Nonalcoholic Steatohepatitis: Natural History and Therapy

非酒精性脂肪性肝病(NAFLD)的特点是脂肪在肝细胞内堆积，并伴有炎症和不同程度的细胞损伤和纤维化。当出现细胞损伤和纤维化时，疾病有可能进展，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，要么有胰岛素抵抗，要么有坦率的糖尿病。由于与肥胖和糖尿病有关，NASH的治疗主要集中在减轻体重和改善胰岛素抵抗上。 从2002年开始，我们在NASH进行了一系列临床研究。最初的研究重点是噻唑烷二酮(TZD)，这是一种广泛用于糖尿病的胰岛素增敏剂。在一项初步研究中，22名患有NASH的非糖尿病患者接受了吡格列酮(每天30毫克)的治疗，并在治疗前和治疗48周结束时对代谢状态、身体成分和肝脏疾病(包括肝脏活检)进行了广泛的测试。根据严格的组织学标准评估改善情况。这项研究的初步报告显示，根据严格的组织学标准，三分之二的患者在治疗后有所改善。改善伴随着肝脏脂肪的显著减少，尽管总体体重和全身脂肪增加。因此，TZDS对NASH的影响似乎是由于脂肪储存从肝脏和中央部位重定向到外围。肝脏的组织学改善不仅体现在脂肪量(脂肪变性)上，而且更显著地体现在细胞损伤、炎症和纤维化方面。在这项研究的后续研究中，对患者的样本进行了一系列细胞因子和脂肪因子的测试。组织学的改善最明显地与脂联素的变化有关，脂联素是一种脂肪因子，可以改善胰岛素信号并诱导脂肪细胞成熟。当停用吡格列酮时，NASH的血清生化和组织学特征发生逆转，停药一年后组织学评分恢复到基线水平。重要的是，在吡格列酮治疗期间出现的体重增加并没有逆转；因此，接受了一年疗程的吡格列酮的患者不再具有组织学上的好处，但比他们治疗前重了很多。这些发现表明，NASH的长期改善需要TZD的长期治疗，而且TZD治疗经常伴随的体重增加最终可能会逆转任何好处。 最近，我们启动了一项关于二甲双胍治疗NASH的前瞻性、开放标签研究。共纳入28例NASH患者。这项研究的设计与吡格列酮的设计类似，患者在48周的二甲双胍(每天2000毫克)疗程结束前和结束时都要接受广泛的身体成分、代谢状态、胰岛素敏感性和肝脏疾病(包括肝脏活检)的评估。主要终点是组织学改善，定义为NASH活动指数改善3点。在入选的28名患者中，26名(13名女性；平均年龄44岁)完成了48周的治疗，并接受了重复的代谢研究、成像和肝脏活检。30%的患者在组织学上有反应。大多数患者体重减轻，平均为6公斤。体重减轻与NASH活动指数和ALT水平的改善显著相关(P&lt；0.01)。胰岛素敏感性也有所改善，但改变的程度与组织学改善无关。因此，二甲双胍可以改善30%的NASH患者的肝脏组织学和丙氨酸氨基转移酶水平，可能是因为它能减轻体重。 NASH的未来研究将针对减肥作为改善这种肝病的一种手段。正在考虑的可能治疗方法包括使用大麻素受体拮抗剂(如利莫那班)和使用大剂量二甲双胍。 为了明确NAFLD、肥胖和代谢综合征之间的遗传联系，我们启动了几项NAFLD的遗传学研究。肥胖是血清丙氨酸(ALT)和天冬氨酸转氨酶(AST)水平的重要相关因素。在第一项研究中，我们试图在社区样本中检查父母肥胖与子代血清ALT和AST水平之间的关系。弗雷明汉后代研究的参与者(n=1732)(50%是女性，平均年龄42岁)进行了血清ALT和AST检测，父母双方都在弗雷明翰原始队列中。研究参与者被分成早发性父母肥胖n=193(至少有一个父母肥胖)、晚发型父母肥胖n=460和无父母肥胖n=1079个亚组。ALT或AST升高与父母肥胖之间的关联被用广义估计方程来解释家族相关性。在包括调整子女肥胖的多变量分析中，父亲早发肥胖者的ALT显著高于非父亲肥胖者(p值=0.02)。早发性父亲肥胖的子女与非父亲肥胖的子女相比，ALT水平更有可能升高(优势比OR 1.75(95%CI 1.06-2.89；p=0.03)。在母亲早发肥胖的子代中，ALT升高与ALT无关(OR1.10，95%CI 0.76-1.59；p=0.61)。父母肥胖与血清AST水平之间没有关联。早发性父亲肥胖，而不是母亲肥胖，会增加子代血清ALT水平升高的几率，这表明更容易出现血清ALT水平升高，这可能是通过家族性早发性肥胖来调节的。

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. Recently, we initiated 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 weight loss as a means of improving this liver disease. Possible therapies that are being considered include use of cannabinoid receptor antagonists (such as rimonabant) and use of high doses of metformin. To define the genetic linkage between NAFLD, obesity, and metabolic syndrome, we have initiated several genetic studies of NAFLD. Obesity is an important correlate of serum alanine (ALT) and aspartate (AST) aminotransferase levels. In the first study, we sought to examine the relations between parental obesity and the serum ALT and AST levels among offspring in a community-based sample. Participants (n=1732) of the Framingham Offspring Study (50% women, mean age 42 years) who had serum ALT and AST measurements and both parents in the Framingham Original cohort, were studied. Study participants were grouped into early-onset parental obesity n=193 (at least one parent obese), later-onset parental obesity n=460, and no parental obesity n=1079 subgroups. The association between elevated ALT or AST and parental obesity was tested using generalized estimating equations to account for familial correlations. In multivariable analysis including adjustment for offspring obesity, significantly higher ALT was observed among individuals with paternal early-onset obesity as compared to those without paternal obesity (p-value=0.02). Offspring with early-onset paternal obesity were more likely to have elevated ALT levels compared with those without paternal obesity (odds ratio OR 1.75 (95% CI 1.06-2.89; p=0.03). There was no association with elevated ALT among offspring with maternal early-onset obesity (OR 1.10, 95% CI 0.76-1.59; p=0.61). There was no association between parental obesity and serum AST levels. Early-onset paternal obesity, but not maternal obesity, increases the odds of elevated serum ALT levels in the offspring, suggesting a predisposition to developing elevated serum ALT levels that may be mediated through familial early-onset obesity.