Biology Reference
In-Depth Information
6.3 Ellagitannins as TNF
α
Secretion Inducers
The ellagitannins' potent antitumor activity through an apparent up-
regulation of the immune system is well founded. Miyamoto's group
suggested that the secretion of IL-1β seen in murine PEC's and
hPBMC's could explain the observed antitumor actions of hydrolyzable
tannins. However, at the time that Miyamoto's group was pursuing the
immunostimulatory experiments, little was known about the “newly
discovered” related cytokine TNFα, and no simple assays were
available. Also given IL-1β's late entry into the cytokine cascade, it was
conceivable that a mediator different than IL-1β was responsible for the
primary activity of the antitumor ellagitannins. Since much post-
Miyamoto research established that TNFα was, indeed, a tumor-lethal
substance, it seemed like a logical target for further tannin-related study.
Additionally, TNFα is among the first cytokines released in response
to immunostimulation and it is known to induce the later production and
release of IL-1β (Dinarello
et al.
, 1986). Finally, a readily available
commercial ELISA-based TNFα assay had become available. Therefore,
some known tumoricidal ellagitannins, an analogue of coriariin A, and
the gallotannin 1,2,3,4,6-penta-
O
-galloyl-beta-D-glucose (β-PGG,
66
)
were tested for their ability to induce TNFα output from hPBMC's
(Feldman
et al.
, 1999).
6.3.1
β
-PGG, agrimoniin, and a model dimer analog of coriariin A
induce TNF
α
secretion from hPBMC's
The initial experiments involved monitoring TNFα generation using a
qualitative test with the L929 murine fibroblast lysis assay (Feldman
et
al.
, 1999). This indirect analysis revealed that significant amounts of
TNFα were present in the supernatant of hPBMC's after 4 hours of
incubation with agrimoniin at 28 μM. Thus, this crude assay provided
the first evidence that the cytokine TNFα was generated by cells treated
with an ellagitannin. Using the same experimental procedure, the
monomeric gallotannin β-PGG (
66
) and the dimer
81
, an analogue of
coriariin A (Fig. 6.15), were assessed quantitatively for their TNFα
inducing capabilities utilizing an ELISA kit. A time-course study
