Methotrexate chemotherapy triggers touch-evoked pain and increased CGRP-positive sensory fibres in the tibial periosteum of young rats

Abstract

Although bone pain caused by cancer chemotherapy is a well-recognized and significant problem, with approximately 1 in 10 childhood cancer patients being reported to experience isolated bone pain along with other skeletal complications, the underlying mechanisms are poorly understood and there is no specific treatment. In this study, effects of methotrexate (MTX) treatment on pain in the hind legs and the extent of sensory innervation of the tibial bone were examined through a 20-day time course in young rats after 5 daily 0.75 mg/kg MTX injections. MTX treatment increased von-Frey filament stimulation-induced mechanical allodynia and palpation nocifensive score in the tibia. MTX-treated rats showed trends in reduced loading (numbers of stands) on hind limbs after palpation, commencing early during treatment and 2 weeks after the end of treatment despite no signs of ongoing pain during normal locomotion. Immunohistochemical analyses showed an increase in innervation of calcitonin gene-related peptide (CGRP)-positive sensory nerve fibres in tibial periosteum on days preceding and overlapping with those rats with touch-evoked pain responses and the bone repair phase. These data suggest that methotrexate chemotherapy triggers touch-evoked pain involving enhanced sensory nerve innervation of the bone.

Differentially expressed miRNAs in bone after methotrexate treatment

“…Furthermore, the involvement of miR‐344g in spinal cord development and pain mechanisms has been previously investigated (Soula et al, 2018). Subcutaneous injections of MTX are known to be in line with a mild amount of pain (Bechard et al, 2014; Zhou et al, 2015). The upregulated miR‐344g observed on Day 3 might be because of subcutaneous injections with MTX, resulting in pain in rats.…”

CGRP-CRLR/RAMP1 signal is important for stress-induced hematopoiesis

“…In the present study, we identified that RAMP1 is specifically expressed in hematopoietic progenitor cells, which led us to speculate that CGRP might be a specific ligand for CRLR in hematopoietic cells. CGRP is a neuropathic peptide that is primarily secreted from sensory nerves after stimulation of transient receptor potential vanilloid receptor-1 (TRPV1), which is distributed in C fibers and upstream, with mechanical stimulation, infection, ischemia, and pain 28–30 . Binding of CGRP to the CRLR/RAMP1 receptor activates adenylate cyclase, which elevates intracellular cAMP and activates protein kinase A (PKA), leading to phosphorylation of multiple targets, such as potassium-sensitive ATP channels, extracellular signal-related kinases (ERKs), and cAMP response element-binding protein (CREB) 28 .…”