Coronavirus disease 2019 (COVID-19) caused by Severe Acute Respiratory Syndrome Coronavirus -2 (SARS-CoV-2) has been reported to 28 infect more than 12 million people worldwide killing 500 thousand people (updated on Jul 10 th , 2020). 1 World Health Organization (WHO) has 29 declared COVID-19 as a public health emergency of international concerns. 2 COVID-19 patients show typical clinical symptoms of fever, 30 fatigue, dry cough and pneumonia. [3] [4] [5] Excessive inflammatory response leads to acute respiratory distress syndrome (ARDS), coagulopathy, and 31 septic shock which can be fatal in critical cases. 3 Gross anatomy identifies the main pathological features including exudation and hemorrhage, 32 epithelium injuries, infiltration of inflammatory immune cells and fibrosis in the lungs of fatal patients. 3, 6-10
A syndrome with a distinct cytokine storm was showed in a subgroup of patients with severe COVID-19, which has also been reported in 34 SARS-CoV infected patients. [11] [12] [13] [14] The cytokine storm refers to an uncontrolled excessive inflammatory response, spreading from a local lesion to 35 the whole body through the systemic circulation. 15, 16 The plasma concentrations of inflammation related cytokines such as interleukins (IL) -2, 36 -6, -7, and -10, tumor necrosis factor-α (TNF-α), interferon-γ-inducible protein 10 (IP10), granulocyte-colony stimulating factor (G-CSF), 37 monocyte chemoattractant protein -1 (MCP-1), and macrophage inflammatory protein 1 alpha (MIP-1α) were significantly increased in the 38 COVID-19 patients. 3, 17, 18 Specially, the activation of alveolar macrophages was a characteristic abnormality. 8
The leading cause of mortality is thought to be ARDS-induced respiratory failure, and patients generally receive supportive management in 40 clinic practice. 17 However, there is still no well-accepted effective treatment for COVID-19. The development of novel therapeutics has been 41 mainly focused on antivirals 19, 20 and vaccines. 11 In addition, the cytokine storm is increasingly being recognized as a key node for the patients 42 deteriorating to severe COVID-19. 3, 11, 17 Therefore, anti-inflammatory therapy has been considered as one of appropriate clinical adjuvant 43 5 treatment options, and the treatments include steroids (e.g., prednisone), 21 selective cytokine blockade (e.g., tocilizumab), 11 JAK inhibition (e.g.,
Baricitinib), 22 intravenous immunoglobulin, Chinese medicines and blood purification. 11, 21
Early in Feb, 2020, 75 of 99 COVID-19 patients received antiviral treatment including oseltamivir. 23 Besides, oseltamivir is noted to have 46 been widely used for confirmed or suspected COVID-19 cases in hospitals in China 24 and Thailand (NCT04303299). The other two clinical trials 47 (NCT04261270 and NCT04255017) involving oseltamivir in the treatment of COVID-19 are currently ongoing. However, the FDA-approved 48 neuraminidase inhibitors including oseltamivir, zanamivir and peramivir were ineffective against the SARS-CoV-2 virus in vitro. 25 There has 49 been no exact evidence to date that oseltamivir is effective in the treatment of COVID-19 in clinic. 19
It is reported that oseltamivir exhibited the antiviral activity of reducing pulmonary viral load, thereby the cytokines production was 51 suppressed. 26 Macrophages play a vital role in both SARS-CoV-2 virus -induced lung lesions and the host cytokine-mediated response. 8 In our 52 previous study, entecavir, a hepatitis B virus (HBV) inhibitor, was demonstrated to directly inhibit the release of cytokines in lipopolysaccharide 53 (LPS) -stimulated macrophage model, 27 which is a classic in vitro model to evaluate the anti-inflammatory activity of the drugs. 28 Herein, we 54 also examined whether these three neuraminidase inhibitors could inhibit the expression of inflammatory cytokines in LPS-stimulated 55 macrophages in the present study. The results showed peramivir had the best ability to inhibit TNF-α by ~70% among the three compounds. 56 Furthermore, we estimated the anti-cytokine storm effect and lung protection of peramivir in vivo. The anti-inflammatory effect of peramivir in 57 human peripheral blood mononuclear cells (hPBMCs) was also observed. 
CCS was induced by a single i.p. injection of LPS (15 mg/kg), as described previously. 29 After 4 h, mice were sacrificed and serum was collected.
After 8 h, the left bronchus was ligated and 1 mL saline was perfused into right lung lobe to collect BALF, and the left lung was fixed with 70 paraformaldehyde for histological analysis. Serum and BALF were further used for multi-cytokine analysis.
To investigate the effect of drugs on the survival time of CSS model mice, a single i.p. injection of saline (n=10), peramivir (20 and 60 mg/kg, 72 n=10) was performed at 1 h before i.p. injection of a lethal dose of LPS (30 mg/kg) to mice, respectively. After modeling, mice survival was 73 recorded every 2 h until 40 h.
Preparation of the peritoneal macrophages 75 The peritoneal macrophages were obtained from the mice after i.p. injection of 3 ml of 3% thioglycolate as described previously. 29 Briefly, the 76 mice were sacrificed, and the macrophages were isolated by lavage with 5 ml of RPMI 1640 (Gibco Life Technologies), washed twice with PBS 77 7 after 4 h of adherence, cultured in RPMI at 37°C and 5% CO 2 , and finally stimulated with 100 ng/ml LPS to harvest supernatants. The isolated 78 cells were used for cytokine analysis and cell viability assays. Anti-inflammatory activity screening 92 We chose an in vitro model of LPS-stimulated peritoneal macrophages to induce TNF-α secretion, and screened potential anti-inflammatory 93 molecules in the antiviral and antibacterial drug library. Briefly, 100 ng/ml LPS stimulated peritoneal macrophages for 4 h with simultaneous The left lung lobes of mice were fixed using formalin, and then the tissues were paraffin-embedded. Sections (5 μm) of formalin-fixed tissues 
Peramivir is an active anti-inflammatory agent without apparent cytotoxicity. 138 The three neuraminidase inhibitors (peramivir, oseltamivir, and zanamivir, Fig. 1a) were explored for their ability to inhibit TNF-α-induced by 139 LPS in macrophages. They inhibit the elevation of TNF-α by 67.2%, 35.6% and 13.1% at 10 µM, respectively (Fig. 1b) . Furthermore, peramivir 140 dose-dependently inhibited TNF-α release with the half-maximal inhibitory concentration (IC 50 ) as 4.3 µM (Fig. 1c) . Given that the inhibitory 141 effect of the drugs on TNF-α might be achieved by cytotoxicity, we tested the cytotoxicity of peramivir in macrophages by a CCK-8 assay. It 142 was demonstrated that no apparent toxicity was observed in the peramivir-treated macrophages at concentrations up to 40 μM (Fig. 1d) .
Peramivir inhibits LPS-induced cytokine storm in mice. 144 We used LPS-induced cytokine storm syndrome (CSS) mouse model to evaluate the in vivo inflammatory inhibitory activity. Peramivir was 145 11 administrated intraperitoneally (i.p.) at the concentration of 60 mg/kg at 1 h before LPS injection, and serum was collected at 4 h after LPS 146 injection for further experiment. Twelve cytokines in total were simultaneously measured using a mouse antivirus panel by flow cytometric bead 147 array. Compared with the control group, 7 cytokines including TNF-α, IL family (IL-6, IL-1β, IL-12), chemokines (MCP-1), interferon family 148 (IFN-α, γ) were significantly decreased by the treatment (Table 1 and Fig. S1 ). The other 5 cytokines including IL-10, IP-10, chemokine (C-C (Fig. 2a) . In contrast, the alveolar structures of mice in the peramivir treated group were relatively intact, inflammatory cell infiltrations were 160 significantly reduced, and mild alveolar thickening and less bleeding points or congestion were observed (Fig. 2a) . Lung injury scores were 161 calculated (Fig. 2b) to show significant protective effects of peramivir (score = 2.6 ± 0.6) to the lung tissues compared with that of control group 162 12 (score = 4.8 ± 0.33). The survival time was prolonged in mice treated with peramivir in a dose-dependent manner after an i.p. injection of a 163 lethal dose of LPS (30 mg/kg) compared with that in control mice (Fig. 2c) .
Peramivir decreases NF-κB transcriptional activity in RAW264.7 and the peritoneal macrophages. 165 NF-κB is an important transcriptional regulator in cells that participated in inflammatory responses, of which the activation induces the 166 expression of multiple genes and production of cytokines consequently leading to cytokine storm. 32 Peramivir dose-dependently inhibited 167 LPS-induced NF-κB transcriptional activity in the RAW264.7 cells with a NF-κB reporter luciferase system (Fig. 2d) . Furthermore, we detected 168 some key factors in inflammation responses by western blot and found that the LPS-induced activation of NF-κB pathway (phosphorylation of 169 p65) and MAPKs (phosphorylation of p38 and Erk1/2) were inhibited after peramivir intervention (Fig. 2e) . Immunofluorescence images of 170 LPS-stimulated peritoneal macrophages treated with or without peramivir indicated that LPS-induced nuclear translocation of p65 was 171 attenuated by peramivir (Fig. 2f) .
Considering the translational value of peramivir in clinical practices, the release of TNF-α was tested in LPS-induced hPBMCs, which were 174 obtained from two healthy donors. Peramivir (Fig. 3a, b and Fig. S3 ) significantly counteracted the level of TNF-α at 6 h and 12 h in a time-and 175 dose-dependent manner without apparent toxicity. The three neuraminidase inhibitors bear similar pharmacophoric side chains (black, Fig. 1a ) and different core scaffolds (red, Fig. 1a ). Peramivir 179 13 has a five-membered cyclopentanol ring, while oseltamivir and zanamivir have six-membered ring, which might be a critical part for the 180 anti-inflammatory activity in the chemical structure of view. anti-inflammatory effect of peramivir in vivo may be due to its antiviral symptomatic treatment, while we tried to investigate whether peramivir 188 can directly inhibit the release of cytokines by inflammatory immune cells.
As the neuraminidase is not expressed in the SARS-CoV-2 virus, oseltamivir, zanamivir and peramivir were ineffective against the virus in 190 vitro. 25 In a clinical study, 75% of the COVID-19 patients received antiviral treatment including oseltamivir and 5 of them simultaneously 191 infected with SARS-CoV-2 and influenza were recovered after treating with oseltamivir. 23 We hypothesized that these neuraminidase inhibitors showed no toxicity toward hPBMCs. *P < 0.05, **P < 0.01, *** P < 0.001. 335 Table 1 . Clinical feature and experimental results of cytokines tested in mouse serum. b Peramivir reduced TNF-α release in dose (2.5, 5, 10 μM)-dependent manner. Peramivir showed no toxicity toward hPBMCs. *P < 0.05, **P <0.01, ***P < 0.005. 369