Corneobiology and corneotherapy--a final chapter.

The text obtained for this review from Professor Albert Kligman was drawn posthumously from a variety of notes that he had been planning to use to write a review on corneobiology and corneotherapy. It was a review that he had dearly hoped to complete--his final 'magnum opus' with reflections on the subject.

Barrier functions of human skin: a holistic view.

The fascinating topic of skin barrier continues to engage researchers from diverse disciplines both in academia and industry. Much of the information on the basic biology of barrier formation, its ontogeny as well as repair and homeostasis comes from studies on animal models. A smaller number of human studies have validated the usefulness of animal models, while highlighting some essential differences. We submit that the human skin barrier is unique in several ways, as much due to our adaptive ability as our control over the environment (macro and micro) that none of the other species have exerted. The human skin is not only exposed to the greatest variations of environment due to our phenomenal mobility but also to the largest number of xenobiotics, both chemical and microbial, resulting from human activity. In this overview, we attempt to evaluate the interdependent relation of skin barriers to environmental stressors hoping to raise interest in some of the lesser known or neglected aspects of human skin barriers as they relate to skin health and dysfunctions.

Histogenesis and progression in ultraviolet light-induced tumors in hairless mice.

Tumor histogenesis and progression were studied in UV-irradiated albino (Skh:hairless-1) and lightly pigmented (Skh:hairless-2) hairless mice. A strongly carcinogenic dose of UV light was used, producing 100% tumor incidence by 35 weeks. The light source emitted mainly UV radiation in the range of 280-320 nm and the less energetic UV radiation up to 400 nm. The resulting epidermal changes and neoplasms resembled those seen in the actinically damaged skin of humans. Microscopic lesions included benign hyperplasia, actinic keratoses, and squamous cell carcinoma in situ and with microinvasion. Clinical tumors were epithelial papillomas, fibropapillomas, keratoacanthomas, cystic keratomas, benign pigmented macules, cutaneous hornlike growth, exophytic and endophytic squamous cell carcinomas of several cytologic types, and fibrosarcomas. Even with this high dose of UV radiation, not all of the small tumors progressed to cancer. Many regressed, including some keratoacanthomas, whereas others remained small and benign for the lifetime of the mouse.

Human models for identification of photosensitizing chemicals.

The human is an appropriate and sensitive animal for identifying photosensitizing drugs administered either topically or systemically. Topically effective phototoxic agents are quite easily revealed when they are applied to normal or scarified skin which is subsequently exposed to 2 X 10(5) J.m-2 of near UV light (UVA, 320-400 nm). Systemically effective phototoxic drugs can be identified by exposing intradermally injected sites to either solar-simulating or UVA radiation. Drugs that cause photocontact allergy can usually be recognized by irradiating pretreated sites six times over a 3-week period with a solar simulator and then challenging the sites with UVA. Existing models, the human model especially, should make it possible to recognize important photosensitizing drugs before they are marketed.

The SLS provocative patch test in allergic contact sensitization.

1. In the increasingly chemical environment of modern life, there are individuals whose marginal state of contact sensitization may not be revealed by standard methods of patch test- ing. The substances are often comparatively weak allergens with extremely limited capacity to penetrate normal skin. 2. Provocative patch tests magnify the manifestations of allergic contact dermatitis. Threshold states of contact sensitization are brought to light. Provocative testing is indispensable in screening new substances for allergenic potentiality. 3. Physical and chemical insults which mildly damage the skin may act as provocative agents. Physical injuries such as sandpapering and ultraviolet radiation are inferior to chemical insults. 4. The promoting effect of provocative tests is mediated by assuring penetration into the immunologic target tissue by damaging the horny layer barrier and by initiating a mild inflammatory response which conditions the tissue to react in an exaggerated but specific way to allergens. 5. Sodium lauryl sulfate (SLS) was the most effective provocative agent. The SLS provocative test is performed by pre-treating the skin for one hour with a 10% aqueous solution of SLS.

Chronic heliodermatitis: a morphologic evaluation of chronic actinic dermal damage with emphasis on the role of mast cells.

Descriptions of actinically damaged human dermis have focused on the late stages of elastotic degeneration. This has diverted attention from preceding events, which are important for understanding the sequence of pathologic changes that culminate in the deranged fibrous structures of elastotic dermis. We studied specimens from the back of the necks (exposed) and inner arms (unexposed) of 24 individuals, aged 35-84 yr, by light and transmission electron microscopy. Intense sunlight exposure was common to all. A previously undescribed finding was the presence of a perivenular, histiocytic-lymphocytic infiltrate in which numerous mast cells, often in close apposition to fibroblasts, were observed. We have termed this "chronic heliodermatitis." We postulate that mast cell-derived mediators in conjunction with enzymes released by the infiltrating cells lead to breakdown of elastic and collagen fibers.

Mechanisms of eccrine anidrosis. I. High level blockade.

The cause of anidrosis of the chronic dermatoses, hydration, and that produced experimentally by protein precipitants is superficial obstruction of the eccrine duct. In each instance, return of sweating in the anidrotic area is effected simply by removal of the stratum corneum with Scotch Tape stripping. The histologic picture common to this type of anidrosis is ductal dilatation following an adequate sweat stress. The presence of an obstruction, whether functional or anatomic, is confirmed by the inability to achieve a methylene blue pore pattern. Parakeratotic plugging of the eccrine ostia is primarily responsible for the obstruction in the spontaneous dermatoses, while actual intraluminal casts are produced chemically by the protein denaturants, high within the stratum corneum portion of the eccrine duct. The PAS positive, diastase resistant casts regularly found in blocked ducts are secondary to the obstruction and are not a primary cause. No adequate explanation has been found for the persistent anidrosis after occlusion of the skin with impermeable plastic dressings.

A method for the assay of inflammatory mediators in follicular casts.

A method is presented whereby inflammatory mediators may be detected and quantified in individual follicular casts. Lysozyme, lactoferrin, IgG, IgM, C3 and material reacting with antiserum to polymorphonuclear leukocytes (PMN) were assayed by functional and immunologic methods. By these techniques, lysozyme, IgG and anti-PMN reactive material were detected in clinically uninflamed follicular casts from acne subjects.

The acute effects of long-wave ultraviolet radiation on human skin.

The erythematogenic and melanogenic properties of polychromatic long-wave ultraviolet light (UV-A) has been re-examined. Redness appeared immediately after exposure and persisted for 24 hr with doses of about 50 Joules/cm2. With threshold erythemal doses, about 13 J/cm2, the redness faded after a few minutes. The response was not biphasic. Pigmentation also appeared immediately after exposure and faded rapidly with threshold doses of 4 J/cm2. With larger doses (18 J/cm2) immediate pigmentation gave way without fading to delayed pigmentation (true melanogenesis). Thus, the acute effects of UV-A, unlike other wavelengths within the UV-spectrum, are immediate and appear without latency. The responses are also most intense immediately after exposure.

Identification of topical photosensitizing agents in humans.

A method is described for the detection of topical photosensitizers in humans. Test agents were applied to the untanned midback under an occlusive dressing for 6 hr and then exposed to broad-spectrum radiation containing UV-A and visible wavelengths from a Xenon arc source. Well-known topical photosensitizers were readily identified. It was found that with certain poorly-penetrating substances, such as water-soluble dyes, applications to scarified skin were necessary to reveal phototoxic activity. In addition, these dyes were activated by wavelengths in the visible region of the spectrum.

Identification of systemic phototoxic drugs by human intradermal assay.

An improved method is presented for the detection of systemically administered photosensitizing drugs in humans. Test agents were injected intradermally in physiologic saline and then exposed to broad spectrum radiation from a Xenon solar simulator. Several clinically recognized photosensitizers were identified by this technique. The activating spectrum depended on the test drug. Sulfonamides and vinblastin were activated by sunburning erythemic radiation (UV-B), while tetracyclines, nalidixic acid and phenothiazines by near UV (UV-A), and chlorothiazide by both. It is suggested that intradermal phototesting offers a means of verifying the phototoxic potential of agents suspected clinically of provoking a photosensitivity eruption.

Cumulative effects from repeated exposures to ultraviolet radiation.

Repeated exposures to subliminal doses of UVR, given at 24-hr intervals, resulted in a lowering of the erythema threshold dose. At erythemogenically equivalent doses, UV-A was the most effective and UV-C the least. A similar and more pronounced effect was observed following repeated exposures to subthreshold doses of UV-A and topically applied 8-methoxypsoralen. These findings provide quantitative evidence for the cumulative nature of acute UVR damage in human skin.

The effect on rhino mouse skin of agents which influence keratinization and exfoliation.

The skin of the rhino mouse, an allelic variant of the hariless mouse, contains deep dermal cysts and huge numbers of hornfilled utriculi which resemble comedones. Chemicals which influence either differentiation or desquamation of horny cells were applied topically twice daily for up to 6 weeks. Except for the dermal cysts, the gross epithelial abnormalities were almost completely corrected by retinoic acid in a dose-dependent fashion. Salicylic acid caused partial emptying of the horny masses, but the utriculi did not regress. Lactic acid, propylene glycol and benzoyl peroxide had minor effects on keratinization and exfoliation. The rhino mouse is a suitable model for assessing chemicals which affect epithelial differentiation (retinoids)or which promote loss of cohesion between horny cells (descaling agents).

Further studies of photoaugmentation in humans: phototoxic reactions.

The addition of modest amounts of long ultraviolet light (UV-A) to 1/2 minimal erythema dose (MED) of sunburning irradiation (UV-B) produced erythema visible at 24 hr, the prototype of the photoaugmentation phenomenon. The results were the same whether UV-A was given before or after UV-B. Photoaugmentation could be demonstrated after an inverval of 6 hr between doses, but not after 1 day. Photoaugmentation has also been demonstrated clinically and histologically with two topical photosensitizers, coal tar and 8-methoxy-psoralen.

Updated in vivo methods for evaluating topical antimicrobial agents on human skin.

Updated and expanded in vivo quantitative testing procedures to determine the efficacy of topical antimicrobial agents are presented. The occlusion test measures the ability of an agent to prevent the expansion of the resident microflora which occurs when an impermeable dressing is applied to the forearm. Measurements are made at 24 and 48 hr. The expanded flora test measures the ability of an agent to suppress a dense population of micro-organisms produced by expansion of the resident flora of the forearm by prior application of an impermeable occlusive dressing. Measurements are made at 6, 24 and 48 hr or after 10 min in the case for agents designed for immediate degerming. The persistence test measures the ability of an agent to establish a reservoir in skin and exert an antimicrobial effect up to 3 days after the last application of the test material. The ecological shift test determines any major alteration in cutaneous microbial ecology following several applications of the material under occlusive dressings. The serum inactivation test determines whether the presence of serum proteins interferes with antimicrobial activity.

Experimental infections with group A streptococci in humans.

Experimental inoculation of 7 strains of Group A streptococci failed to result in either colonization or infection of normal intact skin of human volunteers. All strains rapidly died on normal skin; suppression of the resident microflora did not affect survival and no difference in survival was seen between inoculation on lipid-rich and lipid-poor body areas. Inoculation on skin damaged by superficial scarification resulted in localized infections when 1 x 10(4) or more organisms were inoculated into the wound by rubbing and covered with an impermeable plastic film. Intradermal inoculation resulted in localized cellulitis, regional lymphadenopathy, and fever. All strains were equally effective in producing localized infections in scarified skin.

The influence of UVA and visible radiation on acute damage by short-wave UVR (lambda less than 320 nm).

The influence of UVA and visible radiation on the acute damage by short-wave ultraviolet radiation (UVR) (lambda less than 320 nm) was investigated in human volunteers, using delayed erythema and sunburn cell production as markers of injury. It was found that subsequent exposure to UVA + visible radiation produced a significant reduction of the threshold erythema dose by short-wave UVR, in a dose-dependent manner. Subsequent exposures to varying doses of UVA + visible radiation, as well as to visible light alone failed to influence sunburn cell production. It is concluded that there is a positive interaction between short-wave UVR and UVA in the induction of delayed erythema, but this may not apply to epidermal cell injury. Photorecovery was not observed.

Morphologic investigations on the rebound phenomenon after corticosteroid-induced atrophy in human skin.

Cutaneous atrophy was induced on the forearms of 4 volunteers by continuous occlusive application of clobetasol-17-propionate for 6 weeks, after which time the steroid was discontinued. Epidermal and dermal changes during the subsequent rebound "flare" were monitored for 2 weeks by light and transmission electron microscopy. An exuberant hyperplasia characterized the epidermal response. Within 2 days poststeroid, most basal cells displayed fine structural features typical of highly proliferating cells. "Dark"-staining keratinocytes appeared in large numbers 4 days poststeroid, preceding a 4-fold maximal increase of viable epidermal thickness which occurred at 7 days. The stratum corneum, initially very thin, increased markedly in thickness and displayed the typical basket-weave appearance. By 14 days, Langerhans cells, which were absent immediately poststeroid, were again present. At this time, the epidermis returned to a nearly normal state. Dermal restitution was similarly rapid. Initially, fibroblasts appeared very active as evidenced by widely dilated endoplasmic reticulum filled with flocculent material. Ground substance increased continuously, reaching normal levels by 14 days. An increase in postcapillary venules was noted during the rebound flare. Swift epidermal and dermal changes are evidence that topical corticosteroids are rapidly cleared from the skin. The vigorous epidermal hyperplasia reflects repair of the atrophic, suppressed epidermis as well as a response to desiccation consequent to the loss of the stratum corneum.

Corticosteroid atrophy in human skin. A study by light, scanning, and transmission electron microscopy.

Steroid atrophy was induced in 3 volunteers by the continuous, occlusive application of clobetasol propionate to the forearms for 6 weeks. The changes were followed sequentially by light, scanning, and transmission electron microscopy. a 59% decrease in viable epidermal thickness was noted after the sixth week of treatment, as well as a flattening of the dermal-epidermal junction. The 3-dimensional architecture of the dermis was strikingly reorganized. This was largely brought about by resorption of the ground substance as revealed by a progressive diminution of Hale's stain for acid mucopolysaccharides. Loss of ground substance resulted in decreased spaces between collagen and elastic fibers as shown by scanning and transmission electron microscopy. The fibrous network consequently collapsed, yielding a more compact papillary and reticular dermis. This compression caused the reorientation of both collagen and elastic fibers. However, no differences in collagen and elastin fine structure were noted. Fibroblasts were shrunken but not reduced in density. A marked decrease in number of mast cells was noted in 3-week specimens and virtually no mast cells were observed after 6 weeks. We found that the primary effect of short-term steroid use was a rearrangement of the geometry of the dermal fibrous network. This was not due to alterations in the fibers themselves but a secondary consequence of the loss of ground substance.

The influence of longwave ultraviolet radiation on sunburn cell production by UVB.

The potentiation of sunburn by longwave ultraviolet radiation (photoaugmentation) has been examined with regard to the influence of these waves on sunburn cell production in human skin. It was found that UVA did not enhance sunburn cell production. Photoaugmentation is limited to the erythemal component of the sunburn reaction.