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Abstract
Flavonoids are polyphenolic substances derived from plants that play several pharmacological
activities. They possess anti-viral, anti-microbial, anti-inflammatory and anti-allergic
potential that can be expressed on different cell types, both in animal and human
models. Many of these properties prove inhibitory to a huge panoply of molecular targets
in the micromolar concentration range, either by down-regulating or suppressing many
inflammatory pathways and functions. Flavonoids exert their properties both as purified
aglycone molecules and as plant extracts. Depending on little changes in the flavone-backbone
and on subtle mechanisms of cell behavior and responsiveness, flavonoids can play
a modulating, biphasic and regulatory action on immunity and inflammation; in this
context only few flavones and flavonols have been assayed, mainly because of their
chemical similarity with quercetin, so evidence reported in the literature about the
action of flavonoids is limited to a restricted group of molecules. Many of the effects
reported about flavonoids regard quercetin, as probably the most diffused and known
nature-derived flavonol. Quercetin has shown a biphasic behavior in basophils at nanomolar
doses and hence its action on cells involved in allergic inflammation is here described.
Like many other molecules sharing a flavone ring, quercetin affects immunity and inflammation
by acting mainly on leukocytes and targeting many intracellular signaling kinases
and phosphatases, enzymes and membrane proteins often crucial for a cellular specific
function. This overview collects and discusses the role of flavonoids as anti-infectious
and anti-inflammatory compounds, trying to focus on the complex and modulating interaction
of these polyphenolic substances with cell function. However, the wide group of intracellular
targets and the elevated number of natural compounds potentially effective as anti-inflammatory
therapeutical agents, asks for further insights and evidence to comprehend the role
of these substances in animal cell biology.