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Assess reproducibility of liver transporter function

Assessment of hepatic transporter function in rats using dynamic gadoxetate-enhanced MRI: A reproducibility study 

by Catherine D. G. Hines, Sirisha Tadimalla, Claudia Green, Iina Laitinen, Ebony R. Gunwhy, Steven Sourbron, Issam Ben Khedhiri, Paul D. Hockings, Gunnar Schütz, John C. Waterton

HTN Meeting 2022.


Background: Drug-induced perturbations of liver transporter fluxes contribute to both drug-induced liver injury and drug-drug interactions, which are significant problems in healthcare and in drug development. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using gadoxetate has been proposed for assessing liver transporter-mediated drug injury, with compartmental modelling yielding gadoxetate hepatic plasma clearance (Ktrans) and biliary efflux (kbh) rate constants as biomarkers.  

Purpose/Hypothesis: Quantify the reproducibility and repeatability of gadoxetate Ktrans and kbh in the absence of drugs and investigate robustness by comparing with the effect size of a potent inhibitor, as measured by the TRISTAN rat assay. 

Study Type: data collected from five retroprospective and eight prospective longitudinal substudies. 

Population/Subjects/Phantom/Specimen/Animal Model: 76 male Wistar-Han rats. 

Field Strength/Sequence: Two 4.7T and two 7T Bruker (Rheinstetten, Germany) scanners at three facilities using a T2-weighted (T2W) spin echo sequence for anatomy identification and a retrospectively triggered 3D Fast Low Angle Shot (FLASH) RF-spoiled gradient echo T1W acquisition. 

Assessment: 13 substudies covering three centres, two MRI field strengths, three time periods, and two substances were assessed (ndatasets=108). All 13 substudies included between three to eight rats either scanned once (baseline: Day 1) with saline or study-specific vehicle (nrats=76) or twice (follow-up, 2-7 days apart: Day 2) with saline (nrats=19) or 10 mg/kg of the strong inhibitor rifampicin (nrats=13). 

Methods: Images were analysed using a tracer kinetic (TK) two-compartment exchange model that characterises Ktrans and kbh kinetics of gadoxetate using liver ROIs with a standardised arterial input function derived from a simplified model of the rat circulation. Average Ktrans and kbh values from each study along with 95% confidence intervals were reported as the TRISTAN rat assay. From the assay, reproducibility (between-substudies) and repeatability (between-day) errors were quantified for saline data, only. Reproducibility errors were then deconstructed across centres, field strengths, and time periods to examine the relative impact of different variables. Effect sizes were calculated from data where a follow-up scan of rifampicin was acquired. One-way ANOVAs and paired T-tests were also performed, where p<0.05 was considered to be statistically significant. 

Results: Reproducibility errors were 31% and 43% for Ktrans and kbh. Differences between substudies were significant. When isolating variables, reproducibility errors were as follows for choice of (i) centre: Ktrans<26% (p=0.13), kbh<93% (p=0.03); (ii) field strength: Ktrans<16% (p=0.51), kbh<84% (p=0.34); (iii) time period: Ktrans<29% (p=0.35), kbh<54% (p=0.008). Differences between baseline and follow-up saline data were not significant, with repeatability errors (Ktrans=14+/-2%; kbh=7+/-12%) much smaller than reproducibility errors. Rifampicin significantly reduced Ktrans (-170+/-8%) and kbh (-130+/-23%) across all centres. 

Conclusion: The TRISTAN rat assay is sufficiently robust for quantifying inhibition levels over >50% in absolute or relative terms. This safely includes potent inhibitors like rifampicin (>130% inhibition). For weaker inhibitors (20%-50% inhibition) only relative changes can be measured reliably. Inhibition levels below 20% cannot be quantified. This would require further technical development to reduce the uncertainty caused by the choice of centre, field strength, and drifts over time.