Patients with erythropoietic protoporphyria (EPP) experience symptoms of photosensitivity (erythema, pruritus, burning, and edema) on sunlight exposure.1 This is due to a photo-oxidation reaction sensitized by protoporphyrin, which accumulates because of a defect in the enzyme ferrochelatase. Beta-carotene, an antioxidant and excited species quencher, prevents or lessens the symptoms in many patients1,2 but may be expensive and causes carotenodermia. We had previously found that some thiols quenched photo-oxidative damage induced by endogenous and exogenous porphyrins in various organs of mice, including skin.3 Thiols also quench singlet oxygen and free radicals. Hence, we decided to investigate an alternative therapy using the amino acid cysteine, which also has been shown to act as a radioprotective agent and has excited species quenching activity. Most importantly, unlike other thiol radioprotective agents, cysteine causes little or no toxic effects in man.4
Patients with documented EPP living in the area of Boston,
Roberts JE, Mathews-Roth M. Cysteine Ameliorates Photosensitivity in Erythropoietic Protoporphyria. Arch Dermatol. 1993;129(10):1350–1351. doi:10.1001/archderm.1993.01680310122031
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