Stereoselective sulfation of albuterol in humans. Biosynthesis of the sulfate conjugate by HEP G2 cells

• Published in: Drug metabolism and disposition Vol. 21; no. 1; p. 76
• Main Authors: Walle, T, Walle, U K, Thornburg, K R, Schey, K L
• Format: Journal Article
• Language: English
• Published: United States 01.01.1993
• Subjects: Albuterol - metabolism; Chromatography, High Pressure Liquid - methods; Culture Media; Humans; Kinetics; Liver Neoplasms - metabolism; Mass Spectrometry; Stereoisomerism; Sulfates - metabolism; Tumor Cells, Cultured
• ISSN: 0090-9556

The objective of this study was to test the utility of the human hepatoma cell line Hep G2 for the biosynthesis of the sulfate conjugate of the beta 2-agonist drug albuterol and to determine the stereo-chemistry of the sulfation reaction. Albuterol was, together with Na(2)35SO4, incubated with Hep G2 cells for 48 hr at 37 degrees C. After precipitation of the inorganic sulfate and protein in the medium, the radiolabeled albuterol sulfate formed was isolated by reversed-phase HPLC. The structure of the sulfate conjugate was determined by liquid secondary ion MS and tandem MS, producing a clear molecular ion and a characteristic fragmentation pattern, respectively. The maximum yield from a 100 mm culture dish was 400 micrograms, sufficient for structure identification as well as for development of stereospecific methodology. Efforts to increase the yields by increasing inorganic sulfate or using dexamethasone as an inducer produced only modest effects. Resolution of the albuterol sulfate enantiomers by HPLC, after chiral derivatization, showed a clear preference for the sulfation of (-)-albuterol. This was also shown in kinetic experiments with the individual enantiomers, using cell homogenates, which gave apparent KM values of 115 microM and 528 microM for (-)- and (+)-albuterol, respectively, with an apparent Vmax value 1.7 times higher for (-)-albuterol. The efficiency of sulfation (Vmax/KM) was thus 7.8-fold higher for the pharmacologically more active (-)-enantiomer. Based on these observations, considerably higher bioavailability of (+)- than of (-)-albuterol may be anticipated after oral or inhaled doses of this drug.