The Clinical Efficacy of N-Acetylcysteine in the Treatment of ST Segment Elevation Myocardial Infarction

Myocardial oxidative stress is increased in early reperfusion, but systemic antioxidative therapy does not prevent ischemia-reperfusion arrhythmias in pigs

Background

Arrhythmias in the early phase of reperfusion after myocardial infarction (MI) are common, and can lead to hemodynamic instability or even cardiac arrest. Reactive oxygen species (ROS) are thought to play a key role in the underlying mechanisms, but evidence from large animal models is scarce, and effects of systemic antioxidative treatment remain contentious.

Methods

MI was induced in 7 male and 7 female pigs (Norwegian landrace, 35-40 kg) by clamping of the left anterior descending artery (LAD) during open thorax surgery. Ischemia was maintained for 90 min, before observation for 1 h after reperfusion. Pigs were randomized 1:1 in an operator-blinded fashion to receive either i.v. N-acetylcysteine (NAC) from 70 min of ischemia and onwards, or 0.9% NaCl as a control. Blood samples and tissue biopsies were collected at baseline, 60 min of ischemia, and 5 and 60 min of reperfusion. ECG and invasive blood pressure were monitored throughout.

Results

The protocol was completed in 11 pigs. Oxidative stress, as indicated by immunoblotting for Malondialdehyde in myocardial biopsies, was increased at 5 min of reperfusion compared to baseline, but not at 60 min of reperfusion, and not reduced with NAC. We found no significant differences in circulating biomarkers of myocardial necrosis, nor in the incidence of idioventricular rhythm (IVR), non-sustained ventricular tachycardia (NSVT), ventricular tachycardia (VT) or ventricular fibrillation (VF) between NAC-treated and control pigs during reperfusion.

Conclusion

Myocardial oxidation was increased early after reperfusion in a porcine model of MI, but systemic antioxidative treatment did not protect against reperfusion arrhythmias.

CaMKII and reactive oxygen species contribute to early reperfusion arrhythmias, but oxidation of CaMKIIδ at methionines 281/282 is not a determining factor

BACKGROUND

Available evidence suggest that Ca²⁺/calmodulin-dependent protein kinase type IIδ (CaMKIIδ) and reactive oxygen species (ROS) are important in early ischemia-reperfusion arrhythmias (IRA). Since ROS can activate CaMKIIδ by oxidation of two methionines at positions 281/282, oxidized-CaMKIIδ (Ox-CaMKIIδ) has been proposed to be important for IRA. However, direct evidence for this is missing.

METHODS

We exposed Langendorff-perfused hearts and ventricular cardiomyocytes from C57BL/6 mice to global and simulated ischemia, respectively, and recorded arrhythmic events during early reperfusion. Hearts were collected for immunoblotting of key phosphoproteins. We evaluated the effects of beta-adrenoceptor stimulation, inhibition of CaMKII, and reduced ROS levels with isoprenaline, KN93/AIP and N-acetylcysteine (NAC), respectively. We further tested the importance of Ox-CaMKIIδ by using hearts and cardiomyocytes from mice with CaMKIIδ resistant to oxidation of methionines 281 and 282 (MMVV).

RESULTS

Hearts treated with KN93, AIP or NAC had lower incidence of early IRA, and NAC-treated cardiomyocytes had lower incidence of arrhythmogenic events. However, hearts from MMVV mice had a similar incidence of early IRA to wild type mice (WT), and MMVV and WT cardiomyocytes had a similar frequency of Ca²⁺ waves and Ca²⁺ sparks. Immunoblotting confirmed high levels of oxidation in early reperfusion, but revealed no significant differences in the phosphorylation levels of Ca²⁺-handling proteins in MMVV and WT hearts.

CONCLUSIONS

Although CaMKII and ROS both contribute to early IRA, hearts from mice with CaMKII resistant to oxidation at methionines 281/282 were not protected from such arrhythmias, suggesting that oxidation at these sites is not a determining factor.

Stability Study of Parenteral N-Acetylcysteine, and Chemical Inhibition of Its Dimerization

Parenteral N-acetylcysteine has a wide variety of clinical applications, but its use can be limited by a poor chemical stability. We managed to control parenteral N-acetylcysteine stability, and to study the influence of additives on the decrease of N-acetylcysteine degradation. First, an HPLC-UV dosing method of N-acetylcysteine and its main degradation product, a dimer, was validated and the stability without additive was studied. Then, the influence of several additives (ascorbic acid, sodium edetate, tocopherol and zinc) and of temperature on N-acetylcysteine dimerization was evaluated. Finally, the influence of zinc gluconate at different concentrations (administrable to patients) was investigated. Zinc gluconate at 62.5 µg·mL^-1 allows the stabilization of 25 mg·mL^-1 N-acetylcysteine solution for at least 8 days when stored at 5 ± 3 °C.

The effects of N-acetylcysteine on recovery biomarkers: A systematic review and meta-analysis of controlled trials

N-acetylcysteine (NAC) is one of the antioxidant supplements which is thought to improve recovery. Existing studies regarding NAC and recovery presented conflicting results. This systematic review and meta-analysis evaluated the existing trials and determined the efficacy of acute and chronic NAC administration on recovery biomarkers. PubMed, Web of Science, and Scopus were searched up to July 2021. The random effects or fixed effects model was applied in the meta-analysis. Sensitivity and subgroup analyses were performed. In case of the presence of publication bias, standard methods were applied. The meta-analysis comprised 37 papers (1,388 participants). All included studies were in English language. Acute NAC administration indicated no significant effects on lactate, pH, VO₂ , and CPK-MB ([SMD = -0.06 mmol/L; 95% CI: -0.40, 0.28; p = .714], [SMD = 0.17; 95% CI: -0.28, 0.62; p = .454], [SMD = -0.11 L/min; 95% CI: -0.63, 0.41; p = .686], and [SMD = -0.19 units/L; 95% CI: -0.62, 0.24; p = .395]). Additionally, no evidence of significant influence of chronic NAC administration on lactate, pH, VO₂ , and CK was revealed ([SMD = 0.01 mmol/L; 95% CI: -0.25, 0.27; p = .950], [SMD = -0.51; 95% CI: -1.73, 0.70; p = .424], [SMD = -0.18 L/min; 95% CI: -0.56, 0.20; p = .361], and [SMD = -0.04 units/L; 95% CI: -0.36, 0.29; p = .821]). No considerable effect of NAC on recovery was found. PRACTICAL APPLICATIONS: Previous studies on the influence of NAC administration on recovery biomarkers have presented conflicting results. This systematic review and meta-analysis offers a broad range of detailed information on the influence of chronic and acute NAC supplementation outcomes regarding recovery biomarkers. Overall, the results support that NAC supplementation may not be effective in improving recovery biomarkers. However, subgroup analyses based on NAC dosage indicated the meaningful effect of NAC on CK-MB at the dosage of ≥100 mg/kg.