Phototoxic properties of perfumes containing bergamot oil on human skin: photoprotective effect of UVA and UVB sunscreens

As part of an international cooperative study of the photophysical, photomutagenic and photocarcinogenic properties of bergamot oil and the effect of UVA and UVB sunscreens, the phototoxic properties of model perfumes containing 5, 15 and 50 ppm 5-methoxypsoralen (5-MOP) in bergamot oil with and without a sunscreen have been investigated on human skin. It has been confirmed that the photosensitivity of human skin is maximal 2 h after perfume application. Interestingly the addition of a UVA sunscreen is more efficient for decreasing the phototoxic properties of bergamot oil than is a UVB sunscreen. The addition of sunscreens in a model perfume containing 50 ppm 5-MOP in bergamot oil can reduce the phototoxic properties of this perfume to a toxicity equivalent to that produced by the application of a model perfume containing 15 ppm 5-MOP without sunscreens. However, despite their promising protective effect in vitro, UVB and UVA sunscreens at low concentration (0.5%-1%) in perfumes cannot suppress the phototoxicity of bergamot oil on human skin.     

FAILURE OF UVR DOSE RECIPROCITY FOR SKIN TUMORIGENESIS IN HAIRLESS MICE TREATED WITH 8-METHOXYPSORALEN

Abstract— 8-Methoxypsoralen (8-MOP) phototumorigenesis was studied in hairless albino mice irradiated with solar simulated radiation (SSR). Animals were exposed to three different daily doses of SSR after application of an oily vehicle with or without 8-MOP. Tumor production was dependent on daily SSR dose irrespective of topical treatment. The phototumorigenic potency of SSR was increased by the vehicle and to a much greater extent by inclusion of 8-MOP. Irrespective of topical treatment, a failure in dose reciprocity for tumorigenesis was demonstrated; in terms of cumulative SSR dose, the lower daily doses were more tumorigenic than the higher doses. This reciprocity failure in 8-MOP photosensitized mice is similar to that previously observed for UV-B phototumorigenesis. The relevance of these findings to therapeutic use of psoralens is discussed.     

Genotoxicity of bergapten and bergamot oil in Saccharomyces cerevisiae

In order to determine the genotoxic potential of bergapten (5-methoxypsoralen (5-MOP] and bergamot oil (BO), the genetic effects of 5-MOP and BO (containing equivalent amounts of 5-MOP) were studied in haploid and diploid yeast (Saccharomyces cerevisiae) using solar simulated radiation (SSR). At equal doses of SSR, equal concentrations of 5-MOP alone or 5-MOP in BO have a similar influence on survival and on the induction of cytoplasmic "petite" mutations, reverse and forward mutations, mitotic gene conversion and genetically aberrant colonies including mitotic crossing over. No reciprocity is found between SSR dose and 5-MOP concentration for cytotoxic, mutagenic and recombinogenic effects. In the presence of chemical filters (Parsol 1789, a UVA filter, and Parsol MCX, a cinnamate derivative acting as a UVB filter) considerable protection is observed against the induction of genetic effects by 5-MOP and BO containing 5-MOP in haploid and diploid cells. As indicated by the lower induction kinetics, the protection is higher than expected from the light-absorbing properties, suggesting photochemical interaction. The protection is slightly higher for BO than for 5-MOP. The induction of genetic effects by 5-MOP alone or BO containing 5-MOP is independent of oxygen. Experiments on suction blister fluids taken from patients after topical treatment with BO containing 5-MOP indicate that in comparison with water the bioavailability and thus the genotoxic effects of the compounds are decreased. Moreover, in addition to the filtering effect against the photoinduced genotoxic effects of BO, the presence of chemical filters apparently reduces the penetration of BO containing 5-MOP and provides a reduction in biological effectiveness.     

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)     

8-Methoxypsoralen and long-wave ultraviolet A inhibit the release of proinflammatory mediators and cytokines from human Fc epsilon RI+ cells: an in vitro study

The in vitro effects of 8-MOP (concentrations of 20, 100 and 500 ng/ml) alone or in combination with UVA on mediator release from human basophils and skin mast cells (HSMC), activated with immunological and non-immunological stimuli, were investigated. With respect to basophils activated with anti-IgE serum, the results of this study show that: (i) 8-MOP alone inhibits histamine, LTC(4), IL-4 and IL-13 release concentration dependently with a maximal effect at 500 ng/ml (a concentration not reached in vivo); and (ii) UVA irradiation (5 J/cm(2)), after 8-MOP incubation, enhances this inhibitory effect on all released mediators, but for IL-4 and IL-13 the percentage inhibition is also significant for the 8-MOP concentrations (20-100 ng/ml) employed in vivo during PUVA treatment. Moreover, histamine release from basophils activated with non-immunological stimuli (FMLP and A23187) is inhibited by 8-MOP, alone or in combination with UVA. With respect to the HSMC activated with anti-IgE serum, the results show that: (i) 8-MOP alone reduces histamine release concentration dependently; and (ii) this inhibitory effect is enhanced by UVA irradiation (5 J/cm(2)). Histamine release from HSMC activated with A23187 is not modified either by 8-MOP alone or by 8-MOP plus UVA.     

ENHANCEMENT OF UV-INDUCED SKIN CARCINOGENESIS BY AZATHIOPRINE: ROLE OF PHOTOCHEMICAL SENSITISATION

Abstract The phototoxicity of various drugs (chlorpromazine (CPZ), metronidazole (MET), 8-methoxypsoralen (8-MOP), azathioprine (AZA) and the azathioprine metabolites, 6-mercaptopurine (6-MP), methylnitrothio-imidazole (MNTI), methylnitroimidazole (MNI)) was determined in hairless (Skh-hrl) mice exposed to a light source with broad emission (290–700 nm). Chlorpromazine, MET, 8-MOP, AZA, MNI and 6-MP were phototoxic, as determined by the oedematous response of skin, at doses comparable to those used clinically.
The effects of long-term drug therapy and UV radiation on skin carcinogenesis were then determined. Chlorpromazine and MET, and to a lesser extent AZA, MNTI and 6-MP, enhanced photocarcinogen-esis. In each case, both the tumour yield and the proportion of malignant:benign skin tumours were increased. The results of this study imply that prolonged treatment of mice with low-level phototoxins predisposes to photocarcinogenesis.     

Simple equilibrium dialysis-high-performance liquid chromatographic method for the in vitro assessment of 5-methoxypsoralen bound to human albumin

Increasingly used in therapeutics, 5-methoxypsoralen (5-MOP), a linear furocoumarin, associated with UVA irradiation (PUVA), is now an established treatment for skin diseases such as vitiligo, mycosis funcoides and particularly psoriasis. Successful PUVA therapy depends on a sufficiently high peak 5-MOP plasma concentration coinciding with the UVA irradiation. However, as with most drugs, only the free plasma fraction is able to enter the target cells and has a pharmacological effect. In this work, the binding of 5-MOP to human albumin was studied in vitro, using a dialysis chamber. Bound and free 5-MOP fractions were quantified by a modification of Stolk's high-performance liquid chromatographic method. Dialysis was performed at 37 degrees C and pH 7.4 for 2 h, against a 4% albumin solution in phosphate buffer. The 5-MOP concentrations used were from 5 x 10(-5) to 5 x 10(-2) g/l in 1 x 10(-1) g/l steps. The 5-MOP bound strongly to human albumin in an unsaturable way. The mean 5-MOP binding to albumin was 95.3%. These results are in accordance with those published by Artuc et al. and not with those of Veronese et al., who found a lower saturable fixation (91%). These two research groups used tritiated 5-MOP. The technique used in this work is simple and inexpensive. It can be employed easily in vivo, e.g., for the assessment of 5-MOP free fractions in different therapeutic conditions.     

In vitro photostability and photosensitizing properties of bergamot oil. Effects of a cinnamate sunscreen

Bergamottin, which accounts for about two-thirds of the absorption of UVA and UVB light by bergamot oil, is shown to be fairly unstable on UV irradiation of solutions of bergamot oil (in ethanol-water, 80:20 (w/w)). Bergamottin photodegradation is partly inhibited by molecular oxygen and also by a cinnamate sunscreen acting as a triplet excited state quencher. On UV irradiation of bergamot oil, type II photodynamic properties, i.e. singlet oxygen production, are observed, which can be mainly attributed to the excitation of bergamottin by light. Therefore bergamottin can be considered as a potential photosensitizer in the photobiological activity of bergamot oil.     

Phototoxicity of protoporphyrin IX, diarginine diprotoporphyrinate and N,N-diphenylalanyl protoporphyrin toward human fibroblasts and keratinocytes in vitro: effect of 5-methoxypsoralen

The phototoxicity of two new porphyrin photosensitizers, diarginine diprotoporphyrinate (PP(Arg)2) and N,N-diphenylalanyl protoporphyrin (PP(Phe)2), and the synergistic effect of 5-methoxyposralen (5-MOP) have been studied in comparison with that of protoporphyrin IX (PPIX). Under ultraviolet-A (UV-A) irradiation (lambda=365 nm), the phototoxicity of the porphyrins toward cultured human fibroblasts and keratinocytes decreases in the order: PPIX > PP(Arg)2 > PP(Phe)2. A synergistic effect of 5-MOP on the phototoxicity of PPIX, PP(Arg)2 and PP(Phe)2 has been observed. The combination of PPIX, PP(Arg)2 and PP(Phe)2 with 0.1-0.5 microM 5-MOP significantly potentiates the phototoxicity of the three porphyrins. The most effective potentiation was observed with the water-soluble PP(Arg)2 and 5-MOP concentrations lower than 0.75 microM. Above this 5-MOP concentration this potentiation is abolished. The intracellular concentration of PPIX and PP(Phe)2 is independent of the presence of 5-MOP. On the other hand, the intracellular content of PP(Arg)2 is decreased in a concentration-dependent manner by the psoralen. Illumination with red light, not absorbed by 5-MOP, leads to a weak potentiation of the PP(Arg)2 phototoxic effect in the presence of 5-MOP, suggesting that dark interaction of 5-MOP with cell membranes aggravated by porphyrin photosensitization is involved in the observed phenomena. The results are tentatively explained by differences in hydrophobicity and molecular structures of the examined photosensitizers. PPIX, which is barely soluble in water, has a significantly higher affinity for cell membranes and simultaneously exerts a stronger phototoxic effect than PP(Arg)2 whose solubility in water is high. On the other hand, the weak phototoxicity of PP(Phe)2 could be explained by the steric hindrance brought by the phenylalanyl substituents on the pyrrole ring. The loss in the PP(Arg)2 cell content probably explains the inhibition of the synergistic effect of 5-MOP on the PP(Arg)2 phototoxicity at high 5-MOP concentration. This study suggests that PP(Arg)2 in combination with 5-MOP might reveal a strong phototoxic effect when applied to skin cancer treatment.     

8-METHOXYPSORALEN INCREASES DAYTIME PLASMA MELATONIN LEVELS IN HUMANS THROUGH INHIBITION OF METABOLISM

Abstract It is well established that in healthy humans oral intake of 5-or 8-methoxypsoralen (5-and 8-MOP) is followed by a significant increase in plasma melatonin concentrations. The effect of psoralen on rat melatonin has been studied in vitro and in vivo and a stimulation of release or secretion from the pineal gland has been suggested. In this study we examined the time-related changes in plasma concentrations of 8-MOP, melatonin and 6-sulfatoxymelatonin in 15 patients admitted for routine psoralen plus UVA therapy. On the first day of treatment blood samples were collected before, and 30, 60 , 66 and 90 rnin after intake of 8-MOP (0.6 mg/kg). Although the rate of 8-MOP absorption vaned greatly, a significant increase ( P = 0.0002) in melatonin levels was found 60 min after 8-MOP intake. During UVA exposure a strongly correlated decrease in mean melatonin and mean 8-MOP concentrations was found, indicating an effect of UVA radiation, either direct or 8-MOP mediated, on circulating melatonin levels. Plasma 6-sulfatoxymelatonin concentrations decreased significantly between all time points, suggesting inhibition of melatonin metabolism.     

Photocarcinogenesis in the Tg.AC mouse: lomefloxacin and 8-methoxypsoralen

The Tg.AC mouse is a good predictor of carcinogenic potential when the test article is administered by dorsal painting (Tennant et al. (1995) Environ. Health Perspect. 103, 942). We have used lomefloxacin (LOME) and 8-methoxypsoralen (8-MOP) in combination with UVA to determine whether the Tg.AC transgenic mouse also responds to parenterally administered photocarcinogens. Female Tg.AC mice were given LOME (25 mg/kg intraperitoneal in normal saline) followed by UVA (25 J/cm2) 1-2 h later, five times every 2 weeks on a repetitive schedule. Other groups received LOME, UVA or vehicle alone. After 16 weeks, the mean numbers of papillomas/mouse +/- SD (% responding) were: saline, 0.3 +/- 0.5 (33%); UVA + saline, 1.3 +/- 0.6 (100%); LOME, 1.9 +/- 1.6 (86%) and LOME-UVA, 1.5 +/- 1.9 (64%). Only the 100% incidence of tumors in the UVA group and the maximum tumor yields in the LOME and UVA groups are significant (P < 0.05) when compared with the control. In a second study, Tg.AC mice were administered the classical photocarcinogen 8-MOP (8 mg/kg intragastric in corn oil) followed by 2 J/cm2 UVA 1-2 h later, five times every 2 weeks on a repetitive schedule. The second group received 8-MOP, whereas the third was exposed to UVA alone. Papillomas began to appear at 2 weeks in the 8-MOP-UVA group, and after 17 weeks the mean numbers of papillomas/mouse +/- SD (% responding) were: 8-MOP-UVA, 6.9 +/- 8.6 (93%); UVA + corn oil, 1.1 +/- 1.2 (69%) and 8-MOP, 1.1 +/- 1.6 (50%). The maximum tumor yield in the 8-MOP-UVA group was significantly higher (P < 0.01) than that in the other two groups. Our findings suggest that more studies need to be done before the Tg.AC mouse can be used with confidence to identify parenterally administered photocarcinogens.     

Modulation of 8-Methoxypsoralen-Photoinduced Cutaneous Inflammatory Reactions by Various Chemotherapeutic Agents in vivo

Abstract— Exposure of albino rabbits to UVA-VIS (320-700 nm) radiation after the topical application of 8-methoxypsor-alen (8-MOP) cream is associated with acute cutaneous inflammatory reactions in situ. In the present studies the effects of various agents on 8-MOP plus light induced cutaneous inflammatory response viz. increase in vascular permeability (iVP), accumulation of polymorphonuclear leukocytes (aPMN) and erythema formation were investigated. The inflammatory reactions were induced by a single exposure of 8-MOP-sensitized sites to UVA-VIS (9.4J/cm²) light. Indomethacin, p-bromophenacyl bromide (BPAB), MK886 (trade name of Merck Sharpe & Dome), ibuprofen (IB), nordihydroguaiaretic acid (NDGA) or quinacrine were applied topically in cream base at various times prior to 8-MOP application. The iVP and aPMN were quantitated 24 h postirradiation using ^12SI-HSA and ⁵¹Cr-labeled PMN respectively, while erythema was graded visually. The rate of iVP, aPMN and erythema was inhibited almost completely by indomethacin (7.5-10%) when applied twice, 18 h and 3 h prior to 8-MOP. At lower concentrations of indomethacin (5%) iVP was inhibited whereas aPMN was augmented. The BPAB (0.25%) inhibited more than 90% of 8-MOP-photoinduced iVP and aPMN while there was partial reduction in erythema. The MK886 (0.1%) cream inhibited about 50% of iVP and aPMN but erythema persisted. The agents that are somewhat nonspecific such as IB, quinacrine and NDGA inhibited 8-MOP-photoinduced inflammation only marginally at the concentrations tested. The fact that iVP, aPMN and erythema can be dissociated suggests that there are independent variables in 8-MOP-photoinduced reactions, which involve multifactorial mechanisms probably controlled by different cell-signalling pathways and mediators.     

Evaluation of the protective effect of sunscreens on in vitro reconstructed human skin exposed to UVB or UVA irradiation

We have previously shown that skin reconstructed in vitro is a useful model to study the effects of UVB and UVA exposure. Wavelength-specific biological damage has been identified such as the formation of sunburn cells (SBC) and pyrimidine dimers after UVB irradiation and alterations of dermal fibroblasts after UVA exposure. These specific effects were selected to evaluate the protection afforded by two sunscreens after topical application on the skin surface. Simplified formulations having different absorption spectra but similar sun protection factors were used. One contained a classical UVB absorber, 2-ethylhexyl-p-methoxycinnamate. The other contained a broad-spectrum absorber called Mexoryl SX, characterized by its strong absorbing potency in the UVA range. Both filters were used at 5% in a simple water/oil vehicle. The evaluation of photoprotection on in vitro reconstructed skin revealed good efficiency for both preparations in preventing UVB-induced damage, as shown by SBC counting and pyrimidine dimer immunostaining. By contrast, only the Mexoryl SX-containing preparation was able to efficiently prevent UVA-specific damage such as dermal fibroblast disappearance. Our data further support the fact that skin reconstructed in vitro is a reliable system to evaluate the photoprotection provided by different sunscreens against specific UVB and UVA biological damage.     

High-performance liquid chromatographic measurement of 8-methoxypsoralen in plasma

Summary A simple high-performance liquid chromatographic method for the measurement of 8-Methoxypsoralen (8-MOP) in human plasma following a single 40mg dose has been described. After addition of phosphate-NaOH buffer, pH 12, and internal standard (trimethylpsoralen), the sample is vortex-mixed with diisopropylether. The resulting extract is analysed on a reverse phase column using phosphoric acid (0.05% v/v): acetonitrile (1:1) as mobile phase, and U.V. detection at 220nm. No interference from endogenous sources has been observed. The limit of sensitivity of the assay is 5ng/ml plasma. The measuring range is between 10–700ng 8-MOP/ml plasma, to be expected from oral doses of 0.6mg 8-MOP/kg body weight, and corresponds to the therapeutic plasma concentration. The relative standard deviation at 50ng/ml level of 8-MOP is 3.6%.     

Surfactant adsorption at the metal-oil interface

The structure of the adsorbed palmitic acid at the iron oxide/oil interface has been investigated using polarized neutron reflectometry. The palmitic acid was found to be strongly adsorbed at the oxide/oil interface resulting in a monolayer of thickness 16 ± 4 ? for 150 and 500 ppm palmitic acid concentrations (16 ± 5 ? for the 1000 ppm solution). These layer thicknesses suggest tilt for the palmitic acid molecules with respect to the interface. The model also requires a second diffuse layer extending in the bulk oil. The thickness of this diffuse layer was 35 ± 17 ? for the 150 ppm solution and 45 ± 22 ? for 500 and 1000 ppm solution. The composition profiles at the interface suggest a depletion of the oil in the vicinity of the interface as the concentration of palmitic acid increases.     

Relative affinity of 5-methoxypsoralen and 8-methoxypsoralen towards beta-cyclodextrin: a fluorescence, circular dichroism and chromatographic study

The relative affinity of 5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP) towards beta-cyclodextrin, a good model for the study of lipophilic interactions in biological systems and a potential drug carrier, has been investigated using spectroscopic and chromatographic methods. The fluorescence emission of 5-MOP in aqueous solution containing beta-cyclodextrin (10(-2) M) is found to be markedly blue shifted and enhanced by a factor of 6 whereas no significant changes are observed for 8-MOP. The existence of an induced circular dichroism is evidence for the formation of a 1:1 inclusion complex (association constant K = 400 +/- 50 M-1). Moreover, chromatographic results obtained with a beta-cyclodextrin linked stationary phase are consistent with our spectroscopic results and might have interesting analytical implications. These results clearly demonstrate that, in contrast to 8-MOP, 5-MOP exhibits a strong affinity for hydrophobic medium. Interesting pharmacological and analytical applications may result from the possible inclusion of psoralen derivatives into beta-cyclodextrin.     

ACTIVATION OF THE HUMAN IMMUNODEFICIENCY VIRUS PROMOTER BY UVA RADIATION IN COMBINATION WITH PSORALENS OR ANGELICINS

Abstract— The effects of mono- and bifunctional furocoumarins plus UVA radiation (PUVA and related treatments) on the human immunodeficiency virus-1 (HIV-1) promoter were studied using HeLa cells stably transfected with the chloramphenicol acetyl transferase gene under the control of the HIV-1 promoter. The experiments were performed with three psoralens (5-methoxypsoralen, 5-MOP; 8-methoxypsoralen, 8-MOP; and 4′-aminomethyl-4,8,5′-trimethyl-psoralen, AMT) and four angelicins (angelicin; 4,5′-diniethylangclicin, 4,5′-DMA; 6,4′-dimethylangelicin, 6,4′-DMA; and 4,6,4′-trimethylangelicin, TMA). The drugs alone and UVA radiation alone showed no erect on the HIV promoter. However, when the cells were incubated with the furocoumarins at 0.1–40 μg/mL and then irradiated. the HIV promoter was activated in distinct fluence ranges, i.e. (1) no promoter activity was discernible at low fluences (e.g. at 0.1 μg/mL of 8-MOP up to 100 kJ/m²), (2) as the fluence was increased, the promoter activity increased to reach a maximum (10–50-fold with respect to the unexposcd samples), and (3) as the fluence was further increased, the promoter activity decreased. Similar (although shifted on the fluence scale) pattcrns were observed with either > 340-nm UVA radiation or with UVA radiation contaminated with a small amount of UVB radiation (typical for PUVA lamps). The effective fluences were inversely related to the drug concentration. Experiments with 5-MOP and 8-MOP indicated reciprocity of the drug concentration and radiation hence. The HIV promoter response patterns were similar for monofunctional angelicins and bifunctional psoralens. This indicated that the furocoumarin-DNA crosslinks are not a prerequisite for the promoter activation and that the monoadducts suffice to elicit the HIV promoter response. The HIV promoter-activating effectiveness of diKcrent drugs correlated with their photosensitizing potential. Thus, among psoralens the effectiveness order was AMT >. 5-MOP >8-MOP, and among angelicins: TMA > 6,4′-DMA > 4,5′-DMA > angelicin. The ektiveness did not vary substantially for 5-MOP, 8-MOP, 4,5′-DMA, and 6,4′-DMA. The combined drug and UVA radiation doses were higher than those that elicit cellular responses or those that may be received by the human white blood cells during cxtracorporeal PUVA therapy (photopheresis).     

Sunscreens Protect from UV-Promoted Squamous Cell Carcinoma in Mice Chronically Irradiated with Doses of UV Radiation Insufficient to Cause Edema

Previously we reported that the broad-spectrum sunscreen microfine titanium dioxide (MTD) could completely protect C3H/HeJ mice from UV radiation-induced immunosuppression to a contact sensitizer. In contrast, 2-ethylhexyl p-methoxycinnamate (2-EHMC), a UVB-absorbing sunscreen, only partially protected the skin immune system. In this study we investigated further this differential protection of the skin immune system by comparing the ability of 2-EHMC and MTD to protect these mice from the promotion phase of tumorigenesis. The mice were initiated using a single subcarcinogenic dose of 7,12-dimethylbenz(a)anthracene (DMBA) followed by promotion with chronic low-dose solar-simulated UV radiation for 32 weeks. We used doses of UV insufficient to cause edema in order to simulate daily human exposure to solar UV radiation. Mice were observed for the appearance of squamous cell carcinomas for 48 weeks. The DMBA-initiation alone and DMBA-initiated, sunscreen-treated groups did not develop tumors. Ultraviolet alone induced the appearance of tumors in 46% of mice at week 48 and therefore some tumors were initiated by UV. Initiation with DMBA prior to UV irradiation enhanced tumorigenesis such that 87% of mice at week 48 had tumors. Both 2-EHMC and MTD completely protected these mice from UV-induced promotion as well as from complete carcinogenesis despite the different UV-absorption spectra of the sunscreens and their differential abilities to protect from UV-induced immunosuppression. Furthermore, we have shown that, if UV exposure is not increased to compensate for tolerance to edema, protection from tumorigenesis is afforded by sunscreens.     

Comparative efficacy of Eucalyptus globulus (Labill) hydrodistilled essential oil and temephos as mosquito larvicide

Abstract

In this study Eucalyptus globulus essential oil was tested on major mosquito species and toxicity was compared with temephos. Mortality was calculated after 24?h and 48?h post treatment. In 24?h treatment essential oil show strong larvicidal activity with LC₅₀ and LC₉₀ values were 30.198ppm, 103.389ppm for Anopheles stephensi, 13.578ppm, 106.755ppm for Aedes aegypti; and, 7.469ppm, 32.454ppm for Culex quinquefasciatus and 48?h post treatment LC₅₀ and LC₉₀ values were, 12.576, 49.380ppm for Anopheles stephensi, 7.926, 34.470ppm for Aedes aegypti and 4.408, 21.048ppm for Culex quinquefasciatus. Chemical composition of essential oil using GC-MS and FT-IR analysis shows the presence of 1,8-cineol, (71.7%); α-pinene, (9.14%) as a major compounds. Our findings suggest that essential oil from Eucalyptus globulus leaves can be used for control of mosquito larvae.     

Tracing the Photoaddition of Pharmaceutical Psoralens to DNA

The psoralens 8-methoxypsoralen (8-MOP), 4,5′,8-trimethylpsoralen (TMP) and 5-methoxypsoralen (5-MOP) find clinical application in PUVA (psoralen + UVA) therapy. PUVA treats skin diseases like psoriasis and atopic eczema. Psoralens target the DNA of cells. Upon photo-excitation psoralens bind to the DNA base thymine. This photo-binding was studied using steady-state UV/Vis and IR spectroscopy as well as nanosecond transient UV/Vis absorption. The experiments show that the photo-addition of 8-MOP and TMP involve the psoralen triplet state and a biradical intermediate. 5-MOP forms a structurally different photo-product. Its formation could not be traced by the present spectroscopic technique.