A Serum And Cerebrospinal Fluid Mitochondrial Creatine Kinase Study In Patients With Idiopathic Parkinson’s Disease

ObjectiveIdiopathic Parkinson’s disease(Parkinson’s disease,PD)is the world’s second most common neurodegenerative disease.Patients with PD show a range of motor and non-motor symptoms.At present,there is no conclusion for its cause yet,and there are also lack of effective and easily accessible biomarkers.Mitochondrial dysfunction is considered to be an important component in the pathogenesis of PD.There are many studies on the mitochondrial components in PD,while few studies investigated mitochondrial components in blood and cerebrospinal fluid(CSF).Mitochondrial creatine kinase(MtCK)is an important component of mitochondria.Studies have shown that MtCK is localized in both the peripheral intermembrane space(IMS)and the cristae space.There are two main types,one of which is sarcomeric MtCK(sMtCK),which is mainly expressed in striated muscle tissue;the other is ubiquitous MtCK(uMtCK),which is expressed in many tissues and the brain is one of the main sites.The MtCK and creatine kinase(CK)/phosphocreatine system are important to an intricate,metabolic energy transfer network in the cell,connecting mitochondria with myofibrils,sarcoplasmic reticulum,and even nuclei.In addition,MtCK can form mitochondrial contact sites between the reconstructed inner and outer membrane,and establish permanent contact between mitochondrial membranes.Animal studies had shown that mitochondrial creatine kinase was significantly lost in isolated brain mitochondria exposed to oxidative stress(eg,dopamine oxidation).Obvious oxidative stress has been found in PD patients and is closely related to mitochondrial dysfunction.Changes of mitochondrial components may be expressed in body fluids.Therefore,this study sought to investigate changes of mitochondrial creatine kinase(MtCK)activity(level)in both serum and cerebrospinal fluid as well as serum creatine kinase(CK)and its isoenzyme MB(CK-MB)activity in PD patients,and provide clues for further discovery of Parkinson’s disease biomarkers so as to facilitate its early diagnosis and treatment.MethodsAll the cases of 65 PD patients were from Nanfang Hospital of Southern Medical University and 999 Brain Hospital of Guangdong Province,ranging from May,2016 to October,2017.All of them were in line with the Movement Disorder Society Clinical Diagnostic Criteria for Parkinson’s disease(2015).Secondary Parkinson’s syndrome,Parkinson’s plus syndrome,patients who had undergone anti-Parkinsonism surgery or had drugs that might significantly disturb blood biochemical examination other than anti-Parkinson’s disease drugs,new or chronic glucocorticoid drugs treatment,or diagnosed with myopathy,severe hypertension,diabetes,acute inflammatory reactions,autoimmune diseases,other serious neurological disorders were excluded.40 gender-age-matched control subjects who were interviewed at Nanfang Hospital of Southern Medical University in the same period were recruited according to the inclusion and exclusion criteria strictly.General information was collected for all subjects and vein blood samples or cerebrospinal fluid was collected after 8 h of fasting.Serum ubiquitous mitochondrial creatine kinase,sarcomeric mitochondrial creatine kinase,as well as creatine kinase isoenzymes MB were tested in some of the enrolled subjects using immunosuppressive assays.Phosphocreatine substrate method was applied in the test of serum creatine kinase.CSF ubiquitous mitochondrial creatine kinase of some enrolled subjects were tested using enzyme-linked immunosorbent assay.PD patients were examined in detail by experienced neurologists and evaluated using the MDS-UPDRS,the modified Hoehn&Yahr staging scale and the commonly used neuropsychological questionnaire.The SPSS 19.0 software was used for statistical analysis.ResultThe serum ubiquitous mitochondrial creatine kinase activity of the PD group(3.5 ±1.8 U/L)was significantly lower than that of the control group(5,9± 1.8 U/L)(p<0.01),and the CSF ubiquitous mitochondrial creatine kinase level of the PD group(1.10 ± 0.79 ug/ml)was also significantly lower than that of the control group(2.22±0.71 ug/ml)(p<0.01).Further stratified analysis of serum uMtCK activity according to the severity of the disease showed similar significant differences.The serum creatine kinase activity of the PD group(100.9±48.7 U/L)was significantly higher than the control group(72.7±32.1 U/L)(p<0.05).No significant difference was found between the serum sacromeric mitochondrial kinase activity of the PD group(0.32 ±0.50 U/L)and the control group(0.34±0.48 U/L)(p=0.73),neither between the CK-MB activity of the PD group(10.2±6.7 U/L)and the control group(9.6±5.5 U/L)(p=0.16).Correlation and regression analysis showed that the serum ubiquitous mitochondrial creatine kinase activity in patients with PD was significantly correlated with the rate of disease progression,disease duration and age of onset,but not with H&Y stage and main non-motor symptoms score(MNMSS).The CSF ubiquitous mitochondrial creatine kinase level of PD patients had no significant correlation with the rate of disease progression,disease duration,age of onset,H&Y stage and MNMSS.ConclusionWe first time found that both the serum uMtCK activity and CSF uMtCK level in PD patients were significantly lower than that in the control group subjects.The serum uMtCK activity was positively correlated with the rate of disease progression and age of onset,and was negatively correlated with the disease duration.Serum sMtCK activity did not show significant difference between two groups.This may be due to the difference in the distribution of the two mitochondrial creatine kinases.The uMtCK is extensively expressed in brain and some other tissues,while sMtCK is mainly expressed in striated muscle tissue.The widely distributed uMtCK reflects the changes in the body of PD patients more sensitively.Serum creatine kinase(CK)activity in PD patients was significantly higher than than that in the control group,while the serum CK-MB activity showed no significant difference.Factors affecting MtCK,CK of Parkinson’s disease patients need further study.Serum uMtCK may become a biomarker for the diagnosis of PD,and the study of MtCK in human body fluid can provide useful clues for further exploration of PD biomarkers.