New coal tar extract and coal tar shampoos. Evaluation by epidermal cell DNA synthesis suppression assay

Abstract

Coal tar therapy has been used for many years in the treatment of scaling skin diseases, including psoriasis and eczema. Previous studies of the potential effectiveness of tar have utilized phototoxic erythema assays with long-wave ultraviolet light (UV-A). However, in clinical use, coal tar is rarely used with UV-A, particularly for scalp disease. Therefore, we investigated a nonphototoxic approach to evaluate different coal tar products. Coal tar was found to suppress epidermal cell DNA synthesis in the hairless mouse model, and this is the basis for the assay presented. Using the epidermal cell DNA synthesis suppression assay, we observed that crude coal tar and a new extract of crude coal tar were equally effective and that a concentration gradient effect was achieved. In addition, four commercial coal tar shampoos assayed varied greatly in their ability to suppress epidermal cell DNA synthesis. One shampoo was washed after ten minutes and no significant alteration of suppressive effect was seen.

The pharmacological variability of crude coal tar

“…If the original crude coal tar can vary on a distillation to distillation basis, then so would the final extract or purification of the tar that is used by the patient. In the tar extract process for Neutar® we can demonstrate the equivalence between the tar extract and their crude coal tar parents (Table i; Lowe et al, 1981a;Lowe et al, 1982). Therefore, for manufacturers of purified product it would be beneficial to pre-test the crude coal tar as well as the finished product.…”

“…The epidermal DNA synthesis suppression assay has been used to evaluate many therapeutic agents used in psoriasis treatment, including anthralin (Lowe & Breeding, 1981) and coal tar (Walter, Stoughton & DeQuoy, 1978;Lowe, Wortzman & Breeding, 1981a, 1982 and it reliably predicts efficacy (Lowe et al, 1981b). We have used the DNA synthesis suppression assay to evaluate the variability of biological activity of crude coal tar from different distillations.…”

Duration of Remission of Topical Psoriasis Therapies

“…In murine models, the combination of coal tar and ultraviolet phototherapy decreases DNA synthesis through DNA crosslinking and production of oxygen radicals. [31][32][33] In addition to providing a long duration of remission, Goeckerman and Ingram therapies were well tolerated by patients, and there was no evidence of major adverse effects. Other longer-term studies have failed to demonstrate any increase in the incidence of skin cancer.…”

Management of scalp psoriasis: current perspectives

“…Few studies have evaluated the actual efficacy of these preparations, reporting shampoos have a modest, at best, effect on treating psoriasis of the scalp. 15 There are some studies available that support the use of coal tar shampoo, containing 2%–10% coal tar solution, in scalp psoriasis; 16 , 17 however, no double-blind studies are available to support this practice and many patients do not find tar shampoos cosmetically acceptable. Salicylic acid shampoo, due to its keratolytic effect, has also been used to enhance the penetration of other topical medications including corticosteroids, and has been recommended by The National Psoriasis Foundation as a first-line therapy.…”