| BackgroundAcute Kidney Injury(AKI)is a complicated clinical syndrome characterized by the drastic reduction of renal functions,which is subjected to one or multiple causes.It was reported that there were 2.3 million hospitalized patients who suffered from AKI in china,with a mortality rate of about 24%.The occurrence of AKI increased the financial burden and mortality rate of the inpatients,and meanwhile,caused an autonomous waste of medical resources.Currently,the diagnosis of AKI was based on serum creatinine and urinery output,which were not sensitive in the early stage of AKI and failed to reflect the real kidney injury of the patients.Therefore,the exploration of new biomarkers for the early diagnosis of AKI has been a hot issue,to facilitate problem solving the insufficiency in AKI diagnoses.Kidney participates in the metabolism and excretion process of several amino acids,and regulates the circulatory level ofamino acids in our body.Disorders of amino acids metabolism often subsequently appeared in case of renal damages.Recently,several researches revealed that amino acids were closely related to the renal function and prognosis of patients with kidney disease,such as asymmetric dimethylarginine,symmetric dimethylarginine and S-adenosylhomocysteine.Amino acids may potentially become a new metabolic group for the early diagnosis AKI.AKI and chronic kidney disease(CKD)are closely intertwined,with each disease a risk factor for developing the other and sharing other risk factors in common,as well as sharing causes for the diseases to get worse,and outcomes.For patients with pre-existing CKD,the AKI event can be superimposed on CKD,with acute kidney disease(AKD)existing on a background of CKD.Therefore,in the first,by using UHPLC-MS/MS method,the previously established and verified targeted metabolomics strategy was successfully applied in the assay of 23 plasma/serum amino acids in rats with ischemic acute kidney injury and patients after cardiac surgery,to identify potential amino acid biomarker for AKI.In addition,this targeted metabolomics strategy was performed on CKD patients,to investigate the amino acid metabolism changes.Methods1.To quantitatively profile the amino acid,a MRM-based method established in our lab was further validated for the quantification of 23 amino acids in plasma/serum samples.2.Experimental model of ischemic AKI was induced in rats by bilateral renal artery clamp for 45 min followed by reperfusion.Six time points of 1,2,4,6,10 and 24 h after reperfusion,and 0.6-0.7 mL blood was collected from the posterior obital venous plexus.23 amino acids from all serum samples were assayed by the previously verified targeted metabolomics method,and the diagnostic accuracy for the potential biomarkers was established by using receiver operating characteristic(ROC)analysis.The convential indexes including creatinine,urea nitrogen and neutrophil gelatinaseassociated lipocalin were investigated as well.3.Plasma samples from 2,4,8,12,and 24 h in patients undergoing cardiopulmonary bypass(CPB)were analyzed in the similar way as in the rat experiment,and targeted metabolomics method was also applied to discover diagnostic biomarkers and to identify pathophysiological pathways involved in AKI pathology.4.Plasma samples of chronic kidney disease patients and healthy volunteers were collected for targeted metabolomics method analysis,which was useful clinically for providing a metabolic signature that was associated with the CKD phenotype,to obtain the potential biomarkers for CKD diagnosis in the future.Results1.The levels of the symmetric dimethylarginine,hippuric acid and oxoprolinein the plasma of AKI rats all exhibited excellent diagnostic effects for AKI within 24 h of the injuries.The four amino acid biomarker values peaked,for those with and without AKI,at the 1-hour postoperative time.Among them,hippuric acid and the kynurenine had the best diagnostic effects,higher than that of neutrophil gelatinaseassociated lipocalin by ROC analysis.2.The plasma levels of symmetric dimethylarginine(SDMA)and hippuric acid(Hip)in CPB patients could predict AKI at multiple post-operative time points.Plasma level of SMDA at 1-hour postoperative time can effectively predict the occurrence of AKI,with larger AUC than serum creatinine,which could also be observed at 12-hour postoperative time.Plasma level of HA at 8-hour postoperative time can effectively predict the occurrence of AKI,with larger AUC than serum creatinine.3.CKD patients have altered plasma amino acid profiles when compared to the healthy,including tryptophan,tyrosine,lysine,valine,symmetry dimethyl arginine,methionine,histidine and leucine metabolism disorders.The results showed that as a marker of the renal function,SDMA can not only be used for the diagnosis of AKI,but also showed high correlations with CKD,which indicated that the targeted metabolomics method could be applied as potential biomarker discovery for CKD diagnosis in the future.ConclusionIn summary,we showed that the established and verified targeted metabolomics method could significantly improve the early prediction of AKI cause by prerenal factors,and identify some potential amino acid biomarkers.Amino acid metabolism presented dynamic changes after the incidence of acute renal injury,which process was started very early after surgery in patients by means of plasma biomarker assay,such as SDMA and HA,with higher AUC values that that of serum creatinine.In addition,SDMA was proved to be of relevance for clinical evaluation of CKD patients,which extended the application of this targeted metabolomics method. |
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