A buprenorphine depot formulation provides effective sustained post-surgical analgesia for 72 h in mouse femoral fracture models

CYR61 delivery promotes angiogenesis during bone fracture repair

Compromised vascular supply and insufficient neovascularization impede bone repair, increasing risk of non-union. CYR61, Cysteine-rich angiogenic inducer of 61kD (also known as CCN1), is a matricellular growth factor that has been implicated in fracture repair. Here, we map the distribution of endogenous CYR61 during bone repair and evaluate the effects of recombinant CYR61 delivery on vascularized bone regeneration. In vitro, CYR61 treatment did not alter chondrogenesis or osteogenic gene expression, but significantly enhanced angiogenesis. In a mouse femoral fracture model, CYR61 delivery did not alter cartilage or bone formation, but accelerated neovascularization during fracture repair. Early initiation of ambulatory mechanical loading disrupted CYR61-induced neovascularization. Together, these data indicate that CYR61 delivery can enhance angiogenesis during bone repair, particularly for fractures with stable fixation, and may have therapeutic potential for fractures with limited blood vessel supply.

Local erythropoiesis directs oxygen availability in bone fracture repair

Bone fracture ruptures blood vessels and disrupts the bone marrow, the site of new red blood cell production (erythropoiesis). Current dogma holds that bone fracture causes severe hypoxia at the fracture site, due to vascular rupture, and that this hypoxia must be overcome for regeneration. Here, we show that the early fracture site is not hypoxic, but instead exhibits high oxygen tension (> 55 mmHg, or 8%), similar to the red blood cell reservoir, the spleen. This elevated oxygen stems not from angiogenesis but from activated erythropoiesis in the adjacent bone marrow. Fracture-activated erythroid progenitor cells concentrate oxygen through haemoglobin formation. Blocking transferrin receptor 1 (CD71)-mediated iron uptake prevents oxygen binding by these cells, induces fracture site hypoxia, and enhances bone repair through increased angiogenesis and osteogenesis. These findings upend our current understanding of the early phase of bone fracture repair, provide a mechanism for high oxygen tension in the bone marrow after injury, and reveal an unexpected and targetable role of erythroid progenitors in fracture repair.

Impact of sensory neuropeptide deficiency on behavioral patterns and gait in a murine surgical osteoarthritis model

Substance P (SP) and a calcitonin-related gene alpha (αCGRP-/-) are implicated in musculoskeletal pain perception and were shown to have different effects on the pathogenesis of osteoarthritis (OA). However, it has not been investigated, whether deficiency for SP or αCGRP impacts pain-related behavior and well-being as well as gait during development of experimental OA. We induced OA in the right knee of wild-type (WT) mice and mice either deficient for SP (tachykinin 1, Tac-1) or αCGRP (male, n = 8 per genotype) by destabilizing the medial meniscus (DMM). We monitored body weight and food and water intake as indicators of wellbeing, determined nest building and composite pain score, and performed CatWalk gait analysis over 12 weeks. Cartilage degeneration was determined by OARSI scoring. The 12-week post-DMM, cartilage degradation in the medial compartment was significantly reduced in Tac1-/- mice compared to the WT and to αCGRP-/- mice, coinciding with highest unloading of the operated limb in Tac1-/-. Behavioral and gait analysis revealed only minor differences between the genotypes. Paw print area was most prominently reduced in Tac1-/- over the observation period; at 12 weeks, we found a significant reduction in normalized print area in Tac1-/- compared to presurgery and to the WT at the same time-point. Calculated weight bearing was significantly reduced only in Tac1-/-. Overall, we observed minor impact of DMM on gait and behavior in the present study. The reduced cartilage damage in the absence of SP might be in part due to reduced loading, however, the mechanism is not clear yet.

Refining pain management in mice by comparing multimodal analgesia and NSAID monotherapy for neurosurgical procedures

While neurosurgical interventions are frequently used in laboratory mice, refinement efforts to optimize analgesic management based on multimodal approaches appear to be rather limited. Therefore, we compared the efficacy and tolerability of combinations of the non-steroidal anti-inflammatory drug carprofen, a sustained-release formulation of the opioid buprenorphine, and the local anesthetic bupivacaine with carprofen monotherapy. Female and male C57BL/6J mice were subjected to isoflurane anesthesia and an intracranial electrode implant procedure. Given the multidimensional nature of postsurgical pain and distress, various physiological, behavioral, and biochemical parameters were applied for their assessment. The analysis revealed alterations in Neuro scores, home cage locomotion, body weight, nest building, mouse grimace scales, and fecal corticosterone metabolites. A composite measure scheme allowed the allocation of individual mice to severity classes. The comparison between groups failed to indicate the superiority of multimodal regimens over high-dose NSAID monotherapy. In conclusion, our findings confirmed the informative value of various parameters for assessment of pain and distress following neurosurgical procedures in mice. While all drug regimens were well tolerated in control mice, our data suggest that the total drug load should be carefully considered for perioperative management. Future studies would be of interest to assess potential synergies of drug combinations with lower doses of carprofen.

Embracing ethical research: Implementing the 3R principles into fracture healing research for sustainable scientific progress

As scientific advancements continue to reshape the world, it becomes increasingly crucial to uphold ethical standards and minimize the potentially adverse impact of research activities. In this context, the implementation of the 3R principles-Replacement, Reduction, and Refinement-has emerged as a prominent framework for promoting ethical research practices in the use of animals. This article aims to explore recent advances in integrating the 3R principles into fracture healing research, highlighting their potential to enhance animal welfare, scientific validity, and societal trust. The review focuses on in vitro, in silico, ex vivo, and refined in vivo methods, which have the potential to replace, reduce, and refine animal experiments in musculoskeletal, bone, and fracture healing research. Here, we review material that was presented at the workshop "Implementing 3R Principles into Fracture Healing Research" at the 2023 Orthopedic Research Society (ORS) Annual Meeting in Dallas, Texas.

Evaluating rearing behaviour as a model-specific pain indicator in mouse osteotomy models

To assess pain in mouse models of bone fractures, currently applied assessment batteries use combinations of clinical signs with spontaneous behaviours and model-specific behaviours, including walking and weight-bearing behaviour. Rearing behaviour - an upright position on the hindlimbs - has a motivational and an ambulatory component. Thus, rearing behaviour might have the potential to be an indicator for model-specific pain in mouse fracture models. To date, the assessment of rearing behaviour in bone fracture models using mice is only scarcely described. In this study, we aimed to determine whether the duration of rearing behaviour is affected by osteotomy of the femur in male and female C57BL/6N mice with external fixation (rigid vs. flexible) and could be an additional sign for model-specific pain, such as the presence of limping. Rearing duration was significantly decreased after osteotomy in male and female mice at 24 h, 48 h and 72 h, but was not affected by anaesthesia/analgesia alone. In male mice, the relative rearing duration increased over 72 h (both fixations) and at 10 days in the rigid fixation group but remained significantly lower in the flexible fixation group. In contrast, in female mice, no increase in rearing duration was observed within 72 h and at 10 days post-osteotomy, independent of the fixation. We did not identify any association between relative rearing time and presence or absence of limping. In summary, our results do not provide sufficient evidence that altered rearing behaviour might be an indicative sign for pain in this model.

Development, Validation and Characterization of a Novel Portable Closed Fracture Device

BACKGROUND/AIM

As one of the common clinical diseases, fractures have many causes, mechanisms, healing and influencing factors; especially fracture healing is a long-term and complex process. Animal fracture models can simulate the various states of human fractures, and on this basis, the prevention, mechanism, and treatment of fractures can be studied to further guide clinical practice.

MATERIALS AND METHODS

Here, we developed a novel and portable device to create a closed fracture model in mice. We then compared this novel closed fracture model with the traditional open model in multiple dimensions to evaluate the modelling process of establishment and healing. The two models were evaluated by imaging, immunostaining, and behavioral tests, which fully demonstrated the stability, universality and operability of the modified fracture model in mice.

RESULTS

Surgical quality assessment revealed that the closed fracture model had a shorter operation time and smaller wound than the open model. X-ray and micro-CT results showed no differences between the two models in the evaluation of radiographic and morphological changes during fracture healing. Histological examination revealed the process of the typical intrachondral osteogenic pathway after fracture. Moreover, animal gait analysis indicated reduced postoperative pain in the closed group compared to the open group.

CONCLUSION

This study provides a constructive strategy for a closed fracture model in mice and demonstrates the effectiveness and feasibility of the closed fracture model in studying the typical intrachondral osteogenic pathway of fractures from multiple dimensions.