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SARS-CoV-2 infection of the liver directly contributes
to hepatic impairment in patients with COVID-19
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Our findings suggested that SARS-CoV-2 infection of the liver is a crucial factor contributing to hepatic impairment in patients with COVID-19.
• In this study, we identified the clinical and laboratory characteristics of COVID-19 patients with abnormal liver aminotransferases and firstly reported SARS-CoV-2 is able to infect liver and cause liver impairment of conspicuous cytopathy. In this perspective, a surveillance of viral clearance in liver and long-term outcome of COVID-19 is required. Additional researches on how and to what extent that SARS-COV-2 infection involved in liver enzyme abnormality in distinct COVID-19 population are required.
• through histological, ultrastructural and immunohistochemical examinations on biopsied liver tissues, we found that direct SARS-CoV-2 infection of liver cells significantly contributes to hepatic impairment in patients with COVID-19.
• Coronaviruses have a broad host range and cause a wide variety of respiratory, gastrointestinal, and systemic diseases in animals and humans. Liver enzyme abnormalities developed in as many as 50% of SARS-CoV-2-infected patients reported by various studies. In our study, 41.0% of patients with COVID-19 presented with liver enzyme abnormality, with a prevalence of 23.5% even in the context of mild cases, confirming liver impairment is common in patients with COVID-19. The liver enzyme abnormality was associated with disease severity, as well as a series of laboratory tests, including higher A-aDO2, higher FER, lower albumin, and decreased circulating CD4+ T cells and B lymphocytes. Importantly, we provided the first evidence of SARS-CoV-2 infection directly causing cytopathy of hepatocytes and impairing liver function in patients with COVID-19, although other factors such as drug toxicity or complication-related insults to the liver cannot be excluded.
• SARS-CoV was also reported to cause liver impairment.
Lay summary
Liver enzyme abnormalities are com- mon in patients with coronavirus disease 2019 (COVID-19). We reported the clinical characteristics and liver pathological manifestations of COVID- 19 patients with elevated liver enzymes. Our findings suggested that SARS-CoV-2 infection of the liver is a crucial factor contributing to hepatic impairment in patients with COVID- 19.
EASL COVID-19 and the liver - data from international registries - (09/04/20)
SARS-CoV-2 infection of the liver directly contributes to hepatic impairment in patients with COVID-19
Jnl of Hepatology. Oct 2020. Yijin Wang1,#, Shuhong Liu1,#, Hongyang Liu1,#, Wei Li2,#, Fang Lin3, Lina Jiang1, Xi Li1, Pengfei Xu1, Lixin Zhang1, Lihua Zhao1, Yun Cao2, Jiarui Kang4, Jianfa Yang1, Ling Li1, Xiaoyan Liu1, Yan Li1, Ruifang Nie1, Jinsong Mu3, Fengmin Lu5, Shousong Zhao2, Jiangyang Lu4, Jingmin Zhao1,*
1Department of Pathology and Hepatology, The Fifth Medical Center of Chinese PLA General Hospital, Beijing, China; 2Department of Infectious Diseases, The First Affiliated Hospital of Bengbu Medical College, Bengbu, China; 3Department of Intensive Care Unit, The Fifth Medical Center of Chinese PLA General Hospital, Beijing, China; 4Department of Pathology, The Fourth Medical Center of Chinese PLA General Hospital, Beijing, China; 5Department of Microbiology and Infectious Disease Center, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
Highlights
• Liver enzyme abnormalities in patients with COVID-19 are associated with disease severity.
• Patients with liver enzyme abnormalities have higher A-aDO2 and GGT, lower albumin and decreased circulating CD4+ T cells and B lymphocytes.
• SARS-CoV-2 is able to infect the liver and cause conspicuous hepatic cytopathy.
• Massive apoptosis and binuclear hepatocytes were the predominant histological features of SARS-CoV-2-infected liver.
Background & Aims
Liver enzyme abnormalities are common in patients with coronavirus disease 2019 (COVID-19). Whether or not severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can lead to liver damage per se remains unknown. Herein, we reported the clinical characteristics and liver pathological manifestations of COVID-19 patients with liver enzyme abnormalities.
Methods
We analyzed 156 patients diagnosed with COVID-19 from 2 designated centers in China and compared clinical features between patients with or without elevated aminotransferases. Postmortem liver biopsies were obtained from 2 cases who had elevated aminotransferases. We investigated the patterns of liver impairment by electron microscopy, immunohistochemistry, TUNEL assay and pathological studies.
Results
Sixty-four out of 156 (41.0%) patients with COVID-19 had elevated aminotransferases. The median levels of alanine aminotransferase were 50 U/L vs. 19 U/L, respectively, aspartate aminotransferase were 45.5 U/L vs. 24 U/L, respectively in abnormal and normal aminotransferase groups. Liver enzyme abnormalities were associated with disease severity, as well as a series of laboratory tests including higher alveolar-arterial oxygen partial pressure difference, higher gamma-glutamyltransferase, lower albumin, decreased CD4+ T cells and B lymphocytes. Ultrastructural examination identified typical coronavirus particles, characterized by spike structures, in the cytoplasm of hepatocytes in 2 COVID-19 cases. SARS-CoV-2-infected hepatocytes displayed conspicuous mitochondrial swelling, endoplasmic reticulum dilatation and glycogen granule decrease. Histologically, massive hepatic apoptosis and some binuclear hepatocytes were observed. Taken together, both ultrastructural and histological evidence indicated a typical lesion of viral infection. Immunohistochemical results showed scarce CD4+ and CD8+ lymphocytes. No obvious eosinophil infiltration, cholestasis, fibrin deposition, granuloma, massive central necrosis, or interface hepatitis were observed.
Conclusions
SARS-CoV-2 infection in the liver directly contributes to hepatic impairment in patients with COVID-19. Hence, a surveillance of viral clearance in liver and long-term outcome of COVID-19 is required.
Lay summary
Liver enzyme abnormalities are common in patients with coronavirus disease 2019 (COVID-19). We reported the clinical characteristics and liver pathological manifestations of COVID-19 patients with elevated liver enzymes. Our findings suggested that SARS-CoV-2 infection of the liver is a crucial factor contributing to hepatic impairment in patients with COVID-19.
Discussion
Coronaviruses have a broad host range and cause a wide variety of respiratory, gastrointestinal, and systemic diseases in animals and humans. Liver enzyme abnormalities developed in as many as 50% of SARS-CoV-2-infected patients reported by various studies. In our study, 41.0% of patients with COVID-19 presented with liver enzyme abnormality, with a prevalence of 23.5% even in the context of mild cases, confirming liver impairment is common in patients with COVID-19. The liver enzyme abnormality was associated with disease severity, as well as a series of laboratory tests, including higher A-aDO2, higher FER, lower albumin, and decreased circulating CD4+ T cells and B lymphocytes. Importantly, we provided the first evidence of SARS-CoV-2 infection directly causing cytopathy of hepatocytes and impairing liver function in patients with COVID-19, although other factors such as drug toxicity or complication-related insults to the liver cannot be excluded.
SARS-CoV was also reported to cause liver impairment.
However, the evidence of visible coronavirus particles under TEM examination in liver tissue was absent.
In this study, abundant SARS-CoV-2 viral particles were observed in the cytoplasm of hepatocytes in two COVID-19 cases. The majority of viral particles were noted to harbor a complete envelope with corona-like spikes, indicating SARS-CoV-2 is not only able to enter, but also replicate in hepatocytes. Strikingly, ultrastructural features of conspicuous mitochondria swelling, endoplasmic reticulum dilatation, and impaired cell membrane demonstrated the cytopathy of SARS-CoV-2 in hepatocytes. Moreover, massive hepatic apoptosis and binuclear or a few multinuclear hepatocytes, which were syncytial, rather than proliferative identified by Ki67 immunohistochemistry, were the predominant histological features of viral infection. Meanwhile, immunohistochemistry results showed scarce CD4+ cells and CD8+ cells in liver tissues, suggesting immunopathologic insult might not be favored in liver damage. Taken together, histological and ultrastructural evidence indicated that SARS-CoV-2 dissemination in the liver potentially contributed to abnormal liver aminotransferases.
Angiotensin-converting enzyme 2 (ACE2) is known as cell entry receptor of both SARS-CoV and SARS-CoV-2. SARS-CoV-2 is perceived to be less likely to cause liver infection due to lower ACE2 expression in hepatocytes. However, we found abundant SARS-CoV-2 viral particles in hepatocytes. Usually, the receptor distribution is considered to be concordant with that of infected organs. Nevertheless, there exist notable discordances of ACE2 expression in SARS-CoV targeted multiorgans, such as virus replication in colonic epithelium, which has no ACE2, and no virus infection in endothelial cells, which have ACE2. Evidently, these discrepancies suggested the localization of ACE2 does not fully explain the liver tropism of SARS-CoV-2. We speculate that alternative extra-ACE2 receptors or co-receptors might exist. Another possibility is that the expression of ACE2 in hepatocytes may be upregulated upon sensing virus entry. However, we have no data on the expression of ACE2 in SARS-CoV-2-infected liver and further study is required to address this hypothesis. One of the striking observations in our study was that the A-aDO2 was dramatically higher in patients with liver aminotransferase abnormality, implying that liver damage may be linked to poor pulmonary function in patients with COVID-19. Mechanistically, proinflammatory cytokines were reported to increase significantly in severe COVID-19 cases.
This event often provokes systemic ischemia and hypoxia, which is blamed for inadequate pulmonary ventilation, manifesting as an elevation of A-aDO2. Thus, patients with severe COVID-19 may be predisposed to developing hypoxic-ischemic liver injury. The hallmark of ischemic liver injury is centrilobular necrosis, usually identified by acute and marked increases in serum aminotransferases.
The 2 biopsied cases in the current study did not present the pathological feature of ischemic liver and their serum aminotransferases were increased moderately, implicating the liver impairment in these 2 cases might be independent of pulmonary dysfunction to an extent. Additionally, the involvement of other COVID-19-related complications in liver enzyme abnormality cannot be ruled out. There were only 2 septic patients in our study, 1 with elevated liver enzymes (case 2) and the other with normal liver enzymes, suggesting that sepsis is unlikely to contribute to the high incidence of liver enzyme abnormality in the current cohort. Additionally, the pathological examination in case 2 showed no septic histological features of centrilobular necrosis, canalicular/ductular cholestasis, non-bacterial cholangitis, suggesting that septic insult is unlikely to be the main cause of liver impairment in this case. Nevertheless, due to the limited number of septic patients in our cohort, we could not provide convincing data on the frequency of liver function abnormality in septic patients.
Drug-induced liver injury (DILI) might be an alternative cause of liver damage. According to our results, no significant differences in terms of antiviral and antibiotic medications were found between normal and abnormal liver enzyme groups. Moreover, as hepatotoxicity usually occurs after long-term antiviral therapy, the clinical courses of our patients did not favor antiviral DILI. Indeed, hepatotoxicity may occur in the first few weeks after antibiotic therapy and are typically related to remarkable elevation of liver enzymes, sometimes in conjunction with allergic reactions such as rash. However, our patients had no such obvious adverse reactions, and the median ALT level was 50 (40.0–70.0) U/L in this cohort. Histologically, although both SARS-CoV-2 infection and drugs might result in liver steatosis, the pathological features of no obvious eosinophil infiltration, cholestasis, fibrin deposition, granuloma, massive central necrosis, or interface hepatitis in the 2 biopsied cases were not suggestive of DILI. Nevertheless, we could not exclude DILI as a participating cause since only 2 cases were biopsied.
Several other laboratory variables were shown to associate with aminotransferase abnormalities in COVID-19. The median GGT values in both groups of abnormal and normal aminotransferases were in normal range and no significant differences in levels of DBiL, total bilirubin, or ALP were observed between the 2 groups, suggesting that bile ducts were unlikely the SARS-CoV-2 target sites. Notably, patients with elevated liver enzymes were more likely to have lower serum albumin, suggesting an association of liver synthetic dysfunction and liver enzyme abnormality in patients with COVID-19. Serum ferritin levels were higher in patients with elevated aminotransferases. Physiologically, one-third of ferritin is stored in the liver and circulating ferritin can normally be cleared by liver cells. Therefore, patients with damaged livers may fail to get rid of circulating ferritin, leading to an accumulation of ferritin in serum. Immune disruption, characterized by lymphopenia, decreased levels of CD4+ T cells and B lymphocytes, was more profound in the group with abnormal aminotransferases. However, the serum IL-6 was not higher, but even lower in patients with abnormal aminotransferases. Besides, both lymphopenia and elevated liver enzymes were linked to the severity of COVID-19. We thereafter assumed that immune dysfunction and liver impairment were coincident events, rather than having a cause-effect relationship.
There were limitations in our study. We could only conduct ultrastructural and pathological analysis in 2 biopsies, which is insufficient to represent the entire cohort. Moreover, the cohort was limited to 2 centers. Therefore, large- and multi-cohort studies that contain more cases available for biopsy or autopsy are justified to comprehensively understand liver impairment in COVID-19 patients. However, we believe that our remarkable findings offered crucial clue to liver enzyme abnormality in COVID-19 patients.
In this study, we identified the clinical and laboratory characteristics of COVID-19 patients with abnormal liver aminotransferases and firstly reported SARS-CoV-2 is able to infect liver and cause liver impairment of conspicuous cytopathy. In this perspective, a surveillance of viral clearance in liver and long-term outcome of COVID-19 is required. Additional researches on how and to what extent that SARS-COV-2 infection involved in liver enzyme abnormality in distinct COVID-19 population are required.
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