Reply to: Correspondence relating to “SARS-CoV-2 infection of the liver directly contributes to hepatic impairment in patients with COVID-19”
Authors: Yijin Wang, Fengmin Lu, Jingmin Zhao
Journal: Journal of Hepatology (2020)

SARS-CoV-2 related liver impairment – perception may not be the realityJournal of HepatologyVol. 73Issue 4PreviewThe catastrophic emergence of COVID-19 has led to large volumes of research from epicentres of infection, with some focusing on COVID-19-related liver impairment. In this regard, the study by Wang et al. published in the Journal intrigued us.1 The authors associate very minimal elevations in alanine (ALT) and aspartate aminotransferase (AST; ALT >AST) to disease severity and demonstrate 'specific' COVID-19-related cytopathic changes and virus-like particles on post-mortem liver histopathology (n = 2). Full-Text PDF SARS-CoV-2: Is the liver merely a bystander to severe disease?Journal of HepatologyVol. 73Issue 4PreviewWe read the recent article from Wang et al. with great interest.1 They report that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive patients with ≥1-week history of increased aminotransferases have worse acute pulmonary disease (radiological and physiological) than those without. They also report higher ferritin levels, higher proportions of patients with a low albumin and raised direct bilirubin, and histological features (albeit in only 2 patients) possibly in keeping with viral-mediated liver injury. Full-Text PDF Single cell RNA sequencing analysis did not predict hepatocyte infection by SARS-CoV-2Journal of HepatologyVol. 73Issue 4PreviewIt was with great interest that we read the research article by Wang et al. In their manuscript, the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) particles in hepatocytes is shown with additional arguments for viral replication and cytopathy in infected hepatocytes, which provides a partial explanation for the high prevalence of abnormal liver laboratory tests in patients with COVID-19.1 Full-Text PDF We appreciate the thoughtful comments on our paper. Our study focused on coronavirus disease 2019 (COVID-19)-related liver enzyme abnormalities, rather than acute liver injury. Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could infect the liver, it is not a hepatotropic virus that induces pronounced hepatitis. In keeping with this, abnormal liver function tests during the course of COVID-19 are common and primarily limited to aminotransferases, while clinically severe acute liver injury is rare.[1]Garrido I. Liberal R. Macedo G. Review article: COVID-19 and liver disease - what we know on 1st May 2020.Aliment Pharmacol Ther. 2020; 52: 267-275Crossref PubMed Scopus (119) Google Scholar,[2]Kukla M. Skonieczna-Zydecka K. Kotfis K. Maciejewska D. Loniewski I. Lara L.F. et al.COVID-19, MERS and SARS with concomitant liver injury-systematic review of the existing literature.J Clin Med. 2020; 9: 1420Crossref Scopus (75) Google Scholar This also explains the mild transaminase elevation and other well-preserved parameters, such as lactate, glucose and international normalized ratio, which most likely result from direct virus infection. Regarding biochemical parameters, the median gamma glutamyltransferase (GGT) levels in both groups were in the normal range and there were no significant differences in levels of total or direct bilirubin and alkaline phosphatase, suggesting that cholangiocytes are unlikely the target sites. Aspartate aminotransferase was recently reported to highly correlate with alanine aminotransferase and reflect disease severity throughout the COVID-19 course, whereas the correlation with markers of muscle injury was weak.[3]Bloom P.P. Meyerowitz E.A. Reinus Z. Daidone M. Gustafson J. Kim A.Y. et al.Liver biochemistries in hospitalized patients with COVID-19.Hepatology. 2020; Crossref PubMed Scopus (132) Google Scholar Meanwhile, we noted that the median creatinine kinase (CK) was still in the normal range in the abnormal aminotransferases group, and the frequency of elevated CK was comparable between the 2 groups (17.86 % vs. 13.51%, p = 0.89), indicating that elevated CK and abnormal transaminases might not have a causal relationship. Leakage of albumin from blood vessels due to severe vasculitis was usually accompanied by hydrothorax or ascites. However, the albumin reduction in patients with COVID-19 was usually mild. Taken together, these aberrant blood variables appear to be predominantly the result of hepatic impairment. We stated that SARS-CoV-2 directly contributed to cytopathy based on the ultrastructural findings of conspicuous mitochondria swelling, endoplasmic reticulum dilatation, glycogen granule decrease, and impaired cell membranes. Apoptotic and bi- or multi-nucleated syncytial hepatocytes were also signs of direct viral effects.[4]Chau T.N. Lee K.C. Yao H. Tsang T.Y. Chow T.C. Yeung Y.C. et al.SARS-associated viral hepatitis caused by a novel coronavirus: report of three cases.Hepatology. 2004; 39: 302-310Crossref PubMed Scopus (326) Google Scholar,[5]He L. Ding Y. Zhang Q. Che X. He Y. Shen H. et al.Expression of elevated levels of pro-inflammatory cytokines in SARS-CoV-infected ACE2+ cells in SARS patients: relation to the acute lung injury and pathogenesis of SARS.J Pathol. 2006; 210: 288-297Crossref PubMed Scopus (328) Google Scholar Previous studies demonstrated coronaviruses exerted extensive cytopathic effects through apoptosis, via a caspase-dependent pathway.[4]Chau T.N. Lee K.C. Yao H. Tsang T.Y. Chow T.C. Yeung Y.C. et al.SARS-associated viral hepatitis caused by a novel coronavirus: report of three cases.Hepatology. 2004; 39: 302-310Crossref PubMed Scopus (326) Google Scholar,6Tan Y.J. Fielding B.C. Goh P.Y. Shen S. Tan T.H. Lim S.G. et al.Overexpression of 7a, a protein specifically encoded by the severe acute respiratory syndrome coronavirus, induces apoptosis via a caspase-dependent pathway.J Virol. 2004; 78: 14043-14047Crossref PubMed Scopus (175) Google Scholar, 7Eleouet J.F. Slee E.A. Saurini F. Castagne N. Poncet D. Garrido C. et al.The viral nucleocapsid protein of transmissible gastroenteritis coronavirus (TGEV) is cleaved by caspase-6 and -7 during TGEV-induced apoptosis.J Virol. 2000; 74: 3975-3983Crossref PubMed Scopus (78) Google Scholar, 8Liu C. Xu H.Y. Liu D.X. Induction of caspase-dependent apoptosis in cultured cells by the avian coronavirus infectious bronchitis virus.J Virol. 2001; 75: 6402-6409Crossref PubMed Scopus (80) Google Scholar The 'corona-like' particles are characteristic of coronavirus particles, but not cholesterol crystals which are normally highly electron dense, structureless and inhomogeneous. Hepatocytes manifested no megamitochondria with linear crystalline inclusions, cristae loss, or increased matrix electrondensity, which would be expected in non-alcoholic fatty liver disease (NAFLD).9Lotowska J.M. Sobaniec-Lotowska M.E. Bockowska S.B. Lebensztejn D.M. Pediatric non-alcoholic steatohepatitis: the first report on the ultrastructure of hepatocyte mitochondria.World J Gastroenterol. 2014; 20: 4335-4340Crossref PubMed Scopus (36) Google Scholar, 10Le T.H. Caldwell S.H. Redick J.A. Sheppard B.L. Davis C.A. Arseneau K.O. et al.The zonal distribution of megamitochondria with crystalline inclusions in nonalcoholic steatohepatitis.Hepatology. 2004; 39: 1423-1429Crossref PubMed Scopus (109) Google Scholar, 11Caldwell S.H. Swerdlow R.H. Khan E.M. Iezzoni J.C. Hespenheide E.E. Parks J.K. et al.Mitochondrial abnormalities in non-alcoholic steatohepatitis.J Hepatol. 1999; 31: 430-434Abstract Full Text Full Text PDF PubMed Scopus (434) Google Scholar None of the reported autolytic microscopic modifications in the liver[12]Cocariu E.A. Mageriu V. Staniceanu F. Bastian A. Socoliuc C. Zurac S. Correlations between the autolytic changes and postmortem interval in refrigerated cadavers.Rom J Intern Med. 2016; 54: 105-112PubMed Google Scholar were observed in our biopsies. Clathrins are generally located at the plasma membrane of synapses and play a role in synaptic vesicle reconstitution.[13]Heuser J.E. Reese T.S. Evidence for recycling of synaptic vesicle membrane during transmitter release at the frog neuromuscular junction.J Cell Biol. 1973; 57: 315-344Crossref PubMed Scopus (1653) Google Scholar Clathrin possesses variable morphology, such as multiple coated buds which are formed on endosomes, distinctive from typical coronavirus. In light of the low percentage of hepatocytes expressing ACE2, but not the absolute absence, it is not surprising that SARS-CoV-2 is capable of causing liver injury directly. On the other hand, there exist wide discrepancies between organ symptomatology and ACE2 expression levels.[14]Hamming I. Timens W. Bulthuis M.L. Lely A.T. Navis G. van Goor H. Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis.J Pathol. 2004; 203: 631-637Crossref PubMed Scopus (4177) Google Scholar,[15]Harmer D. Gilbert M. Borman R. Clark K.L. Quantitative mRNA expression profiling of ACE 2, a novel homologue of angiotensin converting enzyme.FEBS Lett. 2002; 532: 107-110Crossref PubMed Scopus (654) Google Scholar For instance, ACE2 expression in the respiratory tract is only moderate compared with that in intestinal epithelia, but respiratory symptomatology is substantially more severe than intestinal.[14]Hamming I. Timens W. Bulthuis M.L. Lely A.T. Navis G. van Goor H. Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis.J Pathol. 2004; 203: 631-637Crossref PubMed Scopus (4177) Google Scholar,[15]Harmer D. Gilbert M. Borman R. Clark K.L. Quantitative mRNA expression profiling of ACE 2, a novel homologue of angiotensin converting enzyme.FEBS Lett. 2002; 532: 107-110Crossref PubMed Scopus (654) Google Scholar It is therefore assumed that direct viral effects on the liver might not operate absolutely through ACE2 expression, and other receptors cannot be excluded. Alternatively, the finding of upregulated ACE2 expression in hepatocytes in cirrhotic liver inspired us to speculate that SARS-CoV-2 infection might induce compensatory hyperplasia of hepatocytes, which are possibly derived from cholangiocytes (with high ACE2 expression).[16]Guan G.W. Gao L. Wang J.W. Wen X.J. Mao T.H. Peng S.W. et al.Zhonghua Gan Zang Bing Za Zhi. 2020; 28: 100-106PubMed Google Scholar This procedure might result in a higher ACE2 expression in regenerative hepatocytes and facilitate viral infection in turn. We acknowledge that fatty liver disease, drug-induced liver injury (DILI), sepsis and multiple organ dysfunction syndromes could be involved in liver damage in the setting of COVID-19, but our clinical and pathological findings do not favor these possibilities, as thoroughly described in our paper. Firstly, the prevalence of transaminase abnormalities was up to 23.5% even in the context of mild cases, precluding the role of COVID-19-related comorbidities. Secondly, despite steatosis, both biopsied cases had neither NAFLD nor other metabolic disorders. The pathological features of no obvious eosinophil infiltration, cholestasis, fibrin deposition, vasculitis, granuloma, massive central necrosis, or interface hepatitis did not comply with DILI. Thirdly, only 7 of 64 (10.9%) cases had sepsis and other severe comorbidities, which could not explain the apparently high rate (41.0%) of liver enzyme abnormality in our cohort. Additionally, the liver pathology in our septic case showed no pathological hallmark of sepsis, suggesting sepsis was not the main insult. All in all, our data fully support a direct role of SARS-CoV-2 in COVID-19-related hepatic impairment. In conclusion, we believe SARS-CoV-2 is capable of infecting the liver and is a crucial factor in liver dysfunction, though other factors cannot be fully excluded. The authors received no financial support to produce this manuscript. JZ and FL contributed to study concept, critical revision of the manuscript; YW contributed to literature search and writing of the manuscript. The authors declare no conflicts of interest. Please refer to the accompanying ICMJE disclosure forms for further details. Download .pdf (.16 MB) Help with pdf files disclosures.pdf