Butyrate Producers as Potential Next-Generation Probiotics: Safety Assessment of the Administration of Butyricicoccus pullicaecorum to Healthy Volunteers

Abstract

Advances in gut microbiota research have triggered interest in developing colon butyrate producers as niche-specific next-generation probiotics, targeted at increasing colon butyrate production and countering disease-associated microbiota alterations. Crucial steps in the development of next-generation probiotics are the design of formulations with a reasonable shelf life as well as the safety demonstration of an intervention in healthy volunteers. One such potential next-generation butyrate-producing probiotic is Butyricicoccus pullicaecorum 25-3^T, with demonstrated safety in in vitro as well as animal models. Here, we examined the strain's safety, tolerability, and impact on microbiota composition and metabolic activity in healthy volunteers in a randomized, double-blind, placebo-controlled crossover study in 30 healthy volunteers. The study design consisted of two 4-week intervention periods (10⁸ CFU B. pullicaecorum [treatment] or maltodextrin [placebo] per day) with a 3-week washout in between. We assessed adverse events, blood parameters (primary endpoints), and fecal microbiota composition and metabolite profiles (secondary endpoints). The number of reported adverse events during the B. pullicaecorum treatment was similar to that of placebo intervention, as were observed changes in blood chemistry parameters, bowel habits, and fecal calprotectin concentrations. Administration of the strain did not induce any disruptive effect in microbiota composition or metabolic activity. In this first human intervention trial with a butyrate-producing Clostridium cluster IV isolate, we demonstrated B. pullicaecorum 25-3^T administration to be both safe and well tolerated by healthy participants. This safety study paves the way for the further development of the strain as a next-generation probiotic. IMPORTANCE This study is the first to determine the safety and tolerance in humans of a butyrate-producing Clostridium cluster IV next-generation probiotic. Advances in gut microbiota research have triggered interest in developing colon butyrate producers as next-generation probiotics. Butyricicoccus pullicaecorum 25-3^T is one such potential probiotic, with demonstrated safety in vitro as well as in animal models. Here, we produced an encapsulated B. pullicaecorum formulation that largely preserved its viability over an 8-month storage period at 4°C. Administration of this formulation to healthy volunteers allowed us to establish the intervention as safe and well tolerated. The probiotic intervention did not cause disruptive alterations in the composition or metabolic activity of health-associated microbiota. The results presented pave the way for the exploration of the impact of the strain on microbiota alterations in a clinical setting.

Keywords: Butyricicoccus pullicaecorum; metabolome; microbiome; next-generation probiotic; safety; tolerance.

FIG 1

Study design. (A) Schematic representation of the study design. Stool diaries and samples were collected as depicted. V1 to V7 represent study visits before, during, and after each intervention and/or washout period. (B) Participant flow diagram showing the number of participants at each stage and reason for dropping out.

FIG 2

(A) Principal-coordinate analysis (PCoA) of interindividual differences in microbiota composition (Bray-Curtis dissimilarity) with samples included in the analysis (n = 188) and 1,106 samples from the Flemish Gut Flora Project. Samples collected during the intervention trial fell within ranges of normal variation, and no separation was observed after intervention compared to baseline. (B) Variation in microbiota richness (Chao1) and in relative abundances of the genus Butyricicoccus after probiotic administration compared to placebo. No significant differences were observed (r = −0.05 and P = 0.747 and r = −0.12 and P = 0.363, respectively).

FIG 3

Fecal metabolite profile analyzed by PLS-DA. No significant difference is found between metabolomes after probiotic intervention compared to baseline (P > 0.05 by RDA).