Differential kinetic profiles and metabolism of primaquine enantiomers by human hepatocytes

作者：Fasinu, Pius S.; Avula, Bharathi; Tekwani, Babu L.; Nanayakkara, N. P. Dhammika; Wang, Yan-Hong; Herath, H. M. T. Bandara; McChesney, James D.; Reichard, Gregory A.; Marcsisin, Sean R.; Elsohly, Mahmoud A.; Khan, Shabana I.; Khan, Ikhlas A.; Walker, Larry A.^*

来源：Malaria Journal, 2016, 15(1): 224.

DOI：10.1186/s12936-016-1270-1

• Enantioselectivity
• Hepatocytes
• Malaria
• Metabolism
• Primaquine enantiomers
• Primaquine metabolites

Background: The clinical utility of primaquine (PQ), used as a racemic mixture of two enantiomers, is limited due to metabolism-linked hemolytic toxicity in individuals with genetic deficiency in glucose-6-phosphate dehydrogenase. The current study investigated differential metabolism of PQ enantiomers in light of the suggestions that toxicity and efficacy might be largely enantioselective. @@@ Methods: Stable isotope C-13-labelled primaquine and its two enantiomers (+)-PQ, (-)-PQ were separately incubated with cryopreserved human hepatocytes. Time-tracked substrate depletion and metabolite production were monitored via UHPLC-MS/MS. @@@ Results: The initial half-life of 217 and 65 min; elimination rate constants (lambda) of 0.19 and 0.64 h(-1); intrinsic clearance (Cl-int) of 2.55 and 8.49 (mu L/min)/million cells, which when up-scaled yielded Cl-int of 6.49 and 21.6 (mL/min)/kg body mass was obtained respectively for (+)-and (-)-PQ. The extrapolation of in vitro intrinsic clearance to in vivo human hepatic blood clearance, performed using the well-stirred liver model, showed that the rate of hepatic clearance of (+)-PQ was only 45 % that of (-)-PQ. Two major primary routes of metabolism were observed-oxidative deamination of the terminal amine and hydroxylations on the quinoline moiety of PQ. The major deaminated metabolite, carboxyprimaquine (CPQ) was preferentially generated from the (-)-PQ. Other deaminated metabolites including PQ terminal alcohol (m/z 261), a cyclized side chain derivative from the aldehyde (m/z 241), cyclized carboxylic acid derivative (m/z 257), a quinone-imine product of hydroxylated CPQ (m/z 289), CPQ glucuronide (m/z 451) and the glucuronide of PQ alcohol (m/z 437) were all preferentially generated from the (-)-PQ. The major quinoline oxidation product (m/z 274) was preferentially generated from (+)-PQ. In addition to the products of the two metabolic pathways, two other major metabolites were observed: a prominent glycosylated conjugate of PQ on the terminal amine (m/z 422), peaking by 30 min and preferentially generated by (+)-PQ; and the carbamoyl glucuronide of PQ (m/z 480) exclusively generated from (+)-PQ. @@@ Conclusion: Metabolism of PQ showed enantioselectivity. These findings may provide important information in establishing clinical differences in PQ enantiomers.

• 出版日期2016-4-19