The Pretreatment Gut Microbiome Is Associated With Lack of Response to Methotrexate in New-Onset Rheumatoid Arthritis

OBJECTIVE

Although oral methotrexate (MTX) remains the anchor drug for rheumatoid arthritis (RA), up to 50% of patients do not achieve a clinically adequate outcome. In addition, there is a lack of prognostic tools for treatment response prior to drug initiation. This study was undertaken to investigate whether interindividual differences in the human gut microbiome can aid in the prediction of MTX efficacy in new-onset RA.

METHODS

We performed 16S ribosomal RNA gene and shotgun metagenomic sequencing on the baseline gut microbiomes of drug-naive patients with new-onset RA (n = 26). Results were validated in an additional independent cohort (n = 21). To gain insight into potential microbial mechanisms, we conducted ex vivo experiments coupled with metabolomics analysis to evaluate the association between microbiome-driven MTX depletion and clinical response.

RESULTS

Our analysis revealed significant associations of the abundance of gut bacterial taxa and their genes with future clinical response (q < 0.05), including orthologs related to purine and MTX metabolism. Machine learning techniques were applied to the metagenomic data, resulting in a microbiome-based model that predicted lack of response to MTX in an independent group of patients. Finally, MTX levels remaining after ex vivo incubation with distal gut samples from pretreatment RA patients significantly correlated with the magnitude of future clinical response, suggesting a possible direct effect of the gut microbiome on MTX metabolism and treatment outcomes.

CONCLUSION

Taken together, these findings are the first step toward predicting lack of response to oral MTX in patients with new-onset RA and support the value of the gut microbiome as a possible prognostic tool and as a potential target in RA therapeutics.

Pilot clinical trial of intravenous doxycycline versus placebo for rheumatoid arthritis

OBJECTIVE

To screen for potential efficacy and assess the feasibility of intravenous (IV) doxycycline as a treatment for rheumatoid arthritis (RA).

METHODS

The study was a (stratified, block) randomized, double blind, 12 week, pilot trial of IV doxycycline 300 mg/day versus identical appearing IV placebo given over 2 h for 14 days. The primary comparison was to a hypothesized placebo rate of 20% as described by Paulus. If a total of 14 consecutive subjects receiving doxycycline treatment did not respond, it would be considered futile to proceed to a Phase III trial. We planned a placebo group of 14 subjects to verify the placebo response rate and estimate sample size required for a definitive Phase III trial, if such a trial was warranted based on the pilot study. American College of Rheumatology (ACR) RA response criteria were used. After 23 subjects entered, the study was closed due to recruitment difficulties.

RESULTS

At baseline, mean (SD) tender joint count was 37 (11.9), swollen joint count 30 (9.6), morning stiffness 317 (319) min, and erythrocyte sedimentation rate 72 mm/h (27.5). Randomization resulted in 10 subjects receiving doxycycline and 13 receiving placebo. Treatment was stopped in 8 subjects: in 6, treatment was ineffective (one taking doxycycline, 5 placebo), and in 2, rashes occurred (one taking doxycycline, one placebo). Only one subject met ACR response criteria in the doxycycline group and none in the placebo group. Having no responders in the placebo group was consistent with placebo response rate of 20% or less. Several patients required peripherally inserted central catheters for venous access.

CONCLUSION

The efficacy of IV doxycycline as a treatment for RA could not be ruled out. However, as the proportion of responders was small, it is unlikely that potential efficacy of IV doxycycline would outweigh potential disadvantages of IV administration.

Association of HLA alleles and clinical features in patients with synovitis of recent onset

OBJECTIVE

To determine how HLA alleles are associated with the clinical disease patterns of patients with synovitis of recent onset.

METHODS

The HLA alleles A, B, C, DRbeta1, and DQbeta1 were determined in a cohort of 211 patients (mean age 42 years, 64% female, 79% white) with recent-onset synovitis in 1 or more peripheral joints. At a mean disease duration of 33 weeks, 98 patients (46%) met the American College of Rheumatology (ACR) criteria for rheumatoid arthritis (RA), 38 (18%) met the European Spondylarthropathy Study Group criteria for spondylarthropathy (SpA), and 75 (36%) were classified as having undifferentiated arthropathy (UA). Controls were racially matched healthy individuals (n = 244).

RESULTS

Shared epitope (SE) alleles were significantly more common in rheumatoid factor-positive (RF+) patients fulfilling the ACR RA criteria than in other patients with early arthritis (65% versus 35%; P < 0.001). In addition, the RA patients had by far the highest frequency of radiographic erosions (52% and 39% in RF+ and RF- RA, respectively, versus 3% and 9% in SpA and UA patients, respectively; P < 0.0001). The presence of SE alleles was a particularly strong predictor of early erosions in the RF- RA patients (odds ratio [OR] 6.8, 95% confidence interval [95% CI] 1.2-45). The presence of 2 SE alleles or an associated DQbeta1*0301 (DQ7) or DQbeta1*0302 (DQ8) allele appeared to modestly increase the risk of early erosions, although these DQ alleles were in strong linkage disequilibrium with DRbeta1*0401, both in the patient and in the control populations. B27 was linked with the presence of SE alleles in the patients, including those patients fulfilling the RA criteria, but not in the controls (12% versus 3%; P < 0.001). Enthesitis was present in 23 (11%) of 211 patients, was highly associated with B27 (OR 4.2, 95% CI 1.5-11.5), and surprisingly, was not a feature specific only to the SpA group. The B8-DR3 haplotype was significantly increased in the patient subgroups compared with controls (17% versus 7%; P < 0.01), although the clinical significance of this association is unclear.

CONCLUSION

This study of HLA associations in a diverse cohort of early synovitis patients emphasizes the complex degree of genetic interaction between alleles at several major histocompatibility complex loci, which regulates clinical phenotypes. In particular, SE and B27, while predisposing patients to characteristic clinical syndromes, had an unexpected degree of association in this cohort, perhaps explaining the overlap in clinical features in many patients.