Structural determination of three new eudesmanolides from Inula helenium

From Monographs to Chromatograms: The Antimicrobial Potential of Inula Helenium L. (Elecampane) Naturalised in Ireland

With antimicrobial resistance rising globally, the exploration of alternative sources of candidate molecules is critical to safeguard effective chemotherapeutics worldwide. Plant natural products are accessible, structurally diverse compounds with antimicrobial potential. The pharmacological applications of plants in medicine can be guided by the attestation of traditional use, as demonstrated in this study. In Irish ethnomedical literature, Inula helenium L. (elecampane) is often indicated for respiratory and dermal ailments. This is the first assessment of antimicrobial sesquiterpene lactones from the roots of elecampane, naturalised in Ireland. Traditional hydro-ethanolic extracts were prepared from multi-origin elecampane roots. A novel clean-up strategy facilitated the bioactivity-guided fractionation of a subset of anti-staphylococcal fractions (the compositions of which were investigated using HPLC-DAD, supported by ¹H NMR). The natural products attributing to the antimicrobial activity, observed in vitro, were identified as alantolactone (1), isoalantolactone (2), igalan (3), and an unseparated mixture of dugesialactone (4) and alloalantolactone (5), as major compounds. The findings suggest that the geographical origin of the plant does not influence the anti-bacterial potency nor the chemical composition of traditional elecampane root. Considering the prevalence of staphylococci-associated infections and associated broad spectrum resistance in Irish hospitals, currently, further research is warranted into the usage of the identified compounds as potential candidates in the control of staphylococcal carriage and infection.

A comprehensive chemical and pharmacological review of three confusable Chinese herbal medicine-Aucklandiae radix, Vladimiriae radix, and Inulae radix

Aucklandiae radix (AR, Muxiang), vladimiriae radix (VR, Chuanmuxiang), and inulae radix (IR, Tumuxiang) are widely used in clinical or folk medicine in China. Their Chinese names all have the Chinese character "Muxiang," which makes it confusable in usage, especially AR and VR, because VR was used as a substitute for AR during a historical period. The National Health Commission of the People's Republic of China has approved AR as a functional food. However, VR and IR are not listed. Many research articles on three kinds of "Muxiang" have been published. However, no review was appeared to compare similarities and differences among the three kinds of "Muxiang." Here, the morphological characterization, phytochemistry, and pharmaceutical effects of AR, VR, and IR were reviewed. We found that only six compounds were common in the three species. Twenty-six compounds were common to AR and VR. Twenty-two compounds were common to AR and IR. Only seven compounds were common to VR and IR. The extracts of AR, VR, and IR were all reported with antiinflammatory effects, which is the most important activity of "Muxiang" species. The volatile oil of AR, VR, and IR had antibacterial activities. Extracts of AR and VR showed anti-gastric ulcers and anti-diarrhea effects. Extracts of AR and IR exhibited anticancer effects. In addition, AR extract had liver protective effect. It is worth mentioning that costunolide and dehydrocostus lactone, which were the common representative compounds of "Muxiang" species, showed antiinflammatory, anticancer, anti-gastric ulcers, and liver protective effects. This review will be a benefit reference for correct understanding and application of the three "Muxiang" species.

Sesquiterpenoids from the roots of Inula helenium inhibit acute myelogenous leukemia progenitor cells

One new eudesmane sesquiterpenoid, 11β-hydroxy-13-chloro-eudesm-5-en-12, 8-olide (1), was isolated from the roots of Inula helenium together with nine eudesmanolides (2-10) and one germacranolide (11). Their structures were elucidated on the basis of detailed spectroscopic analyses. All isolates were evaluated for their antiproliferative activities against human leukemia stem-like cell line KG1a. Compound 10 exhibited the most potent effect with the IC₅₀ value of 3.36 ± 0.18 μM. A further investigation revealed that compound 10 could significantly induce apoptosis of KG1a cells. Additionally, compound 10 had an obvious effect on the levels of apoptosis-related proteins (Bcl-2, Bax, cytochrome c, caspase 9 and caspase 3), indicating that the antiproliferative effect of compound 10 on KG1a cells might be mediated through a mitochondria-dependent apoptotic pathway.

Metabolomic Profile of the Genus Inula

Plants have a long history as therapeutics in the treatment of human diseases and have been used as source of medicines for ages. Searching for new biologically active natural products, many plants and herbs are screened for natural products with pharmacological activities. In this field, the genus Inula, which comprises more than 100 species, several of them being used in traditional medicine, is very important, especially due to the finding that several of the isolated pure secondary metabolites proved to possess important biological activities. Inula species have been reported as rich sources of sesquiterpene lactones, including eudesmanes, germacranes, guaianes, and dimeric structures, and since 2006 ca. 400 secondary metabolites, including more than 100 new natural products, some of them with relevant pharmacological activities, have been identified. Herein, we critically compile and update the information regarding the types of secondary metabolites found in the genus Inula and the progress in their isolation.

Inula sesquiterpenoids: structural diversity, cytotoxicity and anti-tumor activity

INTRODUCTION

The plants of the genus Inula (Asteraceae) are widely distributed throughout Europe, Africa and Asia, and many of these plants have long been used in folk medicine. This genus is a rich source of sesquiterpenoids, which exhibit a wide range of biological activities. Recently, a series of bioactive sesquiterpenoid dimers, with unusual carbon skeletons, have been reported and these have gathered considerable interest.

AREAS COVERED

This article systematically reviews sesquiterpenoids isolated from the genus Inula that have appeared in literature up to August 2013, critically highlighting their anti-tumoral activities and relevant mechanistic insights. The authors also discuss the initial structure-activity relationships for the cytotoxic and anti-tumoral activities of the Inula sesquiterpenoids. Finally, the authors discuss the challenges and potential applications of these sesquiterpenoids in the future.

EXPERT OPINION

Cytotoxic and anti-tumor activities of Inula sesquiterpenoids have been extensively studied since the 1970s. One promising compound, Japonicone A, a dimeric sesquiterpene lactone from traditional herb Inula japonica, has displayed potent in vitro and in vivo anti-tumor activity against Burkitt's lymphoma. Additionally, acetylbritannilactone is thought to be capable of suppressing the abnormal vascular smooth muscle cell proliferation, with the induction of apoptosis in vivo and in vitro. In this regard, it may be worthwhile further investigating acetylbritannilactone in patients with vascular restenosis. Furthermore, given the anti-inflammatory property of britanin, clinical studies on chronic bronchitis and asthma, using the ethanol extract of I. japonica, are currently underway in South Korea. However, despite demonstrating good therapeutic effects, additional pharmacological and toxicological studies are still needed.

Antioxidant and Antimicrobial Activities, and Phenolic Compounds of Selected Inula species from Turkey

Three Inula species, I. viscosa, I. helenium ssp. turcoracemosa and I. montbretiana, collected from different locations of Anatolia were investigated for their antioxidant and antimicrobial potential, and their total phenolic content and phenolic composition. Antioxidant activities of various extracts of the plant parts were measured using DPPH radical scavenging and ABTS assays. Antimicrobial potential of methanol extracts of the plant parts was determined by the agar dilution method against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Candida tropicalis. All the extracts were more active against Gram-positive bacteria and yeasts than Gram-negative bacteria. The extracts exhibited antioxidant and antimicrobial activities in different concentrations. Total phenolic concentration of the extracts was estimated with Folin-Ciocalteu reagent using gallic acid as standard. The total phenolic content varied widely in different parts of the three tested Inula species, ranging from 21.1 ± 0.8 to 190.9 ± 6.1 mg GAE/g extract. Phenolic components, such as chlorogenic acid, caffeic acid, rutin, myricetin, quercetin, luteolin and kaempferol were quantified by HPLC-DAD in the methanol extracts of the Inula species. It was obvious that the antioxidant and antimicrobial properties of the plants were due to the phenolics.