Ultraviolet Light B Irradiation Research Articles

Short-term uvb-irradiation leads to putative limbal stem cell damage and niche cell-mediated upregulation of macrophage recruiting cytokines

Ultraviolet light B (UVB)-irradiation is linked to various ocular pathologies such as limbal stem cell defects in pterygium. Despite the large circumstantial evidence linking UVB irradiation and limbal epithelial stem cell damage, the precise molecular responses of limbal stem cells to UVB irradiation are unclear. Here the effect of UVB irradiation on the putative stem cell phenotype, limbal niche cells and the subsequent effects on corneal (lymph)angiogenic privilege were investigated. Primary human limbal epithelial stem cells and fibroblasts were irradiated with 0.02J/cm2 of UVB, a low dose corresponding to 3min of solar irradiation. UVB irradiation caused significant reduction of limbal epithelial and limbal fibroblast proliferation for 24h, but apoptosis of limbal epithelial stem cells only. Moreover, UVB induced stem-like character loss of limbal epithelial cells, as their colony forming efficiency and putative stem cell marker expression significantly decreased. Interestingly, limbal epithelial cells co-cultured with UVB-irradiated limbal fibroblasts also exhibited loss of stem cell character and decrease of colony forming efficiency. Conditioned media from limbal epithelial cells inhibited lymphatic endothelial cell proliferation and tube network complexity; however this effect diminished following UVB irradiation. In contrast, pro-inflammatory and macrophage-recruiting cytokines such as TNFα, IFNγ and MCP1 were significantly upregulated following cell irradiation of limbal fibroblasts. These data demonstrate the key role of the limbal stem cell niche in response to UVB and subsequent (lymph)angiogenic and inflammatory events. These data suggest that the known pro(lymph)angiogenic effect of UVB irradiation in pterygium is not linked to a direct up-regulation of pro-angiogenic cytokines, but rather to indirect macrophage-recruiting cytokines being upregulated after UVB irradiation.

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Uremic pruritus

Radiosensitization of human breast cancer cells to ultraviolet light by 5-fluorouracil.

Ultraviolet light B (UVB) phototherapy is widely used to treat dermatological diseases and therefore may be a potential optional strategy in the treatment of a skin lesion infiltrated by a malignant tumor. Currently, little is known regarding the effect of UVB phototherapy on human breast cancer cells. The present study aimed to investigate the effect of UVB phototherapy, as well as the potential effect of 5-fluorouracil (5-FU), the first-line anticancer drug for breast cancer, on radiosensitizing MCF-7 human breast cancer cells, in an attempt to develop new therapeutic strategies for the treatment of locoregional recurrence of breast cancer. MCF-7 cells were incubated in the presence of 5-FU for 48 h, and UVB irradiation at 750 mJ/cm(2) was administered in the midterm of 5-FU treatment. The viability of MCF-7 cells was analyzed by the trypan blue staining method. Apoptosis was quantified by flow cytometry and Hoechst 33258 staining. The cell cycle was evaluated by flow cytometry after the staining of cells with propidium iodide. The combination treatment of 5-FU and UVB resulted in a strong potentiation of the inhibitory effect of MCF-7 cell growth, dependent on the intra-S phase cell cycle arrest and induction of apoptosis, when compared to treatment with 5-FU or UVB alone. In conclusion, 5-FU sensitized human breast cancer cells to UVB phototherapy, and this combination therapy is an effective and promising strategy for the treatment of breast cancer, particularly for locoregional recurrence.

Antigenotoxic effects of p53 on spontaneous and ultraviolet light B–induced deletions in the epidermis of gpt delta transgenic mice

Tumor development in the skin may be a multistep process where multiple genetic alterations occur successively. The p53 gene is involved in genome stability and thus is referred to as "the guardian of the genome." To better understand the antigenotoxic effects of p53 in ultraviolet light B (UVB)-induced mutagenesis, mutations were measured in the epidermis of UVB-irradiated p53(+/+) and p53(-/-) gpt delta mice. In the mouse model, point mutations and deletions are separately identified by the gpt and Spi(-) assays, respectively. The mice were exposed to UVB at single doses of 0.5, 1.0, or 2.0 kJ/m(2) . The mutant frequencies (MFs) were determined 4 weeks after the irradiation. All doses of UVB irradiation enhanced gpt MFs by about 10 times than that of unirradiated mice. There were no significant differences in gpt MFs and the mutation spectra between p53(+/+) and p53(-/-) mice. The predominant mutations induced by UVB irradiation were G:C to A:T transitions at dipyrimidines. In contrast, in unirradiated p53(-/-) mice, the frequencies of Spi(-) large deletions of more than 1 kb and complex-type deletions with rearrangements were significantly higher than those of the Spi(-) large deletions in p53(+/+) counterparts. The specific Spi(-) mutation frequency of more than 1 kb deletions and complex types increased in a dose-dependent manner in the p53(+/+) mice. However, no increase of such large deletions was observed in irradiated p53(-/-) mice. These results suggest that the antigenotoxic effects of p53 may be specific to deletions and complex-type mutations induced by double-strand breaks in DNA.

Enhanced contact allergen- and UVB-induced keratinocyte apoptosis in the absence of CD95/Fas/Apo-1

FAS/CD95/Apo-1 is a ubiquitously expressed cell-surface receptor involved in the initiation of programmed cell death. Its function in epidermal keratinocytes has been incompletely defined. Available evidence from in vitro studies points to important roles of Fas in the pathogenesis of contact dermatitis and in keratinocyte apoptosis induced by ultraviolet light. To define functions of Fas in the epidermis in vivo, we have generated mice with epidermis-specific deletion of the fas gene and tested its requirement for 2,4-dinitrofluorobenzene-induced contact dermatitis and for ultraviolet light B (UVB)-induced keratinocyte apoptosis. We report here our unexpected finding that keratinocyte apoptosis induced by both a contact allergen and UVB irradiation was significantly enhanced in Fas-negative epidermis. Expression of Fas by epidermal keratinocytes was neither necessary for the normal development of contact hypersensitivity of the skin, nor required for keratinocyte apoptosis following UVB irradiation. Our study results thus show that in the epidermis in vivo Fas exerts antiapoptotic effects that outweigh its proapoptotic role in contact hypersensitivity responses of the skin and in the tissue response of the epidermis to UVB irradiation.

UVB Irradiation on Melanoma Cells Regulates α4β1 Integrin (VLA‐4) Avidity for Its Ligand VCAM‐1

The major aspect contributing to the mortality of melanoma is its ability to spread, or metastasize. Ultraviolet light B (UVB) is considered an indirect cause of melanoma formation. However, little is known about the potential effects of UVB to melanoma metastasis. Integrins, a large family of cell adhesion molecules expressed on the melanoma cell surface, are important for cell signaling, growth, and migration during metastasis. Most critically, tumor cell tissue invasion is dependent on the initial interaction of tumor cells with vascular endothelium at the target organ, and there is increasing evidence for a prominent role of melanoma VLA‐4 integrin binding to its endothelial ligand vascular cell adhesion molecule‐1 (VCAM‐1) in this process. This research focuses on the quantitative modulation of VLA‐4 integrin expression and function on melanoma cells after UVB irradiation. The present data show that 3 hours post‐UVB irradiation, VLA‐4 expression was unchanged relative to untreated cells, but adhesion to VCAM‐1 decreased ~70%. At 12 hours post‐treatment, VLA‐4 expression was reduced to ~50% of untreated cells, yet adhesion to VCAM‐1 was similar to the 3‐hour time point. Further studies imply that the spatial organization of VLA‐4 in the melanoma membrane contributes the changes in avidity for VCAM‐1. Understanding of the molecular mechanism underlying melanoma‐endothelia interactions upon UVB irradiation can guide the development of clinical advances for melanoma.

Passive cigarette smoke exposure inhibits ultraviolet light B‐induced skin tumors in SKH‐1 hairless mice by blocking the nuclear factor kappa B signalling pathway

Chronic exposure to sunlight [ultraviolet light B (UVB) irradiation] is the most common cause of non-melanoma skin tumors. In the present study, we investigated the effects of passive cigarette smoke superimposed over UVB irradiation, on tumor development, skin pathology and matrix changes in SKH-1 hairless mice. Groups of mice were exposed to 0.1 J/cm(2) of UVB five times per week for 20 weeks and/or exposure to passive cigarette smoke from 40 cigarettes a day over the same time period. UVB exposure resulted in an average of four large squamous cell carcinomas (SCC) and 15 smaller papillomas per mouse, whereas exposing the mice to both UVB + passive cigarette smoke completely prevented SCC formation and averaged less than one small papilloma per mouse. Oxidative DNA damage was investigated and there were no significant changes in the levels of urinary DNA adducts between control, smoke, UV and UV + smoke groups with the exception of 8-oxo guanine which was significantly reduced in the presence of passive cigarette smoke. Immunohistochemistry results revealed that tumor necrosis factor receptor 2 (TNF-R2), glycogen synthase kinase-3 beta, nuclear factor kappa B (NF-kappaB)/p65, KI-67 and cyclooxygenase 2 (COX-2) were markedly up-regulated in the epithelium by UVB exposure, whereas passive smoke exposure combined with the UVB irradiation completely blocked the expression of these proteins. Our results suggest that passive smoke exposure prevents UVB-induced SCC in mice and dramatically reduces the incidence of non-malignant papillomas by altering the NF-kappaB signalling pathway of tumorigenesis.

Anti‐Initiating Activity of 3β‐Methoxy‐13α,14α‐epoxyserratan‐21β‐ol (PJJ‐34) from the Stem Bark of Picea jezoensis Carr. var. jezoensis

Ultraviolet light is the major cause of skin cancers in human, and several effects of ultraviolet light B (UVB) are thought to contribute to skin photocarcinogenesis. 3Beta-methoxy-13alpha,14alpha-epoxyserratan-21beta-ol (PJJ-34; 1) isolated from Picea jezoensis Carr. var. jezoensis showed the strongest antitumor-promoting activity among naturally occurring triterpenoids in the in vivo two-stage mouse skin-carcinogenesis test. To investigate the anti-initiating activity, we further studied mouse models initiated with ultraviolet-B (UVB) and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA). Oral administration of the PJJ-34 (1) during a period before and after the three times of UVB irradiation led to a remarkable effect: oral administration of a 0.0025% solution of 1 only to the test group, which started one week before and ended one week after the irradiation, showed less than half papillomas, and inhibition of tumor incidence and tumor multiplicity in comparison to the control group. Therefore, it was recognized that PJJ-34 (1) showed strong anti-initiating activity as well as anti-promoting activity. After all, 1 seems to be useful as cancer-chemopreventive agent.

Cancer chemopreventive effect of orally administrated lupane-type triterpenoid on ultraviolet light B induced photocarcinogenesis of hairless mouse

Ultraviolet light is the most common cause of skin cancers in human and several effects of ultraviolet light B (UVB) are thought to contribute to skin photocarcinogenesis. The generation of seven triterpenoids from the cones of Liquidamber styraciflua (Hamamelidaceae were examined for their nitric oxide (NO) scavenging activity as the first screening of an in vivo mouse skin anti-initiating assay. 3β,25-epoxy-3α-hydroxylup-20(29)-en-28-oic acid ( 1), which showed the strongest inhibitory effect among these compounds, was studied further for its anti-tumor initiating activity on mouse models initiated with ultraviolet-B (UVB) and promoted with 12- O-tetradecanoylphorbol-13-acetate (TPA). Oral administration of the compound 1 during a period before and after the three times of UVB irradiation exhibited a remarkable effect: administration of 0.0025% solution of the compound 1 given orally only to the test group, which started 1 week before and ended 1 week after the irradiation, showed approximately 50% inhibition of tumor incidence and tumor multiplicity in comparison to the control group. Thus, compound 1 could act as a potent anti-tumor initiator in UVB radiation photocarcinogenesis.

Effects and interactions of low doses of arsenic and UVB on keratinocyte apoptosis.

Although arsenic and ultraviolet light B (UVB) are both causes for skin cancers, lesions of arsenic-induced Bowen's disease are often confined to sun-protected skin. UVB may play a modulatory role in skin carcinogenesis by arsenic. The purpose of this study was to evaluate the effects and interactions of arsenic and UVB on cell cycle progression and apoptosis. Cultured human keratinocytes were treated with sodium arsenite (1 microM) and/or UVB (50 mJ/cm(2)) irradiation in different combinations: (i) arsenic alone, (ii) UVB alone, (iii) arsenic followed by UVB (As-UVB), and (iv) UVB followed by arsenic (UVB-As) treatments. Cell cycle analysis and BrdU pulsing revealed S phase arrest in all treatment groups and growth arrest in As-UVB and UVB-As groups. The terminal deoxynucleotidyl transferase-mediated deoxyuridine nick-end labeling assay showed a higher apoptosis rate in the UVB-As group as compared to that of the As-UVB and UVB groups. UVB irradiation significantly decreased Bcl-2 expression. In either the As-UVB or the UVB-As group, the expression of Bcl-2 was further suppressed as compared to the UVB group. The caspase-3, -8, and -9 relative activities were all increased in the UVB group; however, arsenic significantly enhanced caspase-8 and -3 relative activities in UVB-irradiated keratinocytes (the UVB-As group). Pretreatment with the caspase inhibitor(s) rescued the keratinocytes viability to different degrees with the least in the UVB-As group. Our findings revealed that arsenic enhances UVB-induced keratinocyte apoptosis via suppression of Bcl-2 expression and stimulation of caspase-8 activity. Combined UVB and arsenic treatment resulted in the antiproliferative and proapoptotic effects in keratinocytes. Our results provide the explanation for the rare occurrences of arsenical cancers in the sun-exposed skin and the potential therapeutic role of UVB in arsenic-induced Bowen's disease.

Frequent occurrence of UVB-induced sister chromatid exchanges in telomere regions and its implication to telomere maintenance

Sister chromatid exchanges (SCEs) are symmetrical exchanges between newly replicated chromatids and their sisters. While homologous recombination may be one of the principal mechanisms responsible for SCEs, the full details of their molecular basis and biological significance remain to be elucidated. Following exposure to ultraviolet light B (UVB), mitomycin C (MMC) and cisplatin, we analyzed the location of SCEs on metaphase chromosomes in Chinese hamster CHO cells. The frequency of SCEs increased over the spontaneous level in proportion to the agent’s dose. UVB-induced SCEs occurred frequently in telomere regions, as cisplatin-induced SCEs did, differing from MMC-induced ones. The remarkable difference of intrachromosomal distribution among the three mutagens may be attributed to the specificity of induced DNA lesions and structures of different chromosome regions. Telomeric DNA at the end of chromosomes is composed of multiple copies of a repeated motif, 5′-TTAGGG-3′ in mammalian cells. Telomeric repeats may be potential targets for UVB and cisplatin, which mainly form pyrimidine dimers and intrastrand d(GpG) cross-links, respectively, resulting in SCE formation. UVB irradiation shortened telomeres and augmented the telomerase activity. The possible implications of the frequent occurrence of SCEs in telomere regions are discussed in connection with the maintenance of telomere integrity.

Inhibition of cutaneous ultraviolet light B–mediated inflammation and tumor formation with topical celecoxib treatment

Inflammation, which includes the release of growth factors, proinflammatory cytokines and prostaglandins, the infiltration and activation of inflammatory cells, and the induction of oxidative DNA damage, is known to play a role in cancer development. The combination of damage to the skin resulting from chronic ultraviolet light B (UVB) exposure itself and the inflammatory response it induces is a major source of skin cancer development. Cyclooxygenase-2 (COX-2), an inflammatory enzyme responsible for the production of prostaglandins, is now implicated in the development of epithelial cancers, including squamous cell carcinoma in the skin. Previous work conducted in our laboratory has shown that topical treatment with celecoxib following UVB irradiation inhibits several parameters of acute inflammation, including vascular permeability, the infiltration and activation of neutrophils, and the production of prostaglandin E(2) (PGE(2)). The present studies expanded these observations, demonstrating the ability of topical celecoxib to inhibit acute oxidative damage. In addition, long-term studies illustrate the effectiveness of topical treatment with this drug in reducing chronic inflammation and UVB-induced papilloma/carcinoma formation. This data provides compelling evidence to explore the clinical efficacy of topically applied COX-2 inhibitors for the prevention of human skin cancers.

Immunological responses to ultraviolet light B radiation in Black individuals

Immunological factors are important participants in the pathogenesis of experimental skin tumors. We therefore studied cutaneous immune responses in subjects with either low natural incidence (Black individuals), or a high frequency rate (White individuals) of skin cancer. We performed whole body irradiation with a low dose of ultraviolet light B (UV-B) and evaluated peripheral lymphocytes. UV-B irradiation was associated with small but significant changes in lymphocyte phenotype frequency. In White subjects this consisted of an increased number of CD19 (B cells) and CD 4/29 (inducer of helper T cells); Black subjects had a slight decrease in CD3 (T cells). Natural killer activity, not affected by UV-B in White subjects, increased significantly in Black subjects. UV-B was devoid of immunological effects in vitro for any of the parameters tested. As expected, the low UV-B dose used in this study induced increases of serum vitamin D3 concentrations in White subjects, with lack of response in the Black subjects. We conclude that Black individuals selectively exhibit an increase in Natural Killer activity in response to irradiation with low dose UV-B. This race group-specific immune response to ultraviolet radiation appears to require mediation by the skin. Enhanced Natural Killer activity could underlie at least partly the resistance in Black individuals to the development of photodependent skin cancer.

The photoprotective effect of 1,25-dihydroxyvitamin D 3 on ultraviolet light B-induced damage in keratinocyte and its mechanism of action

We investigated the photoprotective effect of 1,25-dihydroxyvitamin D 3 (1,25(OH) 2D 3) both in vivo and in vitro, revealing its relationship with glutathione, a well-known antioxidant. We also probed into the possible mechanism of photoprotection of 1,25(OH) 2D 3 through immunohistochemical study for metallothionein (MT). At the same time, endogenous antioxidant effect of 1,25(OH) 2D 3 was examined. Survival of cultured human keratinocytes was decreased when the cells were irradiated with ultraviolet light-B (UVB) at doses above 30 mJ/cm 2. But in the presence of 1,25(OH) 2D 3 (12 nM), the decrease of survival of keratinocytes by UVB was diminished. The formation of sunburn cells by UVB irradiation in the skin of ICR mice was inhibited by topical application of 1,25(OH) 2D 3, regardless of prior glutathione depletion. Immunohistochemical staining revealed that 1,25(OH) 2D 3 induced the expression of MT, a potent radical scavenger, mainly in the basal layer of ICR mice skin. 1,25(OH) 2D 3 neither inhibited peroxidation of plasma lipids nor interacted with superoxide, nor removed hydrogen peroxide as an antioxidant. These findings suggest that 1,25(OH) 2D 3 has photoprotective effect not related with glutathione or its endogenous antioxidant property. Rather, it could be attributed to 1,25(OH) 2D 3-induced MT and its capacity to prevent radical-related damage in UVB irradiation.

Inhibition of substance P‐induced histamine release from rat peritoneal mast cells by ultraviolet light B irradiation: decreased intracellular calcium as a partial mechanism

Ultraviolet light irradiation has been shown to suppress immunological reactions of irradiated individuals, however, less attention has been paid to the effects on neurogenic inflammation. We have investigated the effect of ultraviolet light B (UVB) irradiation on substance P (SP)-induced histamine release from rat mast cells. Rat peritoneal mast cells were treated with UVB irradiation and challenged by SP. Histamine release from the cells and intracellular calcium concentrations ([Ca2+]i) in the cells were measured. UVB irradiation at doses used in the present study did not induce histamine release from mast cells. UVB irradiation at doses from 25 to 200 mJ/cm2 inhibited 10(-5) mol/L SP-induced histamine release in a dose-dependent manner. On the other hand, SP-induced increase of [Ca2+]i was inhibited by UVB irradiation only at doses of 100 and 200 mJ/cm2. These data suggest that UVB irradiation inhibits histamine release from SP-activated rat peritoneal mast cells partially through the suppression of an increase in [Ca2+]i.

Abrogation of Allospecific T Lymphocyte Responses in Swine by Ultraviolet Light-B Irradiation

Immunomodulatory effects of ultraviolet-light B (UV-B) irradiation were tested in pigs, using peripheral blood lymphocytes (PBL), with special emphasis on the generation of cytotoxic T lymphocytes (CTL). Stimulator PBL were irradiated with 300–1100 Joules/m 2 (J/m 2) of UV-B (experimental group) and cultured for 24 h prior to being placed in mixed lymphocyte culture (MLC) to determine proliferative responses against alloantigens, or placed in bulk culture with allogeneic PBL to determine the induction of CTL. PBL that received 3000 rads gamma irradiation were used as controls. Proliferative alloresponses against gamma irradiated PBL (control group) were high, with stimulation indices (S.I.) ranging from 13.46 to 81.93. The generation of allospecific CTL activity was also high, ranging from 50.78 % to 95.40 %. In contrast, proliferative responses and generation of allospecific CTL were markedly inhibited (> 49.77 %) against the same donor PBL irradiated with ≥ 500 J/m 2 UV-B. These results demonstrated that ultraviolet light treatment of pig PBL can reduce or prevent allospecific T cell proliferation as well as the generation of specific CTL, similar to results obtained with UV-B irradiation of lymphocytes in rodents.

The Effects of Sunscreens on UVB Erythema and Langerhans Cell Depression

Langerhans cells (LCs) are epidermal antigen-presenting cells capable of initiating a specific T lymphocyte-mediated immune response. It is a well known fact that ultraviolet light B (UVB) suppresses LC number and function. In this study, we confirmed that the sunscreens CITY BLOCK, and TOTAL SUN SHIELD 28 (Clinique Laboratories Tokyo, Japan) protected the epidermis against the depletion of LC number. We also investigated whether or not sunscreens could provide LC protection from ultraviolet ray (UVR) damage other than the prevention of the decrease in the total number of cells. Our data showed that the LC population was depressed after irradiation by 100 mJ/cm2 or 10 mJ/cm2 of UVB, but recovered to within normal levels after 16 days. Both sunscreens provided protection against erythema and LC depression due to UVB irradiation. However, despite the fact that these sunscreens had completely suppressed UVB erythema, shrinkage of LC dendrites was seen. Apparently, sunscreens prevent UVB erythema, but do not protect against functional changes in LC due to UVB. Recently, it has been reported that sunscreens are less effective in protecting against systemic immunosuppression that against inflammation. The shrinkage of LC dendrites despite sunscreen application may help explain this discrepancy.

Adaptation of solitary corals and their zooxanthellae to low light and UV radiation

Adaptation of solitary corals, Fungia repanda and F. echinata, and their zooxanthellae to low light and ultraviolet light B (UV-B) was studied with respect to changes in their protein contents, photosynthetic pigment contents and the photosynthesis-irradiance (P-I) curves. The corals were collected from 1 to 50 m depths in the Republic of Belau (Paulau) in 1990 and 1991. The chlorophyll a content in a unit surface area of the coral did not change significantly with the depth of the habitat, whereas cellular chlorophyll a in the algae increased with the depth. Zooxanthellae density and protein content in a unit surface area of Fungia spp. decreased with the depth. Photosynthetic parameters normalized by a unit surface area of the Fungia spp., maximum gross photosynthetic rate (P gmax area-1) and dark respiration rate (R area-1), were negatively correlated with the depth, while initial slope of the P-I curve (α) did not show significant correlation with the depth. Compensation light intensity (Ic) decreased with the depth. In isolated zooxanthellae, P max chl a -1, and R chl a -1 decreased with the depth, while αchl a was constant. P gmax cell-1 and R cell-1 did not change significantly but αcell increased with the depth. Ic decreased with the depth as in the intact corals. Reduction of protein content in a unit area of the coral from deeper habitat implies decrease of host animal tissues. Reduction of Ic can be explained by decrease of R area-1, which may be due to the diminution of animal tissues. The photoadaptational response to low light intensity of intact Fungia spp. was found to be a combination of the photoadaptation of symbiotic algae and the decrease of host animal tissue. In order to study their adaptation to ultraviolet (UV) radiation, P-I curves of Fungia spp. and isolated zooxanthellae were analyzed before and after UV-B irradiation. 1 h UV-B irradiation showed no effect on the photosynthetic rate of the shallow water (1 m) corals, while it inhibited the photosynthesis of the deep water (30 m) corals and zooxanthellae isolated from both shallow and deep water corals. These results indicate that the host, Fungia spp., in shallow water have protective mechanism for intense UV-B in their habitat. These photoadaptational mechanisms seem to allow the Fungia spp. to have wide vertical distribution where light intensity spans more than two orders of magnitude.

Enhanced prostaglandin synthesis after ultraviolet injury is mediated by endogenous histamine stimulation. A mechanism for irradiation erythema.

Acute ultraviolet light B (UVB) injury is associated with dermal mast cell histamine release. The possibility that histamine-stimulated prostaglandin (PG) synthesis could be a mechanism for irradiation erythema was therefore examined using human skin explants. Explants responded to UV irradiation (120 mJ/cm2) with a fivefold increase in synthesis of prostaglandins E2, F2 alpha and 6-keto PGF1 alpha. Incubating explants with the H1 antihistamines brompheniramine (50 microM) or pyrilamine (30 microM) inhibited PG release from irradiated explants 63 +/- 4.9% (mean +/- SEM) 6 h after UV exposure. Antihistamines did not affect PG synthesis in control explants. Irradiation increased the histamine concentration in explant conditioned medium only 50% over basal values, suggesting that irradiation enhanced histamine responsiveness. Explants were therefore incubated with exogenous histamine. In irradiated explants, PG synthesis was stimulated threefold by 3 microM histamine. Unirradiated explants' PG synthesis was unaffected by histamine. Enhanced histamine sensitivity was also examined in epidermal cell cultures. In irradiated cultures, histamine sensitivity was again markedly potentiated: as little as 1 microM histamine stimulated significant PGE2 release and the response to 10-30 microM histamine was increased six to eight times compared with that of unirradiated cultures. These studies demonstrate that endogenous histamine stimulates PG synthesis in human skin after UV injury by potentiation of histamine-induced prostaglandin release. Potentiated agonist responses induced by UV exposure may contribute to the effects of UVB irradiation injury and in particular to irradiation erythema.

Keratinocyte Prostaglandin Synthesis Is Enhanced by IL-1

Keratinocytes are a rich source of IL-1, a cytokine which stimulates prostaglandin synthesis in many cell types. The effects on arachidonic acid metabolism of this cytokine were therefore studied in cultured adult human keratinocytes. Exogenous IL-1 increased basal cellular prostaglandin synthesis (particularly PGE2) threefold. Increased PGE2 synthesis in response to IL-1 was inhibited by cycloheximide, suggesting a requirement for new protein synthesis. Irradiation of the keratinocytes with low-dose ultraviolet light B (UVB) resulted in the release of increased quantities of both IL-1 and PGE2. The amount of IL-1 released was sufficient to increase PGE2 synthesis when exogenously added to unstimulated cells, suggesting a causal relationship. The time course of accumulation of IL-1 and PGE2 in the medium of irradiated keratinocytes was also consistent with a cause-effect relationship. No feedback inhibition of IL-1 release by the increased PGE2 was detected as demonstrated by the observation that IL-1 production in response to UVB was not augmented by treatment with indomethacin or blunted by the exogenous addition of PGE2. These data suggest that keratinocyte IL-1 may be partially responsible for induction of keratinocyte PGE2 synthesis after UVB irradiation.