The Effect of Various Topical Agents on Sunburn Cell Formation by Ultraviolet Irradiation

Chun, Chung Inn; Lee, Seung Chul; Chun, Inn Ki

Abstract

BACKGROUND: The sunburn cell is an abnormal keratinocyte of the skin induced by ultraviolet (UV) irradiation, and is used as an indicator of cell damage. The sunburn cell is consideredas an apoptotic cell which has been caused by UV irradiation, and many studies have been performed to understand the mechanism of photodamage in relation to apoptosis. The mechanism of photodamage by UV irradiation is still unclear. However, it is suggested that oxygen stress by reactive oxygen species produced by the UV rays may play an important role.
OBJECTIVE
This study was a med at evaluating whether various antioxidants and sunscreen can prevent sunburn cell formation. In addition, we studied whether or not the sunburn cell is identical to an apoptotic cell stained using the TUNEL method.
METHODS
White mice (ICR strain) were used to test the potency of various topical agents which are used in the prevention of sunburn cell formation; the agents were various antioxidants of L-ascorbic acid, tocopherol, catalase, a reduced form of glutathione (GSH), and sunscreen PABA (para-amino benzoic acid). Each agent was topically applied daily for 5 consecutive days on the dorsal skin of the ears. 300 mJ/cm of UV-B was irradiated on the ears 30 mins after the final applicaion, and skin samples were taken 24 hrs after that. The sunburn cells in the H & E stain were counted per 1 mm under the microscope. Also, the same sections for the sunburn cell study were stained by the TUNEL method using the ApopTag In Situ Apoptosis Detection Kit (Oncor, Inc.).
RESULTS
The number of sunburn cells increased in a UV-B dosage-dependent. manner up to 300 mJ/cm2. The potency in the reduction of sunburn cell formation was as follows in order,PABA (0.37 +/- 0,5), GSH (0.87 +/- 0.5), ascorbic acid (1.62 +/- 0.85) and tocopherol (1.75 +/- 1.12). However catalase (2.93 +/- 1.56) did not show any protective effect. Also, the finding that sunburn cells were the same as TUNEL-positive cells confirmed the notion that the sunburn cell is a kind of apototic cell.
CONCLUSION
A sunburn cell is a kind of apoptotic cell that may be caused by reactive oxygen species induced by UV-B irradiation, in view of the fact that sunburn cell formation was inhibited by the topical application of various antioxidants. But the result that physical protection by PABA has the most potent protective effect in relation to sun damage suggests that protection using a combined physical and biochemical approach is important in the development of new topical agents which will inhibit sundamage to the skin.