Loss of Response to Anti-Tumor Necrosis Factor Alpha Therapy in Crohn's Disease Is Not Associated with Emergence of Novel Inflammatory Pathways

While monoclonal antibodies against tumor necrosis factor-alpha (TNF alpha) are effective in treating Crohn's disease (CD), approximately one-third of patients lose response. The mechanisms underlying this loss of response remain elusive. We sought to determine if novel biological pathways, including TNF alpha-independent inflammatory pathways, emerge in those with loss of response to anti-TNF alpha. Using RNA microarray technology in 28 patients with CD, we examined the colonic gene expression differences between those with active inflammation in the setting of loss of response to TNF alpha-antagonist therapy ("loss of responders") compared to anti-TNF alpha na < ve patients with active inflammation and those on anti-TNF therapy in disease remission. Pathway enrichment analyses were performed. We found that colonic expression of chemokines known to drive inflammation (CXCL20, CXCL9, and CXCL10) was elevated in those with loss of response compared to those in remission. Expression of genes critical to modulating oxidative stress burden (DUOX2, DUOXA2, and NOS2) was also elevated. Additionally, MMP3, MMP1, and MMP12 were elevated in those with continued inflammation. Gene enrichment analysis revealed that loss of responders exhibited dysregulation in the cysteine and methionine metabolism pathway, suggesting alteration in oxidative stress burden. There were no differences in genes or pathways between loss of responders and those who were TNF alpha-na < ve. However, loss of response occurred despite the ability of anti-TNF alpha therapy to normalize APO gene expression. Our analyses suggest that loss of response to anti-TNF alpha is not driven by the emergence of pathways that bypass the action or induce resistance to anti-TNF alpha therapy.