Depression and Alzheimer’s disease appear to be linked through several shared biological mechanisms, according to a narrative review examining overlapping molecular pathways between the two conditions.
The review summarizes evidence on biomarkers and pathophysiological processes implicated in both disorders, including oxidative stress, mitochondrial dysfunction, neuroinflammation, and vascular impairment. The authors propose that these intersecting mechanisms may help explain why depressive symptoms frequently occur in patients with Alzheimer’s disease and may contribute to disease progression.
Depression is common in individuals with Alzheimer’s disease, with studies suggesting that up to 90% of patients experience at least one neuropsychiatric symptom during the course of the illness. These symptoms – including mood disturbances, agitation, and anxiety – can complicate disease management and worsen outcomes for both patients and caregivers.
Several biological pathways appear to contribute to both disorders. Oxidative stress – characterized by an imbalance between reactive oxygen species and antioxidant defenses – has been linked to neuronal damage and inflammation in both depression and Alzheimer’s disease. Markers of lipid peroxidation, nucleic acid damage, and protein nitration have been detected in patients with both conditions, suggesting shared molecular processes underlying neurodegeneration and mood dysregulation.
Mitochondrial dysfunction may also play an important role. Disruptions in mitochondrial energy metabolism and calcium regulation can increase oxidative stress and activate inflammatory signaling pathways in the brain. These processes may contribute to neuronal injury and cognitive decline and may also influence depressive symptoms.
Vascular abnormalities represent another proposed area of overlap. Changes in cerebral blood vessels and endothelial function have been associated with both late-life depression and Alzheimer’s disease, potentially affecting amyloid clearance, brain metabolism, and neural network integrity.
The review also highlights emerging evidence that some antidepressants may influence biological pathways involved in Alzheimer’s disease. Preclinical and observational studies suggest that certain antidepressants, including selective serotonin reuptake inhibitors, may reduce amyloid metabolism or inflammatory pathways, although findings remain inconsistent.
The authors add that biomarkers linked to oxidative stress, mitochondrial dysfunction, and vascular injury could help improve early detection and monitoring of Alzheimer's disease in patients with depressive symptoms. Clarifying whether depression functions as a risk factor, prodromal manifestation, or comorbidity of Alzheimer’s disease may be important for developing targeted interventions.
The authors report no conflicts of interest.
Source: Cureus
