The role of plasma inflammatory markers in late-life depression and conversion to dementia: a 3-year follow-up study

Abstract

Abstract Late-life depression (LLD) has been linked to increased likelihood of subsequent dementia, although mechanisms responsible for this association remain largely unknown. One feature frequently observed in both LLD and dementia is elevated levels of plasma inflammatory markers. PRODE (Prognosis of Depression in the Elderly) is a prospective naturalistic study of patients with LLD (N=152; aged 60+). Patients were followed up for 3 years; follow-up data was available for 138 patients, and 36 (26.1%) developed dementia by year 3. Plasma inflammatory markers data were available for 136 patients at baseline for the following range of cytokines and chemokines: IL-1β, IL-1ra, IL-6, IL-10, IL-17a, IL-18, IL-33, TNFα, CD40L, IFN-γ, CCL-2 and CCL-4. Levels of plasma inflammatory markers were compared between 136 LLD patients and healthy controls (n=103), using first multiple linear regression (inflammatory markers as outcome) with stepwise adjustment, and then binary logistic regression with depression status (LLD vs controls) as outcome. Further, we explored whether inflammatory markers and clinical characteristics of LLD (age of onset, course) predicted progression from LLD to dementia using Cox regression. Levels of IL-1ra, IFN-γ, CCL-2, CCL-4 and IL-17a were significantly higher in LLD patients compared to controls. However, none of the inflammatory markers predicted progression from LLD to dementia. Among clinical features, only poor response to treatment significantly predicted higher risk of progression to dementia. In summary, this study replicated previous findings of an increase in inflammatory markers in LLD but did not find evidence they had increased risk of developing future dementia.