Administration of 3,3-dimethyl-1-butanol is immunomodulatory in collagen induced arthritis murine model independent of TMA lyase activity

Abstract Studies of rheumatoid arthritis (RA) and murine collagen-induced arthritis (CIA) link the intestinal microbiome with disease and pathogenic autoantibodies. We have previously identified significant alterations in carnitine metabolism in mice with CIA, providing a potential link between bacterial dysbiosis and autoimmunity. Dietary carnitine is metabolized into trimethylamine (TMA) by bacterial enzyme TMA lyase which is oxidized in the host liver to TMAO. Prior studies determined that 3,3-dimethyl-1-butanol (DMB) and fluoromethylcarnitine (FMC) inhibit TMA lyase. Therefore, we tested if TMA lyase inhibition with DMB or FMC could ameliorate CIA. Male DBA1/j mice at 6 weeks of age were injected with bovine type II collagen in complete Freund’s adjuvant at days 0 and 21. On day 21 drinking water was replaced with vehicle, 1% vol/vol DMB, or 100mg/kg FMC. Mice were monitored for arthritis until day 35. DMB-treated mice had a significant (>50%) reduction in arthritis severity, as well as decreased anti-collagen antibodies, serum IFN-γ, and IL-17 compared to FMC and vehicle-treated mice with CIA. However, only FMC significantly reduced intestinal TMA and circulating TMAO, while DMB did not affect TMA/TMAO, suggesting that the effect of DMB is independent of TMA lyase inhibition. Using gas chromatography, we confirmed that DMB is absorbed and metabolized in mice, thereby identifying a novel metabolite, 3,3-dimethyl-1-butyric acid (DMBut). During CIA, 1% vol/vol DMBut significantly reduced disease, suggesting it is an active metabolite of DMB. Altogether our study suggests that DMB and/or its metabolites are immunomodulatory in CIA. Elucidating its target and mechanism of action may provide directions for RA therapeutic development. Supported by Grants from NIH (U01HL152405, T32AI074491) and from the State of Colorado Office of Economic Development and International Trade Advanced Industries Accelerator Program