Blockade of interleukin-6 signaling enhances hepatic steatosis but improves liver injury in methionine choline-deficient diet-fed mice

Abstract

Inflammatory processes have an important role in the development of hepatic steatosis and progression to nonalcoholic steatohepatitis (NASH). Interleukin-6 (IL-6) is known to be a proinflammatory cytokine, but also promotes liver regeneration and protects the liver against various forms of damage. The role of IL-6/Glycoprotein130 (GP130) in NASH remains unclear. In this study, we determined whether blocking IL-6/GP130 signaling prevents progression of steatohepatitis in a mouse NASH model. Six-week-old male C57/BL6 mice were fed either chow control or a methionine cholinedeficient (MCD) diet for 8 weeks. Half of the MCD diet-fed mice were treated with 15 mg/kg rat anti-mouse IL-6 receptor antibody (MR16-1), intraperitoneally twice weekly, the remainder and chow-fed mice were injected with 15 mg/kg rat IgG as a control. Hepatic steatosis, injury, fibrosis, apoptosis, markers of lipid peroxidation/oxidant stress and IL-6-related gene expressions were evaluated. MR16-1 treatment decreased signal transducer and activator of transcription 3 activities and expression of suppressor of cytokine signaling 3 in MCD diet-treated mouse livers. Although this treatment enhanced intrahepatic lipid accumulation accompanied by increased sterol regulatory element-binding protein 1 and decreased peroxisome proliferator-activated receptor-a expression, elevated plasma alanine aminotransferase levels were improved with decreased plasma free fatty acid levels, lipid peroxidation/oxidant stress and hepatic apoptosis. Blocking IL-6/GP130 signaling by MR16-1 enhanced MCD diet-induced hepatic steatosis, but ameliorated liver injury. These findings suggest that hepatic IL-6 signaling has a protective role against the progression of hepatic steatosis but may enhance liver inflammation.

Blockade of IL-6 signaling exacerbates liver injury and suppresses antiapoptotic gene expression in methionine choline-deficient diet-Fed db/db mice

“…33,34 We found here that MR16-1 treatment did not exacerbate hepatic steatosis (Figure 4a-d) and the expression of lipogenic genes was not altered (data not shown), despite inhibited IL-6 signaling. However, although MR16-1 treatment decreased plasma FFA levels with increased hepatic lipogenic fed wild-type mice (Supplementary Figure 2D, E, 17 ), these were greatly increased in MCD diet-fed db/db mice. This elevation of plasma FFA indicated that excess FFA accumulation in MCD diet-fed db/db mouse livers might have been beyond the capacity of hepatic triglyceride synthesis, in part because the livers of db/db mice were already severely fatty.…”

“…Half of the chow and MCD diet-fed mice were treated with 15 mg/kg rat anti-mouse IL-6 receptor antibody (MR16-1; Cyugai Pharmaceutical, Tokyo, Japan) intraperitoneally twice weekly for 8 or 12 weeks, the remainder were injected with control rat IgG (Equitech-Bio, Kerrville, TX, USA). [17][18][19] All mice were killed 2 days after the final injection of MR16-1. All animal experiments fulfilled the requirements for humane animal care in Kyoto Prefectural University of Medicine.…”

“…[14][15][16] We have reported recently that blockade of IL-6 signaling by neutralizing antibody against the IL-6 receptor (MR16-1), which is a specific antagonist of the mouse IL-6 receptor, enhanced liver steatosis but improved liver injury in wildtype lean mice fed with an MCD diet. 17,18 We interpreted this result as indicating that excess IL-6 produced by an MCD diet may have exerted an effect as a pro-inflammatory cytokine, leading to the progression of NASH. Therefore, blockade of excessive IL-6-mediated signaling improved liver injury in a lean mouse fed with an MCD diet.…”

Inflammation as a potential link between nonalcoholic fatty liver disease and insulin resistance

“…Therefore, several controversies remain to be clarified regarding the pathological role of TNFa in NAFLD. Xu et al (2002) TNFa is present in white adipose tissue and its production is significantly increased in different rodent obesity models Arner (2003) TNFa level correlates with insulin resistance Hotamisligil (2003) Blocking TNFa with an antibody increases insulin sensitivity Uysal et al (1997) Mice lacking TNFa function are protected against obesity-induced insulin resistance Meyer & de Groot (2003) TNFa induces cytotoxicity through regulation of ceramide synthesis Tilg & Diehl (2000) Increased TNFa level in NAFLD patients Lesmana et al (2009) Correlation between TNFa and degree of liver fibrosis in NAFLD subjects Zhou et al (2010) High prevalence of certain TNFa polymorphisms in patients with NAFLD Lee et al (2008) Pharmacological inhibition of TNFa reduces aminotransferase levels in patients with NAFLD IL6 Bastard et al (2002) IL6 produced by white adipose tissue contributes to insulin resistance observed in obese humans El-Assal et al (2004) IL6 protects against ethanol-induced liver injury Wallenius et al (2002) IL6-deficient mice develop mature onset obesity and associated insulin resistance Wieckowska et al (2008) Hepatic IL6 expression correlates with the severity of NAFLD Yamaguchi et al (2010) Blocking IL6 prevents liver damage and enhances liver steatosis In summary, metabolic alterations leading to lipid accumulation promotes local TNFa production (e.g. liver) and kinase activation.…”

“…Thus, although IL6 improves liver injury, it could not be excluded that it may participate to the development of NAFLD. For instance, blocking IL6 in mice presenting a diet-induced NASH prevents liver injury but concomitantly enhances steatosis (Yamaguchi et al 2010). Altogether, these studies provide controversial results for the role of IL6 in NAFLD and insulin resistance that needs to be further investigated.…”