Background/Purpose: Accelerated atherosclerosis has become increasingly recognized as a complication of chronic inflammatory disease, such as in patients with rheumatoid arthritis (RA). RA patients have a 2-fold increased risk of developing coronary artery disease (CAD) regardless of traditional risk factors and cardiovascular complications substantially contribute to their increased mortality. The inflammatory lesions in RA and CAD share the chronicity of tissue-destructive immune responses, with macrophages representing abundant effector cells.

Methods: Patients with RA who fulfilled 2010 ACR/EULAR RA Classification Criteria and patients with CAD (history of at least one myocardial infarction) were enrolled together with healthy age-matched controls. Monocytes were isolated from peripheral blood and differentiated into macrophages with macrophage colony-stimulating factor. Macrophages were polarized into M1 cells with IFN-γ and lipopolysaccharide. Mitochondrial reactive oxygen species (ROS) were quantified by MitoSOX staining and their production was inhibited with the ROS scavenger mitoTEMPO. Cellular ATP concentrations were quantified by fluorometric assay. Glycolytic rates and oxygen consumption were measured by Seahorse Flux Analyzer experiments. Relative gene expression was analyzed by quantitative RT-PCR and adjusted for β-actin transcripts.

Results: Seahorse experiments demonstrated increased glycolytic rates (ECAR) in RA and CAD macrophages compared to age-matched healthy controls. Key enzymes of glycolysis, HK-1 and PKM-2, were upregulated as well as GLUT-1, the main glucose uptake receptor in macrophages. The breakdown of glucose resulted in high mitochondrial activity characterized by an increase in mitochondrial membrane potential and by greater oxygen consumption, with mitochondria from CAD macrophages respiring even more than those from RA macrophages. Pharmaceutical uncoupling of the electron transport chain was used to measure maximal mitochondrial respiration. Notably, CAD mitochondria had explicitly more reserve capacity to work against imminent energy deficits and RA mitochondria still showed higher capacity than healthy ones. A byproduct of enhanced mitochondrial respiration is the generation of mitochondrial ROS, which was confirmed by MitoSOX staining to be substantially higher in patient-derived macrophages. Production of pro-inflammatory key cytokines of the synovial joint and the atherosclerotic plaque was directly related to mitochondrial activity, as indicated by the effective inhibition of IL-6, IL-1b, IL-18, and IL-23 when cells were pretreated with mitoTempo, a ROS-scavenger that specifically targets mitochondria-derived superoxide.

Conclusion: Macrophages from RA and CAD patients share a distinct metabolic profile characterized by upregulated glycolysis and high mitochondrial activity; fueling excess production of ROS and cytokines. Metabolic activity directly regulates the macrophages’ inflammatory potential and might contribute to accelerated atherosclerosis in RA patients.

« Back to 2017 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/metabolic-activity-sustains-macrophage-cytokine-production-in-rheumatoid-arthritis-and-coronary-artery-disease/