Sulphate conjugation enhances reversible binding of drug to human serum albumin.
Reversible binding of model compounds, their conjugated metabolites (sulphates and glucuronides), and also derivatives of the compounds, to human serum albumin (HSA) has been examined using an ultrafiltration method. p-Nitrophenol (p-NP), alpha-naphthol (alpha-NA) and beta-naphthol (beta-NA) were used as model compounds. Reversible binding of 500 microM p-NP sulphate to 4% HSA (96.6 +/- 0.35%, mean +/- s.d. n = 3) was significantly higher (P less than 0.001), whereas reversible binding of p-NP glucuronide to 4% HSA (33.3 +/- 9.82%) was much lower (P less than 0.001) than that of 500 microM p-NP (90.9 +/- 0.60%). Reversible binding of 500 microM p-NP glucopyranoside to 4% HSA (25.8 +/- 2.82%) was comparable with that of the glucuronide, with which it is structurally similar. In contrast, reversible binding of 500 microM p-NP phosphate, an anionic compound like p-NP sulphate, to 4% HSA (61.4 +/- 5.28%) was significantly lower than that of p-NP (P less than 0.001). Similar results were observed in reversible binding of sulphates of alpha-NA and beta-NA. Significant differences of dissociation constants for HSA binding were observed between the parent compound (alpha- or beta-NA) and its sulphate conjugate (P less than 0.005 for alpha-NA and alpha-NA sulphate, P less than 0.001 for beta-NA and beta-NA sulphate), but the number of binding sites was the same. These results indicated that sulphate conjugation enhances reversible binding of a parent compound to HSA by increasing the binding affinity of the parent compound to HSA. This enhancement appeared to be advantageous for preventing random distribution of this metabolite to organs in the body.
Department of Hospital Pharmacy, Toyama Medical and Pharmaceutical University, Japan.
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Mizuma
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Komori
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Ueno
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Horikoshi
D000082:Acetaminophen / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D009284:Naphthols / Q000378:metabolism; D009288:Naproxen / Q000378:metabolism; D009596:Nitrophenols / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011485:Protein Binding; D012709:Serum Albumin / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*
D009284:Naphthols; D009596:Nitrophenols; D004364:Pharmaceutical Preparations; D012709:Serum Albumin; D013431:Sulfates; C029350:1-naphthol; D000082:Acetaminophen; D009288:Naproxen; C028405:2-naphthol; C024836:4-nitrophenol