In the RA patients, PON1 activity toward Hcy thiolactone was negatively correlated with DAS28-ESR (r = −0.78, p < 0.01), CRP (r = −0.52, p < 0.05), and MPO (r = −0.69, p < 0.01) but not with total Hcy, HDL-cholesterol, apolipoprotein A-I, apolipoprotein A-II, or eGFR. Here, MPO is linked to rheumatoid arthritis.