Synthetic derivatives of the alpha- and beta-amyrin triterpenes and their antinociceptive properties

Fifteen different derivatives of an alpha- and beta-amyrin mixture were synthesized by acylation with appropriate anhydride or acid chlorides and oxidation in the presence of tert-butyl chromate or PCC. The molecular structures of the obtained compounds were confirmed by means of IR and (1)H NMR spectra. The compounds were screened for antinociceptive activity using the acetic acid pain model. The 3-O-acyl derivatives alpha- and beta-amyrin propionate 4, alpha- and beta-amyrin hexanoate 6, and alpha- and beta-amyrin octanoate 7 were found to be the most active compounds of the series. In addition, we also have found that alpha- and beta-amyrin octanoate 7 was able to reduce acetic acid-induced abdominal constriction when administered by oral route. Furthermore, this compound reduced the nociceptive response induced by intraplantar injection of formalin.     

5-Alkyl-2-alkylamino-6-(2,6-difluorophenylalkyl)-3,4-dihydropyrimidin-4(3H)-ones, a new series of potent, broad-spectrum non-nucleoside reverse transcriptase inhibitors belonging to the DABO family

2-Alkylamino-6-[1-(2,6-difluorophenyl)alkyl]-3,4-dihydro-5-alkylpyrimidin-4(3H)-ones (F(2)-NH-DABOs) 4, 5 belonging to the dihydro-alkoxy-benzyl-oxopyrimidine (DABO) family and bearing different alkyl- and arylamino side chains at the C(2)-position of the pyrimidine ring were designed as active against wild type (wt) human immunodeficiency virus type 1 (HIV-1) and some relevant HIV-1 mutants. Biological evaluation indicated the importance of the further anchor point of compounds 4, 5 into the non-nucleoside binding site (NNBS): newly synthesized compounds were highly active against both wild type and the Y181C HIV-1 strains. In anti-wt HIV-1 assay the potency of amino derivatives did not depend on the size or shape of the C(2)-amino side chain, but it associated with the presence of one or two methyl groups (one at the pyrimidine C(5)-position and the other at the benzylic carbon), being thymine, alpha-methyluracil or alpha-methylthymine derivatives almost equally active in reducing wt HIV-1-induced cytopathogenicity in MT-4 cells. Against the Y181C mutant strain, 2,6-difluorobenzyl-alpha-methylthymine derivatives 4d, 5h'-n' showed the highest potency and selectivity among tested compounds, both a properly sized C(2)-NH side chain and the presence of two methyl groups (at C(5) and benzylic positions) being crucial for high antiviral action.     

Relaxation induced by N-terminal fragments of chromogranin A in mouse gastric preparations

A definitive role for chromogranin A (CGA)-derived fragments in the control of the gastrointestinal smooth muscle contractility has not been yet established. The purpose of the present study was to evaluate, in vitro, the effects of the recombinant vasostatin 1-78 (VS-1), CGA 7-57 and CGA 47-66 on the mouse gastric mechanical activity, recording the changes of intraluminal pressure. VS-1, CGA 7-57 and CGA 47-66 produced concentration-dependent relaxations. Mouse anti-vasostatin-1 monoclonal antibody 5A8, recognising the region 53-57, abolished the relaxation induced by VS-1, indicating the specificity of the effect. The relaxation was significantly reduced by tetrodotoxin (TTX), blocker of neuronal voltage-dependent Na(+) channels, l-NAME, inhibitor of nitric oxide (NO) synthase, or apamin, blocker of small conductance Ca(2+)-dependent K(+) channels. The joint application of TTX and l-NAME did not show any additive effects, whereas TTX plus apamin abolished the VS-1 response. The results suggest that the N-terminal CGA-derived peptides are able to relax mouse gastric muscle and, therefore, they point out an inhibitory role of vasostatin I in the gastrointestinal tract. The relaxation is mediated in part by neural mechanisms through NO production and in part by non-neural mechanisms involving the opening of small conductance Ca(2+)-dependent K(+) channels.     

Striatum Adenosine A2 Receptors Are Modified During Seizure: Effect of Cyclopentyladenosine Administration

Rat CNS adenosine A_2A receptors were studied after administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) by means of a quantitative autoradiographic method. Specific binding was quantified in striatum only. The highest density was found in caudate-putamen (2.50 fmol/mm²), followed by nuclei accumbens (1.85 fmol/mm²) and the lowest values in the olfactory tubercle (1.26 fmol/mm²). These differerences were statiscally significant. MP administration (150 mg/kg) caused significant increases (12–18%) in caudate-putamen and nuclei accumbens in both stages: seizure and postseizure and no changes in the olfactory tubercle. CPA administration (2 mg/kg) originated a rise of 16% in nuclei accumbens but no change in the other two regions. When CPA was injected 30 minutes before MP, an increase (18 to 45%) in caudate-putamen and nuclei accumbens at seizure and postseizure stages was observed. Saturation results, in striatal membrane fraction, indicate that receptor sites increased their maximal binding capacity (Bmax) while the apparent dissociation constant (Kd) remained unchanged. These results suggest the involvement of the adenosine A_2A receptors in convulsant activity and that CPA administration at the dose selected brings about a rise in neuronal excitability in this area.     

Fluorescence resonance energy transfer detection of synaptophysin I and vesicle-associated membrane protein 2 interactions during exocytosis from single live synapses

To investigate the molecular interactions of synaptophysin I and vesicle-associated membrane protein 2 (VAMP2)/synaptobrevin II during exocytosis, we have used time-lapse videomicroscopy to measure fluorescence resonance energy transfer in live neurons. For this purpose, fluorescent protein variants fused to synaptophysin I or VAMP2 were expressed in rat hippocampal neurons. We show that synaptophysin I and VAMP2 form both homo- and hetero-oligomers on the synaptic vesicle membrane. When exocytosis is stimulated with alpha-latrotoxin, VAMP2 dissociates from synaptophysin I even in the absence of appreciable exocytosis, whereas synaptophysin I oligomers disassemble only upon incorporation of the vesicle with the plasma membrane. We propose that synaptophysin I has multiple roles in neurotransmitter release, regulating VAMP2 availability for the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex and possibly participating in the late steps of exocytosis.     

Oxidative stress in diabetes-induced endothelial dysfunction involvement of nitric oxide and protein kinase C

Reactive oxygen species (ROS) formation plays a major role in diabetes-induced endothelial dysfunction, though the molecular mechanism(s) involved and the contribution of nitric oxide (NO) are still unclear. This study using bovine retinal endothelial cells was aimed at assessing (i) the role of oxygen-dependent vs. NO-dependent oxidative stress in the endothelial cell permeability alterations induced by the diabetic milieu and (ii) whether protein kinase C (PKC) activation ultimately mediates these changes. Superoxide, lipid peroxide, and PKC activity were higher under high glucose (HG) vs. normal glucose throughout the 30 d period. Nitrite/nitrate and endothelial NO synthase levels increased at 1 d and decreased thereafter. Changes in monolayer permeability to 125I-BSA induced by 1 or 30 d incubation in HG or exposure to advanced glycosylation endproduct were reduced by treatment with antioxidants or PKC inhibitors, whereas NO blockade prevented only the effect of 1 d HG. HG-induced changes were mimicked by a PKC activator, a superoxide generating system, an NO and superoxide donor, or peroxynitrite (attenuated by PKC inhibition), but not a NO donor. The short-term effect of HG depends on a combined oxidative and nitrosative stress with peroxynitrite formation, whereas the long-term effect is related to ROS generation; in both cases, PKC ultimately mediates permeability changes.     

Artificial diiron proteins: from structure to function

De novo protein design provides an attractive approach for the construction of models to probe the features required for the function of complex metalloproteins. These minimal models contain the essential elements believed necessary for activity of the protein. In this article, we summarize the design, structure determination, and functional properties of a family of artificial diiron proteins.