are impli-
cated in signal transduction. ROS generation
leads to the expression of specific genes
involved in the development of pathological
conditions such as immunosuppression and
all stages of photocarcinogenesis in skin.
NF-kB is a ubiquitously expressed transcrip-
tion factor that regulates genes involved in
inflammation, immunity, cell-cycle progres-
sion and apoptosis. NF-kB activation is
subject to redox regulation. The AP-1 tran-
scription factor is a dimer composed of pro-
teins from the Fos and Jun families. AP-1
activation, which is also redox regulated,
principally leads to cell proliferation and
transformation. In addition, NF-kB and AP-1
are activated by UVR, either independently
or coordinately regulating the expression of
several target genes whose protein products
are molecular markers of processes such
as inflammation, immunosuppression and

tumour transformation, such as cyclooxy-
genase (COX), nitric oxide synthase (NOS)
and ornithine decarboxylase (ODC) (Afaq
et al ., 2005).

17.2 Photoprotection

Exposure to UVR has several adverse effects
on the skin. Actions recommended to prevent
overexposure to UVR include: avoiding
exposure to the sun; wearing clothing that
protects the neck, arms and legs; using hats
and sunglasses; using sunscreens and block-
ers with a sun protection factor (SPF) of 15
or higher; teaching children to protect them-
selves from the sun; deliberately avoiding
tanning in tanning beds; and examining
the skin regularly to detect the presence of
early cancers (Agarwal and Mukhtar, 1996;
Kullavanijaya and Lim, 2005).
Sunscreens are chemicals that can
absorb UV light efficiently, are applied topi-
cally and protect from the adverse effects of
sunlight, mainly erythema. Most of the com-
mercial formulations contain several active
ingredients for a broad SPF of 280-400 nm
(UVB and UVA). The application of sun-
screen before exposure to UV radiation pre-
vents sunburn, DNA damage and skin
cancer (Pinnell, 2003). However, sunscreens
can induce side effects such as irritation,
allergy, phototoxic reactions, can affect the
synthesis of vitamin D, generate ROS and
act as photosensitizers. These primary
prevention approaches have had limited
success. Therefore, additional efforts are
needed to prevent skin cancer (Kullavanijaya
and Lim, 2005).
Several studies have evaluated the pro-
tective effect of natural products against dam-
age induced by UVR in cells, tissues, animals
and humans. Photochemoprevention is the
use of synthetic or natural substances that
can prevent, delay or reverse the damage
caused by UVR (Agarwal and Mukhtar,
1996; Surh, 1999; Straton et al ., 2000; Afaq
et al ., 2005). The photochemoprevention
involves substances capable of absorbing
the UV and acting as filters, preventing DNA
damage and immunosuppression. In addition,