Preconditioning, anesthetics, and perioperative medication

The Melatonin Receptor Agonist Ramelteon Induces Cardioprotection that Requires MT2 Receptor Activation and Release of Reactive Oxygen Species

Purpose

The melatonin receptor (MT) agonist ramelteon has a higher affinity to MT1 than for MT2 receptors and induces cardioprotection by involvement of mitochondrial potassium channels. Activation of mitochondrial potassium channels leads to release of free radicals. We investigated whether (1) ramelteon-induced cardioprotection is MT2 receptor specific and (2) if free radicals are involved in ramelteon-induced cardioprotection.

Methods

Hearts of male Wistar rats were randomized, placed on a Langendorff system, and perfused with Krebs-Henseleit buffer at a constant pressure of 80 mmHg. All hearts were subjected to 33 min of global ischemia and 60 min of reperfusion. Before ischemia hearts were perfused with ramelteon (Ram) with or without the MT2 receptor inhibitor 4-phenyl-2-propionamidotetralin (4P-PDOT+Ram, 4P-PDOT). In subsequent experiments, ramelteon was administered together with the radical oxygen species (ROS) scavenger N-2-mercaptopropionylglycine (MPG+Ram). To determine whether the blockade of ramelteon-induced cardioprotection can be restored, we combined ramelteon and MPG with mitochondrial permeability transition pore (mPTP) inhibitor cyclosporine A (CsA) at different time points. Infarct size was determined by triphenyltetrazolium chloride (TTC) staining.

Results

Ramelteon-induced infarct size reduction was completely blocked by 4P-PDOT and MPG. Ramelteon and MPG combined with CsA before ischemia were not cardioprotective but CsA at the onset of reperfusion could restore infarct size reduction.

Conclusions

This study shows for the first time that despite the higher affinity to MT1 receptors, (1) ramelteon-induced cardioprotection involves MT2 receptors, (2) cardioprotection requires ROS release, and (3) inhibition of the mPTP can restore infarct size reduction.

Volatile anesthetics versus propofol in the cardiac surgical setting of remote ischemic preconditioning: a secondary analysis of a Cochrane Systematic Review

INTRODUCTION

So far, the concept of remote ischemic preconditioning (RIPC) failed its translation from experimental to clinical studies. In addition to our Cochrane Systematic Review, we systematically assessed the use of the intravenous anesthetic propofol, as a potential confounding factor.

EVIDENCE ACQUISITION

We searched CENTRAL, MEDLINE, Embase and Web of Science. We included randomized controlled trials comparing RIPC with no RIPC in adult patients scheduled for coronary artery bypass graft surgery (with or without valve surgery) receiving either exclusively propofol or exclusively volatile anesthetics. Two authors independently assessed methodological quality and extracted data. We report odds ratios (ORs) with 95% confidence intervals as our summary statistics are based on random-effects models.

EVIDENCE SYNTHESIS

We included 14 studies involving 4060 participants. We found no difference in treatment effect between the propofol and volatile anesthetic groups when RIPC or no RIPC is applied on a composite endpoint (all-cause mortality, non-fatal myocardial infarction and/or any new stroke), all-cause mortality, non-fatal myocardial infarction, stroke, or length of stay on ICU. On cardiac markers, RIPC did show a treatment effect on cardiac troponin T measured as AUC 72 hours (SMD -0.80, CI -1.34, -0.25) in the propofol group. However, these findings have to be interpreted with great caution, to date only a very limited number of patients received volatile anesthetics in RIPC trials (minimum N.=15, maximum N.=232).

CONCLUSIONS

Present data do not permit a final assessment regarding the role of volatile or intravenous anesthetics as a possible confounding factor in RIPC trials.

Remote ischaemic preconditioning versus sham procedure for abdominal aortic aneurysm repair: an external feasibility randomized controlled trial

BACKGROUND

Despite advances in perioperative care, elective abdominal aorta aneurysm (AAA) repair carries significant morbidity and mortality. Remote ischaemic preconditioning (RIC) is a physiological phenomenon whereby a brief episode of ischaemia-reperfusion protects against a subsequent longer ischaemic insult. Trials in cardiovascular surgery have shown that RIC can protect patients' organs during surgery. The aim of this study was to investigate whether RIC could be successfully introduced in elective AAA repair and to obtain the information needed to design a multi-centre RCT.

METHODS

Consecutive patients presenting for elective AAA repair, using an endovascular (EVAR) or open procedure, in a single large city hospital in the UK were assessed for trial eligibility. Patients who consented to participate were randomized to receive RIC (three cycles of 5 min ischaemia followed by 5 min reperfusion in the upper arm immediately before surgery) or a sham procedure. Patients were followed up for 6 months. We assessed eligibility and consent rates, the logistics of RIC implementation, randomization, blinding, data capture, patient and staff opinion, and variability and frequency of clinical outcome measures.

RESULTS

Between January 2010 and December 2012, 98 patients were referred for AAA repair, 93 were screened, 85 (91%) were eligible, 70 were approached for participation and 69 consented to participate; 34 were randomized to RIC and 35 to the sham procedure. There was a greater than expected variation in the complexity of EVAR that impacted the outcomes. Acute kidney injury occurred in 28 (AKIN 1: 23%; AKIN 2: 15% and AKIN 3: 3%) and 7 (10%) had a perioperative myocardial infarction. Blinding was successful, and interviews with participants and staff indicated that the procedure was acceptable. There were no adverse events secondary to the intervention in the 6 months following the intervention.

CONCLUSIONS

This study provided essential information for the planning and design of a multi-centre RCT to assess effectiveness of RIC for improving clinical outcomes in elective AAA repair. Patient consent was high, and the RIC intervention was carried out with minimal disruption to clinical care. The allocation scheme for a definite trial should take into account both the surgical procedure and its complexity to avoid confounding the effect of the RIC, as was observed in this study.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN19332276 (date of registration: 16 March 2012). The trial protocol is available from the corresponding author.

Reduction of myocardial infarct size with ischemic "conditioning": physiologic and technical considerations

A wealth of evidence has revealed that the heart can be "conditioned" and rendered less vulnerable to ischemia-reperfusion injury via the upregulation of endogenous protective signaling pathways. Three distinct conditioning strategies have been identified: (1) preconditioning, the phenomenon where brief episodes of myocardial ischemia (too brief to cause cardiomyocyte death) limit necrosis caused by a subsequent sustained ischemic insult; (2) postconditioning, the concept that relief of myocardial ischemia in a staged or stuttered manner attenuates lethal ischemia-reperfusion injury; and (3) remote conditioning, or upregulation of a cardioprotective phenotype initiated by ischemia in a remote organ or tissue and "transported" to the heart. Progress has been made in defining the technical requirements and limitations of each of the 3 ischemic conditioning models (including the timing and severity of the protective stimulus), as well as elucidating the molecular mechanisms (in particular, the receptor-mediated signaling pathways) responsible for conditioning-induced myocardial protection. Moreover, phase III clinical trials are in progress, seeking to capitalize on the protection that can be achieved by postconditioning and remote conditioning, and applying these strategies in patients undergoing cardiac surgery or angioplasty for the treatment of acute myocardial infarction. There is, however, a potentially important caveat to the clinical translation of myocardial conditioning: emerging data suggest that the efficacy of ischemic conditioning is compromised in aging, diabetic, and hypertensive cohorts, the specific populations in which myocardial protection is most relevant. Successful clinical application of myocardial conditioning will therefore require an understanding of the potential confounding consequences of these comorbidities on the "conditioned" phenotype.

Ischemic preconditioning: the role of mitochondria and aging

Aging represents a triple threat for myocardial infarction (MI). Not only does the incidence of MI increase with age, but the heart becomes more susceptible to MI induced damage and protective interventions such as ischemic preconditioning (IPC) become less effective. Therefore, any rational therapeutic strategy must be built around the ability to combat the detrimental effects of ischemia in aged individuals. To accomplish this, we need to develop a better understanding of how ischemic damage, protection, and aging are linked. In this regard, mitochondria have emerged as a common theme. First, mitochondria contribute to cell damage during ischemia-reperfusion (IR) and are central to cell death. Second, the protective signaling pathways activated by IPC converge on mitochondria, and the opening of mitochondrial ion channels alone is sufficient to elicit protection. Finally, mitochondria clearly influence the aging process, and specific defects in mitochondrial activity are associated with age-related functional decline. This review will summarize the effects of aging on myocardial IR injury and discuss relevant and emerging strategies to protect against MI with an emphasis on mitochondrial function.

[Choice of anaesthetic approach and anaesthetic drugs]

BACKGROUND

All types of anaesthesia should ensure absence of pain, inhibit autonomic responses and provide optimal conditions for surgery. Choice of anaesthetic approach (local, regional or general anaesthesia or a combination of methods) depends on type of surgery and the patients' health and preferences.

MATERIAL AND METHODS

The review is based on literature identified through non-systematic searches in PubMed and own research and experience.

RESULTS

When selecting anaesthetic approach and anaesthetic drugs one has to consider not only the perioperative period, but also postoperative aspects such as pain relief, awakeness, functional ability and absence of nausea. After major surgery, regional anaesthesia (especially epidural anaesthesia) and postoperative analgesia have been shown to reduce pulmonary complications and chronic pain. General anaesthesia can be administered either by volatile agents for inhalation, intravenous hypnotics, potent opioids or a combination (often used). Volatile agents, shown to be cardioprotective during cardiac surgery, are recommended for major non-cardiac surgery in patients with heart disease (even though clinical documentation is limited).

INTERPRETATION

An appropriate anaesthetic approach, taking into account patient characteristics and type of surgery, is important for safety and potential complications. In some situations, the anaesthetic approach and anaesthetic drugs may have an impact on outcome.

A novel mitochondrial K(ATP) channel assay

RATIONALE

The mitochondrial ATP sensitive potassium channel (mK(ATP)) is implicated in cardioprotection by ischemic preconditioning (IPC), but the molecular identity of the channel remains controversial. The validity of current methods to assay mK(ATP) activity is disputed.

OBJECTIVE

We sought to develop novel methods to assay mK(ATP) activity and its regulation.

METHODS AND RESULTS

Using a thallium (Tl(+))-sensitive fluorophore, we developed a novel Tl(+) flux based assay for mK(ATP) activity, and used this assay probe several aspects of mK(ATP) function. The following key observations were made. (1) Time-dependent run down of mK(ATP) activity was reversed by phosphatidylinositol-4,5-bisphosphate (PIP(2)). (2) Dose responses of mK(ATP) to nucleotides revealed a UDP EC(50) of approximately 20 micromol/L and an ATP IC(50) of approximately 5 micromol/L. (3) The antidepressant fluoxetine (Prozac) inhibited mK(ATP) (IC(50)=2.4 micromol/L). Fluoxetine also blocked cardioprotection triggered by IPC, but did not block protection triggered by a mK(ATP)-independent stimulus. The related antidepressant zimelidine was without effect on either mK(ATP) or IPC.

CONCLUSIONS

The Tl(+) flux mK(ATP) assay was validated by correlation with a classical mK(ATP) channel osmotic swelling assay (R(2)=0.855). The pharmacological profile of mK(ATP) (response to ATP, UDP, PIP(2), and fluoxetine) is consistent with that of an inward rectifying K(+) channel (K(IR)) and is somewhat closer to that of the K(IR)6.2 than the K(IR)6.1 isoform. The effect of fluoxetine on mK(ATP)-dependent cardioprotection has implications for the growing use of antidepressants in patients who may benefit from preconditioning.