Potential of 99m Tc-MIBI SPECT imaging for evaluating non-alcoholic steatohepatitis induced by methionine-choline-deficient diet in mice

Background Hepatic mitochondrial dysfunction has been implicated in pathological conditions leading to non-alcoholic steatohepatitis (NASH). Technetium-99 m-2-methoxyisobutyl-isonitrile ( 99m Tc-MIBI), a lipophilic cationic myocardial perfusion agent, is retained in the mitochondria depending on membrane potential. The aim of this study was to investigate the feasibility of 99m Tc-MIBI for evaluating the hepatic mitochondrial dysfunction induced by methionine-choline-deficient (MCD) diet in mice. Methods Male C57Black6J/jcl mice were fed a MCD diet for up to 4 weeks. SPECT scan ( N =6) with 99m Tc-MIBI was performed at 2 and 4 weeks after MCD diet. Mice were imaged with small-animal SPECT/CT under isoflurane anesthesia. Radioactivity concentrations of the liver were measured, and the time of maximum ( T max ) and the elimination half-life ( T 1/2 ) were evaluated. After SPECT scan, liver histopathology was analyzed to evaluate steatosis and inflammation. Non-alcoholic fatty liver disease (NAFLD) activity score was obtained from the histological score of hepatic steatosis and inflammation. Blood biochemistry and hepatic ATP content were also measured ( N =5 to 6). Results Plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were significantly elevated at 2 and 4 weeks after MCD diet. A decrease in hepatic ATP content was also observed in MCD-fed mice. 99m Tc-MIBI SPECT imaging clearly showed the decrease of hepatic 99m Tc-MIBI retention in MCD-fed mice compared to control mice. T 1/2 after 99m Tc-MIBI injection was significantly decreased in the liver of MCD-fed mice (control, MCD 2 weeks, and MCD 4 weeks, T 1/2 = 57.6, 37.6, and 19.8 min, respectively), although no change in T max was observed in MCD-fed mice. SPECT data and histological score showed that the negative correlation ( r = -0.74, p <0.05) between T 1/2 and NAFLD activity score was significant. Conclusions Hepatic 99m Tc-MIBI elimination was increased with increase in NAFLD activity score (NAS) in mice fed MCD diet for 2 and 4 weeks. These results suggest that 99m Tc-MIBI SPECT imaging might be useful for detecting hepatic mitochondrial dysfunction induced by steatosis and inflammation such as NAFLD or NASH.