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Differential kinetic profiles and metabolism of primaquine enantiomers by human hepatocytes.

Fasinu PS, Avula B, Tekwani BL, Nanayakkara NP, Wang YH, Bandara Herath HM, McChesney JD, Reichard GA, Marcsisin SR, Elsohly MA, Khan SI, Khan IA, Walker LA - Malar. J. (2016)

Bottom Line: The major quinoline oxidation product (m/z 274) was preferentially generated from (+)-PQ.Metabolism of PQ showed enantioselectivity.These findings may provide important information in establishing clinical differences in PQ enantiomers.

View Article: PubMed Central - PubMed

Affiliation: The National Center for Natural Products Research, School of Pharmacy, The University of Mississippi, University, MS, 38677, USA.

ABSTRACT

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 (13)C-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 (λ) of 0.19 and 0.64 h(-1); intrinsic clearance (Clint) of 2.55 and 8.49 (µL/min)/million cells, which when up-scaled yielded Clint 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.

No MeSH data available.


Related in: MedlinePlus

A time-course analysis of the in vitro generation of a carboxyprimaquine (1), b primaquine alcohol (2) and c, d their glucuronide conjugates (5, 6), from (+)-, (−)- and (±)-primaquine in human hepatocytes. Each point represents value mean ±SD of four observations
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Fig4: A time-course analysis of the in vitro generation of a carboxyprimaquine (1), b primaquine alcohol (2) and c, d their glucuronide conjugates (5, 6), from (+)-, (−)- and (±)-primaquine in human hepatocytes. Each point represents value mean ±SD of four observations

Mentions: The major deaminated metabolite, CPQ (Fig. 2—1) (75 % of which was generated within 30 min), was preferentially generated from the (−)-PQ, when compared to (+) PQ (about 8:1 at early time points) (Fig. 4a). This metabolite has been shown earlier to be the major product of PQ biotransformation circulating in the plasma of mice [23], monkeys [9] and humans [15]. It is formed through the oxidative deamination of the 8-N-aminoalkyl side chain of PQ to an intermediate PQ aldehyde which is further converted to the carboxylic acid by an aldehyde dehydrogenase. The PQ aldehyde formed from PQ may also undergo a reduction reaction to form the primaquine alcohol (m/z 261; Fig. 2—2), or cyclization of the side chain through the loss of a water molecule (m/z 241, Fig. 2—3). Further metabolism of CPQ involves the elimination of water and cyclization to the 8-amino group forming a lactam product (m/z 257, Fig. 2—4). CPQ and the PQ alcohol undergo conjugation reactions with glucuronides (m/z 451 and 437 respectively; Fig. 2—5, 6) is also formed from hydroxylated CPQ. These metabolites of the oxidative deamination of the amino side chains were preferentially generated from the (−)-PQ compared to (+)-PQ (Fig. 5a, b, c).Fig. 4


Differential kinetic profiles and metabolism of primaquine enantiomers by human hepatocytes.

Fasinu PS, Avula B, Tekwani BL, Nanayakkara NP, Wang YH, Bandara Herath HM, McChesney JD, Reichard GA, Marcsisin SR, Elsohly MA, Khan SI, Khan IA, Walker LA - Malar. J. (2016)

A time-course analysis of the in vitro generation of a carboxyprimaquine (1), b primaquine alcohol (2) and c, d their glucuronide conjugates (5, 6), from (+)-, (−)- and (±)-primaquine in human hepatocytes. Each point represents value mean ±SD of four observations
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4837544&req=5

Fig4: A time-course analysis of the in vitro generation of a carboxyprimaquine (1), b primaquine alcohol (2) and c, d their glucuronide conjugates (5, 6), from (+)-, (−)- and (±)-primaquine in human hepatocytes. Each point represents value mean ±SD of four observations
Mentions: The major deaminated metabolite, CPQ (Fig. 2—1) (75 % of which was generated within 30 min), was preferentially generated from the (−)-PQ, when compared to (+) PQ (about 8:1 at early time points) (Fig. 4a). This metabolite has been shown earlier to be the major product of PQ biotransformation circulating in the plasma of mice [23], monkeys [9] and humans [15]. It is formed through the oxidative deamination of the 8-N-aminoalkyl side chain of PQ to an intermediate PQ aldehyde which is further converted to the carboxylic acid by an aldehyde dehydrogenase. The PQ aldehyde formed from PQ may also undergo a reduction reaction to form the primaquine alcohol (m/z 261; Fig. 2—2), or cyclization of the side chain through the loss of a water molecule (m/z 241, Fig. 2—3). Further metabolism of CPQ involves the elimination of water and cyclization to the 8-amino group forming a lactam product (m/z 257, Fig. 2—4). CPQ and the PQ alcohol undergo conjugation reactions with glucuronides (m/z 451 and 437 respectively; Fig. 2—5, 6) is also formed from hydroxylated CPQ. These metabolites of the oxidative deamination of the amino side chains were preferentially generated from the (−)-PQ compared to (+)-PQ (Fig. 5a, b, c).Fig. 4

Bottom Line: The major quinoline oxidation product (m/z 274) was preferentially generated from (+)-PQ.Metabolism of PQ showed enantioselectivity.These findings may provide important information in establishing clinical differences in PQ enantiomers.

View Article: PubMed Central - PubMed

Affiliation: The National Center for Natural Products Research, School of Pharmacy, The University of Mississippi, University, MS, 38677, USA.

ABSTRACT

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 (13)C-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 (λ) of 0.19 and 0.64 h(-1); intrinsic clearance (Clint) of 2.55 and 8.49 (µL/min)/million cells, which when up-scaled yielded Clint 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.

No MeSH data available.


Related in: MedlinePlus