[Screening of a Lactobacillus casei with monoamine oxidase-inhibitory activity]

To screen for monoamine oxidase (MAO)-inhibiting lactobacillus from healthy human dejecta in an in vitro model, and to provide reference for anti-ageing study in vivo of lactobacillus in the future.

The monoamine oxidase inhibitory model in vitro was applied to screen fermented supernatant and cell-free extracts originated from lactic acid bacteria, and two indices based on screened samples were determined, including biological dosage-effect and the effect of pre-incubated time between MAO and inhibitor on suppression rate. Meanwhile, with membrane separation technology, MAO inhibition from different molecular weight range of samples was measured. Screened strain JH-23 was investigated as target probiotic lactobacillus, identified through the sequence analysis of 16S rDNA gene and API system.

The MAO inhibitory rate of cell-free extracts produced by strain JH-23 reached 33.7%. After samples being vacuum freeze-dried, MAO inhibitory rate was up to 53.2% when the reactive concentration was 16 mg/mL. The inhibition was significantly enhanced with the duration of pre-incubation increased, and then the inhibitory effect became steady after 30 minutes. Crude samples were dialyzed for 48 hours, MAO inhibitory effect of dialysates was significantly increased compared with pre-dialysis. The result of bacteria identification demonstrated that strain JH-23 was ascribed to Lactobacillus casei.

A new screening model in vitro, regarding monoamine oxidase as a target enzyme, was explored in this study. This model was characterized by convenience, rapidity and high sensitivity, and it could be useful for the following anti-aging research in vivo. The cell-free extracts of Lactobacillus casei JH-23 was inhibitory to MAO, and the intracellular small-molecules played a major role in the inhibition.