NADPH oxidase activation and 4-hydroxy-2-nonenal/aquaporin-4 adducts as possible new players in oxidative neuronal damage presents in drug-resistant epilepsy

Abstract

A correlation between epilepsy and cellular redox imbalance has been suggested, although the mechanism by which oxidative stress (OS) can be implicated in this disorder is not clear. In the present study several oxidative stress markers and enzymes involved in OS have been determined. In particular, we examined the levels of 4-hydroxy-2-nonenal protein adducts (HNE-PA), a by-product of lipid peroxidation, and the activation of NADPH oxidase 2 (NOX2), as cellular source of superoxide (O(2)(-)), in surgically resected epileptic tissue from drug-resistant patients (N=50). In addition, we investigated whether oxidative-mediated protein damage can affect aquaporin-4 (AQP4), a water channel implicated in brain excitability and epilepsy. Results showed high levels of HNE-PA in epileptic hippocampus, in both neurons and glial cells and cytoplasmic positivity for p47(phox) and p67(phox) suggesting NOX2 activation. Interestingly, in epileptic tissue immunohistochemical localization of AQP4 was identified not only in perivascular astrocytic endfeet, but also in neurons. Nevertheless, negativity for AQP4 was observed in neurons in degeneration. Of note, HNE-mediated post-translational modifications of AQP4 were increased in epileptic tissues and double immunofluorescence clearly demonstrated co-localization of AQP4 and HNE-PA in epileptic hippocampal structures. The idea is that sudden, disorderly, and excessive neuronal discharges activates NOX2 with O(2)(-) production, leading to lipid peroxidation. The resulting generation of HNE targets AQP4, affecting water and ion balance. Therefore, we suggest that seizure induces oxidative damage as well as neuronal loss, thereby promoting neuronal hyperexcitability, also affecting water and ion balance by AQP4 modulation, and thus generating a vicious cycle.

Impaired enzymatic defensive activity, mitochondrial dysfunction and proteasome activation are involved in RTT cell oxidative damage

“…Indeed, biochemical analyses on muscle biopsy material confirmed reduced activities of NADH cytochrome c reductase, succinate cytochrome c reductase and cytochrome c oxidase, even in mitochondria of physiological appearance [54]. These data correlate with a recent microarray analyses on RTT patient blood samples where we have noticed an up-regulation of several mitochondria-related genes [57]. Specifically, the most significantly regulated transcripts included those encoding for several subunits of mitochondrial respiratory chain complexes and thus linked directly to mitochondrial ATP production and, indirectly, to potential oxidant generation.…”

Differential Transcriptional Profiling of Damaged and Intact Adjacent Dorsal Root Ganglia Neurons in Neuropathic Pain

“…Moreover, brevican, a chondroitin sulphate proteoglycan with growth-inhibiting features, was underexpressed in both damaged and adjacent neurons, as was aquaporin 4. This water channel has very recently been described as absent in degenerative (central) neurons [26]. Another group of upregulated genes hint at the inflammatory component of neuropathic pain, e.g.…”

Status epilepticus results in persistent overproduction of reactive oxygen species, inhibition of which is neuroprotective

“…More recently NADPH oxidase activation has been linked to neuronal damage in human hippocampi from patients suffering from pharmacoresistant epilepsy (Pecorelli et al, 2014), providing a stronger link to human epilepsy. Taken together, these findings suggest that free radical formation via NADPH oxidase represents a novel interventional target to prevent neuronal death following prolonged seizures and in chronic epilepsy.…”