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Biomedical subjects

A Fournier

Publications and source records attributed to A Fournier.

At least 73 records · Page 4Linked to original sources
PubMed2000

Project Medishare: a volunteer program in international health at the University of Miami.

Most U.S. medical schools have programs in international health, but there is a need to find ways to make students (particularly those with little clinical experience) more effective volunteers in international settings. The Department of Family Medicine at the University of Miami School of Medicine developed a program to help prepare students for international work and to ensure that the work they do makes a difference. Over the past four years, this program, Project Medishare, has sent groups of students to Haiti to conduct health fairs. Students prepare all year for their voluntary trips, which take place during the spring and summer breaks; they learn about Haiti's history, culture, language, and health problems. They also raise funds and donations of medicine and supplies. The health fairs, which are one-day events in orphanages and villages, emphasize patient education and preventive medicine. The success of the fairs is evaluated using testimonials from Haitian officials and patients, students' journals, and data collected by the students. Factors critical to Project Medishare's success include (1) having a "critical mass" of culturally and linguistically competent students and faculty; (2) collaboration with local authorities and providers; (3) advance preparation; and (4) using lessons learned from each event to improve the next.

Education, Medical↗
PubMed2000

New short peptide substrates of endothelin-converting enzyme and characterization of the enzyme.

Endothelin (ET) is a 21 amino acid peptide produced following the cleavage of its precursor, big ET, by a metalloprotease, the endothelin-converting enzyme (ECE). In the study reported here we determined the minimal peptide sequence of big ET necessary for enzyme recognition and cleavage at the P1-P1' site. Furthermore, we have explored the role of the amino acids found at the boundaries of the cleavage site. To reach these goals. we synthesized a series of fragments, all containing the P1-P1' cleavage site, Trp21-Val22. Following the incubation of peptide fragments with a partly purified bovine ECE preparation and after analyzing the cleavage pattern by high-performance liquid chromatography (HPLC), we were able to identify big ET(18-23) amide as the minimal peptide core recognized and cleaved by the enzyme. This hydrolysis was inhibited by phosphoramidon but not by thiorphan, a characteristic of the ECE metalloprotease. However, none of the shorter peptides was able to inhibit the cleavage of big ET-1 by ECE, suggesting that they are not recognized by the enzyme. Particularly, it appears that aspartic acid 18 is a key residue for the recognition phenomenon. The delineation of the minimal structure will be a useful tool to further characterize ECE.

Animals↗
PubMed2000

Conformational analysis of endothelin-1 analogs with indolizidinone amino acids incorporated at the C-terminus.

In light of the fact that a beta-turn conformation at the C-terminus of endothelin-1 (ET-1) could be responsible for activity at the ET(B) receptor, the incorporation of (3S, 6S, 9S)-2-oxo-3-amino-1-azabicyclo[4.3.0]nonane-9-carboxylic acid (IAA) should provide an elegant method to establish whether a formyl group on Trp21 plays a role in stabilizing a beta-turn. Eight linear ET-1 analogs, four formylated and four nonformylated, ET-1-(Leu17-Asp18-IAA-Trp21); ET-1-(Leu17-IAA-Ile20-Trp21); ET-1-(Leu17-Asp18-Pro19-Ile20-Trp21) and ET-1-(Leu17-Asp 8-Ile19-Pro20-Trp21) have been analyzed by high-resolution nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Two-dimensional double quantum filtered correlation spectroscopy (DQFCOSY), total correlation spectroscopy (TOCSY) and nuclear Overhausen enhancement spectroscopy (NOESY) were resolved and analyzed for each molecule. Interspatial distance constraints were derived from the intensity of the NOESY connectivities, The formation of hydrogen bonding was monitored from the temperature-dependence of the NH chemical shifts. Molecular models calculated by means of distance geometry, simulated annealing and energy minimization, suggested a global elongated structure for the formylated analogs and a folded arrangement for the nonformylated derivatives, but no hydrogen bonding was detected at the C-terminus of ET-1 analogs.

Endothelin-1↗
PubMed2000

Development of a photolabile ligand for the endothelin-A receptor of endothelin.

Actions of endothelin (ET) are usually mediated through the so-called endothelin-A or -B (ET(A) or ET(B))-receptors. As part of our ongoing research program, we are studying the characterization of the ET(A)-receptor using specific photolabile ligands. Starting with the ET(A)-specific antagonist TTA-386 as a leading compound we developed new ET(A)-specific antagonists containing the photolabile amino acid, p-benzoyl-phenylalanine (Bpa). Following a Bpa peptide scan, with either the L- or D-isomer, we found that D-phenylalanine-6 of TTA-386 can be substituted with either L- or D-Bpa and gives analogs showing antagonistic properties, in an ET(A)-receptor preparation (rat aorta), very similar to those of TTA-386 itself. No agonistic or antagonistic properties were measured with these derivatives in an ET(B) pharmacological preparation (guinea pig lung parenchyma). Thus, these new ligands appear as very promising probes for the characterization of the ET(A)-receptor.

Animals↗
PubMed2000

An improved procedure for the preparation of the endothelin-B-receptor ligand sarafotoxin 6c.

Sarafotoxin 6c (S6c) is a specific agonist for the endothelin-B- (ETB) receptor, being largely used as a standard compound in pharmacological studies related to ETB-receptors. We have developed an improved peptide synthesis prncedure. Using the Fmoc chemistry methodology and an appropriate orthogonal protection scheme, we obtained a crude peptide with a major component identified as [Cys(Acm)(1,15)]S6c. A silver salt (AgBF4) treatment of this crude material completely removed the Acm moieties without the appearance of any major side-products. The free peptide was cyclized using a Fe3+/Fe2+ oxidizing method. Besides the formation of the bridges, no other modification was observed. Thus, the peptide purification was facilitated and an excellent yield of pure sarafotoxin was obtained. The material was characterized by analytical reverse phase-high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Pharmacological properties of the peptide were evaluated in an ETB preparation (guinea pig lung parenchyma strips) and were identical to those of an S6c standard.

Animals↗
PubMed2000

PACAP acts as a neurotrophic factor during histogenesis of the rat cerebellar cortex.

During development of the rat cerebellum, PAC1 receptors are transiently expressed by neuroblasts of the external granule cell layer (EGL). We have previously shown that PACAP is a potent stimulator of granule cell survival in vitro. In the study reported in this paper, we have investigated the effect of PACAP on the development of the rat cerebellar cortex in vivo. PACAP induces a transient increase in the volume of the cerebellar cortex, with a maximum effect at postnatal day 12, which can be accounted for by an increase in the number of granule cells in the EGL, the molecular layer, and the internal granule cell layer (IGL). The effect of PACAP on the number of granule cells is blocked by the antagonist PACAP(6-38), which, by itself, produces a slight inhibition of the number of granule cells in the IGL. These data indicate that PACAP activates proliferation and/or inhibits programmed cell death of granule cells in the developing rat cerebellum. PACAP also stimulates neuronal migration from the EGL to the IGL. Thus, it appears that PACAP can act in vivo as a neurotrophic factor controlling histogenesis of the cerebellar cortex.

Animals↗
PubMed2000

Occurrence and effect of PACAP in the human fetal adrenal gland.

In the study reported in this paper, we characterized PACAP in the human fetal adrenal gland and we investigated the effect of PACAP on steroid secretion from cultured fetal adrenal cells. The adrenal gland from 20-week-old fetuses contained substantial concentrations of PACAP-immunoreactive material (88.6 ng/g wet tissue). HPLC analysis of adrenal extracts revealed the presence of both PACAP27 and PACAP38, the latter being the predominant form. Incubation of cultured fetal adrenal cells with PACAP38 (10(-7) M) significantly increased cortisol and DHEAS secretion. Administration of the beta-adrenoreceptor agonist isoproterenol mimicked the stimulatory effect of PACAP on both steroid secretion whereas preincubation of fetal cells with the beta-adrenoreceptor antagonist propranolol suppressed the steroidogenic effect of PACAP. These data, together with the observation that PACAP receptors are exclusively located on chromaffin cells, suggest that, in the fetal human adrenal gland, the effect of PACAP on steroid secretion is mediated via the local release of catecholamines.

Adrenal Glands↗
PubMed2000

Microbiological high throughput screening: an opportunity for the lead discovery process.

Microbial HTS has been implemented at Rhône-Poulenc Rorer through the development of a dedicated robotic platform. This robot (Turbo) has been designed with the aim of fully integrating microbial HTS into the lead discovery processes. Innovative solutions have been found to reach high throughput as well as flexibility. This opens up new prospects for solid-phase microbial screening, taking advantage of the easy implementation and the very low costs of such screens. The different types of microbial screens done in our laboratory, as well as the throughputs and outputs obtained, are described. Some of the specific aspects of microbial HTS, as compared to biochemical and cell-based assays, are also discussed.

Bacteria↗
PubMed2000

Structural characterization and effects on corticosteroid secretion of endothelin-1 and endothelin-3 from the frog Rana ridibunda.

ABSTRACT Despite the intensive study of endothelin (ET) in mammals, the primary structure and biological activity of the peptide is not known for any species of non-mammalian tetrapod. Extracts of the stomach and the liver of the European green frog Rana ridibunda contained ET-like immunoreactivity measured by RIA using an antiserum raised against human ET-1. The amino acid sequence of the peptide that was isolated in pure form from the stomach extract was identical to that of human ET-1 and the peptide purified from the liver extract was identical to human ET-3 except for a single amino acid substitution (Phe(4)-->Tyr). These observations demonstrate that the amino acid sequences of ET family peptides have been very strongly conserved during evolution of tetrapods and suggest that the pathway of post-translational processing of preproendothelin in the frog is similar to that in mammals. Both frog/human ET-1, frog ET-3 and human ET-3 produced a concentration-dependent increase in the production of corticosteroids from perifused slices of the frog interrenal gland. The maximum responses produced by the peptides (approximately 2-fold increase over basal levels for both corticosterone and aldosterone production) were not significantly different. The potency of ET-1 (-log EC(50)=9.81+/-0.01 (s.e.m.) for corticosterone and 9.52+/-0.29 for aldosterone production) was significantly (P<0.01) greater than that of frog ET-3 (-log EC(50)=8.13+/-1.6 for corticosterone and 8.15+/-0.33 for aldosterone production) but the potencies of frog ET-3 and human ET-3 (-log EC(50)=8.29+/-0.34 and 7.87+/-0.18) were not significantly different.

Adrenal Cortex Hormones↗
PubMed2000

Potent and selective tools to investigate neuropeptide Y receptors in the central and peripheral nervous systems: BIB03304 (Y1) and CGP71683A (Y5).

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y1), T4[NPY33-36]4 (Y2), and CGP71683A (Y5). In rat brain homogenates, BIBO3304 competes for the same population of [125I][Leu31,Pro34] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50 of 0.2 +/- 0.04 nM for BIBO3304 vs. 2.4 +/- 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [125I][Leu31,Pro34]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 microM) were unable to compete for a significant proportion of specific [125I]PYY3-36/Y2 sites. The purported Y2 antagonist T4[NPY33-36]4 competed against [125I]PYY3-36 binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y1, Y2, Y4, or Y5 receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [125I][Leu31,Pro34]PYY binding sites in HEK 293 cells transfected with the rat Y1 receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y5 receptor cDNA. Additionally, both molecules were inactive at Y2 and Y4 receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [125I][Leu31,Pro34]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y1 bioassay (rabbit saphenous vein; pA2 value of 9.04) while being inactive in Y2 (rat vas deferens) and Y4 (rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y1 and Y5 receptor subtypes, respectively, while the purported Y2 antagonist, T4[NPY33-36]4 possesses rather low affinity for this receptor.

Animals↗
PubMed2000

Pituitary adenylate cyclase-activating polypeptide and its receptors: from structure to functions.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid peptide that was first isolated from ovine hypothalamic extracts on the basis of its ability to stimulate cAMP formation in anterior pituitary cells. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-glucagon-growth hormone releasing factor-secretin superfamily. The sequence of PACAP has been remarkably well conserved during the evolution from protochordate to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, and respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide whose activity remains unknown. Two types of PACAP binding sites have been characterized. Type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes, the PACAP-specific PAC1 receptor, which is coupled to several transduction systems, and the two PACAP/VIP-indifferent VPAC1 and VPAC2 receptors, which are primarily coupled to adenylyl cyclase. PAC1 receptors are particularly abundant in the brain and pituitary and adrenal glands whereas VPAC receptors are expressed mainly in the lung, liver, and testis. The wide distribution of PACAP and PACAP receptors has led to an explosion of studies aimed at determining the pharmacological effects and biological functions of the peptide. This report reviews the current knowledge concerning the multiple actions of PACAP in the central nervous system and in various peripheral organs including the endocrine glands, the airways, and the cardiovascular and immune systems, as well as the different effects of PACAP on a number of tumor cell types.

Amino Acid Sequence↗