Acetylcholinesterase Inhibitory Activity After in vitro Gastrointestinal Digestion of Infusions of Mentha Species

Aims: To study the acetylcholinesterase inhibitory activity of Mentha infusions before and after the gastrointestinal digestion and to correlate this activity with the chemical compounds present in these infusions.

Place and Duration of Study: Fresh Mentha x piperita, M. spicata, M. pulegium were bought in a local supermarket. These plants were composed of leaves, stems and flowers for the identification, which was carried out in Plant Biotechnology Centre, Faculty of Sciences, University of Lisbon. The chemical identification of the infusions and the enzymatic tests were carried out in the Center of Chemistry & Biochemistry, Faculty of Science University of Lisbon from September 2010 till June 2011.

Methodology: The compounds present in the infusions were identified by LC-MS. The enzyme activity assay was carried out using a spectrophotometric method. The digestive simulation was accomplished using enzymatic juices prepared in the laboratory and Caco-2 cells lines simulating the intestine barrier.

Results: All the Mentha infusions contained rosmarinic acid. M. spicata infusion contained also eriocitrin and eriodictyol. The IC50 values for acetylcholinesterase inhibitory activity of the infusions, before digestion, stayed between 0.72 and 1.9 mg/mL. These activities are statistically different at p<.05. These activities can be explained by the presence of the phenolic compounds mentioned. Rosmarinic acid has an IC50 equal to 0.439 mg/mL (1.22 mM), eriocitrin and eriodictyol have IC50 equal to 0.439 mg/mL (0.29 mM) and 0.256 mg/mL (0.89 mM) respectively. The presence of these two flavonoids, eriocitrin and eriodictyol, can account for the higher activity detected for M. spicata. The gastric juice or the pancreatic juices used to simulate the gastrointestinal digestion did not originate any difference in the chemical composition of the infusions (analysed by HPLC-DAD). This was also corroborated by the enzymatic tests. The Caco-2 cells did not originate any modification in the enzymatic activity of the infusions. The analysis of the cell homogenate revealed the presence of rosmarinic acid and the phenolic compounds, although in minor amount.

Conclusion: Mentha infusions have the capacity to inhibit acetylcholinesterase, due to the presence of rosmarinic acid, eriocitrin and eriodictyol The composition of the Mentha herbal teas was not modified by the gastro-intestinal juices, or by the intestinal cell line.