Effects of freezing and azide treatment of in vitro human skin on the flux and metabolism of 8-methoxypsoralen.

Abstract

Clinical and in vitro evidence suggests that the physicochemical properties of the skin influence the process by which drugs are transported through skin. The effects of skin storage, preparation and pretreatment on the permeation and metabolism of (8-methoxypsoralen (8-MOP), as a model penetrant, were studied using the flow-through in vitro cell diffusion system. The metabolites and unchanged drug were estimated by thin-layer chromatography. While the permeability of 8-MOP was similar in fresh (445 cm.h-1) and azide-treated (449 cm.h-1) skin (p < 0.01), decreased permeability was observed in frozen skin (406 cm.h-1, p < 0.01). A 2.8-fold increase in the cumulative flux of 8-MOP at 24 h through azide-pretreated (2.5 x 10(-3) mumol.h-1.cm-1) versus fresh skin (9.1 x 10(-4) mumol.h-1.cm-1) was observed (p < 0.01). There was a slight increase in the flux of 8-MOP at 24 h when skin was frozen, compared with untreated skin. Increase in the flux of 8-MOP in frozen skin might result from the alteration of the molecular arrangement of the skin components during freezing. In addition to the obvious differences between frozen and fresh skin, these observations discourage the use of frozen skin. There is a moderate relationship between the permeability and flux of 8-MOP through frozen skin. A similar but nonrelated correlation was observed between the permeability and flux of 8-MOP through azide-treated skin samples (r = 0.6). These findings suggest that azide and freezing treatments lower the skin barrier properties to the transport of 8-MOP. Apparently, factors that may affect the inherent permeability of human skin, particularly those related to the handling, storage and pretreatment of skin with solvents and chemicals, can also influence topical drug delivery. The metabolic capacity of frozen skin and fresh skin remained constant during the period of study. These data may be of value in the development of topical methoxypsoralen systems. Further in vitro and in vivo studies are required to ascertain the generalization of this process.