Chapter 17 Cytokines and pain

Pain and inflammation in women with early-stage breast cancer prior to induction of chemotherapy

CONTEXT

Pain is a commonly experienced and distressing symptom in women with breast cancer (BCA), and recent evidence suggests that immune activation may be associated with pain and other co-occurring symptoms. However, no studies to date have explored the relationships among perceived pain and biomarkers of inflammation in women with early-stage BCA during the initial course of treatment.

OBJECTIVES

The purpose of this research study was to examine the relationships among pro- and anti-inflammatory biomarkers and the presence of pain and other symptoms (anxiety, depression, fatigue, and sleep disorder) prior to induction of chemotherapy.

METHOD

This was a secondary analysis of data that measured perceived symptoms, including the presence of pain and pain interference, and plasma levels of pro- and anti-inflammatory cytokines and C-reactive protein (CRP) in women with early-stage BCA (N = 32) at 1 month postsurgery but prior to induction of chemotherapy.

RESULTS

Women experiencing pain had significantly higher levels of CRP (p < .01), interleukin (IL) 13 (p < .02), and IL-7 (p < .02) and more pain interference (p < .01), depression (p < .01), and sleep disturbance (p < .01) compared to women reporting no pain.

CONCLUSION

The presence of pain during the initial course of treatment in women with early-stage BCA was associated with significantly higher levels of CRP, IL-7, and IL-13, suggesting a potential role of immune activation in perceived pain. Further research to examine the precise effects of these biological factors in modulating pain is needed. Perceived pain was also associated with multiple co-occurring symptoms, and this finding has important implications for symptom management.

Pathophysiological mechanisms of neuropathic pain

Neuropathic pain is a common problem in clinical practice and one that adversely affects patients’ quality of life. Converging evidence from animal and human studies demonstrates that neuropathic pain arises from a lesion in the somatosensory system. Injured peripheral nerve fibers give rise to an intense and prolonged ectopic input to the CNS and, in some cases, also to secondary changes in dorsal horn neuronal excitability. Convincing evidence now suggests that classifying neuropathic pain according to a mechanism-based rather than an etiology-based approach might help in targeting therapy to the individual patient and would be useful in testing new drugs. This article summarizes our current understanding of the peripheral and central pathophysiological mechanisms underlying neuropathic pain and focuses on how symptoms translate into mechanisms.

Early cytokine expression in mouse sciatic nerve after chronic constriction nerve injury depends on calpain

Nerve injury initiates Wallerian degeneration with subsequent alterations of cytokine expression contributing to neuropathic pain. To investigate the very early temporal pattern of cytokine regulation we studied 140 mice of C57Bl/6J background after chronic constriction injury (CCI) of the right sciatic nerve and measured the relative mRNA expression of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1beta) and of the anti-inflammatory cytokines IL-4 and IL-10 with quantitative real-time polymerase chain reaction (qRT-PCR). The measurements were performed in ipsi- and contralateral sciatic nerves and dorsal root ganglia (DRG) 1, 3, 6, 9, 12, 24 h, and 3 and 7 days after CCI. We found an ipsilateral upregulation of TNF, IL-1beta and IL-10 mRNA levels as early as one hour after CCI. To investigate upstream regulatory mechanisms, we used inhibitors to the N-methyl-d-aspartate (NMDA) receptor ((+)-MK-801) and to calpain (MDL-28170). MDL-28170, but not (+)-MK-801 inhibited TNF and IL-1beta upregulation one hour after CCI. This leads us to suggest that calpain is one of the earliest mediators of cytokine upregulation in injured peripheral nerves.