Photoinduced covalent binding of frusemide and frusemide glucuronide to human serum albumin.
OBJECTIVE
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 warfarin-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.
Mizuma
T
T
Department of Biopharmaceutical Science, University of California, San Francisco 94143, USA.
McDonagh
A F
AF
Lin
E T
ET
Benet
L Z
LZ
D001667:Binding, Competitive / Q000528:radiation effects; D004232:Diuretics / Q000737:chemistry / Q000494:pharmacology* / Q000528:radiation effects; D004355:Drug Stability; D005665:Furosemide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology* / Q000528:radiation effects; D006801:Humans; D010777:Photochemistry; D012709:Serum Albumin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013472:Sunlight
D004232:Diuretics; D012709:Serum Albumin; C036234:furosemide glucuronide; D005665:Furosemide