Preconditioning - endogenous defence mechanisms of the heart

The Role of Endogenous Opioids in Cardioprotection

The opioid system involves opioid receptors (OPRs) and endogenous opioid peptides.This chapter will focus on the distribution of OPRs in the cardiovascular system, the expression pattern in the heart, the activation by opioid peptides, and the effects of OPRs activation with potential relevance in cardiovascular performance. In the heart, OPRs are co-expressed with beta adrenergic receptors (β-ARs) in the G-protein-coupled receptor (GPCR) superfamily, functionally cross-talk with β-Ars and modify catecholamine-induced effects. They are involved in cardiac contractility, energy metabolism, myocyte survival or death, vascular resistance. The effects of the opioid system in the regulation of systemic circulation at both the central and peripheral level are presented. The pathways are discussed under physiological (i.e., aging) and pathological conditions (atherosclerosis, heart failure, essential hypertension, ischemic stress). Stimulation of OPRs not only inhibits cardiac excitation-contraction coupling, but also protects the heart against hypoxic and ischemic injury. An enhanced sensitivity to opioids of endocrine organs and neuronal systems is operative in hypertensive patients. The opioid system can be pharmacologically engaged to selectively mimic these responses via cardiac and nervous signaling. The clinical opportunities for the use of cardioprotective effects of opioids require future investigations to provide more specific details of the impact on cardiac performance and electrophysiological properties.

A Review on the Most Important Medicinal Plants Effective in Cardiac Ischemia-Reperfusion Injury

Ischemia, referring to reduction and restriction of perfusion to myocardial tissue which involves coronary artery through the formation of misplaced clots and thrombosis, is one of the most important cardiovascular diseases. Plant-based compounds help to improve or prevent disease by affecting the factors involved in the disease. This review was conducted to report the medicinal plants and factors effective in cardiac ischemiareperfusion (I/R) injury to supplement the knowledge about this disease and its prevention and treatment using certain medicinal plants and their active compounds. For this purpose, medicinal plants and their potential antioxidant activities, effects on lipid levels and plaque formation, atherosclerosis and development of cardiovascular diseases and ischemia were reviewed.

METHODS

To conduct this review, relevant articles published between 1983 and 2018 were retrieved from the Google Scholar, PubMed, Scientific Information Database, Web of Science, and Scopus using search terms antioxidant, ischemia, reperfusion, heart, infarct, inflammation, cholesterol and medicinal plants. Then, the eligible articles were reviewed.

RESULTS

The active compounds of plants, including phenolic compounds, flavonoids, and antioxidant compounds, can be effective on certain pathogenic factors particularly in decreasing cholesterol and blood pressure, preventing an increase in free radicals and ultimately reducing blood clots and vascular resistance to reduce and prevent ischemic disease and its harmful effects.

CONCLUSION

Medicinal plants discussed in this article seem to be able to prevent cardiac damage and the disease progression via affecting the factors that are involved in ischemia.

Remote ischemic conditioning in a rat model of testicular torsion: does it offer testicular protection?

BACKGROUND

Testicular torsion is a surgical emergency mainly affecting adolescent boys, with a relatively high rate of missed torsion and testicular loss secondary to delay in prompt diagnosis and surgical intervention. With ischemic reperfusion injury as its underlying culprit, testicular torsion may respond favorably to remote ischemic conditioning (RIC) where a non-privileged site (e.g. limb) is concurrently rendered ischemic to divert the cascade of reperfusion injury from the privileged organ (e.g. testicle), thus offering a protective effect in improving salvage. This mechanism is established for other organs, whereas it has not been evaluated for testis.

AIM

It was aimed to evaluate RIC in a rat model of testicular torsion as a proof of principle that, similar to what has been demonstrated in other organs, RIC does offer testicular protection.

STUDY DESIGN

This is an animal experimental study. Thirty Sprague-Dawley male rats were divided into control group (n = 15) and experimental group (n = 15). Non-survival surgeries of right-sided spermatic cord torsion (720° counter-clockwise twist) were performed for both the groups (45 min) followed by detorsion and reperfusion (5 min) and then orchiectomy. For the experiment group, an intervention of tail clamping to create RIC was applied 5 min after torsion, then unclamping 5 min before detorsion, followed by detorsion and reperfusion for 5 min and then orchiectomy. The testicles were histologically and immunologically examined using a hypoxia inducible factor (HIF-1α) ELISA Kit. The histological findings on ischemic changes, vascular congestion, and immunohistochemistry were quantified using previously described, validated grading systems.

RESULTS

DISCUSSION: This is the first study to demonstrate the concept of RIC in an animal model of testicular torsion. It is limited by the non-availability of similar studies to compare outcomes and by the caution of extrapolating animal studies on humans. It does lay grounds, however, to subsequent studies to further elaborate on this concept and its clinical applicability.

CONCLUSION

When RIC is applied in the experimental setting of testicular torsion, there is less evidence of hypoxic injury by histology and immunohistochemistry.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.

Volatile Anesthetics and Cardiac Function

All volatile anesthetics have been shown to induce a dose-dependent decrease in myocardial contractility and cardiac loading conditions. These depressant effects decrease myocardial oxygen demand and may, therefore, have a beneficial role on the myocardial oxygen balance during myocardial ischemia. Recently, experimental evidence has clearly demonstrated that in addition to these indirect protective effects, volatile anesthetic agents also have direct protective properties against reversible and irreversible ischemic myocardial damage. These properties have not only been related to a direct preconditioning effect but also to an effect on the extent of reperfusion injury. The implementation of these properties during clinical anesthesia can provide an additional tool in the treatment or prevention, or both, of ischemic cardiac dysfunction in the perioperative period. In the clinical practice, these effects should be associated with improved cardiac function, finally resulting in a better outcome in patients with coronary artery disease. The potential application of these protective properties of volatile anesthetic agents in clinical practice is the subject of ongoing research. This review summarizes the current knowledge on this subject.

Pharmacological Neuroprotection During Cardiac Surgery

Despite more than 30 years of aggressive neuroprotective research by many investigators, neuropsychological deficit after cardiac surgery remains an important cause of postoperative morbidity. Although the neurological outcome is a result of a multifactorial etiology, many physicians world-wide have recognized the importance of this problem, and extensive efforts have been made in attempting to minimize the incidence of neurological and neurocognitive dysfunction. Pharmacological intervention is one of the important potential methods of neuroprotection during cardiac surgery. In vitro studies have identified drugs that are effective protectants against focal cerebral ischemia, hemorrhage, and global ischemia. However, at present there is no solid agreement on the need for prophylactic neuroprotectants in cardiac surgery. Researchers and clinicians must become more cognizant of the pitfalls and paradoxes that have arisen in attempting to translate the results of animal studies into clinical trial, with regard to neuroprotective therapy during cardiac surgery. There is an extensive need for new pharmacological approaches directed at reducing neurologic and neurocognitive injury during cardiac surgery. This article reviews past and present neuroprotective efforts and interventions during cardiac surgery.

Effects of ischemia and omeprazole preconditioning on functional recovery of isolated rat heart

OBJECTIVE

The aim of this study was to compare protective effects of ischemic and potential protective effects of pharmacological preconditioning with omeprazole on isolated rat heart subjected to ischemia/reperfusion.

METHODS

The hearts of male Wistar albino rats were excised and perfused on a Langendorff apparatus. In control group (CG) after stabilization period, hearts were subjected to global ischemia (perfusion was totally stopped) for 20 minutes and 30 minutes of reperfusion. Hearts of group II (IPC) were submitted to ischemic preconditioning lasting 5 minutes before 20 minutes of ischemia and 30 minutes of reperfusion. In third group (OPC) hearts first underwent preconditioning lasting 5 minutes with 100 μM omeprazole, and then submitted 20 minutes of ischemia and 30 minutes of reperfusion.

RESULTS

Administration of omeprazole before ischemia induction had protective effect on myocardium function recovery especially regarding to values of systolic left ventricular pressure and dp/dt max. Also our findings are that values of coronary flow did not change between OPC and IPC groups in last point of reperfusion.

CONCLUSION

Based on our results it seems that ischemic preconditioning could be used as first window of protection after ischemic injury especially because all investigated parameters showed continuous trend of recovery of myocardial function. On the other hand, preconditioning with omeprazole induced sudden trend of recovery with positive myocardium protection, although less effective than results obtained with ischemic preconditioning not withstand, we must consider that omeprazole may be used in many clinical circumstances where direct coronary clamping for ischemic preconditioning is not possible.

Prescription Opioid Use and Risk of Coronary Heart Disease, Stroke, and Cardiovascular Death Among Adults from a Prospective Cohort (REGARDS Study)

OBJECTIVE

Despite unknown risks, prescription opioid use (POU) for nonmalignant chronic pain has grown in the US over the last decade. The objective of this study was to examine associations between POU and coronary heart disease (CHD), stroke, and cardiovascular disease (CVD) death in a large cohort.

DESIGN, SETTING, SUBJECTS

POU was assessed in the prospective cohort study of 29,025 participants of the REasons for Geographic and Racial Differences in Stroke study, enrolled between 2003 and 2007 from the continental United States and followed through December 31, 2010. CHD, stroke, and CVD death were expert adjudicated outcome measures.

METHODS

Cox proportional hazards models adjusted for CVD risk factors were used.

RESULTS

Over a median (SD) of 5.2 (1.8) years of follow-up, 1,362 CHD events, 749 strokes, and 1,120 CVD death occurred (105, 55, and 104, respectively, in the 1,851 opioid users). POU was not associated with CHD (adjusted hazard ratio [aHR]) 1.03 [95% CI 0.83-1.26] or stroke (aHR 1.04 [95% CI 0.78-1.38]), but was associated with CVD death (aHR 1.24 [95% CI 1.00-1.53]) in the overall sample. In the sex-stratified analyses, POU was associated with increased risk of CHD (aHR 1.38 [95% CI 1.05-1.82]) and CVD death (aHR 1.66 [95% CI 1.27-2.17]) among females but not males (aHR 0.70 [95% CI 0.50-0.97] for CHD and 0.78 [95% CI 0.54-1.11] for CVD death).

CONCLUSION

Female but not male POU were at higher risk of CHD and CVD death. POU was not associated with stroke in overall or sex-stratified analyses.

Acute pancreatitis: The stress factor

Acute pancreatitis is an inflammatory disorder of the pancreas that may cause life-threatening complications. Etiologies of pancreatitis vary, with gallstones accounting for the majority of all cases, followed by alcohol. Other causes of pancreatitis include trauma, ischemia, mechanical obstruction, infections, autoimmune, hereditary, and drugs. The main events occurring in the pancreatic acinar cell that initiate and propagate acute pancreatitis include inhibition of secretion, intracellular activation of proteases, and generation of inflammatory mediators. Small cytokines known as chemokines are released from damaged pancreatic cells and attract inflammatory cells, whose systemic action ultimately determined the severity of the disease. Indeed, severe forms of pancreatitis may result in systemic inflammatory response syndrome and multiorgan dysfunction syndrome, characterized by a progressive physiologic failure of several interdependent organ systems. Stress occurs when homeostasis is threatened, and stressors can include physical or mental forces, or combinations of both. Depending on the timing and duration, stress can result in beneficial or harmful consequences. While it is well established that a previous acute-short-term stress decreases the severity of experimentally-induced pancreatitis, the worsening effects of chronic stress on the exocrine pancreas have received relatively little attention. This review will focus on the influence of both prior acute-short-term and chronic stress in acute pancreatitis.

The surmountable effect of FSCPX, an irreversible A(1) adenosine receptor antagonist, on the negative inotropic action of A(1) adenosine receptor full agonists in isolated guinea pig left atria

A1 adenosine receptors (A1 receptors) are widely expressed in mammalian tissues; therefore attaining proper tissue selectivity is a cornerstone of drug development. The fact that partial agonists chiefly act on tissues with great receptor reserve can be exploited to achieve an appropriate degree of tissue selectivity. To the best of our knowledge, the A1 receptor reserve has not been yet quantified for the atrial contractility. A1 receptor reserve was determined for the direct negative inotropic effect of three A1 receptor full agonists (NECA, CPA and CHA) in isolated, paced guinea pig left atria, with the use of FSCPX, an irreversible A1 receptor antagonist. FSCPX caused an apparently pure dextral displacement of the concentration-response curves of A1 receptor agonists. Accordingly, the atrial A1 receptor function converging to inotropy showed a considerably great, approximately 80-92 % of receptor reserve for a near maximal (about 91-96 %) effect, which is greater than historical atrial A1 receptor reserve data for any effects other than inotropy. Consequently, the guinea pig atrial contractility is very sensitive to A1 receptor stimulation. Thus, it is worthwhile considering that even partial A1 receptor agonists, given in any indication, might decrease the atrial contractile force, as an undesirable side effect, in humans.

Partial adenosine A1 receptor agonists for cardiovascular therapies

Adenosine, a purine nucleoside, is present in all cells in tightly regulated concentrations. It has many different physiological effects in the whole body and in the heart. Adenosine activates four G protein-coupled receptors A1, A2a, A2b, and A3. Activation of myocardial A1 receptors has been shown to inhibit a variety of myocardial pathologies associated with ischemia and reperfusion injury, including stunning, arrhythmogenesis, coronary and ventricular dysfunction, acute myocardial infarction, apoptosis, and chronic heart failure, implying several options for new cardiovascular therapies for diseases, like angina pectoris, control of cardiac rhythm, ischemic injury during an acute coronary syndrome, or heart failure. However, the main issue of using full A1 receptor agonists in such indications is the broad physiologic spectrum of cardiac and extracardiac effects. Desired A1 receptor-mediated protective and regenerative cardiovascular effects might be counter-regulated by unintended side effects when considering full A1 receptor agonists. These effects can be overcome by partial A1 agonists. Partial A1 agonists can be used to trigger only some of the physiological responses of receptor activation depending on endogenous adenosine levels and on receptor reserve in different tissues. CV-Therapeutics reported the identification of a partial A1 receptor agonist CVT-3619, and recently, another partial A1 receptor agonist VCP28 was published. Both compounds are adenosine derivatives. Adenosine-like A1 receptor agonists often have the drawback of a short half-life and low bioavailability, making them not suitable for chronic oral therapy. We identified the first non-adenosine-like partial A1 receptor agonist(s) with pharmacokinetics optimal for oral once daily treatment and characterized the qualities of the partial character of the A1 receptor agonist(s) in preclinical and clinical studies.

[Prospects of cardioprotection by volatile anesthetics]

Myocardial ischaemia is followed by some reversibile or ireversibile changes. The aim of cardioplegia is to protect numerous intracellular processes: to spare the intracellular energy stores, to reduce the free oxygen radicals synthesis, to protect the function of the endothelium and myocardial oxygen balance as well as ionic balance. The crystalloid or blood cardioplegia, with anterograde or retrograde infusion, is a basic procedure of the intraoperative cardiac protection. Glucose-insulin-potassium solution was primarily used in a myocardial infarction. After the first promising results, some surgical teams started to use the high glucose-insulin-potassium solution, as a metabolic modulation approach, during a coronary surgery as addition to cardioplegia. During ischaemia, a number of intracellular mechanisms deteriorate with bioenergy misbalance and decrease of cellular functional reserve. In particular, the regulation of contractility in response to loading, alteration in autocrine or paracrine regulation in metabolically stressed hearts and acquired, "learned" tolerance of muscle to deteriorate perfusion (preconditioning) are examples of a variety of the cardiac adaptation. The further improvement in the metabolic modulation during a coronary surgery was made with fluorine ion halogenated volatile aneasthetics used for anaesthesia. The results of some experimental and first clinical studies induced a new approach to the modulation of the intracellular metabolic mechanisms and announced a new concept of anaesthetic preconditioning in coronary surgery. Large, randomized studies are needed to evaluate anaesthetic preconditioning and dependence of its efficiency on type and dose of volatile anaesthetics as well as the role of gene regulation in cardioprotection.

Effect of risedronate on osteocyte viability and bone turnover in paired iliac bone biopsies from early postmenopausal women

It is unclear whether standard clinical doses of risedronate affect osteocyte viability. This study examined osteocyte viability and bone remodeling rate in early postmenopausal women (1-5 years after menopause) who were treated with a standard clinical dose of risedronate (5 mg/day, orally) for 1 year. Paired transiliac bone biopsies were obtained from 19 postmenopausal women at baseline and after 1-year treatment with placebo (n = 8, mean age 52.9 ± 3.4 years) or risedronate 5 mg/day (n = 11, mean age 52.5 ± 3.4 years). In these samples, we measured osteocyte- and bone remodeling-related variables in trabecular bone. In both the placebo and risedronate groups, empty lacunae were significantly decreased after 1-year treatment compared to baseline. There were no significant differences in osteocyte-related variables between placebo and risedronate. Risedronate significantly reduced bone-remodeling indices including mineralizing surface (MS/BS), bone formation rate (BFR/BS), and activation frequency (Ac.f). Risedronate treatment caused significantly lower MS/BS and Ac.f than placebo administration. In conclusion, risedronate 5 mg/day effectively inhibited bone remodeling but did not significantly reduce osteocyte viability in trabecular bone.

Protein misfolding induces hypoxic preconditioning via a subset of the unfolded protein response machinery

Prolonged cellular hypoxia results in energy failure and ultimately cell death. However, less-severe hypoxia can induce a cytoprotective response termed hypoxic preconditioning (HP). The unfolded protein response pathway (UPR) has been known for some time to respond to hypoxia and regulate hypoxic sensitivity; however, the role of the UPR, if any, in HP essentially has been unexplored. We have shown previously that a sublethal hypoxic exposure of the nematode Caenorhabditis elegans induces a protein chaperone component of the UPR (L. L. Anderson, X. Mao, B. A. Scott, and C. M. Crowder, Science 323:630-633, 2009). Here, we show that HP induces the UPR and that the pharmacological induction of misfolded proteins is itself sufficient to stimulate a delayed protective response to hypoxic injury that requires the UPR pathway proteins IRE-1, XBP-1, and ATF-6. HP also required IRE-1 but not XBP-1 or ATF-6; instead, GCN-2, which is known to suppress translation and induce an adaptive transcriptional response under conditions of UPR activation or amino acid deprivation, was required for HP. The phosphorylation of the translation factor eIF2α, an established mechanism of GCN-2-mediated translational suppression, was not necessary for HP. These data suggest a model where hypoxia-induced misfolded proteins trigger the activation of IRE-1, which along with GCN-2 controls an adaptive response that is essential to HP.

Drugs mediating myocardial protection

The occurrence of myocardial ischaemia will result in either reversible or irreversible myocardial dysfunction. Even when revascularization is successful, some reperfusion injury may occur that transiently impairs myocardial function. Therefore, treatment should not only be directed towards prompt restoration of myocardial blood flow but measures should also be taken to prevent or alleviate the consequences of myocardial reperfusion injury. Over the years, various strategies have been developed. The present contribution reviews a number of these strategies focusing on pharmacological treatments that have been developed to address myocardial reperfusion injury.

The effect of post-burn local hyperthermia on the reducing burn injury: The possible role of opioids

PURPOSE

This paper studied the effect of post-burn local hyperthermia on burn induced injury.

METHODS

A second-degree burn injury was induced on the right and left flanks of Balb/c mice. Thirty-two burn wounds were divided into four groups. Opioid receptor blocking was done for groups 3 and 4 by intra-peritoneal administration of Naloxone (NLX) 30 min before the thermal injury. Local hyperthermia (45 degrees C, 30 s) was applied only for the burn wounds of groups 2 and 4. Twenty-four hours after burn injury, the burned wounds were assessed for the level of iNOS (by immunohistochemistry) and the number of hair follicles (as an indicator of tissue injury).

RESULTS

The wounds that received hyperthermia (group 2) had significantly more hair follicles (p < 0.001) compared to the control wounds (group 1). There was no significant difference between the number of hair follicles and acute inflammation of group 1 and group 3 (NLX + burn). Group 4 (NLX + burn + hyperthermia) had significantly fewer hair follicles compared to group 1 (p < 0.001), group 2 (p < 0.001) and group 3 (p < 0.001). The level of iNOS in groups 1, 3 and 4 was not significantly different but significantly more than group 2 (p < 0.001, p < 0.001 and p < 0.001, respectively).

CONCLUSIONS

The results showed that local hyperthermia after second degree burn decreased the tissue injury and iNOS expression. It is also concluded that endogenous opioid response may have a key role in the above mentioned effects of post-burn local hyperthermia.

Iron metabolism in the eye: a review

This review article covers all aspects of iron metabolism, which include studies of iron levels within the eye and the processes used to maintain normal levels of iron in ocular tissues. In addition, the involvement of iron in ocular pathology is explored. In each section there is a short introduction to a specific metabolic process responsible for iron homeostasis, which for the most part has been studied in non-ocular tissues. This is followed by a summary of our current knowledge of the process in ocular tissues.

Endogenous cardiac opioids: enkephalins in adaptation and protection of the heart

Opiates have been used for thousands of years in the form of opium for relief of pain or fever and to induce sleep. However, it was only in the 1970s that the endogenous ligands for the opiate receptors were identified and termed opioid peptides. Opioid peptides activate G protein-coupled receptors in the central and autonomic nervous system, with marked effects on the regulation of pain perception, body temperature, respiration, heart rate and blood pressure. Cardiovascular regulatory effects of endogenous opioids were initially considered to originate from neural centres in the central nervous system, facilitating a regulatory role in neuro-transmission, as demonstrated by the presynaptic co-release from sympathetic neurones of norepinephrine with enkephalin or acetylcholine with enkephalin. However, opioid peptides of myocardial origin have also recently been shown to play a key role in local regulation of the heart. This brief review highlights the key features of the enkephalin opioids in the heart and the current understanding of their role in development, ageing, cardioprotection, hypertension, hypertrophy, and heart failure.

Cardioprotection with Volatile Anesthetics in Cardiac Surgery

Myocardial ischemia during the perioperative period is a major cause of morbidity and mortality after surgery. Experimental data indicate that clinical concentrations of volatile anesthetics protect the myocardium from ischemia and reperfusion injury, as shown by decreased infarct size and more rapid postoperative recovery of contractile function. These anesthetics may also mediate protective effects in other organs, such as the brain and kidney. A number of recent reports have indicated that these experimentally observed protective effects might also be present in the clinical setting. Implementation of such cardioprotection during surgery may provide an additional tool in the treatment and prevention of ischemic cardiac dysfunction in the perioperative period. This review discusses the clinical studies that have focused on the potential cardioprotective effects of volatile anesthetic agents.

Isoflurane attenuates myoglobin release during ischemic and/or reperfusion periods

BACKGROUND

Recently, we have developed cardiac microdialysis for detection of protein leakage from the injured myocardium. We examined whether the exposures to isoflurane would exert a beneficial effect on myocardial injury caused by ischemia or reperfusion.

METHODS

A dialysis probe was implanted into the left ventricle free wall in the rabbits. The dialysate myoglobin level served as an index of myocardial interstitial myoglobin levels. Rabbits were randomly assigned to one of three groups: (1) without exposure to isoflurane (vehicle, n=6), (2) inhale 1 MAC isoflurane once for 30 min (ISO30-1, n=6), and (3) twice for 30 min (ISO30-2, n=6). All rabbits underwent 30 min of coronary occlusion and 60 min of reperfusion. To determine whether the isoflurane induced myocardial protection against chemical hypoxia, sodium cyanide (30 mM) was administered and dialysate myoglobin levels were measured with (n=6) and without pre-exposure to isoflurane twice for 30 min (n=6).

RESULTS

In all three groups dialysate myoglobin levels were increased by coronary occlusion and furthermore augmented by reperfusion. In comparison with the vehicle group, the ISO30-1 group suppressed only the increase in the dialysate myoglobin level during reperfusion. The ISO30-2 group suppressed during both the ischemic and reperfusion periods. Cyanide induced increases in dialysate myoglobin levels. These increments in dialysate myoglobin levels were suppressed by repeated exposure to isoflurane.

CONCLUSION

Repeated exposure to isoflurane suppressed myocardial myoglobin release caused by both ischemia and reperfusion injury. Isoflurane may provide protection against myocardial ischemia/reperfusion and hypoxic injuries.

Ischemic preconditioning of the rat retina: protective role of ferritin

Ischemic preconditioning (IPC) of the retina, accomplished by ischemia of short duration, is highly effective in preventing subsequent severe injury caused by iron-dependent free radical burst after prolonged ischemia. To investigate the mechanistic basis for IPC rescue, we examined changes in the levels of the retinal redox-active and labile iron pool, ferritin, and ferritin-bound iron. Prolonged ischemia severely impaired retinal function, with total loss of the full-field electroretinographic response. IPC provided marked protection against such injury. Histological examination revealed that ischemia-associated structural damage and loss of cells in the outer and inner nuclear layers were largely prevented by IPC. Ferritin levels decreased after prolonged ischemia but remained close to normal when the ischemic episode was preceded by IPC. The protective effect of IPC on retinal function and ferritin was blocked by a zinc-desferrioxamine complex known to interfere with iron signaling. The results suggest a mechanism whereby IPC activates an iron signaling pathway leading to a marked increase in ferritin levels, which mediates resistance to prolonged ischemia.

The protective effect of ischemic preconditioning on rat testis

BACKGROUND

It has been demonstrated that brief episodes of sublethal ischemia-reperfusion, so-called ischemic preconditioning, provide powerful tissue protection in different tissues such as heart, brain, skeletal muscle, lung, liver, intestine, kidney, retina, and endothelial cells. Although a recent study has claimed that there are no protective effects of ischemic preconditioning in rat testis, the protective effects of ischemic preconditioning on testicular tissue have not been investigated adequately. The present study was thus planned to investigate whether ischemic preconditioning has a protective effect on testicular tissue.

METHODS

Rats were divided into seven groups that each contained seven rats. In group 1 (control group), only unilateral testicular ischemia was performed by creating a testicular torsion by a 720 degree clockwise rotation for 180 min. In group 2, group 3, group 4, group 5, group 6, and group 7, unilateral testicular ischemia was performed for 180 min following different periods of ischemic preconditioning. The ischemic preconditioning periods were as follows: 10 minutes of ischemia with 10 minutes of reperfusion in group 2; 20 minutes of ischemia with 10 minutes of reperfusion in group 3; 30 minutes of ischemia with 10 minutes of reperfusion in group 4; multiple preconditioning periods were used (3 x 10 min early phase transient ischemia with 10 min reperfusion in all episodes) in group 5; multiple preconditioning periods were used (5, 10, and 15 min early phase transient ischemia with 10 min reperfusion in all episodes) in group 6; and, multiple preconditioning periods were used (10, 20, and 30 min early phase transient ischemia with 10 min reperfusion in all episodes) in group 7. After the ischemic protocols were carried out, animals were sacrificed by cervical dislocation and testicular tissue samples were taken for biochemical measurements (protein, malondialdehyde, nitric oxide) and histological examination.

RESULTS

Although decreased tissue malondialdehyde levels were detected in the groups of 2, 3, 4, and 5 compared to group 1, significant decreases were observed in only group 2 and group 5 (p < .05). Nitric oxide levels were numerically decreased in all groups compared to the control group but was statistically significant only in group 5 (p < .05). Histopathological examination demonstrated that all groups subjected to ischemic preconditioning had less tissue damage than group 1 (p < .05).

CONCLUSION

These results suggest that ischemic preconditioning provides tissue protection in testicular tissue.

Genotoxic effects of anaesthetics in operating theatre personnel evaluated by the comet assay and micronucleus test

Genetic damage induced by anaesthetic gases in occupationally exposed populations was investigated using the comet assay and micronucleus test. The study included two groups of subjects: 50 operating theatre medical workers (anaesthesiologists, technicians and nurses) and 50 control subjects corresponding in sex, age and smoking habit. The exposed group revealed an increase in genome damage in both tests. In the comet assay, exposure to anaesthetics was a highly significant predictor of the tail length for technicians, while sex proved to be significant predictor of tail moment for women in exposed group. Micronucleus frequency increased significantly, showing threefold increase in exposed groups (RR>3.029). Univariate analysis showed significant influence of duration of exposure, while multivariate analysis showed age to be significant predictor of micronucleus frequency. The obtained results call for further, targeted investigation of exposure risk.

Sevoflurane anesthesia did not affect postoperative cognitive dysfunction in patients undergoing coronary artery bypass graft surgery

PURPOSE

The purpose of this study was to retrospectively examine whether sevoflurane anesthesia had any ameliorative effects on postoperative cognitive dysfunction in patients undergoing coronary artery bypass graft (CABG) surgery.

METHODS

One hundred and nine patients underwent elective CABG surgery at our institution from May 1999 to May 2001. From May 1999 to August 2000, the main anesthetic regime used included a propofol infusion with no volatile anesthetic being administered during the surgery. From September 2000 to May 2001, the main anesthetic regime used was 1.5%-2.0% sevoflurane from the postinduction period until the end of the surgery. All patients underwent a battery of neurological and neuropsychological tests 1 day before and 6 months after the operation.

RESULTS

The use of sevoflurane did not have any significant effects on the postoperative levels of cognitive dysfunction. In contrast, multiple logistic analysis showed that age [odds ratio (OR), 1.3; P = 0.047], diabetes mellitus (OR, 2.5; P = 0.03), and atherosclerosis of the ascending aorta (OR, 1.4; P = 0.047) appeared to be predictive factors of postoperative cognitive dysfunction.

CONCLUSION

This retrospective study showed no relationship between postoperative cognitive dysfunction and the use of sevoflurane.

Cardioprotection with volatile anesthetics: clinical relevance

PURPOSE OF REVIEW

Increasing experimental evidence is indicating that volatile anesthetic agents may exert direct cardioprotective effects. They have been shown to directly precondition or indirectly enhance ischemic preconditioning. This results in protection against reversible and irreversible ischemic myocardial damage. In addition, volatile anesthetics also decrease the extent of the reperfusion injury when administered only during the reperfusion period. The implementation of these properties during clinical anesthesia might provide an additional tool in the treatment and prevention of ischemic cardiac dysfunction in the perioperative period.

RECENT FINDINGS

In clinical practice, these effects should be associated with improved cardiac function, ultimately resulting in a better outcome in patients with coronary artery disease. This potential application of anesthetic agents has only recently been explored and its applicability in clinical practice is the subject of ongoing research.

SUMMARY

This review will summarize the current knowledge in this field and also discuss the potential mechanisms involved in cardioprotection by anesthetic agents.

Temporal and genetic influences on protection against noise-induced hearing loss by hypoxic preconditioning in mice

The protective benefits of hypoxic preconditioning (HPC) against permanent noise-induced hearing loss (NIHL) were investigated in mice. Hypoxia induced by exposure to 8% O2 for 4 h conferred significant protection against damaging broadband noise delivered 24-48 h later in male and female CBA/J (CBA) and CBA/CaJ mice. No protection was found in C57BL/6 (B6) mice, their B6.CAST-Cdh23(CAST) (B6.CAST) congenics, or in CBAxB6 F1 hybrid mice over the same interval, suggesting that the potential for HPC depends on one or a few autosomal recessive alleles carried by CBA-related strains, and is not influenced by the Cdh23 locus. Protection against NIHL in CBA mice was associated with significant up-regulation of hypoxia-inducible factor-1alpha (HIF-1alpha) within the organ of Corti, not found in B6.CAST. In both CBA and B6.CAST mice, some hypoxia-noise intervals shorter than 24 h were associated with exacerbation of NIHL. Cellular cascades underlying the early exacerbation of NIHL by hypoxia are therefore common to both strains, and not mechanistically linked to later protection. Elucidation of the events that underlie HPC, and how these are impacted by genetics, may lead to pharmacologic approaches to mimic HPC, and may help identify individuals with elevated risk of NIHL.

Intestinal ischemic preconditioning in rats and NF-κB activation

Cold preservation prior to small-bowel transplantation can moderate tissue injury, although it is unable to protect the bowel graft from acute reperfusion injury. One method to reduce oxidative stress is ischemic preconditioning (IPC). The limited data regarding IPC of the bowel encouraged us to investigate the key factor in this process, i.e., the activation of nuclear factor-kappa binding (NF-kB) in bowel tissue. The intestine was preconditioned by various cycles of IPC on rats. Activation of NF-kB was detected by a chemiluminescence-based ELISA method. Our findings showed that NF-kB level was elevated significantly 30 min after IPC. One hour following IPC, NF-kB decreased to control level; 2 h after IPC, the level significantly increased again. These changes were independent of the number of IPC cycles. Our experiments with various IPC cycles revealed that even a very short IPC cycle was able to activate the IPC cascade in small-bowel tissue.

Ischemic preconditioning prevents protein aggregation after transient cerebral ischemia

Transient cerebral ischemia leads to protein aggregation mainly in neurons destined to undergo delayed neuronal death after ischemia. This study utilized a rat transient cerebral ischemia model to investigate whether ischemic preconditioning is able to alleviate neuronal protein aggregation, thereby protecting neurons from ischemic neuronal damage. Ischemic preconditioning was introduced by a sublethal 3 min period of ischemia followed by 48 h of recovery. Brains from rats with either ischemic preconditioning or sham-surgery were then subjected to a subsequent 7 min period of ischemia followed by 30 min, 4, 24, 48 and 72 h of reperfusion. Protein aggregation and neuronal death were studied by electron and confocal microscopy, as well as by biochemical analyses. Seven minutes of cerebral ischemia alone induced severe protein aggregation after 4 h of reperfusion mainly in CA1 neurons destined to undergo delayed neuronal death (which took place after 72 h of reperfusion). Ischemic preconditioning reduced significantly protein aggregation and virtually eliminated neuronal death in CA1 neurons. Biochemical analyses revealed that ischemic preconditioning decreased accumulation of ubiquitin-conjugated proteins (ubi-proteins) and reduced free ubiquitin depletion after brain ischemia. Furthermore, ischemic preconditioning also reduced redistribution of heat shock cognate protein 70 and Hdj1 from cytosolic fraction to protein aggregate-containing fraction after brain ischemia. These results suggest that ischemic preconditioning decreases protein aggregation after brain ischemia.

The concept of anaesthetic-induced cardioprotection: clinical relevance

Experimental evidence has clearly demonstrated that volatile anaesthetic agents have direct protective properties against reversible and irreversible ischaemic myocardial damage. These properties have been related to a direct preconditioning effect but also to an effect on the extent of reperfusion injury. The implementation of these properties during clinical anaesthesia can provide an additional tool in the treatment and/or prevention of ischaemic cardiac dysfunction in the perioperative period. In clinical practice, these effects should be associated with improved cardiac function, ultimately resulting in a better outcome in patients with coronary artery disease. This potential application of anaesthetic agents has only recently been explored, and its applicability in clinical practice is the subject of ongoing research. This review summarizes the current knowledge on this subject.

Cardioprotection with volatile anesthetics: mechanisms and clinical implications

Cardiac surgery and some noncardiac procedures are associated with a significant risk of perioperative cardiac morbid events. Experimental data indicate that clinical concentrations of volatile general anesthetics protect the myocardium from ischemia and reperfusion injury, as shown by decreased infarct size and a more rapid recovery of contractile function on reperfusion. These anesthetics may also mediate protective effects in other organs, such as the brain and kidney. Recently, a number of reports have indicated that these experimentally observed protective effects may also have clinical implications in cardiac surgery. However, the impact of the use of volatile anesthetics on outcome measures, such as postoperative mortality and recovery in cardiac and noncardiac surgery, is yet to be determined.

Anti-infarct effect of magnesium is not mediated by adenosine A1 receptors in rat globally ischaemic isolated hearts

1. The aim of present study was to investigate the effects of magnesium (Mg) on cardiac function and infarct size and to compare it effects with those of adenosine. The mechanism of Mg-mediated cardioprotection was explored by combined use of Mg and a selective adenosine A(1) receptor antagonist. 2. Rat isolated hearts were used for Langendorff perfusion. Hearts were either non-preconditioned or preconditioned with Mg (6 mmol/L) or adenosine (1 mmol/L) before 30 min sustained ischaemia followed by 120 min reperfusion. Within each of these protocols, hearts were divided into two groups; one group was exposed to the A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 200 nmol/L). Infarct size was measured by the triphenyltetrazolium chloride method. Left ventricular function was assessed by left ventricular developed pressure (LVDP), the product of heart rate x LVDP and coronary flow (CF). 3. The administration of Mg had an anti-infarct effect independent of its effect on postischaemic functional recovery in rats. Both Mg and adenosine equipotently reduced infarct size, but this effect of Mg was not blocked by the simultaneous administration of DPCPX. Cardiac function was improved by both adenosine and Mg and blockade of adenosine A(1) receptors attenuated these effects for both agents. 4. In conclusion, the results of the present study indicate that stimulation of adenosine A(1) receptors is not responsible for the anti-infarct effect of Mg in ischaemic myocardium in rats, but that the Mg-mediated protection of postischaemic functional recovery in rats is mediated by these receptors.

Effects of Early Phase of Preconditioning on Rat Testicular Ischemia

INTRODUCTION

Brief episodes of ischemia followed by periods of reperfusion generate a powerful protective mechanism in cell, tissue or organ, which increase the resistance to further ischemic damage. This is known as ischemic preconditioning, and has not been investigated in testis. The present experiments were undertaken to determine whether early phase of ischemic preconditioning is evident in rat testis.

MATERIALS AND METHODS

Surgery was conducted under thiopental (60 mg/kg, intraperitoneal) anesthesia in male Wistar rats. Surgical procedures were performed through a midline incision. Group 1 was designed as a sham group. In group 2, which served as the ischemia group, the animals were subjected to unilateral testicular torsion by rotating the left testis 720 degrees in a clockwise direction. Then, this testis was maintained in the torsion position by fixing with a silk suture to the scrotal wall for 90 min. In groups 3 and 4, 5 or 10 min ischemia followed by 10 min reperfusion was introduced, respectively, to induce single cycle ischemic preconditioning. In group 5, which served as the multiple cycle preconditioning group, 3 cycles of 10 min ischemia and 10 min reperfusion were applied prior to 90 min ischemia. Both ipsilateral and contralateral testes were removed from the rats at the end of the experimental periods, and tissue malondialdehyde (MDA), nitric oxide (NO) levels, xanthine oxidase (XO), myeloperoxidase (MPO) and superoxide dismutase (SOD) activities were measured. Both testes were also evaluated histologically, assessing interstitial edema, congestion, hemorrhages, rupture of tubules and Leydig cell proliferation.

RESULTS

90 min ischemia produced a marked increase in MDA level in left testis. However, all ischemic preconditioning protocols used in this study did not show any significant modification in MDA, NO levels or XO, MPO and SOD activities. Histological grading scale was also similar in ischemia and preconditioning groups.

CONCLUSION

These results suggest that there are no protective effects with ischemic preconditioning in rat testis as showed by biochemical analysis and histological examinations.

Protein Kinase C in Cardiac Disease and as a Potential Therapeutic Target

Protein kinase C (PKC) is a member of a large family of serine/threonine kinases that plays an integral role in many of the signaling cascades that govern cellular behavior. As such, it is intricately involved in the processes that mediate disease pathogenesis. Strategies that serve to alter PKC function may prove to be useful in the treatment of numerous disease states. This article reviews the various roles PKC may play in cardiovascular disease, specifically with regard to ischemic heart disease, cardiac hypertrophy, heart failure, hypertension, and atherosclerosis, and suggests the potential for developing therapeutic approaches that can target PKC activity.

EPR oximetry in the beating heart: myocardial oxygen consumption rate as an index of postischemic recovery

Oxygen plays a critical role in the pathophysiology of myocardial injury during both ischemia and subsequent reperfusion (I/R). Thus, oxygen concentration is an important variable to measure during I/R. In the present work, electron paramagnetic resonance (EPR)-based oximetry was used to measure the oxygen concentration during a series of I/R episodes and oxygenation levels were correlated with the contractile and hemodynamic functions of the heart. A custom-developed electronically tunable surface coil resonator working at 1.1 GHz was used to determine tissue pO(2) in the beating heart. Microcrystalline particulate of lithium phthalocyanine was used as an EPR oximetry probe. Isolated and perfused rat hearts were subjected to 1 or 3 hr durations of preischemic perfusion, followed by 15-min I/R cycles. In hearts perfused for 3 hr prior to 15-min I/R cycles, the myocardial pO(2) decreased gradually on subsequent reperfusions of three successive I/R cycles. However, in hearts perfused for 1 hr there was almost 100% recovery of myocardial pO(2) in all three I/R cycles. The extent of oxygenation recovered in each reperfusion cycle correlated with the recovery of hemodynamic and contractile function. The results also showed that the oxygen consumption rate of the heart at the end of each I/R episode decreased in direct proportion to the functional recovery. In summary, it was observed that the amount of myocardial oxygen consumption during I/R could provide a reliable index of functional impairment in the heart.

Cardioprotective effects of desflurane: effect of timing and duration of administration in rat myocardium

BACKGROUND

We compared the cardioprotective effects of 1 minimum alveolar concentration (MAC) desflurane administered before, during or after ischaemia, or throughout the experiment (before, during and after ischaemia) on myocardial infarct size following 30 min occlusion of the left anterior descending coronary artery and 3 h reperfusion in adult rats.

METHODS

Fifty male Sprague-Dawley rats were anaesthetized with pentobarbital, intubated and mechanically ventilated. Blood gases, pH and body temperature (37.5-38 degrees C) were controlled. Heart rate and arterial pressure were measured continuously. Animals were randomly assigned to the following groups (n=10 in each group): pentobarbital only ("Pento"); 15 min desflurane administration followed by 10 min of washout before 30 min ischaemia and 3 h reperfusion ("Precond"); 30 min desflurane administration during ischaemia period ('Isch'); desflurane administration during the 15 first min of reperfusion ("Reperf") and desflurane administration throughout the experiment (before, during and after ischaemia; "Long"). Volumes at risk and infarct sizes were assessed by Indian ink and with 2,3,5-triphenyltetrazolium chloride staining, respectively.

RESULTS

Physiological parameters and volumes at risk were not significantly different between groups. In the Pento group, mean myocardial infarct size was 65 (sd 15)% of the volume at risk; myocardial infarct size was reduced to a significant and comparable extent in the desflurane-treated groups (Precond 42 (14)%; Isch 34 (11)%; Reperf 41 (15)%; Long 33 (10)%; P<0.0002 vs Pento group).

CONCLUSIONS

In rats, desflurane 1 MAC significantly decreased myocardial infarct size whatever the period and duration of administration.

The Challenge of Improving Donor Heart Preservation

Heart transplantation has in recent years become the treatment of choice for end stage heart failure. However while the waiting list for transplantation is growing steadily, the donor pool is not increasing. Therefore, in order to meet demand, transplant programs are using older, "marginal donors" and accepting longer ischaemic times for their donor hearts. As donor organs are injured as a consequence of brain death, during the period of donor management, at organ harvest, preservation, implantation and reperfusion, expansion of acceptance criteria places a great burden on achieving optimal long-term outcomes. However, at each step in the process of transplantation strategies can be employed to reduce the injury suffered by the donor organs. In this review, we set out what steps can be taken to improve the quality of donor organs.

The cardioprotective effects of Na+/H+ exchange inhibition and mitochondrial KATP channel activation are additive in the isolated rat heart

The mechanisms of recovery of the isolated rat heart were studied after 30 min of global ischemia. Functional recovery was assessed by the percentage recovery of developed pressure after 30 min reperfusion and by the magnitude of the contracture on reperfusion. After a control ischemia, developed pressure recovered to only 12+/-2% of pre-ischemic control and the reperfusion contracture was very large (81+/-6 mmHg). Activation of the mitochondrial KATP channel with 100 microM diazoxide present throughout ischemia and reperfusion improved recovery of developed pressure to 36+/-3% and reduced the reperfusion contracture (53+/-4 mmHg). Inhibition of the sodium/hydrogen exchanger with 10 microM cariporide caused a larger recovery of developed pressure to 72+/-4% and further reduced the reperfusion contracture (11+/-3 mmHg). The combination of both drugs increased recovery of developed pressure to 96+/-4% and the reperfusion contracture remained small (11+/-5 mmHg). The effectiveness of the timing of exposure to these drugs was explored. When both diazoxide and cariporide were applied 2 min before the end of ischaemia and remained present during reperfusion the recovery of developed pressure was 81+/-4% and the reperfusion contracture was small (12+/-3 mmHg); neither was significantly different to the recovery when both drugs were present throughout ischemia and reperfusion. We conclude that mitochondrial damage, blocked by diazoxide, and the coupled exchanger pathway, blocked by cariporide, are two of the principal damage pathways and functional recovery appears to be complete when both are blocked. The combination of these drugs is also highly effective when given 2 min before the end of ischemia.

K(ATP) channels and pancreatic islet blood flow in anesthetized rats: increased blood flow induced by potassium channel openers

K(ATP) channels are important for insulin secretion and depolarization of vascular smooth muscle. In view of the importance of drugs affecting K(ATP) channels in the treatment of diabetes, we investigated the effects of these channels on splanchnic blood perfusion in general and pancreatic islet blood flow in particular. We treated anesthetized Sprague-Dawley rats with the K(ATP) channel openers diazoxide or NNC 55-0118 or the K(ATP) channel closer glipizide. Both diazoxide and NNC 55-0118 dose-dependently increased total pancreatic and islet blood flow in the presence of moderate hyperglycemia, but had no effects on the blood perfusion of other splanchnic organs. Diazoxide markedly lowered the mean arterial blood pressure and thus increased vascular conductance in all organs studied. NNC 55-0118 had much smaller effects on the blood pressure. Glipizide did not affect total pancreatic blood flow, but decreased islet blood flow by 50% in the presence of hypoglycemia. We conclude that K(ATP) channels actively participate in the blood flow regulation of the pancreatic islets and that substances affecting such channels may also influence islet blood flow.

[Adaptation of perfusion flow during reperfusion to protect ischemic myocardium from calcium loading]

The aim of this study was (i) to evaluate calcium exchanges occurring during the first stage of reperfusion, and (ii) to investigate the effect of reperfusion flow applied on safe and ischemic hearts. Pig hearts (n = 20) were arrested with cardioplegia and randomly assigned into 2 groups: an ischemic group (1 hour in vitro ischemia at 38 degrees C) versus control group, before being subjected to aortic reperfusion (using 1 and 0.1 ml min-1 g-1 perfusion flow). Both oedema and arterio-venous differences in calcium were analysed during reperfusion. The data showed myocardial Ca++ loading in control hearts reperfused at low flow (p < 0.01) and in ischemic hearts reperfused at high flow (p < 0.01), whereas a low flow reperfusion appeared to protect ischemic hearts. In all groups, reperfusion oedema was greater than 20%. In conclusion, the data suggest that reperfusion flow of arrested hearts should be adapted to the state of the heart: a high flow, necessary for a safe heart, can be deleterious for ischemic heart, whereas a low flow, protective for ischemic hearts, can be deleterious for safe heart.