Effect of sodium selenite-enriched reperfusion solutions on rat cardiac ischemia reperfusion injury

Cardiac surgery often generates oxidative stress leading to ischemia reperfusion injury (I-R). Antioxidants have been shown to prevent this injury and have been added to cardioplegic solutions to assist in recovery. In this study, we tested the effectiveness of sodium selenite in protecting against ischemia reperfusion injury and investigated the mechanisms behind this protection. Hearts from male Wistar rats were subjected to ischemia reperfusion using the Langendorf model. Krebs-Henseleit perfusion solutions were supplemented with 0,0.1, 0.5, 1.0, and 10μM sodium selenite. Hearts were perfused for 30 min and then subjected to 22.5 min of global ischemia followed by 45 min reperfusion. Heart rate, ischemic contracture, end diastolic pressure, and developed ventricular pressure were monitored. At the completion of the experiment, hearts were homogenized and tissue extracts were assayed for glutathione peroxidase (GSH-Px) and thioredoxin reductase (Thx-Red) activity. Sodium selenite, at a concentration of 0.5 μM, demonstrated a protective effect on the recovery of cardiac function following I-R, as evidenced by a lower end diastolic pressure and enhanced recovery of rate pressure product. There was no beneficial effect observed in hearts perfused with 0.1 μM sodium selenite-supplemented buffer, whereas poorer functional recovery was observed in hearts perfused with 10 μM sodium selenite-supplemented buffer. The beneficial effect of sodium selenite was not mediated through increased activity of GSH-Px or Thx-Red. This study demonstrates that the addition of sodium selenite to reperfusion solutions, at an optimal concentration of 0.5 μM, assists in cardiac recovery following ischemia reperfusion.

Myocardial ischemia-reperfusion injury, antioxidant enzyme systems, and selenium : A review

Coronary heart disease (CHD) remains the greatest killer in the Western world, and although the death rate from CHD has been falling, the current increased prevalence of major risk factors including obesity and diabetes, suggests it is likely that CHD incidence will increase over the next 20 years. In conjunction with preventive strategies, major advances in the treatment of acute coronary syndromes and myocardial infarction have occurred over the past 20 years. In particular the ability to rapidly restore blood flow to the myocardium during heart attack, using interventional cardiologic or thrombolytic approaches has been a major step forward. Nevertheless, while 'reperfusion' is a major therapeutic aim, the process of ischemia followed by reperfusion is often followed by the activation of an injurious cascade. While the pathogenesis of ischemia-reperfusion is not completely understood, there is considerable evidence implicating reactive oxygen species (ROS) as an initial cause of the injury.

ROS formed during oxidative stress can initiate lipid peroxidation, oxidize proteins to inactive states and cause DNA strand breaks, all potentially damaging to normal cellular function. ROS have been shown to be generated following routine clinical procedures such as coronary bypass surgery and thrombolysis, due to the unavoidable episode of ischemia-reperfusion. Furthermore, they have been associated with poor cardiac recovery post-ischemia, with recent studies supporting a role for them in infarction, necrosis, apoptosis, arrhythmogenesis and endothelial dysfunction following ischemia-reperfusion. In normal physiological condition, ROS production is usually homeostatically controlled by endogenous free radical scavengers such as superoxide dismutase, catalase, and the glutathione peroxidase and thioredoxin reductase systems. Accordingly, targeting the generation of ROS with various antioxidants has been shown to reduce injury following oxidative stress, and improve recovery from ischemia-reperfusion injury.

This review summarises the role of myocardial antioxidant enzymes in ischemia-reperfusion injury, particularly the glutathione peroxidase (GPX) and the thioredoxin reductase (TxnRed) systems. GPX and TxnRed are selenocysteine dependent enzymes, and their activity is known to be dependent upon an adequate supply of dietary selenium. Moreover, various studies suggest that the supply of selenium as a cofactor also regulates gene expression of these selenoproteins. As such, dietary selenium supplementation may provide a safe and convenient method for increasing antioxidant protection in aged individuals, particularly those at risk of ischemic heart disease, or in those undergoing clinical procedures involving transient periods of myocardial hypoxia.

Effects of ovariectomy and estrogen on ischemia-reperfusion injury in hindlimbs of female rats

The effects of estrogen and ovariectomy on indexes of muscle damage after 2 h of complete hindlimb ischemia and 2 h of reperfusion were investigated in female Sprague-Dawley rats. The rats were assigned to one of three experimental groups: ovariectomized with a 17-estradiol pellet implant (OE), ovariectomized with a placebo pellet implant (OP), or control with intact ovaries (R). It was hypothesized that following ischemia-reperfusion (I/R), muscle damage indexes [serum creatine kinase (CK) activity, calpain-like activity, inflammatory cell infiltration, and markers of lipid peroxidation (thiobarbituric-reactive substances)] would be lower in the OE and R rats compared with the OP rats due to the protective effects of estrogen. Serum CK activity following I/R was greater (P < 0.01) in the R rats vs. OP rats and similar in the OP and OE rats. Calpain-like activity was greatest in the R rats (P < 0.01) and similar in the OP and OE rats. Neutrophil infiltration was assessed using the myeloperoxidase (MPO) assay and immunohistochemical staining for CD43-positive (CD43+) cells. MPO activity was lower (P < 0.05) in the OE rats compared with any other group and similar in the OP and R rats. The number of CD43+ cells was greater (P < 0.01) in the OP rats compared with the OE and R rats and similar in the OE and R rats. The OE rats had lower (P < 0.05) thiobarbituric-reactive substance content following I/R compared with the R and OP rats. Indexes of muscle damage were consistently attenuated in the OE rats but not in the R rats. A 10-fold difference in serum estrogen content may mediate this. Surprisingly, serum CK activity and muscle calpain-like activity were lower (P < 0.05) in the OP rats compared with the R rats. Increases in serum insulin-like growth factor-1 content (P < 0.05) due to ovariectomy were hypothesized to account for this finding. Thus both ovariectomy and estrogen supplementation have differential effects on indexes of I/R muscle damage.

The effects of escitalopram on myocardial apoptosis and the expression of Bax and Bcl-2 during myocardial ischemia/reperfusion in a model of rats with depression

BackgroundMajor depressive disorder (MDD) is an independent risk factor for coronary heart disease (CHD), and influences the occurrence and prognosis of cardiovascular events. Although there is evidence that antidepressants may be cardioprotective after acute myocardial infarction (AMI) comorbid with MDD, the operative pathophysiological mechanisms remain unclear. Our aim was therefore to explore the molecular mechanisms of escitalopram on myocardial apoptosis and the expression of Bax and Bcl-2 in a rat model of depression during myocardial ischemia/reperfusion (I/R).MethodsRats were divided randomly into 3 groups (n = 8): D group (depression), DI/R group (depression with myocardial I/R) and escitalopram + DI/R group. The rats in all three groups underwent the same chronic mild stress and separation for 21 days, at the same time, in the escitalopram + DI/R group, rats were administered escitalopram by gavage (10 mg/kg/day). Ligation of the rat¿s left anterior descending branch was done in the myocardial I/R model. Following which behavioral tests were done. The size of the myocardial infarction was detected using 1.5% TTC dye. The Tunel method was used to detect apoptotic myocardial cells, and both the Rt-PCR method and immunohistochemical techniques were used to detect the expression of Bcl¿2 and Bax.ResultsCompared with the D and DI/R groups, rats in Escitalopram + DI/R group showed significantly increased movements and sucrose consumption (P < .01). Compared with the DI/R group, the myocardial infarct size in the escitalopram + DI/R group was significantly decreased (P < .01). Compared with the D group, there were significantly increased apoptotic myocardial cells in the DI/R and escitalopram + DI/R groups (P < .01); however compared with the DI/R group, apoptotic myocardial cell numbers in the escitalopram + DI/R group were significantly decreased (P < .01). Compared with the DI/R group, there was a down-regulated Bax:Bcl-2 ratio in the escitalopram + DI/R group (P < .01).ConclusionsThese results suggest that in patients with AMI comorbid with MDD, there is an increase in pro-apoptotic pathways that is reversed by escitalopram. This suggests that clinically escitalopram may have a direct cardioprotective after acute myocardial infarction.

Effects of dietary selenium on post-ischemic expression of antioxidant mRNA

Cardiac ischemia reperfusion leads to oxidative stress and poor physiological recovery. Selenium deficiency down-regulates thioredoxin reductase (Txnrd) and glutathione peroxidase (Gpx) activity, impairing recovery from ischemia-reperfusion. Furthermore, selenium supplementation has been shown to be cardioprotective and lessens oxidative stress in reperfused rat hearts. In this study we have investigated the role of selenium in the mRNA expression of these, and related antioxidant proteins, post ischemia-reperfusion. Male rats were fed varying doses of selenium for five weeks. Hearts were isolated and perfused using the Langendorff method with 22.5 min of global ischemia and 45 min reperfusion. RNA was extracted for quantitative real-time PCR analysis of glutathione peroxidase (Gpx)-1 and 4, glutathione reductase (Gsr), thioredoxin peroxidase-2 (Prdx2), thioredoxin (Txn) and thioredoxin reductase (Txnrd)-1 and 2 gene expression. Selenium deficiency produced significant reductions in Gpx-1, Gpx-4, Prdx2, Txnrd-1 and Txnrd-2 expression. Conversely, selenium supplementation of 1000 μg/kg significantly up-regulated Gpx-1, Gpx-4, Txn, Txnrd-1 and Txnrd-2 transcription. Our results show selenium modulates the cardiac mRNA expression of thioredoxin and glutathione related enzymes post ischemia-reperfusion, and impacts on tolerance to ischemia-reperfusion.

Intrinsic resistance of female hearts to an ischemic insult is abrogated in primary cardiac hypertrophy

Important sex differences in cardiovascular disease outcomes exist, including conditions of hypertrophic cardiomyopathy and cardiac ischemia. Studies of sex differences in the extent to which load-independent (primary) hypertrophy modulates the response to ischemia-reperfusion (I/R) damage have not been characterized. We have previously described a model of primary genetic cardiac hypertrophy, the hypertrophic heart rat (HHR). In this study the sex differences in HHR cardiac function and responses to I/R [compared to control normal heart rat (NHR)] were investigated ex vivo. The ventricular weight index was markedly increased in HHR female (7.82 ± 0.49 vs. 4.80 ± 0.10 mg/g; P < 0.05) and male (5.76 ± 0.22 vs. 4.62 ± 0.07 mg/g; P < 0.05) hearts. Female hearts of both strains exhibited a reduced basal contractility compared with strain-matched males [maximum first derivative of pressure (dP/dtmax): NHR, 4,036 ± 171 vs. 4,258 ± 152 mmHg/s; and HHR, 3,974 ± 160 vs. 4,540 ± 259 mmHg/s; P < 0.05]. HHR hearts were more susceptible to I/R (I = 25 min, and R = 30 min) injury than NHR hearts (decreased functional recovery, and increased lactate dehydrogenase efflux). Female NHR hearts exhibited a significantly greater recovery (dP/dtmax) post-I/R relative to male NHR (95.0 ± 12.2% vs. 60.5 ± 9.4%), a resistance to postischemic dysfunction not evident in female HHR (29.0 ± 5.6% vs. 25.9 ± 6.3%). Ventricular fibrillation was suppressed, and expression levels of Akt and ERK1/2 were selectively elevated in female NHR hearts. Thus the occurrence of load-independent primary cardiac hypertrophy undermines the intrinsic resistance of female hearts to I/R insult, with the observed abrogation of endogenous cardioprotective signaling pathways consistent with a potential mechanistic role in this loss of protection.

Auranofin increases apoptosis and ischaemia-reperfusion injury in the rat isolated heart

1. Auranofin, an antirheumatic gold compound, is an inhibitor of selenocysteine enzymes, such as thioredoxin reductase and glutathione peroxidase. These enzymes play an important role in protecting cardiac tissue from oxidative stress generated during ischaemia–reperfusion.

2. Auranofin (100 mg/kg) was administered to rats and their hearts were subjected to an in vitro model of ischaemia–reperfusion. The activity of thioredoxin reductase and glutathione peroxidase was determined in liver and heart tissues in an attempt to correlate enzymatic activity with heart recovery after ischaemia–reperfusion.

3. There was significantly less thioredoxin reductase activity in rat liver extracts, whereas the level of glutathione activity remained unchanged, demonstrating that the dose of auranofin used was able to selectively inhibit one of these enzyme systems. Rats administered auranofin displayed significantly impaired recovery from ischaemic insult. The end diastolic pressure was increased, whereas the rate pressure product was significantly decreased.

4. The level of postischaemic apoptosis was also assessed by examining caspase-3 activity in tissue homogenates. Auranofin significantly increased the degree of postischaemic apoptosis, leading to poor postischaemic recovery.