Background & Aims

Fibromyalgia (FM) is a complex disorder characterised by widespread chronic musculoskeletal pain associated with muscle fatigue[1,2] and reaches 2 to 3% of the world’s population[3]. Activation and recruitment[4,5] of mast cells[5,6,7] seem to be involved in the FM pathophysiology. Mast cells are degranulated under diverse stimuli, releasing inflammatory mediators such as tryptase, histamine, and serotonin, which activate protease-activated receptor-2, H1, and 5-HT2 and 5-HT3 receptors, respectively, expressed on nociceptive neurons, causing peripheral sensitisation. Therefore, peripheral mast cells have a substantial role in pain transmission related to chronic pain conditions[8,9], such as FM[5]. In this sense, FM diagnosis is common in patients with systemic mastocytosis[5,10], and increased mast cells were observed in skin biopsies of FM patients[6]. Thus, we explored the involvement of peripheral mast cells in an experimental model of fibromyalgia induced by reserpine.

Methods

Reserpine (1 mg/kg) subcutaneously (s.c.) or vehicle (0.1% acetic acid in 0.9% NaCl; 10 ml/kg; s.c.) were injected once daily for 3 consecutive days in Swiss male mice (30g; n=6/group) to induce the fibromyalgia (FM) model. From the 4th day after the first reserpine dose, nociceptive [mechanical (von Frey filaments) and cold (acetone drops) allodynia, muscle fatigue (grip test)] and inflammatory [mast cells number (histological analyses) in plantar tissue] parameters were evaluated[11]. The same nociceptive and inflammatory parameters were assessed after mast cell depletion with the compound 48/80 (0.5-4 mg/kg, intraperitoneal (i.p.)). The effect of mast cells membrane stabiliser (ketotifen; 10 mg/kg, oral route (p.o.)), tryptase inhibitor (gabexate; 10 mg/kg, s.c.), or antagonists of receptors PAR-2 (ENMD-1068; 10 mg/kg, i.p.), 5-HT2A (ketanserin; 1 mg/kg, i.p.), 5-HT3 (ondansetron; 1 mg/kg, p.o.), and H1 (promethazine; 1 mg/kg, i.p.) also were evaluated in this FM model.

Results

The fibromyalgia (FM) induction caused mast cell infiltration into the mice’s plantar tissue. The depletion of mast cell mediators with the compound 48/80 or the mast cell membrane stabilizer ketotifen fumarate widely (80-90%) and extensively (from 1 up to 10 days) prevented reserpine-induced mechanical and cold allodynia and muscle fatigue. Compound 48/80 also prevented the reserpine-induced mast cell infiltration to plantar tissue. Finally, we demonstrated that PAR-2, 5-HT2A, 5-HT3, and H1 receptor antagonists expressed in neuronal or mast cells or a tryptase inhibitor seem crucial to mediate FM-related painful symptoms since they reduced the reserpine-induced mechanical and cold allodynia and muscle fatigue.

Conclusions

Studies have suggested the involvement of mast cells in the pain of patients with fibromyalgia (FM). Our findings indicate that mast cells contribute to the development and maintenance of the mechanical and thermal hypersensitivity and muscle fatigue observed in the reserpine-induced experimental FM model, contributing to the substantiated construct validity of this model. It should be noted that many of the drugs used in this study are commercially available to treat other pathologies (e.g.,ketotifen, ondansetron, ketanserin, and promethazine) and would have the potential to be repositioned for FM. Therefore, the clinical use of mast cell membrane stabilizers or antagonism of different receptors targeted downstream to activation of mast cells could effectively treat FM cardinal symptoms of at least a subgroup of patients. Double-blinded, controlled, randomized and large-scale clinical trials of these drugs in patients with FM are needed to understand better their benefits to patients.

References

[1] Clauw, D.J., 2015. Fibromyalgia and Related Conditions. Mayo Clin. Proc. 90, 680–692.
[2] Häuser, W., Ablin, J., Fitzcharles, M.A., Littlejohn, G., Luciano, J. V., Usui, C., Walitt, B., 2015. Fibromyalgia. Nat. Rev. Dis. Prim. 1, 1–16.
[3] Sarzi-puttini, P., Giorgi, V., Marotto, D., 2020. Fibromyalgia: an update on clinical characteristics, aetiopathogenesis and treatment. Nat. Rev. Rheumatol. 16, 645-660.
[4] Littlejohn, G., Guymer, E., 2018. Neurogenic inflammation in fibromyalgia. Semin. Immunopathol. 40, 291–300.
[5] Theoharides, T.C., Tsilioni, I., Bawazeer, M., 2019. Mast Cells, Neuroinflammation and Pain in Fibromyalgia Syndrome. Front. Cell. Neurosci. 13, 1–8.
[6] Blanco, I., Béritze, N., Argüelles, M., Cárcaba, V., Fernández, F., Janciauskiene, S., Oikonomopoulou, K., De Serres, F.J., Fernández-Bustillo, E., Hollenberg, M.D., 2010. Abnormal overexpression of mastocytes in skin biopsies of fibromyalgia patients. Clin. Rheumatol. 29, 1403–1412.
[7] Conti, P., Gallenga, C.E., Caraffa, A., Ronconi, G., Kritas, S.K., 2020. Impact of mast cells in fibromyalgia and low-grade chronic inflammation: Can IL-37 play a role? Dermatol. Ther. 33, e13191.
[8] Héron, A., Dubayle, D., 2013. A focus on mast cells and pain. J. Neuroimmunol. 264, 1–7.
[9] Mai, L., Liu, Q., Huang, F., He, H., Fan, W., 2021. Involvement of Mast Cells in the Pathophysiology of Pain. Front. Cell. Neurosci. 15, 205.
[10] Theoharides, T.C., Tsilioni, I., Arbetman, L., Panagiotidou, S., Stewart, J.M., Gleason, R.M., Russell, I.J., 2015. Fibromyalgia Syndrome in Need of Effective Treatments. J. Pharmacol. Exp. Ther. 355, 255–263.
[11] Brusco, I., Justino, A.B., Silva, C.R., Fischer, S., Cunha, T.M., Scussel, R., Machado-de-Ávila, R.A., Ferreira, J., Oliveira, S.M., 2019. Kinins and their B1 and B2 receptors are involved in fibromyalgia-like pain symptoms in mice. Biochem. Pharmacol. 168, 119–132.

Presenting Author

Sara Marchesan Oliveira

Poster Authors

Sara Marchesan Oliveira, PhD

Professor

Federal University of Santa Maria

Lead Author

Evelyne Silva Brum

PhD

Federal University of Santa Maria

Lead Author

Maria Fialho

Federal University of Santa Maria, Santa Maria, RS, Brazil

Lead Author

Cristina Nogueira

Federal University of Santa Maria

Lead Author

Topics

  • Models: Musculoskeletal