Ezequiel Álvarez

Effects of cis-resveratrol on inflammatory murine macrophages: antioxidant activity and down-regulation of inflammatory genes.

This study investigated for the first time the effects of the cis isomer of resveratrol (c‐RESV) on the responses of inflammatory murine peritoneal macrophages, namely on the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during the respiratory burst; on the biosynthesis of other mediators of inflammation such prostaglandins; and on the expression of inflammatory genes such as inducible nitric oxide synthase (NOS)‐2 and inducible cyclooxygenase (COX)‐2. Treatment with 1–100 μM c‐RESV significantly inhibited intracellular and extracellular ROS production, and c‐RESV at 10–100 μM significantly reduced RNS production. c‐RESV at 1–100 μM was ineffective for scavenging superoxide radicals (O2•−), generated enzymatically by a hypoxanthine (HX)/xanthine oxidase (XO) system and/or for inhibiting XO activity. However, c‐RESV at 10–100 μM decreased nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate (NADH/NADPH) oxidase activity in macrophage homogenates. c‐RESV at 100 μM decreased NOS‐2 and COX‐2 mRNA levels in lipopolysaccharide (LPS) interferon gamma (IFN‐γ)‐treated macrophages. At 10–100 μM, c‐RESV also significantly inhibited NOS‐2 and COX‐2 protein synthesis and decreased prostaglandin E2 (PGE2) production. These results indicate that c‐RESV at micromolar concentrations significantly attenuates several components of the macrophage response to proinflammatory stimuli (notably, production of O2•− and of the proinflammatory mediators NO• and PGE2).

In vitro effects of mangiferin on superoxide concentrations and expression of the inducible nitric oxide synthase, tumour necrosis factor-α and transforming growth factor-β genes

This study investigated the effects of the natural polyphenol mangiferin (MA) on superoxide anion (O(2)(-)) production, xanthine oxidase (XO) activity, vascular contractility, inducible nitric oxide synthase (iNOS) mRNA levels, tumour necrosis factor-alpha (TNF-alpha) mRNA levels, and tumour growth factor-beta (TGF-beta) mRNA levels. O(2)(-) was generated by the hypoxanthine-xanthine oxidase (HX-XO) and phenazine methosulphate (PMS)-NADH systems. XO activity was determined by measurement of uric acid production with xanthine as substrate. Vascular contraction experiments were performed with intact rat aortic rings. iNOS, TNF-alpha and TGF-beta gene expression in rat macrophages stimulated in vivo with 3% thioglycollate and in vitro with 100 ng/mL lipopolysaccharide and 10U/mL of interferon-gamma were evaluated semiquantitatively by the retrotranscriptase-polymerase chain reaction. MA at 10-100 microM, like the known O(2)(-) scavenger superoxide dismutase (1U/mL), scavenged O(2)(-) produced by the HX/XO and PMS-NADH systems. By contrast MA at 1-100 microM, unlike allopurinol (10 microM), was unable to inhibit XO activity. MA at 1-100 microM did not modify resting tone or the contractile responses elicited by 1 microM phenylephrine or 1 microM phorbol 12-myristate 13-acetate in rat aorta. MA at 1-100 microM, like dexamethasone (100 microM), decreased iNOS mRNA levels in activated macrophages. At 100 microM, MA also reduced TNF-alpha mRNA levels, but increased TGF-beta mRNA levels. These results thus indicate that MA is an O(2)(-) scavenger and that it inhibits expression of the iNOS and TNF-alpha genes, suggesting that it may be of potential value in the treatment of inflammatory and/or neurodegenerative disorders. In addition, the finding that MA enhances TGF-beta gene expression suggests that this polyphenol might also be of value in the prevention of cancer, autoimmune disorders, atherosclerosis and coronary heart disease.

Study of the mechanisms involved in the vasorelaxation induced by (−)-epigallocatechin-3-gallate in rat aorta

This study investigated several mechanisms involved in the vasorelaxant effects of (−)‐epigallocatechin‐3‐gallate (EGCG). EGCG (1 μM–1 mM) concentration dependently relaxed, after a transient increase in tension, contractions induced by noradrenaline (NA, 1 μM), high extracellular KCl (60 mM), or phorbol 12‐myristate 13‐acetate (PMA, 1 μM) in intact rat aortic rings. In a Ca2+‐free solution, EGCG (1 μM–1 mM) relaxed 1 μM PMA‐induced contractions, without previous transient contraction. However, EGCG (1 μM–1 mM) did not affect the 1 μM okadaic acid‐induced contractions. Removal of endothelium and/or pretreatment with glibenclamide (10 μM), tetraethylammonium (2 mM) or charybdotoxin (100 nM) plus apamin (500 nM) did not modify the vasorelaxant effects of EGCG. In addition, EGCG noncompetitively antagonized the contractions induced by NA (in 1.5 mM Ca2+‐containing solution) and Ca2+ (in depolarizing Ca2+‐free high KCl 60 mM solution). In rat aortic smooth muscle cells (RASMC), EGCG (100 μM) reduced increases in cytosolic free Ca2+ concentration ([Ca2+]i) induced by angiotensin II (ANG II, 100 nM) and KCl (60 mM) in 1.5 mM CaCl2‐containing solution and by ANG II (100 nM) in the absence of extracellular Ca2+. In RASMC, EGCG (100 μM) did not modify basal generation of cAMP or cGMP, but significantly reversed the inhibitory effects of NA (1 μM) and high KCl (60 mM) on cAMP and cGMP production. EGCG inhibited the enzymatic activity of all the cyclic nucleotide PDE isoenzymes present in vascular tissue, being more effective on PDE2 (IC50∼17) and on PDE1 (IC50∼25). Our results suggest that the vasorelaxant effects of EGCG in rat aorta are mediated, at least in part, by an inhibition of PDE activity, and the subsequent increase in cyclic nucleotide levels in RASMC, which, in turn, can reduce agonist‐ or high KCl concentration‐induced increases in [Ca2+]i.

Glycated albumin, a precursor of advanced glycation end-products, up-regulates NADPH oxidase and enhances oxidative stress in human endothelial cells: molecular correlate of diabetic vasculopathy

Hyperglycaemia induces non‐enzymatic glycation reactions in proteins which generate Amadori products and advanced glycation end‐products; the latter are thought to participate in the vascular complications of diabetic patients. However, the exact mechanisms concerning the effects of glycated proteins on vascular tissue remain to be determined. Therefore, the effects of glycated human serum albumin on human umbilical vein endothelial cells were studied.

Soluble receptor of advanced glycation end products levels are related to ischaemic aetiology and extent of coronary disease in chronic heart failure patients, independent of advanced glycation end products levels: New Roles for Soluble RAGE.

Knowledge of the role of advanced glycation end products (AGE), their receptor (RAGE), and the receptors soluble form (sRAGE), in heart failure (HF) is very limited. We evaluated the clinical role of the AGE–RAGE system in HF and in particular any association it might have with ischaemic aetiology.

Effect of ()-epigallocatechin-3-gallate on respiratory burst of rat macrophages

The toxic effects derived from overproduction of oxygen radicals [reactive oxygen species (ROS)] by immune cells can be partially abolished by the antioxidant activities of plant polyphenols. In the present study, we investigated the antioxidant action of a catechin, (-)-epigallocatechin-3-gallate (EGCG), on the respiratory-burst responses of rat peritoneal macrophages. EGCG at concentrations of 50-200 microM blocked the production of nitric oxide by macrophages stimulated in vivo with sodium thioglycollate then 5 days later in vitro with lipopolysaccharide and gamma-interferon. At 1-100 microM, EGCG also inhibited the extracellular liberation of oxygen radicals by resident peritoneal macrophages stimulated with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA). At low concentrations (1-5 microM), EGCG increased the reduction of nitro blue tetrazolium (NBT) by the superoxide anions generated in the non-enzymatic system NADH/PMS, acting as a pro-oxidant agent, while at concentrations above 10 microM, EGCG acts as a scavenger of superoxide anions. These results show that EGCG is capable of modulating ROS production during the respiratory burst of rat peritoneal macrophages by acting as a superoxide anion scavenger. EGCG may therefore be useful in the prevention and treatment of diseases due to increased free radical production.

Comparative study of the vasorelaxant activity, superoxide-scavenging ability and cyclic nucleotide phosphodiesterase-inhibitory effects of hesperetin and hesperidin

This study investigated the vasorelaxant activity, superoxide radicals (O2•−)-scavenging capacity and cyclic nucleotide phosphodiesterase (PDE)-inhibitory effects of hesperidin and hesperetin, two flavonoids mainly isolated from citrus fruits. Hesperetin concentration-dependently relaxed the isometric contractions induced by noradrenaline (NA, 1 μM) or by a high extracellular KCl concentration (60 mM) in intact rat isolated thoracic aorta rings. However, hesperetin (10 μM–0.3 mM) did not affect the contractile response induced by okadaic acid (OA, 1 μM). Mechanical removal of endothelium and/or pretreatment of aorta rings with glibenclamide (GB, 10 μM), tetraethylammonium (TEA, 2 mM) or nifedipine (0.1 μM) did not significantly modify the vasorelaxant effects of this flavonoid. Hesperetin (10 μM–0.1 mM) did not affect the basal uptake of 45Ca2+ but decreased the influx of 45Ca2+ induced by NA and KCl in endothelium-containing and endothelium-denuded rat aorta. Hesperetin (10 μM–0.1 mM) did not scavenge O2•− generated by the phenazine methosulfate (PMS)-reduced β-nicotinamide adenine dinucleotide (NADH) system. Hesperetin (0.1 mM) significantly reversed the inhibitory effects of NA (1 μM) and high KCl (60 mM) on cyclic nucleotide (cAMP and cGMP) production in cultured rat aortic myocytes. Hesperetin preferentially inhibited calmodulin (CaM)-activated PDE1 and PDE4 isolated from bovine aorta with IC50 values of about 74 μM and 70 μM respectively. In contrast, the 7-rhamnoglucoside of hesperetin, hesperidin (10 μM–0.1 mM), was inactive in practically all experiments, although it inhibited basal and cGMP-activated PDE2 isolated from platelets (IC50 values of 32±4 μM and 137±34 μM respectively). These results suggest that the vasorelaxant effects of hesperetin are basically due to the inhibition of PDE1 and PDE4 activities.

Pravastatin counteracts angiotensin II-induced upregulation and activation of NADPH oxidase at plasma membrane of human endothelial cells.

Endothelial dysfunction has been linked to reactive oxygen species (ROS) production by nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase. Angiotensin II (ANG), which levels are elevated in some cardiovascular diseases, can stimulate this enzyme, whereas statins have been demonstrated pleiotropic effects related with the restoration of endothelial function. Therefore, our purpose was to study the mechanism of the possible beneficial effects of pravastatin on ANG-activated human umbilical vein endothelial cells (HUVEC). ANG induced an increase in the extracellular superoxide anion produced by NADPH oxidase but had no effect in the intracellular ROS production. Pravastatin, which alone did not have any effect on ROS production, totally blocked the stimulating effects of ANG when combined with it. These effects were not due to a direct action of ANG or pravastatin on the activity of NADPH oxidase measured in HUVEC lisates. On the contrary, the results correlated well with other effects of ANG: a Nox4 and p22phox upregulated expression and an enhanced Nox4 translocation to the cell membrane. All these effects were inhibited by pravastatin, which had no effect when incubated alone. These data reveal for the first time that pravastatin interrupts the signaling pathway activated by ANG that leads to an enhanced NADPH oxidase activity at the cell membrane of HUVEC. For that, pravastatin inhibits ANG-induced upregulation of catalytic NADPH oxidase subunits and blocks the migration of them to the endothelial cell membrane.

Current status of NADPH oxidase research in cardiovascular pharmacology

The implications of reactive oxygen species in cardiovascular disease have been known for some decades. Rationally, therapeutic antioxidant strategies combating oxidative stress have been developed, but the results of clinical trials have not been as good as expected. Therefore, to move forward in the design of new therapeutic strategies for cardiovascular disease based on prevention of production of reactive oxygen species, steps must be taken on two fronts, ie, comprehension of reduction-oxidation signaling pathways and the pathophysiologic roles of reactive oxygen species, and development of new, less toxic, and more selective nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors, to clarify both the role of each NADPH oxidase isoform and their utility in clinical practice. In this review, we analyze the value of NADPH oxidase as a therapeutic target for cardiovascular disease and the old and new pharmacologic agents or strategies to prevent NADPH oxidase activity. Some inhibitors and different direct or indirect approaches are available. Regarding direct NADPH oxidase inhibition, the specificity of NADPH oxidase is the focus of current investigations, whereas the chemical structure-activity relationship studies of known inhibitors have provided pharmacophore models with which to search for new molecules. From a general point of view, small-molecule inhibitors are preferred because of their hydrosolubility and oral bioavailability. However, other possibilities are not closed, with peptide inhibitors or monoclonal antibodies against NADPH oxidase isoforms continuing to be under investigation as well as the ongoing search for naturally occurring compounds. Likewise, some different approaches include inhibition of assembly of the NADPH oxidase complex, subcellular translocation, post-transductional modifications, calcium entry/release, electron transfer, and genetic expression. High-throughput screens for any of these activities could provide new inhibitors. All this knowledge and the research presently underway will likely result in development of new drugs for inhibition of NADPH oxidase and application of therapeutic approaches based on their action, for the treatment of cardiovascular disease in the next few years.

PDE4 and PDE5 regulate cyclic nucleotides relaxing effects in human umbilical arteries

Cyclic nucleotides (cAMP and cGMP) are the main second messengers linked to vasodilatation. They are synthesized by cyclases and degraded by different types of phosphodiesterases (PDE). The effect of PDE inhibition and cyclases stimulation on 5-hydroxytryptamine (5-HT; 1 microM) and histamine (10 microM) contracted arteries was analysed. Stimulation of guanylate cyclase or adenylate cyclase relaxed the histamine- and 5-HT-induced contractions indicating that intracellular increase of cyclic nucleotides leads to vasodilatation of the human umbilical artery. We investigated the role of different PDE families in the regulation of this effect. The presence of the different PDE types in human umbilical artery smooth muscle was analysed by RT-PCR and the expression of PDE1B, PDE3A, PDE3B, PDE4C, PDE4D and PDE5A was detected. The unspecific PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX; 50 microM) relaxed histamine-contracted human umbilical artery on 47.4+/-7.2%. This effect seems to be due to PDE4 and PDE5 inhibition because among the selective PDE inhibitors used only the PDE4 inhibitor (rolipram; 1 microM) and the PDE5 inhibitors (dipyridamole and T0156; 3 microM and 1 microM respectively) induced significant relaxation (39.0+/-8.7, 30.4+/-6.0 and 36.3+/-2.8 respectively). IBMX, dipyridamole and T0156 produced similar relaxation on 5-HT-induced contraction. After forskolin, the addition of IBMX or rolipram increased the effect of the adenylate cyclase stimulator and almost completely relaxed the human umbilical artery contracted by histamine (92.5+/-4.9 and 90.9+/-4.7 respectively), suggesting a main role of PDE4. The data obtained with 5-HT contracted arteries confirmed this, because only rolipram and IBMX significantly increased the forskolin vasodilator effect. The administration of dipyridamole and T0156 after sodium nitroprusside (SNP) induced a significant increase of the SNP relaxant effect on histamine-contracted arteries, but PDE1 and PDE3 inhibition did not increase the effect of the guanylate cyclase stimulator. Similar effects were obtained in 5-HT contracted arteries, the SNP induced relaxation was increased by the PDE5 inhibition, but not by PDE1 or PDE3 inhibition. In summary, our results demonstrate that: 1) the increase of cAMP and/or cGMP levels induces relaxation of the human umbilical vascular smooth muscle; 2) four families of PDE are expressed in this smooth muscle: PDE1, PDE3, PDE4 and PDE5; 3) between these families, PDE4 and PDE5 are the key enzymes involved in the regulation of the relaxation associated to cAMP and cGMP, respectively.