Effects of fireweed (Chamerion angustifolium L.) leaf extract and its main component Oenothein B on the viability and cell death of colon cancer (Caco-2) cells

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Introduction Fireweed (Chamerion angustifolium L.) is a medicinal plant, widely used to treat gastrointestinal disorders, such as inflammation and irritation, acid reflux, mucous membrane lesions, wounds healing, swelling [1]. Fireweed is included in a European Medicines Agency (EMA) monograph stating that it can be used to relieve lower urinary tract symptoms associated with benign prostatic hyperplasia [2]. Extracts obtained from fireweed leaf are abundant in polyphenolic compounds (tannins, flavonoids, phenolic acids) and show a variety of pharmacological effects, such as anti-inflammatory, anti-oxidant, antiproliferative, anti-cancer, anti-microbial, anti-bacterial properties [3]. The main compound which is detected in high concentrations in fireweed extract is Oenothein B, a dimeric macrocyclic ellagitannin [1]. Due to the high incidence of colorectal cancer and the need for novel bioactive compounds targeting tumor cell survival, colon cancer is a relevant model to assess the therapeutic potential of fireweed leaf extract and Oenothein B. Aim The aim of the study was to determine the effect of fireweed (Chamerion angustifolium L.) leaf extract and its main component Oenothein B on colon cancer (Caco-2) cell death. Methods The fireweed leaves were collected in Jonava district, Šafarka village (55°00′22″ N; 24°12′22″ E) in 2023 July. The aqueous extracts from unfermented leaves were prepared from plants grown under natural conditions. Colon cancer cells (Caco-2) were treated with different fireweed extract (0.5 mg/mL; 1 mg/mL; 1.5 mg/mL) and Oenothein B (0.05 mg/mL; 0.1 mg/mL; 0.15 mg/mL) concentrations for 48 hours. Control group were untreated colon cancer cells. The amount of viable, apoptotic and necrotic cells was evaluated by Hoechst 33342 (20 µg/mL) and propidium iodide (PI) (10 µg/mL) staining and analyzed with a EVOS M7000 Imaging System (Invitrogen, Thermo Fisher Scientific, Waltham, Massachusetts, U.S.) at 20x magnification. Results We found that the effect of fireweed extract and Oenothein B to colon cancer cell count and viability was dose dependent. An increase in fireweed leaf extract concentration from 0.5 to 1.5 mg/mL resulted in a significant reduction in colon cancer cells by 52–69% (p < 0.05). Similarly, increasing the concentration of Oenothein B from 0.05 mg/mL to 0.15 mg/mL, resulted in a significant reduction of cell number by 50-65% (p < 0.05). The cell viability decreased by 15-91% (p < 0.05) after treatment with fireweed extract (0.5-1.5 mg/mL) and by 11-88% (p< 0.05) after Oenothein B (0.05-0.15 mg/mL). Moreover, a concentrationdependent increase in necrotic cell death was observed following treatment with fireweed extract and Onethein B. Treatment with fireweed extract (0.5-1.5 mg/mL) resulted in an 11–91% increase in necrotic cells, compared to an 8–88% increase observed in the oenothein B-treated group (p< 0.05). Additionally, there was an insignificant amount of apoptotic cell death, 4% in fireweed treated group (0.5 mg/mL) and 2% in Oenothein B treated group (0.05 mg/mL), which completely diminished with increasing concentrations of both the fireweed extract and Oenothein B. Conclusions The aqueous extract of fireweed (Chamerion angustifolium L.) leaves and its main component Oenothein B significantly suppresses the viability of colon cancer cells (Caco-2) in a dose-dependent manner. Notably, both the fireweed leaf extract and Oenothein B exhibited comparable cytotoxic effects, suggesting that Oenothein B may substantially contribute to the anti-cancer activity of the fireweed extract.

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