Cardiac ATP-sensitive potassium channels: a potential target for an anti-ischaemic pharmacological strategy

Brief periods of ischaemia induce in the myocardium an increased resistance to the injury due to a subsequent, more prolonged ischaemic episode. This phenomenon, known as ischaemic pre-conditioning (IPC), articulated in two distinct phases (an early and a delayed one), is ensured by different biological mechanisms. Although an exhaustive comprehension of these mechanisms has not yet been reached, it is widely accepted that among the various signals involved as triggers and/or end-effectors, an important role is undoubtedly played by the activation of cardiac ATP-sensitive potassium channels (K(ATP)). In the myocardial cells, K(ATP) channels have been identified both in the sarcolemmal membrane (sarc-K(ATP)) and in the mitochondrial inner membrane (mito-K(ATP)). Although many experimental findings suggest that a role of sarc-K(ATP) channel activation in IPC cannot be excluded, in the last few years, many authors have indicated that this phenomenon could be attributed to the exclusive (or at least prevalent) activation of the mito-K(ATP) channels. Conversely, drugs modulating the K(ATP) channels (as activators or blockers), on one hand, have been employed as useful experimental tools for basic studies on IPC. On the other hand, K(ATP)-openers have been viewed as promising possible therapeutic agents for limiting the myocardial injury due to ischaemic episodes. In particular, those molecules exhibiting a good degree of selectivity towards the mito-K(ATP) channels have been indicated as potential anti-ischaemic cardio-protective pharmacological tools, devoid of other biological effects (such as negative inotropic activity, hypotension or hyperglycaemia) linked to the activation of cardiac and non-cardiac sarcK(ATP) channels. In this paper, we wish to report the experimental evidence supporting the role of sarc- and mito-K(ATP) channels in IPC, the relative signalling pathways potentially involved in the mechanisms of cardio-protection and, finally, an overview of the most important molecules acting as activators or blockers of K(ATP) channels, with their selectivity profiles.     

Cardioprotection and kallikrein-kinin system in acute myocardial ischaemia in mice

1. Acute myocardial ischaemia and reperfusion trigger cardioprotective mechanisms that tend to limit myocardial injury. These cardioprotective mechanisms remain for a large part unknown, but can be potentiated by performing ischaemic preconditioning or by administering drugs such as angiotensin-I-converting enzyme (kininase II) inhibitors (ACEI). 2. This brief review summarizes the findings concerning the role of tissue kallikrein (TK), a major kinin-forming enzyme, kinins and kinin receptors in the cardioprotection afforded by ischaemic preconditioning (IPC) or by pharmacological postconditioning by drugs originally targeted at the renin-angiotensin system, ACEI and type 1 angiotensin-II receptor blockers (ARB) in acute myocardial ischaemia. Myocardial ischaemia was induced by left coronary occlusion and was followed after 30 min by a 3 h reperfusion period (IR), performed in vivo in mice. The role of the kallikrein-kinin system (KKS) was studied by using genetically engineered mice deficient in TK gene and their wild-type littermates, or by blocking B1 or B2 bradykinin receptors in wild-type mice using selective pharmacological antagonists. 3. Ischaemic preconditioning (three cycles: 3 min occlusion/5 min reperfusion) enhances the ability of the heart of wild-type mice to tolerate IR. Tissue kallikrein plays a major role in the cardioprotective effect afforded by IPC, which is largely reduced in TK-deficient mice. The B2 receptor is the main kinin receptor involved in the cardioprotective effect of IPC. 4. Tissue kallikrein is also required for the cardioprotective effects of pharmacological postconditioning with ACEI (ramiprilat) or ARB (losartan), which are abolished for both classes of drugs in TK-deficient mice. The B2 receptor mediates the cardioprotective effects of these drugs. Activation of angiotensin-II type 2 (AT2) receptor is involved in the cardioprotective effects of losartan, suggesting a functional coupling between AT2 receptor and TK during angiotensin-II type 1 (AT1) receptor blockade. 5. The demonstration of a cardioprotective effect of the KKS in acute myocardial ischaemia involving TK and the B2 receptor and playing a major role in IPC or pharmacological postconditioning by ACEI or ARB, suggests a potential therapeutic approach based on pharmacological activation of the B2 receptor.     

Inflammation in ischaemic brain injury: Current advances and future perspectives

1. Numerous studies have indicated that inflammation plays a key role in ischaemic brain injury. Brain ischaemia–reperfusion‐induced inflammatory responses include increased microglial and astrocyte activity, increased production of cytokines, chemokines, adhesion molecules and metalloproteinases and the infiltration of monocytes and leucocytes into injured brain regions. 2. Although a significant proportion of the inflammatory response appears to exacerbate ischaemic brain injury, certain inflammatory responses are beneficial to ischaemic brains. It is necessary to further identify the detrimental and beneficial inflammatory responses so that therapeutic strategies can be designed for stroke patients to selectively inhibit detrimental responses while enhancing beneficial responses. 3. Increasing evidence also indicates significant changes in the peripheral immune system of stroke patients and animals that undergo cerebral ischaemia. It is worth elucidating the effects of these changes in ischaemic brain damage. 4. There are complex interactions in the ischaemic brain between microglia and other cell types, including neurons, astrocytes, endothelial cells and stem cells. It is of particular interest to determine the mechanisms underlying the roles of high‐mobility group box‐1, advanced glycation end‐products receptors (RAGE), S100B and NADPH oxidase in these interactions. 5. Because brain ischaemia‐induced inflammation is a relatively long‐lasting event with profound effects on brain injury, it is of considerable importance to further investigate the mechanisms underlying inflammation in ischaemic brains.     

Therapeutic potential of anti-inflammatory drugs in focal stroke

The importance of cytokines, especially TNF-α and IL-1β, are emphasised in the propagation and maintenance of the brain inflammatory response to injury. Much data supports the case that ischaemia and trauma elicit an inflammatory response in the injured brain. This inflammatory response consists of mediators (cytokines, chemokines and adhesion molecules) followed by cells (neutrophils early after the onset of brain injury and then a later monocyte infiltration). De novo upregulation of pro-inflammatory cytokines, chemokines and endothelial-leukocyte adhesion molecules occurs soon after focal ischaemia and trauma, as well as at the time when the tissue injury is evolving. The significance of this brain inflammatory response and its contribution to brain injury is now becoming more understood. In this review, we discuss the role of TNF-α and IL-1β in traumatic and ischaemic brain injury and associated inflammation and the co-operative actions of chemokines and adhesion molecules in this process. We also address novel approaches to target cytokines and reduce the brain inflammatory response and thus brain injury, in stroke and neurotrauma. The mitogen-activated protein kinase (MAPK), p38, has been linked to inflammatory cytokine production and cell death following cellular stress. Stroke-induced p38 enzyme activation in the brain has been demonstrated and treatment with a second generation p38 MAPK inhibitor, SB-239063, provides a significant reduction in infarct size, neurological deficits and inflammatory cytokine expression produced by focal stroke. SB-239063 can also provide direct protection of cultured brain tissue to in vitro ischaemia. This robust SB-239063-induced neuroprotection emphasises a significant opportunity for targeting MAPK pathways in ischaemic stroke injury and also suggests that p38 inhibition should be evaluated for protective effects in other experimental models of nervous system injury and neurodegeneration.     

Therapeutic potential of anti-inflammatory drugs in focal stroke

The importance of cytokines, especially TNF-alpha and IL-1beta, are emphasised in the propagation and maintenance of the brain inflammatory response to injury. Much data supports the case that ischaemia and trauma elicit an inflammatory response in the injured brain. This inflammatory response consists of mediators (cytokines, chemokines and adhesion molecules) followed by cells (neutrophils early after the onset of brain injury and then a later monocyte infiltration). De novo upregulation of pro-inflammatory cytokines, chemokines and endothelial-leukocyte adhesion molecules occurs soon after focal ischaemia and trauma, as well as at the time when the tissue injury is evolving. The significance of this brain inflammatory response and its contribution to brain injury is now becoming more understood. In this review, we discuss the role of TNF-alpha and IL-1beta in traumatic and ischaemic brain injury and associated inflammation and the co-operative actions of chemokines and adhesion molecules in this process. We also address novel approaches to target cytokines and reduce the brain inflammatory response and thus brain injury, in stroke and neurotrauma. The mitogen-activated protein kinase (MAPK), p38, has been linked to inflammatory cytokine production and cell death following cellular stress. Stroke-induced p38 enzyme activation in the brain has been demonstrated and treatment with a second generation p38 MAPK inhibitor, SB-239063, provides a significant reduction in infarct size, neurological deficits and inflammatory cytokine expression produced by focal stroke. SB-239063 can also provide direct protection of cultured brain tissue to in vitro ischaemia. This robust SB-239063-induced neuroprotection emphasises a significant opportunity for targeting MAPK pathways in ischaemic stroke injury and also suggests that p38 inhibition should be evaluated for protective effects in other experimental models of nervous system injury and neurodegeneration.     

Ischaemic preconditioning of the vasculature: an overlooked phenomenon for protecting the heart?

Exposing the heart to brief episodes of ischaemia protects the myocardium and vascular endothelial cells against functional damage and cell death caused by subsequent prolonged ischaemia. Elucidation of the mechanisms that are involved in this phenomenon known as 'ischaemic preconditioning' and identification of drugs that mimic the protective response have the potential to improve the prognosis of myocardial infarction and other cardiac syndromes dramatically. This article focuses on recent findings on the effects of ischaemic preconditioning of the coronary vasculature, which highlight the endothelium as an important target for a successful therapeutic approach to myocardial ischaemia-reperfusion injury.     

Inhalational anaesthetics and cardioprotection

The heart has a strong endogenous cardioprotection mechanism that can be triggered by short periods of ischaemia (like during angina) and protects the myocardium during a subsequent ischaemic event (like during a myocardial infarction). This important mechanism, called ischaemic pre-conditioning, has been extensively investigated, but the practical relevance of an intervention by inducing ischaemia is mainly limited to experimental situations. Research that is more recent has shown that many volatile anaesthetics can induce a similar cardioprotection mechanism, which would be clinically more relevant than inducing cardioprotection by ischaemia. In the last few decades, several laboratory investigations have shown that exposure to inhalational anaesthetics leads to a variety of changes in the protein structure of the myocardium. By a functional blockade of these modified (i.e. activated) target enzymes, it was demonstrated that some of these changes in protein structure and distribution can mediate cardioprotection by anaesthetic pre-conditioning. This chapter gives an overview of our current understanding of the signal transduction of this phenomenon. In addition to an intervention before ischaemia (i.e. pre-conditioning), there are two more time windows when a substance may interact with the ischaemia-reperfusion process and might modify the extent of injury: (1) during ischaemia or (2) after ischaemia (i.e. during reperfusion) (postconditioning). In animal experiments, the volatile anaesthetics also interact with these mechanisms (especially immediately after ischaemia), i.e. by post-conditioning. Since ischaemia-reperfusion of the heart routinely occurs in a variety of clinical situations such as during transplant surgery, coronary artery bypass grafting, valve repair or vascular surgery, anaesthetic-induced cardioprotection might be a promising option to protect the myocardium in clinical situations. Initial studies now confirm an effect on surrogate outcome parameters such as length of ICU or in-hospital stay or post-ischaemic troponin release. In this chapter, we will summarize our current understanding of the three mechanisms of anaesthetic cardioprotection exerted by inhalational anaesthetics.     

Drug development for stroke: importance of protecting cerebral white matter.

Multiple pharmacological mechanisms have been identified over the last decade which can protect grey matter from ischaemic damage in experimental models. A large number of drugs targeted at neurotransmitter receptors and related mechanisms involved in ischaemic damage have advanced to clinical trials in stroke and head injury based on their proven ability to reduce grey matter damage in animal models. The outcome to date of the clinical trials of neuroprotective drugs has been disappointing. Although the failure to translate preclinical pharmacological insight into therapy is multifactorial, we propose that the failure to ameliorate ischaemic damage to white matter has been a major factor. The recent development of quantitative techniques to assess ischaemic damage to cellular elements in white matter, both axons and oligodendrocytes, allows rigorous evaluation of pharmacologic mechanisms which may protect white matter in ischaemia. Such pharmacological approaches provide therapeutic opportunities which are both additional or alternatives to those currently being evaluated in man.     

Sex-based differences in cardiac ischaemic injury and protection: therapeutic implications

Ischaemic heart disease (IHD) is the most frequent cause of mortality among men and women. Many epidemiological studies have demonstrated that premenopausal women have a reduced risk for IHD compared with their male counterparts. The incidence of IHD in women increases after menopause, suggesting that IHD is related to declining oestrogen levels. Experimental observations have confirmed the results of epidemiological studies investigating sex-specific differences in cardiac tolerance to ischaemia. Female sex appears also to favourably influence cardiac remodelling after ischaemia/reperfusion injury. Furthermore, sex-related differences in ischaemic tolerance of the adult myocardium can be influenced by interventions during the early phases of ontogenetic development. Detailed mechanisms of these sex-related differences remain unknown; however, they involve the genomic and non-genomic effects of sex steroid hormones, particularly the oestrogens, which have been the most extensively studied. Although the protective effects of oestrogen have many potential therapeutic implications, clinical trials have shown that oestrogen replacement in postmenopausal women may actually increase the incidence of IHD. The results of these trials have illustrated the complexity underlying the mechanisms involved in sex-related differences in cardiac tolerance to ischaemia. Sex-related differences in cardiac sensitivity to ischaemia/reperfusion injury may also influence therapeutic strategies in women with acute coronary syndrome. Women undergo coronary intervention less frequently and a lower proportion of women receive evidence-based therapy compared with men. Although our understanding of this important topic has increased in recent years, there is an urgent need for intensive experimental and clinical research to develop female-specific therapeutic strategies. Only then we will be able to offer patients better evidence-based treatment, a better quality of life and lower mortality.     

The time course of cardioprotection induced by GR79236, a selective adenosine A1-receptor agonist, in myocardial ischaemia-reperfusion injury in the pig

The cardioprotective effects of the selective adenosine A1-receptor agonist, GR79236 (N-[(1S, trans)-2-hydroxycyclopentyl]adenosine), were examined in a porcine model of myocardial ischaemia-reperfusion injury. When pigs were subjected to a 50-min coronary artery occlusion followed by 3-h reperfusion, GR79236 (10 nmol/kg, i.v.) significantly reduced infarct size whether given 10 min before the onset of ischaemia or reperfusion. This effect was independent of the bradycardia induced by GR79236, as it was also observed in animals in which heart rate was maintained by electrical pacing. However, GR79236 administered 10 min after reperfusion did not reduce infarct size. GR79236 had no effect on the incidence or outcome of ventricular dysrhythmias in this pig model of infarction. Similarly, ischaemic preconditioning (IPC, 2 x 10-min ischaemia and 10-min reperfusion) significantly reduced infarct size. The selective adenosine A1-receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 3.3 micromol/kg, i.v.), abolished the haemodynamic and cardioprotective effects of GR79236 and the cardioprotective effects of IPC in anaesthetised pigs. In conclusion, GR79236 exerted a marked cardioprotective effect in a porcine model of myocardial ischaemia-reperfusion injury, provided that it was administered before reperfusion. This suggests that GR79236 may have clinical utility in the treatment of various aspects of ischaemic heart disease.     

Cytochrome P450 2J3/epoxyeicosatrienoic acids mediate the cardioprotection induced by ischaemic post-conditioning, but not preconditioning, in the rat

1. Cytochrome P450 (CYP) epoxygenases and their arachidonic acid metabolites play a protective role against ischaemia-reperfusion injury. In the present study, we investigated whether endogenous CYP2J3/epoxyeicosatrienoic acid (EET) mediates the cardioprotective effects of ischaemic preconditioning (IPC) and ischaemic post-conditioning (IPost). 2. Male Wistar rats were subjected to two cycles of IPC, consisting of 5 min ischaemia and 5 min reperfusion, followed by 45 min occlusion and 2 h reperfusion; IPost consisted of three cycles of 30 s reperfusion and 30 s re-occlusion at the onset of reperfusion. The selective CYP epoxygenase inhibitor N-methylsulphonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH; 3 mg/kg) was administered 10 min before ischaemia or during ischaemia 10 min before reperfusion started. Cardiac function was measured continuously with a angiocatheter connected to a fluid-filled pressure transducer and myocardial infarct size was assessed by triphenyl tetrazolium chloride staining at the end of the experiment. 3. Subjecting rats to IPC and IPost similarly improved cardiac function and reduced myocardial infarct size. Interestingly, IPost, but not IPC, significantly increased CYP2J3 mRNA (1.75 ± 0.22 vs 1.0; P < 0.05) and protein (1.62 ± 0.22 vs 1.0; P < 0.05), as well as 11,12-EET synthesis compared to I/R (6.2 ± 0.2 vs 2.9 ± 0.2 ng/mg wet weight, respectively; P < 0.01). Administration of MS-PPOH before ischaemia significantly decreased 11,12-EET synthesis in both IPC and IPost compared with I/R rats (2.1 ± 0.2, 3.2 ± 0.3 and 2.9 ± 0.2 ng/mg wet weight, respectively; P < 0.01), but decreased the cardioprotective effects, as evidenced by cardiac function and myocardial infarct size, of IPost only. 4. These data indicate that endogenous activation of CYP2J3/EET may be an essential trigger leading to the protective effects of IPost, but not IPC, in the rat heart.     

Endothelin and the ischaemic heart

Soon after its identification as a powerful vasoconstrictor peptide, endothelin (ET-1) was implicated as a detrimental agent involved in determining the outcome of myocardial ischaemia and reperfusion. Early experimental studies demonstrated that ET(A) selective and mixed ET(A)/ET(B) receptor antagonists can reduce infarct size and prevent ischaemia-induced ventricular arrhythmias in models of ischaemia/reperfusion, implying that ET-1 acts through the ET(A) receptor to contribute to injury and arrhythmogenesis. However, as our understanding of the physiology of ET-1 has expanded, the role of ET-1 in the ischaemic heart appears ever more complex. Recent evidence suggests that ET-1 exerts actions on the heart that are not only detrimental (vasoconstriction, inhibition of NO production, activation of inflammatory cells), but which may also contribute to tissue repair, such as inhibition of cardiomyocyte apoptosis. In addition, ET-1-induced mast cell degranulation has been linked to a homeostatic mechanism that controls endogenous ET-1 levels, which may have important implications for the ischaemic heart. Furthermore the mechanism by which ET-1 promotes arrhythmogenesis remains controversial. Some studies imply a direct electrophysiological effect of ET-1, via ET(A) receptors, to increase monophasic action potential duration (MAPD) and induce early after-depolarisations (EADs), while other studies support the view that coronary constriction resulting in ischaemia is the basis for the generation of arrhythmias. Moreover, ET-1 can induce cardioprotection (precondition) against infarct size and ventricular arrhythmias, through as yet incompletely understood mechanisms. To enable us to identify the most appropriate means of targeting this system in a therapeutically meaningful way we need to continue to explore the physiology of ET-1, both in the normal and the ischaemic heart.     

A kallidin-like peptide is a protective cardiac kinin, released by ischaemic preconditioning of rat heart

Bradykinin is thought to play a major role among the endogenous cardioprotective candidates of ischaemic preconditioning (IPC). Little attention has been paid to the fact that in the tissue kallidin (KAL), rather than bradykinin might be the physiological mediator of the kallikrein-kinin system. In order to evaluate the importance of one or the other peptide the release and effect of both kinins has been investigated in isolated rat hearts following IPC. Bradykinin- and a KAL-like peptide were measured in the effluent of the rat isolated Langendorff heart with two different specific radioimmunoassays. The creatine kinase activity in the effluent was judged as degree of cardiac injury caused by ischaemia. During IPC, which consists of three 5 min no-flow and 5 min reperfusion cycles prior to the 30 min ischaemia, the bradykinin level in the effluent did not change significantly (15.4-19.4 pg ml(-1)). In the control group the bradykinin levels were 15.9-16.6 pg ml(-1). During IPC KAL-like peptide (Arg(1)-, instead of Lys(1)-KAL), which has recently been verified by mass spectrometry, displays 5.8-fold higher levels in the effluent and significantly increases in the same time interval from 90.4 to 189 pg ml(-1).After 30 min ischaemia the bradykinin levels in the IPC group were not significantly different to those of the control group (18.7 vs 14.4 pg ml(-1)). The KAL-like peptide levels in the IPC group vs the control group were 105 vs 86.1 pg ml(-1). By the 30 min ischaemia the creatine kinase activity in the IPC group increased from 0.367 to 8.93 U l(-1) (before and 10-30 min after ischaemia). In the control group during the same time period the creatine kinase levels increased from 0.277 to 34.9 U l(-1). The low increase in creatine kinase activity following IPC was taken as equivalent of the cardioprotective action. A KAL antibody or HOE140 (kinin B(2)-receptor antagonist) completely abolished this beneficial effect of IPC (36.6 and 53.0 U l(-1)) when added to the perfusion medium during the reperfusion cycles of IPC prior to the 30 min ischaemia. Our data suggest that in rat hearts KAL-like peptide rather than bradykinin is the physiological compound activated by IPC and acting via the cardiac kinin B(2)-receptor. Thus, endogenously generated KAL-like peptide seems to play a major role in the cardioprotection of IPC.     

Therapeutic approaches to organ preservation injury

The long-term preservation of organ explants and protection from cold ischaemia and subsequent rewarming reperfusion injury is essential to successful allografting and instrumental in enlarging the international donor pool. Current hypothermic preservation solutions may have reached the limit of what is possible in terms of explant longevity and viability, and research attention has been turned to novel organoprotective pharmacotherapeutics that could provide the next generation of explant/transplant nurture. Organoprotection is equally paramount during surgical procedures requiring a period of ischaemia as in coronary artery bypass grafting, angioplasty or stenting. Similarly, the phenomenon of non-freezing cold injury (NFCI), associated with microcirculatory and neuronal damage in exposed and often immersed extremities, also involves ischaemia–reperfusion injury. Whilst additions to cold storage solutions of antioxidants and modulators of cellular metabolism may extend their preservative efficacy, pharmacological triggers of ischaemic preconditioning and the hibernation phenotype may offer breakthroughs in the prevention of ischaemia–reperfusion injury.     

Mast cells,peptides and cardioprotection – an unlikely marriage?

1 Mast cells have classically been regarded as the ‘bad guys’ in the setting of acute myocardial ischaemia, where their released contents are believed to contribute both to tissue injury and electrical disturbances resulting from ischaemia. Recent evidence suggests, however, that if mast cell degranulation occurs in advance of ischaemia onset, this may be cardioprotective by virtue of the depletion of mast cell contents that can no longer act as instruments of injury when the tissue becomes ischaemic. 2 Many peptides, such as ET‐1, adrenomedullin, relaxin and atrial natriuretic peptide, have been demonstrated to be cardioprotective when given prior to the onset of myocardial ischaemia, although their physiological functions are varied and the mechanisms of their cardioprotective actions appear to be diverse and often ill defined. However, one common denominator that is emerging is the ability of these peptides to modulate mast cell degranulation, raising the possibility that peptide‐induced mast cell degranulation or stabilization may hold the key to a common mechanism of their cardioprotection. 3 The aim of this review was to consolidate the evidence implying that mast cell degranulation could play both a detrimental and protective role in myocardial ischaemia, depending upon when it occurs, and that this may underlie the cardioprotective effects of a range of diverse peptides that exerts physiological effects within the cardiovascular system.     

Anti-inflammatory effects of limb ischaemic preconditioning are mediated by sensory nerve activation in rats

We have shown that ischaemic preconditioning ameliorates both the local periosteal and the systemic leukocyte activation evoked by limb ischaemia–reperfusion. We hypothesized that the activation of chemosensitive afferent nerves by transient ischaemia contributes to the protective mechanisms of ischaemic preconditioning via a calcitonin gene-related peptide (CGRP)-dependent mechanism. In Sprague–Dawley rats, 60-min complete limb ischaemia was followed by 180 min of reperfusion. In further experiments, the CGRP analogue hCGRP (0.3 μg kg^?1) or ischaemic preconditioning (2?×?10-min ischaemia/10-min reperfusion) was applied prior to the ischaemia–reperfusion insult. Ischaemic preconditioning was performed in three subgroups in which animals received the CGRP receptor antagonist CGRP_8–37 (30 μg kg^?1 h^?1), the chemosensitive afferent nerve inactivator resiniferatoxin (3?×?15 μg kg^?1, sc), or vehicle. The effects of CGRP_8-37 and resiniferatoxin on ischaemia–reperfusion without ischaemic preconditioning were also evaluated. In the tibial periosteum of rats, intravital fluorescence microscopy and immunohistochemistry revealed significant attenuations of ischaemia-reperfusion-induced post-ischaemic leukocyte–endothelial interactions (rolling and adherence in the postcapillary venules) and tissue intracellular adhesion molecule expression following ischaemic preconditioning or hCGRP administration. Administration of CGRP_8-37 or pretreatment of animals with resiniferatoxin reversed the anti-inflammatory effects of limb ischaemic preconditioning, but failed to affect the microcirculatory consequences of ischaemia–reperfusion without ischaemic preconditioning. The results suggest that activation of the chemo- (capsaicin-) sensitive afferent nerves is involved in the mechanisms of microcirculatory anti-inflammatory protection provided by limb ischaemic preconditioning. Controlled activation of chemosensitive C-fibres or the CGRP receptors by the induction of ischaemic preconditioning or other means may furnish therapeutic benefit by ameliorating the periosteal microcirculatory consequences of tourniquet ischaemia.     

3',4'-Dihydroxyflavonol reduces infarct size and injury associated with myocardial ischaemia and reperfusion in sheep

1 The antioxidant properties of flavonols in vivo and their potential benefits in myocardial ischaemia/reperfusion (I/R) injury have been little investigated. We evaluated the ability of a synthetic flavonol, 3',4'-dihydroxyflavonol (DiOHF) to scavenge superoxide in post-I/R myocardium and to prevent myocardial I/R injury. 2 Anaesthetized sheep were studied in four groups (n=5-6): control, ischaemic preconditioning (IPC), vehicle and DiOHF (before reperfusion, 5 mg kg(-1), i.v.). The left anterior descending coronary artery was occluded distal to the second diagonal branch for 1 h followed by 2 h of reperfusion. Infarct size, myocardial function, NADPH-activated superoxide generation and biochemical markers of injury were measured. 3 DiOHF (10(-8)-10(-4) m) incubated in vitro with post-I/R myocardium from the vehicle group suppressed superoxide production dose-dependently. 4 DiOHF administered in vivo also significantly reduced superoxide generation in vitro. DiOHF and IPC markedly reduced infarct size, which was 73+/-2% of the area at risk in vehicle, 50+/-4% in DiOHF, 75+/-5% in control and 44+/-4% in IPC. Post-I/R segment shortening within the ischaemic zone was greater in DiOHF (2.3+/-0.7%; P<0.01) and IPC (1.7+/-0.5%; P<0.01) than those in corresponding controls (-1.7+/-0.4; -2.1+/-0.4%). 5 DiOHF and IPC improved coronary blood flow to the ischaemic area and preserved higher levels of nitric oxide metabolites in the venous outflow from the ischaemic zone. 6 DiOHF attenuated superoxide production in post-I/R myocardium, and significantly reduced infarct size and injury following I/R in anaesthetized sheep. The extent of protection by DiOHF is comparable to that afforded by IPC. Thus, DiOHF has clinical potential for improving recovery from acute myocardial infarction and other ischaemic syndromes.     

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.     

AMPA receptor antagonists with additional mechanisms of action: new opportunities for neuroprotective drugs?

Ischaemic stroke of the brain accounts for about one third of all deaths in industrialized countries. Many of the patients who survive are severily impaired. Thus, there is an enormous need for pharmacotherapy for the treatment of ischaemic stroke. Why is such a treatment not available yet? Are the pathophysiological sequelae of brain ischaemia not well understood? Have there been no attempts for clinical development of neuroprotective drugs? Everyone who is engaged in stroke research knows that the opposite is true: The cellular processes occuring after brain ischaemia have been studied for a long time, and we have a thorough understanding of the cellular processes which are involved. Many compounds underwent clinical trials, but most of them failed. One hypothesis to explain this disappointing fact might be that the cellular consequences of stroke are manyfold, but that the clinically tested compounds were selective for only one molecular mechanism. The aim of this review is to give a summary of the pathophysiological mechanisms which occur during and after an ischaemic stroke, and to comment on the preclinical studies where multiple disease-related mechanisms were targeted pharmacologically. Moreover, a novel class of neuroprotective compounds, the oxadiazole derivatives, will be presented. Compounds of this chemical class target two key mechanisms which are important for the pathophysiology of stroke, namely voltage-gated sodium channels, as well as glutamate receptors of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype.