Dynamic weight-bearing test during jumping: A sensitive outcome measure of chronic osteoarthritis pain in rats.

Pain due to osteoarthritis (OA) often occurs during locomotion in the vertical direction when joints are subjected to high mechanical load, e.g. during standing up from a chair or using stairs. To investigate joint pain in OA rat models, dynamic weight-bearing or gait analysis is traditionally conducted during horizontal walking on a flat surface. However, in chronic models of OA, which are of particular translational relevance for the disease, differences in the readouts between OA and control rats are often weak and of high variability leading to an insufficient assay window for drug profiling. To measure pain-related symptoms more sensitively, we conducted a dynamic weight-bearing test in the moment of a strong voluntary mechanical load. For that, we permanently housed rats in a four-story rat colony cage (RCC) and determined hind paw forces during voluntary jumping from one level to the next. This outcome measure was named jump incapacitance. After inducing OA by destabilizing the medial meniscus (DMM), we found that during jumps the average ipsilateral over contralateral hind paw forces were significantly reduced compared with healthy controls (jump incapacitance) from early- (day 7) to late-stage disease (day 90). An intra-articular injection of Zilretta (triamcinolone acetonide extended-release injectable suspension) attenuated OA-induced jump incapacitance after 8 days compared with DMM rats receiving vehicle (p = 0.069). In contrast, a CatWalk test for gait disturbance failed to detect any significant alterations in the chronic course of the DMM model. In conclusion, the dynamic weight-bearing test during jumping represents a novel method to characterize joint pain symptoms even in a slowly progressive OA rat model. It is sensitive, observer independent, relates to clinically relevant endpoints and demonstrates backtranslation of a drug that is approved for the treatment of OA knee pain.

Systematic analysis reveals that colony housing aligns gait profiles and strengthens link between histological and micro-CT bone markers in rat models of osteoarthritis.

Osteoarthritis (OA) etiopathogenesis is complex with strong environmental/lifestyle determinants that, in laboratory animals, extend to social context and stress levels. This study seeks to identify whether colony housing of rats exerts a social impact on locomotion behaviors to influence alignment between symptomatic (gait) and structural (bone micro-CT measures, cartilage morphometry, and histology) OA outcome measures. Rats were randomly allocated to conventional (type IV; n = 48) or rat colony cage (RCC; n = 30) housing, further randomized to OA surgical models (ACLT + tMx, MMT or DMM) or no surgery (control), and maintained for 19 weeks during which multiple gait recordings were made. Standard histological grading and bone micro-CT data were collected at necropsy. Principal component analysis was used to summarize the variation in gait, micro-CT or histology. Linear mixed effects model or two-way ANOVA was employed to evaluate the impact of the housing system, surgery and time on gait, or micro-CT and histology components Analyses reveal that RCC exaggerates trends in gait change via a combined effect of the housing system and surgery. Intriguingly, RCC-housed nonoperated control rats showed similar gait changes to rats subjected to surgery; the latter exhibited significant structural joint changes in both systems. Stronger correlation between histological and micro-CT bone changes were found in medial and lateral tibia joint compartments of rats housed in RCC system. This study has established that rat social housing exaggerates outcomes in traditional histological measures of OA, generates stronger links between histology and micro-CT bone changes and removes gait differences as a variable in their etiology.

Automated Tracking of Motion and Body Weight for Objective Monitoring of Rats in Colony Housing.

Living together in large social communities within an enriched environment stimulates self-motivated activity in rats. We developed a modular housing system in which a single unit can accommodate as many as 48 rats and contains multiple functional areas. This rat colony cage further allowed us to remotely measure body weight and to continuously measure movement, including jumping and stair walking between areas. Compared with pair-housed, age-, strain-, and weight-matched rats in conventional cages, the colony-housed rats exhibited higher body mass indices, had more exploratory behavior, and were more cooperative during handling. Continuous activity tracking revealed that the amount of spontaneous locomotion, such as jumping between levels and running through the staircase, fell after surgery, blood sampling, injections, and behavioral tests to a similar extent regardless of the specific intervention. Data from the automated system allowed us to identify individual rats with significant differences (>2 SD) from other cohoused rats; these rats showed potential health problems, as verified using conventional health scoring. Thus, our rat colony cage permits social interaction and provides a variety of functional areas, thereby perhaps improving animal wellbeing. Furthermore, automated online tracking enabled continuous quantification of spontaneous motion, potentially providing objective measures of animal behavior in various disease models and reducing the need for experimental manipulation. Finally, health monitoring of individual rats was facilitated in an objective manner.

Development and characterisation of a novel and rapid lung eosinophil influx model in the rat.

Eosinophils play a major role in the development and severity of asthma. Robust and rapid preclinical animal models are desirable to profile novel therapeutics inhibiting the influx of eosinophils into the airways. To develop a rapid, airway eosinophil recruitment model in the rat, Brown-Norway (BN) rats were immunised with ovalbumin (OVA)/alum on day 0, 1 and 2 and challenged with OVA aerosol on day 5 and 6. On day 7 bronchoalveolar lavage fluid (BALF) was analysed for eosinophil numbers, eosinophil peroxidase (EPO) activity and cytokines. Lung sections were also examined. The immunised animals showed a strong selective influx of eosinophils into the airways correlating with enhanced EPO activity, Interleukin (IL-4), IL-5 and monocytes chemo attractant protein levels in the BALF in comparison to sham-sensitised rats. In addition the immunised rats developed goblet cell metaplasia in the lung and showed OVA specific IgG1 and IgE levels in the serum but no airway hyperreactivity after metacholine challenge. Airway inflammation was suppressed by applying the steroids Budesonide (intra tracheally) and Prednisolone (per orally), Roflumilast a phosphodiesterase-4 inhibitor, and the H1 receptor antagonists Epinastine and Ketotifen. Montelukast, a Leukotriene receptor antagonist and Chromoglycate, a mast cell stabiliser, had no effect in this model. In summary, in this novel preclinical rat model therapeutics expected to inhibit the development of airway eosinophilia can rapidly be tested.