Glycine protects cardiomyocytes against lethal reoxygenation injury by inhibiting mitochondrial permeability transition

Remifentanil preconditioning confers delayed cardioprotection in the rat †

BACKGROUND

Preconditioning with remifentanil (RPC) provides immediate cardioprotection in rats via all three types of opioid (OP) receptor. This study sought to investigate whether remifentanil also confers delayed cardioprotection via OP receptors.

METHODS

Male rats received preconditioning either by ischaemia (IPC; 5 min occlusion, 5 min reperfusion x 3) or with remifentanil (RPC; 1, 5, 10, and 20 microg kg(-1) min(-1), 20 min infusion). After 24 h, all animals were subjected to 30 min occlusion of the left coronary artery and 2 h of reperfusion. Subsequently, the time-course effect of RPC (10 microg kg(-1) min(-1), 20 min infusion) was determined at 12, 16, 24, 32, 36, and 48 h intervals, using the same experimental procedure. The effect of RPC (10 microg kg(-1) min(-1), 20 min infusion) and IPC in the presence of selective OP receptor antagonists was evaluated at the 24 h interval. Infarct size (IS), as a percentage of the area at risk (AAR), was determined.

RESULTS

Pre-treatment with remifentanil at 1, 5, 10, and 20 microg kg(-1) min(-1) significantly reduced the IS/AAR at 24 h with the maximum effect at 10 microg kg(-1) min(-1). Remifentanil at 10 microg kg(-1) min(-1) significantly reduced the IS at 12 h [32.5 (sd 9.1)%]; 16 h [26.1 (2.8)%]; 24 h [19.5 (5.0)%]; 32 h [31.2 (9.1)%]; and 36 h [36.4 (9.4)%] after drug administration. The maximal reduction in IS was seen at 24 h and the effect completely disappeared at 48 h [36.4 (9.4)%]. The protective effect of RPC was abolished or significantly attenuated by blockade of any of the three OP receptors with selective antagonists.

CONCLUSIONS

Like IPC, remifentanil produces delayed cardioprotection in anaesthetized rats 12-36 h after administration. The protective effect is mediated via all three OP receptors.

Effect of glycine on the calcium signal of thrombin-stimulated platelets

In treatment of hemorrhagic shock, small-volume infusion of 7.5% NaCl gives immediate hemodynamic improvement, but in vitro experiments suggest it depresses the hemostatic system. Since previous reports showed that hyperosmotic glycine solutions preserved the platelet function better than hyperosmotic NaCl solutions, we investigated whether glycine changes the intracellular calcium ([Ca]i) signal. Platelets were incubated in hyperosmotic solutions containing sodium glycine or glycine base and stimulated with 0.1 IU/ml thrombin. [Ca]i increases were compared with an isosmotic control. Platelets incubated in zero calcium/EGTA were used to study separately the effect of glycine on calcium mobilization from intracellular stores and extracellular calcium entry. When NaCl was replaced by sodium glycine, the [Ca]i increase produced by thrombin was enhanced, because the calcium entry increased without changes in the mobilization of stored calcium. The addition of 50 mmol/l glycine base to the HEPES-buffered media increases the thrombin-induced entry of calcium or manganese. This study demonstrates that hyperosmotic glycine solutions increase the entry of calcium. This effect contrasts with the impairment of the thrombin-induced calcium signals by NaCl. The addition of low amounts of glycine in resuscitation solutions would be useful to reduce dysfunctional inflammatory responses without the risk of bleeding; however, concentrated solutions could cause toxic effects.

Heart slice NMR

Nuclear magnetic resonance (NMR) spectroscopy of the heart is normally carried out using whole heart preparations under coronary perfusion. In such preparations, either radical changes in ionic composition of the perfusate or applications of numerous drugs would affect coronary microcirculation. This report communicates the first (31)P NMR spectroscopy study using a heart slice preparation (left ventricular slices) superfused with extracellular medium. The ratio of phosphocreatine concentration to ATP concentration was approximately 2.1. Also, intracellular pH and Mg(2+) concentration ([Mg(2+)](i)), estimated from the chemical shifts of inorganic phosphate and ATP, were comparable with those under retrograde perfusion. [Mg(2+)](i) was significantly increased by the removal of extracellular Na(+), supporting the essential role of Na(+)-coupled Mg(2+) transport in Mg(2+) homeostasis of the heart. Heart slice preparation could also be used to evaluate the potency of cardiac drugs, regardless of their possible effects on coronary microcirculation.

Effects of hypoxia, glucose deprivation and acidosis on phosphatidylcholine synthesis in HL-1 cardiomyocytes. CTP:phosphocholine cytidylyltransferase activity correlates with sarcolemmal disruption

A decrease in [3H]Cho (choline) incorporation in to PtdCho (phos-phatidylcholine) preceded the onset of LDH (lactate dehydrogenase) release in HL-1 cardiomyocytes submitted to simulated ischaemia. This observation led us to examine the role of PtdCho synthesis in sarcolemmal disruption in HL-1 cardiomyocytes. To address this objective we analysed the individual effects of hypoxia, glucose deprivation and acidosis, three prominent components of ischaemia, on the different steps of the Kennedy pathway for the synthesis of PtdCho. Pulse and pulse-chase experiments with [3H]Cho, performed in whole HL-1 cells submitted to hypoxia or normoxia, in the presence or absence of glucose at different pHs indicated first, that CK (choline kinase) was inhibited by hypoxia and acidosis, whereas glucose deprivation exacerbated the inhibition caused by hypoxia. Second, the rate-limiting reaction in PtdCho synthesis, catalysed by CCT (CTP:phosphocholine cytidylyltransferase), was inhibited by hypoxia and glucose deprivation, but unexpectedly activated by acidosis. In cellfree system assays, acidosis inhibited both CK and CCT. In experiments performed in whole cells, the effect of acidosis was likely to be direct on CK, but indirect or intact-cell-dependent on CCT. Since hypoxia and glucose deprivation favoured membrane disruption, but acidosis prevented it, we hypothesized that the modulation of CCT could be an important determinant of cell survival. Supporting this hypothesis, we show that CCT activity in whole-cell experiments clearly correlated with LDH release, but not with ATP concentration. Altogether our results suggest a significant role for CCT activity in sarcolemmal disruption during ischaemia.

Atractyloside and 5-hydroxydecanoate block the protective effect of puerarin in isolated rat heart

The aim of the present study was to determine whether the clinically effective cardioprotection conferred by puerarin (Pue) against ischemia and reperfusion is mediated by mitochondrial transmembrane pores and/or channels. Hearts isolated from male Sprague-Dawley rats were perfused on a Langendorff apparatus and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The production of formazan, which provides an index of myocardial viability, was measured by absorbance at 550 nm, and the level of lactate dehydrogenase (LDH) in the coronary effluent was determined. In this model, Pue (0.0024-2.4 mmol/l) had a dose-dependent, negatively inotropic effect. Pretreatment with Pue at 0.24 mmol/l for 5 min before ischemia increased myocardial formazan content, reduced LDH release, improved recovery of left ventricular end-diastolic pressure and rate-pressure product (left ventricular developed pressure multiplied by heart rate) during reperfusion. Administration of atractyloside (20 micromol/l), an opener of the mitochondrial permeability transition pore, for the first 20 min of reperfusion, and 5-hydroxydecanoate (100 micromol/l), the mitochondrial-specific ATP-sensitive potassium channel blocker, for 20 min before ischemia, attenuated the protective effects of Pue. In mitochondria isolated from hearts pretreated with 0.24 mmol/l Pue for 5 min, a significant inhibition of Ca(2+)-induced swelling was observed, and this inhibition was attenuated by 5-hydroxydecanoate. In isolated ventricular myocytes, pretreatment with Pue prevented ischemia-induced cell death and depolarization of the mitochondrial membrane, and atractyloside and 5-hydroxydecanoate attenuated the effects of Pue. These findings indicate that puerarin protects the myocardium against ischemia and reperfusion injury via inhibiting mitochondrial permeability transition pore opening and activating the mitochondrial ATP-sensitive potassium channel.

Glutamine's protection against cellular injury is dependent on heat shock factor-1

Glutamine (GLN) has been shown to protect cells, tissues, and whole organisms from stress and injury. Enhanced expression of heat shock protein (HSP) has been hypothesized to be responsible for this protection. To date, there are no clear mechanistic data confirming this relationship. This study tested the hypothesis that GLN-mediated activation of the HSP pathway via heat shock factor-1 (HSF-1) is responsible for cellular protection. Wild-type HSF-1 (HSF-1(+/+)) and knockout (HSF-1(-/-)) mouse fibroblasts were used in all experiments. Cells were treated with GLN concentrations ranging from 0 to 16 mM and exposed to heat stress injury in a concurrent treatment model. Cell viability was assayed with phenazine methosulfate plus tetrazolium salt, HSP-70, HSP-25, and nuclear HSF-1 expression via Western blot analysis, and HSF-1/heat shock element (HSE) binding via EMSA. GLN significantly attenuated heat-stress induced cell death in HSF-1(+/+) cells in a dose-dependent manner; however, the survival benefit of GLN was lost in HSF-1(-/-) cells. GLN led to a dose-dependent increase in HSP-70 and HSP-25 expression after heat stress. No inducible HSP expression was observed in HSF-1(-/-) cells. GLN increased unphosphorylated HSF-1 in the nucleus before heat stress. This was accompanied by a GLN-mediated increase in HSF-1/HSE binding and nuclear content of phosphorylated HSF-1 after heat stress. This is the first demonstration that GLN-mediated cellular protection after heat-stress injury is related to HSF-1 expression and cellular capacity to activate an HSP response. Furthermore, the mechanism of GLN-mediated protection against injury appears to involve an increase in nuclear HSF-1 content before stress and increased HSF-1 promoter binding and phosphorylation.

Is glycine effective against elevated blood pressure?

PURPOSE OF REVIEW

Glycine, a non-essential amino acid, has been found to protect against oxidative stress in several pathological situations, and it is required for the biosynthesis of structural proteins such as elastin. As hypertension is a disease in which free radicals and large vessel elasticity are involved, this article will examine the possible mechanisms by which glycine may protect against high blood pressure.

RECENT FINDINGS

The addition of glycine to the diet reduces high blood pressure in a rat model of the metabolic syndrome. Also, glycine supplemented to the low protein diet of rat dams during pregnancy has a beneficial effect on blood pressure in their offspring. The mechanism by which glycine decreases high blood pressure can be attributed to its participation in the reduction of the generation of free radicals, increasing the availability of nitric oxide. In addition, as glycine is required for a number of critical metabolic pathways, such as the synthesis of the structural proteins collagen and elastin, the perturbation of these leads to impaired elastin formation in the aorta. This involves changes in the aorta's elastic properties, which would contribute to the development of hypertension.

SUMMARY

The use of glycine to lower high blood pressure could have a significant clinical impact in patients with the metabolic syndrome and with limited resources. On the other hand, more studies are needed to explore the beneficial effect of glycine in other models of hypertension and to investigate possible side-effects of treatment with glycine.

Reduction of all-trans-retinoic acid–induced teratogenesis in the rat by glycine administration

BACKGROUND

Prenatal rat embryo exposure to retinoids induces severe malformations in various organs; the most active and teratogenic metabolite is all-trans-retinoic acid (atRA). The mechanisms of this embryopathy are only partly known. In the present study, the influence of glycine on the teratogenicity of atRA was investigated.

METHODS

Embryos from 5 groups of white rats were studied: Group 1 remained untreated; Group 2 received glycine 2% in drinking water ad libitum from the first gestational day (GD 1); Group 3 was administered vehicle (corn oil); Group 4 was treated with atRA (50 mg/kg of body weight) injected (IP); and Group 5 was treated with atRA (50 mg/kg of body weight IP) plus glycine 2% in drinking water ad libitum from GD 1. atRA was administrated daily from GD 8-10. Dams were killed on the 21st day of pregnancy, and their fetuses were examined to detect external, visceral, and skeletal malformations.

RESULTS

The results show that the atRA-administered dose is not toxic for the dams, and that although fetal death was not observed, it produced abnormalities in the fetuses. Glycine reduced atRA-induced teratogenic effects (external and skeletal defects).

CONCLUSIONS

The results indicate that glycine effectively reduces the teratogenic effects of atRA. Thus, glycine might be useful for the prevention of vitamin A teratogenicity.

The mitochondrial permeability transition pore and the Ca2+-activated K+ channel contribute to the cardioprotection conferred by tumor necrosis factor-alpha

Pretreatment with tumor necrosis factor-alpha (TNF-alpha) is known to trigger cardioprotection and it can activate multiple downstream signaling cascades. However, it is not known whether the mitochondrial permeability transition pore and the Ca(2+)-activated K(+) channel (K(Ca) channel) are involved in the TNF-alpha-induced cardioprotection. In the present study, we examined whether TNF-alpha inhibits pore opening and activates the K(Ca) channel in the cardioprotection. In isolated rat hearts subjected to 30 min of regional ischemia and 120 min of reperfusion, pretreatment with 10 U/ml TNF-alpha for 7 min followed by 10 min washout improved the recovery of rate-pressure product (RPP=left ventricular developed pressure x heart rate) and coronary flow (CF) during reperfusion, and reduced the infarct size and release of lactate dehydrogenase (LDH). Administration of 20 micromol/L atractyloside, a pore opener, for the last 5 min of ischemia and first 15 min of reperfusion, and pretreatment with 1 micromol/L paxilline, an inhibitor of the K(Ca) channel, for 5 min before ischemia, attenuated the recovery of RPP and CF, and the reductions of infarct size and release of LDH induced by TNF-alpha. On the other hand, administration of 10 micromol/L NS 1619, an opener of the K(Ca) channel, for 10 min before ischemia, decreased the infarct size and LDH release, and improved contractile functions and CF; these effects were attenuated by atractyloside. Pretreatment with 0.2 micromol/L cyclosporin A for the last 5 min of ischemia and first 15 min of reperfusion showed similar effects to those of TNF-alpha, and they were not attenuated by paxilline. In mitochondria isolated from hearts pretreated with 10 U/ml TNF-alpha for 7 min, a significant inhibition of Ca(2+)-induced swelling was observed. Furthermore, paxilline attenuated the inhibition of Ca(2+)-induced mitochondrial swelling by TNF-alpha. These findings indicate that TNF-alpha protects the myocardium against ischemia and reperfusion injury by inhibiting mitochondrial permeability transition pore opening as well as activating K(Ca) channels, probably the mitochondrial K(Ca) channel, which is upstream from the pore.

Effect of sarcolemmal rupture on myocardial electrical impedance during oxygen deprivation

Plasma membrane disruption is a characteristic feature of cell death induced by hypoxia or ischemia. Here, we investigated whether analysis of tissue electrical impedance allows detection of ongoing cell membrane rupture and necrotic cell death in hypoxic or ischemic myocardium. Twenty-eight isolated rat hearts were submitted to 5 h of ischemia (n = 8) or hypoxia (n = 20). Myocardial electrical impedance and lactate dehydrogenase (LDH) release were monitored. The time course of hypoxia-induced cell death was modified by altering pH (pH 7.4 or 6.4, 5 h) or by adding 3 or 10 mM glycine. Ischemia and hypoxia induced an increase in electrical impedance, followed by a plateau, and later a reduction. During hypoxia, LDH release started after a prolonged lapse of time (80.00 +/- 8.37 min at pH 7.4 and 122.50 +/- 11.82 min at pH 6.4). The onset of LDH release was followed by the onset of the late reduction in electrical impedance, and both were delayed by acidic pH (P < 0.05) and by glycine (P < 0.05). The times of onset of LDH release and of late electrical changes were significantly correlated (r = 0.752, P < 0.001). In separate experiments, induction of sarcolemmal rupture with Triton X-100 (n = 6) mimicked the late effects of ischemia or hypoxia on tissue impedance. The protective effects of glycine and acidosis on membrane disruption were confirmed (propidium iodide) in energy-deprived HL-1 cardiomyocytes. These results describe for the first time a late fall in electrical impedance in myocardium submitted to prolonged oxygen deprivation and demonstrate that this fall allows detection of ongoing cell necrosis.