Severe Disease Activity and Liver Fibrosis Are Associated With a Lack of Hepatic Mitochondrial Adaptation in Patients With NASH

Dysfunctional mitochondrial function is believed to play a vital role in the progression of nonalcoholic steatohepatitis (NASH) to advanced fibrosis and cirrhosis. However, most evidence arises from animal models while there is limited data in humans. The characteristic histological finding of NASH is hepatocellular injury with ballooning and inflammation, often associated with fibrosis in advanced disease. The aim of this study was to assess the role of mitochondrial function (eg, oxidative phosphorylation [OXPHOS] in patients with vs. without NASH and fibrosis. To this end, we recruited 38 patients with NAFLD with risk factors (obesity and/or type 2 diabetes) for NASH (age: 52±12 years; 37% male; BMI: 39.6±8.5 kg/m(2); HbA1c: 6.8±1.4%) in whom we assessed mitochondrial respiration and also performed measurements of insulin resistance (IR). Tissue was obtained by either a Tru-cut percutaneous liver biopsy (n=26) or a wedge biopsy during bariatric surgery (n=12). After tissue was separated for histological diagnosis, small liver samples (2–4 mg) were processed to quantify OXPHOS by measuring the mitochondrial oxygen consumption rate in individual complexes of mitochondria, expressed as pmol×mg wet weight(-1)×s(-1), using high-resolution respirometry, Oxygraph-2k. Based on liver histology, patients with NASH (n=18) compared to without NASH (n=20), had worse hyperinsulinemia and HOMA-IR (25.2±10.5 vs 14.9± 6.7 µU/ml and 8.9±4.3 vs. 4.9±2.9 mg/dl × µU/ml, respectively) and higher OXPHOS (all p<0.05), although well matched for age, BMI, HbA1c and % with diabetes. This was likely an adaptation to IR and higher FFA flux to the liver. We then examined patients based specifically on disease activity, using a combined score of hepatocyte ballooning and inflammation (necroinflammation score [NIS]) and divided as mild (n=16), moderate (n=14) or severe (n=8) NIS (also well matched for relevant clinical parameters). Patients in the moderate vs. mild NIS group disease activity had increased mitochondrial respiration as represented by OXPHOS (45.9±11.8 vs. 31.3±9.8), electron transport chain activity (ETC) (61.0±17.6 vs. 46.4±15.2) and state 3 respiration induced by ADP (20.7±4.9 vs. 16.4±4.6 pmol×mg wet weight(-1)×s(-1); all p<0.05). There was a trend for these parameters to decline in patients with severe vs. moderate disease activity, that was further accentuated when patients with NASH also had clinically significant fibrosis compared to those with mild or no fibrosis (OXPHOS: 37.9±7.8 vs. 49.8±12.5, p=0.04; and ETC: 49.8±13.4 vs. 67.5±16.1, p=0.02). Conclusion: In patients with NASH, there is an early hepatic mitochondrial adaptation to account for the state of more severe insulin resistance in steatohepatitis compared to simple steatosis. This adaptation is impaired when disease activity worsens and is most evident once patients develop steatohepatitis with significant fibrosis.