Study of rat hepatocytes in primary culture submitted to hypoxia and reoxygenation: action of the cytoprotectors prostaglandin E1, superoxide dismutase, allopurinol and verapamil

Histidine-Rich Glycoprotein Alleviates Liver Ischemia/Reperfusion Injury in Mice With Nonalcoholic Steatohepatitis

Hepatic ischemia/reperfusion injury (IRI) is a major complication of liver surgery and transplantation, especially in patients with nonalcoholic steatohepatitis (NASH). The mechanism of NASH susceptibility to IRI has not been fully clarified. We investigated the role of liver-produced histidine-rich glycoprotein (HRG) in NASH IRI. A NASH mouse model was established using C57BL/6J mice fed a methionine-choline-deficient diet (MCDD) for 6 weeks. The MCDD and standard diet groups were exposed to 60 minutes of partial hepatic ischemia/reperfusion (I/R). We further evaluated the impact of HRG in this context using HRG knockdown (KD) mice. IRI increased HRG expression in the standard diet group, but not in the MCDD group after I/R. HRG expression was inversely correlated with neutrophil infiltration and the formation of neutrophil extracellular traps (NETs). HRG KD mice showed severe liver injury with neutrophil infiltration and the formation of NETs. Pretreatment with supplementary HRG protected against I/R with the inhibition of neutrophil infiltration and the formation of NETs. In vitro, hepatocytes showed that the expression of HRG was upregulated under hypoxia/reoxygenation conditions, but not in response to oleic acid-treated hepatocytes. The decrease in HRG expression in fatty hepatocytes was accompanied by decreased farnesoid X receptor and hypoxia inducible factor 2 alpha subunit expression. HRG is a hepatoprotective factor during hepatic IRI because it decreases neutrophil infiltration and the formation of NETs. The decrease in HRG is a cause of susceptibility to IRI in steatotic livers. Therefore, HRG is a new therapeutic target for minimizing liver damage in patients with NASH.

Hepatic Accumulation of Hypoxanthine: A Link Between Hyperuricemia and Nonalcoholic Fatty Liver Disease

BACKGROUND

An elevated level of plasma uric acid has been widely recognized as a risk factor for non-alcoholic fatty liver disease (NAFLD), where oxidative stress and inflammation play an important role in the pathophysiology of the disease. Although the complete molecular mechanisms involved remain unknown, while under physiological conditions uric acid presents antioxidant properties, hyperuricemia has been linked to oxidative stress, chronic low-grade inflammation, and insulin resistance, basic signs of NAFLD.

AIM OF STUDY

Employing in vivo experimentation, we aim to investigate whether a high-fat diet rich in cholesterol (HFD), modifies the metabolism of purines in close relationship to molecular events associated with the development of NAFLD. In vitro experiments employing HepG2 cells are also carried out to study the phenomenon of oxidative stress.

METHODS

Adult male rabbits were fed for 8 weeks an HFD to induce NAFLD. At the beginning of the experiment and every 15 d until the completion of the study, plasma levels of lipids, lipoproteins, and uric acid were measured. Liver tissue was isolated, and histology performed followed by the biochemical determination of hypoxanthine, protein expression of xanthine oxidoreductase (XOR) by western blot analysis, and xanthine oxidase (XO) activity using an enzymatic kinetic assay. Furthermore, we employed in vitro experimentation studying HepG2 cells to measure the effect of hypoxanthine and H₂O₂ upon the production of radical oxygen species (ROS), XO activity, and cell viability.

RESULTS AND CONCLUSION

Hepatic tissue from rabbits fed the HFD diet showed signs of NAFLD associated with an increased ROS concentration and an altered purine metabolism characterized by the increase in hypoxanthine, together with an apparent equilibrium displacement of XOR towards the xanthine dehydrogenase (XDH) isoform of the enzyme. This protein shift visualized by a western blot analysis, associated with an increase in plasma uric acid and hepatocyte hypoxanthine could be understood as a compensatory series of events secondary to the establishment of oxidative stress associated with the chronic establishment of fatty liver disease.

Protective effects of fish oil, allopurinol, and verapamil on hepatic ischemia-reperfusion injury in rats

Background:

The major aim of this work was to study the protective effects of fish oil (FO), allopurinol, and verapamil on hepatic ischemia-reperfusion (IR)-induced injury in experimental rats.

Materials and Methods:

Sixty male Wistar albino rats were randomly assigned to six groups of 10 rats each. Group 1 served as a negative control. Group 2 served as hepatic IR control injury. Groups 3, 4, 5, and 6 received N-acetylcysteine (standard), FO, allopurinol, and verapamil, respectively, for 3 consecutive days prior to ischemia. All animals were fasted for 12 h, anesthetized and underwent midline laparotomy. The portal triads were clamped by mini-artery clamp for 30 min followed by reperfusion for 30 min. Blood samples were withdrawn for estimation of serum alanine transaminase (ALT) and aspartate transaminase (AST) activities as well as hepatic thiobarbituric acid reactive substances, reduced glutathione, myeloperoxidase, and total nitrate/nitrite levels, in addition to histopathological examination.

Results:

Fish oil, allopurinol, and verapamil reduced hepatic IR injury as evidenced by significant reduction in serum ALT and AST enzyme activities. FO and verapamil markedly reduced oxidative stress as compared to control IR injury. Levels of inflammatory biomarkers in liver were also reduced after treatment with FO, allopurinol, or verapamil. In accordance, a marked improvement of histopathological findings was observed with all of the three treatments.

Conclusion:

The findings of this study prove the benefits of FO, allopurinol, and verapamil on hepatic IR-induced liver injury and are promising for further clinical trials.

Differential roles of prostaglandin E-type receptors in activation of hypoxia-inducible factor 1 by prostaglandin E1 in vascular-derived cells under non-hypoxic conditions

Prostaglandin E₁ (PGE₁), known pharmaceutically as alprostadil, has vasodilatory properties and is used widely in various clinical settings. In addition to acute vasodilatory properties, PGE₁ may exert beneficial effects by altering protein expression of vascular cells. PGE₁ is reported to be a potent stimulator of angiogenesis via upregulation of VEGF expression, which is under the control of the transcription factor hypoxia-inducible factor 1 (HIF-1). However, the molecular mechanisms behind the phenomenon are largely unknown. In the present study, we investigated the mechanism by which PGE₁ induces HIF-1 activation and VEGF gene expression in human aortic smooth muscle cells (HASMCs) and human umbilical vein endothelial cells (HUVECs), both vascular-derived cells. HUVECs and HASMCs were treated with PGE₁ at clinically relevant concentrations under 20% O₂ conditions and HIF-1 protein expression was investigated. Expression of HIF- 1α protein and the HIF-1-downstream genes were low under 20% O₂ conditions and increased in response to PGE₁ treatment in both HUVECs and HASMCs in a dose- and time-dependent manner under 20% O₂ conditions as comparable to exposure to 1% O₂ conditions. Studies using EP-receptor-specific agonists and antagonists revealed that EP1 and EP3 are critical to PGE₁-induced HIF-1 activation. In vitro vascular permeability assays using HUVECs indicated that PGE₁ increased vascular permeability in HUVECs. Thus, we demonstrate that PGE₁ induces HIF- 1α protein expression and HIF-1 activation under non-hypoxic conditions and also provide evidence that the activity of multiple signal transduction pathways downstream of EP1 and EP3 receptors is required for HIF-1 activation.

Immediate graft histological assay, post pig's liver transplantation

PURPOSE

To describe the vascular and tissue histopathological changes in seven sequential experimental liver transplantations in pigs.

METHODS

Fourteen female pigs, Sus domesticus species, with body mass between 5 and 8 kg were utilized. After the end of all anastomoses of the graft implantation in the receptor, the animal was monitored for 30 minutes, and at its end one of the biopsies was collected for histological analysis. The histological criteria utilized were: lytic hepatocyte necrosis, density of septal and portal inflammatory infiltrated, sinusoidal congestion and hemorrhage. The analysis was performed separately for the portal region in zone 1, 2 and 3.

RESULTS

Among the structural changes undergone by the graft, those with greater frequency and intensity were vascular congestion and steatosis, which stood out in transplantations 5, 6 and 7.

CONCLUSIONS

The technique demonstrated vascular alterations represented by vasocongestion, edema and minimum inflammatory reaction. In relation to the parenchyma, was observed macrovacuolar pan-acinar steatosis, focal lytic and occasional hemorrhages, beyond the accumulation of hemosiderin in Kuppfer's cells.

Variable responses of small and large human hepatocytes to hypoxia and hypoxia/reoxygenation (H-R)

Hypoxia and hypoxia-reoxygenation (H-R) regulate human hepatocyte cell death by mediating the accumulation of reactive oxygen species (ROS). Hepatocytes within the liver are organised into peri-portal (PP) and peri-venous (PV) subpopulations. PP and PV hepatocytes differ in size and function. We investigated whether PP and PV human hepatocytes exhibit differential susceptibility to hypoxic stress. Isolated hepatocytes were used in an in vitro model of hypoxia and H-R. ROS production and cell death were assessed using flow cytometry. PV, and not PP hepatocytes, accumulate intracellular ROS in a mitochondrial dependent manner during hypoxia and H-R. This increased ROS regulates hepatocyte apoptosis and necrosis via a mitochondrial pathway. These findings have implications on the understanding of liver injury and application of potential therapeutic strategies.