No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Helenalin - A Sesquiterpene Lactone with Multidirectional Activity
Abstract
Sesquiterpene lactones, secondary metabolites of plants, present in a large number of species mostly from the Asteracea family, were used in the traditional medicine of many countries for the treatment of various pathological conditions. They exert a broad range of activities, including anti-inflammatory, anti-bacterial and anti-cancer properties. The best known sesquiterpene lactones which are already used as drugs or are in clinical trials are artemisinin, thapsigargin and parthenolide. Yet another sesquiterpene lactone, helenalin, an active component of Arnica montana, known for its strong anti-inflammatory activity, has been used for centuries in folk medicine to treat minor injuries. Unfortunately, helenalin's ability to cause allergic reactions and its toxicity to healthy tissues prevented so far the development of this sesquiterpene lactone as an anticancer or antiinflammatory drug. Recently, the new interest in the biological properties, as well as in the synthesis of helenalin analogs has been observed. This review describes helenalin's major biological activities, molecular mechanisms of action, its toxicity and potential for further research.
... Jest ona klasyfikowana jako pseudo--guaianolid, a jej efekty działania w komórkach polegają m.in. na zdolności hamowania aktywności enzymów i czynników transkrypcji poprzez ich alkilację [21]. Do udokumentowanych aktywności ekstraktów z arniki oraz pochodnych helenaliny należą m.in.: działanie przeciwobrzękowe, przeciwreumatyczne, przeciwbólowe i przeciwdrobnoustrojowe. ...
... Do udokumentowanych aktywności ekstraktów z arniki oraz pochodnych helenaliny należą m.in.: działanie przeciwobrzękowe, przeciwreumatyczne, przeciwbólowe i przeciwdrobnoustrojowe. Badania ekstraktów z arniki, helenaliny oraz wybranych preparatów żelowych zawierających nalewkę arnikową prowadzono na modelach in vitro, in vivo oraz w kilku testach klinicznych [18][19][20][21]. Helenalina jest obecnie analizowana m.in. ...
... Badania kolejnych pochodnych helenaliny skupiają się m.in. na poszukiwaniu związków o korzystniejszym profilu farmakologicznym [18,19,21]. ...
Lecznicze zastosowanie arniki górskiej (Arnica montana L.) ma w Europie długą tradycję, a obecnie potwierdzoną i udokumentowaną aktywność biologiczną ekstraktów z jej kwiatów i wyizolowanej z nich helenaliny. Główne grupy wyspecjalizowanych metabolitów występujących w Arnicae flos to: laktony seskwiterpenowe, flawonoidy, kwasy fenolowe. Za działanie przeciwzapalne, które uzasadnia większość zastosowań arniki, odpowiadają przede wszystkim pochodne helenaliny, które obecnie są badane również m.in. w zakresie działania przeciwnowotworowego, a także przeciw wybranym pierwotniakom pasożytniczym wywołującym choroby tropikalne. Opracowanie nowych rozwiązań pozyskiwania znacznych ilości arniki dla przemysłu farmaceutycznego i kosmetycznego oraz poszukiwanie wydajnego źródła pochodnych helenaliny jest zatem uzasadnione aktywnością biologiczną i poszerzającym się zakresem możliwych zastosowań leczniczych. Wysokie zapotrzebowanie na surowiec roślinny oraz zakaz pozyskiwania ze stanowisk naturalnych ściśle chronionej arniki górskiej przyczyniły się do optymalizacji uprawy tego gatunku, poszukiwania materiału roślinnego o porównywalnych cechach jakościowych i ilościowych od innych gatunków (przede wszystkim arniki łąkowej), a także stosowania metod biotechnologicznych w roślinnych hodowlach in vitro. W tym obszarze najliczniej pojawiają się publikacje dotyczące opracowania wydajnego mikrorozmnażania arniki do upraw. Procedury biotechnologiczne w metodach otrzymywania pochodnych helenaliny z roślinnych kultur in vitro mają zarówno wartość naukowo-badawczą, jak i gospodarczą, a potencjał ten może być również objęty ochroną patentową. W niniejszym opracowaniu przedstawiamy tradycyjne zastosowania arniki górskiej w Europie w XX wieku oraz podsumowujemy dotychczasowe kierunki badań w XXI wieku, ze szczególnym uwzględnieniem wykorzystania roślinnych kultur in vitro. Poza dokumentami historycznymi, cytowane prace opisują pozyskiwanie materiału roślinnego z arniki i są to wybrane oryginalne prace badawcze oraz publikacje poglądowe dostępne w międzynarodowych bazach publikacyjnych (PubMed, ScienceDirect). Wymieniamy także rośliny innych gatunków z rodziny Asteraceae, które nazywane są potocznie „arniką” w rejonach Brazylii czy Meksyku (znane również jako: arnika brazylijska, arnika meksykańska, arnika fałszywa), i które również są przedmiotem prac badawczych z zakresu fitochemii i aktywności biologicznej.
... A number of SQLs have been reported to exhibit significant anticancer activity and many of the SQLs are currently undergoing clinical trials [8]. Helenalin is an important SQL having significant pharmacological potential, with its bioactivities ranging from antimicrobial to anticancer [9,10]. It has been reported to cause growth inhibition of cancer cells through multiple mechanisms [10]. ...
... Helenalin is an important SQL having significant pharmacological potential, with its bioactivities ranging from antimicrobial to anticancer [9,10]. It has been reported to cause growth inhibition of cancer cells through multiple mechanisms [10]. However, the anticancer effects of Helenalin have not been explored against doxorubicin-resistant leukemia cells. ...
... Owing to this, there has been increased pursuit to identify and characterize molecules that could used as lead molecules for the treatment of different types of cancers including leukemia [18]. Helenalin is an important SQL that has been reported to halt the growth of cancer cells [10] and has also been reported to induce autophagy in cancer cells [19]. In yet another study it has been reported to induce apoptosis of renal cancer cells [20]. ...
Purpose:
The main purpose of the current study was to investigate the antitumor effects of helenalin - a plant derived sesquiterpene lactone, against doxorubicin-resistant acute myeloid leukemia HL60 cells, along with evaluating its effects on apoptosis induction, mitochondrial membrane potential (MMP), cell migration and inhibition and PI3K/AKT/M-TOR signalling pathway.
Methods:
Antiproliferative effects were evaluated with CCK8 cell viability assay and colony formation assay. Cell apoptotic effects were studied by (acridine orange) AO/ethidium bromide (EB) staining assay. To further estimate the extent of apoptosis, flow cytometry using annexin V assay was used. Effects on MMP were estimated by flow cytometry, while transwell migration assay was used to study the effects on cell migration and invasion. Protein expression was estimated by western blot method.
Results:
The results showed that helenalin inhibits the growth of the HL60 cells significantly and exhibited an IC50 of 23.5 µM. In addition, it was observed that the anticancer effects of helenalin are due to induction of mitochondrial-mediated apoptosis which was also associated with enhancement of the expression of Bax and decrease in the expression of Bcl-2. Helenalin also caused loss of MMP in the doxorubicin-resistant HL-60 cells and also inhibited their migratory and invasive properties via modulation of the PI3K/AKT/M-TOR signalling pathway.
Conclusions:
In conclusion, the present study reveals that helenalin sesquiterpene lactone exhibits significant antitumor activity in doxorubicin-resistant acute myeloid leukemia HL60 cells by targeting some key pathways and as such this molecule could prove to be a potential drug candidate for future investigations.
... Typically, trichlamide is a commercial broad-spectrum fungicide containing a salicylaldehyde skeleton. 16 ⊍-Methylene-γ-butyrolactone, a five-membered lactone moiety, is widely present in numerous NPs and biologically active molecules, such as parthenolide, 17 helenalin, 18 neurolenin A, 19 and goyazensolide 20 ( Fig. 1(b)). This privileged structure has attracted much attention due to its various pharmacological activities, including anticancer, 21 anti-inflammatory, 18 antibacterial, 22 antimalarial 23 and antiviral activities. ...
... 16 ⊍-Methylene-γ-butyrolactone, a five-membered lactone moiety, is widely present in numerous NPs and biologically active molecules, such as parthenolide, 17 helenalin, 18 neurolenin A, 19 and goyazensolide 20 ( Fig. 1(b)). This privileged structure has attracted much attention due to its various pharmacological activities, including anticancer, 21 anti-inflammatory, 18 antibacterial, 22 antimalarial 23 and antiviral activities. 24 In recent years, the ⊍-methylene-γ-butyrolactone scaffold has also been introduced to investigate antimicrobial activities for the control of plant diseases. ...
BACKGROUND
Plant diseases caused by phytopathogenic fungi and oomycetes pose a serious threat to ensuring crop yield and quality. Finding novel fungicidal candidates based on natural products is one of the critical methods for developing effective and environmentally friendly pesticides. In this study, a series of salicylaldehyde derivatives containing an α‐methylene‐γ‐butyrolactone moiety were designed, synthesized, and their fungicidal activities were evaluated.
RESULTS
The bioassay studies indicated that compound C3 displayed an excellent in vitro activity against Rhizoctonia solani with a half‐maximal effective concentration (EC50) value of 0.65 μg/mL, higher than that of pyraclostrobin (EC50 = 1.44 μg/mL) and comparable to that of carbendazim (EC50 = 0.33 μg/mL). For Valsa mali and Phytophthora capsici, compound C3 also showed good fungicidal activities with EC50 values of 0.91 and 1.33 μg/mL, respectively. In addition, compound C3 exhibited promising protective in vivo activity against R. solani (84.1%) at 100 μg/mL, which was better than that of pyraclostrobin (78.4%). The pot experiment displayed that compound C3 had 74.8% protective efficacy against R. solani at 200 μg/mL, which was comparable to that of validamycin (78.2%). The antifungal mode of action research indicated that compound C3 could change the mycelial morphology and ultrastructure, increase cell membrane permeability, affect respiratory metabolism by binding to complex III, and inhibit the germination and formation of sclerotia, thereby effectively controlling the disease.
CONCLUSION
The present study provides support for the application of these salicylaldehyde derivatives as promising potential pesticides with remarkable and broad‐spectrum fungicidal activities against phytopathogenic fungi and oomycetes in crop protection. © 2023 Society of Chemical Industry.
... Helenalin is a natural sesquiterpene lactone that has been seen in the alcoholic extraction of Arnica chamissonis and Arnica Montana flowers that have anti-cancer and anti-inflammatory therapeutics effects (Figure 1) (Drogosz and Janecka, 2019;. ...
... Helenalin also has displayed an inhibitory efficacity on expression of human telomerase reverse transcriptase gene (hTERT), decreasing telomerase activity in breast cancer cells (Drogosz and Janecka, 2019;Bajaj et al., 2020). ...
Objective:
The telomerase gene is overexpressed in the majority of tumors and cancers compared to normal and healthy cells, and on the other hand, this enzymatic protein is overactive, therefore, the telomerase enzyme is considered a primary target for diagnostic and therapeutic purposes in most cancers. This has been hypothesized that Helenalin has anti-telomerase activity in a wide range of cancers and Tumor tissues. In this study, we investigated the inhibitory effect of helenalin extract on telomerase gene expression in the T47D breast cancer cell line.
Methods:
We used the MTT assay to evaluate the cytotoxic effect of different concentrations of helenalin on the T47D breast cancer cell line at 24, 48, and 72 hours. Besides, the expression of the hTERT gene in T47D cell lines treated with 1.0 and 5.0 µM helenalin after 24, 48, and 72 h incubation times was investigated through real-time PCR.
Results:
According to the MTT assay, the inhibitory effect of helenalin on T47D cell proliferation is time and dose-dependent. Moreover, the results of Real-time PCR showed that exposure of T47D cell lines to helenalin led to a significant Decreasing in the expressional values of the hTERT gene as a time and dose-dependent procedure compared with the control group (P ≤ 0.05).
Conclusion:
These preliminary results demonstrated the cytotoxic potential of helenalin through inhibition of hTERT against T47D breast cancer cells.
... Thanks to this diversity, it is an extremely interesting group that exhibits several important biological properties. Among these activities, the most frequently mentioned are cytotoxic [12][13][14], anti-inflammatory [15,16], antiplasmodial [17], antiviral [18], and antibacterial. Therefore, a wide selection of articles provides an overview of those biological properties or most often presents, in detail, the anticancer properties [4,5,9,19]. ...
... Appalasamy et al. [28] indicated that artemisinin can be an effective drug against not only Gram-negative Salmonella sp. but also Gram-positive Staphylococcus aureus, diarrhea and malaria. One of the eudesmanolide sesquiterpene lactones-blumeoidolide-A (16), isolated from the aerial parts of this plant, demonstrated limited but interesting antibacterial activity against B. subtilis ATCC 6633 and two Staphylococcus strains [34] ( Table 1). ...
The development of bacterial resistance to antibiotics and the consequent lack of effective therapy is one of the biggest problems in modern medicine. A consequence of these processes is an urgent need to continuously design and develop novel antimicrobial agents. Among the compounds showing antimicrobial potential, lactones are a group to explore. For centuries, their antimicrobial activities have been used in folk medicine. Currently, novel lactone compounds are continuously described in the literature. Some of those structures exhibit high antimicrobial potential and some are an inspiration for design and synthesis of future drugs. This paper describes recent developments on antimicrobial lactones with smaller ring sizes, up to seven membered ε-lactones. Their isolation from natural sources, chemical synthesis, synergistic activity with antibiotics, and effects on quorum sensing are presented herein.
... Even though various STLs, with helenalin among them, have been considered interesting as anti-cancer drugs or leads already in the 1970s, these compounds were later abandoned mainly because of toxicity issues (literature reviewed in [71,73,88]). However, the concentrations of HAC and GOY needed to block C/EBPβ function and thereby to inhibit transcription in the MYB assay are in the submicromolar range and we could show selectivity of this effect in comparison with an unspecific cytotoxicity [77]. ...
... Our findings on C/EBPβ inhibition by STLs are also very important with respect to the well-known anti-inflammatory activity of STLs. Helenalin and its derivatives such as HAC and various other STLs are quite well known for their anti-inflammatory activity (literature reviewed by [72,73,88]). It is quite important to note at this point that the inhibitory activity of STLs on another transcription factor, NF-B, has been known for more than 20 years and is widely associated with these anti-inflammatory properties of STLs [90][91][92]. ...
The transcription factor MYB is expressed predominantly in hematopoietic progenitor cells, where it plays an essential role in the development of most lineages of the hematopoietic system. In the myeloid lineage, MYB is known to cooperate with members of the CCAAT box/enhancer binding protein (C/EBP) family of transcription factors. MYB and C/EBPs interact with the co-activator p300 or its paralog CREB-binding protein (CBP), to form a transcriptional module involved in myeloid-specific gene expression. Recent work has demonstrated that MYB is involved in the development of human leukemia, especially in acute T-cell leukemia (T-ALL) and acute myeloid leukemia (AML). Chemical entities that inhibit the transcriptional activity of the MYB-C/EBPβ-p300 transcription module may therefore be of use as potential anti-tumour drugs. In searching for small molecule inhibitors, studies from our group over the last 10 years have identified natural products belonging to different structural classes, including various sesquiterpene lactones, a steroid lactone, quinone methide triterpenes and naphthoquinones that interfere with the activity of this transcriptional module in different ways. This review gives a comprehensive overview on the various classes of inhibitors and the inhibitory mechanisms by which they affect the MYB-C/EBPβ-p300 transcriptional module as a potential anti-tumor target. We also focus on the current knowledge on structure-activity relationships underlying these biological effects and on the potential of these compounds for further development.
... The presence of the two so-called Michael acceptors conditions to a certain extent the pharmacological activity of helenalin as the removal of either one or both moieties by means of reduction leads to a significant decrease or even complete loss of activity (Hall et al. 1980(Hall et al. , 1979Lee 1973;Lee and Furukawa 1972). Helenalin is a broad-spectrum active compound, featuring in particular anti-inflammatory, antitumor, and antiprotozoal activity (Drogosz and Janecka 2019). In vitro, it acts as a selective inhibitor of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) (Lyss et al. 1997) binding directly to Cys38 within the DNA binding domain of NF-κB subunit p65/RelA (Garcia-Pineres et al. 2001;Lyss et al. 1998). ...
... Although the pharmacological activities of helenalin have been extensively investigated (Drogosz and Janecka 2019;Lin et al. 2014;Li et al. 2019), insufficient information exists regarding its metabolism and pharmacokinetic behavior (Kriplani and Guarve 2020). Helenalin, quantified as helenalin isobutyrate, was found to penetrate in and permeate through the stratum corneum of porcine skin. ...
Sesquiterpene lactone helenalin is used as an antiphlogistic in European and Chinese folk medicine. The pharmacological activities of helenalin have been extensively investigated, yet insufficient information exists about its metabolic properties. The objectives of the present study were (1) to investigate the in vitro NADPH-dependent metabolism of helenalin (5 and 100 µM) using human and rat liver microsomes and liver cytosol, (2) to elucidate the role of human cytochrome P450 (CYP) enzymes in its oxidative metabolism, and (3) to study the inhibition of human CYPs by helenalin. Five oxidative metabolites were detected in NADPH-dependent human and rat liver microsomal incubations, while two reduced metabolites were detected only in NADPH-dependent human microsomal and cytosolic incubations. In human liver microsomes, the main oxidative metabolite was 14-hydroxyhelenalin, and in rat liver microsomes 9-hydroxyhelenalin. The overall oxidation of helenalin was several times more efficient in rat than in human liver microsomes. In humans, CYP3A4 and CYP3A5 followed by CYP2B6 were the main enzymes responsible for the hepatic metabolism of helenalin. The extrahepatic CYP2A13 oxidized helenalin most efficiently among CYP enzymes, possessing the Km value of 0.6 µM. Helenalin inhibited CYP3A4 (IC50 = 18.7 µM) and CYP3A5 (IC50 = 62.6 µM), and acted as a mechanism-based inhibitor of CYP2A13 (IC50 = 1.1 µM, KI = 6.7 µM, and kinact = 0.58 ln(%)/min). It may be concluded that the metabolism of helenalin differs between rats and humans, in the latter its oxidation is catalyzed by hepatic CYP2B6, CYP3A4, CYP3A5, and CYP3A7, and extrahepatic CYP2A13.
... In this class of natural products, the subgroup of pseudo-guaianolides (or pseudo-guaiacanes) has been less investigated than other SLs. This subgroup includes the lead compound helenalin being potently active but causing allergic reactions [5]. The subclass also includes analogues such as mexicanin I, damsin and neoambrosin [6][7][8]. ...
... Therefore, the bioactivity of SL compounds cannot be attributed to the modification of a unique target. Their mechanism of action has been qualified as being polytargeted, leading to a multidirectional activity [5]. This multimodal action confers potent anticancer activities to helenalin, but also enhances the risk of unwanted toxicity. ...
Sesquiterpene lactones (SLs) are abundant in plants and display a large spectrum of bioactivities. The compound britannin (BRT), found in different Inula species, is a pseudoguaianolide-type SL equipped with a typical and highly reactive α-methylene-γ-lactone moiety. The bioproperties of BRT and related pseudoguaianolide SLs, including helenalin, gaillardin, bigelovin and others, have been reviewed. Marked anticancer activities of BRT have been evidenced in vitro and in vivo with different tumor models. Three main mechanisms are implicated: (i) interference with the NFκB/ROS pathway, a mechanism common to many other SL monomers and dimers; (ii) blockade of the Keap1-Nrf2 pathway, with a covalent binding to a cysteine residue of Keap1 via the reactive α-methylene unit of BRT; (iii) a modulation of the c-Myc/HIF-1α signaling axis leading to a downregulation of the PD-1/PD-L1 immune checkpoint and activation of cytotoxic T lymphocytes. The non-specific reactivity of the α-methylene-γ-lactone moiety with the sulfhydryl groups of proteins is discussed. Options to reduce or abolish this reactivity have been proposed. Emphasis is placed on the capacity of BRT to modulate the tumor microenvironment and the immune-modulatory action of the natural product. The present review recapitulates the anticancer effects of BRT, some central concerns with SLs and discusses the implication of the PD1/PD-L1 checkpoint in its antitumor action.
... Helenalin has been shown to exert strong anti-inflammatory and antiprotozoal effects and to suppress the proliferation of cancer cells. The ability of helenalin to selectively target the p50/p65 transcription factor heterodimer, the most downstream proteins in the NF-κB signaling pathway, can be regarded as its most important action [18] . ...
... It decreases inflammation by preventing immune cells from functioning, especially macrophages and neutrophils [46] . Also, helenalin has been demonstrated to have potent antitumor activity and the mechanisms underlying its action are entirely unexplained [18] . ...
Arnica montana, of the family Asteraceae, is used for its anti-inflammatory and wound healing properties, especially for bruises, tissue injuries and other traumas. However, its cellular and molecular mechanisms are not yet fully known. Its main active ingredient is helenalin, a sesquiterpene lactone, known as one of the main active ingredients of Asteraceae species. The aim of this study was to investigate cell proliferation, wound healing and anti-inflammatory activity of helenalin on human keratinocyte cells treated with lipopolysaccharide stimulated human monocytic cell line. Human keratinocyte cells were treated with different helenalin concentrations (0.095-50 μM) to determine toxic and nontoxic concentrations. Then, the effects of nontoxic (0.02 and 0.2 μM) and toxic (2 μM) helenalin concentrations on human keratinocyte cell proliferation and migration were determined using the real time cell analysis system. The scratch assay was performed to determine wound healing activity and supernatants were collected to determine the effects of helenalin on cytokine levels of human keratinocyte cells under inflammatory and non-inflammatory conditions. Under inflammatory conditions, 0.02 and 0.2 μM helenalin increased keratinocyte proliferation and induced the most wound healing and anti-inflammatory activity in human keratinocyte cells. Cell proliferation and migration, wound healing and anti-inflammatory effects were higher in cells exposed to 0.02 μM helenalin than 0.2 μM. Helenalin has been found to decrease the production of inflammatory cytokines, especially under inflammatory conditions and increase wound closure by increasing cell proliferation and migration.
... In summary, of the 63 compounds identified, the predominant groups were phenolic compounds, including terpenoids and flavonoids, likely associated with observed biological activity. For instance, as previously reported, sesquiterpene lactones, such as helenalin and its derivatives, might be responsible for the observed cytotoxicity (Heilmann et al. 2001;Drogosz and Janecka 2019). On the other hand, some flavonoids and terpenes can be accountable for attenuated virulence, as previously reported for Klebsiella pneumoniae (Adeosun et al. 2022). ...
Abstract
The rise of antibiotic-resistant bacterial strains represents an important challenge for global health, underscoring the critical need for innovative strategies to confront this threat. Natural products and their derivatives have emerged as a promising reservoir for drug discovery. The social amoeba Dictyostelium discoideum is a potent model organism in this effort. Employing this invertebrate model, we introduce a novel perspective to investigate natural plant extracts in search of molecules with potential antivirulence activity. Our work established an easy-scalable developmental assay targeting a virulent strain of Klebsiella pneumoniae, with Helenium aromaticum as the representative plant. The main objective was to identify tentative compounds from the Helenium aromaticum extract that attenuate the virulence of K. pneumoniae virulence without inducing cytotoxic effects on amoeba cells. Notably, the methanolic root extract of H. aromaticum fulfilled these prerequisites compared to the dichloromethane extract. Using UHPLC Q/Orbitrap/ESI/MS/MS, 63 compounds were tentatively identified in both extracts, 47 in the methanolic and 29 in the dichloromethane, with 13 compounds in common. This research underscores the potential of employing D. discoideum-assisted pharmacognosy to discover new antivirulence agents against multidrug-resistant pathogens.
... For instance, sesquiterpene lactones, such as helenalin and its derivatives, might be responsible for the observed cytotoxicity, as previously reported 18,19 . On the other hand, some flavonoids and terpenes can be accountable for attenuated virulence, as previously reported for Klebsiella pneumoniae 20 . ...
The rise of antibiotic-resistant bacterial strains poses a significant global health challenge, underscoring the critical need for innovative strategies to address this threat. Natural products and their derivatives have emerged as a promising reservoir for drug discovery. The social amoeba Dictyostelium discoideum is an advantageous model organism in this effort. Using this invertebrate model, we introduce a novel perspective to screen natural plant extracts for molecules with potential antivirulence activity. As a proof of concept, we established a simple high-throughput assay to screen for antivirulence molecules targeting Klebsiella pneumoniae among extracts of Helenium aromaticum . Thus, we aimed to identify compounds attenuating K. pneumoniae virulence without inducing cytotoxic effects on amoeba cells. Notably, the methanolic root extract of H. aromaticum but not other extracts fulfilled these prerequisites. Further analysis via UHPLC-ESI-MS/MS led to the identification of 24 chemical compounds boasting potential antivirulence attributes. This research underscores the potential of employing D. discoideum -assisted pharmacognosy for unearthing novel antivirulence agents against multidrug-resistant pathogens.
Table of Content Graphic
... H also has antitelomerase activity in a variety of cancers and tumor tissues; it shows a cytotoxic effect in the T47D breast cancer line and decreases the expressional values of the hTERT gene in a dose-dependent manner [52]. H promotes apoptosis by the release of cytochrome c from mitochondria and arrests the G2/M-phase of the cell cycle [53]. Potential applications of H and DH are reserved in over 100 patents related to medical and cosmetic uses, from shampoos and wound healing accelerators, substances eliminating the effects of bites, to specifics for capillary skin. ...
Arnica montana is a valuable plant with high demand on the pharmaceutical and cosmetic market due to the presence of helenalin (H) and 11α, 13-dihydrohelenalin (DH) sesquiterpene lactones (SLs), with many applications and anti-inflammatory, anti-tumor, analgesic and other properties. Despite the great importance of these compounds for the protection of the plant and their medicinal value, the content of these lactones and the profile of the compounds present within individual elements of florets and flower heads have not been studied so far, and attempts to localize these compounds in flower tissues have also not been conducted. The three studied Arnica taxa synthesize SLs only in the aerial parts of plants, and the highest content of these substances was found in A. montana cv. Arbo; it was lower in wild species, and a very small amount of H was produced by A. chamissonis. Analysis of dissected fragments of whole inflorescences revealed a specific distribution pattern of these compounds. The lactones content in single florets increased from the top of the corolla to the ovary, with the pappus calyx being a significant source of their production. Histochemical tests for terpenes and methylene ketones indicated the colocalization of lactones with inulin vacuoles.
... The activity of many plants used in traditional folk medicine is related to the presence of this group of compounds [6][7][8]. This is because lactones exhibit several valuable biological properties, such as cytotoxic [9,10], antibacterial [11,12], antifeedant [13,14] and anti-inflammatory [15,16]. However, biologically active compounds are found in natural sources in small amounts and in mixtures composed of substances of similar structure, making their isolation and separation difficult. ...
The microbial transformations of lactones with a halogenoethylocyclohexane moiety were performed in a filamentous fungi culture. The selected, effective biocatalyst for this process was the Absidia glauca AM177 strain. The lactones were transformed into the hydroxy derivative, regardless of the type of halogen atom in the substrate structure. For all lactones, the antiproliferative activity was determined toward several cancer cell lines. The antiproliferative potential of halolactones was much broader than that observed for the hydroxyderivative. According to the presented results, the most potent was chlorolactone, which exhibited significant activity toward the T-cell lymphoma line (CL-1) cell line. The hydroxyderivative obtained through biotransformation was not previously described in the literature.
... Helenalin (Figure 3), a sesquiterpene lactone found in the flowers of wolf's bane (Arnica montana) and Chamisso arnica (Arnica chamissonis), has been shown to have antiinflammatory, immunomodulatory, and anticancer activities [210,211]. Although it has been used for many years as a treatment for minor injuries in folk medicine, its ability to cause allergic reactions poses a challenge for its use as an anticancer drug [212]. Helenalin was investigated for its anticancer effects on human RCC Caki cells. ...
Renal cell carcinoma (RCC) is associated with about 90% of renal malignancies, and its incidence is increasing globally. Plant-derived compounds have gained significant attention in the scientific community for their preventative and therapeutic effects on cancer. To evaluate the anticancer potential of phytocompounds for RCC, we compiled a comprehensive and systematic review of the available literature. Our work was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria. The literature search was performed using scholarly databases such as PubMed, Scopus, and ScienceDirect and keywords such as renal cell carcinoma, phytochemicals, cancer, tumor, proliferation, apoptosis, prevention, treatment, in vitro, in vivo, and clinical studies. Based on in vitro results, various phytochemicals, such as phenolics, terpenoids, alkaloids, and sulfur-containing compounds, suppressed cell viability, proliferation and growth, showed cytotoxic activity, inhibited invasion and migration, and enhanced the efficacy of chemotherapeutic drugs in RCC. In various animal tumor models, phytochemicals suppressed renal tumor growth, reduced tumor size, and hindered angiogenesis and metastasis. The relevant antineoplastic mechanisms involved upregulation of caspases, reduction in cyclin activity, induction of cell cycle arrest and apoptosis via modulation of a plethora of cell signaling pathways. Clinical studies demonstrated a reduced risk for the development of kidney cancer and enhancement of the efficacy of chemotherapeutic drugs. Both preclinical and clinical studies displayed significant promise of utilizing phytochemicals for the prevention and treatment of RCC. Further research, confirming the mechanisms and regulatory pathways, along with randomized controlled trials, are needed to establish the use of phytochemicals in clinical practice.
... The anticancer activity of various components of A. montana has been investigated thoroughly, particularly sesquiterpene lactones, the main active compound of the plant (Lee et al., 1972;Lyß et al., 1998;Willuhn, 1998;Douglas et al., 2004;Huang P.-R. et al., 2005;Ghantous et al., 2010;Chaturvedi, 2011;Lim et al., 2012;Chadwick et al., 2013;Jakobs et al., 2016;Drogosz and Janecka, 2019;Kriplani and Guarve, 2020). The essential oils of the plant have been shown to possess cytotoxic activity on cells of anaplastic astrocytoma and glioblastoma multiforme (Sugier et al., 2019(Sugier et al., , 2020, while ethanol extracts of the plant also inhibited melanogenesis (Usui et al., 2015). ...
Arnica montana L. flower heads are known for their antioxidant, antimicrobial, and anticancer activity. The aim of this work was to optimize the process of supercritical CO2 extraction, to achieve high extraction yield and high content of biologically active components, and to confirm the antimicrobial and anticancer activity of the extract. The influence of pressure and temperature on the total phenolic content, antioxidant activity, and proanthocyanidin content was evaluated. The pressure and temperature were found to be interdependent. A temperature of 60°C and a pressure of 30 MPa resulted in a high extraction yield, antioxidant activity and phenolic content. The content of proanthocyanidins was highest at a pressure between 18 and 24 MPa. The extracts inhibited three different microorganisms successfully; Staphylococcus aureus, Escherichia coli and Candida albicans, at concentrations ranging from 0.1 to 5.16 mg/ml and showed anticancer activity decrease up to 85% at a concentration of 0.5 mg/ml.
... C00003211 (Helenalin Acetate) found in plant Balduina angustifolia has anti-in ammatory and anti-cancer activities. Helenalin Acetate reduces the phospholipase A2 activity and inhibits human neutrophil migration, chemotaxis, and platelet aggregation40,41 . The inhibitory effect of helenalin on the biosynthesis of leukotrienes promotes ...
Sequences of different spike proteins of COVID-19 are collected and classified by constructing a sequence similarity graph and applying clustering algorithms. Binding affinity of small molecules to those spike proteins is searched by assessing the similarity between spike proteins and different human protein sequences. Selected binding molecules are then compared with natural products mainly plant secondary metabolites based on Tanimoto similarity measure. A tripartite graph is created among spike proteins, binding molecules, and secondary metabolites and a scoring scheme is proposed to measure the strength of a tripartite relation in such a graph. Based on this tripartite graph and scoring scheme, some natural compounds are selected which are likely to be effective against COVID-19. The medicinal and biological activities of the selected compounds are discussed depicting their likelihood to be covid drugs based on scientific literatures.
... It is endemic to Europe with predominant distribution in mountainous areas from South-Norway, Latvia in the Baltic region to South-Portugal, the northern Apennines in Italy and the southern Carpathians in Romania (Kahmen and Poschlod, 2000;Luijten et al., 2000;Falniowski et al., 2011;Maurice et al., 2012;Hollmann et al., 2020). For centuries A. montana has been a well-known, commercial medicinal plant used for various diseases such as arthritis, rheumatic disorders, inflammation and blunt injuries (Klaas et al., 2002;ESCOP, 2003;Drogosz and Janecka, 2019). The therapeutic value of A. montana is attributed to secondary metabolites (Dall'Acqua et al., 2011;Kowalski et al., 2015;Sugier et al., 2017). ...
Arnica montana L. (AM, Asteraceae) is a perennial, herbaceous vascular plant species of commercial importance. The flower heads’ pharmacological properties are attributed mainly to sesquiterpene lactones (SLs), with phenolic acids and flavonoids also considered of relevance. The botanical drug is still partly collected in different European mountain regions. The SL content can be influenced by genetic factors and environmental conditions (altitude, temperature and rainfall). Surprisingly, the influence of the soil on SL-content have rarely been investigated. However, the soil determines the occurrence, distribution and overall fitness of AM. Equally, environmental factors are crucial determinants for the biosynthesis and fluctuations in plant secondary metabolites. Therefore, different abiotic (pH, C/N ratio, base saturation, cation exchange capacity) and biotic (species richness, vegetation cover) parameters need to be assessed as potential drivers of the variable content of AM’s secondary metabolites. Consequently, we developed an in situ experimental design aiming to cover a wide range of soil pH conditions. We detected and investigated different AM populations growing in grassland on acidic soils, on siliceous as well as calcareous geologies within the same geographical region and altitudinal belt. The total SL content and most single SL contents of the AM flower heads differed significantly between the two geologies. AM flower heads of plants growing on loam on limestone showed a significant higher total SL content than the flower heads of plants growing in siliceous grasslands. Furthermore, the SL contents were significantly correlated with geobotanical species richness and vegetation cover pointing toward an effect of species interactions on the production of SLs. Moreover, the ratios of the main SLs helenalin to dihydrohelenalin esters were significantly correlated to environmental parameters indicating that SL composition might be a function of habitat conditions. The findings of this study shed light upon the often ignored, complex interactions between environmental conditions and plant secondary metabolites. We highlight the importance of both abiotic and biotic habitat parameters for SLs in AM.
... We found that ROS levels in RMS cells increased after helenalin treatment in a dose-dependent manner, indicating that helenalin could sabotage the antioxidant enzyme system in RMS cells. Oxidative stress triggered by helenalin was also reported in previous studies [8,58]. NAC, which is a known ROS scavenger, antagonised the helenalin-induced ROS generation in both RD and RH30 cells and consequently reduced ROS levels. ...
Rhabdomyosarcoma (RMS) is the most frequent soft tissue sarcoma in paediatric patients. Relapsed or refractory RMS shows very low 5-year survival rates, which urgently necessitates new chemotherapy agents. Herein, the sesquiterpene lactone, helenalin, was investigated as a new potential therapeutic agent against the embryonal RMS (eRMS) and alveolar RMS (aRMS) cells. We have evaluated in vitro antiproliferative efficacy of helenalin on RMS cells by the MTT and wound healing assay, and estimated several cell death pathways by flow cytometry, confocal microscopy and immunoblotting. It was shown that helenalin was able to increase reactive oxygen species levels, decrease mitochondrial membrane potential, trigger endoplasmic reticulum stress and deactivate the NF-𝛋B pathway. Confirmation was obtained through the use of antagonistic compounds which alleviated the effects of helenalin in the corresponding pathways. Our findings demonstrate that oxidative stress is the pivotal mechanism of action of helenalin in promoting RMS cell death in vitro.
... Similarly, the biosynthesis of alantolactone (Fig. 3) in Inula helenium requires investigation as multiple studies proved its effectiveness in cancer treatment [Babaei et al. 2021]. Helenalin (Fig. 3) and 11,13-dihydrohelenalin, the major active substances of the extracts prepared from Arnica montana, a very old medicinal plant, are known to demonstrate anti-inflammatory and antibacterial properties [Drogosz and Janecka 2019]. Nevertheless, their biosynthesis is still poorly understood. ...
Asteraceae family is a rich source of many sesquiterpene lactones (STLs). These secondary metabolites exhibit multidirectional activity including anti-tumor, anti-inflammatory or antimicrobial, just to name a few. Promising approach of metabolic engineering offers a way of increasing the production of STLs by reconstruction of their biosynthetic pathway in a heterologous system. Moreover, their production in host plants might be increased through overexpression of biosynthetic genes and/or transcription factors (TFs) positively regulating the pathway. Either of the strategies requires extensive knowledge on the genetic background of STLs biosynthesis pathway. This review summarizes molecular investigations concerning biosynthesis of these medicinally essential metabolites.
... Sesquiterpene lactones constitute a major class of phytochemicals in many medicinal plants from the Asteraceae family. They seem to be important contributors to the Asteraceae species' broad bioactivity spectrum, including antimicrobial and antiviral antidiabetic, antimalarial, antiproliferative, and antiparasitic activities (Ren et al., 2016;Adekenov, 2019;Drogosz and Janecka, 2019;Cheong et al., 2020). Sesquiterpene lactones modulate many processes that influence multiple targets of inflammatory reactions, for example, oxidative phosphorylation in neutrophils, chemotaxis and migration of lymphocyte, as well as the secretion of histamine, serotonin and proinflammatory cytokines (Koch et al., 2001;Merfort, 2011 Rayan et al., 2011;Mathema et al., 2012;Chadwick et al., 2013;Shi et al., 2013;Acevedo et al., 2017;Kim and Choi, 2019;Coricello et al., 2020). ...
Plant-derived substances have been shown to affect potential targets in inflammatory diseases. We have previously purified from the desert plant Achillea fragrantissima , a sesquiterpene lactone named achillolide A, and demonstrated its anti-inflammatory activities in cultured brain macrophages named microglial cells. In the present study, we further investigated achillolide A in alleviating atopic dermatitis, a chronic and recurring inflammatory skin disease. We investigated achillolide A for its in vivo anti-inflammatory activity using the oxazolone model of atopic dermatitis in mice, in which oxazolone induces ear swelling. Our results show that mice treated with achillolide A showed a significant decrease in the oxazolone-induced ear swelling. Since macrophages are inflammatory cells that play a pivotal role in the pathogenesis of atopic dermatitis, the anti-inflammatory effects of achillolide A were also studied in spleen cells. We demonstrated that achillolide A reduced the levels of LPS-induced inflammatory cytokines IL-2, IL-6, TNFα, IFNγ and IL-12 that were secreted from cultured splenocytes. These data suggest that achillolide A should be considered for further research in treating atopic dermatitis.
... Especially, some derivatives such as 3-methyl piperidine derivative (1) has stronger cytotoxicity and higher safety index than COS. Actually, due to toxicity and a tendency to cause allergic dermatitis for patients with Asteraceae sensitization [118,119], many SLs have not always been considered favorably as potential anticancer agents, although there are several compounds have been evaluated in clinical trials [120]. But according to relevant researches about COS and DEH, we think that COS, DEH and their derivatives maybe become the promising anticancer drugs by structural modification or chemosynthesis. ...
Costunolide (COS) and dehydrocostus lactone (DEH) are two natural sesquiterpene lactones with potential antitcancer activity against a range of cancer cell types both in vitro and in vivo, particularly for breast cancer and leukemia. There are many researches that have been taken to characterize these pathways and to reveal their anticancer mechanisms of action of COS and DEH. However, while there is a great deal of evidence detailing the effects of COS and DEH on considerable signaling pathways and cellular functions, a global view of their mechanism of action remains elusive. This review systematically summarizes the antitumor activity and mechanism of COS and DEH in the recent reports, and discusses the effect of the key active part (α-methylene-γ-butyrolactone) of COS and DEH against cancer. Moreover, we also discuss the antineoplastic activity of COS and DEH derivatives to improve the cytotoxicity and safety index. We believe this review can provide a systemic reference to develop COS and DEH as anticancer agents.
Traditional Chinese Medicine (TCM), as a unique medical model in China, has been shown to be effective in the treatment of many diseases. It has been proven that TCM can increase the pain threshold, increase the level of endorphins and enkephalins in the body, and reduce the body's response to adverse stimuli. In recent years, TCM scholars have made valuable explorations in the field of pain treatment, using methods such as internal and external application of TCM and acupuncture to carry out research on pain treatment and have achieved more satisfactory results. TCM treats pain in a variety of ways, and with the discovery of a variety of potential bioactive substances for pain treatment. With the new progress in the research of other TCM treatment methods for pain, TCM will have greater potential in the clinical application of pain.
Cancer represents a complex disease category defined by the unregulated proliferation and dissemination of anomalous cells within the human body. According to the GLOBOCAN 2020 report, the year 2020 witnessed the diagnosis of approximately 19.3 million new cases of cancer and 10.0 million individuals succumbed to the disease. A typical cell eventually becomes cancerous because of a long-term buildup of genetic instability and replicative immortality. Telomerase is a crucial regulator of cancer progression as it induces replicative immortality. In cancer cells, telomerase inhibits apoptosis by elongating the length of the telomeric region, which usually protects the genome from shortening. Many nanoparticles are documented as being available for detecting the presence of telomerase, and many were used as delivery systems to transport drugs. Furthermore, telomere homeostasis is regulated by the circadian time-keeping machinery, leading to 24-hour rhythms in telomerase activity and TERT mRNA expression in mammals. This review provides a comprehensive discussion of various kinds of nanoparticles used in telomerase detection, inhibition, and multiple drug-related pathways, as well as enlightens an imperative association between circadian rhythm and telomerase activity from the perspective of nanoparticle-based anticancer therapeutics.
This systematic review identified various bioactive compounds which have the potential to serve as novel drugs or leads against acute myeloid leukemia. Acute myeloid leukemia is a heterogeneous hematopoietic malignancy that arises from the dysregulation of cell differentiation, proliferation, and cell death. The risk factors associated with the onset of AML include long-term exposure to radiations and chemicals such as benzene, smoking, genetic disorders, blood disorders, advancement in age and others. Although novel strategies to manage AML, including a refinement of the conventional chemotherapy regimens, hypomethylating agents and molecular targeted drugs, have been developed in recent years, resistance and relapse remain the main clinical problems. In this study, three databases, PubMed/MEDLINE, ScienceDirect and Google Scholar were systematically searched to identify various bioactive compounds with antileukemic properties. A total of 518 articles were identified out of which 59 were viewed as eligible for the current report. From the data extracted, over 60 bioactive compounds were identified and divided into 5 major groups: flavonoids, alkaloids, organosulfur compounds, terpenes and terpenoids, and other known and emerging bioactive compounds. The mechanism of actions of the analyzed individual bioactive molecules differ remarkably and include disrupting chromatin structure, upregulating the synthesis of certain DNA repair proteins, inducing cell cycle arrest and apoptosis, and inhibiting/regulating Hsp90 activities, DNA-methyltransferase 1 and histone deacetylase 1.
Organocatalytic asymmetric Michael additions of aldehydes to 2-furanones are successfully conducted. This study provides an efficient approach to produce highly functionalized chiral γ-lactones with three consecutive stereogenic carbons accompanied with...
Castor (Ricinus communis; family: Euphorbiaceae) oil extracted from castor seed is a nonedible, nontoxic, yellowish color liquid that has become an essential bioresource material for industrial uses. The castor oil is rich in ricinoleic acid; this is a key precursor of the production of lactones. The presence of a double bond and hydroxyl and carboxylic groups with a long hydrocarbon chain in ricinoleic acid proposes several possibilities for converting it into valuable compounds. γ-Decalactone is an aroma compound having peach-like essence, generally utilized in food industries. Lipase-mediated biotransformation is used to produce γ-decalactone from ricinoleic acid under controlled conditions. Several studies and industrial approaches have explained the genetic and metabolic engineering and bioprocess engineering strategies in the enrichment of aroma compounds, but few studies have been available on the utilization of castor oil as a natural raw material for the synthesis of aroma compounds. As a result, this review draws attention to the importance of castor oil in the production of value-added aroma compounds with their estimated global market prospective. The review gives information about the properties of castor oil and its geographical accessibility and its exploitation as a bio-based resource for the production of various value-added materials. In addition, this review emphasizes the utilization of ricinoleic acid or castor oil as a renewable source for the production of aroma compounds. Though chemical transformation for the production of lactone derivatives is known, the products are chiral mixtures. On the other hand, the lipase-based conversion is enantiospecific, and this product is categorized as nature-identical and considered safe for using in food products.KeywordsCastor oilFlavourFragranceLipase medicated biotransformation
Objective:
An important factor in the aging of the face is a reduction in the volume of adipose tissue. This reduction in adipose tissue contributes to decreased skin elasticity, which is also part of the aging process. Overall, these lead to wrinkle formation. Fat injection is a common means of addressing this issue and is used to reduce the effects of aging on the face and to increase the fullness of the lips and breasts. However, fat injection is an invasive surgical procedure. This study aimed to discover novel cosmetic ingredients that increase the volume of subcutaneous (pre)adipocytes to create the appearance of more youthful skin.
Methods:
We focused on the number of subcutaneous preadipocytes and the accumulation of lipid droplets. To discover natural ingredients that increase both of these, extracts of 380 natural products were prepared and screened for their effects on both growth and differentiation (i.e., lipid droplet accumulation) of human subcutaneous preadipocytes. One extract was found to have the desired effects, and this was further studied to determine the active compounds. We then evaluated its efficacy in a human clinical study.
Results:
We found that Arnica montana L. flower extract (AFE) accelerates both the growth and differentiation of human subcutaneous preadipocytes. AFE was found to significantly increase the volume of adipocyte spheroids. The active compounds 6-O-methacryloylhelenalin and 6-O-isobutyrylhelenalin were found to be responsible for the effects of AFE on preadipocytes. In a human clinical study, gels containing 1% AFE successfully enhanced the volume of the lips and face with reduction of wrinkles with no adverse reactions.
Conclusion:
This is the first report to demonstrate that AFE and the included compounds, 6-O-methacryloylhelenalin and 6-O-isobutyrylhelenalin, act on preadipocytes. AFE would be ideal for use in products that plump the face to reduce wrinkles and create a more youthful appearance.
Background
Centipeda minima (L.) A. Braun & Asch (C. minima) has been used as a traditional Chinese herbal medicine to treat multiple diseases, including sinusitis, rhinitis, headache, and allergy. To date, the anticancer properties of C. minima have drawn considerable attention owing to the anticancer potential of C. minima extracts, the identification of active components, and the elucidation of underlying molecular mechanisms. However, the anticancer properties and significance of active components in C. minima have rarely been summarized.
Purpose
This review presents a comprehensive summary of the anticancer properties exhibited by active components of C. minima.
Methods
An extensive search for published articles on the anticancer activities and active components of C. minima was performed using Web of Science, PubMed, Science Direct, and Google Scholar.
Results
C. minima extracts exhibited both anticancer and chemosensitizing effects. Phytochemical studies have identified the active anticancer components of C. minima extracts. Sesquiterpene lactones, such as 6-O-angeloylplenolin (6-OAP, or brevilin A) and arnicolide D, have similar structures and anticancer mechanisms. As the most abundant sesquiterpene lactone in C. minima, 6-OAP exhibits anticancer activities mainly by targeting Skp1-Cullin1-F-box protein (SCF) E3 ubiquitin ligase and signal transducers and activators of transcription 3 (STAT3). Clinical trials have assessed the potential of 6-OAP in patients with vertex balding and alopecia areata, given its effect on JAK-STATs signaling. Chlorogenic acid, a representative organic acid in C. minima, reportedly possesses anticancer potential and inhibits tumor growth by affecting tumor microenvironment and has been approved for phase II clinical trials in patients with glioma in China.
Conclusion
In the present review, we highlight intriguing anticancer properties mediated by active compounds isolated from C. minima extracts, particularly sesquiterpene lactones, which might provide clues for developing novel anticancer drugs. Relevant clinical trials on chlorogenic acid and 6-OAP can promote anticancer clinical applications. Therefore, it is worth comprehensively elucidating underlying anticancer mechanisms and conducting clinical trials on C. minima and its active components.
The enantiomeric pure and natural (+)-Lactones (C ≤ 14) with aromas obtained from fruits and milk are considered flavoring compounds. The flavoring value is related to the lactones' ring size and chain length, which blend in varying concentrations to produce different stone-fruit flavors. The nature-identical and enantiomeric pure (+)-lactones are only produced through whole-cell biotransformation of yeast. The industrially important γ-decalactone and δ-decalactone are produced by a four-step aerobic-oxidation of ricinoleic acid (RA) following the lactonization mechanism. Recently, metabolic engineering strategies have opened up new possibilities for increasing productivity. Another strategy for increasing yield is to immobilize the RA and remove lactones from the broth regularly. Besides flavor impact, γ-, δ-, ε-, ω-lactones of the carbon chain (C8-C12), the macro-lactones and their derivatives are vital in pharmaceuticals and healthcare. These analogues are isolated from natural sources or commercially produced via biotransformation and chemical synthesis processes for medicinal use or as active pharmaceutical ingredients. The various approaches to biotransformation have been discussed in this review to generate more prospects from a commercial point of view. Finally, this work will be regarded as a magical brick capable of containing both traditional and genetic engineering technology while contributing to a wide range of commercial applications.
This review summarizes the current knowledge on lactones, a class of biologically active natural products isolated from a wide range of living organisms. Butenolide, 5,6-dihydropyran-2-one, and sesquiterpene lactones display an impressive variety of bioactivities and are the most abundant in nature. This paper provides a compilation of ring construction strategies for the synthesis of small, medium, and macrolactones and discusses their biological activities and industrial, pharmaceutical, and agrochemical applications.
Introduction
Nuclear magnetic resonance (NMR) measurement of ¹J CC coupling by two‐dimensional (2D) INADEQUATE (incredible natural abundance double quantum transfer experiment), which is a special case of double‐quantum (DQ) spectroscopy that offers unambiguous determination of ¹³C–¹³C spin–spin connectivities through the DQ transitions of the spin system, is especially suited to solving structures rich in quaternary carbons and poor in hydrogen content (Crews rule).
Objective
To review published literature on the application of NMR methods to determine structure in the liquid‐state, which specifically considers the interaction of a pair of carbon‐13 (¹³C) nuclei adjacent to one another, to allow direct tracing out of contiguous carbon connectivity using 2D INADEQUATE.
Methodology
A comprehensive literature search was implemented with various databases: Web of Knowledge, PubMed and SciFinder, and other relevant published materials including published monographs. The keywords used, in various combinations, with INADEQUATE being present in all combinations, in the search were 2D NMR, ¹J CC coupling, natural product, structure elucidation, ¹³C–¹³C connectivity, cryoprobe and CASE (computer‐assisted structure elucidation)/PANACEA (protons and nitrogen and carbon et alia ).
Results
The 2D INADEQUATE continues to solve “intractable” problems in natural product chemistry, and using milligram quantities with cryoprobe techniques combined with CASE/PANACEA experiments can increase machine time efficiency. The ¹³C–¹³C‐based structural elucidation by dissolution single‐scan dynamic nuclear polarisation NMR can overcome disadvantages of ¹³C insensitivity at natural abundance. Selected examples have demonstrated the trajectory of INADEQUATE spectroscopy from structural determination to clarification of metabolomics analysis and use of DFT (density functional theory) and coupling constants to clarify the connectivity, hybridisation and stereochemistry within natural products.
Conclusions
Somewhat neglected over the years because of perceived lack of sensitivity, the 2D INADEQUATE NMR technique has re‐emerged as a useful tool for solving natural products structures, which are rich in quaternary carbons and poor in hydrogen content.
Background
Arnica montana containing helenalin as its principal active constituent, is the most widely used plant to treat various ailments. Recent studies indicate that Arnica and helenalin provides significant health benefits, including anti-inflammatory, neuroprotective, antioxidant, cholesterol-lowering, immunomodulatory and most important, anticancer properties.
Objective
The objective of the present revie w is to overview the recent patents of Arnica and its principal constituent helenalin, including new methods of isolation, and their use in the prevention of cancer and other ailments.
Methods
Current prose and patents emphasizing the anticancer potential of helenalin and Arnica, incorporated as anti-inflammary agent in anticancer preparations have been identified and reviewed with particular emphasis on their scientific impact and novelty.
Results
Helenalin has shown its anticancer potential to treat multiple types of tumors, both in vitro and in vivo. It has also portrayed synergistic effects when given in combination with other anticancer drugs or natural compounds. New purification/isolation techniques are also developing with novel helenalin formulations and its synthetic derivatives have been developed to increase its solubility and bioavailability.
Conclusion
The promising anticancer potential of helenalin in various preclinical studies may open new avenues for therapeutic interventions in different tumors. Thus clinical trials validating its tumor suppressing and chemopreventive activities particularly in conjunction with standard therapies, are immediately required.
Objective
Helenalin is a natural anti-inflammatory agent that is proving its efficacy to treat various medical conditions. The objective of the review is to summarize various mechanisms of helenalin to treat inflammatory disorders and cancers, adverse effects and avenues of further research.
Key Findings
Helenalin is found to cure chronic conditions like rheumatoid arthritis, ulcers and malignancies like stomach, colon, breast, larynx, lung and skin cancers via various mechanisms.
Conclusion
This review article will help us to systemically analyze the wealth of information concerning the medicinal properties of helenalin and to recognize the gaps which have vetoed its pervasive application in the medical community.
The increase in the application of herbal medicines and dietary products over the last decades has been accompanied with a substantial increase in case reports of herb-induced toxicities. Metabolic activation of relatively inert functional groups to chemically reactive metabolites is often considered to be an obligatory event in the etiology of drug-induced adverse reactions. Circumstantial evidence suggests that several herb-induced toxicities are a result of transformation of herbal constituents to electrophilic reactive metabolites that can covalently bind to vital macromolecules in the body, exemplified by aristolochic acids and pyrrolizidine alkaloids. At physiologically relevant concentrations, bioactivation of furanocoumarins and methylenedioxyphenyl compounds leads to mechanism-based inactivation of drug metabolizing enzymes and clinically manifested herb-drug interactions. Of particular interest is that several organic functional groups embedded in herbal constituents act as a toxicophore as well as a pharmacophore, resembling the electrophilic warheads in the development of targeted covalent inhibitors. The aim of this review is to provide a cataloging of bioactivation mechanisms of herbal substructures, structure-activity relationships, biological targets, and assist in circumventing the structural liability in the development of more effective and safer herb-based NCEs.
The highly efficient addition of phosphorus and carbon pronucleophiles to α-methylene-γ-butyrolactones (tulipalin A and arglabin) under n-Bu3P catalysis is reported. Kinetic experiments indicate that the unprecedentedly high reactivity of α-methylene-γ-butyrolactones results from the rigid s-cis geometry of the 1-oxa-1,3-butadiene moiety that favors generation of zwitterionic intermediate stabilized by interaction between the phosphonium center and adjacent carbonyl oxygen. The presented strategy offers an economical and practical method for functionalization of natural biologically active α-methylene-γ-butyrolactones with high levels of chemo- and stereoselectivity.
A series of group VIII carbamoyl complexes, [M(2-NHC(O)C 5 H 4 N)(CO) 2 (2-SC 5 H 4 N)] [where M = Fe, Ru and Os], was found to be efficient and regioselective catalysts for the intramolecular hydroxycarboxylation of α,ω-alkynoic acids, yielding exocyclic enol lactones for ring sizes up to 7 atoms, and endocyclic enol lactones for ring sizes up to 12 atoms. They also catalysed the regioselective intermolecular hydroxycarboxylation reaction between propargylic alcohol and carboxylic acids to form β-oxo-esters. These complexes could also function as electrocatalysts in proton reduction, and evaluation of their redox potentials revealed that the iron complex was much more efficient than the ruthenium or osmium analogues.
Plants are a significant reservoir of cytotoxic agents, including compounds with the ability to interfere with multidrug-resistant (MDR) cells. With the aim of finding promising candidates for chemotherapy, 91 native and naturalized plants collected from the central region of Argentina were screened for their cytotoxic effect toward sensitive and MDR P-glycoprotein (P-gp) overexpressing human leukemia cells by means of MTT assays. The ethanol extracts obtained from Aldama tucumanensis , Ambrosia elatior , Baccharis artemisioides , Baccharis coridifolia , Dimerostemma aspilioides , Gaillardia megapotamica , and Vernonanthura nudiflora presented outstanding antiproliferative activity at 50 μ g/mL, with inhibitory values from 93 to 100%, when tested on the acute lymphoblastic leukemia (ALL) cell line CCRF-CEM and the resistant derivative CEM-ADR5000, while 70–90% inhibition was observed against the chronic myelogenous leukemia (CML) cell K562 and its corresponding resistant subline, Lucena 1. Subsequent investigation showed these extracts to possess marked cytotoxicity with IC 50 values ranging from 0.37 to 29.44 μ g/mL, with most of them being below 7 μ g/mL and with ALL cells, including the drug-resistant phenotype, being the most affected. G. megapotamica extract found to be one of the most effective and bioguided fractionation yielded helenalin (1) . The sesquiterpene lactone displayed IC 50 values of 0.63, 0.19, 0.74, and 0.16 μ g/mL against K562, CCRF-CEM, Lucena 1, and CEM/ADR5000, respectively. These results support the potential of these extracts as a source of compounds for treating sensitive and multidrug-resistant leukemia cells and support compound 1 as a lead for developing effective anticancer agents.
Leishmaniases are neglected infectious diseases caused by parasites of the ‘protozoan’ genus Leishmania. Depending on the parasite species, different clinical forms are known as cutaneous, muco-cutaneous, and the visceral leishmaniasis (VL). VL is particularly fatal and the therapy presents limitations. In the search for new anti-leishmanial hit compounds, seven natural sesquiterpene lactones were evaluated against promastigotes and intracellular amastigotes of Leishmania (Leishmania) infantum, a pathogen causing VL. The pseudoguaianolides mexicanin I and helenalin acetate demonstrated the highest selectivity and potency against intracellular amastigotes. In addition, promastigotes treated with helenalin acetate were subject to an ultrastructural and biochemical investigation. The lethal action of the compound was investigated by fluorescence-activated cell sorting and related techniques to detect alterations in reactive oxygen species (ROS) content, plasma membrane permeability, and mitochondrial membrane potential. Helenalin acetate significantly reduced the mitochondrial membrane potential and the mitochondrial structural damage was also confirmed by transmission electron microscopy, displaying an intense organelle swelling. No alteration of plasma membrane permeability or ROS content could be detected. Additionally, helenalin acetate significantly increased the production of nitric oxide in peritoneal macrophages, probably potentiating the activity against the intracellular amastigotes. Helenalin acetate could hence be a useful anti-leishmanial scaffold for further optimization studies.
Arnica montana has been widely used as a homeopathic remedy for the treatment of several inflammatory conditions in pain management and postoperative settings. This review gives an overview of the therapeutic use of Arnica montana in the above-mentioned fields also focusing on its mechanisms of action learned from animal models and in vitro studies. Arnica montana is more effective than placebo when used for the treatment of several conditions including post-traumatic and postoperative pain, edema, and ecchymosis. However, its dosages and preparations used have produced substantial differences in the clinical outcome. Cumulative evidence suggests that Arnica montana may represent a valid alternative to non-steroidal anti-inflammatory drugs, at least when treating some specific conditions.
Background:
Nowadays, the encapsulation of cytotoxic chemotherapeutic agents is attracting interest as a method for drug delivery. We hypothesized that the efficiency of helenalin might be maximized by encapsulation in β-cyclodextrin nanoparticles. Helenalin, with a hydrophobic structure obtained from flowers of Arnica chamissonis and Arnica Montana, has anti-cancer and anti-inflammatory activity but low water solubility and bioavailability. β-Cyclodextrin (β-CD) is a cyclic oligosaccharide comprising seven D-glucopyranoside units, linked through 1,4-glycosidic bonds.
Materials and methods:
To test our hypothesis, we prepared β-cyclodextrin- helenalin complexes to determine their inhibitory effects on telomerase gene expression by real-time polymerase chain reaction (q-PCR) and cytotoxic effects by colorimetric cell viability (MTT) assay.
Results:
MTT assay showed that not only β-cyclodextrin has no cytotoxic effect on its own but also it demonstrated that β-cyclodextrin- helenalin complexes inhibited the growth of the T47D breast cancer cell line in a time and dose-dependent manner. Our q-PCR results showed that the expression of telomerase gene was effectively reduced as the concentration of β-cyclodextrin-helenalin complexes increased.
Conclusions:
β-Cyclodextrin-helenalin complexes exerted cytotoxic effects on T47D cells through down-regulation of telomerase expression and by enhancing Helenalin uptake by cells. Therefore, β-cyclodextrin could be superior carrier for this kind of hydrophobic agent.
Leaf-cutting ants of the Attini tribe are a major pest of agricultural and forestry productions in the New World. Economic losses caused by these ants were estimated at several million dollars per year. These ants need to live in symbiosis with a basidiomycete fungus. Due to their mutualistic interaction with the symbiotic fungus, management of Attini ants can be done with insecticides or fungicides or both. So far, synthetic pesticides were the main control means, albeit with negative effects on the environment. Very few studies describe alternative methods for the control of leaf-cutting ants such as the use of insecticidal and fungicidal plant extracts. There is therefore a need of knowledge on phytochemicals and plants that could be used as insecticides and fungicides. Here, we review chemicals of plant origin and species with insecticidal and fungicidal activities. We establish a list of plants and phytochemicals that could manage leaf-cutting ants and also other insects, notably insects that use fungus-based agriculture. An exhaustive literature search of 1965 references from 1923 to 2010 was conducted using scientific databases, chemical databases, botanical databases, and books to identify published papers related to insecticidal and fungicidal chemical compounds stemmed from plant species. The major points are the following: (1) 119 and 284 chemicals have been cited in the literature for their insecticidal and fungicidal activities, respectively; (2) 656 and 1,064 plant species have significant insecticidal and fungicidal activities, respectively; (3) 3 main chemical classes were most cited for these activities: alkaloids, phenolics, and terpenoids; (4) 20 interesting chemicals with the both insecticidal and fungicidal activities were found; and (5) 305 plant species containing these chemicals were cited. To conclude, 20 chemicals: caryophyllene oxide, cinnamaldehyde, eugenol, helenalin, linalool, menthone, myristicin, pulegone, thymol, anethole, anisaldehyde, elemicin, isopimpinellin, plumbagin, podophyllotoxin, psoralen, xanthotoxin, anonaine, solamargine, and tomatine; two main plant families, Lamiaceae and Apiaceae; and 17 species of these families were particularly interesting for the management of leaf-cutting ants.
Some medicinal plants, which are known to produce allergic reactions, are also specifically used as antiinflammatory agents. Among the more relevant plants, we report species with cinnamaldehyde, cinnamic alcohol, geraniol, hydroxycitronellal, eugenol and isoeugenol are all potential allergens. In addition, fragrances, which are mixtures of small-molecular-weight compounds, may induce allergic contact dermatitis due to fragrance-specific CD4+ and CD8+ T lymphocytes. Plants from the Asteraceae family used in folk medicine as anti-inflammatories can cause allergic contact dermatitis because of its content in sesquiterpene lactones, which have been reported as the antiinflammatory principles in this species. Species with flavonoids, iridoids, terpenoids and alkaloids have been described as inhibitors of contact dermatitis. Scrophularia auriculata, Poria cocos, Santolina chamaecyparissus, Ranunculus sceleratus and Helichrysum italicum all showed activity in different experimental protocols of contact dermatitis, thus justifying the potential use of these medicinal plants as anti-allergens and inhibitors of contact dermatitis reactions produced by allergens and chemicals. Hydroquinone derivatives such as 1-O-b-glucopyranosyl-2-(3'-hydroxymethyl-3'-methylallyl) hydroquinone and arbutin, flavonoids such as kaempferol, apigenin and genistein, sesquiterpene lactones such as helenalin, diterpenes such as triptonide, triterpenes such as tripterine and bryonolic acid, iridoids such as scrovalentinoside, alkaloids such as indirubin, dehydrocorydaline, magnoflorine hydroxide and phellodendrine acetate, and polysaccharides such as fucoidin have been reported as inhibitors of contact dermatitis reactions.
Allergic contact dermatitis due to plants is common. Potentially allergenic plants and plant products are found in many everyday environments, such as the home, the garden, the workplace, and recreational settings. By improving our knowledge of allergenic plant-derived chemical compounds, we will be better positioned to identify novel allergens. We review the most relevant chemical allergens that contribute to plant allergic contact dermatitis and propose a clinical classification system based on 5 major families of chemical sensitizers: α-methylene-γ-butyrolactones, quinones, phenol derivatives, terpenes, and miscellaneous structures (disulfides, isothiocyanates, and polyacetylenic derivates). We also describe the different clinical pictures of plant allergic contact dermatitis and review currently available patch test materials. A better understanding of the specific allergens involved in plant allergic contact dermatitis will help to predict cross-reactivity between different plant species or families.
Numerous studies have demonstrated that autophagy plays a vital role in maintaining cellular homeostasis. Interestingly, several anticancer agents were found to exert their anticancer effects by triggering autophagy. Emerging data suggest that autophagy represents a novel mechanism that can be exploited for therapeutic benefit. Pharmacologically active natural compounds such as those from marine, terrestrial plants and animals represent a promising resource for novel anticancer drugs. There are several prominent examples from the past proving the success of natural products and derivatives exhibiting anticancer activity. Helenalin, a sesquiterpene lactone has been demonstrated to have potent anti-inflammatory and antitumor activity. Albeit previous studies demonstrating helenalin's multi modal action on cellular proliferative and apoptosis, the mechanisms underlying its action are largely unexplained.
To deduce the mechanistic action of helenalin, cancer cells were treated with the drug at various concentrations and time intervals. Using western blot, FACS analysis, overexpression and knockdown studies, cellular signaling pathways were interrogated focusing on apoptosis and autophagy markers.
We show here that helenalin induces sub-G1 arrest, apoptosis, caspase cleavage and increases the levels of the autophagic markers. Suppression of caspase cleavage by the pan caspase inhibitor, Z-VAD-fmk, suppressed induction of LC3-B and Atg12 and reduced autophagic cell death, indicating caspase activity was essential for autophagic cell death induced by helenalin. Additionally, helenalin suppressed NF-κB p65 expression in a dose and time dependent manner. Exogenous overexpression of p65 was accompanied by reduced levels of cell death whereas siRNA mediated suppression led to augmented levels of caspase cleavage, autophagic cell death markers and increased cell death.
Taken together, these results show that helenalin mediated autophagic cell death entails inhibition of NF-κB p65, thus providing a promising approach for the treatment of cancers with aberrant activation of the NF-κB pathway.
Acute Tyyoxicity of Helenalin in BDF1 Mice. CHAPMAN, D. E., ROBERTS, G. B., REYNOLDS, D. J., GRIPPO, A. A., HOLBROOK, D. J., HALL, I. H., CHANEY, S. G., CHANG, J., AND LEE, K. H. (1988). Fundam. Appl. Toxicol 10, 302-312. The acute toxicity of helenalin, a sesquiter-pene lactone isolated from Helenium microcephalum , was examined in male BDF1 mice. The 14-day LD50 for a single ip dose of helenalin in male mice was 43 mg/kg. A single ip injection of 25 mg helenalin/kg increased serum alanine aminotransferase (ALT), lactate dehydrogenase (LDH), urea nitrogen (BUN), and sorbitol dehydrogenase within 6 hr of treatment. Multiple helenalin exposures, ip injection of 25 mg helenalin/kg for 3 days, increased differential poly-morphonuclear leukocyte counts and decreased lymphocyte counts. Serum ALT, BUN, and cholesterol levels were also increased by multiple helenalin exposures at 25 mg helenalin/kg/ day. Helenalin significantly reduced liver, thymus, and spleen relative weights and histologic evaluation revealed substantial effects of multiple helenalin exposures on lymphocytes of the thymus, spleen, and mesenteric lymph nodes. No helenalin-induced histologic changes were observed in the liver or kidney. Multiple helenalin exposures (25 mg/kg/day) significantly inhibited hepatic microsomal enzyme activities (aminopyrine demethylase and aniline hydroxylase) and decreased microsomal cytochromes P-450 and 65 contents. Three concurrent days of diethyl maleate (DEM) pretreatment (3.7 mmol DEM/kg, 0.5 hr before helenalin treatment) significantly increased the toxicity of helenalin exposure. The present studies indicate that the hepatic microsomal drug metabolizing system and lymphoid organs are particularly vulnerable to the effects of helenalin. In addition, helenalin toxicity is increased by DEM pretreatments which have been shown to decrease glutathione concentrations.
Helenalin is a naturally occuring sesquiterpene lactone extracted from Arnica montana and Arnica chamissonis ssp. foliosa. Helenalin and its derivatives are known for anti-cancer and anti-inflammatory effects via inhibiting NF-kappaB and telomerase activity and impairing protein and DNA synthesis, suggesting that helenalin is a potential candidate for the treatment of deregulated and unwanted T cell-mediated immune responses. Here we show that helenalin induces apoptosis in activated CD4+ T cells by triggering the mitochondrial pathway of apoptosis. Induction of apoptosis is accompanied by rapid stabilization of p53, nuclear localization of p53 and AIF, and an increase in ROS production that results in loss of mitochondrial membrane potential (DeltaPsim). Activated CD4+ T cells which survive exposure to helenalin undergo inhibition of proliferation by induction of G2/M cell cycle arrest. Cell cycle arrest is accompanied by the accumulation of cell cycle regulator proteins p21(WAF/CIP1), p2(KIP1) and cyclin D2, whereas abundance of cyclin A and B(1) is decreased. Cell surface expression of the activation-associated receptors CD25, CD27, CD28, CD120b as well as production of IL-2 are impaired. Transcriptional activation of genes encoding for CD25, IL-2 and IFN-gamma is mediated by transcription factors of the NFAT family, and we demonstrate that helenalin suppresses nuclear translocation of NFATc2 in activated CD4+ T cells. Thus, helenalin can be defined as a new immunosuppressive compound suited for the treatment of deregulated and unwanted T cell-mediated immune responses.
Prompted by results of our previous studies where we found high activity of some sesquiterpene lactones (STLs) against Trypanosoma brucei rhodesiense (which causes East African sleeping sickness), we have now conducted a structure-(in-vitro)-activity study on a set of 40 STLs against T. brucei rhodesiense, T. cruzi, Leishmania donovani and Plasmodium falciparum. Furthermore, cytotoxic activity against L6 rat skeletal myoblast cells was assessed. Some of the compounds possess high activity, especially against T. brucei (e.g. helenalin and some of its esters with IC(50)-values of 0.05-0.1 microM, which is about 10 times lower than their cytotoxic activity). It was found that all investigated antiprotozoal activities are significantly correlated with cytotoxicity and the major determinants for activity are a,b-unsaturated structural elements, also known to be essential for other biological activities of STLs. It was observed, however, that certain compounds are considerably more toxic against protozoa than against mammalian cells while others are more cytotoxic than active against the protozoa. A comparative QSAR analysis was therefore undertaken, in order to discern the antiparasitic activity of STLs against T. brucei and cytotoxicity. Both activities were found to depend to a large extent on the same structural elements and molecular properties. The observed variance in the biological data can be explained in terms of subtle variations in the relative influences of various molecular descriptors.
Available chemotherapeutics take advantage of the fast proliferation of cancer cells. Consequently slow growth makes androgen refractory prostate cancer resistant towards available drugs. No treatment is available at the present, when the cancer has developed metastases outside the prostate (T4 stage). Cytotoxins killing cells irrespective of the phase of the cell cycle will be able to kill slowly proliferating prostate cancer cells. Lack of selectivity, however, prevents their use as systemic drugs. Prostate cancer cells secrete characteristic proteolytic enzymes, e.g. PSA and hK2, with unusual substrate specificity. Conjugation of cytotoxins with peptides, which are selective substrates for PSA or hK2, will afford prodrugs, from which the active drug only will be released in close vicinity of the cancer cells. Based on this strategy prodrugs targeted at prostate cancer cells have been constructed and evaluated as potential drugs for prostate cancer. The potency of the thapsigargins as apoptotic agents make these naturally occurring sesquiterpene lactones attractive lead compounds. Intensive studies on structure-activity relationships and chemistry of the thapsigargins have enabled construction of potent derivatives enabling conjugation with peptides. Studies on the mechanism of action of the thapsigargins have revealed that the cytoxicity is based on their ability to inhibit the intracellular sarco-/endoplasmtic calcium pump.
An analytical RPLC method for sesquiterpene lactones in Arnica montana has been extended to include quantitative analyses of dihydrohelenalin esters. LC-ESI-MS-MS distinguished the isomeric helenalin and dihydrohelenalin esters. The dihydrohelenalin esters have lower response factors for UV detection than do helenalin esters, which must be taken into account for quantitative analyses. Analyses of flowers from 16 different wild populations of A. montana in Spain showed differing proportions of helenalin and dihydrohelenalin esters. For the first time a chemotype with high levels of helenalin esters (total helenalins 5.2-10.3 mg/g dry weight) is reported in Spanish A. montana. These samples were from heath lands at high altitude (1330-1460 m), whereas samples from meadows and peat bogs at lower altitudes were the expected chemotype with high levels of dihydrohelenalin esters (total dihydrohelenalins 10.9-18.2 mg/g). The phenolic compounds, both flavonoid glycosides and caffeoylquinic acids, in Spanish A. montana are reported for the first time. The levels of several of these compounds differed significantly between samples from heath lands and samples from peat bogs or meadows, with the heath land samples being most similar to central European A. montana in their phenolic composition.
Naturally occurring sesquiterpene lactones and their semisynthetic derivatives, such as the O = C-C = CH-bearing helenalin and its esters, have been shown to demonstrate potent cytotoxicity against the growth of murine L1210 lymphoid leukemia and human Tmolt3 leukemia, colon adenocarcinoma, HeLaS3, lung bronchogenic, KB, osteosarcoma, and glioma cells. The modes of action of helenalin in L1210 cells are the inhibition of DNA, RNA, and protein syntheses. This study confirms that thiol bearing enzymes of nucleic acid metabolism were significantly inhibited, e.g. DNA polymerase alpha, IMP hydrogenase, and ribonucleoside reductase. The addition of GSH to the reaction medium demonstrated total recovery of L1210 ribonucleoside reductase activity. Helenalin reduced cellular GSH levels in L1210 cells. Helenalin also reduced all four pool levels of d(NTP)s which would account for part of the observed inhibition of DNA synthesis. Reductions in the ribonucleotide pool levels were also generally evident after drug treatment. Thus, the sesquiterpene lactones appear to have more than one mode of action in L1210 cells. All of the modes of actions of helenalin are feasible mechanisms to lower nucleic acid synthesis and cause cell death of the L1210 leukemia cells.
Helenalin is a pseudoguaianolide natural product that targets Cys38 within the DNA binding domain of NF-κB transcription factor p65 (RelA). Helenalin contains two Michael acceptors that covalently modify cysteines: a α-methylene-γ-butyrolactone and a cyclopentenone. We recently reported two simplified helenalin analogues that mimic the biological activity of helenalin and contain both electrophilic moieties. To determine the individual contributions of the Michael acceptors toward NF-κB inhibition, we synthesized a small library of helenalin-based analogues containing various combinations of α-methylene-γ-butyrolactones and cyclopentenones. The kinetics of thiol addition to a subset of the analogues was measured to determine the relative thiol reactivities of the embedded electrophiles. Additionally, the cellular NF-κB inhibitory activities of the analogues were determined to elucidate the contributions of each Michael acceptor to biological potency. Our studies suggest the α-methylene-γ-butyrolactone contributes most significantly to the NF-κB inhibition of our simplified helenalin analogues.
Extracts of Arnica spp. are traditionally used due to their anti-inflammatory effects for the topical treatment of e.g. haematoma or muscle distortions. One of the main active compounds is Helenalin, a sesquiterpene lactone that can be found in various Asteraceae. However, immunotoxic effects of the compound are only poorly analysed. In this study, a 2D gel electrophoresis based proteomic approach together with a membrane based proteomic assay, metabolomics and the detection of intracellular reactive oxygen species (iROS) were used to investigate potential immunotoxic properties of Helenalin on the human immune cell lines Jurkat and THP-1 and on human peripheral blood mononuclear cells (PBMC). The study revealed a dose-dependent cytotoxicity towards both tested cell lines and the PBMC. However, the cell lines were less sensitive to the Helenalin treatment than the PBMC. The proteomic assays showed strong effects on the carbohydrate metabolism and the protein folding in THP-1 cells but only weak impact on Jurkat cells. Metabolomic studies as well as iROS detection in THP-1 cells verified the results of the proteomic analysis. In summary, the approaches used in this study were able to identify target pathways of Helenalin especially in THP-1 monocytes and thus enable a risk assessment of the substance.
The Asteraceae is characterized by structurally diverse sesquiterpene lactones and furanosesquiterpenes. In this review the tribal, subtribal and generic distribution of sesquiterpene lactones is examined and the compounds’ utility as taxonomic characters discussed. Sesquiterpene lactones fulfill the major requirements for good analytic and synthetic characters. Studies of infraspecific sesquiterpene lactone variation indicate that different elements within complex taxa are often defined by distinct chemistries, termed chemotypes. Chemotypes have been identified within many of the thoroughly investigated taxa:Ambrosia camphorata, A. chamissonis, A. confertiflora, theA. cumanensis-A. psilostachya-A. artemisiifolia complex,A. dumosa, Artemisia tridentata, Gaillardia pulchella andMelampodium leucanthum. Such an analytic usage is mostly restricted to the infraspecific level. Synthetic usage at the interspecific level and above profits from the application of a biogenetically based methodology for sorting out the complex molecules’ carbon-skeletal and substitutional features into unit characters. Cladistics or Hennigian phylogenetic systematics provides a useful framework for such an analysis. Preliminary surveys indicate that sesquiterpene lactones are especially good characters for differentiating subtribes within several major tribes: the Vernonieae, Heliantheae and Mutisieae. As yet, too few data are available for other tribes to discern such patterns. Species surveys inVernonia, Ambrosia, Iva, Parthenium,Tetragonotheca andArtemisia demonstrate that sesquiterpene lactones are useful in discerning infrageneric groups. The biogenetic cladistic analysis of the interspecific sesquiterpene lactone variation inIva shows the efficacy of this analytical methodology. At present, such biogenetically based approaches are impeded by limited biosynthetic evidence and the erratic distribution of sesquiterpene lactones within the family. Instances of apparent displacement of sesquiterpene lactones by other terpenoids (i.e. sesquiterpene furans, alcohols and acids, diterpenes, diterpene acids, etc.) at various taxonomic levels suggest that ultimately sesquiterpene lactones must be interpreted as taxonomic characters in the context of the family’s total terpene chemistry. All taxa from which sesquiterpene lactones have been reported are listed together with the compound names, major structural features and the literature cited. A less-complete listing is provided for taxa producing furanosesquiterpenes. Structures for all reported compounds are included. Two appendices listing alphabetically taxa and compounds and relevant text page numbers permit cross-indexing of plants and compounds.
Background:
The up-regulation of telomerase gene expression occurs in numerous cancers such as breast cancer. A recent study used the PLGA-PEG-helenalin complex, and free helenalin, to inhibit the expression of telomerase in the breast cancer cell line. The purpose of this study was to examine whether nano encapsulating helenalin improves the anti-cancer effect of free helenalin in the T47D breast cancer cell line.
Method:
The breast cancer cell line (T47D) was grown in the RPMI 1640 medium, supplemented with 10% FBS. The helenalin was encapsulated by the double emulsion method. Then, the drug loading was calculated and its morphology identified by SEM. Other properties of this copolymer were characterized by Fourier transform infrared (FTIR) spectroscopy and H nuclear magnetic resonance (H NMR) spectroscopy. The assessment of drug cytotoxicity on the growth of the breast cancer cell line was carried out through MTT assay. After treating the cells with a given amount of drug, RNA was extracted and cDNA was synthesized. In order to assess the amount of telomerase gene expression, real-time PCR was performed.
Results:
With regard to the amount of the drug loaded, IC50 value was significantly decreased in nanocapsulated (NC) helenalin, in comparison with that of free helenalin. This finding has been proved through the decrease of telomerase gene expression by real-time PCR.
Conclusion:
In this study, we demonstrated that the NC-helenalin complex is more effective than free helenalin in inhibiting the growth of breast cancer cells.
NF-κB comprises a family of five transcription factors that form distinct protein complexes, which bind to consensus DNA sequences at promoter regions of responsive genes regulating cellular processes. The past three decades have witnessed remarkable progress in understanding the NF-κB signaling pathway in physiologic and pathologic conditions. The role of NF-κB in human cancer initiation, development, metastasis, and resistance to treatment has drawn particular attention. A significant number of human cancers have constitutive NF-κB activity due to the inflammatory microenvironment and various oncogenic mutations. NF-κB activity not only promotes tumor cells' proliferation, suppresses apoptosis, and attracts angiogenesis, but it also induces epithelial-mesenchymal transition, which facilitates distant metastasis. In certain circumstances, NF-κB activation may also remodel local metabolism and anergize the immune system to favor tumor growth. Suppression of NF-κB in myeloid cells or tumor cells usually leads to tumor regression, which makes the NF-κB pathway a promising therapeutic target. However, because of its vital role in various biologic activities, components of the NF-κB pathway need to be carefully selected and evaluated to design targeted therapies. Cancer Immunol Res; 2(9); 823-30. ©2014 AACR.
Background:
Chagas disease or American Trypanosomiasis is caused by the flagellated protozoan parasite Trypanosoma cruzi (T. cruzi) and is recognized by the WHO as one of the world's 17 neglected tropical diseases. Only two drugs (Benznidazol, Bz and Nifurtimox, Nx) are currently accepted for treatment, however they cause severe adverse effects and their efficacy is still controversial. It is then important to explore for new drugs.
Purpose:
Programmed cell death (PCD) in parasites offers interesting new therapeutic targets. The aim of this work was to evaluate the induction of PCD in T. cruzi by two natural sesquiterpene lactones (STLs), dehydroleucodine (DhL) and helenalin (Hln) as compared with the two conventional drugs, Bz and Nx.
Material and methods:
Hln and DhL were isolated from aerial parts of Gaillardia megapotamica and Artemisia douglassiana Besser, respectively. Purity of compounds (greater than 95%) was confirmed by (13)C-nuclear magnetic resonance, melting point analysis, and optical rotation. Induction of PCD in T. cruzi epimastigotes and trypomastigotes by DhL, Hln, Bz and Nx was assayed by phosphatidylserine exposure at the parasite surface and by detection of DNA fragmentation using the TUNEL assay. Trypanocidal activity of natural and synthetic compounds was assayed by measuring parasite viability using the MTT method.
Results:
The two natural STLs, DhL and Hln, induce programmed cell death in both, the replicative epimastigote form and the infective trypomastigote form of T. cruzi. Interestingly, the two conventional antichagasic drugs (Bz and Nx) do not induce programmed cell death. A combination of DhL and either Bz or Nx showed an increased effect of natural compounds and synthetic drugs on the decrease of parasite viability.
Conclusion:
DhL and Hln induce programmed cell death in T. cruzi replicative epimastigote and infective trypomastigote forms, which is a different mechanism of action than the conventional drugs to kill the parasite. Therefore DhL and Hln may offer an interesting option for the treatment of Chagas disease, alone or in combination with conventional drugs.
Although sesquiterpene lactones are terpenoid compounds characteristic of the Asteraceae (Compositae) they are also known from other angiosperm families as well as from some gymnosperms. The wide variety of chemical structures so far discovered is matched by a diversity of biological activities. Compounds that have cytotoxic, anti-tumourgenic, anti-bacterial and anti-fungal properties are widely distributed. Various sesquiterpene lactones are known to be toxic to human and animal parasites, insects and vertebrates. Many of these compounds or plants containing them are a cause of allergic contact dermatitis in humans but some of them have been used for their pharmacological activity. Sesquiterpene lactones also act as plant growth regulators and are responsible for allelopathic properties of many plants. Various activities of sesquiterpene lactones suggest their evolutionary significance in plants as deterrents against herbivores and anti-fungal, anti-bacterial allelopathic agents. This review summarizes the present knowledge regarding the biological activities of sesquiterpene lactones and their structure-activity relationships.
The NF-kappaB family of transcription factors has an essential role in inflammation and innate immunity. Furthermore, NF-kappaB is increasingly recognized as a crucial player in many steps of cancer initiation and progression. During these latter processes NF-kappaB cooperates with multiple other signaling molecules and pathways. Prominent nodes of crosstalk are mediated by other transcription factors such as STAT3 and p53 or the ETS related gene ERG. These transcription factors either directly interact with NF-kappaB subunits or affect NF-kappaB target genes. Crosstalk can also occur through different kinases, such as GSK3-beta, p38, or PI3K, which modulate NF-kappaB transcriptional activity or affect upstream signaling pathways. Other classes of molecules that act as nodes of crosstalk are reactive oxygen species and miRNAs. In this review, we provide an overview of the most relevant modes of crosstalk and cooperativity between NF-kappaB and other signaling molecules during inflammation and cancer.
Alcoholic extracts prepared form Arnicae flos, the collective name for flowerheads from Arnica montana and A. chamissonis ssp. foliosa, are used therapeutically as anti-inflammatory remedies. The active ingredients mediating the pharmacological effect are mainly sesquiterpene lactones, such as helenalin, 11 alpha,13-dihydrohelenalin, chamissonolid and their ester derivatives. While these compounds affect various cellular processes, current data do not fully explain how sesquiterpene lactones exert their anti-inflammatory effect. We show here that helenalin, and, to a much lesser degree, 11 alpha,13-dihydrohelenalin and chamissonolid, inhibit activation of transcription factor NF-kappa B. This difference in efficacy, which correlates with the compounds' anti-inflammatory potency in vivo, may be explained by differences in structure and conformation. NF-kappa B, which resides in an inactive, cytoplasmic complex in unstimulated cells, is activated by phosphorylation and degradation of its inhibitory subunit, I kappa B. Helenalin inhibits NF-kappa B activation in response to four different stimuli in T-cells, B-cells and epithelial cells and abrogates kappa B-driven gene expression. This inhibition is selective, as the activity of four other transcription factors, Oct-1, TBP, Spl and STAT 5 was not affected. We show that inhibition is not due to a direct modification of the active NF-kappa B heterodimer. Rather, helenalin modifies the NF-kappa B/I kappa B complex, preventing the release of I kappa B. These data suggest a molecular mechanism for the anti-inflammatory effect of sesquiterpene lactones, which differs from that of other nonsteroidal anti-inflammatory drugs (NSAIDs), indomethacin and acetyl salicylic acid.
The acute toxicity of helenalin, a sesquiterpene lactone isolated from Helenium microcephalum, was examined in male BDF1 mice. The 14-day LD50 for a single ip dose of helenalin in male mice was 43 mg/kg. A single ip injection of 25 mg helenalin/kg increased serum alanine aminotransferase (ALT), lactate dehydrogenase (LDH), urea nitrogen (BUN), and sorbitol dehydrogenase within 6 hr of treatment. Multiple helenalin exposures, ip injection of 25 mg helenalin/kg for 3 days, increased differential polymorphonuclear leukocyte counts and decreased lymphocyte counts. Serum ALT, BUN, and cholesterol levels were also increased by multiple helenalin exposures at 25 mg helenalin/kg/day. Helenalin significantly reduced liver, thymus, and spleen relative weights and histologic evaluation revealed substantial effects of multiple helenalin exposures on lymphocytes of the thymus, spleen, and mesenteric lymph nodes. No helenalin-induced histologic changes were observed in the liver or kidney. Multiple helenalin exposures (25 mg/kg/day) significantly inhibited hepatic microsomal enzyme activities (aminopyrine demethylase and aniline hydroxylase) and decreased microsomal cytochromes P-450 and b5 contents. Three concurrent days of diethyl maleate (DEM) pretreatment (3.7 mmol DEM/kg, 0.5 hr before helenalin treatment) significantly increased the toxicity of helenalin exposure. The present studies indicate that the hepatic microsomal drug metabolizing system and lymphoid organs are particularly vulnerable to the effects of helenalin. In addition, helenalin toxicity is increased by DEM pretreatments which have been shown to decrease glutathione concentrations.
Sesquiterpene lactones are pharmacologically interesting compounds of the flowerheads of Arnica chamissonis Less. spp. foliosa (Nutt.) Maguire, officinal as Arnicae Flos (DAB 9 and 2.AB-DDR). For the qualitative and quantitative determination of these compounds, high-performance liquid chromatographic (HPLC) and gas chromatographic (GC) methods, have been developed using Hypersil-ODS columns with a water-methanol elution gradient and UV detection at 225 nm in the HPLC system and an OV-01-CB capillary column with flame ionization detection in the GC system. The procedure includes the extraction of the sesquiterpene lactones from the plant material and a rapid sample clean-up on Extrelut columns. Based on different reference substances and different methods of calculation, the sesquiterpene lactone contents varied from 0.6 to 1.7% [relative standard deviation 4.40% by GC and 4.59% by HPLC system (n = 8)].
Sesquiterpenoids, and specifically sesquiterpene lactones from Asteraceae, may play a highly significant role in human health, both as part of a balanced diet and as pharmaceutical agents, due to their potential for the treatment of cardiovascular disease and cancer. This review highlights the role of sesquiterpene lactones endogenously in the plants that produce them, and explores mechanisms by which they interact in animal and human consumers of these plants. Several mechanisms are proposed for the reduction of inflammation and tumorigenesis at potentially achievable levels in humans. Plants can be classified by their specific array of produced sesquiterpene lactones, showing high levels of translational control. Studies of folk medicines implicate sesquiterpene lactones as the active ingredient in many treatments for other ailments such as diarrhea, burns, influenza, and neurodegradation. In addition to the anti-inflammatory response, sesquiterpene lactones have been found to sensitize tumor cells to conventional drug treatments. This review explores the varied ecological roles of sesquiterpenes in the plant producer, depending upon the plant and the compound. These include allelopathy with other plants, insects, and microbes, thereby causing behavioural or developmental modification to these secondary organisms to the benefit of the sesquiterpenoid producer. Some sesquiterpenoid lactones are antimicrobial, disrupting the cell wall of fungi and invasive bacteria, whereas others protect the plant from environmental stresses that would otherwise cause oxidative damage. Many of the compounds are effective due to their bitter flavor, which has obvious implications for human consumers. The implications of sesquiterpenoid lactone qualities for future crop production are discussed.
Many sesquiterpene lactones (SLs) possess considerable anti-inflammatory activity. They inhibit the transcription factor NF-κB by selectively alkylating its p65 subunit probably by reacting with cysteine residues. Here we assayed 28 sesquiterpene lactones for their ability to inhibit NF-κB. The majority of the potent NF-κB inhibitors possess two reactive centers in form of an α-methylene-γ-lactone group and an α,β- or α,β,γ,δ-unsaturated carbonyl group. Based on computer molecular modelling we propose a molecular mechanism of action, which is able to explain the p65 selectivity of the SLs and the observed correlation of high activity with alkylant bifunctionality. A single bifunctional SL molecule can alkylate the cysteine residue (Cys 38) in the DNA binding loop 1 (L1) and a further cysteine (Cys 120) in the nearby E’ region. This cross link alters the position of tyrosine 36 and additional amino acids in such a way that their specific interactions with the DNA become impossible. We also created a model for monofunctional SLs.
Helenalin, a sesquiterpene lactone, exhibits anti-inflammatory and anti-tumor activities. Here, we investigated whether helenalin could induce apoptosis in human renal carcinoma Caki cells. Helenalin increased apoptosis in dose dependent manner in Caki cells, and also induced apoptosis in other carcinoma cells, such as human renal carcinoma ACHN cells, human colon carcinoma HT29 and HCT116 cells. We found that helenalin markedly induced endoplasmic reticulum (ER) stress-related genes, such as regulated in development and DNA damage responses (REDD) 1, activating transcription factor-4 (ATF4) and/or the CCAAT enhancer-binding protein-homologous protein (CHOP). However, down-regulation of ATF4 and/or CHOP expression by siRNA had no effect on helenalin-induced apoptosis in Caki and HCT116 cells. Helenalin increased production of intracellular reactive oxygen species (ROS). Furthermore, ROS scavengers, N-acetylcystine (NAC), and glutathione ethyl ester (GEE), reduced helenalin-induced apoptosis. Taken together, helenalin induced apoptosis via ROS generation in human renal carcinoma Caki cells.
Helenalin, a natural plant product with significant antitumor activities, decreased male BDF1 mouse hepatic microsomal cytochrome P450 contents in vivo and in vitro. A single i.p. dose of 25 mg helenalin/kg body weight significantly (P < 0.05) decreased microsomal cytochrome P450 contents and inhibited cytochrome P450-dependent mixed-function oxidase activities within 1–2 hr post-exposure. Helenalin (1.0 mM) decreased microsomal cytochrome P450 contents in vitro by 11% in the absence of NADPH and by 32% in the presence of NADPH. These in vitro and in vivo decreases in cytochrome P450 were accompanied by comparable decreases in total microsomal heme contents. Helenalin (1.0 mM) increased mouse hepatic microsomal oxygen consumption and NADPH utilization by 3.2 and 5.4 nmol/min/mg protein respectively. Helenalin (1.0 mM) significantly (P < 0.05) increased microsomal lipid peroxidation in vitro, and this helenalin-induced increase in lipid peroxidation was inhibited completely by the addition of 0.05 mM EDTA. However, microsomal cytochrome P450 contents were equally affected by helenalin in the presence or absence of EDTA, suggesting that lipid peroxidation did not contribute to the helenalin-induced decrease in cytochrome P450. The addition of 0.05 mM hemin to microsomes treated in vitro with 1.0 mM helenalin resulted in a 58% recovery of cytochrome P450 contents. This ability of hemin to reconstitute cytochrome P450 in helenalin-treated microsomes suggests that helenalin produced a selective loss of heme from the cytochrome P450 holoprotein, and that the resulting cytochrome P450 apoprotein remained intact after helenalin treatment. The increased loss of microsomal cytochrome P450 produced by helenalin in the presence of NADPH suggests that a helenalin metabolite may be responsible for heme loss and the in vitro destruction of cytochrome P450.
The nuclear factor-κB (NF-κB) transcription factor family has been considered the central mediator of the inflammatory process and a key participant in innate and adaptive immune responses. Coincident with the molecular cloning of NF-κB/RelA and identification of its kinship to the v-Rel oncogene, it was anticipated that NF-κB itself would be involved in cancer development. Oncogenic activating mutations in NF-κB genes are rare and have been identified only in some lymphoid malignancies, while most NF-κB activating mutations in lymphoid malignancies occur in upstream signaling components that feed into NF-κB. NF-κB activation is also prevalent in carcinomas, in which NF-κB activation is mainly driven by inflammatory cytokines within the tumor microenvironment. Importantly, however, in all malignancies, NF-κB acts in a cell type-specific manner: activating survival genes within cancer cells and inflammation-promoting genes in components of the tumor microenvironment. Yet, the complex biological functions of NF-κB have made its therapeutic targeting a challenge.
α-Methylene-γ- and δ-lactones, as well as α-methylene-γ- and δ-lactams, are plant-derived compounds often used in traditional medicine for the treatment of inflammatory diseases. In recent years, the anticancer properties of these compounds and the molecular mechanisms of their action have been studied extensively. In the search for modern anticancer drugs, various synthetic analogs of α-methylene-γ- and δ-lactones and lactams have been synthesized and tested for their cytotoxic activity. In this review, we give a brief description of the occurrence and biological activity of such compounds isolated from plants and their diverse synthetic analogs.
Evasion of cell death by overexpression of anti-apoptotic proteins, such as Bcl-2, is commonly observed in cancer cells leading to a lack of response to chemotherapy. Hence, there is a need to find new chemotherapeutic agents that are able to overcome chemoresistance mediated by Bcl-2 and to understand their mechanisms of action. Helenalin, a sesquiterpene lactone (STL), induces cell death and abrogates clonal survival in a highly apoptosis-resistant Bcl-2 overexpressing Jurkat cell line as well as in two other Bcl-2 overexpressing solid tumor cell lines (mammary MCF-7; pancreatic L6.3pl). This effect is not achieved by directly affecting the mitochondria-protective function of Bcl-2 in the intrinsic pathway of apoptosis since Bcl-2 overexpressing Jurkat cells do not show cytochrome c release and dissipation of mitochondrial membrane potential upon helenalin treatment. Moreover, helenalin induces an atypical form of cell death with necrotic features in Bcl-2 overexpressing cells, neither activating classical mediators of apoptosis (caspases, AIF, Omi/HtrA2, Apaf/apoptosome) nor ER-stress mediators (BiP/GRP78 and CHOP/GADD153), nor autophagy pathways (LC3 conversion). In contrast, helenalin was found to inhibit NF-κB activation that was considerably increased in Bcl-2 overexpressing Jurkat cells and promotes cell survival. Moreover, we identified reactive oxygen species (ROS) and free intracellular iron as mediators of helenalin-induced cell death whereas activation of JNK and abrogation of Akt activity did not contribute to helenalin-elicited cell death. Our results highlight the NF-κB inhibitor helenalin as a promising chemotherapeutic agent to overcome Bcl-2-induced cell death resistance.
Sesquiterpene lactones are a large group of secondary plant metabolites mostly known from the Asteraceae family. They exert a broad variety of different biological activities. This review attempts to critically summarise the knowledge on the anti-inflammatory and cytotoxic activity of SLs, with a special focus on parthenolide and helenalin. Recent advances on their molecular modes of action, allergic potential and also QSAR studies with SLs are presented. Therapeutic areas are highlighted in which SLs may play a role in the future. Thus, SLs may possess therapeutic relevance as single components for the local treatment of inflammation, such as rheumatoid complaints. In cancer therapy, SLs may be favourable in dual therapy or in the inhibition of leukaemia cell growth. In each case, native SLs serve as leads that have to be optimised in terms of their specificity, pharmacokinetics and absorption, distribution, metabolism and excretion (=ADME) properties. Finally, appropriate in vivo studies will decide whether SLs will become therapeutics or remain interesting research compounds.
Artemisinins are efficacious antimalarial drugs widely employed as first-line treatment in endemic countries under the form of combined therapies. Different molecular modes of action have been postulated to explain the parasiticidal effect of these compounds; however, none has been unequivocally accepted, and their physiological relevance is still questioned. Similarly, no definite genetic determinant of Plasmodium sensitivity to artemisinins has been identified so far. A better understanding of the mode of action of artemisinins and the genetic basis of laboratory-induced or field-observed altered susceptibility is crucial for malaria control. In this review different models of artemisinins' molecular action are briefly presented, focusing on recent advances, and the evidence of potential association between various gene polymorphisms and artemisinin resistance is comprehensively reviewed.
Multiple cell death mechanisms operate in both uni- and multicellular organisms. Hence, research during the past forty years has revealed that apoptosis is not the only cell death program involved in the regulation of tissue homeostasis and the removal of unwanted cells in biological organisms. While the molecular pathways of apoptosis and necrosis are now relatively well established, the precise mechanisms of other cell death modalities, and their cross-talk, require additional study. This is particularly important, since many human disorders can be attributed, directly or indirectly, to defective cell death mechanisms. In this review we shall discuss the characteristics and cross-talk between various modes of cell death and their role in cell death-related disorders, notably, neurodegenerative disease and cancer.
Sesquiterpene lactones such as helenalin have generally been considered as highly promising compounds for the treatment of inflammatory disorders. Although sesquiterpene lactones are known to inhibit signaling through transcription factor nuclear factor-kappaB (NF-kappaB), the nature of their molecular targets remains controversial. To characterize the interactions of helenalin with putative target proteins, a surface plasmon resonance-based method was developed and validated to analyze the interactions of helenalin with the NF-kappaB protein p65/RelA, with recombinant IkappaB kinases (IKKs) alpha and beta, and with the intracellular antioxidant glutathione, all immobilized on sensor chips. At pH 7.4, helenalin is interacting with RelA (K(D)=4.8microM), yet it failed to bind either IKKalpha or IKKbeta. When DNA with NF-kappaB binding sites was immobilized on sensor chips, the binding of RelA was inhibited by helenalin with an IC(50) of 5.0microM. At pH 8.0, helenalin was also able to interact with reduced, but not oxidized, glutathione with a K(D) of 24microM, but no significant interaction was observed at pH 7.4. Thus, with this optimized method, we showed that the sesquiterpene lactone helenalin interacts with the NF-kappaB protein RelA but not with IKKalpha or IKKbeta. Moreover, at physiological pH, helenalin does not interact with glutathione to any significant extent.
Among plant secondary metabolites, terpenoids are the most abundant and structurally diverse group. In addition to their important roles in pollinator attraction and direct and indirect plant defense, terpenoids are also commercially valuable due to their broad applications in the cosmetic, food, and pharmaceutical industries. Because of their functional versatility and wide distribution, great efforts have been made to decipher terpenoid biosynthetic pathways, to investigate the molecular mechanism determining their structural diversity, and to understand their biosynthetic regulation. Recent progress on the manipulation of terpenoid production in transgenic plants not only holds considerable promise for improving various plant traits and crop protection but also increases our understanding of the significance of terpenoid metabolites in mediating plant-environment interactions.
Allergic contact dermatitis (ACD) is an inflammatory skin disease of great and steadily increasing importance as an occupational health problem. The disease is induced by chemicals and metal ions which penetrate the skin and form complexes with host proteins. This process is accompanied by a strong, allergen-induced inflammatory reaction and leads to the migration of allergen-carrying dendritic cells (DC) from the skin to regional lymph nodes, where they promote generation of allergen-specific T cells. The latter are the ultimate effector cells of the disease. Re-exposure to the causative agent leads to the recruitment of the T effector cells, which then elicit the typical skin inflammatory reaction at the site of contact. Although DC and effector T cells play a protagonistic role in the sensitization and elicitation phase of ACD, respectively, other cell types including keratinocytes, NK cells, mast cells and B cells contribute to the pathogenesis of the disease. In this review the authors summarize recent findings that identify stress responses and innate immune pathways triggered by contact allergens and review recent data regarding the adaptive T cell response. The new data were collected mainly from studies on contact hypersensitivity (CHS), the corresponding experimental mouse model of human ACD. The elucidation of the molecular events involved in contact allergen-induced innate responses will help to design new treatment strategies and may allow to develop predictive in vitro assays for the identification of contact allergens.
Previously, we designed and synthesized a potent NF-kappaB inhibitor, DHMEQ. Although DHMEQ showed potent anti-inflammatory and anticancer activities in animals, its molecular target has not been elucidated. In the present study, its target protein was found to be p65 and other Rel homology proteins. We found that (-)-DHMEQ bound to p65 covalently with a 1:1 stoichiometry by conducting SPR and MALDI-TOF MS analyses. MS analysis of the chymotrypsin-digested peptide suggested the binding of (-)-DHMEQ to a Cys residue. Formation of Cys/(-)-DHMEQ adduct in the protein was supported by chemical synthesis of the adduct. Substitution of specific Cys in p65 and other Rel homology proteins resulted in the loss of (-)-DHMEQ binding. (-)-DHMEQ is the first NF-kappaB inhibitor that was proven to bind to the specific Cys by chemical methodology. These findings may explain the highly selective inhibition of NF-kappaB and the low toxic effect of (-)-DHMEQ in cells and animals.
Some sesquiterpene lactones and related compounds were tested for anti-inflammatory activity in rodents. In the edema-induced carrageenan inflammation screen, the alpha-methylene-gamma-lactone moiety of the sesquiterpene lactones was required for inhibitory activity. The 6-hydroxy group of helenalin also was required for potency. In the tenulin series, the 2,3-epoxy derivatives were marginally active. The same structure was required for inhibition of the writhing reflex. In the chronic adjuvant arthritic screen, compounds containing the alpha-methylene-gamma-lactone moiety, the beta-unsubstituted cyclopentenone ring, and the alpha-epoxy cyclopentenone system afforded significant inhibition at 2.5 mg/kg/day. The sesquiterpene lactones were marginally effective against induced pleurisy. The delayed hypersensitivity was suppressed by these agents whereas immunoglobulin synthesis was slightly stimulated. No delerious side effects were observed with these agents from the limited tests performed.
Several novel cyclopentenone bearing lactams and related derivatives have been synthesized as potential alkylating antitumor agents. The synthesis of these compounds involved the reaction of helenalin with sym-dimethylethylenediamine. These lactams were initially formed by a Michael addition of the amine to the α-methylene grouping of the γ-lactone ring, followed by a nucleophilic ring closure by the attack of the second amine group on the γ-lactone carbonyl. Reaction of helenalin (1) with dimethylamine gave, in addition to the single Michael reaction adduct (2) of the γ-lactone ring, a new double Michael addition product (9). The regeneration of 1 from 2 could be effected in 50% yield by silica gel column chromatography. In vitro assay for the cytotoxicity of these compounds against the growth of tissue culture cells originating from human epidermoid carcinoma of the larynx (H.Ep.-2) showed decreased significant activity due to the loss of the α-methylene-γ-lactone alkylating moiety. Cytotoxicity and in vivo antitumor activity in Walker 256 carcinosarcoma screen were enhanced with the introduction of a cinnamate ester group to the parent molecule. Preliminary in vivo tumor assay also indicated that compounds possessing a cyclopentenone and a C-6 hydroxyl group in either a bicyclic ring system or a tricyclic ring system with a saturated α-methylene grouping of the γ-lactone ring were active against Walker 256 carcinosarcoma growth in rats and marginally active against P-388 lymphocytic leukemia in mice.
Studies with smallhead sneezeweed (Helenium microcephalum DC) indicated that a sesquiterpene lactone, helenalin, is the only significant toxic constituent present. The oral median lethal dose of helenalin for 5 mammalian species was between 85 and 105 mg/kg.
Several epoxides of helenalin related derivatives have been synthesized in an effort to evaluate the potential significance of the epoxycyclopentanone moiety for cytotoxic activity against the growth of tissue culture cells originating from human epidermoid carcinoma of larynx (H.Ep-2). Helenalin (1) was converted to the monoepoxy derivative 2 and the diepoxy derivative 3 by alkaline hydrogen peroxide at different temperatures. Alternative synthesis of 2 was achieved by a convenient method of protecting the alpha-methylene grouping of the gamma-lactone, i.e., epoxidation of helenalin dimethylamine adduct 4, followed by treatment of the reaction product 5 with m-chloroperbenzoic acid. 2,3-Epoxy-11,13-dihydrohelenalin (8) was prepared by direct epoxidation of 11,13-dihydrohelenalin (7). Treatment of mexicanin A (9) with m-chloroperbenzoic acid gave, in addition to the 1,2-epoxy derivative 10, 1-alpha-hydroxyhelenalin (11) which furnished an acetate (12) upon acetylation. Catalytic hydrogenation of 10 yielded the dihydroepoxide 13. Treatment of 1 or acetylhelenalin (15) with Ac2O-p-TsOH gave the same acetyl dienol acetate (14). Epoxidation of 14 with m-chloroperbenzoic acid gave 1,beta hydroxyhelenalin (19) and a mixture of monoepoxides (17 and 18) which yielded 19 and 11 upon silica gel chromatography. The results of the cytotoxicity test of the compounds studied indicate that either an alpha- or a beta-epoxycyclopentanone moiety in helenalin related derivatives contributes significantly to the cytotoxicity. Furthermore, this cytotoxicity appears to be independent of the presence or absence of an alpha-epoxy-gamma-lactonic moiety.
This study investigates the effect on human platelet function of two sesquiterpene lactones from Arnica montana L., helenalin (H) and 11 alpha,13-dihydrohelenalin (DH). Both compounds inhibited collagen-induced platelet aggregation, thromboxane formation and 5-hydroxytryptamine secretion in a concentration-dependent manner at 3-300 microM. When arachidonic acid was used as stimulus, thromboxane formation remained unaffected despite of inhibition of platelet aggregation. Both H and DH reduced the number of acid-soluble sulfhydryl groups in platelets, by up to 78% at anti-aggregatory concentrations. Moreover, H- and DH-induced platelet inhibition could be prevented by the thiol containing amino acid cysteine. It is concluded that H and DH inhibit platelet function via interaction with platelet sulfhydryl groups, probably associated with reduced phospholipase A2 activity.
Hymenoxon and helenalin are toxic sesquiterpene lactones present in the toxic range plants Hymenoxys odorata and Helenium microcephalum. Helenalin (25 mg/kg) or hymenoxon (30 mg/kg) administered to immature male ICR mice caused a rapid decrease in hepatic glutathione levels and were lethally toxic to greater than 60% of the animals within 6 d. L-2-Oxothiazolidine 4-carboxylate (OTC), a compound that elevates cellular glutathione levels, administered to mice 6 or 12 h before either helenalin or hymenoxon protected against hepatic glutathione depletion and the lethal toxicity of these toxins. OTC administered at the same time as the sesquiterpene lactones was not protective, suggesting that the critical events against which glutathione is protective occur within the first 6 h. In primary rat hepatocyte cultures, hymenoxon and helenalin (4-16 microM) caused a rapid lethal injury as determined by the release of lactate dehydrogenase. Cotreatment of cultures with N-acetylcysteine at high concentrations (4 mM) afforded significant protection against lethal injury by both toxins. In contrast, BCNU, which inhibits glutathione reductase, or diethylmaleate, which depletes hepatocellular glutathione, potentiated the hepatotoxicity of helenalin and hymenoxon in monolayer rat hepatocytes. These studies suggest that the in vivo and in vitro toxicity of hymenoxon and helenalin is strongly dependent on hepatic glutathione levels, which hymenoxon and helenalin rapidly deplete at very low concentrations.