Intra‐articular etanercept attenuates pain and hypoxia from TMJ loading in the rat

Abstract

Mechanical overloading of the temporomandibular joint (TMJ) and biochemical changes, like inflammation and hypoxia, contribute to cartilage degeneration and pain associated with osteoarthritis (OA). Yet, how overloading contributes to early dysregulation of chondrocytes is not understood, limiting the development of diagnostics and treatments for TMJ OA. Hypoxia‐inducible factors (HIF)‐1α/2α in chondrocytes were evaluated at Days 8 and 15 in a rat TMJ pain model induced by jaw loading (1 h/day for 7 days) using immunohistochemistry and compared between cases that induce persistent (3.5 N), acute (2 N), or no (0 N) sensitivity. Hypoxia was measured on Day 8 by immunolabeling of the tracer EF5 and 18F‐EF5 PET imaging. To assess the role of tumor necrosis factor (TNF) in painful TMJ loading, intra‐articular etanercept was given before loading. Orofacial sensitivity was evaluated during and after loading. Facial grimace, TNF‐α, HIF‐2α, and hypoxia levels in the TMJ were measured after loading. HIF‐2α was elevated (P = .03) after 3.5 N loading at Day 8, but HIF‐1α was unchanged. EF5 uptake increased on Day 8 in the 3.5 N group (P < .048) by tissue assay and 18F‐EF5 PET. At Day 8, both HIF‐2α (P = .01) and EF5 uptake (P = .005) were correlated with loading magnitude. Etanercept attenuated sensitivity (P < .01) and the facial grimace on Day 7 (P = .01). It also reduced (P < .01) HIF‐2α and EF5 uptake on Day 8; but TNF‐α levels were not different from controls at that time. Findings suggest that TMJ loading that induces persistent sensitivity upregulates the catabolic factor HIF‐2α and reduces oxygen levels in the cartilage, which may be TNF‐driven.

Intra-articular collagenase in the spinal facet joint induces pain, DRG neuron dysregulation and increased MMP-1 absent evidence of joint destruction

“…3b) also differs from osteoarthritis models reporting HIFs are elevated with pain-like behaviors 30,31 . It is possible that HIF-1α may play a role in an earlier, yet transient, chondrocyte response to the intra-articular collagenase 31 . Yet, the lack of other evidence of cartilage damage (Fig.…”

“…4, 5) adds to growing evidence that trauma-and osteoarthritis-induced joint sensitivity is regulated by dysregulation of a host of neurotransmitters, cell signaling proteins, and matrix-altering proteins in the DRG 3,29,48,49 . Further, this occurs absent joint space narrowing, cartilage lesions, osseous changes, or chondrocyte disruption, all of which are pronounced in loading-induced osteoarthritis 30,31 and with intra-articular crude collagenase [24][25][26] . Collagenase-induced changes in neural and joint outcomes (Figs.…”

“…HIF-1α expression was probed using immunolabeling to assess the health of chondrocytes in C6/C7 articular cartilage 30,31 . Immunohistochemical protocols are described previously 31 and used a primary antibody for rabbit anti-HIF-1α (1:250; Abcam Cambridge, MA) and a biotinylated horse antirabbit IgG secondary antibody (1:1000; Vector Laboratories; Burlingame, CA). Tissue sections without primary antibodies were included as negative controls and to verify antibody specificity for all immunolabeling assays.…”

“…3b). An assessor blinded to groups counted both the number of HIF-1α-positive and total number of cells in each image 31 ; the percentage HIF-1α-positive cells was taken as an average for each animal.…”

“…Effects on joint structure were quantified using histology of the capsular ligament and cartilage at day 21, a timepoint that allows for any detectable joint damage to develop 24 . Hypoxia-inducible factor 1α (HIF-1α), a protein that regulates chondrocyte survival in pathologically hypoxic environments, was also probed for its role in homeostatic maintenance in the cartilage 30,31 . Substance P, a neuropeptide involved in nociception 7,12 , and phosphorylated ERK (pERK), a mitogen-activated kinase indicative of noxious injury 32,33 , were investigated in the DRG and spinal cord.…”