Longwave ultraviolet radiation (UVA)-induced alteration of epidermal DNA synthesis

N2 laser-induced oxidation of hemoproteins in red blood cell lysate

Irradiation of red blood cell lysate with a N(2) laser (337 nm) was observed to induce oxidation of hemoproteins. This process showed a strong dependence on the concentration of red blood cell lysate and the dose of radiation. Studies of mechanisms and experiments with deoxygenated red blood cell lysate rule out involvement of any reactive oxygen species and suggest that the process is not a photodynamic reaction.

Topical application of alpha-tocopherol modulates the antioxidant network and diminishes ultraviolet-induced oxidative damage in murine skin

The aim of this study was to investigate the effects of topical alpha-tocopherol application on epidermal and dermal antioxidants and its ability to prevent ultraviolet (UV)-induced oxidative damage. Hairless mice received topical applications of alpha-tocopherol 24 h before a single, acute UV irradiation (10 x minimal erythemal dose). The four major antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase and glutathione peroxidase), hydrophilic and lipophilic antioxidants, and lipid hydroperoxides, markers of oxidative damage, were assayed in both epidermis and dermis of hairless mice. Topical alpha-tocopherol treatment increased dermal superoxide dismutase activity by 30% (P < 0.01) and protected epidermal glutathione peroxidase and superoxide dismutase from depletion after UV irradiation. Total and reduced glutathione levels in the epidermis increased by 50% after the topical treatment (P < 0.05), as did dermal ascorbate levels (by 40%: P < 0.01). The topical treatment increased alpha-tocopherol levels both in the epidermis (62-fold) and the dermis (22-fold: P < 0.001 in each layer). Furthermore, alpha-tocopherol treatment significantly reduced the formation of epidermal lipid hydroperoxides after UV irradiation (P < 0.05). These results demonstrate that topical administration of alpha-tocopherol protects cutaneous tissues against oxidative damage induced by UV irradiation in vivo, and suggest that the underlying mechanism of this effect involves the up-regulation of a network of enzymatic and non-enzymatic antioxidants.

Cell cycle effects and concomitant p53 expression in hairless murine skin after longwave UVA (365 nm) irradiation: a comparison with UVB irradiation

Ultraviolet A (UVA, 315-400 nm) radiation is known to be a complete carcinogen, but in contrast to UVB (280-315 nm) radiation, much of the cell damage is oxygen dependent (mediated through reactive oxygen species), and the dominant premutational DNA lesion(s) remains to be identified. To investigate further the basic differences in UVA and UVB carcinogenesis, we compared in vivo cellular responses, viz. cell cycle progression and transient p53 expression in the epidermis, after UVA1 (340-400 nm) exposure with those after broadband UVB exposure of hairless mice. Using flow cytometry we found a temporary suppression of bromodeoxyuridine (BrdU) uptake in S-phase cells both after UVB and UVA1 irradiation, which only in the case of UVB is followed by an increase to well over control levels. With equally erythemogenic doses (1-2 MED), the modulation of BrdU uptake was more profound after UVB than after UVA1 irradiation. Also, a marked transient increase in the percentage of S-phase cells occurred both after UVB and after UVA1 irradiation, but this increase evolved more rapidly after UVA1 irradiation. Further, p53 expression increased both after UVB and UVA1 irradiations, with peak expression already occurring from 12 to 24 h after UVA1 exposure and around 24 h after UVB exposure. Overall, UVA1 radiation appears to have less of an impact on the cell cycle than UVB radiation, as measured by the magnitude and duration of changes in DNA synthesis and cells in S phase. These differences are likely to reflect basic differences between UVB and UVA1 in genotoxicity and carcinogenic action.

Drug photosensitivity, idiopathic photodermatoses, and sunscreens

Photosensitization may be defined as a process in which a reaction to normally innocuous radiation is induced by the introduction of a specific radiation-absorbing substance (the photosensitizer) that causes another component (the substrate) to be changed by the radiation. This review focuses on photosensitization produced by exogenous chemicals. Idiopathic photodermatoses, including polymorphous light eruption and its variants, solar urticaria and chronic actinic dermatitis, are also discussed. Clinical recognition patterns of the photodermatoses are stressed as well as several diagnostic procedures available for confirmation of the condition. Finally, descriptions, therapeutic uses, and adverse reactions of sunscreens are provided.

Photoprotection due to pigmentation and epidermal thickness after repeated exposure to ultraviolet light and psoralen plus ultraviolet A therapy

Tanning and thickening of the epidermis are cardinal defensive responses of human skin to ultraviolet (UV) radiation that lead to increased photoprotection. Earlier studies have shown that skin pigmentation can be used to predict minimal erythema dose and minimal phototoxic dose. In this study it was calculated how much of the increase in photoprotection after 4 weeks of repeated exposure to suberythemogenic doses of either UVA or UVB radiation sources or psoralen plus UVA (PUVA) therapy that was attributable to melanogenesis. The backs of 12 volunteers were exposed to 6 different UVA and UVB radiation sources 9 times during 4 weeks. Skin pigmentation was assessed by skin reflectance measuring. Photoprotection was determined from the minimal erythema dose. Melanogenesis accounted for 63-95% of the increase in photoprotection after 4 weeks of exposure to UVA radiation. Exposure to two UVB sources induced a significant increase in photoprotection but not in pigmentation. Melanogenesis accounted only for 6-11% of the increase in photoprotection after 4 weeks of UVB exposure. The pigmentary and photoprotective responses to PUVA therapy were followed in 14 patients. After 2 weeks of exposure, the increase in photoprotection was significantly higher than predicted from the increase in skin pigmentation. After 4 weeks, melanogenesis accounted for only 36% of the increase in photoprotection. This study shows that melanogenesis accounts for the increased photoprotection after 2 weeks of exposure to UVA radiation, but after 4 weeks other protective mechanisms occur. During suberythemal UVB exposure and during PUVA therapy the importance of skin pigmentation in the overall photoprotection gradually decreases during a 4-week irradiation period.

Determinants of antioxidant status in humans

Antioxidant status in humans reflects the dynamic balance between the antioxidant system and prooxidants and has been suggested as a useful tool in estimating the risk of oxidative damage. This paper reviews determinants of antioxidant status such as diet including antioxidant nutrient and nonnutrient intake, absorption and bioavailability, dietary components such as polyunsaturated fatty acids and transition metals, food storage and processing, chemical form, chirality and formulation of supplemental compounds and alcohol intake; environmental factors such as pollutants, ultraviolet radiation and smoking; injury and disease, medications and other medical treatments such as radiation; strenuous exercise; and physiological stage or conditions such as those in premature babies and the elderly. It is proposed that, in addition to current focus on tissues, the antioxidant status of digesta should be considered because of its effect on specific tissues and potential health implications.

Protection by zinc against UVA- and UVB-induced cellular and genomic damage in vivo and in vitro

For many years, zinc salts have been used both topically and orally to treat minor burns and abrasions as well as to enhance wound repair in man and animals. In this study we describe the protective effects of zinc against UV-induced genotoxicity in vitro and against sunburn cell formation in mouse skin in vivo. Cultured skin cells from neonatal mice showed a dramatic increase in the number of micronuclei as a result of UVA and UVB irradiation. Inclusion of zinc at 5 micrograms/mL in the medium significantly reduced the frequency of micronuclei and of micronucleated cells. In hairless mice, topical application of zinc chloride for 5 consecutive days or a single application 2 h prior to UV exposure reduced the number of sunburn cells in the epidermis as did application of zinc 1 h after exposure. Application 2 h after irradiation also tended to have a protective effect, although there was a large variation between animals. It is proposed that an influx of zinc can protect epidermal cells against some of the more delayed effects of UV-induced damage.

On the induction of protective responses in Salmonella typhimurium strain TA1535/pSK1002 by UVA (365 nm)

Exposure to UVA (365 nm) led to growth delay, loss of viability and inhibition of 3H-thymidine incorporation into the cells of Salmonella typhimurium strain TA1535 containing multiple copies of a plasmid pSK1002 carrying a umuC'-'lacZ fusion gene. Ultraviolet-A induced umu gene expression, as monitored by the estimation of beta-galactosidase, in a linear fluence-dependent manner. The induction of umu gene expression increased with the increase of postirradiation incubation period of the cells in the LB-ampicillin (LBA) medium at 37 degrees C and leveled off from 2 h onward. The induction of gene expression depended on concomitant protein synthesis and represented the induction of the SOS response in the particular S. typhimurium cells used. The exposure to low fluences (sublethal) of UVA also led to the induction of an adaptive response in the same bacterial cells, which made them resistant to subsequent challenge by a much higher fluence of the same radiation. The adaptive response, as monitored by the assays of viability and beta-galactosidase units, increased with the period of exposure to sublethal fluences of UVA, attained a maximum at the UVA exposure of 4.5 kJ/m2 (15 min) and thereafter gradually decreased with further increase of UVA exposure period. Modulation studies involving D2O, LBA growth medium, different scavengers of free radicals and quenchers of activated oxygen species indicated the involvement of both hydroxyl free radicals and singlet oxygen in the UVA-induced umu gene expression.

UVA-induced peroxidation of lipid in the dried film state

Exposure of a dried lipid thin film to UVA produced a dose-dependent linear increase in the three peroxidation products, conjugated diene, lipid hydroperoxide and malondialdehyde (MDA). All three lipid peroxidation products exhibited an inverse dose rate effect. Identical amounts of malondialdehyde were produced when the lipid film was exposed to UVA either directly or through the thickness of the Corning glass on which the film was cast. Antioxidants, alpha-tocopherol, butylated hydroxytoluene (BHT) and the singlet oxygen quencher beta-carotene significantly inhibited the UVA-induced peroxidation of the lipid film. The biological implications of the UVA-induced peroxidation of the dried lipid film are discussed.

The influence of topical and systemic vitamin E on ultraviolet light-induced skin damage in hairless mice

Hairless mice were fed diets containing different levels of vitamin E or received topical applications of the vitamin for three weeks before a single exposure equivalent to one minimal erythematous dose of ultraviolet light provided by an artificial sunlight source. Lipid peroxidation and suppression of incorporation of thymidine into DNA were used to estimate the degree of damage caused by the radiation. Restriction of dietary vitamin E had little effect on degree of epidermal lipid peroxidation or on thymidine incorporation into DNA. High dietary levels of the vitamin did not alter the degree of lipid peroxidation; however, the incorporation of thymidine was restored to levels comparable to those of unirradiated animals. Topical administration of a 1% solution of the vitamin in ethanol 1 or 24 hours before irradiation also restored thymidine incorporation and reduced the degree of lipid peroxidation. The results suggest that both dietary and topical vitamin E are effective in protecting the epidermis against some of the early damage induced by ultraviolet radiation.

Specific mRNAs accumulate in long-wavelength UV-irradiated mouse epidermis

Total RNA from hairless mice epidermis was analysed by RNA-DNA hybridization on slot blots at various times following irradiation with long-wavelength UV light (UV-B or UV-B plus UV-A). Densitometric scanning of the autoradiographies indicates that the amount of RNA which hybridizes with an Ha-ras DNA probe remains constant for up to 72 h after irradiation. The amount of the transcript which hybridizes to a c-fos DNA probe increases dose dependently from 15 min to 2 h after irradiation. RNA which hybridizes to a tubulin DNA probe accumulates in parallel with the increase in mitotic index associated with the radiation-induced hyperplasia.

Prevention of skin cancer

Our understanding of the carcinogenic process as it relates to human skin cancer is growing rapidly. As this understanding increases, so will our ability to alter the process in a positive fashion. Presently, sun exposure is known to be the major carcinogen in human skin. The use of sunscreens is, and will continue to be, the most effective method of preventing human skin cancer. As these agents become more effective, especially against long-wave UV radiation, and as patients begin to use them more conscientiously, we should experience a decrease in skin cancer rates. In addition, a number of chemical agents are presently being investigated as anticarcinogens, especially in those patients who are at high risk for the development of skin cancers. A number of these hold promise as safe and effective chemopreventatives in reducing the morbidity and mortality of cancer in human skin.