Dear Editor,

Coronavirus disease 2019 (COVID-19) is a type of novel coronavirus and no specific treatment is currently available. Apart from damages to the lung, COVID-19 is also able to trigger liver injury. Numerous observational studies have revealed that elevation of liver enzymes, including alanine aminotransferase (ALT) and aspartate aminotransferase (AST), was detected in some COVID-19 patients, especially in severe cases.1 Unfortunately, the underlying mechanisms and risk factors of COVID-19-induced liver damage have not been completely elucidated. Therefore, identification of novel risk factors in liver injury of COVID-19 patients is essential for the prevention and treatment of liver damage. In this study, 192 patients with COVID-19 hospitalized in Chongqing Public Health Center were recruited to identify the risk factors in COVID-19 patients with liver injury.

The characteristics of 163 mild and 29 severe patients with COVID-19 were analyzed in this study. The results indicated that age and hospitalization time of severe patients were significantly higher compared to mild cases (P < 0.05, Supplementary Table S1). Additionally, the respiratory (fever, shortness of breath, and chest tightness) and gastrointestinal symptoms (anorexia) in severe patients were more obvious (P < 0.05, Supplementary Table S1). Furthermore, liver injury was more commonly detected in the severe group, in whom the expression levels of inflammatory cytokines (procalcitonin, C-reactive protein, erythrocyte sedimentation rate, interleukin (IL)-6, IL-10, and IL-17A) were remarkably elevated (P < 0.05, Supplementary Table S1). The numbers of T lymphocyte subsets (CD3+, CD4+ and CD8+ T cells) in patients with severe COVID-19 were notably decreased compared to mild patients (P < 0.05, Supplementary Table S1).

Further studies on liver function alterations in patients with mild and severe COVID-19 suggested that the levels of albumin were significantly reduced, and the production of ALT, AST, and lactate dehydrogenase (LDH) was remarkably elevated in patients with severe COVID-19 at admission. Furthermore, the severity of liver injury in patients was aggravated during hospitalization, and the levels of ALT, AST, alkaline phosphatase and LDH in severe patients with COVID-19 were significantly increased compared to the mild group (Supplementary Fig. S2). When the patients tested negative for COVID-19 and reached the discharge standard, liver function of both the experimental groups was significantly improved. These findings suggested that, during the development of COVID-19, liver injury could be aggravated. Taken all together, age, respiratory and gastrointestinal symptoms, the levels of inflammatory cytokines, numbers of T lymphocyte subsets, and degree of liver injury were associated with COVID-19 severity.

To further analyze the risk factors in liver injury of COVID-19 patients, 75 patients (39.06%) with liver injury and 117 patients without liver injury were recruited at admission. More male participants were found in the liver injury group compared to patients without liver injury (P < 0.05, Supplementary Table S2). In addition, more obvious gastrointestinal symptoms (anorexia), reduced number of T lymphocyte subsets (CD3+ and CD4+ T cells), and upregulation of inflammatory cytokines (r-interferon, tumor necrosis factor (TNF)-α, IL-2, IL-4, IL-10, and IL-17A) were detected in patients with severe COVID-19. Logistic regression was performed to identify potential risk factors in COVID-19 patients with liver injury at admission. Univariate analysis revealed that gender, TNF-α, IL-2, IL-4, IL-17A, CD3+ T, and CD4+ T cells were novel risk factors in COVID-19 patients with liver injury (P < 0.05,Supplementary Table S3). Multivariate analysis indicated that gender (odds ratio (OR) = 0.31, 95% confidence interval (CI) = 0.11–0.80, P = 0.007), IL-2 (OR = 4.07, 95% CI = 1.25–14.20, P < 0.001), IL-17A (OR = 1.63, 95% CI = 1.23–2.40, P = 0.004), and CD4+ T (OR = 3.90, 95% CI = 1.41–12.17, P < 0.001) cells were independent risk factors in COVID-19 patients with liver injury (P < 0.05, Supplementary Table S3).

During hospitalization, the number of patients with liver injury was increased significantly, as liver injury was detected in 133 COVID-19 patients (69.27%), while 59 patients exhibited no liver damage. Interestingly, liver injury was detected in 25 out of 29 (86.21%) severe COVID-19 patients. The results suggested that the proportion of male patients, nausea, and ritonavir/antibiotics treatment were significantly higher in participants with liver injury (P < 0.05, Supplementary Table S4). In addition, patients with liver injury exhibited reduced number of T lymphocyte subsets (CD3+, CD4+ and CD8+ T cells), and increased levels of inflammatory cytokines (TNF-α, IL-2, IL-6, and IL-10) during hospitalization (P < 0.05, Supplementary Table S4). Logistic regression was carried out to identify putative risk factors in COVID-19 patients with liver injury during hospitalization. Univariate analysis revealed that ritonavir, IL-2, IL-6, IL-10, CD4+ T, and CD8+ T cells were novel risk factors of COVID-19 patients with liver injury during hospitalization (P < 0.05, Table 1). Multivariate analysis suggested that ritonavir (OR = 4.75, 95% CI = 1.89–16.55, P < 0.001), IL-6 (OR = 3.27, 95% CI = 2.09–5.60, P < 0.001), CD4+ (OR = 0.99, 95% CI = 0.95–1.23, P = 0.010) and CD8+ T cells (OR = 1.38, 95% CI = 0.97–1.96, P < 0.001) were independent risk factors in COVID-19 patients with liver injury (P < 0.05, Table 1).

Table 1 Univariate and multivariate analyses of potential risk factors in COVID-19 patients with liver injury during hospitalization
Full size table

Dysregulation of immune response was observed in COVID-19 patients.2 During the development of COVID-19, the expression of programmed cell death receptor 1 and Tim-3 in T lymphocytes was increased, suggesting the depletion of T cells.3 In consistence with these findings, the results of this study suggested that the numbers of T lymphocyte subsets (CD3+, CD4+ and CD8+ T cells) were significantly reduced in patients with liver injury during hospitalization. In addition, CD4+ T cells were an independent risk factor in COVID-19 patients with liver injury at admission. Furthermore, CD4+ and CD8+ T cells were potential independent risk factors in COVID-19 patients with liver injury during hospitalization. Taken all together, depletion of T lymphocytes was detected to serve essential roles on liver injury in COVID-19 patients.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-mediated production of inflammatory cytokines could contribute to liver injury.4 In this study, the expression levels of r-interferon, TNF-α, IL-2, IL-4, IL-10, and IL-17A were remarkably elevated in patients with liver injury at admission. Multivariate analysis indicated that IL-2 and IL-17A were independent risk factors in COVID-19 patients with liver injury at admission, suggesting IL-2 and IL-17A were key inflammatory cytokines that could lead to liver injury. However, the inflammatory factors continued to change during the development of COVID-19. The results of this study revealed that COVID-19 patients with liver injury exhibited increased levels of inflammatory cytokines (TNF-α, IL-2, IL-6, and IL-10) compared to participants without liver injury. Furthermore, multivariate analysis revealed that IL-6 was an independent risk factor in COVID-19 patients with liver injury during hospitalization. In summary, an increased production of inflammatory cytokines was detected in COVID-19 patients, which was associated with liver injury. In clinical practice, alteration of inflammatory cytokines should be closely monitored during the treatment.

At present, no specific treatment is available for COVID-19 patients. The commonly used antiviral drugs lopinavir/ritonavir are mainly metabolized in the liver, and the side effects include liver dysfunction. Previous studies have suggested that use of lopinavir/ritonavir was associated with significantly aggravated liver injury.5 In this study, the proportion of ritonavir- and antibiotics-treated cases was significantly increased in COVID-19 patients with liver injury. Multivariate analysis indicated that ritonavir treatment was an independent risk factor in COVID-19 patients with liver injury.

In conclusion, liver injury was found in many COVID-19 patients, especially those with severe symptoms. The underlying mechanisms of liver injury in COVID-19 patients mainly involve SARS-CoV-2-mediated liver damage, immune response, and cytokine production, as well as drug-induced liver injury. Therefore, during the treatment of COVID-19, intervention targeting CD4+ and CD8+ T cells, antagonist of inflammatory cytokines, could be a promising therapeutic strategy for the treatment of liver injury in COVID-19 patients, and drug-induced liver damage should also be avoided.