A NEW BROAD-SPECTRUM SUNSCREEN 81 PF 0-8 4-4 6-2 8-0 MDC-Boehmite/P-MCX% Figure 17. Preventive effect of MDC-boehmite (1/1) combined with P-MCX on delayed pigmentation induced by natural sunlight on human back skin. The samples of W/O-type emulsion containing MDC- boehmite (1/1) and P-MCX were treated (2 mg/cm 2) ten minutes before sun exposure. n = 6. PF = protection factor. jects. In several combinations with Parsol MCX, they demonstrate an SPF near 2, while Parsol MCX alone had no effect (Figure 18). DISCUSSION 4-Methoxydibenzoylmethane-2-carboxylic acid (MDC) was developed as a new sun- screen agent. It is characterized by varying UVA and UVB absorption spectra with cationic metal compounds such as boehmite, and such complexation induces an increase in the molecular absorbance coefficient in the UVA range and a decrease in the UVB range. In accordance with changes in the molecular absorbance coefficient (MAC), the MDC-boehmite complex is found to provide a high and dose-dependent protection against both PUVA- and UVB-induced erythema. An increase in MAC by 10,000 in the UVA range induces an increase in SPF by about 3.8, while a decrease in MAC by 4,000 at UVB range is associated with a decrease in SPF by about 1.2, although the appearance of a minimum value at the 6/6 ratio of MDC-boehmite does not exactly correspond to the changes in the MAC. Since prostaglandins have frequently been implicated as inflammatory mediators in ery- thema induced by UVB irradiation as well as that induced by PUVA (8-13), the

82 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS PF 0-8 4-4 6-2 8-0 MDC-Boehmite/P-MCX% Figure 18. Preventive effect of MDC-bochmitc (1/1) combined with P-MCX on immediate tanning in- duced by glass-filtered natural sunlight on human back skin. The samples of W/O-type emulsion con- taining MDC-boehmite (1/1) and P-MCX were treated (2 mg/cm 2) ten minutes before sun exposure. n = 11. PF = protection factor. preventive effect of our new sunscreen was evaluated by measuring the level of prosta- glandins released in the medium of organ culture after exposure to UVB or PUVA. Our recent studies have demonstrated that the organ culture system is a convenient method of determining the level of prostaglandin synthesis for the evaluation of inflammation genesis attributable to UV irradiation (6). Assay of prostaglandins reveals that the prior application of MDC-boehmite complex markedly suppresses the prostaglandin release induced by PUVA and UVB up to the nonexposed level, demonstrating a distinct preventive effect on UV-induced biologic events. For protection against UV-induced pigmentation, brownish yellow guinea pig skin, which has a moderate number of functioning melanocytes in the epidermis and responds well even to a single UV exposure to induce a visibly well-defined hyperpigmentation (14), may serve as an ideal model. It appears to be comparable to human skin, especially mongoloid, for elucidating several UV pigmentation processes that generally involve a numerical increase in the number of epidermal active melanocytes. MDC-boehmite complex also demonstrates a remarkable effect in preventing hyperpigmentation in- duced by repeated exposure of tortoiseshell guinea pigs to UVB or UVA wave bands. This preventive effect is accompanied by a decrease in the melanocyte population, but