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 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 6 21 ml/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.

Deconvolution of plasma pharmacokinetics from dynamic heart imaging data obtained by SPECT/CT imaging

“…The modeling approach for deconvolution of plasma PK from dynamic heart imaging data is very useful because: a) plasma PK analysis and imaging studies can be conducted in a single cohort of animals, substantially reducing the number of animals and conserving resources; b) it improves the accuracy and precision of Patlak plot parameter estimates since the plasma PK and dynamic imaging data are obtained from the same mouse. Although bulk heart imaging data has been found to agree with plasma PK of probes that are restricted to the vascular space (Bao, Vasquez et al 2019), it is not applicable to molecules that are substantially taken up by the heart tissue. For example, a previous study reported that heart ROI time-activity curves (TACs) can overestimate the actual blood concentration of 18 F-FDG especially at later time points after injection.…”

“…Recent studies conducted by Bao et.al compared noninvasive heart fluorescence molecular tomography (FMT) and serial blood sampling to determine blood PK of probes ranging from 2-150 kDa. They found excellent agreement in kinetic profiles and associated PK parameters between these two methods and further applied FMT to estimate glomerular filtration rate under various pathological conditions (Bao, Vasquez et al 2019).…”

“…Recent studies conducted by Bao et.al compared noninvasive heart fluorescence molecular tomography (FMT) and serial blood sampling to determine blood PK of probes ranging from 2-150 kDa. They found excellent agreement in kinetic profiles and associated PK parameters between these two methods and further applied FMT to estimate glomerular filtration rate under various pathological conditions (Bao, Vasquez et al 2019). However, for molecules such as insulin and Aβ, which have been the focus of research in our lab, this method can overpredict plasma levels because both proteins, especially Aβ, exhibit considerable accumulation in heart tissue (Troncone, Luciani et al 2016, Martinez-Naharro, Hawkins et al 2018).…”

Insulin Signaling Differentially Regulates the Trafficking of Insulin and Amyloid Beta Peptides at the Blood–Brain Barrier

“…To construct the plots for [ 125 I]­iodo-Aβ42 and [ 125 I]­iodo-Aβ40, the concentrations measured in the heart ROI during the imaging experiment were used as a surrogate for the plasma concentrations. The use of heart imaging data as a surrogate for plasma pharmacokinetics is a well-established method, but was not suitable for the [ 125 I]­iodoinsulin studies due to substantial accumulation of insulin in the heart tissue. Although the concentrations derived from heart ROI do not reflect the true plasma concentrations, this approach still allows for a relative comparison of K i estimates between groups.…”

Methods for Assessment of the Glomerular Filtration Rate in Laboratory Animals

“…However, the sample size was small ( n = 3), and the PK curve of the fluorescent signal of the kidneys was inconsistent with that of the plasma concentration. The author did not explain possible reasons for this difference [ 72 ]. Additionally, this method requires continuous anesthesia, which may influence the GFR.…”