The broad spectrum mixed-lineage kinase 3 inhibitor URMC-099 prevents acute microgliosis and cognitive decline in a mouse model of perioperative neurocognitive disorders

Patients with pre-existing neurodegenerative disease commonly experience fractures that require orthopedic surgery. Perioperative neurocognitive disorders (PND), including delirium and postoperative cognitive dysfunction, are serious complications that can result in increased 1-year mortality when superimposed on dementia. Importantly, there are no disease-modifying therapeutic options for PND. Our lab developed the "broad spectrum" mixed-lineage kinase 3 inhibitor URMC-099 to inhibit pathological innate immune responses that underlie neuroinflammation-associated cognitive dysfunction. Here, we test the hypothesis that URMC-099 can prevent surgery-induced neuroinflammation and cognitive impairment.

These findings show that prophylactic URMC-099 treatment is sufficient to prevent surgery-induced microgliosis and cognitive impairment without affecting fracture healing. Together, these findings provide compelling evidence for the advancement of URMC-099 as a therapeutic option for PND.

Orthopedic surgery was performed by fracturing the tibia of the left hindlimb with intramedullary fixation under general anesthesia and analgesia. In a pilot experiment, 9-month-old mice were treated five times with URMC-099 (10 mg/kg, i.p.), spaced 12 h apart, with three doses prior to surgery and two doses following surgery. In this experiment, microgliosis was evaluated using unbiased stereology and blood-brain barrier (BBB) permeability was assessed using immunoglobulin G (IgG) immunostaining. In follow-up experiments, 3-month-old mice were treated only three times with URMC-099 (10 mg/kg, i.p.), spaced 12 h apart, prior to orthopedic surgery. Two-photon scanning laser microscopy and CLARITY with light-sheet microscopy were used to define surgery-induced changes in microglial dynamics and morphology, respectively. Surgery-induced memory impairment was assessed using the "What-Where-When" and Memory Load Object Discrimination tasks. The acute peripheral immune response to surgery was assessed by cytokine/chemokine profiling and flow cytometry. Finally, long-term fracture healing was assessed in fracture callouses using micro-computerized tomography (microCT) and histomorphometry analyses.

Orthopedic surgery induced BBB disruption and microglial activation, but had no effect on microglial process motility. Surgically treated mice exhibited impaired object place and identity discrimination in the "What-Where-When" and Memory Load Object Discrimination tasks. Both URMC-099 dosing paradigms prevented the neuroinflammatory sequelae that accompanied orthopedic surgery. URMC-099 prophylaxis had no effect on the mobilization of the peripheral innate immune response and fracture healing. Conclusions: These findings show that prophylactic URMC-099 treatment is sufficient to prevent surgery-induced microgliosis and cognitive impairment without affecting fracture healing. Together, these findings provide compelling evidence for the advancement of URMC-099 as a therapeutic option for PND.