Evaluation of Nonalcoholic Fatty Liver Disease in C57BL/6J Mice by Using MRI and Histopathologic Analyses

Abstract

Nonalcoholic fatty liver disease (NAFLD) can lead to cirrhosis, hepatocellular carcinoma, and ultimately death. Magnetic resonance techniques are accurate, noninvasive methods for evaluating hepatic steatosis but, in animals, have not been fully validated against histologic findings. We sought to validate the MRI fat-signal fraction (MRI-FSF) used for diagnosing NAFLD in human nonclinical trials by comparing MRI data with histopathologic findings in C57BL/6J mice (n = 24) fed normal chow (controls) or a methionine- and choline-deficient (MCD) diet to induce NAFLD. Axial T2-weighted fast spin-echo images were used to examine the entire liver. For histopathologic analyses, liver slides were evaluated for hepatic steatosis according to the NAFLD activity score. Pearson correlation coefficient and receiver operating characteristics analyses were performed. According to the fat-fraction signal, the mean percentage of liver fat in mice with induced NAFLD was 57%, which correlated with the histologically determined steatosis grade. The proton-density fat fraction effectively distinguished severe from mild hepatic steatosis, with an AUC of 0.92. Evaluation accuracy decreased when lobular inflammation and hepatocellular ballooning were considered. This study showed strong concurrence between MRI-FSF and histopathologic steatosis in a murine model of NAFLD. MRI-FSF had moderate sensitivity and specificity in this context. These results confirm that the MRI is a useful biomarker of hepatic steatosis in NAFLD in murine model.

Figure 1.

Sections of liver from (A) normal C57BL/6J mice, (B) mice fed an MCD diet for 8 wk, and (C) mice fed an MCD diet for12 wk. Much greater lobular inflammation is present in mice fed MCD for 12 wk (panel C) than for 8 wk (B). Hematoxylin and eosin stain; magnification, 200×.

Figure 2.

Signal fat-fraction (FSF) obtained using a fat-suppression MRI technique. (A) Images of the liver acquired without fat saturation in normal mice, (B) with fat saturation, (C) MR images acquired as no fat saturation– fat saturation, showingthe fat signal, (D) images of the liver acquired with no fat saturation in mice fed an MCD diet, (E) with fat saturation, (F) MRI fat signals revealed greater fat infiltration in the liver of MCD mice than in that of normal mice (white arrow).

Figure 3.

Comparison of normal mice and mice fed an MCD diet for 8 wk. MRI–FSF revealed a greater percentage (P < 0.0001) of fat in the livers of MCD mice than in control mice.

Figure 4.

Comparison of normal mice and mice fed an MCD diet for 12 wk. MRI–FSF revealed a greater percentage (P = 0.0046) of fat in the livers of MCD mice than in control mice.

Figure 5.

In liver with induced NAFLD, MRI–FSF measurements of hepatic fat content (%) and histologic measurements of steatosis (%) are highly correlated (P = 0.0053).

Figure 6.

Receiver operating characteristic analysis of MRI–FSF and the histologically determined grade of steatosis for mice with induced NAFLD. MRI–FSF can distinguish between histologic degrees of steatosis: moderate (33% to 66%) and severe (66% to 100%) hepatic steatosis. (B) Receiver operating characteristic curve of MRI–FSF for steatosis.

Figure 7.

Receiver operating characteristic analysis of MRI–FSF for histologically determined NAS grades for mice with NAFLD. (A) MRI–FSF discriminates between moderate (score; 4 to 5) and severe (score; 6 to 7) NAS grade. (B) The receiver operating characteristic curve for NAS grade showed a lower sensitivity and specificity than that for steatosis.