Circulating AIM as an Indicator of Liver Damage and Hepatocellular Carcinoma in Humans

et al. (2014) Circulating AIM as an Indicator of Liver Damage and Hepatocellular Carcinoma in Humans. PLoS ONE 9(10): e109123. doi:10.1371/journal.pone.0109123 Circulating AIM as an Indicator of Liver Damage and Hepatocellular Carcinoma in Humans Tomoko Yamazaki Mayumi Mori Satoko Arai Ryosuke Tateishi Masanori Abe Mihoko Ban Akemi Nishijima Maki Maeda Takeharu Asano Toshihiro Kai Kiyohiro Izumino Jun Takahashi Kayo Aoyama Sei Harada Toru Takebayashi Toshiaki Gunji Shin Ohnishi Shinji Seto Yukio Yoshida Yoichi Hiasa Kazuhiko Koike Ken-ichi Yamamura Ken-ichiro Inoue Toru Miyazaki Kalpana Ghoshal, The Ohio State University, United States of America Background: Hepatocellular carcinoma (HCC), the fifth most common cancer type and the third highest cause of cancer death worldwide, develops in different types of liver injuries, and is mostly associated with cirrhosis. However, non-alcoholic fatty liver disease often causes HCC with less fibrosis, and the number of patients with this disease is rapidly increasing. The high mortality rate and the pathological complexity of liver diseases and HCC require blood biomarkers that accurately reflect the state of liver damage and presence of HCC. Methods and Findings: Here we demonstrate that a circulating protein, apoptosis inhibitor of macrophage (AIM) may meet this requirement. A large-scale analysis of healthy individuals across a wide age range revealed a mean blood AIM of 4.9961.8 mg/ml in men and 6.0662.1 mg/ml in women. AIM levels were significantly augmented in the younger generation (20s-40s), particularly in women. Interestingly, AIM levels were markedly higher in patients with advanced liver damage, regardless of disease type, and correlated significantly with multiple parameters representing liver function. In mice, AIM levels increased in response to carbon tetrachloride, confirming that the high AIM observed in humans is the result of liver damage. In addition, carbon tetrachloride caused comparable states of liver damage in AIM-deficient and wild-type mice, indicating no influence of AIM levels on liver injury progression. Intriguingly, certain combinations of AIM indexes normalized to liver marker score significantly distinguished HCC patients from non-HCC patients and thus could be applicable for HCC diagnosis. Conclusion: AIM potently reveals both liver damage and HCC. Thus, our results may provide the basis for novel diagnostic strategies for this widespread and fatal disease. Current address; Omics Group; Genomic Science Laboratories; Dainippon Sumitomo Pharma Co; Ltd; Osaka; Japan - Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This work was supported by Grants-in-Aid for Scientific Research (A) (Japan Society for the Promotion of Science), CREST (JST), research grants by ONSENDO Co., Ltd. (to TM), Grants-in-Aid for Scientific Research (B) (Japan Society for the Promotion of Science) (to SA), research grants by The Tokyo Biochemical Research Foundation, Takeda Science Foundation and Ono Medical Research Foundation (to MM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: Although the authors received funding from a commercial source (ONSENDO Co., Ltd), this funding was solely for research activity, and was not used for employment, consultancy, patents, products in development, or marketed products related to either commercial source. This funding does not alter the authors adherence to PLOS ONE policies on sharing data and materials. Chronic liver injury is one of the most common and fatal diseases in modern society. It has multiple causes including hepatitis virus infection mostly due to hepatitis C virus (HCV) and to a lesser extent hepatitis B virus (HBV), alcohol injury, autoimmunity, and genetic disorders such as hemochromatosis [13]. In addition, the non-alcoholic fatty liver disease (NAFLD), which is associated with obesity, has been observed in a rapidly growing number of patients due to recent and drastic changes in lifestyle. NAFLD comprises a wide variety of disease criteria ranging from benign simple steatosis to progressive inflammation and fibrosis, called non-alcoholic steatohepatitis (NASH) [4,5]. Such chronic liver diseases exhibit continuous inflammation and fibrosis and are a prominent risk for the development of hepatocellular carcinoma (HCC) [68]. In contrast to patients with HCV infection, who display a high susceptibility to HCC, only a limited proportion of NAFLD patients progress to carcinoma [911]. Intriguingly, recent evidence has revealed that although HCC develops largely on the basis of severe liver fibrosis/cirrhosis, it often occurs without cirrhosis in NAFLD/ NASH patients exhibiting mild inflammation and fibrosis [1218]. However, the mechanism of how each pathological background induces HCC remains to be elucidated. With such increasing risks and complicated pathogenesis, biomarkers that reflect the state of liver damage and the presence of HCC are important, particularly for the early diagnosis of HCC development. Ideally, markers that indicate an individuals susceptibility to HCC may be desirable from the prognostic and preventive views of HCC. The circulating protein, apoptosis inhibitor of macrophage (AIM), also called CD5L, was initially identified as an apoptosis inhibitor that supports macrophage survival [19]. AIM is produced solely by tissue macrophages under transcriptional regulation by nuclear receptor liver X receptor alpha (LXRa) [20 22], and as a secreted molecule, AIM is detected in both human and mouse blood [19,23]. Interestingly, AIM associates with the immunoglobulin (Ig)M pentamer in the blood, and this association protects AIM from renal excretion, thereby maintaining circulating AIM at a relatively high concentration (approximately 2 5 mg/ml) in mice [23,24]. However, AIMs precise levels in healthy individuals and patients with various diseases remain controversial [2528]. We recently identified that AIM is incorporated into adipocytes via CD36-mediated endocytosis where it inactivates cytoplasmic fatty acid synthase (FASN) through direct binding. This response reduces the production of lipid droplet-coating proteins such as fat-specific protein 27 (FSP27) and perilipin, thereby decreasing triacylglycerol deposition within adipocytes [29,30]. Consistent with this effect, adipocyte hypertrophy was found to be more advanced with a greater mass of visceral adipose tissue in AIMdeficient (AIM-/-) mice than in wild-type (AIM+/+) mice fed a highfat diet (HFD) [29]. We also found that AIM prevents lipid storage in the liver, as in adipocytes [31]. Because a consensus has rapidly emerged that hepatocytic lipid metabolism impacts the pathogenesis of not only NAFLD but also other liver injuries, as w (...truncated)