Blood Pharmacokinetics Imaging by Noninvasive Heart Fluorescence Tomography and Application to Kidney Glomerular Filtration Rate Assessment.

ABSTRACT

In mouse pharmacokinetic (PK) studies, current standard methods often require large numbers of animals to support collection of blood samples serially over a defined time range. We have developed and validated a noninvasive fluorescence molecular tomography (FMT) heart imaging approach for blood PK quantification that uses small numbers of mice and has the advantage of repeated, longitudinal live imaging. This method was validated using a variety of near infrared (NIR) fluorescent-labeled molecules, ranging in size from 1.3 to 150 kDa, that were assessed by microplate blood assays as well as by noninvasive FMT 4000 imaging. Excellent agreement in kinetic profiles and calculated PK metrics was seen for the two methods, establishing the robustness of this noninvasive optical imaging approach. FMT heart imaging was further assessed in the challenging application of inulin-based glomerular filtration rate (GFR) measurement. After a single bolus injection of an NIR fluorescent-labeled inulin probe in small cohorts of mice (n = 5 per group), 2-minute heart scans (at 2, 6, 15, 30, and 45 minutes) were performed by FMT imaging. GFR was calculated using two-compartment PK modeling, determining an average rate of 240 ± 21 µl/min in normal mice, in agreement with published mouse GFR ranges. Validation of GFR assessment in unilaterally nephrectomized mice and cyclosporin A-treated mice both measured ∼50% decreases in GFR. Imaging results correlated well with ex vivo plasma microplate assays for inulin blood kinetics, and the decreases in GFR were accompanied by increases in plasma creatinine and blood urea nitrogen.