Alteration in energy expenditure or metabolism is the most accused risk issue for the onset and for the course of neurodegenerative cognitive disorders. Neuropeptides are suggested to be related with learning and memory. Phoenixin (PNX) is the most recently reported neuropeptide and we aimed to compare the plasma level in people with subjective memory complaints, patients with mild cognitive impairment, and mild Alzheimer's disease (AD).

Ninety two participants enrolled in the study. After screening tests, all participants were assessed with a neuropsychological battery for further cognitive evaluations. We used ELISA kit to assay the level of Human PNX.

Patients with AD were significantly older than people in subjective memory complaint group (p = 0.02). There was no significant difference between groups according to gender (p = 0.435). Mean plasma PNX level was not significantly different between groups (p = 0.279). Mean plasma PNX level in MCI group was positively correlated with BMI (r = 0.402 and p = 0.028), serum HDL level (r = 0.454 and p = 0.012), blood systolic pressure (r = 0.428 and p = 0.018) and negatively correlated with logical memory (r=−0.335 and p=0.031). The mean plasma PNX level was positively correlated with immediate recall in subjective memory complaint group (r = 0.417 and p = 0.034).

This study is the first studying the association of plasma PNX level and cognitive complaints or decline. The knowledge about the role, interaction, and physiological functions of PNX is lacking. Lower plasma PNX level might be important in prodromal stages as MCI and the predictive role of PNX should be investigated in further studies.