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Biomedical subjects

P Lefebvre

Publications and source records attributed to P Lefebvre.

At least 91 records · Page 5Linked to original sources
PubMed1996

Effect of neurotrophic factors on the inner ear: clinical implications.

Loss of auditory neurons is commonly associated with sensorineural deafness, and may result from either direct neuronal injury or be a consequence of sensory hair cell loss (i.e. loss of source of trophic factors). Developmental studies and in vitro studies of adult neurons have begun to identify growth factors important for the development, maintenance, and rescue/repair of auditory neurons. Specific neurotrophic factors have been shown to enhance the auditory neurons' ability to withstand traumatic loss of target tissue connections and toxic injury. Promising initial in vivo studies confirm that specific neurotrophins are able to support neuronal survival and promote neuronal repair in an intact animal following injury to the cochlea. Further study into unique methods and routes of growth factor delivery will provide insights into the possibility of neurotrophic growth factors to act as drugs for the treatment of injured or stressed auditory neurons.

Animals↗
PubMed1996

[Livedo vasculitis: report of a case].

Livedo vasculitis is an occlusive thrombotic hyalinizing vessel disease characterized by parietal hyalinization, endothelial proliferation, fibrin deposits and formation of thrombi within the superficial and deep dermal vessels. Diagnosis, essentially clinical, emphasizes the clinical and histopathological features of livedo vasculitis. We conducted an etiological investigation in our case, as required to diagnose idiopathic livedo vasculitis. Several therapies have been suggested with inconstant results and recurrence after withdrawal. In our case, treatment with recombinant tissue plasminogen activator was successful but was unable to prevent recurrence.

Adult↗
PubMed1996

The role of the neurotrophins in maturation and maintenance of postnatal auditory innervation.

Auditory hair cells produce trophic factors that directly affect maturation and survival of auditory neurons. These factors include two members of the neurotrophin family: brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). Loss of hair cells, as a result of either noise trauma or ototoxic damage, results in the degeneration of auditory neurons. An in vitro model of early postnatal rat organ of Corti/spiral ganglion explants was used to study the effects of deprivation and supplementation of nerve growth factor (NGF), BDNF, and NT-3 on neuronal survival. Immunolocalization of receptors for these neurotrophins correlated with their effectiveness as promoters of neuronal survival. BDNF affected early neuronal survival, whereas NT-3 was the most important survival factor for maturing auditory neurons. NGF was shown to maintain axonal morphology. Our results support the hypothesis that changes in the expression of these neurotrophins and their specific receptors in the maturing cochlea may control the postnatal processes of neuronal apoptosis and maturation of the innervation of both inner and outer hair cells. The results suggest that these growth factors have potential for preventing neuronal degeneration as well as enhancing the repair of damaged neuronal processes in the traumatized auditory system.

Animals↗
PubMed1996

[Spontaneous dissection of the internal carotid artery: apropos of a case].

Dissections of the extracranial internal carotid artery are probably underestimated in the general population. They are often unrecognized and asymptomatic as shown in this case report and are only the cause of 1 to 4% of cerebral ischaemic accidents. However, they are responsible for 5 to 20% of such accidents in adults younger than 30 years of age. The nontraumatic nature of the carotid artery dissection in our case has been suggested by the medical history although minor trauma could have been missed. A skin biopsy has enabled us to eliminate elastopathies such as Marfan's or Ehlers-Danlos' syndrome. The diagnosis of dissection has been suggested by a Doppler colour echography ; it was confirmed by the arteriography which revealed a long dissection looking like "string sign" at the level of the internal carotid artery just over the carotid bulb. As far as the evolution is concerned, a medical treatment made it quickly favourable.

Aortic Dissection↗
PubMed1995

Characterization of nuclear retinoic acid binding activity in sensitive leukemic cell lines: cell specific uptake of ATRA and RAR alpha protein modulation.

The diverse effects of all-trans retinoic acid (ATRA) on growth, differentiation and homeostasis of vertebrate organisms are mediated by three distinct isoforms of retinoic acid receptors (RARs). Although it is not known to what extent each RAR contributes to the different effects of ATRA, several studies have demonstrated that ATRA induced granulocytic differentiation in human myeloid leukemic cell lines is mediated by RAR alpha. In this study, we investigated ATRA binding affinity of the endogenous nuclear receptors of HL-60 and NB4 leukemic cells. Scatchard plot analysis yielded an apparent dissociation constant of 5 +/- 0.3 nM and 1400 +/- 80 receptor sites per cell in HL-60 cells, whereas the NB4 promyelocytic leukemic cell line showed a lower affinity (8.5 +/- 0.5 nM and 900 +/- 30 receptor sites per cell). Modulation of RAR alpha protein (5 fold excess) was found in NB4 cells after 24 hours ATRA exposure, whereas HL-60 cells required a 72-hour culture period to weakly increase the RAR alpha protein level. These data were closely related to the ATRA intracellular concentration and kinetics of terminal differentiation of the cells.

Animals↗
PubMed1995

NT-3 combined with CNTF promotes survival of neurons in modiolus-spiral ganglion explants.

Auditory neurons depend upon the integrity of both their peripheral (auditory hair cells) and central (cochlear nucleus) targets for survival. One proposed trophic mechanism is the production of neurotrophin-3 (NT-3) by auditory hair cells. Modiolus-spiral ganglion explants from adult rats that closely mirror cell-cell interactions and in vivo tissue relationships within this ganglion provide a model for testing trophic factors. Brain derived neurotrophic factor (BDNF), NT-3 and ciliary neurotrophic factor (CNTF) were tested for their ability, both individually and in combination, to support neuronal survival. NT-3 was the strongest individual promoter of survival, while CNTF (a cytokine) with NT-3 (a neurotrophin) was the most effective combination for promoting the survival of auditory neurons.

Animals↗
PubMed1995

Protein phosphatases 1 and 2A regulate the transcriptional and DNA binding activities of retinoic acid receptors.

To determine which factors may regulate the DNA binding and transcriptional properties of retinoic acid receptors (RARs and RXRs), we investigated the sensitivity of reporter genes bearing various retinoic acid response elements (RAREs) to protein phosphatases (PPases) inhibition. PPases inhibition by okadaic acid led to an increase of the reporter genes activity in a RARE-dependent and ligand-independent manner and was dependent on the type of response element used. Overexpression of protein phosphatases 2A and 1 (PP2A and PP1) decreased the inducibility of the reporter genes tested. Nuclear extracts from okadaic acid-treated COS cells displayed an 2-5-fold increased level of receptor binding to RAREs in vitro, suggesting that PPases inhibition increased the DNA binding activity of retinoid receptors. Treatment of receptors extracted from COS cells by alkaline phosphatase and partially purified PP1 and PP2A decreased their DNA binding activity, but heterodimers bound to DNA were not sensitive to phosphatase treatment. Reconstitution experiments showed that phosphorylation of both receptors increased the DNA binding activity of RXR/RAR heterodimers. Taken together, these data show that the modulation of the phosphorylation state of RARs and RXRs represents an other level of regulation of the retinoid signaling pathway.

Animals↗
PubMed1995

Structural determinants of the ligand-binding site of the human retinoic acid receptor alpha.

The ligand-dependent transactivating properties of retinoic acid receptors are controlled through a complex structure at the C-terminus of these proteins, commonly referred to as the hormone binding domain. This domain is involved not only in ligand recognition but also in protein-protein interactions such as homo- and heterodimerization processes. To identify more precisely regions of the human all-trans-retinoic acid receptor alpha (hRAR alpha) that are involved in ligand binding, we constructed a series of deletion mutants of this molecule and overexpressed them in bacteria. We found that the C-terminal part of the D domain (amino acids 186-198) was necessary for ligand binding. The F domain and the 10 C-terminal amino acids of the E domain were dispensable for high-affinity binding of various natural and synthetic retinoids. A further deletion to position 403 resulted in a moderate decrease in affinity for all-trans-(ATRA) and 9-cis-retinoic acids, whereas the binding of two RAR alpha-specific ligands (Am80 and Am580) was abolished. In addition, hRAR alpha and the minimal hormone binding domain (amino acids 186-410) bound ATRA with a positive, cooperative mechanism. This behavior was not observed with CD367, a conformationally restricted synthetic retinoid. The positive cooperativity could be correlated with stable ATRA binding to RAR homodimers, whose formation was triggered by ligand. In the same conditions, only monomeric CD367-RAR alpha complexes were detected. These data indicate that ligand binding to hRAR alpha requires the presence of part of the D domain, whereas the C-terminal end of the E domain is involved in more subtle ligand recognition processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Simultaneous determination of all-trans and 13-cis retinoic acids and their 4-oxo metabolites by adsorption liquid chromatography after solid-phase extraction.

All-trans retinoic acid (all-trans RA), the active metabolite of vitamin A, has been demonstrated to be an efficient alternative to chemotherapy in the treatment of acute promyelocytic leukemia (APL), the AML3 subtype of the FAB cytological classification. Complete remission is obtained by inducing terminal granulocytic differentiation of the leukemic cells. To study all-trans RA pharmacokinetics in patients with APL, a rapid, precise and selective high-performance liquid chromatographic (HPLC) assay was developed. This method is easy and shows good repeatability (C.V. = 8.41-12.44%), reproducibility (C.V. = 9.19-14.73%), accuracy (C.V. = 3.5-11%) and sensitivity with a detection limit of 5 pmol/ml. The analysis is performed using normal-phase HPLC in an isocratic mode with UV detection after solid-phase extraction on octadecyl (C18) columns. The mobile phase is hexane-dichloromethane-dioxane (78:18:4, v/v) containing 1% acetic acid.

Adsorption↗
PubMed1995

All-trans retinoic acid pharmacokinetics and bioavailability in acute promyelocytic leukemia: intracellular concentrations and biologic response relationship.

PURPOSE: This study investigated the in vitro pharmacologic behavior and disposition kinetics of all-trans retinoic acid (ATRA) in acute myeloid leukemic (AML) cells, their sensitivity to its differentiating effect, and the in vivo response of acute promyelocytic leukemia (APL) patients after therapy. PATIENTS AND METHODS: Fresh leukemic cells from 14 AML patients (nine APL and five non-APL), were incubated in suspension culture in the absence or presence of 10(-6) mol/L ATRA. Intracellular ATRA concentration and ATRA metabolism was determined by high-performance liquid chromatography (HPLC). RESULTS: Immediate uptake is observed with maximal intracellular levels (Cmax) achieved after 24 hours of incubation. At this time, ATRA levels were variable, ranging from 20 to 230 pmol/10(6) cells (median, 100 pmol/10(6) cells). Comparison of ATRA intracellular levels with the in vitro response of patients' cell samples as measured by the percentage of nitro blue tetrazolium (NBT)-positive cells after a 3-day incubation period allowed us to discriminate a group of APL patients (n = 6) with high Cmax (group A; median, 200 pmol/10(6) cells) and maximal differentiation at day 3 (median, 80%), and a group of patients (n = 8, three APL and five non-APL) with low Cmax (group B; median, 35 pmol/10(6) cells) and poor in vitro response (median, 40%; APL cases only). Interestingly, all APL patients, except one included in group A (rapid in vitro ATRA uptakers), achieved a complete remission. CONCLUSION: These findings suggest that intracellular ATRA concentrations are determinant for ATRA response and should be taken into account when monitoring the efficacy of ATRA differentiation therapeutic trials in malignant disorders.

Adolescent↗
PubMed1995

Differential uptake of all-trans retinoic acid by acute promyelocytic leukemic cells: evidence for its role in retinoic acid efficacy.

All-trans retinoic acid (ATRA) has been demonstrated to be an efficient alternative to chemotherapy in the treatment of acute promyelocytic leukemia (APL or AML3). Complete remission is obtained by inducing granulocytic differentiation of the leukemic cells. To date, the exact mechanism through which ATRA exerts its differentiating effect is not known. The present investigation was initiated to characterize ATRA intracellular concentrations achieved in human myeloid leukemic cells in relation to their different sensitivity to ATRA differentiating effect. During the first 24 h of incubation, a significant decrease of ATRA in the culture medium and a marked increase in the intracellular concentrations were observed. Maximal uptake by the leukemic cells was reached within minutes, with levels between 20 and 260 pmol/10(6) cells (median = 100). Interestingly, a correlation between ATRA-induced differentiation and the intracellular ATRA concentration achieved was observed. In fact, patients with intracellular levels below 60 pmol/10(6) cells defined slow uptakers, never exceeded 40% differentiated cells at day 3. On the other hand, cells with 2-4-fold higher concentration (100-250 pmol/10(6) cells) achieved 100% differentiated cells at day 3. This report suggests that intracellular ATRA concentration is a key pharmacological parameter that should be taken into account to gain further insights into ATRA sensitivity in APL patients.

Adolescent↗