Individual variations in the correlation between erythemal threshold, UV-induced DNA damage and sun-burn cell formation

A linear correlation between erythema intensity and DNA damage upon exposur e to UV has not been firmly established. Many of the deleterious effects of UV exposure do occur after exposure to suberythemal doses. After DNA damag e, cells undergo DNA repair. It is commonly accepted that when the burden o f damage is beyond the repair capacities, the cell undergoes programmed cel l death or apoptosis. The aim of this study is to quantify the amount of UV -induced DNA damage (estimated via the measurement of DNA repair or unsched uled DNA synthesis or UDS) and cellular damage (estimated via the determina tion of the density of sunburn cells or SBC). If DNA damage and erythema ar e correlated, similar intensity of UDS and similar density of SBC should be found in volunteers irradiated with a UV dose equal to two minimal erythem a doses (MED). Our results show that in 15 different individuals the same r elative dose (2 MEDs) provokes UDS values, which vary within a factor of 4. An even larger variability affects SBC counts after the same relative dose . When DNA damage or SBC are plotted versus the absolute dose (i.e. the dos e expressed in J/m(2)), there is a rough correlation (with several exceptio ns) between dose and extent of UDS and SBC counts. It seems possible to div ide the volunteers into two subpopulations with different susceptibilities to UV damage. It is well known that UDS and SBC measurements are often affe cted by large experimental indeterminacy, yet, the analysis of our results makes it plausible to suggest that for the triggering of erythema, a common threshold value for DNA damage or for SBC count are not to be found. In co nclusion, the erythema response seems to be loosely correlated with DNA dam age. This suggests that the protection offered by the sunscreens against DN A damage, the molecular basis of UV-induced mutagenesis, might not be relat ed to the sun protection factor (SPF) indicated on the label of sunscreens, which is evaluated using the erythema as an endpoint. (C) 2001 Elsevier Sc ience B.V. All rights reserved.