OBJECTIVES: Major medical indications of probiotic bacteria are conditions associated with the gastrointestinal tract. They exhibit not only the local but also systemic effects, the molecular mechanisms of which are poorly understood. We hypothesized that the action at remote sites of the body could be at least partially attributed to substances of the low molecular mass released from digested bacteria and able to cross the intestinal barrier. The aim of the study was the analysis of immunobiological properties of bacterial lysates and characterization of chemical constituents participating on this mode of action.
METHODS: Lactobacillus casei probiotic strain DN-114001 was employed. Lysates were prepared by passing bacteria through a French press (1500 psi) followed by lyophilisation. The fractions were prepared by the microfiltration of the crude lysate using the 3-, 10-, 30-, 50-, and 100-kDa cutoff filters (Amicon® Ultra 0.5 ml, Millipore Corp.). This procedure completely removes biologically active bacterial macromolecules such as peptidoglycan (PGN), lipoteichoic acid (LTA) and lipopolysaccharide (LPS). Effects of microfiltrates on the in vitro production of nitric oxide (NO), cytokines, and prostaglandin E2 (PGE2) were investigated in rat peritoneal cells.
RESULTS: The original crude lysate (≤10 µg/ml) activated the biosynthesis of NO, PGE2, and secretion of cytokines. The amount of the lysate needed for the preparation of microfiltered fractions exhibiting immunostimulatory effects was 10-fold higher (100 µg/ml). The molecules with the molecular mass ≤3 kDa were responsible for approximately 45% and 83% of the NO- and PGE2-enhancing activities of the crude lysate, respectively. The microfiltered fractions of the lysate also enhanced secretion of interleukin-6 and tumor necrosis factor-α but not that of interleukin-10 and interferon-γ.
CONCLUSION: The Lactobacillus casei probiotic strain DN-114001 contains low molecular mass (≤3 kDa) molecules possessing immunostimulatory properties. Their chemical nature remains to be identified.