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Biomedical subjects

S Bénazeth

Publications and source records attributed to S Bénazeth.

9 recordsLinked to original sources
PubMed2005

Almost all about citrulline in mammals.

Citrulline (Cit, C6H13N3O3), which is a ubiquitous amino acid in mammals, is strongly related to arginine. Citrulline metabolism in mammals is divided into two fields: free citrulline and citrullinated proteins. Free citrulline metabolism involves three key enzymes: NO synthase (NOS) and ornithine carbamoyltransferase (OCT) which produce citrulline, and argininosuccinate synthetase (ASS) that converts it into argininosuccinate. The tissue distribution of these enzymes distinguishes three "orthogonal" metabolic pathways for citrulline. Firstly, in the liver, citrulline is locally synthesized by OCT and metabolized by ASS for urea production. Secondly, in most of the tissues producing NO, citrulline is recycled into arginine via ASS to increase arginine availability for NO production. Thirdly, citrulline is synthesized in the gut from glutamine (with OCT), released into the blood and converted back into arginine in the kidneys (by ASS); in this pathway, circulating citrulline is in fact a masked form of arginine to avoid liver captation. Each of these pathways has related pathologies and, even more interestingly, citrulline could potentially be used to monitor or treat some of these pathologies. Citrulline has long been administered in the treatment of inherited urea cycle disorders, and recent studies suggest that citrulline may be used to control the production of NO. Recently, citrulline was demonstrated as a potentially useful marker of short bowel function in a wide range of pathologies. One of the most promising research directions deals with the administration of citrulline as a more efficient alternative to arginine, especially against underlying splanchnic sequestration of amino acids. Protein citrullination results from post-translational modification of arginine; that occurs mainly in keratinization-related proteins and myelins, and insufficiencies in this citrullination occur in some auto-immune diseases such as rheumatoid arthritis, psoriasis or multiple sclerosis.

Animals↗
PubMed2004

Spectroscopic and structural study of metal-metal bonded metalloporphyrinic derivatives: the case of rhodium-indium.

The synthesis and spectroscopic characterization of heterometallic porphyrinate derivatives containing rhodium-indium metal-metal bonds are reported. The investigated compounds are represented by the formula [(Porph)RhIn(Porph')], where Porph and Porph' are OEP, TPP, beta-Cl(4)TPP, beta-Cl(8)TPP, or TPyP. UV-Visible spectroscopy of the title complexes confirms the presence of a strong pi-pi interaction between the macrocycles in each derivative and denotes the effect of the nontransition metal in their optical features. For comparison purposes, a new bimetallic complex with a rhodium-thallium metal-metal bond is also presented. According to (1)H and (13)C NMR data, we were able to distinguish two major NMR regions: the endo- between the metal-metal bonded macrocycles and the exo-, which are characteristic features of porphyrinic complexes at very close proximity. X-ray absorption spectroscopy (XAS) structural characterization of Rh-In bond was performed on the [(OEP)RhIn(OEP)] complex, in the fluorescence mode, and we essentially focused on the metal-metal distance determination. Finally, the distance of 2.543(3) A was deduced from the X-ray structure of a new [(TPP)RhIn(TPyP)] derivative.

Journal Article↗
PubMed2001

XAFS study of gadolinium and samarium bisporphyrinate complexes.

The comparative X-ray absorption spectroscopy study of gadolinium and samarium bisporphyrinate complexes represented by the formulas Gd(III)H(oep)(tpp), Gd(III)(oep)(2), Gd(III)H(tpp)(2) and Sm(III)H(oep)(tpp), Sm(III)(oep)(2), Sm(III)H(tpp)(2) is reported. The XAFS spectra are recorded on the LURE-DCI storage ring (Orsay, France) in transmission mode on the microcrystalline samples at the Gd and Sm L(3) edges. The local environment for Ln(3+) ions has been reconstructed applying one-shell and two-shell XAFS analysis procedures. The protonated and nonprotonated bisporphyrinate complexes present different XAFS features. After our analysis on the title derivatives, the gadolinium ion (at 80 K) is found to be bonded: (i) to eight nitrogen atoms at R(Gd-N) 2.50 A, for Gd(III)(oep)(2) [Debye-Waller (DW) factor 0.004 A(2)]; (ii) to seven nitrogen atoms at R(Gd-N) 2.49 A, for Gd(III)H(oep)(tpp) [DW factor 0.005 A(2)] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Gd-N) 2.50 A [DW factor 0.006 A(2)] and two nitrogen atoms at long distance for Gd(III)H(tpp)(2). A similar coordination sphere has been detected for the corresponding Sm derivatives. So, the samarium ion (at room temperature) is bonded: (i) to eight nitrogen atoms at R(Sm-N) 2.53 A, for Sm(III)(oep)(2) [DW factor 0.006 A(2)]; (ii) to seven nitrogen atoms at R(Sm-N) 2.53 A, for Sm(III)H(oep)(tpp) [DW factor 0.006 A(2)] and one nitrogen at long distance; and (iii) to six nitrogen atoms at R(Sm-N) 2.50 A, for Sm(III)H(tpp)(2) [DW factor 0.006 A(2)] and two nitrogen atoms at long distance. As far as concerns Ln(III)(oep)(2) complexes, the increase of Ln-N distance in the series Gd(3+) < Eu(3+) < Sm(3+) reflects an increase in the ionic radii, which are in good agreement with previously published XRD data on Eu(III)(oep)(2). Moreover, the protonated Ln(III)H(oep)(tpp) and Ln(III)H(tpp)(2) complexes possess systematically shorter distances of about 0.02 A between the XAFS and XRD data. This difference is attributed to the asymmetry of the distribution concerning Ln-N distances.

Journal Article↗
PubMed2001

XAS applied to pharmaceuticals: drug administration and bioavailability.

We present selected XAS applications, focused towards practical hospital questions of drug administration and bioavailability, where the technique is driven up to its limits of sensitivity. i) XAS was used to study the interactions between the components of parenteral nutrition solutions, in particular zinc and aminoacids, possibly modifying their bioavailability. ii) We studied by EXAFS a series of binary and ternary copper-aminoacid complexes, in view of the development of an efficient oral drug against copper deficiencies in Menkes disease. iii) EXAFS and XANES analysis allowed us to characterise the solution form of a new arsenic containing drug against leukaemia. In parallel to the XAS measurements, we analysed trace elements levels along patients' hairs, using X-ray fluorescence excited by synchrotron radiation. The measurements along the hair allow for a monitoring of essential trace elements during therapy.

Arsenic Trioxide↗
PubMed1999

Cerium-doped diosmectite for topical application studies of the cerium-clay interaction.

Cerium is used for its antiseptic and immunomodulatory properties in burn injury. We have developed a cerium-doped clay to replace existing ointments. Adsorption and release of cerium (Ce3+) by diosmectite were studied at 22+/-2 degrees C, in the presence of various other cationic species. Simple spectrofluorimetric determination of cerium was used (lambdaexc=240 nm/lambdaem=360 nm). Cerium binding reached a plateau within 2 min and was a function of the electrolyte content of the solution in contact with the clay. Langmuir isotherm treatment led to a maximal binding capacity of 66 mg of Ce3+ per gram of clay. Partial release occurred within 2 min (19% in the presence of isotonic NaCl solution). The ionic strength of the solution, and the ionic radius and charge of the electrolytes present in the bathing solution significantly influenced cerium release, in contrast to pH and temperature changes. These results strongly point to a cationic exchange mechanism between diosmectite and cerium solution.

Administration, Topical↗