Development of a Selective Adsorbing Material for Binding of Pyrrolizidine Alkaloids in Herbal Extracts, Based on Molecular Group Imprinting.

Abstract

Pyrrolizidine alkaloids are secondary plant constituents that became a subject of public concern because of their hepatotoxic, pneumotoxic, genotoxic, and cytotoxic effects. Due to disregardful harvesting and/or contamination with pyrrolizidine alkaloid-containing plants, there is a high risk of ingesting these substances with plant extracts or natural products. The limit for the daily intake was set to 0.007 µg/kg body weight. If contained in an extract, cleanup methods may help to minimize the pyrrolizidine alkaloid concentration. For this purpose, a material for depleting pyrrolizidine alkaloids in herbal preparations was developed based on the approach of molecular imprinting using monocrotaline. Molecular imprinted polymers are substances with specific binding characteristics, depending on the template used for imprinting. By means of group imprinting, only one molecule is used for creating selective cavities for many molecular pyrrolizidine alkaloid variations. Design of Experiment was used for the development using a 25 screening plan resulting in 64 polymers (32 MIPs/32 NIPs). Rebinding trials revealed that the developed material can compete with common cation exchangers and is more suitable for depleting pyrrolizidine alkaloids than C18- material. Matrix trials using an extract from Chelidonium majus show that there is sufficient binding capacity for pyrrolizidine alkaloids (80%), but the material is lacking in selectivity towards pyrrolizidine alkaloids in the presence of other alkaloids with similar functional groups such as berberine, chelidonine, and coptisine. Beyond this interaction, the selectivity could be proven for other structurally different compounds on the example of chelidonic acid.