Comparison of the Metabolic Capacity Between Human and Porcine Liver Microsomes

Organ transplantation is currently the treatment of choice for end stage organ diseases. However, organ shortages have greatly limited the number of patients who may receive organ transplantation. Even with the use of organs from living-donors, the number of patients on the waiting list continues to increase every day. It is critical to find a solution for the organ shortages. Xenotransplantation, a process of transplanting organs from one species to another has received much attention over the past several years. Pig has been identified as an ideal organ donor for xenotransplantation. Researchers have successfully produced pigs with gene editing and human gene insertion. Liver is the second most transplanted organ and the primary organ that metabolizes endogenous and exogenous chemicals. Given that transplant patients receive treatment with several drugs that are metabolized, it is essential to understand the metabolic capacity of pig livers. This study compares the metabolism of testosterone by human and porcine liver microsomes. The formation of five typical testosterone metabolites were evaluated, highlighting the metabolic differences between the two species. Comparison of enzyme activities and production rates of major and minor metabolites revealed that both human and pig microsomes primarily produced 6β-hydroxytestosterone (6β-OHT) as the major metabolite. Human microsomes generally produced more 6β-OHT and exhibited higher enzyme activity compared to pig microsomes. Among the minor metabolites, human microsomes produced 2⍺-hydroxytestosterone (2⍺-OHT) and 6⍺-hydroxytestosterone (6⍺-OHT), while pig microsomes did not produce any detectable amount of 2⍺-OHT. The study observed a decline in the enzyme activity for 6β-OHT production over time for both human and pig microsomes, potentially due to NADPH depletion, autoinhibition, or enzyme denaturation. At 60 minutes, the concentrations of certain metabolites, including 6β-OHT and 16β-hydroxytestosterone (16β-OHT), were lower than at earlier time points, suggesting further transformation or breakdown of metabolites. By providing detailed metabolic profiles and enzyme activity comparisons, this research contributes to the foundational knowledge necessary for understanding drug metabolism in human and porcine liver microsomes, which will be critical for advancing xenotransplantation of the liver.