The mistletoe Viscum coloratum is used in
traditional Chinese medicine to treat inflammatory diseases. In this study, a cellular model in isolated human neutrophils, which are important in the pathogenesis of
rheumatoid arthritis,
chronic obstructive pulmonary disease, and other inflammatory diseases, was established to elucidate the anti-inflammatory functions of V. coloratum. The partially purified extract of V. coloratum (PPE-SVC) potently inhibited formyl-L-methionyl-L-leucyl-
L-phenylalanine (FMLP)-induced
superoxide anion generation and
elastase release in a concentration-dependent manner with IC(50) values of 0.58+/-0.03 and 4.93+/-0.54 microg/ml, respectively. Furthermore, a new
chalcone derivative,
viscolin (4',4''-dihydroxy-2',3',6',3''-tetramethoxy-1,3-diphenylpropane), was isolated from PPE-SVC.
Viscolin was demonstrated to inhibit
superoxide anion generation and
elastase release, as well as to accelerate resequestration of cytosolic
calcium in FMLP-activated human neutrophils. Furthermore, the inhibitory effects of
viscolin were reversed by
protein kinase A (
PKA) inhibitor, suggesting that PKA mediates the
viscolin-caused inhibitions.
Viscolin induced a substantial increase in cAMP levels, and that occurred through the inhibition of
phosphodiesterase (PDE) activity but not an increase in
adenylate cyclase function. Consistent with this,
viscolin potentiated the PGE(1)-caused inhibition of
superoxide anion release and
calcium mobilization, as well as elevation of cAMP formation. These results demonstrate that inhibition of inflammatory responses in human neutrophils by
viscolin is associated with an elevation of cellular cAMP through inhibition of PDE. Comparable results were also observed by PPE-SVC, indicating that the effect of PPE-SVC is at least partly mediated by
viscolin. In summary,
viscolin is a novel inhibitor of PDE and might be useful for treatment of neutrophilic
inflammation.