Nonalcoholic Steatohepatitis: Natural History, Pathogenesis and Therapy

非酒精性脂肪性肝病（NAFLD）的特征是脂肪在肝细胞中的积累，伴随炎症和不同程度的细胞损伤和纤维化。 当细胞损伤和纤维化存在时，疾病有可能进展，并被称为非酒精性脂肪性肝炎（NASH）。 NASH的病因尚不清楚，但大多数患者超重或肥胖，并患有胰岛素抵抗或明显的糖尿病。 由于这种与肥胖和糖尿病的联系，NASH的治疗重点是减轻体重和改善胰岛素抵抗。 从2002年开始，我们在NASH中进行了一系列临床研究。 最初的研究集中在噻唑烷二酮类（TZDs），广泛用于糖尿病的胰岛素增敏剂。在一项初步研究中，22例非糖尿病NASH患者接受吡格列酮（每日30 mg）治疗，并在48周治疗前和治疗结束时接受了代谢状态、身体组成和肝脏疾病（包括肝活检）的广泛检测。 通过严格的组织学标准评估改善。 这项研究的初步报告显示，根据严格的组织学标准判断，三分之二的患者在治疗后有所改善。 尽管体重和全身脂肪总体增加，但改善伴随着肝脂肪的显著减少。 因此，TZD在NASH中的作用似乎是由于脂肪储存从肝脏和中心部位重定向到外周。 肝脏的组织学改善不仅是脂肪量（脂肪变性），而且在细胞损伤，炎症和纤维化方面更显着。 在本研究的后续研究中，对来自患者的样品进行了细胞因子和脂肪因子的测试。 组织学改善与脂联素的变化相关性最明显，脂联素是一种脂肪因子，可改善胰岛素信号传导并诱导脂肪细胞成熟。 停用吡格列酮后，NASH的血清生化和组织学特征逆转，组织学评分在停用吡格列酮后一年恢复至基线水平。重要的是，吡格列酮治疗期间发生的体重增加没有逆转;因此接受吡格列酮1年疗程的患者不再具有组织学获益，但比治疗前明显加重。 这些发现表明，NASH的长期改善需要TZD的长期治疗，并且通常伴随TZD治疗的体重增加可能最终逆转任何益处。 我们完成了一项二甲双胍治疗NASH的前瞻性、开放性研究。 共入组了28例NASH患者。 该研究的设计与吡格列酮相似，在二甲双胍（每日2000 mg）48周疗程之前和结束时，对患者的身体组成、代谢状态、胰岛素敏感性和肝脏疾病（包括肝脏活检）进行了广泛评价。 主要终点是组织学改善，定义为NASH活动指数改善3分。 在入组的28例患者中，26例（13例女性;平均年龄44岁）完成了48周的治疗，并接受了重复代谢研究、成像和肝活检。 30%的患者获得了组织学缓解。大多数患者体重减轻，平均为6公斤。体重减轻与NASH活性指数和ALT水平的改善之间存在显著相关性（两者，p <0.01）。胰岛素敏感性也有所改善，但变化程度与组织学改善无关。 因此，二甲双胍导致30%的NASH患者的肝脏组织学和ALT水平改善，可能是由于其引起体重减轻的作用。 NASH的未来研究将针对改善这种肝脏疾病的其他方法。 正在考虑的可能疗法包括使用维生素E。我们还在开展NAFLD和/或代谢综合征患者的代谢和生理研究。 全基因组关联（GWA）研究确定了与肝脂肪增加或肝酶升高相关的单核苷酸多态性（SNP），可能反映了非酒精性脂肪性肝病（NAFLD）。我们启动了一项研究，以调查这些SNPs是否与NAFLD患者的组织学严重程度相关。在NASH临床研究网络和美国国立卫生研究院临床中心研究中招募的1117名（894名成人/223名儿童）患有组织学证实的NAFLD的个体针对GWA研究中与肝脂肪或肝酶相关的6种SNP进行基因分型。 在成人中，22号染色体上的3个SNP与非酒精性脂肪性肝炎（NASH）的组织学参数相关。在调整年龄、性别、糖尿病和饮酒量后，PNPLA 3基因中的非同义编码SNP rs738409 C/G的次要等位基因，编码I148 M改变的脂蛋白基因与脂肪变性相关（p=0.03），门静脉炎症（p=2.5x10-4）、小叶炎症（p=0.005）、Mallory-Denk小体（p=0.015）、NAFLD活动性评分（NAS，p=0.004）和纤维化（p=7.7x10-6）。SAMM 50-PNPLA 3簇中的另外两个SNP表现出类似的关联。CPN 1-ERLIN 1-CHUK区域10号染色体上的三个SNP与纤维化独立相关（p=0.010）。在儿童中，没有SNP与组织学严重程度相关。然而，在多变量分析中，rs738409 G等位基因与活检时的年轻年龄相关（p=0.045）。在这个组织学证实的NAFLD的大型队列中，我们证实了rs738409 G等位基因与脂肪变性的相关性，并描述了其与组织学严重程度的相关性。在儿科患者中，高风险rs738409 G等位基因与疾病的早期表现相关。我们还描述了迄今为止未知的10号染色体基因座的SNP与NASH纤维化严重程度之间的关联。

Nonalcoholic fatty liver disease (NAFLD) is marked by accumulation of fat in liver cells with accompanying inflammation and variable degrees of cell injury and fibrosis. When cell injury and fibrosis are present, the disease has a potential to progress and is referred to as nonalcoholic steatohepatitis (NASH). The etiology of NASH is not clear, but most patients are overweight or obese and have either insulin resistance or frank diabetes. Because of this association with obesity and diabetes, therapies for NASH have focused upon weight loss and improvement in insulin resistance. Starting in 2002, we conducted a series of clinical research studies in NASH. An initial study focused on the thiazolidinediones (TZDs), insulin sensitizing agents that are used widely in diabetes. In a pilot study, 22 non-diabetic patients with NASH were treated with pioglitazone (30 mg daily) and underwent extensive testing for metabolic status, body composition and liver disease (including liver biopsy) before and at the end of 48 weeks of therapy. Improvement was assessed by strict histological criteria. A preliminary report on this study showed that two-thirds of patients improved on therapy as judged by strict histological criteria. Improvements were accompanied by a marked decrease in hepatic fat despite an overall increase in body weight and total body fat. Thus, the effects of TZDs in NASH appeared to be due to the redirection of fat storage from the liver and central sites to the periphery. The histological improvements in the liver were not just in amount of fat (steatosis), but more strikingly in cell injury, inflammation and fibrosis. In follow up of this study, samples from patients were tested for a battery of cytokines and adipokines. Histological improvements correlated most clearly with changes in adiponectin, a adipokine that improves insulin signaling and induces maturation of adipocytes. When pioglitazone was stopped, the serum biochemical and histological features of NASH were reversed, histological scores returning to baseline by a year after discontinuation of pioglitazone. Importantly, the weight gain that occurred during pioglitazone therapy was not reversed; so that patients who received a one-year course of pioglitazone no longer had the histological benefit but were considerably heavier than before they were treated. These finds indicate that long-term improvement in NASH would require long-term therapy with a TZD and that the weight gain that often accompanies TZD therapy is likely to ultimately reverse any benefit. We completed a prospective, open-labelled study of metformin as therapy for NASH. A total of 28 patients with NASH were enrolled. The design of the study was similar to that for pioglitazone, in that patients underwent extensive evaluation of body composition, metabolic status, insulin sensitivity and liver disease (including liver biopsy) before and at the end of a 48 week course of metformin (2000 mg daily). The primary endpoint was histologic improvement, defined as a 3-point improvement in the NASH activity index. Of 28 patients enrolled, 26 (13 females; average age 44 years) completed 48 weeks of treatment and underwent repeat metabolic studies, imaging and liver biopsy. Thirty percent achieved a histologic response. Most patients lost weight, the average being 6 kg. There was a marked association between weight loss and improvements in NASH activity index and ALT levels (both, p <0.01). Insulin sensitivity also improved, but the degree of change did not correlate with histologic improvement. Thus, metformin leads to improvements in liver histology and ALT levels in 30% of patients with NASH probably by its effects in causing weight loss. Future studies in NASH will be directed at other means of improving this liver disease. Possible therapies that are being considered include use of Vitamin E. We are also develop metabolic and physiologic studies of patients with NAFLD and/or metabolic syndrome. Genome wide association (GWA) studies identified single nucleotide polymorphisms (SNPs) that are associated with increased hepatic fat or elevated liver enzymes, presumably reflecting nonalcoholic fatty liver disease (NAFLD). We initiated a study to investigate whether these SNPs are associated with histological severity in a large cohort of NAFLD patients. 1117 (894 adults/223 children) individuals enrolled in NASH-Clinical Research Network and National Institutes of Health Clinical Center studies with histologically-confirmed NAFLD were genotyped for six SNPs that are associated with hepatic fat or liver enzymes in GWA studies. In adults, 3 SNPs on chromosome 22 showed associations with histological parameters of nonalcoholic steatohepatitis (NASH). After adjustment for age, gender, diabetes and alcohol consumption, the minor allele of rs738409C/G, a nonsynonymous coding SNP in the PNPLA3 (adiponutrin) gene encoding an I148M change, was associated with steatosis (p=0.03), portal inflammation (p=2.5x10-4), lobular inflammation (p=0.005), Mallory-Denk bodies (p=0.015), NAFLD activity score (NAS, p=0.004) and fibrosis (p=7.7x10-6). Two other SNPs in the SAMM50-PNPLA3 cluster demonstrated similar associations. Three SNPs on chromosome 10 in the CPN1-ERLIN1-CHUK region were independently associated with fibrosis (p=0.010). In children, no SNP was associated with histological severity. However, the rs738409 G allele was associated with younger age at the time of biopsy in multivariate analysis (p=0.045). In this large cohort of histologically-proven NAFLD, we confirm the association of the rs738409G allele with steatosis and describe its association with histological severity. In pediatric patients, the high-risk rs738409G allele is associated with an earlier presentation of disease. We also describe a hitherto unknown association between SNPs at a chromosome 10 locus and the severity of NASH fibrosis.