D-4F, an ApoA-I mimetic peptide ameliorating TRPA1-mediated nocifensive behaviour in a model of neurogenic inflammation

Abstract

Background: High doses of capsaicin are recommended for the treatment of neuropathic pain. However, low doses evoke mechanical hypersensitivity. Activation of the capsaicin chemosensor transient receptor potential vanilloid 1 (TRPV1) induces neurogenic inflammation. In addition to the release of pro-inflammatory mediators, reactive oxygen species are produced. These highly reactive molecules generate oxidised phospholipids and 4-hydroxynonenal (4-HNE) which then directly activate TRP ankyrin 1 (TRPA1). The apolipoprotein A-I mimetic peptide D-4F neutralises oxidised phospholipids. Here, we asked whether D-4F ameliorates neurogenic hypersensitivity in rodents by targeting reactive oxygen species and 4-HNE in the capsaicin-evoked pain model. Results: Co-application of D-4F ameliorated capsaicin-induced mechanical hypersensitivity and allodynia as well as persistent heat hypersensitivity measured by Randell-Selitto, von Frey and Hargreaves test, respectively. In addition, mechanical hypersensitivity was blocked after co-injection of D-4F with the reactive oxygen species analogue H 2 O 2 or 4-HNE. In vitro studies on dorsal root ganglion neurons and stably transfected cell lines revealed a TRPA1-dependent inhibition of the calcium influx when agonists were pre-incubated with D-4F. The capsaicin-induced calcium influx in TRPV1-expressing cell lines and dorsal root ganglion neurons sustained in the presence of D-4F. Conclusions: D-4F is a promising compound to ameliorate TRPA1-dependent hypersensitivity during neurogenic inflammation.

Pain Control by Targeting Oxidized Phospholipids: Functions, Mechanisms, Perspectives

“…D-4F blocks H 2 O 2 , 4-HNE, and OxPAPC, but not capsaicin- or AITC-induced calcium influx in TRPA1- or TRPV1-expressing HEK293 cells or dorsal root ganglion neurons ( 10 , 14 ). Apart from OxPL scavenging, other mechanisms of function are discussed for D-4F.…”

“…Research on inflammatory pain in the early years focused on stable biomolecules like prostaglandins and peptides/proteins such as cytokines which trigger the action potential firing of nociceptors ( 8 ). Recently, works by our group and others have identified OxPL as proalgesic compounds in preclinical pain models ( 10 , 11 , 14 , 15 ). Mechanistically, the highly reactive, transient, endogenous irritants directly activate ion channels on nociceptive C-fiber neurons.…”

“…OxPAPC as well as its corresponding metabolites excite nociceptors and pain behaviour in different models for inflammatory pain ( 10 , 11 , 14 , 15 , 28 , 29 ). Specific OxPAPC components such as PGPC and POVPC as well as the OxPL degradation product lysophosphatidylcholine (LPC) are increased in chloroform-based lipid extracts from inflamed tissue by MALDI-TOF ( 10 ).…”

“…Advances in lipidomics give the opportunity to identify lipids that may serve as biomarkers or treatment targets. Based on the idea that proalgesic OxPL are preferentially produced locally and non-enzymatically, OxPL neutralization was thought to be a feasible strategy to target the proalgesic function of OxPL, at least in rodent pain models ( 10 , 14 , 15 ). Targeting enzymatic OxPL production with small molecule inhibitors, for instance oxazolone-derived compounds for lipoxygenase inhibition, is antinociceptive ( 50 ).…”

“…It may be that 4-HNE, a lipid peroxidation downstream product, is the functional target of D-4F. 4-HNE could possibly bind to the lysine residues in D-4F and consecutively being inactivated ( 14 ). Indeed, in a murine asthma model, 4-HNE production was decreased after D-4F treatment.…”