Cadinane-Type Sesquiterpenoids from Heterotheca inuloides: Absolute Configuration and Anti-inflammatory Activity

Evaluation of selected natural sesquiterpenes as sensitizing agents of β-lactam-resistant bacterial strains

AIMS

To evaluate the capacity of fourteen sesquiterpenes to enhance the action of known antibiotics against two β-lactam resistant strains, and to determine a possible mechanism of antibiotic sensitization by assessing their ability to inhibit a β-lactamase enzyme.

METHODS AND RESULTS

The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of β-lactams cefuroxime (CEFM) and cefepime (CPM) against Staphylococcus aureus 23MR and Escherichia coli 82MR strains in the absence and presence of subinhibitory concentrations of fourteen natural sesquiterpenes. (1R,4R)-4H-1,2,3,4-tetrahydro-1-hydroxycadalen-15-oic acid (5), xerantolide (8), estafiatin (11), and ambrosin (12) exhibited the best sensitizing effects in both strains. These compounds were able to reduce the MIC of CEFM by 2-fold (from 15.0 to 7.5 µg/mL) and CPM by 15-fold (from 0.9 to 0.06 µg/mL) in S. aureus 23MR. For E. coli 82MR, the MIC of CEFM was reduced up to 8-fold (from 120.0 to 15.0 µg/mL). In this strain, the activity of 8 and 11 surpassed that of clavulanic acid (positive reference), which reduced the MIC of CEFM from 120.0 to 60.0 µg/mL. To elucidate a possible mechanism of antibiotic sensitization, molecular docking studies were conducted with β-lactamases. These studies revealed an affinity with the enzymes (energies > -4.93 kcal/mol) by the formation of hydrogen bonds with certain conserved amino acid residues within the active sites. However, the in vitro results indicated only marginal inhibition, with percentages <50%.

CONCLUSIONS

The bioevaluations indicate that nine of fourteen sesquiterpenes enhance the action of CEFM and CPM against the β-lactam resistant strains, and these compounds displayed moderate activity as inhibitors of β-lactamase.

New Techniques of Structure Elucidation for Sesquiterpenes

The most significant new techniques that have been used in the twenty-first century for the structure elucidation of sesquiterpenes and some derivatives are reviewed in this chapter. A distinctive feature of these methodologies is the combination of accurate experimental measurements with theoretical data obtained by molecular modeling calculations that allow to visualize, understand, and quantify many structural characteristics. This has been the case for NMR spectroscopy, which has expanded its potential for solving complex structural problems by means of comparison with quantum mechanical molecular models. Ab initio and density functional theory calculations of chemical shifts, coupling constants, and residual chemical shift anisotropies have played important roles in the solution of many structures of sesquiterpenes. The assignments of their absolute configurations by evaluation of calculated and experimental chiroptical properties as electronic and vibrational circular dichroism are also reviewed. This chapter also includes the use of X-ray diffraction analysis with emphasis on calculations of the Flack and Hooft parameters, which are applicable to all molecules that crystallize in non-centrosymmetric space groups. The accurate molecular models of sesquiterpenes, validated by concordance with their experimental properties, are nowadays essential for the interpretation of the effects of these natural products on biological systems.

Chemo-sensitizing activity of natural cadinanes from Heterotheca inuloides in human uterine sarcoma cells and their in silico interaction with ABC transporters

Sensitizing activities exerted by 3,4-dihydro-7-hydroxycadalene (1), rac-3,7-dihydroxy-3(4H)-isocadalen-4-one (4) and (1R,4R)-4H-1,2,3,4-tetrahydro-1-hydroxycadalen-15-oic acid (9), the major cadinanes isolated from Heterotheca inuloides, towards multidrug-resistant MES-SA/MX2 and parental MES-SA epithelial human uterine sarcoma cell lines were evaluated. We also evaluated the in silico interactions (expressed as ΔG_binding in kcal/mol) of cadinanes 1, 4 and 9 in an in vitro assay, and also tested several structurally related natural compounds with the multidrug resistance protein (MDR1, P-glycoprotein), human multidrug resistance protein 1 (MRP1), and breast cancer resistance protein (BCRP) structures as pharmacological targets using AutoDock and AutoDock Vina. Compound 1 potentiated the cytotoxicity of doxorubicin and mitoxantrone drugs in resistant MES-SA/MX2 cells, compared to cells treated with each drug alone. Compound 1 could reverse the resistance to doxorubicin 12.44 fold at a concentration of 5 μM. It also re-sensitized cells to mitoxantrone 3.94 fold. Hence, compound 1 may be considered as a potential chemosensitizing agent to overcome multidrug resistance in cancer. The docking analysis suggested that there are interactions between cadinanes from H. inuloides and MDR1, MRP1, and BCRP proteins mainly through π-π interactions and hydrogen bonds.

Human disorders associated with inflammation and the evolving role of natural products to overcome

Inflammation is a biological function which triggered after the mechanical tissue disruption or from the responses by the incidence of physical, chemical or biological negotiator in body. These responses are essential act provided by the immune system during infection and tissue injury to maintain normal tissue homeostasis. Inflammation is a quite complicated process at molecular level with the involvement of several proinflammatory expressions. Several health problems are associated with prolonged inflammation, which effects nearly all major to minor diseases. The molecular and epidemiological studies jagged that the inflammation is closely associated with several disorders with their specific targets. It would be great achievement for human health around the world to overcome on inflammation. Mostly used anti-inflammatory drugs are at high risk of side effects and also expensive. Hence, the plant-based formulations gained a wide acceptance by the public and medical experts to treat it. Due to extensive dispersal, chemical diversity and systematically established biological potentials of natural products have induced renewed awareness as a gifted source for medications. However, today's urgent need to search for cheaper, more potent and safe anti-inflammatory medications to overcome on current situation. The goal of this review to compile an update on inflammation, associated diseases, molecular targets, inflammatory mediators and role of natural products. The entire text concise the involvement of various cytokines in pathogenesis of various human disorders. This assignment discussed about 321 natural products with their promising anti-inflammatory potential discovered during January 2009 to December 2018 with 262 citations.

Unusual cadinane-type sesquiterpene glycosides with α-glucosidase inhibitory activities from the fruit of Cornus officinalis Sieb. et Zuuc

Five novel and rare cadinane-type sesquiterpene glycosides, cornucadinoside A-E (1-5) were isolated from water extract of the fruit of Cornus officinalis Sieb. et Zuuc.. The new chemical structures, together with their absolute configurations, were elucidated on the basis of extensive spectroscopic analysis, including a comparison of their experimental and calculated electronic circular dichroism (ECD) spectra. Their structures, which possess a naphthalene skeleton, are the first report on the occurrence of cadinane sesquiterpene glycosides in Cornus. Additionally, all the compounds exhibited marked α-glucosidase inhibitory activity except for 3in vitro.

Effect of natural and semi-synthetic cadinanes from Heterotheca inuloides on NF-κB, Nrf2 and STAT3 signaling pathways and evaluation of their in vitro cytotoxicity in human cancer cell lines

The effects of ten natural cadinane sesquiterpenoids isolated from Heterotheca inuloides on the pathways of the NF-κB, Nrf2 and STAT3 transcription factors were studied for the first time. The main constituent in this species, 7-hydroxy-3,4-dihydrocadalene (1), showed anti-NF-κB activity and activated the antioxidant Nrf2 pathway, which may explain the properties reported for the traditional use of the plant. In addition to the main metabolite, a structurally similar compound, 7-hydroxy-cadalene (2), also displayed anti-NF-κB activity. Thus, both natural compounds were used as templates for the preparation of a novel semi-synthetic derivative set, including esters and carbamates, which were evaluated for their potential in vitro antiproliferative activities against six human cancer cell lines. Carbamate derivatives 32 and 33 were found to exhibit potent activity against human colorectal adenocarcinoma and showed important selectivity in cancer cells. Among ester derivatives, compound 13 was determined to be a more potent NF-κB inhibitor and Nrf2 activator than its parent, 7-hydroxy-3,4-dihydrocadalene (1). Furthermore, this compound decreases levels of phospho-IκBα, a protein complex involved in the NF-κB activation pathway. Molecular simulations suggest that all active compounds interact with the activation loop of the IKKβ subunit in the IKK complex, which is the responsible of IκBα phosphorylation. Thus, we identified two natural, and one semi-synthetic, NF-κB and Nrf2 modulators and two new promising cytotoxic compounds.

Mexican Arnica (Heterotheca inuloides Cass. Asteraceae: Astereae): Ethnomedical uses, chemical constituents and biological properties

ETHNOPHARMACOLOGICAL RELEVANCE

Heterotheca inuloides Cass. (Asteraceae) has been traditionally used to treat a wide range of diseases in Mexico in the treatment of rheumatism, topical skin inflammation, muscular pain colic, and other painful conditions associated with inflammatory processes, additionally has been used to treat dental diseases, and gastrointestinal disorders. This species has also been used for the treatment of cancer and diabetes. This review provides up-to-date information on the botanical characterization, traditional uses, chemical constituents, as well as the biolological activities of H. inuloides.

MATERIAL AND METHODS

A literature search was conducted by analyzing the published scientific material. Information related to H. inuloides was collected from various primary information sources, including books, published articles in peer-reviewed journals, monographs, theses and government survey reports. The electronic search of bibliographic information was gathered from accepted scientific databases such as Scienfinder, ISI Web of Science, Scielo, LILACS, Redalyc, Pubmed, SCOPUS and Google Scholar.

RESULTS

To date, more than 140 compounds have been identified from H. inuloides, including cadinane sesquiterpenes, flavonoids, phytosterols, triterpenes, benzoic acid derivatives, and other types of compounds. Many biological properties associated with H. inuloides. Many studies have shown that the extracts and some compounds isolated from this plant exhibit a broad spectrum of biological activities such as antioxidant, antitumor, anti-inflammatory, cytotoxic, and chelating activities, as well as insecticidal and phytotoxic activity. To date, reports on the toxicity of H. inuloides are limited.

CONCLUSIONS

A comprehensive analysis of the literature obtained through the above-mentioned sources confirmed that ethnomedical uses of H. inuloides have been recorded in Mexico to treat rheumatism, pain, and conditions associated with inflammatory processes. Pharmacological studies have demonstrated the activity of certain compounds associated with the traditional use of the plant such as the anti-inflammatory and cytotoxic activities of the species. The available literature showed that cadinene sesquiterpenes are the major bioactive components of H. inuloides with potential pharmacological activities. Further investigations are needed to fully understand the mode of action of the major active constituents.