Sepsis is still a common critical disease with high morbidity and mortality in intensive care unit. Recently, a meta-analysis showed that reversible myocardial depression occurs early in severe sepsis and septic shock. In other words, sepsis myocardial injury would be reversed with early intervention. The clinical evidence for ES for septic cardiomyopathy is still insufficient, and it is not a first-line drug. The use of ES in the treatment of patients with sepsis has been debated for a long time. Presently, several studies have shown that heart rate control with selective beta-1 blockers in septic shock is safe. Moreover, a meta-analysis suggested that ES may improve survival in patients with tachycardia sepsis. Many clinical trials have also shown that ES can protect heart function by lowering heart rate at the early time and reducing the work of the heart muscle. Our experiment broadly confirmed the protective effect of ES on myocardial injury.
The specific mechanism of ES on myocardial injury in sepsis remains unclear. A certain animal study confirmed that ES can suppress inflammation and apoptosis in the intestinal tissue via the overexpression of NF-kappa B-p65 in the early stage. Early-stage use of ES might be an ideal treatment method for sepsis. The effect of esmolol on autophagy has been reported in the post-resuscitation model of cardiac arrest, but not in this model of septic myocardial injury. Our experiment is necessary for elucidating the significance of ES in the treatment of septic cardiomyopathy.
Autophagy pathways are complex and varied, and are closely related to apoptosis and inflammation. The molecules involved are very diverse and the regulatory mechanisms among them are complex. The autophagic proteins preserve mitochondrial integrity. AMPK plays a major regulatory role in cellular energy homeostasis by directly phosphorylating metabolic enzymes and nutrient transporters and indirectly promoting the transactivation of nuclear genes involved in mitochondrial biogenesis and function. AMPK-ULK1 signaling is important in skeletal muscle, and ULK1 activation is dependent on AMPK. Beclin-1 may promote mitochondrial biogenesis through up-regulation of AMPK/ULK1, in addition to removing damaged mitochondria through mitochondrial autophagy. The amount of LC3-II is correlated with the extent of autophagosome formation. The results showed that the autophagy pathway was significantly inhibited at 6, 12, 24h under LPS induction, leading to increased myocardial injury in rats. In the group pretreated with ES, myocardial injury improved significantly. According to the expression of autophagic protein, ES may protect myocardium by promoting the autophagy of AMPK-ULK1 single signaling pathway.
In the experiment, we added rapamycin and 3-MA treatment groups to confirm the mechanism of ES on autophagy. Rapamycin is well known as an undisputed autophagy activator[30–32]. Rapamycin has been shown to be cardioprotective in pressure‑overloaded and ischemic heart diseases by regulating the mechanistic target of rapamycin (mTOR) signaling network[33, 34]. Our results showed that although rapamycin is cardioprotective in septic myocardial damage, its myocardial protection is not as good as ES. Furthermore, 3-MA, an inhibitor of PI3K, plays a vital role in forming and developing autophagosomes. We also found that 3-MA showed no significant difference in LPS-induced autophagy protein expression. It is still unclear which part of the autophagy pathway ES participates in and which targets it applies.
Therefore, whether this pathway exists in the myocardium becomes the entry point of our experiment. By measuring the protein expression of p-AMPK, p-mTOR and p-ULK1, we found that ES can activate the expression of p-AMPK, which leads to the opening of energy regulation pathway, thus achieving the effect of autophagy promotion, and playing a positive protective role in the myocardium of septic rats.
During the experiment, we wrapped the front end of the catheter with aluminum skin to effectively prevent rats from biting the catheter during intravenous pumping. The single-cage pumping mode was used in each rat. However, due to the stenosis of blood vessels and catheters in rats as well as the complexity of time points, we failed to find the blocking of pumping drugs in some rats in time, which ultimately led to treatment failure. Moreover, rats may be affected by the experimental environment and batch, and many confounding factors are inevitable.
In conclusion, our results are still problematic and need to be verified by more experiments. It has to be said that ES may protect myocardial injury by promoting autophagy, which provides a new idea for the subsequent treatment of myocardial injury in sepsis.