Limosilactobacillus reuteri enables oral-to-systemic absorption of iberiotoxin for treatment of collagen-induced arthritis in rats.

Background: Rheumatoid arthritis (RA) is an autoimmune disease characterized by joint inflammation and damage in which fibroblast-like synoviocytes (FLS) play a central role. Invasiveness and proliferation of FLS in RA is dependent on activity of the K_Ca1.1 potassium channel. Peptide blockers of K_Ca1.1, such as iberiotoxin (IbTX), can be delivered subcutaneously to treat animal models of RA. We tested whether an engineered probiotic oral delivery platform could effectively deliver IbTX systemically in a rat model of RA.

Results: A plasmid for inducible secretion of IbTX was constructed and transformed into probiotic Limosilactobacillus reuteri ATCC PTA-6475 to generate LrIbTX. No differences in growth rate between LrIbTX and the control strain were detected in vitro, and live LrIbTX was recovered from the feces of rats following oral gavage. IbTX was detected in the sera of healthy rats orally gavaged with LrIbTX by a K_Ca1.1 competitive binding assay using a biotinylated IbTX analog and streptavidin-conjugated fluorophore. Collagen-induced arthritis (CIA), an animal model of RA, was used to measure the effect of LrIbTX versus injected IbTX or control L. reuteri expressing an irrelevant protein on clinical score, histologic inflammation, and bone density. Oral LrIbTX and injected IbTX had similar efficacy in treating CIA in rats as measured by clinical joint swelling and histologic inflammation, which were significantly improved versus control bacteria or vehicle injection. No treatments induced measurable levels of anti-IbTX IgG, and there were no differences in macroscopic bone damage or anti-collagen II IgM and IgG levels between CIA groups. Injected IbTX and oral LrIbTX were also equivalent in inhibiting an active delayed-type hypersensitivity (DTH) reaction in rats.

Conclusions: This work describes the effective oral delivery of a candidate therapeutic peptide, IbTX, via engineered L. reuteri to treat an animal model of autoimmune disease and demonstrates systemic distribution of an intestinally produced peptide. We anticipate that oral delivery of engineered microbes may be a generalizable strategy for enhancing the oral bioavailability of peptide therapeutics.