Link N as a therapeutic agent for discogenic pain

Abstract

Neurotrophins (NTs) are the major contributors of sensory axonal sprouting, neural survival, regulation of nociceptive sensory neurons, inflammatory hyperalgesia, and neuropathic pain. Intervertebral disc (IVD) cells constitutively express NTs. Their expression is upregulated by proinflammatory cytokines present in the IVD during degeneration, which can promote peripheral nerve ingrowth and hyperinnervation, leading to discogenic pain. Currently, there are no targeted therapies that decrease hyperinnervation in degenerative disc disease. Link N is a naturally occurring peptide with a high regenerative potential in the IVD. Therefore, the suitability of Link N as a therapeutic peptide for suppressing NTs, which are known modulators and mediators of pain, was investigated. The aim of the present study is to determine the effect of Link N on NTs expression, nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), and their cognate receptors TrkA and TrkB as they are directly correlated with symptomatic back pain. Furthermore, the neurotransmitter (substance P) was also evaluated in human annulus fibrosus (AF) cells stimulated with cytokines. Human AF cells isolated from normal IVDs were stimulated with interleukin‐1β (IL‐1β) and tumor necrosis factor‐α (TNF‐α) in the presence or absence of Link N. NGF release in the media was evaluated by Western blotting. Total RNA was isolated and gene expression was measured using real‐time PCR. Gene expression of NGF, BDNF, TrkA, and TrkB significantly decreased in human disc cells stimulated with either IL‐1β or TNF‐α supplemented with Link N when compared to the cells stimulated only with IL‐1β or TNF‐α. NGF protein expression was also suppressed in AF cells coincubated with Link N and IL‐1β when compared to the cells stimulated only with IL‐1β. Link N can suppress the stimulation of NGF, BDNF, and their receptors TrkA and TrkB in AF cells in an inflammatory milieu. Thus, coupled with previous observations, this suggests that administration of Link N has the potential to not only repair the discs in early stages of the disease but also suppress pain.

Optimization of a rat lumbar IVD degeneration model for low back pain

“…These changes have been shown to be induced by pro-inflammatory cytokines, including TNFα. 17,18 The importance of TNF-α in the induction of painful IVD degeneration has been recently shown in a study demonstrating that inhibition of TNF-α at the time of induced IVD injury limits long-term pain and degeneration in a rat model. 18 While imaging-based diagnosis including MRI provides detailed images of the IVD tissue, it fails to clearly differentiate between a pathologically painful disc and a disc that does not generate pain.…”

Tungsten accumulates in the intervertebral disc and vertebrae stimulating disc degeneration and upregulating markers of inflammation and pain

“…An extracellular matrix with a high proteoglycan to collagen ratio can be used as a means to identify an NP-like phenotype in vivo as an indicator of disc degeneration (Mwale et al, 2004). In control discs, the GAG to collagen ratio in the disc was on average 3.7 : 1 (Fig.…”

“…VEGF was analysed to determine the effect of tungsten exposure on nerve ingrowth. In addition, several animal models of disc degeneration show increased IVD innervation by the identification of CGRP (Johnson et al, 2015;Noorwali et al, 2018). CGRP is a neurotransmitter that acts as a pain modulator and its increased production can cause hyperexcitability and sensitisation (Schou et al, 2017).…”

“…The spine is composed of vertebral segment units consisting of a bony vertebrae and the IVD. IVDs link two adjacent vertebrae and are composed of the collagen-rich AF, the central gel-like proteoglycanrich NP and two endplates of hyaline cartilage that sandwich the AF and NP (Oegema, 1993;Vo et al, 2016). The compressive ability of the NP is achieved by the attraction of water molecules from the GAG chains present on individual aggrecan monomers (the principal proteoglycan in the disc) (Oegema, 1993;Watanabe et al, 1998).…”

“…This process results in the degradation of aggrecan and, as the NP losses water, it becomes more fibrotic, eventually leading to the formation of clefts that can also affect the integrity of the AF. Sequelae of enhanced inflammatory cytokines eventually lead to increases in the expression of the neurotrophic factors NGF and BDNF from disc cells, resulting in hyperinnervation of the IVD (Johnson et al, 2015;Noorwali et al, 2018).…”