Background/Purpose:   High levels of rheumatoid arthritis (RA) disease activity have been
associated with abnormal function of circulating high density lipoproteins
(HDL) and increased cardiovascular risk.  Oxidative modifications to the HDL
particle by enzymes such as myeloperoxidase (MPO) occur in atherosclerotic
plaques of non-RA patients and adversely affect HDL function.  In the current
work, we evaluated the oxidant environment and anti-oxidant function of HDL in
synovial fluid (SF) from RA patients compared to patients with non-inflammatory
arthritis (NIA).

Methods: HDL
was isolated from synovial fluid of 10 RA patients and 11 NIA patients by
dextran bead precipitation.  HDL’s anti-oxidant function was measured by a cell
free assay as described previously (A&R 2009; 60(10): 2870-9). MPO
and paraoxonase 1 (PON1) activity (using both paraoxonase and arylesterase
assays), were measured in SF by previously published assays with minor
modifications (ARD 2012 Jul;71(7):1157-62, A&R 2012; 64(6):1828-37).  Oxidation products of arachidonic acid and
linoleic acid including 5 hydroxyeicosatetraenoic acid (HETE), 12-HETE,
15-HETE, 9-hydroxyoctadecadienoic acid (HODE) and 13-HODE were measured in
synovial fluid by mass spectrometry as described previously with minor
modifications (Drug Metab Lett. 2010; 4(3): 139-48). Total and HDL
cholesterol (HDL-C) levels in SF were determined by standard methods.

Results: HDL
in SF from RA patients had significantly worse anti-inflammatory, anti-oxidant
function as measured by a higher mean HDL inflammatory index (HII) compared to
SF HDL from patients with NIA (see table).  RA SF had significantly higher MPO
activity and higher levels of 15-HETE which were most strongly correlated with
SF macrophage cell counts (r values= 0.7 and 0.6 respectively, p values
<0.05) and showed trends for correlations with the HII (r = 0.5 and 0.3
respectively, p values =0.2).  Higher levels of total cholesterol, HDL-C, and
PON1 activity were noted in RA SF compared to NIA SF (see table).

Conclusion: HDL
is increased in RA SF and is pro-inflammatory and pro-oxidant compared to HDL
from NIA SF. These findings suggest a potential mechanism by which circulating
HDL in active RA patients lose their protective capacity by exposure to the
pro-oxidant joint milieu, linking high RA disease activity to abnormal HDL
function, and potentially increased CV risk.

HII=HDL
Inflammatory Index; F = Female; WBC = White blood cell; Ct = count; Neut =
neutrophil; Mac = macrophage; TC = total cholesterol; Aryl = Arylesterase. *p
value < 0.05 compared to NIA.