Purpose: Laparoscopic serial liver biopsy sampling has been effectively used in preclinical large animal studies to obtain samples at designated times without requiring a terminal procedure or multiple major invasive surgeries. This sampling procedure therefore reduces the number of animals required on a given study and also allows for serial rather than sparse sampling design. The minor liver damage caused by this procedure is presumed to have minimal impact on liver functionality as it relates to simultaneous pharmacokinetic (PK) measurements in a given study design; however, this assessment has not previously been quantitatively evaluated. As such, the re-use of the animals that have previously undergone serial liver biopsies for additional PK studies (for example, in a colony setting) is conservatively limited in order to minimize possible variants in PK evaluations.
Methods: Acetaminophen, a common analgesic and antipyretic drug known to have extensive liver metabolism, was administered orally to non-naïve male cynomolgus monkeys before and after multiple serial liver biopsy procedures. At selected timepoints following each dose administration, blood was collected and plasma was analyzed by LC-MS/MS to determine concentrations of acetaminophen and its glucuronide and sulfate conjugate metabolites. During the biopsy phase of the study, animals underwent 5 laparoscopic liver biopsy procedures over a 29-day period; minimum recovery time between biopsies was 24 hours. Doses of acetaminophen were administered at least 2 days prior to the first biopsy and at least 7 days following the final biopsy. Laparoscopic liver biopsy procedures were performed according to internal SOPs, adhering to strict sterile surgical technique, including anesthesia and analgesics. General health of the animals was assessed by clinical pathology, in addition to frequent physical and cageside examinations for up to 6 months.
Results: After multiple liver biopsies, the mean concentrations and pharmacokinetics of acetaminophen, acetaminophen sulfate, and acetaminophen glucuronide were generally similar compared to pre-biopsy results (<2-fold differences for all parameters).
Animals were generally healthy through the evaluation period. Body weight was maintained and no adverse clinical observations were reported. Clinical pathology results confirm the initial liver injury during the biopsy phase of the study, with expected decreases in ALT and AST, in addition to moderate decreases in BUN and electrolytes and slight decreases in albumin. However, parameters generally rebounded during the subsequent 6 month evaluation.
Conclusion: In conclusion, the pharmacokinetics of acetaminophen, acetaminophen-sulfate, and acetaminophen-glucuronide were similar before and after multiple serial liver biopsy sampling, suggesting that these animals should not necessarily be precluded from re-use for additional, non-surgical preclinical pharmacokinetic studies. It is suggested that routine health checks are performed to monitor liver enzymes and albumin levels to confirm that further re-use is appropriate.