In Vitro Assessment of in Vivo Damage to the Barrier Properties of Pig Skin Caused by a Complex Mixture

Abstract

The purpose of this study was to determine if an in vitro method can be used to measure changes in the barrier properties of skin caused by in vivo or in vitro topical exposure to a test chemical. The effect of a test chemical (liquid gun propellant [LP], a highly irritating mixture of hydroxylammonium nitrate, triethanolammonium nitrate, and water) on the barrier function of skin was assessed in vitro by measuring the penetration of [¹⁴C]benzoic acid following exposure to LP. Weanling pigs were topically exposed to single doses (25μl/cm²) of saline (control) or LP. LP-induced changes in the barrier properties of the skin were determined by measuring the permeability to [¹⁴C]benzoic acid. After 1-5 days, pigs were euthanized and skin sections excised from the sites of application. Skin sections were mounted in in vitro penetration chambers to measure cumulative 24 hr penetration of [¹⁴C]benzoic acid. Topical treatment with undiluted LP resulted in an 8.2-fold increase in permeability to [¹⁴C]benzoic acid at 1 day after exposure. The permeability declined progressively during the succeeding 4 days. In a parallel study, untreated skin was excised, placed in penetration chambers, and then exposed to saline or LP for 1 day. In vitro skin exposure to LP resulted in a 3.9-fold increase in penetration of [¹⁴C]benzoic acid. These studies demonstrate that the effect of LP on skin barrier properties is greatest at 1 day postexposure and steadily decreases thereafter and that both in vivo and in vitro dermal exposure to LP alters the barrier properties of skin. This in vitro method, which is the quantitation of transdermal transport of benzoic acid, can be used to assess the effect of chemical or physical agents on barrier function and time course of return to normal barrier function of skin.