Three hundred and thirteen extracts
from 136 Brazilian plant species belonging to 36 families were tested for their
suppressive activity on phytohemaglutinin (PHA) stimulated proliferation of human
peripheral blood mononuclear cells (PBMC). The proliferation was evaluated by
the amount of [
3H]-thymidine incorporated by the cells. Twenty extracts
inhibited or strongly reduced the proliferation in a dose-dependent manner at
doses between 10 and 100 µg/ml. Three of these extracts appeared to be non-toxic
to lymphocytes, according to the trypan blue permeability assay and visual inspection
using optical microscopy. Bioassay-guided fractionation of
Alomia myriadenia
extract showed that myriadenolide, a labdane diterpene known to occur in this
species, could account for the observed activity of the crude extract. Using a
similar protocol, an active fraction of the extract from
Gaylussacia brasiliensis
was obtained. Analysis of the
1H and
13C
NMR spectra of this fraction indicates the presence of an acetylated triterpene
whose characterization is underway. The extract of
Himatanthus obovatus
is currently under investigation.
