Background/Purpose:

Numerous studies have reported increased
cardiovascular morbidity and mortality in rheumatoid arthritis (RA) patients
that cannot be explained by traditional risk factors. In a non-RA cohort, our
collaborators identified specific biomarkers of nitrative stress which act to
impair endothelium dependent nitric oxide function and were found to be
predictive of future CV events in an at risk population.  These biomarkers [asymmetric
dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and N-mono-methylarginine
(MMA)] are produced by methylation of arginine, the sole nitrogen source for NO
synthesis. We believe these biomarkers of subclinical endothelial dysfunction may
serve as an early non-invasive predictor of accelerated atherosclerosis in RA patients.
The aim of this study is to investigate if these biomarkers of endothelial
dysfunction are increased in patients with RA compared to healthy controls and
to examine the effects of disease modifying treatments, statin therapy, and
seropositive status on levels of these biomarkers.

Methods:

The plasma from 119 RA patients (83.6%
female, 60.2± 13.6 yrs of
age) seen in a tertiary care center from October 2014 to April 2015 was
analyzed for ADMA, SDMA and MMA levels by stable isotope dilution HPLC with
online electrospray ionization tandem mass spectrometry compared to controls.
The Arginine Methylation Index (ArgMI) was estimated by the ratio of
[(ADMA+SDMA)/MMA]. The effects of statin and DMARD therapy, as well as
seropositivity (anti-CCP antibody or RF>20) on these biomarkers were
evaluated. The Student t test or Wilcoxon Rank sum test for continuous
variables and chi squared test for categorical variables were used in
statistical analysis.

Results:

ADMA and SDMA
biomarker levels and ArgMI were statistically larger in the RA cohort
(p<.0001) when compared with their age and gender matched healthy controls
(see Table 1). Surprisingly, seronegative patients exhibited statistically
significant higher ArgMI compared with seropositive patients. Statin and DMARD therapy
showed no significant effect on any nitrative stress biomarkers.

Conclusion:

These elevated nitrative stress
biomarkers in RA patients suggest an important avenue for detecting subclinical
endothelial dysfunction in RA. Surprisingly, DMARD treatment, known to decrease
systemic inflammation, did not suppress biomarkers of nitrative stress, which points
towards a disconnect between systemic inflammation and endothelial dysfunction.
Furthermore the elevated ArgMI seen in seronegative patients, a group that is
perceived as having a more benign course and CV risk phenotype, warrants additional
study. Future studies which prospectively follow patients for CV outcomes have
the potential to identify RA patients at increased CV risk and provide them
with appropriate preventative intervention.

Table 1.

Data
represented as Median (IQR)