Many studies report an elevated circulating level of extracellular vesicles (EVs) in liver disease patients, however whether these changes are a result of liver injury or whether they also mediate disease is not understood. Non-alcoholic steatohepatitis (NASH) is defined by liver lipid accumulation, inflammation and in severe cases fibrosis and cirrhosis. Progression from simple steatosis to more severe injury is difficult to detect and there is no reliable diagnostic biomarker, with disease staging only possible through biopsy. As this progression can change cell activation and stress and alters packaging of molecules into EVs, we hypothesize that the profile of these membrane structures change with disease progression.
We investigated the EVs present in the circulation and liver of C57Bl/6 male mice fed either a high-fat diet (HFD; 45%kcal fat) or chow for 12 and 52 weeks. EVs were obtained by ultracentrifugation of plasma or conditioned media from liver slices, and quantified using NanoSight™. These values were compared to degree of steatosis measured by lipid staining with Oil Red O and circulating markers of liver injury.
An increase in circulating EVs was observed in HFD mice, while liver-derived EVs were decreased in these animals. When compared against liver lipid, plasma and liver-derived EVs showed positive and negative correlations, respectively (both p<0.001). In addition to the effect of diet, aging also contributed to EV number. In plasma, EVs were increased around 10-fold for both diets, although the effect was much stronger in HFD (p=0.001) than chow (p=0.021).
This data suggests that circulating EVs may be a useful indicator of steatosis, however care must be taken as values may be confounded by aging. As liver-derived EVs decrease with steatosis, it is unlikely that they contribute to the increased circulating population, however their mechanism of action in the context of NASH is currently being investigated.