Neuroprotective role of phosphodiesterase inhibitor ibudilast on neuronal cell death induced by activated microglia

The phosphodiesterase inhibitor, ibudilast, has many effects on lymphocytes, endothelial cells, and glial cells. We examined the neuroprotective role of ibudilast in neuron and microglia co-cultures. Ibudilast significantly suppressed neuronal cell death induced by the activation of microglia with lipopolysaccharide (LPS) and interferon (IFN)-gamma. To examine the mechanisms by which ibudilast exerts a neuroprotective role against the activation of microglia, we examined the production of inflammatory and anti-inflammatory mediators and trophic factors following ibudilast treatment. In a dose-dependent manner, ibudilast suppressed the production of nitric oxide (NO), Reactive Oxygen Species, interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha and enhanced the production of the inhibitory cytokine, IL-10, and additional Neurotrophic Factors, including nerve growth factor (NGF), glia-derived neurotrophic factor (GDNF), and neurotrophin (NT)-4 in activated microglia. Thus, ibudilast-mediated neuroprotection was primarily due to the inhibition of inflammatory mediators and the upregulation of neurotrophic factor. In the CA1 region of hippocampal slices, long-term potentiation (LTP) induced by high frequency stimulation (HFS) could be inhibited with LPS and interferon-gamma stimulation. Ibudilast returned this LTP inhibition to the levels observed in controls. These results suggest that ibudilast may be a useful neuroprotective and anti-dementia agent counteracting neurotoxicity in activated microglia.