Evaluation of the ¹³C-octanoate breath test as a surrogate marker of liver damage in animal models

Background: Octanoate (also known as sodium octanoate), a medium-chain fatty acid metabolized in the liver, is a potential substrate for non-invasive breath testing of hepatic mitochondrial β-oxidation. Methods: We evaluated the ¹³C-octanoate breath test (OBT) for assessing injury in acute hepatitis and two rat models of liver cirrhosis, first testing octanoate absorption (per os or intraperitoneally (i.p.)) in normal rats. We then induced acute hepatitis with thioacetamide (300 mg/kg/i.p., 24-h intervals). Liver injury end points were serum aminotransferase levels and ¹³C-OBT (24 and 48 h following initial injection). Thioacetamide (200 mg/kg/i.p., twice per week, 12 weeks) was used to induce liver cirrhosis. OBT and liver histological assessment were performed every 4 weeks. Bile duct ligation (BDL) was used to induce cholestatic liver injury. We completed breath tests with ¹³C-OBT and ¹³C-methacetin (MBID), liver biochemistry, and liver histology in BDL and sham-operated rats (baseline, 6, 14, 20 days post-BDL). Results: Octanoate absorbs well by either route. Peak amplitudes and cumulative percentage dose recovered at 30 and 60 min (CPDR30/60), but not peak time, correlated with acute hepatitis. Fibrosis stage 3 at week 8 significantly correlated with each OBT parameter. Cholestatic liver injury (serum bilirubin, ALP, gamma-GT, liver histology) was associated with significant suppression of the maximal peak values and CPDR30/60, respectively (P < 0.05), using MBID but not ¹³C-octanoate. Conclusions: OBT is sensitive for potentially evaluating liver function in rat models of acute hepatitis and thioacetamide-induced liver cirrhosis but not in cholestatic liver injury. The MBID test may be better for evaluation of cholestatic liver disease in this model.