Background: The aim of this study is to determine the impact of species and tissue differences on the glucuronidation of diclofenac in vitro. Method: Microsomes from different species (rat, monkey, mouse, dog, and human) and rat and human tissues (liver, intestine, and kidney) were used to assess the rate of glucuronidation reaction of diclofenac. The metabolites were quantified using ultra high-performance liquid chromatography (UHPLC) and fitted into a Michaelis–Menten model to determine the metabolic kinetic parameters. Results: The results showed higher rates of metabolism in the liver as compared to that of the intestine and kidney by both human and rat tissues microsomes. There were also differences in the rate of metabolism in the liver across the tested species, with mouse liver microsome having the highest maximum reaction rate (V_max) at 7.22 nmol/min/mg followed by human liver microsome at 6.66 ± 0.33 nmol/min/mg, dog liver microsome at 5.05 ± 0.42 nmol/min/mg, monkey liver microsome at 3.88 ± 0.15 nmol/min/mg, and rat liver microsome at 0.83 ± 0.04 nmol/min/mg. Conclusions: This study demonstrated that the liver is the major organ for the glucuronidation of diclofenac. In addition, glucuronidation of diclofenac was different across the tested species; therefore, the influence of species should be taken into consideration in the pharmacological, pharmaceutical, and toxicological study of diclofenac.

Background: Peclinical and clinical studies have revealed that ezetimibe, an approved cholesterol-absorption inhibitor, is rapidly and extensively metabolized to a more potent metabolite, ezetimibe glucuronide. Since different species are commonly used in the pharmacokinetic and pharmacodynamic studies of ezetimibe, it is essential to determine the species difference in glucuronidation of ezetimibe in order to accurately evaluate ezetimibe’s pharmacokinetics and pharmacodynamics. The purpose of the study was to compare species differences in ezetimibe glucuronidation rates using intestinal microsomes from humans, rats, mice, monkeys, and dogs. Method: Intestinal microsomes from different species were used to assess the ezetimibe glucuronidation rates. Multiple substrate concentrations at 0.5, 2, 5, 10, 20, 30, 40, and 50 µM were tested and fitted into the Michaelis–Menten model to determine the enzyme kinetic parameters. Results: The results showed that the glucuronidation rates with these tested species were significantly different. Kinetic studies revealed that the maximum metabolic rate (V_max) was higher in monkeys (3.87 ± 0.22 nmol/mg/min) than that in rat (2.40 ± 0.148 nmol/mg/min) and mouse (2.23 ± 0.10 nmol/mg/min), and then human (1.90 ± 0.08 nmol/mg/min) and dog (1.19 ± 0.06 nmol/mg/min). The CLint was an 8.17-fold difference among these species, following the order of mouse > dog > human > rat = monkey. Conclusions: The study revealed that the rate of ezetimibe glucuronidation in the intestine was different in different species and has an impact on ezetimibe glucuronidation in the intestine. When analyzing the pharmacodynamics, pharmacokinetics, or toxicology of ezetimibe using different models, these species differences must be taken into consideration.

Alvocidib, an approved drug for the treatment of acute myeloid leukemia, undergoes glucuronidation metabolism.

Background: Diarrhea induced by an excessive amount of fat is a prevalent gastrointestinal disorder. Currently, there are limited animal models and treatment options for diarrhea associated with fat. This study aims to develop a mouse model of high-fat-associated diarrhea using glyceryl-trioleate (GTO) and evaluate the potential of montmorillonite clay (MMT) in mitigating this condition. Methods: GTO was administered to mice at different doses through oral gavage to induce diarrhea. Clay was treated through oral gavage to evaluate its anti-diarrhea effect. Fecal conditions were monitored. Intestinal tissues were subjected to histological examination to assess structural integrity. The total fecal bile acids were evaluated using a bile acid assay kit to determine the mechanism of action. Results: The results showed that a diarrhea model was established by administering GTO at 2000 mg/kg. When the animals were treated with clay, diarrhea incidence and severity were decreased significantly in a dose-dependent manner. Compared to the untreated group receiving GTO alone, clay co-administration at 2000 mg/kg reduced diarrhea scores by approximately 48%, while the higher dose of 4000 mg/kg achieved an 83% reduction. Fecal bile acid analysis showed that diarrhea is associated with total bile acid levels in the feces. Histological exams showed that diarrhea is associated with tissue inflammation in the colon. Conclusions: This study showed that GTO administration induced diarrhea in mice, and clay effectively alleviates fat-induced diarrhea through modulation of fecal bile acid composition. These findings suggest that this model can be used to evaluate diarrhea associated with excessive amounts of fat and clay that can be further tested for diarrhea attenuation.