Extracting and Analyzing Pyrrolizidine Alkaloids in Medicinal Plants: A Review.

Pyrrolizidine alkaloids (PAs) are distributed in plant families of Asteraceae, Boraginaceae, and Fabaceae and serve in the chemical defense mechanism against herbivores. However, they became a matter of concern due to their toxicity associated with the high risk of intake within herbal preparations, e.g., phytopharmaceutical formulations, medicinal teas, or other plant-derived drug products. In 1992, the German Federal Ministry of Health established the first limits of PA content for fourteen medicinal plants. Because of the toxic effects of PAs, the Federal Institute of Risk Assessment (BfR) established more stringent limits in 2011, whereby a daily intake <0.007 µg/kg body weight was recommended and valid until 2018. A threefold higher limit was then advised by BfR. To address consumer safety, there is the need for more efficient extraction procedures along with robust, selective, and sensitive analytical methods to address these concerns. With the increased prevalence of, e.g., phytopharmaceutical formulations, this timely review comprehensively focuses on the most relevant extraction and analysis strategies for each of those fourteen plant genera. While a variety of extraction procedures has been reported, differences in PA content of up to 1110 ppm (0.11% (w/w)) were obtained dependent on the nature of the solvent and the applied extraction technique. It is evident that the efficient extraction of PAs requires further improvements or at least standardization of the extraction conditions. Comparing the various analytical techniques applied regarding selectivity and sensitivity, LC-MS methods appear most suited. This review shows that both standardized extraction and sensitive determination of PAs is required for achieving appropriate safety levels concerning public health in future.

Stability-indicating colorimetric assay for indicine N-oxide using TLC.

Aliquots of aqueous solutions in which indicine N-oxide may be degraded were mixed with 0.5 M formic acid (1:3) to adjust the pH to approximately 2-4 to quench the reaction and to ensure adequate TLC resolution. Silica-coated aluminum sheets were used to isolate indicine N-oxide by cutting the appropriate region from the chromatogram. By a modification of a known procedure, the silica gel then was treated with an acetic anhydride-diglyme mixture, and the mixture was heated to convert the drug to a pyrrole, which was then coupled with 4-dimethylaminobenzaldehyde to produce a color. The absorbance of the resulting solution was determined at 566 nm, and the apparent molar absorptivity, epsilon, based on the final indicine N-oxide concentration was 6.13 x 10(4). The recovery was approximately 92%, and the assays were readily reproducible with a coefficient of variation of 4.4%.