Factors affecting the reliability of behavioral assessments for rodent osteoarthritis models

The translational value of osteoarthritis (OA) models is often debated because numerous studies have shown that animal models frequently fail to predict the efficacy of therapies in humans. In part, this failing may be due to the paucity of preclinical studies that include behavioral assessments in their metrics. Behavioral assessments of animal OA models can provide valuable data on the pain and disability associated with disease-sequelae of significant clinical relevance. Clinical definitions of efficacy for OA therapeutics often center on their palliative effects. Thus, the widespread inclusion of behaviors indicative of pain and disability in preclinical animal studies may contribute to greater success identifying clinically relevant interventions. Unfortunately, studies that include behavioral assays still frequently encounter pitfalls in assay selection, protocol consistency, and data/methods transparency. Targeted selection of behavioral assays, with consideration of the array of clinical OA phenotypes and the limitations of individual behavioral assays, is necessary to identify clinically relevant outcomes in OA animal models appropriately. Furthermore, to facilitate accurate comparisons across research groups and studies, it is necessary to improve the transparency of methods. Finally, establishing agreed-upon and clear definitions of behavioral data will reduce the convolution of data both within and between studies. Improvement in these areas is critical to the continued benefit of preclinical animal studies as translationally relevant data in OA research. As such, this review highlights the current state of behavioral analyses in preclinical OA models.

Functional Measures of Grip Strength and Gait Remain Altered Long-term in a Rat Model of Post-traumatic Elbow Contracture

Post-traumatic joint contracture (PTJC) is a debilitating condition, particularly in the elbow. Previously, we established an animal model of elbow PTJC quantifying passive post-mortem joint mechanics and histological changes temporally. These results showed persistent motion loss similar to what is experienced in humans. Functional assessment of PTJC in our model was not previously considered; however, these measures would provide a clinically relevant measure and would further validate our model by demonstrating persistently altered joint function. To this end, a custom bilateral grip strength device was developed, and a recently established open-source gait analysis system was used to quantify forelimb function in our unilateral injury model. In vivo joint function was shown to be altered long-term and never fully recover. Specifically, forelimb strength in the injured limbs showed persistent deficits at all time points; additionally, gait patterns remained imbalanced and asymmetric throughout the study (although a few gait parameters did return to near normal levels). A quantitative understanding of these longitudinal, functional disabilities further strengthens the clinical relevance of our rat PTJC model enabling assessment of the effectiveness of future interventions aimed at reducing or preventing PTJC.

A graphic user interface for the evaluation of knee osteoarthritis (GEKO): an open-source tool for histological grading

OBJECTIVE

In osteoarthritis (OA) models, histology is commonly used to evaluate the severity of joint damage. Unfortunately, semi-quantitative histological grading systems include some level of subjectivity, and quantitative grading systems can be tedious to implement. The objective of this work is to introduce an open source, graphic user interface (GUI) for quantitative grading of knee OA.

METHODS

Inspired by the 2010 OARSI histopathology recommendations for the rat, our laboratory has developed a GUI for the evaluation of knee OA, nicknamed GEKO. In this work, descriptions of the quantitative measures acquired by GEKO are presented and measured in 42 histological images from a rat knee OA model. Using these images, across-session and within-session reproducibility for individual graders is evaluated, and inter-grader reliability across different levels of OA severity is also assessed.

RESULTS

GEKO allowed histological images to be quantitatively scored in less than 1 min per image. In addition, intra-class coefficients (ICCs) were largely above 0.8 for across-session reproducibility, within-session reproducibility, and inter-grader reliability. These data indicate GEKO aided in the reproducibility and repeatability of quantitative OA grading across graders and grading sessions.

CONCLUSIONS

Our data demonstrate GEKO is a reliable and efficient method to calculate quantitative histological measures of knee OA in a rat model. GEKO reduced quantitative grading times relative to manual grading systems and allowed grader reproducibility and repeatability to be easily assessed within a grading session and across time. Moreover, GEKO is being provided as a free, open-source tool for the OA research community.

The Open Source GAITOR Suite for Rodent Gait Analysis

Locomotive changes are often associated with disease or injury, and these changes can be quantified through gait analysis. Gait analysis has been applied to preclinical studies, providing quantitative behavioural assessment with a reasonable clinical analogue. However, available gait analysis technology for small animals is somewhat limited. Furthermore, technological and analytical challenges can limit the effectiveness of preclinical gait analysis. The Gait Analysis Instrumentation and Technology Optimized for Rodents (GAITOR) Suite is designed to increase the accessibility of preclinical gait analysis to researchers, facilitating hardware and software customization for broad applications. Here, the GAITOR Suite’s utility is demonstrated in 4 models: a monoiodoacetate (MIA) injection model of joint pain, a sciatic nerve injury model, an elbow joint contracture model, and a spinal cord injury model. The GAITOR Suite identified unique compensatory gait patterns in each model, demonstrating the software’s utility for detecting gait changes in rodent models of highly disparate injuries and diseases. Robust gait analysis may improve preclinical model selection, disease sequelae assessment, and evaluation of potential therapeutics. Our group has provided the GAITOR Suite as an open resource to the research community at www.GAITOR.org, aiming to promote and improve the implementation of gait analysis in preclinical rodent models.

Unique spatiotemporal and dynamic gait compensations in the rat monoiodoacetate injection and medial meniscus transection models of knee osteoarthritis

OBJECTIVE

In rodent osteoarthritis (OA) models, behavioral changes are often subtle and require highly sensitive methods to detect these changes. Gait analysis is one assay that may provide sensitive, quantitative measurement of these behavioral changes. To increase detection sensitivity of gait assessments relative to spatiotemporal gait collection alone, we combined our spatiotemporal and dynamic gait collection systems. Using this combined system, gait was assessed in the rat medial meniscus transection (MMT) model and monoiodoacetate (MIA) injection model of knee OA.

DESIGN

36 male Lewis rats were separated into MMT (n = 8), medial collateral ligament transection (MCLT) (n = 8), skin incision (n = 4), MIA injection (n = 8), and saline injection (n = 8) groups. After initiation of OA, gait data were collected weekly in each group out to 4 weeks.

RESULTS

The MMT and MIA injection models produced unique pathologic gait profiles, with MMT animals developing a shuffling gait and MIA injection animals exhibiting antalgic gait. Spatiotemporal changes were also observed in the MMT model at week 1 (P < 0.01), but were not observed in the MIA injection model until week 3 (P < 0.01). Dynamic gait changes were observed in both models as early as 1 week post-surgery (P < 0.01).

CONCLUSION

Combined analysis of spatiotemporal and dynamic gait data increased detection sensitivity for gait modification in two rat OA models. Analyzing the combined gait data provided a robust characterization of the pathologic gait produced by each model. Furthermore, this characterization revealed different patterns of gait compensations in two common rat models of knee OA.

Peri-implant tissue response and biodegradation performance of a Mg-1.0Ca-0.5Sr alloy in rat tibia

Biodegradable magnesium (Mg) alloys combine the advantages of traditional metallic implants and biodegradable polymers, having high strength, low density, and a stiffness ideal for bone fracture fixation. A recently developed Mg-Ca-Sr alloy potentially possesses advantageous characteristics over other Mg alloys, such as slower degradation rates and minimal toxicity. In this study, the biocompatibility of this Mg-Ca-Sr alloy was investigated in a rat pin-placement model. Cylindrical pins were inserted in the proximal tibial metaphyses in pre-drilled holes orthogonal to the tibial axis. Implant and bone morphologies were investigated using μCT at 1, 3, and 6 weeks after implant placement. At the same time points, the surrounding tissue was evaluated using H&E, TRAP and Goldner's trichrome staining. Although gas bubbles were observed around the degrading implant at early time points, the bone remained intact with no evidence of microfracture. Principle findings also include new bone formation in the area of the implant, suggesting that the alloy is a promising candidate for biodegradable orthopedic implants.

A novel operant-based behavioral assay of mechanical allodynia in the orofacial region of rats

BACKGROUND

Detecting behaviors related to orofacial pain in rodent models often relies on subjective investigator grades or methods that place the animal in a stressful environment. In this study, an operant-based behavioral assay is presented for the assessment of orofacial tactile sensitivity in the rat.

NEW METHODS

In the testing chamber, rats are provided access to a sweetened condensed milk bottle; however, a 360° array of stainless steel wire loops impedes access. To receive the reward, an animal must engage the wires across the orofacial region. Contact with the bottle triggers a motor, requiring the animal to accept increasing pressure on the face during the test. To evaluate this approach, tolerated bottle distance was measured for 10 hairless Sprague Dawley rats at baseline and 30 min after application of capsaicin cream (0.1%) to the face. The experiment was repeated to evaluate the ability of morphine to reverse this effect.

RESULTS

The application of capsaicin cream reduced tolerated bottle distance measures relative to baseline (p<0.05). As long as morphine did not cause reduced participation due to sedation, subcutaneous morphine dosing reduced the effects of capsaicin (p<0.001). Comparison with existing method: For behavioral tests, experimenters often make subjective decisions of an animal's response. Operant methods can reduce these effects by measuring an animal's selection in a reward-conflict decision. Herein, a method to measure orofacial sensitivity is presented using an operant system.

CONCLUSIONS

This operant device allows for consistent measurement of heightened tactile sensitivity in the orofacial regions of the rat.