Photoprotective Activity of some Mexican Plants - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 262

Table 17.3. Sun protection factor (SPF) of the substances evaluated in guinea pigs.

Compounds (2 mg/cm 2 ) SPF Exposition time without erythema (min)

Without protection - 20 ± 2.0

OMC 2.0 ± 0.10 40 ± 4.5

MeOH extract of B. perfoliata 3.0 ± 0.09 60 ± 1.8

MeOH extract of B. scordioides 3.0 ± 0.09 60 ± 1.8

Linarin 9.0 ± 0.30 160 ± 6.0

Linarin acetate 5.0 ± 0.2 80 ± 4.0

Verbascoside 24.0 ± 0.7 440 ± 14

MeOH extract of Y. periculosa 3.4 ± 0.5 68 ± 9.5

Naringenin 3.6 ± 0.6 72 ± 10.1

Resveratrol 5.0 ± 0.7 100 ± 12.3

MS 5.6 ± 0.5 112 ± 8.5

MS: trans -3,3 ′ ,5,5 ′ -tetrahydroxy-4-methoxystilbene; OMC: Octyl- p -methoxy- trans -cinnamate.

17.8 Photoprotective Activity
Against UVB-induced Skin Damage:
Histological Study

UVR. Finally, those animals treated with
verbascoside retarded the appearance of
erythema at about ~440 min.
Many agents, like UV light filters, affect
the transmission of UV light to human skin.
In addition, there are agents like antioxidants
that can modulate the effects of UV light on
the skin. Most of the naturally occurring che-
mopreventive phenolics exert multifaceted
action, and any clinical applications using
these substances should be based on the pre-
cise understanding of the physiologically
relevant action mechanisms.

A histological evaluation was also per-
formed on the guinea pig skin exposed to
UVR, both the unprotected skin and the
skin protected by each of the substances.
The histological changes after 20 min of UV
irradiation in guinea pig skin compared
with normal skin (Fig. 17.4a) include thick-
ening of stratum corneum and epidermis,
intra/intercellular and perivascular oedema,
perivascular infiltration and spongiosis, as
shown in Fig. 17.4b. The guinea pigs treated
with a topical, sub-minimal erythema dose
of the methanolic extracts, the isolated com-
pounds or OMC did not show these UVB-
induced inflammatory changes, as shown
in Fig. 17.4c-17.4l. The histopathological
study of the skin samples exposed at MED
with protection showed that a topical appli-
cation of each of the experimental treatments
had a different effect on the skin, which
could be an indication that the protection
afforded was also linked to the modulation
of cellular processes. The appearance of
erythema in animals treated with resvera-
trol, linarin, linarin acetate and MS occurred
at ~100 min, while those animals treated
with naringenin or the methanol extracts of
plants had an appearance of erythema at
~70 min, and with OMC had an appearance
of erythema after ~40 min of exposure to

17.9 Conclusion

The increase in skin cancer morbidity and
mortality is alarming and expensive, in
both human and economic terms. New
strategies are needed to combat this disease.
The development of promising chemopre-
ventive agents is a demanding process that
requires continuous research. The natural
products constitute an important group
of pharmacological agents capable of pre-
venting the occurrence and reducing the
severity of UVR-induced skin diseases. The
research of natural products with chemo-
preventive properties has focused on the
antioxidant, anti-inflammatory and antimuta-
genic activities of the compounds. In addi-
tion, this chapter shows that the phenolic
compounds isolated from B. perfoliata,