The genus Calea L.: A review on traditional uses, phytochemistry, and biological activities

Bioguided isolation of a selective compound from Calea phyllolepis leaves against breast cancer cells

Plants of the Calea genus have been reported to contain lipophilic compounds, such as sesquiterpene lactones, with cytotoxic effect against different cancer cell lines. The aim of this manuscript was to investigate the chemical profile and cytotoxic activity of different fractions from Calea phylolepis leaves on different human cancer cell lines. The fractions were prepared using solvent extraction of increasing polarity, yielding hexane, ethyl acetate and methanolic fractions. All fractions were chemically analysed by thin layer chromatography (TLC), and their cytotoxic activity against HT-29 (colon adenocarcinoma), MCF-7 (breast cancer), U-251MG (malignant glioblastoma) and L929 (mouse fibroblast) cell lines was investigated. Among these, the hexane and ethyl acetate fractions showed higher cytotoxic effects, while the methanolic fraction did not show any cytotoxic effects. The major bioactive compound from the hexane fraction (12.15%) was isolated using chromatographic methods and was identified by nuclear magnetic resonance spectroscopy (NMR) and gas chromatography-mass spectrometry (GC-MS) analysis as 6-epi-β-verbesinol coumarate. This compound showed activity against breast cancer cells (IC₅₀  = 5.8 ± 1.0 μg/ml), similar to etoposide. Furthermore, 6-epi-β-verbesinol coumarate showed low cytotoxicity to normal fibroblast cells, suggesting a high selectivity index (SI = 7.39) against breast cancer cells.

Chemical Characterization of Plant Extracts and Evaluation of their Nematicidal and Phytotoxic Potential

Nacobbus aberrans ranks among the "top ten" plant-parasitic nematodes of phytosanitary importance. It causes significant losses in commercial interest crops in America and is a potential risk in the European Union. The nematicidal and phytotoxic activities of seven plant extracts against N. aberrans and Solanum lycopersicum were evaluated in vitro, respectively. The chemical nature of three nematicidal extracts (EC_50,48h ≤ 113 µg mL^-1) was studied through NMR analysis. Plant extracts showed nematicidal activity on second-stage juveniles (J2): (≥87%) at 1000 µg mL^-1 after 72 h, and their EC₅₀ values were 71.4-468.1 and 31.5-299.8 µg mL^-1 after 24 and 48 h, respectively. Extracts with the best nematicidal potential (EC_50,48h < 113 µg mL^-1) were those from Adenophyllum aurantium, Alloispermum integrifolium, and Tournefortia densiflora, which inhibited L. esculentum seed growth by 100% at 20 µg mL^-1. Stigmasterol (1), β-sitosterol (2), and α-terthienyl (3) were identified from A. aurantium, while 1, 2, lutein (4), centaurin (5), patuletin-7-β-O-glucoside (6), pendulin (7), and penduletin (8) were identified from A. integrifolium. From T. densiflora extract, allantoin (9), 9-O-angeloyl-retronecine (10), and its N-oxide (11) were identified. The present research is the first to report the effect of T. densiflora, A. integrifolium, and A. aurantium against N. aberrans and chemically characterized nematicidal extracts that may provide alternative sources of botanical nematicides.

Secondary Metabolites of Plants as Modulators of Endothelium Functions

According to the World Health Organization, cardiovascular diseases are the main cause of death worldwide. They may be caused by various factors or combinations of factors. Frequently, endothelial dysfunction is involved in either development of the disorder or results from it. On the other hand, the endothelium may be disordered for other reasons, e.g., due to infection, such as COVID-19. The understanding of the role and significance of the endothelium in the body has changed significantly over time—from a simple physical barrier to a complex system encompassing local and systemic regulation of numerous processes in the body. Endothelium disorders may arise from impairment of one or more signaling pathways affecting dilator or constrictor activity, including nitric oxide–cyclic guanosine monophosphate activation, prostacyclin–cyclic adenosine monophosphate activation, phosphodiesterase inhibition, and potassium channel activation or intracellular calcium level inhibition. In this review, plants are summarized as sources of biologically active substances affecting the endothelium. This paper compares individual substances and mechanisms that are known to affect the endothelium, and which subsequently may cause the development of cardiovascular disorders.

Extracts from Six Native Plants of the Yucatán Peninsula Hinder Mycelial Growth of Fusarium equiseti and F. oxysporum, Pathogens of Capsicum chinense

Fusarium equiseti strain FCHE and Fusarium oxysporum strain FCHJ were isolated from the roots of wilting habanero pepper (Capsicum chinense Jacq.) seedlings with root rot. Toward developing a biorational control of these serious phytopathogenic strains, ethanolic (EE) and aqueous (AE) extracts of different vegetative parts of 40 tropical native plants of the Yucatán Peninsula were screened for antifungal activity. Extracts of six out of 40 assayed plants were effective, and the most inhibitory extracts were studied further. EEs from Mosannona depressa (bark from stems and roots), Parathesis cubana (roots), and Piper neesianum (leaves) inhibited mycelial growth of both strains. Each active EE was then partitioned between hexane and acetonitrile. The acetonitrile fraction from M. depressa stem bark (MDT-b) had the lowest minimum inhibitory concentration of 1000 µg/mL against both pathogens and moderate inhibitory concentration (IC₅₀) of 462 against F. equiseti and 472 µg/mL against F. oxysporum. After 96 h treatment with EE from M. depressa stem bark, both strains had distorted hyphae and conidia and collapsed conidia in scanning electron micrographs. Liquid chromatography–ultraviolet–high resolution mass spectrometry analysis revealed that the major component of the fraction was α-asarone. Its antifungal effect was verified using a commercial standard, which had an IC₅₀ of 236 µg/mL against F. equiseti and >500 µg/mL against F. oxysporum. Furthermore, the P. cubana hexane fraction and P. neesianum acetonitrile fraction had antifungal activity against both Fusarium pathogens. These compounds provide new options for biorational products to control phytopathogenic fungi.

Sesquiterpene Lactones from Calea pinnatifida: Absolute Configuration and Structural Requirements for Antitumor Activity

This work describes the chromatographic fractionation of the aerial parts of Calea pinnatifida and the structural characterization and determination of the absolute configuration of the isolated compounds as well as their antitumor potential. The HPLC fractionation of the CH₂Cl₂ phase of the MeOH extract from the leaves of C. pinnatifida led to the isolation of two related sesquiterpene lactones (STLs): calein C (1) and calealactone B (2). Additionally, during the purification process, a derivative of calein C (3) was formed as a product of the Michael addition of MeOH. The structures of Compounds 1–3 were established based on spectroscopic and spectrometric data, while the absolute stereochemistry was established by vibrational circular dichroism. In order to evaluate the effect of the conjugated double bonds on the cytotoxic activity of STLs, Compounds 1–3 were tested against anaplastic (KTC-2) and papillary (TPC-1) thyroid carcinoma cells. Calein C was the most active of the STLs, and displayed activity against both KTC-2 and TPC-1. On the other hand, the calein C derivative (3) was the least cytotoxic of all the compounds tested. These results are promising and suggest the importance of studying sesquiterpene lactones isolated from C. pinnatifida in terms of antitumor activity, especially considering the effects of α,β-unsaturated carbonyl systems.

Computationally aided stereochemical assignment of undescribed bisabolenes from Calea urticifolia

Calea urticifolia (Mill.) DC. (Compositae) is a medicinal plant found in El Salvador. Calea is used in folkloric medicine as a psychoactive principle with calming effect, as well as in the treatment of diarrhea and fever. Three undescribed bisabolenes, named caleanolenes A-C, as well as, three known sesquiterpene lactones 2,3-epoxyjuanislamin, calealactone B, calein C, and the flavonoid acacetin, were isolated from the chloroform extract of the leaves of C. urticifolia. The chemical structures of the isolated compounds were determined on the basis of HRMS, IR, CD, and from 1D and 2D NMR spectroscopic studies. The absolute configurations of the caleanolenes have been partly established using GIAO NMR and ECD calculations. The isolated compounds were evaluated for cytotoxicity against the CA46 and Raji lymphoma, and the MCF7 breast cancer cell lines, with 2,3-epoxyjuanislamin showing the best activity in all cell lines (IC₅₀ value range 2.9-12.3 μM).