Rheumatoid arthritis: pathological mechanisms and modern pharmacologic therapies

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease that primarily affects the lining of the synovial joints and is associated with progressive disability, premature death, and socioeconomic burdens. A better understanding of how the pathological mechanisms drive the deterioration of RA progress in individuals is urgently required in order to develop therapies that will effectively treat patients at each stage of the disease progress. Here we dissect the etiology and pathology at specific stages: (i) triggering, (ii) maturation, (iii) targeting, and (iv) fulminant stage, concomitant with hyperplastic synovium, cartilage damage, bone erosion, and systemic consequences. Modern pharmacologic therapies (including conventional, biological, and novel potential small molecule disease-modifying anti-rheumatic drugs) remain the mainstay of RA treatment and there has been significant progress toward achieving disease remission without joint deformity. Despite this, a significant proportion of RA patients do not effectively respond to the current therapies and thus new drugs are urgently required. This review discusses recent advances of our  understanding of RA pathogenesis, disease modifying drugs, and provides perspectives on next generation therapeutics for RA.

Background The adaptive immune response in rheumatoid arthritis (RA) is influenced by an interaction between host genetics and environment, particularly the host microbiome. Association of the gut microbiota with various diseases has been reported, though the specific components of the microbiota that affect the host response leading to disease remain unknown. However, there is limited information on the role of gut microbiota in RA. In this study we aimed to define a microbial and metabolite profile that could predict disease status. In addition, we aimed to generate a humanized model of arthritis to confirm the RA-associated microbe. Methods To identify an RA biomarker profile, the 16S ribosomal DNA of fecal samples from RA patients, first-degree relatives (to rule out environment/background as confounding factors), and random healthy non-RA controls were sequenced. Analysis of metabolites and their association with specific taxa was performed to investigate a potential mechanistic link. The role of an RA-associated microbe was confirmed using a human epithelial cell line and a humanized mouse model of arthritis. Results Patients with RA exhibited decreased gut microbial diversity compared with controls, which correlated with disease duration and autoantibody levels. A taxon-level analysis suggested an expansion of rare taxa, Actinobacteria, with a decrease in abundant taxa in patients with RA compared with controls. Prediction models based on the random forests algorithm suggested that three genera, Collinsella, Eggerthella, and Faecalibacterium, segregated with RA. The abundance of Collinsella correlated strongly with high levels of alpha-aminoadipic acid and asparagine as well as production of the proinflammatory cytokine IL-17A. A role for Collinsella in altering gut permeability and disease severity was confirmed in experimental arthritis. Conclusions These observations suggest dysbiosis in RA patients resulting from the abundance of certain rare bacterial lineages. A correlation between the intestinal microbiota and metabolic signatures could determine a predictive profile for disease causation and progression. Electronic supplementary material The online version of this article (doi:10.1186/s13073-016-0299-7) contains supplementary material, which is available to authorized users.

To evaluate the efficacy and safety of adalimumab (D2E7), a fully human monoclonal tumor necrosis factor alpha antibody, in combination with methotrexate (MTX) in patients with active rheumatoid arthritis (RA) despite treatment with MTX. In a 24-week, randomized, double-blind, placebo-controlled study, 271 patients with active RA were randomly assigned to receive injections of adalimumab (20 mg, 40 mg, or 80 mg subcutaneously) or placebo every other week while continuing to take their long-term stable dosage of MTX. The primary efficacy end point was the American College of Rheumatology criteria for 20% improvement (ACR20) at 24 weeks. An ACR20 response at week 24 was achieved by a significantly greater proportion of patients in the 20-mg, 40-mg, and 80-mg adalimumab plus MTX groups (47.8%, 67.2%, and 65.8%, respectively) than in the placebo plus MTX group (14.5%) (P < 0.001). ACR50 response rates with the 20-mg, 40-mg, and 80-mg adalimumab dosages (31.9%, 55.2%, and 42.5%, respectively) were significantly greater than that with placebo (8.1%) (P = 0.003, P < 0.001, and P < 0.001, respectively). The 40-mg and 80-mg doses of adalimumab were associated with an ACR70 response (26.9% and 19.2%, respectively) that was statistically significantly greater than that with placebo (4.8%) (P < 0.001 and P = 0.020). Responses were rapid, with the greatest proportion of adalimumab-treated patients achieving an ACR20 response at the first scheduled visit (week 1). Adalimumab was safe and well tolerated; comparable numbers of adalimumab-treated patients and placebo-treated patients reported adverse events. The addition of adalimumab at a dosage of 20 mg, 40 mg, or 80 mg administered subcutaneously every other week to long-term MTX therapy in patients with active RA provided significant, rapid, and sustained improvement in disease activity over 24 weeks compared with MTX plus placebo.