Photoprotective Activity of some Mexican Plants - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 259

Table 17.1. Absorption in the UVB range of the methanolic extracts and molar extinction coefficient of
the compounds from B. perfoliata, B. scordioides and Y. periculosa , and several commercial sunscreens.

Substance l max (nm) e (M −1 cm −1 )

Methanolic extract B. perfoliata 282, 320 n.d.

Methanolic extract B. scordioides 279, 316 n.d.

Linarin 334 18,832

Linarin acetate 320 32,335

Verbascoside 291, 332 26,130, 35,113

Methanolic extract Y. periculosa 232, 313 n.d.

Naringenin 212, 288 12,555, 7,745

Resveratrol 218, 305 29,823, 37,895

trans -3,3 ′ ,5,5 ′ -tetrahydroxy-4-methoxystilbene (MS) 227, 316 40,278, 45,374

Commercial sunscreens
Octyl- p -methoxy- trans -cinnamate (OMC)
(Pattanaargson et al ., 2004)

310 24,000

Octylsalicylate (Shaath, 2005) 308 4,900

Avobenzone (Shaath, 2005) 351 30,500

p -aminobenzoic acid (Shaath, 2005) 293 14,000

Padimate-O (Shaath, 2005) 307 27,300

n.d., not determined.

17.6 Photoprotective Effect Against

UVB-induced Cell Death

it was less active than octyl- p -methoxy-
trans-cinnamate (OMC) as a protective con-
trol (cell death at 35 min). Methanol extracts
of the Mexican plants studied (Fig. 17.3b) and
resveratrol protected their respective bacteria
populations in a similar manner to OMC and
did not reach cell death until 60 min. Linarin
and MS protect against cell death in bacterial
population to 120 min. Linarin acetate and
verbascoside protected the bacteria more effi-
ciently than the positive control; the bacterial
population protected by those compounds
did not reach cell death until 120 min of irra-
diation with UVB (Fig. 17.3c).
The constant mortality K is a parameter
that indicates the range of inactivation of
E. coli . The data in Fig. 17.3b and 17.3c
show the photoprotective effect of the meth-
anolic extracts of B. perfoliata, B. scordio-
ides and Y. periculosa tested. All substances
(OMC, methanolic extracts, linarin, linarin
acetate, verbascoside, naringenin, resveratrol
and MS) protected the bacterial population
from the lethal effects of UVR. All substances
presented K values lower than experiments
without protection (Table 17.2). In the
experiments with protection, the K ranged
from 0.03 to 0.27. Verbascoside and linarin
acetate showed a strong photoprotective

The protective effect against UVB-induced
cell death was evaluated using E. coli as a
cell model. The bacterial decay depends
mainly on the dose of radiation that induces
damage to DNA. E. coli was inactivated when
exposed to UV. The effectiveness of UV light
in the biological inactivation primarily
results from the fact that DNA molecules
absorb UV photons between 200 and 320 nm,
with peak absorption at 265nm. In case of
lethal damage, DNA replication is blocked
by DNA alterations, mainly cyclobutane
pyrimidine dimer (CPD) and the pyrimidine
(6-4) pyrimidinone (6-4PP), which ulti-
mately results in reproductive cell death.
The exposure of a bacterial culture to UVB
produces the rapid decline in population
caused by damage to the DNA (Oguma et al .,
2001; Taghipour, 2004).
Our results showed that the bacteria pop-
ulation (≈10 8 ) without protection reached cell
death at 10 min, with a mortality rate (K) of
0.8276 (Fig. 17.3a) (García-Bores et al., 2010).
Naringenin possesses pronounced photopro-
tective activity when compared with the neg-
ative control; although the results show that