Analysis of herbal teas made from the leaves of comfrey (Symphytum officinale): reduction of N-oxides results in order of magnitude increases in the measurable concentration of pyrrolizidine alkaloids

• Published in: Public health nutrition 2004-10, Vol.7 (7), p.919-924
• Main Authors: Oberlies, Nicholas H, Kim, Nam-Cheol, Brine, Dolores R, Collins, Bradley J, Handy, Robert W, Sparacino, Charles M, Wani, Mansukh C, Wall, Monroe E
• Format: Article
• Language: English
• Subjects: Beverages - analysis; Chemical reduction; Chromatography; Chromatography, Gas; Comfrey; Comfrey - chemistry; Echimidine; Herbal tea; Leaves; N-oxide; Nitrogen Oxides - analysis; Nitrogen Oxides - metabolism; Oxidation-Reduction; Oxides; Plant Extracts - analysis; Plant Extracts - toxicity; Plant Leaves - chemistry; Pyrrolizidine; Pyrrolizidine Alkaloids - analysis; Pyrrolizidine Alkaloids - toxicity; Symphytine; Symphytum officinale; Tea
• ISSN: 1368-9800; 1475-2727
• DOI: 10.1079/PHN2004624

To determine the relative quantities of two hepatotoxic pyrrolizidine alkaloids, symphytine and echimidine, in teas prepared from comfrey leaves (Symphytum officinale), and to determine the potential contribution of the N-oxide forms of these alkaloids to levels of the parent alkaloids. Comfrey leaves were purchased from three commercial sources and used to prepare tea in a manner consistent with the methods used by consumers. An extraction scheme was devised for extraction of the alkaloids, and a gas chromatographic method was developed to quantify the two major alkaloids, symphytine and echimidine. Recognising that the N-oxide derivatives of these alkaloids have also been identified in comfrey preparations, chemical reduction was applied to determine the total quantities of the alkaloids as free bases and as N-oxide derivatives. The concentration of symphytine and echimidine varied considerably between teas prepared from leaves purchased from the different vendors of plant material. Moreover, a much higher concentration of symphytine was found in the tea when steps were included to reduce N-oxides prior to analysis. The treatment of pure symphytine with hot water did not generate the N-oxide derivative de novo. Since the pyrrolizidine alkaloids are known to be hepatotoxic, consumption of herbal teas made from comfrey leaves may be ill-advised. The concentration of pyrrolizidine alkaloids in such teas may be underestimated substantially unless the concentration of N-oxides is taken into consideration.