Angiotensin II induces tumor necrosis factor biosynthesis in the adult mammalian heart through a protein kinase C-dependent pathway

Involvement of tumor necrosis factor-alpha in natriuretic response to systemic infusion of nitric oxide synthase inhibitor in anesthetized mice

Systemic infusion of TNF-alpha exerts renal vasoconstriction but caused marked natriuresis in mice. Similar renal responses were also observed during systemic infusion of nitric oxide (NO) synthase inhibitors as opposed to their usual antinatriuretic responses when administered intrarenally. In the present study, we examined the hypothesis that acute NO blockade systemically induces TNF-alpha generation. which induces this natriuretic response. Renal responses to intravenous infusion of the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME; 0.2 microg x min(-1) x g body wt(-1) for 85 min) and its impact on the plasma level of TNF-alpha were evaluated in anesthetized mice. Plasma TNF-alpha was undetected in untreated mice (n = 7) but was elevated in L-NAME-treated mice (109 +/- 22 pg/ml; P < 0.01 vs. untreated group; n = 7) along with an increase in TNF-alpha protein expression in kidney tissue. L-NAME infusion caused a usual increase in mean arterial pressure (MAP; 98 +/- 3 to 122 +/- 3 mmHg; P < 0.01) and decreases in renal blood flow (RBF; 8.6 +/- 0.3 to 4.4 +/- 0.2 ml x min(-1) x g(-1); P < 0.01) and glomerular filtration rate (GFR; 1.14 +/- 0.07 to 0.77 +/- 0.04 ml x min(-1) x g(-1); P < 0.01) with a marked increase in sodium excretion (U(Na)V; 0.48 +/- 0.10 to 3.52 +/- 0.85 micromol x min(-1) x g(-1); P < 0.01). Interestingly, in mice (n = 7) pretreated with the TNF-alpha blocker etanercept (5 mg/kg sc), the U(Na)V response to l-NAME infusion was markedly blunted (0.58 +/- 0.08 to 1.22 +/- 0.28 micromol x min(-1) x g(-1); P = NS) although responses for MAP, RBF, and GFR were mostly unchanged. However, pretreatment with the superoxide scavenger tempol in mice (n = 7) did not alter the U(Na)V response to L-NAME. These data demonstrate that L-NAME-induced natriuresis is mediated, at least in part, by concomitant generation of TNF-alpha during NO blockade.

Autoantibody-mediated angiotensin receptor activation contributes to preeclampsia through tumor necrosis factor-alpha signaling

Preeclampsia is a prevalent life-threatening hypertensive disorder of pregnancy for which the pathophysiology remains largely undefined. Recently, a circulating maternal autoantibody, the angiotensin II type I (AT(1)) receptor agonistic autoantibody (AA), has emerged as a contributor to disease features. Increased circulating maternal tumor necrosis factor alpha (TNF-alpha) is also associated with the disease; however, it is unknown whether this factor directly contributes to preeclamptic symptoms. Here we report that this autoantibody increases the proinflammatory cytokine TNF-alpha in the circulation of AT(1)-AA-injected pregnant mice but not in nonpregnant mice. Coinjection of AT(1)-AA with a TNF-alpha neutralizing antibody reduced cytokine availability in AT(1)-AA-injected pregnant mice. Moreover, TNF-alpha blockade in AT(1)-AA-injected pregnant mice significantly attenuated the key features of preeclampsia. Autoantibody-induced hypertension was reduced from 131+/-4 to 110+/-4 mm Hg, and proteinuria was reduced from 212+/-25 to 155+/-23 microg of albumin per milligram of creatinine (both P<0.05). Injection of AT(1)-AA increased the serum levels of circulating soluble fms-like tyrosine kinase 1 and soluble endoglin (34.1+/-5.1, 2.4+/-0.3 ng/mL, respectively) and coinjection with the TNF-alpha blocker significantly reduced their levels (21.7+/-3.4 and 1.2+/-0.4 ng/mL, respectively). Renal damage and placental abnormalities were also decreased by TNF-alpha blockade. Lastly, the elevated circulating TNF-alpha in preeclamptic patients is significantly correlated with the AT(1)-AA bioactivity in our patient cohort. Similarly, the autoantibody, through AT(1) receptor-mediated TNF-alpha induction, contributed to increased soluble fms-like tyrosine kinase 1, soluble endoglin secretion, and increased apoptosis in cultured human villous explants. Overall, AT(1)-AA is a novel candidate that induces TNF-alpha, a cytokine that may play an important pathogenic role in preeclampsia.

Caveolin-1 ablation reduces the adverse cardiovascular effects of N-omega-nitro-L-arginine methyl ester and angiotensin II

Caveolae are the major cellular membrane structure through which extracellular mediators transmit information to intracellular signaling pathways. In vascular tissue (but not ventricular myocardium), caveolin-1 (cav-1) is the main component of caveolae; cav-1 modulates enzymes and receptors, such as the endothelial nitric oxide synthase and the angiotensin II (AngII) type 1 receptor. Evidence suggests that AngII and aldosterone (ALDO) are important mediators of ventricular injury. We have described a model of biventricular damage in rodents that relies on treatment with N-omega-nitro-l-arginine methyl ester (L-NAME (nitric oxide synthase inhibitor)) and AngII. This damage initiated at the vascular level and was observed only in the presence of ALDO and an activated mineralocorticoid receptor (MR). We hypothesize that cav-1 modulates the adverse cardiac effects mediated by ALDO in this animal model. To test this hypothesis, we assessed the ventricular damage and measures of inflammation, in wild-type (WT) and cav-1 knockout (KO) mice randomized to either placebo or L-NAME/AngII treatment. Despite displaying cardiac hypertrophy at baseline and higher blood pressure responses to L-NAME/AngII, cav-1 KO mice displayed, as compared with WT, decreased treatment-induced biventricular damage as well as decreased transcript levels of the proinflammatory marker plasminogen activator inhibitor-1. Additionally, L-NAME/AngII induced an increase in cardiac MR levels in WT but not cav-1-ablated mice. Moreover and despite similar circulating ALDO levels in both genotypes, the myocardial damage (as determined histologically and by plasminogen activator inhibitor-1 mRNA levels) was less sensitive to ALDO levels in cav-1 KO vs. WT mice, consistent with decreased MR signaling in the cav-1 KO. Thus, we conclude that the L-NAME/AngII-induced biventricular damage is mediated by a mechanism partially dependent on cav-1 and signaling via MR/ALDO.

Globular adiponectin inhibits angiotensin II-induced nuclear factor kappaB activation through AMP-activated protein kinase in cardiac hypertrophy

Activation of nuclear factor kappaB (NF-kappaB) has been found necessary for cardiac hypertrophic growth in vivo and in vitro experiments. Adiponectin, an adipocyte-derived polypeptide, suppresses cardiac hypertrophy in response to pressure overload. Here we investigated the potential effect of adiponectin on NF-kappaB activation in hypertrophic neonatal rat ventricular myocytes (NRVMs) and related signal transduction pathway. We treated NRVMs with globular adiponectin (gAd) before angiotensin II (AngII) stimulation. Pretreating cells with gAd reduced the increased incorporation of [(3)H]-leucine and the mRNA levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) stimulated by AngII, indicating gAd inhibited AngII-induced cardiac hypertrophic signaling. Moreover, gAd pretreatment suppressed inhibitory protein kappaB (I-kappaB) phosphorylation and decreased p65 nuclear translocation, DNA-binding and transcription activity of NF-kappaB. Meanwhile, gAd promoted AMP-activated protein kinase (AMPK) phosphorylation, which is a downstream signaling mediator of adiponectin. Pharmacological activator of AMPK could inhibit AngII-induced NF-kappaB translocation, and inhibitor of AMPK or a dominant-negative AMPK adenovirus suppressed gAd-mediated inhibition of I-kappaB phosphorylation and NF-kappaB activation. When AMPK was inhibited, the suppressive effect of gAd on ANP mRNA expression was reduced. Our data indicate that gAd inhibits cardiac hypertrophic signaling through AMPK mediated suppression of NF-kappaB activation.

The detrimental role of angiotensin receptor agonistic autoantibodies in intrauterine growth restriction seen in preeclampsia

Growth-restricted fetuses are at risk for a variety of lifelong medical conditions. Preeclampsia, a life-threatening hypertensive disorder of pregnancy, is associated with fetuses who suffer from intrauterine growth restriction (IUGR). Recently, emerging evidence indicates that preeclamptic women harbor AT₁ receptor agonistic autoantibodies (AT₁-AAs) that contribute to the disease features. However, the exact role of AT₁-AAs in IUGR and the underlying mechanisms have not been identified. We report that these autoantibodies are present in the cord blood of women with preeclampsia and retain the ability to activate AT₁ receptors. Using an autoantibody-induced animal model of preeclampsia, we show that AT₁-AAs cross the mouse placenta, enter fetal circulation, and lead to small fetuses with organ growth retardation. AT₁-AAs also induce apoptosis in the placentas of pregnant mice, human villous explants, and human trophoblast cells. Finally, autoantibody-induced IUGR and placental apoptosis are diminished by either losartan or an autoantibody-neutralizing peptide. Thus, these studies identify AT₁-AA as a novel causative factor of preeclampsia-associated IUGR and offer two possible underlying mechanisms: a direct detrimental effect on fetal development by crossing the placenta and entering fetal circulation, and indirectly through AT₁-AA–induced placental damage. Our findings highlight AT₁-AAs as important therapeutic targets.

Angiotensin II and tumour necrosis factor alpha as mediators of ATP-dependent potassium channel remodelling in post-infarction heart failure

AIMS

Angiotensin II (Ang II) and tumour necrosis factor alpha (TNFalpha) are involved in the progression from compensated hypertrophy to heart failure. Here, we test their role in the remodelling of ATP-dependent potassium channel (K(ATP)) in heart failure, conferring increased metabolic and diazoxide sensitivity.

METHODS AND RESULTS

We observed increased expression of both angiotensinogen and TNFalpha in the failing rat myocardium, with a regional gradient matching that of the K(ATP) subunit Kir6.1 expression. Both angiotensinogen and TNFalpha expression correlated positively with Kir6.1 and negatively with Kir6.2 expression across the post-infarction myocardium. To further identify a causal relationship, cardiomyocytes isolated from normal rat hearts were exposed in vitro to Ang II or TNFalpha. We observed increased Kir6.1 and SUR subunit and reduced Kir6.2 subunit mRNA expression in cardiomyocytes cultured with Ang II or TNFalpha, similar to what was observed in failing hearts. In patch-clamp experiments, cardiomyocytes cultured with Ang II or TNFalpha exhibited responsiveness to diazoxide, in terms of both K(ATP) current and action potential shortening. This was not observed in untreated cardiomyocytes and resembles the diazoxide sensitivity of failing cardiomyocytes that also overexpress Kir6.1. Ang II exerted its effect through induction of TNFalpha expression, because TNFalpha-neutralizing antibody abolished the effect of Ang II, and in failing hearts, regional expression of angiotensinogen matched TNFalpha expression. Finally, Ang II and TNFalpha regulated K(ATP) subunit expression, possibly through differential expression of Forkhead box transcription factors.

CONCLUSION

This study identifies Ang II and TNFalpha as mediators of the remodelling of K(ATP) channels in heart failure.

Curcumin ameliorates renal failure in 5/6 nephrectomized rats: role of inflammation

TNF-α and NF-κB play important roles in the development of inflammation in chronic renal failure (CRF). In hepatic cells, curcumin is shown to antagonize TNF-α-elicited NF-κB activation. In this study, we hypothesized that if inflammation plays a key role in renal failure then curcumin should be effective in improving CRF. The effectiveness of curcumin was compared with enalapril, a compound known to ameliorate human and experimental CRF. Investigation was conducted in Sprague-Dawley rats where CRF was induced by 5/6 nephrectomy (Nx). The Nx animals were divided into untreated (Nx), curcumin-treated (curcumin), and enalapril-treated (enalapril) groups. Sham-operated animals served as a control. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was significantly reduced by curcumin and enalapril treatment. However, only enalapril significantly improved blood pressure. Compared with the control, the Nx animals had significantly higher plasma and kidney TNF-α, which was associated with NF-κB activation and macrophage infiltration in the kidney. These changes were effectively antagonized by curcumin and enalapril treatment. The decline in the anti-inflammatory peroxisome proliferator-activated receptor γ (PPARγ) seen in Nx animals was also counteracted by curcumin and enalapril. Studies in mesangial cells were carried out to further establish that the anti-inflammatory effect of curcumin in vivo was mediated essentially by antagonizing TNF-α. Curcumin dose dependently antagonized the TNF-α-mediated decrease in PPARγ and blocked transactivation of NF-κB and repression of PPARγ, indicating that the anti-inflamatory property of curcumin may be responsible for alleviating CRF in Nx animals.

Angiotensin II downregulates the fatty acid oxidation pathway in adult rat cardiomyocytes via release of tumour necrosis factor-alpha

AIMS

Advanced heart failure is often associated with reduced myocardial fatty acid oxidation capacity. We have previously observed that failing hearts of mice with overexpression of angiotensinogen in the myocardium exhibit marked reduction of key regulatory proteins of fatty acid oxidation. In the present study, we determined whether exposure of adult rat cardiac (ARC) myocytes to angiotensin II (Ang II) influences expression of fatty acid translocase, muscle-type carnitine palmitoyl transferase-I, and medium-chain acyl-CoA dehydrogenase.

METHODS AND RESULTS

Ang II reduced mRNA expression of the three regulatory proteins in ARC myocytes during the entire 14-days culture period. However, protein expression and palmitate oxidation rate remained unaltered for 7 days, but subsequently markedly decreased. The decrease of protein expression and of fatty acid oxidation coincided with the onset of increased protein expression of tumour necrosis factor-alpha (TNF-alpha). The effect of Ang II was completely abolished by either blocking TNF-alpha formation through inhibition of reactive oxygen species-mediated activation of nuclear factor-kappaB or by neutralizing TNF-alpha with a specific antibody. Activation of peroxisome proliferator-activated receptor-alpha (PPARalpha) and PPARbeta/delta counteracted Ang II-mediated reduction of the fatty acid oxidation pathway.

CONCLUSION

Prolonged exposure of cardiac myocytes to Ang II elicits downregulation of the fatty acid oxidation pathway mediated by enhanced synthesis of TNF-alpha.

Tumor necrosis factor-alpha induces renal vasoconstriction as well as natriuresis in mice

Tumor necrosis factor-α (TNF-α) has been implicated in the pathogenesis of hypertension and renal injury. However, the direct effects of TNF-α on renal hemodynamic and excretory function are not yet clearly defined. We examined the renal responses to infusion of TNF-α (0.33 ng·g⁻¹·min⁻¹) in anesthetized mice. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by PAH and inulin clearance. The urine was collected from a cannula inserted into the bladder. Following the 60-min control clearance period, TNF-α infusion was initiated and 15 min were given for stabilization followed by another 60-min clearance period. TNF-α alone (n = 7) caused decreases in RBF (7.9 ± 0.3 to 6.4 ± 0.3 ml·min⁻¹·g⁻¹) and GFR (1.04 ± 0.06 to 0.62 ± 0.08 ml·min⁻¹·g⁻¹) as well as increases in absolute (0.8 ± 0.3 to 1.4 ± 0.3 μmol·min⁻¹·g⁻¹) and fractional excretion of sodium (0.5 ± 0.2 to 1.5 ± 0.4%) without affecting arterial pressure. TNF-α also increased 8-isoprostane excretion (8.10 ± 1.09 to 11.13 ± 1.34 pg·min⁻¹·g⁻¹). Pretreatment with TNF-α blocker etanercept (5 mg/kg sc; 24 and 3 h before TNF-α infusion; n = 6) abolished these responses. However, TNF-α induced an increase in RBF and caused attenuation of the GFR reduction in mice pretreated with superoxide (O₂⁻) scavenger tempol (2 μg·g⁻¹·min⁻¹; n = 6). Pretreatment with nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (0.1 μg·g⁻¹·min⁻¹; n = 6) resulted in further enhancement in vasoconstriction while natriuresis remained unaffected in response to TNF-α. These data suggest that TNF-α induces renal vasoconstriction and hypofiltration via enhancing the activity of O₂⁻ and thus reducing the activity of NO. The natriuretic response to TNF-α is related to its direct effects on tubular sodium reabsorption.

Expression of renin-angiotensin system and peroxisome proliferator-activated receptors in alcoholic cardiomyopathy

BACKGROUND

Alcoholic cardiomyopathy (ACM) develops in response to chronic alcohol intake and it is hypothesized that activation of the renin-angiotensin system (RAS) and disorders in energy metabolism may play important roles in its onset. Given that the expression of peroxisome proliferator-activated receptors (PPARalpha and PPARgamma) changes with alterations in cardiac metabolism and myocardial remodeling, this study was designed to test the hypothesis that protein expression of PPARalpha and PPARgamma is correlated with RAS activation in ACM.

METHODS

For the first experiment, rats were divided into 3 groups: 30 received alcohol (intragastric administration with ad libitum drinking), 30 received alcohol and irbesartan (5 mg/kg/d, p.o.), and 30 served as controls. RAS activity and protein expression of PPARalpha and PPARgamma were evaluated in rats following 6 months of alcohol feeding using radioimmunoassay, reverse transcriptase PCR, and Western blot methods. For the second experiment, rats were divided into 4 groups: 10 rats received alcohol/irbesartan (5 mg/kg/d, p.o.)/PD98059 (methyl ethyl ketone [MEK]-1 inhibitor) (0.3 mg/kg/d, p.o.), 10 rats received alcohol/PD98059, 10 rats received alcohol/irbesartan, and 10 rats received alcohol alone. Myocardial PPARalpha and PPARgamma protein expression was detected following 6 months of alcohol feeding using Western blot method.

RESULTS

Compared with controls, myocardial angiotensin (Ang) I, Ang II, and renin levels were progressively increased at 2, 4, and 6 months of alcohol intake. mRNA expression of renin, angiotensinogen, angiotensin-converting enzyme (ACE), and AT1 was increased at 6 months. Moreover, activated RAS downregulated PPARalpha and upregulated PPARgamma protein expression as ACM progressed. Finally, extracellular signal regulated kinase 1 and 2 (ERK1/2) was shown to play a key role in the regulation of protein expression of PPARalpha and PPARgamma.

CONCLUSION

These results suggest that RAS is activated during the development of ACM. Moreover, ERK1/2 plays a key role in the regulation of protein expression of PPARalpha and PPARgamma by RAS in ACM.

Aldosterone induces interleukin-18 through endothelin-1, angiotensin II, Rho/Rho-kinase, and PPARs in cardiomyocytes

Aldosterone (Aldo) is recognized as an important risk factor for cardiovascular diseases. IL-18 induces myocardial hypertrophy, loss of contractility of cardiomyocytes, and apoptosis leading myocardial dysfunction. However, so far, there have been few reports concerning the interaction between Aldo and IL-18. The present study examined the effects and mechanisms of Aldo on IL-18 expression and the roles of peroxisome proliferator-activated receptor (PPAR) agonists in rat cardiomyocytes. We used cultured rat neonatal cardiomyocytes stimulated with Aldo to measure IL-18 mRNA and protein expression, Rho-kinase, and NF-kappaB activity. We also investigated the effects of PPAR agonists on these actions. Aldo, endothelin-1 (ET-1), and angiotensin II (ANG II) increased IL-18 mRNA and protein expression. Mineralocorticoid receptor antagonists, endothelin A receptor antagonist, and ANG II receptor antagonist inhibited Aldo-induced IL-18 expression. Aldo induced ET-1 and ANG II production in cultured media. Moreover, Rho/Rho-kinase inhibitor and statin inhibited Aldo-induced IL-18 expression. On the other hand, Aldo upregulated the activities of Rho-kinase and NF-kappaB. PPAR agonists attenuated the Aldo-induced IL-18 expression and NF-kappaB activity but not the Rho-kinase activity. Our findings indicate that Aldo induces IL-18 expression through a mechanism that involves, at a minimum, ET-1 and ANG II acting via the Rho/Rho-kinase and PPAR/NF-kappaB pathway. The induction of IL-18 in cardiomyocytes by Aldo, ET-1, and ANG II might, therefore, cause a deterioration of the cardiac function in an autocrine and paracrine fashion. The inhibition of the IL-18 expression by PPAR agonists might be one of the mechanisms whereby the beneficial cardiovascular effects are exerted.

Involvement of tumor necrosis factor-alpha in angiotensin II-mediated effects on salt appetite, hypertension, and cardiac hypertrophy

Hypertension is considered a low-grade inflammatory condition induced by various proinflammatory cytokines, including tumor necrosis factor (TNF)-alpha. Recent studies have implicated an involvement of TNF-alpha in the development of salt-sensitive hypertension induced by angiotensin II (Ang II). To understand further the relationship between TNF-alpha and Ang II, we examined the responses to Ang II in TNF-alpha knockout (TNF-alpha(-/-)) mice in the present study. A continuous infusion of Ang II (1 microg/kg per minute) for 2 weeks was given to both TNF-alpha(-/-) and wild-type (WT) mice with implanted osmotic minipumps. Daily measurement of water intake, salt intake, and urine output were performed using metabolic cages. Blood pressure was monitored continuously with implanted radiotelemetry. Ang II administration for 2 weeks caused increases in salt (0.2+/-0.07 to 5.6+/-0.95 mL/d) and water (5.4+/-0.34 to 11.5+/-1.2 mL/d) intake and in mean arterial pressure (115+/-1 to 151+/-3 mm Hg) in wild-type mice, but these responses were absent in TNF-alpha(-/-) mice (0.2+/-0.04 to 0.3+/-0.09 mL/d, 5.5+/-0.2 to 6.1+/-0.07 mL/d, and 113+/-2 to 123+/-3 mm Hg, respectively). Cardiac hypertrophy induced by Ang II was significantly attenuated in TNF-alpha(-/-) mice compared with wild-type mice. In a group of TNF-alpha(-/-) mice, when replacement therapy was made with recombinant TNF-alpha, Ang II induced similar responses in salt appetite, mean arterial pressure, and cardiac hypertrophy, as observed in wild-type mice. These results suggest that TNF-alpha plays a mechanistic role in mediating chronic Ang II-induced effects on salt appetite and blood pressure, as well as on cardiac hypertrophy.

Interruption of endothelin signaling modifies membrane type 1 matrix metalloproteinase activity during ischemia and reperfusion

The matrix metalloproteinases (MMPs), in particular, membrane type 1 MMP (MT1-MMP), are increased in the context of myocardial ischemia and reperfusion (I/R) and likely contribute to myocardial dysfunction. One potential upstream induction mechanism for MT1-MMP is endothelin (ET) release and subsequent protein kinase C (PKC) activation. Modulation of ET and PKC signaling with respect to MT1-MMP activity with I/R has yet to be explored. Accordingly, this study examined in vivo MT1-MMP activation during I/R following modification of ET signaling and PKC activation. With the use of a novel fluorogenic microdialysis system, myocardial interstitial MT1-MMP activity was measured in pigs (30 kg; n = 9) during I/R (90 min I/120 min R). Local ET(A) receptor antagonism (BQ-123, 1 microM) and PKC inhibition (chelerythrine, 1 microM) were performed in parallel microdialysis probes. MT1-MMP activity was increased during I/R by 122 +/- 10% (P < 0.05) and was unchanged from baseline with ET antagonism and/or PKC inhibition. Selective PKC isoform induction occurred such that PKC-betaII increased by 198 +/- 31% (P < 0.05). MT1-MMP phosphothreonine, a putative PKC phosphorylation site, was increased by 121 +/- 8% (P < 0.05) in the I/R region. These studies demonstrate for the first time that increased interstitial MT1-MMP activity during I/R is a result of the ET/PKC pathway and may be due to enhanced phosphorylation of MT1-MMP. These findings identify multiple potential targets for modulating a local proteolytic pathway operative during I/R.

Acute phase proteins and systolic dysfunction in subjects with acute myocardial infarction

AIM

To investigate correlations between plasmatic concentrations of acute phase proteins (APPs) and left ventricular systolic function during the early phase of acute myocardial infarction.

METHODS

Plasmatic concentrations of alpha-1-anti-trypsin (A1AT), alpha 1 glyco-protein (A1GP), haptoglobin (HG), caeruloplasmin (CP) and C-reactive protein (CRP) were evaluated in 123 patients with ST elevation acute myocardial infarction (STEMI) within 12 h after onset of chest pain. Systolic function was assessed with bi-dimensional echography and incidence of in-hospital adverse events was compared to APPs levels.

RESULTS

A1AT, A1GP, HG and CP showed a statistically significant correlation with admission CRP concentrations (P < 0.001). Left ventricular ejection fraction inversely correlated with plasmatic concentrations of A1GP, A1AT, CP and HG. Incidence of acute heart failure correlated with values of APPs and, in a stepwise analysis, CP values were the most significant markers of acute heart failure.

CONCLUSIONS

Systolic dysfunction in STEMI patients seems to be associated with an inflammatory response featured by a rise in plasmatic concentration of APPs; increase in APPs concentrations seems to own a short-term prognostic relevance.

Nuclear factor-kappaB signaling contributes to severe, but not moderate, angiotensin II-induced left ventricular remodeling

OBJECTIVE

The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated in cardiomyocyte hypertrophy in vitro as well as in vivo; however, it is unknown if activation of NF-kappaB plays a mandatory role in the hypertrophic process. Here we characterize the importance of NF-kappaB signaling in moderate and severe left ventricular (LV) hypertrophy in rats with chronic pressure overload induced by angiotensin II (Ang II) infusion.

METHODS AND RESULTS

Electrophoretic mobility shift assay analysis revealed that Ang II infusion (2.5 microg/kg per min) for 6 days increased LV NF-kappaB/DNA-binding activity in a biphasic manner in Sprague-Dawley rats. Pyrrolidine dithiocarbamate (PDTC) (100 mg/kg per day), an NF-kappaB inhibitor, abolished Ang II-induced NF-kappaB activation and concomitant increase in tumor necrosis factor-alpha gene expression, while activator protein-1/DNA binding was not affected. Inhibition of NF-kappaB signaling for 6 days significantly attenuated Ang II-induced increases in LV/body weight ratio, LV mean wall thickness and cardiomyocyte cross-sectional area, without compromising LV systolic function. Moreover, PDTC abolished Ang II-induced cardiomyocyte apoptosis and interstitial fibrosis, and attenuated the gene expression of type I collagen. In contrast, a moderate LV hypertrophy induced by Ang II at a lower dose (0.5 microg/kg per min) was not associated with a significant activation of NF-kappaB, and PDTC treatment had no effect on the hypertrophic indices.

CONCLUSION

Our in-vivo data indicate a critical role of NF-kappaB signaling in the advanced stage of the remodeling process, whereas development of moderate LV hypertrophy is not dependent on NF-kappaB activation.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

CARMA3/Bcl10/MALT1-dependent NF-kappaB activation mediates angiotensin II-responsive inflammatory signaling in nonimmune cells

Angiotensin II (Ang II) is a peptide hormone that, like many cytokines, acts as a proinflammatory agent and growth factor. After injury to the liver, the hormone assists in tissue repair by stimulating hepatocytes and hepatic stellate cells to synthesize extracellular matrix proteins and secrete secondary cytokines and by stimulating myofibroblasts to proliferate. However, under conditions of chronic liver injury, all of these effects conspire to promote pathologic liver fibrosis. Much of this effect of Ang II results from activation of the proinflammatory NF-kappaB transcription factor in response to stimulation of the type 1 Ang II receptor, a G protein-coupled receptor. Here, we characterize a previously undescribed signaling pathway mediating Ang II-dependent activation of NF-kappaB, which is composed of three principal proteins, CARMA3, Bcl10, and MALT1. Blocking the function of any of these proteins, through the use of either dominant-negative mutants, RNAi, or gene targeting, effectively abolishes Ang II-dependent NF-kappaB activation in hepatocytes. In addition, Bcl10(-/-) mice show defective hepatic cytokine production after Ang II treatment. Evidence also is presented that this pathway activates NF-kappaB through ubiquitination of IKKgamma, the regulatory subunit of the IkappaB kinase complex. These results elucidate a concrete series of molecular events that link ligand activation of the type 1 Ang II receptor to stimulation of the NF-kappaB transcription factor. These findings also uncover a function of the CARMA, Bcl10, and MALT1 proteins in cells outside the immune system.

Telmisartan inhibits β2-integrin MAC-1 expression in human T-lymphocytes

OBJECTIVE

The pathogenesis of atherosclerosis, a chronic inflammatory disease, is influenced by the renin-angiotensin system and especially by angiotensin II subtype 1 (AT1) receptor activation. Although pro-inflammatory properties of angiotensin II as well as anti-inflammatory effects of AT1 receptor antagonists are well known, the underlying mechanisms are poorly understood.

METHOD AND RESULTS

In a prospective double-blind study, patients with hypertension and coronary artery disease were treated with either 40 mg telmisartan (n = 21) or placebo (n = 21) for 12 weeks. General markers of inflammation, such as high-sensitivity C-reactive protein (hs-CRP) and interleukin-6 (IL-6), and cell adhesion molecules, such as soluble intercellular adhesion molecule (s-ICAM-1) and the leucocyte adhesion molecule soluble-L-selectin (sL-selectin), as well as the lymphocytic expression of the beta2 integrin MAC-1, were assessed before and after treatment. Telmisartan therapy significantly decreased the lymphocyte beta2 integrin MAC-1 expression, whereas hs-CRP, IL-6, s-ICAM and sL-selectin remained unaltered. In-vitro experiments were conducted to clarify the mode of action. Cultured human lymphocytes were stimulated with either angiotensin II or phorbol-12-myristate-13-acetate (PMA)/ionomycin, alone or after pretreatment with telmisartan. Whereas angiotensin II exerted no effect on beta2-integrin MAC-1 expression in lymphocytes, telmisartan dose-dependently inhibited beta2-integrin expression in lymphocytes in the absence or presence of angiotensin II.

CONCLUSION

The AT1 receptor antagonist telmisartan inhibits the expression of the pro-inflammatory beta2-integrin MAC-1 expression in lymphocytes independently of angiotensin II, suggesting an AT1 receptor-independent atheroprotective effect of this AT1 receptor antagonist.

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

The renin-angiotensin system is a central component of the physiological and pathological responses of cardiovascular system. Its primary effector hormone, angiotensin II (ANG II), not only mediates immediate physiological effects of vasoconstriction and blood pressure regulation, but is also implicated in inflammation, endothelial dysfunction, atherosclerosis, hypertension, and congestive heart failure. The myriad effects of ANG II depend on time (acute vs. chronic) and on the cells/tissues upon which it acts. In addition to inducing G protein- and non-G protein-related signaling pathways, ANG II, via AT(1) receptors, carries out its functions via MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases [PDGF, EGFR, insulin receptor], and nonreceptor tyrosine kinases [Src, JAK/STAT, focal adhesion kinase (FAK)]. AT(1)R-mediated NAD(P)H oxidase activation leads to generation of reactive oxygen species, widely implicated in vascular inflammation and fibrosis. ANG II also promotes the association of scaffolding proteins, such as paxillin, talin, and p130Cas, leading to focal adhesion and extracellular matrix formation. These signaling cascades lead to contraction, smooth muscle cell growth, hypertrophy, and cell migration, events that contribute to normal vascular function, and to disease progression. This review focuses on the structure and function of AT(1) receptors and the major signaling mechanisms by which angiotensin influences cardiovascular physiology and pathology.

Overexpression of angiotensinogen in the myocardium induces downregulation of the fatty acid oxidation pathway

Heart failure is associated with downregulation of the fatty acid oxidation pathway in the ventricular myocardium. Since angiotensin II plays a critical role in myocardial phenotypic changes associated with heart failure, we investigated the effect of chronic angiotensin II stimulation on the fatty acid oxidation pathway in transgenic (TG) mice with targeted overexpression of angiotensinogen in the myocardium (TG1306/1R mice). TG1306/R1 mice progressively developed left ventricular hypertrophy. After 12 months, approximately half of the mice exhibited signs of heart failure including increased lung weight index [>+2 SD of age-matched wild-type (WT) mice] and 5-fold increase of myocardial brain natriuretic peptide expression. Myocardial mRNA and protein expression of peroxisome proliferator-activated receptor alpha (PPARalpha) progressively decreased in both WT and TG1306/R1 mice during the 12 months observation period, but much more pronounced in TG1306/R1 mice. Concomitantly, mRNA expression of enzymes of fatty acid oxidation (medium-chain acyl CoA dehydrogenase, MCAD; carnitine palmitoyl transferase I, CPT-I) was reduced in TG1306/R1 compared with age-matched WT mice. However, protein expression of MCAD and CPT-I was decreased concomitantly only in TG mice with criteria of heart failure. Correspondingly, myocardial oxidation of palmitate, measured during ex vivo working heart perfusion, was reduced by 25% in TG1306/R1 mice with heart failure. These results demonstrate that angiotensin II-induced cardiac hypertrophy is associated with reduction of PPARalpha and of mRNA expression of enzymes of fatty acid metabolism relative to age-matched WT mice. However, both protein expression of fatty acid oxidation enzymes and the rate of fatty acid oxidation remain unchanged unless heart failure occurs, suggesting the involvement of posttranscriptional mechanisms in the metabolic changes associated with heart failure.

Angiotensin II in the failing heart. Short communication

In the failing heart, the local angiotensin II concentration is increased, and the extent of cardiac angiotensin II release is related to the clinical signs of heart failure. The enzymes involved in myocardial generation of angiotensin II are the angiotensin-converting enzyme (ACE) and chymases. While myocardial angiotensin II is mainly generated by chymases in the human heart, ACE inhibitors nevertheless improve left ventricular (LV) function, attenuate LV remodelling and reduce mortality in heart failure patients. These beneficial actions of ACE inhibitors, however, relate to their beneficial effect on kinin metabolism. Angiotensin II type 1 receptor (AT1) antagonists also mediate part of their beneficial effects through increased bradykinin formation. However, in contrast to ACE inhibitors, AT1 receptor antagonists attenuate downstream signalling of angiotensin II-induced AT1 receptor activation, which increases the activity of existing proteins (e.g. NADPH oxidase) and the de novo synthesis of proteins (e.g. inducible nitric oxide synthase, tumor necrosis factor-alpha ) in cardiomyocytes. Given the multiple actions of AT1 receptor activation on cardiomyocyte and non-cardiomyocyte function in the presence of an increased myocardial AngII concentration, the reduction of cardiovascular mortality and rate of hospitalization following AT1 receptor blockade in heart failure patients not receiving ACE inhibitors is not surprising. Most importantly, the beneficial effects of AT1 receptor blockade are not only achieved when used as an alternative to ACE inhibition, but also when used on top of ACE inhibitors.

Convergence of protein kinase C and JAK-STAT signaling on transcription factor GATA-4

Angiotensin II (AII), a potent vasoactive hormone, acts on numerous organs via G-protein-coupled receptors and elicits cell-specific responses. At the level of the heart, AII stimulation alters gene transcription and leads to cardiomyocyte hypertrophy. Numerous intracellular signaling pathways are activated in this process; however, which of these directly link receptor activation to transcriptional regulation remains undefined. We used the atrial natriuretic factor (ANF) gene (NPPA) as a marker to elucidate the signaling cascades involved in AII transcriptional responses. We show that ANF transcription is activated directly by the AII type 1 receptor and precedes the development of myocyte hypertrophy. This response maps to STAT and GATA binding sites, and the two elements transcriptionally cooperate to mediate signaling through the JAK-STAT and protein kinase C (PKC)-GATA-4 pathways. PKC phosphorylation enhances GATA-4 DNA binding activity, and STAT-1 functionally and physically interacts with GATA-4 to synergistically activate AII and other growth factor-inducible promoters. Moreover, GATA factors are able to recruit STAT proteins to target promoters via GATA binding sites, which are sufficient to support synergy. Thus, STAT proteins can act as growth factor-inducible coactivators of tissue-specific transcription factors. Interactions between STAT and GATA proteins may provide a general paradigm for understanding cell specificity of cytokine and growth factor signaling.

Anti-stress and anti-anxiety effects of centrally acting angiotensin II AT1 receptor antagonists

The brain and the peripheral (hormonal) angiotensin II systems are stimulated during stress. Activation of brain angiotensin II AT(1) receptors is required for the stress-induced hormone secretion, including CRH, ACTH, corticoids and vasopressin, and for stimulation of the central sympathetic activity. Long-term peripheral administration of the angiotensin II AT(1) antagonist candesartan blocks not only peripheral but also brain AT(1) receptors, prevents the hormonal and sympathoadrenal response to isolation stress and prevents the formation of stress-induced gastric ulcers. The mechanisms responsible for the prevention of stress-induced ulcers by the AT(1) receptor antagonist include protection from the stress-induced ischemia and inflammation (neutrophil infiltration and increase in ICAM-1 and TNF-alpha) in the gastric mucosa and a partial blockade of the stress-induced sympathoadrenal stimulation, while the protective effect of the glucocorticoid release during stress is maintained. AT(1) receptor antagonism prevents the stress-induced decrease in cortical CRH(1) and benzodiazepine binding and is anxiolytic. Blockade of brain angiotensin II AT(1) receptors offers a novel therapeutic opportunity for the treatment of anxiety and other stress-related disorders.

AT1 Receptor Blockade Prevents Cardiac Dysfunction after Myocardial Infarction in Rats

Myocardial infarction (MI) can induce severe alterations of contractile function that can, in turn, lead to heart failure. In a previous study, we have demonstrated that TNF-alpha was involved in cardiac contractile dysfunction 7 days after coronary artery ligation in rats. Since Angiotensin II type 1 (AT1) receptor can be involved in TNF-alpha production, we have investigated whether early short-term treatment with irbesartan, an AT1 receptor blocker, is able to limit TNF-alpha production within the heart and to improve cardiac function and geometry following MI in rats. Male Wistar rats were subjected to permanent coronary artery ligation and received either a placebo or irbesartan (50 mg/kg/day) per os daily from day 3 to day 6 after surgery. On day 7, cardiac TNF-alpha was significantly reduced in MI rats receiving irbesartan (p < 0.05). Moreover, irbesartan improved residual LV end-diastolic pressure under both basal conditions and after volume overload (p < 0.01). In addition, a significant leftward shift of the pressure-volume curve in the irbesartan-treated group was found versus placebo. Finally, infarct expansion index was also significantly improved by irbesartan (p < 0.01). In conclusion, early, short-term AT1 receptor blockade limits post-infarct cardiac TNF-alpha production and diminishes myocardial alterations observed 7 days after MI in the rat.

A review of the renal and neurohormonal effects of B-type natriuretic peptide

Adverse neurohormonal activation is an essential component in the pathogenesis of acute decompensated congestive heart failure (CHF). Consequently, blunting this activation is an important therapeutic goal. B-type natriuretic peptide (BNP) is a counterregulatory hormone produced by the ventricles in response to pressure and volume load. Endogenous BNP levels are significantly elevated in patients with acute CHF, but these levels are frequently inadequate to overcome the excess neurohormonal activation present in this condition. Infusion of nesiritide, a recombinant form of endogenous human BNP, increases circulating BNP levels by several-fold, augmenting the counterregulatory effects of this hormone. Clinical trials demonstrate that in patients with acute decompensated CHF, nesiritide produces arterial and venous vasodilation, reducing both preload and afterload; blunts adverse neurohormones, including renin, aldosterone, norepinephrine, and endothelin-1; and improves renal hemodynamics and tubular function. As a result, nesiritide quickly reduces clinical symptoms and improves mortality in patients with acute CHF.

A potential role for angiotensin II in obesity induced cardiac hypertrophy and ischaemic/reperfusion injury

BACKGROUND

The mechanisms for obesity induced myocardial remodelling and subsequent mechanical dysfunction are poorly understood. There is good evidence that angiotensin II and TNFalpha have strong growth promoting properties and are elevated with obesity. In addition, these two peptides may interact to exacerbate myocardial ischaemic/reperfusion injury.

HYPOTHESIS

Obesity increases systemic and myocardial renin-angiotensin system (RAS) activity and TNFalpha levels and contributes to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

METHODS

Male Wistar rats were placed on a standard rat chow diet or cafeteria diet for 16 weeks. Two additional groups of rats received the respective diets and losartan (30 mg/ kg/d) in their drinking water. Hearts were perfused on the isolated working rat heart perfusion system and mechanical function was documented before and after 15 min normothermic total global ischaemia. Blood and myocardial samples were collected for angiotensin II, TNFalpha and NADPH oxidase activity determinations.

RESULTS

The rats on the cafeteria diet became obese compared to rats on the standard rat chow (438 +/- 5.9 g vs 393 +/- 7.3 g for control, p < 0.05). Obesity was associated with elevated serum angiotensin II (0.050 +/- 0.015 pmol/ml vs. 0.035 +/- 0.003 pmol/ml, p < 0.05) and TNFalpha levels (42.8 +/- 5.93 pg/ml vs. 13.18 +/- 2.50 pg/ml, p < 0.05), and increased heart to body weight ratios (3.1 +/- 0.04 mg/g vs. 2.8 +/- 0.03 mg/g, p < 0.05). Losartan had no effect on body weight but decreased basal myocardial angiotensin II and TNFAlpha levels as well as heart to body weight ratio in the obese and lean controls (2.5 +/- 0.05 mg/g and 2.6 +/- 0.04 mg/g relative to their controls, p < 0.05). Hearts from obese rats had lower reperfusion aortic outputs (AO) than their concurrent controls (18.42 +/- 1.17 ml/min vs. 27.8 +/- 0.83 ml/min, p < 0.05). Losartan improved aortic output recoveries in obese rats (23.0 +/- 1.71 ml/min, p < 0.05).

CONCLUSIONS

Obesity increased serum angiotensin II and TNFalpha levels, blood pressure, and heart weight to body weight ratios. These changes were associated with decreased basal and post-ischaemic myocardial mechanical function. Chronic AT(1) receptor antagonism prevented the adverse changes in heart weight, mechanical function and susceptibility to ischaemic/reperfusion injury. Although current data do not exclude additional mechanisms for obesity induced cardiac remodelling, they suggest that angiotensin II may contribute to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

Irbesartan inhibits human T-lymphocyte activation through downregulation of activator protein-1

1 Irbesartan is a promising antihypertensive drug with beneficial effects on atherosclerotic processes. In the progression of atherosclerosis, human T-lymphocytes play an important role, but it is not yet known how irbesartan modulates human T-lymphocytes activation. To gain insight into the mechanisms by which irbesartan acts, we investigated its effects on human T-lymphocytes. 2 Primary human T-lymphocytes were isolated from whole blood. Cytokines were determined by ELISA. Activator protein-1 (AP-1) and related protein activities were determined by electrophoretic mobility shift assays, kinase assays, Western blotting and transfection assays. 3 Irbesartan inhibited the production of both tumor necrosis factor-alpha and interferon-gamma by activated T-cells, especially at therapeutic concentrations. Further investigation at the molecular level indicated that the inhibition of activated human T-lymphocytes specifically correlated with the downregulation of AP-1 DNA-binding activity. In the Jurkat T-cell line, irbesartan also inhibited AP-1 transcriptional activity. Finally, we revealed that irbesartan is unique in its ability to inhibit the activation of both c-Jun NH2-terminal protein kinase and p38 MAPK. 4 Our studies show that irbesartan may modulate inflammation-based atherosclerotic diseases through a cell-mediated mechanism involving suppression of human T-lymphocytes activation via downregulation of AP-1 activity.

Regulation of the human tumor necrosis factor-alpha promoter by angiotensin II and lipopolysaccharide in cardiac fibroblasts: different cis-acting promoter sequences and transcriptional factors

We recently showed that angiotensin (ANG) II as well as mechanical stretch stimulated production of tumor necrosis factor (TNF) in cardiac fibroblasts. Presently, we examined the molecular mechanisms by which ANGII and lipopolysaccharide (LPS) upregulate TNF-alpha gene expression. In neonatal rat cardiac fibroblasts, increased transcription of TNF-alpha mRNA was detected as luciferase activity associated with activity of the TNF-alpha promoter. Progressive deletion from this promoter located the LPS-responsive region between -200 and -120 bp from the transcription initiation site, while the sequence between -120 and -70 bp was required for ANGII-induced expression. Next, we examined which cis-acting sequences in the TNF-alpha promoter region were essential for induction of TNF-alpha transcription. Competition analysis by electrophoretic mobility shift assay with and without specific antibodies showed that LPS increased binding of Sp1 and Sp3 to the Sp1-binding site, while Egr-1 was unimportant. With ANGII, binding of ATF-2/c-jun to the CRE site was required for TNF-alpha gene induction; neither Ets nor NF-kappaB was essential. Mutation analysis confirmed that response to LPS relied upon the Sp1 site in the TNF-alpha promoter, while the CRE-binding site was essential for stimulation by ANGII. We concluded that since TNF-alpha gene expression is transcriptionally activated by ANGII or LPS in cardiac fibroblasts via different cis-acting sequences in the TNF-alpha promoter and different transcriptional factors, mechanisms inducing TNF production differ between heart failure or cardiac hypertrophy and infectious disease.

Attenuation of virus-induced myocardial injury by inhibition of the angiotensin II type 1 receptor signal and decreased nuclear factor-kappa B activation in knockout mice

OBJECTIVES

This study examined the role of angiotensin II (Ang-II) in a murine model of viral myocarditis.

BACKGROUND

Ang-II plays an important role in the pathophysiology of various cardiovascular disorders. However, the role of Ang-II in inflammatory heart diseases is not known.

METHODS

Four-week-old wild-type (WT) and Ang-II type 1 receptor (AT(1)R) knockout (KO) mice were inoculated with the encephalomyocarditis virus (EMCV). Survival, histopathology, expression of proinflammatory cytokines, and activity of nuclear factor-kappa B (NF-kB) in the heart were examined.

RESULTS

The 14-day survival was significantly increased in KO compared with WT mice. Histopathologic scores for myocardial necrosis (0.86 +/- 0.69 vs. 2.44 +/- 0.88, p < 0.01) and cellular infiltration (0.86 +/- 0.38 vs. 2.33 +/- 0.50, p < 0.01) were lower in KO than in WT mice. The expression of tumor necrosis factor-alpha (TNF-alpha) was increased 43.2-fold, that of interleukin-1-beta (IL-1-beta) 45.8-fold, and the activity of NF-kB 2.24-fold by EMCV inoculation in WT mice (each p < 0.01), but not in KO mice (5.9-fold, 6.3-fold, and 1.12-fold, respectively, each p = NS). The AT(1)R blocker also significantly attenuated the expression of proinflammatory cytokines and the activation of NF-kB in virus-inoculated WT mice. Intravenous Ang-II injection enhanced the activation of NF-kB (2.28-fold, p < 0.01) and increased the expression of TNF-alpha (2.31-fold, p < 0.01) and IL-1-beta (2.45-fold, p < 0.01) in heart tissue of WT but not KO mice.

CONCLUSIONS

These results indicate that the AT(1)R signal is obligatory for the development of virus-induced myocardial injury through the proinflammatory action of Ang-II via the NF-kB/cytokine pathway.

Role of angiotensin AT1 and AT2 receptors in cardiac hypertrophy and cardiac remodelling

1. Left ventricular hypertrophy (LVH) is an independent cardiovascular risk factor. Angiotensin AT1 receptor antagonism has been considered as a specific approach to block the renin-angiotensin system and been demonstrated to be able to prevent or regress LVH by interfering with the remodelling process of the heart. 2. Angiotensin AT1 receptor blockade induces a marked increase in angiotensin (Ang) II, which may stimulate the AT2 receptors. Gene expression of AT1 and AT2 receptors increases in a time-dependent manner in cardiac remodelling following myocardial infarction. 3. Considerable efforts have been made to clarify the role of AT2 receptors in cardiac hypertrophy and remodelling since the mid-1990s, resulting in controversial reports: the AT2 receptor mediates actions either opposite to or in coordination with those of the AT1 receptor. Moreover, there are many reports of no significant effects mediated by AT2 receptors. 4. Based on the studies reviewed in the present article, we assume that the predominant effect of AngII in cardiac hypertrophy and cardiac remodelling is growth promoting and that this effect is mediated mainly via AT1 receptors. The AT2 receptors may affect the hypertrophic process by interacting with other cardiac membrane proteins, enzymes and autacoids. Before coming to a conclusion as to whether AT2 receptor stimulation or antagonism is beneficial to the heart, more studies should be performed in different LVH models, especially long-term treatment protocols in vivo.

Angiotensin II-induced MMP-2 release from endothelial cells is mediated by TNF-alpha

Angiotensin II (ANG II) has been etiologically linked to vascular disease; however, its role in the alterations of endothelial function that occur in vascular disorders is not completely understood. Matrix metalloproteinases (MMPs) and proinflammatory cytokines are involved in the pathological remodeling of blood vessels that occurs in vascular disease. In this study we evaluated the effects of ANG II on tumor necrosis factor (TNF)-alpha and MMP-2 production in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were stimulated with ANG II (0.1-10 microM) for 24 h, in the presence or absence of antagonists of ANG II type 1 (AT(1)R) and type 2 (AT(2)R) receptors, and the production and release of TNF-alpha and MMP-2 were assessed. ANG II increased TNF-alpha mRNA and protein expression and the release of bioactive TNF-alpha. Moreover, ANG II induced MMP-2 release and reduced the secretion of tissue inhibitor of MMP (TIMP)-2 from endothelial cells. To elucidate whether endogenous TNF-alpha could mediate the effects of ANG II on MMP-2 release, cells were pretreated with anti-TNF-alpha neutralizing antibodies or pentoxifylline (an inhibitor of TNF-alpha synthesis). TNF-alpha inhibition prevented the secretion of MMP-2 induced by ANG II. Furthermore, AT(1)R antagonism with candesartan prevented the formation of MMP-2 and TNF-alpha and the reduction of TIMP-2 induced by ANG II. These results indicate that ANG II, via AT(1)R, modulates the secretion of TNF-alpha and MMP-2 from endothelial cells and that TNF-alpha mediates the effects of ANG II on MMP-2 release.

Anti-inflammatory effects of angiotensin II AT1 receptor antagonism prevent stress-induced gastric injury

Stress reduces gastric blood flow and produces acute gastric mucosal lesions. We studied the role of angiotensin II in gastric blood flow and gastric ulceration during stress. Spontaneously hypertensive rats were pretreated for 14 days with the AT1 receptor antagonist candesartan before cold-restraint stress. AT1 receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. AT1 blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after cold-restraint stress, reduced the increase in adrenomedullary epinephrine and tyrosine hydroxylase mRNA without preventing the stress-induced increase in adrenal corticosterone, decreased the stress-induced expression of TNF-alpha and that of the adhesion protein ICAM-1 in arterial endothelium, decreased the neutrophil infiltration in the gastric mucosa, and decreased the gastric content of PGE2. AT1 receptor blockers prevent stress-induced ulcerations by a combination of gastric blood flow protection, decreased sympathoadrenal activation, and anti-inflammatory effects (with reduction in TNF-alpha and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and PGE2 release. Angiotensin II has a crucial role, through stimulation of AT1 receptors, in the production and progression of stress-induced gastric injury, and AT1 receptor antagonists could be of therapeutic benefit.

Oxidative stress is a critical mediator of the angiotensin II signal in human neutrophils: involvement of mitogen-activated protein kinase, calcineurin, and the transcription factor NF-kappaB

Neutrophils are mobilized to the vascular wall during vessel inflammation. Published data are conflicting on phagocytic nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase activation during the hypertensive state, and the capacity of angiotensin II (Ang II) to modulate the intracellular redox status has not been analyzed in neutrophils. We here describe that Ang II highly stimulates endogenous and extracellular O2- production in these cells, consistent with the translocation to the cell membrane of the cytosolic components of NADPH oxidase, p47phox, and p67phox. The Ang II-dependent O2- production was suppressed by specific inhibitors of AT1 receptors, of the p38MAPK and ERK1/2 pathways, and of flavin oxidases. Furthermore, Ang II induced a robust phosphorylation of p38MAPK, ERK1/2, and JNK1/2 (particularly JNK2), which was hindered by inhibitors of NADPH oxidase, tyrosine kinases, and ROS scavengers. Ang II increased cytosolic Ca2+ levels-released mainly from calcium stores-enhanced the synthesis de novo and activity of calcineurin, and stimulated the DNA-binding activity of the transcription factor NF-kappaB in cultured human neutrophils. Present data demonstrate for the first time a stimulatory role of Ang II in the activation of phagocytic cells, underscore the relevant role of ROS as mediators in this process, and uncover a variety of signaling pathways by which Ang II operates in human neutrophils.

Gemfibrozil reduces release of tumor necrosis factor-alpha in peripheral blood mononuclear cells from healthy subjects and patients with coronary heart disease

BACKGROUND

Inflammatory process plays an important role in the pathogenesis of coronary heart disease (CHD). With the growing use of gemfibrozil and other fibrates, their anti-inflammatory effects have been noted. But little is known about the effect of gemfibrozil on tumor necrosis factor (TNF)-alpha secretion in peripheral blood mononuclear cells (PBMC) from patients with coronary heart disease.

METHODS

PBMC were obtained from CHD patients (n=16) and healthy controls (n=13). PBMC (2x10(6) cells/ml) were cultured in 24-well plates with or without Ang II (10(-8), 10(-7), 10(-6) mol/l), or Ang II (10(-6) mol/l) plus gemfibrozil (10(-6), 10(-5), 10(-4) mol/l). After 24-h incubation, the supernatants were separated, and TNF-alpha was measured by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Spontaneous release of TNF-alpha was 299.2+/-110.7 pg/ml in PBMC from CHD patients and 179.3+/-78.2 pg/ml in PBMC from control subjects (P<0.05). Incubated with Ang II (10(-8), 10(-7), 10(-6) mol/l), TNF-alpha secretion was 307.7+/-141.8, 318.9+/-135.6, 328.6+/-123.9 pg/ml in PBMC from CHD patients, and 225.3+/-135.4, 224.1+/-141.0,218.7+/-134.8 pg/ml in PBMC from control subjects, respectively. Ang II did not significantly trigger TNF-alpha secretion in both groups. Compared with that incubated with Ang II (10(-6) mol/l) alone, release of TNF-alpha intervened by gemfibrozil (10(-6),10(-5),10(-4) mol/l) decreased to 279.4+/-132.2, 268.0+/-132.7, 226.6+/-102.7 pg/ml in PBMC from CHD patients, and 177.6+/-94.4, 156.1+/-69.4, 105.3+/-52.7 pg/ml in the control group, respectively. Gemfibrozil (10(-5),10(-4) mol/l) significantly inhibited TNF-alpha secretion in both groups (P<0.05).

CONCLUSIONS

Our data demonstrated that gemfibrozil reduced release of TNF-alpha in PBMC both from CHD patients and controls. This effect may partially be relevant to the clinical benefits of gemfibrozil in the treatment of dyslipidemia and atherosclerosis.

The therapeutic effect of natriuretic peptides in heart failure; differential regulation of endothelial and inducible nitric oxide synthases

The abnormal regulation of nitric oxide synthase activity represents an underlying feature of heart failure. Increased peripheral vascular resistance, and decreased renal function may be in part related to impaired endothelium-dependent nitric oxide (NO) synthesis. Paradoxically, the chronic production of NO by inducible nitric oxide synthase (iNOS) in heart failure exerts deleterious effects on ventricular contractility, and circulatory function. Consequently, pharmacologically improving endothelium-dependent NO synthesis and the concomitant inhibition of iNOS activity would be therapeutically advantageous. Interestingly, natriuretic peptides have been shown to differentially regulate endothelial NOS (eNOS) and iNOS activity. Moreover, in both patients and animal models of heart failure, pharmacologically increasing plasma natriuretic peptide levels ameliorated vascular tone, renal function, and ventricular contractility. Based on these observations, the following review will explore whether the therapeutic benefit of the natriuretic peptide system in heart failure may occur in part via the amelioration of endothelium-dependent NO synthesis, and the concomitant inhibition of cytokine-mediated iNOS expression.

Tumor necrosis factor-alpha-induced AT1 receptor upregulation enhances angiotensin II-mediated cardiac fibroblast responses that favor fibrosis

Extracellular matrix (ECM) remodeling after myocardial infarction (MI) is an important determinant of cardiac function. Tumor necrosis factor-alpha (TNF-alpha) and angiotensin (Ang) II levels increase after MI and both factors affect fibroblast functions. The type 1 (AT1) receptor that mediates most Ang II effects is upregulated after MI in cardiac fibroblasts, and there is evidence that this is caused by TNF-alpha. We sought to determine if TNF-alpha-induced AT1 receptor upregulation alters fibroblast responsiveness to Ang II and if this effect differs from direct TNF-alpha effects on fibroblast functions. In cultured neonatal rat cardiac fibroblasts, TNF-alpha reduced cellular [3H]-proline incorporation, increased matrix metalloproteinase-2 (MMP-2) activity and protein, and increased TIMP-1 protein levels. In cardiac fibroblasts with TNF-alpha-induced AT1 receptor upregulation, Ang II-stimulated [3H]proline incorporation and TIMP-1 protein production was approximately 2-fold greater than in nonpretreated fibroblasts. Angiotensin II reduced MMP-2 activity and protein level only in TNF-alpha-pretreated fibroblasts. Angiotensin II effects were inhibited by selective AT1 (but not AT2) receptor blockers. Thus, TNF-alpha-induced AT1 receptor upregulation enhances Ang II-mediated functions that favor fibrosis. These effects are mostly directionally opposite of direct TNF-alpha effects on cardiac fibroblasts. Recognition of multifaceted TNF-alpha effects provides new insights into post-MI ECM remodeling.