Metabolomic Signature Of Amino Acids And Polyamines In The Serum Of Osteoarthritis Patients

Purpose: Metabolomic analysis holds great potential for improving the understanding about osteoarthritis (OA) caused metabolomic shifts associated with systemic inflammation and oxidative stress (OxS). Amino acids and polyamines are closely involved in maintaining the balance between reactive oxygen species (ROS) and antioxidant system. The main aim of the study was to map the systemic changes of amino acids and polyamines in the severe OA compared with asymptomatic matched controls and identify systemic serum biomarkers that have the potential to be used in clinical practise. Methods: Knee and hip OA patients who met the American College of Rheumatology criteria for knee and hip OA were included in the study. The study participants were recruited prospectively. The control group was matched to age and gender and recreuited from the family medicine practices. The exclusion criteria were posttraumatic OA, infectious arthropathy, endocrine arthropathy, malignancy, acute inflammatory disease, insufficiency of kidneys (eGFR < 60ml/min/1.73m2), clinically significant heart failure, diabetes. The fasting serum of 70 knee and hip OA patients and 82 controls were assessed via targeted approach using the AbsoluteIDQ™ p180 kit. The blood samples were collected in the morning after an overnight fast and abstinence from tobacco and alcohol. The samples were held in at -70 °C until assessment. Standard preoperative radiographs were used for the grading of OA severity according to Kellgren and Lawrence by two independent raters. A consensus score was used for the analysis.The level of metabolites (amino acids and polyamines) has been expressed as μM ± standard deviation. Results: The two study groups had similar age and gender proportions, but OA group had significantly higher BMI. Inflammatory markers (white blood cell count and high sensitivity C-reactive protein) were higher in the OA group.Tabled 1General description of study groupsOsteoarthritis (n=70)Controls (n=82)p-valueAge (years)62 ± 761 ± 80.173Male/Female (n)36 / 3438 / 440.871BMI (kg/m2)27.8 ± 3.226.0 ± 3.50.001hs-CRP (mg/l)1.9 ± 1.11.5 ± 1.20.014WBC (109/l)6.5 ± 1.45.7 ± 1.90.001 Open table in a new tab There were several significant differences in the amino acid and polyamine levels across the study groups. The present study demonstrates significantly higher levels of arginine (Arg), asparagine (Asn), leucine (Leu), serine (Ser), asymmetric dimethylarginine (ADMA), phenylalanine (Phe), spermidine and lower levels of serotonin and spermine/spermidin ratio in the OA group after adjusting for BMI.Tabled 1Amino acid and polyamine levels of the study groupsOsteoarthritis (n=70)Controls (n=82)p-valueArginine105.2 ± 22.496.3 ± 23.50.020Glycine280.8 ± 116.2289.8 ± 114.60.794Leucine180.9 ± 50.0156.7 ± 39.50.008ADMA0.618 ± 0.1560.559 ± 0.1330.037Spermidine0.188 ± 0.0510.161 ± 0.0460.001Spermine0.158 ± 0.0140.159 ± 0.0160.677Spermine-spermidine ratio0.898 ± 0.2271.060 ± 0.279<0.001Serine137.4 ± 29.1121.8 ± 27.60.001 Open table in a new tab Several changes in the serum levels of amino acids of the OA patients compared with controls suggest systemic inflammation in severe OA patients. We found increased levels of Arg and ADMA in OA group and the severity of OA was correlated to Arg levels. Arg remained an independent determinant of OA severity in the multiple regression model after including potential covariates. The increase of 1 grade in the radiographic OA severity was equal to an average of 10.0 μM higher level of serum Arg. ADMA and Arg play important role in nitric oxide (NO) production. Arg is the precursor for NO and ADMA is the major endogenous inhibitor of NO synthase (NOS). The combination of increased Arg and ADMA levels in OA group suggest inhibited NOS activity that leads to Arg accumulation. NO has been linked to inflammation in OA pathogenesis and also anabolic mechanisms so the specific details remain to be elucidated in further research.Tabled 1Regression model with arginine as the dependent variable in the osteoarthritis patients groupBStd ErrorBetap- valueOA severity9.124.10.280.031Gender5.775.60.130.310Age-0.310.37-0.100.392BMI-0.240.86-0.0330.782Glucose-7.114.15-0.210.092 Open table in a new tab We found that OA patients had higher levels of Ser and severe OA was associated with lower levels of serum Gly. The correlation was further analyzed in a multiple regression model and remained independent after including potential covariates. An increase of 1 grade in the radiographic OA severity was equal to an average of 46.4 μM of lower level of Gly in the OA group. The changes indicate Gly deficiency and Ser accumulation in the severe OA that might be related to enzyme Ser hydroxymethyltranferase impairment and lead to decreased collagen synthesis in the affected joint. Ser hydroxymethyltranferase activity has been also found to be altered in metabolic syndrome and obesity, conditions that are closely related to OA.Tabled 1Regression model with glycine as the dependent variable in the osteoarthritis patients groupBStd ErrorBetap- valueOA severity-43.220.6-0.250.040Gender-64.728.1-0.280.025Age0.51.80.030.777BMI3.04.30.080.483Glucose-25.320.7-0.150.227 Open table in a new tab The significantly higher Leu levels in OA might reflect the increased collagen breakdown due to cartilage degeneration and muscle atrophy. Furthermore, lower spermin to spermidine ratio and increased spermidine in the OA group might indicate excessive OxS in OA. The spermine-spermidine system protects against OxS by scavenging free radicals. The increased level of spermidine in OA patients might be caused by lower activity of spermine synthase, an enzyme that converts spermidine to spermine. The accumulation of spermidine might impair the lysosome function, thus leading to increased OxS. Conclusions: The present study demostrates significant changes in the amino acid and polyamine profiles of OA patients that highlight the role of inflammation and excessive OxS in the pathogenesis of OA.