| Background With the increasing aging of the population, the prevalence of Alzheimer's disease (AD) is rising, and 10%~20% of AD patients are also diagnosed with chronic obstructive pulmonary disease (COPD). Compared to patients with a single disease, those with both AD and COPD exhibit more severe cognitive impairment, poorer quality of life, and a greater disease burden. Abnormal neurotransmitter levels have been observed in both AD and COPD patients, which may contribute to cognitive dysfunction. However, the alterations in neurotransmitter levels in patients with comorbid AD and COPD and their association with cognitive function remain unclear. Objective To investigate the changes in neurotransmitter levels in patients with comorbid AD and COPD, and to explore their correlation with cognitive function, in order to provide reference for the improvement of cognitive function in patients with AD combined with COPD. Methods A total of 40 patients who were hospitalized at Mianyang Third People's Hospital between January and September 2024 and met the diagnostic criteria for Alzheimer's disease (AD) as defined by the International Classification of Diseases, 10th Edition (ICD-10), were included in the AD group. Another 40 patients who met the diagnostic criteria for chronic obstructive pulmonary disease (COPD) according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2023 guidelines were included in the COPD group. Additionally, 40 patients who met the diagnostic criteria for both conditions were included in the AD combined with COPD group. Additionally, 40 healthy individuals undergoing physical examination at the same hospital during the same period were selected as the control group. Encephalofluctuograph was used to detect levels of γ-aminobutyric acid (GABA), glutamate (Glu), norepinephrine (NE), serotonin (5-HT), acetylcholine (Ach), and dopamine (DA).Cognitive function of the subjects was assessed using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment Scale (MoCA). Spearman correlation analysis and multiple linear regression were performed to examine the relationship between MMSE scores and neurotransmitter levels in patients with comorbid AD and COPD. Results ①There was a statistically significant overall difference in MMSE and MoCA scores among the four groups(H=126.323, 128.489, P<0.01). The MMSE and MoCA scores in the AD combined with COPD group were both lower than those in the COPD group, AD group, and control group, with the differences being statistically significant( P<0.05). ②Statistically significant differences were found in the levels of GABA, Glu, NE, Ach, and DA among the four groups (H=64.602, 46.635, 135.594, 14.237, 127.967, P<0.01). The levels of GABA, Ach, and DA in the AD combined with COPD group were lower than those in the COPD group, AD group, and control group, with the differences being statistically significant (P<0.05). Conversely, the Glu level in the the AD combined with COPD group was higher than that in the COPD group, AD group, and control group, with the differences being statistically significant (P<0.05). ③In the the AD combined with COPD group, levels of GABA, ACh, and DA showed a positive correlation with MMSE scores (r=0.633, 0.876, 0.580, P<0.05), while Glu levels were negatively correlated with MMSE scores (r=-0.377, P=0.016). ④Multiple linear regression analysis showed that the levels of Ach（B=0.253，95% CI：0.153~0.352）and Glu（B=0.137，95% CI：0.013~0.261）were influencing factors for MMSE scores. Conclusion Compared with the COPD group, AD group, and control group, patients with AD combined with COPD exhibited more severe cognitive impairment, lower levels of GABA, ACh, and DA, and higher levels of Glu in the brain. Ach and GABA levels are potential influencing factors of cognitive function in patients with AD combined with COPD. |