The cardioprotective effect of S. africana caerulea/Blue Sage in ischaemia and reperfusion induced oxidative stress

Background: Since antiquity, alternative herbal remedies, such as S. africana caerulea/Blue Sage (BLS) water infusion extract (WIE) has been used by traditional healers, for the effective treatment of various chronic inflammatory disorders associated with reduced cellular antioxidant defense mechanisms and free radical cellular damage. In the heart, ischaemia-reperfusion (I/R) induced oxidative stress becomes an early crucial event in the pathogenesis of ischaemia-reperfusion injury (I/RI) and subsequent heart failure. Purpose/Aim: To investigate whether BLS WIE treatment during ischaemia and/or reperfusion may be cardioprotective. Study design: Isolated perfused rat hearts were exposed to 35 min regional ischaemia (RI) and 60 min reperfusion. The BLS WIE was applied: i) for the last 10 min of RI (PerT) or ii) from onset of reperfusion (PostT) or iii) both (PerT) + (PostT). Methods: Endpoints were functional recovery and infarct size (IS). In another set of experiments, left ventricles were freeze-clamped after RI and 10 min reperfusion for detection of total and phosphorylated p-ERK p44/p42, p-Akt, p-p38-MAPK, p-JNK, Nrf-2, NF-kB, Bax, Bcl-2, Caspase-3, and PGC-1α by Western blot analysis. Results: BLS (PostT) significantly increased ERK p44, p-Akt, Nrf-2, and Bcl-2 levels; significantly decreased p-p38-MAPK as well as p-JNK p46 phosphorylation; did not affect Bax levels and significantly decreased Bax/Bcl-2 ratios. This was associated with significantly reduced Caspase-3 levels and increased PGC-1α phosphorylation, particlarly when BLS WIE was administered as PostT. Conclusion: The administration of polyphenol-rich BLS WIE at different stages of ischaemia and/or reperfusion, activate/inhibit several signaling events simultaneously and mediate cardioprotection in a multitarget manner.

Cardioprotective Effects of Beta3-Adrenergic Receptor (β3-AR) Pre-, Per-, and Post-treatment in Ischemia-Reperfusion

The β3-AR (beta3-adrenergic receptor) is resistant to short-term agonist-promoted desensitization and delivers a constant intracellular signal, making this receptor a potential target in acute myocardial infarction (AMI).

AIM

To investigate whether selective modulation of β3-AR prior to or during ischemia and/or reperfusion may be cardioprotective.

METHODS

Isolated perfused rat hearts were exposed to 35-min regional ischemia (RI) and 60-min reperfusion. The β3-AR agonist (BRL37344, 1 μM) or antagonist (SR59230A, 0.1 μM) was applied: (i) before RI (PreT) or (ii) last 10 min of RI (PerT) or (iii) onset of reperfusion (PostT) or (iv) during both PerT+PostT. Nitric oxide (NO) involvement was assessed, using the NOS inhibitor, L-NAME (50 μM). Endpoints were functional recovery, infarct size (IS), cGMP levels, and Western blot analysis of eNOS, ERKp44/p42, PKB/Akt, and glycogen synthase kinase-3β (GSK-3β).

RESULTS

Selective treatment with BRL significantly reduced IS. L-NAME abolished BRL-mediated cardioprotection. BRL (PreT) and BRL (PerT) significantly increased cGMP levels (which were reduced by L-NAME) and PKB/Akt phosphorylation. BRL (PostT) produced significantly increased cGMP levels, PKB/Akt, and ERKp44/p42 phosphorylation. BRL (PerT+PostT) caused significant eNOS, PKB/Akt, ERKp44/p42, and GSK-3β phosphorylation.

CONCLUSION

β3-AR activation by BRL37344 induced significant cardioprotection regardless of the experimental protocol. However, the pattern of intracellular signaling with each BRL treatment differed to some degree and suggests the involvement of cGMP, eNOS, ERK, GSK-3β, and particularly PKB/Akt activation. The data also suggest that clinical application of β3-AR stimulation should preferably be incorporated during late ischemia or/and early reperfusion.

Melatonin has profound effects on mitochondrial dynamics in myocardial ischaemia/reperfusion

Research focus recently shifted to mitochondrial dynamics and the role of fusion and fission in cardioprotection. The aim of this study was to evaluate (i) the function and dynamics of mitochondria isolated from hearts exposed to ischaemia/reperfusion (I/R) (ii) the effects of melatonin, a powerful cardioprotectant, on mitochondrial dynamics in I/R. Isolated perfused rat hearts were stabilized for 30 min, subjected to 20 min global ischaemia, followed by 30 min reperfusion. Tissue was collected, mitochondria isolated for measurement of mitochondrial oxidative function and lysates from mitochondrial and cytosolic fractions prepared for western blotting. Melatonin (0.3 or 50 μM) was administered for 10 min immediately before the onset of ischaemia and for 10 min at the onset of reperfusion. Infarct size was assessed after 35 min regional ischaemia/60 min reperfusion using triphenyltetrazolium staining. The results show that reperfusion significantly reduced mitochondrial QO2 (states 3 and 4), with minor effects by melatonin. Cytosolic Beclin 1 and the LC3 II/I ratio were reduced by ischaemia and increased by reperfusion. Both ischaemia and reperfusion reduced mitochondrial PINK1 and Parkin levels, while reperfusion increased p62. An alternative mitophagy pathway mediated by Rab9 is activated during myocardial ischaemia/reperfusion. Ischaemia reduced and reperfusion increased cytosolic ULK1 expression, associated with redistribution of Rab9 and Drp1 between the cytosol and mitochondria. Melatonin significantly reduced mitochondrial p62 expression upon reperfusion. Throughout the protocol, melatonin significantly (i) increased cytosolic total (t) and phospho (p) ULK1, and Rab9 levels (ii) increased the cytosolic and reduced the mitochondrial pDrp1 levels and p/t Drp1 ratio, suggesting inhibition of mitochondrial fission. Fusion was affected to a lesser extent. Cardioprotection by melatonin is associated with substantial effects on mitophagy, the significance thereof remains to be established.

Antiretroviral drug-induced endothelial dysfunction is improved by dual PPARα/γ stimulation in obesity

Obesity rates are rising in HIV-infected populations; however, the putative role of highly active antiretroviral therapy (HAART) in the development of endothelial and cardiovascular derangements in the presence of pre-existing overweight/obesity is unclear. Although dual peroxisome proliferator-activated receptors-alpha/gamma (PPARα/γ) stimulation mitigates HAART-induced metabolic dysfunction, vascular effects are unresolved. To investigate whether HAART induces vascular dysfunction in obesity and to explore the underlying mechanisms of PPARα/γ stimulation, male Wistar rats were placed on a high-calorie diet for 16 weeks. After 10 weeks, HAART (lopinavir/ritonavir, azidothymidine/lamivudine) with/without PPARα/γ agonist, Saroglitazar, was administered daily for six weeks. Excised thoracic aorta rings were subjected to isometric tension studies and Western blot measurements. HAART+Saroglitazar-treated obese animals recorded lower adiposity indices (4.3 ± 0.5%) vs. HAART only-treated obese rats (5.6 ± 0.3%; p < .01). Maximum acetylcholine-induced vasorelaxation (R_max), was lower in obese+HAART group (76.10 ± 3.58%) vs. obese control (101.40 ± 4.75%; p < .01). However, R_max was improved in obese+ HAART+Saroglitazar (101.00 ± 3.12%) vs. obese+HAART rats (p < .001). The mean LogEC₅₀ was improved in obese+HAART+Saroglitazar vs. obese+HAART group; p = .003. Improved endothelial function in obese+ HAART+Saroglitazar group was associated with upregulation of eNOS, PKB/Akt and downregulated p22-phox expression vs. obese+HAART group. Therefore, PPARα/γ stimulation attenuated HAART-induced endothelial dysfunction by upregulating vasoprotective eNOS, PKB/Akt signaling and downregulating pro-oxidative p22-phox expression.

The significance of the washout period in preconditioning

AIMS

Exposure of the heart to 5 min global ischaemia (I) followed by 5 min reperfusion (R) (ischaemic preconditioning, IPC) or transient Beta 2-adrenergic receptor (B2-AR) stimulation with formoterol (B2PC), followed by 5 min washout before index ischaemia, elicits cardioprotection against subsequent sustained ischaemia. As the washout period during preconditioning is essential for subsequent cardioprotection, the aim of this study was to investigate the involvement of protein kinase A (PKA), reactive oxygen species (ROS), extracellular signal-regulated kinase (ERK), PKB/Akt, p38 MAPK and c-jun N-terminal kinase (JNK) during this period.

METHODS

Isolated perfused rat hearts were exposed to IPC (1x5min I / 5min R) or B2PC (1x5min Formoterol / 5min R) followed by 35 min regional ischaemia and reperfusion. Inhibitors for PKA (Rp-8CPT-cAMP)(16μM), ROS (NAC)(300μM), PKB (A-6730)(2.5μM), ERKp44/p42 (PD98,059)(10μM), p38MAPK (SB239063)(1μM) or JNK (SP600125)(10μM) were administered for 5 minutes before 5 minutes global ischaemia / 5 min reperfusion (IPC) or for 5 minutes before and during administration of formoterol (B2PC) prior to regional ischaemia, reperfusion and infarct size (IS) determination. Hearts exposed to B2PC or IPC were freeze-clamped during the washout period for Western blots analysis of PKB, ERKp44/p42, p38MAPK and JNK.

RESULTS

The PKA blocker abolished both B2PC and IPC, while NAC significantly increased IS of IPC but not of B2PC. Western blot analysis showed that ERKp44/p42 and PKB activation during washout after B2PC compared to IPC was significantly increased. IPC compared to B2PC showed significant p38MAPK and JNKp54/p46 activation. PKB and ERK inhibition or p38MAPK and JNK inhibition during the washout period of B2PC and IPC respectively, significantly increased IS.

CONCLUSION

PKA activation before regional ischaemia is a prerequisite for cardioprotection in both B2PC and IPC. However, ROS was crucial only in IPC. Kinase activation during the washout phase of IPC and B2PC, albeit different, affords the same cardioprotective response.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

High carbohydrate and high fat diets protect the heart against ischaemia/reperfusion injury

Background

Although obesity is still considered a risk factor in the development of cardiovascular disorders, recent studies suggested that it may also be associated with reduced morbidity and mortality, the so-called “obesity paradox”. Experimental data on the impact of diabetes, obesity and insulin resistance on myocardial ischaemia/reperfusion injury are controversial. Similar conflicting data have been reported regarding the effects of ischaemic preconditioning on ischaemia/reperfusion injury in hearts from such animals. The aim of the present study was to evaluate the susceptibility to myocardial ischaemia/reperfusion damage in two models of diet-induced obesity as well as the effect of ischaemic and pharmacological preconditioning on such hearts.

Methods

Three groups of rats were fed with: (i) normal rat chow (controls) (ii) a sucrose-supplemented diet (DIO) (iii) a high fat diet (HFD). After 16 weeks, rats were sacrificed and isolated hearts perfused in the working mode and subjected to 35 min regional ischaemia/60 min reperfusion. Endpoints were infarct size and functional recovery. Infarct size was determined, using tetrazolium staining. Activation of PKB/Akt and ERKp44/p42 (RISK pathway) during early reperfusion was determined using Western blot. Statistical evaluation was done using ANOVA and the Bonferroni correction.

Results

Infarct sizes of non-preconditioned hearts from the two obese groups were significantly smaller than those of the age-matched controls. Ischaemic as well as pharmacological (beta-adrenergic) preconditioning with a beta2-adrenergic receptor agonist, formoterol, caused a significant reduction in infarct size of the controls, but were without effect on infarct size of hearts from the obese groups. However, ischaemic as well as beta-preconditioning caused an improvement in functional performance during reperfusion in all three groups. A clear-cut correlation between the reduction in infarct size and activation of ERKp44/p42 and PKB/Akt was not observed: The reduction in infarct size observed in the non-preconditioned hearts from the obese groups was not associated with activation of the RISK pathway. However, beta-adrenergic preconditioning caused a significant activation of ERKp44/p42, but not PKB/Akt, in all three groups.

Conclusions

Relatively long-term administration of the two obesity-inducing diets resulted in cardioprotection against ischaemia/reperfusion damage. Further protection by preconditioning was, however, without effect on infarct size, while an improvement in functional recovery was observed.

The cardioprotective effect of an aqueous extract of fermented rooibos (Aspalathus linearis) on cultured cardiomyocytes derived from diabetic rats

Diabetic cardiomyopathy (DCM) is a disorder of the heart muscle that contributes to cardiovascular deaths in the diabetic population. Excessive generation of free radicals has been directly implicated in the pathogenesis of DCM. The use of antioxidants, through dietary supplementation, to combat increased cellular oxidative stress has gained popularity worldwide. Aspalathus linearis (rooibos) is a popular herbal tea that contains a novel antioxidant, aspalathin. Literature has reported on the antidiabetic, anti-inflammatory and free radical scavenging effects of rooibos. However, its protective effect against DCM has not been established. Therefore, this study investigated whether chronic exposure to an aqueous extract of fermented rooibos (FRE) has an ex vivo cardioprotective effect on hearts obtained from streptozotocin (STZ) induced diabetic rats. Adult Wistar rats were injected with 40 mg/kg of STZ. Two weeks after STZ injection, cardiomyocytes were isolated and cultured. Cultured cardiomyocytes were treated with FRE (1 and 10 μg/ml), vitamin E (50 μg/ml), and n-acetyl cysteine (1mM) for 6h, before exposure to either hydrogen peroxide (H2O2) or an ischemic solution. Cardiomyocytes exposed to H2O2 or an ischemic solution showed a decrease in metabolic activity and glutathione content with a concomitant increase in apoptosis and intracellular reactive oxygen species. Pretreatment with FRE was able to combat these effects and the observed amelioration was better than the known antioxidant vitamin E. This study provides evidence that an aqueous extract of fermented rooibos protects cardiomyocytes, derived from diabetic rats, against experimentally induced oxidative stress and ischemia.

Abstract 181: β-Adrenergic Preconditioning Is Adenosine Mediated

This study investigated the roles of adenosine, oxygen free radicals (ROS), the K + ATP channels and the PI 3 K/PKB/Akt and ERK signal transduction pathways during the triggering and mediation phases of beta-adrenergic preconditioning (BPC)

Methods : Using the isolated working rat heart, BPC was elicited by administration of denopamine (B 1 receptor agonist, 10 -7 M), isoproterenol (B 1 /B 2 receptor agonist, 10 -7 M) or formoterol (B 2 receptor agonist, 10 -9 M) for 5 min followed by 5 min washout. Index ischemia was 35 min regional ischemia followed by 2h reperfusion and infarct size was determined with the tetrazolium method. The role of adenosine was studied using selective adenosine receptor antagonists. Involvement of ROS, PKC, the mitochondrial K + ATP channels, endogenous opioids and bradykinin was studied by using N-acetyl cysteine (NAC), bisindolylmaleimide, 5-HD, naloxone or HOE140, respectively. Wortmannin and PD98,059 were used to inhibit PI 3 K and ERK respectively. Phosphorylation of these kinases was determined by Western blot.

Results: Preconditioning with all three B-adrenergic receptor agonists caused a significant (40-60%) reduction in infarct size and improvement in postischemic function. BPC with isoproterenol and denopamine was abolished by the adenosine A 3 receptor antagonist MRS1191 during both the triggering and mediation phases, while being effective during reperfusion only in formoterol preconditioned heart s. B 1 /B 2 PC was attenuated by MRS1754 (adenosine A 2B receptor antagonist) during the triggering and mediation phases. The mediation phase of B 1 /B 2 PC was also abolished by ZM241385 (A 2A receptor blocker). The adenosine A 1 receptor blocker, DPCPX, was without effect. The ROS scavenger NAC caused a significant attenuation of cardioprotection induced by all three B-adrenergic receptor agonists. 5-HD, naloxone and Hoe140 were without effect on BPC. Activation of ERK and PI3K/PKB/Akt during both triggering and reperfusion phases are required for cardioprotection.

Conclusion: BPC in rat hearts is dependent on activation of the A 3 adenosine receptors by endogenous adenosine and production of free radicals during the triggering and mediation phases while the A 2A and A 2B receptors participate mainly during reperfusion.

The mechanism of beta-adrenergic preconditioning: roles for adenosine and ROS during triggering and mediation

The aim of this study was to investigate the mechanism of beta-adrenergic preconditioning (BPC). The roles of adenosine and its receptor subtypes, the generation of oxygen free radicals (ROS) and activation of the K(ATP) channels as well as the phosphoinositide-3-kinase (PI(3)K)/PKB/Akt and extracellular signal-regulated kinase (ERK) signal transduction pathways during the triggering and mediation phases were evaluated. Using the isolated working rat heart, BPC was elicited by administration of denopamine (beta1 adrenergic receptor agonist, 10(-7) M), isoproterenol (beta1/beta2 adrenergic receptor agonist, 10(-7) M) or formoterol (beta2 adrenergic receptor agonist, 10(-9) M) for 5 min followed by 5 min washout. Index ischaemia was 35 min regional ischaemia and infarct size determined using the tetrazolium method. The role of adenosine was studied using adenosine deaminase and selective antagonists as well as the PI(3)K and ERK inhibitors, wortmannin and PD98,059, bracketing the triggering and mediating phases. Involvement of ROS, PKC, the mitochondrial K(ATP) channels, release of endogenous opioids and bradykinin was studied by administration of N-acetyl cysteine (NAC), bisindolylmaleimide, the K(ATP) channel blocker 5-hydroxydecanoate (5-HD), naloxone or HOE140, respectively. Activation of PKB/Akt and ERKp44/p42 during triggering and reperfusion was determined by Western blot. Preconditioning with all three beta-adrenergic receptor agonists caused a reduction in infarct size and an improvement in postischaemic function. BPC preconditioning with isoproterenol, denopamine or formoterol was abolished by the adenosine A3 receptor antagonist MRS1191 during both the triggering and mediation phases. Isoproterenol-induced preconditioning (beta1/beta2 PC) was attenuated by MRS1754, an adenosine A(2B) receptor antagonist, during the triggering phase and abolished during reperfusion. The mediation phase of beta1/beta2 PC was also abolished by ZM241385, an adenosine A(2A) antagonist. The free radical scavenger NAC caused a significant attenuation of cardioprotection induced by isoproterenol when administered during both trigger and mediation phases, while being effective during the trigger phase with denopamine and during reperfusion in formoterol preconditioned hearts. The mitochondrial K(ATP) channel blocker, 5-HD, was without effect on beta1/beta2 PC during both triggering and mediation phases. BPC in rat hearts is dependent on activation of the A(3) adenosine receptors by endogenously produced adenosine and production of free radicals during the triggering and mediation phases while the A(2A) and A(2B) adenosine receptors participate mainly during reperfusion. The mitochondrial K(ATP) channels do not contribute to cardioprotection at any stage. Activation of ERK and PI3K/PKB/Akt during the triggering and reperfusion phases is associated with cardioprotection.

Effect of sildenafil on reperfusion function, infarct size, and cyclic nucleotide levels in the isolated rat heart model

We have previously shown that NO-donor induced elevation in myocardial cGMP levels is associated with improved reperfusion function of the isolated rat heart. The phosphodiesterase 5 (PDE 5) inhibitor, sildenafil could potentially increase myocardial cGMP levels and thus protect the heart against ischaemic/reperfusion injury.

METHODS

To test our hypothesis we treated the isolated working rat heart with vehicle, OR sildenafil (10, 20, 50, 100, 200 nM), OR sildenafil (50 nM) plus a sarcolemmal (HMR 1098) or a mitochondrial (5-Hydroxydecanoate (5-HD)) K(ATP) channel blocker. Hearts were then subjected to 20 min global, or 35 min regional ischaemia at 37( composite function)C before reperfusion function (aortic output, coronary flow and aortic pressure) and infarct size were documented. Pre-ischaemic, ischaemic and reperfusion myocardial cAMP and cGMP concentrations were determined.

RESULTS

Low concentrations of sildenafil (10, 20 and 50 nM) improved reperfusion aortic output (AO) recovery (61.4+/- 4.5%, 64.8 +/- 5.2% and 62.3 +/- 5.0% vs. 45.4 +/- 3.8% for controls (p < 0.05)) and infarct size, while high concentrations (200 nM) worsened AO recovery (24.9 +/- 4.9.0%, p < 0.05). Myocardial cGMP levels of ischaemic tissue were elevated (34.7 +/- 2.4 vs. 27.3 +/- 2.2 pmol/g ww) and cAMP levels were suppressed (0.59 +/- 0.03 vs. 0.87 +/- 0.06 nmol/g ww) in the sildenafil (50 nM) treated hearts. Co-perfusion with sildenafil plus HMR 1098 decreased AO recovery (21.7 +/- 7.6% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (29.7 +/- 2.04% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05).Similarly, sildenafil plus 5-HD decreased reperfusion AO recovery (44.4 +/- 6.0% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (33.8 +/- 1.62% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05).

CONCLUSIONS

(1) Pretreatment with low concentrations of sildenafil (20-50 nM) improves, while higher concentrations (200 nM) worsen reperfusion function in this model. (2) Low concentrations of sildenafil (20-50 nM) decrease infarct size while the higher concentrations had no effect. (3) These protective properties of low concentrations of sildenafil may be related to its cGMP elevating and cAMP suppressing effects in the ischaemic heart. (4) Possible end-effectors for sildenafil in the ischaemic heart include the mitochondrial and sarcolemmal K(ATP) channel.

The temporal relationship between p38 MAPK and HSP27 activation in ischaemic and pharmacological preconditioning

An ischaemic preconditioning protocol and subsequent sustained ischaemia were characterized by activation and attenuation of p38 MAPK phosphorylation, respectively. However, the significance of events downstream of p38 MAPK needs investigation. Therefore the temporal relationship between phosphorylation of p38 MAPK and its downstream substrate HSP27 was studied during either an ischaemic or beta-adrenergic preconditioning protocol and during sustained ischaemia. Isolated rat hearts were preconditioned (with or without a p38 MAPK inhibitor, SB203580) with 1 x 5 min or 3 x 5 min global ischaemia or 5 min beta-adrenergic stimulation (10(-7) M isoproterenol), followed by 25 min sustained ischaemia and 30 min reperfusion. Hearts were freeze-clamped at different time intervals and fractionated to determine p38 MAPK and HSP27 phosphorylation, via Western blotting. Significant phosphorylation of cytosolic p38 MAPK and membrane (myo-fibrillar) HSP27 occurred at the end of the first preconditioning episode. However, p38 MAPK phosphorylation disappeared during subsequent preconditioning episodes, while HSP27 phosphorylation was maintained for the duration of the protocol. Similar changes in p38 MAPK and HSP27 occurred with 5 min beta-adrenergic preconditioning. After 25 min ischaemia, significant phosphorylation of cytosolic and membrane HSP27 was observed, while p38 MAPK phosphorylation was attenuated in ischaemic and beta-adrenergic preconditioned compared to non-preconditioned hearts. SB203580-induced abolishment of p38 MAPK and HSP27 phosphorylation during the triggering phase of both preconditioning protocols reversed the changes in these parameters seen after sustained ischaemia. The results suggest that p38 MAPK activation triggers HSP27 phosphorylation during both the preconditioning protocols and during sustained ischaemia. Protection of preconditioned hearts during sustained ischaemia was characterized by phosphorylation of both cytosolic and myofibrillar HSP27.

A mechanism for zinc toxicity in neuroblastoma cells

Zinc is an important component of proteins essential for normal functioning of the brain. However, it has been shown in vitro that this metal, at elevated levels, can be toxic to cells leading to their death. We investigated possible mechanisms of cell death caused by zinc: firstly, generation of reactive oxygen species, and secondly, the activation of the MAP-kinase pathway. Cell viability was assessed by means of the methyl-thiazolyl tetrazolium salt (MTT) assay and confirmed by tetramethylrhodamine methyl ester (TMRM) staining. We measured the phosphorylation status of Erk and p38 as indicators of MAP-kinase activity, using Western Blot techniques. A time curve was established when neuroblastoma (N2alpha) cells were exposed to 100 microM of zinc for 4, 12, and 24 h. Zinc caused a significant reduction in cell viability as early as 4 h, and indirectly stimulated the accumulation of reactive oxygen species as determined by 2.7 dichlorodihydrofluorescein diacetate (DCDHF) staining and confocal microscopy. Investigation of the MAP-kinase pathway indicated that Erk was downregulated, while p38 was stimulated. Our results therefore led us to conclude that in vitro, zinc toxicity involved the generation of reactive oxygen species and the activation of the MAP-kinase pathway.

The role of the MAP-kinase superfamily in beta-amyloid toxicity

The mitogen-activated protein kinase (MAP kinase) pathway participates in a number of reactions of the cell when responding to various external stimuli. These stimuli include growth factor binding to its receptor as well as stressful situations such as hypoxia and oxidative stress. It has been postulated that one of the mechanisms by which beta-amyloid exerts its toxic effects is to produce oxidative stress. This study therefore investigated whether the MAP-kinase pathway was activated in cells following exposure to beta-amyloid. Neuroblastoma (N2alpha) cells were used in all experiments. The cells were exposed to 50, 100, and 500 microM glutamate, and 10, 30, and 50 microM beta-amyloid, for 24 h. The methylthiazolyl tetrazolium salt (MTT) assay was performed to determine the degree of toxicity. The generation of hydrogen peroxide was detected by fluorescence microscopy using the dye dihydrochlorofluorescein diacetate (DCDHF). Extracellular-signal-regulated kinase (ERK) and p38 MAP-kinase phosphorylation, as representatives of the MAP-kinase pathway, was determined. Treating N2alpha cells with beta-amyloid resulted in a greater than 50% reduction in cell viability. These cells also showed a significantly higher presence of hydrogen peroxide. Western Blot analysis revealed that the phosphorylation of p38 MAP kinase was dose-dependently increased in cells exposed to glutamate and beta-amyloid. On the other hand, the phosphorylation of ERK was significantly reduced in these cells. These data therefore suggest that the toxic effects of beta-amyloid involve the generation of hydrogen peroxide, leading to the activation of p38 and the down-regulation of ERK.

Melatonin protects against ischaemic-reperfusion myocardial damage

OBJECTIVES

Melatonin, a hormonal product of the pineal gland, is now known to be a multi-faceted free radical scavenger and anti-oxidant. Since little information is available regarding the action of melatonin on the heart, we studied the effects of melatonin on adult ventricular myocytes subjected to chemical hypoxia and reoxygenation.

METHODS

Adult rat ventricular myocytes were preloaded with tetramethylrhodamine (TMRM) in combination with one of the following fluorophores: dichlorodihydrofluorescein diacetate (DCDHF), dihydrorhodamine 123 (DHR) or fluo 3 (Fluo) and then investigated with confocal laser scanning microscopy. Chemical hypoxia was induced by addition of 1.5 mM KCN and 20 mM deoxyglucose to the superfusion buffer. Melatonin (50-100 microM) was added at intervals during the protocol.

RESULTS

Cells subjected to 12.5 min chemical hypoxia showed marked morphological changes, increased fluorescence intensity of DCDHF, DHR and Fluo, suggesting Ca2+ accumulation and generation of H2O2 and reactive oxygen species. The number of cells showing increased fluorescence also increased significantly. Melatonin (50 and 100 microM) caused a significant reduction in morphological changes, number of cells with increased fluorescence and fluorescence intensity of DHR and Fluo, (but not DCDHF).

CONCLUSION

Melatonin effectively reduced damage induced by chemical hypoxia in adult cardiomyocytes, probably by virtue of its effects on reactive oxygen species generation and intracellular Ca2+ accumulation.

Halothane protects the isolated rat myocardium against excessive total intracellular calcium and structural damage during ischemia and reperfusion

A recent study from our laboratory demonstrated halothane to be a powerful protectant of the isolated rat heart during reperfusion after normothermic cardioplegic arrest. It was speculated that this protective effect might be due to prevention of excessive intracellular calcium. The aim of the present study was to evaluate the effect of halothane on the total intracellular calcium (Ca2+) content and on myocardial structure both at the end of normothermic cardioplegic arrest and at the end of reperfusion. Isolated perfused rat hearts were perfused for a control period of 30 min, followed by 40 min of normothermic cardioplegic arrest with or without reperfusion for 30 min. Halothane (1.5%) was administered continuously before and after arrest. Halothane caused a significant decrease of intracellular Ca2+ at the end of normothermic cardioplegic arrest and after reperfusion. Myocardial morphology was assessed by extensive light microscopy and ultrastructure was evaluated by electron microscopy. Grading of ischemic damage showed that exposure to normothermic cardioplegia resulted in marked ischemic injury, regardless of whether the hearts were treated with halothane. Reperfusion in the presence of halothane caused a significant reversal of ischemic damage and almost complete ultrastructural repair, whereas untreated hearts still exhibited severe edema, contracture, and contracture bands. Our results indicate that the beneficial effects of halothane on myocardial structural recovery during reperfusion is associated with a reduction in excessive intracellular Ca2+. The exact mechanism of this protective action is under investigation.

Effect of captopril on changes in rats' hearts induced by long-term irradiation

The aim of this study was to test the efficacy of captopril, an angiotensin-converting enzyme inhibitor and a known suppressor of fibrosis, in preventing late radiation-induced cardiac pathology. Myocardial functional, histochemical and ultrastructural-morphometric studies were done on perfused hearts of rats isolated 3 and 6 months after 60Co gamma irradiation with 20 Gy and age-matched controls. At each time the animals were divided into the following groups: nonirradiated controls; irradiated once with 20 Gy; irradiated as above and given daily doses of captopril; daily doses of captopril without irradiation. The results showed that captopril, while ameliorating the decrease in the indices of capillary function, increase in mast cells, fibrosis, number of atrial granules, and changes in nerve terminals, failed to prevent the progressive functional deterioration of the hearts after irradiation. These findings suggest that an intramyofiber derangement may be involved in the long-term myocardial complications of irradiation.