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Peripheral Administration of an Opioid Peptide Analog Ameliorates Morphine-Produced Hyperalgesia in a Spared Nerve Injury Model

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Abstract

Traditional opioids have proven analgesic effects in clinical applications but are also associated with side effects, especially hyperalgesia. Reducing the occurrence of hyperalgesia is part of effective clinical pain management. In this study, we investigated the difference between MEL-0614, a novel endomorphin analog that can effectively penetrate the blood–brain barrier, and morphine in inducing hyperalgesia. Under mechanical and thermal stimulation conditions, intravenous administration of morphine led to hyperalgesia even at low concentrations, which was not observed with MEL-0614 even at high concentrations. In a spared nerve injury model, significantly less aggravation of allodynia was caused by an intravenous injection of MEL-0614 compared with that caused by morphine, and the allodynia symptoms occurred later. Notably, MEL-0614 significantly relieved the symptoms of morphine-induced allodynia. The activation of N-methyl-d-aspartic acid receptor and expression of inflammatory mediators differed in spinal microglia after intravenous injections of MEL-0614 and morphine. Intravenous injections of morphine induced increases in the number of microglia and overexpression of inflammatory factors, including tumor necrotic factor and interleukin-1β. Conversely, the effects of MEL-0614 administration did not differ from those of saline, and there was no inflammatory mediator overexpression. Especially in the spared nerve injury model, the cross-administration of morphine and MEL-0614 could reduce the expression of Toll-like receptor 4 and other related genes to different degrees compared with the use of morphine alone. Concurrently, the results could also explain the alleviating effect of MEL-0614 on morphine-induced pain sensitivity in behavioral experiments. Our findings may provide important information regarding the clinical treatment of neuropathic pain in the future.

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Data Availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Abbreviations

ANOVA:

Analysis of variance

AUC:

Area under the curve

BBB:

Blood–brain barrier

BDNF:

Brain-derived growth factor

EMs:

Endomorphins

IV:

Intravenous

IL-1β:

Interleukin-1β

NMDA:

N-methyl-d-aspartic acid

P2X7R:

P2X receptor 7

qPCR:

Quantitative PCR

SNI:

Spared nerve injury

TLR4:

Toll-like receptor 4

TNF-α:

Tumor necrosis factor-α

WT:

Withdrawal threshold

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Acknowledgements

The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (21432003, 21402076 and 81502904), the Program for Chang-Jiang Scholars (IRT_15R27), the Natural Science Foundation of Gansu Province (20JR5RA285, 18JR2RA031), and the Fundamental Research Funds for the Central Universities (561221002, lzujbky-2018-Kb11).

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Authors and Affiliations

Authors

Contributions

RW, YW and XL designed the experiments. YW and MM wrote the manuscript. MM, JW, CH, KL, QR, and NL performed experiments. MM calculated the date and prepared the figures. All authors reviewed the manuscript.

Corresponding authors

Correspondence to Xin Liu or Rui Wang.

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Conflict of interest

The authors declare no potential conflict of interests.

Ethical Approval

The experiments conducted in this study met the ethical and moral requirements. To reduce the suffering of animals, each mouse was used only once. All experiments in this study were approved by the ethics committee of Lanzhou University (License Number: SYXK Gan 2009-0005).

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Wang, Y., Ma, Mt., Wang, J. et al. Peripheral Administration of an Opioid Peptide Analog Ameliorates Morphine-Produced Hyperalgesia in a Spared Nerve Injury Model. Int J Pept Res Ther 28, 12 (2022). https://doi.org/10.1007/s10989-021-10319-4

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  • DOI: https://doi.org/10.1007/s10989-021-10319-4

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