Branched chain amino acids and carbohydrate restriction exacerbate ketogenesis and hepatic mitochondrial oxidative dysfunction during NAFLD.

Mitochondrial adaptation during non-alcoholic fatty liver disease (NAFLD) include remodeling of ketogenic flux and sustained tricarboxylic acid (TCA) cycle activity, which are concurrent to onset of oxidative stress. Over 70% of obese humans have NAFLD and ketogenic diets are common weight loss strategies. However, the effectiveness of ketogenic diets toward alleviating NAFLD remains unclear. We hypothesized that chronic ketogenesis will worsen metabolic dysfunction and oxidative stress during NAFLD. Mice (C57BL/6) were kept (for 16-wks) on either a low-fat, high-fat, or high-fat diet supplemented with 1.5X branched chain amino acids (BCAAs) by replacing carbohydrate calories (ketogenic). The ketogenic diet induced hepatic lipid oxidation and ketogenesis, and produced multifaceted changes in flux through the individual steps of the TCA cycle. Higher rates of hepatic oxidative fluxes fueled by the ketogenic diet paralleled lower rates of de novo lipogenesis. Interestingly, this metabolic remodeling did not improve insulin resistance, but induced fibrogenic genes and inflammation in the liver. Under a chronic "ketogenic environment," the hepatocyte diverted more acetyl-CoA away from lipogenesis toward ketogenesis and TCA cycle, a milieu which can hasten oxidative stress and inflammation. In summary, chronic exposure to ketogenic environment during obesity and NAFLD has the potential to aggravate hepatic mitochondrial dysfunction.

Muyyarikkandy MS ，McLeod M ，Maguire M ，Mahar R ，Kattapuram N ，Zhang C ，Surugihalli C ，Muralidaran V ，Vavilikolanu K ，Mathews CE ，Merritt ME ，Sunny NE ... -  《-》

Branched-chain amino acids alter cellular redox to induce lipid oxidation and reduce de novo lipogenesis in the liver.

Surugihalli C ，Muralidaran V ，Ryan CE ，Patel K ，Zhao D ，Sunny NE ... -  《-》

Cross-talk between branched-chain amino acids and hepatic mitochondria is compromised in nonalcoholic fatty liver disease.

Sunny NE ，Kalavalapalli S ，Bril F ，Garrett TJ ，Nautiyal M ，Mathew JT ，Williams CM ，Cusi K ... -  《-》

Hepatic ketogenic insufficiency reprograms hepatic glycogen metabolism and the lipidome.

d'Avignon DA ，Puchalska P ，Ercal B ，Chang Y ，Martin SE ，Graham MJ ，Patti GJ ，Han X ，Crawford PA ... -  《JCI Insight》

The ketogenic diet prevents steatosis and insulin resistance by reducing lipogenesis, diacylglycerol accumulation and protein kinase C activity in male rat liver.

Obesity-associated insulin resistance plays a major role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). The accumulation of diacylglycerol (DAG), ceramides and inflammation are key factors that cause NAFLD. In recent years, the ketogenic diet (KD) has emerged as an effective non-pharmacological intervention for the treatment of NAFLD and other obesity-related metabolic disorders. What remains undetermined is how the KD affects DAG and ceramide content and insulin sensitivity in the liver. Thus, this research was designed to assess these variables, as well as glucose and fat metabolism and markers of inflammation in livers of rats exposed for 8 weeks to one of the following diets: standard chow (SC), obesogenic high-fat, sucrose-enriched diet (HFS) or a KD. Despite having a higher fat content than the HFS diet, the KD did not cause steatosis and preserved hepatic insulin signalling. The KD reduced DAG content and protein kinase C-ε activity, but markedly increased liver ceramide content. However, whereas the KD increased ceramide synthase 2 (CerS2) expression, it suppressed CerS6 expression, an effect that promoted the production of beneficial very long-chain ceramides instead of harmful long-chain ceramides. The KD also enhanced the liver expression of key genes involved in mitochondrial biogenesis and fatty acid oxidation (Pgc-1α and Fgf21), suppressed inflammatory genes (Tnfα, Nf-kb, Tlr4 and Il6), and shifted substrate away from de novo lipogenesis. Thus, through multiple mechanisms the KD exerted anti-steatogenic and insulin-sensitizing effects in the liver, which supports the use of this dietary intervention to treat NAFLD. KEY POINTS: The accumulation of diacylglycerol (DAG), ceramides and inflammation are key factors that cause insulin resistance and non-alcoholic fatty liver disease (NAFLD). This study provides evidence that a ketogenic diet (KD) rich in fat and devoid of carbohydrate reduced DAG content and preserved insulin signalling in the liver. The KD shifted metabolism away from lipogenesis by enhancing genes involved in mitochondrial biogenesis and fatty acid oxidations in the liver. The KD also promoted the production of beneficial very long-chain ceramides instead of potentially harmful long-chain ceramides. Through multiple mechanisms, the KD exerted anti-steatogenic and insulin-sensitizing effects in the liver, which supports the use of this dietary intervention to treat NAFLD.

Jani S ，Da Eira D ，Stefanovic M ，Ceddia RB ... -  《-》