Background and aims: Management of neuropathic pain remains therapeutic challenge to modern medicine, due to limited efficacy of the conventional analgesics and accompanying adverse effects. One of the reason for the lack of optimally efficient therapies is the not fully-known pathomechanism of neuropathy. The complex neuroimmunological interactions mediated by chemokines are suggested to be involved in the development and persistence of this kind of pain. Recently the C-C chemokine receptor e.g. type 1 (CCR1) [1] and 3 (CCR3) [2] selective and dual antagonists [3] have been suggested to reduce hypersensitivity in rodent model of neuropathic pain. However the role of some of their endogenous ligands, namely CCL2, CCL7 and CCL8, which collectively belong to the monocyte chemotactic proteins family, have not been extensively studied. Therefore, the aim of the following experiments were to evaluate the mRNA/protein time-course changes of CCL2, CCL7 and CCL8 after sciatic nerve injury, as well as verification whether this chemokines evoke the hypersensitivity after intrathecal injection. Next step was to investigate if blockade of CCL2, CCL7 and CCL8 by inhibitor of their synthesis, bindarit, can decrease the hypersensitivities in different phases of neuropathic pain. 

Methods: The present study was performed in the use of Albino Swiss male mice. In order to evaluate the properties of tested chemokines, the single intrathecal administrations of reconstituted CCL2, CCL7 and CCL8 at the dose of 0.3 μg/5 μL were performed in naive mice. To induce neuropathic pain-like behavior, animals were exposed to the chronic constriction injury of the sciatic nerve (CCI model) in accordance to the procedure described by Bennet and Xie [3]. The study of analgesic potency of bindarit was tested in the frame of three independent sets of experiments: the CCI-exposed mice received repeated (3 injections, once per day) administrations of bindarit (10 or 40 μg/5 μL) 0, 1st and 2nd day after CCI (first group) or 10th, 11th and 12th days post CCI (second group) or 26th, 27th and 28th days post CCI (third group). To assess the tactile and thermal hypersensitivity of mice, the von Frey and cold plate tests were used, respectively. Analysis of mRNA and protein by RT-qPCR and ELISA was performed in the spinal cord, which was collected from mice at different time points post-CCI.

Results: Animals exposed to CCI expressed strong tactile and thermal hypersensitivity as measured 2-28 days after surgery. Simultaneously, biochemical analysis revealed that CCL2, CCL7 and CCL8 mRNA and protein levels in spinal cord were elevated at this time points. Single intrathecal injection of above mentioned, reconstituted chemokines induced mechanical and thermal hypersensitivity in naive animals. The repeated administration of bindarit reduced tactile and thermal hypersensitivity which was observed in early, middle and late phase of neuropathic pain development.

Conclusions: The following experiments demonstrated that CCL2, CCL7 and CCL8, which exerts strongly pronociceptive properties, play an important role in neuropathy. Importantly it was showed that inhibition of their synthesis by bindarit attenuated pain-related behaviors similarly in different phases of neuropathic pain development in mice. Interestingly, it brought analgesic effects even in fully-developed neuropathy. Obtained data suggest that bindarit might be a promising tool for neuropathic pain management in the future.

References:

1.      doi: 10.1111/imm.13172.

2.      doi: 10.3389/fimmu.2021.781310.

3.      doi: 10.3390/cells12010098

4.      doi: 10.1016/0304-3959(88)90209-6.

Relevance for Patient Care: Currently, bindarit is in the second phase of clinical trials for type 2 diabetic nephropathy patients, therefore we believe that considering it as a potential drug to alleviate the symptoms of neuropathic pain could also be useful in the management of this kind of pain, although it would require further, in-depth research.

Acknowledgments: This research was funded by the National Science Centre, Poland grants, OPUS 22 2021/43/B/NZ7/00230, PRELUDIUM 2018/29/N/NZ7/00287, and statutory funds from the Maj Institute of Pharmacology Polish Academy of Sciences.