Lamotrigine is an anticonvulsant that undergoes biotransformation by Phase II GST and UGT enzymes to yield a variety of glucuronidation and sulfation products. The major product in human is the N2-glucuronide conjugate, which is only observed in small concentrations in the rodent. Instead the rodent has a tendency to generate the primary oxidation product of the UGT pathway and the an assortment of sulfation products associated with the GST pathway. This study aimed to determine if significant levels of humanization allowed for more production of the N2-glucuronide products as one would expect to see in human.
Conjugation of glucuronic acid involves a hypothesized quaternary amine intermediate step that generates either the N2, or N5-glucuronide product of the parent molecule. The N2-glucuronide is the major product generated in humans.
The sulfation pathway has been shown experimentally to involve CYP2A6 aryl epoxide intermediates that are then converted to many unique glutathione products though GST enzymes. The chimeric animals demonstrate many of these conjugates both in wild-type and humanized strains.
Over the previous three year, the staff at Yecuris have run multiple experiments using lamotrigine as a probe substrate and have aggregated the data for illustrative purposes. The first sets of experiments involved the examination of the non-repopulated models (muFRG) to better understand what the baseline state of the models are. Wild-type C57Bl/6 and NOD male and female mice we compared against RG and FRG KO mice on the same strains and genders. No substantive differences were observed between any of the strains or genders, though we note that in other experiments with different compounds the immune deficient strains have demonstrated differences in physiological effect as compared to the wild-type controls. Here we include the combined data from all of the background experiments in one plot to compare the humanized animals against.
When humanized to any extent, we observe a modest increase in glutathione products. Significant increases in the desired human-specific metabolite, M3, are not seen in animals that reach 50% reconstitution. However, in animals that reach above 80% chimerism, significant formation of the M3 peak is observed.
