Role of aldehyde desidrogenase-2 and 4-hydroxynonenal on pain

Abstract

Aldehyde-dehydrogenase 2 (ALDH-2) is a mitochondrial enzyme responsible for the metabolism of toxic aldehydes, including the removal of 4-hydroxynonenal (4-HNE), an aldehyde generated during mitochondrial lipid peroxidation. 4-HNE accumulation has been recently related to increased pain through direct activation of TRPA1. Our preliminary results in collaboration with Dr. Daria Mochly-Rosen - Stanford University-EUA show that activation of ALDH2, using a small molecule developed by the group (Alda-1), displays a potent antinoceptive effect in a model of carrageenan-induced hyperalgesia (intraplantar, i.pl) in rats. Biochemical analysis show that carrageenan increases 4-HNE-protein adducts (high affinity chemical bindings) in the paw of carrageenan-treated animals, and Alda-1 decreases the adduct formation. In addition, we observed that Alda-1 reverts carrageenan-induced ALDH2 inactivation. These data show for the first time that ALDH-2 activation induces analgesia by reducing 4-HNE adduct formation. However, the role of ALDH-2 in pain control as well as the mechanisms involved in this effect are still unknown. Moreover, preliminary data obtained by our group and data from the literature have shown protein kinase C epsilon (PKCe) is involved in the carrageenan-induced hyperalgesia, and this kinase can be modulated by 4-HNE. However, the association between PKCe activation and 4-HNE accumulation in pain has never been investigated. Therefore, we propose to characterize the involvement of 4-HNE in the hyperalgesia. Indeed, we plan to investigate the role of ALDH2 in pain control. To address this question we will investigate (a) whether 4-HNE release during inflammation activates TRPV1 and TRPA1 receptors through adducts formation; (b) whether carrageenan induces formation of 4-HNE adducts in both plantar tissue and DRG using proteomics and mass spectrometry analysis (results will be validated by using Alda-1); (c) whether 4-HNE activates PKCe and contributes to the TRP activation in plantar, DRG tissue or primary culture of DRG; (d) whether PKCe activation is involved in carrageenan- or 4-HNE induced nociception in wild type and PKCe knock-out mice, or using selective PKCe activators and inhibitors; (e) whether the endogenous ALDH2 is involved in carrageenan-induced hyperalgesia in wild type and dominant negative transgenic mice for the ALDH2, or using selective ALDH2 inhibitor and Alda-1. Taken together, our proposal will contribute to the identification of a new molecular process involved in hyperalgesia as well as the development of new pharmacological tools in pain control. Finally, this proposal will extend the experimental approaches currently applied in the laboratory and provide an international collaboration. (AU)