Naltrindole attenuates irreversible Hypercontracture during Myocardial Ischemia by a Novel Mechanism and elicits robust cardioprotective effects in Myocardial Ischemia/Reperfusion Injury
Authors: Stinson Cameron , Le Mai An , Clair Logan , Ramsarran James , Boakye Tanoh Desmond , Humayun Annam , Melnik Juliet 
Published: May 2024

Introduction: Previous studies have shown that naltrindole (NTI) produced robust cardioprotective effects (e.g.~80% reduction of infarct size) in both ex-vivo (2.5-5μM) and in-vivo (3.75-7.5 mg/kg) rat myocardial ischemia-reperfusion (MIR) injury models. We recently showed that NTI 100-200μM attenuated phorbol 12-myristate 13-acetate (PMA) induced polymorphonuclear leukocytes (PMNs) superoxide (SO) release by a novel mechanism of action (MOA) devoid of opioid receptors. We hypothesize NTI’s novel MOA is a reduction of intracellular calcium (Ca2+). To test this hypothesis, we conducted PMN SO release and isolated perfused MIR assays using KB-R7943(KB). KB is known to reduce intracellular Ca2+ via inhibition of reverse mode Na+/Ca2+ exchanger and therefore should attenuate PMN SO release, myocardial ischemic hypercontracture, infarct size, and left ventricular end diastolic pressure (LVEDP). Methods: PMNs and hearts isolated from anesthetized male Sprague Dawley (SD) rats (~400g SO release assay, ~300g for perfused hearts). PMN SO release was stimulated using PMA (100nM) ± NTI 10-200 μM, KB 5-20 μM, or vehicle (0.5% DMSO; controls) and measured spectrophotometrically as a change in absorbance @ 550nm over 390 secs and cell viability was determined using 0.2% Trypan blue exclusion. We then infused NTI 1.25-5μM, KB 10-20μM, or naloxone (NX; negative control) 10μM for 5 min into perfused hearts, just prior to global I (30min)/R(45min). Cardiac LV function was measured via a pressure transducer and infarct size using 1% triphenyltetrazolium chloride staining in MIR assay. Data were analyzed using ANOVA and Fischers post-hoc analysis, with p<0.05 considered statistically significant. Results: PMN SO release assay: KB 10 μM, KB 20 μM, NTI 100 μM (~3.75 mg/kg), and NTI 200 μM(~7.5 mg/kg) significantly attenuated PMA induced PMN SO release by ~40% (KB 10μM, n=7, p<0.05), ~50% ((KB 20μM, n=7, p<0.05), ~30% (NTI 100 μM, n=7, p<0.05), 75% (NTI 200μM, n=7, p<0.05) respectively when compared to untreated control (n=10). MIR assay: NTI 5μM, 2.5μM, 1.25μM and KB 20 μM reduced infarct size (4.8±3%, n=5, p<0.05), (6.8±0.8%, n=6, p<0.05), (12.2±3%, n=5), and (2.9±2%, n=5, p<0.05) respectively compared to vehicle (14.1±2%, n=9) and NX 10μM controls (18±3%, n=3). NTI 5 μM and KB 20 μM had significantly improved LVEDP to (32.4±11%, n=5, p<0.05) and (22.8±4%, n=5, p<0.05) respectively compared to vehicle control (72.4±6%, n=9) and NX 10μM controls(54.2±8%, n=3) Conclusion: NTI and KB showed concentration-dependent effects on reducing PMN SO release. Both NTI (2.5μM, 5μM) and KB (20μM) reduced infarct size and improved LVEDP. The novel MOA of NTI is most likely mediated via a reduction in intracellular Ca2+ and subsequent hypercontracture during myocardial ischemia. The infarct reducing effect of NTI can benefit patients who will undergo elective PCI, CABG, and transplants. Funding: This study was funded by the Philadelphia College of Osteopathic Medicine, Department of Biomedical Sciences, Division of Research, and the Center for Chronic Diseases of Aging and Young Therapeutics, LLC. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.