EGLN1 Inhibition and Rerouting of α-Ketoglutarate Suffice for Remote Ischemic Protection

Glucagon-like peptide-1 (GLP-1) mediates cardioprotection by remote ischaemic conditioning

Aims

Although the nature of the humoral factor which mediates cardioprotection established by remote ischaemic conditioning (RIc) remains unknown, parasympathetic (vagal) mechanisms appear to play a critical role. As the production and release of many gut hormones is modulated by the vagus nerve, here we tested the hypothesis that RIc cardioprotection is mediated by the actions of glucagon-like peptide-1 (GLP-1).

Methods and results

A rat model of myocardial infarction (coronary artery occlusion followed by reperfusion) was used. Remote ischaemic pre- (RIPre) or perconditioning (RIPer) was induced by 15 min occlusion of femoral arteries applied prior to or during the myocardial ischaemia. The degree of RIPre and RIPer cardioprotection was determined in conditions of cervical or subdiaphragmatic vagotomy, or following blockade of GLP-1 receptors (GLP-1R) using specific antagonist Exendin(9–39). Phosphorylation of PI3K/AKT and STAT3 was assessed. RIPre and RIPer reduced infarct size by ∼50%. In conditions of bilateral cervical or subdiaphragmatic vagotomy RIPer failed to establish cardioprotection. GLP-1R blockade abolished cardioprotection induced by either RIPre or RIPer. Exendin(9–39) also prevented RIPre-induced AKT phosphorylation. Cardioprotection induced by GLP-1R agonist Exendin-4 was preserved following cervical vagotomy, but was abolished in conditions of M3 muscarinic receptor blockade.

Conclusions

These data strongly suggest that GLP-1 functions as a humoral factor of remote ischaemic conditioning cardioprotection. This phenomenon requires intact vagal innervation of the visceral organs and recruitment of GLP-1R-mediated signalling. Cardioprotection induced by GLP-1R activation is mediated by a mechanism involving M3 muscarinic receptors.

Metabolic Signature of Remote Ischemic Preconditioning Involving a Cocktail of Amino Acids and Biogenic Amines

BACKGROUND

Remote ischemic preconditioning (RIPC) is an attractive therapeutic procedure for protecting the heart against ischemia/reperfusion injury. Despite evidence of humoral mediators transported through the circulation playing a critical role, their actual identities so far remain unknown. We sought to identify plasmatic RIPC-induced metabolites that may play a role.

METHODS AND RESULTS

Rat plasma samples from RIPC and control groups were analyzed using a targeted metabolomic approach aimed at measuring 188 metabolites. Principal component analysis and orthogonal partial least-squares discriminant analysis were used to identify the metabolites that discriminated between groups. Plasma samples from 50 patients subjected to RIPC were secondarily explored to confirm the results obtained in rats. Finally, a combination of the metabolites that were significantly increased in both rat and human plasma was injected prior to myocardial ischemia/reperfusion in rats. In the rat samples, 124 molecules were accurately quantified. Six metabolites (ornithine, glycine, kynurenine, spermine, carnosine, and serotonin) were the most significant variables for marked differentiation between the RIPC and control groups. In human plasma, analysis confirmed ornithine decrease and kynurenine and glycine increase following RIPC. Injection of the glycine and kynurenine alone or in combination replicated the protective effects of RIPC seen in rats.

CONCLUSIONS

We have hereby reported significant variations in a cocktail of amino acids and biogenic amines after remote ischemic preconditioning in both rat and human plasma.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01390129.

Remote ischaemic conditioning in the context of type 2 diabetes and neuropathy: the case for repeat application as a novel therapy for lower extremity ulceration

An emerging treatment modality for reducing damage caused by ischaemia–reperfusion injury is ischaemic conditioning. This technique induces short periods of ischaemia that have been found to protect against a more significant ischaemic insult. Remote ischaemic conditioning (RIC) can be administered more conveniently and safely, by inflation of a pneumatic blood pressure cuff to a suprasystolic pressure on a limb. Protection is then transferred to a remote organ via humoral and neural pathways. The diabetic state is particularly vulnerable to ischaemia–reperfusion injury, and ischaemia is a significant cause of many diabetic complications, including the diabetic foot. Despite this, studies utilising ischaemic conditioning and RIC in type 2 diabetes have often been disappointing. A newer strategy, repeat RIC, involves the repeated application of short periods of limb ischaemia over days or weeks. It has been demonstrated that this improves endothelial function, skin microcirculation, and modulates the systemic inflammatory response. Repeat RIC was recently shown to be beneficial for healing in lower extremity diabetic ulcers. This article summarises the mechanisms of RIC, and the impact that type 2 diabetes may have upon these, with the role of neural mechanisms in the context of diabetic neuropathy a focus. Repeat RIC may show more promise than RIC in type 2 diabetes, and its potential mechanisms and applications will also be explored. Considering the high costs, rates of chronicity and serious complications resulting from diabetic lower extremity ulceration, repeat RIC has the potential to be an effective novel advanced therapy for this condition.

HIF1α and metabolic reprogramming in inflammation

HIF1α is a common component of pathways involved in the control of cellular metabolism and has a role in regulating immune cell effector functions. Additionally, HIF1α is critical for the maturation of dendritic cells and for the activation of T cells. HIF1α is induced in LPS-activated macrophages, where it is critically involved in glycolysis and the induction of proinflammatory genes, notably Il1b. The mechanism of LPS-stimulated HIF1α induction involves succinate, which inhibits prolyl hydroxylases (PHDs). Pyruvate kinase M2 (PKM2) is also induced and interacts with and promotes the function of HIF1α. In another critical inflammatory cell type, Th17 cells, HIF1α acts via the retinoic acid-related orphan receptor-γt (RORγt) to drive Th17 differentiation. HIF1α is therefore a key reprogrammer of metabolism in inflammatory cells that promotes inflammatory gene expression.

Cardioprotection by Remote Ischemic Preconditioning is Blocked in the Aged Rat Heart in Vivo

OBJECTIVES

In animal studies, remote ischemic preconditioning (RIPC) is a powerful tool to protect the heart from ischemia and reperfusion injury. Unfortunately, this effect was not seen consistently in recent large clinical trials. Aging was shown to be a confounding factor for the effect of direct preconditioning in experimental studies, but whether aging also can influence the effect of RIPC and thus be responsible for the contradictory clinical effect is unknown. The aim of this study was to investigate whether the cardioprotective effect of RIPC was abolished by aging.

DESIGN

Randomized, prospective, blinded laboratory investigation.

SETTING

Experimental laboratory.

PARTICIPANTS

Male Wistar rats.

INTERVENTIONS

Anesthetized young (Y, 2-3 months) and aged (A, 22-24 months) male Wistar rats were randomized to 4 groups (n = 6 per group). Control animals (Y-Con and A-Con) were not treated further; RIPC groups (Y-RIPC and A-RIPC) received 4 cycles of 5 minutes of bilateral hind limb ischemia interspersed with 5 minutes reperfusion before myocardial ischemia and reperfusion. All animals underwent 25 minutes of regional myocardial ischemia and 120 minutes of reperfusion. At the end of reperfusion, infarct size was determined by TTC staining.

MEASUREMENTS AND MAIN RESULTS

In the control group of young rats, infarct size was 56±9% of the area at risk. RIPC reduced infarct size to 31±9% (p<0.05 v Y-Con). Cardioprotection by RIPC was abolished completely in the aged rat heart (A-RIPC: 62±8%, A-Con: 63±4%; ns).

CONCLUSIONS

The results of the authors' study showed that cardioprotection induced by remote ischemic preconditioning was blocked in the aged rat heart.

In vivo assessment of behavioral recovery and circulatory exchange in the peritoneal parabiosis model

The sharing of circulation between two animals using a surgical procedure known as parabiosis has created a wealth of information towards our understanding of physiology, most recently in the neuroscience arena. The systemic milieu is a complex reservoir of tissues, immune cells, and circulating molecules that is surprisingly not well understood in terms of its communication across organ systems. While the model has been used to probe complex physiological questions for many years, critical parameters of recovery and exchange kinetics remain incompletely characterized, limiting the ability to design experiments and interpret results for complex questions. Here we provide evidence that mice joined by parabiosis gradually recover much physiology relevant to the study of brain function. Specifically, we describe the timecourse for a variety of recovery parameters, including those for general health and metabolism, motor coordination, activity, and sleep behavior. Finally, we describe the kinetics of chimerism for several lymphocyte populations as well as the uptake of small molecules into the brains of mice following parabiosis. Our characterization provides an important resource to those attempting to understand the complex interplay between the immune system and the brain as well as other organ systems.