Hepatic steatosis is defined by an increased content of hepatocellular lipids (HCLs) and is frequently observed in insulin-resistant states including type 2 diabetes mellitus. A dietary excess of saturated fat contributes significantly to HCL accumulation. Elevated HCL levels mainly account for hepatic insulin resistance, which is probably mediated by partitioning of free fatty acids to the liver (fat overflow) and by an imbalance of adipocytokines (decreased adiponectin and/or increased proinflammatory cytokines). Both free fatty acids and adipocytokines activate inflammatory pathways that include protein kinase C, the transcription factor nuclear factor kappaB, and c-Jun N-terminal kinase 1 and can thereby accelerate the progression of hepatic steatosis to nonalcoholic steatohepatitis and cirrhosis. Proton magnetic resonance spectroscopy has made it possible to quantify HCL concentrations and to detect even small changes in these concentrations in clinical settings. Moderately hypocaloric, fat-reduced diets can decrease HCL levels by approximately 40-80% in parallel with loss of up to 8% of body weight. Treatment with thiazolidinediones (e.g. pioglitazone and rosiglitazone) reduces HCL levels by 30-50% by modulating insulin sensitivity and endocrine function of adipose tissue in type 2 diabetes. Metformin improves hepatic insulin action without affecting HCL levels, whereas insulin infusion for 67 h increases HCL levels by approximately 18%; furthermore, HCL levels positively correlate with the insulin dosage in insulin-treated type 2 diabetes. In conclusion, liver fat is a critical determinant of metabolic fluxes and inflammatory processes, thereby representing an important therapeutic target in insulin resistance and type 2 diabetes mellitus.

译文

肝脂肪变性是由肝细胞脂质(HCL)含量增加所定义的,并且经常在包括2型糖尿病在内的胰岛素抵抗状态中观察到。饮食中饱和脂肪过多会大大增加HCL的积累。 HCL水平升高主要是肝脏胰岛素抵抗的原因,这可能是由游离脂肪酸在肝脏中的分配(脂肪溢出)和脂肪细胞因子的失衡(脂联素减少和/或促炎细胞因子增加)介导的。游离脂肪酸和脂肪细胞因子均激活包括蛋白激酶C,转录因子核因子kappaB和c-Jun N端激酶1在内的炎症途径,从而可以加速肝脂肪变性发展为非酒精性脂肪性肝炎和肝硬化。质子磁共振波谱使量化HCL浓度和检测临床环境中这些浓度的微小变化成为可能。适度低热量,低脂肪饮食可将HCL水平降低约40-80%,同时最多可减少8%的体重。噻唑烷二酮类药物(例如吡格列酮和罗格列酮)治疗可通过调节2型糖尿病的胰岛素敏感性和脂肪组织的内分泌功能将HCL水平降低30-50%。二甲双胍在不影响HCL水平的情况下改善了肝胰岛素的作用,而胰岛素输注67 h可使HCL水平增加约18%。此外,在用胰岛素治疗的2型糖尿病中,HCL水平与胰岛素剂量呈正相关。总之,肝脏脂肪是代谢通量和炎症过程的关键决定因素,因此代表胰岛素抵抗和2型糖尿病的重要治疗靶标。

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