10 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1 0 7 I 0 6 1 o 5 I I o 5 Cultu re Day Figure 6b. Effect of ZPT on the growth of JTC-17 cells seeded in different concentrations. A: Cells were initially cultured at a 3.0 x 10 4 cell density with simultaneous addition of ZPT at indicated concentrations. B: Cells were initially cultured at a 3.2 x 10 5 cell density with simultaneous addition of ZPT at indicated concentrations. Arrow represents the time of the addition of drugs. Since actual inhibition of DNA synthesis by ZPT requires penetration of ZPT into epidermis as well as sequential contact with epidermal basal cells, whether or not the suppression of dandruff by ZPT could reasonably be interpreted in the terms of the inhibition of DNA synthesis observed here, remains to be established not only with regard to ZPT's permeability into the scalp skin but also for its actual in vivo cellular metabolic action. Our previous microbial study (1) has suggested that of greater significance for induction of clinical effectiveness is the factor of penetration of ZPT into the skin. This observation is based on the fact that the presence of ZPT molecules on scalp in concentrations capable of maintaining the continuous suppression of P. ovale does not necessarily result in reduction of dandruff. In a biological estimation of actually adsorbed ZPT molecules by in vitro minimum inhibitory concentration (MIC) values for its anti-yeast action, there seems to be at least 10 ppm of ZPT present within the upper layers of the scalp (1). Furthermore, surfactants used as main constituents of antidandruff shampoos because of their enhanced surface activities may accelerate percutaneous absorption (12). There is some evidence that dandruff scalp has a

EFFECT OF ZINC PYRITHIONE ON SKIN CELLS 11 decreased number of horny layers as compared to normal scalp (13). Therefore, the clinical effectiveness on dandruff through inhibition of DNA synthesis by ZPT seems aided through the enhanced permeability of dandruff scalp. This also suggests, as supported by clinical noneffectiveness of ZPT on mild dandruff subjects (14), that the restoration of the normal number of horny cell layers, because of decreased permeability, may generally diminish the potency of ZPT in exerting its inhibition of DNA synthesis. Scalp epidermal kinetics have revealed that dandruff is a disorder of hyperproliferation (15). Therefore, our findings that the highly active antidandruff agents ZPT and DS have an inhibiting effect on DNA synthesis of mammalian cells, support the hypothesis that the antidandruff effect by ZPT may primarily be due to its anti-metabolic effect rather than its anti-yeast effect. Since pyrithione is a general inhibitor of membrane transport processes in fungi (16), it seems likely that the decrease of P. ovale concomitant with the decrease in dandruff caused by ZPT as observed previously (1), involves similarities in cellular metabolisms between anti-yeast and anti-DNA synthe- sizing actions, both of which are related to a marked decrease in the activities of a variety of independently regulated transport systems within cells. REFERENCES (1) G. Imokawa, H. Shimizu, and K. Okamoto, Antimicrobial effect of zinc pyrithione, J. Soc. Cosmet. Chem., 33, 27-37 (1982). (2) J. j. Leyden, K. J. McGinley, and A.M. Kligman, Role of microorganisms in dandruff, Arch. Dermatol., 112, 333-338 (1976). (3) R. W. VanderWyk and K. E. Hechemy, A comparison of the bacterial and yeast flora of the human scalp and their effect upon dandruff production, J. Soc. Cosmet. Chem., 18, 629-634 (1967). (4) J. Fukuyama, Y. Mori, and H. Kikkawa, A male bearing XX sex chromosome constitution in humans, Proc. XII Intern. Congr. Genety., 1,216-217 (1968). (5) A. Sato, Changes in chromatin pattern during long term tissue culture of human male skin cells exhibiting XX chromosome, 26th Meeting of Japan. Tissue Culture Assoc. (1968). (6) E. Christophers, Growth stimulation of cultured postembryonic epidermal cells by vitamin A acid,J. Invest. DermatoL, 63,450-455 (1974). (7) T. Ebina, K. Ohtsuki, M. Seto, and N. Ishida, Specific G 2 block in HeLa-S3 cells by neocarzinostatin, Eur. J. Cancer, 11,155-158 (1975). (8) G. C. Priestley and J. C. Brown, Acute toxicity of zinc pyrithione to human skin cells in vitro, Acta Dermatovener (Stockholm), 60, 145-148 (1980). (9) G. Piewig and A.M. Kligman, The effect of selenium sulfide on epidermal turnover of normal and dandruff scalps,J. Soc. Cosmet. Chem., 20, 767-775 (1969). (10) M. Gloor, M. Dressel, and U. W. Schnyder, The effect of coal tar distillate, cadmium sulfide, ichtyol sodium and omadine MDS on the epidermis of the guinea pig, Dermatologica, 156, 238-243 (1978). (11) H. W. Young, G. Schochetman, S. Hodas, and M. E. Balis, Inhibition of DNA synthesis by hydroxyurea: structure-activity relationships, Cancer Res., 27, 535-540 (1967). (12) G. Imokawa and Y. Mishima, Cumulative effect of surfactants on cutaneous horny layers: lysosome labilizing action, Contact Dermatitis, 5,151-162 (1979). (13) A. B. Ackerman and A.M. Kligman, Some observations on dandruff, J. Soc. Cosmet. Chem., 20, 81-101 (1969). (14) A.M. Kligman, R. R. Marpies, L. R. Lantis, and K.J. McGinley, Appraisal of efficacy of antidandruff formulations,J. Soc. Cosmet. Chem., 25, 73-91 (1974). (15) A.M. Kligman, K.J. McGinley, and J. J. Leyden, The nature of dandruff, J. Soc. Cosmet. Chem., 27, 111-139 (1976). (16) C. J. Chandler and I. H. Segel, Mechanism of the antimicrobial action of pyrithione: effects on membrane transport, ATP levels, and protein synthesis, Antimicrobial Agents and Chemotherapy, 14, 60-68 (1978).