Evaluation of the test method for skin irritation as prescribed by oecd and EEC

Percutaneous absorption and skin irritation upon low-level prolonged dermal exposure to nonane, dodecane and tetradecane in hairless rats

Even though the dermal toxicity of hydrocarbon fuels has been well established in the literature, there is little information available on the dermal penetration kinetics and irritation potential of the individual hydrocarbons. The penetration and skin retention of nonane, dodecane and tetradecane was assessed in vitro using hairless rats’ skin. The effects of unocclusive dermal exposures of these chemicals (15 mL every 2 h for 8 h a day for four days) on the transepidermal water loss (TEWL) and erythema were measured in CD hairless rats. The expression of interleukin 1a (IL-1a) and TNF-a in the skin and blood were measured at the end of dermal exposures. The flux of dodecane was 3- and 77-fold higher than nonane and tetradecane. The retention of chemicals in stratum corneum (SC) was in the order of tetradecane-dodecane-nonane, and directly correlated to the log Kp (r2-0.9900) and molecular weight of the chemicals (r2-0.8782). The TEWL and erythema data indicate that irritation was in the following order: tetradecane-dodecane-nonane. Likewise, the expression of IL-1a in the blood and TNF-a in the skin after dermal exposures was higher for tetradecane followed by dodecane and nonane compared to control. In conclusion, the aliphatic hydrocarbon chemicals of the present study induced cumulative irritation upon low-level repeat exposures for a four-day period. The affinity of the chemicals to SC and their gradual accumulation in the skin in the present study is the probable cause for the differences in the skin irritation profiles of different aliphatic chemicals. The findings of the present study will be helpful in understanding the skin irritation response of the chemicals in humans; indeed the reality check arises from dermal exposures in humans and human experience in occupational handling of these chemicals.

Evaluation of a non-invasive human and an in vitro cytotoxicity method as alternatives to the skin irritation test on rabbits

5 substances were investigated for their primary irritant effect by means of different protocols. The cutaneous blood flow values (CBFV) were measured in humans: in a 1st series of experiments 12 h after application of the pure substances for 48 h and in a 2nd series of experiments 1, 24, 48 and 72 h after application of the 10% diluted substances (subclinical concentration) for 3 h. Rabbit skin erythema scores were obtained 1, 24, 48 and 72 h after application of the undiluted substances for 4 h. The uridine uptake inhibition assay on KB cells was included as a cytotoxicity test. Results obtained for both protocols on humans are compared with each other and with the test data obtained on rabbits, and with the cytotoxicity data. Application of the undiluted substances for 48 h on human skin or for only 3 h at a 10% dilution resulted in the same ranking between the substances. The CBFV in the human correlated very well (r = 0.99) with erythema scores obtained on rabbits. A poor correlation was observed between the in vitro and the in vivo results. From this study, it can be concluded that CBFV measurement is a valid method for the detection of erythema at subclinical concentrations.