Pretreatment with D-myo-inositol trisphosphate reduces infarct size in rabbit hearts: role of inositol trisphosphate receptors and gap junctions in triggering protection

Repeated Remote Ischemic Conditioning Effect on Ankle-brachial Index in Diabetic Patients - A Randomized Control Trial

Background:

Remote ischemic preconditioning (RIPC) is a phenomenon where a short period of ischemia in one organ protects against further ischemia in the other organs. We hypothesized that RIPC occurring in diabetic patients with ankle brachial index (ABI) between 0.70 and 0.90 were included with peripheral arterial disease, would make the better coronary flow resulted in the increasing ABI.

Materials and Methods:

This randomized clinical trial study was done in the Afshar Cardiovascular Hospital in Yazd between 2013 and 2014. Sixty participants were randomly divided into two groups (intervention and control groups). The intervention group was undergoing RIPC, and the control group was tested without RIPC. RIPC was stimulated by giving three cycles of 5 min of ischemia followed by 5 min of reperfusion of both upper arms using a blood pressure cuff inflated to 200 mm Hg (n = 30). This was compared with no RIPC group which consisted of placing a deflated blood pressure cuff on the upper limbs (n = 30).

Results:

The mean of ABI level before intervention in the RIPC and control group group was 0.82 ± 0.055 and 0.83 ± 0.0603 (P = 0.347) respectively, with no significant difference. It was 0.86 ± 0.066 in the RIPC group compared the control 0.83 ± 0.0603 (P = 0.046). So levels of ABI were greater after intervention in the RIPC group. The mean of ABI level increase from 0.82 ± 0.05 to 0.86 ± 0.06 in RIPC group (P = 0.008). So the intervention group showed a significant increase in ABI.

Conclusions:

RIPC through using a simple, noninvasive technique, composing three cycles of 5 min-ischemia of both upper arms, showing a significant increase in ABI level in diabetic patients.

Pharmacological options to protect the aged heart from ischemia and reperfusion injury by targeting the PKA-BK(Ca) signaling pathway

The beneficial effects of many cardioprotective strategies including ischemic or pharmacological conditioning are reduced in the aged heart. The underlying reason(s) for the age-dependent loss of cardioprotection is unclear. Recently, we demonstrated that protein kinase A (PKA) dependent cardioprotection is lost in the aged heart. However, activation of large-conductance Ca(2+)-sensitive K(+) (BK(Ca)) channels, a putative PKA downstream target, initiated cardioprotection also in the aged heart. Therefore, we aimed to investigate whether 1) BK(Ca) channels are critically involved in PKA activation induced cardioprotection and 2) the age-dependent loss of cardioprotection is caused by differences in PKA regulation. Using an in vivo rat model with regional myocardial ischemia, we treated young (2-4 months) and aged (22-24 months) Wistar rats with PKA activator forskolin, BK(Ca) channel activator NS1619 and/or BK(Ca) channel blocker iberiotoxin. Forskolin induced infarct size reduction was 1) age-dependent and 2) prevented by iberiotoxin. The effect of forskolin on myocardial PKA activity was comparable in young and aged animals. In addition, NS1619 initiated cardioprotection also in the aged heart both when administered before ischemia and during early reperfusion phase. Activation of BK(Ca) channels is critically involved in forskolin induced cardioprotection. The age-dependency of forskolin induced cardioprotection is not caused by age-dependent differences in PKA activation. Pharmacological targeting of BK(Ca) channels before or after myocardial ischemia is a promising therapeutic strategy to protect the aged heart from ischemia and reperfusion injury.

Role of gap junctions and hemichannels in parasitic infections

In vertebrates, connexins (Cxs) and pannexins (Panxs) are proteins that form gap junction channels and/or hemichannels located at cell-cell interfaces and cell surface, respectively. Similar channel types are formed by innexins in invertebrate cells. These channels serve as pathways for cellular communication that coordinate diverse physiologic processes. However, it is known that many acquired and inherited diseases deregulate Cx and/or Panx channels, condition that frequently worsens the pathological state of vertebrates. Recent evidences suggest that Cx and/or Panx hemichannels play a relevant role in bacterial and viral infections. Nonetheless, little is known about the role of Cx- and Panx-based channels in parasitic infections of vertebrates. In this review, available data on changes in Cx and gap junction channel changes induced by parasitic infections are summarized. Additionally, we describe recent findings that suggest possible roles of hemichannels in parasitic infections. Finally, the possibility of new therapeutic designs based on hemichannel blokers is presented.

A matter of life, death and diseases: mitochondria from a proteomic perspective

Mitochondria are highly ordered, integrated organelles that energize cellular activities and contribute to programmed death by initiating disciplined apoptotic cascades. This review seeks to clarify our understanding of mitochondrial structural-functional integrity beyond the resolved nuclear genome by unraveling the dynamic mitochondrial proteome and elucidating proteome/genome interplay. The roles of mechanochemical coupling between mitoskeleton and cytoskeleton and crosstalk with other organelles in orchestrating cellular outcomes are explained. The authors also review the modulation of mitochondrial-related oxidative stress on apoptosis and cancer development and the context is applied to interpret pathogenetic events in neurodegenerative disorders and cardiovascular diseases. The accumulated proteomics evidence is used to describe the integral role that mitochondria play and how they influence other intracellular organelles. Possible mitochondrial-targeted therapeutic interventions are also discussed.

Remote ischemic preconditioning in patients with intermittent claudication

OBJECTIVE

Remote ischemic preconditioning (RIPC) is a phenomenon in which a short period of sub-lethal ischemia in one organ protects against subsequent bouts of ischemia in another organ. We hypothesized that RIPC in patients with intermittent claudication would increase muscle tissue resistance to ischemia, thereby resulting in an increased ability to walk.

METHODS

In a claudication clinic, 52 ambulatory patients who presented with complaints of intermittent claudication in the lower limbs associated with an absent or reduced arterial pulse in the symptomatic limb and/or an ankle-brachial index <0.90 were recruited for this study. The patients were randomly divided into three groups (A, B and C). All of the patients underwent two tests on a treadmill according to the Gardener protocol. Group A was tested first without RIPC. Group A was subjected to RIPC prior to the second treadmill test. Group B was subjected to RIPC prior to the first treadmill test and then was subjected to a treadmill test without RIPC. In Group C (control group), both treadmill tests were performed without RIPC. The first and second tests were conducted seven days apart. Brazilian Clinical Trials: RBR-7TF6TM.

RESULTS

Group A showed a significant increase in the initial claudication distance in the second test compared to the first test.

CONCLUSION

RIPC increased the initial claudication distance in patients with intermittent claudication; however, RIPC did not affect the total walking distance of the patients.

IP3, a small molecule with a powerful message

Research conducted over the past two decades has provided convincing evidence that cell death, and more specifically apoptosis, can exceed single cell boundaries and can be strongly influenced by intercellular communication networks. We recently reported that gap junctions (i.e. channels directly connecting the cytoplasm of neighboring cells) composed of connexin43 or connexin26 provide a direct pathway to promote and expand cell death, and that inositol 1,4,5-trisphosphate (IP3) diffusion via these channels is crucial to provoke apoptosis in adjacent healthy cells. However, IP3 itself is not sufficient to induce cell death and additional factors appear to be necessary to create conditions in which IP3 will exert proapoptotic effects. Although IP3-evoked Ca(2+) signaling is known to be required for normal cell survival, it is also actively involved in apoptosis induction and progression. As such, it is evident that an accurate fine-tuning of this signaling mechanism is crucial for normal cell physiology, while a malfunction can lead to cell death. Here, we review the role of IP3 as an intracellular and intercellular cell death messenger, focusing on the endoplasmic reticulum-mitochondrial synapse, followed by a discussion of plausible elements that can convert IP3 from a physiological molecule to a killer substance. Finally, we highlight several pathological conditions in which anomalous intercellular IP3/Ca(2+) signaling might play a role. This article is part of a Special Issue entitled:12th European Symposium on Calcium.

Autophagy as a therapeutic target for ischaemia /reperfusion injury? Concepts, controversies, and challenges

Autophagy is the tightly orchestrated cellular 'housekeeping' process responsible for the degradation and disposal of damaged and dysfunctional organelles and protein aggregates. In addition to its established basal role in the maintenance of normal cellular phenotype and function, there is growing interest in the concept that targeted modulation of autophagy under conditions of stress (most notably, ischaemia/reperfusion) may represent an adaptive mechanism and render the myocardium resistant to ischaemia/reperfusion injury. Our aims in this review are to: (i) provide a balanced overview of the emerging hypothesis that perturbation of autophagy may serve as a novel, intriguing, and powerful cardioprotective treatment strategy and (ii) summarize the controversies and challenges in exploiting autophagy as a therapeutic target for ischaemia/reperfusion injury.

Pharmacological modulation of connexin-formed channels in cardiac pathophysiology

Coordinated electrical activity in the heart is supported by gap junction channels located at the intercalated discs of cardiomyocytes. Impaired gap junctional communication between neighbouring cardiomyocytes contributes to the development of re-entry arrhythmias after myocardial ischaemia. Current antiarrhythmic therapy is hampered by a lack of efficiency and side effects, creating the need for a new generation of drugs. In this review, we focus on compounds that increase gap junctional communication, thereby increasing the conduction velocity and decreasing the risk of arrhythmias. Some of these compounds also inhibit connexin 43 (Cx43) hemichannels, thereby limiting adenosine triphosphate loss and volume overload following ischaemia/reperfusion, thus potentially increasing the survival of cardiomyocytes. The compounds discussed in this review are: (i) antiarrythmic peptide (AAP), AAP10, ZP123; (ii) GAP-134; (iii) RXP-E; and (vi) the Cx mimetic peptides Gap 26 and Gap 27. None of these compounds have effects on Na(+) , Ca(2+) and K(+) channels, and therefore have no proarrhythmic activity associated with currently available antiarrhythmic drugs. GAP-134, RXP-E, Gap 26 and Gap 27 are pharmalogical agents with a favorable clinical safety profile, as already confirmed in phase I clinical trials for GAP-134. These agents show an excellent promise for treatment of arrhythmias in patients with ischaemic cardiomyopathy.

Role of the gap junction in ischemic preconditioning in the heart

The gap junction plays roles not only in electrical coupling of cardiomyocytes but also in intercellular transport of biologically active substances. Furthermore, the gap junction participates in decision making on cell survival versus cell death in various types of cells, and a part of reperfusion injury in the heart has been indicated to be gap junction mediated. The contribution of gap junction communication (GJC) and/or mitochondrial “hemichannels” to protective signaling during the trigger phase of ischemic preconditioning (IPC) is suggested by observations that IPC failed to protect the heart when GJC was blocked during IPC. Although ischemia suppresses both electrical and chemical GJC, chemical GJC persists for a considerable time after electrical GJC is lost. IPC facilitates the ischemia-induced suppression of chemical GJC, whereas IPC delays the reduction of electrical GJC after ischemia. The inhibition of GJC during sustained ischemia and reperfusion by GJC blockers mimics the effect of IPC on myocardial necrosis. IPC induces distinct effects on the interaction of connexin-43 with protein kinases, and the phosphorylation of connexin-43 at Ser368 by PKCε is a primary mechanism of inhibition of chemical GJC by IPC. Several lines of evidence support the notion that the modulation of GJC is a part of the mechanism of IPC-induced protection against myocardial necrosis and arrhythmias, though what percentage of IPC protection is attributable to the inhibition of GJC during ischemia-reperfusion still remains unclear.

Mimetic peptides as blockers of connexin channel-facilitated intercellular communication

There is a dearth of chemical inhibitors of connexin-mediated intercellular communication. The advent of short "designer" connexin mimetic peptides has provided new tools to inhibit connexin channels quickly and reversibly. This perspective describes the development of mimetic peptides, especially Gap 26 and 27 that are the most popular and correspond to specific sequences in the extracellular loops of connexins 37, 40 and 43. Initially they were used to inhibit gap-junctional coupling in a wide range of mammalian cells and tissues. Currently, they are also being examined as therapeutic agents that accelerate wound healing and in the early treatment of spinal cord injury. The mimetic peptides bind to connexin hemichannels, influencing channel properties as shown by lowering of electrical conductivity and potently blocking the entry of small reporter dyes and the release of ATP by cells. A mechanism is proposed to help explain the dual action of connexin mimetic peptides on connexin hemichannels and gap-junctional coupling.

The gap junction cellular internet: connexin hemichannels enter the signalling limelight

Cxs (connexins), the protein subunits forming gap junction intercellular communication channels, are transported to the plasma membrane after oligomerizing into hexameric assemblies called connexin hemichannels (CxHcs) or connexons, which dock head-to-head with partner hexameric channels positioned on neighbouring cells. The double membrane channel or gap junction generated directly couples the cytoplasms of interacting cells and underpins the integration and co-ordination of cellular metabolism, signalling and functions, such as secretion or contraction in cell assemblies. In contrast, CxHcs prior to forming gap junctions provide a pathway for the release from cells of ATP, glutamate, NAD+ and prostaglandin E2, which act as paracrine messengers. ATP activates purinergic receptors on neighbouring cells and forms the basis of intercellular Ca2+ signal propagation, complementing that occuring more directly via gap junctions. CxHcs open in response to various types of external changes, including mechanical, shear, ionic and ischaemic stress. In addition, CxHcs are influenced by intracellular signals, such as membrane potential, phosphorylation and redox status, which translate external stresses to CxHc responses. Also, recent studies demonstrate that cytoplasmic Ca2+ changes in the physiological range act to trigger CxHc opening, indicating their involvement under normal non-pathological conditions. CxHcs not only respond to cytoplasmic Ca2+, but also determine cytoplasmic Ca2+, as they are large conductance channels, suggesting a prominent role in cellular Ca2+ homoeostasis and signalling. The functions of gap-junction channels and CxHcs have been difficult to separate, but synthetic peptides that mimic short sequences in the Cx subunit are emerging as promising tools to determine the role of CxHcs in physiology and pathology.

Translocation of connexin 43 to the inner mitochondrial membrane of cardiomyocytes through the heat shock protein 90-dependent TOM pathway and its importance for cardioprotection

We have previously shown that connexin 43 (Cx43) is present in mitochondria, that its genetic depletion abolishes the protection of ischemia- and diazoxide-induced preconditioning, and that it is involved in reactive oxygen species (ROS) formation in response to diazoxide. Here we investigated the intramitochondrial localization of Cx43, the mechanism of Cx43 translocation to mitochondria and the effect of inhibiting translocation on the protection of preconditioning. Confocal microscopy of mitochondria devoid of the outer membrane and Western blotting on fractionated mitochondria showed that Cx43 is located at the inner mitochondrial membrane, and coimmunoprecipitation of Cx43 with Tom20 (Translocase of the outer membrane 20) and with heat shock protein 90 (Hsp90) indicated that it interacts with the regular mitochondrial protein import machinery. In isolated rat hearts, geldanamycin, a blocker of Hsp90-dependent translocation of proteins to the inner mitochondrial membrane through the TOM pathway, rapidly (15 minutes) reduced mitochondrial Cx43 content by approximately one-third in the absence or presence of diazoxide. Geldanamycin alone had no effect on infarct size, but it ablated the protection against infarction afforded by diazoxide. Geldanamycin abolished the 2-fold increase in mitochondrial Cx43 induced by 2 preconditioning cycles of ischemia/reperfusion, but this effect was not associated with reduced protection. These results demonstrate that Cx43 is transported to the inner mitochondrial membrane through translocation via the TOM complex and that a normal mitochondrial Cx43 content is important for the diazoxide-related pathway of preconditioning.

First molecular evidence that inositol trisphosphate signaling contributes to infarct size reduction with preconditioning

Considerable attention has focused on the role of protein kinase C (PKC) in triggering the profound infarct-sparing effect of ischemic preconditioning (PC). In contrast, the involvement of inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)], the second messenger generated in parallel with the diacylglycerol-PKC pathway, remains poorly understood. We hypothesized that, if Ins(1,4,5)P(3) signaling [i.e., release of Ins(1,4,5)P(3) and subsequent binding to Ins(1,4,5)P(3) receptors] contributes to PC-induced cardioprotection, then the reduction of infarct size achieved with PC would be attenuated in mice that are deficient in Ins(1,4,5)P(3) receptor protein. To test this concept, hearts were harvested from 1) B6C3Fe-a/a-Itpr-1(opt+/-)/J mutants displaying reduced expression of Ins(1,4,5)P(3) receptor-1 protein, 2) Itpr-1(opt+/+) wild types from the colony, and 3) C57BL/6J mice. All hearts were buffer-perfused and randomized to receive two 5-min episodes of PC ischemia, pretreatment with d-myo-Ins(1,4,5)P(3) [sodium salt of native Ins(1,4,5)P(3)], the mitochondrial ATP-sensitive K(+) channel opener diazoxide, or no intervention (controls). After the treatment phase, all hearts underwent 30-min global ischemia followed by 2 h of reperfusion, and infarct size was delineated by tetrazolium staining. In both wild-type and C57BL/6J cohorts, area of necrosis in hearts that received PC, d-myo-Ins(1,4,5)P(3), and diazoxide averaged 28-35% of the total left ventricle (LV), significantly smaller than the values of 52-53% seen in controls (P < 0.05). In contrast, in Itpr-1(opt+/-) mutants, protection was only seen with diazoxide: neither PC nor d-myo-Ins(1,4,5)P(3) limited infarct size (52-58% vs. 56% of the LV in mutant controls). These data provide novel evidence that Ins(1,4,5)P(3) signaling contributes to infarct size reduction with PC.

Reduction of infarct size with d-myo-inositol trisphosphate: role of PI3-kinase and mitochondrial KATP channels

Prophylactic treatment with d- myo-inositol 1,4,5-trisphosphate hexasodium [d- myo-Ins(1,4,5)P3], the sodium salt of the endogenous second messenger Ins(1,4,5)P3, triggers a reduction of infarct size comparable in magnitude to that seen with ischemic preconditioning (PC). However, the mechanisms underlying d- myo-Ins(1,4,5)P3-induced protection are unknown. Accordingly, our aim was to investigate the role of four archetypal mediators implicated in PC and other cardioprotective strategies (i.e., PKC, PI3-kinase/Akt, and mitochondrial and/or sarcolemmal KATP channels) in the infarct-sparing effect of d- myo-Ins(1,4,5)P3. Fifteen groups of isolated buffer-perfused rabbit hearts [5 treated with d- myo-Ins(1,4,5)P3, 5 treated with PC, and 5 control cohorts] underwent 30 min of coronary artery occlusion and 2 h of reflow. One set of control, d- myo-Ins(1,4,5)P3, and PC groups received no additional treatment, whereas the remaining sets were infused with chelerythrine, LY-294002, 5-hydroxydecanoate (5-HD), or HMR-1098 [inhibitors of PKC, PI3-kinase, and mitochondrial and sarcolemmal ATP-sensitive K+ (KATP) channels, respectively]. Infarct size (delineated by tetrazolium staining) was, as expected, significantly reduced in both d- myo-Ins(1,4,5)P3- and PC-treated hearts versus controls. d- myo-Ins(1,4,5)P3-induced cardioprotection was blocked by 5-HD but not HMR-1098, thereby implicating the involvement of mitochondrial, but not sarcolemmal, KATP channels. Moreover, the benefits of d- myo-Ins(1,4,5)P3 were abrogated by LY-294002, whereas, in contrast, chelerythrine had no effect. These latter pharmacological data were corroborated by immunoblotting: d- myo-Ins(1,4,5)P3 evoked a significant increase in expression of phospho-Akt but had no effect on the activation/translocation of the cardioprotective ε-isoform of PKC. Thus PI3-kinase/Akt signaling and mitochondrial KATP channels participate in the reduction of infarct size afforded by prophylactic administration of d- myo-Ins(1,4,5)P3.

Effects of Heptanol on Neurogenic Contractions of Vas Deferens: A Comparative Study of Stimulation Frequency in Guinea Pig and Rat

This study examines the role of gap junctional communication in smooth muscle in relation to the frequency of stimulation and the innervation density of the tissue in the generation of neurogenic contractions. Toward this end the effects of heptanol, a gap junctional blocker, on the neurogenic contractions of guinea pig and rat vas deferens at different frequencies of stimulation (single pulse, 5, 10, 20, 40, 60, and 80 Hz) were studied. In both the prostatic and epididymal halves of these tissues, heptanol abolished the neurogenic contractions at the lower frequencies of stimulation. At higher frequencies, contractions were resistant to heptanol action. The effect of heptanol on the neurogenic contractions was found to decrease with increasing stimulation frequency. The neurogenic contractions of rat vas deferens were more resistant to heptanol than those of guinea pig vas deferens. Our data indicate that gap junctional communication is significant in the generation of neurogenic contractions in both guinea pig and rat vas deferens in a frequency-dependent manner, and we discuss the mechanisms underlying these findings.

Inositol phospholipids localized to caveolae in rat heart are regulated by alpha1-adrenergic receptors and by ischemia-reperfusion

Postischemic reperfusion of rat or mouse hearts causes generation of inositol (1,4,5)trisphosphate [Ins(1,4,5)P3] and the initiation of arrhythmias. In the current study we investigated the possibility that the enhanced Ins(1,4,5)P3 generation in postischemic reperfusion was associated with an increased availability of the precursor lipid phosphatidylinositol(4,5)bisphosphate (PIP2) for alpha1-adrenergic receptor-activated phospholipase C (PLC). Isolated-perfused rat hearts were labeled with [3H]inositol and subjected to ischemia-reperfusion or stimulation with norepinephrine under normoxic conditions. Caveolar fractions were prepared by buoyant density sucrose gradient centrifugation. [3H]PIP2 was concentrated in caveolae, along with Galphaq and PLCbeta1b. Caveolae contained only 27.3 +/- 6.9% (means +/- SE, n = 6) of the total alpha1-adrenergic receptor complement of the heart. These did not migrate to PIP2-containing caveolar fractions with norepinephrine stimulation under normoxic conditions, even though caveolar PIP2 was depleted. In contrast, [3H]PIP2 in caveolae increased during 2 min of reperfusion, independently of norepinephrine release and thus of alpha1-adrenergic receptor activation. The increased PIP2 in the caveolar fractions where signaling proteins are concentrated may be critical for the heightened generation of Ins(1,4,5)P3 in early reperfusion.