The Multimodal MOPr/DOPr Agonist LP2 Reduces Allodynia in Chronic Constriction Injured Rats by Rescue of TGF-β1 Signalling.

Annamaria Fidilio,Federica Maria Spitale,Salvatore Spoto,Giuseppe Caruso,Nunzio Vicario,Lorella Pasquinucci,Nicolò Musso,Agostino Marrazzo,Santina Chiechio,Rosalba Parenti,Margherita Grasso,Carmela Parenti,Rita Turnaturi,Filippo Caraci

doi:10.3389/fphar.2021.749365

Abstract

Neuropathic pain is one of the most disabling forms of chronic pain and it is characterized by hyperalgesia and allodynia linked to an aberrant processing of pain transmission and to neuroinflammation. Transforming growth factor-β1 (TGF-β1) is an anti-inflammatory cytokine, which protects against neuroinflammation. It has been demonstrated that TGF-β1 and opioid receptors signalling crosstalk results in an improvement of endogenous opioid analgesia, but it is not known whether mu opioid peptide receptor (MOPr) or delta opioid peptide receptor (DOPr) agonists can positively modulate TGF-β1 pathway. In the present study, we examined the correlation between anti-allodynic effect of LP2, a dual-target MOPr/DOPr agonist, and TGF-β1 signalling in the chronic constriction injury (CCI) model. We detected a significant decrease of active TGF-β1 and of its type II receptor TGFβ-R2 levels in the spinal cord from CCI rats and a selective deficit of TGF-β1 in microglia cells both at days 11 and 21 post-ligature, as assessed by immunofluorescence analysis. LP2, when administered from the 11 days post-ligature to 21 days, was able to reduce CCI-induced mechanical allodynia by rescue of TGF-β1 and TGFβ-R2 levels. Our data suggest that the rescue of TGF-β1 signalling by dual-target MOPr/DOPr agonist LP2 could be mediated by DOPr activation in spinal microglia, thus the dual-target approach could represent a novel pharmacological approach to increase the analgesic efficacy of MOPr agonists.

Highlights

Neuropathic pain, one of the most complex and disabling forms of chronic pain, is currently defined as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system” (Treed et al, 2008)
We found that constriction injury (CCI) significantly decreased the expression levels of Transforming growth factor-β1 (TGF-β1) (Figure 2A) and of its receptor TGFβ-R2 (Figure 2B), while raised both IL-6 (Figure 2C) and IL-1β (Figure 2D) mRNA expression levels compared to the rats belonging to the SHAM group (p < 0.05 for all cytokines)
We have previously demonstrated that the multimodal mu opioid peptide receptor (MOPr)/delta opioid peptide receptor (DOPr) agonist LP2 produced a significant anti-nociceptive and anti-inflammatory effect in tail-flick and formalin test, respectively (Pasquinucci et al, 2017; Pasquinucci et al, 2019)

Summary

INTRODUCTION

Neuropathic pain, one of the most complex and disabling forms of chronic pain, is currently defined as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system” (Treed et al, 2008). In rats subjected to unilateral sciatic nerve chronic constriction injury (CCI), we already showed that LP2 significantly inhibits the development of mechanical allodynia and prevents CCI-induced Cx43 alterations and proapoptotic signalling in the CNS (Vicario et al, 2019a). These findings prompted us to further examine the molecular mechanisms underlying the analgesic effects of the MOPr/ DOPr agonist LP2 in the CCI model. In the present study we examined the hypothesis that CCI can induced an impairment of the TGF-β1 pathway and that the anti-allodynic effects of LP2 in the CCI rat model can be mediated by an increased expression of TGF-β1 and its type 2 receptor (TGFβ-R2) at spinal cord level along the time course of neuropathic pain

MATERIALS AND METHODS

Evaluation of Mechanical Allodynia

RESULTS

DISCUSSION

ETHICS STATEMENT