Claire André

Treatment with the arginase inhibitor Nω-hydroxy-nor-L-arginine improves vascular function and lowers blood pressure in adult spontaneously hypertensive rat

Objective High vascular arginase activity and subsequent reduction in vascular nitric oxide production were recently reported in animal models of hypertension. The present study investigated the effects of in-vivo arginase inhibition on blood pressure and vascular function in adult spontaneously hypertensive rats. Methods Ten-week-old spontaneously hypertensive rats and normotensive age-matched Wistar–Kyoto rats were treated with or without the selective arginase inhibitor Nω-hydroxy-nor-L-arginine for 3 weeks (10 or 40 mg/kg per day, intraperitoneally). Systolic blood pressure and cardiac rate were measured before and during treatment. Flow and pressure-dependent reactivity as well as remodeling of mesenteric arteries, acetylcholine-dependent vasodilation of aortic rings, cardiac hypertrophy, arginase activity and nitric oxide production were investigated in 13-week-old spontaneously hypertensive rats. Results In spontaneously hypertensive rats, Nω-hydroxy-nor-L-arginine treatment decreased arginase activity (30–40%), reduced blood pressure (∼35 mmHg) and improved the reactivity of mesenteric vessels. However, vascular and cardiac remodeling was not different between treated and untreated spontaneously hypertensive rats. In Wistar–Kyoto rats, Nω-hydroxy-nor-L-arginine did not affect blood pressure. Finally, arginase inhibition was associated with increased nitric oxide production. Consistent with this, the response of aortic rings to acetylcholine was fully restored by Nω-hydroxy-nor-L-arginine, and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the effect of Nω-hydroxy-nor-L-arginine on flow-dependent vasodilation. Conclusion Pharmacological inhibition of arginase in adult spontaneously hypertensive rats decreases blood pressure and improves the reactivity of resistance vessels. These data represent in-vivo argument in favor of selective arginase inhibition as a new therapeutic strategy against hypertension.

A novel stationary phase based on amino derivatized nanotubes for HPLC separations: theoretical and practical aspects.

A novel column based on silica containing immobilized carbon nanotubes (CNTs) was developed and evaluated in terms of its binding efficiency and resolution. First, CNT functionalized with amino groups (CNT-NH(2)) were prepared via chemical modification of carboxylic groups introduced on the CNT surface. Secondly the covalent immobilization of CNT-NH(2) was carried out by using glutardialdehyde activating agent on aminopropyl (AP)-silica surface. This CNT stationary phase was applied to the HPLC separation of two molecule series, i.e. polychlorinated biphenyl (PCB) isomers with different degrees of substitution in the ortho-position (non-ortho to tetra-ortho substituted) and terpenes (linalool, geraniol, thymol, alpha-terpineol). The retention behavior of these solute molecules was measured under isocratic conditions with different mobile phase compositions, ranging from 0.05-0.70 v/v of toluene in cyclohexane. The retention factors of the solute molecule do not depend linearly on the toluene fraction but follow a quadratic relationship. This CNT stationary phase was a very useful column for the separation of PCB congeners and terpenes. It was demonstrated that a planar conformation of the solute molecule enhanced the solute retention on this CNT stationary phase. As well, a quantitative structure relationship derived, demonstrated the significant input to retention was due to the structurally selective dipole-dipole and charge transfer interactions with the solutes. These results were compared with those obtained on the AP stationary phase. The proposed CNT stationary phase for the separation possess distinctive and interesting retentive properties, and chemometric analysis of retention data of appropriate designed series of test solutes appears to be a convenient, objective and quantitative method to prove a new phase specificity.

Cardiovascular effects of arginase inhibition in spontaneously hypertensive rats with fully developed hypertension

AIMS Growing evidence suggests that arginase misregulation plays a key role in the pathophysiology of essential hypertension. In the present study, we investigated the potential cardiovascular therapeutic effects of a long-term treatment with an arginase inhibitor in adult spontaneously hypertensive rats (SHR) with fully developed hypertension. METHODS AND RESULTS Treatment of 25-week-old SHR with the arginase inhibitor N(omega)-hydroxy-nor-L-arginine (nor-NOHA, 40 mg/day for 10 weeks) sustainably reduced systolic blood pressure (-30 mmHg, P < 0.05). The antihypertensive effect of nor-NOHA was associated with changes on mesenteric artery reactivity including the restoration of angiotensin-II-induced contraction and acetylcholine-induced vasodilation to the values of normotensive Wistar Kyoto rats. Both nitric oxide synthase and cyclooxygenase-dependent mechanisms account for the improvement of endothelial function afforded by the arginase inhibitor, which in addition blunted hypertension-induced endothelial arginase I overexpression in mesenteric arteries. Nor-NOHA also prevented the remodelling of aorta as measured by collagen content and media/lumen ratio, and improved the compliance of carotid artery in SHR. Cardiac fibrosis assessed by collagen content of left heart ventricle was reduced by nor-NOHA, with no significant effect on cardiac hypertrophy. CONCLUSION Our results report that a long-term treatment with an arginase inhibitor reduced blood pressure, improved vascular function, and reduced cardiac fibrosis in SHR with fully developed hypertension. These data suggest that arginase represents a promising novel target for pharmacological intervention in essential hypertension.

Incorporation of carbon nanotubes in a silica HPLC column to enhance the chromatographic separation of peptides: Theoretical and practical aspects

The retention mechanism of a series of peptides on a single-wall carbon nanotube (SWCNT) stationary phase inside an HPLC column was investigated over a wide range of mobile phase compositions. While the similar size C18 column exhibited an efficiency of 11.5 μm, the SWCNT column increased the efficiency, i.e. 7.10 μm at a flow rate of 0.8 mL/min, and significantly affected the separation quality of the peptides. The values of enthalpy (ΔH) and entropy (ΔS(*)) of transfer of the peptides from the mobile to the SWCNT stationary phase were determined. The method studied each factor, i.e. ACN fraction x in the ACN/water mixture and column temperature. The changes in retention factor, ΔH and ΔS(*) as a function of the ACN fraction in the mobile phase were examined. These variations are explained using the organization of ACN in clusters in the ACN/water mixture and on the steric and electronic forces implied in the retention process. The information obtained in this work makes this SWCNT stationary phase useful for peptide research and demonstrated the role of ACN to improve the separation quality.

Peculiarities of a novel bioenzymatic reactor using carbon nanotubes as enzyme activity enhancers: application to arginase.

Multiwalled carbon nanotubes have been entrapped in a porous monolithic chromatographic support. This support was used for the covalent immobilization of the arginase enzyme a novel target in hypertension. The effect of the nanotube (NT) amount into the monolith was analyzed. The obtained results demonstrated the ability of carbon nanotubes to increase significantly the performance of this novel bioactive support.

Non-covalent functionalisation of monolithic silica for the development of carbon nanotube HPLC stationary phases

In this paper, an effective and simple method was used for the immobilization of single wall carbon nanotubes (SWCNTs) on a monolithic HPLC material containing 2 μm macropore sizes and 13 nm mesopore sizes. The chromatographic support was coated with ultra short SWCNTs in a noncovalent way to preserve the sp(2) nanotube structure and thus their physico-chemical properties. It was demonstrated that the amino-surface of the monolith stabilized with 1-methyl-2-pyrrolidinone efficiently and stably adsorbed SWCNTs onto the chromatographic support. It was shown that this novel stationary phase was very useful for the HPLC isocratic mode separation of a series of small aromatic compounds in a very short analysis time. The comparison with a classical equivalent C18 monolithic column showed that the SWCNT column presented the best efficiency in similar chromatographic conditions.

Analysis of the progesterone displacement of its human serum albumin binding site by β-estradiol using biochromatographic approaches: effect of two salt modifiers

The mechanisms of (i) the binding of two sex-hormones (i.e. progesterone and beta-estradiol) to human serum albumin (HSA) and (ii) the progesterone displacement of its HSA binding cavity by beta-estradiol were studied by biochromatography using three different methods. In the first time, zonal elution method was used to prove the direct competition effect between the two sex-hormone. In the second time, the competition effect between beta-estradiol and progesterone to bound on the same HSA site was analysed by the competitive bi-Langmuir approach. Finally, the thermodynamic data of these two binding processes were studied. The Gibbs free energy value (Delta(approximately)G degrees) of the displacement equilibrium was negative demonstrating that beta-estradiol displaced progesterone of its HSA binding cavity. Moreover, the effect of two chloride modifiers (i.e. Na(+), Mg(2+)) on these two binding processes were analysed. Results showed that in the salt biological concentration ranges, the Mg(2+) cation enhanced strongly the bioavailable progesterone, whereas the Na(+) cation interacted slowly on the progesterone displacement of its HSA binding site by beta-estradiol. This study showed that it must be useful to carry out more in vivo test on the magnesium supplementation effect for women who suffer from estrogen dominance syndrome.

Boron nitride nanotubes and their functionalization via quinuclidine-3-thiol with gold nanoparticles for the development and enhancement of the HPLC performance of HPLC monolithic columns

In this paper, a new and effective method was described for attaching gold nanoparticles (Au-NPs) on to the surface of thiol-terminated Boron Nitride Nanotubes (BNNT) functionalized with quinuclidine-3-thiol, acting as a bridging agent. The quinuclidine-3-thiol was first grafted onto the surface of the BNNTs via strong interactions between the electron pair from the nitrogen atom of the quinuclidine structure and the electronic gap from the boron atom of the BNNT. The bare surface of Au-NPs facilitates to attach on the thiol group of the thiol-terminated BNNTs. These two nanomaterials (pristine BNNTs and Au-BNNTs) were then incorporated into a monolithic polymer. The obtained monolithic BNNT and AuBNNT stationary phases were very useful columns for the HPLC isocratic mode separation of a series of benzene and naphtalene derivatives. The retention on these two stationary phases was due to the different intermolecular interactions including the dispersion interaction (area of the delocalized π bond), the dipole-dipole interactions, and the electrostatic repulsion. The presence of Au-NPs on the BNNT surface improved significantly the retention and column efficiency for compounds with thiol groups in their structure. As well, it was shown that both retention and column efficiency linearly increased with the nanotube (NT) amount in the polymerization mixture. This manuscript thus established for the first time the fact that BNNT was a very useful nanomaterial for the development of novel HPLC stationary phases and increased the performance of classical equivalent C18 monolithic columns.

A novel chiral column for the HPLC separation of a series of dansyl amino and arylalkanoic acids

In a previous paper [C. Andre, M. Thomassin, A. Umrayami, L. Ismaili, B. Refouvelet, Y.C. Guillaume, Talanta 71 (2007) 1817] a novel cyclic hexapeptide molecule dissolved in the mobile phase was evaluated as a chiral selector (CS) for the enantiomer separation of a series of dansyl amino and arylalkanoic acids using high performance liquid chromatography (HPLC). In this paper, this CS was immobilized to the surface of a monolithic support and the enantioselectivity and the performance of this novel column are discussed.

The protease activity of transthyretin reverses the effect of pH on the amyloid-β protein/heparan sulfate proteoglycan interaction: A biochromatographic study

Patients suffering of Alzheimers disease (AD) are characterized by a low transthyretin (TTR) level in the brain. The effect of pH and TTR concentration in the medium on the β-amyloid protein (Aβ)/heparan sulfate proteoglycan (HSPG) association mechanism were studied using a biochromatographic approach. For this purpose, HSPG was immobilized via amino groups onto the amino propyl silica pre-packed column, activated with glutaraldehyde, by using the Schiff base method. Using an equilibrium perturbation method, it was clearly shown that Aβ can be bound with HSPG. This approach allowed the determination of the thermodynamic data of this binding mechanism. The role of the pH was also analyzed. Results from enthalpy-entropy compensation and the plot of the number of protons exchanged versus pH showed that the binding mechanism was dependent on pH with a critical value at pH=6.5. This value agreed with a histidine protonation as an imidazolium cation. Moreover, the corresponding thermodynamical data showed that at pH>6.5, van der Waals and hydrogen bonds due to aromatic amino acids as tyrosine or phenylalanine present in the N-terminal (NT) part governed the Aβ/HSPG association. Aβ remained in its physiological structure in a random coil form (i.e. the non-amyloidogenic structure) because van der Waals interactions and hydrogen bonds were preponderant. At acidic pH (pH<6.5), ionic and hydrophobic interactions, created by histidine protonation and hydrophobic amino acids, appeared in the Aβ/HSPG binding. These hydrophobic and ionic interactions led to the conversion of the random coil form of Aβ into a β-sheet structure which was the amyloidogenic folding. When TTR was incubated with Aβ, the Aβ/HSPG association mechanism was enthalpy driven at all pH values. The affinity of Aβ for HSPG decreased when TTR concentration increased due to the complexation of Aβ with TTR. Also, the decrease of the peak area with the increase of TTR concentration demonstrated that this Aβ/TTR association led to the cleavage of Aβ full length to a smaller fragment. For acidic pH (pH<6.5), it was shown that the importance of the hydrophobic and ionic interactions decreased when TTR concentration increased. This result confirmed that Aβ was cleaved by TTR in a part containing only the NT part. Our results demonstrated clearly that TTR reversed the effect of acidic pH and thus played a protective role in AD.