Biomedical subjects

Jean-Philippe David

Publications and source records attributed to Jean-Philippe David.

6 recordsLinked to original sources

PubMed2003

Factors influencing the toxicity of xenobiotics against larval mosquitoes.

In order to examine the factors influencing xenobiotic toxicity against larval mosquitoes, the larvicidal performances of two conventional insecticides (temephos and Bacillus thuringiensis var. israelensis: Bti) and a new potential phyto-insecticide (decomposed leaf litter) were compared under different conditions against three detritivorous larval mosquito types. Bioassays performed under standard conditions indicated differential tolerance levels according to the xenobiotic and the larval type. Bioassays performed under different conditions of xenobiotic dose and geometry of the water column indicated differential effects of those parameters on mortality rates. This allowed us to distinguish the performances of temephos versus those of Bti and leaf litter. These toxicological performances were examined as indicators for analysis of xenobiotic bioavailability for mosquito larvae in environmental water, and also for their comparative interest in field mosquito control.

Aedes↗

PubMed2002

Taste sensitivity of detritivorous mosquito larvae to decomposed leaf litter.

Dietary leaf litter chemistry is known to play an important ecotoxicological role in the plant-mosquito interaction in subalpine flooded areas surrounded by vegetation because of differential larvicidal effects of insoluble polyphenols formed during the leaf decaying process. This dietary interaction was investigated through comparative evaluation of the role of toxic/nontoxic leaf litter in both larval foraging and feeding behavior, by using different samples of decomposed alder leaf litter and larval Aedes aegypri as experimental references. Track analysis showed significant differences in larval foraging behavior in the absence or presence of leaf litter. Comparative alimentary preference investigations and further track analysis suggested that larvae are unable to detect leaf litter toxicity. These characteristics of the larval behavioral feeding pattern suggested that: (1) decomposed leaf litter may be involved as an important attractive food source in the habitat selection and evolutionary history of culicids, and (2) preingestive behavioral mechanisms appear to be minimally involved in the differential larval dietary adaptation to toxic leaf litter. These results may have interesting consequences for culicid biological control.

Aedes↗

PubMed2002

Progressive decrease of amyloid precursor protein carboxy terminal fragments (APP-CTFs), associated with tau pathology stages, in Alzheimer's disease.

Amyloid precursor protein (APP) dysfunction is a key aetiologic agent in Alzheimer's disease (AD). The processing of this transmembrane protein generates carboxy terminal fragments (CTFs) upstream of beta-amyloid peptide (Abeta) production. The physiologic significance of APP-CTFs is still poorly understood, as well as the relationship that could link APP dysfunction and tau pathology in familial and non-familial AD (non-FAD). In the present study, we have investigated the quantitative and qualitative changes of APP-CTFs in different brain areas of non-demented and demented patients from a prospective and multidisciplinary study. A significant decrease of the five APP-CTFs was observed, which correlated well with the progression of tau pathology, in most cases with infraclinical AD and AD, either familial or non-FAD. Furthermore, solubility properties and the ratio between the five bands were also modified, both in the Triton-soluble and/or -insoluble fractions. Together, we show here for the first time a modification directly observed on APP-CTFs upstream of Abeta products and its relationship with tau pathology, which could reflect the basic aetiological mechanisms of AD.

Aged↗

PubMed2002

Neurosteroid quantification in human brain regions: comparison between Alzheimer's and nondemented patients.

Some neurosteroids have been shown to display beneficial effects on neuroprotection in rodents. To investigate the physiopathological significance of neurosteroids in Alzheimer's disease (AD), we compared the concentrations of pregnenolone, pregnenolone sulfate (PREGS), dehydroepiandrosterone, dehydroepiandrosterone sulfate (DHEAS), progesterone, and allopregnanolone, measured by gas chromatography-mass spectrometry, in individual brain regions of AD patients and aged nondemented controls, including hippocampus, amygdala, frontal cortex, striatum, hypothalamus, and cerebellum. A general trend toward decreased levels of all steroids was observed in all AD patients' brain regions compared with controls: PREGS and DHEAS were significantly lower in the striatum and cerebellum, and DHEAS was also significantly reduced in the hypothalamus. A significant negative correlation was found between the levels of cortical beta-amyloid peptides and those of PREGS in the striatum and cerebellum and between the levels of phosphorylated tau proteins and DHEAS in the hypothalamus. This study provides reference values for steroid concentrations determined by gas chromatography-mass spectrometry in various regions of the aged human brain. High levels of key proteins implicated in the formation of plaques and neurofibrillary tangles were correlated with decreased brain levels of PREGS and DHEAS, suggesting a possible neuroprotective role of these neurosteroids in AD.

Aged↗

PubMed2002

Larvicidal properties of decomposed leaf litter in the subalpine mosquito breeding sites.

The larvicidal properties of the dietary leaf litter originating from the vegetation surrounding the subalpine mosquito breeding sites were investigated by using 10-month decomposed alder leaf litter against different field collections of culicine taxa of various ecological origin (Aedes cantans, Aedes caspius, Aedes cataphylla, Aedes detritus, Aedes punctor, Aedes pullatus, Aedes rusticus, Anopheles claviger, Culex hortensis, Culex pipiens, Culiseta morsitans). Larvae originating from sites with polyphenol-poor vegetation appeared more sensitive to ingested leaf litter than those originating from sites with polyphenol-rich vegetation. Within a given taxon (e.g., A. rusticus, A. cataphylla, C. hortensis), the overall levels of cytochrome P450 monooxygenase and esterase activities appeared higher in larvae able to feed on leaf litter than in pupae and adults unable to feed on leaf litter. This suggests the involvement of these enzymes in the detoxification mechanisms responsible for larval tolerance to polyphenols of the dietary leaf litter. Such a tolerance of the larval stage thus appears as fundamental in the ecotoxicological adaptation of mosquito taxa to the polyphenolic profiles of the riparian vegetation.

Alnus↗

PubMedDate not supplied

Tau aggregation in the hippocampal formation: an ageing or a pathological process?

Tauopathy is a concept to describe different genetic or metabolic dysfunctions of tau proteins that generate most of the known dementing disorders. Tauopathy is a degenerating process that also affects the entorhinal formation, and then the hippocampal formation in ageing. In Alzheimer's disease (AD), a disease due to APP dysfunction, a similar tauopathy process in observed in neocortical areas, well correlated to cognitive impairment. One important gap of knowledge is the relationship between tauopathy in the hippocampal formation, ageing, AD, and cognitive impairment. Here we show that the multidisciplinary analysis of numerous brains from non-demented and demented patients suggests the following observations: tauopathy of the hippocampal formation in humans is age-related but not an age-dependent process, also independent of AD, but amplified by APP dysfunctions. Tauopathy in the entorhinal and hippocampal formation could be another type of pathological dysfunction of tau proteins, and a therapeutic target to delay AD. Relevant animal models are desperately needed to address this issue.

Aged↗