Heightened inflammatory activity has been proposed as a mechanism for the development of cancer-related fatigue (CRF), a common and distressing condition that can negatively affect quality of life. Inflammation is also implicated in the pathogenesis of depression, and depression is a strong predictor of CRF. Thus, the role of the pro-inflammatory cytokine network in CRF may be mediated by depression or both conditions may share similar underlying physiological processes. The current study investigated associations between fatigue, depression and inflammatory cytokine (IFN-γ, IL-6, TNF-α) and CRP concentrations, as well as kynurenine pathway (KP) activation, in 61 breast cancer patients prior to chemotherapy. Changes in inflammatory markers and KP activation over time were also explored, and associations with changes in fatigue and depression were examined. Higher levels of CRP were significantly correlated with fatigue and depression before chemotherapy; nevertheless, CRP predicted fatigue independently of depression. Although greater kynurenine concentrations were associated with increased immune activation, there was no evidence that the KP played a role in fatigue or depression. Furthermore, no relationships emerged between either fatigue or depression and IFN-γ, IL-6, or TNF-α before chemotherapy. Nevertheless, kynurenine levels pre- and post-treatment significantly predicted changes in depression, suggesting that heightened KP activation may contribute to depressive symptoms in patients treated for cancer. In addition, IL-6 significantly covaried with fatigue. These preliminary findings provide some support for the idea that low-grade inflammation contributes to the development of CRF, independently of depression; however, there was no evidence that this is mediated by KP activity.
Keywords: CRP; Cancer; Cancer-related fatigue; Cytokine; Depression; IFN-γ; IL-6; Inflammation; Kynurenine; TNF-α.
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