Background & Aims

Fibromyalgia is a chronic and widespread pain characterised by significant muscle disorders, fatigue, mood swings, depression, and sleep disturbances, which affects 2 to 4% of the world’s population 1–3. Its aetiology is still not completely elucidated, and the parameters for defining it still lack precision, which makes its treatment challenging 4,5. The proposed pharmacological approaches have limited efficacy and marked adverse effects and do not effectively contribute to improving patients’ quality of life 1. Oxidative stress and releasing of reactive oxygen species have been proposed as the focal point of painful diseases, including fibromyalgia 6,7. Studies show that the sustaining of pain by oxidative stress is mediated by the action of macrophages, causing inflammation and chronic pain 8. Therefore, we aimed to investigate the involvement of oxidative stress stimulated by macrophages in a reserpine-induced fibromyalgia model.

Methods

The fibromyalgia model was induced by a daily subcutaneous (s.c.) injection of reserpine (1 mg/kg) or vehicle (0.1% acetic acid in saline) for 3 consecutive days 9 in C57BL6J male or Macrophage Fas-Induced Apoptosis (MaFIA) mice (IACUC #1194/2015PR; #5070100119/2019). The involvement of oxidative stress was verified after oral (p.o.) administration of ?-lipoic acid (100 mg/kg) 8, or intraperitoneal (i.p.) injection of PBN (100 mg/kg) 6. To assess the involvement of macrophages, MaFIA mice received 5 consecutive injections of AP20187 (2 mg/kg, i.p.) 8. Paw withdrawal threshold test (PWT) using von Frey filaments, acetone drops test, thigmotaxis behaviour, grip test, and forced swim test (FST) were evaluated as well the measurement of hydrogen peroxide (H2O2) levels 7,10. The sciatic nerve was collected and labelled with an F4/80+ monoclonal antibody to visualise the presence of macrophages 8. Data was expressed as mean±SEM and analysed by one- or two-way ANOVA-Bonferroni post hoc test.

Results

Reserpine-induced mechanical allodynia (reduced PWT by the von Frey test) and cold allodynia (increased sensitivity to acetone drops) were attenuated by the antioxidant alpha-lipoic acid and the ROS scavenger, PBN. Both treatments reduced the decrease in muscle strength (grip test), immobility time in the FST and sciatic nerve H2O2 levels increased by the reserpine-induced fibromyalgia model. None of the treatments had any effect on the reserpine-induced thigmotaxis behaviour. Reserpine, but not its vehicle, induced an increase in macrophages (F4/80+ cells) in the sciatic nerve of C57BL6J mice. Reserpinized MaFIA mice treated with B/B homodimerizer AP20187 had no macrophages in the sciatic nerve. The lack of macrophages reversed the mechanical and cold allodynia and immobility time in the FST induced by reserpine. No changes were observed in thigmotaxis behaviour or muscle strength.

Conclusions

The fibromyalgia model in mice, mimicked by consecutive injections of reserpine, induces pain and anxiety and depression-like behaviours, characteristics of the clinical manifestation of the disease 5,7,10,11. This study observed the involvement of oxidative stress in the reserpine-induced fibromyalgia model, highlighted by antioxidants-caused decrease in nociceptive parameters, depressive-like behaviours, and levels of reactive oxygen species 6,7. Macrophages are known to contribute to pain models through oxidative stress 8; here, we demonstrate by using MaFIA mice that macrophages, through releasing reactive oxygen species, contribute to pain and depressive-like behaviours in the reserpine-induced fibromyalgia model. Therefore, we propose that decreasing oxidative stress from macrophages may be a promising target for treating fibromyalgia in patients.

References

1.Sarzi-Puttini, P., Giorgi, V., Marotto, D. & Atzeni, F. Fibromyalgia: an update on clinical characteristics, aetiopathogenesis and treatment. Nat. Rev. Rheumatol. 16, 645–660 (2020).

2.Huynh, C. N., Yanni, L. M. & Morgan, L. A. Fibromyalgia: Diagnosis and management for the primary healthcare provider. J. Women’s Heal. 17, 1379–1387 (2008).

3.Sumpton, J. E. & Moulin, D. E. Fibromyalgia. Handb. Clin. Neurol. 119, 513–527 (2014).
4.Häuser, W. et al. Fibromyalgia. Nat. Rev. | Dis. Prim. 1, 1–16 (2015).

5.Brum, E. S., Becker, G., Fialho, M. F. P. & Oliveira, S. M. Animal models of fibromyalgia: What is the best choice? Pharmacol. Ther. 230, 107959 (2022).

6.De Logu, F. et al. Oxidative stress mediates thalidomide-induced pain by targeting peripheral TRPA1 and central TRPV4. BMC Biol. 18, (2020).

7.Brum, E. da S. et al. Relevance of Mitochondrial Dysfunction in the Reserpine-Induced Experimental Fibromyalgia Model. Mol. Neurobiol. 57, 4202–4217 (2020).

8.De Logu, F. et al. Macrophages and Schwann cell TRPA1 mediate chronic allodynia in a mouse model of complex regional pain syndrome type I. Brain. Behav. Immun. 88, 535–546 (2020).

9.Nagakura, Y., Oe, T., Aoki, T. & Matsuoka, N. Biogenic amine depletion causes chronic muscular pain and tactile allodynia accompanied by depression: A putative animal model of fibromyalgia. Pain 146, 26–33 (2009).

10.Fischer, S. P. M. et al. Involvement of TRPV1 and the efficacy of ?-spinasterol on experimental fibromyalgia symptoms in mice. Neurochem. Int. 134, 104673 (2020).

11.Brusco, I. et al. Kinins and their B1 and B2 receptors are involved in fibromyalgia-like pain symptoms in mice. Biochem. Pharmacol. 168, 119–132 (2019).

Presenting Author

Samuel Atuati

Poster Authors

Samuel Felipe Atuati

Master's Degree student

Federal Univesity of Santa Maria

Lead Author

E-mail

Evelyne Silva Brum

PhD

Federal University of Santa Maria

Lead Author

E-mail

Maria Fialho

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

Lead Author

E-mail

Daniel Doctor Araújo

PhD

University of Florence

Lead Author

E-mail

Lorenzo Doctor Landini

PhD

University of Florence

Lead Author

E-mail

Matilde Doctor Marini

PhD

University of Florence

Lead Author

E-mail

Mustafa Doctor Titiz

PhD

University of Florence

Lead Author

E-mail

Pierangelo Doctor Geppetti

PhD

University of Florence

Lead Author

E-mail

Romina Nassini

University of Florence

Lead Author

E-mail

Francesco De Logu

Lead Author

E-mail

Sara Marchesan Oliveira

PhD

Federal University of Santa Maria

Lead Author

E-mail

Topics

  • Specific Pain Conditions/Pain in Specific Populations: Fibromyalgia