Pseudoepidermis, constructed in vitro, for use in toxicological and pharmacological studies

Evaluation of transdermal penetration enhancers using a novel skin alternative

A novel alternative to animal skin models was developed in order to aid in the screening of transdermal penetration enhancers. The skin alternative consists of a dermal layer containing human fibroblasts dispersed in a collagen matrix and an epidermal layer of differentiated and stratified human keratinocytes. Skin alternatives were placed in modified Franz diffusion cells (receptor volume 12 mL, donor area 3.14 cm2, n = 5) and enhancer solution (0.4 M in propylene glycol (PG)) was applied. Following 1 h of pretreatment, 10 microL of saturated hydrocortisone (HC) solution in PG was applied, and the cells were occluded with Parafilm. Samples were removed from the receptor compartment over 24 h, replaced with fresh receptor solution, and analyzed for steroid content using HPLC. Skin HC content was also determined. Receptor concentration at 24 h (Q24) for full-thickness skin alternative (control) was 28.6 +/- 13.7 microM and permeability (P) was 8.3 x 10(-4) +/- 5.5 x 10(-4) cm h-1. Azone (1) produced a Q24 of 105.0 +/- 36.1 microM and a P of 11.3 x 10(-4) +/- 1.8 x 10(-4) cm h-1, while the novel penetration enhancer 1-dodecyl-2-pyrrolidinone (2) produced a Q24 of 164.8 +/- 61.2 microM and a P of 33.3 x 10(-4) +/- 6.6 x 10(-4) cm h-1. Compound 3 produced the highest values for all permeability parameters tested with a P of 48.0 +/- 36.8 cm h-1 and a Q24 of 186.1 +/- 45.1 microM. When compared to the control, compound 1 gave an enhancement ratio (ER) of 3.7 for Q24 and 1.4 for P. Compound 2 gives an ER 5.8 for Q24 and 4.0 for P. These enhancement ratios are similar to those found using HC and human skin.

Use of human pseudo-epidermis to evaluate the toxicity of bis-(2-chloroethyl)sulfide (BCES) on water permeation barrier formation and function

Human pseudo-epidermis was used to investigate the effects of bis-(2-chloroethyl)sulfide (BCES) on the formation and function of the water permeation barrier. To generate the culture, 2 million viable basal cells derived from human skin were placed on a Puropore nylon microporous membrane pre-coated with calf skin collagen. Addition of bovine pituitary extract and epidermal growth factor to the medium favored the formation of homogeneous cultures and better barrier function. The water permeation constant (Kp) was shown to decrease significantly and reached 25 +/- 6 x 10(-3) when it was calculated from 71% of the cultures prepared. The effects of topically applied BCES on the incorporation of [14C]linoleic acid, as a marker for lipid synthesis, and Kp, as a measure of water permeation, were studied. Compared with untreated cultures, there was no difference in the Kp immediately after exposure to 1-10 nmol BCES/cm2 for 30 min. On the other hand, [14C]linoleic acid incorporation was dose-dependently decreased immediately after exposure and then returned to normal by 48 h later. These data suggest that BCES produces no direct damage to the water permeation barrier but may affect barrier formation by inhibiting lipid synthesis.

The effect of 2,2'-dichlorodiethyl sulfide on DNA synthesis of a murine stratified keratinocyte culture system

A primary stratified keratinocyte culture resembling the epidermis in situ was used as a model for studying the effects of exposure to 2,2'-dichlorodiethyl sulfide, or sulfur mustard (SM), on DNA synthesis. A method that distinguishes between semi-conservative (s.c.) DNA synthesis and repair synthesis was used to determine if the former was inhibited following treatment with SM. In this method the density of the newly synthesized DNA was increased by incorporation of 5-bromo-2-deoxyuridine. Density gradient centrifugation was then used to isolate the heavy DNA for quantification. It was demonstrated that topically applied SM in the dose range of 1-10 nmole/cm2 inhibited s.c. DNA synthesis (replication) in a dose and time related manner. Inhibition of DNA replication by SM would result in inhibition of cell division which must be preceded by s.c. DNA synthesis. This failure to replace damaged germinative cells may lead to the destruction of the basal layer which is observed in vivo and in our epidermal culture following exposure to SM. This may also be related to development of vesication observed in exposed intact human skin.

Assessment of the role of DNA damage and repair in the survival of primary cultures of rat cutaneous keratinocytes exposed to bis(2-chloroethyl)sulfide

Toxicity manifests itself as vesication in human skin exposed topically to bis(2-chloroethyl)sulfide (BCES). The destruction of the proliferating population of epidermal cells is a major component of the pathogenic process. Available data strongly suggest that damage to cellular DNA is a critical factor in the loss of these cells. However, the influence of DNA repair on this toxic response has not been adequately studied. Therefore, a study was undertaken to ascertain the influence of DNA repair on the survival of primary monolayer cultures of rat cutaneous keratinocytes exposed to BCES. The sensitive nucleoid sedimentation assay was employed for the determination of DNA damage in cultures exposed to very low levels of BCES. Initial experiments demonstrated that within 1 hr of exposure to as little as 0.1 microM BCES the structural integrity of cellular DNA was compromised, presumably resulting from the appearance of single-strand breaks in the nucleic acid. This same effect was demonstrated in basal cells derived from a stratified, cornified culture grown at the air-liquid interface and exposed topically to the vesicant. Further studies with the monolayer culture demonstrated that the gross structural integrity of the DNA in cells exposed to as much as 5 microM BCES was completely restored within the first 22 hr following the exposure. However, this repair process appeared to be inefficient since a depression of thymidine incorporation into DNA and a significant loss of DNA were exhibited in exposed cultures as long as 72 hr after the initial exposure.