Ischemic preconditioning-like effect of polyunsaturated fatty acid-rich diet on hepatic ischemia/reperfusion injury

Ischemic preconditioning modifies mortality and inflammatory response

PURPOSE

To evaluate the effect of ischemic preconditioning on mortality, inflammatory mediators and oxidative stress after intestinal ischemia and reperfusion.

METHODS

Male Wistar rats were allocated according to the period of ischemia with or without ischemic preconditioning which consist on clamping the superior mesenteric artery for 10 minutes followed by reperfusion for 10 minutes before the sustained ischemia period. Mortality was assessed in Phase 1 study, and the CINC-1, CINC-2 and MDA levels in the lungs were analyzed in Phase 2.

RESULTS

Mortality was lower in the ischemic preconditioning group subjected to 90 minutes of ischemia compared to the group without ischemic preconditioning (I-90: 50% and IPC-90: 15%, p=0.018), and it was lower in the ischemic preconditioning group as a whole compared to the groups without ischemic preconditioning (IPC-14% and I=30%, p=0.006). Lower levels of MDA, CINC-1, and CINC-2 were observed in the animals that were subjected to ischemic preconditioning compared to the animals that were not (MDA: I-45=1.23 nmol/mg protein, and IPC-45=0.62 nmol/mg protein, p=0.0333; CINC-1: I-45=0.82 ng/mL and IPC-45=0.67 ng/mL, p=0.041; CINC-2: I-45=0.52 ng/mL and IPC-45=0.35 ng/mL, p=0.032).

CONCLUSION

Ischemic preconditioning reduces mortality, inflammatory process and oxidative stress in rats subjected to intestinal ischemia and reperfusion.

An ω-3-enriched diet alone does not attenuate CCl4-induced hepatic fibrosis

Exposure to the halogenated hydrocarbon carbon tetrachloride (CCl₄) leads to hepatic lipid peroxidation, inflammation and fibrosis. Dietary supplementation of ω-3 fatty acids has been increasingly advocated as being generally anti-inflammatory, though its effect in models of liver fibrosis is mixed. This raises the question of whether diets high in ω-3 fatty acids will result in a greater sensitivity or resistance to liver fibrosis as a result of environmental toxicants like CCl₄. In this study, we fed CCl₄-treated mice a high ω-3 diet (using a mix of docosahexaenoic acid and eicosapentaenoic acid ethyl esters). We also co-administered an inhibitor of soluble epoxide hydrolase, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), which has been shown to boost anti-inflammatory epoxy fatty acids that are produced from both ω-3 and ω-6 dietary lipids. We showed that soluble epoxide inhibitors reduced CCl₄-induced liver fibrosis. Three major results were obtained. First, the ω-3-enriched diet did not attenuate CCl₄-induced liver fibrosis as judged by collagen deposition and collagen mRNA expression. Second, the ω-3-enriched diet raised hepatic tissue levels of several inflammatory lipoxygenase metabolites and prostaglandins, including PGE2. Third, treatment with TPPU in drinking water in conjunction with the ω-3-enriched diet resulted in a reduction in liver fibrosis compared to all other groups. Taken together, these results indicate that dietary ω-3 supplementation alone did not attenuate CCl₄-induced liver fibrosis. Additionally, oxylipin signaling molecules may play role in the CCl₄-induced liver fibrosis in the high ω-3 diet groups.

Trisulfate Disaccharide Decreases Calcium Overload and Protects Liver Injury Secondary to Liver Ischemia/Reperfusion

Background

Ischemia and reperfusion (I/R) causes tissue damage and intracellular calcium levels are a factor of cell death. Sodium calcium exchanger (NCX) regulates calcium extrusion and Trisulfated Disaccharide (TD) acts on NCX decreasing intracellular calcium through the inhibition of the exchange inhibitory peptide (XIP).

Objectives

The aims of this research are to evaluate TD effects in liver injury secondary to I/R in animals and in vitro action on cytosolic calcium of hepatocytes cultures under calcium overload.

Methods

Wistar rats submitted to partial liver ischemia were divided in groups: Control: (n = 10): surgical manipulation with no liver ischemia; Saline: (n = 15): rats receiving IV saline before reperfusion; and TD: (n = 15): rats receiving IV TD before reperfusion. Four hours after reperfusion, serum levels of AST, ALT, TNF-α, IL-6, and IL-10 were measured. Liver tissue samples were collected for mitochondrial function and malondialdehyde (MDA) content. Pulmonary vascular permeability and histologic parameters of liver were determined. TD effect on cytosolic calcium was evaluated in BRL3A hepatic rat cell cultures stimulated by thapsigargin pre and after treatment with TD.

Results

AST, ALT, cytokines, liver MDA, mitochondrial dysfunction and hepatic histologic injury scores were less in TD group when compared to Saline Group (p<0.05) with no differences in pulmonary vascular permeability. In culture cells, TD diminished the intracellular calcium raise and prevented the calcium increase pre and after treatment with thapsigargin, respectively.

Conclusion

TD decreases liver cell damage, preserves mitochondrial function and increases hepatic tolerance to I/R injury by calcium extrusion in Ca2+ overload situations.

Analysis of polyunsaturated fatty acids and the omega-6 inflammatory pathway in hepatic ischemia/re-perfusion injury

The aim of the present study was to assess omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) in liver tissue and evaluate changes in the n‑6-associated inflammatory pathway following liver ischemia/re‑perfusion (IR) injury. Male Wistar rats which were allowed free access to standard rat chow were included in the study. Blood vessels supplying the median and left lateral hepatic lobes were occluded with an arterial clamp for 60 min, followed by 60 min of re‑perfusion. Levels of arachidonic acid (AA, C20:4n‑6), dihomo‑gamma‑linolenic acid (DGLA, C20:3n‑6), eicosapentaenoic acid (EPA, C20:5n‑3) and docosahexaenoic acid (DHA, C22:6n‑3) in liver tissue were determined by an optimized multiple reaction monitoring method using ultra fast‑liquid chromatography coupled with tandem mass spectrometry. Phospholipase A2 (PLA2), cyclooxygenase (COX) and prostaglandin E2 (PGE2) were measured in tissue samples to evaluate changes in the n‑6 inflammatory pathway. Total histopathological score of cellular damage were significantly increased following hepatic IR injury. n‑3 and n‑6 PUFA levels were significantly increased in post‑ischemic liver tissue compared to those in non‑ischemic controls. No significant difference was observed in the AA/DHA and AA/EPA ratio in post‑ischemic liver tissues compared with that in the control. Tissue activity of PLA2 and COX as well as PGE2 levels were significantly increased in post‑ischemic liver tissues compared to those in non‑ischemic controls. The results of the present study suggested that increased hydrolysis of fatty acids via PLA2 triggers the activity of COX and leads to increased PGE2 levels. Future studies evaluating agents which block the formation of eicosanoids derived from n‑6 PUFAs may facilitate the development and application of treatment strategies in liver injury following IR.

GPR120 on Kupffer cells mediates hepatoprotective effects of ω3-fatty acids

BACKGROUND & AIMS

Many of the beneficial effects of ω3-fatty acids (ω3FAs) are being attributed to their anti-inflammatory properties. In animal models, ω3FAs also protect from hepatic ischemia reperfusion injury (IRI), a significant cause of complications following liver surgery. Omegaven®, a clinical ω3FA-formulation, might counteract the exaggerated inflammatory response underlying IRI, but the according mechanisms are unresearched. Recently, GPR120 has been identified as a first receptor for ω3FAs, mediating their anti-inflammatory effects. Here, we sought to investigate whether Omegaven® protects from hepatic IRI through GPR120.

METHODS

Using a mouse model of liver IRI, we compared the effects of a GPR120 agonist with those of Omegaven®.

RESULTS

GPR120 in liver was located to Kupffer cells (KCs). Agonist and Omegaven® provided similar protection from IRI, which was abolished by clodronate-depletion of KCs or by pretreatment with an αGpr120-siRNA. In vitro and in vivo, both agents dampened the NFκB/JNK-mediated inflammatory response. Dampening was associated with an M1>M2 macrophage polarization shift as assessed by marker expression. In αGpr120-siRNA-pretreated mice with or without ischemia, Omegaven® was no more able to promote M2 marker expression, indicating its anti-inflammatory properties are dependent on GPR120 in liver.

CONCLUSIONS

These findings establish KC-GPR120 as a key mediator of Omegaven® effects and suggest GPR120 as a therapeutic target to mitigate inflammatory stress in liver.

Inhibition of neutral sphingomyelinase decreases arachidonic acid mediated inflammation in liver ischemia-reperfusion injury

This study aimed to determine the role of selective neutral sphingomyelinase (N-SMase) inhibition on arachidonic acid (AA) mediated inflammation following liver ischemia-reperfusion (IR) injury. Selective N-SMase inhibitor was administered via intraperitoneal injections. Liver IR injury was created by clamping blood vessels supplying the median and left lateral hepatic lobes for 60 min, followed by 60 min reperfusion. Levels of AA in liver tissue were determined by multiple reaction monitoring (MRM) using ultra fast-liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Phospholipase A₂ (PLA₂), cyclooxygenase (COX) and prostaglandin E₂ (PGE₂) were measured in liver tissue. Arachidonic acid levels, activity of PLA₂, COX and PGE₂ levels were significantly increased in postischemic liver tissue compared to nonischemic controls. N-SMase inhibition significantly decreased COX activity and PGE₂ levels in postischemic liver. Future studies evaluating agents blocking N-SMase activity can facilitate the development of treatment strategies to alleviate inflammation in liver I/R injury.

Lobe-specific heterogeneity and matrix metalloproteinase activation after ischemia/reperfusion injury in rat livers

Studies assessing the effects of partial-hepatic ischemia/reperfusion (I/R) injury focused on the damage to the ischemic-lobe, whereas few data are available on non-ischemic lobe. This study investigated whether acute liver I/R does affect non-ischemic lobe function via modulation of extracellular matrix remodeling. Male Sprague-Dawley rats underwent left lateral- and median-lobe ischemia for 30 min and reperfusion for 60 min or sham operation. After reperfusion, blood samples and hepatic biopsies from both the ischemic (left-lobe, LL) and the non-ischemic lobe (right-lobe, RL) were collected. Serum hepatic enzymes and TNF-alpha, tissue matrix metalloproteinases (MMP-2, MMP-9), liver morphology, malondialdehyde (MDA), and myeloperoxidase (MPO) were evaluated. Liver I/R injury was confirmed by altered increased hepatic enzymes and TNF-alpha. I/R induced an altered morphology and an increase in MMP-2 and MMP-9 activity not only in left-ischemic lobe (LL) but also in the right-non-ischemic (RL) lobe. A lobar difference was detected for MDA formation and MPO activity in both sham and I/R submitted rats, with higher levels in the left lobe for both groups. This study indicates that an increase in MMPs, which may be TNF-alpha-mediated, occurs in both the ischemic- and the non-ischemic lobes; the heterogeneous lobe concentrations of MDA and MPO suggest that the random sampling of liver tissue should be avoided.