Transmissible gastroenteritis virus (TGEV) is a porcine coronavirus.
Lithium chloride (LiCl) has been found to be effective against several DNA viruses, such as Herpes simplex virus and vaccinia virus. Recently, we and others have reported the inhibitory effect of LiCl on avian infectious
bronchitis coronavirus (IBV)
infection, an RNA virus. In the current study, the action mechanism of LiCl on cell
infection by TGEV was investigated. Plaque assays and 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenyl tetrazoliumbromide (MTT) assays showed that the cell
infection by TGEV was inhibited in a dose-dependent manner, when LiCl was added to virus-infected cells; the cell
infection was not affected when either cells or viruses were pretreated with the
drug. The inhibition of TGEV
infection in vitro by LiCl was observed at different virus doses and with different cell lines. The inhibitory effect of LiCl against TGEV
infection and transcription was confirmed by RT-PCR and real-time PCR targeting viral S and 3CL-protease genes. The time-of-addition effect of the
drug on TGEV
infection indicated that LiCl acted on the initial and late stage of TGEV
infection. The production of virus was not detected at 36 h post-
infection due to the
drug treatment. Moreover, immunofluorescence (IF) and flow cytometry analyses based on staining of
Annexin V and
propidium iodide staining of nuclei indicated that early and late cell apoptosis induced by TGEV was inhibited efficiently. The ability of LiCl to inhibit apoptosis was investigated by IF analysis of
caspase-3 expression. Our data indicate that LiCl inhibits TGEV
infection by exerting an anti-apoptotic effect. The inhibitory effect of LiCl was also observed with porcine epidemic
diarrhea coronavirus. Together with other reports concerning the inhibitory effect of
lithium salts on IBV in cell culture, our results indicate that LiCl may be a potent agent against porcine and avian coronaviruses.