Cytokine Dynamics, Diagnosis and Treatment of Neuroinflammation In Chronic Constriction Injury Rat Model

Chronic neuropathic pain is a serious, worldwide health problem leading to life-long treatment and the possibility of significant disability. In this study, neuropathic pain was modeled using the chronic constriction injury (CCI) in rats. The CCI rats exhibited hypersensitivity (typical neuropathic pain symptom) to mechanical stimulation of the affected paw 11 days post-surgery, at a time when sham surgery animals did not. It is known that immune cells play a role in the development of neuropathic pain and to further explore the relationship between neuropathic pain and immune cells, we hypothesized that the infiltration of immune cells into the affected sciatic nerve can be monitored in vivo by optical imaging. To test this hypothesis, an intravenous injection of a novel perfluorocarbon (PFC) nanoemulsion developed by J. M. Janjic (PharmD, PhD) and co-workers was used. Post-injection, the nanoemulsion is endocytosed by inflammatory cells (e.g. monocytes and macrophages) in a CCI rat. The nanoemulsion carried two distinct imaging agents, a near-infrared (NIR) lipophilic fluorescence reporter (DiR) and a 19F magnetic resonance imaging (MRI) tracer (PFC). This study showed that in live rats, NIR fluorescence was concentrated in the area of the affected sciatic nerve. Furthermore, the 19F MRI signal was observed in the affected sciatic nerve in the perfusion fixed rats. Histological examination of the CCI sciatic nerve sections revealed significant infiltration of CD68 positive macrophages. These results demonstrate that the infiltration of immune cells into the sciatic nerve can be visualized in live animals using these methods. Using the same strategy, a theranostic nanoemulsion containing an anti-inflammatory drug, celecoxib, along with NIR dye and 19F tracer, was used for the targeted delivery of the drug into the inflammatory cells at the site of injury while at the same time providing the ability to track inflammation. A single intravenous injection of the nanoemulsion carrying a low dose of celecoxib (0.24 mg/kg), a normally highly insoluble drug, appears to have provided a direct delivery of the drug into the inflammatory cells. Single dose intravenous injection of the theranostic nanoemulsion resulted in significant relief from the hypersensitivity behavior (mechanical allodynia) that persisted for at least four days post-injection. These findings demonstrated that celecoxib-containing theranostic nanoemulsion based therapy is an effective tool for the simultaneous tracking and treatment of the neuroinflammation in a CCI rat model. Inflammation is known to be associated with peripheral neuropathy, however the interplay among cytokines, chemokines and neurons is still unclear. We hypothesized that the neuroinflammatory interaction can be defined by using a computational modeling approach, based on the dynamics of the protein expression of various inflammatory mediators in the sciatic nerve of the CCI rats. Using Dynamic Bayesian Network inference, we identified Interleukin (IL)-18 as a central node associated with neuropathic pain in the CCI rat model. Immunofluorescence supported a role for inflammasome activation and induction of IL-18 at the site of injury. Combined in-vivo and in-silico approaches may thus highlight novel molecular targets associated with peripheral neuropathy that can be the target of future theranostic nanoemulsion-based therapy