Effect of coal tar fractions on guinea-pig and human skin

Abstract

Summary In this study, the effect of topical applications of coal tar and of fractions derived from it were investigated in guinea‐pigs and humans. Coal tar and its fractions produced thickening of guinea‐pig epidermis in various degrees which were accurately measured. There was great variability in the epidermal thickening caused by different batches of coal tar. Separation into ether soluble and insoluble fractions yielded products which caused greater epidermal thickening than the parent substance. The acid soluble and alkali soluble extracts caused only minimal skin changes. The acid soluble fraction appeared to have similar activity to that of coal tar in the treatment of psoriasis, whereas the alkali soluble extract was without activity in patients with psoriasis. Coal tar incorporated in emulsifying ointment as well as a mixture of bases known to be present in coal tar and incorporated into emulsifying ointment produced suppression of epidermal thickening in guinea‐pigs when compared with appropriate controls. It must be concluded that coal tar contains both irritant (inflammation producing) and anti‐inflammatory substsnces. Their precise relationship to therapeutic effectiveness is not clear.

Pharmacological variability of crude coal tar

“…Furthermore, their observations on the pharmacological variability of coal tar are not new. This was first demonstrated by Downing & Bauer (1948) and confirmed in later studies (Wrench & Britten, 1975;Sarkany & Gaylarde, 1976). In addition we reported data on the effect of various coal tar fractions on epidermal thickness and showed that coal tar and certain of its fractions could suppress epidermal thickening induced by a topically applied irritant.…”

“…They cited previous publications which supported their work. They ignored the majority of reports which disagreed with their findings and which reported an increase in mitotic rate labelling index or epidermal thickness (Jambon, 1909;Combes, 1943;Kaidbey & Kligman, 1974;Elgjo & Larsen, 1973;Saldfeld & Orth, 1965;Wrench & Britten, 1975;Foreman et al, 1979;Sarkany & Gaylarde, 1976).…”

The atrophogenic effect of crude coal tar on human epidermis

“…Furthermore, Jambon (1909) observed an increased mitotic rate when tar was applied to normal human skin. Epidermal hyperplasia has also been found in hairless mice (Elgjo & Larscn, 1973) and guinea-pigs (Sarkany & Gaylarde, 1976). However, in all of these studies the duration was short (4 weeks or less).…”

“…In a recent study in whleh the effects of coal tar and vitamin A acid on membrane coating granules were analyzed (Lavker, Grove & Leyden, 1979), we gained the impression that the epidermis was thinner after the tar treatment. This was a paradoxical result for coal tar is known to produce hyperplasia and hyperkeratosis in man (Jambon, 1909;Combes, 1943Combes, ,1944Kaidbey& Kligman, 1974) and animals (Sarkany & Gaylarde, 1976;Elgjo & Larscn, 1973).…”

The Potential of the Essential Fatty Acid-Deficient Hairless Rat as a Psoriasis Screening Model for Topical Anti-Proliferative Drugs

“…The action of the dithranol vehicle on the epidermis measured in this study is probably due to the presence of coal tar. Coal tar stimulates epidermal turnover in normal skin but causes suppression of epidermal hyperplasia in psoriasis [27] and of thickening induced by irritants [28]. A suppression of epidermal DNA synthesis has been suggested [29].…”