Reactive metabolites of acetaminophen activate and sensitize the capsaicin receptor TRPV1

Mirjam J Eberhardt,Florian Schillers,Jeanne De La Roche,Esther M Eberhardt,Linus Risser,Christine Herzog,Andreas Leffler,Frank Echtermeyer

doi:10.1038/s41598-017-13054-3

Abstract

The irritant receptor TRPA1 was suggested to mediate analgesic, antipyretic but also pro-inflammatory effects of the non-opioid analgesic acetaminophen, presumably due to channel activation by the reactive metabolites parabenzoquinone (pBQ) and N-acetyl-parabenzoquinonimine (NAPQI). Here we explored the effects of these metabolites on the capsaicin receptor TRPV1, another redox-sensitive ion channel expressed in sensory neurons. Both pBQ and NAPQI, but not acetaminophen irreversibly activated and sensitized recombinant human and rodent TRPV1 channels expressed in HEK 293 cells. The reducing agents dithiothreitol and N-acetylcysteine abolished these effects when co-applied with the metabolites, and both pBQ and NAPQI failed to gate TRPV1 following substitution of the intracellular cysteines 158, 391 and 767. NAPQI evoked a TRPV1-dependent increase in intracellular calcium and a potentiation of heat-evoked currents in mouse spinal sensory neurons. Although TRPV1 is expressed in mouse hepatocytes, inhibition of TRPV1 did not alleviate acetaminophen-induced hepatotoxicity. Finally, intracutaneously applied NAPQI evoked burning pain and neurogenic inflammation in human volunteers. Our data demonstrate that pBQ and NAQPI activate and sensitize TRPV1 by interacting with intracellular cysteines. While TRPV1 does not seem to mediate acetaminophen-induced hepatotoxicity, our data identify TRPV1 as a target of acetaminophen with a potential relevance for acetaminophen-induced analgesia, antipyresia and inflammation.

Highlights

Acetaminophen is one of the most commonly used analgesics worldwide, and it is generally assumed that it induces analgesia and antipyresia mainly by inhibiting cyclooxygenase[1]
(C) 1 μM NAPQI (5 min) sensitizes ramp currents generated by TRPV1, and these can be transiently blocked by BCTC. (D) Increasing concentrations of acetaminophen (APAP 10 μM, 100 μM, 1000 μM, each applied for 4 minutes) has no effects on ramp currents evoked in hTRPV1-expressing cells
Measuring ramp currents by depolarization from −100 to +100 mV applied within 500 ms, 1 μM pBQ activated slowly developing membrane currents with a strong outward rectification in all cells which generated capsaicin (1 μM)-induced currents due to expression of hTRPV1 (n = 8, Fig. 1A)

Summary

Introduction

Acetaminophen is one of the most commonly used analgesics worldwide, and it is generally assumed that it induces analgesia and antipyresia mainly by inhibiting cyclooxygenase[1]. Activation of TRPA1 by at least pBQ seems to involve a modification of several cysteines[12] Both metabolites result from a cytochrome P450-dependent metabolism of acetaminophen mainly in the liver, but they can be detected in the upper laminae of the spinal cord as well as in the lung following systemic administration of acetaminophen[5]. While intrathecal injection of acetaminophen, pBQ and NAPQI produces analgesic effects in rodents, intraplantar injections of acetaminophen are ineffective[5]. Our data clearly indicate that TRPV1 is a relevant target of NAPQI and pBQ

Methods

Results

Conclusion