Influence of acidosis and hypoxia on liver ischemia and reperfusion injury in an in vivo rat model

Optimal Use of 2',7'-Dichlorofluorescein Diacetate in Cultured Hepatocytes

Oxidative stress is a state that arises when the production of reactive transients overwhelms the cell's capacity to neutralize the oxidants and radicals. This state often coincides with the pathogenesis and perpetuation of numerous chronic diseases. On the other hand, medical interventions such as radiation therapy and photodynamic therapy generate radicals to selectively damage and kill diseased tissue. As a result, the qualification and quantification of oxidative stress are of great interest to those studying disease mechanisms as well as therapeutic interventions. 2',7'-Dichlorodihydrofluorescein-diacetate (DCFH₂-DA) is one of the most widely used fluorogenic probes for the detection of reactive transients. The nonfluorescent DCFH₂-DA crosses the plasma membrane and is deacetylated by cytosolic esterases to 2',7'-dichlorodihydrofluorescein (DCFH₂). The nonfluorescent DCFH₂ is subsequently oxidized by reactive transients to form the fluorescent 2',7'-dichlorofluorescein (DCF). The use of DCFH₂-DA in hepatocyte-derived cell lines is more challenging because of membrane transport proteins that interfere with probe uptake and retention, among several other reasons. Cancer cells share some of the physiological and biochemical features with hepatocytes, so probe-related technical issues are applicable to cultured malignant cells as well. This study therefore analyzed the in vitro properties of DCFH₂-DA in cultured human hepatocytes (HepG2 cells and differentiated and undifferentiated HepaRG cells) to identify methodological and technical features that could impair proper data analysis and interpretation. The main issues that were found and should therefore be accounted for in experimental design include the following: (1) both DCFH₂-DA and DCF are taken up rapidly, (2) DCF is poorly retained in the cytosol and exits the cell, (3) the rate of DCFH₂ oxidation is cell type-specific, (4) DCF fluorescence intensity is pH-dependent at pH < 7, and (5) the stability of DCFH₂-DA in cell culture medium relies on medium composition. Based on the findings, the conditions for the use of DCFH₂-DA in hepatocyte cell lines were optimized. Finally, the optimized protocol was reduced to practice and DCFH₂-DA was applied to visualize and quantify oxidative stress in real time in HepG2 cells subjected to anoxia/reoxygenation as a source of reactive transients.

Protective effect of apelin preconditioning in a rat model of hepatic ischemia reperfusion injury; possible interaction between the apelin/APJ system, Ang II/AT1R system and eNOS

Introduction

Hepatic ischemic reperfusion injury occurs in multiple clinical settings. Novel potential protective agents are still needed to attenuate this injury. Apelin preconditioning protects against ischemic reperfusion injury in different organs. However, the protective mechanism of apelin on hepatic ischemic reperfusion injury is not yet clear.

Aim

Evaluate the effect of apelin-13 preconditioning on hepatic ischemic reperfusion injury and clarify possible interactions between apelinergic, renin-angiotensin systems and endothelial nitric oxide synthase.

Methods

In total, 60 rats were assigned to four groups: control sham-operated, ischemic reperfusion, apelin-treated ischemic reperfusion and apelin + N-nitro-L-arginine methyl ester-treated ischemic reperfusion. Apelin 2 µg/kg/day and N-nitro-L-arginine methyl ester 10 mg/kg/day were injected intraperitoneally daily for 3 days and 2 weeks respectively before hepatic ischemic reperfusion. Serum aminotransferase, aspartate aminotransferase, hepatic malondialdehyde, apelin, gene expression of caspase-3, endothelial nitric oxide synthase and angiotensin type 1 receptor and liver histopathology were compared between groups.

Results

Apelin significantly reduced serum aminotransferase, aspartate aminotransferase, hepatic malondialdehyde, caspase-3 and angiotensin type 1 receptor expression, whereas hepatic apelin and endothelial nitric oxide synthase expression were significantly increased with improved hepatic histopathology. N-nitro-L-arginine methyl ester co-administration partially reversed this hepatoprotective effect.

Conclusion

Apelin-13 reduced hepatic ischemic reperfusion injury. This protection could be related to the suppression of hepatic angiotensin type 1 receptor expression and elevation of hepatic apelin level and endothelial nitric oxide synthase expression, which counteracts the pathologic effects of Ang II/angiotensin type 1 receptor. An interaction exists between apelinergic, renin-angiotensin systems and endothelial nitric oxide synthase in hepatic ischemic reperfusion pathophysiology.

Bicarbonate Increases Ischemia-Reperfusion Damage by Inhibiting Mitophagy

During an ischemic event, bicarbonate and CO2 concentration increase as a consequence of O2 consumption and lack of blood flow. This event is important as bicarbonate/CO2 is determinant for several redox and enzymatic reactions, in addition to pH regulation. Until now, most work done on the role of bicarbonate in ischemia-reperfusion injury focused on pH changes; although reperfusion solutions have a fixed pH, cardiac resuscitation protocols commonly employ bicarbonate to correct the profound acidosis associated with respiratory arrest. However, we previously showed that bicarbonate can increase tissue damage and protein oxidative damage independent of pH. Here we show the molecular basis of bicarbonate-induced reperfusion damage: the presence of bicarbonate selectively impairs mitophagy, with no detectable effect on autophagy, proteasome activity, reactive oxygen species production or protein oxidation. We also show that inhibition of autophagy reproduces the effects of bicarbonate in reperfusion injury, providing additional evidence in support of this mechanism. This phenomenon is especially important because bicarbonate is widely used in resuscitation protocols after cardiac arrest, and while effective as a buffer, may also contribute to myocardial injury.

Plasma-Lyte 148: A clinical review

AIM

To outline the physiochemical properties and specific clinical uses of Plasma-Lyte 148 as choice of solution for fluid intervention in critical illness, surgery and perioperative medicine.

METHODS

We performed an electronic literature search from Medline and PubMed (via Ovid), anesthesia and pharmacology textbooks, and online sources including studies that compared Plasma-Lyte 148 to other crystalloid solutions. The following keywords were used: “surgery”, “anaesthesia”, “anesthesia”, “anesthesiology”, “anaesthesiology”, “fluids”, “fluid therapy”, “crystalloid”, “saline”, “plasma-Lyte”, “plasmalyte”, “hartmann’s”, “ringers”“acetate”, “gluconate”, “malate”, “lactate”. All relevant articles were accessed in full. We summarized the data and reported the data in tables and text.

RESULTS

We retrieved 104 articles relevant to the choice of Plasma-Lyte 148 for fluid intervention in critical illness, surgery and perioperative medicine. We analyzed the data and reported the results in tables and text.

CONCLUSION

Plasma-Lyte 148 is an isotonic, buffered intravenous crystalloid solution with a physiochemical composition that closely reflects human plasma. Emerging data supports the use of buffered crystalloid solutions in preference to saline in improving physicochemical outcomes. Further large randomized controlled trials assessing the comparative effectiveness of Plasma-Lyte 148 and other crystalloid solutions in measuring clinically important outcomes such as morbidity and mortality are needed.

The case for 0.9% NaCl: is the undefendable, defensible?

Although 0.9% NaCl solution is by far the most-used fluid for fluid therapy in resuscitation, it is difficult to find a paper advocating its use over other types of crystalloid solutions. Literature on the deleterious effects of 0.9% NaCl has accumulated over the last decade, but critical appraisal of alternative crystalloid solutions is lacking. As such, the literature seems to suggest that 0.9% NaCl should be avoided at all costs, whereas alternative crystalloid solutions can be used without scrutiny. The basis of this negative evaluation of 0.9% NaCl is almost exclusively its effect on acid-base homeostasis, whereas the potentially deleterious effects present in other types of crystalloids are neglected. We have the challenging task of defending the use of 0.9% NaCl and reviewing its positive attributes, while an accompanying paper will argue against the use of 0.9% NaCl. It is challenging because of the large amount of literature, including our own, showing adverse effects of 0.9% NaCl. We will discuss why 0.9% NaCl solution is the most frequently used resuscitation fluid. Although it has some deleterious effects, all fluids share common features of concern. As such the emphasis on fluid resuscitation should be on volume rather than on composition and should be accompanied by a physiological assessment of the impact of fluids. In this paper, we hope to discuss the context within which fluids, specifically 0.9% NaCl, can be given in a safe and effective manner.

The ideal crystalloid - what is 'balanced'?

PURPOSE OF REVIEW

This review explores the contemporary definition of the term 'balanced crystalloid' and outlines optimal design features and their underlying rationale.

RECENT FINDINGS

Crystalloid interstitial expansion is unavoidable, but also occurs with colloids when there is endothelial glycocalyx dysfunction. Reduced chloride exposure may lessen kidney dysfunction and injury with a possible mortality benefit. Exact balance from an acid-base perspective is achieved with a crystalloid strong ion difference of 24 mEq/l. This can be done simply by replacing 24 mEq/l of chloride in 0.9% sodium chloride with bicarbonate or organic anion bicarbonate substitutes. Potassium, calcium and magnesium additives are probably unnecessary. Large volumes of mildly hypotonic crystalloids such as lactated Ringer's solution reduce extracellular tonicity in volunteers and increase intracranial pressure in nonbrain-injured experimental animals. A total cation concentration of 154 mmol/l with accompanying anions provides isotonicity. Of the commercial crystalloids, Ringer's acetate solution is close to balanced from both acid-base and tonicity perspectives, and there is little current evidence of acetate toxicity in the context of volume loading, in contrast to renal replacement.

SUMMARY

The case for balanced crystalloids is growing but unproven. A large randomized controlled trial of balanced crystalloids versus 0.9% sodium chloride is the next step.

Repercussões pulmonares após isquemia hepática parcial e reperfusão: modelo experimental

OBJETIVO: Descrever um modelo experimental de lesão de isquemia/reperfusão hepática com manifestações sistêmicas, representadas pelo envolvimento pulmonar, que possa ser utilizado por aqueles que pretendem compreender esse fenômeno. MÉTODOS: Ratos Wistar machos (200-250g) foram usados. Quatorze foram alocados em dois grupos, sendo G1 com oito submetidos somente à laparotomia e G2, seis à isquemia e reperfusão hepática. As funções hepática (aminotransferases séricas, respiração mitocondrial, histologia) e pulmonar (teste do azul de Evans) foram analisadas. RESULTADOS: houve diferença estatística significativa entre G1 e G2 ao se comparar valores de AST (24,3 ± 108 e 5406 ± 2263), ALT (88,5 ± 28,5 e 5169 ± 2690), razão de controle respiratório (3,41 ± 0,17 e 1,91 ± 0,55) e relação ADP/O (1,93 ± 0,03 e 1,45 ± 0,27), lesões histológicas (necrose, células inflamatórias, hemorragia, microesteatose) e teste do azul de Evans (194,31 ± 53 e 491,8 ± 141). CONCLUSÃO: O modelo mostrou-se útil para o estudo de lesão de isquemia/reperfusão hepática.

Hypothermic protection in an acute hypoxia model in rats: Acid-base and oxidant/antioxidant profiles

AIM OF THE STUDY

Recent works demonstrate the benefits of hypothermia when used to preserve brain, cardiac, hepatic, and intestinal function against hypoxic-ischemic injury. However, it is also known that hypothermia affects systemic parameters and also induces the generation of reactive oxygen species in cells and tissues. Here we studied the acid-base related parameters and the antioxidant-oxidant effects of deep hypothermia induction before an acute hypoxic insult in rats.

METHODS

Acid-base indicators and parameters related to oxidative stress were analyzed in hypothermic rats (21-22 degrees C) breathing room air during 2h (control hypothermia), and hypothermic animals switched to hypoxic air (10% O(2)) during the second hour (hypothermia hypoxia group), and they were compared with corresponding normothermia groups maintained at 37 degrees C (control normothermia and normothermia hypoxia groups).

RESULTS

Mild metabolic acidosis appeared early in arterial blood during hypothermia. After exposure to hypoxia, evidence of tissue injury (plasma transaminases and blood lactate) and oxidative stress (increase in lipid peroxidation, decrease in glutathione levels and in the glutathione reduction potential in liver) was found. In contrast, in the hypothermia hypoxia group, plasmatic parameters remained as the control values, and the hepatic glutathione reduction potential were significantly more negative when compared with the normothermia hypoxia group.

CONCLUSIONS

We propose that acidosis induced by hypothermia contributes to the maintenance of intracellular reduction potential in liver, regarding the GSSG/2GSH couple and may help to increase plasmatic antioxidant pool. Our findings provide new insights into the protective effects of hypothermia in vivo.

Acid-base and bio-energetics during balanced versus unbalanced normovolaemic haemodilution

Fluids balanced to avoid acid-base disturbances may be preferable to saline, which causes metabolic acidosis in high volume. We evaluated acid-base and bio-energetic effects of haemodilution with a crystalloid balanced on physical chemical principles, versus crystalloids causing metabolic acidosis or metabolic alkalosis. Anaesthetised, mechanically ventilated Sprague-Dawley rats (n=32, allocated to four groups) underwent six exchanges of 9 ml crystalloid for 3 ml blood. Exchange was with one of three crystalloids with strong ion difference (SID) values of 0, 24 (balanced) and 40 mEq/l. Controls did not undergo haemodilution. Mean haemoglobin concentration fell to approximately 50 g/l after haemodilution. With SID 24 mEq/l fluid, metabolic acid-base remained unchanged. Dilution with SID 0 mEq/l and 40 mEq/l fluids caused a progressive metabolic acidosis and alkalosis respectively. Standard base excess (SBE) and haemoglobin concentration were directly correlated in the SID 0 mEq/l group (R2 = 0.61), indirectly correlated in the SBE 40 mEq/l group (R2 = 0.48) and showed no correlation in the SID 24 mEq/l group (R2 = 0.003). There were no significant differences between final ileal values of CO2 gap, nucleotides concentration, energy charge, or luminal lactate concentration. SID 40 mEq/l crystalloid dilution caused a significant rise in subcutaneous lactate. In this group mean kidney ATP concentration was significantly less than controls and renal energy charge significantly lower than SID 0 mEq/l and control groups. We conclude that a crystalloid SID of 24 mEq/l provides balanced haemodilution. Bio-energetic perturbations with higher SID haemodilution may be more severe and need further investigation.

IL-10 attenuates hepatic I/R injury and promotes hepatocyte proliferation

BACKGROUND

One of the most important determinants of the outcome of hepatic ischemia and reperfusion (I/R) injury is the onset of the inflammatory response. Interleukin-10 (IL-10) is a potent anti-inflammatory cytokine. It inhibits the production of interleukin-6 (IL-6), which however, also is involved in priming hepatocyte proliferation. The aim of this study was to examine the protective effects and the influence on the regenerative response of exogenous as well as endogenous IL-10 in a rat model of hepatic I/R injury.

MATERIALS AND METHODS

Seventy percent Liver I/R was induced in male Wistar rats for 60 min followed by 24 h reperfusion. One group underwent a midline laparotomy with recombinant rat (rr)IL-10 administration (SHAM + IL-10). The other groups underwent 60 min ischemia with administration of saline (I/R + saline), rrIL-10 [at two different time-points, i.e., I/R + IL-10pre(ischemia) and I/R + IL-10end(ischemia)] or anti-rat IL-10 antibody (I/R + antiIL-10).

RESULTS

Parenchymal damage, as assessed by plasma alanine aminotransferase and aspartate aminotransferase, was significantly reduced by rrIL-10 and by endogenous IL-10 (P < 0.05). Also, rrIL-10 significantly reduced IL-6 production and the accumulation of neutrophils in liver and lung tissue, as measured by myeloperoxidase activity. Necrosis and apoptosis were significantly reduced and hepatocyte proliferation was stimulated by rrIL-10.

CONCLUSIONS

RrIL-10 and, to a lesser extent, endogenous IL-10, attenuate damage and inflammation, while rrIL-10 also promotes proliferation after hepatic I/R injury in rats. Therefore, rrIL-10 has potential use to prevent I/R injury and to promote liver regeneration after partial liver resection with temporary inflow occlusion.

Peritoneal tissue-oxygen tension during a carbon dioxide pneumoperitoneum in a mouse laparoscopic model with controlled respiratory support

BACKGROUND

Previous animal studies suggested that the peritoneal environment during a carbon dioxide (CO(2)) pneumoperitoneum is hypoxic and that this may contribute to the formation of intra-abdominal adhesions or the growth of malignant cells. There is no study, however, that investigates the relationship between anaesthesia, ventilation and the laparoscopic peritoneal environment to the development of hypoxia. The objective of this study is to monitor the peritoneal tissue-oxygen tension (PitO(2)) under various conditions including anaesthesia alone, during a CO(2) pneumoperitoneum at both low and high intraperitoneal pressure (IPP), and laparotomy, in animal models with controlled respiratory support (CRS).

METHODS

C57BL6 mice were divided into eight groups (n = 5) consisting of anaesthesia alone or with CO(2) pneumoperitoneum at low (2 mmHg) or high (8 mmHg) IPP or undergoing laparotomy. Groups were further subdivided into those with or without CRS with endotracheal intubation and mechanical ventilation. Over the course of the 1 h procedure, PitO(2) was continuously monitored.

RESULTS

Protocol 1. The PitO(2) levels (104.2 +/- 7.8 mmHg, mean +/- SEM) in non-injured peritoneum during a CO(2) pneumoperitoneum at a low IPP were elevated approximately 2-fold over the levels during laparotomy (49.8 +/- 15.0 mmHg) in ventilated mice. Protocol 2. After insufflation with CO(2), the PitO(2) was immediately elevated and maintained at a higher level. Following laparotomy, it decreased immediately. This elevation was not seen with air insufflation.

CONCLUSION

In mice, a significant elevation in PitO(2) occurs during a CO(2) pneumoperitoneum at low IPP with CRS.

Selective portal clamping to minimize hepatic ischaemia-reperfusion damage and avoid accelerated outgrowth of experimental colorectal liver metastases

BACKGROUND

Temporary vascular clamping during local ablation for colorectal liver metastases increases destruction volumes. However, it also causes ischaemia-reperfusion (IR) injury to the liver parenchyma and accelerates the outgrowth of microscopic tumour deposits. The aim of this study was to investigate the effects of selective portal clamping on hepatocellular damage and tumour growth.

METHODS

Mice carrying pre-established hepatic colorectal micrometastases underwent either simultaneous clamping of both the portal vein and the hepatic artery or selective clamping of the portal vein to the median and left liver lobes for 45 min. Sham-operated mice served as controls. Hepatic injury and tumour growth were assessed over time.

RESULTS

Standard inflow occlusion resulted in a rise in liver enzymes, a local inflammatory response and hepatocellular necrosis. The outgrowth of pre-established micrometastases was accelerated three- to fourfold in clamped compared with non-clamped liver lobes (27.4 versus 7.8 per cent, P < 0.010). Conversely, selective portal clamping induced minimal liver injury, tissue inflammation or hepatocellular necrosis, and completely stopped the accelerated outgrowth of micrometastases.

CONCLUSION

Selective portal clamping does not induce liver tissue damage or accelerate micrometastasis outgrowth and may therefore be the preferable clamping method during local ablative treatment of hepatic metastases.

Inhibition of classical complement activation attenuates liver ischaemia and reperfusion injury in a rat model

Activation of the complement system contributes to the pathogenesis of ischaemia/reperfusion (I/R) injury. We evaluated inhibition of the classical pathway of complement using C1-inhibitor (C1-inh) in a model of 70% partial liver I/R injury in male Wistar rats (n = 35). C1-inh was administered at 100, 200 or 400 IU/kg bodyweight, 5 min before 60 min ischaemia (pre-I) or 5 min before 24 h reperfusion (end-I). One hundred IU/kg bodyweight significantly reduced the increase of plasma levels of activated C4 as compared to albumin-treated control rats and attenuated the increase of alanine aminotransferase (ALT). These effects were not better with higher doses of C1-inh. Administration of C1-inh pre-I resulted in lower ALT levels and higher bile secretion after 24 h of reperfusion than administration at end-I. Immunohistochemical assessment indicated that activated C3, the membrane attack complex C5b9 and C-reactive protein (CRP) colocalized in hepatocytes within midzonal areas, suggesting CRP is a mediator of I/R-induced, classical complement activation in rats. Pre-ischaemic administration of C1-inh is an effective pharmacological intervention to protect against liver I/R injury.

Ischemia/reperfusion accelerates the outgrowth of hepatic micrometastases in a highly standardized murine model

Mortality in colorectal cancer is associated with the development of liver metastases. Surgical removal of these tumors is the only hope for cure, but recurrence is common. During liver surgery, ischemia/reperfusion (I/R) often occurs as a result of hemorrhage or vascular clamping. Although the adverse effects of I/R on postoperative liver function are well documented, the influence of I/R on the outgrowth of residual micrometastases is unknown. We used a highly standardized mouse model of partial hepatic I/R to study the effects of I/R on the outgrowth of preestablished colorectal micrometastases. Five days following intrasplenic injection of C26 colon carcinoma cells, the vascular structures of the left lobe were clamped for 45 minutes under hemodynamically stable conditions. Tissue glutathione, plasma liver enzymes, hepatocellular necrosis, and tumor growth were assessed over time. I/R caused oxidative stress and early liver tissue damage. The outgrowth of micrometastases in occluded liver lobes was accelerated five- to sixfold compared with nonoccluded lobes and was associated with areas of necrotic liver tissue surrounded by inflammatory cells and apoptotic hepatocytes. Accelerated tumor growth and tissue necrosis were completely prevented by occluding blood flow intermittently. In contrast, ischemic preconditioning or treatment with the antioxidants alpha-tocopherol or ascorbic acid failed to protect against late tissue necrosis and tumor growth, although early hepatocellular damage was largely prevented by these methods. In conclusion, I/R is a strong stimulus of recurrent intrahepatic tumor growth. Measures to prevent I/R-induced late tissue necrosis cross-protect against this phenomenon.

Mild hypothermia protects liver against ischemia and reperfusion injury

AIM: To determine whether mild hypothermia could protect liver against ischemia and reperfusion injury in pigs.

METHODS: Twenty-four healthy pigs were randomly divided into normothermia, mild hypothermia and normal control groups. The experimental procedure consisted of temporary interruption of blood flow to total hepatic lobe for different lengths of time and subsequent reperfusion. Hepatic tissue oxygen pressure (P_tiO₂) and aspartate aminotransferase (AST) values were evaluated, and ultrastructural analysis was carried out for all samples.

RESULTS: Serum AST was significantly lower, and hepatic P_tiO₂ values were significantly higher in the mild hypothermia group than in the normothermia group during liver ischemia-reperfusion periods (P = 0.032, P = 0.028). Meanwhile, the histopathologic injury of liver induced by ischemia-reperfusion was significantly improved in the mild hypothermia group, compared with that in the normothermia group.

CONCLUSION: Mild hypothermia can protect the liver from ischemia-reperfusion injury in pigs.

Hypocapnia attenuates mesenteric ischemia-reperfusion injury in a rat model

PURPOSE

Hypocapnia, a recognized complication of high frequency oscillation ventilation, has multiple adverse effects on lung and brain physiology in vivo, including potentiation of free radical injury. We hypothesized that hypocapnia would potentiate the effects of mesenteric ischemia-reperfusion on bowel, liver and lung injury.

METHODS

Anesthetized male Sprague-Dawley rats were ventilated with high frequency oscillation and were randomized to one of four groups, exposed to either mesenteric ischemia-reperfusion or sham surgery, and to either hypocapnia or normocapnia.

RESULTS

All animals survived the protocol. Ischemia-reperfusion caused significant histologic bowel injury. Bowel 8-isoprostane generation was greater in ischemia-reperfusion vs sham, but was attenuated by hypocapnia. Laser-Doppler flow studies of bowel perfusion confirmed that hypocapnia attenuated reperfusion following ischemia. Plasma alanine transaminase, reflecting overall hepatocellular injury, was not increased by ischemia-reperfusion but was increased by hypocapnia; however, hepatic isoprostane generation was increased by ischemia-reperfusion, and not by hypocapnia. Oxygenation was comparable in all groups, and compliance was impaired by ischemia-reperfusion but not by hypocapnia.

CONCLUSION

Hypocapnia, although directly injurious to the liver, attenuates ischemia-reperfusion induced lipid peroxidation in the bowel, possibly through attenuation of blood flow during reperfusion.