Nitrosative and Oxidative Stresses Contribute to Post-Ischemic Liver Injury Following Severe Hemorrhagic Shock: The Role of Hypoxemic Resuscitation

Purpose: Hemorrhagic shock and resuscitation is frequently associated with liver ischemia-reperfusion injury. The aim of the study was to investigate whether hypoxemic resuscitation attenuates liver injury. Methods: Anesthetized, mechanically ventilated New Zealand white rabbits were exsanguinated to a mean arterial pressure of 30 mmHg for 60 minutes. Resuscitation under normoxemia (Normox-Res group, n = 16, PaO2 = 95–105 mmHg) or hypoxemia (Hypox-Res group, n = 15, PaO 2 = 35–40 mmHg) followed, modifying the FiO 2. Animals not subjected to shock constituted the sham group (n = 11, PaO 2 = 95–105 mmHg). Indices of the inflammatory, oxidative and nitrosative response were measured and histopathological and immunohistochemical studies of the liver were performed. Results: Normox-Res group animals exhibited increased serum alanine aminotransferase, tumor necrosis factor- alpha, interleukin (IL)-1b and IL-6 levels compared with Hypox-Res and sham groups. Reactive oxygen species generation, malondialdehyde formation and myeloperoxidase activity were all elevated in Normox-Res rabbits compared with Hypox-Res and sham groups. Similarly, endothelial NO synthase and inducible NO synthase mRNA expression was up-regulated and nitrotyrosine immunostaining increased in animals resuscitated normoxemically, indicating a more intense nitrosative stress. Hypox-Res animals demonstrated a less prominent histopathologic injury which was similar to sham animals. Conclusions: Hypoxemic resuscitation prevents liver reperfusion injury through attenuation of the inflammatory respons

A20 Modulates Lipid Metabolism and Energy Production to Promote Liver Regeneration

Background: Liver Regeneration is clinically of major importance in the setting of liver injury, resection or transplantation. We have demonstrated that the NF-$\kappa$B inhibitory protein A20 significantly improves recovery of liver function and mass following extended liver resection (LR) in mice. In this study, we explored the Systems Biology modulated by A20 following extended LR in mice. Methodology and Principal Findings: We performed transcriptional profiling using Affymetrix-Mouse 430.2 arrays on liver mRNA retrieved from recombinant adenovirus A20 (rAd.A20) and rAd.$\beta$galactosidase treated livers, before and 24 hours after 78% LR. A20 overexpression impacted 1595 genes that were enriched for biological processes related to inflammatory and immune responses, cellular proliferation, energy production, oxidoreductase activity, and lipid and fatty acid metabolism. These pathways were modulated by A20 in a manner that favored decreased inflammation, heightened proliferation, and optimized metabolic control and energy production. Promoter analysis identified several transcriptional factors that implemented the effects of A20, including NF-$\kappa$B, CEBPA, OCT-1, OCT-4 and EGR1. Interactive scale-free network analysis captured the key genes that delivered the specific functions of A20. Most of these genes were affected at basal level and after resection. We validated a number of A20's target genes by real-time PCR, including p21, the mitochondrial solute carriers SLC25a10 and SLC25a13, and the fatty acid metabolism regulator, peroxisome proliferator activated receptor alpha. This resulted in greater energy production in A20-expressing livers following LR, as demonstrated by increased enzymatic activity of cytochrome c oxidase, or mitochondrial complex IV. Conclusion: This Systems Biology-based analysis unravels novel mechanisms supporting the pro-regenerative function of A20 in the liver, by optimizing energy production through improved lipid/fatty acid metabolism, and down-regulated inflammation. These findings support pursuit of A20-based therapies to improve patients' outcomes in the context of extreme liver injury and extensive LR for tumor treatment or donation

High plasma uric acid concentration: causes and consequences

High plasma uric acid (UA) is a precipitating factor for gout and renal calculi as well as a strong risk factor for Metabolic Syndrome and cardiovascular disease. The main causes for higher plasma UA are either lower excretion, higher synthesis or both. Higher waist circumference and the BMI are associated with higher insulin resistance and leptin production, and both reduce uric acid excretion. The synthesis of fatty acids (tryglicerides) in the liver is associated with the de novo synthesis of purine, accelerating UA production. The role played by diet on hyperuricemia has not yet been fully clarified, but high intake of fructose-rich industrialized food and high alcohol intake (particularly beer) seem to influence uricemia. It is not known whether UA would be a causal factor or an antioxidant protective response. Most authors do not consider the UA as a risk factor, but presenting antioxidant function. UA contributes to > 50% of the antioxidant capacity of the blood. There is still no consensus if UA is a protective or a risk factor, however, it seems that acute elevation is a protective factor, whereas chronic elevation a risk for disease

Formation and role of plasma S-nitrosothiols in liver ischemia-reperfusion injury

Plasma S-nitrosothiols (RSNOs) may act as a circulating form of nitric oxide that affects vascular function and platelet aggregation. Their role in liver ischemia/reperfusion (I/R) injury is largely unknown. The aim of the present study was to investigate the changes in plasma RSNOs following liver I/R injury. Two groups of New Zealand white rabbits were used (n=6, each): the I/R group underwent 60 min lobar liver ischemia and 7 h reperfusion, while the sham group underwent laparotomy but no liver ischemia. Serial RSNO levels were measured in plasma by electron paramagnetic resonance (EPR) spectrometry, nitrite/nitrates by capillary electrophoresis, hepatic microcirculation by laser Doppler flowmetry, redox state of hepatic cytochrome oxidase by near-infrared spectroscopy, liver iNOS mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR) and the oxidation of dihydrorhodamine to rhodamine by fluorescence. The effect of the antioxidant N-acetylcysteine (NAC) on RSNOs formation and DHR oxidation was tested in a third group of animals (n=6) undergoing lobar liver I/R. Hepatic I/R was associated with a significant increase in plasma RSNOs, plasma nitrites, hepatic iNOS mRNA expression, impairment in hepatic microcirculation, decrease in the redox state of cytochrome oxidase, and significant production of rhodamine. The changes were more obvious during the late phase of reperfusion (> 4 h). NAC administration decreased plasma RSNOs and oxidation of DHR to RH (P < 0.05, 5 and 7 h postreperfusion, respectively). These results suggest that significant upregulation of nitric oxide synthesis during the late phase of reperfusion is associated with impairment in microcirculation and mitocbondrial dysfunction. Plasma S-nitrosothiols are a good marker of this nitric oxide-mediated hepatotoxicity. (c) 2007 Elsevier Inc. All rights reserved