Measurement of in vivo sunscreen immune protection factors in humans

This study investigates the level of protection provided by sunscreens against solar-simulated UV radiation-induced immunosuppression in humans. The in vivo immune protection factors (IPF) of two broad-spectrum sunscreens were determined by assessing their ability to prevent UV-induced suppression of nickel contact hypersensitivity (CHS) in 15 nickel-allergic volunteers. Each volunteer was irradiated on unprotected skin of the back with different doses of UV daily for 4 days. Multiples of these UV doses were concurrently delivered to sunscreen-treated sites on the contralateral back. Nickel patches were then applied to both irradiated sites and adjacent, unirradiated control sites. Nickel-induced erythema at each site was measured 72 h later with a reflectance spectrometer. Comparison of the nickel reactions of irradiated and unirradiated skin revealed linear UV dose-responses for immunosuppression in both unprotected and sunscreen-treated skin. The minimum level of immunosuppression that can be reliably detected with this method is 20%. Therefore, the UV dose that reduces mean nickel CHS by 20% is the minimal immune suppression dose (MISD). Sunscreen IPF were determined by dividing the mean MISD of sunscreen-treated skin by that of unprotected skin. The sunscreens, with sun protection factors of 9 and 24, had IPF of 6.5 and > 25, respectively.     

No adaptation to UV-induced immunosuppression and DNA damage following exposure of mice to chronic UV-exposure

It is well known that ultraviolet (UV) radiation induces erythema, immunosuppression and carcinogenesis. We hypothesized that chronic exposure to solar UV radiation induces adaptation that eventually prevents the suppression of acquired immunity. We studied adaptation for UV-induced immunosuppression after chronic exposure of mice to a suberythemal dose of solar simulated radiation (SSR) with Cleo Natural lamps, and subsequent exposure to an immunosuppressive dose of solar or UVB radiation (TL12). After UV dosing, the mice were sensitized and challenged with either diphenylcyclopropenone (DPCP) or picryl chloride (PCl). To assess the adaptation induced by solar simulated radiation, we measured the proliferative response and cytokine production of skin-draining lymph node cells after immunization to DPCP, the contact hypersensitivity (CHS) response to PCl, and thymine-thymine (T-T) cyclobutane dimers in the skin of mice. After induction of immunosuppression by SSR or by TL12 lamps, the proliferative response of draining lymph node cells after challenge with DPCP, or the CHS after challenge with PCl, showed significant suppression of the immune response. Chronic irradiation from SSR preceding the immunosuppressive dose of UV failed to restore the suppressed immune response. Reduced lipopolysaccharide-triggered cytokine production (of IL-12p40, IFN-gamma, IL-6 and TNF-alpha) by draining lymph node cells of mice sensitized and challenged with DPCP indicated that no adaptation is induced. In addition, the mice were not protected from T-T dimer DNA damage after chronic solar irradiation. Our studies reveal no evidence that chronic exposure to low doses of SSR induces adaptation to UV-induced suppression of acquired immunity.     

Viability of the antigen determines whether DNA or urocanic acid act as initiator molecules for UV-induced suppression of delayed-type hypersensitivity

UV radiation suppresses the immune response, and UV-induced immune suppression contributes to UV-induced photocarcinogenesis. For UV-induced immune suppression to occur, electromagnetic energy (i.e. UV radiation) must be converted to a biological signal. Two photoreceptors have been identified in the skin that serves this purpose, epidermal DNA and trans-urocanic acid (UCA). Although compelling evidence exists to support a role for each pathway (UV-induced DNA damage or photoisomerization of UCA) in UV-induced immune suppression, it is not clear what determines which photoreceptor pathway is activated. To address this question, we injected UV-irradiated mice with a monoclonal antibody with specificity for cis-UCA or applied liposomes containing DNA repair enzymes to the skin of UV-irradiated mice. The effect that each had on UV-induced suppression of delayed-type hypersensitivity was measured. We asked whether the light source used (FS-40 sunlamps vs solar-simulated UV radiation) altered whichever pathway of immune suppression was activated. Different doses of UV radiation and the viability of the antigen were also considered. Neither the dose of UV nor the light source had any influence on determining which pathway was activated. Rather, we found that the viability of the antigen was the critical determinant. When live antigens were used, UV-induced immune suppression was blocked with monoclonal anti-cis-UCA but not with T4 endonuclease V-containing liposomes. The reverse was observed when formalin-fixed or killed antigens were used. Our findings indicate that antigen viability dictates which photoreceptor pathway predominates after UV exposure.     

LACK OF INHIBITION OF ULTRAVIOLET RADIATION-INDUCED ORNITHINE DECARBOXYLASE ACTIVITY BY RETINOIC ACID

Abstract— Normally present at low levels, ornithine decarboxylase (ODC) activity is induced to higher levels in animal skin by such disparate agents as tumor promoter 12–0-tetradecanoylphorbol-13-acetate (TPA), UV radiation, and hair plucking. Retinoids are known to inhibit induction by TPA. Repeated applications of retinoic acid (RA) in acetone have also been reported to inhibit UV-induced ODC in hairless mice. As a preliminary study, it was of interest to know whether RA in a cream vehicle would have the same effect. Groups of Skh-hairless-1 albino mice were irradiated once with Westinghouse FS-20 lamps (0.045 Joules/cm^/). Immediately post-irradiation, RA was applied to the dorsum in different concentrations (0.001%, 0.002%, 0.02%), vehicles (cream and acetone) and on various time schedules (1–5 times). Sacrifice was by cervical dislocation 24 h later. Epidermis was obtained by mild heat separation and two epidermal sheets were pooled for each extract. In all experiments, the 70-fold increase in UV-induced ODC activity was further increased by retinoic acid by a factor ∼ 1.6. Since ODC levels are usually elevated in proliferating systems, the results are in concordance with the fact that both UV radiation and RA induce epidermal hyperplasia.     

ULTRAVIOLET-B DOSE-RESPONSE CURVES FOR LOCAL AND SYSTEMIC IMMUNOSUPPRESSION ARE IDENTICAL

Irradiation of mice with UVB suppresses contact hypersensitivity either "locally", i.e. when sensitizer is applied to the UV irradiated site, or "systemically", i.e. when sensitizer is applied to a site distal to the site of irradiation. It has been suggested that local suppression requires lower doses of UV than does systemic suppression, and that different mechanisms are therefore responsible. We undertook a detailed analysis of the dose-response and kinetics of UV-induced local and systemic suppression of contact hypersensitivity to trinitrochlorobenzene in two strains of mice, C57BL/6 and BALB/c. We found that the UV dose-responses for systemic and local suppression were identical within the same strain. Comparison, however, of UV dose-responses between strains indicated that C57BL/6 mice required 6.4 times less UV than did BALB/c mice to generate an equivalent amount of suppression. In both strains, local suppression was initiated if sensitizer was applied immediately, or 1 or 3 days after completion of a single dose of UV. In contrast, systemic suppression was initiated only if sensitizer was applied 3 days after UV irradiation. Thus local suppression was generated in the absence of significant systemic suppression (but not vice versa), and this was dependent on time of application of sensitizer after UV irradiation, not on the dose of UV administered. Filtration of the UV source with Mylar indicated that UVB was responsible for initiating both local and systemic suppression. In summary, these results indicate that (1) genetically determined differences in susceptibility to UV suppression exist, (2) the time courses of generation of local and systemic suppression are identical, and therefore use of the terms "low dose" and "high dose" to refer respectively to local and systemic suppression by UV irradiation are incorrect. We conclude that a common mechanism initiates UV-induced local and systemic suppression of contact hypersensitivity by the immediate formation, at the site of UV irradiation, of an immunosuppressive signal which takes between 1 and 3 days to act systemically.     

Using ultra-weak photon emission to determine the effect of oligomeric proanthocyanidins on oxidative stress of human skin

Exposure of skin to ultraviolet (UV) radiation triggers oxidative stress in skin tissue that can lead to erythema, early skin aging or even cancer. It is suggested that oligomeric proanthocyanidins (OPCs), phytonutrients that belong to the polyphenol family have an anti-oxidant/anti-inflammatory activity on the skin. Measuring ultra-weak photon emission (UPE) is a non-invasive, fairly-sensitive and convenient technique for continuously monitoring oxidative stress. The present study was undertaken to confirm anti-oxidant activity of the specific OPCs cream formulation in human skin by measuring UPE of skin. In the present study 25 healthy female subjects participated. As a baseline measurement of skin, UPE was recorded from the dorsal surface of the subjects’ hands before (spontaneous UPE) and after exposure to UV (UV-induced UPE). The effects of the OPCs cream on spontaneous and UV-induced UPE were measured using a fractionated UV exposure protocol. UV exposure resulted in an increase in UPE from both hands. Repeat UV exposure also resulted in a long-term increase of spontaneous UPE. This is likely due to depletion of anti-oxidant capacity of skin resulting in sensitization of skin to UV. It was assessed by measuring spontaneous UPE at 80 min after each UV exposure. Application of the OPCs cream immediately after UV exposure resulted in a significant (approx. 30%) decrease in UV-induced UPE. Topical OPCs cream application also reduced sensitization of skin to UV following repeated UV exposure (i.e., reduced long-term increase in spontaneous UPE). This study indicates that the specific OPCs cream formulation significantly decreases UV-induced oxidative stress in human skin based on UPE measurement. It therefore suggests that regular use of this OPCs cream might protect skin from harmful effects of UV.     

UV protective effects of DNA repair enzymes and RNA lotion

Solar UV radiation is known to cause immune suppression, believed to be a critical factor in cutaneous carcinogenesis. Although the mechanism is not entirely understood, DNA damage is clearly involved. Sunscreens function by attenuating the UV radiation that reaches the epidermis. However, once DNA damage ensues, repair mechanisms become essential for prevention of malignant transformation. DNA repair enzymes have shown efficacy in reducing cutaneous neoplasms among xeroderma pigmentosum patients. In vitro studies suggest that RNA fragments increase the resistance of human keratinocytes to UVB damage and enhance DNA repair but in vivo data are lacking. This study aimed to determine the effect of topical formulations containing either DNA repair enzymes ( Micrococcus luteus ) or RNA fragments (UVC-irradiated rabbit globin mRNA) on UV-induced local contact hypersensitivity (CHS) suppression in humans as measured in vivo using the contact allergen dinitrochlorobenzene. Immunohistochemistry was also employed in skin biopsies to evaluate the level of thymine dimers after UV. Eighty volunteers completed the CHS portion. A single 0.75 minimum erythema dose (MED) simulated solar radiation exposure resulted in 64% CHS suppression in unprotected subjects compared with unirradiated sensitized controls. In contrast, UV-induced CHS suppression was reduced to 19% with DNA repair enzymes, and 7% with RNA fragments. Sun protection factor (SPF) testing revealed an SPF of 1 for both formulations, indicating that the observed immune protection cannot be attributed to sunscreen effects. Biopsies from an additional nine volunteers showed an 18% decrease in thymine dimers by both DNA repair enzymes and RNA fragments, relative to unprotected UV-irradiated skin. These results suggest that RNA fragments may be useful as a photoprotective agent with in vivo effects comparable to DNA repair enzymes.     

Isoflavonoid compounds from red clover (Trifolium pratense) protect from inflammation and immune suppression induced by UV radiation

Isoflavones derived from many edible plants have been reported to possess significant antioxidant, estrogenic and tyrosine kinase inhibitory activity. Genistein has been found previously to provide protection from oxidative damage induced by UV radiation both in vitro and following dietary administration. We have therefore examined the potential of a number of isoflavones from red clover (Trifolium pratense) and some metabolically related compounds to offer protection from UV irradiation in hairless mice by topical application after UV exposure. We show that whereas the primary isoflavones, daidzein, biochanin A and formononetin, were inactive, 20 microM lotions of genistein and the metabolites equol, isoequol and the related derivative dehydroequol had powerful potential to reduce the inflammatory edema reaction and the suppression of contact hypersensitivity induced by moderate doses of solar-simulated UV radiation. For equol the protection was concentration dependent and 5 microM equol markedly reduced the UV-induced inflammation but abrogated the UV-induced immunosuppression. Equol protected similarly from immunosuppression induced by the putative epidermal mediator, cis-urocanic acid (UCA), indicating a potential mechanism of action involving inactivation of this UV-photoproduct. Since immunosuppression induced by both UV radiation and by cis-UCA appears to be an oxidant-dependent response our observations support the actions of these topically applied isoflavones and their metabolites as antioxidants. They also indicate that lotions containing equol, unlike topical UV sunscreens, more readily protect the immune system from photosuppression than from the inflammation of the sunburn reaction, even when applied after exposure, and thus such compounds may have a future role as sun-protective cosmetic ingredients.     

ULTRAVIOLET-INDUCED CELL DEATH IS INDEPENDENT OF DNA REPLICATION IN RAT KANGAROO CELLS

Rat kangaroo (Potorous tridactylus) cells have an efficient repair system for photoreactivation of lethal lesions induced by 254 nm UV. However, this ability is lost with increasing time after UV, being completely ineffective after 24 h. Critical events leading to UV-induced cell death must occur within this period of time. DNA synthesis was inhibited by the DNA polymerase inhibitor aphidicolin and the loss of the capability to photorepair lethal lesions was maintained as for replicating cells. Similar data were obtained in synchronized cells UV irradiated immediately before S phase. Under the same conditions, the ability to remove cyclobutane pyrimidine dimers by photoreactivation in these cells remained unchanged 24 h after irradiation. These data indicate that the critical events responsible for UV-induced cell death occur in the absence of DNA replication.     

Suppression of UVB-induced cutaneous erythema by a previous UVB exposure

People who vacation in sunny places are exposed to the sun on multiple occasions at least on a daily basis. The clinical assessment of sun exposure is erythema in the first 48 h after exposure and pigmentation at times greater than 3-5 days. The purpose of this investigations was to determine the extent to which consecutive erythemogenic exposures result in additive erythema responses. Studies were conducted in which volunteers were first exposed to a graded series of fluences of UVB radiation and then on subsequent days (1-3 days) the same sites along with the surrounding unexposed skin were challenged with varying fluences of UVB radiation. The erythema reactions were assessed clinically and were objectively documented with diffuse reflectance spectroscopy. The sites that received two exposures always showed a reduced erythema response compared to a single erythemogenic exposure. The suppression of erythema was more pronounced when the second exposure was given 48 h after the first. The erythema suppression was maximal when the first exposure was at 1.3 minimum erythema dose (MED). The pigment response to the first exposure was completely suppressed for fluences less than 1.5 MED. We thus provide evidence for a decoupling of the classical sequence of erythema-pigmentation response. We also show that the erythema induced by a second exposure may be substantially suppressed by an earlier exposure, and that this cannot be due to melanin photoprotection or due to substantial thickening of the stratum corneum. We propose that the cause may be some diffusible element of yet unknown origin.     

RESTRICTION ENZYME CLEAVAGE OF UV-IRRADIATED DNA: A COMPARISON OF FAR-UV AND MID-UV WAVELENGTHS

UV-irradiated DNA is less susceptible to restriction by Type II endonucleases than unirradiated DNA presumably due to photolesions formed in the recognition sites. Previous reported studies have used 254 nm radiation or 313 nm plus acetophenone, both treatments which introduce pyrimidine dimers in preference to other photolesions. To assess the effect of a longer wavelength, at which the ratio of pyrimidine dimer formation to the formation of other photolesions is reduced, two different DNAs were irradiated with UV of either 254 or 313 nm and restricted with suitable restriction endonucleases. Restriction patterns were analysed for novel fragments resulting from UV-induced alteration of enzyme recognition sites. EcoRI restriction of 254 nm irradiated lambda DNA produced six novel bands, only three of which were observed following restriction of 313 nm irradiated lambda. These three represented the largest fragments resulting from single site blocks. Novel fragments involving adjacent site blocks observed at 254 nm were not found with 313 nm radiation. Comparison of 254 nm irradiated pSV₂gpt to that irradiated at 313 nm, both restricted with Dral, revealed a more complex pattern. Although all sites were singly blocked by radiation of both wavelengths, multiple site blocks produced by 313 nm radiation did not occur in the order predicted by the 254 nm radiation dose response. These data suggest that certain sites in pSV₂gpt may be more refractory to multiple site blocks than others when irradiated at 313 nm.     

Individual variations in the correlation between erythemal threshold, UV-induced DNA damage and sun-burn cell formation.

A linear correlation between erythema intensity and DNA damage upon exposure to UV has not been firmly established. Many of the deleterious effects of UV exposure do occur after exposure to suberythemal doses. After DNA damage, cells undergo DNA repair. It is commonly accepted that when the burden of damage is beyond the repair capacities, the cell undergoes programmed cell death or apoptosis. The aim of this study is to quantify the amount of UV-induced DNA damage (estimated via the measurement of DNA repair or unscheduled DNA synthesis or UDS) and cellular damage (estimated via the determination of the density of sunburn cells or SBC). If DNA damage and erythema are correlated, similar intensity of UDS and similar density of SBC should be found in volunteers irradiated with a UV dose equal to two minimal erythema doses (MED). Our results show that in 15 different individuals the same relative dose (2 MEDs) provokes UDS values, which vary within a factor of 4. An even larger variability affects SBC counts after the same relative dose. When DNA damage or SBC are plotted versus the absolute dose (i.e. the dose expressed in J/m(2)), there is a rough correlation (with several exceptions) between dose and extent of UDS and SBC counts. It seems possible to divide the volunteers into two subpopulations with different susceptibilities to UV damage. It is well known that UDS and SBC measurements are often affected by large experimental indeterminacy, yet, the analysis of our results makes it plausible to suggest that for the triggering of erythema, a common threshold value for DNA damage or for SBC count are not to be found. In conclusion, the erythema response seems to be loosely correlated with DNA damage. This suggests that the protection offered by the sunscreens against DNA damage, the molecular basis of UV-induced mutagenesis, might not be related to the sun protection factor (SPF) indicated on the label of sunscreens, which is evaluated using the erythema as an endpoint.     

Topical trans-4-aminomethylcyclohexanecarboxylic acid prevents ultraviolet radiation-induced pigmentation

We have studied the effect of a plasmin inhibitor, trans-4-aminomethylcyclohexanecarboxylic acid (trans-AMCHA), on skin pigmentation induced by ultraviolet (UV) exposure in Weiser-Maples guinea pigs. When guinea pigs are exposed to UV radiation (840 mJ cm-2), skin pigmentation is clearly observed from seven days after exposure and continued to increase to 29 days. Post-exposure applications of 2 and 3% solutions of trans-AMCHA to the exposed regions prevent or inhibit the pigmentation process. When the skin is removed and stained by the Fontana-Masson method, melanin content in the basal layer of UV-exposed epidermis is significantly reduced in the regions to which 2 and 3% trans-AMCHA solutions have been applied, compared with the vehicle control. As plasmin is known to contribute to the release of arachidonic acid (AA) and the production of prostaglandins (PGs), we have examined the effects of trans-AMCHA on AA-induced pigmentation in guinea pig skin. Topical application of trans-AMCHA causes a dose-dependent decrease in AA-induced pigmentation. These results suggest that trans-AMCHA reduces melanocyte tyrosinase activity by suppressing the production of PGs, UV-induced melanogens, through the suppression of the UV-induced increase in epidermal plasmin activity.     

Nicotinamide Prevents Ultraviolet Radiation-induced Cellular Energy Loss

UV radiation is carcinogenic by causing mutations in the skin and also by suppressing cutaneous antitumor immunity. We previously found nicotinamide (vitamin B3) to be highly effective at reducing UV-induced immunosuppression in human volunteers, with microarray studies on in vivo irradiated human skin suggesting that nicotinamide normalizes subsets of apoptosis, immune function and energy metabolism-related genes that are downregulated by UV exposure. Using human adult low calcium temperature keratinocytes, we further investigated nicotinamide’s effects on cellular energy metabolism. We found that nicotinamide prevented UV-induced cellular ATP loss and protected against UV-induced glycolytic blockade. To determine whether nicotinamide alters the effects of UV-induced oxidative stress posttranslationally, we also measured UV-induced reactive oxygen species (ROS). Nicotinamide had no effect on ROS formation, and at the low UV doses used in these studies, equivalent to ambient daily sun exposure, there was no evidence of apoptosis. Hence, nicotinamide appears to exert its UV protective effects on the skin via its role in cellular energy pathways.     

UV erythema reducing capacity of mizolastine compared to acetylsalicylic acid or both combined in comparison to indomethacin.

UV light exerts hazardous effects such as induction of skin cancer and premature skin aging. In this study we evaluated an assumptive anti-inflammatory effect of the nonsedative histamine H1-receptor antagonist, mizolastine, on UV-induced acute sunburn reaction. Therefore, a clinical, randomized, double-blind, four-arm, crossover study was conducted in healthy young female volunteers (skin type II) comparing the UV sensitivity under mizolastine, acetyl-salicylic acid (ASA), indomethacin or a mizolastine/ASA combination. Moreover, HaCaT keratinocytes were incubated with mizolastine under various UV treatment modalities in vitro to study its effect on the release of inflammatory cytokines, i.e. interleukin (IL)-1 alpha, IL-6 and tumor necrosis factor alpha (TNF-alpha). All three drugs were effective in suppressing the UVB-, UVA- and combined UVA/UVB-erythema. However, the strongest effects were observed using the combined treatment with both 250 mg ASA and 10 mg mizolastine. An inhibitory effect in vitro of 10 nM mizolastine upon UV-induced cytokine release from HaCaT keratinocytes was observed for IL-1 alpha at 24 h after 10 J/cm2 UVA1, for IL-6 at 48 h after 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, and also for TNF-alpha at 4 h after 10 J/cm2 UVA, 10 J/cm2 UVA1 and 30 mJ/cm2 UVB, respectively. The combination of mizolastine and ASA can be strongly recommended as a protective measure against UV erythema development with a lower unwanted side effect profile than that of the hitherto treatment modality, i.e. indomethacin.     

Isomerization of urocanic acid after ultraviolet radiation is influenced by skin pigmentation

Exposure to ultraviolet (UV) radiation may induce erythema, DNA damage and suppression of immune responses. Melanin pigmentation offers protection against the first two of these effects, but immunosuppression seems to occur irrespective of the subject's pigmentation. Cis-urocanic acid (cis-UCA), produced by isomerization of trans-UCA in the stratum corneum on UV exposure, initiates some of the immunomodulatory effects of UV radiation. In the present study the relationship between skin pigmentation and UCA isomerization has been examined in 28 healthy individuals of skin types I-IV. Pigmentation is measured in five areas of not recently exposed back skin before irradiation with 0, 0.45, 0.9, 1.8 and 3.6 standard erythema dose (SED) of filtered broadband UV-B (1 SED = 10 mJ cm-2 at 298 nm). The concentration of UCA isomers is measured immediately after the irradiation. With 3.6 SED, the relative production of cis-UCA is close to the maximum obtainable, irrespective of skin type. A significant negative correlation is found between pigmentation and relative production of cis-UCA at 0.45 and 1.8 SED, and between pigmentation and absolute production of cis-UCA at 0.45 SED. At doses of 0.45 and 0.9 SED the relative and absolute production of cis-UCA are higher in the group with skin types I and II when compared with the group with skin types III and IV. The higher isomerization in the lightly pigmented subjects than in the more pigmented ones may indicate that people with fair skin are at a relatively higher risk of immunosuppression when exposed to low doses of UV radiation.     

LACK OF CORRELATION BETWEEN SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND PHOTOISOMERIZATION OF EPIDERMAL UROCANIC ACID IN THE HAIRLESS MOUSE

Abstract 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.     

SUPPRESSION OF CONTACT HYPERSENSITIVITY BY UV RADIATION AND ITS RELATIONSHIP TO UV-INDUCED SUPPRESSION OF TUMOR IMMUNITY

Abstract— In this study, we examine some of the photobiologic and immunologic characteristics of the suppression of contact hypersensitivity (CHS) by UV radiation. BALB/c mice were irradiated on the shaved dorsal skin with FS40 sunlamps and sensitized 5 days later by applying a contact sensitizer lo the shaved abdomen. The suppression of CHS resulting from exposure to a given total dose of UV radiation was unaffected by changes in dose fractionation over a 5-day period and by changes in dose-rate over a 10-fold range. Elimination of wavelengths below 315 nm with a mylar filter abrogated the suppressive effect of the sunlamps, even when the same total energy was administered. Irradiation of unshaved mice required 14 times more energy to produce 50% suppression than was required for shaved mice, suggesting that the exposed skin is the primary target of this effect. Contact sensitization of UV-irradiated, but not unirradiated, mice induced the appearance of antigen-specific suppressor T lymphocytes in their spleen. The photobiologic and immunologic similarities between the suppression of CHS by UV radiation and the UV-mediated suppression of tumor rejection that we described previously suggest that these two immunosuppressive effects of UV exposure share certain steps in their pathways.     

Thioridazine induces immediate and delayed erythema in photopatch test

Thioridazine is a phenothiazine derivative that has been used as an antipsychotic; it rarely causes photosensitization. However, we noticed that this drug induced an erythematous reaction in a photopatch test. Six volunteers were patch tested with various concentrations of thioridazine and irradiated with a range of UVA doses, and the time courses of the color of and blood flow to the test sites were monitored. The free-radical metabolites of thioridazine generated under UVA irradiation and its effects on ascorbate radical formation were examined with an electron paramagnetic resonance (EPR) spectrometer in vitro. As a result, immediate erythema developed during UVA irradiation in most subjects when 1% thioridazine was applied for 48 h and irradiation doses were higher than 4 J cm(-2). Another peak of erythematous reaction was observed 8-12 h after irradiation. The in vitro examination detected an apparent EPR signal, which appeared when 2 mM thioridazine in air-saturated phosphate buffer was irradiated with UVA, whereas this reaction was attenuated under anaerobic conditions. The EPR signal of the ascorbate radical was augmented under both aerobic and anaerobic conditions. Thioridazine-derived oxidants and/or thioridazine radicals generated during UVA irradiation seem to play an important role in this unique phototoxic reaction.     

In vitro antioxidant and in vivo photoprotective effects of an association of bioflavonoids with liposoluble vitamins

A new tendency in cosmetic formulations is the association of botanical extracts and vitamins to improve skin conditions by synergic effects. The objective of this study was to determine the antioxidant activity of associated bioflavonoids, retinyl palmitate (RP), tocopheryl acetate (TA) and ascorbyl tetraisopalmitate (ATIP), as well as their photoprotective effects in preventing increased erythema, transepidermal water loss (TEWL) and sunburn cell formation in hairless mouse skin. The antioxidant activity of solutions containing the association or each substance separately was evaluated in vitro by a chemiluminescence assay. The photoprotective effect was evaluated by means of in vivo tests. Dorsal skin of hairless mice was treated daily by topical applications for 5 days with formulations containing or not containing (vehicle) the flavonoid-vitamins association (5%). The skin was irradiated (UVA/B) 15 minutes after the last application. The results showed that bioflavonoids had in vitro antioxidant properties and also that when they were associated with vitamins their antioxidant activity was more pronounced. On the other hand, erythema and UV damage to the permeability barrier function (TEWL) was not significantly reduced by previous treatment with the flavonoid-vitamin-association formulations, when compared to the irradiated vehicle-treated area. However, the treatment protected the skin from UV damage because it reduced the number of sunburn cells, when compared to the vehicle-treated area. Finally, the association of vitamins and bioflavonoids added to a dermocosmetic formulation showed a relevant biological activity in terms of photoprotection, because the association of bioflavonoids and vitamins acted by different mechanisms, such as antioxidation and absorption of UV radiation, which suggests its use in antiaging and photoprotective products.