The Cardioprotective Effects of Novel Na+/H+ Exchanger Inhibitor TY-51924 on Ischemia/Reperfusion Injury:

The Role of Plasma Membrane Sodium/Hydrogen Exchangers in Gastrointestinal Functions: Proliferation and Differentiation, Fluid/Electrolyte Transport and Barrier Integrity

The five plasma membrane Na⁺/H⁺ exchanger (NHE) isoforms in the gastrointestinal tract are characterized by distinct cellular localization, tissue distribution, inhibitor sensitivities, and physiological regulation. NHE1 (Slc9a1) is ubiquitously expressed along the gastrointestinal tract in the basolateral membrane of enterocytes, but so far, an exclusive role for NHE1 in enterocyte physiology has remained elusive. NHE2 (Slc9a2) and NHE8 (Slc9a8) are apically expressed isoforms with ubiquitous distribution along the colonic crypt axis. They are involved in pH_i regulation of intestinal epithelial cells. Combined use of a knockout mouse model, intestinal organoid technology, and specific inhibitors revealed previously unrecognized actions of NHE2 and NHE8 in enterocyte proliferation and differentiation. NHE3 (Slc9a3), expressed in the apical membrane of differentiated intestinal epithelial cells, functions as the predominant nutrient-independent Na⁺ absorptive mechanism in the gut. The new selective NHE3 inhibitor (Tenapanor) allowed discovery of novel pathophysiological and drug-targetable NHE3 functions in cystic-fibrosis associated intestinal obstructions. NHE4, expressed in the basolateral membrane of parietal cells, is essential for parietal cell integrity and acid secretory function, through its role in cell volume regulation. This review focuses on the expression, regulation and activity of the five plasma membrane Na⁺/H⁺ exchangers in the gastrointestinal tract, emphasizing their role in maintaining intestinal homeostasis, or their impact on disease pathogenesis. We point to major open questions in identifying NHE interacting partners in central cellular pathways and processes and the necessity of determining their physiological role in a system where their endogenous expression/activity is maintained, such as organoids derived from different parts of the gastrointestinal tract.

DJ-1: A promising therapeutic candidate for ischemia-reperfusion injury

DJ-1 is a multifaceted protein with pleiotropic functions that has been implicated in multiple diseases, ranging from neurodegeneration to cancer and ischemia-reperfusion injury. Ischemia is a complex pathological state arising when tissues and organs do not receive adequate levels of oxygen and nutrients. When the blood flow is restored, significant damage occurs over and above that of ischemia alone and is termed ischemia-reperfusion injury. Despite great efforts in the scientific community to ameliorate this pathology, its complex nature has rendered it challenging to obtain satisfactory treatments that translate to the clinic. In this review, we will describe the recent findings on the participation of the protein DJ-1 in the pathophysiology of ischemia-reperfusion injury, firstly introducing the features and functions of DJ-1 and, successively highlighting the therapeutic potential of the protein.

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DJ-1 has been shown to confer protection in ischemia-reperfusion injury models.

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DJ-1 protection relies on the activation of antioxidant signaling pathways.

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DJ-1 regulates mitochondrial homeostasis during ischemia and reperfusion.

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DJ-1 seems to modulate ion homeostasis during ischemia and reperfusion.

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DJ-1 may represent a promising therapeutic target for ischemia-reperfusion injury.

Inhibition of Na+/H+ Exchanger With EMD 87580 does not Confer Greater Cardioprotection Beyond Preconditioning on Ischemia-Reperfusion Injury in Normal Dogs

Postischemic accumulation of intracellular Na⁺ promotes calcium overload and contributes to cellular necrosis. Cardioprotection afforded by pharmacologic blockade of the sodium-hydrogen exchanger subtype 1 (NHE1) is thought to be more remarkable than that obtained by ischemic conditioning (IC). The window of protection provided by IC pretreatment is maintained even when performed up to 48 hours before ischemia. In addition, the perception exists that combined NHE1 inhibition plus IC produces greater than additive protection against ischemic injury. The current study compared the efficacy of NHE1 blockade by N-[2-methyl-4,5-bis(methylsulfonyl)-benzoyl]-guanidine (EMD 87580 5 mg/kg) combined with first- or second-window IC on ischemic tolerance in dogs subject to 90-minute acute ischemia and 180-minute reperfusion. Infarct size (tetrazolium staining), vascular responses, and myocardial perfusion (microspheres) were assessed. EMD 87580 given before ischemia or before reperfusion did not reduce infarct size (compared to vehicle-treated group). Significant protection against tissue necrosis was obtained by both first- and second-window IC, but additive cardioprotection (ie, greater than that afforded by IC) was not observed by treatment with EMD 87580. Vascular reactivity in the infarct-related artery was not preserved after ischemia-reperfusion in any of the experimental groups. Likewise, either the pharmacologic or the nonpharmacologic interventions did not modify myocardial perfusion. These data demonstrate that EMD 87580 did not protect against ischemia-reperfusion injury regardless of the time of drug administration. Combined EMD 87580 and IC did not antagonize protection that was achieved by either first- or second-window IC alone; no additive protection beyond preconditioning was obtained. Further study is necessary to assess the value of NHE1 blockers as protective agents against myocardial injury.

Randomized controlled trial of TY-51924, a novel hydrophilic NHE inhibitor, in acute myocardial infarction

BACKGROUND

In patients with ST-elevation acute myocardial infarction (STEMI), reperfusion therapy limits infarct size, but can directly evoke myocardial reperfusion injury. Activation of the Na(+)/H(+) exchanger (NHE) plays an important role in reperfusion injury. TY-51924, a novel NHE inhibitor, significantly reduced infarct size in animal studies and was well tolerated in early-phase clinical trials. This study aim was to evaluate the efficacy and safety of TY-51924 in patients with STEMI.

METHODS

In this multicenter, randomized, double-blind, placebo-controlled Phase II trial, 105 patients with first anterior STEMI undergoing primary percutaneous coronary intervention (pPCI) were randomly assigned to receive an intravenous infusion of either TY-51924 or placebo. Primary endpoints were myocardial salvage index (MSI) as determined by single photon emission computed tomography (SPECT) 3-5 days after pPCI and safety up to 7 days.

RESULTS

Baseline characteristics were similar in the two groups. MSI 3-5 days after pPCI (0.200 vs. 0.290, p=0.56), 3 months after pPCI (0.470 vs. 0.500, p=0.76), and the incidences of side effects did not differ between the two groups as a whole. However, on post hoc analysis of 52 patients with a large area at risk (AAR) (≥38%) and no antegrade coronary flow, MSI by SPECT at 3 months after pPCI was significantly higher in TY-51924 group (0.450 vs. 0.320, p=0.03). TY-51924 did not adversely influence hemodynamics.

CONCLUSIONS

TY-51924 did not improve MSI or increase side effects as a whole. However, TY-51924 is potentially cardioprotective in the presence of a large AAR and no antegrade coronary flow.