Ultraviolet A radiation (320-400 nm) protects hairless mice from immunosuppression induced by ultraviolet B radiation (280-320 nm) or cis-urocanic acid.

T cell-mediated immune function, here measured as the contact hypersensitivity reaction, is readily suppressed by moderate exposure of mice to ultraviolet B (UVB) or solar-simulated radiation (SSUV), or by topical application of cis-urocanic acid. The effect of ultraviolet A (UVA) radiation on immune function has been unclear. Here we have demonstrated that when UVA radiation from a fluorescent tube source was rigorously filtered to remove contaminating UVB radiation, it was immunologically innocuous at physiologically relevant doses. Furthermore, we have found that mice exposed to UVA radiation, either immediately after, or up to 24 h before, immunosuppressive treatment with either UVB radiation, SSUV or cis-urocanic acid, became refractory to the immunosuppression and retained more normal contact hypersensitivity. A greater UVA exposure reversed the immunosuppression more effectively. The results suggest that there are immunologically significant interactions between UV wavebands, and that UVA exposure may induce a relatively long-lived immunoprotective photoproduct, as yet unidentified, that can inhibit the activity of epidermal cis-urocanic acid and thus provide protection from photoimmunosuppression.

Dependence of photocarcinogenesis and photoimmunosuppression in the hairless mouse on dietary polyunsaturated fat.

A series of semi-purified diets containing 20% fat by weight, of increasing proportions (0, 5%, 10%, 15% or 20%) of polyunsaturated sunflower oil mixed with hydrogenated saturated cottonseed oil, was fed to groups of Skh:HR-1 hairless mice during induction and promotion of photocarcinogenesis. The photocarcinogenic response was of increasing severity as the polyunsaturated content of the mixed dietary fat was increased, whether measured as tumour incidence, tumour multiplicity, progression of benign tumours to squamous cell carcinoma, or reduced survival. At the termination of the study approximately 6 months following the completion of the 10-week chronic UV irradiation treatment, when most mice bore tumours, the contact hypersensitivity (CHS) reactions in those groups supporting the highest tumour leads (fed 15% or 20% polyunsaturated fat), were significantly suppressed in comparison with the mice bearing smaller tumour loads (fed 0, 5% or 10% polyunsaturated fat). When mice were exposed acutely to UV radiation (UVR), a diet of 20% saturated fat provided almost complete protection from the suppression of CHS, whereas feeding 20% polyunsaturated fat resulted in 57% suppression; the CHS of unirradiated mice was unaffected by the nature of the dietary fat. These results suggest that the enhancement of photocarcinogenesis by the dietary polyunsaturated fat component is mediated by an induced predisposition to persistent immunosuppression caused by the chronic UV irradiation, and supports the evidence for an immunological role in dietary fat modulation of photocarcinogenesis in mice.

Dietary butter protects against ultraviolet radiation-induced suppression of contact hypersensitivity in Skh:HR-1 hairless mice.

Dietary fats modulate a wide variety of T cell functions in mice and humans. This study examined the effects of four different dietary fats, predominantly polyunsaturated sunflower oil, margarine, and predominantly saturated butter, clarified butter, on the T cell-mediated, systemic suppression of contact hypersensitivity by ultraviolet radiation in the Skh:HR-1 hairless mouse. Diets containing either 200 g/kg or 50 g/kg butter or clarified butter as the sole fat source protected against systemic photoimmunosuppression, whether the radiation source was unfiltered ultraviolet B (280-320 nm) or filtered solar simulated ultraviolet radiation (290-400 nm), in comparison with diets containing either 200 or 50 g/kg margarine or sunflower oil. There was a linear relationship (r > 0.9) between protection against photoimmunosuppression and the proportion of clarified butter in mice fed a series of 200 g/kg mixed fat diets that provided varying proportions of clarified butter and sunflower oil. The dietary fats did not modulate the contact hypersensitivity reaction in unirradiated animals. The observed phenomena were not primary due to the carotene, tocopherol, cholecalciferol, retinol, lipid hydroperoxide or the nonfat solid content of the dietary fats used and appeared to be a result of the different fatty acid composition of the fats.

The protective effect of indomethacin on photocarcinogenesis in hairless mice.

Orally administered indomethacin at 10-600 micrograms per mouse per day has been shown to inhibit UV radiation-induced erythema dose responsively. At the higher doses tested (200-600 micrograms) there was evidence of drug toxicity. Indomethacin administered orally at 20 micrograms per mouse daily during photocarcinogenesis induction both increased the probability of remaining tumour free and reduced the average tumour multiplicity. When indomethacin was administered only during the UV irradiation period (initiation), a reduction in tumour multiplicity and in the progression of tumours to malignant squamous cell carcinomas was observed; when administered only during the post-irradiation promotion period, there was a significant increase in the probability of remaining tumour free. Thus both tumour initiation and promotion by UV radiation appear to be indomethacin-sensitive, possibly affected by different mechanisms.

Pyridoxine supplementation protects mice from suppression of contact hypersensitivity induced by 2-acetyl-4-tetrahydroxybutylimidazole (THI), ultraviolet B radiation (280-320 nm), or cis-urocanic acid.

Evidence exists implicating the epidermal ultraviolet B (UVB) photoproduct cis-urocanic acid as an immunogenic mediator of the systemic suppression of T cell-mediated immunity by UVB exposure. Cis-urocanic acid appears to act via histamine receptor pathways, and histamine receptor antagonists and other imidazole ring compounds may modify its immune suppressing action. A component of the food coloring substance ammonia caramel, 2-acetyl-4-tetrahydroxybutylimidazole (THI), which is known to cause lymphopenia in rats, appears to suppress immunity by a similar pathway when the contact hypersensitivity reaction has been the immune function assay in mice. The induction of lymphopenia in rats by THI is inhibited by the vitamin pyridoxine. This study demonstrates that the suppression of contact hypersensitivity in mice by UVB radiation, cis-urocanic acid, or THI is strongly inhibited by supplemental pyridoxine, fed at 30 mg/kg diet, in comparison with the normal diet, which supplies 7 mg pyridoxine/kg diet. These results suggest that pyridoxine competes with cis-urocanic acid and THI for the same binding site or receptor, which we postulate to be a histamine-like T lymphocyte receptor, and that a role may exist for the control of photoimmunosuppression by this vitamin.

Differential photoimmunoprotection by sunscreen ingredients is unrelated to epidermal cis urocanic acid formation in hairless mice.

A series of experimental sunscreen preparations based on a common vehicle, containing increasing concentrations of either octyl-N-dimethyl-p-aminobenzoate (o-PABA) or 2-ethylhexyl-p-methoxycinnamate (2-EHMC) as the ultraviolet B (UVB) absorber, has been tested in the hairless mouse for the ability to protect from erythema, from the systemically suppressive effects of UVB (280-320 nm) radiation on contact hypersensitivity, and from photoisomerization of epidermal urocanic acid. All the preparations protected efficiently from the edema component of the erythema response when mice were exposed to UVB radiation equivalent to three times the minimal erythema dose (MED). However, when mice were exposed to UVB radiation equivalent to 15 x MED, protection from erythema was observed only at the higher concentrations of each UVB absorber (10% 2-EHMC and 10% or 15% o-PABA). Protection from the UVB-induced suppression of contact hypersensitivity was shown to be dependent on both the nature of the UVB absorber and its concentration. Photoimmunoprotection by the sunscreens containing 2-EHMC was evident at lower concentrations (5% and 10% 2-EHMC) than with o-PABA, following both 3 x MED and 15 x MED of UVB exposure. Photoimmunoprotection by o-PABA-containing sunscreens was observed only at 15% o-PABA following 3 x MED, and failed at all tested concentrations after 15 x MED of UVB exposure. Regardless of the photoimmunoprotective capacity, sunscreen preparations containing either of the UVB absorbers prevented the UVB-induced formation of cis urocanic acid in the mouse epidermis and in vitro under all conditions tested. Thus, there appeared to be a correlation between protection from edema and from cis urocanic acid formation at 3 x MED of UVB, but a dissociation of these variables at 15 x MED of UVB. There was no relation apparent at either UVB dose between either edema or cis urocanic acid formation and protection from suppression of contact hypersensitivity.

Lack of correlation between suppression of contact hypersensitivity by UV radiation and photoisomerization of epidermal urocanic acid in the hairless mouse.

The immunological consequences of exposure to UVA (320-400 nm) radiation are unclear. This study describes the relationship between the generation of epidermal cis-urocanic acid and the ability to respond to a contact-sensitizing agent, in hairless mice exposed to different UV radiation sources, which incorporate successively greater short-wavelength cutoff by filtration of the radiation from fluorescent UV tubes. Mice were exposed to these radiation sources at doses systematically varying in UVB radiation content but supplying increasing proportions of UVA radiation. All radiation sources were found to generate approximately 35% cis-urocanic acid in the epidermis, thus normalizing the sources for cis-urocanic acid production. However, only those sources richest in short-wavelength UVB resulted in suppression of the systemic contact hypersensitivity response. These sources also induced the greatest erythema reaction, measured as its edema component, in the exposed skin. A strong correlation was thus demonstrated between the induction of edema and the suppression of contact hypersensitivity, but there appeared to be no correlation between the generation of epidermal cis-urocanic acid and suppression of contact hypersensitivity. The sources richest in UVA content did not result in suppression of contact hypersensitivity; furthermore mice previously irradiated with such UVA-rich sources were refractory to the immunosuppressive action of exogenous cis-urocanic acid. A protective effect of the increased UVA content thus appeared to be inhibiting immunosuppression by the available endogenously generated or exogenously applied cis-urocanic acid.

A garlic extract protects from ultraviolet B (280-320 nm) radiation-induced suppression of contact hypersensitivity.

Lyophilized aged garlic extract has been incorporated at concentrations of 0.1%, 1% and 4% by weight into semipurified powdered diets and fed to hairless mice. Under moderate UVB exposure conditions resulting in 58% suppression of the systemic contact hypersensitivity response in control-fed mice, a dose-responsive protection was observed in the garlic-fed mice; contact hypersensitivity in the UVB-exposed mice fed 4% garlic extract was suppressed by only 19%. If the UVB exposure was replaced by topical application of one of a series of lotions containing increasing concentrations of cis-urocanic acid, a dose-responsive suppression of contact hypersensitivity was demonstrated in control-fed mice (urocanic acid at 25, 50, 100 and 200 micrograms per mouse resulting in 22-46% suppression). Mice fed a diet containing 1% aged garlic extract were partially protected from cis-urocanic acid-induced suppression of contact hypersensitivity, with greater protection from the lower concentrations of urocanic acid. Mice fed a diet containing 4% aged garlic extract were protected from all concentrations of urocanic acid. The results indicate that aged garlic extract contains ingredient(s) that protect from UVB-induced suppression of contact hypersensitivity and suggest that the mechanism of protection is by antagonism of the cis-urocanic acid mediation of this form of immunosuppression.

Suppressive effect of 2-acetyl-4-tetrahydroxybutylimidazole on contact hypersensitivity in the Skh: HR hairless mouse.

The compound 2-acetyl-4-tetrahydroxybutylimidazole (THI), a component of ammonia caramel, has been shown to cause lymphopenia and to impair several immune functions in rats and mice. In this study we show that THI effectively suppresses contact hypersensitivity dose responsively in the hairless mouse, whether administered topically or orally. The suppression was shown to be prevented by topical administration of the histamine antagonist, cimetidine, and by the dipeptide, carnosine. Splenocytes from THI-treated mice failed to elicit normal contact hypersensitivity when transferred to naive mice. This suggests that THI acts by modifying splenocyte function, perhaps via a histamine-like receptor site(s).

Differential protection by two sunscreens from UV radiation-induced immunosuppression.

A controversy has arisen concerning the ability of sunscreens to protect mice from the immunosuppressive effects of UV radiation. We have assessed the photoprotection in hairless mice of two sun protection factor (SPF)15 sunscreens containing different UVB (280-320-nm) absorbers, namely, octyl-N-dimethyl-p-aminobenzoate (o-PABA) or 2-ethylhexyl-p-methoxycinnamate (2-EHMC). Following three minimum erythemal exposures to UV radiation, both systemic suppression of contact hypersensitivity to 2,4-dinitrofluorobenzene and induction of susceptibility to transplanted UV radiation-induced tumor cells was established. Topically applied 2-EHMC sunscreen protected totally from both forms of immunosuppression, but the o-PABA sunscreen failed to protect, although both sunscreens were equally effective in protection from UV radiation-induced erythema and edema.

Effect of ultraviolet (UV) radiation and UVB-absorbing sunscreen ingredients on 7,12-dimethylbenz(a)anthracene-initiated skin tumorigenesis in hairless mice.

These experiments describe the enhancement of 7,12-dimethylbenz(a)anthracene (DMBA)-initiated skin tumorigenesis in hairless mice by subsequent chronic ultraviolet (UV) irradiation of the same skin site. Each carcinogen was administered at a level that separately resulted in threshold tumorigenesis. The cocarcinogenic response was evident as a marked increase in tumour incidence, tumour multiplicity and degree of tumour malignancy. Irradiation through the topically applied UVB (290-315 nm)-absorbing sunscreen ingredient, 2-ethylhexyl-p-methoxycinnamate, totally protected from the photoenhancement. However, irradiation through an alternative UVB absorber, octyl-N-dimethyl-p-aminobenzoate, failed to protect from photoenhancement. A possible immunologic role for the enhancement of DMBA tumorigenesis by UV radiation is proposed.

Effect on topical 5-methoxypsoralen on tumorigenesis induced in albino and pigmented hairless mouse skin by UV irradiation.

A new line of the Skh:HRII hairless pigmented mouse (black juvenile coat) is described which has been selectively bred for the capacity to respond consistently to simulated solar UV radiation with a continuous and strong tan. This mouse demonstrates a degree of protection from chronic UV-induced tumorigenesis when compared with the Skh:HRI hairless albino mouse, and has been used here to study the effect of induced melanogenesis on phototumorigenesis. Mice were irradiated for 10 weeks with incremental doses of simulated solar UV radiation (UVA + B) from a fluorescent tube source which induced tumours in 100% of albino mice and 93% of black mice by 200 days (minimally oedemal), or with 60% of this dose (sub-oedemal) which induced tumours in 85% of albino mice and 65% of black mice. Mice were also exposed to the UVA component of these radiation sources, obtained by window glass filtration. The effect of topical 5-methoxypsoralen (5-MOP) was examined, at either 0.003% with minimally oedemal UVA + B or its UVA component alone, or at 0.01% with sub-oedemal UVA + B or its UVA component alone, in both albino and black mice. The 5-MOP concentrations were selected as the maximum concentration which did not increase the erythema and oedema responses after a single exposure to minimally oedemal or sub-oedemal UVA + B. At 200 days, the tumorigenic response to sub-oedemal UVA + B was significantly increased by topical 5-MOP, to 100% in albinos and 93% in black mice. In contrast, tumorigenesis in response to minimally oedemal UVA + B was unaffected by topical 5-MOP. The UVA component alone of either irradiation regime was not tumorigenic under these conditions. When combined with topical 5-MOP, the UVA of minimally oedemal UVA + B became moderately tumorigenic, and resulted in a tumour incidence of 23% in albinos and 14.5% in black mice. However, the UVA component of sub-oedemal UVA + B, when combined with topical 5-MOP, was highly tumorigenic specifically in albino mice, inducing tumours in 93% of albino mice but in only 27% of black mice. Tan intensity resulting from minimally oedemal UVA + B was not enhanced by topical 5-MOP, and its UVA component combined with 5-MOP resulted in only a minimal tan. However, the tan intensity resulting from sub-oedemal UVA + B with topical 5-MOP was strongly increased, although its UVA component combined with 5-MOP did not produce a perceptible tan.(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of u.v.-induced skin carcinogenesis in the hairless mouse by inoculation with cell-free extracts of skin tumours.

The presence of papillomaviral-like DNA has been described in ultraviolet light-induced tumours in the skin of the hairless mouse (14). Here we describe the effects of the inoculation of cell-free extracts of ultraviolet light-induced tumours into the scarified skin of normal hairless mice, prior to exposure of the mice to a cumulative carcinogenic dose of ultraviolet light. Extracts from papillomas or squamous cell carcinomas enhanced the susceptibility of the inoculated mice to ultraviolet light-induced tumorigenesis, if the extracts contained papillomaviral DNA sequences detected by cross-hybridization with Mastomys natalensis papillomaviral DNA. The recipient mice developed a greater tumour incidence, tumour yield, tumour diameter and degree of malignancy.

Topical urocanic acid enhances UV-induced tumour yield and malignancy in the hairless mouse.

Epidermal urocanic acid has been postulated to be the mediator of the specific state of immunosuppression induced by UV irradiation, by which UV-initiated tumour cells are able to evade normal recognition and can survive to grow progressively into malignant tumours. These experiments demonstrate that topical application of UV-irradiated urocanic acid systemically suppresses the contact type hypersensitivity response to oxazolone in hairless mice. In addition, topically applied urocanic acid markedly increases the overt tumour yield and the degree of malignancy in hairless mice exposed chronically to daily minimally erythemal doses of simulated solar UV light. Topical urocanic acid also increases the number of latent UV-initiated tumours, detectable by croton oil promotion. Therefore UV photoproducts of urocanic acid can both systemically suppress contact hypersensitivity in the epidermis, and also enhance early survival of UV-initiated tumour cells resulting in augmentation of UV photocarcinogenesis.