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.