WaterLOGSY as a method for primary NMR screening: practical aspects and range of applicability.

WaterLOGSY represents a powerful method for primary NMR screening in the identification of compounds interacting with macromolecules, including proteins and DNA or RNA fragments. Several relay pathways are used constructively in the experiment for transferring bulk water magnetization to the ligand. The method is particularly useful for the identification of novel scaffolds of micromolar affinity that can be then optimized using directed screening, combinatorial chemistry, medicinal chemistry and structure-based drug design. The practical aspects and range of applicability of the WaterLOGSY experiment are analyzed in detail here. Competition binding and titration WaterLOGSY permit, after proper correction, the evaluation of the dissociation binding constant. The high sensitivity of the technique in combination with the easy deconvolution of the mixtures for the identification of the active components, significantly reduces the amount of material and time needed for the NMR screening process.

Correction of dyslipoproteinaemia of casein-fed rabbit by FCE 27677, a potent novel ACAT inhibitor.

Rabbits fed a wheat starch casein diet develop hypercholesterolaemia characterized by the plasma elevation of low density lipoprotein (LDL) that is caused by oversecretion of apoB-100 containing lipoproteins by the liver and by the suppression of the EDTA-sensitive hepatic beta- very low density lipoprotein (VLDL)-LDL receptor. In this study, the effect of FCE 27677 ((-)N-[2,6-bis(1-methylethyl)phenyl]-N'-[(4R,5R)-2-(4-dimethylaminoph eny l)-4,5-dimethyl-dioxolan-2-yl]methylurea) a novel potent systemic acylCoA:cholesterol acetyltransferase (ACAT, EC 2.3.1.26) inhibitor, has been evaluated. When New Zealand White rabbits were fed with casein for 4 weeks, LDL cholesterol increased from 14 +/- 3 mg/dl-1 to 77 +/- 6 mg/dl-1. By contrast the animals receiving FCE 27677 (10 mg kg-1 d-1) mixed with the casein diet maintained a normal LDL concentration (22 +/- 3 mg dl-1). This hypolipidaemic effect was also observed when rabbits previously made hypercholesterolaemic by being fed casein for 4 weeks were then treated for a month with FCE 27677. [125I]LDL plasma turnover studies and [125I]LDL binding studies to liver membranes were carried out with the purpose of investigating the mechanism of action of the drug. The LDL apoB-100 production rate in chow-fed, casein-fed, and casein-fed rabbits receiving FCE 27677, was respectively 10.5, 22.4, and 12.5 mg kg-1 d-1. The turnover rate of [125I]LDL in the animals receiving the drug was not, however, different from that in the rabbits fed the casein diet alone (2.381 vs 2.079 pools d-1). Both values were lower than that in chow-fed animals (3.271 pools d-1). FCE 27677 did not normalize the activity of the hepatic beta-VLDL-LDL EDTA-sensitive receptor which is suppressed by casein feeding. Altogether the results are consistent with the idea that FCE 27677 by acting through inhibition of the cholesterol esterification in the liver normalizes the LDL synthetic rate. ACAT inhibitors may be useful drugs for the treatment of human dyslipoproteinaemia secondary to derangement of the apoB-100 synthetic rate.

Oxidized lipoproteins induce long-lasting inhibition of nitric oxide synthase from a murine endothelioma cell line (bEnd.4).

BACKGROUND: The vascular endothelium produces nitric oxide, which has vasodilatory properties. It has been postulated that some lipoproteins may increase arterial vascular tone by decreasing the availability of endothelium-derived nitric oxide. The mechanism underlying this effect, however, is still poorly understood. METHODS: We investigated the effect of native and oxidized human low- and high-density lipoproteins on the nitric oxide synthetic activity of an endothelioma cell line (bEnd.4). Oxidized lipoproteins were obtained by incubation with CuSO4. The production of nitric oxide by the cells was monitored by quantifying the nitrite concentration in the medium using Greiss reagent. RESULTS: The synthesis of nitric oxide by the bEnd.4 cell line was calcium-dependent and was abolished by a selective inhibitor of the constitutive nitric oxide synthase. Incubation with oxidized lipoproteins caused a time- and dose-dependent inhibition of nitric oxide synthetic activity. At a concentration of 100 micrograms/ml cholesterol, oxidized low- and high-density lipoproteins inhibited the production of nitric oxide by 27 and 51%, respectively, within 6h. The lipid fraction obtained from the native or the oxidized lipoproteins mimicked the effect of the intact lipoproteins. CONCLUSION: These results support the involvement of oxidized lipoproteins in the modulation of endothelial functions relevant to the pathogenesis of cardiovascular disease.

Prolonged in vitro exposure of rat brain slices to adenosine analogues: selective desensitization of adenosine A1 but not A2 receptors.

Agonist-induced desensitization of adenosine A1 and A2 receptors was studied in rat striatum slices maintained in carbo-oxygenated Krebs buffer. Slices were exposed to adenosine analogues (either cyclo-pentyl-adenosine or N-ethyl-carboxamido-adenosine) for selected time periods (15-60 min) and repeatedly washed at the end of agonist exposure. Agonist-induced changes of adenosine receptors were then evaluated in P2 fractions prepared from slices by measuring A1 and A2 receptor-regulated adenylate cyclase. A1 receptors were rapidly desensitized by agonist exposure, as shown by a gradual loss of A1 receptor-mediated inhibition of basal cyclase activity and cAMP formation, which was evident within 15-30 min after addition of the adenosine analogue. Agonist-induced desensitization of A1 receptors was dose- and time-dependent, and seemed quicker in onset with cyclo-pentyl-adenosine, according to the higher A1 selectivity of this receptor agonist, with respect to N-ethyl-carboxamido-adenosine. Binding of the A1-selective agonist [3H]cyclo-hexyl-adenosine was unaffected by the desensitization procedure at any of the exposure periods utilized, suggesting that an uncoupling of A1 receptors from their transduction system is indeed responsible for the loss of functional activity. Loss of A1 receptor function was accompanied by a time-dependent amplification of A2 receptor-mediated stimulation of adenylate cyclase activity, likely due to an 'unmasking' of A2 stimulatory receptor function as a consequence of the desensitization of A1 inhibitory receptors. All these effects could be completely counteracted by the concomitant exposure to an adenosine receptor antagonist, and specifically involved the coupling mechanisms of adenosine receptors with their effector system.(ABSTRACT TRUNCATED AT 250 WORDS)