Prevention and reversal of hepatic steatosis with a high-protein diet in mice

The hallmark of NAFLD is steatosis of unknown etiology. We tested the effect of a high-protein (HP)²2AA: arachidonic acid; Acac: acetyl-CoA carboxylase; Acox: acyl-coenzyme A oxidase; Akt: thymoma viral proto-oncogene 1 (a.k.a. PKB-protein kinase B); Alas1: aminolevulinic acid synthase 1; Arntl (a.k.a. Bmal1): aryl hydrocarbon receptor nuclear translocator-like protein; BCAA: branched-chain amino acids; BHB: β-hydroxybutyrate; ITGAM: Integrin-αM; Chop/Ddit3: C/EBP-homologous protein/DNA damage-inducible transcript 3 protein; Chrebp: carbohydrate-responsive element-binding protein; Cpt1: carnitine palmitoyltransferase 1; DHA: docosahexaenoic acid; eIF2α: eukaryotic translation-initiation factor 2α; Elovl: elongation of very long-chain fatty acids; en%: energy percent; EPA: eicosapentaenoic acid; Fasn: fatty acid synthase; Fgf21: fibroblast growth factor 21; FFA: free fatty acids; G6Pase: glucose-6-phosphatase; GCN2: general control nonrepressed 2; HF: high fat; HF/LPres: high fat, low protein restricted; HP: high protein; LF: low fat; LP: low protein; Mcp1: monocyte chemotactic protein 1; Mlxipl (a.k.a. Chrebp): Mlx-interacting protein-like; mAco: mitochondrial aconitase; mmBCFA: monomethyl branched-chain fatty acid; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; Nfil3: nuclear factor interleukin-3-regulated protein; NFκB: nuclear factor κB; Nr1d1 (a.k.a. rev-erbα): nuclear receptor subfamily 1, group D, member 1; PCK1: phosphoenolpyruvate carboxykinase 1; PERK: protein kinase RNA-like endoplasmic reticulum kinase; Pgc1α: pparγ-coactivator1-α, PL: choline-containing phospholipids; Ppar: peroxisome proliferator-activated receptor; r_s: Spearman correlation coefficient; Scd1: stearoyl-CoA desaturase 1; Srebf: sterol regulatory element-binding transcription factor; TC: total cholesterol; TG: triglycerides. diet on diet-induced steatosis in male C57BL/6 mice with and without pre-existing fatty liver. Mice were fed all combinations of semisynthetic low-fat (LF) or high-fat (HF) and low-protein (LP) or HP diets for 3weeks. To control for reduced energy intake by HF/HP-fed mice, a pair-fed HF/LP group was included. Reversibility of pre-existing steatosis was investigated by sequentially feeding HF/LP and HF/HP diets. HP-containing diets decreased hepatic lipids to ~40% of corresponding LP-containing diets, were more efficient in this respect than reducing energy intake to 80%, and reversed pre-existing diet-induced steatosis. Compared to LP-containing diets, mice fed HP-containing diets showed increased mitochondrial oxidative capacity (elevated Pgc1α, mAco, and Cpt1 mRNAs, complex-V protein, and decreased plasma free and short-chain acyl-carnitines, and [C₀]/[C₁₆+C₁₈] carnitine ratio); increased gluconeogenesis and pyruvate cycling (increased PCK1 protein and fed plasma-glucose concentration without increased G6pase mRNA); reduced fatty-acid desaturation (decreased Scd1 expression and [C_16:1n-7]/[C_16:0] ratio) and increased long-chain PUFA elongation; a selective increase in plasma branched-chain amino acids; a decrease in cell stress (reduced phosphorylated eIF2α, and Fgf21 and Chop expression); and a trend toward less inflammation (lower Mcp1 and Cd11b expression and less phosphorylated NFκB). Conclusion: HP diets prevent and reverse steatosis independently of fat and carbohydrate intake more efficiently than a 20% reduction in energy intake. The effect appears to result from fuel-generated, highly distributed small, synergistic increases in lipid and BCAA catabolism, and a decrease in cell stress.