Wetting properties of porous high temperature polymer electrolyte fuel cells materials with phosphoric acid

The influence of phosphoric acid temperature and concentration on the wetting behavior of porous high temperature polymer electrolyte fuel cell materials is investigated.

Homogeneity and elemental distribution in self-assembled bimetallic Pd-Pt aerogels prepared by a spontaneous one-step gelation process

Multi-metallic aerogels have recently emerged as a novel and promising class of unsupported electrocatalyst materials due to their high catalytic activity and improved durability for various electrochemical reactions. Aerogels can be prepared by a spontaneous one-step gelation process, where the chemical co-reduction of metal precursors and the prompt formation of nanochain-containing hydrogels, as a preliminary stage for the preparation of aerogels, take place. However, detailed knowledge about the homogeneity and chemical distribution of these three-dimensional Pd-Pt aerogels at the nano-scale as well as at the macro-scale is still unclear. Therefore, we used a combination of spectroscopic and microscopic techniques to obtain a better insight into the structure and elemental distribution of the various Pd-rich Pd-Pt aerogels prepared by the spontaneous one-step gelation process. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDX) were employed in this work to uncover the structural architecture and chemical composition of the various Pd-rich Pd-Pt aerogels over a broad length range. The Pd80Pt20, Pd60Pt40 and Pd50Pt50 aerogels showed heterogeneity in the chemical distribution of the Pt and Pd atoms inside the macroscopic nanochain-network. The features of mono-metallic clusters were not detected by EXAFS or STEM-EDX, indicating alloyed nanoparticles. However, the local chemical composition of the Pd-Pt alloys strongly varied along the nanochains and thus within a single aerogel. To determine the electrochemically active surface area (ECSA) of the Pd-Pt aerogels for application in electrocatalysis, we used the electrochemical CO stripping method. Due to their high porosity and extended network structure, the resulting values of the ECSA for the Pd-Pt aerogels were higher than that for a commercially available unsupported Pt black catalyst. We show that the Pd-Pt aerogels possess a high utilization of catalytically active centers for electrocatalytic applications based on the nanostructured bimetallic framework. Knowledge about the homogeneity and chemical distribution of the bimetallic aerogels can help to further optimize their preparation by the spontaneous one-step gelation process and to tune their electrocatalytic reactivity.

A highly flexible electrochemical flow cell designed for the use of model electrode materials on non-conventional substrates

We present a novel electrochemical flow cell based on a wall-jet configuration to carry out electrochemical investigations under controlled mass transport conditions. The described setup can be applied for investigations similar to those performed with a common rotating disc electrode setup but allows the use of non-conductive and square substrates. This setup thus opens the possibility for the characterization of a new range of materials on a broad range of substrates. Cyclic voltammograms were recorded to assess the cleanliness and good saturation of the cell with inert gas. The performance of the flow cell regarding hydrodynamic experiments was evaluated by probing the oxygen reduction reaction on differently prepared platinum catalysts, including Pt on non-conductive substrates. The high reproducibility of the limiting currents for these samples demonstrates the good functionality, adaptability, and flexibility of the cell.

Quantifying phosphoric acid in high-temperature polymer electrolyte fuel cell components by X-ray tomographic microscopy

Synchrotron-based X-ray tomographic microscopy is investigated for imaging the local distribution and concentration of phosphoric acid in high-temperature polymer electrolyte fuel cells. Phosphoric acid fills the pores of the macro- and microporous fuel cell components. Its concentration in the fuel cell varies over a wide range (40-100 wt% H3PO4). This renders the quantification and concentration determination challenging. The problem is solved by using propagation-based phase contrast imaging and a referencing method. Fuel cell components with known acid concentrations were used to correlate greyscale values and acid concentrations. Thus calibration curves were established for the gas diffusion layer, catalyst layer and membrane in a non-operating fuel cell. The non-destructive imaging methodology was verified by comparing image-based values for acid content and concentration in the gas diffusion layer with those from chemical analysis.

Dual spectrum neutron radiography: identification of phase transitions between frozen and liquid water

In this Letter, a new approach to distinguish liquid water and ice based on dual spectrum neutron radiography is presented. The distinction is based on arising differences between the cross section of water and ice in the cold energy range. As a significant portion of the energy spectrum of the ICON beam line at Paul Scherrer Institut is in the thermal energy range, no differences can be observed with the entire beam. Introducing a polycrystalline neutron filter (beryllium) inside the beam, neutrons above its cutoff energy are filtered out and the cold energy region is emphasized. Finally, a contrast of about 1.6% is obtained with our imaging setup between liquid water and ice. Based on this measurement concept, the temporal evolution of the aggregate state of water can be investigated without any prior knowledge of its thickness. Using this technique, we could unambiguously prove the production of supercooled water inside fuel cells with a direct measurement method.

Developments and perspectives of oxide-based catalysts for the oxygen evolution reaction

Activity, selectivity and stability of oxygen evolution catalysts for water electrolyzers: an interplay between composition, morphology, preparation and processing.

Pt nanoparticles supported on Sb-doped SnO2 porous structures: developments and issues

Control of the metal oxide surface properties leads in the case of Sb–SnO₂ to a support material for Pt nanoparticles with tailored catalyst corrosion stability and activity.

The potential of secondary metabolites from plants as drugs or leads against protozoan neglected diseases - part II

Infections with protozoan parasites are a major cause of disease and mortality in many tropical countries of the world. Diseases caused by species of the genera Trypanosoma (Human African Trypanosomiasis and Chagas Disease) and Leishmania (various forms of Leishmaniasis) are among the seventeen "Neglected Tropical Diseases" (NTDs) defined by the WHO. Furthermore, malaria (caused by various Plasmodium species) can be considered a neglected disease in certain countries and with regard to availability and affordability of the antimalarials. Living organisms, especially plants, provide an innumerable number of molecules with potential for the treatment of many serious diseases. The current review attempts to give an overview on the potential of such plant-derived natural products as antiprotozoal leads and/or drugs in the fight against NTDs. In part I, a general description of the diseases, the current state of therapy and need for new therapeuticals, assay methods and strategies applied in the search for new plant derived natural products against these diseases and an overview on natural products of terpenoid origin with antiprotozoal potential were given. The present part II compiles the current knowledge on natural products with antiprotozoal activity that are derived from the shikimate pathway (lignans, coumarins, caffeic acid derivatives), quinones of various structural classes, compounds formed via the polyketide pathways (flavonoids and related compounds, chromenes and related benzopyrans and benzofurans, xanthones, acetogenins from Annonaceae and polyacetylenes) as well as the diverse classes of alkaloids. In total, both parts compile the literature on almost 900 different plant-derived natural products and their activity data, taken from over 800 references. These data, as the result of enormous efforts of numerous research groups world-wide, illustrate that plant secondary metabolites represent an immensely rich source of chemical diversity with an extremely high potential to yield a wealth of lead structures towards new therapies for NTDs. Only a small percentage, however, of the roughly 200,000 plant species on earth have been studied chemically and only a small percentage of these plants or their constituents has been investigated for antiprotozoal activity. The repository of plant-derived natural products hence deserves to be investigated even more intensely than it has been up to present.

Inhibition of Myb-dependent gene expression by the sesquiterpene lactone mexicanin-I

The c-myb proto-oncogene encodes a transcription factor that is highly expressed in the progenitor cells of the hematopoietic system, where it regulates the expression of genes important for lineage determination, cell proliferation and differentiation. There is strong evidence that deregulation of c-myb expression is involved in the development of human tumors, particularly of certain types of leukemia, and breast and colon cancer. The c-Myb protein is therefore an interesting therapeutic target. Here, we have investigated the potential of natural sesquiterpene lactones (STLs), a class of compounds that are active constituents of a variety of medicinal plants, to suppress Myb-dependent gene expression. We have developed a test system that allows screening of compounds for their ability to interfere with the activation of Myb target genes. Using this assay system, we have identified the STL mexicanin-I as the first cell-permeable, low-molecular-weight inhibitor of Myb-induced gene expression.

Pharmacological properties of the extract and some isolated compounds of Clausena lansium stem bark: anti-trichomonal, antidiabetic, anti-inflammatory, hepatoprotective and antioxidant effects

ETHNOPHARMACOLOGICAL RELEVANCE

Clausena lansium (Fool's Curry Leaf) is used for various ethnomedical conditions in some countries, including bronchitis, malaria, viral hepatitis, acute and chronic gastro-intestinal inflammation, and as a spicy substitute of the popular Curry leaf tree (Murraya koenigii).

AIM OF THE STUDY

This study was to evaluate the ethnomedical uses of the stem bark in inflammatory conditions, hepatotoxicity and to determine the anti-diabetic and anti-trichomonal properties of the plant.

MATERIALS AND METHOD

Anti-trichomonal, in vivo and in vitro antidiabetic and insulin stimulating, anti-inflammatory, hepatoprotective and anti-oxidant activities using Trichomonas gallinae, glucose loaded rats and in vitro insulin secreting cell line (INS-1 cell), carrageenin-induced rat paw oedema, CCl(4)-induced hepatotoxicity and DPPH scavenging ability methods respectively for the extracts and some isolates were determined.

RESULTS

A dichloromethane extract was superior over methanolic extract with respect to an anti-trichomonal activity which was measured after 24 and 48 h. The isolated compounds imperatorin and 3-formylcarbazole had the main anti-trichomonal activity (LC(50)s of 6.0, 3.0 and 3.6, 9.7 microg/mL after 24 and 48 h, respectively). Methanolic extract (100 mg/kg) induced maximum and significant (p<0.05) anti-hyperglycaemic activity of 15.8% at 30 min and a 38.5% increase in plasma insulin at 60 min, compared to control. The increase in plasma insulin after 60 min, compared to 0 min, was 62.0% (p<0.05). The significant 174.6% increase of insulin release from INS-1 cells (in vitro) at 0.1 mg/ml indicates that it mediates its antidiabetic action mainly by stimulating insulin release. Imperatorin and chalepin were the major active constituents increasing in vitro insulin release to 170.3 and 137.9%, respectively. 100 mg/kg of the methanolic extract produced an anti-inflammatory activity after 4 h. A sedative effect was not observed. 100 and 200 mg/kg of methanolic extract administered i.p., reduced CCl4-induced hepatotoxicity firstly by 5.3 and 8.4% reduction in phenobarbitone-sleeping time respectively, secondly by reversing the reduction in serum liver proteins by 7.0-8.8%, serum AST, ALT and ALP activities by 27.7-107.9% and thirdly by diminishing increased values of plasma AST, ALT and ALP activities by 13.2-83.8%. The extract exhibited antioxidant activities.

CONCLUSION

The hepatoprotective activity of C. lansium is partly due to its anti-oxidant and anti-inflammatory properties and confirms its folkloric use in the treatment of gastro-intestinal inflammation, bronchitis and hepatitis. In addition the use of C. lansium stem bark would be useful in diabetes and trichomoniasis.

Evaluation of analytical markers characterising different drying methods of parsley leaves (Petroselinum crispum L.)

Drying process of parsley leaves from Petroselinum crispum L. can influence the sensory qualities and aromatic taste of this herbal product. Beside oven-dried material, freeze-dried parsley is getting increasingly into the market. In the course of a search for analytical tools to differentiate oven-dried and lyophilised parsley, a HPLC determination of the 6"-O-malonylapiin to apiin ratio was shown to be a suitable marker system. While the ratio is high for fresh and lyophilised leave material, oven-drying leads to demalonylation and, subsequently, to a low malonylapiin--apiin ratio. Additionally, L*a*b colour measurement can be used for quality control to differentiate between different dried parsley raw materials.

Lignans from Linum species of sections Syllinum and Linum

The aryltetralin lignans 6-methoxypodophyllotoxin, 5'-demethoxy-6-methoxypodophyllotoxin as well as the corresponding 8'-epimers 6-methoxypicropodophyllin, and 5'-demethoxy-6-methoxypicropodophyllin were isolated from suspension cultures of Linum cariense, and 4'-demethyl-6-methoxypodophyllotoxin together with 6-methoxypodophyllotoxin from plants of L. tauricum, which both belong to section Syllinum of the genus Linum. Cell cultures of L. altaicum, L. austriacum ssp. euxinum and L. lewisii belonging to section Linum accumulate the naphthalene lignans justicidin B and isojusticidin B. The different lignans were identified by HPLC and spectroscopic methods.

Hypoglycaemic constituents of Stachytarpheta cayennensis leaf

The aqueous infusion (tea) of Stachytarpheta cayennensis leaves is used ethnomedically in Peru, Nigeria and other tropical countries for the management of diabetes. Oral administration (p. o.) of aqueous (125 mg/kg) and methanolic (2000 mg/kg) extracts of the leaves to alloxan-diabetic rats showed significant blood glucose reductions by 43 and 53%, respectively, at the end of a 4 hour period similar to the strong effect of glibenclamide (5 mg/kg, P. O.). The methanolic extract was successively partitioned into ethyl acetate, butanol and water fractions, and the same test showed that the butanol fraction (2000 mg/kg) had the highest (50%) hypoglycaemic activity at 4 hours after oral administration. It was also the most active fraction when tested in vitro [insulin release from an insulin secreting cell line (INS-1)] and was also active in normal rats and rats made hyperglycaemic by a glucose load. Its activity was comparable to that of glibenclamide (positive control) in these models. This active butanol fraction was subjected to chromatographic subfractionation; some subfractions reduced hyperglycaemia in alloxan-diabetic rats to 60 and 78% and induced insulin release from the INS-1 cells; other subfractions, however, gave hyperglycaemic activities IN VIVO and inhibition of insulin release from the INS-1 cells. Three major compounds of the butanol fraction were isolated and characterised as 6beta-hydroxyipolamide, ipolamide and isoverbascoside; they increased insulin secretion from INS-1 cells to 125, 128 and 127%, respectively, whereas glibenclamide increased insulin secretion to 157%. The results justify the ethnomedical use of the plant in the management of diabetes and suggest that the butanol fraction and some of its isolated constituents mediate their actions primarily by stimulating insulin release directly.

Accumulation of lignans in suspension cultures of Linum mucronatum ssp. armenum (Bordz.) Davis

For the first time callus and suspension cultures of Linum mucronatum ssp. annenum were initiated, grown in darkness at 25 degrees C and analyzed for lignans. 6-Methoxypodophyllotoxin was the main lignan besides smaller amounts of podophyllotoxin isolated and identified by chromatographic methods as well as by 1H NMR.

Cysteine 38 in p65/NF-kappaB plays a crucial role in DNA binding inhibition by sesquiterpene lactones

Sesquiterpene lactones (SLs) have potent anti-inflammatory properties. We have shown previously that they exert this effect in part by inhibiting activation of the transcription factor NF-kappaB, a central regulator of the immune response. We have proposed a molecular mechanism for this inhibition based on computer molecular modeling data. In this model, SLs directly alkylate the p65 subunit of NF-kappaB, thereby inhibiting DNA binding. Nevertheless, an experimental evidence for the proposed mechanism was lacking. Moreover, based on experiments using the SL parthenolide, an alternative mode of action has been proposed by other authors in which SLs inhibit IkappaB-alpha degradation. Here we report the construction of p65/NF-kappaB point mutants that lack the cysteine residues alkylated by SLs in our model. In contrast to wild type p65, DNA-binding of the Cys(38) --> Ser and Cys(38,120) --> Ser mutants is no longer inhibited by SLs. In addition, we provide evidence that parthenolide uses a similar mechanism to other SLs in inhibiting NF-kappaB. Contrary to previous reports, we show that parthenolide, like other SLs, inhibits NF-kappaB most probably by alkylating p65 at Cys(38). Although a slight inhibition of IkappaB degradation was detected for all SLs, the amount of remaining IkappaB was too low to explain the observed NF-kappaB inhibition.

Inhibitory effects of helenalin and related compounds on 5-lipoxygenase and leukotriene C(4) synthase in human blood cells

The sesquiterpene lactone helenalin, which can be isolated from several plant species of the Asteraceae family, is a potent anti-inflammatory and antineoplastic agent. In agreement, alcohol extracts of these plants are used for local external treatment of inflammatory conditions. Since leukotrienes are important mediators in inflammatory processes, the inhibitory effects of helenalin and some derivatives on leukotriene (LT) biosynthesis were studied. Treatment of human platelets with helenalin provoked irreversible inhibition of LTC(4) synthase in a concentration- and time-dependent manner with an IC(50) of 12 microM after a 60 min preincubation. 11alpha,13-Dihydrohelenalin acetate was less potent. Interestingly, individual donors could be divided into two distinct groups with respect to the efficacy of helenalin to suppress platelet LTC(4) synthase. In human granulocytes, helenalin inhibited both the 5-lipoxygenase (IC(50) 9 microM after 60 min preincubation) and LTC(4) synthase in a concentration- and time-dependent fashion. In contrast, the drug was without effect on LTA(4) hydrolase. The GSH-containing adducts (2beta-(S-glutathionyl)-2,3-dihydrohelenalin and 2beta-(S-glutathionyl)-2,3,11alpha,13-tetra hydrohelenalin acetate) did not significantly inhibit LTC(4) synthase. The present results indicate a mechanism for the anti-inflammatory effect of helenalin and related compounds.

The influence of glutathione and cysteine levels on the cytotoxicity of helenanolide type sesquiterpene lactones against KB cells

The biological activities of sesquiterpene lactones have been attributed to their reactivity with the cysteine residues of functional proteins forming covalent bonds via Michael type addition. In the present study we investigated the influence of different L-cysteine (cys) and glutathione (GSH) concentrations on the cytotoxicity of the sesquiterpene lactones (STLs) helenalin, 11alpha,13-dihydrohelenalin acetate and chamissonolide against KB cells. Due to the significantly higher reactivity of the alpha-methylene-gamma-lactone (ML) towards cys as compared with the cyclopentenone (CP) site at physiological pH, addition of 20, 50 and 100 molar equivalents of cys decreased the cytotoxicity of helenalin and chamissonolide, whereas the cytotoxicity of 11alpha,13-dihydrohelenalin acetate remained unaffected. In contrast, the influence of GSH addition on the cytotoxicity of 11alpha,13-dihydrohelenalin acetate depends on the concentration of GSH added. Concentration-effect curves obtained for chamissonolide and GSH resembled the decline in cytotoxicity after cys addition. Helenalin showed a biphasic shape of the concentration-effect curve for the 100:1 GSH/helenalin ratio resembling at higher doses the chamissonolide and in lower doses the 11alpha,13-dihydrohelenalin acetate curve at 50-fold excess. These results can be explained by the different reactivity and equilibrium conditions for thiol addition of the two reactive centers of bifunctional STLs in cellular test systems and verified a clear correlation between the different reactivity of their electrophilic centers and the observed biological effects in in-vitro cell systems.

The alpha-subunit of the epithelial sodium channel is an aldosterone-induced transcript in mammalian collecting ducts, and this transcriptional response is mediated via distinct cis-elements in the 5'-flanking region of the gene

Aldosterone stimulates Na(+) reabsorption in the collecting ducts by increasing the activity of the epithelial sodium channel, ENaC. Systemic administration of aldosterone increases alpha ENaC mRNA expression in mammalian kidney, suggesting that the alpha ENaC gene is a target for aldosterone action in the distal nephron. To determine whether aldosterone increases alpha ENaC gene transcription, a portion of the alpha ENaC 5'- flanking region coupled to luciferase was transfected into MDCK-C7 cells, a collecting duct cell line with aldosterone-stimulated Na(+) transport. Both dexamethasone and aldosterone stimulated alpha ENaC-coupled reporter gene activity via the glucocorticoid receptor (GR), and this response correlated with the effect of these hormones on endogenous alpha ENaC expression. The aldosterone-stimulated alpha ENaC expression was blocked by actinomycin D, and aldosterone had no effect on alpha ENaC mRNA decay, confirming a transcriptional effect. In HT-29 cells, a GR/mineralocorticoid receptor (MR)-deficient colonic cell line with constitutive alpha ENaC expression, cotransfection with GR or MR restored aldosterone-stimulated alpha ENaC gene transcription, although aldosterone had a functional preference for MR. Analysis of deletion constructs confirmed that a single imperfect glucocorticoid response element (GRE) is necessary and sufficient to confer the aldosterone responsiveness to the alpha ENaC gene promoter in MDCK-C7 and HT-29 cells. These results confirm that alpha ENaC is an aldosterone-induced transcript in the collecting duct and delineates the molecular mechanism for this effect.

New allo-cedrane type sesquiterpene hemiketals and further sesquiterpene lactones from fruits of Illicium floridanum

Three new tetracyclic sesquiterpene hemiketals possessing the very rare allo-cedrane carbon skeleton, debenzoyl-7-deoxo-1 alpha,7 alpha-dihydroxytashironin, debenzoyl-7-deoxo-7 alpha-hydroxytashironin, and debenzoyl-7-deoxo-7 alpha-hydroxy-3-oxotashironin (1--3), were isolated from the fruits of Illicium floridanum ELLIS (American Star Anise, Star bush). Their structures were elucidated by mass and NMR spectroscopic analyses. The molecular structure of 1, including absolute stereochemistry, was determined by single-crystal X-ray diffraction of its monohydrate. Only one compound of this type, tashironin, has previously been isolated from Illicium tashiroi. Furthermore, a new sesquiterpene lactone of the seco-prezizaane type, 3,4-anhydro-13,14-dihydroxyfloridanolide (4), and the known anislactone B (5) were isolated. The occurrence of further allo-cedrane sesquiterpenes in another Illicium species confirms the hypothesis of previous authors that this type of compound is a biogenetic precursor of the typical seco-prezizaane sesquiterpene lactones found in this genus. Moreover, regarding their co-occurrence with anislactone B as reported here, they may also be considered precursors for the anislactone skeletal type.

Tetrahydrofuran lignans from Illicium floridanum and their activity in a luminol enhanced chemiluminescence assay

Two lignans of the tetrahydrofuran type, di-O-methyltetrahydrofuroguaiacin B (1) and (+)-veraguensin (2) were isolated from fruits and leaves of Illicium floridanum Ellis (Illiciaceae). These compounds are the first genuine lignans isolated from the genus Illicium. We investigated their radical scavenging potency towards 1,1-diphenyl-2-picrylhydrazyl radical reagent and their influence on luminol enhanced chemiluminescence (CHL) induced by different stimuli in human polymorphonuclear neutrophils (PMN). Both compounds were inactive in the TLC assay for chemical radical scavenge. In the PMN assay, the symmetric lignan 1 at concentrations below 1.0 microM displayed a strong inhibition of CHL induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP). At concentrations above 5 microM, 1 led to a pronounced increase of fMLP induced CHL. When CHL was stimulated with opsonized zymosan, both compounds were completely inactive. Thus, 1 must interfere selectively with a step in the signal cascade evoked by fMLP. In addition to their known PAF-receptor antagonism tetrahydrofuran lignans may thus also interfere with inflammatory responses by inhibition of free radical formation.

On the stability of sesquiterpene lactones in the officinal Arnica tincture of the German pharmacopoeia

An investigation of sesquiterpene lactone content in Arnica tincture (German Pharmacopoeia) after storage for three years at different temperatures (+4, +25 and +30 degrees C) was carried out by GC and GC-MS analysis. A decrease (13, 32 and 37%, respectively) in the content of the main active compounds in this preparation, 11 alpha,13-dihydrohelenalin esters, correlating with storage temperature was found. This change was shown to be caused by addition of ethanol to the cyclopentenone structure of these molecules leading to 2-ethoxy-2,3,11,13-tetrahydrohelenalin derivatives.

Glutathione adducts of helenalin and 11 alpha,13-dihydrohelenalin acetate inhibit glutathione S-transferase from horse liver

The 2-mono- and 2,13-bis-glutathionyl adducts of helenalin and the 2-monoglutathionyl adduct of 11 alpha,13-dihydrohelenalin acetate were previously shown to be formed by spontaneous Michael addition at physiological pH. In living cells, glutathione (GSH) conjugation of many types of electrophilic agents is catalysed by a family of GSH S-transferase enzymes (GST). The capability of a glutathione S-transferase from horse liver to catalyze the reaction of helenalin and other helenanolides with GSH was investigated. The enzyme did not accelerate GSH conjugation of helenalin, 11 alpha,13-dihydrohelenalin, or 2-deacetyl-6-deoxychamissonolide. The GSH-adducts, formed by spontaneous reaction, were found to be inhibitors of this enzyme. Free helenalin, a potent inhibitor of many enzymes containing free sulfhydryl groups, did not show any inhibitory activity on GST. It was thus demonstrated that GSH-adducts of sesquiterpene lactones possess their own specific biological activity. Two further enzymes using GSH as substrate, glutathione reductase and glyoxalase I, were not influenced by free helenalin or its GSH-adducts.

Helenanolide type sesquiterpene lactones. Part 5: the role of glutathione addition under physiological conditions

Sesquiterpene lactones (STLs) are known to exert most of their numerous biological activities through inhibition of enzymes and other functional proteins by forming covalent bonds with free cysteine residues in these macromolecules. The question arises how these drugs can alkylate such vital target structures instead of being quickly deactivated by reaction with the cysteine group of glutathione (GSH) which is present in high concentrations in all cells. We have measured in this study the pH dependent kinetics of GSH addition to the cyclopentenone and alpha-methylene-gamma-lactone group of helenanolide type sesquiterpene lactones using UV-spectrophotometry. The reaction with GSH at physiological pH proceeds very quickly but is reversible so that a fraction of STL molecules will always be available for reaction with protein targets. In agreement with these chemical data, helenalin-mono- and -bis-glutathionyl adducts were demonstrated to inhibit the nuclear transcription factor NF-kappaB at concentrations similar to the free sesquiterpene lactone.

The molecular structure of 2alpha-hydroxyneoanisatin and structure-activity relationships among convulsant sesquiterpenes of the seco-prezizaane and picrotoxane types

The molecular structure of 2alpha-hydroxyneoanisatin, a positional isomer of the potent neurotoxin anisatin, was determined by X-ray crystallographic analysis. This compound and four further seco-prezizaane type sesquiterpene lactones previously isolated from Illicium floridanum, which represent different structural types with respect to the mode of cyclisation, did not induce anisatin/picrotoxinin-like convulsions in mice. Based on these results and literature data for other seco-prezizaanes, structural requirements for convulsant activity are discussed. Comparison of the three dimensional molecular shape and electrostatic properties of active and inactive seco-prezizaane type lactones with compounds of the picrotoxane type resulted in the identification of a common pharmacophore structure for these different skeletal classes of convulsant natural products.

Inhibition of transcription factor NF-kappaB by sesquiterpene lactones: a proposed molecular mechanism of action

Many sesquiterpene lactones (SLs) possess considerable anti-inflammatory activity. They inhibit the transcription factor NF-kappaB by selectively alkylating its p65 subunit probably by reacting with cysteine residues. Here we assayed 28 sesquiterpene lactones for their ability to inhibit NF-kappaB. The majority of the potent NF-kappaB inhibitors possess two reactive centers in form of an alpha-methylene-gamma-lactone group and an alpha,beta- or alpha,beta,gamma,delta-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.

Functional and energetic consequences of chronic myocardial creatine depletion by beta-guanidinopropionate in perfused hearts and in intact rats

Oral feeding with the creatine analogue beta-guanidinopropionate (beta-GP) reduces myocardial phosphocreatine and creatine concentrations by about 80%in vitro, this is accompanied by reduced contractile performance. We hypothesized, thus, that beta-GP feeding leads to hemodynamic changes in vivo characteristic of heart failure. beta-GP was fed to Wistar rats for up to 8 weeks. In isolated hearts, function was measured isovolumically, myocardial energetics were followed with (31)P-NMR spectroscopy. In vivo hemodynamics were measured with Millar-Tip-catheters and an electromagnetic flow probe. Beta-GP feeding did not alter heart weight. In vitro, diastolic pressure-volume curves indicated structural left ventricular dilatation, and a 36% reduction of left ventricular developed pressure was found; phosphocreatine was reduced by approximately 80%, ATP unchanged and creatine kinase reaction velocity ((31)P-MR saturation transfer) decreased by approximately 90%. The total creatine pool (high-pressure liquid chromatography) was reduced by up to approximately 70%. In contrast to in vitro findings, in vivo cardiac hemodynamics (including left ventricular developed pressure, d P/d t(max), cardiac output and peripheral vascular resistance) at rest and during acute volume loading showed no alterations after beta-GP feeding. The only functional impairment observed in vivo was a 14% reduction of maximum left ventricular developed pressure during brief aortic occlusion. In the intact rat, cardiac and/or humoral compensatory mechanisms are sufficient to maintain normal hemodynamics in spite of a 90% reduction of creatine kinase reaction velocity. However, chronic beta-GP feeding leads to structural left ventricular dilatation.

Novel seco-prezizaane sesquiterpenes from north american illicium species

Three novel seco-prezizaane sesquiterpenes (1-3) were isolated from leaves of Illicium parviflorum (swamp star anise, yellow star anise), a species occurring endemically in central Florida. Compound 1, named cycloparvifloralone, possesses a hitherto unknown ring system with a cagelike acetal/hemiketal structure. Lactones 2 (cycloparviflorolide) and 3 (parviflorolide) which were obtained as an inseparable mixture, coexist in a hemiketal/keto equilibrium. It could be shown that a 4,7-hemiketal (4) occurs in an analogous fashion to pseudoanisatin 5, a known constituent of other Illicium species. From the fruits of Illiciumfloridanum the novel ortholactone 6 was isolated. The structures of the new compounds were elucidated by interpretation of their 1D and 2D homo- and heteronuclear NMR spectroscopic data. The modes of cyclization observed in 1, 2, 4, and 6 have not been described previously, and a biogenetic sequence is proposed for these compounds and further seco-prezizaane sesquiterpenes.

The anti-inflammatory sesquiterpene lactone helenalin inhibits the transcription factor NF-kappaB by directly targeting p65

The sesquiterpene lactone helenalin is a potent anti-inflammatory drug whose molecular mechanism of action remains unclear despite numerous investigations. We have previously shown that helenalin and other sesquiterpene lactones selectively inhibit activation of the transcription factor NF-kappaB, a central mediator of the human immune response. These drugs must target a central step in NF-kappaB pathway, since they inhibit NF-kappaB induction by four different stimuli. It has previously been reported that sesquiterpene lactones exert their effect by inhibiting degradation of IkappaB, the inhibitory subunit of NF-kappaB. These data contradicted our report that IkappaB is not detectable in helenalin-treated, ocadaic acid-stimulated cells. Here we use confocal laser scanning microscopy to demonstrate the presence of IkappaB-released, nuclear NF-kappaB in helenalin-treated, tumor necrosis factor-alpha stimulated cells. These data show that neither IkappaB degradation nor NF-kappaB nuclear translocation are inhibited by helenalin. Rather, we provide evidence that helenalin selectively alkylates the p65 subunit of NF-kappaB. This sesquiterpene lactone is the first anti-inflammatory agent shown to exert its effect by directly modifying NF-kappaB.

Structure revision of xanthalongin and further sesquiterpene lactones from flowers of Arnica longifolia

In addition to the helenanolide and xanthanolide type sesquiterpene lactones previously isolated from A. longifolia D.C. Eaton, we report on 13 further sesquiterpene lactones (7 helenanolides, 1 xanthanolide, 3 1,5-trans-guaianolides, 1 1,5-cis-guaianolide and 1 eudesmanolide) occurring in the flowerheads of this species. The structure of xanthalongin is revised to a 10beta-methyl configurated xanthanolide on the basis of new NMR spectral evidence. Furthermore, the 1,5-cis-guaianolide 2- O-acetylarnimollin, in contrast with our previous assignment, possesses a 2alpha-O-acyl configuration. A sesquiterpene lactone pattern as diverse as that of A. longifolia consisting of 1,5-trans-guaianolides and pseudoguaianolides (helenanolides), 1,5-cis-guaianolides and xanthanolides as well as eudesmanolides, which are postulated to be derived from three different biogenetic pathways, is particularly remarkable.

Aggravation of left ventricular remodeling by a novel specific endothelin ET(A) antagonist EMD94246 in rats with experimental myocardial infarction

An endothelin (ET(A)) antagonist reduced mortality and an ET(A) + ET(B) antagonist prevented left ventricular dilatation in rats with large myocardial infarction. This study tested the hypothesis that long-term blockade of the ET(A) receptor would have beneficial effects on left ventricular function and remodeling. Three hours after coronary artery ligation or sham operation in rats, EMD94246 (100 mg/kg/day, n=62) or placebo (n=62) was given by gavage. Eight weeks later, left ventricular hemodynamic measurements were performed and left ventricular volume determined with a double-lumen catheter after KCl-induced cardiac arrest. EMD94246 treatment had no effects on mortality or hemodynamic parameters. In rats with large infarcts, EMD94246 significantly increased left ventricular volume (2.5+/-0.1 vs. 2.2+/-0.1 ml/kg; p < 0.05). The nonpeptide ET(A)-selective antagonist EMD94246 promoted chronic left ventricular dilatation in rats with large myocardial infarction.

Sesquiterpene lactone content in leaves of in vitro and field cultivated Arnica montana

On the basis of GC and GC/MS analyses we report on the full qualitative and quantitative sesquiterpene lactone (STL) content of in vitro cultivated A. montana plantlets consisting of helenalin and 11alpha,13-dihydrohelenalin esters in approximately equal amounts. The accumulation of STL was shown to be correlated with tissue differentiation in the above-ground parts. The seasonal variation of STL content in leaves of A. montana cultivated in the proving field was investigated. Changes in the composition of the STL fraction were detected. While young plants accumulate mainly helenalin derivatives, the content of such compounds decreases to almost zero within about 6 weeks from the beginning of leaf formation while that of dihydrohelenalin type compounds increases at the same rate and remains constant for a longer period.

Agonist-specific modulation of glucocorticoid receptor-mediated transcription by immunosuppressants

Although the immunosuppressive drugs FK506, rapamycin and cyclosporin A have been reported to potentiate transcriptional activation mediated by a non-saturating concentration of the glucocorticoid receptor agonist dexamethasone, the precise mechanism(s) underlying these responses remains unclear. The murine L-929-derived LMCAT cell line stably transfected with the mouse mammary tumor virus promoter-chloramphenicol acetyl transferase reporter gene construct was utilized in the present study to further investigate the mechanism(s) underlying this dexamethasone potentiation as well as the possible agonist specificity of this potentiation. The present data demonstrate that pretreatment (2 h) of LMCAT cells with 10 microM FK506, rapamycin or cyclosporin A results in the potentiation of reporter gene transcription mediated not only by dexamethasone (approximately 12-fold), but also by hydrocortisone (approximately 6-fold) and triamcinolone acetonide (approximately 2.5-fold). In sharp contrast, the data show for the first time that pretreatment with any one of these immunosuppressive drugs suppresses (approximately 2-8-fold) the transcriptional responses mediated by corticosterone, deoxycorticosterone, and cortexolone. Pretreatment of intact LMCAT cells with FK506 increases the subsequent whole cell specific binding of [3H]dexamethasone, but does not increase specific cytoplasmic binding when the tritiated agonist is added directly to cytosolic extracts prepared from the pretreated cells. These data suggest that the FK506-mediated potentiation of the transcriptional responses induced by some agonists, like dexamethasone, may be related to the ability of this immunosuppressant to inhibit the membrane-associated multidrug resistance (MDR) P-glycoprotein, which actively extrudes some steroids from cells. Identical pretreatment with FK506 has no detectable effect on the subsequent whole cell specific binding of [3H]corticosterone, a steroid which is not effectively extruded by the MDR pump. Two additional MDR pump inhibitors, verapamil and quinidine, potentiate (30-fold) the dexamethasone-mediated transcriptional response as expected, but have no detectable effects on a corticosterone-mediated transcriptional response. Unlike immunosuppressive drugs, these ion channel blockers do not bind to receptor-associated immunophilins (FK506-binding proteins or cyclophilins). Collectively, these results suggest that immunosuppressants potentiate a dexamethasone-mediated transcriptional response in LMCAT cells by inhibiting efflux of this steroid. In contrast, these drugs appear to suppress a corticosterone-mediated transcriptional response by a different mechanism, perhaps one involving their binding to glucocorticoid receptor-associated immunophilins.

New Sesquiterpene Lactones from Illicium floridanum

In continuation of our phytochemical investigation of Illicium floridanum Ellis (American star anise, star bush), three new sesquiterpene lactones possessing the anisatin-type carbon skeleton (8,9-seco-prezizaane skeleton), 14-acetoxy-3-oxofloridanolide (1), 13-acetoxy-14-(n-butyryloxy)floridanolide (2), and 3beta-acetoxy-14-n-butyryloxy-10-deoxyfloridanolide (3), were isolated from fruits of this plant. Their structures were elucidated by 1D and 2D NMR measurements. The molecular structure of 1 was obtained by single crystal X-ray diffraction. The 11,3-delta-lactone structure of the compound previously described as debenzoyldunnianin in our previous communication, on grounds of NMR spectral evidence and X-ray crystallographic analysis is revised to a delta-lactone closed between C-11 and C-7 (compound 4). The neurotoxic sesquiterpene lactone anisatin (5) and its isomer 2alpha-hydroxyneoanisatin (3-deoxy-2alpha-hydroxyanisatin, 6) were also isolated and identified by spectroscopic means. The presence of the neurotoxin 5 in relatively high amounts in the fruits and leaves confirms and explains early reports on the toxicity of this plant.

Helenalin, an anti-inflammatory sesquiterpene lactone from Arnica, selectively inhibits transcription factor NF-kappaB

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, 11alpha,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, 11alpha,13-dihydrohelenalin and chamissonolid, inhibit activation of transcription factor NF-kappaB. This difference in efficacy, which correlates with the compounds' anti-inflammatory potency in vivo, may be explained by differences in structure and conformation. NF-kappaB, which resides in an inactive, cytoplasmic complex in unstimulated cells, is activated by phosphorylation and degradation of its inhibitory subunit, IkappaB. Helenalin inhibits NF-kappaB activation in response to four different stimuli in T-cells, B-cells and epithelial cells and abrogates kappaB-driven gene expression. This inhibition is selective, as the activity of four other transcription factors, Oct-1, TBP, Sp1 and STAT 5 was not affected. We show that inhibition is not due to a direct modification of the active NF-kappaB heterodimer. Rather, helenalin modifies the NF-kappaB/IkappaB complex, preventing the release of IkappaB. 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.

Trans-retinoic acid and glucocorticoids synergistically induce transcription from the mouse mammary tumor virus promoter in human embryonic kidney cells

Human embryonic kidney (K293) cells transfected with a mouse mammary tumor virus (MMTV) promoter-luciferase reporter construct (pHH-Luc) were utilized to investigate the potential effects of trans-retinoic acid (tRA), either by itself or in combination with glucocorticoid (GC) hormones, on a well-characterized, GC-sensitive transcriptional response. tRA or the synthetic GC hormone dexamethasone induced transcription from the MMTV promoter in a dose-dependent manner, with 1 micromol tRA and 1 micromol dexamethasone alone causing a four- to six-fold and a 40-fold induction of basal transcription, respectively. Simultaneous treatment with 1 micromol dexamethasone and 1 micromol tRA resulted in a synergistic transcriptional response that was 120-fold higher than basal level and 2.5 times the predicted response, based on a simple additive effect of both agonists. tRA does not appear to mediate this synergistic transcriptional response by enhancing GC receptor (GR) binding capacity, affinity, or nuclear translocation. tRA was unable to potentiate GC-induced transcriptional activity from a minimal GC response element (GRE), and GC were unable to potentiate tRA-induced transcriptional activity from a minimal retinoic acid response element (RARE). These data rule out direct protein-protein interactions between GC and retinoid receptors as a mechanism for the observed synergism. tRA also synergized with aldosterone-induced, mineralocorticoid receptor (MR)-mediated, transcriptional activation of the MMTV promoter, resulting in a response that was 1.7 times the predicted additive response. The MMTV GRE located between -187 and -165 was required for GC-induced and synergistic activation of the MMTV promoter, whereas sequences located within -151 to +5 were sufficient for tRA-induced transcription from the MMTV promoter. Mutation of a consensus RARE half-site (CCAAGT) identified at position -65 to -60 within the MMTV-LTR did not affect either tRA-induced transcriptional activation or synergism with GC. We propose that the tRA-induced transcriptional response from the MMTV promoter, as well as synergism with GC, may be mediated by the activation or induction of a factor(s) that either directly binds to the MMTV promoter or indirectly stabilizes binding of another transcription factor to these sequences.