OBJECTIVE To investigate the activity and mechanism of tetrandrine (TET) against influenza A virus in vitro and in vivo. METHODS (1) Cell experiments. ① Human non-small cell lung cancer cells (A549) were divided into TET 0 (cell control), 1.25, 2.5, 5, 10, 20 and 25 μmol·L-1 groups, and H1N1+TET 0, 1.25, 2.5, 5, 10, 20 and 25 μmol·L-1 groups. The TET groups were treated with the corresponding concentrations of TET while the H1N1+TET groups were infected with H1N1 for 1 h before the corresponding concentrations of TET were added. After 48 h, cell viability was detected using the CCK-8 method. ② The cells were divided into cell control, H1N1+TET 0, 2.5, 5, and 10 μmol·L-1 groups and treated as in ①. After 24 h of incubation, the mRNA expressions of matrix protein 1(M1), hemagglutinin (HA), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interferon-β (IFN-β) were tested by the real-time quantitative PCR (RT-qPCR). The expression levels of M1, HA, neuraminidase (NA), nucleoprotein (NP), and phosphorylation of signal transducer and activator of transcription 3 (STAT3) protein were detected by Western blotting. (2) Animal experiments. ① Male BALB/c mice were randomly divided into the solvent control group, H1N1 group, H1N1+oseltamivir phosphate (Ose) 20 mg·kg-1 group, and H1N1+TET 25, 50 and 100 mg·kg-1 groups. The solvent control group and the H1N1 group were ig administered with 0.5% carboxymethyl cellulose sodium (CMC-Na), while the H1N1+Ose group and the H1N1+TET 25, 50 and 100 mg·kg-1 groups were ig given suspensions of the respective concentrations of drugs in 0.5% CMC-Na. After three consecutive days of pretreatment, all these groups except the solvent control group were intranasally inoculated with H1N1 to establish an influenza-infected mouse model. The survival rate and body mass of mice were monitored and recorded for 15 consecutive days post-H1N1 infection. ② The grouping and treatment were the same as ①. After infection, mice were sacrificed on day 3 and 5. The expression levels of M1, HA, TNF-α, IL-1β and IL-6 in lung tissues were detected by RT-qPCR, and those of M1, HA, NA, NP, and phosphorylation of STAT3 protein in mice lung tissues by Western blotting. Hematoxylin-Eosin (HE) staining was performed to observe the pathological changes of lung tissues in mice. The levels of IL-6, TNF-α and IFN-β in bronchoalveolar lavage fluid (BALF) were determined by enzyme-linked immunosorbent assays (ELISA). RESULTS (1)① The half maximal inhibitory concentration study showed a value of 18.06 μmol·L-1 for A549 effected by TET. Compared with the H1N1 group, TET 2.5, 5 and 10 μmol·L-1 significantly increased cell viability. ② The expression levels of M1, HA mRNA and M1, HA, NA protein in the TET 2.5, 5 and 10 μmol·L-1 groups were significantly lowered compared with the H1N1 group. TET 5 μmol·L-1 significantly decreased H1N1-induced IL-6, TNF-α and IFN-β mRNA expression levels in A549 cells. TET 5 and 10 μmol·L-1 could significantly mitigate the phosphorylation of STAT3. (2) ① Compared with the H1N1 group, TET 50 mg·kg-1 significantly improved the survival rate of H1N1-infected mice while TET 25 mg·kg-1 significantly elevated the body-weight of H1N1-infected mice. In the TET 50 mg·kg-1 group, expressions of HA and M1 mRNA, and HA, M1, NA and NP protein in the lung tissues of H1N1-infected mice were significantly reduced compared with the H1N1 group. Compared with the H1N1 group, TET 50 mg·kg-1 significantly decreased the lung index, improved inflammatory lesions in lung tissues, inhibited the mRNA expressions of TNF-α, IL-6 and IFN-β in lung tissues, and down regulated the expressions of TNF-α, IL-6 and IFN-β proinflammatory cytokines in the BALF of the H1N1-infected mice. In addition, TET 50 mg·kg-1 also significantly inhibited STAT3 phosphorylation in lung tissues of mice infected with H1N1. CONCLUSION TET can inhibit H1N1 infection both in vivo and in vitro. The potential mechanism may be related to the inhibition of the IL-6/STAT3 pathway, which subsequently suppresses the inflammatory response induced by H1N1.
