Participação da aldeído desidrogenase-2 na neuroinflamação induzida pela constrição do nervo isquiático

Abstract

Background: Aldehyde dehydrogenase-2 (ALDH2) is a mitochondrial enzyme responsible for detoxifying aldehydes generated from the lipid peroxidation. We previously showed that Alda-1, a small molecule that activates ALDH2, has a potent antinociceptive effect in a chronic neuropathic pain model induced by the chronic constriction injury of the sciatic nerve (CCI) in mice, by decreasing reactive aldehydes, such as 4-hydroxynonenal (4-HNE) at the injured site. One of the most important mechanisms involved in the neuropathic pain onset and chronification is

the activation of immune and glial cells. Considering that reactive aldehydes are pro- inflammatory and pro-nociceptive, we hypothesized that 4-HNE is involved in the

central sensitization in CCI-induced neuropathy model. Methods: The nociceptive threshold was assessed by the up and down method using von Frey filaments, before (0), 7-, and 14-days post-injury (DPI). The ALDH2 function was modulated by Alda-1 (16 mg/Kg/day, s.c. osmotic pump) or by using a transgenic mice model with an inactivating mutation found commonly in Asiatic populations that impairs ~95% in ALDH2 activity (ALDH2*2). The 4-HNE protein adducts and the activation of glial cells in the dorsal horn of the spinal cord was assessed by using

immunofluorescence techniques, followed by microglia morphology, and co- localization analysis. Moreover, axonal degeneration was assessed by evaluating the

cell infiltration and fragmentation of myelin in histological preparation of sciatic nerve. Results: CCI decreases the nociceptive threshold in 7 and 14DPI, in wildtype (WT) and ALDH2*2 animals, and Alda-1 prevents CCI-induced hypernociception in both periods and genotypes. Also, CCI increases the immunostaining for 4-HNE adducts, GFAP (astrocyte), Iba-1 (microglia) along with a change in microglia morphology to pro-inflammatory profile in wild type mice. Alda-1 prevents 4-HNE adducts formation and glial cells activation, as measured in microglia morphology. Interestingly, the

impairment in ALDH2 activity contributes to changes in glial activation dynamic. Alda- 1 reduces 4-HNE levels in ALDH2*2 mice, without interfering with IBA-1 and GFAP

expressions. However, the microglia morphology analysis revealed that Alda-1 might

induce a shift from inflammatory to anti-inflammatory profile. The co-localization study showed that 4-HNE accumulates in afferent axons, Schwann cells, as well as spinal cord neurons and oligodendrocytes. Finally, we also showed that CCI induced sciatic nerve degeneration in both genotypes, which was prevented by the treatment with Alda-1. Conclusion: The data suggest that 4-HNE plays an important role in neuropathic hypernociception by controlling aldehyde levels and central neuroinflammation, as well as regulates axonal degeneration and peripheral inflammation in this model. Interestingly, the genetic impairment in ALDH2 activity changes the dynamics of glial activation upon nerve injury. Finally, Alda-1 is a promising molecule for neuropathic pain treatment.