ABSTRACT (274 words)
Tetracyclines have recently emerged as possible therapeutic agents for
several diseases of the central nervous system. Chemically modified
tetracycline 3 (also known as Incyclinide, CMT-3 or COL-3), a
tetracycline derivative without antibiotic activity that crosses the
blood–brain barrier, has been recently validated as a potent
anti-inflammatory molecule. The present study discloses a possible
mechanism through which COL-3 induces an anti-inflammatory response in
cultured microglial cells activated by two different inflammogens: the
standard bacterial component lipopolysaccharide (LPS) and the amyloid
fibrils of the synaptic protein α-Synuclein (αSa). Under LPS and αSa
treatment, COL-3 effectively reduced the production of prototypical
proinflammatory markers, as the cytokine TNF-α and the microglial
protein Iba-1. COL-3 effects were reproduced by doxycycline (DOX), a
tetracycline used as reference molecule and dexamethasone, a classic
anti-inflammatory drug. Surprisingly, COL-3 avoided the increase in
glucose uptake induced by LPS and αSa in microglial cells, an outcome
also observed with the inhibitor of NADPH oxidase apocynin, high
concentration of glucose and with its non-metabolized analog
2-deoxy-glucose. COL-3 and DOX, as well as apocynin and 2-deoxy-glucose
also reduced glucose-derived NADPH, a cofactor required for NADPH
oxidase activation and reactive oxygen species (ROS) generation.
Comforting these data, our results showed that LPS- and αSa-induced ROS
production was also blunted in the presence of COL-3 and DOX, as well as
apocynin and the anti-oxidant vitamin E analog trolox. Accordingly,
apocynin and 2-deoxy-glucose mimicked the TNF-α reduction induced by
COL-3 in LPS and αSa-treated cells. In this way, we propose that the
anti-inflamatory mechanism of action of COL-3 is the consequence of its
capacity to block glucose consumption and consequent glucose- and
NADPH-dependent ROS production in microglial cells.
Keywords: 2-deoxyglucose uptake; α-synuclein; CMT-3;
doxycycline, glia; glucose metabolism; incyclinide; microglia; NADPH;
NADPH oxidase; neuroinflammation; pentose-phosphate shunt; ROS.