Quantifying renal lipid accumulation in obese murine models using Magnetic Resonance Imaging (MRI).

Renal cortical lipid content is increased in obesity and contributes to obesity-related kidney dysfunction. Studying this phenomenon requires reliable tools to quantitate renal cortical lipid in preclinical models. However, most current preclinical methods require euthanizing the model. MRI has been used to measure lipid content in other organ systems but, to our knowledge, has not been employed in quantifying kidney lipid in mice. Eleven-week old male C57BL/6 mice were fed either standard chow (ND) (12 % fat) or high fat diet (HFD) (45 % fat) for 12 weeks. At the end of this period, a 9.4 T Bruker MRI was utilized to perform fat-water separation imaging based on the Dixon method. These images were utilized to calculate a proton-density fat fraction for regions of interest within the renal cortex. For validation, frozen kidney sections underwent immunofluorescent LipidSpot™ staining for quantitation of lipid droplet area. After 12 weeks on diet, the average body weight of HFD fed mice was 34.63g compared to 27.84g in ND controls (p < 0.001). Consistent with prior studies, MRI demonstrated increased hepatic fat content of 13.34 % in HFD fed mice compared to 8.3 % in ND controls (p < 0.05). Renal cortical lipid measured by MRI averaged 7.35 % in HFD fed mice compared to 4.75 % in ND controls (p < 0.05). On histologic analysis, HFD fed mice had a ratio of lipid droplet area to DAPI of 0.866 compared to 0.221 in ND fed mice (p < 0.05). These results demonstrate that MRI can be used effectively to measure changes in renal cortical lipid content in mice.