An investigation of the roles of TRPV1, TRPA1 and Hydrogen Sulfide in thermoregulation

Abstract

The Transient Receptor Potential Vanilloid 1 (TRPV1) ion channel is an integrator of noxious stimuli, including noxious heat (>43°C), low pH (<6) and capsaicin (the pungent component of chilli peppers). Transient Receptor Potential Ankyrin 1 (TRPA1) is a closely related channel, activated by reactive oxygen species, hydrogen sulfide (H2S) and mustard oil. Their expression on primary sensory neurons is well characterised. Recent studies show that they are also expressed in non‐neuronal tissue. Whilst TRPV1 and TRPA1 antagonism is a promising analgesic and anti‐inflammatory strategy, early generation TRPV1 antagonists produced a poorly understood cross‐species side effect of hyperthermia. H2S is a vasodilator and TRPA1 activator. Inhalation of H2S can suspend animation, a state that includes a decreased body temperature. The role of TRPA1 and H2S in TRPV1‐mediated hyperthermia was investigated using TRPV1 and TRPA1 antagonists, knockout mice, H2S donors and modulators of endogenous H2S producing enzymes. The effects of TRPV1 antagonists SB366791 and JNJ17203212 and TRPA1 antagonists HC030031 and TCS5861528 on thermal and mechanical nociceptive thresholds of naïve mice were determined using the Hargreaves and automated Von Frey techniques, respectively. Antagonist‐induced changes in core body temperature of conscious, ambulatory mice were determined using radiotelemetry. Only JNJ17203212 produced a significant increase in core body temperature. The effects of the same antagonists on capsaicin‐ and mustard oil‐ induced blood flow changes in the pinna and knee were investigated, using full‐field laser Doppler perfusion. The capsaicin‐induced increase in pinna blood flow demonstrated a neuronal response; in the knee decreased flux demonstrated nonneuronal TRPV1 activation. Mustard oil similarly increased flux in the pinna and knee: TRPA1 does not exhibit any vasoconstrictor activity in this model. JNJ17203212 significantly attenuated capsaicin‐induced blood flow changes in the pinna and knee. No inhibition was observed with SB366791. HC030031 significantly reduced mustard oil‐induced blood flow increases in the pinna and knee whilst TCS5861528 had no effect. Finally, the involvement of TRPA1 blockade and H2S in JNJ17203212‐mediated hyperthermia was determined, using HC030031 and GYY4137, respectively. Whilst TRPA1 was not directly involved in our model, GYY4137 attenuated the hyperthermia elicited by JNJ17203212, suggesting H2S may have a role in TRPV1 antagonist‐mediated hyperthermia.

Date of Award	2015
Original language	English
Awarding Institution	King's College London
Supervisor	David Mountford (Supervisor), Julie Keeble (Supervisor) & Stuart Bevan (Supervisor)