A new Italian study has found that obese patients with longstanding rheumatoid arthritis (RA) who are put on anti-tumor necrosis factor (anti-TNF) therapies are less likely to achieve remission than their thinner counterparts.

The research, published online in Arthritis Care & Research recently, also found that, when it comes to obese patients, not all anti-TNFs are equal. Obese people who were taking infliximab (Remicade) were less likely to achieve remission than obese patients taking etanercept (Enbrel) or adalimumab (Humira).

There are five anti-TNFs – biologic medications that target the immune system – currently approved for RA: infliximab, etanercept, adalimumab, certolizumab pegol (Cimzia) and golimumbab (Simponi). The study did not include certolizumab pegol or golimumab, which are much newer than the others.

A growing body of research has shown that body fat (adipose tissue) produces inflammation that may make diseases such as RA worse. But researchers don’t yet completely understand why that happens or how treatment should be changed for people who are obese.

“Adipose tissue is a source of pro-inflammatory cytokines [proteins], and thus it may contribute to the inflammatory burden of the RA patient, creating a more inflammatory and therapy-resistant state,” explains lead author Elisa Gremese, MD, a researcher at the Catholic University of the Sacred Heart in Rome, Italy. “It has also been shown that obese RA patients have a more severe disease than normal weight patients, and this may also lead to a poorer therapy effect.”

The study involved 641 RA patients in Italy with established RA. All had tried taking methotrexate without benefit and so were stepped up to an anti-TNF. The participants were treated either with infliximab, adalimumab or etanercept and assessed at the start of the study as well as month three, six and 12. Remission was defined as having a DAS28 of less than 2.6 lasting for at least three months. DAS28 – Disease Activity Score in 28 joints – is a measure of disease burden and tender/swollen joints.