Antioxidative and Anti-Borrelia Effects of Plantago Species ^†

Borrelia burgdorferi sensu lato bacteria are the causative agent of Lyme disease, Europe’s most common vector-borne disease. In Estonia, the number of ticks carrying pathogenic bacteria and the case numbers of the illness are rapidly rising [1]. The infection can affect multiple organ systems and withstand several rounds of antibiotic treatment [2]. Therefore, novel treatment options are needed to combat the persister forms of the bacteria responsible for the chronic illness [3]. The screening of natural resources has shown promise in helping discover lead compounds with distinct anti-Borrelia activity for future therapeutic approaches. The antioxidative and antibacterial properties of several plants found in Estonia have been demonstrated by our group. This presentation discusses the chemical characterisation and anti-Borrelia activity determination of Plantago major and Plantago lanceolata. The plants’ main groups of bioactive compounds were quantified by colorimetric tests, total polyphenols by the Folin–Ciocalteu, total flavonoids by the AlCl₃, and total iridoids by the Trim–Hill method. The results show that dried aerial parts of P. major and P. lanceolata contain up to 32.7 and 47.1 mg/g gallic acid equivalents of phenolic compounds, up to 10.0 and 14.4 mg/g quercetin equivalents of flavonoids, and up to 11.4 and 23.4 mg/g asperuloside equivalents of iridoids, respectively. The extracts were chemically characterised using HPLC–DAD–MS/MS. The antioxidative activity of all extracts was evaluated using the ORAC_FL method, and found to be up to 12.3 or 14.6 mg/g Trolox equivalents for P. major and P. lanceolata, respectively. The anti-Borrelia activity of the plant extracts was tested on the latent bacterial forms using the SYBR Green I and Propidium Iodide assay. The residual viability of B. burgdorferi bacteria after incubation with the plant extracts was as low as 18.7% for P. major species, and 23.6% for P. lanceolata species. Therefore, as our results demonstrate that both P. major and P. lanceolata contain considerable amounts of phytochemicals with antioxidant properties and show significant anti-Borrelia effects on the latent forms of B. burgdorferi, these plants should be considered for further therapeutic research.