Safety and Tolerability of Lactobacillus reuteri DSM 17938 and Effects on Biomarkers in Healthy Adults: Results from a Randomized Masked Trial

BACKGROUND There are few carefully-designed studies investigating the safety of individual probiotics approved under Investigational New Drug policies. OBJECTIVES The primary aim of this prospective, double-blind placebo-controlled trial was to investigate if daily treatment of adults with Lactobacillus reuteri DSM 17938 (LR) for 2 months is safe and well-tolerated. Our secondary aim was to determine if LR treatment has immune effects as determined by regulatory T cell percentages, expression of toll-like receptors (TLR)-2 and -4 on circulating peripheral blood mononuclear cells (PMBCs), cytokine expression by stimulated PBMC, and intestinal inflammation as measured by fecal calprotectin. METHODS Forty healthy adults were randomized to a daily dose of 5 × 10(8) CFUs of LR (n = 30) or placebo (n = 10) for 2 months. Participants completed a daily diary card and had 7 clinic visits during treatment and observation. RESULTS There were no severe adverse events (SAEs) and no significant differences in adverse events (AEs). There were no differences in PBMC subclasses, TLRs, or cytokine expression after treatment. The probiotic-treated group had a significantly higher fecal calprotectin level than the placebo group after 2 months of treatment: 50 µg/g (IQR 24-127 µg/g) vs. 17 µg/g (IQR 11-26 µg/g), p = 0.03, although values remained in the normal clinical range (0-162.9 µg/g). LR vials retained >10(8) CFUs viable organisms/ml. CONCLUSIONS LR is safe and well tolerated in adults, without significant changes in immunologic markers. There was a small but significant increase in fecal calprotectin, perhaps indicating some element of immune recognition at the intestinal level. TRIAL REGISTRATION Clinical Trials.gov NCT00922727.