Salmon and Human Thrombin Differentially Regulate Radicular Pain, Glial-Induced Inflammation and Spinal Neuronal Excitability through Protease-Activated Receptor-1

Abstract

Chronic neck pain is a major problem with common causes including disc herniation and spondylosis that compress the spinal nerve roots. Cervical nerve root compression in the rat produces sustained behavioral hypersensitivity, due in part to the early upregulation of pro-inflammatory cytokines, the sustained hyperexcitability of neurons in the spinal cord and degeneration in the injured nerve root. Through its activation of the protease-activated receptor-1 (PAR1), mammalian thrombin can enhance pain and inflammation; yet at lower concentrations it is also capable of transiently attenuating pain which suggests that PAR1 activation rate may affect pain maintenance. Interestingly, salmon-derived fibrin, which contains salmon thrombin, attenuates nerve root-induced pain and inflammation, but the mechanisms of action leading to its analgesia are unknown. This study evaluates the effects of salmon thrombin on nerve root-mediated pain, axonal degeneration in the root, spinal neuronal hyperexcitability and inflammation compared to its human counterpart in the context of their enzymatic capabilities towards coagulation substrates and PAR1. Salmon thrombin significantly reduces behavioral sensitivity, preserves neuronal myelination, reduces macrophage infiltration in the injured nerve root and significantly decreases spinal neuronal hyperexcitability after painful root compression in the rat; whereas human thrombin has no effect. Unlike salmon thrombin, human thrombin upregulates the transcription of IL-1β and TNF-α and the secretion of IL-6 by cortical cultures. Salmon and human thrombins cleave human fibrinogen-derived peptides and form clots with fibrinogen with similar enzymatic activities, but salmon thrombin retains a higher enzymatic activity towards coagulation substrates in the presence of antithrombin III and hirudin compared to human thrombin. Conversely, salmon thrombin activates a PAR1-derived peptide more weakly than human thrombin. These results are the first to demonstrate that salmon thrombin has unique analgesic, neuroprotective and anti-inflammatory capabilities compared to human thrombin and that PAR1 may contribute to these actions.

Salmon-derived thrombin inhibits development of chronic pain through an endothelial barrier protective mechanism dependent on APC

“…BSCB permeability was investigated by immunolabeling the spinal cord for IgG, a blood protein that is not present in the CNS under normal conditions, at day 1 and day 7. Those time points were selected since they correspond to the development and maintenance of pain in this injury model (13,38-41). To investigate indicators of inflammation to pain and BSCB breakdown, serum levels of a panel of inflammatory cytokines were assayed at day 1, which corresponds to maximal BSCB breakdown.…”

“…Salmon thrombin (15min+STh, n=5) or human (15min+HTh, n=4) thrombin solutions were delivered directly on top of the C7 nerve root immediately after removal of the compression (38,39,43). A control group received 20μl of NB media alone to account for the effects of the vehicle (vehicle, n=5).…”

“…Specifically, thrombin derived from salmon exhibits nearly indistinguishable clotting capabilities, but initiates different cell signaling cascades compared to human thrombin (36-39). Salmon thrombin induces lower levels of platelet aggregation and astrocytic transcription of pro-inflammatory cytokines compared to human thrombin at the same concentration (37,38). We have shown that salmon thrombin uniquely inhibits the development of neuropathic pain after a nerve root compression injury and activates PAR1 to a lower degree than human thrombin (38,39).…”

“…Salmon thrombin induces lower levels of platelet aggregation and astrocytic transcription of pro-inflammatory cytokines compared to human thrombin at the same concentration (37,38). We have shown that salmon thrombin uniquely inhibits the development of neuropathic pain after a nerve root compression injury and activates PAR1 to a lower degree than human thrombin (38,39). We hypothesize that salmon thrombin may prevent neural pain by exhibiting a higher affinity for protein C than mammalian thrombin promoting its ability to provide vascular protection.…”

Superoxide Dismutase‐Loaded Porous Polymersomes as Highly Efficient Antioxidants for Treating Neuropathic Pain

“…[9] Several animal models of nerve root compression have shown that even a transient, 15-minute compression applied to the nerve root is sufficient to induce sustained pain. [10, 11] In addition to pain, axonal damage and myelin degeneration are evident in the nerve root by 7 days after compression. [11] Such damage is hypothesized to relate to and cause neuronal dysfunction and contribute to the maintenance of pain by impaired axonal transport in the nerve root and disrupting the afferent signals that communicate to synapses in the spinal cord dorsal horn.…”