Reactive dicarbonyl compounds cause Calcitonin Gene-Related Peptide release and synergize with inflammatory conditions in mouse skin and peritoneum

Abstract

The plasmas of diabetic or uremic patients and of those receiving peritoneal dialysis treatment have increased levels of the glucose-derived dicarbonyl metabolites like methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG). The elevated dicarbonyl levels can contribute to the development of painful neuropathies. Here, we used stimulated immunoreactive Calcitonin Gene–Related Peptide (iCGRP) release as a measure of nociceptor activation, and we found that each dicarbonyl metabolite induces a concentration-, TRPA1-, and Ca2+-dependent iCGRP release. MGO, GO, and 3-DG were about equally potent in the millimolar range. We hypothesized that another dicarbonyl, 3,4-dideoxyglucosone-3-ene (3,4-DGE), which is present in peritoneal dialysis (PD) solutions after heat sterilization, activates nociceptors. We also showed that at body temperatures 3,4-DGE is formed from 3-DG and that concentrations of 3,4-DGE in the micromolar range effectively induced iCGRP release from isolated murine skin. In a novel preparation of the isolated parietal peritoneum PD fluid or 3,4-DGE alone, at concentrations found in PD solutions, stimulated iCGRP release. We also tested whether inflammatory tissue conditions synergize with dicarbonyls to induce iCGRP release from isolated skin. Application of MGO together with bradykinin or prostaglandin E2 resulted in an overadditive effect on iCGRP release, whereas MGO applied at a pH of 5.2 resulted in reduced release, probably due to an MGO-mediated inhibition of transient receptor potential (TRP) V1 receptors. These results indicate that several reactive dicarbonyls activate nociceptors and potentiate inflammatory mediators. Our findings underline the roles of dicarbonyls and TRPA1 receptors in causing pain during diabetes or renal disease.

Spontaneous activity of specific C‐nociceptor subtypes from diabetic patients and mice: Involvement of reactive dicarbonyl compounds and (sensitized) transient receptor potential channel A1

“…The slower Ca 2+ kinetics of GO were reflected in a slower but much prolonged rise of the stimulated CGRP release from cutaneous nerve endings. It has previously been demonstrated that GO -like MGO-stimulated CGRP release depends on TRPA1 (but not TRPV1) activation, 38 and the reduction of GO-induced nociceptor firing by the TRPA1 antagonist A967079 corroborated this finding (Figure 3C). Interestingly, however, the 37% of units presenting with this enhanced spontaneous activity in diabetes did not (significantly) respond to GO and MGO superfusion with an increased discharge rate, quite in contrast to the fibers with "normal" spontaneous activity (Figure 5B).…”

“…The neuropeptide release stimulated by GO was not reversible (within 5 min wash-out) in contrast to MGO-stimulated release, as it has already been shown before. 38 Surprisingly, no difference could be detected when GO 3 mM-induced release was compared between healthy and diabetic mice (Figure 6C, left and right panel).…”

“…16,87 We therefore conclude that in the mouse heat-and mechanosen- and hyperalgesia when microinjected in human skin. [37][38][39][40] Very similar to MGO, GO mainly excited the peptidergic, polymodal (C-MH, C-MHC) fibers rather than the mechanosensitive C-HTM units that are also largely insensitive to mustard oil stimulation, probably lacking TRPA1 expression.…”

“…21 In the past, we have shown that TRPA1 receptor stimulation induces CGRP release from peptidergic fibers innervating hairy skin. 38,39 Convergent evidence from skin immunohistochemistry and from Calca (CGRPα)…”

“…MGO and related dicarbonyl compounds are electrophilic TRPA1 agonists which at high extracellular concentrations, as required for their slow membrane permeation, cause a robust activation of cultured DRG neurons and cutaneous nociceptors. 10,[37][38][39] MGO elicits TRPA1-dependent painful sensations and long-lasting hyperalgesia when injected into skin of healthy subjects. 40 Intracellular MGO causes posttranslational modifications of TRPA1 that lead to formation of disulfide bonds, which is an accepted TRPA1 activation mechanism.…”