Biomedical subjects

L Dinan

Publications and source records attributed to L Dinan.

36 records · Page 2Linked to original sources

PubMed2000

Resveratrol-type oligostilbenes from Iris clarkei antagonize 20-hydroxyecdysone action in the Drosophila melanogaster B(II) cell line.

Bioassay-guided high-performance liquid chromatography analysis of a MeOH extract of Iris clarkei seeds yielded the resveratrol-type oligomeric stilbenes, ampelopsin B and alpha-viniferin, which antagonize the action of 20-hydroxyecdysone; with a 20-hydroxyecdysone concentration of 50 nM, the ED50 values were 33 microM and 10 microM, respectively. The structures of these compounds were determined by spectroscopic analysis, notably ultraviolet, liquid secondary ion mass spectrometry and modern one- and two-dimensional nuclear magnetic resonance techniques.

Animals↗

PubMed1999

Phytoecdysteroids in seeds and plants of Rhagodia baccata (Labill.) Moq. (Chenopodiaceae).

Seeds of Rhagodia baccata afforded, in addition to 20-hydroxy-ecdysone and polypodine B, a novel phytoecdysteroid, (20R)-22-deoxy-20,21-dihydroxyecdysone, the structure of which was elucidated unequivocally by UV, LSIMS and NMR techniques. This compound possessed agonistic activity in the Drosophila melanogaster BII cell bioassay, with an ED50 value of 2.0 x 10(-7)M (ED50 value for 20-hydroxyecdysone = 7.5 x 10(-9)M). The distribution of ecdysteroids in plants of R. baccata has been determined. Highest levels are associated with the youngest aerial tissues and with the roots. Ecdysteroid profiles are qualitatively very similar throughout the plant, with 20-hydroxyecdysone and polypodine B predominating in all plant parts tested.

Animals↗

PubMed1999

An extensive ecdysteroid CoMFA.

The ecdysteroid agonist activity of 71 HPLC-purified ecdysteroids was measured in the Drosophila melanogaster BII tumorous blood cell line assay. The resultant log(ED50) values, spanning almost 6 orders of magnitude, were used to construct a comparative molecular field analysis (CoMFA) model in which conformations were selected by homology to the crystal structure of ecdysone. Model A was constructed by utilization of the region-focused electrostatic indicator field (q2 = 0.631, r2 = 0.903, 5 components, 4 outliers). Model B made use of region-focused electrostatic and steric indicator fields along with MlogP (q2 = 0.694, r2 = 0.892, 5 components, 4 outliers). The model and its underlying bioassay data support a pharmacophore hypothesis in which ecdysteroid binding is understood to be due principally to the summation of localized interactions from approximately six specific loci. This is in contrast to previous structure-activity relationship hypotheses which are formulated in terms of the presence or absence of essential functional groups, without which ecdysteroid receptor affinity would be completely absent. The present CoMFA model is utilized to predict the activities of heretofore unknown ecdysteroids.

Animals↗

PubMed1998

1 alpha,20R-dihydroxyecdysone from Axyris amaranthoides.

Bioassay/RIA-directed phytochemical examination of the seeds of Axyris amaranthoides afforded a new ecdysteroid: 1 alpha,20R-dihydroxyecdysone [1-epi-integristerone A], together with 20-hydroxyecdysone and polypodine B. The structure of 1 alpha,20R-dihydroxyecdysone was determined unequivocally by UV, LSIMS, and a combination of 1D and 2D NMR techniques.

Ecdysone↗

PubMed1998

Somatic mutation of immunoglobulin V(H)6 genes in human infants.

Infants respond to antigen by making antibody that is generally of low affinity for antigen. Somatic hypermutation of immunoglobulin genes, and selection of cells expressing mutations with improved affinity for antigen, are the molecular and cellular processes underlying the maturation of antibody affinity. We have reported previously that neonates and infants up to 2 months of age, including individuals undergoing strong immunological challenge, show very few mutated V(H)6 sequences, with low mutation frequencies in mutated sequences, and little evidence of selection. We have now examined immunoglobulin genes from healthy infants between 2 and 10 months old for mutation and evidence of selection. In this age group, the proportion of V(H)6 sequences which are mutated and the mutation frequency in mutated sequences increase with age. There is evidence of selection from 6 months old. These results indicate that the process of affinity maturation, which depends on cognate T-B cell interaction and functional germinal centres, is approaching maturity from 6 months old.

Adult↗

PubMed1997

Cucurbitacins are insect steroid hormone antagonists acting at the ecdysteroid receptor.

Two triterpenoids, cucurbitacins B and D, have been isolated from seeds of Iberis umbellata (Cruciferae) and shown to be responsible for the antagonistic activity of a methanolic extract of this species in preventing the 20-hydroxyecdysone (20E)-induced morphological changes in the Drosophila melanogaster BII permanent cell line. With a 20E concentration of 50 nM, cucurbitacins B and D give 50% responses at 1.5 and 10 microM respectively. Both cucurbitacins are able to displace specifically bound radiolabelled 25-deoxy-20-hydroxyecdysone (ponasterone A) from a cell-free preparation of the BII cells containing ecdysteroid receptors. The Kd values for cucurbitacins B and D (5 and 50 microM respectively) are similar to the concentrations required to antagonize 20E activity with whole cells. Cucurbitacin B (cucB) prevents stimulation by 20E of an ecdysteroid-responsive reporter gene in a transfection assay. CucB also prevents the formation of the Drosophila ecdysteroid receptor/Ultraspiracle/20E complex with the hsp27 ecdysteroid response element as demonstrated by gel-shift assay. This is therefore the first definitive evidence for the existence of antagonists acting at the ecdysteroid receptor. Preliminary structure/activity studies indicate the importance of the Delta23-22-oxo functional grouping in the side chain for antagonistic activity. Hexanorcucurbitacin D, which lacks carbon atoms C-22 to C-27, is found to be a weak agonist rather than an antagonist. Moreover, the side chain analogue 5-methylhex-3-en-2-one possesses weak antagonistic activity.

Animals↗

PubMed1997

Two limonoids from Turraea obtusifolia (Meliaceae), prieurianin and rohitukin, antagonise 20-hydroxyecdysone action in a Drosophila cell line.

Bioassay-assisted HPLC analyses yielded two prieurianin-type limonoids, prieurianin and rohitukin, from the seeds of Turraea obtusifolia, which act as antagonists of 20-hydroxyecdysone action in the Drosophila melanogaster BII cell line. With a 20-hydroxyecdysone concentration of 5 x 10(-8) M, the ED50 values for prieurianin and rohitukin are 10(-5) M and 1.25 x 10(-4) M, respectively.

Animals↗

PubMed1997

Biological activity of natural and synthetic ecdysteroids in the BII bioassay.

The potencies of 19 ecdysteroids are compared in the BII bioassay, which reflects the affinity of binding to the ligand binding site of the Drosophila melanogaster ecdysteroid receptor. The compounds tested represent either natural products isolated from plants (phytoecdysteroids) or fungi (mycoecdysteroids) or synthetic analogues based on insect metabolites (zooecdysteroids). None of the tested compounds showed any antagonistic activity, but all possessed quantifiable agonistic activity. All the mycoecdysteroids were less potent than the major insect ecdysteroid, 20-hydroxyecdysone (20E). Also, conjugation of 20E with a glucose moiety results, as expected, in considerable reduction in biological activity, but the remaining activity is dependent on the position of conjugation. The implications of these findings for the structure/activity relationship of ecdysteroids are discussed.

Biological Assay↗

PubMed1997

Endogenous ecdysteroid levels and rates of ecdysone acylation by intact ovaries in vitro in relation to ovarian development in adult female crickets, Acheta domesticus.

Ecdysteroid titres have been determined in adult female house crickets (Acheta domesticus) in relation to reproductive maturation. Ecdysteroid levels in newly emerged adult females are low except in the gut and carcass, which probably reflects the remnants of the preecdysial ecdysteroid peak. Ecdysteroid levels in all compartments increase markedly once ovarian weight surpasses 10 mg. Apolar ecdysteroid conjugates (ecdysone 22-fatty acyl esters) predominate in ovarian tissue throughout ovarian maturation, but low levels of free ecdysteroid and polar conjugated ecdysteroids are also present. During this period, two peaks of ecdysteroids (mainly free and apolar conjugated ecdysteroids) are observed in the haemolymph, gut, and carcass compartments. The peaks in the haemolymph occur when the ovarian mass reaches 30 and 100 mg. The gut and carcass may be acting as sinks or sites of metabolism for the hormone released from the ovaries. The rate of ecdysone acylation by ovaries was found to be developmentally regulated, increasing from low levels in the immature ovaries of newly emerged females as the ovaries increase in size. A semiquantitative assay has been developed to identify compounds which inhibit the conversion of [3H]ecdysone into 22-fatty acyl [3H]ecdysone by ovaries in vitro. A number of ecdysteroids possessing a free hydroxyl group as C-22 as well as the side-chain stereochemistry of ecdysone effectively inhibit this conversion, probably by acting as competitive substrates. In the cases of 20-hydroxyecdysone and ponasterone A, it was clearly demonstrated that these compounds are converted to a mixture of C-22 fatty acyl esters. Several other compounds which have been suggested to affect ecdysteroid metabolism/mode of action in other systems were also tested for their effects on the acyltransferase activity of ovaries in vitro.

Acylation↗

PubMed1997

Cucurbitane-type compounds from Hemsleya carnosiflora antagonize ecdysteroid action in the Drosophila melanogaster BII cell line.

The ecdysteroid agonist and antagonist activities of 3 cucurbitanes, 2 cucurbitane glycosides and 2 cucurbitacins isolated from Hemsleya carnosiflora (Cucurbitaceae) have been determined in the Drosophila melanogaster BII bioassay. Carnosiflogenins A and C and carnosiflosides II and VI possess antagonistic activity. Carnosiflogenin A was also found to induce the formation of spindle-shaped cells with high frequency in both the agonist and antagonist assays. At 10(-3) M, carnosiflogenins B and C were cytotoxic, 23,24-Dihydrocucurbitacin F and 25-acetoxy-23,24-dihydrocucurbitacin F are also antagonistic at high concentrations. The concentration dependencies of the antagonistic activities of these two cucurbitacins, carnosiflosides II and VI and carnosiflogenin C are presented. The biological and ecological significance of these results are discussed in relationship to the concentrations present in the rhizomes of H. carnosiflora.

Animals↗

PubMed1997

24(24(1))[Z]-dehydroamarasterone B, a phytoecdysteroid from seeds of Leuzea carthamoides.

A new phytoecdysteroid, 24(24(1))[Z]-dehydroamarasterone B, has been isolated from seeds of Leuzea (Rhaponticum) carthamoides. It has been unambiguously identified by CIMS, 13C NMR and 1H NMR spectroscopy. The biological activity of the ecdysteroid has been determined in the Drosophila melanogaster BII bioassay. The ED50 (5.2 x 10(-7) M) is 70-fold higher than that for 20-hydroxyecdysone (7.5 x 10(-9) M).

Animals↗

PubMed1996

Maternal immunization with Haemophilus influenzae type b polysaccharide-tetanus protein conjugate vaccine in The Gambia.

OBJECTIVE: To evaluate maternal responses to Haemophilus influenzae type b (Hib) polysaccharide-tetanus protein conjugate (polyribosylribitol phosphate-tetanus or PRP-T) given to pregnant Gambian women, the transplacental transfer of antibody, and the effect of maternal immunization on infant responses to the vaccine. DESIGN: An open, randomized immunogenicity study. SETTING: A busy urban health center in The Gambia. STUDY PARTICIPANTS: A total of 451 pregnant women enrolled during the third trimester of pregnancy. INTERVENTION: Study participants were randomized to three groups. In one group, mothers were given PRP-T during the third trimester and their infants were given PRP-T at 2, 3, and 4 months of age. In the second group, mothers received PRP-T and infants were given inactivated poliovirus vaccine. In the third group, mothers received meningococcal A and C vaccine, and their infants received PRP-T. MAIN OUTCOME MEASURES: Anti-PRP antibody measurements of maternal cord, and infant blood. RESULTS: Vaccinated women had a marked increase in total anti-PRP antibody (geometric mean titer 9.0 micrograms/mL), which was greatest in women in their first or second pregnancy. Previous tetanus vaccination during the same pregnancy and high concentrations of antitetanus antibody were associated with lower anti-PRP responses. In infants of PRP-T recipients, cord blood anti-PRP IgG concentrations were 61% of simultaneous maternal concentrations. In vaccinated infants of vaccinated mothers, geometric mean anti-PRP antibody concentrations at birth, 2 months of age, and 5 months of age were 1.92, 0.35 and 2.84 micrograms/mL, respectively, while in vaccinated infants of unvaccinated mothers, the corresponding concentrations were 0.29, 0.12, and 3.91 micrograms/mL. At 2 months of age, 60% of infants of vaccinated mothers and 26% of infants of unvaccinated mothers had anti-PRP antibody concentrations considered to be protective (>0.15 micrograms/mL). CONCLUSIONS: In areas where much invasive Hib disease occurs in infants younger than 6 months, maternal immunization may help to reduce the risk of Hib disease in infants too young for immunization.

Antibodies, Bacterial↗

PubMed1988

Formation of apolar ecdysteroid conjugates by ovaries of the house cricket Acheta domesticus in vitro.

The newly laid eggs of the house cricket Acheta domesticus contain apolar ecdysteroid conjugates, which we have hypothesized to be ecdysone long-chain fatty acyl esters [Whiting & Dinan (1988) J. Insect Physiol., in the press]. The ovaries of mature adult female A. domesticus in vitro convert [3H]ecdysone into apolar conjugates identical with those found in newly laid eggs. Comparison of the radioactive metabolites produced on incubation of [3H]ecdysone with various organs of adult female A. domesticus in vitro indicate that the fat-body is the major producer of polar ecdysteroid metabolites at this stage of development, whereas the ovaries are the major site of production of apolar metabolites. Apolar metabolites are also produced to a lesser extent by the crop, gut sections and the fat-body. Hydrolysis of radioactive metabolites produced by the ovaries with Helix enzymes releases only [3H]ecdysone, and thus ecdysone is not metabolized before conjugation by the ovaries. Formation of chemical derivatives (acetonide and acetates) of these 3H-labelled apolar conjugates strongly indicates that the position of conjugation is through the hydroxy group at C-22 of ecdysone. Extensive chromatographic analysis of the 3H-labelled apolar metabolites produced by the ovaries by t.l.c. and h.p.l.c. and comparison with authenticated reference compounds have conclusively demonstrated that the conjugates consist of ecdysone esterified at C-22 to a mixture of common long-chain fatty acids. The major fatty acyl esters have been identified and their percentage contribution to the mixture determined: laurate (0.5%), myristate (2.8%), palmitate (25.8%), stearate (8.4%), arachidate (1.0%), oleate (15.7%), linoleate (38.8%) and linolenate (2.1%). In addition there are three minor unidentified peaks, one of which has been tentatively identified as ecdysone 22-palmitoleate (2.6%). Comparison of this percentage composition with the previously published fatty acid composition of A. domesticus haemolymph [Wang & Patton (1969) J. Insect Physiol. 15, 851-860] reveals remarkable similarities, indicating that the acyl transferase(s) forming the conjugates have a broad specificity with regard to the fatty acyl substrate.

Animals↗

PubMed1988

The chemical synthesis of ecdysone 22-long-chain fatty acyl esters in high yield.

Eight ecdysone 22-long-chain fatty-acyl esters (laurate, myristate, palmitate, stearate, oleate, linoleate, linolenate and arachidate) have been chemically synthesised in high yield. Ecdysone was first converted to the 2,3-acetonide derivative and then acylated selectively at C-22 with the appropriate acyl anhydride. The protecting acetonide group is then removed by mild acid treatment to yield the ecdysone 22-acyl ester. Reaction conditions have been optimised to maximise the overall yield (ca. 70%). The ecdysone acyl esters and their 2,3-acetonide derivatives have been characterised by 1H- and 13C-NMR and high-resolution FAB-mass-spectrometry.

Acylation↗

PubMed1978

Preparation of 3-epi-ecdysone and 3-epi-20-hydroxyecdysone.

3-Dehydro-ecdysone and 3-dehydro-20-hydroxyecdysone were prepared and characterized. Reduction of these compounds with NaBH4 gave 3-epi-ecdysone and 3-epi-20-hydroxyecdysone, which were characterized fully by mass and p.m.r. spectrometry as well as by derivative formation.

Chemical Phenomena↗

PubMedDate not supplied

Phytoecdysteroid profiles in seeds of Sida spp. (Malvaceae).

Procedures are presented for the assessment of the phytoecdysteroid profiles in small plant samples (ca. 25 mg), using seeds of Sida spp. as an example. The procedures are suitable for the analysis of minute or valuable samples and provide copious information for chemotaxonomic purposes. Methanolic extracts of the plant material, after partitioning against hexane, were separated by reversed-phase gradient HPLC monitored by PAD, RIA and bioassay. Aliquots of the fractions were also treated with Helix pomatia hydrolases, followed by RIA and bioassay, in order to assess the presence of hydrolysable ecdysteroid conjugates. Further information could also be obtained by separation of samples using normal-phase gradient HPLC. Among 11 species of Sida examined, seed extracts of S. acuta (= S. carpinifolia) and S. rhombifolia were found to contain significant amounts of ecdysteroids, seed extracts of S. filicaulis contained only moderate levels, whilst the remaining species showed no detectable levels of ecdysteroids. The ecdysteroid profiles of the extracts of the three positive species were significantly different, demonstrating that phytoecdysteroids have chemotaxonomic value in this genus.

Animals↗

PubMedDate not supplied

4D-QSAR analysis of a set of ecdysteroids and a comparison to CoMFA modeling.

The ecdysteroid-responsive Drosophila melanogaster B(II) cell line is a prototypical homologous inducible gene expression system. A training set of 71 ecdysteroids, for which the -log(EC(50)) potencies in the ecdysteroid-responsive B(II) cell line were measured, was used to construct 4D-QSAR models. Four nearly equivalent optimum 4D-QSAR models, for two modestly different alignments, were identified (Q(2) = 0.76-0.80). These four models, together with two CoMFA models, were used in consensus modeling to arrive at a three-dimensional pharmacophore. The C-2 and C-22 hydroxyls are identified as hydrogen-bond acceptor sites which enhance activity. A hydrophobic site near C-12 is consistent with increasing activity. The side-chain substituents at C-17 are predicted to adopt semiextended "active" conformations which could fit into a cylinder-shaped binding pocket lined largely with nonpolar residues for enhanced activity. A test set of 20 ecdysteroids was used to evaluate the QSAR models. Two 4D-QSAR models for one alignment were identified to be superior to the others based on having the smallest average residuals of prediction for the prediction set (0.69 and 1.13 -log[EC(50)] units). The correlation coefficients of the optimum 4D-QSAR models (R(2) = 0.87 and 0.88) are nearly the same as those of the best CoMFA model (R(2) = 0.92) determined for the same training set. However, the cross-validation correlation coefficient of the CoMFA model is less significant (Q(2) = 0.59) than those of the 4D-QSAR models (Q(2) = 0.80 and 0.80).

Animals↗

PubMedDate not supplied

Limnantheoside C (20-hydroxyecdysone 3-O-beta-D-glucopyranosyl-[1-->3]-beta-D-xylopyranoside), a phytoecdysteroid from seeds of Limnanthes alba (limnanthaceae).

A new ecdysteroid glycoside, limnantheoside C (20-hydroxyecdysone 3-O-beta-D-glucopyranosyl-[-->3]-beta-D-xylopyranoside [1]), together with limnantheoside A (20-hydroxyecdysone 3-O-beta-D-xylopyranoside [2]) and 20-hydroxyecdysone (3) have been isolated by bioassay/RIA-directed HPLC analyses of a methanol extract of the seedmeal of Limnanthes alba Hartw. ex Benth. The structure of the novel ecdysteroid glycoside (1) was determined unambiguously by UV, LSIMS and a combination of 1D- and 2D-NMR experiments. These three compounds are isolated from Limnanthes alba for the first time.

Animals↗