Sleep disorders in Parkinson's disease: clinical features, iron metabolism and related mechanism

To investigate clinical features, iron metabolism and neuroinflammation in Parkinson's disease (PD) patients with sleep disorders (SD). 211 PD patients were evaluated by Pittsburgh Sleep Quality Index (PSQI) and a body of scales for motor symptoms and non-motor symptoms. 94 blood and 38 cerebral spinal fluid (CSF) samples were collected and iron and its metabolism-relating proteins, neuroinflammatory factors were detected and analyzed. 136 cases (64.5%) of PD patients were accompanied by SD. Factor with the highest score in PSQI was daytime dysfunction. Depression, restless leg syndrome, autonomic symptoms and fatigue contributed 68.6% of the variance of PSQI score. Transferrin level in serum and tumor necrosis factor-α level in CSF decreased, and the levels of iron, transferrin, lactoferrin and prostaglandin E2 in CSF increased in PD patients with SD compared with those without SD. In CSF, prostaglandin E2 level was positively correlated with the levels of transferrin and lactoferrin, and tumor necrosis factor-α level was negatively correlated with the levels of iron, transferrin and lactoferrin in CSF. Depression, restless leg syndrome, autonomic disorders and fatigue are the important contributors for the poor sleep in PD patients. Abnormal iron metabolism may cause excessive iron deposition in brain and be related to SD in PD patients through dual potential mechanisms, including neuroinflammation by activating microglia and neurotoxicity by targeting neurons. Hence, inhibition of iron deposition-related neuroinflammation and neurotoxicity may cast a new light for drug development for SD in PD patients.