Involvement of the transient receptor potential ankyrin-1 (TRPA1) channel in the thermoregulatory effects of hydrogen-sulfide

HV Wilson1, R Riahi1, M Solymar2, E Pakai2, V Tekus2, E Pinter2, M Whiteman3, JE Keeble1, A Garami2,1. 1King's College London, London, UK, 2University of Pecs, Pecs, Hungary, 3University of Exeter, Exeter, UK

Hydogen sulfide (H2S) is an endogenous gaseous mediator, synthesized predominantly by cystathionine β-synthase (central) and cystathionine gamma-lyase (peripheral) enzymes. It plays a role in a variety of physiological processes, for example, in inflammation and cardiovascular regulation. Recently, inhaled H2S has been shown to induce suspended animation in mice, a process with close links to thermoregulation (Blackstone et al., 2005). The aim of the present study was to determine whether H2S-induced thermoregulatory changes are mediated through Transient Receptor Potential Ankyrin-1 (TRPA1) receptors and whether H2S influences lipopolysaccharide (LPS)–induced fever.

All experiments were carried out in accordance with the EU Directive 86/609/EEC. Male (25–30 g) C57BL/6, TRPA1 wild type (WT) and TRPA1 knock out (KO) mice were used. I.c.v. cannula implantation was performed under ketamine (81.7 mg/kg)/ xylazine (9.3 mg/kg) anaesthesia and antibiotic protection (gentamycin, 6 mg/kg i.p. or i.m.). Animals were allowed to recover for 1–3 days before experiments were performed. The effects of the H2S donors, sodium sulphide (Na2S, fast H2S release, 0.5–1 mg/kg, i.c.v.) and GYY4137 (slow H2S release, 3 mg/kg, i.c.v.), or vehicle (saline, 3 μl) on core temperature (TC) and oxygen consumption (VO2) were studied using thermocouple and respirometry setups (see Garami et al., 2011). In a separate set of experiments, GYY4137 (3 mg/kg) or saline (3.3 ml/kg) was delivered in 0.1 ml/30g i.p. as a –120 min pre-treatment to LPS (120 µg/kg, 3.3 ml/kg i.p.).

In agreement with previous literature, Na2S (i.c.v.) induced dose-dependent hypothermia with a nadir of -0.8±0.4 and -1.5±0.5°C at 0.5 and 1 mg/kg, respectively. In paired studies of TRPA1 WT and KO mice, the absence of TRPA1, in part, inhibited H2S-induced hypothermia and hypometabolism. The i.c.v. injection of GYY4137 also induced significant (P<0.05) hypothermia (-1.9±0.5°C) and hypometabolism (-74±26 ml/kg/min). Both donor compounds were assessed peripherally (i.p.) for thermoregulatory effects, of which both reported negative data. This suggests that H2S acts centrally, consistent with the knowledge that thermoregulation is centrally controlled within the preoptic area of the hypothalamus. GYY4137-mediated effects were far slower than Na2S, which was consistent with the “slow-releasing” characterisation of GYY4137. Furthermore, GYY4137-induced hypothermia was attenuated in TRPA1 KO animals compared to WT controls with nadirs of -1.3±0.4 vs. -3.2±0.4°C, respectively. Finally, GYY4137 had no significant effect on LPS-induced fever compared to vehicle (maximal Tc of 1.8+0.7 vs. 1.6+0.4°C for saline vs. GYY4137 pre-treatment, respectively).

This study provides novel, in vivo evidence for TRPA1-mediated effect of H2S in thermoregulation. The present study supported previous findings that H2S has cryogenic properties and, to the authors’ knowledge, this is the first study to clearly report that H2S-induced hypothermia and hypometabolism is, at least in part, TRPA1-mediated.

References:

1. Blackstone et al. (2005). Science, 308: 518.

2. Garami et al. (2011). J. Neuroscience, 31: 1721-1733.