RA patients who use methotrexate have been shown to have lower cardiovascular mortality compared to non-users; however, the mechanism underlying this protection is unclear. Here, Reiss et al (Arthritis Rheum 2008; 58(12): 3675) explore the atheroprotective effects of methotrexate in an experimental model of atherogenesis.
THP-1 monocytes/macrophages and human donor peripheral blood mononuclear cells (PBMCs) were cultured and exposed singly and in varying combinations to increasing concentrations of methotrexate, pro-atherogenic factors (IFNγ and the COX-2 inhibitor NS398), and the adenosine A2A receptor agonist CGS21680 and antagonist ZM241385. Differences in mRNA and protein expression for the anti-atherogenic proteins cholesterol 27-hydroxylase (27-OHase) and ATP-binding cassette transporter A1 (ABCA1), key mediators of the reverse cholesterol transport process, and the formation of macrophage foam cells after incubation with acetylated LDL were compared for the different exposure groups.
Exposure to methotrexate increased mRNA and protein expression for the anti-atherogenic reverse cholesterol transport mediator 27-OHase while the COX-2 inhibitor NS398 reduced 27-OHase mRNA levels. The effect of NS398 on 27-OHase mRNA levels was blocked when co-incubated with methotrexate. Similarly, methotrexate abrogated the reduction in 27-OHase levels induced by incubation with IFNγ. The effect of methotrexate on enhancing 27-OHase increased with increasing concentration of methotrexate. Similar findings were seen when human PBMCs were used.
Both NS398 and IFNγ reduced mRNA levels of the anti-atherogenic protein ABCA1. Co-incubation with methotrexate abrogated these effects and was associated with higher ABCA1 levels than in controls, despite the presence of NS398 and IFNγ. Adding the adenosine A2A receptor antagonist reduced the beneficial effect of methotrexate, suggesting that methotrexate exerts its beneficial effect through the adenosine A2A receptor.
THP-1 macrophages incubated with LDL transformed readily into foam cells when exposed to INFγ or the COX-2 inhibitor NS398. Foam cell transformation was reduced when co-exposed to methotrexate. Methotrexate was not effective at reducing foam cell transformation when the adenosine A2A receptor was blocked with ZM241385.
Methotrexate upregulated important anti-atherogenic proteins involved in the reverse cholesterol transport process and abrogated the detrimental effect of COX-2 inhibition and IFNγ on these proteins and macrophage foam cell transformation.
These are a very elegant set of experiments that help to explain why methotrexate, in contrast to other non-biologic DMARDs, appears to convey a cardiovascular mortality benefit in users. It should be notes, however, that these results are from an in vitro experimental model of atherogenesis, and may function differently in vivo in the environment of an actual artery. Regardless, these results suggesting cardioprotection provide additional justification for methotrexate as the cornerstone of therapy for inflammatory arthritis.