Vagus Nerve Stimulation Alleviates Hepatic Ischemia and Reperfusion Injury by Regulating Glutathione Production and Transformation

Vagus nerve stimulation: A targeted approach for reducing tissue-specific ischemic reperfusion injury

Vagus Nerve Stimulation (VNS), a neuromodulation technique of applying controlled electrical impulses to the vagus nerve, has now emerged as a potential therapeutic approach for ischemia-reperfusion insults. It provides a pivotal link in improving functional outcomes for the central nervous system and multiple target organs affected by ischemia-reperfusion injury (I/RI). Reduced blood flow during ischemia and subsequent resumption of blood supply during reperfusion to the tissue compromises cellular health because of the combination of mitochondrial dysfunction, oxidative stress, cytokine release, inflammation, apoptosis, intracellular calcium overload, and endoplasmic reticulum stress, which ultimately leads to cell death and irreversible tissue damage. Furthermore, inflammation and apoptosis also play critical roles in the acute progression of ischemic injury pathology. Emerging evidence indicates that VNS in I/RI may act in an anti-inflammatory capacity, reducing oxidative stress and apoptosis, while also improving endothelial and mitochondrial function leading to reduced infarct sizes and cytoprotection in skeletal muscle, gastrointestinal tract, liver, kidney, lung, heart, and brain tissue. In this review, we attempt to shed light on the mechanistic links between tissue-specific damage following I/RI and the therapeutic approach of VNS in attenuating damage, considering both direct and remote I/RI scenarios. Thus, we want to advance the understanding of VNS that could further warrant its clinical implementation, especially as a treatment for I/RI.

Melatonin attenuates liver ischemia-reperfusion injury via inhibiting the PGAM5-mPTP pathway

Phosphoglycerate mutase/protein phosphatase (PGAM5)-mediated cell death plays an important role in multiple liver diseases. However, few studies have confirmed the regulatory mechanism of melatonin acting on PGAM5-mediated cell death in the context of liver ischemia-reperfusion (I/R) injury. The liver I/R injury model and cell hypoxia-reoxygenation model were established after melatonin pretreatment. Liver injury, cell activity, cell apoptosis, oxidative stress index, and PGAM5 protein expression were detected. To investigate the role of PGAM5 in melatonin-mediated liver protection during I/R injury, PGAM5 silencing, and overexpression were performed before melatonin pretreatment. Our results indicated that PGAM5 was significantly elevated by I/R injury, and predominantly localized in the necrosis area. However, treatment with melatonin blocked PGAM5 activation and conferred a survival advantage of hepatocytes in liver I/R injury, similar to the results achieved by silencing PGAM5. In terms of mechanism, we illustrated that activated PGAM5 promoted mitochondrial permeability transition pore (mPTP) opening, and administration of melatonin inhibited mPTP opening and interrupted hepatocytes death via blocking PGAM5. Our data indicated that the PGAM5-mPTP axis is responsible for I/R-induced liver injury. In contrast, melatonin supplementation blocked the PGAM5-mPTP axis and thus decreased cell death, providing a protective advantage to hepatocytes in I/R. These results established a new paradigm in melatonin-mediated hepatocyte protection under the burden of I/R attack.

The protective role of vagus nerve stimulation in ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) encompasses the damage resulting from the restoration of blood supply following tissue ischemia. This phenomenon commonly occurs in clinical scenarios such as hemorrhagic shock, severe trauma, organ transplantation, and thrombolytic therapy. Despite its prevalence, existing treatments exhibit limited efficacy against IRI. Vagus nerve stimulation (VNS) is a widely utilized technique for modulating the autonomic nervous system. Numerous studies have demonstrated that VNS significantly reduces IRI in various organs, including the heart, brain, and liver. This article reviews the pathological processes during IRI and summarizes the role and possible mechanisms of VNS in IRI of different organs. Furthermore, this review addresses the current challenges of VNS clinical applications, providing a novel perspective on IRI treatment.

Effects of a single session of noninvasive auricular vagus nerve stimulation on sports performance in elite athletes: an open-label randomized controlled trial

OBJECTIVES

The purpose of this study was to investigate the efficacy of noninvasive auricular vagus nerve stimulation (AVNS) on sports performance.

METHODS

The intervention group (n = 30) received a single session of AVNS, while the control group (n = 30) received a single session of sham AVNS. Pre- and post-treatment isometric quadriceps muscle strength, heart rate, lower extremity balance, and grip strength were measured.

RESULTS

It was ascertained that the differences in heart rate (-0.73 pulse/min, p = 0.032) and modified Star Balance Test scores (anterior 2.72 cm, p = 0.000, posterolateral 3.65 cm, p = 0.000 and posteromedial 2.43 cm, p = 0.000) before and after AVNS were significant in subjects in the experimental group. The results of the one-way ANOVA analysis show that the differences obtained in all measurement parameters are not statistically significant (p > 0.05). Considering the partial eta squared (η2) obtained from the measurements, a small descriptive effect in favor of experimental group was obtained for the quadriceps strength (0.016) and anterior balance (0.054) measurements.

CONCLUSION

This study demonstrates that a single AVNS session compared to sham AVNS shows a modest benefit though not statistically significant improvement in athletic performance. Single-use of AVNS seems not effective in improving athletic performance.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov identifier NCT05436821.

Vagus nerve stimulation attenuates acute kidney injury induced by hepatic ischemia/reperfusion injury in rats

Hepatic ischemia/reperfusion (I/R) injury, caused by limited blood supply and subsequent blood supply, is a causative factor resulting in morbidity and mortality during liver transplantation and liver resection. Hepatic I/R injury frequently contributes to remote organ injury, such as kidney, lung, and heart. It has been demonstrated that vagus nerve stimulation (VNS) is effective in remote organ injury after I/R injury. Here, our aim is to investigate the potential action of VNS on hepatic I/R injury-induced acute kidney injury (AKI) and explore its underlying mechanisms. To test this hypothesis, male Sprague-Dawley rats were randomly assigned into three experimental groups: Sham group (sham operation, n = 6); I/R group (hepatic I/R with sham VNS, n = 6); and VNS group (hepatic I/R with VNS, n = 6). VNS was performed during the entire hepatic I/R process. Our results showed that throughout the hepatic I/R process, VNS significantly regulated the expression levels of various iconic factors and greatly enhanced the protein expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and hemeoxygenase-1 (HO-1) in the kidneys. These findings suggested that VNS may ameliorate hepatic I/R injury-induced AKI by suppressing inflammation, oxidative stress, and apoptosis probably through activating the Nrf2/HO-1 signaling pathway.

Ferroptosis increases obesity: Crosstalk between adipocytes and the neuroimmune system

Ferroptosis requires not only the accumulation of iron ions, but also changes in many ferroptosis-related regulators, including a decrease in GPX4 and inhibition of SLC7A11 for classical ferroptosis, a deletion of FSP1 or GCH1. Surprisingly, adipose tissue (AT) in the obesity conditions is also accompanied by iron buildup, decreased GSH, and increased ROS. On the neurological side, the pro-inflammatory factor released by AT may have first caused ferroptosis in the vagus nerve by inhibiting of the NRF2-GPX4 pathway, resulting in disorders of the autonomic nervous system. On the immune side, obesity may cause M2 macrophages ferroptosis due to damage to iron-rich ATMs (MFe^hi) and antioxidant ATMs (Mox), and lead to Treg cells ferroptosis through reductions in NRF2, GPX4, and GCH1 levels. At the same time, the reduction in GPX4 may also trigger the ferroptosis of B1 cells. In addition, some studies have also found the role of GPX4 in neutrophil autophagy, which is also worth pondering whether there is a connection with ferroptosis. In conclusion, this review summarizes the associations between neuroimmune regulation associated with obesity and ferroptosis, and on the basis of this, highlights their potential molecular mechanisms, proposing that ferroptosis in one or more cells in a multicellular tissue changes the fate of that tissue.

Long-term normothermic machine preservation of human livers: what is needed to succeed?

Although short-term machine perfusion (≤24 h) allows for resuscitation and viability assessment of high-risk donor livers, the donor organ shortage might be further remedied by long-term perfusion machines. Extended preservation of injured donor livers may allow reconditioning, repairing, and regeneration. This review summarizes the necessary requirements and challenges for long-term liver machine preservation, which requires integrating multiple core physiological functions to mimic the physiological environment inside the body. A pump simulates the heart in the perfusion system, including automatically controlled adjustment of flow and pressure settings. Oxygenation and ventilation are required to account for the absence of the lungs combined with continuous blood gas analysis. To avoid pressure necrosis and achieve heterogenic tissue perfusion during preservation, diaphragm movement should be simulated. An artificial kidney is required to remove waste products and control the perfusion solution's composition. The perfusate requires an oxygen carrier, but will also be challenged by coagulation and activation of the immune system. The role of the pancreas can be mimicked through closed-loop control of glucose concentrations by automatic injection of insulin or glucagon. Nutrients and bile salts, generally transported from the intestine to the liver, have to be supplemented when preserving livers long term. Especially for long-term perfusion, the container should allow maintenance of sterility. In summary, the main challenge to develop a long-term perfusion machine is to maintain the liver's homeostasis in a sterile, carefully controlled environment. Long-term machine preservation of human livers may allow organ regeneration and repair, thereby ultimately solving the shortage of donor livers.

Vagus Nerve Stimulation Attenuates Acute Skeletal Muscle Injury Induced by Hepatic Ischemia/Reperfusion Injury in Rats

Vagus nerve stimulation (VNS) has a protective effect on distal organ injury after ischemia/reperfusion (I/R) injury. We aimed to investigate the protective efficacy of VNS on hepatic I/R injury-induced acute skeletal muscle injury and explore its underlying mechanisms. To test this hypothesis, male Sprague-Dawley rats were randomly divided into three groups: sham group (sham operation, n = 6); I/R group (hepatic I/R with sham VNS, n = 6); and VNS group (hepatic I/R with VNS, n = 6). A hepatic I/R injury model was prepared by inducing hepatic ischemia for 1 h (70%) followed by hepatic reperfusion for 6 h. VNS was performed during the entire hepatic I/R process. Tissue and blood samples were collected at the end of the experiment for biochemical assays, molecular biological preparations, and histological examination. Our results showed that throughout the hepatic I/R process, VNS significantly reduced inflammation, oxidative stress, and apoptosis, while significantly increasing the protein levels of silent information regulator 1 (SIRT1) and decreasing the levels of acetylated forkhead box O1 and Ac-p53, in the skeletal muscle. These data suggest that VNS can alleviate hepatic I/R injury-induced acute skeletal muscle injury by suppressing inflammation, oxidative stress, and apoptosis, potentially via the SIRT1 pathway.

Downregulation of miR-497-5p prevents liver ischemia-reperfusion injury in association with MED1/TIMP-2 axis and the NF-κB pathway

Liver ischemia-reperfusion (I/R) injury is a common clinical pathological phenomenon, which is accompanied by the occurrence in liver transplantation. However, the underlying mechanism is not yet fully understood. MicroRNAs (miRNAs) play an important role in liver I/R injury. Therefore, the study of miRNAs function will contribute a new biological marker diagnosis of liver I/R injury. This study aims to evaluate effects of miR-497-5p in liver I/R injury in mice. The related regulatory factors of miR-497-5p in liver I/R injury were predicted by bioinformatics analysis. Vascular occlusion was performed to establish the liver I/R injury animal models. Hypoxia/reoxygenation (H/R) was performed to establish the in vitro models. Hematoxylin-eosin (HE) staining was conducted to assess liver injury. The inflammatory factors were evaluated by enzyme-linked immunosorbent assay (ELISA). Flow cytometry was adopted to assess the cell apoptosis. The expression of miR-497b-5p was increased in liver I/R injury. Knockdown of miR-497b-5p inhibited the production of inflammatory factors and cell apoptosis. Overexpression of mediator complex subunit 1 (MED1) and tissue inhibitor of metalloproteinase 2 (TIMP2) inhibited cell apoptosis to alleviate liver I/R injury. miR-497b-5p could activate the nuclear factor kappa-B (NF-κB) pathway by inhibiting the MED1/TIMP-2 axis to promote liver I/R injury. This study may provide a new strategy for the treatment of liver I/R injury.

Hepatic ischemia reperfusion injury: effect of moderate intensity exercise and oxytocin compared to l-arginine in a rat model

Background

Hepatic ischemia reperfusion (IR) injury is considered as a main cause of liver damage and dysfunction. The l-arginine/nitric oxide pathway seems to be relevant during this process of IR. Although acute intense exercise challenges the liver with increased reactive oxygen species (ROS), regular training improves hepatic antioxidant status. Also, oxytocin (Oxy), besides its classical functions, it exhibits a potent antistress, anti-inflammatory, and antioxidant effects. This study was designed to evaluate the hepatic functional and structural changes induced by hepatic IR injury in rats and to probe the effect and potential mechanism of moderate intensity exercise training and/or Oxy, in comparison to a nitric oxide donor, l-arginine, against liver IR-induced damage.

Results

Compared to the sham-operated control group, the hepatic IR group displayed a significant increase in serum levels of ALT and AST, plasma levels of MDA and TNF-α, and significant decrease in plasma TAC and nitrite levels together with the worsening of liver histological picture. L-Arg, Oxy, moderate intensity exercise, and the combination of both Oxy and moderate intensity exercises ameliorated these deleterious effects that were evident by the significant decrease in serum levels of ALT and AST, significant elevation in TAC and nitrite, and significant decline in lipid peroxidation (MDA) and TNF-α, besides regression of histopathological score regarding hepatocyte necrosis, vacuolization, and nuclear pyknosis. Both the moderate intensity exercise-trained group and Oxy-treated group showed a significant decline in TNF-α and nitrite levels as compared to l-Arg-treated group. The Oxy-treated group showed statistical insignificant changes in serum levels of ALT, AST, and plasma levels of nitrite, MDA, TAC, and TNF-α as compared to moderate intensity exercise-trained group.

Conclusion

The combination of both moderate intensity exercise and Oxy displayed more pronounced hepatoprotection on comparison with l-Arg which could be attributed to their more prominent antioxidant and anti-inflammatory effects but not due to their NO-enhancing effect.

Blocking the Hepatic Branch of the Vagus Aggravates Hepatic Ischemia-Reperfusion Injury via Inhibiting the Expression of IL-22 in the Liver

Liver ischemia-reperfusion injury (IRI) is an inevitable process during liver transplantation, hemorrhagic shock, resection, and other liver surgeries. It is an important cause of postoperative liver dysfunction and increased medical costs. The protective effects of the vagus nerve on hepatic IRI have been reported, but the underlying mechanism has not been fully understood. We established a hepatic vagotomy (Hv) mouse model to study the effect of the vagus on liver IRI and to explore the underlying mechanism. Liver IRI was more serious in mice with Hv, which showed higher serum ALT and AST activities and histopathological changes. Further experiments confirmed that Hv significantly downregulated the expression of IL-22 protein and mRNA in the liver, blocking the activation of the STAT3 pathway. The STAT3 pathway in the livers of Hv mice was significantly activated, and liver injury was clearly alleviated after treatment with exogenous IL-22 recombinant protein. In conclusion, Hv can aggravate hepatic IRI, and its mechanism may be related to inhibition of IL-22 expression and downregulation of the STAT3 pathway in the liver.