Key result
UGT1A1 preferentially metabolizes R-carvedilol while UGT2B7 prefers S-carvedilol, and genetic mutations in these enzymes reduce metabolic capacity without altering stereoselectivity.
Genetic mutations in UGT1A1 (G71R) and UGT2B7 (A71S, H268Y) reduce the metabolic capacity for carvedilol but do not alter the stereoselective preference of these enzymes.
May inform carvedilol exposure in UGT variant carriers; leaves open human translation and clinical relevance.
Carvedilol, an alpha- and beta-adrenergic blocking drug, is mainly metabolized by CYP2D6, UGT1A1, UGT2B4 and UGT2B7. This drug is administered orally as a racemic mixture of R(+)- and S(-)-enantiomers. It has been reported that CYP2D6 prefers metabolizing S-carvedilol to R-carvedilol stereoselectively. On the other hand, stereoselective metabolism of carvedilol by UGTs is still unclear. Moreover, we have reported that patients with chronic heart failure who had polymorphism in CYP2D6, UGT1A1 and/or UGT2B7 had lower metabolic activity and oral clearance than did patients with no polymorphism. The aim of this study was to clarify stereoselective metabolism of carvedilol by UGT1A1 and UGT2B7 and to determine by using a recombinant enzyme-introduced mutation whether genetic mutation in UGT1A1 and UGT2B7 causes reduction in metabolic activity for carvedilol. A glucuronidation assay using human liver microsomes and recombinant UGT1A1 and UGT2B7 expressed in HeLa cells demonstrated that UGT1A1 prefers metabolizing R-carvedilol to S-carvedilol. On the other hand, UGT2B7 prefers metabolizing S-carvedilol to R-carvedilol. Moreover, G71R mutation of UGT1A1 reduced both affinity and capacity but did not affect stereoselective metabolism. On the other hand, both A71S and H268Y mutations of UGT2B7 reduced capacity but did not affect affinity and, as a result, the efficiency of metabolism was remarkably reduced. However, as in the case of UGT1A1, neither of the mutations affected stereoselective metabolism.
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Takekuma et al. (2007) studied this question. Carvedilol enantiomers (R- and S-carvedilol) was evaluated on Stereoselective glucuronidation and kinetic parameters (Km, Vmax). UGT1A1 preferentially metabolizes R-carvedilol while UGT2B7 prefers S-carvedilol, and genetic mutations in these enzymes reduce metabolic capacity without altering stereoselectivity.
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