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Photoinduced covalent binding of frusemide and frusemide glucuronide to human serum albumin
Author(s) -
Mizuma§ Takashi,
McDonagh Antony F.,
Lin Emil T.,
Benet Leslie Z.
Publication year - 1999
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1046/j.1365-2125.1999.00970.x
Subject(s) - human serum albumin , chemistry , covalent bond , binding site , phototoxicity , quenching (fluorescence) , naproxen , tryptophan , fluorescence , photochemistry , biochemistry , organic chemistry , amino acid , medicine , physics , alternative medicine , pathology , quantum mechanics , in vitro
Aims To study reaction of photoactivated frusemide (F) and F glucuronide (Fgnd metabolite) with human serum albumin in order to find a clue to clarify a mechanism of phototoxic blisters from high frusemide dosage.Methods F was exposed to light in the presence of human serum albumin (HSA). HSA treated with this method (TR‐HSA) was characterized by fluorescence spectroscopic experiment, alkali treatment and reversible binding experiment.Results Less 4‐hydroxyl‐N ‐furfuryl‐5‐sulphamoylanthranilic acid (4HFSA, a photodegradation product of F) was formed in the presence of HSA than in the absence of HSA. A new fluorescence spectrum excited at 320 nm was observed for TR‐HSA. Alkali treatment of TR‐HSA released 4HFSA. Quenching of the fluorescence due to the lone tryptophan near the warfarin‐binding site of HSA was observed in TR‐HSA. The reversible binding of F or naproxen to the warfarin‐binding site of TR‐HSA was less than to that of native HSA. These results indicate the photoactivated F was covalently bound to the warfarin‐binding site of HSA. The covalent binding of Fgnd, which is also reversibly bound to the wafarin‐binding site of HSA, was also induced by exposure to sunlight. Fgnd was more photoactive than F, indicating that F could be activated by glucuronidation to become a more photoactive compound.Conclusions The reactivity of photoactivated F and Fgnd to HSA and/or to other endogenous compounds may cause the phototoxic blisters that result at high F dosage.