EFFICACY OF MICRONIZED TITANIUM DIOXIDE-CONTAINING COMPOUNDS IN PROTECTION AGAINST UVB-INDUCED IMMUNOSUPPRESSION IN HUMANS IN-VIVO

Micronized pigment-containing sunscreens may provide a good alternativ e to chemical sunscreens in protection against ultraviolet (UV) B-indu ced immunosuppression. The metal particles in these products are likel y to remain on the skin surface where they can offer broadband protect ion for both the UVA and UVB regions. We have tested the protective ca pacity of three titanium dioxide (TiO2)-containing compounds in humans in vivo. The effect on sunburn cell formation has been investigated u sing transmission electron microscopy, while the mixed epidermal cell lymphocyte reaction (MECLR) has been used as a model for immunosuppres sion. Furthermore, the influence of titanium on the integrity of the s tratum corneum barrier (intercellular lipids and desmosomes) has been examined using freeze fracture electron microscopy. We find that all t hree compounds protect against sunburn cell formation. The immunoprote ction studies show that one of the three compounds does not prevent UV B-induced changes of the MECLR responses. Application of this compound without subsequent UVB irradiation also induces a significant decreas e of the MECLR responses. Moreover, the same compound affects the inte rcellular lipid layers, and desmosomes cannot be detected. The deleter ious effect of this compound is probably caused by an incomplete hydro lysis during the TiO2 synthesis. Our findings indicate that micronized pigment-containing compounds can offer good protection against shea-t erm UVB-induced immunomodulation in humans in vivo. However, accurate screening of the synthesis of these compounds is a prerequisite for th eir safe use as sunscreening agents in human subjects. (C) 1998 Elsevi er Science S.A. All rights reserved.