title: Energy Metabolism Disorder as a Contributing Factor of Rheumatoid Arthritis: A Comparative Proteomic and Metabolomic Study.
abstract: OBJECTIVE
  To explore the pathogenesis of rheumatoid arthritis (RA), the different metabolites were screened in synovial fluid by metabolomics.
  
  
  METHODS
  Synovial fluid from 25 RA patients and 10 normal subjects were analyzed by GC/TOF MS analysis so as to give a broad overview of synovial fluid metabolites. The metabolic profiles of RA patients and normal subjects were compared using multivariate statistical analysis. Different proteins were verified by qPCR and western blot. Different metabolites were verified by colorimetric assay kit in 25 inactive RA patients, 25 active RA patients and 20 normal subjects. The influence of hypoxia-inducible factor (HIF)-1α pathway on catabolism was detected by HIF-1α knockdown.
  
  
  RESULTS
  A subset of 58 metabolites was identified, in which the concentrations of 7 metabolites related to energy metabolism were significantly different as shown by importance in the projection (VIP) (VIP ≥ 1) and Student's t-test (p<0.05). In the 7 metabolites, the concentration of glucose was decreased, and the concentration of lactic acid was increased in the synovial fluid of RA patients than normal subjects verified by colorimetric assay Kit. Receiver operator characteristic (ROC) analysis shows that the concentration of glucose and lactic acid in synovial fluid could be used as dependable biomarkers for the diagnosis of active RA, provided an AUC of 0.906 and 0.922. Sensitivity and specificity, which were determined by cut-off points, reached 84% and 96% in sensitivity and 95% and 85% in specificity, respectively. The verification of different proteins identified in our previous proteomic study shows that the enzymes of anaerobic catabolism were up-regulated (PFKP and LDHA), and the enzymes of aerobic oxidation and fatty acid oxidation were down-regulated (CS, DLST, PGD, ACSL4, ACADVL and HADHA) in RA patients. The expression of HIF-1α and the enzymes of aerobic oxidation and fatty acid oxidation were decreased and the enzymes of anaerobic catabolism were increased in FLS cells after HIF-1α knockdown.
  
  
  CONCLUSIONS
  It was found that enhanced anaerobic catabolism and reduced aerobic oxidation regulated by HIF pathway are newly recognized factors contributing to the progression of RA, and low glucose and high lactic acid concentration in synovial fluid may be the potential biomarker of RA.
authors.affiliation: Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Xin Yu
authors.initials: XY
authors.lastname: Yang
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Kai Di
authors.initials: KD
authors.lastname: Zheng
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Ke
authors.initials: K
authors.lastname: Lin
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Guifeng
authors.initials: G
authors.lastname: Zheng
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Hai
authors.initials: H
authors.lastname: Zou
authors.affiliation: Department of Rheumatology, Jiamusi Central Hospital, Jiamusi, China.
authors.forename: Jian Min
authors.initials: JM
authors.lastname: Wang
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Yao Yao
authors.initials: YY
authors.lastname: Lin
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Chifundo Martha
authors.initials: CM
authors.lastname: Chuka
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Ren Shan
authors.initials: RS
authors.lastname: Ge
authors.affiliation: Department of Orthopaedic Surgery, Shanghai Guanghua Special Hospital for Rheumatoid Arthritis, Shanghai, China.
authors.forename: Weitao
authors.initials: W
authors.lastname: Zhai
authors.affiliation: Department of Biochemistry, School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, China.
authors.forename: Jian Guang
authors.initials: JG
authors.lastname: Wang
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000209:etiology / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007719:Knee Joint / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D050356:Lipid Metabolism; D008297:Male; D055432:Metabolomics; D008875:Middle Aged; D010084:Oxidation-Reduction; D040901:Proteomics; D015398:Signal Transduction; D013582:Synovial Fluid / Q000378:metabolism*; D013583:Synovial Membrane / Q000378:metabolism
chemical_list: D015415:Biomarkers; D019344:Lactic Acid; D005947:Glucose