Houttuynia cordata
Thunb. is a medicinal plant widely used in folk medicine in several Asian countries. It
has been reported that a water extract of
H. cordata
exhibits activity against herpes simplex virus (HSV)
and the virus of severe acute respiratory syndrome (SARS), although the mechanisms are not fully under-
stood yet. Previous studies have demonstrated absolute requirement of NF-
j
B activation for efficient rep-
lication of HSV-1 and HSV-2 and inhibition of NF-
j
B activation has been shown to suppress HSV
infection. Here we show that a hot water extract of
H. cordata
(HCWE) inhibits HSV-2 infection through
inhibition of NF-
j
B activation. The IC
50
was estimated at 50
l
g/ml of lyophilized HCWE powder. At 150
and 450
l
g/ml, HCWE blocked infectious HSV-2 production by more than 3 and 4 logs, respectively. The
inhibitory activity was concomitant with an inhibition of NF-
j
B activation by HSV-2 infection. Although
activation of NF-
j
B and Erk MAPK has been implicated for HSV replication and growth, HCWE showed no
effect on HSV-2-induced Erk activation. Furthermore, we show that treatment with quercetin, quercitrin
or isoquercitrin, major water extractable flavonoids from
H. cordata
, significantly blocked HSV-2 infec-
tion. These results together demonstrated that
H. cordata
blocks HSV-2 infection through inhibition of