DOP43 Histologic improvement, attenuation of inflammation and microbiome modulation by engineered high acetate producing Saccharomyces boulardii in DSS-induced colitis

Abstract

Abstract Background The probiotic Saccharomyces cerevisiae var. boulardii (Sb) may be optimized for therapeutic use in ulcerative colitis by enhancing its acetate production, as acetate is a key factor for its probiotic efficacy and was shown to have anti-inflammatory and barrier-protective effects in vitro (Deleu, 2023). Therefore, higher acetate producing Sb strains have been engineered which were preclinically evaluated in an acute DSS mice model of colitis. Methods Nine-week-old female C57/Bl6 mice (N=120) were allocated to 12 treatment groups receiving drinking water or 2.75% DSS in combination with PBS (control), Baker’s yeast (non-probiotic control), SDH1 (no-acetate Sb), ENT (transient acetate strain-probiotic Enterol control), SbP (high acetate Sb) and ENT3 (extra high acetate Sb). Disease activity including weight loss, diarrhoea and the presence of occult blood were scored daily. On day 7, the DSS groups were transferred to regular drinking water and on day 14 mice were sacrificed. Colonic tissue and faeces (0, 9, 14d) were collected for resp. histology, RNA, and 16S rRNA sequencing. Results Disease activity in DSS subgroups (Fig.A), determined by the area under the curve, was lower for SbP compared to PBS and Baker’s yeast (both p<0.05). Sb SDH1 showed higher disease activity compared to the Sb strains ENT, SbP and ENT3 (all p<0.05). At sacrifice, the macroscopic damage score in DSS was lower for SbP and ENT3 (both p<0.05) compared to Sb SDH1, and the colon weight/length-ratio was decreased for ENT and SbP compared to Sb SDH1 (resp. p=0.06 and p=0.08). Higher histologic inflammation was noted in the non- or transient-acetate producing strains on DSS compared to healthy PBS control (all p<0.05), whereas this increase was not observed for both high-acetate producing strains SbP and ENT3 on DSS (p=NS) indicating a production dependent response. Anti-inflammatory findings were confirmed by transcriptomic analysis of differentially expressed genes e.g. decreased expression of Tnf, Il1b and S100a8/9, predominantly expressed as calprotectin, upon stimulation with the highest acetate producing strain ENT3 (all adj.p<0.1; except PBS adj.p=0.16). Subsequent, microbial analysis showed a superior effect of ENT3 in maintaining a stable alpha diversity (p=0.58, Fig.E), which was not observed for the other strains. Conclusion Engineered high acetate producing Sb strains attenuated DSS-induced colitis, with its anti-inflammatory effects further supported by transcriptomic analysis and superiority in maintaining a stable microbiome composition. Together with our previous in vitro work in patient-derived organoids, these data indicate a role for high-acetate producing Sb- in attenuating intestinal inflammation.