It is known that the majority of
cocaine users also consume alcohol. Alcohol can react with
cocaine to produce a significantly more cytotoxic compound,
cocaethylene. Hence a truly valuable
cocaine-metabolizing
enzyme as treatment for
cocaine abuse/overdose should be efficient for not only
cocaine itself, but also
cocaethylene. The catalytic parameters (kcat and KM) of human BChE (
butyrylcholinesterase) and two mutants (known as
cocaine hydrolases E14-3 and E12-7) for
cocaethylene are characterized in the present study, for the first time, in comparison with those for
cocaine. On the basis of the obtained kinetic data, wild-type human BChE has a lower catalytic activity for
cocaethylene (kcat=3.3 min(-1), KM=7.5 μM and kcat/KM=4.40 × 10(5) M(-1)·min(-1)) compared with its catalytic activity for (-)-
cocaine. E14-3 and E12-7 have a considerably improved catalytic activity against
cocaethylene compared with the wild-type BChE. E12-7 is identified as the most efficient
enzyme for hydrolysing
cocaethylene in addition to its high activity for (-)-
cocaine. E12-7 has an 861-fold improved catalytic efficiency for
cocaethylene (kcat=3600 min(-1), KM=9.5 μM and kcat/KM=3.79 × 10(8) M(-1)·min(-1)). It has been demonstrated that E12-7 as an exogenous
enzyme can indeed rapidly metabolize
cocaethylene in rats. Further kinetic modelling has suggested that E12-7 with an identical concentration as that of the endogenous BChE in human plasma can effectively eliminate (-)-
cocaine,
cocaethylene and
norcocaine in simplified kinetic models of
cocaine abuse and overdose associated with the concurrent use of
cocaine and alcohol.