Ultraviolet phototoxicity

Sambuco (1985) has described the sunburn response of the Yucatan minipig to ultraviolet (UV) light, suggesting that this species would also make a good model in phototoxicity as well as photocontact dermatitis studies. Thirty 12-cm sites were demarcated, permitting the study of 15 different dermal dosages of UV radiation. 

As public consciousness of the harmful effects of exposure to ultraviolet light (skin cancer, premature ageing, etc.) has increased, there has been a substantial increase in the use of sunscreens. These sunscreens have, however, been associated with a number of reported problems such as phototoxicity and photoallergy. The use of p-aminobenzoic acid (PABA) and its derivatives has been discontinued due to their ability to... 

A well-investigated group of potent phototoxic compounds are the/wra-nocoumarins (psoralens) (Fig. 11.16), compounds that are also used as fish poisons. Furocoumarins absorb ultraviolet at around 330 nm and are converted to triplet stages these, in turn, produce singlet oxygen that damages amino acids (Fig. 11.17). 

Components of pitch and coal tar produce cutaneous photosensitization skin eruptions usually are limited to areas exposed to ultraviolet light. " Most of the phototoxic agents will induce hypermelanosis of the skin if chronic photodermatitis is severe and prolonged, leukoderma may occur." Some oils containing PNAs have been associated with follicular and sebaceous gland changes, which commonly take the form of acne. ... 

Photosensitivity Photosensitization (photoallergy or phototoxicity) may occur therefore, caution patients to take protective measures (ie, sunscreens, protective clothing) against exposure to sunlight or ultraviolet light (eg, tanning beds) until tolerance is determined. 

Phototoxicity Moderate-to-severe phototoxic reactions have occurred in patients exposed to direct or indirect sunlight or to artificial ultraviolet light (eg, sunlamps) during or following treatment with lomefloxacin, sparfloxacin, or ofloxacin. 

Ultraviolet and visible light Phototoxicity potential assessed by 3T3 phototoxicity test... 

Phototoxicity occurs when skin exposed to sunlight, especially in the UVA region of 320 to 400 nm, reddens and develops blisters as a consequence of the presence of certain chemical species. The phototoxic chemical species that result in such reactions are ones to which an individual is exposed either directly on the skin or systemically. These compounds absorb ultraviolet radiation and, like the porphyrins discussed above, enter excited states interacting with 02 to generate destructive oxidant species and free radicals. Numerous chemical species, including furocoumarins, polycyclic aromatic hydrocarbons, tetracyclines, and sulfonamides, can be phototoxic. 

Furanocoumarins Also called furocoumarins, methoxypsoralens or bergaptenes. Found in cold-pressed citrus oils, e.g. bergamot. An oxygen-containing cyclic structure associated with phototoxicity on exposure to ultraviolet light. 

Phototoxicity Phototoxicity, for example, severe sunburn, occurs when the patient receiving a tetracycline is exposed to sun or ultraviolet rays. This toxicity is encountered most frequently with tetracycline, doxycydine, and demeclocycline [dem e kloe SYE kleen],... 

An Australian dermatologist has reported three cases of phototoxic reactions to St. John s wort (14). The patients were fair-skinned and had had significant exposure to ultraviolet light. In two cases St. John s wort was applied topically. In all cases complete recovery occurred after withdrawal of St. John s wort and cessation of exposure to ultraviolet light. 

Phototoxic reactions occurred in 10 patients with malignant melanoma when they were given dacarbazine (6). In five patients who were tested there was increased sensitivity to ultraviolet A patch-testing in six showed no type IV allergies. In five patients oral temozolomide did not cause phototoxicity. 

Precautions are necessary to avoid ultraviolet radiation after taking photoreactive drugs (38). Metabolism of hn-comycin can lead to the formation of reactive oxygen species and cause tissue injury and damage to various cellular macromolecules, which can result in phototoxicity. Typical photosensitivity with a maculopapular eruption has been observed with hncomycin in two patients treated intramuscularly (6). 

Two patients had localized and disseminated bullous phototoxic skin reactions 48-72 hours after exposure to bergamot aromatherapy and ultraviolet light (4). One developed bullous skin lesions after exposure to aerosolized aromatherapy oil in a sauna. 

Acetylenic isobutylamides and polyacetylenes occurring in Echinacea have been shown to inhibit the growth of yeast strains of Saccharomyces cerevisiae, Candida shehata, Candida kefyr, Candida albicans, Candida steatulytica, and Candida tropicalis. This growth inhibition occurred to a greater extent under ultraviolet irradiation than without it. There are other compounds in Echinacea that are suspected to be phototoxic to microbes, but this has yet to be demonstrated (16). 

Fluoroquinolones such as ofloxacin, enoxacin, lomefloxacin and ciprofloxacin have been shown to cause cutaneous phototoxicity and photosensitivity in mice induced by oral administration followed by ultraviolet-A irradiation. These reactions have further been shown to be mediated via reactive oxygen species such as hydroxyl radicals and singlet oxygens and not by generation of toxic photoproducts (44). 

In vitro studies have demonstrated that. vera latex derived anthraquinones in presence to ultraviolet light A (UVA) exhibited significant photo-oxidative damage to both cellular RNA and DNA 61). Several studies on photostability and phototoxicity of A vera extracts indicate that in presence of UV light it can generate the formation of free radicals 62, 63). 

R.A. Larson, M.R. Berenbaum (1988). Environmental phototoxicity solar ultraviolet radiation affects the toxicity of natural and man-made chemicals. Environ. Sci. Technol., 22, 354-360. 

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