Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCB303

Poster Communications

Dicarbonyls from the diabetic metabolism activate nociceptors

A. K. Becker1, P. Reeh1, B. Namer1, S. K. Sauer1

1. Institute of Physiology and Pathophysiology, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen, Germany.

In about one third of diabetes patients neuropathy affects primary sensory neurons and causes loss of cutaneous sensitivity and/or pain. There is growing evidence that certain metabolites arising from the glycolytic metabolism are responsible for neuronal hyperexcitability or damage. These reactive dicarbonyls such as methylglyoxal (MG), glyoxal and 3-deoxyglucosone (3-DG) accumulate and lead to non-enzymatic glycation of ion channels that are responsible for transduction of sensory stimuli, generation and finally conduction of action potentials. It has already been shown that MG directly activates cutaneous nociceptors through TRPA1 receptors (Eberhardt et al. 2012, Andersson et al. 2013) and causes pain-related behaviour when applied systemically in mice (Bierhaus et al. 2012). Here we investigate the impact of different dicarbonyls on the excitability of cutaneous nociceptors. Using the isolated skin-saphenous nerve preparation the effects of the metabolites on characterized C and A-delta fibers are investigated. Response properties as well as mechanical and thermal thresholds before and after stimulation with the dicarbonyls are compared as well as their potencies. TRPA1 involvement is tested using TRPA1 knockout animals or the TRPA1 antagonist A967079. These experiments are complemented by measurement of stimulated CGRP release from isolated mouse hind paw skin flaps in vitro using an enzyme-immuno-assay (Bertin Pharma France). The ex vivo animal research plan was approved by the Government of Central Franconia in Würzburg. Recordings from cutaneous nociceptors from C57Bl/6J control mice showed that 86% of classical polymodal nociceptors (n=15) respond to glyoxal (10mM) superfusion of their receptive fields with an ongoing low frequency discharge that comprises about 128 ± 25 S.E.M. spikes/10min (n=13). 30% of low threshold, rapidly adapting A-delta fibers (n=23) were activated by MG (10mM) and, in contrast to C fibers, exhibited a high frequency and long lasting discharge pattern with about 1095 ± 409 S.E.M. spikes/10min (n=7). Regarding the C fibers a clear tendency of threshold changes could not be detected whereas 43% of the responding A-delta fibers (n=3) showed an increase of mechanical thresholds by more than 362mN. We could also show that 77% of the C-fiber responses were TRPA1 dependent. MG (1, 3, 5mM), glyoxal (1, 3, 5, 10mM) and 3-DG (1, 3, 5mM) induced a TRPA1- and concentration-dependent increase of CGRP release (n=6-10 each). While the MG-induced release was reversible, a clearly prolonged CGRP release was found when the skin was stimulated with glyoxal or 3-DG. These data show that beside MG also glyoxal and 3-DG activate nociceptors in a differential manner. The dicarbonyls accumulate with different time courses and reach different concentrations. Our future work will focus on a possible cooperation of these metabolites. Supported by the DFG (SA-2126/2-1).

Where applicable, experiments conform with Society ethical requirements