Invasive Plant Extracts Show DNA-Protective Power in Yeast Safety Tests

Two of Europe’s most aggressive invasive plants, the false indigo bush (Amorpha fruticosa) and the tree of heaven (Ailanthus altissima), may be more than ecological nuisances. A new study published in the journal BioRisk reports that chemical extracts prepared from the fruit of the false indigo bush and the bark of the tree of heaven showed no detectable genotoxic, mutagenic, or carcinogenic activity in a battery of yeast-based tests. More strikingly, the extracts protected cells against DNA damage inflicted by a powerful mutagenic agent, suggesting that these troublesome invaders could become a cheap and abundant source of biologically active, DNA-protective compounds.

The research team set out to answer a question that has long been underexplored for both species: are their chemical constituents safe at the genetic level, and might they even shield living cells from damage? Both plants are prolific invaders. Amorpha fruticosa, a shrub native to North America, and Ailanthus altissima, a tree native to China introduced to Europe and North America at the end of the eighteenth century, tolerate a wide range of habitats and spread aggressively because few herbivores keep them in check. Their unchecked spread is considered a significant driver of biodiversity loss, so any pharmacological use that encourages large-scale harvesting could double as a habitat-protection strategy.

Both species also carry long histories in traditional medicine. Tree of heaven preparations have been applied against asthma, epilepsy, bleeding, dysentery, and eye diseases, while false indigo bush has been used for stomach pain, intestinal worms, eczema, neuralgia, and rheumatism. Chemically, the plants are well stocked with interesting molecules. The fruit of Amorpha fruticosa is rich in isoflavonoids, rotenoids, and prenylated stilbenoids, including the diverse amorfrutin group. The bark of Ailanthus altissima contains more than 221 reported compounds, among them alkaloids, quassinoids, phenylpropanoids, triterpenoids, and volatile oils. Yet despite this pharmacological promise, the authors note that toxicity data for these extracts remain scarce, which is precisely the gap the new study set out to fill.

The researchers prepared three extracts. Fruit of Amorpha fruticosa, collected near Sofia, Bulgaria, was first defatted with chloroform and then extracted with 70 percent methanol to yield the AF extract. Tree of heaven bark was macerated with hexane to produce a lipophilic extract, AAEH, and the remaining defatted material was percolated with 70 percent methanol to give a hydrophilic extract, AAEM. Each extract was then tested at three concentrations, 10, 100, and 1000 micrograms per milliliter, across a suite of assays designed to probe both DNA-damaging and DNA-protective behavior.

The first round of testing measured antioxidant capacity in vitro. In the DPPH radical scavenging assay, which tracks the color change of a stable radical from purple to yellow, the AF extract performed best, with an IC50 value of 63.71 micrograms per milliliter, followed by AAEM at 696.12 and AAEH at 1396.97 micrograms per milliliter. Ascorbic acid, the standard, came in at 15.94 micrograms per milliliter, so even the best plant extract showed only slight to moderate radical scavenging by comparison. A complementary DNA topology assay, which monitors whether supercoiled plasmid DNA stays intact or relaxes into a damaged circular form, produced a consistent ranking, AF greater than AAEM greater than AAEH. Notably, the hexane extract displayed a moderate pro-oxidant potential, meaning it could itself inflict single-strand damage on plasmid DNA under certain conditions.

The heart of the study, however, took place in living cells of the baker’s yeast Saccharomyces cerevisiae, a workhorse model whose major stress-response pathways closely resemble those of human cells. Using yeast also aligns with the European Union’s Directive 2010/63/EU, which enshrines the principle of replacing, reducing, and refining animal experimentation. The team employed two classic yeast systems: Zimmermann’s test on the diploid strain D7ts1, which measures mitotic gene conversion, reverse point mutations, and mitotic crossing-over, and the Ty1 retrotransposition test on haploid strain 551, a proxy for carcinogenic potential. Zeocin, a radiomimetic antibiotic of the bleomycin family that shreds DNA much like ionizing radiation, served as the positive control.

The safety results were unambiguous. When yeast cells were treated with the extracts alone, survival remained comparable to untreated controls at all three concentrations, and the frequencies of convertants, revertants, and total aberrants matched baseline levels. No Ty1 retrotransposition was induced by any extract. According to the authors, this is the first demonstration that Amorpha fruticosa fruit extract and Ailanthus altissima bark extracts are neither genotoxic, mutagenic, nor carcinogenic in this test system, a foundational finding for any future pharmacological development.

The protective results were even more compelling. When cells were pre-treated with an extract before a one-minute exposure to 100 micrograms per milliliter of Zeocin, survival rose roughly twofold compared with Zeocin alone, and the burden of genetic damage fell dramatically. Reverse point mutations dropped to levels comparable with untreated cells after pre-treatment with AF and AAEM, and total aberrants were significantly reduced across the board. The AF extract stood out as the only one capable of reducing Zeocin-induced mitotic gene conversion at every concentration tested, an effect the researchers attribute to its isoflavonoid-rich composition, possibly through activation of homologous recombination repair and modulation of chromatin structure. In the Ty1 assay, pre-treatment with AF and AAEH reduced transposition rates to near-control levels, indicating genuine anticarcinogenic activity, while only the lowest AAEM concentration failed to protect cells.

Not every interaction was benign. Pre-treatment with the lowest concentration of the hexane extract, 10 micrograms per milliliter, actually potentiated Zeocin’s recombinogenic effect, increasing gene conversion frequencies. The authors point out that AAEH is dominated by phytosterols, and previous work has shown that sterols can enhance the activity of bleomycin, a close relative of Zeocin. This concentration-dependent twist underscores a central lesson of the study: biological effects track phytochemical composition. The protective hierarchy, AF greater than AAEM greater than AAEH, mirrors the flavonoid and stilbenoid content of the extracts, and flavonoids are already well known for antimutagenic properties.

Perhaps the most intriguing mechanistic insight is what the protection does not depend on. Because the extracts showed only mild to moderate antioxidant activity in vitro, the researchers suggest that the reduction of mutations and retrotransposition events is not primarily an antioxidant effect. Instead, they speculate that the extracts may activate protective enzymes independent of the homologous recombination machinery, since reverse mutation frequency is a readout of error-prone recombination. The team, which included Ekaterina Kozuharova, who identified and extracted the plants, emphasizes that further experiments are needed to pin down the mode of action and identify the active constituents. Still, the message is clear: two plants that choke wetlands and crack through pavement may owe their next chapter to the laboratory bench, where their abundant, inexpensive chemistry could be transformed from invasive liability into DNA-protective asset.

Subject of Research: Genotoxicity, mutagenicity, and protective effects of Amorpha fruticosa and Ailanthus altissima extracts in yeast

Article Title: Screening of Amorpha fruticosa and Ailanthus altissima extracts for genotoxicity/antigenotoxicity, mutagenicity/antimutagenicity and carcinogenicity/anticarcinogenicity

Article References: Todorova, T., Boyadzhiev, K., Shkondrov, A., Parvanova, P., Dimitrova, M., Ionkova, I., Krasteva, I., Kozuharova, E., & Chankova, S. (2022). Screening of Amorpha fruticosa and Ailanthus altissima extracts for genotoxicity/antigenotoxicity, mutagenicity/antimutagenicity and carcinogenicity/anticarcinogenicity. BioRisk, 17, 201-212. https://doi.org/10.3897/biorisk.17.77327

Image Credits: AI Generated

DOI: 10.3897/biorisk.17.77327

Keywords: Amorpha fruticosa, Ailanthus altissima, invasive species, genotoxicity, antimutagenicity, Saccharomyces cerevisiae, Zeocin, antioxidant activity, Ty1 retrotransposition, phytochemistry, flavonoids, DNA repair