Ultralow concentrations of bupivacaine exert anti-inflammatory effects on inflammation-reactive astrocytes.

Bupivacaine is a widely used, local anesthetic agent that blocks voltage-gated Na(+) channels when used for neuro-axial blockades. Much lower concentrations of bupivacaine than in normal clinical use, < 10(-8)  m, evoked Ca(2+) transients in astrocytes from rat cerebral cortex, that were inositol trisphosphate receptor-dependent. We investigated whether bupivacaine exerts an influence on the Ca(2+) signaling and interleukin-1ß (IL-1ß) secretion in inflammation-reactive astrocytes when used at ultralow concentrations, < 10(-8)  m. Furthermore, we wanted to determine if bupivacaine interacts with the opioid-, 5-hydroxytryptamine- (5-HT) and glutamate-receptor systems. With respect to the µ-opioid- and 5-HT-receptor systems, bupivacaine restored the inflammation-reactive astrocytes to their normal non-inflammatory levels. With respect to the glutamate-receptor system, bupivacaine, in combination with an ultralow concentration of the µ-opioid receptor antagonist naloxone and µ-opioid receptor agonists, restored the inflammation-reactive astrocytes to their normal non-inflammatory levels. Ultralow concentrations of bupivacaine attenuated the inflammation-induced upregulation of IL-1ß secretion. The results indicate that bupivacaine interacts with the opioid-, 5-HT- and glutamate-receptor systems by affecting Ca(2+) signaling and IL-1ß release in inflammation-reactive astrocytes. These results suggest that bupivacaine may be used at ultralow concentrations as an anti-inflammatory drug, either alone or in combination with opioid agonists and ultralow concentrations of an opioid antagonist.

Anti-inflammatory substances can influence some glial cell types but not others.

In rat microglial enriched cultures, expressing Toll-like receptor 4, we studied cytokine release after exposure with 1 ng/ml LPS for 0.5-24 h. Dexamethasone and corticosterone exposure served as controls. We focused on whether naloxone, ouabain, and bupivacaine, all agents with reported anti-inflammatory effects on astrocytes, could affect the release of TNF-α and IL-1ß in microglia. Our results show that neither ultralow (10(-12) M) nor high (10(-6) M) concentrations of these agents had demonstrable effects on cytokine release in microglia. The results indicate that anti-inflammatory substances exert specific influences on different glial cell types. Astrocytes seem to be functional targets for anti-inflammatory substances while microglia respond directly to inflammatory stimuli and are thus more sensitive to anti-inflammatory substances like corticoids. The physiological relevance might be that astrocyte dysfunction influences neuronal signalling both due to direct disturbance of astrocyte functions and in the communication within the astrocyte networks. When the signalling between astrocytes is working, then microglia produce less pro-inflammatory cytokines.