RAT MONOSODIUM IODOACETATE (MIA) MODEL

Animals

Studies are conducted in adult male and female Sprague Dawley rats (Envigo) in an AAALAC-accredited facility with approval from an Institutional Animal Care and Use Committee, and implemented in accordance with the Guide for the Care and Use of Laboratory Animals 8th Edition (National Research Council, 2011) with standards set by the National Institutes of Health.

Induction of joint pain

The monosodium iodoacetate (MIA) model in rats is an established model of knee joint pain induced by an intra-articular injection of MIA into the knee joint (Fernihough et al., 2004, Pomonis et al., 2005), which inhibits glyceraldehyde-3-phosphatase dehydrogenase, inducing the progressive loss of chondrocytes, leading to histologic and morphologic changes to the articular cartilage closely resembling those seen in human osteoarthritis. In this model, cartilage degeneration, localized inflammation, and pain behaviors are observed.

Under anesthesia, animals receive a single injection of MIA into the left hind limb knee joint through the patellar tendon. Animals are carefully monitored throughout the experiment.

Study design

In the MIA model, mechanical allodynia using von Frey filaments and dynamic weight bearing are assessed in separate cohorts using appropriate group sizes determined by power analysis. Male and female rats (n=8-10) are evaluated in separate cohorts. Dose-responses are investigated, and vehicle and positive control groups are included to establish the validity of the experiment. The experimenter is blinded to the treatments, and dosing is performed by an independent experimenter.

The area of the paw tested with von Frey filaments is located in the center of the plantar surface, avoiding the foot pads (X on Figure 1A). The experimental design for the assessment of mechanical allodynia and weight bearing is presented in Figure 1B.

Experimental outcomes

Hind paw mechanical allodynia testing using von Frey filaments

Paw withdrawal threshold (PWT) is assessed using the up-down method (Chaplan et al., 1994) for both the ipsilateral and contralateral hind paws prior to MIA injection (Figure 1B). Post-induction PWT baseline is determined 4 days after MIA injection, and animals with ipsilateral PWT ≤4.0g are included in the subsequent testing of the asset’s efficacy to treat mechanical allodynia in MIA rats.

Hind paw dynamic weight bearing assessment

Changes in normal weight bearing of the paws is assessed by measuring the weight distribution of each paw of the rat (Philpott et al., 2017) with the Dynamic Weight Bearing Device prior to MIA injection (Figure 1B). Post-induction weight bearing baseline is determined 4 days after MIA injection, and the asset’s efficacy to treat weight bearing deficits in MIA rats is tested subsequently.

This work was conducted by PsychoGenics Inc. (Paramus, NJ) in collaboration with PSPP, NINDS, NIH under contract # 75N95019D00026