Peripherally Acting Opioids in Orofacial Pain.

Qing Liu,Wenguo Fan,Fang Huang,Shengyan Yang,Hongwen He,Lijia Mai

doi:10.3389/fnins.2021.665445

Qing Liu, Wenguo Fan + Show 4 more

Open Access

https://doi.org/10.3389/fnins.2021.665445

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Abstract

The activation of opioid receptors by exogenous or endogenous opioids can produce significant analgesic effects in peripheral tissues. Numerous researchers have demonstrated the expression of peripheral opioid receptors (PORs) and endogenous opioid peptides (EOPs) in the orofacial region. Growing evidence has shown the involvement of PORs and immune cell-derived EOPs in the modulation of orofacial pain. In this review, we discuss the role of PORs and EOPs in orofacial pain and the possible cellular mechanisms involved. Furthermore, the potential development of therapeutic strategies for orofacial pain is also summarized.

Highlights

It has been well established that opioid receptors are widely distributed throughout the central and peripheral sensory nervous systems (Machelska and Celik, 2020)
Intrathecal morphine results in a reduction in the number of β-endorphin-containing cells within the inflamed tissues, and peripheral endogenous antinociceptive effects are significantly decreased. These findings suggest the role of central mechanisms in modulating peripheral endogenous opioid analgesia (Schmitt et al, 2003)
Inflammation or injury of peripheral nerves causes an increase in the expression of peripheral opioid receptors (PORs) on peripheral nerve terminals and production of immunocyte-derived endogenous opioid peptides (EOPs)

Summary

INTRODUCTION

It has been well established that opioid receptors are widely distributed throughout the central (spinal cord, brain) and peripheral (trigeminal and dorsal root ganglia) sensory nervous systems (Machelska and Celik, 2020). A growing body of literature has noted that interactions involving peripheral opioid receptors (PORs) and immune cell-derived endogenous opioid peptides (EOPs) produce potent analgesia in painful conditions (Machelska and Stein, 2006; Hua, 2016). MOR, DOR, and KOR proteins can be detected in astrocytes and oligodendrocytes in the mouse brain (Stiene-Martin et al, 2001), but no study has shown the expression of opioid receptors in satellite glial cells. Classical EOPs are categorized as endorphins, enkephalins, and dynorphins, which are derived from three precursor proteins, proopiomelanocortin (POMC), proenkephalin (PENK), and prodynorphin (PDYN), respectively (Stein, 2018) These opioid peptides exhibit different affinity and selectivity for MOR (endorphins, enkephalins), DOR (enkephalins, endorphins) and KOR (dynorphins) (Machelska, 2007).

Methods

CONCLUSION