Abstract
Background
Brachial plexus root avulsion (BPRA), a disabling peripheral nerve injury, induces substantial motoneuron death, motor axon degeneration and denervation of biceps muscles, leading to the loss of upper limb motor function. Acetylglutamine (N-acetyl-L-glutamine, NAG) has been proven to exert neuroprotective and anti-inflammatory effects on various disorders of the nervous system. Thus, the present study mainly focused on the influence of NAG on motor and sensory recovery after BPRA in rats and the underlying mechanisms.
Methods
Male adult Sprague Dawley (SD) rats were subjected to BPRA and reimplantation surgery and subsequently treated with NAG or saline. Behavioral tests were conducted to evaluate motor function recovery and the mechanical pain threshold of the affected forelimb. The morphological appearance of the spinal cord, musculocutaneous nerve, and biceps brachii was assessed by histological staining. Quantitative real-time PCR (qRT‒PCR) was used to measure the mRNA levels of remyelination and regeneration indicators in myocutaneous nerves. The protein levels of inflammatory and pyroptotic indicators in the spinal cord anterior horn were measured using Western blotting.
Results
NAG significantly accelerated the recovery of motor function in the injured forelimbs, enhanced motoneuronal survival in the anterior horn of the spinal cord, inhibited the expression of proinflammatory cytokines and pyroptosis pathway factors, facilitated axonal remyelination in the myocutaneous nerve and alleviated atrophy of the biceps brachii. Additionally, NAG attenuated neuropathic pain following BPRA.
Conclusion
NAG promotes functional motor recovery and alleviates neuropathic pain by enhancing motoneuronal survival and axonal remyelination and inhibiting the pyroptosis pathway after BPRA in rats, laying the foundation for the use of NAG as a novel treatment for BPRA.
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Introduction
Over the years, the increase in the number of domestic motorcycles and the lack of safety awareness of drivers has been paralleled by an increase in traffic accidents, leading to a surge in the prevalence of brachial plexus root avulsion (BPRA) [1]. BPRA induces the massive death in motoneurons, the degeneration of motor axons and targeted biceps muscle denervation, eventually leading to the loss of motor function in the upper extremity [2, Behavioral tests The Terzis grooming test was performed to determine motor function recovery of the affected forelimb as previously described [Mechanical withdrawal threshold Mechanical pain threshold testing was performed to determine changes in neuropathic pain behavior as previously described [36]. In our study, we found that NAG could efficiently alleviate muscle atrophy in rats subjected to avulsion/reimplantation, which was associated increased biceps muscle weight and volume, larger fiber size and decreased number of fibroblast nuclei. Neurogenic pain is a common and refractory complication after BPRA injury [37]. In addition to motor and sensory deficits, pain can be equally debilitating. BPRA pain has been characterized as rapid (an effect that occurs immediately after the trauma) and intermittent shooting pain, which may be observed at sites distant from the lesion. The pain states are generated and maintained by the activation of microglia and astrocytes in the spinal cord, which typically lasts 3 months after BPA [38]. Various nociceptive stimuli can activate c-Fos (a marker associated with pain) in the spinal cord [20]. NGF and CGRP have been shown to play critical roles in the molecular mechanisms of inflammatory-mediated disorders and are closely associated with nerve pain. Consistently, we observed that NAG could significantly reduce the MWT and protein levels of NGF and CGRP, suggesting that NAG alleviates pain. Overall, this study is the first to provide compelling evidence that acetylglutamine promotes functional motor recovery by enhancing motoneuronal survival and axonal remyelination after brachial plexus root avulsion in rats. Moreover, acetylglutamine can inhibit pyroptosis and attenuate the inflammatory response in the anterior horn of the spinal cord, leading to improved motoneuron survival. Importantly, we demonstrated that acetylglutamine could reduce neuropathic pain following brachial plexus avulsion. Although the results seem exciting, because promoting the survival of injured motor neurons is a prerequisite for functional motor recovery after BPRA, so, in our present study, we mainly concentrated on promoting the motoneuron survival to facilitate motor recovery. Further studies related to the effect of NAG on regeneration of motoneuron after BPRA are no doubt needed to be performed. Overall, acetylglutamine has robust prospects for clinical applications to treat brachial plexus avulsion.Terzis grooming test
Availability of data and materials
All data generated or analyzed during this study are included in this published article.
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Funding
We thank the Key Scientific Research Project of Hunan Provincial Department of Education (Grant no. 22A0314), Hunan Provincial Natural Science Foundation of China (Grant nos. 2021JJ30625, 2021JJ70114), the Hunan Provincial Innovation Foundation For Postgraduate (No. CX20221001), Clinical Medical Technology Innovation Guidance Project in Hunan Province (Grant no. 2021SK51822), Scientific research project of Hunan Health Committee (Grant no. 20201963) for support.
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Conceptualization, Z.X.; Methodology, L.W., S.C, and S.H.F.; Investigation, M.C., K.S., C.P. S.V, and S.H.F.; Writing—Original Draft, M.C., K.S., C.P., and S.H.F.; Writing—Review & Editing, M.C, K.S., C.P., and S.H.F.; Funding Acquisition,S.H.F.; Supervision, M.C., K.S., and S.H.F. All authors read and approved the final manuscript.
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Wu, L., Chen, S., He, B. et al. Acetylglutamine facilitates motor recovery and alleviates neuropathic pain after brachial plexus root avulsion in rats. J Transl Med 21, 563 (2023). https://doi.org/10.1186/s12967-023-04399-7
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DOI: https://doi.org/10.1186/s12967-023-04399-7