Fish oil-supplemented feeding does not attenuate warm liver ischemia and reperfusion injury in the rat

Beneficial effects of natural compounds on experimental liver ischemia-reperfusion injury

Liver ischemia-reperfusion injury (IRI) is a phenomenon inherent to hepatic surgery that severely compromises the organ functionality, whose underlying mechanisms involve cellular and molecular interrelated processes leading to the development of an excessive inflammatory response. Liver resident cells and those recruited in response to injury generate pro-inflammatory signals such as reactive oxygen species, cytokines, chemokines, proteases and lipid mediators that contribute to hepatocellular necrosis and apoptosis. Besides, dying hepatocytes release damage-associated molecular patterns that actívate inflammasomes to further stimulate inflammatory responses leading to massive cell death. Since liver IRI is a complication of hepatic surgery in man, extensive preclinical studies have assessed potential protective strategies, including the supplementation with natural compounds, with the objective to downregulate nuclear factor-κB functioning, the main effector of inflammatory responses. This can be accomplished by either the activation of peroxisome proliferator-activated receptor-α, G protein-coupled receptor 120 or antioxidant signaling pathways, the synthesis of specific pro-resolving mediators, downregulation of Toll-like receptor 4 activity or additional contributory mechanisms that are beginning to be understood. The latter aspect is a crucial issue to be accomplished in preclinical studies, in order to establish adequate conditions for the supplementation with natural products before major liver surgeries in man involving warm IR, such as hepatic trauma or resection of large intrahepatic tumors.

Nutrition in kidney transplantation

Organ transplantation has progressively established itself as the preferred therapy for many end-stage organ failures. However, many of these chronic diseases and their treatments can negatively affect nutritional status, leading to malnutrition and mineral deficiencies.Nutritional status is an important determinant of the clinical outcome of kidney transplant recipients.Malnutrition and obesity may represent a contraindication to transplantation in many cases and may increase the risk of postoperative complications after the transplantation. Nutritional support in kidney transplant recipients is challenging, since it must take into account the pre-transplant nutritional status, the side effects of immunosuppression, the function of the transplanted graft, the presence of infection, and the general status of the patient at the time of the transplantation.With these considerations in mind, we reviewed current literature on the impact of nutritional status on the outcome of kidney transplantation.

Temporal changes in hepatic antioxidant enzyme activities after ischemia and reperfusion in a rat liver ischemia model

This study investigated the hypothesis that administration of tilapia fish oil diet would attenuate warm liver ischemia/reperfusion injury (IRI) and whether fish oil modulates prooxidant/antioxidant status. Male Wistar rats were subjected to 30 min of approximately 70% hepatic ischemia followed by 1, 12, and 24 h reperfusion. Rats were randomly divided into three groups: sham-operated group (SO), control–warm hepatic ischemia (WI) group, and Oil–WI group given tilapia oil for 3 weeks followed by liver IRI. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were measured in the plasma. Levels of thiobarbituric acid reactive substances (TBARS) and antioxidant enzymes as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities were measured in liver fractions.

In the sham group, there was no enzymatic or histological change. I/R caused significant increase in serum AST, ALT, and tissue TBARS levels. As compared to the control group, animals treated with tilapia oil experienced a significant decrease ( p < 0.05) in AST and ALT levels in reperfusion periods. Tissue TBARS levels in Oil–WI group were significantly ( p < 0.05) reduced as compared to control group at 60 min after reperfusion. After ischemia, 1, 12, and 24 h of reperfusion, CAT, SOD, and GPx values were the lowest in the Oil–WI group and highest in the control group and were statistically significant ( p < 0.05). Histological analysis also revealed that fish oil provided some protection compared with the control group.

Tilapia oil exerts a protective effect during the early phase of reperfusion, and it modulates prooxidant/antioxidant status of rat liver subjected to warm IRI.

Omega 3 - Omega 6: What is right for the liver?

Linoleic and alpha-linolenic acids are the fatty acids designated as "essential" since they are not synthesized by mammalian cells and must be provided in the diet. The recent dietary shift towards the consumption of n-6 (omega-6) at the expense of n-3 (omega-3) polyunsaturated fatty acids (PUFAs) is thought to be a primary cause of many diseases related to the Western diet. The body converts linoleic acid to arachidonic acid and derives eicosapentaenoic acid from alpha-linolenic acid. Ideally the effects of these fatty acids and their eicosanoid derivatives are tailored to the specific biological needs of the body. The balance between n-3 and n-6 PUFAs is essential for metabolism and maintenance of the functions of both classes. The availability of n-3 long chain PUFAs plays a major role in regulating both fat accumulation and its elimination by the liver. Derangement of hepatic n-6:n-3 PUFA ratio impacts on the histological pattern of fatty liver through modulation of the amount of intrahepatic lipids. Moreover, the influence of PUFAs and their eicosanoid products on hepatic microcirculation and ischemia/reperfusion injury has been demonstrated in many studies. This concise review article will focus on the role of PUFAs and eicosanoids in hepatic steatosis, microcirculation and ischemia/reperfusion injury.

Prevention of reperfusion injury and microcirculatory failure in macrosteatotic mouse liver by omega-3 fatty acids

Macrovesicular hepatic steatosis has a lower tolerance to reperfusion injury than microvesicular steatosis with an abnormally high ratio of omega-6 (n-6): omega-3 (n-3) polyunsaturated fatty acids (PUFAs). We investigated the influence of PUFAs on microcirculation in steatotic livers and the potential to minimize reperfusion injury in the macrosteatotic liver by normalization of PUFAs. Ob/ob mice were used as a model of macrovesicular hepatic steatosis and C57/Bl6 mice fed a choline-deficient diet for microvesicular steatosis. Steatotic and lean livers were subjected to 45 minutes of ischemia and 3 hours of reperfusion. Hepatic content of omega-3 and omega-6 PUFAs was determined. Microcirculation was investigated using intravital fluorescence microscopy. A second group of ob/ob mice was supplemented with dietary omega-3 PUFAs and compared with the control diet-fed group. Microcirculation, AST, and Kupffer cell activity were assessed. Macrosteatotic livers had significant microcirculatory dysfunction correlating with high omega-6: omega-3 PUFA ratio. Dietary omega-3 PUFA resulted in normalization of this ratio, reduction of intrahepatic lipids, and decrease in the extent of macrosteatosis. Defective microcirculation was dramatically ameliorated with significant reduction in Kupffer cell activity and protection against hepatocellular injury both before ischemia and after reperfusion.

CONCLUSION

Macrosteatotic livers disclosed an abnormal omega-6: omega-3 PUFA ratio that correlates with a microcirculatory defect that enhanced reperfusion injury. Thus, protective strategies applied during or after ischemia are unlikely to be useful. Preoperative dietary omega-3 PUFAs protect macrosteatotic livers against reperfusion injury and might represent a valuable method to expand the live liver donor pool.

Intralipid minimizes hepatocytes injury after anoxia-reoxygenation in an ex vivo rat liver model

OBJECTIVE

Ischemia-reperfusion injury is a determinant in liver injury occurring during surgical procedures, ischemic states, and multiple organ failure. The pre-existing nutritional status of the liver, i.e., fasting, might contribute to the extent of tissue injury. This study investigated whether Intralipid, a solution containing soybean oil, egg phospholipids, and glycerol, could protect ex vivo perfused livers of fasting rats from anoxia-reoxygenation injury.

METHODS

The portal vein was cannulated, and the liver was removed and perfused in a closed ex vivo system. Isolated livers were perfused with glucose 5.5 and 15 mM, and two different concentrations of Intralipid, i.e., 0.5:100 and 1:100 (v/v) Intralipid 10%:medium (n = 5 in each group). The experiment consisted of perfusion for 15 min, warm anoxia for 60 min, and reoxygenation during 60 min. Hepatic enzymes, potassium, glucose, lactate, bilirubin, dienes, trienes, and cytochrome-c were analyzed in perfusate samples. The proportion of glycogen in hepatocytes was determined in biopsies.

RESULTS

Intralipid attenuated transaminases, lactate dehydrogenase, potassium, diene, and triene release in the perfusate (dose-dependant) during the reoxygenation phase when compared with glucose-treated groups. The concentration of cytochrome-c in the medium was the highest in the 5.5-mM glucose group. The glycogen content was low in all livers at the start of the experiment.

CONCLUSION

Intralipid presents, under the present experimental conditions, a better protective effect than glucose in anoxia-reoxygenation injury of the rat liver.

Experimental studies defining omega-3 fatty acid antiinflammatory mechanisms and abrogation of tumor-related syndromes

Clinical and experimental evidence has supported a benefit for the inclusion of fish oils (a primary source of omega-3 fatty acids) as a component of a normal healthy diet. Polyunsaturated omega-3 fatty acids have been demonstrated to be of benefit in a number of inflammation-associated disease states, including atherosclerosis, autoimmune disorders, malignancy, and sepsis. The beneficial effects of omega-3 fatty acids are thought to occur through the postulated antiinflammatory actions of omega-3 fats; however, the specific mechanism(s) of action has not been completely defined. In this review, we discuss the recent progress made in our laboratory on defining the mechanisms of omega-3 fatty acids activity.

Renal effects of parenteral fish oil administered to heart-beating organ donors and renal-transplant recipients: a tolerance study

BACKGROUND & AIMS

Nutrition can interfere with organ function during the different stages of transplantation. Oral fish oil supplementation to kidney transplant recipients has been found to improve renal function. The aim of the present study was to determine the safety and tolerance of intravenous administration of fish-oil emulsion to heart-beating brain-dead donors and, subsequently, to the kidney recipients, and to assess its effects on renal function.

METHODS

A lipid emulsion enriched with omega-3 fatty acids (MLF 541) was given intravenously to 8 heart-beating, brain-dead organ donors for up to 4 h before organ harvesting and to the kidney recipients for 5 days postoperatively. Hemodynamic, biochemistry and hematological parameters were measured before and at the end of lipid administration in the donors and on posttransplantation days 1, 5, 30 and 180 in the recipients. Findings in the recipients were compared with a concurrent control group.

RESULTS

There were no significant changes in hemodynamic or laboratory parameters during the MLF infusion in the donors or the 5 days of MLF administration in the recipients. Blood urea nitrogen and serum creatinine levels decreased over time in both the study and control recipients (P < 0.05 for both), with no significant between-group difference at any of the time points studied.

CONCLUSIONS

Administration of MLF 541 is safe in organ donors and in kidney recipients. Further studies involving nutrients as pharmacological agents in organ transplantation are warranted.

Omega-3 fatty acid lipid emulsion reduces LPS-stimulated macrophage TNF-alpha production

BACKGROUND

Omega-3 (omega-3) fatty acids (FA), specifically eicosapentaenoic acid (EPA), attenuate cytokine-mediated inflammation. Currently, in the United States, there is no commercial source of omega-3 lipid for clinical use. A clinically used European lipid emulsion, Omegaven, has been shown to have beneficial antiinflammatory effects; however, the mechanisms of its action are not well defined. In the present work, this omega-3 FA emulsion has been evaluated in order to define its effects on TNF-alpha production in a model of LPS-stimulated macrophages.

MATERIALS AND METHODS

RAW 264.7 cells (1 x 10(6) cell/well) were incubated with DMEM, Omegaven, or an isoenergetic omega-6 lipid emulsion, Lipovenos for 4 h. Cells were washed and then stimulated with LPS (1 microg/mL) or media alone for 3 h. Plate well supernatants were collected and assayed for TNF-alpha production by ELISA. Statistical analysis was performed by ANOVA and post-hoc analyses; the significance was defined as p < 0.05.

RESULTS

Unstimulated RAW cell TNF-alpha production was similar in all groups and < 60 pg/mL. Lipovenos pretreatment did not alter TNF-alpha production from that of baseline compared to LPS-stimulated cells. Four-hour Omegaven pretreatment significantly reduced TNF-alpha production in LPS-stimulated cells, with a 46% reduction in TNF-alpha from baseline observed.

CONCLUSION

Four-hour omega-3 FA emulsion pretreatment significantly attenuated LPS-stimulated macrophage TNF-alpha production. These data support the contention that antiinflammatory effects of omega-3 FA occur at least in part through the inhibition of macrophage TNF-alpha production in response to endotoxin. Further studies to define the antiinflammatory mechanisms of omega-3 FA on macrophages are warranted. The availability of Omegaven as an experimental treatment and Lipovenos as an equivalent control will be useful for future studies.

Long-chain n-3 fatty acids and inflammation: potential application in surgical and trauma patients

Lipids used in nutritional support of surgical or critically ill patients have been based on soybean oil, which is rich in the n-6 fatty acid linoleic acid (18:2n-6). Linoleic acid is the precursor of arachidonic acid (20:4n-6). In turn, arachidonic acid in cell membrane phospholipids is the substrate for the synthesis of a range of biologically active compounds (eicosanoids) including prostaglandins, thromboxanes, and leukotrienes. These compounds can act as mediators in their own right and can also act as regulators of other processes, such as platelet aggregation, blood clotting, smooth muscle contraction, leukocyte chemotaxis, inflammatory cytokine production, and immune function. There is a view that an excess of n-6 fatty acids should be avoided since this could contribute to a state where physiological processes become dysregulated. One alternative is the use of fish oil. The rationale of this latter approach is that fish oil contains long chain n-3 fatty acids, such as eicosapentaenoic acid. When fish oil is provided, eicosapentaenoic acid is incorporated into cell membrane phospholipids, partly at the expense of arachidonic acid. Thus, there is less arachidonic acid available for eicosanoid synthesis. Hence, fish oil decreases production of prostaglandins like PGE2 and of leukotrienes like LTB4. Thus, n-3 fatty acids can potentially reduce platelet aggregation, blood clotting, smooth muscle contraction, and leukocyte chemotaxis, and can modulate inflammatory cytokine production and immune function. These effects have been demonstrated in cell culture, animal feeding and healthy volunteer studies. Fish oil decreases the host metabolic response and improves survival to endotoxin in laboratory animals. Recently clinical studies performed in various patient groups have indicated benefit from this approach.

n-3 Polyunsaturated fatty acid-enriched diet does not protect from liver injury but attenuates mortality rate in a rat model of systemic endotoxemia

OBJECTIVE

We investigated the potential of dietary fish oil containing n-3 polyunsaturated fatty acids to attenuate hepatic injury and mortality rate of rats in response to systemic endotoxemia.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University laboratory.

SUBJECTS

A total of 43 male Sprague Dawley rats.

INTERVENTIONS

Rats were fed either fish oil supplement or regular standard lab chow. After 8 wks of feeding, each diet group was subjected to a single exposure of lipopolysaccharide (Escherichia coli, 10 mg/kg intravenously) or saline. Hepatic microvascular response and liver injury were assessed by in vivo analysis of Kupffer cell phagocytic activity, leukocyte-endothelial cell interaction, nutritive sinusoidal perfusion failure, and parenchymal cell apoptosis (intravital fluorescence epi-illumination technique) as well as bile flow, serum liver enzyme activities, and tissue histomorphology.

MEASUREMENTS AND MAIN RESULTS

In animals fed a standard diet, livers at 16 hrs after lipopolysaccharide-exposure exhibited depressed Kupffer cell phagocytic activity, enhanced hepatic microvascular leukocyte activation, leukocytic tissue infiltration, sinusoidal perfusion failure, and parenchymal cell apoptosis. Hepatic microvascular injury was further accompanied by reduced bile flow and enhanced liver enzyme release. The fish oil enriched diet did not significantly change the multiple features of endotoxemia-associated liver injury; however, it maintained arterial blood pressure, systemic leukocyte count, and acid base balance and showed a tendency toward improved survival on lipopolysaccharide exposure with a 16 hr-survival rate of 80% (p =.06 vs. survival rate of 40% in animals fed a regular diet). Moreover, slightly increased serum concentrations of interleukin-10 coincided with enhanced concentrations of interleukin-6 in fish oil fed endotoxemic animals. Healthy, non-lipopolysaccharide-exposed, fish oil fed animals did not differ from those fed with the regular diet, except for dampened Kupffer cell phagocytic activity.

CONCLUSIONS

Fish oil feeding does not protect from local endotoxemia-induced hepatic microvascular dysfunction. However, dietary modulation of inflammatory mediator response by macrophages, constituting an appropriate immune response, could add to the survival advantage seen in fish oil-fed animals on exposure to lipopolysaccharide.

Effect of nutritional state of brain-dead organ donor on transplantation

OBJECTIVE

We describe the effect of the metabolic and nutritional modifications caused by severe illness or injury in brain-dead organ donors on transplant organ function. Malnutrition is frequently found in brain-dead organ donors and nutrients may interfere with different organ functions.

METHODS

Literature was obtained from MEDLINE using the key words organ donation, brain death, transplantation, nutrition, fish oil, amino acids.

RESULTS

In the liver, infusion of large quantities of dextrose can restore glycogen reserves but may induce hyperglycemia and a hyperosmolar hepatic state. Feeding improves protein synthesis in hepatocytes, and fat (fish oil) administration in particular increases the hepatic energy and adenosine triphosphate content. Amino acids have a significant effect on regenerating hepatic tissue when given with fat and glucose. In the heart, free fatty acids administered during reperfusion improve cardiac functional recovery, and administration of propofol, a general anesthetic agent enriched with fatty acids, have protective effects on ischemia-and-reperfusion injury. Glutamine also can induce graft protection during ischemia-and-reperfusion injury. Renal function is improved by fish oil supplementation. In addition, effective renal plasma flow, glomerular filtration rate, and renal blood flow are increased, apparently by a reduction in thromboxane B2 production. Glycine or alanine can protect renal tubules from stress injury.

CONCLUSION

Nutrition plays an important role in the modulation of organ function after transplantation.

Efficacy of nutritional pharmacology in surgical patients

The present article reviews the current concepts of immune enhancement through nutritional support for the surgical patient as they are derived experimentally and clinically. Although the potential for altering outcome in surgical patients through nutritional enhancement exists, the authors caution against overzealous application of laboratory data in the clinical arena. Available clinical studies have, at best, only demonstrated modest benefits. It is appropriate that the current literature be critically reviewed to assess the efficacy of the agent(s) purported to be of clinical benefit. Although present reports of immune-enhancing nutrition regimens demonstrate no overwhelming benefits in the critically ill or immunocompromised patient, the pursuit of this science remains undaunted. Lessons learned from the past are leading to reinvestigations in the laboratory, as well as better designs of clinical trials that are free of distracting post-hoc analysis and performed clearly in an intention-to-treat manner.