Differential inhibition of noradrenaline release mediated by inhibitory A1-adenosine receptors in the mesenteric vein and artery from normotensive and hypertensive rats.

Mesenteric arteries and veins are densely innervated by sympathetic nerves and are crucial in the regulation of peripheral resistance and capacitance, respectively, thus, in the control of blood pressure. Presynaptic adenosine receptors are involved in vascular tonus regulation, by modulating noradrenaline release from vascular postganglionic sympathetic nerve endings. Some studies also suggest that adenosine receptors (AR) may have a role in hypertension. We aim at investigating the role of presynaptic adenosine receptors in mesenteric vessels and establish a relationship between their effects (in mesenteric vessels) and hypertension, using the spontaneously hypertensive rats (SHR) as a model of hypertension. Adenosine receptor-mediated modulation of noradrenaline release was investigated through the effects of selective agonists and antagonists on electrically-evoked [(3)H]-noradrenaline overflow. CPA (A1AR selective agonist: 1-100 nM) inhibited tritium overflow, but the inhibition was lower in SHR mesenteric vessels. IB-MECA (A3AR selective agonist: 1-100 nM) also inhibited tritium overflow but only in WKY mesenteric veins. CGS 21680 (A2AAR selective agonist: up to 100 nM) failed to facilitate noradrenaline release in mesenteric veins, from both strains, but induced a similar facilitation in the mesenteric arteries. NECA (non-selective AR agonist: 1, 3 and 10µM), in the presence of A1 (DPCPX, 20 nM) and A3 (MRS 1523, 1 µM) AR selective antagonists, failed to change tritium overflow. In summary, the modulatory effects mediated by presynaptic adenosine receptors were characterized, for the first time, in mesenteric vessels: a major inhibition exerted by the A1 subtype in both vessels; a slight inhibition mediated by A3 receptors in mesenteric vein; a facilitation mediated by A2A receptors only in mesenteric artery (from both strains). The less efficient prejunctional adenosine receptor mediated inhibitory effects can contribute to an increase of noradrenaline in the synaptic cleft (both in arteries and veins), which might conduce to increased vascular reactivity.

Guidelines for the management of chronic medication in the perioperative period: systematic review and formal consensus.

WHAT IS KNOWN AND OBJECTIVE: The worldwide volume of surgery is huge and the number of interventions performed is increasing as a result of advances in technological resources and refinement of medical teams' expertise, in a progressively elderly and sick population. Consequently, half of the general surgical patients take medications unrelated to surgery. Evidence-based guidelines for perioperative medication management are therefore critically needed to improve safety in surgery. The purpose of this work was to develop practice recommendations for the management of chronic medication in the perioperative period. METHODS: A systematic review and a formal consensus were performed. A search in Medline, Embase, ISI Web of Knowledge and Medscape were conducted in September 2008. Two independent investigators assessed the quality of selected studies. Evidence-based guidelines with strength classification were found for some therapeutic groups. Those guidelines were adopted and no further analysis was performed. For the other therapeutic groups, a formal consensus was used, based on a modified nominal group technique: 32 statements were formulated considering the literature retrieved. A selected panel of experts was asked by electronic mail to rate their level of agreement with each statement. Then, a meeting was convened and a second round survey was used to determine the final level of agreement. The statements which met the established criteria of consensus were developed into practice recommendations, supported by the results of the formal consensus and the evidence-based findings from systematic review. RESULTS AND DISCUSSION: A total of 23 studies were included in the systematic review; three randomized controlled trials (RCTs), 13 cohorts, two case-controls and three clinic-cases. Twenty-two practice recommendations for the management of chronic medication in the perioperative period resulted from formal consensus. WHAT IS NEW AND CONCLUSION: Epidemiological studies concerning the perioperative management of chronic medications are clinically heterogeneous and there are few RCTs available. However, the formal consensus method proved to be a helpful tool to integrate different strands of evidence for the development of practice guidelines.

The anticancer properties of dietary polyphenols and its relation with apoptosis.

Aberrantly regulated apoptosis is involved in the pathogenesis of several diseases and defective apoptosis leads to uncontrolled cell proliferation and tumorigenesis. Cancer is an example of a pathologic condition where the normal mechanisms of cell cycle regulation are dysfunctional either by excessive cell proliferation, inhibited/suppressed apoptosis or both. Dietary habits are estimated to contribute to, at least, one third of all human cancers, showing that dietary components can exacerbate or interfere with carcinogenesis. However, several epidemiological studies have revealed that some dietary factors can decrease the risk of different types of cancer. Apoptosis is suggested to be a crucial mechanism for the chemopreventive properties associated with several dietary factors by eliminating potentially deleterious (damaged/mutated) cells. Food, a readily available item, contains several promising chemopreventive agents. Polyphenols are serious candidates since they are responsible for the cancer protective properties of a diet rich in vegetables and fruits: numerous phenolic compounds showed antiproliferative and cytotoxic effects, and more specifically pro-apoptotic activities, in several cancer cells lines and animal tumor models. The aim of the present review is to analyze and summarize several aspects related to the molecular mechanisms of apoptosis induced by dietary factors with particular emphasis on polyphenols. Dietary factors that can activate cell death signals and induce apoptosis, preferentially in precancerous or malignant cells, and the study of their apoptotic inducing targets can represent a mean to devise new strategies for cancer prevention in the future.

Ligands and therapeutic perspectives of adenosine A(2A) receptors.

Adenosine A(2A) receptors are members of the G protein-coupled receptor family and mediate multiple physiological effects of adenosine, both at the central nervous system (CNS) and at peripheral tissues, by activating several pathways or interacting with other receptors or proteins. Increasing evidence relate A(2A) receptors with pharmacological stress testing, neurodegenerative disorders (such as Parkinson's disease) and inflammation, renewing the interest in these receptors, increasingly viewed as promising therapeutic targets. Series of agonists and antagonists have been developed by medicinal chemistry artwork either by structure activity relationship (SAR) or quantitative structure activity relationship (QSAR) studies. These studies have allowed identification of the structural and electrostatic requirements for high affinity A(2A) receptor binding and, therefore, contributing to the rational design of A(2A) receptor ligands. Additional rational chemical modifications of the existing A(2A) receptor ligands may further improve their affinity/selectivity. The purpose of this review is to analize and summarize aspects related to the medicinal chemistry of A(2A) receptor ligands, their present and potencial therapeutic applications by exploring the molecular structure and physiological and pathophysiological roles of A(2A) receptors.

New insights on the anticancer properties of dietary polyphenols.

Cancer, one of the major causes of death across the world, has shown to be a largely preventable disease, highly susceptible to modulation by dietary factors. Phenolic compounds, abundant in vegetables and fruits ubiquitous in diet, were described to play an important role as chemopreventive agents. Since conventional therapeutic and surgical approaches have not been able to control the incidence of most cancer types, the development of chemopreventive strategies is an urgent priority in public health. The current diet phenolic intake is often insufficient to protect from mutagens (either exogenous or endogenous), which leads to the need for dietary supplementation as an alternative approach. Research efforts are placing increasing emphasis on identifying the biological mechanisms and in particular the signal transduction pathways related to the chemopreventive activities of these compounds. These effects are believed to occur by the regulation of signaling pathways such as nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) or mitogen-activated protein kinases (MAPK). Dietary polyphenols can exert their effects on these pathways separately or sequentially and in addition the occurrence of crosstalk between these pathways cannot be overlooked. By modulating cell signaling pathways, polyphenols activate cell death signals and induce apoptosis in precancerous or malignant cells resulting in the inhibition of cancer development or progression. However, regulation of cell signaling pathways by dietary polyphenols can also lead to cell proliferation/survival or inflammatory responses due to increased expression of several genes. The present review summarizes the most recent advances providing new insights into the molecular mechanisms underlying the promising anticarcinogenic activity of dietary polyphenols.

Differential activation by daphnetoxin and mezerein of PKC-isotypes alpha, beta I, delta and zeta.

Daphnetoxin, a mezerein derivative, was isolated from the stem bark of Daphne gnidium. Mezerein is a PKC activator that exhibits antileukemic properties. However, daphnetoxin and its analogue 12-hydroxydaphnetoxin were described as being devoid of this effect. In the present study daphnetoxin and mezerein were compared as PKC activators on classical (alpha and beta I), novel (delta) and atypical (zeta) isoforms, using an alternative in vivo yeast phenotypic assay. The aim was to clarify if daphnetoxin is a PKC activator and if the differences between the antiproliferative effect of mezerein and of its analogue daphnetoxin may be ascribed to differences on their potency or selectivity as PKC activators. Yeast samples expressing each of the mammalian PKC isoforms tested were incubated with daphnetoxin or mezerein. Growth inhibition caused by these drugs was assumed to be due to PKC activation since it did not occur when expression was not induced. Mezerein inhibited the growth of yeast expressing PKC alpha (IC(50) = 1190 +/- 237 nM; n = 20), PKC beta I (IC(50) = 908 +/- 46 nM; n = 20), and PKC delta (IC(50) = 141 +/- 25 nM; n = 20) but not of yeast expressing PKC zeta. Daphnetoxin also inhibited the growth of yeast expressing isoforms alpha, beta I and delta, being more potent than mezerein on PKC alpha (IC(50) = 536 +/- 183 nM; n = 20; P < 0.05), as potent as mezerein on PKC beta I (IC(50) = 902 +/- 129 nM; n = 20) and less potent than mezerein upon PKC delta (IC(50) = 3370 +/- 492 nM; n = 20; P < 0.05). These results show that daphnetoxin is a potent PKC activator but with a selectivity different from that of mezerein. It is suggested that the lack of antileukemic and antiproliferative effects of daphnetoxin may be due to its lower potency to activate PKC delta.

Chromium(VI)-mediated DNA damage: oxidative pathways resulting in the formation of DNA breaks and abasic sites.

Inside cells chromium(VI) is activated to its ultimate carcinogenic form by reducing agents including glutathione (GSH) and ascorbate (AsA). The precise mechanism by which DNA damaging species are formed is unclear. In earlier in vitro work with isolated DNA we have shown that chromium(VI) in combination with GSH or AsA is able to induce similar numbers of single strand breaks and apurinic/apyrimidinic sites (AP-sites). Moreover, the formation of both lesions followed a similar temporal pattern. It is conceivable that the two forms of DNA damage arise from a common precursor lesion (e.g. hydrogen abstraction at C4' of the DNA sugar moiety) with a partitioning along two pathways, one yielding an AP-site, the other a single strand break (SSB) and a base propenal. The present study is intended to test this hypothesis by analysing whether oxidation products of deoxyribose can be formed in the presence of chromium(VI) and GSH or AsA. It was found that mixtures of chromium(VI) and GSH or AsA were able to oxidise 2-deoxyribose to yield malondialdehyde, which was detected by reaction with thiobarbituric acid. The characteristic pink chromogen, which forms upon reaction with thiobarbituric acid, was also observed with calf thymus DNA as the substrate. In both experimental systems the addition of catalase prevented the formation of deoxyribose breakdown products. Hydroxyl radicals did not seem to be important for the generation of DNA damage as the characteristic modified DNA bases could not be detected by using gas chromatography-mass spectrometry. These results lead us to conclude that the formation of SSB during the reductive conversion of chromium(VI) proceeds primarily via hydrogen abstraction from C4'. The observation that Fenton chemistry is not involved in these processes is intriguing and necessitates further research into the ways in which chromium can activate molecular oxygen to form DNA damaging species.

Taurine release in the rat vas deferens is modulated by Ca2+ and is independent of contractions.

Electrical field stimulation induces taurine release in rat vas deferens. In the present study, it was investigated if this release is secondary to contraction. The influence of Ca2+ and of the stimulation conditions was also studied. Contractions evoked by electrical field stimulation (5 Hz/270 pulses, transverse or longitudinal) were recorded and released taurine was quantified by high performance liquid chromatography with fluorimetric detection. Ca2+ removal abolished contractions, but not the overflow of taurine. Overflow elicited by longitudinal electrical field stimulation was higher than that elicited by transverse electrical field stimulation. Increasing the current strength also increased taurine overflow. In Ca2+-free medium, taurine overflow was decreased by caffeine (5 mM) or ryanodine (10 microM) but increased by dantrolene (50 microM). The results indicate that taurine release evoked by electrical field stimulation is (i) independent of contraction, (ii) modulated by Ca2+, (iii) potential dependent, and may be due to a decrease in taurine affinity for the plasma membrane and/or to an increase of Na+-dependent outward transport.

The reductive conversion of the carcinogen chromium (VI) and its role in the formation of DNA lesions.

The potential of Cr(VI), in combination with glutathione (GSH) or ascorbate (AsA) to induce apurinic/apyrimidinic sites (AP-sites) and single strand breaks (SSB) in isolated deoxyribonucleic acid (DNA) was investigated. The observation that both lesions were formed with equal probability and followed a similar time course suggests that they might arise from attack of a reactive species at C4' of the DNA sugar moeity. This idea is further substantiated by the finding that malondialdehyde-like products are released in chromate/GSH- and chromate/AsA-treated DNA. The generation of AP-sites and SSB was dependent on molecular oxygen and could be suppressed by the addition of catalase. Our results rule out hydroxyl radicals as the DNA damaging species. Furthermore, Cr(V), an intermediate formed during reaction with GSH or AsA, is not directly involved in the generation of DNA damage, unless activated by molecular oxygen. Our findings indicate that a superoxo- or peroxo-complex involving Cr(V) or Cr(IV) might be the species responsible for DNA damage. Evidence is presented that the DNA lesions arising from chromate/AsA have the potential to cause gene mutations.

The reductive conversion of chromium (VI) by ascorbate gives rise to apurinic/apyrimidinic sites in isolated DNA.

The formation of apurinic/apyrimidinic sites (AP-sites) and single strand breaks (SSB) by chromate and ascorbate (AsA) in isolated DNA was investigated using a number of agents that cleave DNA at AP-sites (putrescine, exonuclease III, the tripeptide Lys-Trp-Lys, and an AP-endonuclease containing fraction isolated from human fibroblasts). Relative to the number of SSB caused by chromate and AsA alone, all these agents induced additional nicking, indicating the induction of AP-sites. Chromate/AsA-induced AP-sites contain aldehyde groups, as cleavage by putrescine could be prevented by treatment with borohydride which reduced the aldehyde. The time course for the formation of both DNA lesions was very similar, and there was a 1:1 ratio of the number of SSB to the number of AP-sites. The addition of catalase to incubation mixtures containing chromate/AsA led to an almost complete suppression of AP-sites and SSB. In systems containing lower concentrations of chromate/AsA, the exclusion of oxygen inhibited the formation of both lesions. It is suggested that AP-sites and SSB arise from attack by reactive species deriving from chromate/AsA on one single site at DNA, probably the sugar moiety. In view of the known mutagenicity of AP-sites, these results could aid an understanding of the mechanisms underlying chromium(VI) carcinogenicity.

The formation of DNA cleaving species during the reduction of chromate by ascorbate.

A detailed study of the ability of chromate in combination with ascorbate to induce DNA single-strand breaks in the absence of iron(II) and copper(II) has been carried out. In solutions containing 1 mM ascorbate and chromate in the range 0.1-1 mM extensive DNA cleavage occurred. Chromate alone or the final product of the chromate/ascorbate reaction were not responsible for the cleavage observed. Evidence is presented that an intermediate generated during the reduction of chromate is the reactive species. No strand breaks occurred upon addition of catalase, pointing to a role for peroxidic species in the steps leading to the generation of the cleaving species. The exclusion of oxygen led to a substantial decrease in the number of strand breaks. Furthermore, the formation of strand breaks declined with decreasing concentrations of phosphate in the phosphate buffers used as the incubation medium. No DNA strand breaks were induced in medium containing HEPES. These observations rule out chromium(V) as the agent directly responsible for the DNA degradation, as chromium(V) is formed during the reduction of chromate by ascorbate in HEPES buffer. Our results lead us to suggest that the DNA-damaging ability of chromate upon reduction by ascorbate arises from the activation of oxygen exacerbated by phosphate and points to a peroxo or superoxo complex involving chromium(V) or chromium(IV) as a possible candidate.