Fd. Olivarius et al., Isomerization of urocanic acid after ultraviolet radiation is influenced by skin pigmentation, J PHOTOCH B, 48(1), 1999, pp. 42-47
Citations number
30
Categorie Soggetti
Biochemistry & Biophysics
Journal title
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
Exposure to ultraviolet (UV) radiation may induce erythema, DNA damage and
suppression of immune responses. Melanin pigmentation offers protection aga
inst the first two of these effects, but immunosuppression seems to occur i
rrespective of the subject's pigmentation. Cis-urocanic acid (cis-UCA), pro
duced by isomerization of trans-UCA in the stratum corneum on UV exposure,
initiates some of the immunomodulatory effects of UV radiation. In the pres
ent study the relationship between skin pigmentation and UCA isomerization
has been examined in 28 healthy individuals of skin types I-IV. Pigmentatio
n is measured in five areas of not recently exposed back skin before irradi
ation with 0, 0.45, 0.9, 1.8 and 3.6 standard erythema dose (SED) of filter
ed broadband UV-B (1 SED = 10 mJ cm(-2) at 298 nm). The concentration of UC
A isomers is measured immediately after the irradiation. With 3.6 SED, the
relative production of cis-UCA is close to the maximum obtainable, irrespec
tive of skin type. A significant negative correlation is found between pigm
entation and relative production of cis-UCA at 0.45 and 1.8 SED, and betwee
n pigmentation and absolute production of cis-UCA at 0.45 SED. At doses of
0.45 and 0.9 SED the relative and absolute production of cis-UCA are higher
in the group with skin types I and II when compared with the group with sk
in types III and IV. The higher isomerization in the lightly pigmented subj
ects than in the more pigmented ones may indicate that people with fair ski
n are at a relatively higher risk of immunosuppression when exposed to low
doses of UV radiation. (C) 1999 Elsevier Science S.A. All rights reserved.