Synthetic triterpenoids target the Arp2/3 complex and inhibit branched actin polymerization

Synthetic triterpenoids are anti-tumor agents that affect numerous cellular functions including apoptosis and growth inhibition. Here, we used mass spectrometric and protein array approaches and uncovered that triterpenoids associate with proteins of the actin cytoskeleton, including actin-related protein 3 (Arp3). Arp3, a subunit of the Arp2/3 complex, is involved in branched actin polymerization and the formation of lamellipodia. 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO)-Im and CDDO-Me were observed to 1) inhibit the localization of Arp3 and actin at the leading edge of cells, 2) abrogate cell polarity, and 3) inhibit Arp2/3-dependent branched actin polymerization. We confirmed our drug effects with siRNA targeting of Arp3 and observed a decrease in Rat2 cell migration. Taken together, our data suggest that synthetic triterpenoids target Arp3 and branched actin polymerization to inhibit cell migration.

Ardipusilloside I purified from Ardisia pusilla competitively binds VEGFR and induces apoptosis in NCI-H460 cells

The present study was to evaluate the effects of Ardipusilloside I isolated from Ardisia pusilla on the growth, vascular endothelial growth factor receptor (VEGFR) expression and apoptosis of NCI-H460 cell line by MTT, ELISA and flow cytometer, respectively. The docking assay between Ardipusilloside I and VEGFR was studied by Sybyl/Sketch module. The change of microstructure was observed by transmission electron microscope (TEM). DNA fragmentation was visualized by agarose gel electrophoresis. The protein expression of Bax and Bcl-2 was detected by immunohistochemistry (IHC). A series of changes were observed in NCI-H460 cell treated by Ardipusilloside I, including microstructure, DNA fragmentation, protein expression of VEGFR, Bax and Bcl-2. The results showed Ardipusilloside I had a good docking with VEGFR and could inhibit growth and induce apoptosis of NCI-H460 cell in a dose-dependent manner. Cell cycle was significantly stopped at the G(1) phase. Under electronic microscope, the morphology of NCI-H460 cell treated with Ardipusilloside I showed nuclear karyopycnosis, chromatin agglutination and typical apoptotic body. VEGFR and Bcl-2 expression were decreased and Bax expression was increased. In conclusion, all these results demonstrate that Ardipusilloside I has a good docking with VEGFR and has an inhibitory effect on growth of NCI-H460 cell and can induce its apoptosis.

Resistance in the plant, Barbarea vulgaris, and counter-adaptations in flea beetles mediated by saponins

Three saponins and two sapogenins had differential effects on food consumption in five near-isogenic flea beetle lines, which differ in their ability to utilize a novel host plant, Barbarea vulgaris (Brassicaceae). The ability to live on this plant is controlled by major, dominant R-genes in the flea beetle, Phyllotreta nemorum (Coleoptera: Chrysomelidae: Alticinae). A susceptible genotype (rr) is unable to live on the plant, whereas resistant genotypes (RR and Rr) can utilize the novel host plant. Among compounds isolated from B. vulgaris, hederagenin cellobioside (hederagenin-3-O-(4-O-beta-D-glucopyranosyl)-beta-D-glucopyranoside) inhibited feeding, whereas the effect of oleanolic acid cellobioside was much weaker. The aglycones (sapogenins) were inactive. Although hederagenin cellobioside was active against all flea beetle lines, its effect on food consumption was much stronger on the susceptible genotype (rr) compared to the resistant genotype (Rr). Susceptible and resistant flea beetle genotypes were equally sensitive to a non-host saponin, alpha-hederin (hederagenin-3-O-(2-O-alpha-L-rhamnopyranosyl)-alpha-L-arabinopyranoside). These results suggest that R-alleles in flea beetles might be specific adaptations to defensive saponins in B. vulgaris. A possible mechanism of action of the R-alleles might be to encode for an enzyme (e.g. a glucosidase), which is able to cleave glycosidic bonds in hederagenin cellobioside, but not in alpha-hederin. The potential role of saponins as defensive compounds in B. vulgaris and as targets for counter-adaptations in flea beetles and other insects is discussed.

Overexpression of a grapevine R2R3-MYB factor in tomato affects vegetative development, flower morphology and flavonoid and terpenoid metabolism

Although the terpenoid pathway constitutes, with the phenylpropanoid metabolism, the major pathway of secondary metabolism in plants, little is known about its regulation. Overexpression of a Vitis vinifera R2R3-MYB transcription factor (VvMYB5b) in tomato induced pleiotropic changes including dwarfism, modified leaf structure, alterations of floral morphology, pigmented and glossy fruits at the "green-mature" stage and impaired seed germination. Two main branches of secondary metabolism, which profoundly influence the organoleptic properties of the fruit, were affected in the opposite way by VvMYB5b overexpression. Phenylpropanoid metabolism was down regulated whereas the amount of beta-carotene was up regulated. This is the first example of the independent regulation of phenylpropanoid and carotenoid metabolism. The strongest modification concerns a decrease in beta-amyrin, the precursor of the oleanolic acid, which is the major component of grape waxes. Scanning electron microscopy analysis of fruits and leaves confirms the alteration of wax metabolism and a modification of cell size and shape. This may potentially impact resistance/tolerance to biotic and abiotic stresses. The results are compared with a similar approach using heterologous expression of VvMYB5b in tobacco.

Accumulation and dynamic trends of triterpenoid saponin in vegetative organs of Achyranthus bidentata

The relationship between structural features of various vegetative organs and triterpenoid saponin accumulation in Achyranthus bidentata Blume was investigated using anatomy, histochemistry and phytochemistry. The results showed that the primary and secondary structures of roots, and the structures of stems and leaves of A. bidentata, were similar to those of ordinary dicotyledonous plants. The enlargement of its roots, however, was primarily associated with growth and differentiation of tertiary structures. There were collateral medullary vascular bundles in addition to the normal vascular bundles in the stem. The tertiary structure was not only main parts in the roots of A. bidentata, but also important storage region of triterpenoid saponin in its growth and development. The stem may be the essential transport organ of triterpenoid saponin, while palisade parenchyma may be the primary synthesis location. In November, the total quantity of triterpenoid saponin and overall biomass in the roots reach a maximum level. This was the best time, therefore, to harvest the roots and corresponded to the traditional harvest period. Despite the withered appearance of leaves, stems also contained substantial amounts of triterpenoid saponin, and it was recommended that the stems of A. bidentata should be used.

2070-DTI, A Topoisomerase Inhibitor Produced byStreptomycessp. Strain No. 2070

A novel inhibitor of topoisomerase II designated as 2070-DTI was isolated from the culture filtrate of Streptomyces sp. strain No. 2070. The structure was determined to be that of the known soyasaponin I on the basis of spectroscopic methods (NMR and MS). 2070-DTI strongly inhibited the decatenation activity of human placenta topoisomerase II in a noncompetitive manner, and weakly inhibited or was inert towards the relaxation activities of various topoisomerase I's and DNA-related enzymes. 2070-DTI is an inhibitor belonging to the cleavable complex-nonforming type without DNA intercalation.

Localization and dynamic change of saikosaponin in root of Bupleurum chinense

Anatomical, histochemical and phytochemical methods were used to investigate the structure, the localization and content changes of total saikosaponin and saikosaponin-a of the roots of Bupleurum chinense DC. at different developmental stages. Results showed that saikosaponin was mainly distributed in pericycle and primary phloem in the young root; but in the mature root, it was mainly distributed in vascular cambium and secondary phloem. During the whole growth period from the pre-blossom, blossom, fruit, and fruit mature periods until the pre-withering period, it was in the fruit mature period that both the total saikosaponin content and the saikosaponin-a content reached the highest level. So the last 20 d of October was considered as the right collecting season for the drug of B. chinense. In addition, the quality of 1-year-old drug was better than that of 2-year-old drug due to its higher saikosaponin content. On the other hand, judging from the external characteristics of the drug, the one with an acerose taproot and more lateral roots was of better quality. The results offered theoretical bases for selecting medicinal material of high quality and determining the most appropriate harvesting stage and part of B. chinense.

[Structural development of root and their relationship to accumulation of triterpenoid saponins in Achyranthes bidentata Bl]

A study concerning the relationship of dynamic accumulation of triterpenoid saponins and anatomical characteristics of Achyranthes bidentata Bl roots was undertaken by anatomical, histochemical and phytochemical method respectively. Results revealed that the primary and secondary structures of the root resembled those of usual dicots. The continual thickening growth of root principally resulted from the differentiation and development of the tertiary structure. The first ring of supernumerary cambium originated from the parenchyma and vascular ray cells of secondary phloem and each of the followed rings initiated in the outmost foundamental parenchyma cells which were derived from the immediate preceding ring. In the supernumerary cambiums, there had not distinction between the fusiform initial and the ray initial. Its cells present stratifide arranged from a longitudinal section through root. Regular and concentric rings of tertiary vascular bundles who differentiate centrifugally were enclosed by the connective parenchyma. The number of the rings continually increase with the development of the root itself. Triterpenoid saponins accumulated mainly in pericycle, primary phloem and parenchyma between primary phloem and xylem in the primary structure of root but came into existence in cells of secondary phloem and phelloderm with secondary structure development of root, and as well as in supernumerary cambium and phloem of tertiary vascular bundle after the tertiary structure maturated gradually in the roots. The investigation provides indications that the tertiary structure were not only main parts in the roots of Achyranthes bidentata Bl, but also important storage region of triterpenoid saponins in its growth and development. In addition, the analysis of using the HPLC showed that dynamic increasing trend oleanolic acid was as "S" curve during the roots growth and development and up to the highest content of triterpenoid saponins after plants grew 120 days. Meanwhile, the number of the rings of tertiary vascular bundles, length and diameter of the roots were the same as the triterpenoid saponins increasing trend. It should be optimal season for harvest.

Biotransformation of betulinic and betulonic acids by fungi

Betulinic acid (1), a triterpenoid found in many plant species, has attracted attention due to its important pharmacological properties, such as anti-cancer and anti-HIV activities. The closely related, betulonic acid (2) also has similar properties. In order to obtain derivatives potentially useful for detailed pharmacological studies, both compounds were submitted to incubations with selected microorganisms. In this work, both were individually metabolized by the fungi Arthrobotrys, Chaetophoma and Dematium, isolated from the bark of Platanus orientalis as well as with Colletotrichum, obtained from corn leaves; such fungal transformations are quite rare in the scientific literature. Biotransformations with Arthrobotrys converted betulonic acid (2) into 3-oxo-7beta-hydroxylup-20(29)-en-28-oic acid (3), 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4) and 3-oxo-7beta,30-dihydroxylup-20(29)-en-28-oic acid (5); Colletotrichum converted betulinic acid (1) into 3-oxo-15alpha-hydroxylup-20(29)-en-28-oic (6) acid whereas betulonic acid (2) was converted into the same product and 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4); Chaetophoma converted betulonic acid (2) into 3-oxo-25-hydroxylup-20(29)-en-28-oic acid (7) and both Chaetophoma and Dematium converted betulinic acid (1) into betulonic acid (2). Those fungi, therefore, are useful for mild, selective oxidations of lupane substrates at positions C-3, C-7, C-15, C-25 and C-30.

Dammarenediol-II synthase, the first dedicated enzyme for ginsenoside biosynthesis, in Panax ginseng

Panax ginseng produces triterpene saponins called ginsenosides, which are classified into two groups by the skeleton of aglycones, namely dammarane type and oleanane type. Dammarane-type ginsenosides dominate over oleanane type not only in amount but also in structural varieties. However, their sapogenin structure is restricted to two aglycones, protopanaxadiol and protopanaxatriol. So far, the genes encoding oxidosqualene cyclase (OSC) responsible for formation of dammarane skeleton have not been cloned, although OSC yielding oleanane skeleton (beta-amyrin synthase) has been successfully cloned from this plant. In this study, cDNA cloning of OSC producing dammmarane triterpene was attempted from hairy root cultures of P. ginseng by homology based PCR method. A new OSC gene (named as PNA) obtained was expressed in a lanosterol synthase deficient (erg7) Saccharomyces cerevisiae strain GIL77. LC-MS and NMR analyses identified the accumulated product in the yeast transformant to be dammarenediol-II, demonstrating PNA to encode dammarenediol-II synthase.

Identification of beta-amyrin and sophoradiol 24-hydroxylase by expressed sequence tag mining and functional expression assay

Triterpenes exhibit a wide range of structural diversity produced by a sequence of biosynthetic reactions. Cyclization of oxidosqualene is the initial origin of structural diversity of skeletons in their biosynthesis, and subsequent regio- and stereospecific hydroxylation of the triterpene skeleton produces further structural diversity. The enzymes responsible for this hydroxylation were thought to be cytochrome P450-dependent monooxygenase, although their cloning has not been reported. To mine these hydroxylases from cytochrome P450 genes, five genes (CYP71D8, CYP82A2, CYP82A3, CYP82A4 and CYP93E1) reported to be elicitor-inducible genes in Glycine max expressed sequence tags (EST), were amplified by PCR, and screened for their ability to hydroxylate triterpenes (beta-amyrin or sophoradiol) by heterologous expression in the yeast Saccharomyces cerevisiae. Among them, CYP93E1 transformant showed hydroxylating activity on both substrates. The products were identified as olean-12-ene-3beta,24-diol and soyasapogenol B, respectively, by GC-MS. Co-expression of CYP93E1 and beta-amyrin synthase in S. cerevisiae yielded olean-12-ene-3beta,24-diol. This is the first identification of triterpene hydroxylase cDNA from any plant species. Successful identification of a beta-amyrin and sophoradiol 24-hydroxylase from the inducible family of cytochrome P450 genes suggests that other triterpene hydroxylases belong to this family. In addition, substrate specificity with the obtained P450 hydroxylase indicates the two possible biosynthetic routes from triterpene-monool to triterpene-triol.

Induced accumulation of oleanolic acid and ursolic acid in cell suspension cultures of Uncaria tomentosa

Increasing sucrose from 20 to 50 g l(-1) in Uncaria tomentosa cell suspension cultures enhanced ursolic acid and oleanolic acid production from 129 +/- 61 to 553 +/- 193 microg g(-1) cell dry wt. The maximal concentration of both triterpenes (1680 +/- 39 microg g(-1) cell dry wt) was 8 days after elicitation by jasmonic acid, while yeast extract or citrus pectin treatments produced 1189 +/- 20 or 1120 +/- 26 microg g(-1) cell dry wt, respectively. The ratio of ursolic acid:oleanolic acid was constant at 70:30.

Function and clustered expression of MaxiK channels in cerebral myocytes remain intact with aging

The incidence of stroke increases significantly in the aging population where stroke related deaths boost at >75 years and survivors are often permanently disabled. Aging is known to decrease cerebral blood flow likely due to an increase in arterial tone. Although MaxiK channels are key regulators of cerebral arterial tone their pattern of expression and function in cerebral blood vessels during aging is unknown. Using specific antibodies against the alpha-subunit of MaxiK channels and current recordings, we now demonstrate that in aging cerebral myocytes, MaxiK channels remain healthy. Furthermore, we show for the first time that in the vasculature, MaxiK channels are expressed in clusters. Clusters have an estimated radius of approximately 200 nm in young rats (3-5 month old Fisher 344 rats) which remains normal in old (25-30 month rats) cerebral myocytes. Consistent with a healthy MaxiK channel expression in old cerebral arteries, MaxiK current density, kinetics and Ca(2+) sensitivity were practically identical in young and old myocytes. Sensitivity to nanomolar concentrations of dehydrosoyasaponin-I that activates channels formed by alpha and beta subunits is also the same in young and old myocytes. These results demonstrate that MaxiK channels maintain normal expression during cerebral aging which is in sharp contrast to our previous finding of loss of expression in aging coronary arteries. It seems therefore, that cerebral myocytes have developed a protective anti-aging mechanism leading to the continued expression of MaxiK channels.

Soyasaponin I and sapongenol B have limited absorption by Caco-2 intestinal cells and limited bioavailability in women

A human study was conducted to evaluate soyasaponin bioavailability in humans. Eight healthy women ingested a single dose of concentrated soy extract containing 434 micromol of group B soyasaponins, the predominant form of soyasaponins in soybeans. Neither soyasaponins nor their metabolites were detected in a 24-h urine collection. Soyasapogenol B, a major metabolite of group B soyasaponins, was found (36.3 +/- 10.2 micromol) in a 5-d fecal collection but no group B soyasaponins were detected. A human colon cancer Caco-2 cell model was used to evaluate the absorbability of soyasaponins at the mucosal level. The mucosal transfers of soyasaponin I and soyasapogenol B were 0.5-2.9 and 0.2-0.8%, respectively, after 4-h incubation on the Caco-2 monolayer. The apical to basolateral absorptions of soyasaponin I and soyasapogenol B were low with P(app) of 0.9 to 3.6 x 10(-6) and 0.3 to 0.6 x 10(-6) cm/s, respectively. The transport rate and cell uptake of soyasaponin I were saturable and concentration-independent. In contrast, soyasapogenol B was taken up by Caco-2 cells in a concentration-dependent manner. Soyasaponin I had no apparent cytotoxic effect on Caco-2 cells at concentrations up to 3 mmol/L, whereas soyasapogenol B at 1 mmol/L or more significantly reduced cell viability. Therefore, ingested soyasaponins have low absorbability in human intestinal cells and seem to be metabolized to soyasapogenol B by human intestinal microorganisms in vivo and excreted in the feces.

Human fecal metabolism of soyasaponin I

The metabolism of soyasaponin I (3-O-[alpha-L-rhamnopyranosyl-beta-D-galactopyranosyl-beta-D-glucuronopyranosyl]olean-12-ene-3beta,22beta,24-triol) by human fecal microorganisms was investigated. Fresh feces were collected from 15 healthy women and incubated anaerobically with 10 mmol soyasaponin I/g feces at 37 degrees C for 48 h. The disappearance of soyasaponin I in this in vitro fermentation system displayed apparent first-order rate loss kinetics. Two distinct soyasaponin I degradation phenotypes were observed among the subjects: rapid soyasaponin degraders with a rate constant k = 0.24 +/- 0.04 h(-)(1) and slow degraders with a k = 0.07 +/- 0.02 h(-)(1). There were no significant differences in the body mass index, fecal moisture, gut transit time, and soy consumption frequency between the two soyasaponin degradation phenotypes. Two primary gut microbial metabolites of soyasaponin I were identified as soyasaponin III (3-O-[beta-D-galactopyranosyl-beta-D-glucuronopyranosyl]olean-12-ene-3beta,22beta,24-triol) and soyasapogenol B (olean-12-ene-3beta,22beta,24-triol) by NMR and electrospray ionized mass spectroscopy. Soyasaponin III appeared within the first 24 h and disappeared by 48 h. Soyasapogenol B seemed to be the final metabolic product during the 48 h anaerobic incubation. These results indicate that dietary soyasaponins can be metabolized by human gut microorganisms. The sugar moieties of soyasaponins seem to be hydrolyzed sequentially to yield smaller and more hydrophobic metabolites.

Dynamics of β2-Adrenergic Receptor−Ligand Complexes on Living Cells†

The agonist-induced dynamic regulation of the beta(2)-adrenergic receptor (beta(2)-AR) on living cells was examined by means of fluorescence correlation spectroscopy (FCS) using a fluorescence-labeled arterenol derivative (Alexa-NA) in hippocampal neurons and in alveolar epithelial type II cell line A549. Alexa-NA specifically bound to the beta(2)-AR of neurons with a K(D) value of 1.29 +/- 0.31 nM and of A549 cells with a K(D) of 5.98 +/- 1.62 nM. The receptor density equaled 4.5 +/- 0.9 microm(-2) in neurons (rho(N)) and 19.9 +/- 2.0 microm(-2) in A549 cells (rho(A549)). Kinetic experiments revealed comparable on-rate constants in both cell types (k(on) = 0.49 +/- 0.03 s(-1) nM(-1) in neurons and k(on) = 0.12 +/- 0.02 s(-1) nM(-1) in A549 cells). In addition to the free ligand diffusing with a D(free) of (2.11 +/- 0.04) x 10(-6) cm(2)/s, in both cell types receptor-ligand complexes with two distinct diffusion coefficients, D(bound1) (fast lateral mobility) and D(bound2) (hindered mobility), were observed [D(bound1) = (5.23 +/- 0.64) x 10(-8) cm(2)/s and D(bound2) = (6.05 +/- 0.23) x 10(-10) cm(2)/s for neurons, and D(bound1) = (2.88 +/- 1.72) x 10(-8) cm(2)/s and D(bound2) = (1.01 +/- 0.46) x 10(-9) cm(2)/s for A549 cells]. Fast lateral mobility of the receptor-ligand complex was detected immediately after addition of the ligand, whereas hindered mobility (D(bound2)) was observed after a delay of 5 min in neurons (up to 38% of total binding) and of 15-20 min in A549 cells (up to 40% of total binding). Thus, the receptor-ligand complexes with low mobility were formed during receptor regulation. Consistently, stimulation of receptor internalization using the adenylate cyclase activator forskolin shifted the ratio of receptor-ligand complexes toward D(bound2). Intracellular FCS measurements and immunocytochemical studies confirmed the appearance of endocytosed receptor-ligand complexes in the cytoplasm subjacent to the plasma membrane after stimulation with the agonist terbutaline (1 microM). This regulatory receptor internalization was blocked after preincubation with propranolol and with a cholesterol-complexing saponin alpha-hederin.

A novel saponin hydrolase from Neocosmospora vasinfecta var. vasinfecta

We isolated a soybean saponin hydrolase from Neocosmospora vasinfecta var. vasinfecta PF1225, a filamentous fungus that can degrade soybean saponin and generate soyasapogenol B. This enzyme was found to be a monomer with a molecular mass of about 77 kDa and a glycoprotein. Nucleotide sequence analysis of the corresponding gene (sdn1) indicated that this enzyme consisted of 612 amino acids and had a molecular mass of 65,724 Da, in close agreement with that of the apoenzyme after the removal of carbohydrates. The sdn1 gene was successfully expressed in Trichoderma viride under the control of the cellobiohydrolase I gene promoter. The molecular mass of the recombinant enzyme, about 69 kDa, was smaller than that of the native enzyme due to fewer carbohydrate modifications. Examination of the degradation products obtained by treatment of soyasaponin I with the recombinant enzyme showed that the enzyme hydrolyzed soyasaponin I to soyasapogenol B and triose [alpha-L-rhamnopyranosyl (1-->2)-beta-D-galactopyranosyl (1-->2)-D-glucuronopyranoside]. Also, when soyasaponin II and soyasaponin V, which are different from soyasaponin I only in constituent saccharides, were treated with the enzyme, the ratio of the reaction velocities for soyasaponin I, soyasaponin II, and soyasaponin V was 2,680:886:1. These results indicate that this enzyme recognizes the fine structure of the carbohydrate moiety of soyasaponin in its catalytic reaction. The amino acid sequence of this enzyme predicted from the DNA sequence shows no clear homology with those of any of the enzymes involved in the hydrolysis of carbohydrates.

Recycling plant wax constituents for chemical defense: hemi-biosynthesis of triterpene saponins from ?-amyrin in a leaf beetle

Several species of Doryphorina leaf beetles from Central- and South America produce oleanane triterpene glycosides in their defensive glands. The presence of pentacyclic triterpenes in insects is intriguing since they lack the key enzymes necessary to synthesize these compounds. Since beta-amyrin is a common constituent of leaf waxes, we hypothesized that these leaf beetles use this compound as a precursor to their oleanane glycosides. To test this hypothesis we first confirmed the presence of beta-amyrin in Ipomoea batatas, the food plant of Platyphora kollari. Next, adults of P. kollari were fed for 10 days with I. batatas leaf disks painted with a solution of [2,2,3-(2)H(3)]beta-amyrin ([2,2,3-(2)H(3)]-1). The secretion from their defensive glands was collected and analyzed by HPLC-ESIMS. The results demonstrated that the secretion of beetles fed with an amount of [2,2,3-(2)H(3)]beta-amyrin corresponding to the quantity of unlabeled (natural) beta-amyrin present in the leaf disks contained on average 5.1% of [2,2,3-(2)H(3)]-3- O-beta- d-glucopyranosyl-(1-->4)-beta- d-glucuronopyranosyl-hederagenin ([2,2,3-(2)H(3)]-2), whereas the secretions of beetles fed with 10 times this amount of [2,2,3-(2)H(3)]beta-amyrin contained on average 23.9% of [2,2,3-(2)H(3)]-2. In both series of experiments, the percentage of labeled versus unlabeled triterpene glycoside in the secretion was positively correlated with the amount of deuterated beta-amyrin ingested. These results demonstrate for the first time that some leaf beetles are able to metabolize a widespread triterpenic constituent of leaf wax into more complex glycosides that are stored in their defensive glands.

Ethanol sensitivity of BK(Ca) channels from arterial smooth muscle does not require the presence of the beta 1-subunit

Ethanol inhibition of large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channels in aortic myocytes may contribute to the direct contraction of aortic smooth muscle produced by acute alcohol exposure. In this tissue, BK(Ca) channels consist of pore-forming (bslo) and modulatory (beta) subunits. Here, modulation of aortic myocyte BK(Ca) channels by acute alcohol was explored by expressing bslo subunits in Xenopus oocytes, in the absence and presence of beta(1)-subunits, and studying channel responses to clinically relevant concentrations of ethanol in excised membrane patches. Overall, average values of bslo channel activity (NP(o), with N = no. of channels present in the patch; P(o) = probability of a single channel being open) in response to ethanol (3-200 mM) mildly decrease when compared with pre-ethanol, isosmotic controls. However, channel responses show qualitative heterogeneity at all ethanol concentrations. In the majority of patches (42/71 patches, i.e., 59%), a reversible reduction in NP(o) is observed. In this subset, the maximal effect is obtained with 100 mM ethanol, at which NP(o) reaches 46.2 +/- 9% of control. The presence of beta(1)-subunits, which determines channel sensitivity to dihydrosoyaponin-I and 17beta-estradiol, fails to modify ethanol action on bslo channels. Ethanol inhibition of bslo channels results from a marked increase in the mean closed time. Although the voltage dependence of gating remains unaffected, the apparent effectiveness of Ca(2+) to gate the channel is decreased by ethanol. These changes occur without modifications of channel conduction. In conclusion, a new molecular mechanism that may contribute to ethanol-induced aortic smooth muscle contraction has been identified and characterized: a functional interaction between ethanol and the bslo subunit and/or its lipid microenvironment, which leads to a decrease in BK(Ca) channel activity.

Up-regulation of soyasaponin biosynthesis by methyl jasmonate in cultured cells of Glycyrrhiza glabra

Exogenously applied methyl jasmonate (MeJA) stimulated soyasaponin biosynthesis in cultured cells of Glycyrrhiza glabra (common licorice). mRNA level and enzyme activity of beta-amyrin synthase (bAS), an oxidosqualene cyclase (OSC) situated at the branching point for oleanane-type triterpene saponin biosynthesis, were up-regulated by MeJA, whereas those of cycloartenol synthase, an OSC involved in sterol biosynthesis, were relatively constant. Two mRNAs of squalene synthase (SQS), an enzyme common to both triterpene and sterol biosyntheses, were also up-regulated by MeJA. In addition, enzyme activity of UDP-glucuronic acid: soyasapogenol B glucuronosyltransferase, an enzyme situated at a later step of soyasaponin biosynthesis, was also up-regulated by MeJA. Accumulations of bAS and two SQS mRNAs were not transient but lasted for 7 d after exposure to MeJA, resulting in the high-level accumulation (more than 2% of dry weight cells) of soyasaponins in cultured licorice cells. In contrast, bAS and SQS mRNAs were coordinately down-regulated by yeast extract, and mRNA accumulation of polyketide reductase, an enzyme involved in 5-deoxyflavonoid biosynthesis in cultured licorice cells, was induced transiently by yeast extract and MeJA, respectively.

Biosynthesis of sterols and triterpenes in cell suspension cultures of Uncaria tomentosa

Pectin administered to Uncaria tomentosa cell suspension cultures, was found to increase the production of triterpene acids (ursolic and oleanolic acid), however, neither growth nor sterol accumulation were affected. Cell cultures showed that pectin treatment caused a rapid threefold increase in the activities of enzymes involved in the biosynthesis of C(5) and C(30 )isoprenoid, such as isopentenyl diphosphate isomerase and squalene synthase. The activity of a farnesyl diphosphatase, which could divert the flux of farnesyl diphosphate to farnesol, was two times lower in elicited than in control cells. Elicited cells also transformed more rapidly a higher percentage of [5-(3)H]mevalonic acid into triterpene acids. Interestingly, addition of terbinafine, an inhibitor of squalene epoxidase, to elicited cell cultures inhibited sterol accumulation while triterpene production was not inhibited. These results suggest that in U. tomentosa cells, both the previously mentioned enzymes and those involved in squalene 2,3-oxide formation play an important regulatory role in the biosynthesis of sterols and triterpenes.

UDP-glucuronic acid:soyasapogenol glucuronosyltransferase involved in saponin biosynthesis in germinating soybean seeds

We detected UDP-glucuronic acid:soyasapogenol glucuronosyltransferase (UGASGT) activity in the microsomal fraction from germinating soybean (Glycine max [L.] Merr.) seed. A microsomal fraction was isolated from germinating soybean seed and treated with various detergents to solubilize the enzyme. UGASGT activity was monitored throughout purification using UDP-[U-(14)C]glucuronic acid and soyasapogenol B as substrates. Purification of UGASGT was achieved by HiTrap Q, Superdex 200, and HiTrap Blue chromatography procedures. This resulted in >205-fold enrichment relative to the starting homogenate. UGASGT was found to require divalent cations for activity. Studies on the substrate specificity of UGASGT demonstrated that the specificity for the sugar residue transferred was very high, as activity was scarcely found when UDP-glucuronic acid was replaced by other UDP sugars: UDP-glucose and UDP-galactose. Soyasapogenols, which are the aglycons of soybean saponin, are usable acceptors, but glycyrrhetinic acid, sophoradiol, beta-amyrin, and flavonoids are not. These findings suggest that this UGASGT was a specific enzyme for UDP-glucuronic acid as a donor and soyasapogenols as acceptors, and that it was related to the biosynthesis of the sugar chain in soybean saponin. This study provides a basis for the molecular characterization of a key enzyme in saponin biosynthesis in soybean. The isolation of the gene may enable its use in the elucidation of the biosynthesis and physiological role of saponins in soybean.

Detoxification of lantana hepatotoxin, lantadene A, using Alcaligenes faecalis

Detoxification of lantadene A (LA), the hepatotoxin from Lantana camara var. aculeata, by the bacterial strain Alcaligenes faecalis has been investigated. Lantadene A induced hepatotoxicity concomitant with increases in plasma bilirubin, blood plasma enzymes and histopathological lesions that typify lantana toxicity. The extract of fermentation broth in which LA was incubated with A. faecalis did not elicit any alterations in blood enzyme prolife or liver histopathology, which were comparable with the control group. It is concluded that A. faecalis detoxified LA and no noxious product was formed on incubation of LA with A. faecalis.

A synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), is a ligand for the peroxisome proliferator-activated receptor gamma

A novel synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), previously reported to have potent differentiating, antiproliferative, and antiinflammatory activities, has been identified as a ligand for the peroxisome proliferator-activated receptor gamma (PPARgamma). CDDO induces adipocytic differentiation in 3T3-L1 cells, although it is not as potent as the full agonist of PPARgamma, rosiglitazone. Binding studies of CDDO to PPARgamma using a scintillation proximity assay give a Ki between 10(-8) to 10(-7) M. In transactivation assays, CDDO is a partial agonist for PPARgamma. The methyl ester of CDDO, CDDO-Me, binds to PPARgamma with similar affinity, but is an antagonist. Like other PPARgamma ligands, CDDO synergizes with a retinoid X receptor (RXR)-specific ligand to induce 3T3-L1 differentiation, while CDDO-Me is an antagonist in this assay. The partial agonism of CDDO and the antagonism of CDDO-Me reflect the differences in their capacity to recruit or displace cofactors of transcriptional regulation; CDDO and rosiglitazone both release the nuclear receptor corepressor, NCoR, from PPARgamma, while CDDO-Me does not. The differences between CDDO and rosiglitazone as either partial or full agonists, respectively, are seen in the weaker ability of CDDO to recruit the coactivator CREB-binding protein, CBP, to PPARgamma. Our results establish the triterpenoid CDDO as a member of a new class of PPARgamma ligands.

Biotransformation of lantadene A (22 beta-angeloyloxy-3-oxoolean-12-en-28-oic acid), the pentacyclic triterpenoid, by Alcaligenes faecalis

A bacterial strain capable of biotransformation of lantadene A (22 beta-angeloyloxy-3-oxo-olean-12-en-28-oic acid), the pentacyclic hepatotoxin of lantana (Lantana camara var. aculeata) has been isolated from soil using lantadene A as the sole carbon source. The organism is Gram negative, rod shaped, motile, catalase positive and has been identified as Alcaligenes faecalis. The isolate has been found to be specific for lantadene A and did not utilize lantadene B. In studies using sucrose as an additional carbon source, A. faecalis elicited biotransformation of lantadene A to its trans isomer 22 beta-tigloyloxy-3-oxoolean-12-en-28-oic acid, designated as lantadene X and two other minor metabolites which could not be isolated in pure state.