Evaluation of EWRR Abstracts

Gut dysbiosis and Vagus Nerve: a pathway to chronic pain in Rheumatoid Arthritis?

Background

Emerging evidence highlights the pivotal role of the vagus nerve (VN) in rheumatoid arthritis (RA), with reduced VN activity preceding the disease onset and vagotomy identified as a potential risk factor for RA development. This phenomenon is linked to the VN's immunomodulatory properties but may also integrate its role in the gut-brain axis. Both preclinical and clinical studies suggest that VN stimulation may alleviate chronic pain, including fibromyalgia, abdominal pain, and headaches. Despite achieving clinical and biological remission, approximately 30% of RA patients continue to experience persistent pain. Interestingly, dysbiosis—a disruption in gut microbiota composition—is present in RA and may even precede the development of articular symptoms. Using heart rate variability (HRV) analysis from telemetric electrocardiograms, our team demonstrated that fecal microbiota transplantation (FMT) from RA patients altered VN activity in recipient mice compared to FMT from healthy controls (HC), mimicking the VN dysfunction observed in RA. We hypothesize that chronic pain in RA may partly stem from dysbiosis and its effects on the VN and gut-brain axis. Here, we explore the interplay between gut microbiota, VN activity, and pain using a mouse model.

Methods

FMT was performed using gut microbiota from RA patients (RA-FMT) or HC (HC-FMT) in male C57/Bl6 mice. VN activity was assessed via calcium imaging of vagal afferent neurons isolated from nodose/jugular ganglia. Neurons were stimulated with pharmacological agents, including serotonin and nicotine, to evaluate their responses. Behavioral experiments were conducted to assess mechanical sensitivity (Von Frey Test) and anxiodepressive-related behaviors (Sucrose Splash Test). Statistical analyses were performed using Mann-Whitney tests.

Results

RA-FMT (n = 136 neurons, N = 10 mice) did not alter the proportion of nodose neurons responding to serotonin and nicotine compared to HC-FMT (n = 98 neurons, N = 5 mice), with response rates of 52% and 71% for RA-FMT versus 48% and 75% for HC-FMT, respectively. However, RA-FMT neurons exhibited a significant reduction in nicotine response amplitude (p = 0.038, n = 48 RA-FMT neurons vs. 70 HC-FMT neurons). No difference in serotonin response amplitude was observed (n = 30 RA-FMT neurons; 46 HC-FMT neurons). In vivo, RA-FMT did not affect mechanical sensitivity but induced depressive-like behaviors, evidenced by reduced grooming time in the Sucrose Splash Test (p = 0.067, n = 6 RA-FMT mice; 4 HC-FMT mice).

Conclusion

Our findings, supported by HRV analysis and calcium imaging, suggest that gut microbiota from RA patients modulates VN afferent neuronal responses and may contribute to depressive-related behaviors in vivo. Ongoing studies aim to elucidate the underlying mechanisms of this

modulation. Targeting the gut microbiota-VN axis represents a promising therapeutic avenue for managing chronic pain in RA.

Intra-articular slow-release treatment with microspheres containing colchicine is efficient in an inflammatory arthritis rat model.

Purpose: Gout is a common disease causing painful and disabling flares. Approved treatments for acute gout flares are slow acting and associated with poor safety profiles. There is a clear unmet medical need for a more effective treatment for acute pain, with a rapid onset of action and a good safety profile. We aimed to evaluate the efficacy of a novel intra-articular (IA) combination of sustained-release colchicine (SR-COL) and ropivacaine (ROPI) (PKM-01) in a rat model of acute inflammatory arthritis.

Methods: This treatment (PKM-01) combines the anesthetic ropivacaine (ROPI), with colchicine (COL) formulated within a biodegradable poly(lactic-co-glycolic acid) (PLGA) polymer matrix. COL was encapsulated within microspheres of PLGA polymer for sustained release. To evaluate the effect of this treatment, we adapted a model of intra-articular carrageenan (CAR)-induced arthritis in the knees or ankles. A total of 50 µL of 2% CAR was injected intra-articularly (IA) in Sprague Dawley rats, and acute arthritis occurred in the hours following the injection. Treatments were administered IA with less than a one-minute delay after CAR injection: PBS, ROPI, dexamethasone (DXM), encapsulated COL, or PKM-01. Pain was evaluated using von Frey filaments or weight-bearing assessments. Histological semi-quantitative scores were used to evaluate joint inflammation and destruction.

Results: All animals developed acute, painful, and destructive arthritis after CAR injection. DXM exerted a significant effect on pain, inflammation, and joint destruction. ROPI was effective for pain relief but not to prevent inflammation or destruction. Colchicine was effective for all three parameters. PKM-01 exerted a strong analgesic effect (Figure 1A) and demonstrated anti-inflammatory properties, which were histologically detected in joint inflammation (Figure 1B) and destruction (Figure 1C). In addition, colchicine concentration in blood over 72 hours after ankle injections remained at very low levels and significantly below toxic thresholds.

Conclusions: Taken together, these data indicate in this model that PKM-01 could be an option for treating acute inflammatory arthritis. Since oral treatment with colchicine is limited by toxicity, PKM-01 could be useful for patients, including those with comorbidities for whom glucocorticoids are contraindicated or not tolerated. A clinical trial in humans is already planned.

Key words : arthritis, colchicine, microsphere

Figure 1 : Postural pain evaluation scores AUC along the study (A). B and C: Histological inflammation (B) and destruction (C). COL + ROPI corresponds to PKM-01. Kruskal-Wallis test was performed. * p ≤ 0.05, ** p ≤ 0.01, ***p ≤ 0.001. 

‘Fibroblast–Neuron Interactions Driving Persistent Pain in Rheumatoid Arthritis’ (FiND-Pain RA) - a study protocol

Key words: Fibroblasts, Rheumatoid arthritis, Pain

Abstract

Background

Pain in patients with rheumatoid arthritis (RA) is an unmet clinical need. Targeting joint inflammation with disease modifying antirheumatic drugs (DMARDs) has not resulted in the anticipated reduction in pain for many patients. This can partly be explained by the concept of central sensitisation whereby spinal and supraspinal pathways have a lower threshold of activation leading to increased perception of pain.

Synovial stromal cells such as fibroblasts are also thought to play a role through peripheral sensitisation of nerves in the joint. Synovial fibroblasts are known to produce pro-algesic mediators such as interleukin 6 (IL-6) and nerve growth factor (NGF) at the mRNA level. These pro-algesic mediators could activate sensory nerve fibres that send signals from the joint to the spinal cord, thereby driving persistent pain in RA. The purpose of this study is to evaluate which pro-algesic mediators are produced by lining versus sublining fibroblasts and whether the level of these mediators correlates with clinical measures of pain in patients with RA.  

Methods

FiND-Pain RA is a multi-centre observational study which will recruit 50 patients with seropositive RA who attend the rheumatology department of Guy’s and St Thomas’ Hospital, London and the Nuffield Orthopaedic Centre, Oxford. Clinical examination, pain-focused patient reported outcome measures (PROMs), ultrasound examination and ultrasound guided synovial biopsy of the knee will be performed. The levels of known and putative pro-algesic mediators will be measured in fibroblasts from the lining and sublining layer of the synovium. The location and spatial morphology of sensory nerve fibres and their proximity to the lining and sub-lining fibroblasts will be characterized.

Results

The primary outcome will be to determine whether the knee pain scores of participants correlate with the level of leukaemia inhibitory factor (LIF), a novel putative pain mediator expressed in sublining fibroblasts. Publicly available transcriptomic datasets of synovial tissue from patients with RA have shown LIF to be highly expressed at the gene level, and increased levels of LIF protein in RA synovial fluid compared to serum have been demonstrated in unpublished work from our group. The exact source and role of LIF in RA and pain are yet to be elucidated.

The secondary outcomes will be to determine whether other pro-algesic mediators produced by lining or sub-lining fibroblasts correlate with clinical measures of pain and to assess the location and proximity of sensory nerve fibres to lining versus sub-lining fibroblasts.

Discussion

Fibroblast-neuron interaction including their derived cytokines would be an exciting new therapeutic target in RA, with further understanding of the mechanisms hopefully leading to novel analgesics and other interventions.

This work has been granted ethical approval by the Bromley Research Ethics Committee and is funded by a Wellcome Trust collaborative award.