The Roles of Caloric Restriction Mimetics in Central Nervous System Demyelination and Remyelination

The dysfunction of myelinating glial cells, the oligodendrocytes, within the central nervous system (CNS) can result in the disruption of myelin, the lipid-rich multi-layered membrane structure that surrounds most vertebrate axons. This leads to axonal degeneration and motor/cognitive impairments. In response to demyelination in the CNS, the formation of new myelin sheaths occurs through the homeostatic process of remyelination, facilitated by the differentiation of newly formed oligodendrocytes. Apart from oligodendrocytes, the two other main glial cell types of the CNS, microglia and astrocytes, play a pivotal role in remyelination. Following a demyelination insult, microglia can phagocytose myelin debris, thus permitting remyelination, while the developing neuroinflammation in the demyelinated region triggers the activation of astrocytes. Modulating the profile of glial cells can enhance the likelihood of successful remyelination. In this context, recent studies have implicated autophagy as a pivotal pathway in glial cells, playing a significant role in both their maturation and the maintenance of myelin. In this Review, we examine the role of substances capable of modulating the autophagic machinery within the myelinating glial cells of the CNS. Such substances, called caloric restriction mimetics, have been shown to decelerate the aging process by mitigating age-related ailments, with their mechanisms of action intricately linked to the induction of autophagic processes.

Monitoring of Levosimendan Administration in Patients with Pulmonary Hypertension Undergoing Cardiac Surgery and Effect of Two Different Dosing Schemes on Hemodynamic and Echocardiographic Parameters

INTRODUCTION

The perioperative management of patients with pulmonary hypertension (PH) undergoing cardiac surgery represents one of the most challenging clinical scenarios. This fact mainly depends on the relationship existing between PH and right ventricular failure (RVF). Levosimendan (LS) is an inodilator that might be an effective agent in the treatment of PH and RVF. The aim of this study was to examine the impact of the duration of cardiopulmonary bypass (CPB) on the therapeutic drug monitoring of LS and to evaluate the effect of preemptive administration of LS on perioperative hemodynamic and echocardiographic parameters in cardiac surgical patients with preexisting PH.

MATERIALS AND METHODS

In this study, LS was administered in adult patients undergoing cardiac surgery before CPB in order to prevent exacerbation of preexisting PH and subsequent right ventricular dysfunction. Thirty cardiac surgical patients with preoperatively confirmed PH were randomized to receive either 6 μg/kg or 12 μg/kg of LS after the induction of anesthesia. The plasma concentration of LS was measured after CPB. In this study, a low sample volume was used combined with a simple sample preparation protocol. The plasma sample was extracted by protein precipitation and evaporated; then, the analyte was reconstituted and detected using specific and sensitive bioanalytical liquid chromatography with mass spectrometry (LC-MS/MS) methodology. The clinical, hemodynamic, and echocardiographic parameters were registered and evaluated before and after the administration of the drug.

RESULTS

A fast bioanalytical LC-MS/MS methodology (a run time of 5.5 min) was developed for the simultaneous determination of LS and OR-1896, its main metabolite in human plasma. The LC-MS/MS method was linear over a range of 0.1-50 ng/mL for LS and 1-50 ng/mL for its metabolite OR-1896. Measured plasma concentrations of LS were inversely related to the duration of CPB. LS administration before CPB during cardiac surgery was effective in reducing pulmonary artery pressure and improving hemodynamic parameters after CPB, with a more pronounced and durable effect of the drug at the dose of 12 μg/kg. Additionally, administration of LS at a dose of 12 μg/kg in cardiac surgical patients with PH before CPB improved right ventricular function.

CONCLUSION

LS administration decreases pulmonary artery pressure and may improve right ventricular function in patients with PH undergoing cardiac surgery.