Delayed energy protection of ischemic preconditioning on hepatic ischemia/reperfusion injury in rats

Attenuation of Oxidative Stress by Ischemic Preconditioning in an Experimental Model of Intraabdominal Hypertension

PURPOSE

Increased intra-abdominal pressure, as used in laparoscopic surgery or seen in intraabdominal hypertension (IAH), is associated with tissue ischemia and oxidative stress. Ischemic preconditioning (IP) is a method successfully used in liver and transplant surgery, in order to attenuate the detrimental effects of ischemia and reperfusion. In this experimental study, we tested the ability of IP to modify oxidative stress induced by extremely high intraabdominal pressures.

METHODS

Twenty-five female pigs were studied and divided in three groups: a control group, a pneumoperitoneum group (with pressure of 30 mmHg), and an ischemic preconditioning group (initially subjected to preconditioning with pressure of 25 mmHg for 15 min and desufflation for 15 min and then to pneumoperitoneum as in pneumoperitoneum group). Blood samples were obtained at identical time intervals in the three groups. Total oxidative capacity, total antioxidative capacity and total nitric oxide (NO), nitrite and nitrate concentrations were measured and compared between groups.

RESULTS

IP increased total antioxidative capacity (p = .045) and protective mediators like nitrite (p = .022). It was also associated with a trend toward lower levels of total oxidative capacity at the end of the abdominal desufflation period but statistical significance was not met.

CONCLUSIONS

IP attenuated oxidative stress induced by IAH, mainly by increasing antioxidative capacity and the levels of protective mediators. The fact that IP was effective, even when used at extremely high levels of intraabdominal pressure, reinforces the interest on this method but further studies are needed to clarify its mechanism of action and potential clinical applications.

Identical MicroRNAs Regulate Liver Protection during Anaesthetic and Ischemic Preconditioning in Rats: An animal study

Anaesthetic preconditioning (APC) and ischemic preconditioning (IPC) ameliorate liver ischemia-reperfusion (I/R) injury and are important for regulating hepatic I/R injury. MicroRNAs (miRNAs) are short, noncoding RNA molecules of 21-23 nucleotides in length, and are currently under intensive investigation regarding their ability to regulate gene expression in a wide range of species. miRNA activity is involved in controlling a wide range of biological functions and processes. We evaluated whether APC and IPC are mediated by the same miRNAs by performing comprehensive miRNA screening experiments in a rat model of hepatic I/R injury. Twenty-one rats were randomly divided into three groups (n = 7/group): control (mock preconditioning), APC, and IPC. Control rats were subjected to 60 min of hepatic ischemia followed by 4 h of reperfusion, whereas the APC and IPC groups were preconditioned with 2% sevoflurane and hepatic ischemia for 10 min prior to ischemia-reperfusion, respectively. Liver samples were collected to measure miRNA levels after 3 h of reperfusion, and gene networks and canonical pathways were identified using Ingenuity Pathway Analysis (IPA). Blood samples were collected to measure the levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Although haemodynamic parameters did not vary among the groups, AST and ALT levels were significantly higher in the control group than in the APC and IPC groups. Comprehensive miRNA screening experiments revealed that most miRNAs altered in the APC group were common to those in the IPC group. IPA identified five miRNAs related to the Akt-glycogen synthase kinase-3β (GSK-3β)-cyclin D1 pathway that were significantly affected by both preconditioning strategies. The application of either APC or IPC to ameliorate hepatic I/R injury results in expression of several common miRNAs that are related to the Akt-GSK-cyclin D1 pathway.

Arginase induction and activation during ischemia and reperfusion and functional consequences for the heart

Induction and activation of arginase is among the fastest responses of the heart to ischemic events. Induction of arginase expression and enzyme activation under ischemic conditions shifts arginine consumption from nitric oxide formation (NO) to the formation of ornithine and urea. In the heart such a switch in substrate utilization reduces the impact of the NO/cGMP-pathway on cardiac function that requires intact electromechanical coupling but at the same time it induces ornithine-dependent pathways such as the polyamine metabolism. Both effects significantly reduce the recovery of heart function during reperfusion and thereby limits the success of reperfusion strategies. In this context, changes in arginine consumption trigger cardiac remodeling in an unfavorable way and increases the risk of arrhythmia, specifically in the initial post-ischemic period in which arginase activity is dominating. However, during the entire ischemic period arginase activation might be a meaningful adaptation that is specifically relevant for reperfusion following prolonged ischemic periods. Therefore, a precise understanding about the underlying mechanism that leads to arginase induction as well as of it's mechanistic impact on post-ischemic hearts is required for optimizing reperfusion strategies. In this review we will summarize our current understanding of these processes and give an outlook about possible treatment options for the future.

Hepatic ischemic preconditioning increases portal vein flow in experimental liver ischemia reperfusion injury

BACKGROUND

Ischemic preconditioning (IPC) has been shown to decrease liver injury and to increase hepatic microvascular perfusion after liver ischemia reperfusion. This study aimed to evaluate the effects of IPC on hemodynamics of the portal venous system.

METHODS

Thirty-two rats were randomized into two groups: IPC group and control group. The rats of the IPC group underwent IPC by 10 minutes of liver ischemia followed by 10 minutes of reperfusion before liver ischemia, and the rats of the control group were subjected to 60 minutes of partial liver ischemia. Non-ischemic lobes were resected immediately after reperfusion. The animals were studied at 4 hours and 12 hours after reperfusion. Mean arterial pressure, heart rate, portal vein flow and pressure were analyzed. Blood was collected for the determination of the levels of aspartate aminotransferase, alanine aminotransferase, calcium, lactate, pH, bicarbonate, and base excess.

RESULTS

IPC increased the mean portal vein flow at 4 hours and 12 hours after reperfusion. IPC recovered 78% of the mean portal vein flow at 12 hours after reperfusion. IPC decreased the levels of aspartate aminotransferase, alanine aminotransferase and lactate, and increased the levels of ionized calcium, bicarbonate and base excess at 12 hours after reperfusion.

CONCLUSIONS

This study demonstrated that IPC increases portal vein flow and enhances hepatoprotective effects in liver ischemia reperfusion. The better recovery of portal vein flow after IPC may be correlated with the lower levels of transaminases and with the better metabolic profile.

Arginase as a target for treatment of myocardial ischemia-reperfusion injury

Two distinct enzymes of arginase (1 and 2) are critically regulating nitric oxide (NO) bioavailability by competing with NO synthase for their common substrate l-arginine. Increased expression and activity of arginase is observed in atherosclerosis and myocardial ischemia-reperfusion (I/R). Several studies have demonstrated a key pathophysiological role of increased activity of arginase during I/R. Pharmacological inhibition of arginase results in restoration of NO availability and salvage of myocardium during I/R. Arginase inhibition might be a promising therapeutic strategy for the limitation of myocardial injury in acute myocardial infarction. Current understanding of the role of arginase and efficacy of arginase inhibition during myocardial I/R is reviewed in the present article.

Dihydrolipoyl histidinate zinc complex, a new antioxidant, attenuates hepatic ischemia-reperfusion injury in rats

BACKGROUND AND AIMS

Ischemia/reperfusion (I/R) injury is characterized by significant oxidative stress, which induces characteristic changes in the antioxidant system and organ injury leading to significant morbidity and mortality. The aim of this study was to evaluate the protective effect of dihydrolipoyl histidinate zinc complex (DHLHZn) on oxidative damage after severe hepatic I/R injury.

METHODS

Thirty male Wistar rats were subjected to 45 min of hepatic ischemia by clamping of the hepatic artery and portal vein, followed by a 6-h reperfusion period. DHLHZn (10 mg/kg) (I/R + DHLHZn group) or saline (I/R group) was administered intraperitoneally twice, 30 min before ischemia and at the beginning of the reperfusion. Sham-operated animals (sham group) received equal amounts of saline. The rats were killed at the end of the reperfusion period. Serum levels of aspartate aminotransferase and alanine aminotransferase were determined, and histological examination and oxidative stress were evaluated in liver tissues. In addition, antimycin A-stimulated RAW264.7 cells (murine macrophage-like cells) were treated with DHLHZn to estimate its antioxidant effect.

RESULTS

Serum aspartate aminotransferase and alanine aminotransferase levels were increased in the I/R group, but these increases were significantly inhibited in the I/R + DHLHZn group. Similarly, liver tissue damage observed in the I/R group was attenuated in the I/R + DHLHZn group. Cells treated in vitro with both DHLHZn and antimycin A showed reduced reactive oxygen species activity compared to cells treated with antimycin A alone.

CONCLUSION

The new antioxidant DHLHZn may have potential for therapeutic application in liver I/R injury, although this is a limited animal study.

Nitric oxide is an essential mediator of the protective effects of remote ischaemic preconditioning in a mouse model of liver ischaemia/reperfusion injury

NO (nitric oxide) may protect the liver from IR (ischaemia/reperfusion) injury. RIPC (remote ischaemic preconditioning) also protects against liver IR injury; however, the molecular mediator(s) of RIPC are currently unknown. The aim of the present study was to assess the role of NO in hindlimb RIPC-induced protection against liver IR injury. Mice were allocated to the following groups: sham group; RIPC group (six cycles of 4×4 min IR of hindlimb); IR group [40 min lobar (70%) hepatic ischaemia and 2-h reperfusion]; RIPC+IR group (RIPC followed by IR group procedures); and C-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt]+RIPC+IR group [C-PTIO (a direct NO scavenger) was administered, followed by the RIPC+IR group procedure]. Hepatic MBF (microcirculatory blood flow) was measured throughout the experiment. Circulating NOx (nitrite and nitrate) levels, plasma liver transaminases, hepatic histopathological and TEM (transmission electron microscopy) studies were performed at the end of the experiment. NOx concentrations were significantly elevated (P<0.05) in the RIPC and RIPC+IR groups. Compared with liver IR alone, RIPC+IR preserved hepatic MBF during liver reperfusion (P<0.05). In contrast, C-PTIO+RIPC+IR reduced MBF compared with RIPC+IR (P<0.05). RIPC+IR reduced plasma transaminases (P<0.05), and histopathological and ultrastructural features of injury compared with IR alone. The protective effects of RIPC+IR in reducing liver IR injury were abrogated in the group that received antecedent C-PTIO (C-PTIO+RIPC+IR). In conclusion, NO is an essential mediator of the protection afforded by hindlimb RIPC against liver IR injury. The mechanisms underlying this protection involve preservation of the sinusoidal structure and maintenance of blood flow through the hepatic microcirculation.

Grape seed extract treatment reduces hepatic ischemia-reperfusion injury in rats

This study was designed to determine the possible protective effect of grape seed extract (GSE), a widely used antioxidant dietary supplement, on hepatic ischemia/reperfusion (I/R) injury. Wistar albino rats were subjected to 45 min of hepatic ischemia, followed by a 60 min reperfusion period. GSE was administered in a dose of 50 mg/kg/day orally for 15 days before I/R injury and repeated before the reperfusion period. Liver samples were taken for histological examination or determination of hepatic malondialdehyde (MDA), glutathione (GSH) and myeloperoxidase (MPO) activity. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were determined to assess liver functions. Lactate dehydrogenase (LDH) and cytokines (TNF-alpha and IL-1 beta) were also assayed in serum samples for the evaluation of generalized tissue damage. Ischemia/reperfusion caused a significant decrease in hepatic GSH, and significant increases in MDA level, and MPO activity. Serum AST and ALT levels, as well as LDH activity and plasma TNF-alpha and IL-1beta levels were also elevated in the I/R group. Treatment with GSE reversed all these biochemical parameters as well as histological alterations induced by I/R. In conclusion, GSE reduced I/R-induced organ injury through its ability to balance the oxidant-antioxidant status, to inhibit neutrophil infiltration and to regulate the release of inflammatory mediators.

Alpha-lipoic acid protects against hepatic ischemia-reperfusion injury in rats

BACKGROUND AND AIM

To evaluate the protective effect of alpha-lipoic acid in reducing oxidative damage after severe hepatic ischemia/reperfusion (IR) injury.

METHODS

Wistar albino rats were subjected to 45 min of hepatic ischemia, followed by 60 min reperfusion period. Lipoic acid (100 mg/kg i.p.) was administered 15 min prior to ischemia and immediately before reperfusion period. At the end of the reperfusion period aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) activity, and cytokine, TNF-alpha and IL-1beta levels were determined in serum samples. Malondialdehyde (MDA), and glutathione (GSH) levels and myeloperoxidase (MPO) activity were determined in the liver tissue samples while formation of reactive oxygen species was monitored by using chemiluminescence (CL) technique with luminol and lucigenin probes. Tissues were also analyzed histologically.

RESULTS

Serum ALT, AST, and LDH activities and TNF-alpha and IL-1beta levels were elevated in the I/R group, while this increase was significantly lower in the group of animals treated concomitantly with lipoic acid. Hepatic GSH levels, significantly depressed by I/R, were elevated back to control levels in lipoic acid-treated I/R group. Furthermore, increases in tissue luminol and lucigenin CL, MDA levels and MPO activity due to I/R injury were reduced back to control levels with lipoic acid treatment.

CONCLUSION

Since lipoic acid administration alleviated the I/R-induced liver injury and improved the hepatic structure and function, it seems likely that lipoic acid with its antioxidant and oxidant-scavenging properties may be of potential therapeutic value in protecting the liver against oxidative injury due to ischemia-reperfusion.

Liver and lung late alterations following hepatic reperfusion associated to ischemic preconditioning orN-acetylcysteine

This study aimed the effect of n-acetylcysteine or ischemic preconditioning in hepatic and pulmonary damage after liver ischemia-reperfusion injury. Twenty-four male Wistar-EPM rats were assigned into four groups: (IR) Hepatic ischemia-reperfusion; (IPC) IPC achieved before hepatic ischemia; (NAC) Animals received NAC pretreatment; and Sham operated group. After 24 h of hepatic reperfusion, blood, liver, and pulmonary samples were evaluated. Nonparametric tests were used (P <or= 0.05). Aspartate aminotransferase levels were similar among experimental groups. Lower alanine aminotrasnferase levels were observed in sham group (P = 0.04). IPC and NAC groups prevented from necrosis (P = 0.027), apoptosis (P = 0.003), and microvesicular steatosis (P = 0.0007), but not from neutrophil infiltration in liver tissue. IPC and NAC treatment reduced alveolar septal edema (P = 0.014), but did not prevent from neutrophil infiltration or vascular congestion. In conclusion, IPC and NAC attenuated hepatic and pulmonary damage after hepatic ischemia-reperfusion injury.