Serum methylarginines and incident depression in a cohort of older adults.

Background: Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in depression. This study measured serum concentrations of l-arginine, asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in a representative sample of older community-dwelling adults and determined their association with incident depression over 6-years of follow-up.

Methods: Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and l-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults (Median age=64 years; IQR=60-70) from the Hunter Community Study. Clinical depression was defined as a Centre for Epidemiological Studies Depression Scale (CES-D) score ≥16 or use of antidepressant medications.

Results: In adjusted analyses ADMA (Q3), SDMA (Q2), l-arginine (Q2), gender, and asthma remained statistically significant predictors of incident depression at follow-up. Quartile 3 of ADMA concentration was associated with 3.5 times the odds of developing depression compared with Q1 (OR=3.54; 95% CI: 1.25-9.99).

Limitations: Limitations of our study include the use of a subjective self-reported questionnaire tool using a dichotomous cut-off, together with use of antidepressant medications, as proxies for clinical depression. Moreover, similarly to most population studies on methylated arginines, the measurement of ADMA and SDMA from blood does not necessarily reflect intracellular concentrations of these compounds. Finally, there were no measures of nitric oxide metabolites to determine if these levels were altered in the presence of elevated methylarginines and depression.

Conclusions: After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum ADMA was independently associated with incident depression at 6-years follow-up.