## 4 Discussion  
Our study assessed whether naringenin, a small-molecule inhibitor of MARK4, could augment hemodynamics, cardiomyocyte contractility, and \(\alpha\)-tubulin tyrosination in a rat model of MI. We found that naringenin, when encapsulated in a PEG-PCL micelle and injected into rats' left ventricular myocardium immediately after MI, results in an improved ejection fraction one day after MI. It also showed that micellized naringenin increases left ventricular cardiomyocyte contraction and relaxation velocity and decreases left ventricular \(\alpha\)-tubulin detyrosination. Finally, this study demonstrated that micellized naringenin achieved these effects without any renal, hepatic, or cardiac toxicity, measured by serum assays of creatinine, ALT, AST, and troponin I. Collectively, this study demonstrates the potential efficacy and safety of micellized naringenin as an intropic agent in the setting of acute MI. A growing body of the literature has linked \(\alpha\)-tubulin detyrosination to increased myocyte stiffness and impaired myocyte contractility [17; 18; 19]. Our study builds on data that show that mitigating \(\alpha\)-tubulin detyrosination may augment myocyte contractility and hemodynamics. In 2018, [PERSON] et al. found that cardiomyocytes from failing human hearts had an increased ratio of detyrosinated to total microtubules relative to those from non-failing hearts [20]. They also demonstrated that suppressing tubulin detyrosination with parthenolide in failing human cardiomyocytes in vitro increases their contraction and relaxation velocity. Subsequent work by [PERSON] et al. linked elevated MARK4 protein and mRNA expression in mouse hearts after MI to increased tubulin detyrosination [12]. They found that mice with genetically knocked out MARK4 had a preserved ejection fraction at 1, 2, and 4 weeks after MI. Our study is the first to demonstrate an association between the in vivo pharmacologic inhibition of tubulin detyrosination and the subsequent augmentation of cardiomyocyte contraction and relaxation velocity, as well as global hemodynamics. Additionally, it is the first to show that these improvements in cardiomyocyte contractility and hemodynamics occur as early as one day following both MI and treatment. Figure 4: Serologic assessments of nephrotoxicity, hepatotoxicity, and cardiotoxicity in rats one day post-myocardial infarction, stratified by treatment group. ALT: alanine aminotransferase. AST: aspartate aminotransferase. *: \(p<0.05\). ***: \(p<0.001\). ***: \(p<0.0001\). Micellized naringenin and naringenin dissolved in DMSO have comparable effects on cardiomyocyte contractility and global hemodynamics, but our study did not directly compare the impact of these two treatments on tubulin dyrovination itself. Both groups likely had similar effects on metrics such as stroke work due to naringenin's ability to augment the contractility and lusitropy of viable heart muscle post-MI. It is unclear why only the MI-NarDMSO cohort, but not the MI-NarMic cohort, had improved cardiac output relative to MI-Untreated cohort. However, given that Sham rats did not show improved cardiac output relative to the MI-Untreated cohort, cardiac output is likely not as reliable of a reflection of global hemodynamics as stroke work and ejection fraction are. The significance of our study's primary finding lies in the translatability of micellized naringenin as a suppressor of \(\alpha\)-tubulin dyrovination. It is not feasible to genetically knock out MARK4 in humans at risk of MI. Similarly, parthenolate--an agent that mitigates tubulin dyrovination by inhibiting tubulin carboxypeptidase--is not expected to be effective in vivo given its off-target effects such as the prolongation of intracellular calcium ion transients [20]. Naringenin is a relatively inexpensive small molecule that potentially inhibits MARK4 (IC50 of 4.11 \(\upmu\)M) and has antioxidant, anti-inflammatory, and pro-angiogenic effects, which may contribute to its hemodynamic benefits after MI [14; 21; 22; 23].