Novel in vivo and ex vivo hybrid in vivo imaging system (IVIS) imaging offers a convenient and precise way to measure the glomerular filtration rate in conscious mice

Introduction: In pharmacology and toxicology studies, the glomerular filtration rate (GFR) is the gold standard for the assessment of renal function, and the renal clearance of inulin in blood measured by photometers is known as a filtration marker for the determination of GFR. Preclinically, a non-invasive GFR measurement method was recently developed in which near-infrared fluorescently labelled inulin (GFR-Vivo 680) was scanned with fluorescence molecular tomography (FMT). However, measurement of GFR using FMT has major disadvantages and technical challenges, such as requiring experienced skills in animal handling and rapid and precise time management. Additionally, fur and skin pigmentation may severely compromise imaging due to tissue fluorescence absorption. To overcome these drawbacks of FMT imaging, we have developed an in- and ex vivo hybrid method for measuring GFR using the in vivo imaging system (IVIS).

Methods: An IVIS-based imaging method was tested to determine the clearance kinetics of plasma GFR-Vivo 680 after a single bolus injection in conscious C57BL/6 mice administered vehicle or cyclosporine A (CsA, 80 mg/kg) for 14 days.

Results: Based on a two-compartment model fitting, the estimated GFR was 235 ± 53 and 189 ± 19 μL/min in vehicle-treated and CsA-treated male mice, respectively (p < 0.01). Our assay revealed the decreased GFR, similar to the sensitivity of FMT imaging, which yielded comparable GFR values (229 ± 61 and 151 ± 35 μL/min in vehicle-treated and CsA-treated mice, respectively, p < 0.01), and to those previously reported in the literature.

Discussion: These studies demonstrate the feasibility of IVIS imaging measurement of inulin clearance in untreated, vehicle-treated and cyclosporine A-treated mice. We propose this new method as an alternative, simple, and versatile way to measure GFR in vivo and ex vivo in pharmacological and toxicological studies.