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.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Oberlies
Nicholas H
NH
Natural Products Laboratory, RTI International, Research Triangle Park, NC 27709, USA. oberlies@rti.org
Kim
Nam-Cheol
NC
Brine
Dolores R
DR
Collins
Bradley J
BJ
Handy
Robert W
RW
Sparacino
Charles M
CM
Wani
Mansukh C
MC
Wall
Monroe E
ME
D001628:Beverages / Q000032:analysis*; D002849:Chromatography, Gas; D020844:Comfrey / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000032:analysis / Q000378:metabolism*; D010084:Oxidation-Reduction; D010936:Plant Extracts / Q000032:analysis / Q000633:toxicity; D018515:Plant Leaves / Q000737:chemistry; D011763:Pyrrolizidine Alkaloids / Q000032:analysis* / Q000633:toxicity
D009589:Nitrogen Oxides; D010936:Plant Extracts; D011763:Pyrrolizidine Alkaloids; C020639:symphytine