This study is a pilot, proof of concept study to determine the effects of administering an oral short chain fatty acid (SCFA) supplement along with methotrexate as first line treatment of new onset rheumatoid arthritis (NORA) patients. Up to 50 participants will be included to obtain a sample size of at least 16 participants taking the oral supplement. The study team hypothesizes that oral SCFA will change the participants' gut microbiome and regulatory immune responses. Clinical data to assess for adverse events, stool, urine samples and peripheral blood will be collected at baseline, 2 and 4 months with an optional 6-month time point. Fecal microbiome will be analyzed. Adaptive immune responses will be analyzed from participant blood samples.

Inclusion Criteria:

1. New diagnosis of rheumatoid arthritis (RA) (<6 months) meeting 2010 ACR/EULAR for RA
2. Scheduled to begin treatment with methotrexate at any dose as standard medical care
3. Able and willing to provide written informed consent prior to any study specific procedures
4. Age 18 years and above at time of enrollment
5. Subjects not excluded based on race or ethnicity

Exclusion Criteria:

1. Participants who are pregnant or are currently breastfeeding
2. History of sensitivity to study compound or any of their excipients
3. Previous intolerance to SCFA or related compounds
4. Current (within 3 months of screening) treatment with csDMARDs
5. Current or past (ever) treatment with biologic therapies (including but not limited to anti-TNF, anti-IL-17, anti-IL-12/23)
6. Current antibiotic treatment (within 3 months of screening)
7. Current consumption of probiotics (within 3 months of screening)
8. Severe hepatic impairment (eg, ascites and/or clinical signs of coagulopathy)
9. Renal failure (eGFR <30 or requiring dialysis) by history
10. History of other autoimmune disease
11. Current immunodeficiency state (e.g., cancer, HIV, others)

Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices) will be available upon reasonable request.

Beginning 9 months and ending 36 months following article publication or as required by a condition of awards and agreements supporting the research.

The investigator who proposed to use the data will have access to the data upon reasonable request. Requests should be directed to Rebecca.Blank@nyulangone.org. To gain access, data requestors will need to sign a data access agreement.