Two Sensitive in Vitro Monitors of Chemical Toxicity to Human and Animal Skin (in Short-Term Organ Culture): I. Paranuclear Vacuolization in glycol Methacrylate Tissue Sections II. Interference with [14C]Leucine Incorporation

Toxicity of mustard gas skin lesions

Although the exact pathogenesis of mustard gas-induced dermal toxicity remains elusive, morphopathological data gathered in controlled animal and in vitro investigations is providing important clues as to approximate mechanisms. Our laboratory has been studying dermal effects of the chemical warfare agent, sulfur mustard, in a variety of animal models, cultured isolated human cells, and in vitro organotypic skin models. Published anatomical, pathological, and ultrastructural results of these studies have documented consistent cellular and basement membrane zone effects irrespective of the model. Cellular effects include the early targeting of basal cells of the stratum basale to the exclusion of other epidermal cells, with nuclear and cytoplasmic indications of cell injury and cell death. Effects on the basement membrane zone include the formation of characteristic microvesicles in the lamina lucida of those models which possessed structural components of a true basement membrane. We are now investigating effects on proteins of the basement membrane microenvironment and correlate in the present paper the morphopathology of sulfur mustard dermal lesions with immunohistochemical study of bullous pemphigoid antigen, laminin, type IV collagen, and type VII collagen.

Antigen-specific IgG1-mediated epidermal cell injury: a component of contact hypersensitivity reactions in guinea pigs, measurable in vitro in full-thickness skin explants

Guinea pigs were sensitized by the topical application of either dinitrochlorobenzene (DNCB) or oxazolone on days 1, 2, 3, and 10. Seventeen days after the first treatment with the sensitizer, full-thickness 1.0-cm2 explants of untreated areas of skin were topically exposed in vitro to these contactants. Compared to the response of skin from control guinea pigs, skin from specifically sensitized animals showed a dose-related increase in the number of epidermal cells containing vacuoles. A specific increase in epidermal microblistering paralleled the increase in epidermal vacuolization. In addition, skin explants from sensitized animals (exposed to the contactant) showed a specific decrease in the incorporation of [14C]leucine. Full-thickness skin explants from unsensitized guinea pigs were sensitized in vitro by the intradermal injection of serum IgG1 fraction from oxazolone-sensitized guinea pigs. In such passively sensitized explants, the specific contactant produced an increase in the number of epidermal vacuoles, an increase in the amount of microblistering, and a decrease in the number of mast cells detectable by Giemsa staining. To elicit this specific response, the concentration of the specific contactant had to be mildly injurious, as well as antigenic. This requirement for nonspecific injury could be met by topically exposing skin explants to a nonspecific irritant followed by a sub-threshold concentration of the specific contactant. In contrast to vacuole formation and blistering, contactant-specific degranulation of mast cells (measured by the decrease in their number) did not require irritant levels of the contactant. These studies show that several components of contact sensitivity reactions can be reproduced in vitro by the passive transfer of sera containing antigen-specific immunoglobulins. Banks of such sera might, therefore, be useful in identifying (in human populations) many pre-existing sensitivities to chemical compounds.

Mediators, initiating the inflammatory response, released in organ culture by full-thickness human skin explants exposed to the irritant, sulfur mustard

Mediators released from injured human skin that initiate the inflammatory response have not been adequately identified. Organ culture of full-thickness skin explants enables us to do so, because injury to the skin can be made in vitro, eliminating the rapid leakage of serum and infiltration of leukocytes that occur in vivo. In our studies, the military vesicant sulfur mustard (SM) (10 microliters of a 0.01 to 1.0% dilution) was topically applied to injure the epidermis of the explant. Then, the explants were cultured in small Petri dishes, usually for 18 h at 36 degrees C, and the organ-culture fluids were assayed for various inflammatory mediators. We found that the culture fluids from SM-exposed and control explants contained similar amounts of angiotensin-converting enzyme, trypsin-like and chymotrypsin-like proteases, acid phosphatase, beta-glucuronidase, beta-galactosidase, lysozyme, deoxyribonuclease, ribonuclease, interleukin 1, and lactic dehydrogenase. However, the culture fluids from SM-exposed explants contained increased amounts of histamine and plasminogen-activating activity, and often prostaglandin E2, when compared to culture fluids from control explants. After 3 to 4 d in culture, full-thickness human skin explants, when exposed to 0.2% SM (but not when exposed to 1.0% SM), sometimes showed separation of the epidermis and increased collagenase activity (i.e., hydroxyproline release). Thus, histamine (from local mast cells), and prostaglandin E2 and plasminogen-activating activity (probably from both mast cells and epidermal cells) are apparently involved in early mediation of the inflammatory response.

Effects of nicotinamide on biochemical changes and microblistering induced by sulfur mustard in human skin organ cultures

Blister formation due to sulfur mustard (HD) exposure was studied in an ex vivo human skin model. Pieces of fresh human skin were exposed to HD vapor and subsequently incubated in medium for 48 hr. During this culture period cellular NAD+ levels and uptake of glucose from the medium decreased relative to the duration of the exposure to HD. In light microscopic sections of skin that were exposed to HD for 6 min. clefts of variable size could be clearly observed between the epidermis and the dermis after a 48-hr culture period. Immunohistochemical staining of collagen type IV demonstrated that separation occurred between the basal membrane and the basal keratinocytes. The described ex vivo human skin model mimicked the in vivo process quite well. Since it was reported that nicotinamide could protect cellular NAD+ levels after HD exposure, HD-treated skin pieces were incubated in medium containing 10 mM nicotinamide. Although this incubation caused an elevation of cellular NAD+ levels and of glucose uptake from the medium compared to control values, it did not result in a substantial reduction of cell death or microblister formation as observed by light microscopy in tissue sections. It was concluded that depletion of cellular NAD+ levels is not the only cause of HD-induced cell death.

Full-thickness human skin explants for testing the toxicity of topically applied chemicals

This report describes a model organ-culture system for testing the toxicity of chemical substances that are topically applied to human skin. In this system, the viable keratinocytes in the full-thickness skin explants are protected by the same keratinized layer as skin remaining on the donor, and toxicity can be assessed microscopically and/or biochemically. The human skin specimens were discards from a variety of surgical procedures. They were cut into full-thickness 1.0-cm2 explants, and briefly exposed to the military vesicant sulfur mustard (SM), which was used as a model toxicant. The explants were then organ cultured in small Petri dishes for 24 h at 36 degrees C. In the 0.03-1.0% dosage range, a straight-line dose-response relationship occurred between the concentration of SM applied and the number of paranuclear vacuoles seen histologically in the epidermis. Within the same SM dosage range, there was also a proportional decrease in 14C-leucine incorporation by the explants. Thus, the number of paranuclear vacuoles reflected decreases in protein synthesis by the injured epidermal cells. The epidermis of full-thickness untreated (control) human skin explants usually remained viable for 7 d when stored at 4 degrees C in culture medium. During storage, a relatively small number of paranuclear vacuoles developed within the epidermis, but the explants were still quite satisfactory for testing SM toxicity. Incubation (for 4 or 24 h at 36 degrees C) of such control skin explants reduced (often by 50%) the small number of paranuclear vacuoles produced during 4-7 d of storage. This reduction was probably caused by autolysis of many of the vacuolated cells. Two types of paranuclear vacuoles could be identified by both light and electron microscopy: a storage type and a toxicant type. The storage type seemed to be caused by autolysis of cell components. The toxicant type seemed to be caused by an invagination of the plasma membrane. Only toxicant-type vacuoles increased appreciably in number when skin explants were exposed to mustard, and to other toxicants.

Two-compartment model for rabbit skin organ culture

A new method was developed for rabbit skin organ culture. In a two-compartment model, skin discs were cultured on a Millicell-HA insert unit with a microporous membrane which allows transport of culture medium via the dermis into the epidermis, whereas the epidermal side remains free of direct contact with culture medium. In this relatively simple two-compartment organ culture model, rabbit skin could be cultured for 7 d in RPMI 1640 medium supplemented with fetal bovine serum, or for 2 d in RPMI 1640 medium supplemented with cofactors. The histomorphology and ultrastructure of 7-d cultured rabbit skin discs was essentially similar to that of freshly isolated rabbit skin. Keratinocytes in the stratum basale continued to divide during organ culture. The terminal differentiation of the epidermis continued in vitro as was found by the presence of keratohyalin granules, the intact stratum corneum, and keratin expression. Furthermore, glucose consumption continued until culture Day 7, but thereafter it declined rapidly. Concomitantly, degenerative changes were found. At the end of the 7-d culture period the distance between single dermal collagen fibrils had increased as compared to noncultured skin. This model of skin organ cultures can be used to study biological processes, dermal toxicity, and penetration and metabolism of xenobiotics in intact skin. Furthermore, within certain limits, processes responsible for repair and regeneration of damaged skin can also be studied in this model because the rabbit skin can be cultured for 7 d.