Nitric oxide (NO) induces nitration of protein kinase Cepsilon (PKCepsilon ), facilitating PKCepsilon translocation via enhanced PKCepsilon -RACK2 interactions: a novel mechanism of no-triggered activation of PKCepsilon

Thioredoxin reduces post-ischemic myocardial apoptosis by reducing oxidative/nitrative stress

BACKGROUND AND PURPOSE

Thioredoxin (Trx) is an oxidoreductase that prevents free radical-induced cell death in cultured cells. Here we assessed the mechanism(s) underlying the cardioprotective effects of Trx in vivo.

EXPERIMENTAL APPROACH

The effects of myocardial ischemia (30 min) and reperfusion were measured in mice, with assays of myocardial apoptosis, superoxide production, NOx and nitrotyrosine content, and myocardial infarct size. Recombinant human Trx (rhTrx, 0.7-20 mg kg(-1), i.p.) was given 10 min before reperfusion.

KEY RESULTS

Treatment with 2 mg kg(-1) rhTrx significantly decreased myocardial apoptosis and reduced infarct size (P<0.01). Nitrotyrosine content of cardiomyocytes was markedly reduced in rhTrx-treated animals (P<0.01). To further identify the mechanisms by which rhTrx may exert its anti-nitrative effect, iNOS expression and production of NOx and superoxide were determined. Treatment with rhTrx had no significant effect on iNOS expression or NOx content in the ischemic/reperfused heart. However, it markedly upregulated mSOD and reduced tissue superoxide content. To further establish a causative link between the anti- peroxynitrite effect and the cardioprotective effect of rhTrx, cultured adult cardiomyocytes were incubated with SIN-1, a peroxynitrite donor, (50 microM for 3 h) resulting in a nitrotyrosine content comparable to that seen in the ischemic/reperfused heart and causing significant cardiomyocyte apoptosis (P<0.01). Treatment with rhTrx markedly decreased SIN-1 induced apoptosis (P<0.01).

CONCLUSIONS AND IMPLICATIONS

These results demonstrate that Trx is a novel anti-apoptotic and cardioprotective molecule that exerts its cardioprotective effects by reducing ischemia/reperfusion-induced oxidative/nitrative stress.

Role of nitric oxide in mast cells: controversies, current knowledge, and future applications

Mast cells (MC) are important effector cells in allergic disorders. Recently, the role of MC in innate and adaptive immunity is gaining prominence. Nitric oxide is an important signaling molecule and its production in mast cell has been reported widely. However, controversy exists about whether MC produce NO. This review addresses the role of NO in MC biology and the reasons behind the controversy and discusses effects of NO in regulation of MC phenotype and function.

Protein kinase Cepsilon interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

We have previously identified a phorbol ester-induced PKCepsilon (protein kinase Cepsilon) interaction with the ( approximately 18 kDa) COIV [CO (cytochrome c oxidase) subunit IV] in NCMs (neonatal cardiac myocytes). Since PKCepsilon has been implicated as a key mediator of cardiac PC (preconditioning), we examined whether hypoxic PC could induce PKCepsilon-COIV interactions. Similar to our recent study with phorbol esters [Ogbi, Chew, Pohl, Stuchlik, Ogbi and Johnson (2004) Biochem. J. 382, 923-932], we observed a time-dependent increase in the in vitro phosphorylation of an approx. 18 kDa protein in particulate cell fractions isolated from NCMs subjected to 1-60 min of hypoxia. Introduction of a PKCepsilon-selective translocation inhibitor into cells attenuated this in vitro phosphorylation. Furthermore, when mitochondria isolated from NCMs exposed to 30 min of hypoxia were subjected to immunoprecipitation analyses using PKCepsilon-selective antisera, we observed an 11.1-fold increase in PKCepsilon-COIV co-precipitation. In addition, we observed up to 4-fold increases in CO activity after brief NCM hypoxia exposures that were also attenuated by introducing a PKCepsilon-selective translocation inhibitor into the cells. Finally, in Western-blot analyses, we observed a >2-fold PC-induced protection of COIV levels after 9 h index hypoxia. Our studies suggest that a PKCepsilon-COIV interaction and an enhancement of CO activity occur in NCM hypoxic PC. We therefore propose novel mechanisms of PKCepsilon-mediated PC involving enhanced energetics, decreased mitochondrial reactive oxygen species production and the preservation of COIV levels.

H11 Kinase Prevents Myocardial Infarction by Preemptive Preconditioning of the Heart

Ischemic preconditioning confers powerful protection against myocardial infarction through pre-emptive activation of survival signaling pathways, but it remains difficult to apply to patients with ischemic heart disease, and its effects are transient. Promoting a sustained activation of preconditioning mechanisms in vivo would represent a novel approach of cardioprotection. We tested the role of the protein H11 kinase (H11K), which accumulates by 4- to 6-fold in myocardium of patients with chronic ischemic heart disease and in experimental models of ischemia. This increased expression was quantitatively reproduced in cardiac myocytes using a transgenic (TG) mouse model. After 45 minutes of coronary artery occlusion and reperfusion, hearts from TG mice showed an 82+/-5% reduction in infarct size compared with wild-type (WT), which was similar to the 84+/-4% reduction of infarct size observed in WT after a protocol of ischemic preconditioning. Hearts from TG mice showed significant activation of survival kinases participating in preconditioning, including Akt and the 5'AMP-activated protein kinase (AMPK). H11K directly binds to both Akt and AMPK and promotes their nuclear translocation and their association in a multiprotein complex, which results in a stimulation of survival mechanisms in cytosol and nucleus, including inhibition of proapoptotic effectors (glycogen synthase kinase-3beta, Bad, and Foxo), activation of antiapoptotic effectors (protein kinase Cepsilon, endothelial and inducible NO synthase isoforms, and heat shock protein 70), increased expression of the hypoxia-inducible factor-1alpha, and genomic switch to glucose utilization. Therefore, activation of survival pathways by H11K preemptively triggers the antiapoptotic and metabolic response to ischemia and is sufficient to confer cardioprotection in vivo equally potent to preconditioning.

Statin-induced expression of CD59 on vascular endothelium in hypoxia: a potential mechanism for the anti-inflammatory actions of statins in rheumatoid arthritis

Hypoxia, which leads to dysfunctional cell metabolism, and complement activation both play central roles in the pathogenesis of rheumatoid arthritis (RA). Recent studies have reported that mice deficient for the complement-inhibitory protein CD59 show enhanced susceptibility to antigen-induced arthritis and reported that statins have anti-inflammatory effects in RA. We hypothesized that the anti-inflammatory effect of statins in RA relates in part to their ability to increase CD59 expression in hypoxic conditions and therefore to reduce complement activation. Flow-cytometric analysis showed that CD59 expression on endothelial cells (EC) was unaffected by atorvastatin in normoxia (21% O2), whereas in hypoxic conditions (1% O2) an up to threefold dose-dependent increase in CD59 expression was seen. This effect of hypoxia was confirmed by treatment of EC with chemical mimetics of hypoxia. The upregulation of CD59 protein expression in hypoxia was associated with an increase in steady-state mRNA. L-Mevalonate and geranylgeraniol reversed the response, confirming a role for inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase and geranylgeranylation. Likewise, inhibition by NG-monomethyl-L-arginine and NG-nitro-L-arginine methyl ester confirmed that CD59 upregulation in hypoxia was nitric oxide dependent. The expression of another complement-inhibitory protein, decay-accelerating factor (DAF), is known to be increased by atorvastatin in normoxia; this response was also significantly enhanced under hypoxic conditions. The upregulation of CD59 and DAF by atorvastatin in hypoxia prevented the deposition of C3, C9 and cell lysis that follows exposure of reoxygenated EC to serum. This cytoprotective effect was abrogated by inhibitory anti-CD59 and anti-DAF mAbs. The modulation of EC CD59 and DAF by statins under hypoxic conditions therefore inhibits both early and late complement activation and may contribute to the anti-inflammatory effects of statins in RA.

Role of MMP-2 in PKCδ-mediated inhibition of Na+ dependent Ca2+ uptake in microsomes of pulmonary smooth muscle: Involvement of a pertussis toxin sensitive protein

Treatment of bovine pulmonary artery smooth muscle with the O2 *- generating system hypoxanthine plus xanthine oxidase stimulated MMP-2 activity and PKC activity; and inhibited Na+ dependent Ca2+ uptake in the microsomes. Pretreatment of the smooth muscle with SOD (the O2 *- scavenger) and TIMP-2 (MMP-2 inhibitor) prevented the increase in MMP-2 activity and PKC activity, and reversed the inhibition of Na+ dependent Ca2+ uptake in the microsomes. Pretreatment with calphostin C (a general PKC inhibitor) and rottlerin (a PKCdelta inhibitor) prevented the increase in PKC activity and reversed O2 *- caused inhibition of Na+ dependent Ca2+ uptake without causing any change in MMP-2 activity in the microsomes of the smooth muscle. Treatment of the smooth muscle with the O2 *- generating system revealed, respectively, 36 kDa RACK-1 and 78 kDa PKCdelta immunoreactive protein profile along with an additional 38 kDa immunoreactive fragment in the microsomes. The 38 kDa band appeared to be the proteolytic fragment of the 78 kDa PKCdelta since pretreatment with TIMP-2 abolished the increase in the 38 kDa immunoreactive fragment. Co-immunoprecipitation of PKCdelta and RACK-1 demonstrated O2 *- dependent increase in PKCdelta-RACK-1 interaction in the microsomes. Immunoblot assay elicited an immunoreactive band of 41 kDa G(i)alpha in the microsomes. Treatment of the smooth muscle tissue with the O2 *- generating system causes phosphorylation of G(i)alpha in the microsomes and pretreatment with TIMP-2 and rottlerin prevented the phosphorylation. Pretreatment of the smooth muscle tissue with pertussis toxin reversed O2 *- caused inhibition of Na+ dependent Ca2+ uptake without affecting the protease activity and PKC activity in the microsomes. We suggest the existence of a pertussis toxin sensitive G protein mediated mechanism for inhibition of Na+ dependent Ca2+ uptake in microsomes of bovine pulmonary artery smooth muscle under O2 *- triggered condition, which is regulated by PKCdelta dependent phosphorylation and sensitive to TIMP-2 for its inhibition.

Regulation of p53 by activated protein kinase C-delta during nitric oxide-induced dopaminergic cell death

Selective cell death of dopaminergic neurons in the substantia nigra is the major cause of Parkinson disease. Current evidence suggests that this cell death could be mediated by nitric oxide by-products such as nitrate and peroxynitrite. Because protein kinase C (PKC)-delta is implicated in apoptosis of various cell types, we studied its roles and activation mechanisms in nitric oxide (NO)-induced apoptosis of SN4741 dopaminergic cells. When cells were treated with sodium nitroprusside (SNP), a NO donor, endogenous PKC-delta was nitrated and activated. Immunoprecipitation revealed that p53 co-immunoprecipitated with PKC-delta and was phosphorylated at the 15th serine residue in SNP-treated cells. An in vitro kinase assay revealed that p53 was directly phosphorylated by SNP-activated PKC-delta. The p53 Ser-15 phosphorylation was suppressed in SNP-treated cells when the NO-mediated activation of PKC-delta was inhibited by rottlerin or (-)-epigallocatechin gallate. Within 3 h of p53 phosphorylation, its protein levels increased because of decreased ubiquitin-dependent proteosomal proteolysis, whereas the protein levels of MDM2, ubiquitin-protein isopeptide ligase, were down-regulated in a p53 phosphorylation-dependent fashion. Taken together, these results demonstrate that nitration-mediated activation of PKC-delta induces the phosphorylation of the Ser-15 residue in p53, which increases its protein stability, thereby contributing to the nitric oxide-mediated apoptosis-like cell death pathway. These findings may be expanded to provide new insight into the cellular mechanisms of Parkinson disease.

Explaining the phenomenon of nitrate tolerance

During the last century, nitroglycerin has been the most commonly used antiischemic and antianginal agent. Unfortunately, after continuous application, its therapeutic efficacy rapidly vanishes. Neurohormonal activation of vasoconstrictor signals and intravascular volume expansion constitute early counter-regulatory responses (pseudotolerance), whereas long-term treatment induces intrinsic vascular changes, eg, a loss of nitrovasodilator-responsiveness (vascular tolerance). This is caused by increased vascular superoxide production and a supersensitivity to vasoconstrictors secondary to a tonic activation of protein kinase C. NADPH oxidase(s) and uncoupled endothelial nitric oxide synthase have been proposed as superoxide sources. Superoxide and vascular NO rapidly form peroxynitrite, which aggravates tolerance by promoting NO synthase uncoupling and inhibition of soluble guanylyl cyclase and prostacyclin synthase. This oxidative stress concept may explain why radical scavengers and substances, which reduce oxidative stress indirectly, are able to relieve tolerance and endothelial dysfunction. Recent work has defined a new tolerance mechanism, ie, an inhibition of mitochondrial aldehyde dehydrogenase, the enzyme that accomplishes bioactivation of nitroglycerin, and has identified mitochondria as an additional source of reactive oxygen species. Nitroglycerin-induced reactive oxygen species inhibit the bioactivation of nitroglycerin by thiol oxidation of aldehyde dehydrogenase. Both mechanisms, increased oxidative stress and impaired bioactivation of nitroglycerin, can be joined to provide a new concept for nitroglycerin tolerance and cross-tolerance. The consequences of these processes for the nitroglycerin downstream targets soluble guanylyl cyclase, cGMP-dependent protein kinase, cGMP-degrading phosphodiesterases, and toxic side effects contributing to endothelial dysfunction, such as inhibition of prostacyclin synthase, are discussed in this review.

Copper, oxidative stress, and human health

Copper (Cu), a redox active metal, is an essential nutrient for all species studied to date. During the past decade, there has been increasing interest in the concept that marginal deficits of this element can contribute to the development and progression of a number of disease states including cardiovascular disease and diabetes. Deficits of this nutrient during pregnancy can result in gross structural malformations in the conceptus, and persistent neurological and immunological abnormalities in the offspring. Excessive amounts of Cu in the body can also pose a risk. Acute Cu toxicity can result in a number of pathologies, and in severe cases, death. Chronic Cu toxicity can result in liver disease and severe neurological defects. The concept that elevated ceruloplasmin is a risk factor for certain diseases is discussed. In this paper, we will review recent literature on the potential causes of Cu deficiency and Cu toxicity, and the pathological consequences associated with the above. Finally, we will review some of the potential biochemical lesions that might underlie these pathologies. Given that oxidative stress is a characteristic of Cu deficiency, the role of Cu in the oxidative defense system will receive special attention. The concept that excess Cu may be a precipitating factor in Alzheimer's disease is discussed.

Antecedent ethanol ingestion prevents postischemic microvascular dysfunction

Prolonged ischemia followed by reperfusion (I/R) results in impaired endothelial cell function in all segments of the microvasculature. Moreover, microcirculatory dysfunction plays a major role in the genesis of the reperfusion component of total tissue injury in I/R. Thus, preservation of endothelial function is an important therapeutic goal for ameliorating injury in tissues subjected to I/R. An accumulating body of evidence indicates that low to moderate ethanol consumption produces an adaptive transformation to a protected phenotype in both microvascular endothelium and parenchymal cells such that they are rendered resistant to the pathologic effects of I/R. The purpose of this review is to summarize our current understanding of the signaling pathways underlying the development of the preconditioned state induced by antecedent ethanol in arteriolar, capillary, and venular endothelium. In addition, we will highlight understudied areas with regard to microvascular protection afforded by antecedent ethanol in the hopes that this will stimulate investigation of its underlying mechanisms. Understanding these signaling pathways may provide a mechanistic rationale for the development of novel treatment interventions that target both the microcirculatory and parenchymal sequelae to I/R, thereby maximizing the therapeutic potential of the protected phenotypes produced by pharmacologic preconditioning.

Male castration increases neuronal nitric oxide synthase activity in the rat mesenteric artery through protein kinase C activation

The objective of the present study was to assess the effect of endogenous male sex hormones on the activity of protein kinase C (PKC), as well as the regulatory effect of this kinase on the neuronal nitric oxide (NO) release induced by electrical field stimulation (EFS; 200 mA; 0.3 ms; 1-16 Hz). For this purpose, superior mesenteric arteries from control and orchidectomized male Sprague-Dawley rats were used. PKC activity was greater in arteries from orchidectomized than control rats. Basal and EFS-induced NO release was similar in arteries from both groups despite the lower nNOS expression in arteries from orchidectomized rats. Phorbol 12,13-dibutyrate (PDBu), a PKC activator, EFS-induced NO release was higher in arteries from control compared to orchidectomized rats. Calphostin C, a non-selective PKC inhibitor, or Gö6976, a PKC inhibitor partially selective for conventional isoforms,abolished the EFS-induced NO release in arteries from control animals, while it was decreased in arteries from orchidectomized animals. The PKCzeta pseudosubstrate inhibitor decreased EFS-induced NO release equally in both groups. The NO synthase (NOS) inhibitor Nomega-nitro-L-arginine-methyl ester (L-NAME) enhanced the EFS-elicited contractions in arteries from both groups. Calphostin C increased the contractions elicited by EFS in arteries from control and orchidectomized rats. This increase was further enhanced by calphostin C plus L-NAME only in orchidectomized rats. PDBu reduced EFS-induced contraction in arteries from controls but did not affect it in orchidectomized rats. The further addition of L-NAME increased the responses in both types of arteries. These results show that PKC activity is enhanced in mesenteric arteries from orchidectomized rats, which may be the responsible for the greater nNOS activity in these arteries. Conventional and atypical PKCzeta isoforms positively regulate nNOS activity in arteries from both control and orchidectomized rats, but the contribution of conventional PKC isoforms to enhanced nNOS activity seems to be greater in arteries from orchidectomized rats.

Angiotensin II induces tyrosine nitration and activation of ERK1/2 in vascular smooth muscle cells

Angiotensin II (Ang II) induces a prominent and sustained nitration and activation of ERK1/2 in rat vascular smooth muscle cells, both mediated via AT1 receptor. Nitration and activation was also shown for recombinant non-activated extracellular signal-regulated kinase (ERK) and MEK. Nitration and phosphorylation of ERK1/2 by Ang II was significantly inhibited by NAD(P)H inhibitors and scavengers of oxygen and nitrogen reactive species and completely blocked by a selective inducible nitric-oxide synthase inhibitor. MEK inhibitor U0126 did not affect ERK nitration but completely blocked activation. These data indicate that Ang II nitrates and activates ERK1/2 via a reactive species-sensitive pathway.

Peroxynitrite activates ERK via Raf-1 and MEK, independently from EGF receptor and p21Ras in H9C2 cardiomyocytes

Peroxynitrite is a potent oxidant and nitrating species proposed as a direct effector of myocardial damage in a wide range of cardiac diseases. Whether peroxynitrite also acts indirectly, by modulating cell signal transduction pathways in the myocardium, has not been investigated. Here, we examined the ability of peroxynitrite to activate extracellular signal-related kinase (ERK), a MAP kinase which has been linked with hypertrophic and anti-apoptotic responses in the heart, in cultured H9C2 cardiomyocytes. Peroxynitrite elicited a concentration- and time-dependent activation of ERK, secondary to the upstream activation of MEK 1 (ERK kinase). Activation of MEK-ERK by peroxynitrite was related to the upstream activation of Raf-1 kinase, as ERK and MEK phosphorylation were prevented by the Raf-1 inhibitor BAY43-9006. These effects of peroxynitrite were not associated with the activation of p21(Ras), known as a common signaling target of cellular oxidative stress. In contrast to ERK activation mediated by the epidermal growth factor (EGF), ERK activation by peroxynitrite was not prevented by AG1478 (EGF receptor inhibitor). Peroxynitrite acted through oxidative, but not nitrative chemistry, as ERK remained activated while nitration was prevented by the flavanol epicatechin. In addition to ERK, peroxynitrite also potently activated two additional members of the MAP kinase family of signaling proteins, JNK and p38. Thus, peroxynitrite activates ERK in cardiomyocytes through an unusual signaling cascade involving Raf-1 and MEK 1, independently from EGFR and P21(Ras), and also acts as a potent activator of JNK and p38. These results provide the novel concept that peroxynitrite may represent a previously unrecognized signaling molecule in various cardiac pathologies.

Proteolytic activation of protein kinase Calpha by peroxynitrite in stimulating cytosolic phospholipase A2 in pulmonary endothelium: involvement of a pertussis toxin sensitive protein

We sought to determine the roles of PKCalpha and G(i)alpha in regulating cPLA(2) activity in bovine pulmonary artery endothelial cell membrane under peroxynitrite (ONOO(-)) stimulation. Treatment of bovine pulmonary artery endothelial cells with ONOO(-) markedly stimulates the cell membrane associated protease activity, protein kinase C (PKC) activity, phospholipase A(2) (PLA(2)) activity, and arachidonic acid (AA) release from the cells. ONOO(-) significantly increases (Ca(2+))(i) in the cells, and pretreatment with the intracellular Ca(2+) chelator BAPTA-AM prevents the increase in (Ca(2+))(i), protease activity, PKC activity, and cPLA(2) activity in the cell membrane and AA release from the cells. Pretreatment of the cells with arachidonyl trifluoromethyl ketone (AACOCF(3)) (a cPLA(2) inhibitor) prevents ONOO(-)-stimulated cPLA(2) activity and AA release without producing a significant alteration of the protease activity. Pretreatment with vitamin E and aprotinin prevents ONOO(-)-induced increase in the protease activity, PKC activity, and cPLA(2) activity in the cell membrane and AA release from the cells. Pretreatment with the PKC inhibitor calphostin C prevents ONOO(-)-caused increase in PKC activity and cPLA(2) activity in the cell membrane and AA release from the cells. An immunoblot study of the cell membrane isolated from the ONOO(-)-treated cells with polyclonal PKCalpha antibody elicited an increase in the 80 kDa immunoreactive protein band along with an additional 47 kDa immunoreactive fragment. An immunoblot study with anti-nitrotyrosine antibody revealed that ONOO(-) induces nitration of tyrosine residues in PKCalpha. Pretreatment of the cells with aprotinin abolished the 47 kDa immunoreactive fragment in the immunoblot. An immunoblot study of the endothelial cell membrane with polyclonal cPLA(2) antibody revealed that treatment of the cells with ONOO(-) markedly increases the cPLA(2) immunoreactive protein profile in the membrane. Pretreatment of the endothelial cells with Go6976, a PKCalpha inhibitor, prevents the increase in PKC activity and cPLA(2) activity in the cell membrane under ONOO(-)-triggered condition. It, therefore, appears from the present study that treatment of the cells with ONOO(-) causes an increase in the protease activity, and that plays an important role in activating PKCalpha, which subsequently stimulates cPLA(2) activity in the cell membrane and AA release from the cells. An immunoblot assay with polyclonal G(i)alpha antibody elicited an immunoreactive band having a molecular mass of 41 kDa. Pretreatment of the cells with pertussis toxin markedly inhibits ONOO(-)-induced increase in cPLA(2) activity and AA release without significantly altering (Ca(2+))(i), protease activity, and PKC activity in the cell membrane. Treatment of the cells with ONOO(-) causes phosphorylation of G(i)alpha in the cell membrane, and pretreatment with Go6976 prevents its phosphorylation. We suggest the existence of a pertusssis toxin sensitive G protein-mediated mechanism for activation of cPLA(2) by ONOO(-) in bovine pulmonary artery endothelial cell membrane, which is regulated by PKCalpha-dependent phosphorylation and sensitive to aprotinin for its inhibition.

Delayed Preconditioning-Mimetic Actions of Nitroglycerin in Patients Undergoing Exercise Tolerance Tests

Background— Nitroglycerin (NTG) induces delayed preconditioning (PC)-mimetic effects in animal models and in humans during coronary angioplasty. We tested the hypothesis that NTG mitigates ischemia and enhances functional capacity during an exercise tolerance test (ETT) in patients with coronary artery disease.

Methods and Results— Twenty-eight patients with stable angina and ischemia documented by a stress test were randomized in a double-masked, crossover design to receive a titrated intravenous infusion of NTG or normal saline over 4 hours. At 24 to 28 hours after study medication infusion, each patient underwent 2 ETTs separated by a 1-week washout period. Compared with control patients, pretreatment with NTG was associated with a dose-dependent increase in exercise duration averaging 40 seconds (412±19 versus 372±24 seconds, P =0.014) and an improvement in ECG manifestations of ischemia, as shown by a decrease in maximal ST-segment depression (1.84±0.14 versus 1.63±0.13 mm, P =0.011), sum of ST-segment depressions in 12 leads (7.64±1.01 versus 6.61±0.83 mm, P =0.027), and time to resolution of ST-segment depression (229±30 versus 207±28 s, P =0.018). These benefits occurred despite an increase in myocardial workload after NTG, as indicated by a higher peak rate-pressure product (24 492±1054 versus 22 536±1019 mm Hg/min, P =0.015).

Conclusions— NTG produces a late PC-mimetic effect that mitigates the ECG manifestations of ischemia during exercise and improves exercise capacity. To our knowledge, this is the first study to demonstrate that NTG can alleviate exercise-induced ischemia 24 hours after its administration, long after the hemodynamic effects have subsided. The finding that nitrate-induced late PC ameliorates a common manifestation of coronary artery disease has potentially significant implications for the management of this disorder and for the design of clinical trials.

Integrated pharmacological preconditioning and memory of cardioprotection: role of protein kinase C and phosphatidylinositol 3-kinase

Although protein kinase C (PKC) and phosphatidylinositol 3 (PI3)-kinase are implicated in cardioprotective signal transduction mediated by ischemic preconditioning, their role in pharmacological preconditioning (PPC) has not been determined. Cultured neonatal rat cardiomyocytes (CMCs) were subjected to simulated ischemia for 2 h followed by 15 min of reoxygenation. PPC of CMCs consisted of administration of 50 microM adenosine, 50 microM diazoxide, and 50 microM S-nitroso-N-acetylpenicillamine (SNAP), each alone or in combination, for 15 min followed by 30 min of washout before simulated ischemia. Although PKC-epsilon and PI3-kinase were significantly activated during treatment with adenosine, activation of these kinases dissipated after washout. In contrast, PPC combined with adenosine, diazoxide, and SNAP elicited sustained activation of PKC-epsilon and PI-3 kinase after washout. The combined-PPC, but not the single-PPC, protocol conferred antiapoptotic and antinecrotic effects after reoxygenation. The PKC inhibitor chelerythrine (5 microM) or the PI3-kinase inhibitor LY-294002 (10 microM) given during the washout period partially blocked the activation of PKC-epsilon and PI3-kinase mediated by the combined-PPC protocol, whereas combined addition of chelerythrine and LY-294002 completely inhibited activation of PKC-epsilon and PI3-kinase. Chelerythrine or LY-294002 partially blocked antiapoptotic and antinecrotic effects mediated by the combined-PPC protocol, whereas combined addition of chelerythrine and LY-294002 completely abrogated antiapoptotic and antinecrotic effects. These results suggest that the combined-PPC protocol confers cardioprotective memory through sustained and interdependent activation of PKC and PI3-kinase.

Cytochrome c oxidase subunit IV as a marker of protein kinase Cepsilon function in neonatal cardiac myocytes: implications for cytochrome c oxidase activity

We have previously demonstrated that low concentrations of phorbol esters stimulate the selective translocation of protein kinase C (PKC) alpha and epsilon from the cell soluble to the particulate fraction in NCMs (neonatal rat cardiac myocytes). We therefore determined if the in vitro phosphorylation of substrates in these fractions could be used as assays of PKCalpha or epsilon activation. Intact cell phorbol ester treatment caused a decline in the in vitro (32)P-incorporation into several proteins in the cell-soluble fraction. These declines occurred in the presence or absence of in vitro Ca(2+) and probably reflected the exit of PKC isoenzymes from the soluble fraction. In contrast, an approx. 18 kDa protein incorporated (32)P in particulate fractions isolated from 4beta-PMA-treated cells in a Ca(2+)-independent manner. Proteomic and immunoprecipitation analyses indicated that the protein is subunit IV of the cytochrome c oxidase complex (COIV). In vitro phosphorylation of COIV was attenuated by PKC pseudosubstrate peptides. Introduction of an PKCepsilon-selective translocation inhibitor [Johnson, Gray, Chen and Mochly-Rosen (1996) J. Biol. Chem. 271, 24962-24966] into NCMs before 4beta-PMA treatments also attenuated the in vitro phosphorylation of COIV. In mitochondrial extracts from 4beta-PMA-treated NCMs, the PKCepsilon isoenzyme coimmunoprecipitated with COIV, and cytochrome c oxidase activity was enhanced 2-fold. The in vitro phosphorylation of COIV reflects a novel approach for monitoring PKCepsilon function in NCMs. Furthermore, PKCepsilon probably interacts with COIV in NCM mitochondria to enhance electron-transport chain complex IV activity.

Mapping Sites of Tyrosine Nitration by Matrix‐Assisted Laser Desorption/Ionization Mass Spectrometry

Protein tyrosine nitration is an important part of nitric oxide biology. This posttranslational modification occurs under normal physiological conditions and is substantially enhanced under various pathological conditions. Studies reveal that protein tyrosine nitration is a dynamic and selective process that influences protein function and turnover and can be considered a diagnostic biomarker of pathology. The identification of nitrated tyrosine residues directly within any given nitrated protein is important for studies on in vivo mechanisms of nitration and for the explanation of functional consequences of nitration. Specific nitrated tyrosines in given proteins may be also more informative as oxidative biomarkers than overall nitrotyrosine levels. However, localization of the sites of nitration remains a methodological challenge. Mass spectrometry (MS) is an ideal method for identifying nitrated tyrosines in proteins because of its sensitivity and specificity. This chapter is not intended to thoroughly discuss the various MS-based approaches for nitrotyrosine identification and merely focuses on the analysis of peptides containing nitrotyrosine by matrix-assisted laser desorption ionization MS (MALDI-MS). The data summarized show that the MALDI-MS pattern of a tyrosine-nitrated peptide includes the unique combination of ions that provides unequivocal evidence for the presence of nitrotyrosine in a given peptide and could be used for mapping sites of tyrosine nitration in proteins.

New insight into the signalling pathways of heat stress-induced myocardial preconditioning: protein kinase Cepsilon translocation and heat shock protein 27 phosphorylation

1. Heat stress (HS) is known to induce delayed preconditioning against myocardial infarction 24 h later, but the exact signalling pathway of this response remains to be elucidated. In previous studies, we have shown evidence for the implication of protein kinase C (PKC) and p38 mitogen-activated protein kinase (MAPK) in the HS-induced reduction in infarct size. Furthermore, in their phosphorylated state, small heat shock proteins (Hsp27) seem to confer cytoskeletal protection. In the present study, we sought to determine the effect of HS on the subcellular distribution of PKC isoforms and on Hsp27 phosphorylation. 2. Rats were subjected to either HS (42 degrees C for 15 min; HS group) or sham anaesthesia (sham group) before their hearts were excised. Myocardial tissue extracts obtained 20 min or 24 h after HS were processed for western blot analysis. 3. In the HS group, PKCepsilon translocated from the cytosolic to the particulate fraction (4426 +/- 128 vs 6258 +/- 316 arbitrary units; P = 0.002). Chelerythrine (5 mg/kg, i.p.), a PKC inhibitor, abolished this translocation. Western blot analysis of Hsp27 24 h after HS showed a marked increase in protein expression and phosphorylation in the particulate fraction. 4. In the present study, we have shown that HS induces the translocation of PKCepsilon from the cytosolic to the particulate fraction. Along with our previous observation that PKC is a trigger of HS-induced myocardial preconditioning, the results of the present study suggest an important role of the epsilon isoform of PKC in this cardioprotective mechanism. Furthermore, we have also demonstrated that the cytoprotective protein Hsp27 is phosphorylated following HS. Therefore, we can conclude that PKC and MAPK/Hsp27 are involved in the signalling pathway of HS-induced cardioprotection.

PKC-interacting proteins: from function to pharmacology

Protein kinase C (PKC) is a ubiquitously expressed family of kinases that have key roles in regulating multiple cellular activities. The activity of this family is controlled tightly by several molecular mechanisms, including interaction with binding-partner proteins. These PKC-interacting proteins (C-KIPs) confer specificity for individual PKC isoforms by regulating the activity and cellular localization of PKC isoforms and, subsequently, the ability of these isoforms to specifically regulate cellular functional events. Although many C-KIPs have been identified by genome and proteome-mining approaches, it is important to address the specificity and function of the interactions in greater detail because they might form novel drug targets. In this article, we review recent work on C-KIPs and the implications for pharmacological and therapeutic development.

NO donor-activated PKC-delta plays a pivotal role in ischemic myocardial protection through accelerated opening of mitochondrial K-ATP channels

Nitric oxide (NO) can activate protein kinase C (PKC) and the activation of mitochondrial ATP-sensitive potassium (K-ATP) channels is cardioprotective. However, interactions among NO, PKC, and mitochondrial K-ATP channels remain vague. To clarify the cardioprotective mechanism induced by nicorandil, we compared its ability to activate PKC isoforms with that of the mitochondrial K-ATP channel opener, diazoxide. We induced myocardial infarction in rats by 30 minutes of ischemia followed by reperfusion, then assessed the infarct size 3 weeks later. We also examined the translocation of PKC isoforms in the isolated perfused rat heart. Nicorandil and diazoxide reduced infarct size, and the effect of nicorandil, but not of diazoxide attenuated by the PKC inhibitor, chelerythrine, or by the NO quencher, carboxy PTIO. Immunoblotting revealed that nicorandil translocated PKC-delta to the mitochondria, and that this was inhibited by carboxy PTIO. The protective effect of nicorandil against myocardial infarction partly depended on the translocation of PKC-delta to the mitochondria, which we attributed to the NO donor effect of nicorandil. The PKC-delta- dependent activation of mitochondrial K-ATP channel opening might be synergistic with its direct effect, making nicorandil an efficient opener of such channels.

Increased release of excitatory amino acids by the actions of ATP and peroxynitrite on volume-regulated anion channels (VRACs) in astrocytes

Rapid swelling of astrocytes in primary culture by exposure to hyposmotic medium (or slower swelling by exposure to high K+ medium) leads to release of the excitatory amino acids (EAAs) glutamate and aspartate. One question that arises is whether these phenomena are only relevant to pathological states such as ischemia and trauma where marked astrocytic swelling occurs or whether much smaller astrocytic volume changes, that might be encountered under physiological states, will cause such release. We have recently found that extracellular ATP strongly potentiated volume-regulated anion channels (VRACs)-mediated-excitatory amino acid release in non-swollen and osmotically swollen primary astrocyte cultures. However, ATP does not seem to directly activate but instead positively modulates VRACs and we postulate that a minor fraction of these are active under isoosmotic conditions based on the finding that in hyperosmotic media the ATP-induced increase was inhibited. Agonist and inhibitor analysis suggests that the effect of ATP is mediated by several subtypes of metabotropic P2Y receptors. Thus, the concept of volume transmission may be extended to volume-mediated transmission, whereby moderate cell swelling causes release of neurotransmitter substances. The product of the superoxide oxygen radical and nitric oxide, peroxynitrite, formed under pathological conditions such as cerebral ischemia, also potentiated the release of D-[3H]aspartate from astrocyte cultures exposed to limited or marked swelling via intracellular signaling mechanisms involving tyrosine kinases (TKs). Thus, the enhancement of cell volume-dependent release of excitatory amino acids from astrocytes can be physiological or pathological and its magnitude depends on the degree of the cell volume increase.

Oxidative stress in the placenta

Pregnancy is a state of oxidative stress arising from increased placental mitochondrial activity and production of reactive oxygen species (ROS), mainly superoxide anion. The placenta also produces other ROS including nitric oxide, carbon monoxide, and peroxynitrite which have pronounced effects on placental function including trophoblast proliferation and differentiation and vascular reactivity. Excessive production of ROS may occur at certain windows in placental development and in pathologic pregnancies, such as those complicated by preeclampsia and/or IUGR, overpowering antioxidant defenses with deleterious outcome. In the first trimester, establishment of blood flow into the intervillous space is associated with a burst of oxidative stress. The inability to mount an effective antioxidant defense against this results in early pregnancy loss. In late gestation increased oxidative stress is seen in pregnancies complicated by diabetes, IUGR, and preeclampsia in association with increased trophoblast apoptosis and deportation and altered placental vascular reactivity. Evidence for this oxidative stress includes increased lipid peroxides and isoprostanes and decreased expression and activity of antioxidants. The interaction of nitric oxide and superoxide produces peroxynitrite, a powerful prooxidant with diverse deleterious effects including nitration of tyrosine residues on proteins thus altering function. Nitrative stress, subsequent to oxidative stress is seen in the placenta in preeclampsia and diabetes in association with altered placental function.

Dual actions of nitric oxide on angiogenesis: possible roles of PKC, ERK, and AP-1

Regulation of angiogenesis by nitric oxide (NO) is controversial since NO has been shown to have both pro- and anti-angiogenic effects. In this study, we examined the effect of the NO donor, S-nitro-N-acetyl-penicillamine (SNAP), on in vitro angiogenesis, and the mechanisms involved: PKC activity, ERK and c-Jun phosphorylation, and AP-1 DNA binding activity, in microvascular endothelial cells. SNAP, at 0.5-4 mM, significantly and dose-dependently inhibited angiogenesis, PKC activity, and ERK and c-Jun phosphorylation up to 80%, 83%, and 63% and 73%, respectively. SNAP at concentrations > 2mM also abolished AP-1 binding activity. Lower concentrations of SNAP (0.1-0.3 mM) significantly increased angiogenesis, PKC activity, and ERK and c-Jun phosphorylation up to 46%, 60%, and 61% and 180%, respectively. These findings indicate that the dual pro- and anti-angiogenic actions of NO are dose-dependent and suggest that they are mediated by PKC and ERK acting on AP-1.

Nitric oxide, oxidants, and protein tyrosine nitration

The occurrence of protein tyrosine nitration under disease conditions is now firmly established and represents a shift from the signal transducing physiological actions of (.)NO to oxidative and potentially pathogenic pathways. Tyrosine nitration is mediated by reactive nitrogen species such as peroxynitrite anion (ONOO(-)) and nitrogen dioxide ((.)NO2), formed as secondary products of (.)NO metabolism in the presence of oxidants including superoxide radicals (O2(.-)), hydrogen peroxide (H2O2), and transition metal centers. The precise interplay between (.)NO and oxidants and the identification of the proximal intermediate(s) responsible for nitration in vivo have been under controversy. Despite the capacity of peroxynitrite to mediate tyrosine nitration in vitro, its role on nitration in vivo has been questioned, and alternative pathways, including the nitrite/H2O2/hemeperoxidase and transition metal-dependent mechanisms, have been proposed. A balanced analysis of existing evidence indicates that (i) different nitration pathways can contribute to tyrosine nitration in vivo, and (ii) most, if not all, nitration pathways involve free radical biochemistry with carbonate radicals (CO3(.-)) and/or oxo-metal complexes oxidizing tyrosine to tyrosyl radical followed by the diffusion-controlled reaction with (.)NO2 to yield 3-nitrotyrosine. Although protein tyrosine nitration is a low-yield process in vivo, 3-nitrotyrosine has been revealed as a relevant biomarker of (.)NO-dependent oxidative stress; additionally, site-specific nitration focused on particular protein tyrosines may result in modification of function and promote a biological effect. Tissue distribution and quantitation of protein 3-nitrotyrosine, recognition of the predominant nitration pathways and individual identification of nitrated proteins in disease states open new avenues for the understanding and treatment of human pathologies.

Regulation of hypertrophic and apoptotic signaling pathways by reactive oxygen species in cardiac myocytes

Increasing evidence suggests that oxidative and nitrosative stress play an important role in regulation of cardiac myocyte growth and survival. The cardiovascular system is continuously exposed to both reactive oxygen species (ROS) and nitrogen species (RNS), collectively termed reactive inflammatory species (RIS), and imbalances between the enzymes that regulate their bioavailability are associated with cardiac hypertrophy and the pathogenesis of cardiomyopathies, myocardial infarction and heart failure. It is now clear that RIS act as critical regulators of cardiac myocyte hypertrophy and apoptosis through control of redox-sensitive signaling cascades, such as tyrosine kinases and phosphatases, protein kinase C, and mitogen-activated protein kinases. This review will focus on the mechanisms by which ROS/RNS modulate cardiac myocyte growth and apoptosis induced by neurohormones and cytokines, and will discuss evidence for a role in the pathophysiology of heart failure.

Roles of superoxide, peroxynitrite, and protein kinase C in the development of tolerance to nitroglycerin

A current hypothesis states that tolerance to nitroglycerin (GTN) involves increased formation of superoxide (O2*-). Studies showing that inhibitors of protein kinase C (PKC) prevent tolerance to GTN suggest the involvement of PKC activation, which can also increase O2*-. We examined the roles of O2*-, peroxynitrite (ONOO-), and PKC activation in GTN tolerance. Pre-exposure of rat aortic rings to GTN (5 x 10(-4) M) for 2 h caused tolerance to the vasodilating effect of GTN, as evidenced by a substantial rightward shift of GTN concentration-relaxation curves. This shift was reduced by treatment of the rings with the antioxidants uric acid, vitamin C, or tempol or the PKC inhibitor chelerythrine. We also found that O2*- generation via xanthine/xanthine oxidase in the bath induced tolerance to GTN. However, responses to nitroprusside were not affected. In vivo tolerance produced in rats by 3-day i.v. infusion of GTN was also almost completely prevented by coinfusion of tempol. In bovine aortic endothelial cells (EC), addition of GTN produced a marked increase in tyrosine nitrosylation, indicating increased ONOO- formation. This action was blocked by prior treatment with uric acid, superoxide dismutase, NG-nitro-L-arginine methyl ester, or chelerythrine. We also demonstrated that GTN translocates the alpha- and epsilonPKC isoforms in EC. However, PKCzeta was not affected by GTN treatment. In conclusion, tolerance to GTN involves enhanced production of O2*- and ONOO- and activation of NO synthase. Furthermore, sustained activation of alpha- and epsilonPKC isozymes in EC by GTN may play a role in development of tolerance.

Glucocorticoid receptor nitration leads to enhanced anti-inflammatory effects of novel steroid ligands

It has recently emerged that posttranslational modification of proteins via nitration of tyrosine residues can alter their function. In this study, we describe that specific nitration of the glucocorticoid receptor (GR) by NCX-1015, a novel NO-donating prednisolone derivative (prednisolone 21-[4'-(nitrooxymethyl)benzoate), results in an enhancement of GR-mediated events. Incubation of PBMC and U937 cells with 1-10 micro M NCX-1015 caused faster activation of GR as assessed by augmented 1) binding to [(3)H]dexamethasone, 2) dissociation from heat shock protein 90, and 3) nuclear translocation. PBMCs treated with NCX-1015 contained GR that had undergone tyrosine nitration. The chemistry facilitating the increase in steroid binding capacity observed with NCX-1015 is specific, because changing the position of the NO-donating group or ubiquitous nitration by addition of an NO donor was unable to mimic this event. In vivo treatment with NCX-1015 provoked GR nitration and faster heat shock protein 90 dissociation as assessed in peritoneal cells. Accordingly, NCX-1015, but not prednisolone or other derivatives, produced a rapid inhibition of the early neutrophil recruitment and mediator generation in a model of peritonitis. In conclusion, we report here for the first time that posttranslational modification of GR by this novel nitrosteroid is associated with its enhanced anti-inflammatory activity.

Combined pharmacological preconditioning with a G-protein-coupled receptor agonist, a mitochondrial KATP channel opener and a nitric oxide donor mimics ischaemic preconditioning

1. Although pharmacological preconditioning (PPC) has emerged as an alternative to ischaemic preconditioning (IPC) in cardioprotection, the efficacy of PPC compared with IPC has not been investigated. Because IPC is mediated by complex signalling cascades arising from multiple triggers, we have hypothesized that combined PPC is necessary to mimic IPC. 2. Isolated and perfused rat hearts underwent IPC by three cycles of 5 min ischaemia and 5 min reperfusion before 30 min global ischaemia followed by 120 min reperfusion. Adenosine (30 micromol/L), diazoxide (50 micromol/L) and s-nitroso-N-acetylpenicillamine (SNAP; 50 micromol/L) were added for 25 min just before (pretreatment modality) or 45 min before (PPC modality) the index ischaemia. 3. Ischaemic preconditioning significantly improved isovolumic left ventricular (LV) function and reduced infarct size. Although pretreatment with adenosine, diazoxide or SNAP alone was capable of reducing infarct size, PPC with each drug alone or in a combination of two drugs except for diazoxide plus SNAP failed to reduce infarct size. In contrast, PPC in combination with adenosine, diazoxide and SNAP (triple combination PPC) conferred significant improvement of LV function and reduction of infarct size that was as effective as IPC. 4. Cardioprotection afforded by triple combination PPC was abolished by the Gi/o-protein inhibitor pertussis toxin, the mitochondiral KATP channel inhibitor 5-hydroxydecanoate or the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO). 5. Protein kinase C (PKC)-epsilon in the particulate fraction was activated throughout preconditioning ischaemia and reperfusion. Although PKC-epsilon was activated during treatment with adenosine, diazoxide or SNAP alone, it was inactivated after washout. In contrast, PKC-epsilon remained activated after triple combination PPC. The PKC inhibitor chelerythrine abolished activation of PKC-epsilon and cardioprotection afforded by IPC and triple combination PPC. 6. These results demonstrate that combined PPC with a G-protein-coupled receptor agonist, a mitochondrial KATP channel opener and an NO donor is necessary to mimic IPC and such synergistic cardioprotection is associated with enhanced and sustained activation of PKC-epsilon.

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

In the past few years, nuclear DNA damage-sensing mechanisms activated by ionizing radiation have been identified, including ATM/ATR and the DNA-dependent protein kinase. Less is known about sensing mechanisms for cytoplasmic ionization events and how these events influence nuclear processes. Several studies have demonstrated the importance of cytoplasmic signaling pathways in cytoprotection and mutagenesis. For cytoplasmic signaling, radiation-stimulated reactive oxygen species (ROS) and reactive nitrogen species (RNS) are essential activators of these pathways. This review summarizes recent studies on the chemistry of radiation-induced ROS/RNS generation and emphasizes interactions between ROS and RNS and the relative roles of cellular ROS/RNS generators as amplifiers of the initial ionization events. Cellular mechanisms for regulating ROS/RNS levels are discussed. The mechanisms by which cells sense ROS/RNS are examined in terms of how ROS/RNS modify protein structure and function, for example, interactions with metal-thiol clusters, protein tyrosine nitration, protein cysteine oxidation, S-thiolation and S-nitrosylation. We propose that radiation-induced ROS are the initiators and that nitric oxide (NO*) or derivatives are the effectors activating these signal transduction pathways. In responding to cellular ionization events, the cell converts an oxidative signal to a nitrosative one because ROS are too reactive and unspecific in their reactions for regulatory purposes and the cell is equipped to precisely modulate NO* levels.

Dose-dependent effects of acute exercise on PKC levels in rat heart: is PKC the heart's prophylactic?

Epidemiological studies have demonstrated that chronic exercise is cardioprotective, and recent evidence from our laboratory suggests a key role for protein kinase C (PKC)-dependent pathways, at least in part, as a cellular basis for this response. However, the dose-response relationship linking exercise volume and the time course of isoform-specific PKC activation are poorly understood.

AIM

The purpose of this investigation was to determine the effects of acute exercise of varying durations on PKC subcellular distribution and phosphorylation in the rat left ventricle.

METHODS

Adult (5 months) male Fischer-344 more rats were subjected to a single bout (OB) or 7 days (SB) of treadmill running (n = 6/group; 23 m min-1, 20 min), and compared with sedentary controls (SED; n = 8). Hearts were isolated immediately after [early window (EW); n = 3/group] or 24 h after the last exercise bout [late window (LW); n = 3/group] in OB and SD, respectively. Total PKC and subcellular distribution for the alpha, delta, epsilon, betaI, and betaII isoforms, as well as phosphorylated (phospho-) PKC epsilon (pSer729), PKC alpha (pSer657) and PKCdelta (pThr507) levels were assessed by western blotting. Protein kinase C epsilon and PKC alpha mRNA levels were assessed by real time polymerase chain reaction.

RESULTS

Following OB, PKCbetaI protein levels were reduced, while total phospho-PKC epsilon (pSer729), PKC alpha (pSer657) and PKC delta (pThr507) levels were increased during EW (P < 0.05). Interestingly, total PKC delta (31%) and membrane-associated PKC alpha (24%) levels decreased from EW to LW (P < 0.05). In contrast, SB yielded chronic increases in total PKC epsilon (80.5%) levels and PKC delta (20.0%) levels (P < 0.03), with reversal of effects on phospho-PKC epsilon (Ser729), phospho-PKC alpha (Ser657) and phospho-PKC delta (Thr507) levels observed with OB. Reductions in total phospho-PKC alpha (Ser657) persisted at SB (26.1%; P < 0.02). Interestingly, mRNA levels for PKC epsilon were significantly increased following SB while PKC alpha mRNA levels were reduced, respectively.

CONCLUSION

These data suggest that divergent patterns of PKC activation occur following OB and SB at both the transcriptional and translational levels. That similar patterns of PKC translocation are observed in experimental models of ischaemic preconditioning and genetic PKC manipulation provide evidence for a dose-dependent cardioprotective phenotype induced by physical activity.

Age, cell signalling and cardioprotection

For many years investigators have been researching methods of preconditioning the myocardium against ischaemia-induced damage; however, a majority of this research has been carried out in young animals and cells. Normal ageing is accompanied by changes in the human myocardium that decrease its capacity to tolerate and respond to various forms of stress. Also, the likelihood of experiencing an ischaemic stress and other cardiovascular complications increases as an individual ages; therefore, an aged population would benefit most from cardioprotective treatments. Methods currently known to provide cardioprotection (or preconditioning) include exercise, heat stress, oxidative stress, brief ischaemia, stretch and certain pharmacological interventions. It is unclear whether the aged myocardium can adapt to a preconditioning stimulus; however, many researchers have observed age-related alterations in the expression and activation of proteins key to the cardioprotective process. These proteins include heat shock protein 70 (HSP70), nitric oxide synthase (NOS), the sodium-hydrogen exchanger (NHE), and the mitogen-activated protein (MAP) kinases c-Jun N-terminal Kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Therefore, the purpose of the current review will be to outline the current knowledge of these cardioprotective agents in an aged myocardium. Interactions among the cardioprotective agents outlined herein suggest that age-related changes in the myocardium will need to be better understood before cardioprotective interventions that have been proved effective in young animals can be applied to an aged human population.

Late preconditioning by ethanol is initiated via an oxidant-dependent signaling pathway

Ingestion of alcoholic beverages at low to moderate levels 24 h prior to ischemia and reperfusion (I/R) prevents postischemic leukocyte/endothelial cell adhesive interactions, a phenomenon referred to as late ethanol preconditioning (EtOH-PC). The aim of this study was to determine whether oxidants act as initiators of late EtOH-PC. Ethanol was instilled into the stomachs of C57BL/6 mice as a bolus by gavage at a dose that produced a peak plasma concentration of 45 mg/dl 30 min after administration and returned to control levels 60 min after ingestion. Twenty four hours later, the superior mesenteric artery was occluded for 45 min followed by 70 min of reperfusion. The numbers of rolling and firmly adherent leukocytes were quantified in postcapillary venules of the small intestine in sham animals (no EtOH-PC, no I/R), in mice subjected to I/R alone or EtOH-PC + I/R, and in animals treated with Mn-TBAP (a cell-permeant superoxide dismutase mimetic), oxypurinol (a XO inhibitor), the NAD(P)H oxidase inhibitors PR-39 or apocynin, or oxypurinol plus PR39 during the period of EtOH-PC on Day 1 followed by I/R on Day 2. In separate groups of mice, oxypurinol or apocynin were also administered 1 h after ethanol ingestion on Day 1, with induction of I/R 24 h later. I/R induced marked increases in leukocyte rolling and adherence, effects that were completely prevented by EtOH-PC. Coincident treatment with Mn-TBAP, oxypurinol, PR-39, apocynin, or oxypurinol plus PR-39 with ethanol attenuated these anti-inflammatory actions of EtOH-PC. However, administration of oxypurinol or apocynin 1 h after ethanol ingestion failed to prevent these protective effects of EtOH-PC. Our results indicate that reactive oxygen species formed during the period of ethanol exposure on Day 1 trigger the development of an anti-inflammatory phenotype that renders the small bowel resistant to the proadhesive effects of I/R 24 h later.

Peroxynitrite enhances astrocytic volume-sensitive excitatory amino acid release via a src tyrosine kinase-dependent mechanism

Volume-regulated anion channels (VRACs) are critically important for cell volume homeostasis, and under pathological conditions contribute to neuronal damage via excitatory amino (EAA) release. The precise mechanisms by which brain VRACs are activated and/or modulated remain elusive. In the present work we explored the possible involvement of nitric oxide (NO) and NO-related reactive species in the regulation of VRAC activity and EAA release, using primary astrocyte cultures. The NO donors sodium nitroprusside and spermine NONOate did not affect volume-activated d-[3H]aspartate release. In contrast, the peroxynitrite (ONOO-) donor 3-morpholinosydnomine hydrochloride (SIN-1) increased volume-dependent EAA release by approx. 80-110% under identical conditions. Inhibition of ONOO- formation with superoxide dismutase completely abolished the effects of SIN-1. Both the volume- and SIN-1-induced EAA release were sensitive to the VRAC blockers NPPB and ATP. Further pharmacological analysis ruled out the involvement of cGMP-dependent reactions and modification of sulfhydryl groups in the SIN-1-inducedmodulation of EAA release. The src family tyrosine kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo [3,4-d]pyrimidine (PP2), but not its inactive analog PP3, abolished the effects of SIN-1. A broader spectrum tyrosine kinase inhibitor tyrphostin A51, also completely eliminated the SIN-1-induced EAA release. Our data suggest that ONOO- up-regulates VRAC activity via a src tyrosine kinase-dependent mechanism. This modulation may contribute to EAA-mediated neuronal damage in ischemia and other pathological conditions favoring cell swelling and ONOO- production.