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Biomedical subjects

J P David

Publications and source records attributed to J P David.

At least 19 recordsLinked to original sources
PubMed2006

Involvement of cytochrome P450 monooxygenases in the response of mosquito larvae to dietary plant xenobiotics.

The response of mosquito larvae to plant toxins found in their breeding sites was investigated by using Aedes aegypti larvae and toxic arborescent leaf litter as experimental models. The relation between larval tolerance to toxic leaf litter and cytochrome P450 monooxygenases (P450s) was examined at the toxicological, biochemical and molecular levels. Larvae pre-exposed to toxic leaf litter show a higher tolerance to those xenobiotics together with a strong increase in P450 activity levels. This enzymatic response is both time- and dose-dependent. The use of degenerate primers from various P450 genes (CYPs) allowed us to isolate 16 new CYP genes belonging to CYP4, CYP6 and CYP9 families. Expression studies revealed a 2.3-fold over-expression of 1 CYP gene (CYP6AL1) after larval pre-exposure to toxic leaf litter, this gene being expressed at a high level in late larval and pupal stages and in fat bodies and midgut. The CYP6AL1 protein has a high level of identity with other insect's CYPs involved in xenobiotic detoxification. The role of CYP genes in tolerance to natural xenobiotics and the importance of such adaptive responses in the capacity of mosquitoes to colonize new habitats and to develop insecticide resistance mechanisms are discussed.

Adaptation, Biological↗
PubMed2003

Mosquito larval consumption of toxic arborescent leaf-litter, and its biocontrol potential.

Previously we described the mosquito larvicidal properties of decomposed leaf-litter from deciduous trees, especially the alder Alnus glutinosa (L) Gaertn., due to toxic polyphenols and other secondary compounds. To further examine the biocontrol potential of toxic leaf-litter for mosquito control, feeding rates of third-instar mosquito larvae were assessed for examples of three genera: Anopheles stephensi Liston, Aedes aegypti (L) and Culex pipiens L. (Diptera: Culicidae). When immersed in a suspension of non-toxic leaf-litter particles (approximately 0.4 mm), pre-starved larvae of all three species ingested sufficient material in 30 min to fill the anterior gut lumen (thorax plus two to three abdominal segments). Gut filling peaked after 1-2 h ingestion time, filling the intestine up to six to seven abdominal segments for Ae. aegypti, but maxima of five abdominal segments for Cx. pipiens and An. stephensi. Using three methods to quantify consumption of three materials by third-instar larvae of Ae. aegypti, the average amount of leaf-litter (non-toxic 0.4 mm particles) ingested during 3 h was determined as approximately 20 microg/larva (by dry weight and by lignin spectrophotometric assay). Consumption of humine (approximately 100 microm particles extracted from leaf-litter) during 3 h was approximately 80 microg/larva for Ae. aegypti, but only approximately 30 microg/larva for Cx. pipiens and 15 microg/larva for An. stephensi, with good concordance of determinations by dry weight and by radiometric assay. Cellulose consumption by Ae. aegypti was intermediate: approximately 40 microg/larva determined by radiometric assay. Apparent differences between the amounts of these materials ingested by Ae. aegypti larvae (humine four-fold, cellulose two-fold more than leaf-litter) may be attributed to contrasts in palatability (perhaps related to particle size or form), rather than technical discrepancies, because there was good concordance between results of both methods used to determine the amounts of humine and leaf-litter ingested. Bioassays of toxic leaf-litter (decomposed 10 months) with 4-h exposure period (ingestion time) ranked the order of sensitivity: Ae. aegypti (LC50 < 0.03 g/L) > An. stephensi (LC50 = 0.35 g/L) > Cx. pipiens (LC20 > 0.4 g/L). When immersed in the high concentration of 0.5 g/L toxic leaf-litter (0.4 mm particles), as little as 15-30 min ingestion time (exposure period) was sufficient to kill the majority of larvae of all three species, as soon as the gut lumen was filled for only the first few abdominal segments. Possibilities for mosquito larval control with toxic leaf-litter products and the need for standardized ingestion bioassays of larvicidal particles are discussed.

Aedes↗
PubMed2003

The role of environment in shaping the genetic diversity of the subalpine mosquito, Aedes rusticus (Diptera, Culicidae).

The relative involvement of larval dietary tolerance to the leaf-litter toxic polyphenols in shaping population genetic structure of the subalpine mosquito Aedes rusticus was examined. This was compared with other parameters such as geographical range, type of vegetation surrounding the breeding site, and occurrence of annual larvicidal treatments. Population genetic structure was analysed at 10 presumed neutral polymorphic isoenzyme loci. Toxicological comparisons involved standard bioassays performed on larvae fed on toxic decomposed leaf litter. Significant overall genetic differentiation was observed among the 22 studied populations and within the five defined geographical groups. Analysis of molecular variance revealed an absence of relation between genetic and environmental parameters, genetic variance being essentially found within populations. This suggested that the larval dietary tolerance to the toxic leaf litter and the other studied parameters poorly influence population genetic structure. The local adaptation of subalpine mosquito populations to the surrounding vegetation thus appears as a labile trait. Such a dynamic adaptation is also suggested by the correlation between geographical and toxicological distances and the correlation between dietary tolerance to the leaf-litter toxic polyphenols and annual larvicidal treatments.

Aedes↗
PubMed2001

[Geriatrics and rehabiliation: role of the hospital in healthcare networks?].

OBJECTIVE: There is no accepted definition of geriatric post-acute or rehabilitation care. The exact role within the healthcare network and the function of units providing such care remain to be clarified. We describe the activity of geriatric post-acute or rehabilitation care units in four French hospitals to identify common features and provide elements of practical interest concerning their role in the healthcare network. METHODS: Data from 4 healthcare institutions in France recorded in the 1999 Medical Information System were analyzed. RESULTS: Geriatric post-acute or rehabilitation units generally provided care for patients over 80 years of age in short-stay wards. These patients were dependent and recovering from an acute illness. In addition to rehabilitation and medical care, given according to the patients' needs, the units also provided social counseling and acute care as in other short-stay wards. A wide variety of pathological conditions was observed. At discharge most patients returned to their home or were transferred to a nursing home. CONCLUSION: Geriatric post-acute or rehabilitation units meet the requirements proposed in French legislation and in addition provide social counseling and acute care services, which is evidence of the deficiencies in the healthcare network in the field of elderly patient care.

Acute Disease↗
PubMed2001

c-Jun NH2-terminal kinase (JNK)1 and JNK2 have similar and stage-dependent roles in regulating T cell apoptosis and proliferation.

Apoptotic and mitogenic stimuli activate c-Jun NH2-terminal kinases (JNKs) in T cells. Although T cells express both JNK1 and JNK2 isozymes, the absence of JNK2 alone can result in resistance to anti-CD3-induced thymocyte apoptosis and defective mature T cell proliferation. Similar defects in thymocyte apoptosis and mature T cell proliferation, the latter due to reduced interleukin 2 production, are also caused by JNK1 deficiency. Importantly, T cell function was compromised in Jnk1(+/-)Jnk2(+/-) double heterozygous mice, indicating that JNK1 and JNK2 play similar roles in regulating T cell function. The reduced JNK dose results in defective c-Jun NH2-terminal phosphorylation in thymocytes but not in peripheral T cells, in which nuclear factors of activated T cells (NK-ATs)-DNA binding activity is affected. Thus, JNK1 and JNK2 control similar functions during T cell maturation through differential targeting of distinct substrates.

Animals↗
PubMed2001

Carbonic anhydrase II is an AP-1 target gene in osteoclasts.

c-Fos, a member of the AP-1 family of transcription factors, is necessary for osteoclast differentiation but to date, none of the osteoclast-phenotypic markers have been identified as AP-1 target genes. Here, we demonstrate that carbonic anhydrase II (CA II), an enzyme necessary for osteoclast activity, is transcriptionally upregulated by c-Fos/AP-1. A functional AP-1 binding site is present in the CA II promoter and is necessary for this regulation. Furthermore, we show that AP-1 binding activity, mainly composed of Fra-2 and JunD, is induced by treatment of bone marrow cultures with the osteoclastogenic hormone 1,25 dihydroxyvitamin D(3). Fra-2 and JunD are found in mature osteoclasts as well. Thus, our data demonstrate that cFos/AP-1 can directly regulate the expression of this osteoclast marker and that AP-1 activity is upregulated in osteoclast progenitors in response to osteoclastogenic signals.

Animals↗
PubMed2001

Alkyl phenols and derivatives from Tapirira obtusa.

From the bark of Tapiria obtusa, six alkyl phenol derivatives were isolated: 1-hydroxy-3-[(Z)-7'-nonadecenyl]-benzene, 1-hydroxy-3-[(Z)-7'-heptadecenyl]-benzene, 1-hydroxy-3-[14'-phenyltetradecyl]-benzene, and 1-hydroxy-3-[16'-phenyltetradecyl]-benzene, and their possible biogenetic precursors, 1-(16'-phenyl-12'Z-hexadecenyl)-4-Z-cyclohexene-(1S*,3S*)-diol and (4S*,6S*)-dihydroxy-6-(14'Z-nonadecenyl)-2-cyclohexenone. The structures of these compounds were elucidated by chemical and spectroscopic analysis, (4S*,6S*)-Dihydroxy-6-(14'Z-nonadecenyl)-2-cyclohexenone showed cytotoxic activity.

Magnetic Resonance Spectroscopy↗
PubMed2001

Involvement of ligninlike compounds in toxicity of dietary alder leaf litter against mosquito larvae.

The toxicological characteristics of dietary decomposed alder leaf litter against mosquito larvae were further investigated through enzymatic and chemical purification of a phenoliclike cell-wall fraction isolated from crude litter. The toxicity of the subfractions obtained was controlled by standard bioassays on third instars of Aedes aegypti chosen as a reference target species. Enzymatic hydrolyses of the cell-wall fraction were performed with caylase, pectolyase, esterase, and beta-glycosidase, in order to release, respectively, cellulose material and phenolic compounds bound to lignins. These treatments did not affect the larvicidal activity and the phenolic activity of the cell-wall fraction. Chemical alkaline and acid hydrolyses were carried out to break ester and glycosidic bonds of the cell-wall fraction. Comparison of HPLC profiles of the hydrolysates from both toxic and nontoxic fractions did not reveal differences between the phenolic acids released. Aluminum chloride, known for its phenolic complexing activity, counteracted the larvicidal activity of the cell-wall fraction. Altogether, these results suggest the involvement of ligninlike compounds in the toxicity of dietary alder leaf litter against larval mosquitoes. The toxicity of this fraction, which was very sensitive to drastic and smooth oxidations, seemed to be associated with a strong oxidative potential. These results are discussed in relation to a possible mode of action of lignins in the plant-mosquito interactions.

Aedes↗
PubMed2001

Dynamic recruitment of Cdc2 to specific microtubule structures during mitosis.

A-type cyclin-dependent kinases (CDKs), also known as cdc2, are central to the orderly progression of the cell cycle. We made a functional Green Fluorescent Protein (GFP) fusion with CDK-A (Cdc2-GFP) and followed its subcellular localization during the cell cycle in tobacco cells. During interphase, the Cdc2-GFP fusion protein was found in both the cytoplasm and the nucleus, where it was highly resistant to extraction. In premitotic cells, a bright and narrow equatorial band appeared on the cell surface, resembling the late preprophase band, which disintegrated within 10 min as followed by time-lapse images. Cdc2-GFP was not found on prophase spindles but left the chromatin soon after this stage and associated progressively with the metaphase spindle in a microtubule-dependent manner. Arresting cells in mitosis through the stabilization of microtubules by taxol further enhanced the spindle-localized pool of Cdc2-GFP. Toward the end of mitosis, Cdc2-GFP was found at the midzone of the anaphase spindle and phragmoplast; eventually, it became focused at the midline of these microtubule structures. In detergent-extracted cells, the Cdc2-GFP remained associated with mitotic structures. Retention on spindles was prevented by pretreatment with the CDK-specific inhibitor roscovitine and was enhanced by the protein phosphatase inhibitor okadaic acid. Furthermore, we demonstrate that both the endogenous CDK-A and Cdc2-GFP were cosedimented with taxol-stabilized plant microtubules from cell extracts and that Cdc2 activity was detected together with a fraction of polymerized tubulin. These data provide evidence that the A-type CDKs associate physically with mitotic structures in a microtubule-dependent manner and may be involved in regulating the behavior of specific microtubule arrays throughout mitosis.

CDC2 Protein Kinase↗
PubMed2000

Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots.

New information on the electron-hole wave functions in InAs-GaAs self-assembled quantum dots is deduced from Stark effect spectroscopy. Most unexpectedly it is shown that the hole is localized towards the top of the dot, above the electron, an alignment that is inverted relative to the predictions of all recent calculations. We are able to obtain new information on the structure and composition of buried quantum dots from modeling of the data. We also demonstrate that the excited state transitions arise from lateral quantization and that tuning through the inhomogeneous distribution of dot energies can be achieved by variation of electric field.

Journal Article↗
PubMed2000

Comparative ability to detoxify alder leaf litter in field larval mosquito collections.

The larvicidal effects of polyphenols from dietary alder leaf litter were investigated in different field collections of three detritivorous Aedes taxa (Ae. detritus, Ae. cataphylla, Ae. rusticus) and compared to the cytochrome P450 monooxygenase, glutathione S-transferase, and esterase activities. Larvae from polyphenol-rich habitats had a higher tolerance for polyphenols and higher midgut cytochrome P450 and esterase activities than larvae from polyphenol-poor habitats. Furthermore, the role of P450 enzymes in the mechanism of resistance to alder polyphenols was suggested by the synergistic effect in vivo of piperonyl butoxide in the resistant Ae. rusticus. This confirms the importance of polyphenols to larval mosquito performance, and provides evidence for the importance of specific detoxification mechanisms for tolerance to dietary polyphenols. Arch.

Aedes↗
PubMed2000

Toxicity of vegetable tannins on crustacea associated with alpine mosquito breeding sites.

The impact of tannins from the environmental vegetation naturally polluting Alpine mosquito breeding sites was experimentally investigated by studying the toxicity of tannic acid, a natural hydrolyzable tannin, on the nontarget crustacean fauna associated with culicine populations. Bioassays indicate that exposure to tannic acid at concentrations from 0.06 to 2.0 mM is more deleterious to Chydorus sphaericus, Diaptomus castor, and Eucypris fuscata, than to Daphnia pulex, Acanthocyclops robustus, and Eucypris virens. Histopathological investigations after treatment with tannic acid at concentrations from 0.125 to 0.500 mM reveal sequential degenerative patterns of the midgut epithelium depending on the taxon, duration of the treatment, and concentrations assayed. These differential toxic effects on Crustacea are compared with those previously observed in larval Diptera, in order to evaluate the plant tannins as potentially useful products in integrated mosquito management programs.

Animals↗
PubMed2000

Differential toxicity of leaf litter to dipteran larvae of mosquito developmental sites.

The relative toxicity of leaf litter to nematocerous dipteran larvae characteristic of mosquito developmental sites was investigated. Culicidae, Chironomidae, and Simuliidae taxa originating from alpine hydrosystems were tested together with two laboratory nonindigenous culicid taxa. Bioassays indicate that ingestion of 10-month-old decaying leaves from Alnus glutinosa, Populus nigra, and Quercus robur by larvae is more deleterious for Aedes aegypti, A. albopictus, Culex pipiens, Simulium variegatum, and Chironomus annularius than for A. rusticus. Histopathological observations reveal that the midgut epithelium is the main target organ of the toxic effect of dietary leaf litter, which appears to be stronger than that of previously reported tannic acid. There is a general response of the nematocerous larval midgut epithelium to dietary tannins-phenolic compounds: clear cells of the anterior midgut showing symptoms of intoxication before dark cells of the posterior midgut.

Animals↗
PubMed2000

A-type proanthocyanidin antioxidant from Dioclea lasiophylla.

The A-type proanthocyanidin, epigallocatechin-(2beta-->7,4beta-->8)-epicatechin, together with the known epicatechin, luteolin 3'beta-D-glucopyranoside, chrysoeriol 7beta-D-glucopyranoside and 2-methylpentan-2,4-diol, were isolated from leaves of Dioclea lasiophilla. The structures were established on the basis of their spectral data. Antioxidant activities of isolates were measured using the autooxidation of beta-carotene in a linolenic acid suspension method.

Anthocyanins↗
PubMed2000

Constituents of Caesalpinia pyramidalis.

Two new glycosyl phenylpropenoid acids, 4-O-beta-glucopyranosyloxy-(Z)-7-hydroxycinnamic acid (1) and 4-O-beta-glucopyranosyloxy-(Z)-8-hydroxycinnamic acid (2), besides lupeol and aghatisflavone, were isolated from the leaves of Caesalpinia pyramidalis.

Cinnamates↗
PubMed2000

Role of vegetable tannins in habitat selection among mosquito communities from the Alpine hydrosystems.

The role of vegetable tannins in habitat selection among mosquito communities in Alpine hydrosystems was investigated through ecotoxicological comparison of 19 arthropod species characteristic of 12 breeding sites known for their abiotic environmental factors and their different riparian vegetation. The toxicity of tannins was experimentally compared among species representative of both the dipteran fauna and the crustacean fauna associated with the mosquito breeding sites. Bioassays using tannic acid solutions at concentrations from 0.1 to 11 mM separated the dipteran taxa into five groups of differential sensitivity and the crustacean taxa into four groups. The different levels of sensitivity among taxa were correlated with the various amounts of total phenolics and tannins found in the most prominent plant types associated with the different breeding sites. This suggested that tannins and, more generally, phenolic compounds may be involved in plant-arthropod interactions in Alpine hydrosystems.

Animal Feed↗
PubMed2000

Increased bone formation and osteosclerosis in mice overexpressing the transcription factor Fra-1.

Bone formation by osteoblasts is essential for skeletal growth and remodeling. Fra-1 is a c-Fos-related protein belonging to the AP-1 family of transcription factors. Here we show that transgenic mice overexpressing Fra-1 in various organs develop a progressive increase in bone mass leading to osteosclerosis of the entire skeleton, which is due to a cell-autonomous increase in the number of mature osteoblasts. Moreover, osteoblast differentiation, but not proliferation, was enhanced and osteoclastogenesis was also elevated in vitro. These data indicate that, unlike c-Fos, which causes osteosarcomas, Fra-1 specifically enhances bone formation, which may be exploited to stimulate bone formation in pathological conditions.

Animals↗