Biology Reference
In-Depth Information
Table 17.2.
Coefficient of determination (R
2
) and mortality constant (K) of bacterial irradiation
experiments with and without protection.
Substance
K
R
2
Protection of cell death (min)
Without protection
0.8276
0.9363
5
OMC
0.1349
0.9832
30
Methanolic extract
B. perfoliata
0.1404
0.9723
30
Methanolic extract
B. scordioides
0.1357
0.9547
30
Linarin
0.0971
0.9790
60
Linarin acetate
0.0323
0.9623
120
Verbascoside
0.0347
0.9912
120
Methanolic extract
Y. periculosa
0.1306
0.9482
30
Naringenin
0.2766
0.9911
15
Resveratrol
0.1372
0.9915
30
MS
0.0746
0.8549
60
MS:
trans
-3, 3
′
, 5, 5
′
-tetrahydroxy-4-methoxystilbene; OMC: Octyl-
p
-methoxy-
trans
-cinnamate
effect against UVB-induced cell death; the
K (0.03) was 27.5-fold below the K without
protection (0.82). Our research shows the
potential photoprotective effect of extracts and
compounds isolated from Mexican plants.
used to protect against the acute effects of
UVR. OMC is a widely used UVB filter in
various cosmetic formulations. It is known
that all organic sunscreen agents may induce
adverse effects such as irritation, allergic
contact reaction, photoallergy or phototoxic-
ity. Kullavanijaya and Lim (2005) reported
photosensitization and/or photoallergic
reactions induced by this compound.
Because of this, it is important to develop
research focused on the search for natural
substances with photoprotective activity.
The SPF of all substances was deter-
mined on guinea pigs in our laboratory (Table
17.3). The negative control (guinea pigs with
vehicle) showed perceptible erythema at 20 ±
2 min; this time was considered as the MED.
All the substances were more active than
OMC (SPF 2.0 ± 0.1), because a significant
difference was observed in comparison with
controls. The SPFs obtained from plant
extracts and naringenin were ≅3, and from
linarin acetate, resveratrol and MS were ≅5.
Linarin and verbascoside were the com-
pounds with the highest photoprotective
activity: their SPFs were 9 and 24, respec-
tively (Avila
et al
., 2005; García-Bores
et al
.,
2010). Verbascoside retarded the appearance
of erythema at about ~440 min. The meth-
anolic extracts and the phytochemicals have
maximum absorptions in the UVB region of
the electromagnetic spectrum and will be,
therefore, potentially photoprotective sub-
stances (Table 17.1). This explains the protec-
tive properties from these Mexican plants.
17.7 Photoprotective Activity
Against UVB-induced Skin Damage:
Sun Protection Factor (SPF)
Sunburn erythema is the most conspicuous
and well-recognized acute cutaneous response
to UV irradiation, and it is the most widely
used end point in dermatological photobiol-
ogy. The molecules responsible for light
absorption (chromophores) that initiate
sunburn inflammation have not been pre-
cisely identified. However, the action spec-
trum of erythema is consistent with the
hypothesis that UV interactions with DNA
are of major importance. Indirect oxidative
damage might also occur secondarily to
endogenous photosensitization reactions
(Matsumura and Ananthaswamy, 2004).
A widely accepted method for sun-
screen efficacy measurements is SPF, which
is defined as the ratio of the dose of UVR
(290-400 nm) required to produce 1 Minimal
Erythema Dose (MED) on sunscreen-
protected skin (after application of 2 mg/cm
2
of product) over the dose required to pro-
duce 1 MED on unprotected skin (Bissett
et al
., 1991). Sunscreens have long been
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