Research Article

A Laboratory Evaluation of Medicinal Herbs Used in China for the Treatment of Hand, Foot, and Mouth Disease

Figure 2

HCT directly inactivates EV71 virion, whereas MHB blocks CVA16 infection by targeting both the virion and cellular factors. (a) Time course study of HCT and MHB antiviral activity. HCT at 40 μg/mL and MHB at 200 μg/mL were added at 2 hr prior to (−2 hr), during (0 hr), or postvirus inoculation at times as indicated (2 hr, 4 hr, 8 hr, 10 hr, 12 hr, and 24 hr PI). Virus infection was determined at 72 hr PI by measuring cell viability colorimetrically. Data are presented as an inhibition rate which is calculated as described in Materials and Methods. (b, c) Coincubation of EV71 with HCT abolishes EV71 infectivity, and MHB inhibits CVA16 infection likely through viral and cellular factors. EV71 (b) or CVA16 (c) in 20 μL culture medium was mock-treated or treated with HCT at a concentration of 40 μg/mL or MHB at 200 μg/mL in a 37°C water bath, respectively, for 2 hr (virus). The treated samples were then added to 1.0 mL fresh culture medium and used to infect Vero cells (final MOIs at 0.2 and final concentrations of HCT and MHB were at 0.8 μg/mL and 4 μg/mL, resp.). In parallel experiments, Vero cells were pretreated with HCT at 40 μg/mL or with MHB at 200 μg/mL at 37°C for 2 hr. The drugs were replaced with fresh culture medium (cell) or left in the culture medium (plus drug). The cells were then infected with EV71 or with CVA16 at equal MOIs. Virus infection was assayed by secondary infection assays at 48 hr PI. Pretreatment of EV71 but not Vero cells with HCT abolished the infectivity of EV71 virus. Treatment of CVA16 or Vero cells with MHB blocked CVA16 infection. Data are presented as mean ± SE of triplicate samples. The results are representative of two independent experiments.