Osteoarthritis: Nerve ablation - a new treatment for OA pain?

Molecular pathogenesis of OA pain: Past, present, and future

OBJECTIVE

To provide a historical perspective and narrative review on research into the molecular pathogenesis of osteoarthritis pain.

DESIGN

PubMed databases were searched for combinations of "osteoarthritis", "pain" and "animal models" for papers that represented key phases in the history of osteoarthritis pain discovery research including epidemiology, pathology, imaging, preclinical modeling and clinical trials.

RESULTS

The possible anatomical sources of osteoarthritis pain were identified over 50 years ago, but relatively slow progress has been made in understanding the apparent disconnect between structural changes captured by radiography and symptom severity. Translationally relevant animal models of osteoarthritis have aided in our understanding of the structural and molecular drivers of osteoarthritis pain, including molecules such as nerve growth factor and C-C motif chemokine ligand 2. Events leading to persistent osteoarthritis pain appear to involve a two-step process involving changes in joint innervation, including neo-innervation of the articular cartilage, as well as sensitization at the level of the joint, dorsal root ganglion and central nervous system.

CONCLUSIONS

There remains a great need for the development of treatments to reduce osteoarthritis pain in patients. Harnessing all that we have learned over the past several decades is helping us to appreciate the important interaction between structural disease and pain, and this is likely to facilitate development of new disease modifying therapies in the future.

Hydrogen sulfide inhibits endoplasmic reticulum stress through the GRP78/mTOR pathway in rat chondrocytes subjected to oxidative stress

The activation of oxidative stress is a primary cause of chondrocyte apoptosis in osteoarthritis (OA). The 78‑kDa glucose‑regulated protein (GRP78)/mammalian target of rapamycin (mTOR) signaling pathway has been demonstrated to be linked with the endoplasmic reticulum (ER) and autophagy. Hydrogen sulfide (H2S) has been reported to exert antioxidant effects. The present study investigated oxidative stress levels via 2',7'‑dichlorofluorescin diacetate and MitoSOX staining, apoptosis rates via flow cytometry and the expression levels of ER stress‑related proteins in GYY4137 (donor of H2S)‑treated chondrocytes (CHs). CHs were isolated from the bilateral hip joints of male rats to examine mitochondrial permeability transition pore opening‑ and mTOR signaling pathway‑related proteins. The results demonstrated that tert‑Butyl hydroperoxide (TBHP) increased CH apoptosis, and treatment with GYY4137 ameliorated TBHP‑mediated the generation of ROS and CH apoptosis. Moreover, TBHP‑treated CHs displayed elevated ER stress sensor expression levels and apoptotic rates; however, the TBHP‑induced protein expression levels were decreased following GYY4137 treatment. In the present study, treatment with either GYY4137 or transfection with GRP78 siRNA both suppressed the activation of p‑P70S6k and p‑mTOR. H2S played an important role in regulating ER stress in TBHP‑stimulated CHs. GYY4137 promoted autophagy, which was accompanied by the inhibition of ER stress. On the whole, the present study demonstrates that TBHP‑induced oxidative stress stimulates ER interactions and CH apoptosis, which are suppressed by exogenous H2S via modulating the GRP78/mTOR signaling pathway.

What is new in pain modification in osteoarthritis?

There is a big need for the development of novel therapies for the safe management of chronic pain associated with OA. Here we reviewed PubMed (2015 onward) and ClinicalTrials.gov for ongoing and recently completed trials where pain in OA is the primary outcome measure. Three broad categories were identified: biological therapies, small molecules and cryoneurolysis. The most promising new strategy is blockade of nerve growth factor with antibodies. Two anti-nerve growth factor antibodies, tanuzemab and fasinumab, are in active development after the 2010 hold on trials was lifted in 2015. In addition, several active clinical trials are testing distinct mechanism-based interventions, including cytokine inhibition, selective μ, δ or κ opioid receptor agonists, zoledronate and intra-articular capsaicin. In addition to pharmacological approaches, cryoneurolytic strategies that directly target peripheral nerves may play a role in OA pain management, but efficacy profiles and long-term effects of such treatments need more study. Clearly, the therapeutic landscape for OA pain is rapidly expanding. Since symptomatic OA is a heterogeneous disease, the challenge will be to identify patients that will benefit the most from specific approaches.