Vagus Nerve Attenuates Hepatocyte Apoptosis upon Ischemia-Reperfusion via α7 Nicotinic Acetylcholine Receptor on Kupffer Cells in Mice

PRIAM1 participates in the inhibition of inflammation and acetylcholinesterase activity in goose fatty liver formation

Goose fatty liver, a product of short-term overfeeding, is notable for its high nutritional value and unique tolerance to severe steatosis without inflammation, in contrast to human nonalcoholic fatty liver disease (NAFLD). It is known that choline can alleviate nonalcoholic steatohepatitis and liver cirrhosis, inhibit cell apoptosis, promote lecithin synthesis and fat transportation out of the liver, and relieve cardiovascular disease-related symptoms (e.g., hyperlipidemia and hypercholesterolemia). This study investigates the role of Proline Rich Membrane Anchor 1 (PRIMA1) in inhibiting inflammation through choline metabolism during goose fatty liver formation. Overfeeding of geese resulted in increased body and liver weights, elevated fat content, and significantly higher expression of PRIMA1, accompanied by decreased LITAF and CRP (important pro-inflammatory cytokines) expression and reduced acetylcholinesterase (AchE) activity, which was assessed by the amount of produced choline. The overexpression of PRIMA1 in goose primary hepatocytes (GPHs) enhanced AchE activity. Consistently, glucose-induced upregulation of PRIMA1 expression in GPHs was accompanied by increased AchE activity. Further combined treatment with glucose and PRIMA1 knockdown in GPHs showed that downregulation of PRIMA1 attenuated the suppression of LITAF and CRP expression caused by glucose addition, but had no effect on the rise in AchE activity. These findings indicate that PRIMA1 may play a role in promoting choline metabolism and protecting against liver inflammation, offering insights into potential therapeutic targets for NAFLD.

Activation of α7 Nicotinic Acetylcholine Receptors Inhibits Hepatic Necroptosis and Ameliorates Acute Liver Injury in Mice

BACKGROUND

Acute liver injury is a disease characterized by severe liver dysfunction, caused by significant infiltration of immune cells and extensive cell death with a high mortality. Previous studies demonstrated that the α7 nicotinic acetylcholine receptor (α7nAChR) played a crucial role in various liver diseases. The hypothesis of this study was that activating α7nAChR could alleviate acute liver injury and investigate its possible mechanisms.

METHODS

Acute liver injury was induced by intraperitoneal injection of lipopolysaccharide (LPS)/D-galactosamine (D-Gal) in wild type, α7nAChR knockout (α7nAChR-/-) and stimulator of interferon gene (STING) mutation (Stinggt/gt) mice in the presence or absence of a pharmacologic selective α7nAChR agonist (PNU-282987). The effects of α7nAChR on hepatic injury, inflammatory response, mitochondrial damage, necroptosis, and infiltration of immune cells during acute liver injury were assessed.

RESULTS

The expression of α7nAChR in liver tissue was increased in LPS/D-Gal-induced acute liver injury mice. Compared to the age-matched wild-type mice, α7nAChR deficiency decreased the survival rate, exacerbated the hepatic injury accompanied with enhanced inflammatory response and oxidative stress, and aggravated hepatic mitochondrial damage and necroptosis. Conversely, pharmacologic activation of α7nAChR by PNU-282987 displayed the opposite trends. Furthermore, PNU-282987 significantly reduced the proportion of infiltrating monocyte-derived macrophages (CD45+CD11bhiF4/80int), M1 macrophages (CD45+CD11b+F4/80+CD86hiCD163low), and Ly6Chi monocytes (CD45+CD11b+MHC [major histocompatibility complex] ⅡlowLy6Chi), but increased the resident Kupffer cells (CD45+CD11bintF4/80hiTIM4hi) in the damaged hepatic tissues caused by LPS/D-Gal. Interestingly, α7nAChR deficiency promoted the STING signaling pathway under LPS/D-Gal stimulation, while PNU-282987 treatment significantly prevented its activation. Finally, it was found that Sting mutation abolished the protective effects against hepatic injury by activating α7nAChR.

CONCLUSIONS

The authors' study revealed that activating α7nAChR could protect against LPS/D-Gal-induced acute liver injury by inhibiting hepatic inflammation and necroptosis possibly via regulating immune cells infiltration and inhibiting STING signaling pathway.

EDITOR’S PERSPECTIVE

Modafinil lightens apoptosis and inflammatory response in hepatic ischemia-reperfusion injury through inactivation of TLR9/Myd88/p38 signaling

Hepatic ischemia/reperfusion injury (IRI) remains a severe threat during liver surgery and transplantation, accounting for unfavorable clinical outcomes. Modafinil (MOD), a wakefulness-inducing compound, is increasingly disclosed to protect against IRI. However, the specific literatures covering the association between MOD and hepatic IRI are few. Here, this paper is committed to unraveling the role and response mechanism of MOD in hepatic IRI. After the establishment of hepatic IRI mice model and cell model, relevant assay kits measured the concentrations of biochemical indicators of hepatotoxicity and hematoxylin and eosin staining estimated liver morphology. Enzyme-linked immunosorbent assay, reverse-transcription quantitative polymerase chain reaction, and western blot evaluated inflammatory levels. Terminal-deoxynucleoitidyl transferase-mediated nick end labeling assay and western blot appraised apoptosis. Western blot also analyzed the expression of Toll-like receptor 9 (TLR9)/myeloid differentiation primary response gene 88 (MyD88)/p38 signaling-associated proteins. Cell counting kit-8 method judged cell viability. MOD was discovered to mitigate liver dysfunction and morphological damage, inflammatory response, apoptosis in vivo and improve cell viability, suppress inflammatory response and apoptosis in vitro. In addition, MOD inactivated TLR9/Myd88/p38 signaling both in vitro and in vivo. Further, TLR9 elevation reversed the inhibitory role of MOD in inflammatory response and cell apoptosis in vitro. Anyway, MOD blocked TLR9/Myd88/p38 signaling to exhibit anti-inflammatory and anti-apoptotic properties in hepatic IRI.

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.

The Novel MyD88 Inhibitor TJ-M2010-5 Protects Against Hepatic Ischemia-reperfusion Injury by Suppressing Pyroptosis in Mice

BACKGROUND

. With the development of medical technology and increased surgical experience, the number of patients receiving liver transplants has increased. However, restoration of liver function in patients is limited by the occurrence of hepatic ischemia-reperfusion injury (IRI). Previous studies have reported that the Toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88) signaling pathway and pyroptosis play critical roles in the development of hepatic IRI.

METHODS

. A mouse model of segmental (70%) warm hepatic IRI was established using BALB/c mice in vivo. The mechanism underlying inflammation in mouse models of hepatic IRI was explored in vitro using lipopolysaccharide- and ATP-treated bone marrow-derived macrophages. This in vitro inflammation model was used to simulate inflammation and pyroptosis in hepatic IRI.

RESULTS

. We found that a MyD88 inhibitor conferred protection against partial warm hepatic IRI in mouse models by downregulating the TLR4/MyD88 signaling pathway. Moreover, TJ-M2010-5 (a novel MyD88 inhibitor, hereafter named TJ-5) reduced hepatic macrophage depletion and pyroptosis induction by hepatic IRI. TJ-5 treatment inhibited pyroptosis in bone marrow-derived macrophages by reducing the nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells, decreasing the release of high-mobility group box-1, and promoting endocytosis of lipopolysaccharide-high-mobility group box-1 complexes.

CONCLUSIONS

. Inhibition of MyD88 may protect the liver from partial warm hepatic IRI by reducing pyroptosis in hepatic innate immune cells. These results reveal the mechanism underlying the development of inflammation in partially warm hepatic IRI and the induction of cell pyroptosis.

NAMPT inhibition reduces macrophage inflammation through the NAD+/PARP1 pathway to attenuate liver ischemia-reperfusion injury

BACKGROUND

Liver ischemia-reperfusion injury (IRI) is a major complication in the perioperative period and often leads to liver failure and even systemic inflammation. Previous studies have suggested that the inflammatory response participated in the liver damage during liver IRI. Nicotinamide phosphoribosyl transferase (NAMPT) is required for the maintenance of cellular nicotinamide adenine dinucleotide (NAD+) levels, catalyzing the rate-limiting step in the NAD + salvage pathway. NAMPT is strongly upregulated during inflammation and constitutes an important mechanistic link between inflammatory, metabolic, and transcriptional pathways. The aim of our study was to investigate the role of NAMPT in liver IRI.

METHODS

We investigated the effect of pharmacological inhibition of NAMPT with FK866 in models of liver IRI. Liver damage was assessed by HE staining, serum ALT/AST, and TUNEL staining. To examine the mechanism, primary hepatocytes, liver macrophages and RAW264.7 cells were treated with or without NAMPT inhibitors before hypoxia-reoxygenation. Liver macrophages and RAW 264.7 cells activation in vitro was evaluated by western blotting, flow cytometry, and ELISA.

RESULT

We found that NAMPT was upregulated in liver IRI. Treatment with the NAMPT inhibitor FK866 ameliorated liver IRI and suppressed inflammation in mice. Although NAMPT plays an important role both in hepatocytes and liver macrophages, we focused on the impact of NAMPT on liver macrophages. The mechanism revealed that FK866 potently inhibited NAMPT activity, as demonstrated by reduced liver NAD+ and intracellular NAD+, resulting in reduced abundance and activity of NAD + -dependent enzymes, including poly (ADP-ribose) polymerase 1 (PARP1), thus inhibiting macrophage M1 polarization by reducing CD86, iNOS, TNF-α, and interleukin (IL)-1β. Taken together, our data suggested that NAMPT can regulate macrophage polarization through NAD+/PARP1 to ameliorate liver injury, and that FK866-mediated NAMPT blockade may be a therapeutic approach in liver IRI.

Activating α7nAChR ameliorates abdominal aortic aneurysm through inhibiting pyroptosis mediated by NLRP3 inflammasome

Abdominal aortic aneurysm (AAA) is defined as a dilated aorta in diameter at least 1.5 times of a normal aorta. Our previous studies found that activating α7 nicotinic acetylcholine receptor (α7nAChR) had a protective effect on vascular injury. This work was to investigate whether activating α7nAChR could influence AAA formation and explore its mechanisms. AAA models were established by angiotensin II (Ang II) infusion in ApoE-/- mice or in wild type and α7nAChR-/- mice. In vitro mouse aortic smooth muscle (MOVAS) cells were treated with tumor necrosis factor-α (TNF-α). PNU-282987 was chosen to activate α7nAChR. We found that cell pyroptosis effector GSDMD and NLRP3 inflammasome were activated in abdominal aorta, and inflammatory cytokines in serum were elevated in AAA models of ApoE-/- mice. Activating α7nAChR reduced maximal aortic diameters, preserved elastin integrity and decreased inflammatory responses in ApoE-/- mice with Ang II infusion. While α7nAChR-/- mice led to aggravated aortic injury and increased inflammatory cytokines with Ang II infusion when compared with wild type. Moreover, activating α7nAChR inhibited NLRP3/caspase-1/GSDMD pathway in AAA model of ApoE-/- mice, while α7nAChR deficiency promoted this pathway. In vitro, N-acetylcysteine (NAC) inhibited NLRP3 inflammasome activation and NLRP3 knockdown reduced GSDMD expression, in MOVAS cells treated with TNF-α. Furthermore, activating α7nAChR inhibited oxidative stress, reduced NLRP3/GSDMD expression, and decreased cell pyroptosis in MOVAS cells with TNF-α. In conclusion, our study found that activating α7nAChR retarded AAA through inhibiting pyroptosis mediated by NLRP3 inflammasome. These suggested that α7nAChR would be a potential pharmacological target for AAA.

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.

Activation of vagovagal reflex prevents hepatic ischaemia-reperfusion-induced lung injury via anti-inflammatory and antioxidant effects

NEW FINDINGS

What is the central question of this study? Does vagus nerve stimulation have protective effects against both direct liver damage and distant lung injury in a rat model of hepatic ischaemia-reperfusion? What is the main finding and its importance? Vagus nerve stimulation provides protection through anti-inflammatory and anti-oxidative stress effects, possibly achieved by the vagovagal reflex.

ABSTRACT

Hepatic ischaemia-reperfusion (I/R) is not an isolated event; instead, it can result in remote organ dysfunction. The aim of this study was to investigate whether vagus nerve stimulation (VNS) can alleviate hepatic I/R-induced lung injury and to explore the underlying mechanism. Thirty male Sprague-Dawley rats were randomly allocated into five groups (n = 6 each): the sham group (without I/R or VNS), the I/R group (hepatic I/R) and three different VNS treatment groups (hepatic I/R plus VNS). The hepatic I/R group was subjected to occlusion of the portal vein and hepatic artery for 1 h, followed by 6 h of reperfusion. The intact afferent and efferent cervical vagus nerves were stimulated throughout the I/R process. During VNS, cervical neural activity was recorded. At the end of the experiment, liver function, the wet-to-dry lung weight ratio, histology of the liver and lung and inflammatory/oxidative indices were evaluated. We found that VNS significantly mitigated lung injury, as demonstrated by alleviation of pulmonary oedema and pathological alterations, by limiting inflammatory cytokine infiltration and increasing antioxidant capability. This proof-of-concept study suggested that VNS might protect patients from lung injury induced by hepatic I/R related to various circumstances.

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.

Fenofibrate Ameliorates Hepatic Ischemia/Reperfusion Injury in Mice: Involvements of Apoptosis, Autophagy, and PPAR-α Activation

Hepatic ischemia and reperfusion injury is characterized by hepatocyte apoptosis, impaired autophagy, and oxidative stress. Fenofibrate, a commonly used antilipidemic drug, has been verified to exert hepatic protective effects in other cells and animal models. The purpose of this study was to identify the function of fenofibrate on mouse hepatic IR injury and discuss the possible mechanisms. A segmental (70%) hepatic warm ischemia model was established in Balb/c mice. Serum and liver tissue samples were collected for detecting pathological changes at 2, 8, and 24 h after reperfusion, while fenofibrate (50 mg/kg, 100 mg/kg) was injected intraperitoneally 1 hour prior to surgery. Compared to the IR group, pretreatment of FF could reduce the inflammatory response and inhibit apoptosis and autophagy. Furthermore, fenofibrate can activate PPAR-α, which is associated with the phosphorylation of AMPK.

The dual role of alpha7 nicotinic acetylcholine receptor in inflammation-associated gastrointestinal cancers

Alpha7 nicotinic acetylcholine receptor (α7nAChR) is one of the main subtypes of nAChRs that modulates various cancer-related properties including proliferative, anti-apoptotic, pro-angiogenic and pro-metastatic activities in most of the cancers. It also plays a crucial role in inflammation control through the cholinergic anti-inflammatory pathway in numerous pathophysiological contexts. Such diverse physiological and pathological functions that initiate from this receptor may have significant impacts in determining the outcome of different cancers. Various tissues of gastrointestinal (GI) cancers such as gastric, colorectal, pancreatic and liver cancers have shown the up-regulated expression of α7nAChR as compared to normal adjacent tissues. According to the well-established connection between inflammation and tumorigenesis in the digestive system, there are mounting studies demonstrated either stimulatory or inhibitory effects of α7nAChR signaling in the development of GI cancers. To date, the precise underlying mechanisms related to this receptor in patients with GI cancers have not been fully elucidated. Regarding the paradoxical modulatory effects of this receptor in carcinogenesis, in this review, we aim to summarize the accumulated evidence about the involvement of α7nAChR in inflammation-associated GI cancers. It seems that the complex influences of α7nAChR may be a promising target in designing novel strategies in the treatment of such pathologic conditions.

Vagus nerve regulates the phagocytic and secretory activity of resident macrophages in the liver

The gastrointestinal (GI) tract harbors commensal microorganisms as well as invasive bacteria, toxins and other pathogens and, therefore, plays a pivotal barrier and immunological role against pathogenic agents. The vagus nerve is an important regulator of the GI tract-associated immune system, having profound effects on inflammatory responses. Among GI tract organs, the liver is a key site of immune surveillance, as it has a large population of resident macrophages and receives the blood drained from the guts through the hepatic portal circulation. Although it is widely accepted that the hepatic tissue is a major target for vagus nerve fibers, the role of this neural circuit in liver immune functions is still poorly understood. Herein we used in vivo imaging techniques, including confocal microscopy and scintigraphy, to show that vagus nerve stimulation increases the phagocytosis activity by resident macrophages in the liver, even on the absence of an immune challenge. The activation of this neural circuit in a non-lethal model of sepsis optimized the removal of bacteria in the liver and resulted in the production of anti-inflammatory and pro-regenerative cytokines. Our findings provide new insights into the neural regulation of the immune system in the liver.

Vagus Nerve Stimulation Attenuates Hepatic Ischemia/Reperfusion Injury via the Nrf2/HO-1 Pathway

It has been demonstrated that vagus nerve stimulation (VNS) plays a protective role in ischemia/reperfusion (I/R) injury of various organs. The present study investigates the protective effect of VNS on hepatic I/R injury and the potential mechanisms. Male Sprague-Dawley rats were randomly allocated into three groups: the sham operation group (Sham; n = 6, sham surgery with sham VNS); the I/R group (n = 6, hepatic I/R surgery with sham VNS); and the VNS group (n = 6, hepatic I/R surgery plus VNS). The I/R model was established by 1 hour of 70% hepatic ischemia. Tissue samples and blood samples were collected after 6 hours of reperfusion. The left cervical vagus nerve was separated and stimulated throughout the whole I/R process. The stimulus intensity was standardized to the voltage level that slowed the sinus rate by 10%. VNS significantly reduced the necrotic area and cell death in I/R tissues. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) were also decreased by VNS. In addition, VNS suppressed inflammation, oxidative stress, and apoptosis in I/R tissues. VNS significantly increased the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) in the liver. These data indicated that VNS may attenuate hepatic I/R injury by inhibiting inflammation, oxidative stress, and apoptosis possibly via the Nrf2/HO-1 pathway.

Fenofibrate improves vascular endothelial function in diabetic mice

Microvascular and macrovascular complications are major causes of disability and death in diabetic patients. High levels of blood glucose sabotage the integrity of blood vessels and induce endothelial dysfunction. Fenofibrate is an agonist of peroxisome proliferator-activated receptor α and can reduce the incidence of cardiovascular events in diabetic patients. This study tested the hypothesis that fenofibrate could ameliorate endothelium-dependent vasodilation in diabetic mice and relieve high glucose-induced endothelial dysfunction via activating endothelial nitric oxide synthase (eNOS) and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. A streptozotocin (STZ)-induced diabetic model was established by intraperitoneal injection of STZ (dissolved in sodium citrate buffer) at a dose of 60 mg/kg for 5 consecutive days. Mice were administered fenofibrate (100 mg/kg/d, i.g.) for 14 days. The endothelial function of extracted mouse aortae was examined by evaluating acetylcholine induced endothelium-dependent relaxation combined with phenylephrine-induced vasoconstriction and sodium nitroprusside-induced endothelium-independent relaxation. Superoxide onion (O₂^-) was determined using dihydroethidium staining of aortae. Functions of mouse aortic endothelial cells (MAECs) were assessed, and expression levels of eNOS and AMPK were determined by Western blotting. Fenofibrate ameliorated the impaired endothelium-dependent relaxation in diabetic mice and decreased the level of intracellular O₂- in diabetic mouse aortae. In-vitro, fenofibrate treatment improved the impaired function of MAECs, increased nitric oxide production, and decreased the O₂- level, as well as activated eNOS and AMPK phosphorylation in cultured MAECs by high glucose. Fenofibrate could ameliorate endothelium-dependent vasodilation in diabetic mice and relieve high glucose-induced endothelial dysfunction, which was possibly related to the activation of eNOS and AMPK phosphorylation.

Rivastigmine prevents injury induced by ischemia and reperfusion in rat liver

PURPOSE

To evaluate whether pre-treatment with rivastigmine is able to attenuate the I/R induced lesions in rat liver.

METHODS

SHAM animals or those submitted to I/R, non-treated or pre-treated with rivastigminine (2mg/kg) either 50 or 15 minutes before ischemia, were used. After I/R protocol, these animals were killed and their livers were harvested to measurement of the mitochondrial swelling as well as the malondialdehyde (MDA), nitrite and nitrate tissue concentration. Blood was also harvested for serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) determinations.

RESULTS

I/R promoted a significant increase of mitochondrial swelling in the studied animals. This increase of mitochondrial swelling was partially prevented by rivastigmine, but only if administered 50 minutes before ischemia. No significant modification of MDA, nitrite or nitrate tissue concentrations was observed in consequence of I/R, followed or not by rivastigmine treatments. In addition, I/R elevated both AST and ALT. These elevations of serum enzymes were not reversed by the different rivastigmine treatments.

CONCLUSIONS

Rivastigmine administered 50 minutes before ischemia attenuates I/R-induced mitochondrial swelling, that indicates liver injury. This protective effect may be related to a greater stimulation of α7nAChR present in the Kupffer cells by the non-methabolized ACh, leading to an attenuation of I/R-induced inflammation.

Revisiting the Cardioprotective Effects of Acetylcholine Receptor Activation against Myocardial Ischemia/Reperfusion Injury

Acute myocardial infarction (AMI) is the most common cause of acute myocardial injury and its most clinically significant form. The most effective treatment for AMI is to restore an adequate coronary blood flow to the ischemic myocardium as quickly as possible. However, reperfusion of an ischemic region can induce cardiomyocyte death, a phenomenon termed “myocardial ischemia/reperfusion (I/R) injury”. Disruption of cardiac parasympathetic (vagal) activity is a common hallmark of a variety of cardiovascular diseases including AMI. Experimental studies have shown that increased vagal activity exerts cardioprotective effects against myocardial I/R injury. In addition, acetylcholine (ACh), the principle cardiac vagal neurotransmitter, has been shown to replicate the cardioprotective effects of cardiac ischemic conditioning. Moreover, studies have shown that cardiomyocytes can synthesize and secrete ACh, which gives further evidence concerning the importance of the non-neuronal cholinergic signaling cascades. This suggests that the activation of ACh receptors is involved in cardioprotection against myocardial I/R injury. There are two types of ACh receptors (AChRs), namely muscarinic and nicotinic receptors (mAChRs and nAChRs, respectively). However, the effects of AChRs activation in cardioprotection during myocardial I/R are still not fully understood. In this review, we summarize the evidence suggesting the association between AChRs activation with both electrical and pharmacological interventions and the cardioprotection during myocardial I/R, as well as outline potential mechanisms underlying these cardioprotective effects.

Nicotinic acetylcholine receptor α7 subunit improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide; yet, the pathogenesis of the disorder is not completely understood. The nicotinic acetylcholine receptor α7 subunit (α7nAChR) plays an indispensable role in the vagus nerve-regulated cholinergic anti-inflammatory pathway.

METHODS

In the present study, we investigated the key role of α7nAChR in NAFLD development. Male wild-type (WT) and α7nAChR knockout (α7nAChR^-/-) mice were fed a normal chow or a high-fat diet (HFD) for 16weeks to induce NAFLD.

RESULTS

We found that both the mRNA and protein levels of α7nAChR in the liver tissue of NAFLD mice were significantly higher than those in mice fed normal chow. There were no differences in food intake, body weight, hepatic cholesterol and triglyceride contents, and insulin sensitivity between WT and α7nAChR^-/- mice under normal condition. When the WT and α7nAChR^-/- mice were challenged with HFD, the body weight of α7nAChR^-/- mice became higher than that of WT mice. The oxygen consumption and energy expenditure in HFD-fed α7nAChR^-/- mice were significantly lower than that in HFD-fed WT mice. The HFD-fed α7nAChR^-/- mice also showed more aggravated hepatic lipid accumulation, steatosis and oxidative stress than HFD-fed WT mice. Macrophage infiltration; mRNA levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β; and liver fibrosis were significantly accelerated in HFD-fed α7nAChR^-/- mice compared to that in HFD-fed WT mice. In addition, the bolus insulin injection-activated insulin signaling pathway, which was reflected by the phosphorylation of insulin receptor at Tyr1162/Tyr1163 site (p-IR^{Tyr1162/Tyr1163}), insulin receptor substrate-1 at Tyr612 site (p-IRS-1^Tyr612) and Akt at Ser473 (p-Akt^Ser473), was significantly compromised in liver tissues of HFD-fed α7nAChR^-/- mice relative to HFD-fed WT mice. Finally, pharmacologically activation of α7nAChR in HFD-fed mice, with a selective agonist PNU-282987, remarkably ameliorated the hepatic steatosis, inflammatory cell infiltration and fibrosis.

CONCLUSION

In conclusion, our results demonstrate that activation of α7nAChR improves energy homeostasis and inhibits inflammation in nonalcoholic fatty liver disease.

Cholinergic Anti-Inflammatory Pathway and the Liver

The hepatic vagus branches innervate the liver and serve an important role in liver-brain connection. It appears that brain modulates inflammatory responses by activation of vagal efferent fibers. This activation and subsequent acetylcholine releases from vagus nerve terminals leads to inhibition of inflammatory cytokines through α7 nicotinic acetylcholine receptors (α7nAChRs) which located on the surface of different cell types such as liver Kupffer cells. This protective role of vagus-α7nAChR axis in liver diseases has been shown in several experimental studies. On the other hand, accumulated evidence clearly demonstrate that, autonomic dysfunction which is reduced functioning of both vagal and sympathetic nervous system, occurs during chronic liver disease and is well-known complication of patients suffering from cirrhosis. This review describes the impact and significance of cholinergic anti-inflammatory pathway in the liver and discusses about its disease-related dysfunction on the progression of cirrhosis. Considering the fact that sepsis is major cause of death in cirrhotic patients, convergence of these findings, may lead to designing novel therapeutic strategies in the field of chronic liver diseases management involving selective drug targeting and electrical nerve stimulation.

Cholinergic anti-inflammatory pathway inhibits neointimal hyperplasia by suppressing inflammation and oxidative stress

Neointimal hyperplasia as a consequence of vascular injury is aggravated by inflammatory reaction and oxidative stress. The α7 nicotinic acetylcholine receptor (α7nAChR) is a orchestrator of cholinergic anti-inflammatory pathway (CAP), which refers to a physiological neuro-immune mechanism that restricts inflammation. Here, we investigated the potential role of CAP in neointimal hyperplasia using α7nAChR knockout (KO) mice. Male α7nAChR-KO mice and their wild-type control mice (WT) were subjected to wire injury in left common carotid artery. At 4 weeks post injury, the injured aortae were isolated for examination. The neointimal hyperplasia after wire injury was significantly aggravated in α7nAChR-KO mice compared with WT mice. The α7nAChR-KO mice had increased collagen contents and vascular smooth muscle cells (VSMCs) amount. Moreover, the inflammation was significantly enhanced in the neointima of α7nAChR-KO mice relative to WT mice, evidenced by the increased expression of tumor necrosis factor-α/interleukin-1β, and macrophage infiltration. Meanwhile, the chemokines chemokine (C-C motif) ligand 2 and chemokine (CXC motif) ligand 2 expression was also augmented in the neointima of α7nAChR-KO mice compared with WT mice. Additionally, the depletion of superoxide dismutase (SOD) and reduced glutathione (GSH), and the upregulation of 3-nitrotyrosine, malondialdehyde and myeloperoxidase were more pronounced in neointima of α7nAChR-KO mice compared with WT mice. Accordingly, the protein expression of NADPH oxidase 1 (Nox1), Nox2 and Nox4, was also higher in neointima of α7nAChR-KO mice compared with WT mice. Finally, pharmacologically activation of CAP with a selective α7nAChR agonist PNU-282987, significantly reduced neointima formation, arterial inflammation and oxidative stress after vascular injury in C57BL/6 mice. In conclusion, our results demonstrate that α7nAChR-mediated CAP is a neuro-physiological mechanism that inhibits neointima formation after vascular injury via suppressing arterial inflammation and oxidative stress. Further, these results imply that targeting α7nAChR may be a promising interventional strategy for in-stent stenosis.

α7 nicotinic acetylcholine receptor agonist inhibits the damage of rat hippocampal neurons by TLR4/Myd88/NF‑κB signaling pathway during cardiopulmonary bypass

The present study aimed to investigate the effect of α7 nicotinic acetylcholine receptor (α7nAChR) agonist on the damage of hippocampal neurons and the expression of toll like receptor 4 (TLR4)/myeloid differentiation primary response 88 (Myd88)/nuclear factor (NF)‑κB signal pathway‑associated factors in cardiopulmonary bypass (CPB). Sprague Dawley rats were randomly divided into five groups: Sham operation (Sham); CPB; CPB + α7nAChR agonist PHA568487 (PHA); CPB + α7nAChR inhibitor MLA (MLA); and CPB + PHA568487 + TLR4 antagonist (CPT). Blood and brain tissue samples were harvested at 12 h following the withdrawal of CPB. Levels of serum inflammatory factors [interleukin (IL)‑1β, IL‑6 and tumor necrosis factor (TNF)‑α] and brain injury markers [S‑100β and neuron‑specific enolase (NSE)] were measured using ELISA. In addition, pathological histology and apoptosis changes were observed using hematoxylin and eosin staining, and Tunnel assays. Quantitative polymerase chain reaction and western blot assays were used to determine the expression of TLR4, Myd88 and NF‑κB mRNA, and protein in the hippocampus. The morphology of hippocampal pyramidal cells in the Sham group was observed to be normal. Pyramidal cells in the CPB, MLA and CPT groups were loosely arranged, and the baselines had disappeared, with clear nucleus pyknosis and neuronal apoptosis. Furthermore, the cells in the PHA group were slightly damaged. IL‑1β, IL‑6, TNF‑α, S‑100β and NSE expression levels in the CPB, MLA, and CPT groups were significantly higher compared with that in the Sham group (P<0.05). Compared with CPB group, the expression of inflammatory cytokines in the PHA group was significantly lower (P<0.05). The expression of TLR4, Myd88 and NF‑κB mRNA, and protein in the hippocampus of CPB, MLA and CPT groups were significantly higher compared with that in the Sham group, and the PHA group expression was significantly lower compared with the CPB group (P<0.05). α7nAChRs agonist can inhibit the apoptosis of rat brain neurons induced by CPB, and may protect against brain injury through the TLR4/Myd88/NF‑κB signaling pathway.