Absence of mutagenic effects of a particular Symphytum officinale L. liquid extract in the bacterial reverse mutation assay

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Comfrey (Symphytum officinale L.) root preparations are traditionally used for the topical treatment of contusions, strains and sprains. Besides allantoin and phenolcarbonic acids (e.g. rosmarinic acid) which are discussed as pharmacologically active principles, the drug contains pyrrolizidine alkaloids (PAs) (e.g. intermedine, lycopsamine, symphytine, echimidine) and their N-oxides which are known for their hepatotoxic, carcinogenic and mutagenic properties [1]. The commercially available herbal medicinal products Kytta-Salbe® f (ointment) and Kytta-Plasma® f (paste for cataplasms) contain a liquid extract from comfrey root (DER 1:2; extraction solvent: ethanol 60% v/v) as active substance. The aim of this study was to demonstrate the absence of genotoxic effects of this particular extract in the bacterial reverse mutation assay (Ames test). Briefly, comfrey root liquid extract was investigated for its ability to induce gene mutations in Salmonella typhimurium strains TA 98, TA 100, TA 102, TA 1535 and TA 1537 with and without metabolic activation using the mammalian microsomal fraction S9 mix. Reference mutagens were used to check the validity of the experiments [2]. The investigated comfrey root fluid extract showed no biologically relevant increases in revertant colony numbers of any of the five tester strains, neither in the presence nor in the absence of metabolic activation. In conclusion, the comfrey root fluid extract contained in Kytta-Salbe® f and Kytta-Plasma® f was not mutagenic in the bacterial reverse mutation assay.