Inhibition of Human Parainfluenza Virus Type 2 Growth in Vitro by Catechin is caused by the Inhibition of Genome and mRNA Syntheses and by the Disruption of Cytoskeleton, and that by Tannic Acid is Mainly Caused by Genome Synthesis Inhibition and the Disruption of Cytoskeleton

The antiviral activities of catechin mixture (catechin) and tannic acid against human parainfluenza virus type 2 (hPIV-2) were investigated in vitro. Catechin and tannic acid both inhibited cell fusion induced by hPIV-2 in LLCMK2 cells. However, high concentrations of them caused cell toxicity. Both catechin and tannic acid reduced the number of viruses released from the cells. Real time PCR showed that catechin almost completely inhibited virus genome RNA synthesis, and tannic acid largely inhibited it. Virus nucleoprotein (NP), fusion (F) and hemaggulutinin-neuraminidase (HN) gene syntheses were largely inhibited by catechin, and mRNA syntheses of these proteins were partly inhibited by catechin. However, tannic acid did not cause inhibition. An indirect immunofluorescence study showed that catechin partly inhibited virus NP, F and HN protein syntheses, but tannic acid did not inhibit either virus NP, F or HN protein syntheses. Using a recombinant green fluorescence protein (GFP)-expressing hPIV-2 without matrix protein (rhPIV-2∆MGFP), it was found that virus entry into the cells was not inhibited by catechin or tannic acid, and that spreading of virus to the adjacent cells was not blocked by them. Catechin and tannic acid disrupted both actin microfilaments and microtubules. These results indicated that the inhibitory effect of catechin was caused by the inhibitions of both viral genome RNA and mRNA syntheses, and by the disruption of actin microfilaments and microtubules. However, inhibition by tannic acid was mainly caused by vial genome synthesis inhibition and the disruption of cytoskeleton.