title: Effect of sialic acid residues of human alpha 1-acid glycoprotein on stereoselectivity in basic drug-protein binding.
abstract: The function of sialic acid groups at the terminal of sugar chains of human alpha 1-acid glycoprotein (AGP) was investigated with respect to chiral discrimination between optical isomers of basic drugs, using high-performance capillary electrophoresis/frontal analysis (HPCE/FA), a novel analytical method developed for the determination of unbound drug concentration with ultramicrosample volume (100-200 nl). Native human AGP and desialylated AGP were used as test proteins, and propranolol (PRO) and verapamil (VER) were used as model drugs. The unbound concentration of (S)-VER was 1.31 times higher than that of (R)-VER in native AGP solution. This selectivity was not affected by desialylation. Further, enzymatic elimination of galactose residues, which neighbored sialic acid groups, did not change the binding of either isomer of VER. On the other hand, the unbound concentration of (R)-PRO was 1.27 times higher than that of (S)-PRO in native AGP solution. Desialylation caused the unbound concentration of (S)-PRO to rise to the same level of (R)-PRO, resulting in loss of enantioselectivity. Thus, it follows that sialic acid groups of AGP, as a whole, are not responsible for chiral recognition between enantiomers of VER but are involved in enantioselectivity toward the isomers of PRO.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kyoto University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Shiono
authors.forename: A
authors.initials: A
authors.lastname: Shibukawa
authors.forename: Y
authors.initials: Y
authors.lastname: Kuroda
authors.forename: T
authors.initials: T
authors.lastname: Nakagawa
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000737:chemistry / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D019075:Electrophoresis, Capillary; D006801:Humans; D009961:Orosomucoid / Q000737:chemistry*; D011433:Propranolol / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D012794:Sialic Acids / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D014700:Verapamil / Q000737:chemistry / Q000378:metabolism
chemical_list: D000319:Adrenergic beta-Antagonists; D001798:Blood Proteins; D002121:Calcium Channel Blockers; D009961:Orosomucoid; D012794:Sialic Acids; D011433:Propranolol; D014700:Verapamil