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

Abstract

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, highfat, 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.

Coordinated pyruvate kinase activity is crucial for metabolic adaptation and cell survival during mitochondrial dysfunction

“…Recently, improvement of adult-onset mitochondrial myopathy was achieved by intervention of NAD + levels with niacin ( 41 ). Moreover, the protection of liver function through supplement of branched amino acids has also been reported ( 42–45 ). Altogether, these studies suggest that supporting the metabolic balance might be a treatment strategy to be evaluated.…”

β-Cell Dysfunction, Hepatic Lipid Metabolism, and Cardiovascular Health in Type 2 Diabetes: New Directions of Research and Novel Therapeutic Strategies

“…Given the insulin secretion stimulatory effect of BCAAs on β-cells [ 130 ], the high levels of BCAAs observed in obesity and T2DM may suggest a deleterious long-term effect or resistance to their function similar to what happens to FGF-21 in obesity [ 128 , 129 , 138 ]. Restriction of BCAAs was reported recently to worsen ketogenesis and cause oxidative dysfunction of the mitochondria in mice [ 206 ]. A ketogenic diet could be a useful approach to burn excess calories and harness less energy by the cell theoretically, although randomized controlled trials have shown only a minor effect [ 207 ].…”

Dietary Macronutrient Composition Differentially Modulates the Remodeling of Mitochondrial Oxidative Metabolism during NAFLD

“…The TCA cycle intermediates in the liver tissue (≈15 mg) and isolated mitochondrial protein (500 µg) were extracted with 750 µL of chloroform: methanol (2:1) and 250 µL of water. The aqueous phase was dried under nitrogen, and the TCA cycle intermediates were converted to their oximes with 20 µL of 2% methoxamine hydrochloride in pyridine ( w / v ) by microwaving for 90 s, which is followed by conversion to their respective TBDMS (Tert-butyldimethylsilyl) derivatives [ 42 ]. Serum (25 µL) samples were processed following deproteinization with 750 µL of cold acetonitrile and the conversion of metabolites to their oxime with 20 µL of 2% methoxamine hydrochloride in pyridine, followed by TBDMS derivatization.…”

“…Metabolites were separated on a HP-5MS UI column (30 m × 0.25 mm × 0.25 μm; Agilent, Santa Clara, CA, USA) and fragmented under electrical ionization. Fragments of interest were detected using single ion monitoring (SIM) on a GC-MS (5973N-Mass Selective Detector, 6890-Series GC, Agilent, Santa Clara, CA, USA) [ 42 ].…”