在男性B型肝炎病毒帶原者中PNPLA3基因變異與非酒精性脂肪肝和肝細胞癌罹病風險之相關性：前瞻研究

Abstract

研究背景：PNPLA3 (Patatin like phospholipase domain containing 3)主要表現於肝臟，具有水解肝臟三酸甘油脂的能力。PNPLA3 rs738409 C>G位點的變異，會使PNPLA3蛋白失去功能。非肥胖型脂肪肝在亞洲地區很常見，並認為與遺傳基因有很大的關係，但其機制尚不清楚。過去的研究發現B型肝炎病毒(hepatitis B virus, HBV)感染與非酒精性脂肪肝(nonalcoholic fatty liver disease, NAFLD)之間存在負相關。 研究目的：利用長期追蹤慢性HBV帶原者肝細胞癌(hepatocellular carcinoma, HCC)自然史的世代研究，探討PNPLA3 rs738409基因變異與脂肪肝發展為HCC的過程，並針對非肥胖型的人進行討論。 材料與方法：研究樣本分別是使用2853位進行PNPLA3 rs738409定序之公保世代(Government Employees’ Central Clinics cohort study)個案。樣本皆為HBsAg陽性且沒有發生肝癌的男性公務員，並於1989至1992年納入研究，追蹤至2010年。PNPLA3基因型與脂肪肝對長期追蹤HCC發生的相關性是使用1050位由公保世代所延伸的病例世代研究在考慮HBV病毒量(HBV viral load)後，進行驗證。脂肪肝與肝癌是透過腹部超音波進行診斷。PNALA3基因定序是使用TaqMan SNP assay。長期追蹤資料是利用廣義估計方程式(generalized-estimating equation model, GEE)進行估計。風險比(hazard ratios, HRs)及其95%信賴區間(confidence intervals, CIs)是使用Cox model進行分析。病例世代研究的分析則是透過Weighted Cox 迴歸模型。 研究結果：本研究總共有174人於追蹤過程中發生HCC。PNPLA3 GG型會增加HCC發生的風險(HR=1.60, 95%CI=1.02-2.51)，並且與脂肪肝(odds ratio [OR]=1.73, 95%CI=1.44-2.08)及增高ALT(OR=1.44, 95%CI=1.19-1.75)存在正相關。但是脂肪肝卻與以超音波進行重複測量的肝硬化呈負相關(OR=0.29, 95%CI=0.23-0.37)。除此之外，在調整HBV病毒量之後脂肪肝依然會減少HCC發生的風險(HR=0.29, 95%CI=0.17-0.49)。相較於過重或是肥胖的人，PNPLA3 GG型對HCC的作用在體態正常或是過瘦的人身上較為明顯(HR=2.42, 95%CI=1.19-4.90)。 結論：在慢性HBV帶原者中，PNPLA3 基因變異與脂肪肝、HCC的發生具有相關性，特別是在非肥胖的人身上。但是共同存在慢性HBV感染及脂肪肝的患者與HCC的發生是呈現負相關。因此，HBV帶原者其NAFLD的致病機制尚須未來研究做進一步討論。

Background: Patatin-like phospholipase domain-containing 3 (PNPLA3) has hydrolase activity towards triglyceride, which is highly expressed in hepatocytes. The variant rs738409 C>G p.I148M leads to loss of function of PNPLA3. The mechanism of nonobese nonalcoholic fatty liver disease (NAFLD), which is found more frequently in Asians, is not fully understood and may be associated with genetic background. Prior studies have shown an inverse association between chronic hepatitis B virus (HBV) infection and NAFLD. Specific aims: Using a long-term cohort study on the natural history of hepatocellular carcinoma (HCC) in chronic HBV carriers, we investigated the contribution of PNPLA3 rs738409 variant and fatty liver in the natural course of developing HCC, particularly among nonobese individuals. Materials and Methods: Genotyping of PNPLA3 rs738409 was performed in the Government Employees’ Central Clinics cohort study of 2853 HBsAg positive men who were recruited between 1989 and 1992 and followed until 2010. The prospective associations of PNPLA3 genotypes and fatty liver with HCC risk were validated after taking into account hepatitis B viral load in a case-cohort study of 1050 participants within the cohort study. Fatty liver and liver cirrhosis were diagnosed by ultrasonography. PNPLA3 genotyping was performed by TaqMan SNP assay. Generalized-estimating equation model was used for longitudinal data analysis. Cox models was used to estimate hazard ratios (HRs) and their 95% confidence intervals (CIs). Weighted Cox regression was used in case-cohort analysis. Results: A total of 174 incident HCC cases were identified. PNPLA3 GG genotype was associated with incident HCC (HR=1.60, 95%CI=1.02-2.51). It also showed a positive longitudinal relationship with fatty liver (odds ratio [OR]=1.73, 95%CI=1.44-2.08) and elevated ALT (OR=1.44, 95%CI=1.19-1.75). In contrast, fatty liver had a negative relationship with liver cirrhosis (OR=0.29, 95%CI=0.23-0.37) in repeated ultrasonographic measurements and incident HCC even after adjustment for plasma HBV DNA levels (HR=0.29, 95%CI=0.17-0.49). The impact of PNPLA3 GG genotype on incident HCC was greater in subjects who were normal-weight or underweight (HR=2.42, 95%CI=1.19-4.90) than in those with overweight or obesity. Conclusions: PNPLA3 rs738409 variant was associated with fatty liver and the development of HCC in chronic HBV carriers, especially in nonobese individuals. However, concurrent fatty liver in chronic hepatitis B patients was negatively related to incident HCC. Further studies on the pathogenesis of NAFLD in the condition of coexisting HBV are warranted.