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Biomedical subjects

J A Pickett

Publications and source records attributed to J A Pickett.

At least 19 recordsLinked to original sources
PubMed2002

Characterization of (1'R,4S,4aR,7S,7aR)-dihydronepetalactol as a semiochemical for lacewings, including Chrysopa spp. and Peyerimhoffina gracilis.

The enantiomerically pure diastereoisomers (1R,4S,4aR,7S,7aR)- (1) and (1R,4R,4aR,7S,7aR)-dihydronepetalactol (2) were synthesized diastereoselectively from a renewable resource, (4aS,7S,7aR)-nepetalactone (3), isolated as the main constituent of the essential oil of the catmint plant Nepeta cataria. The stereochemistry of the compounds was determined by NMR spectroscopy and X-ray crystallography, and the compounds were identified, respectively, as neomatatabiol and isoneomatatabiol, natural products from Actinidia polygama, for which the lactol stereochemistry was previously incompletely defined. Compound 1 was found to catch significant numbers of three species of lacewing in the field: in Korea. Chrysopa cognata, and in the United Kingdom, Nineta vittata and most notably Peverimhoffina gracilis. All species caught in significant numbers were found more frequently in traps releasing 1 than 2, while more C. cognata, C. formosa, and C. phyllochroma were found in traps releasing (1R,4aS,7S,7aR)-nepetalactol (4). The catch of P. gracilis with 1 is of particular interest as this lacewing has only recently been recorded in the United Kingdom. Where sexed, the lacewings of all species trapped were found to be male, implying a possible pheromonal role for these or structurally related compounds.

Animals↗
PubMed2001

CYP83b1 is the oxime-metabolizing enzyme in the glucosinolate pathway in Arabidopsis.

CYP83B1 from Arabidopsis thaliana has been identified as the oxime-metabolizing enzyme in the biosynthetic pathway of glucosinolates. Biosynthetically active microsomes isolated from Sinapis alba converted p-hydroxyphenylacetaldoxime and cysteine into S-alkylated p-hydroxyphenylacetothiohydroximate, S-(p-hydroxyphenylacetohydroximoyl)-l-cysteine, the next proposed intermediate in the glucosinolate pathway. The production was shown to be dependent on a cytochrome P450 monooxygenase. We searched the genome of A. thaliana for homologues of CYP71E1 (P450ox), the only known oxime-metabolizing enzyme in the biosynthetic pathway of the evolutionarily related cyanogenic glucosides. By a combined use of bioinformatics, published expression data, and knock-out phenotypes, we identified the cytochrome P450 CYP83B1 as the oxime-metabolizing enzyme in the glucosinolate pathway as evidenced by characterization of the recombinant protein expressed in Escherichia coli. The data are consistent with the hypothesis that the oxime-metabolizing enzyme in the cyanogenic pathway (P450ox) was mutated into a "P450mox" that converted oximes into toxic compounds that the plant detoxified into glucosinolates.

Arabidopsis↗
PubMed2001

Switching on plant genes by external chemical signals.

During the past decade there has been rapidly increasing interest in the role of plant volatiles in insect-plant interactions and the induction of plant defence systems by both pathogens and herbivores. Scientists are striving to link the proximate studies elucidating pathways and genes with the ultimate adaptive studies that attempt to explain their ecological role. However, we still do not know whether plants 'talk' to one another by employing 'phytopheromones'.

Acetates↗
PubMed2001

Response of the ladybird parasitoid Dinocampus coccinellae to toxic alkaloids from the seven-spot ladybird, Coccinella septempunctata.

Electrophysiological and behavioral responses of the ladybird parasitoid Dinocampus coccinellae to volatiles from the seven-spot ladybird, Coccinella septempunctata, were investigated to identify semiochemicals involved in host location. Coupled gas chromatography-electroantennography (GC-EAG) with D. coccinellae located a small peak of prominent activity in an extract of volatiles from adult C. septempunctata. The active compound was identified by coupled GC-mass spectrometry and by comparison with an authentic sample as the free-base alkaloid precoccinelline, which forms part of the toxic defense of this ladybird. Behavioral studies in an olfactometer showed that D. coccinellae was significantly attracted to the volatile extract and also to the alkaloid. Myrrhine, a stereoisomer of precoccinelline found in low amounts in C. septempunctata and in other ladybird species, was shown to be electrophysiologically active and significantly attractive. Perception of ladybird alkaloids by D. coccinellae is a rare example of toxicants acting as aerially transmitted cues for interactions between the third and fourth trophic levels.

Alkaloids↗
PubMed2001

Volatile components in dorsal gland secretions of the white-lipped peccary, Tayassu pecari, from Bolivia.

Secretions from the dorsal gland of male and female free-ranging adult white-lipped peccaries (Tayassu pecari) from Bolivia were analyzed by gas chromatography-mass spectrometry. Fifty compounds were identified, some provisionally. Secretions of both sexes contain saturated and unsaturated C5-C18 carboxylic acids as well as isomers of the diterpene springene. The females' secretions uniquely possess farnesyl esters of C8 and C10 carboxylic acids, whereas the males' secretions uniquely showed two compounds provisionally identified as monounsaturated C16 lactones. Saturated high-molecular-weight esters of C10 carboxylic acids are more abundant in the females' secretions than in those of the males. The secretions of both sexes also contain monoalkanoate esters of methylhydroquinone as major components.

Animals↗
PubMed2001

Electroantennogram and behavioural responses of the malaria vector Anopheles gambiae to human-specific sweat components.

Afrotropical malaria vectors of the Anopheles gambiae complex (Diptera: Culicidae), particularly An. gambiae sensu stricto, are attracted mainly to human hosts. A major source of human volatile emissions is sweat, from which key human-specific components are the carboxylic acids (E)- and (Z)-3-methyl-2-hexenoic acid and 7-octenoic acid. Electrophysiological studies on the antennae of An. gambiae s.s. showed selective sensitivity to these compounds, with a threshold at 10(-6) g comparable to that of known olfactory stimulants 1-octen-3-ol, p-cresol, isovaleric acid, and lower than threshold sensitivity to L-lactic acid and the synthetic mosquito repellent N,N-diethyltoluamide (DEET). A combination of the acids released at concentrations > 10(-5) g in wind tunnel bioassays significantly reduced the response to CO2, the major attractant released by human hosts, for strains of An. gambiae s.s. originating from East and West Africa. Field trials with odour-baited entry traps (OBETs) in Burkina Faso showed that 7-octenoic acid significantly increased (by 1.7-fold) the catch of females of An. gambiae sensu lato (comprising two sibling species: An. arabiensis Patton and An. gambiae s.s.) in OBETs baited with CO2, whereas combinations of the acids significantly reduced the catch in CO2-baited traps (by 2.1-fold) and in whole human odour-baited traps (by 1.5-fold). The pure (E) and (Z) geometric isomers of 3-methyl-2-hexenoic acid gave comparable results to the (EIZ) isomer mixture. These results provide the first experimental evidence that human-specific compounds affect the behaviour of highly anthropophilic An. gambiae s.l. mosquitoes. The compounds appear to inhibit the upwind flight' response to known long-range attractants, and may serve either to mask' the attractants present or, more probably, to 'arrest' upwind flight when mosquitoes arrive at a host under natural conditions. In the final approach to hosts, vectors are known to reduce their flight speed and increase their turning rate, to avoid overshooting the source. In our experimental apparatus, these changes in flight behaviour would reduce the number of mosquitoes entering the ports of the collection devices.

Animals↗
PubMed2000

Cytochrome p450 CYP79F1 from arabidopsis catalyzes the conversion of dihomomethionine and trihomomethionine to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates.

Glucosinolates are natural plant products that have received rising attention due to their role in interactions between pests and crop plants and as chemical protectors against cancer. Glucosinolates are derived from amino acids and have aldoximes as intermediates. We report that cytochrome P450 CYP79F1 catalyzes aldoxime formation in the biosynthesis of aliphatic glucosinolates in Arabidopsis thaliana. Using recombinant CYP79F1 functionally expressed in Escherichia coli, we show that both dihomomethionine and trihomomethionine are metabolized by CYP79F1 resulting in the formation of 5-methylthiopentanaldoxime and 6-methylthiohexanaldoxime, respectively. 5-methylthiopentanaldoxime is the precursor of the major glucosinolates in leaves of A. thaliana, i.e. 4-methylthiobutylglucosinolate and 4-methylsulfinylbutylglucosinolate, and a variety of other glucosinolates in Brassica sp. Transgenic A. thaliana with cosuppression of CYP79F1 have a reduced content of aliphatic glucosinolates and a highly increased level of dihomomethionine and trihomomethionine. The transgenic plants have a morphological phenotype showing loss of apical dominance and formation of multiple axillary shoots. Our data provide the first evidence that a cytochrome P450 catalyzes the N-hydroxylation of chain-elongated methionine homologues to the corresponding aldoximes in the biosynthesis of aliphatic glucosinolates.

Arabidopsis↗
PubMed2000

New roles for cis-jasmone as an insect semiochemical and in plant defense.

cis-jasmone, or (Z)-jasmone, is well known as a component of plant volatiles, and its release can be induced by damage, for example during insect herbivory. Using the olfactory system of the lettuce aphid to investigate volatiles from plants avoided by this insect, (Z)-jasmone was found to be electrophysiologically active and also to be repellent in laboratory choice tests. In field studies, repellency from traps was demonstrated for the damson-hop aphid, and with cereal aphids numbers were reduced in plots of winter wheat treated with (Z)-jasmone. In contrast, attractant activity was found in laboratory and wind tunnel tests for insects acting antagonistically to aphids, namely the seven-spot ladybird and an aphid parasitoid. When applied in the vapor phase to intact bean plants, (Z)-jasmone induced the production of volatile compounds, including the monoterpene (E)-beta-ocimene, which affect plant defense, for example by stimulating the activity of parasitic insects. These plants were more attractive to the aphid parasitoid in the wind tunnel when tested 48 h after exposure to (Z)-jasmone had ceased. This possible signaling role of (Z)-jasmone is qualitatively different from that of the biosynthetically related methyl jasmonate and gives a long-lasting effect after removal of the stimulus. Differential display was used to compare mRNA populations in bean leaves exposed to the vapor of (Z)-jasmone and methyl jasmonate. One differentially displayed fragment was cloned and shown by Northern blotting to be up-regulated in leaf tissue by (Z)-jasmone. This sequence was identified by homology as being derived from a gene encoding an alpha-tubulin isoform.

Amino Acid Sequence↗
PubMed1999

Exploiting insect responses in identifying plant signals.

Plants produce compounds which can act as semiochemicals, i.e. as signals modifying the behaviour and development of other organisms without having direct physiological activity, and which generally have extremely benign toxicological properties. Such semiochemicals include plant stress signals and possibly also phytopheromones associated with the induction of defence systems but which may also be exploited by colonizing organisms. Since it is now possible to use sophisticated electrophysiological techniques to investigate insect interactions with phytopheromones, the detection and characterization of such signalling systems is greatly facilitated, particularly when combined with behavioural techniques for confirming the biological relevance of the signals. As well as the contribution of these studies to the understanding of plant-insect and plant-plant interactions, plant signals are potentially valuable in the regulation of gene expression for improved or alternative approaches to crop protection. It would also be possible to use these signals to 'switch on', when required, other genes associated with beneficial agronomic or nutritional crop traits.

Animals↗
PubMed1999

Production of (5R,6S)-6-acetoxy-5-hexadecanolide, the mosquito oviposition pheromone, from the seed oil of the summer cypress plant, Kochia scoparia (Chenopodiaceae).

The oviposition pheromone for the pathogen-vectoring mosquitoes in the genus Culex (Diptera: Culicidae), that is, (5R, 6S)-6-acetoxy-5-hexadecanolide, is efficiently synthesized, in admixture with the inactive (5S,6R) enantiomer ( approximately 33% w/w), from the fixed oil extracted from the seeds of the summer cypress plant, Kochia scoparia (Chenopodiaceae), cultivated on an industrial scale. Oviposition bioassays using gravid females of Culex quinquefasciatus, a vector of filariasis in human beings, showed that the product was attractive, with activity comparable to that of a pure synthetic sample containing the same amount of the active enantiomer. Production of the pheromone in the form of a biologically active crude material via a cheap and renewable plant suitable for development as a new industrial crop provides the basis for control of Cx. quinquefasciatus and other congeneric vectors of pathogens in resource-poor areas of the world.

Animals↗
PubMed1999

A survey of epidural analgesia for labour in the United Kingdom.

A postal survey of obstetric units throughout the UK was conducted to obtain information about the provision of epidural analgesia for labour. Ninety per cent of units offered a 24-h epidural service and the average epidural rate was 24%. The most commonly administered epidural test dose was 3 ml of bupivacaine 0.5% and bupivacaine 0. 25% was most often used as the initial epidural top-up. Continuous infusions of low-dose bupivacaine and opioid mixtures were the most popular method of maintenance epidural analgesia. Twenty-four per cent of units offered combined spinal-epidural analgesia in addition to standard epidural analgesia. Midwives played a prominent role in the administration of epidural bolus top-ups and also in the assessment and maintenance of continuous epidural infusions.

Analgesia, Epidural↗
PubMed1996

The role of mosquito olfaction in oviposition site location and in the avoidance of unsuitable hosts.

Developments in the exploitation of mosquito olfaction are traced, in collaborative studies with various groups, from the first identification of a mosquito pheromone through to a discussion of non-host avoidance. The characterization of the oviposition pheromone for mosquitoes in the genus Culex, e.g. Culex quinquefasciatus, as a novel chiral lactone ester provided the impetus for a number of sophisticated asymmetric syntheses and economical large-scale routes to racemic products. The latter have provided material for successful field trials in three continents. During the course of this field work, we obtained evidence that semiochemicals originating directly from the oviposition site are essential for activity of the oviposition pheromone. Recent studies are elucidating the nature of these agents and their geographical variability. Initially, we used synthetic oviposition pheromone to attract mosquitoes to sites treated with a biorational larvicide. However, recyclable biological control agents offer better prospects for resource-poor regions. A biotechnological approach to pheromone production has been devised involving the generation of inexpensive starting materials by the cultivation of a higher plant. New studies on dipterous pests feeding on farm animals indicate a semiochemically based mechanism by which unsuitable individuals within the host species are avoided. There appears to be an analogous process in which mosquitoes avoid certain potential human hosts, thereby raising prospects for the development of novel, rationally identified repellents once the semiochemical/olfactory interactions have been fully elucidated.

Animals↗
PubMed1996

The aphid sex pheromone cyclopentanoids: synthesis in the elucidation of structure and biosynthetic pathways.

Identification of a range of aphid sex pheromones as comprising the cyclopentanoids (4aS,7S,7aR)-nepetalactone, (1R,4aS,7S,7aR)-nepetalactol and the (1S)- and (1R,4aR,7S,7aS)-nepetalactols required samples authenticated by 1H and 13C NMR. These and related compounds were provided by small scale synthesis and extraction from plants in the genus Nepeta (Lamiaceae). The subsequent discovery that the synthetic sex pheromones could attract males, and also parasitic wasps that attack aphids, has created a need for large scale syntheses of the cyclopentanoids. This is afforded by cyclisation of the 8-oxo-1-enamine of citronellal as originally developed by Schreiber and co-workers (1986). Investigation into the biosynthesis of the cyclopentanoids by plants for exploiting aphid sex pheromones in crop protection by means of molecular biology required synthesis of putative biosynthetic intermediates, some with radioactive isotopic labelling, particularly 8-oxidised monoterpene alcohols and aldehydes.

Animals↗
PubMed1996

Diagnostic indicators in the early recognition of severe cocaine intoxication.

Acute cocaine intoxication is an ever increasing problem in the United Kingdom. Aggressive resuscitation linked to early diagnosis is essential in preventing death. Three cases of severe cocaine toxicity are presented to highlight certain diagnostic indicators in recognising the condition in patients presenting in a collapsed state to the accident and emergency department. Acidosis was a striking feature. The acute management of such patients is supportive and should involve methods to minimize continuing absorption.

Acidosis↗
PubMed1995

Purification and characterization of an acyclic monoterpene primary alcohol:NADP+ oxidoreductase from catmint (Nepeta racemosa).

A soluble monoterpene primary alcohol:NADP+ oxidoreductase has been purified to apparent homogeneity from leaves of the catmint, Nepeta racemosa. The purified enzyme consisted of two polypeptides, with molecular masses of 42,000 and 40,000 Da, and contained zinc ions. A number of monoterpene alcohols (geraniol, nerol, citronellol, and their hydroxylated derivatives) were substrates, but the enzyme was inactive toward ethanol. The enzyme required NADP(H) as cofactor, with NAD(H) ineffective. Gas chromatographic and coupled mass spectrometric analysis of the reaction products showed that 10-hydroxygeraniol and 10-hydroxynerol were oxidized by the enzyme in the presence of NADP+, at both C-1 and C-10. These results are consistent with a role for this enzyme in the biosynthesis of iridoid monoterpenes.

Alcohol Oxidoreductases↗