Background & Aims

Osteoarthritis (OA), the most common form of arthritis, is typically associated with chronic pain (inflammatory and neuropathic), which varies considerably in affected patients (1). Chronic pain management is a significant unmet medical need as current drugs are either ineffective or produce undesirable side effects such as sedation, ulcers, and addiction. Despite several approaches, including physical therapy, non-steroidal anti-inflammatory drugs, and corticosteroids, OA-associated pain remains inadequately managed (2). In addition, developing new pain management drugs is complicated by the poor clinical translational value and the absence of objective measures for chronic pain perception in existing animal models (3).
This study aimed to set up and compare two surgical OA rat models for use in the pharma industry. The medial meniscus tear (MMT) and the medial meniscectomy (MNX) models were studied behaviorally and validated pharmacologically with pregabalin.

Methods

MMT and MNX models were implemented in adult male Sprague Dawley rats. The rats were assessed in mechanical sensitivity with a manual von Frey test, and dynamic weight-bearing measured in the CatWalk gait analysis device at baseline and weekly post-surgery.
As soon as there was a significant difference in phenotypes between MMT/MNX and sham rats, one group of the MMT/MNX-operated rats was treated with pregabalin (30 mg/kg p.o.), and 3 h later the effect on behavioral phenotype in mechanical sensitivity was assessed.
At the end of the study, the knees were dissected, fixed in 10% formalin, decalcified, embedded in paraffin, sectioned, stained with Toluidine Blue, and used for pathology scoring following the guidelines recommended by the Osteoarthritis Research Society International (OARSI) histopathology initiative for rat.

Results

A statistically significant increase in mechanical hypersensitivity in MMT rats was achieved six weeks post-surgery. MNX rats had a faster progression than MMT rats, the pain phenotype was achieved already three weeks post-surgery. Dynamic weight-bearing did not show differences between MMT/MNX and sham rats or between models.
Pregabalin treatment significantly attenuated mechanical hypersensitivity in MMT/MNX rats compared to vehicle-treated rats, providing successful pharmacological validation of the models. However, a slight variation was observed in behavioral data from the MNX+vehicle group, which was most probably caused by the stress due to the oral administration of a large volume of vehicle.
OARSI scoring demonstrated robust loss of cartilage matrix and increased total pathology score in the operated knees.

Conclusions

Surgical MMT and MNX models in rodents are valuable tools for studying OA pathology progression. They recapitulate the temporal development of knee pathology much better than chemically induced models and thus are very useful for the development of disease-modifying therapies for OA. However, their validity for assessing OA-related pain remains controversial, mostly due to very mild pain phenotype. In this study, a mild increase was demonstrated in mechanical hypersensitivity following MMT/MNX surgeries, and studied the temporal progression of this phenotype. Moreover, the models were successfully validated with the well-known painkiller drug pregabalin. In drug discovery, fast and translational in vivo models are preferred. MNX model progresses faster than the MMT model, making it more suitable for drug research. However, the MNX model needs further optimization of surgical procedures and more objective measurements to reduce experimental variation.

References

1.Dimitroulas, T., Duarte, R. V., Behura, A., Kitas, G. D., & Raphael, J. H. (2014). Neuropathic pain in osteoarthritis: A review of pathophysiological mechanisms and implications for treatment. In Seminars in Arthritis and Rheumatism (Vol. 44, Issue 2). https://doi.org/10.1016/j.semarthrit.2014.05.011
2.Krishnamurthy, A., Lang, A. E., Pangarkar, S., Edison, J., Cody, J., & Sall, J. (2021). Synopsis of the 2020 US Department of Veterans Affairs/US Department of Defense Clinical Practice Guideline: The Non-Surgical Management of Hip and Knee Osteoarthritis. In Mayo Clinic Proceedings (Vol. 96, Issue 9). https://doi.org/10.1016/j.mayocp.2021.03.017
3.Sadler, K. E., Mogil, J. S., & Stucky, C. L. (2022). Innovations and advances in modelling and measuring pain in animals. In Nature Reviews Neuroscience (Vol. 23, Issue 2). https://doi.org/10.1038/s41583-021-00536-7

Presenting Author

Paula Lehtinen

Poster Authors

Paula Lehtinen

MSc

University of Turku and Orion Corporation

Lead Author

Andrii Domanskyi

PhD

Orion Corporation

Lead Author

Carina Stenfors

Orion Corporation

Lead Author

Topics

  • Models: Musculoskeletal