Effects of systemic indomethacin, meclizine, and BW755C on chronic ultraviolet B-induced effects in hairless mouse skin

A New Topical Candidate in Acne Treatment: Characterization of the Meclozine Hydrochloride as an Anti-Inflammatory Compound from In Vitro to a Preliminary Clinical Study

Acne is a chronic inflammatory multifactorial disease involving the anaerobic bacterium Cutibacterium acnes (C. acnes). Current acne treatments are associated with adverse effects, limiting treatment compliance and use. We showed that meclozine, an anti-histaminic H1 compound, has anti-inflammatory properties. In Vitro, meclozine reduced the production of CXCL8/IL-8 and IL-1β mRNA and protein by C. acnes-stimulated human keratinocytes and monocytes. No cell toxicity was observed at the IC50. Meclozine prevented the phosphorylation of ERK and JNK. In Vivo, 1% meclozine gel significantly decreased C. acnes-mouse ear induced inflammation by 26.7% (p = 0.021). Ex vivo experiments on human skin explants showed that meclozine decreased the production of GM-CSF, IL-1β and TNF-α at transcriptional and translational levels. In a randomized, double-blind, placebo-controlled proof-of-concept clinical trial on 60 volunteers, 2% meclozine pharmaceutical gel decreased by 20.1% (p < 0.001) the ASI score in the treated group after 12 weeks of treatment. No adverse event was reported. Together, these results indicate that meclozine is a potent topical anti-inflammatory compound of potential value for acne treatment.

Does Photosensitivity Predict Photococarcinogenicity?

Assessment of short-term and long-term effects of light (pho—totesting) is part of the safety evaluation of drugs. Results are incorporated into drug package inserts to advise patients and health care providers about the use of drug products on sun—exposed skin. We undertook an exhaustive literature search and a search of archived studies at the Center for Drug Evaluation and Research (CDER), Food and Drug Administration (FDA), in order to evaluate the potential of short—term photoassays to predict long—term effects of drugs used in sunlight (280–700 nm). The correlation between the findings from the photococarcinogenicity assays in mice that used exposure to simulated sunlight and those from photogenotoxicity and photosensitivity studies was examined. Results indicated that photosensitivity and photogenotoxicity assays did not necessarily predict effects in photococarcinogenicity studies in mice. Effects of drugs on skin that are not due to photoactivation of drug can be important factors in enhancement of UV—induced skin carcinogenesis.

Dietary Lutein/Zeaxanthin Partially Reduces Photoaging and Photocarcinogenesis in Chronically UVB-Irradiated Skh-1 Hairless Mice

Lutein and zeaxanthin are xanthophyll carotenoids with potent antioxidant properties protecting the skin from acute photodamage. This study extended the investigation to chronic photodamage and photocarcinogenesis. Mice received either a lutein/zeaxanthin-supplemented diet or a standard nonsupplemented diet. Dorsal skin of female Skh-1 hairless mice was exposed to UVB radiation with a cumulative dose of 16,000 mJ/cm(2) for photoaging and 30,200 mJ/cm(2) for photocarcinogenesis. Clinical evaluations were performed weekly, and the animals were sacrificed 24 h after the last UVB exposure. For photoaging experiments, skin fold thickness, suprapapillary plate thickness, mast cell counts and dermal desmosine content were evaluated. For photocarcinogenesis, samples of tumors larger than 2 mm were analyzed for histological characterization, hyperproliferation index, tumor multiplicity, total tumor volume and tumor-free survival time. Results of the photoaging experiment revealed that skin fold thickness and number of infiltrating mast cells following UVB irradiation were significantly less in lutein/zeaxanthin-treated mice when compared to irradiated animals fed the standard diet. The results of the photocarcinogenesis experiment were increased tumor-free survival time, reduced tumor multiplicity and total tumor volume in lutein/zeaxanthin-treated mice in comparison with control irradiated animals fed the standard diet. These data demonstrate that dietary lutein/zeaxanthin supplementation protects the skin against UVB-induced photoaging and photocarcinogenesis.

Vascular endothelial growth factor-A mediates ultraviolet B-induced impairment of lymphatic vessel function

UVB irradiation of the skin induces erythema, epidermal hyperplasia, vascular hyperpermeability, and edema formation. Previous studies have revealed that the cutaneous blood vasculature plays a critical role in the mediation of photodamage. In contrast, the role of lymphatic vessels, which play an essential role in the maintenance of tissue fluid balance, in the response to UVB irradiation has remained unknown. We report here that both acute and chronic UVB irradiation of murine skin results in prominent enlargement of lymphatic vessels. Surprisingly, these enlarged lymphatic vessels were functionally impaired and hyperpermeable, as detected by intravital lymphangiography. The expression levels of vascular endothelial growth factor (VEGF)-A but not of the known lymphangiogenesis factors VEGF-C or VEGF-D, were enhanced in UVB-irradiated epidermis. Targeted overexpression of VEGF-A in the epidermis of transgenic mice led to increased enlargement and leakage of lymphatic vessels after acute UVB irradiation, whereas systemic blockade of VEGF-A signaling largely prevented lymphatic vessel abnormalities and photodamage induced by UVB. Together, these findings identify lymphatic vessels as novel targets for UVB-induced cutaneous photodamage and suggest that VEGF-A mediates impairment of lymphatic vessel function, thereby contributing to the adverse effects of UVB irradiation on the skin.

Genomic instability in radial growth phase melanoma cell lines after ultraviolet irradiation

BACKGROUND/AIMS

Although ultraviolet (UV) irradiation, apoptosis, and genomic instability are all potentially involved in the pathogenesis of melanoma, in vitro studies investigating these changes in the radial growth phase of this neoplasm are still lacking; therefore, this study was designed to investigate these changes.

METHOD

An in vitro system consisting of three radial growth phase Wistar melanoma cell lines (WM35, WM3211, and WM1650) was established. Cells were UV irradiated (10 mJ/cm2 for UVB and 6 J/cm2 for UVA), harvested after UV exposure, and evaluated for viability and apoptosis using Trypan blue and terminal deoxynucleotidyl transferase mediated dUTP digoxigenin nick end labelling assays, respectively. Polymerase chain reaction based microsatellite assays were used to examine the cell lines for the presence of microsatellite instability (MSI) using 21 markers at the 1p, 2p, 3p, 4q, 9p, and 17p regions.

RESULTS

Exposure to UV initiated progressive cell death associated with pronounced apoptosis, with UVA having a greater effect than UVB. MSI was found in UVB (WM35 and WM3211) and UVA (WM35) irradiated cell lines at 1p, 9p, and 17p, but not in non-irradiated cells. The prevalence of MSI was higher after UVB irradiation (14%) than UVA irradiation (4.7%), and was most frequently found at D1S233.

CONCLUSIONS

The ability of erythemogenic UV irradiation to induce both apoptosis and MSI in radial growth phase melanoma cells is suggestive of its role in melanoma pathogenesis. This instability may reflect a hypermutability state, oxidative stress induced DNA damage, replication infidelity, or a combination of these factors.

Vascular endothelial growth factor promotes sensitivity to ultraviolet B-induced cutaneous photodamage

Acute ultraviolet B (UVB) irradiation of the skin results in erythema, vasodilation, edema, and angiogenesis, which is associated with the expression of vascular endothelial growth factor (VEGF) by epidermal keratinocytes. It is unclear, however, whether VEGF is required for the damage or repair process that occurs in the skin on UVB exposure. We subjected transgenic mice that overexpress VEGF, and their wild-type littermates, to graded doses of acute UVB irradiation. The skin of VEGF-overexpressing mice was highly photosensitive and became erythematic when exposed to half the UVB dose required to induce erythema in wild-type mice. Erythema was associated with proliferating dermal endothelial cells, cutaneous edema, and inflammatory cell infiltration. When subjected to 10 weeks of low-level UVB irradiation, no major changes were observed in wild-type mice, whereas VEGF transgenic mice developed skin damage associated with degradation of the dermal matrix and enhanced vascularization. Systemic treatment with an anti-VEGF blocking antibody reduced the sensitivity of wild-type mice to acute UVB irradiation without inhibiting post-UVB repair. Our results reveal that VEGF promotes the cutaneous damage that occurs after UVB exposure and that the VEGF signaling pathway might serve as a novel target for the prevention of UVB-induced photodamage.

Possible involvement of gelatinases in basement membrane damage and wrinkle formation in chronically ultraviolet B-exposed hairless mouse

A number of studies indicate that matrix metalloproteinase might be involved in photoaging, but little is known about their direct contribution to ultraviolet-induced histologic and morphologic changes in the skin in vivo. This study reports the relationship between changes of matrix metalloproteinase activities and ultraviolet B-induced skin changes in hairless mouse. The role of matrix metalloproteinase in the skin changes was studied by topical application of a specific matrix metalloproteinase inhibitor. The backs of mice were exposed to ultraviolet B three times a week for 10 wk. Histologic studies showed that the basement membrane structure was damaged, with epidermal hyperplasia, in the first 2 wk of ultraviolet B irradiation, followed by the appearance of wrinkles, which gradually extended in the latter half of the ultraviolet B irradiation period. We observed enhancement of type IV collagen degradation activity, but not collagenase or matrix metalloproteinase-3 activity, in extracts of ultraviolet B-irradiated, wrinkle-bearing skin. Gelatin zymographic analysis revealed that gelatinases, matrix metalloproteinase-9 and matrix metalloproteinase-2, were significantly increased in the extract. In situ zymographic study clarified that the activity was specifically localized in whole epidermis of ultraviolet B-irradiated, wrinkled skin in comparison with normal skin. The activity was induced around the basal layer of the epidermis by a single ultraviolet exposure of at least one minimal erythema dose. Furthermore, topical application of a specific matrix metalloproteinase inhibitor, CGS27023A, inhibited ultraviolet B-induced gelatinase activity in the epidermis, and its repeated application prevented ultraviolet B-induced damage to the basement membrane, as well as epidermal hyperplasia and dermal collagen degradation. Ultraviolet B-induced wrinkles were also prevented by administration of the inhibitor. These results, taken together, suggest that ultraviolet B-induced enhancement of gelatinase activity in the skin contributes to wrinkle formation through the destruction of basement membrane structure and dermal collagen in chronically ultraviolet B-exposed hairless mouse, and thus topical application of matrix metalloproteinase inhibitors may be an effective way to prevent ultraviolet B-induced wrinkle formation.

Targeted overexpression of the angiogenesis inhibitor thrombospondin-1 in the epidermis of transgenic mice prevents ultraviolet-B-induced angiogenesis and cutaneous photo-damage

Chronic ultraviolet-B irradiation of the skin results in epidermal hyperplasia, degradation of extracellular matrix molecules, and formation of wrinkles. To characterize the biologic role of the vascular system in the mediation of ultraviolet-B-induced skin damage, we performed quantitative analyses of cutaneous blood vessels of mice after 10 wk of ultraviolet-B irradiation. Skin vascularization was greatly increased after chronic ultraviolet-B exposure with a significant increase of both the number and the size of dermal blood vessels, associated with upregulation of vascular endothelial growth factor expression in the hyperplastic epidermis. To directly study whether inhibition of angiogenesis may diminish ultraviolet-B-induced cutaneous damage, wild-type and transgenic mice with skin-specific overexpression of the endogenous angiogenesis inhibitor thrombospondin-1 were subjected to the same ultraviolet-B irradiation regimen. Ultraviolet-B-irradiated thrombospondin-1 transgenic mice showed a significantly reduced skin vascularization, decreased endothelial cell proliferation, and increased endothelial cell apoptosis rates, compared with wild-type mice. Moreover, dermal photo-damage and wrinkle formation were greatly reduced in thrombospondin-1 transgenic mice. These results reveal an important role of the cutaneous vascular system in mediating ultraviolet-B-induced skin damage and suggest inhibition of angiogenesis as a potential new approach for the prevention of chronic cutaneous photo-damage.

Quantitative and qualitative effects of chemical peeling on photo-aged skin: an experimental study

Chemical peel reverses the visible stigmata of photo aging in human skin. The qualitative and, in particular, the quantitative changes in the dermis that effect this transformation are unclear. This study used a recognized photo-aged animal model, the Skh:HR-1 hairless mouse, to quantify and qualify the changes that occurred in collagen and glycosaminoglycan content after chemical peel. One hundred Skh:HR-1 hairless mice were photo-aged by use of chronic ultraviolet B irradiation for 14 weeks. After irradiation the animals were randomly distributed into five groups of 20 mice each: group 1, control; group 2, 50% glycolic acid peel; group 3, 30% trichloroacetic acid peel; group 4, 50% trichloroacetic acid peel; group 5, phenol peel (Baker-Gordon formula). The respective peeling agent was applied to the dorsal skin of each animal while it was fully anesthetized. Punch biopsies were taken at several times after peel for histological and biochemical analysis. Glycosaminoglycan content was assessed at 14, 28, and 60 days using a colorimetric assay. Collagen content per unit volume increased initially 3 days after the procedure in all chemical peel groups, declining on day 7, and peaking again on day 28. Significant elevations (p < 0.04) were seen in the 30% trichloroacetic acid, 50% trichloroacetic acid, and phenol peels on days 3 and 28 in comparison with controls. This increase in collagen content was not maintained and returned to control values by 60 days. Glycosaminoglycan content per unit volume was elevated initially after peel with significant elevation (p < 0.02) in the 50% trichloroacetic acid and phenol groups on days 14 and 28. This increase in glycosaminoglycan content was not maintained beyond 28 days and declined to control values by day 60 in all groups. Histological examination demonstrated an increase in dermal thickness in the 50% trichloroacetic acid and phenol groups in comparison with controls by day 60. Under polarized light all chemical peel groups at day 60 demonstrated a reorganization of collagen in the reticular and papillary dermis. The elastotic masses that are pathognomonic of photo aging were present in the control group but were absent in the peel groups and demonstrated a reorganization of the elastic fibers in the dermis. This effect was deeper in the dermis in the deeper peel groups (50% trichloroacetic acid and phenol peel). The beneficial effects of chemical peel were due to a combination of two findings; a reorganization in dermal structural elements and an increase in dermal volume. These effects were more pronounced in the deeper peel groups.

Delayed induction of pigmented spots on UVB-irradiated hairless mice

Human skin exposed to solar radiation for a long time subsequently develops pigmented spots, which are named solar lentigines. Since no animal model of this process is currently available, we attempted to induce similar spots in pigmented hairless mice. The mice were irradiated at 38 or 94 mJ/cm(2) three times/week for various periods of time (1-8 weeks) under an ultraviolet light source (Toshiba FL-SE; UVB). Skin pigmentation of irradiated mice was visually observed and skin color was determined with a colorimeter for 78 weeks. Uniform pigmentation was induced, but persisted only during exposure, disappearing completely within 2 weeks after cessation of exposure. At about 28 weeks after the first exposure, pigmented spots suddenly began to appear. These pigmented spots were less than 2 mm in diameter and light brown in color. The length of the latent period until appearance and the extent of development of these spots were dependent on the exposure period. Histological examination revealed increased numbers of active melanocytes and melanin granules in the affected epidermis. These pigmented spots closely resemble solar lentigines in humans, and the mice should be useful as an animal model of solar lentigines.

Efficacy of potential chemopreventive agents on rat colon aberrant crypt formation and progression

We assessed the effects of 78 potential chemopreventive agents in the F344 rat using two assays in which the inhibition of carcinogen-induced aberrant crypt foci (ACF) in the colon was the measure of efficacy. In both assays ACF were induced by the carcinogen azoxymethane (AOM) in F344 rats by two sequential weekly injections at a dose of 15 mg/kg. Two weeks after the last AOM injection, animals were evaluated for the number of aberrant crypts detected in methylene blue stained whole mounts of rat colon. In the initiation phase protocol agents were given during the period of AOM administration, whereas in the post-initiation assay the chemopreventive agent was introduced during the last 4 weeks of an 8 week assay, a time when ACF had progressed to multiple crypt clusters. The agents were derived from a priority listing based on reports of chemopreventive activity in the literature and/or efficacy data from in vitro models of carcinogenesis. During the initiation phase carboxyl amidoimidazole, p-chlorphenylacetate, chlorpheniramine maleate, D609, diclofenac, etoperidone, eicosatetraynoic acid, farnesol, ferulic acid, lycopene, meclizine, methionine, phenylhexylisothiocyanate, phenylbutyrate, piroxicam, 9-cis-retinoic acid, S-allylcysteine, taurine, tetracycline and verapamil were strong inhibitors of ACF. During the post-initiation phase aspirin, calcium glucarate, ketoprofen, piroxicam, 9-cis-retinoic acid, retinol and rutin inhibited the outgrowth of ACF into multiple crypt clusters. Based on these data, certain phytochemicals, antihistamines, non-steroidal anti-inflammatory drugs and retinoids show unique preclinical promise for chemoprevention of colon cancer, with the latter two drug classes particularly effective in the post-initiation phase of carcinogenesis.

Histological increase in inflammatory infiltrate in sun-exposed skin of female subjects: the possible involvement of matrix metalloproteinase-1 produced by inflammatory infiltrate on collagen degradation

To investigate morphological changes occurring during cutaneous photoageing, a correlation between the number of infiltrating cells in the dermis and the degree of collagen damage was examined using sections from clinically normal chronically sun-exposed and sun-protected skin of Japanese female subjects. Haematoxylin and eosin-stained sections from 134 sun-exposed (subjects aged 3-82 years) and 73 sun-protected (subjects aged 1-86 years) areas demonstrated a predominant lymphoid cell and to a lesser extent histiocyte infiltration. The mean +/- SD number of lymphoid cells and histiocytes in the sun-exposed skin sections (427.0+/-192.2 and 147.8+/-83.3 cells/mm2, respectively) was significantly higher than in the sun-protected skin sections (292.6+/-98.3 and 125.9+/-59.0 cells/mm2, respectively) (P < 0.001 and P < 0.05, respectively), and the number of lymphoid cells in the sun-exposed skin sections increased significantly with age up to 50 years (r = 0.400, P < 0.001). Sun-exposed skin sections with severe collagen degeneration had a significantly higher number of lymphoid cells than those with slightly degenerated collagen (mean 626.3 vs. 482.4 cells/mm2, P < 0.01). The mean count of mast cells in sun-exposed skin was 202.0 cells/mm2; this did not vary with the age of the subjects or the level of collagen damage. Immunohistochemical studies using 24 frozen sections identified most of the lymphoid cells infiltrating sun-exposed skin as memory T lymphocytes (CD3+, CD4+ and CD45RO+). The number of cells which displayed immunoreactivity to matrix metalloproteinase (MMP)-1 in the sun-exposed skin sections was significantly higher than in the sun-protected skin sections (mean 170.2 vs. 113.6 cells/mm2, P < 0.05). Among these cells were observed CD3 and MMP-1 double-stained T lymphocytes, and T lymphocytes contacting MMP-1-positive cells. These morphological observations suggest that T lymphocytes infiltrating photodamaged skin may play a part in the degeneration and reduction of collagen through MMP-1 activity.

An extract of Polypodium leucotomos appears to minimize certain photoaging changes in a hairless albino mouse animal model. A pilot study

Chronic ultraviolet B (UVB) exposure of human or murine skin is known to induce cutaneous photoaging and enhanced carcinogenic risk. An extract of Polypodium leucotomos (PL), a tropical fern plant, has been known to exhibit interesting antioxidant and photoprotective properties against acute exposure to ultraviolet radiation. The objective of this preliminary (or pilot) study was to determine the photoprotective role of topically applied Polypodium leucotomos extract in the prevention or amelioration of cutaneous changes of photoaging in hairless mice. PL-treated mice showed significant reduction of skinfold thickness than those observed in PL-untreated controls. Additionally, PL-treated mice showed a significantly lower degree of histologic parameters of photoaging damage, including dermal elastosis, compared with positive control mice. Interestingly, PL treatment also showed reduction in the number of mice showing skin tumors at 8 weeks after the cessation of the UVB exposure protocol. The results of this preliminary study illustrate that PL treatment helped to ameliorate and to partially inhibit some of the histologic damage associated with photoaging of skin and appeared to contribute to a decrease in the prevalence of UVB-induced skin tumors in mice.

The effects of radicals compared with UVB as initiating species for the induction of chronic cutaneous photodamage

There is substantial evidence that ultraviolet radiation induces the formation of reactive oxygen species which are implicated as toxic intermediates in the pathogenesis of photoaging. The aim of this study was to determine whether repeated topical treatment with benzoyl peroxide, a source of free radicals, produced the same cutaneous effects as chronic ultraviolet B radiation. Three concentrations of benzoyl peroxide (0.1, 1.5, 5.0% wt/wt) and three cumulative fluences of ultraviolet B radiation (0.9, 2.2, 5.1 J per cm2) used alone and in all combinations along with appropriate controls. Female SKH1 (hr/hr) albino hairless mice were treated 5 d per wk for 12 wk. Extracellular matrix molecules and histologic parameters were assessed. Ultraviolet B radiation induced a fluence-dependent and time-dependent increase in skin-fold thickness. Fluence dependence was seen for epidermal thickness, sunburn cell numbers, dermal thickness, glycosaminoglycan content, mast cell numbers, and skin-fold thickness. Benzoyl peroxide treatment alone caused less marked increases in epidermal and dermal measures compared with ultraviolet B under the conditions used. A benzoyl peroxide concentration-dependent increase was only observed for elastin content, although the highest concentration of benzoyl peroxide increased epidermal thickness and glycosaminoglycan content. A synergistic interaction between ultraviolet B and benzoyl peroxide was not found. These results indicate that repeated administration of benzoyl peroxide produces skin changes in the hairless mouse that qualitatively resemble those produced by ultraviolet B and suggest that common mechanisms may be involved. In addition, any potential synergistic effect of ultraviolet B and benzoyl peroxide was below the level of detection used in this study.

Endogenous skin fluorescence includes bands that may serve as quantitative markers of aging and photoaging

Aging and photoaging cause distinct changes in skin cells and extracellular matrix. Changes in hairless mouse skin as a function of age and chronic UVB exposure were investigated by fluorescence excitation spectroscopy. Fluorescence excitation spectra were measured in vivo, on heat-separated epidermis and dermis, and on extracts of mouse skin to characterize the absorption spectra of the emitting chromophores. Fluorescence excitation spectra obtained in vivo on 6 wk old mouse skin had maxima at 295, 340, and 360 nm; the 295 nm band was the dominant band. Using heat separated tissue, the 295 nm band predominantly originated in the epidermis and the bands at 340 and 360 nm originated in the dermis. The 295 nm band was assigned to tryptophan fluorescence, the 340 nm band to pepsin digestable collagen cross-links fluorescence and the 360 nm band to collagenase digestable collagen cross-links fluorescence. Fluorescence excitation maxima remained unchanged in chronologically aged mice (34-38 wk old), whereas the 295 nm band decreased in intensity with age and the 340 nm band increased in intensity with age. In contrast, fluorescence excitation spectra of chronically UVB exposed mice showed a large increase in the 295 nm band compared with age-matched controls and the bands at 340 and 350 nm were no longer distinct. Two new bands appeared in the chronically exposed mice at 270 nm and at 305 nm. These reproducible changes in skin autofluorescence suggest that aging causes predictable alterations in both epidermal and dermal fluorescence, whereas chronic UV exposure induces the appearance of new fluorphores.

Histological and biochemical changes induced by total bile duct ligation in the rat

The aim of the present investigation was to assess in a correlated biochemical and morphological study the dynamics of fibrogenesis after bile duct ligation and to compare the time course of alterations with those occurring in thioacetamide induced liver fibrosis. The data show that, after bile duct obstruction, the deposition of connective tissue elements and formation of ductular proliferates rapidly set in. The index of fibroplasia correlated well with the changes of the OH-proline concentration of the liver. Comparing the biliary fibrosis with the thioacetamide induced liver fibrosis, the progress of the former occurred more rapidly, even though in both cases only a few necroses were observed. Therefore, we suggest that in biliary fibrosis other mechanisms are responsible for the rapid onset of production of extracellular material and proliferative processes than in thioacetamide-induced liver fibrosis.

All-trans-retinoic acid enhances collagen gene expression in irradiated and non-irradiated hairless mouse skin

All-trans-retinoic acid (t-RA) can repair some of the tissue damage caused by chronic exposure of skin to UV radiation. In the present study, we have investigated its effect on collagen and collagenase gene expression in hairless mouse skin. Hairless mice (SKH-hr 1) were irradiated dorsally with increasing doses of UVB radiation (total, 4.8 J cm-2) for 10 weeks. The animals were then topically treated with 0.05% t-RA dissolved in a vehicle or with the vehicle alone three times a week for up to 10 weeks. Non-irradiated animals underwent the same treatment. In our experimental conditions, UVB irradiation alone induced no changes in type I, III and VI collagen mRNA levels in dorsal and ventral skin. The mRNA level of collagenase I was also unchanged. Topically applied t-RA increased the steady state levels of type I and III collagen mRNA in irradiated and non-irradiated dorsal skin. The mean increase was about 2.2- and 2.7-fold in non-irradiated skin and 2.4- and 2.5-fold in irradiated skin for type I and III collagen mRNA respectively. The increase in irradiated skin was partly due to the vehicle alone, which exerted a stimulating effect on the steady state levels of alpha 1(I) and alpha 1(III) mRNA. The mRNA level of type VI collagen was also significantly increased by t-RA, but only in irradiated skin. The mRNA level of collagenase was significantly decreased only in irradiated t-RA-treated skin. In addition, t-RA exerted a systemic effect because the mRNA levels of collagen were enhanced by factors of 1.9 and 2.5 for alpha 1(I) and 2.0 and 2.0 for alpha 1(III) in the ventral skin of irradiated and non-irradiated animals respectively. This study leads to the conclusion that topical t-RA exerts directly and/or indirect effects on the expression of collagen genes in irradiated and non-irradiated hairless mouse skin.

Hyaluronic acid and dermatan sulfate are selectively stimulated by retinoic acid in irradiated and nonirradiated hairless mouse skin

All-trans retinoic acid (RA) has been shown to enhance subepidermal repair in photoaged hairless mice. The current study assesses the effects of RA on the glycosaminoglycan (GAG) content in irradiated and nonirradiated mouse skin. Mice were exposed to ultraviolet B (UVB) for 10 wk, after which they were treated either with 0.05% RA or with an ethanolpolyethylene glycol 400 vehicle three times a week for 10 or 20 wk. When assessed at the end of 10 wk of UVB irradiation, the GAG content had doubled, without a change in the hyaluronic acid (HA) to dermatan sulfate (DS) ratio. When irradiation was discontinued, the GAG content decreased progressively until the end of the experimental period. This decline was totally inhibited by RA treatment and could be ascribed to a marked increase in hyaluronic acid (78%), whereas no significant change in DS was observed. In nonirradiated skin, however, topical RA increased GAG levels mainly by a pronounced increase in the content (50%) and the synthesis (40%) of DS. In untreated mice, the HA/DS ratio decreased significantly with age in both irradiated and nonirradiated mice. Interestingly, RA maintained this ratio only in animals exposed to UVB. In addition, there was a marked stimulation in the heparin content, up to approximately 20-fold, after irradiation, whereas the amount of heparin in both irradiated and nonirradiated skin increased about 2- to 3-fold with RA treatment. In summary, the alterations induced in HA and DS contents in irradiated and nonirradiated skin indicate the specificity of the RA-induced effects for the various GAGs.

Cutaneous cell and extracellular matrix responses to ultraviolet-B irradiation

The present study examined fibroblasts and keratinocytes in monolayers and cultured within dermal and skin substitutes and their use in assessing the effect of UVB irradiation on cutaneous cells and extracellular matrix organization. Dermal substitutes (DS) were produced by incorporating normal fibroblasts into a collagen lattice and skin substitutes (SS) were obtained by seeding normal keratinocytes onto the DS. Keratinocyte monolayers, fibroblast monolayers, DS, and SS were exposed once a day to a UVB source (10 mJ/cm2). The irradiation protocol was stopped when the keratinocytes of the non-irradiated cultures (control groups) had reached confluence. Microscopic observations revealed that UVB radiation decreased both fibroblast and keratinocyte growth and enhanced their differentiation resulting in (1) less fibroblasts in the DS and SS, and (2) incomplete coverage of the DS by keratinocytes. Microscopic observations and histological analyses revealed major morphological changes. Both cell types became bigger and presented wide nuclei and vacuoles in the cytoplasm. No organized deep epidermal layer was observed in irradiated compared to non-irradiated SS. Irradiated DS and SS extracellular matrices showed an irregular aggregating collagen fiber organization with serious discrepancies suggesting large defects in the structural properties of the extracellular matrix. The present study demonstrated that exposure to a UVB source led to profound morphological and functional disturbances in both cutaneous cells and in the extracellular matrices of the DS and SS. The present technology would be of great interest for step-by-step studies of UVR effects on cutaneous cell morphology and functional properties, and could be an alternative to using animals for pharmacological and toxicological evaluations.

Chronic UVB- and all-trans retinoic-acid-induced qualitative and quantitative changes in hairless mouse skin

Histochemical and ultrastructural studies have already demonstrated that chronic exposure to UV radiation induces profound alterations in all structural elements of the skin and that topical all-trans retinoic acid (tRA) can substantially correct much of the tissue damage. However, previous biochemical studies on dermal components of the extracellular matrix have led to contradictory results, particularly with regard to the effect of chronic UV exposure. The aim of our study was to investigate changes in collagen content and other dermal modifications induced by tRA in irradiated and non-irradiated hairless mouse skin. Hairless mice were exposed to increasing doses of UVB for 10 weeks (the cumulative total dose was 4.6 J cm-2). After the UV irradiation period the animals were treated with 0.05% tRA or with ethanol-polyethylene glycol vehicle alone three times a week for up to 10 weeks. Non-irradiated animals underwent the same treatments. The main clinical and histological changes induced by UVB exposure were erythema, wrinkling, keratosis and epidermal thickening. Following UVB exposure, tRA treatment did not improve the clinical aspect but increased the width of the dermal repair zone. Fibronectin, laminin and type I and VI collagens were detected by indirect immunofluorescence techniques in this zone. Type I and III collagens were quantitated in skin fragments after cyanogen bromide digestion and polyacrylamide gel electrophoresis. Under our experimental conditions, UVB irradiation alone induced neither changes in total collagen nor in type I and III collagen levels. tRA treatment of irradiated skin significantly increased both type I and III collagen levels by factors of 1.33 and 1.88 respectively. The ratio of type III to types I + III increased significantly. Topical tRA also increased collagen type levels in non-irradiated hairless mouse skin. Type I collagen increased proportionally to type III. This study leads to the conclusion that topical tRA exerts direct or indirect effects on collagen metabolism in irradiated as well as non-irradiated hairless mouse skin.

Experimental photoaging in C3H/HeN, C3H/HeJ, and Balb/c mice: comparison of changes in extracellular matrix components and mast cell numbers

Chronic exposure of human or murine skin to ultraviolet B (UVB) radiation alters dermal extracellular matrix composition and increases the number of mast cells and inflammatory cells. Experiments were designed to test the possible role of UVB-induced tumor necrosis factor-alpha in these photoaging changes based on reports that C3H/HeN, but not C3H/HeJ or Balb/c mice, produce excess TNF-alpha in response to UVB exposure. Pigmented C3H/HeN and C3H/HeJ strains were exposed to a total of 75 J/cm2 of UVB radiation, and unpigmented Balb/c mice were exposed to 19 J/cm2. The UVB-induced increases in collagen, glycosaminoglycans, and neutrophil number were similar or the same in all three strains. The elastin increase was greater in C3H/HeJ than in C3H/HeN mice. The most striking difference between the strains was a 7.7-fold UVB-induced increase in mast cells in C3H/HeN mice compared to no increase in irradiated C3H/HeJ mice and a 2.3-fold increase in Balb/c mice. These results suggest that excess TNF-alpha (or other mediator) produced in C3H/HeN skin (but not C3H/HeJ skin) in response to UVB exposure is involved in the mast cell increase and partial inhibition of elastin increase, but that neither these mediators nor mast cell products are important mediators for the chronic UVB-induced increases in neutrophils, glycosaminoglycans, and collagen. When a possible source of the excess TNF-alpha was investigated, it was found that isolated epidermal cells from all three strains produced increases in TNF-alpha in response to UVB radiation. These results, as well as the previous results showing differences between these strains in UVB-induced effects on cutaneous immune function, are consistent with a model in which UVB-induced mediators from the epidermis stimulate another cell type to produce excess TNF-alpha (and other mediators) in the C3H/HeN but not C3H/HeJ or Balb/c mice.

Dietary fish-oil supplementation in humans reduces UVB-erythemal sensitivity but increases epidermal lipid peroxidation

Ultraviolet radiation (UVR)-induced erythema may be mediated in part by free radical-generated tissue damage, including lipid peroxidation. We have examined the effect of dietary fish oil rich in omega-3 fatty acids upon susceptibility to UVB-induced erythema and epidermal lipid peroxidation. Fifteen volunteers took 10 g fish oil, containing 18% eicosapentaenoic acid and 12% docosahexaenoic acid, daily for 3 or 6 months. Sensitivity to UVB was assessed at intervals on fish oil, and 2.5 months after stopping treatment. Paired skin shave biopsies were taken from six subjects, at baseline and 3 months, from both irradiated and control skin. Fatty acid composition was analyzed and thiobarbituric acid-reactive substances measured as an index of lipid peroxidation. With increasing time on fish oil the minimal erythema dose rose progressively, from 18.9 +/- 13.9 mJ/cm2 (mean +/- SD) at baseline to 41.1 +/- 16.6 mJ/cm2 at 6 months, p < 0.01. Ten weeks after stopping fish oil the minimal erythema dose fell to 23.1 +/- 4.9 mJ/cm2, p < 0.05. Epidermal total omega-3 fatty acids rose from 1.8 +/- 0.4% total fatty acids (mean +/- SEM) to 24.2 +/- 3.9% at 3 months, p < 0.01. This was accompanied by a rise in thiobarbituric acid-reactive substances in irradiated skin from 6 +/- 0.3 (mean +/- SEM) to 18.5 +/- 2.6 A532/g skin, p < 0.01. Hence dietary omega-3 fatty acids produce a pronounced reduction in UVB-erythemal sensitivity, although susceptibility of skin to lipid peroxidation is increased. Thus, omega-3 fatty acids may act as an oxidizable buffer, protecting more vital structures from free radical damage.