S-Allylmercaptocysteine improves alcoholic liver disease partly through a direct modulation of insulin receptor signaling

Abstract

Alcoholic liver disease (ALD) causes insulin resistance, lipid metabolism dysfunction, and inflammation. We investigated the protective effects and direct regulating target of S-allylmercaptocysteine (SAMC) from aged garlic on liver cell injury. A chronic ethanol-fed ALD in vivo model (the NIAAA model) was used to test the protective functions of SAMC. It was observed that SAMC (300 mg/kg, by gavage method) effectively ameliorated ALD-induced body weight reduction, steatosis, insulin resistance, and inflammation without affecting the health status of the control mice, as demonstrated by histological, biochemical, and molecular biology assays. By using biophysical assays and molecular docking, we demonstrated that SAMC directly targeted insulin receptor (INSR) protein on the cell membrane and then restored downstream IRS-1/AKT/GSK3β signaling. Liver-specific knock-down in mice and siRNA-mediated knock-down in AML-12 cells of Insr significantly impaired SAMC (250 μmol/L in cells)-mediated protection. Restoration of the IRS-1/AKT signaling partly recovered hepatic injury and further contributed to SAMC's beneficial effects. Continuous administration of AKT agonist and recombinant IGF-1 in combination with SAMC showed hepato-protection in the mice model. Long-term (90-day) administration of SAMC had no obvious adverse effect on healthy mice. We conclude that SAMC is an effective and safe hepato-protective complimentary agent against ALD partly through the direct binding of INSR and partial regulation of the IRS-1/AKT/GSK3β pathway.

Keywords: ADIPOQ, adiponectin; AKT; ALD, alcoholic liver disease; ALDH2, aldehyde dehydrogenase 2; ALT, alanine aminotransferase; AMPK, adenosine 5′-monophosphate (AMP)-activated protein kinase; AST, aspartate aminotransferase; ATGL, adipose triglyceride lipase; Alcoholic liver disease; CPT1, carnitine palmitoyltransferase I; CYP2E1, cytochrome P450 2E1; FDA, U.S. Food and Drug Administration; FFA, free fatty acids; GRB14, growth factor receptor-bound protein 14; GSK3β; GSK3β, glycogen synthase kinase 3 beta; GTT, glucose tolerance test; HSL, hormone sensitive lipase; IGF-1, insulin-like growth factors-1; IL, interleukin; INSR, insulin receptor; IRS, insulin receptor substrate; IRS-1; IRTK, insulin receptor tyrosine kinase; Insulin receptor; Insulin resistance; LDLR, low-density lipoprotein receptor; LRP6, low-density lipoprotein receptor related protein 6; MTT, 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide; NAC, N-acetyl-cysteine; NAFLD, non-alcoholic fatty liver disease; NAS, NAFLD activity score; NF-κB, nuclear factor kappa B; NIAAA, National Institute on Alcohol Abuse and Alcoholism; NRF2, nuclear factor erythroid 2-related factor 2; ORF, open reading frame; PA, palmitate acid; PPARα, peroxisome proliferator-activated receptor alpha; RER, respiratory exchange ratio; S-Allylmercaptocysteine; SAMC, S-allylmercaptocysteine; SPR, surface plasmon resonance; SREBP-1c, sterol regulatory element-binding protein 1c; Safety; TC, total cholesterol; TCF/LEF, T-cell factor/lymphoid enhancer factor; TG, triglyceride; TNF, tumor necrosis factor; TSA, thermal shift assay; WAT, white adipose tissues; WT, wild-type.