Figure 3.

Putative Mechanisms of Increased Risk of COPD Patients to Mood Disorders. Reactive oxygen species from exposure to cigarette smoking accumulate in the lungs and trigger local inflammation. The lung inflammatory mediators spill into the plasma, where systemic inflammation sets in. Systemic inflammation activates the Kynurenine pathway. Hence, more tryptophan is degraded into kynurenines, limiting its transport into the brain for serotonin synthesis, leading to anxiety and depression. In addition, inflammatory mediators cross the blood–brain barrier, causing neurodegeneration and reduced synthesis of neurotransmitters, also resulting in anxiety and depression. Furthermore, hypoxia associated with COPD could lead to neuronal damage, thus interfering with the production of neurotransmitters. COPD: chronic obstructive pulmonary disease.