Abstract-Oxidative stress plays a critical role in the pathogenesis of hypertension. The NADPH oxidase constitutes a major source of superoxide anion in phagocytic cells, and its activation is associated with matrix metalloproteinase (MMP)-9 secretion by these cells. We investigated the effects of the angiotensin II type 1 receptor antagonist losartan and its metabolites (EXP3174 and EXP3179) on NADPH oxidase activity and MMP-9 secretion in human phagocytic cells. ⅐Ϫ in the vessel wall, and they are present in endothelial cells, smooth muscle cells, fibroblasts, and infiltrated monocytes/macrophages. 3,4 Protein kinase C (PKC)-dependent p47phox phosphorylation and translocation are major mechanisms involved in phagocytic NADPH oxidase activation. 3 Phagocytic NADPH oxidase is overactivated in essential hypertension. 5,6 Clinical studies have demonstrated that treatment with losartan improves endothelial function and decreases blood pressure through a reduction in oxidative stress. 7,8 Moreover, several experimental studies have demonstrated beneficial effects of losartan treatment on vascular alterations by blocking NADPH oxidase activation. 9 -12 Losartan is hepatically metabolized by the cytochrome-P450 pathway and exerts its antihypertensive actions predominantly by EXP3174, its main metabolite and the pharmacological blocker of the angiotensin II type 1 receptor (AT 1 R). 13,14 Interestingly, during losartan metabolism, the liver also produces the EXP3179 metabolite, which has no AT 1 R-blocking properties. 14,15 In recent years, several studies have reported that the EXP3179 metabolite exerts AT 1 Rindependent actions. [15][16][17][18] Krämer et al 15 demonstrated that EXP3179 mediates the anti-inflammatory properties of losartan by abolishing cyclooxygenase-2 upregulation. Furthermore, EXP3179 stimulates endothelial NO synthase and suppresses tumor necrosis factor-␣-induced apoptosis. 16 Schupp et al 17 have demonstrated that EXP3179 acts as a peroxisome proliferator-activated receptor-␥ agonist. Finally, the ability of EXP3179 to inhibit collagen-dependent platelet activation has also been described. 18 Therefore, we hypothesized that EXP3179 metabolite might inhibit NADPH oxidase in phagocytic cells by AT 1 R-

In the ischemic-reperfused (I/R) heart, renin-containing mast cells (MC) release enzymatically active renin, activating a local renin-angiotensin system (RAS), causing excessive norepinephrine release and arrhythmic dysfunction. Activation of G-receptors on MC and/or ischemic preconditioning (IPC) prevent renin release, thus providing anti-RAS cardioprotection. We questioned whether sphingosine-1-phosphate (S1P), a sphingolipid produced in the I/R heart, might afford anti-RAS cardioprotection by activating G-coupled S1P receptors (S1PR) on MC. We report that activation of G-coupled S1PR in cardiac MC confers IPC-like anti-RAS cardioprotection due to S1PR-mediated inhibition of I/R-induced cardiac MC degranulation and renin release. This results from an initial translocation of protein kinase C subtype- and subsequent activation of aldehyde dehydrogenase type 2 (ALDH2), culminating in the elimination of the MC-degranulating effects of acetaldehyde and other toxic species produced during I/R. Inhibition of toxic aldehydes-induced MC-renin release prevents local RAS activation, reduces infarct size, and alleviates arrhythmias. Notably, these cardioprotective effects are lacking in hearts and MC from gene-targeted knock-in mice (ALDH2*2) in which ALDH2 enzymatic activity is maximally reduced. Thus, ALDH2 appears to play a pivotal role in this protective process. Our findings suggest that MC S1PR may represent a new pharmacologic and therapeutic target for the direct alleviation of RAS-induced cardiac dysfunctions, including ischemic heart disease and congestive heart failure.

Hypoxia increased CT-1 levels in cardiac cells (in vitro and in vivo) through a direct regulation of CTF1 promoter by HIF-1α. This CT-1 activation by hypoxia may protect cells from apoptosis, thus supporting a protective role for CT-1 as a survival factor for cardiomyocytes.

We reported previously that natriuretic peptides, including brain natriuretic peptide (BNP), promote norepinephrine release from cardiac sympathetic nerves and dopamine release from differentiated pheochromocytoma PC12 cells. These proexocytotic effects are mediated by an increase in intracellular calcium secondary to cAMP/protein kinase A (PKA) activation caused by a protein kinase G (PKG)-mediated inhibition of phosphodiesterase type 3 (PDE3). The purpose of the present study was to search for novel means to prevent the proadrenergic effects of natriuretic peptides. For this, we focused our attention on neuronal inhibitory G␣ i/o -coupled histamine H 3 and H 4 receptors. Our findings show that activation of neuronal H 3 and H 4 receptors inhibits the release of catecholamines elicited by BNP in cardiac synaptosomes and differentiated PC12 cells. This effect results from a decrease in intracellular Ca 2ϩ due to reduced intracellular cAMP/PKA activity, caused by H 3 and H 4 receptor-mediated PKG inhibition and consequent PDE3-induced increase in cAMP metabolism. Indeed, selective H 3 and H 4 receptor agonists each synergized with a PKG inhibitor and a PDE3 activator in attenuating BNP-induced norepinephrine release from cardiac sympathetic nerve endings. This indicates that PKG inhibition and PDE3 stimulation are pivotal for the H 3 and H 4 receptor-mediated attenuation of BNP-induced catecholamine release. Cardiac sympathetic overstimulation is characteristic of advanced heart failure, which was recently found not to be improved by the administration of recombinant BNP (nesiritide), despite the predicated beneficial effects of natriuretic peptides. Because excessive catecholamine release is likely to offset the desirable effects of natriuretic peptides, our findings suggest novel means to alleviate their adverse effects and improve their therapeutic potential.

Renin is a newly discovered constituent of mast cells. Given that mast cells play a major role in IgE-mediated allergic hypersensitivity, we investigated whether activation of the high-affinity IgE receptor FcεRI elicits release of mast-cell renin. Cross-linking of FcεRI on the surface of mature bone marrow-derived mast cells elicited release of enzymatically active renin protein. The angiotensin I-forming activity of the renin protein was completely blocked by the selective renin inhibitor BILA 2157, which excludes formation of angiotensin I by proteases other than renin. FcεRI-mediated mast-cell renin release was inhibited by dexamethasone and potentiated by the proinflammatory mediator PGE2. Furthermore, cross-linking of mast-cell FcεRI in ex vivo murine hearts passively sensitized with monoclonal anti-DNP IgE also resulted in mast-cell degranulation and overflow of renin. Our findings indicate that IgE-mediated allergic hypersensitivity provokes release of renin from both cultured and resident cardiac mast cells, a process likely to be exacerbated in a chronic inflammatory background. Given the widespread distribution of mast cells, and the presence of angiotensinogen and angiotensin-converting enzyme in many tissues, renin release in immediate hypersensitivity reactions could result in local angiotensin II generation and multiorgan dysfunctions.