Nitrite, a novel method to decrease ischemia/reperfusion injury in the rat liver

Effects of iNOS in Hepatic Warm Ischaemia and Reperfusion Models in Mice and Rats: A Systematic Review and Meta-Analysis

Warm ischaemia is usually induced by the Pringle manoeuver (PM) during hepatectomy. Currently, there is no widely accepted standard protocol to minimise ischaemia-related injury, so reducing ischaemia-reperfusion damage is an active area of research. This systematic review and meta-analysis focused on inducible nitric oxide synthase (iNOS) as an early inflammatory response to hepatic ischaemia reperfusion injury (HIRI) in mouse- and rat-liver models. A systematic search of studies was performed within three databases. Studies meeting the inclusion criteria were subjected to qualitative and quantitative synthesis of results. We performed a meta-analysis of studies grouped by different HIRI models and ischaemia times. Additionally, we investigated a possible correlation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) regulation with iNOS expression. Of 124 included studies, 49 were eligible for the meta-analysis, revealing that iNOS was upregulated in almost all HIRIs. We were able to show an increase of iNOS regardless of ischemia or reperfusion time. Additionally, we found no direct associations of eNOS or NO with iNOS. A sex gap of primarily male experimental animals used was observed, leading to a higher risk of outcomes not being translatable to humans of all sexes.

Long-term co-administration of sodium nitrite and sodium hydrosulfide inhibits hepatic gluconeogenesis in male type 2 diabetic rats: Role of PI3K-Akt-eNOS pathway

OBJECTIVE

A deficiency in hydrogen sulfide (H₂S) and nitric oxide (NO) contributes to the development of type 2 diabetes (T2D). An inhibitory effect on liver gluconeogenesis has been reported in rats with T2D with co-administration of sodium nitrite and sodium hydrosulfide (NaSH); the underlying mechanisms have however not yet been elucidated. The aim of this study is to determine the long-term effects of co-administering sodium nitrite and NaSH on expression of genes involved in liver gluconeogenesis in rats with T2D.

METHODS

T2D was induced using a high fat diet combined with low-dose of streptozotocin (30 mg/kg). Rats were divided into 5 groups (n = 7/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite+NaSH. Nitrite (50 mg/L) and NaSH (0.28 mg/kg) were administered for 9 weeks. Intraperitoneal pyruvate tolerance test (PTT) was performed at the end of the ninth week and mRNA expressions of PI3K, Akt, eNOS, PEPCK, G6Pase, and FBPase were measured in the liver.

RESULTS

Co-administration of nitrite and NaSH decreased elevated serum glucose concentrations during PTT. Compared to T2D + nitrite, co-administration of nitrite and NaSH resulted in significant increases in mRNA expression of PI3K, Akt, and eNOS and significant decreases in mRNA expression of G6Pase and FBPase but had no effect on PEPCK expression.

CONCLUSION

Long-term NaSH administration at low-dose, potentiated the inhibitory effects of nitrite on mRNA expression of key liver gluconeogenic enzymes in rats with T2D. This inhibitory effect of nitrite and NaSH co-administration on gluconeogenesis were associated with increased gene expression of PI3K, Akt, and eNOS in the liver.

Inorganic nitrite bioactivation and role in physiological signaling and therapeutics

The bioactivation of inorganic nitrite refers to the conversion of otherwise 'inert' nitrite to the diatomic signaling molecule nitric oxide (NO), which plays important roles in human physiology and disease, notably in the regulation of vascular tone and blood flow. While the most well-known sources of NO are the nitric oxide synthase (NOS) enzymes, another source of NO is the nitrate-nitrite-NO pathway, whereby nitrite (obtained from reduction of dietary nitrate) is further reduced to form NO. The past few decades have seen extensive study of the mechanisms of NO generation through nitrate and nitrite bioactivation, as well as growing appreciation of the contribution of this pathway to NO signaling in vivo. This review, prepared for the volume 400 celebration issue of Biological Chemistry, summarizes some of the key reactions of the nitrate-nitrite-NO pathway such as reduction, disproportionation, dehydration, and oxidative denitrosylation, as well as current evidence for the contribution of the pathway to human cardiovascular physiology. Finally, ongoing efforts to develop novel medical therapies for multifarious conditions, especially those related to pathologic vasoconstriction and ischemia/reperfusion injury, are also explored.

Oxygen and nitrite reduction by heme-deficient sulphite oxidase in a patient with mild sulphite oxidase deficiency

Isolated sulphite oxidase deficiency (iSOD) is an autosomal recessive inborn error in metabolism characterised by accumulation of sulphite, which leads to death in early infancy. Sulphite oxidase (SO) is encoded by the SUOX gene and forms a heme- and molybdenum-cofactor-dependent enzyme localised in the intermembrane space of mitochondria. Within SO, both cofactors are embedded in two separated domains, which are linked via a flexible 11 residue tether. The two-electron oxidation of sulphite to sulphate occurs at the molybdenum active site. From there, electrons are transferred via two intramolecular electron transfer steps (IETs) via the heme cofactor and to the physiologic electron acceptor cytochrome c. Previously, we reported nitrite and oxygen to serve as alternative electron acceptors at the Moco active site, thereby overcoming IET within SO. Here, we present evidence for these reactions to occur in an iSOD patient with an unusual mild disease representation. In the patient, a homozygous c.427C>A mutation within the SUOX gene leads to replacement of the highly conserved His143 to Asn. The affected His143 is one of two heme-iron-coordinating residues within SO. We demonstrate, that the H143N SO variant fails to bind heme in vivo leading to the elimination of SO-dependent cytochrome c reduction in mitochondria. We show, that sulphite oxidation at the Moco domain is unaffected in His143Asn SO variant and demonstrate that nitrite and oxygen are able to serve as electron acceptors for sulphite-derived electrons in cellulo. As result, the patient H143N SO variant retains residual sulphite oxidising activity thus ameliorating iSOD progression.

Nitrite attenuates mitochondrial impairment and vascular permeability induced by ischemia-reperfusion injury in the lung

Primary graft dysfunction (PGD) is directly related to ischemia-reperfusion (I/R) injury and a major obstacle in lung transplantation (LTx). Nitrite (NO2-), which is reduced in vivo to form nitric oxide (NO), has recently emerged as an intrinsic signaling molecule with a prominent role in cytoprotection against I/R injury. Using a murine model, we provide the evidence that nitrite mitigated I/R-induced injury by diminishing infiltration of immune cells in the alveolar space, reducing pulmonary edema, and improving pulmonary function. Ultrastructural studies support severe mitochondrial impairment in the lung undergoing I/R injury, which was significantly protected by nitrite treatment. Nitrite also abrogated the increased pulmonary vascular permeability caused by I/R. In vitro, hypoxia-reoxygenation (H/R) exacerbated cell death in lung epithelial and microvascular endothelial cells. This contributed to mitochondrial dysfunction as characterized by diminished complex I activity and mitochondrial membrane potential but increased mitochondrial reactive oxygen species (mtROS). Pretreatment of cells with nitrite robustly attenuated mtROS production through modulation of complex I activity. These findings illustrate a potential novel mechanism in which nitrite protects the lung against I/R injury by regulating mitochondrial bioenergetics and vascular permeability.

Hydrogen sulfide potentiates the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats

OBJECTIVE

Decreased nitric oxide (NO) bioavailability and hydrogen sulfide (H₂S) deficiency have been linked with the pathophysiology of type 2 diabetes (T2D). Restoration of NO levels by nitrite have been associated with favorable metabolic effects in T2D. Moreover, H₂S can potentiate the effects of NO in the cardiovascular system. The aim of this study was to determine the effects of long-term co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on carbohydrate metabolism in type 2 diabetic rats.

METHODS

T2D was induced using chronic high fat diet (HFD) feeding combined with low dose streptozotocin (STZ) regimen. Rats were divided into 5 groups (N = 10/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite + NaSH. Nitrite (50 mg/L in drinking water) and NaSH (0.28 mg/kg, daily i. p. injection) were administered for 9 weeks. Fasting serum glucose, insulin, lipid profile, liver function tests, and oxidative stress indices were measured. Intraperitoneal glucose tolerance test (GTT) was performed at the end of the eighth week, and three days later, intraperitoneal pyruvate tolerance test (PTT) was done. Protein levels and mRNA expression of glucose transporter type 4 (GLUT4) in soleus muscle and epididymal adipose tissue as well as mRNA expression of H₂S-producing enzymes in the liver, soleus muscle, and epididymal adipose tissue were measured at the end of the study.

RESULTS

Compared to the controls, HFD and STZ treated rats developed metabolic dysfunction. Nitrite treatment improved carbohydrate metabolism, liver function, and oxidative stress indices whereas NaSH treatment per se had no significant effects. However, co-administration of NaSH and nitrite resulted in further improvement in serum insulin level, GTT, PTT, liver function, oxidative stress, protein level and mRNA expression of GLUT4, as well as mRNA expression of H₂S-producing enzymes in diabetic rats.

CONCLUSION

Low dose of NaSH per se had no effect on carbohydrate metabolism while it potentiated the favorable metabolic effects of inorganic nitrite in type 2 diabetic rats. These favorable effects were associated with decreased oxidative stress and increased GLUT4 expression in insulin-sensitive tissues as well as improvement of liver function.

Prediction of rat liver transplantation outcomes using energy metabolites measured by microdialysis

BACKGROUND

Warm ischemia jeopardizes graft quality and recipient survival in donation after cardiac death (DCD) transplantation. Currently, there is no system to objectively evaluate the liver quality from DCD. The present study tried to use energy metabolites to evaluate the donor liver quality.

METHODS

We divided 195 Sprague-Dawley rats into five groups: the control (n = 39), warm ischemic time (WIT) 15 min (n = 39), WIT 30 min (n = 39), WIT 45 min (n = 39), and WIT 60 min (n = 39) groups. Three rats from each group were randomly selected for pretransplant histologic evaluation of warm ischemia-related damage. The remaining 36 rats were randomly divided into donors and recipients of 18 liver transplantations, and were subjected to postoperative liver function and survival analyses. Between cardiac arrest and cold storage, liver energy metabolites including glucose, lactate, pyruvate, and glycerol were measured by microdialysis. The lactate to pyruvate ratio (LPR) was calculated.

RESULTS

The changes in preoperative pathology with warm ischemia were inconspicuous, but the trends in postoperative pathology and aminotransferase levels were consistent with preoperative energy metabolite measurements. The 30-day survival rates of the control and WIT 15, 30, 45, and 60 min groups were 100%, 81.82%, 76.92%, 58.33%, and 25.00%, respectively. The areas under the receiver operating characteristic curves of glucose, lactate, glycerol, and LPR were 0.87, 0.88, 0.88, and 0.92, respectively.

CONCLUSION

Glucose, lactate, glycerol, and LPR are predictors of graft quality and survival outcomes in DCD transplantation.

Tuning constitutive and pathological inflammation in the gut via the interaction of dietary nitrate and polyphenols with host microbiome

Chronic inflammation is currently recognized as a critical process in modern-era epidemics such as diabetes, obesity and neurodegeneration. However, little attention is paid to the constitutive inflammatory pathways that operate in the gut and that are mandatory for local welfare and the prevention of such multi-organic diseases. Hence, the digestive system, while posing as a barrier between the external environment and the host, is crucial for the balance between constitutive and pathological inflammatory events. Gut microbiome, a recently discovered organ, is now known to govern the interaction between exogenous agents and the host with ensued impact on local and systemic homeostasis. Whereas gut microbiota may be modulated by a myriad of factors, diet constitutes one of its major determinants. Thus, dietary compounds that influence microbial flora may thereby impact on inflammatory pathways. One such example is the redox environment in the gut lumen which is highly dependent on the local generation of nitric oxide along the nitrate-nitrite-nitric oxide pathway and that is further enhanced by simultaneous consumption of polyphenols. In this paper, different pathways encompassing the interaction of dietary nitrate and polyphenols with gut microbiota will be presented and discussed in connection with local and systemic inflammatory events. Furthermore, it will be discussed how these interactive cycles (nitrate-polyphenols-microbiome) may pose as novel strategies to tackle inflammatory diseases.

Hepatic ischemia reperfusion injury: A systematic review of literature and the role of current drugs and biomarkers

Hepatic ischemia reperfusion injury (IRI) is not only a pathophysiological process involving the liver, but also a complex systemic process affecting multiple tissues and organs. Hepatic IRI can seriously impair liver function, even producing irreversible damage, which causes a cascade of multiple organ dysfunction. Many factors, including anaerobic metabolism, mitochondrial damage, oxidative stress and secretion of ROS, intracellular Ca(2+) overload, cytokines and chemokines produced by KCs and neutrophils, and NO, are involved in the regulation of hepatic IRI processes. Matrix Metalloproteinases (MMPs) can be an important mediator of early leukocyte recruitment and target in acute and chronic liver injury associated to ischemia. MMPs and neutrophil gelatinase-associated lipocalin (NGAL) could be used as markers of I-R injury severity stages. This review explores the relationship between factors and inflammatory pathways that characterize hepatic IRI, MMPs and current pharmacological approaches to this disease.

The Effect of Etoricoxib on Hepatic Ischemia-Reperfusion Injury in Rats

Ischemia-reperfusion (I/R) damage is known to be a pathological process which continues with the increase of oxidants and expands with the inflammatory response. There is not any study about protective effect of etoricoxib on the liver I/R damage in literature.

OBJECTIVE

This study investigates the effect of etoricoxib on oxidative stress induced by I/R of the rat liver.

MATERIAL AND METHODS

Experimental animals were divided into four groups as liver I/R control (LIRC), 50 mg/kg etoricoxib + liver I/R (ETO-50), 100 mg/kg etoricoxib + liver I/R (ETO-100), and healthy group (HG). ETO-50 and ETO-100 groups were administered etoricoxib, while LIRC and HG groups were orally given distilled water by gavage. Hepatic artery was clamped for one hour to provide ischemia, and then reperfusion was provided for 6 hours. Oxidant, antioxidant, and COX-2 gene expressions were studied in the liver tissues. ALT and AST were measured.

RESULTS

Etoricoxib in 50 and 100 mg/kg doses changed the levels of oxidant/antioxidant parameters such as MDA, MPO, tGSH, GSHRd, GST, SOD, NO, and 8-OH/Gua in favour of antioxidants. Furthermore, etoricoxib prevented increase of COX-2 gene expression and ALT and AST levels. This important protective effect of etoricoxib on the rat liver I/R can be tested in the clinical setting.