N-acetylcysteine treatment normalizes serum tumor necrosis factor-alpha level and hinders the progression of cardiac injury in hypertensive rats

Glutathione deficiency in cardiac patients is related to the functional status and structural cardiac abnormalities

Background

The tripeptide glutathione (L-gamma-glutamyl-cysteinyl-glycine) is essential to cell survival, and deficiency in cardiac and systemic glutathione relates to heart failure progression and cardiac remodelling in animal models. Accordingly, we investigated cardiac and blood glutathione levels in patients of different functional classes and with different structural heart diseases.

Methods

Glutathione was measured using standard enzymatic recycling method in venous blood samples obtained from 91 individuals, including 15 healthy volunteers and 76 patients of New York Heart Association (NYHA) functional class I to IV, undergoing cardiac surgery for coronary artery disease, aortic stenosis or terminal cardiomyopathy. Glutathione was also quantified in right atrial appendages obtained at the time of surgery.

Results

In atrial tissue, glutathione was severely depleted (−58%) in NYHA class IV patients compared to NYHA class I patients (P = 0.002). In patients with coronary artery disease, this depletion was related to the severity of left ventricular dysfunction (P = 0.006). Compared to healthy controls, blood glutathione was decreased by 21% in NYHA class I patients with structural cardiac disease (P<0.01), and by 40% in symptomatic patients of NYHA class II to IV (P<0.0001). According to the functional NYHA class, significant depletion in blood glutathione occurred before detectable elevation in blood sTNFR1, a marker of symptomatic heart failure severity, as shown by the exponential relationship between these two parameters in the whole cohort of patients (r = 0.88).

Conclusions

This study provides evidence that cardiac and systemic glutathione deficiency is related to the functional status and structural cardiac abnormalities of patients with cardiac diseases. These data also suggest that blood glutathione test may be an interesting new biomarker to detect asymptomatic patients with structural cardiac abnormalities.

The cannabinoid receptor type 2 promotes cardiac myocyte and fibroblast survival and protects against ischemia/reperfusion-induced cardiomyopathy

Post-myocardial infarction (MI) heart failure is a major public health problem in Western countries and results from ischemia/reperfusion (IR)-induced cell death, remodeling, and contractile dysfunction. Ex vivo studies have demonstrated the cardioprotective anti-inflammatory effect of the cannabinoid type 2 (CB2) receptor agonists within hours after IR. Herein, we evaluated the in vivo effect of CB2 receptors on IR-induced cell death, fibrosis, and cardiac dysfunction and investigated the target role of cardiac myocytes and fibroblasts. The infarct size was increased 24 h after IR in CB2(-/-) vs. wild-type (WT) hearts and decreased when WT hearts were injected with the CB2 agonist JWH133 (3 mg/kg) at reperfusion. Compared with WT hearts, CB2(-/-) hearts showed widespread injury 3 d after IR, with enhanced apoptosis and remodeling affecting the remote myocardium. Finally, CB2(-/-) hearts exhibited exacerbated fibrosis, associated with left ventricular dysfunction 4 wk after IR, whereas their WT counterparts recovered normal function. Cardiac myocytes and fibroblasts isolated from CB2(-/-) hearts displayed a higher H(2)O(2)-induced death than WT cells, whereas 1 microM JWH133 triggered survival effects. Furthermore, H(2)O(2)-induced myofibroblast activation was increased in CB2(-/-) fibroblasts but decreased in 1 microM JWH133-treated WT fibroblasts, compared with that in WT cells. Therefore, CB2 receptor activation may protect against post-IR heart failure through direct inhibition of cardiac myocyte and fibroblast death and prevention of myofibroblast activation.

Sphingomyelinases: their regulation and roles in cardiovascular pathophysiology

Sphingomyelinases (SMases) hydrolyse sphingomyelin, releasing ceramide and creating a cascade of bioactive lipids. These lipids include sphingosine and sphingosine-1-phosphate, all of which have a specific signalling capacity. Sphingomyelinase activation occurs in different cardiovascular system cell types, namely cardiac myocytes, endothelial and vascular smooth muscle cells, mediating cell proliferation, cell death, and contraction of cardiac and vascular myocytes. Three main types of SMases contribute to cardiovascular physiology: the lysosomal and secreted acidic SMases (L- and S-ASMases, respectively) and the membrane neutral SMase (NSMase). These three enzymes have common activators, including ischaemia/reperfusion stress and proinflammatory cytokines, but they differ in their enzymatic properties and subcellular locations that determine the final effect of enzyme activation. This review focuses on the recent advances in the understanding of ASMase and NSMase pathways and their specific contribution to cardiovascular pathophysiology. Current knowledge indicates that the inhibitors of the different SMase types are potential tools for the treatment of cardiovascular diseases. Acid SMase inhibitors could be tools against post-ischaemia reperfusion injury and in the treatment of atherosclerosis. Neutral SMase inhibitors could be tools for the treatment of atherosclerosis, heart failure, and age-related decline in vasomotion. However, the design of bioavailable and more specific SMase-type inhibitors remains a challenge.

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.

Renal antioxidant enzymes and glutathione redox status in leptin-induced hypertension

Previously, we have demonstrated that leptin increases blood pressure (BP) in the rats through two oxidative stress-dependent mechanisms: stimulation of extracellular signal-regulated kinases (ERK) by H(2)O(2) and scavenging of nitric oxide (NO) by superoxide (O(2-.)). Herein, we examined if renal glutathione system and antioxidant enzymes determine the mechanism of prohypertensive effect of leptin. Leptin administered at 0.5 mg/kg/day for 4 or 8 days increased BP and renal Na(+),K(+)-ATPase activity and reduced fractional sodium excretion; these effects were prevented by NADPH oxidase inhibitor, apocynin. Superoxide scavenger, tempol, abolished the effect of leptin on BP and renal Na(+) pump in rats receiving leptin for 8 days, whereas ERK inhibitor, PD98059, was effective in animals treated with leptin for 4 days. Leptin administered for 4 days decreased glutathione (GSH) and increased glutathione disulfide (GSSG) in the kidney. In animals receiving leptin for 8 days GSH returned to normal level, which was accompanied by up-regulation of gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme of the GSH biosynthetic pathway. In addition, superoxide dismutase (SOD) activity was decreased, whereas glutathione peroxidase (GPx) was increased in rats receiving leptin for 8 days. Cotreatment with gamma-GCS inhibitor, buthionine sulfoximine (BSO), accelerated, whereas GSH precursor, N-acetylcysteine (NAC), attenuated leptin-induced changes in gamma-GCS, SOD, and GPx. In addition, coadministration of BSO changed the mechanism of BP elevation from H(2)O(2)-ERK to (O(2-.))-NO dependent in animals receiving leptin for 4 days, whereas NAC had the opposite effect in rats treated with leptin for 8 days. These results suggest that initial change in GSH redox status induces decrease in SOD/GPx ratio, which results in greater amount of (O)2-.)) versus H(2)O(2) in later phase of leptin treatment, thus shifting the mechanism of BP elevation from H(2)O(2)-ERK to (O(2-.))-NO dependent.

Oxidative stress mediates cardiac fibrosis by enhancing transforming growth factor-beta1 in hypertensive rats

Cardiac fibrosis represented as perivascular/interstial fibrosis occurs in patients with hypertension. Oxidative stress has been demonstrated to contribute to such structural remodeling. The underlying mechanisms, however, remain to be elucidated. Herein, we tested the hypothesis that oxidative stress mediates cardiac fibrogenesis by stimulating transforming growth factor (TGF)-beta1 expression, which in turn triggers a series of fibrogenic responses. Sprague-Dawley rats were treated with angiotensin (Ang)II (9 microg/h s) for 4 weeks with/without co-treatment of combined antioxidants, apocynin, and tempol (120 mg/kg/day each, oral). Untreated rats served as controls. Appearance of cardiac oxidative stress and its potential effect on the expression of TGF-beta1, population of myofibroblasts, collagen synthesis/degradation, and fibrosis in hearts were examined. Chronic AngII infusion elevated systemic blood pressure (210 +/- 5 mmHg). Extensive perivascular and interstitial fibrosis was found in both ventricles, which were co-localized with oxidative stress represented as upregulated NADPH oxidase (gp91(phox) subunit) expression. Co-treatment with antioxidants led to: (1) markedly decreased cardiac gp91(phox); (2) significantly attenuated gene expression of TGF-beta1, type-I collagen, and tissue inhibitors of matrix metalloproteinase (TIMP)-I/II in the heart; (3) largely reduced population of myofibroblasts at sites of fibrosis; (4) significantly reduced cardiac collagen volume; (5) and partially suppressed blood pressure (190 +/- 4 mmHg). Thus, cardiac oxidative stress promotes the development of cardiac fibrosis by upregulating TGF-beta1 expression, which subsequently enhances cardiac collagen synthesis and suppresses collagen degradation in hypertensive rats.

TNFR1 and TNFR2 Signaling Interplay in Cardiac Myocytes

Tumor necrosis factor alpha (TNFalpha) plays a major role in chronic heart failure, signaling through two different receptor subtypes, TNFR1 and TNFR2. Our aim was to further delineate the functional role and signaling pathways related to TNFR1 and TNFR2 in cardiac myocytes. In cardiac myocytes isolated from control rats, TNFalpha induced ROS production, exerted a dual positive and negative action on [Ca(2+)] transient and cell fractional shortening, and altered cell survival. Neutralizing anti-TNFR2 antibodies exacerbated TNFalpha responses on ROS production and cell death, arguing for a major protective role of the TNFR2 pathway. Treatment with either neutralizing anti-TNFR1 antibodies or the glutathione precursor, N-acetylcysteine (NAC), favored the emergence of TNFR2 signaling that mediated a positive effect of TNFalpha on [Ca(2+)] transient and cell fractional shortening. The positive effect of TNFalpha relied on TNFR2-dependent activation of the cPLA(2) activity, independently of serine 505 phosphorylation of the enzyme. Together with cPLA(2) redistribution and AA release, TNFalpha induced a time-dependent phosphorylation of ERK, MSK1, PKCzeta, CaMKII, and phospholamban on the threonine 17 residue. Taken together, our results characterized a TNFR2-dependent signaling and illustrated the close interplay between TNFR1 and TNFR2 pathways in cardiac myocytes. Although apparently predominant, TNFR1-dependent responses were under the yoke of TNFR2, acting as a critical limiting factor. In vivo NAC treatment proved to be a unique tool to selectively neutralize TNFR1-mediated effects of TNFalpha while releasing TNFR2 pathways.

Thiol supplementation inhibits metalloproteinase activity independent of glutathione status

Matrix metalloproteinases (MMPs) are proteolytic enzymes that regulate both integrity and composition of the extracellular matrix (ECM). Excessive ECM breakdown by MMPs is implicated in many physiological and pathological conditions, such as atherosclerosis. Activated macrophages, especially in the atherosclerotic lesion, are a major source of reactive oxygen species (ROS). Antioxidants protect against ROS-induced MMPs activation and inhibit gelatinolytic activity. We sought to determine whether the antioxidants glutathione (GSH), N-acetylcysteine (NAC), or lipoic acid (LA) affect gelatinase production and secretion. The results show that thiol compounds affect MMPs expression and activity in different ways. MMP-2 activity is directly inhibited by NAC and GSH, while LA is ineffective. On the contrary, MMP-9 expression is inhibited by LA at a pretrascriptional level, and MMP-9 activity is stimulated by GSH through a direct interaction with the gelatinase itself. Although all thiols, these compounds have different properties and different cellular uptakes and metabolic characteristics, and this could explain, at least in part, their differential effects on MMPs.

Neutral sphingomyelinase inhibition participates to the benefits of N-acetylcysteine treatment in post-myocardial infarction failing heart rats

Deficiency in cellular thiol tripeptide glutathione (L-gamma glutamyl-cysteinyl-glycine) determines the severity of several chronic and inflammatory human diseases that may be relieved by oral treatment with the glutathione precursor N-acetylcysteine (NAC). Here, we showed that the left ventricle (LV) of human failing heart was depleted in total glutathione by 54%. Similarly, 2-month post-myocardial infarction (MI) rats, with established chronic heart failure (CHF), displayed deficiency in LV glutathione. One-month oral NAC treatment normalized LV glutathione, improved LV contractile function and lessened adverse LV remodelling in 3-month post-MI rats. Biochemical studies at two time-points of NAC treatment, 3 days and 1 month, showed that inhibition of the neutral sphingomyelinase (N-SMase), Bcl-2 depletion and caspase-3 activation, were key, early and lasting events associated with glutathione repletion. Attenuation of oxidative stress, downregulation of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and its TNF-R1 receptor were significant after 1-month NAC treatment. These data indicate that, besides glutathione deficiency, N-SMase activation is associated with post-MI CHF progression, and that blockade of N-SMase activation participates to post-infarction failing heart recovery achieved by NAC treatment. NAC treatment in post-MI rats is a way to disrupt the vicious sTNF-alpha/TNF-R1/N-SMase cycle.

Necrostatin-1 protects against glutamate-induced glutathione depletion and caspase-independent cell death in HT-22 cells

Glutamate, a major excitatory neurotransmitter in the CNS, plays a critical role in neurological disorders such as stroke and Parkinson's disease. Recent studies have suggested that glutamate excess can result in a form of cell death called glutamate-induced oxytosis. In this study, we explore the protective effects of necrostatin-1 (Nec-1), an inhibitor of necroptosis, on glutamate-induced oxytosis. We show that Nec-1 inhibits glutamate-induced oxytosis in HT-22 cells through a mechanism that involves an increase in cellular glutathione (GSH) levels as well as a reduction in reactive oxygen species production. However, Nec-1 had no protective effect on free radical-induced cell death caused by hydrogen peroxide or menadione, which suggests that Nec-1 has no antioxidant effects. Interestingly, the protective effect of Nec-1 was still observed when cellular GSH was depleted by buthionine sulfoximine, a specific and irreversible inhibitor of glutamylcysteine synthetase. Our study further demonstrates that Nec-1 significantly blocks the nuclear translocation of apoptosis-inducing factor (a marker of caspase-independent programmed cell death) and inhibits the integration of Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (a pro-death member of the Bcl-2 family) into the mitochondrial membrane. Taken together, these results demonstrate for the first time that Nec-1 prevents glutamate-induced oxytosis in HT-22 cells through GSH related as well as apoptosis-inducing factor and Bcl-2/adenovirus E1B 19 kDa-interacting protein 3-related pathways.

Cytokines in HIV-associated cardiomyopathy

Among the multiple cardiac manifestations occurring in HIV-infected patients, cardiomyopathy is one of the most challenging. Its incidence has only slightly decreased since the introduction of highly active antiretroviral therapy (HAART). Also, its pathogenesis remains relatively unclear. Although several studies demonstrated the presence of HIV genome in the heart of patients, more recent developments found that viral infection plays an indirect role only, as well as they recognized the contribution of proinflammatory cytokines in the progression of the disease. Experimental studies on animals and cultured myocytes have established the signalling pathway triggered by proinflammatory cytokines in heart failure and cardiomyopathy. Tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1) and IL-6 promote expression of inducible nitric oxide synthase (iNOS) in cardiomyocytes through activation of p38 mitogen-activated protein kinase (p38 MAPK) and nuclear factor kappaB (NFkappaB). TNF-alpha and high concentrations of NO also induce cardiomyocyte apoptosis by TNF type 1 receptor activation. This biological framework, which is also involved in progression of cardiomyopathy in humans, is more pronounced in HIV-infected patients, in whom proinflammatory cytokines TNF-alpha, IL-1 and IL-6 are increased, resulting in an enhanced expression of cardiac iNOS, especially in patients with a low CD4 T cell count. This may account for the worse outcome of heart failure in HIV-infected patients. However, there are only few data today to support future therapeutic implications of cytokines antagonism in treatment of HIV-infected patients with cardiomyopathy. Whether modulation of TNF production or selective inhibition of p38 MAPK pathway could be useful approaches remains uncertain.

N-acetylcysteine -- passe-partout or much ado about nothing?

In experimental studies, the old mucolytic agent N-acetylcysteine (NAC) has had beneficial effects in disorders supposedly linked to oxidative stress. Numerous, mainly small clinical trials with variable doses have yielded inconsistent results in a wide variety of diseases. NAC added to the conventional therapy of human immunodeficiency virus infection might be of benefit; in respect of chronic obstructive pulmonary disease, systematic reviews and meta-analyses suggested that prolonged treatment with NAC is efficacious, but a recent multicentre study has questioned this. In a large intervention trial on cancer recurrence, NAC was ineffective. NAC infusions have been widely used in acute hepatic failure but convincing evidence of its benefits is lacking. A preliminary study reported that NAC is effective in preventing radiocontrast-induced nephropathy but thereafter highly mixed results have been published, and even meta-analyses disagree on its efficacy. In intensive care NAC has mostly been a disappointment but recently it has 'given promises' in surgery with cardiopulmonary bypass. NAC therapy is routine only in paracetamol intoxication.

Oxidative modification of tropomyosin and myocardial dysfunction following coronary microembolization

AIMS

We addressed a potential mechanism of myocardial dysfunction following coronary microembolization at the level of myofibrillar proteins.

METHODS AND RESULTS

Anaesthetized pigs underwent intracoronary infusion of microspheres. After 6 h, the microembolized areas (MEA) had decreased systolic wall thickening to 38 +/- 7% of baseline and a 2.62 +/- 0.40-fold increase in the formation of disulphide cross-bridges (DCB) in tropomyosin relative to that in remote areas. The impairment in contractile function correlated inversely with DCB formation (r = -0.68; P = 0.015) and was associated with increased TNF-alpha content. DCB formation was reflected by increased tropomyosin immunoreactivity and abolished in vitro by dithiothreitol. Ascorbic acid prevented contractile dysfunction as well as increased DCB and TNF-alpha. In anaesthetized dogs, 8 h after intracoronary microspheres infusion, contractile function was reduced to 8+/-10% of baseline and DCB in MEA was 1.48+/-0.12 higher than that in remote areas. In conscious dogs, 6 days after intracoronary microspheres infusion, myocardial function had returned to baseline and DCB was no longer different between remote and MEA. Again contractile function correlated inversely with DCB formation (r = -0.83; P = 0.005).

CONCLUSION

Myofibrillar protein oxidation may represent a mechanistic link between inflammation and contractile dysfunction following coronary microembolization.

A nutritional supplement formula for influenza A (H5N1) infection in humans

By early February 2006, the World Health Organization had reported 165 human cases of H5N1 influenza since December 2003, with 88 fatalities. However, the avian H5N1 influenza virus apparently is not yet efficiently transmitted between humans. Though a near-term possibility of a global H5N1 influenza pandemic remains, currently there is no vaccine or anti-viral drug that is proven to be safe and effective in preventing or treating H5N1 influenza in humans. There is thus a compelling public interest in developing alternative prophylaxis and treatment strategies for H5N1 influenza, which would need to address the complex pathogenesis of H5N1 influenza that is responsible for its apparently unusually high virulence. The authors present here a significant body of medical and scientific evidence to support the prophylactic use of a carefully designed nutritional supplement formulation that may antagonize the major pathogenic processes of H5N1 influenza in humans. Through several independently-mediated mechanisms, the formulations may: (a) degrade H5N1 virulence by directly affecting the virus itself, (b) inhibit H5N1 viral replication by maintaining cellular redox equilibrium in host cells, (c) inhibit H5N1 replication by a blockade of the nuclear-cytoplasmic translocation of the viral ribonucleoproteins and reduced expression of late viral proteins related to the inhibition of protein kinase C activity and its dependent pathways, (d) down-regulate activation and proliferation of proinflammatory cytokines in respiratory epithelial cells and macrophages that are implicated in the pathogenesis of H5N1 influenza, and (e) protect the lungs and other vital organs from virus- and cytokine-induced oxidative stress by supplying and maintaining sufficient levels of exogenous and endogenous antioxidants. Key mediators in these processes include selenium, vitamin E, NAC/glutathione, resveratrol, and quercetin. Taken prophylactically, and throughout the duration and recovery of an H5N1 infection, the nutritional supplement formula may aid humans infected with H5N1 influenza to survive with a reduced likelihood of major complications, and may provide a relatively low-cost strategy for individuals as well as government, public-health, medical, health-insurance, and corporate organizations to prepare more prudently for an H5N1 pandemic. Some evidence also indicates that the supplement formulation may be effective as an adjunctive to H5N1 vaccine and anti-viral treatments, and should be tested as such.