Aging, depression and dementia: The inflammatory process

Population aging that we are currently witnessing has led to an increase in chronic age-related diseases, with dementia and depression being highlighted. Several studies establish a relationship between dementia and depression, although without defining the mechanism that links them. Some studies establish depression as a prodrome of dementia, while others consider it a risk factor for dementia. One of the events that is common between dementia and depression is the inflammatory process. In depression, an increase in inflammatory cytokines has been described, which would justify the serotonergic, noradrenergic and dopaminergic dysfunction of depression. This increase entails altering the activity of the hypothalamic-pituitary-adrenal (HPA) axis, thus linking chronic stress to depression, and the consequent weakening of the blood-brain barrier (BBB), facilitating the passage of pro-inflammatory factors. In this line, recent studies suggest that inflammation could direct the development of the pathogenesis of dementia, particularly Alzheimer's disease (AD), once the pathology has begun. In addition, sustained exposure to pro-inflammatory cytokines characteristic of aging could alter the microglial function and the expression of enzymes responsible for amyloid peptide metabolism, aggravating the pathological process. In view of the involvement of the inflammatory process in both conditions, it is necessary to investigate the events which both conditions share, such as the inflammatory process, to know the involvement of the inflammatory process in both dementia and depression, possible relationship of these 2 conditions, and consequently, to establish the clinical approach to both conditions.