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

Health implications of high dietary omega-6 polyunsaturated Fatty acids

Omega-6 (n-6) polyunsaturated fatty acids (PUFA) (e.g., arachidonic acid (AA)) and omega-3 (n-3) PUFA (e.g., eicosapentaenoic acid (EPA)) are precursors to potent lipid mediator signalling molecules, termed "eicosanoids," which have important roles in the regulation of inflammation. In general, eicosanoids derived from n-6 PUFA are proinflammatory while eicosanoids derived from n-3 PUFA are anti-inflammatory. Dietary changes over the past few decades in the intake of n-6 and n-3 PUFA show striking increases in the (n-6) to (n-3) ratio (~15 : 1), which are associated with greater metabolism of the n-6 PUFA compared with n-3 PUFA. Coinciding with this increase in the ratio of (n-6) : (n-3) PUFA are increases in chronic inflammatory diseases such as nonalcoholic fatty liver disease (NAFLD), cardiovascular disease, obesity, inflammatory bowel disease (IBD), rheumatoid arthritis, and Alzheimer's disease (AD). By increasing the ratio of (n-3) : (n-6) PUFA in the Western diet, reductions may be achieved in the incidence of these chronic inflammatory diseases.

Role of hepatic de novo lipogenesis in the development of fasting-induced fatty liver in the American mink (Neovison vison)

American mink (Neovison vison) develop fatty liver quickly in response to food deprivation, which results in preferential mobilisation of n-3 PUFA. The altered n-3:n-6 PUFA ratio in the liver may activate the endocannabinoid system resulting in increased lipid synthesis. The objective of the present study was to investigate the effects of feeding intensity (80 or 120% RDA), dietary fat source (n-3, n-6 or n-9 fatty acids (FA)) and short-term fasting (1-7 d) on hepatic de novo lipogenesis (DNL) and the development of fatty liver in mink. Significantly elevated expression of mRNA encoding for acetyl-CoA carboxylase-1 (ACC-1) and FA synthase (FAS) was observed in the liver of mink fasted for 5-7 d, while upon re-feeding for 28 d after a 7 d food deprivation, DNL returned to pre-fasting levels. The females had a higher expression of ACC-1 and FAS mRNA than the males. In the non-fasted animals, dietary fat source and feeding intensity had significant effects on ACC-1 mRNA. The highest levels were observed in the mink fed the rapeseed oil (n-9) diet at 80% RDA, while the lowest levels were seen when the same diet was fed at 120% RDA. For FAS, the highest gene expression was seen in the fasted mink fed at 80% RDA and the lowest in the non-fasted mink fed at 80%. It is concluded that short-term food deprivation induces hepatic lipidosis in mink and that during this process, hepatic DNL further exacerbates liver fat accumulation.

Chemical composition of hepatic lipids mediates reperfusion injury of the macrosteatotic mouse liver through thromboxane A(2)

BACKGROUND & AIMS

Chemical composition of hepatic lipids is an evolving player in steatotic liver ischemia/reperfusion (I/R) injury. Thromboxane A(2) (TXA(2)) is a vasoactive pro-inflammatory lipid mediator derived from arachidonic acid (AA), an omega-6 fatty acid (Ω-6 FA). Reduced tolerance of the macrosteatotic liver to I/R may be related to increased TXA(2) synthesis due to the predominance of Ω-6 FAs.

METHODS

TXA(2) levels elicited by I/R in ob/ob and wild type mice were assessed by ELISA. Ob/ob mice were fed Ω-3 FAs enriched diet to reduce hepatic synthesis of AA and TXA(2) or treated with selective TXA(2) receptor blocker before I/R.

RESULTS

I/R triggered significantly higher hepatic TXA(2) production in ob/ob than wild type animals. Compared with ob/ob mice on regular diet, Ω-3 FAs supplementation markedly reduced hepatic AA levels before ischemia and consistently blunted hepatic TXA(2) synthesis after reperfusion. Sinusoidal perfusion and hepatocellular damage were significantly ameliorated despite downregulation of heme oxygenase-1. Hepatic transcript and protein levels of IL-1β and neutrophil recruitment were significantly diminished after reperfusion. Moreover, TXA(2) receptor blockage conferred similar protection without modification of the histological pattern of steatosis. A stronger protection was achieved in the steatotic compared with lean animals.

CONCLUSIONS

Enhanced I/R injury in the macrosteatotic liver is explained, at least partially, by TXA(2) mediated microcirculatory failure rather than size-related mechanical compression of the sinusoids by lipid droplets. TXA(2) blockage may be a simple strategy to include steatotic organs and overcome the shortage of donor organs for liver transplantation.

Intravenous administration of multipotent stromal cells prevents the onset of non-alcoholic steatohepatitis in obese mice with metabolic syndrome

BACKGROUND & AIMS

Metabolic syndrome is secondary to obesity and characterized by dyslipidemia, insulin resistance, and hypertension. Non-alcoholic fatty liver disease is its hepatic manifestation, whose progression-limiting step is non-alcoholic steatohepatitis (NASH). The latter is characterized by lipid accumulation, hepatocyte damage, leukocyte infiltration, and fibrosis. NASH is a prodrome to cirrhosis and hepatocellular carcinoma. Multipotent stromal cells (MSCs) have been shown to be immunomodulatory and contribute to liver regeneration in acute failure conditions. Our aim was to evaluate whether MSC administration prevents the onset of NASH in obese mice with metabolic syndrome.

METHODS

C57BL/6 mice were chronically fed with high-fat diet. At week 33, mice received intravenously either the vehicle (obese untreated) or two doses of 0.5×10(6) syngeneic MSCs (obese MSC-treated). Four months later, liver function and structure, and metabolic syndrome markers were assessed. The persistence of donor MSCs(GFP) in obese mice was evaluated 17 weeks after their administration.

RESULTS

Obese untreated mice presented high plasma levels of hepatic enzyme, hepatomegaly, liver fibrosis, inflammatory cell infiltration, and hepatic triglyceride accumulation. Furthermore, they showed high expression levels of fibrosis markers and pro-inflammatory cytokines. By contrast, obese MSC-treated mice only presented steatosis. Mice kept obese, hypercholesterolemic, hyperglycemic, and insulin resistant irrespective of whether they received MSCs or not. Donor MSCs(GFP) were found in liver, bone marrow, heart, and kidney of obese mice.

CONCLUSIONS

MSC administration prevents the onset of NASH in obese mice. Observed hepatoprotection is not related to a reversion of the metabolic syndrome but to the preclusion of the inflammatory process.

Dietary saturated and monounsaturated fats protect against acute acetaminophen hepatotoxicity by altering fatty acid composition of liver microsomal membrane in rats

Background

Dietary polyunsaturated fats increase liver injury in response to ethanol feeding. We evaluated the effect of dietary corn oil (CO), olive oil (OO), and beef tallow (BT) on fatty acid composition of liver microsomal membrane and acute acetaminophen hepatotoxicity.

Methods

Male Sprague-Dawley rats were fed 15% (wt/wt) CO, OO or BT for 6 weeks. After treatment with acetaminophen (600 mg/kg), samples of plasma and liver were taken for analyses of the fatty acid composition and toxicity.

Results

Treatment with acetaminophen significantly elevated levels of plasma GOT and GPT as well as hepatic TBARS but reduced hepatic GSH levels in CO compared to OO and BT groups. Acetaminophen significantly induced protein expression of cytochrome P450 2E1 in the CO group. In comparison with the CO diet, lower levels of linoleic acid, higher levels of oleic acids and therefore much lower ratios of linoleic to oleic acid were detected in rats fed OO and BT diets.

Conclusions

Dietary OO and BT produces similar liver microsomal fatty acid composition and may account for less severe liver injury after acetaminophen treatment compared to animals fed diets with CO rich in linoleic acid. These findings imply that types of dietary fat may be important in the nutritional management of drug-induced hepatotoxicity.

Hepatic lipid composition analysis using 3.0-T MR spectroscopy in a steatotic rat model

PURPOSE

To investigate the feasibility of in vivo assessment of hepatic lipid composition using 3.0-T proton magnetic resonance spectroscopy ((1)H-MRS) in a steatotic rat model and compare it to histopathological and biochemical assessment.

MATERIALS AND METHODS

Hepatic steatosis was induced by feeding rats with a methionine/choline-deficient (MCD) diet for 1, 2, 3, 5 or 7 weeks (n=5 per group). At the end of the diet period, (1)H-MRS of the liver was performed, and rats were sacrificed for histopathological and biochemical assessment of the liver. Spectra were acquired in a single voxel (1.2 cc) using a point-resolved spectroscopic sequence with TE/TR=35/2000 ms and 64 signal acquisitions. From the MR spectra, peak area ratios were calculated to estimate hepatic lipid composition.

RESULTS

During MCD diet periods, hepatic steatosis significantly increased on histopathology (P<.001). The (1)H-MRS measurements of total hepatic fat content [1.3/(1.3+4.65) ppm] correlated strongly with histological macrovesicular hepatic steatosis (r=0.93, P<.001) and with the biochemical total hepatic fatty acids (r=0.94, P<.001). Total unsaturated fatty acids [TUFA, 5.4/(1.3+4.65) ppm] estimated with (1)H-MRS strongly correlated with the biochemical unsaturated fatty acids (r=0.90, P<.001). Polyunsaturated fatty acids [PUFA, 2.8/(1.3+4.65) ppm] estimated with (1)H-MRS strongly correlated with biochemical PUFA (r=0.91, P<.001). The proportion of total unsaturated fatty acids relative to the amount of total fatty acids (rTUFA, 5.4/1.3 ppm) measured with (1)H-MRS strongly correlated with the biochemical amount of unsaturated relative to total hepatic fatty acids (r=0.81, P<.001). The proportion of PUFA relative to the amount of total fatty acids (rPUFA, 2.8/1.3 ppm) measured with (1)H-MRS correlated with the biochemical amount of PUFA relative to total fatty acids (r=0.59, P=0.005,) and with the biochemical amount of omega-6 PUFA relative to total fatty acids (r=0.73, P<.001). PUFA at (1)H-MRS correlated with the histopathologically assessed degree of lobular inflammation in the liver (r=0.57, P=.001).

CONCLUSION

3.0 T (1)H-MRS is able to measure poly- and unsaturated hepatic fatty acids and this strongly correlates with biochemical assessment. This study provides evidence that 3.0-T (1)H-MRS is a noninvasive technique to assess hepatic lipid composition.

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

Liver conversion of docosahexaenoic and arachidonic acids from their 18-carbon precursors in rats on a DHA-free but α-LNA-containing n-3 PUFA adequate diet

The long-chain polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and arachidonic acid (AA, 20:4n-6), are critical for health. These PUFAs can be synthesized in liver from their plant-derived precursors, α-linolenic acid (α-LNA, 18:3n-3) and linoleic acid (LA, 18:2n-6). Vegetarians and vegans may have suboptimal long-chain n-3 PUFA status, and the extent of the conversion of α-LNA to EPA and DHA by the liver is debatable. We quantified liver conversion of DHA and other n-3 PUFAs from α-LNA in rats fed a DHA-free but α-LNA (n-3 PUFA) adequate diet, and compared results to conversion of LA to AA. [U-(13)C]LA or [U-(13)C]α-LNA was infused intravenously for 2h at a constant rate into unanesthetized rats fed a DHA-free α-LNA adequate diet, and published equations were used to calculate kinetic parameters. The conversion coefficient k(⁎) of DHA from α-LNA was much higher than for AA from LA (97.2×10(-3) vs. 10.6×10(-3)min(-1)), suggesting that liver elongation-desaturation is more selective for n-3 PUFA biosynthesis on a per molecule basis. The net daily secretion rate of DHA, 20.3μmol/day, exceeded the reported brain DHA consumption rate by 50-fold, suggesting that the liver can maintain brain DHA metabolism with an adequate dietary supply solely of α-LNA. This infusion method could be used in vegetarians or vegans to determine minimal daily requirements of EPA and DHA in humans.

Serum fatty acids, antioxidants, and treatment response in hepatitis C infection: greater polyunsaturated fatty acid and antioxidant levels in hepatitis C responders

BACKGROUND

Patients suffering from chronic hepatitis C (CHC) may exhibit impaired liver functions such as disturbances of fatty acid storage, synthesis and degradation.

OBJECTIVE

Possible associations between serum fatty acid (SFA) profiles, antioxidant status and treatment response were investigated in a trans-sectional study of untreated and treated CHC patients in comparison to a healthy control group.

METHODS

SFA composition and antioxidant status were examined in female patients with CHC: 9 were naïve to Interferon-α and ribavirin treatment (IFR), 21 sustained treatment responders, 21 were nonresponders, and 21 were healthy control group members. Additionally, in all CHC patients gammaglutamyl transferase (GGT), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured.

RESULTS

Responders and healthy control group members had significantly higher antioxidant (P < .001), eicosapentaenoic (P < .001) and arachidonic acid (P < .004) levels, but lower stearic acid (P < .001) concentrations than non-responders and untreated patients. ALT was higher in untreated CHC patients than in treated ones (P < .028). GGT and AST did not differ significantly between patient groups, however GGT levels were associated with serum Gamma-Linolenic-Acid concentration (P = .009).

CONCLUSION

SFA profiles and antioxidant status in female CHC patients differ markedly from those of healthy controls, a phenomenon which is possibly related with their effect of HCV replication.

Liver transplantation using fatty livers: always feasible?

Steatotic liver grafts represent the most common type of "extended criteria" organs that have been introduced during the last two decades due to the disparity between liver transplant candidates and the number available organs. A precise definition and reliable and reproducible method for steatosis quantification is currently lacking and the potential influence of the chemical composition of hepatic lipids has not been addressed. In our view, these shortcomings appear to contribute significantly to the inconsistent results of studies reporting on graft steatosis and the outcome of liver transplantation. In this review, various definitions, prevalence and methods of quantification of liver steatosis will be covered. Ischemia/reperfusion injury of the steatotic liver and its consequences on post-transplant outcome will be discussed. Selection criteria for organ allocation and a number of emerging protective strategies are suggested.

Protection against in vivo liver ischemia-reperfusion injury by n-3 long-chain polyunsaturated fatty acids in the rat

N-3 polyunsaturated fatty acids (n-3 PUFA) affect inflammatory processes. This study evaluated the effects of dietary supplementation with fish oil on hepatic ischemia-reperfusion (IR) injury in the rat. Parameters of liver injury (serum transaminases and histology) and oxidative stress (serum 8-isoprostanes and hepatic GSH and GSSG), were correlated with NF-kappaB DNA binding and FA composition and inflammatory cytokine release. N-3 PUFA supplementation significantly increased liver n-3 PUFA content and decreased n-6/n-3 PUFA ratios. IR significantly modified liver histology and enhanced serum transaminases, 8-isoprotanes and inflammatory cytokines, with net reduction in liver GSH levels and net increment in those of GSSG. Early increase (3 h) and late reduction (20 h) in NF-kappaB activity was induced. All IR-induced changes were normalized by n-3 PUFA supplementation. In conclusion, prevention of liver IR-injury was achieved by n-3 PUFA supplementation, with suppression of oxidative stress and recovery of pro-inflammatory cytokine homeostasis and NF-kappaB functionality lost during IR.

Omega-3 Long Chain Polyunsaturated Fatty Acids for Treatment of Parenteral Nutrition–Associated Liver Disease: A Review of the Literature

Parenteral nutrition–associated liver disease (PNALD) is a complex disease that is diagnosed by clinical presentation, biochemical markers of liver injury, concurrent use of parenteral nutrition (PN), and negative workup for other causes of liver disease. For the past 30 years, clinicians have had few effective treatments for PNALD and when disease progressed to liver cirrhosis it was historically associated with poor outcomes. Within the past 5 years there has been some encouraging evidence for the potential benefits of fish oils, rich in omega-3 long-chain polyunsaturated fatty acids (ω3PUFA), in reversing liver injury associated with PN. This article reviews the current literature relating to ω3PUFA and PNALD.

Isolation and analysis of bioactive constituents of sour cherry (Prunus cerasus) seed kernel: an emerging functional food

A plant-based diet reduces the risk for the development of several chronic diseases, such as ischemic heart disease or cancer due to natural compounds found in plants. Numerous cereals, berries, fruits, and vegetables, including sour cherry (Prunus cerasus), which is a favored fruit worldwide, contain biological active components. The antioxidant components of the sour cherry seed kernel have not been investigated until now. The aim of our study was to isolate and analyze the bioactive constituents of sour cherry seed kernel. We separated the oil fraction of the kernel; then the remaining solid fraction was dried, and the oil-free kernel extract was further analyzed. Our results show that sour cherry seed kernel oil contains vegetable oils including unsaturated fatty acids, oleic acids, alpha-tocopherol, tocotrienols, and tocopherol-like components. The components of the solid fraction include various bioactive structures such as polyphenols, flavonoids, vegetable acids, and pro- and anthocyanidins, which could have useful therapeutic effects in the prevention of various vascular diseases.

Treatment with omega-3 fatty acids but not exendin-4 improves hepatic steatosis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease in the Western world. The aim of this study was to evaluate the biochemical and histological effects of omega-3 fatty acid and exendin-4 treatment on NAFLD in an animal model.

METHODS

Sixty-three 8-week-old outbred Sprague-Dawley male rats were used for this study. Three animals were used as procedure controls, and 30 rats were fed a methionine and choline deficient (MCD) diet and 30 were fed a regular chow diet. In each group of 30 animals, 10 served as controls, 10 received exendin-4, and 10 received omega-3 fatty acids. After 75 days of treatment, the animals were euthanized, the tissues and serum were harvested, and the livers were formalin-fixed for histology.

RESULTS

The MCD diet was exceptionally efficient at producing fatty livers. The MCD control animals had a liver steatosis score of 38+/-6.7 (of 50 possible); treatment with exendin-4 was not associated with a significant reduction of steatosis (44+/-5.16, P=0.07) and the omega-3 fatty acid treatment was associated with a significant decrease in the liver steatosis score (15.6+/-13.46, P<0.001) compared with both the controls and the exendin-4 groups. The omega-3 fatty acid treatment increased serum aspartate aminotransferase significantly, whereas exendin-4 had no effect.

CONCLUSION

In an animal model of NAFLD, the omega-3 fatty acid therapy was associated with significant improvement in hepatic steatosis compared with exendin-4. These data suggest that omega-3 fatty acid supplements may have a potential therapeutic role in patients with NAFLD.

Quantifying conversion of linoleic to arachidonic and other n-6 polyunsaturated fatty acids in unanesthetized rats

Isotope feeding studies report a wide range of conversion fractions of dietary shorter-chain polyunsaturated fatty acids (PUFAs) to long-chain PUFAs, which limits assessing nutritional requirements and organ effects of arachidonic (AA, 20:4n-6) and docosahexaenoic (DHA, 22:6n-3) acids. In this study, whole-body (largely liver) steady-state conversion coefficients and rates of circulating unesterified linoleic acid (LA, 18:2n-6) to esterified AA and other elongated n-6 PUFAs were quantified directly using operational equations, in unanesthetized adult rats on a high-DHA but AA-free diet, using 2 h of intravenous [U-(13)C]LA infusion. Unesterified LA was converted to esterified LA in plasma at a greater rate than to esterified gamma-linolenic (gamma-LNA, 18:3n-6), eicosatrienoic acid (ETA, 20:3n-6), or AA. The steady-state whole-body synthesis-secretion (conversion) coefficient k*(i) to AA equaled 5.4 x 10(-3) min(-1), while the conversion rate (coefficient x concentration) equaled 16.1 micromol/day. This rate exceeds the reported brain AA consumption rate by 27-fold. As brain and heart cannot synthesize significant AA from circulating LA, liver synthesis is necessary to maintain their homeostatic AA concentrations in the absence of dietary AA. The heavy-isotope intravenous infusion method could be used to quantify steady-state liver synthesis-secretion of AA from LA under different conditions in rodents and in humans.

Review article: omega-3 fatty acids - a promising novel therapy for non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease affects 10-35% of the adult population worldwide; there is no consensus on its treatment. Omega-3 fatty acids have proven benefits for hyperlipidaemia and cardiovascular disease, and have recently been suggested as a treatment for non-alcoholic fatty liver disease.

AIMS

To review the evidence base for omega-3 fatty acids in non-alcoholic fatty liver disease and critically appraise the literature relating to human trials.

METHODS

A Medline and PubMed search was performed to identify relevant literature using search terms 'omega-3', 'N-3 PUFA', 'eicosapentaenoic acid', 'docosahexaenoic acid', 'non-alcoholic fatty liver disease' and 'NAFLD'.

RESULTS

Omega-3 fatty acids are important regulators of hepatic gene transcription. Animal studies demonstrate that they reduce hepatic steatosis, improve insulin sensitivity and reduce markers of inflammation. Clinical trials in human subjects generally confirm these findings, but have significant design inadequacies.

CONCLUSIONS

Omega-3 fatty acids are a promising treatment for non-alcoholic fatty liver disease which require to be tested in randomized placebo-controlled trials.

Nonalcoholic fatty liver disease: pathology and pathogenesis

Nonalcoholic fatty liver disease (NAFLD) is recognized as the leading cause of chronic liver disease in adults and children. NAFLD encompasses a spectrum of liver injuries ranging from steatosis to steatohepatitis with or without fibrosis. Fibrosis may progress to cirrhosis and complications including hepatocellular carcinoma. Histologic findings represent the complexity of pathophysiology. NAFLD is closely associated with obesity and is most closely linked with insulin resistance; the current Western diet, high in saturated fats and fructose, plays a significant role. There are several mechanisms by which excess triglycerides are acquired and accumulate in hepatocytes. Formation of steatotic droplets may be disordered in NAFLD. Visceral adipose tissue dysfunction in obesity and insulin resistance results in aberrant cytokine expression; many cytokines have a role in liver injury in NAFLD. Cellular stress and immune reactions, as well as the endocannabinoid system, have been implicated in animal models and in some human studies.

Classification of genes and putative biomarker identification using distribution metrics on expression profiles

Background

Identification of genes with switch-like properties will facilitate discovery of regulatory mechanisms that underlie these properties, and will provide knowledge for the appropriate application of Boolean networks in gene regulatory models. As switch-like behavior is likely associated with tissue-specific expression, these gene products are expected to be plausible candidates as tissue-specific biomarkers.

Methodology/Principal Findings

In a systematic classification of genes and search for biomarkers, gene expression profiles (GEPs) of more than 16,000 genes from 2,145 mouse array samples were analyzed. Four distribution metrics (mean, standard deviation, kurtosis and skewness) were used to classify GEPs into four categories: predominantly-off, predominantly-on, graded (rheostatic), and switch-like genes. The arrays under study were also grouped and examined by tissue type. For example, arrays were categorized as ‘brain group’ and ‘non-brain group’; the Kolmogorov-Smirnov distance and Pearson correlation coefficient were then used to compare GEPs between brain and non-brain for each gene. We were thus able to identify tissue-specific biomarker candidate genes.

Conclusions/Significance

The methodology employed here may be used to facilitate disease-specific biomarker discovery.

Methionine limitation results in increased hepatic FAS activity, higher liver 18:1 to 18:0 fatty acid ratio and hepatic TAG accumulation in Atlantic salmon, Salmo salar

The current experiment aimed to study whether interactions with lipid metabolism possibly might explain the relative increased liver weight obtained in fish fed sub-optimal methionine levels. A basal diet based on a blend of plant proteins which is low in methionine (1.6 g Met/16 g N) was compared to a methionine adequate diet (2.2 g Met/16 g N) prepared by adding DL-methionine (2.4 g/kg) to the basal diet in the expense of wheat grain. Fish oil was used as the lipid source. The diets were balanced in all nutrients except methionine. The diets were fed to Atlantic salmon (500 g BW) for a period of 3 months. Feed intake did not differ, rendering the intake of all nutrients except methionine equal. Fish fed the low methionine diet had an increased liver size relative to body weight, indicating fat deposition in the liver. Fish given the sub-optimal methionine diet showed about six times higher fatty acid synthase (FAS) activity as compared to the fish fed the adequate methionine diet, indicating a higher de novo lipogenesis. A significant rise in the liver 18:1 to 18:0 fatty acid ratios also supported storage of lipids over fatty acid oxidation. Indeed, methionine limitation resulted in significantly higher TAG concentrations in the liver. Sub-optimal dietary methionine also resulted in lower hepatic taurine concentrations and the total bile acids concentrations were reduced in faeces and tended to be reduced in plasma. Taken together, our data show that salmon fed sub-optimal methionine levels had increased relative liver weight and developed signs commonly described in the early stage of non-alcoholic fatty liver disease in rodent models (increased FAS activity, changed fatty acid ratios and TAG accumulation).

Assessment of hepatic steatosis by expert pathologists: the end of a gold standard

BACKGROUND

The presence of fat in the liver is considered a major risk for postoperative complication after liver surgery and transplantation. The current standard of quantification of hepatic steatosis is microscopic evaluation by pathologists, although consistency in such assessment remains unclear. Computerized image analysis is an alternative method for objective assessment of the degree of hepatic steatosis.

METHODS

High resolution images of hematoxylin and eosin stained liver sections from 46 consecutive patients, initially diagnosed with liver steatosis, were blindly assessed by 4 established expert pathologists from different institutions. Computerized analysis was carried out simultaneously on the same sections. Interobserver agreement and correlation between the pathologists' and computerized assessment were evaluated using intraclass correlation coefficients (ICC), Spearman rank correlation coefficients, or descriptive statistics.

RESULTS

Poor agreement among pathologists (ICC: 0.57) was found regarding the assessment of total steatosis, (ICC >0.7 indicates acceptable agreement). Pathologists' estimation of micro- and macrosteatosis disclosed also poor correlation (ICC: 0.22, 0.55, respectively). Inconsistent assessment of histological features of steatohepatitis (lobular inflammation, portal inflammation, hepatocyte ballooning, and Mallory hyaline) was documented. Poor conformity was also shown between the computerized quantification and ratings of 3 pathologists (Spearman rank correlation coefficients: 0.22, 0.82, 0.28, and 0.38).

CONCLUSION

Quantification of hepatic steatosis in histological sections is strongly observer-dependent, not reproducible, and does not correlate with the computerized estimation. Current standards of assessment, previously published data and the clinical relevance of hepatic steatosis for liver surgery and transplantation must be challenged.

Response to Fasting in an Unnaturally Obese Carnivore, the Captive European Polecat Mustela putorius

The European polecat ( Mustela putorius) is a naturally lean carnivore prone to excessive weight gain in captivity. This study assessed its suitability to investigate the natural history of the obese phenotype displayed in overweight humans, domestic animals, and seasonally obese wild mammals. Ten farm-bred polecats were subjected to a 5-day fast with 10 controls. Obesity (40% body fat) was associated with an unfavorable plasma lipid profile and high glucose and insulin concentrations. The polecats were in phase II of fasting with normoglycemia, low liver carbohydrate stores, and decreased plasma concentrations of urea and most amino acids. Although the plasma nonesterified fatty acid (NEFA) levels were elevated, the adipose tissue lipase activities suggested a blunted lipolytic response. Lipid mobilization was more efficient from intraabdominal fat. The animals developed hepatic lipidosis with elevated NEFA influx into the liver and losses of n-3 polyunsaturated fatty acids and arginine as hypothetical etiological factors. The plasma leptin, insulin, and triiodothyronine levels decreased but were not accompanied by reduced sex steroid or increased stress hormone concentrations. The blunted lipolytic response often encountered in obesity suggests that the organism is trying to defend the obese phenotype. Liver lipidosis and decreased insulin and triiodothyronine levels seem to be among the most consistent responses to fasting manifested in diverse mammalian orders and different levels of body fatness. The polecat could be recommended as an easily accessible carnivorean model to study the natural history of the obese phenotype and its comorbidities.

n-3 and n-6 Polyunsaturated fatty acids suppress sterol regulatory element binding protein activity and increase flow of non-esterified cholesterol in HepG2 cells

The plasma lipid-lowering effect of PUFA, one of their main beneficial effects, is considered to be related to the regulation of lipid biosynthesis through transcription factors including sterol regulatory element binding proteins (SREBP). In the present study, we compared the effect of different PUFA on SREBP activity in HepG2 cells, using a sterol regulatory element–luciferase reporter construct as a probe. Supplementation with different fatty acids reduced SREBP activity in the order 20 : 5n-3 = 18 : 2n-6 = 20 : 4n-6≫18 : 3n-3 = 22 : 6n-3 = 22 : 5n-6≫18 : 1n-9. The suppression of SREBP activity greatly depended on the degree of incorporation of the supplemented PUFA into cellular lipids, and correlated positively with the unsaturation index (r 0·831; P < 0·01) of total cell lipids. Supplemented PUFA were also metabolised to longer and more unsaturated species. These processing activities were higher for n-3 than n-6 PUFA (P < 0·01). We studied the effect of PUFA on the intracellular distribution of non-esterified cholesterol, using filipin staining and fluorescence microscopy with or without the cholesterol traffic blocker U18666A. The data show that the incorporation of PUFA increases non-esterified cholesterol flow from the plasma membrane to intracellular membranes. We conclude that suppression of SREBP activity by PUFA depends on the degree of incorporation into cellular lipids, and is associated with increased flow of non-esterified cholesterol between the plasma membrane and intracellular membranes.

A role for complement in the enhanced susceptibility of steatotic livers to ischemia and reperfusion injury

Hepatic steatosis typically renders the donor organ unusable, as donor organs with >30% steatosis are more likely to develop graft failure. The mechanisms leading to failure are not well defined, but steatosis enhances hepatic susceptibility to ischemia reperfusion injury (IRI). We investigated the role of complement in hepatic IRI in lean and steatotic (diet-induced) mice. Steatotic mice were significantly more susceptible to total warm hepatic IRI than lean mice as determined by serum alanine aminotransferase, histopathologically assessed damage, and 24-h survival. C3 deficiency protected both lean and steatotic mice from IRI, as determined by all measured outcomes. Furthermore, treatment of wild-type mice with the complement inhibitor CR2-Crry provided protection equivalent to that seen in C3-deficient mice. Importantly, although steatotic livers were much more susceptible to IRI than lean livers, by most measures there was no statistical difference between the level of IRI to steatotic or lean livers when complement was inhibited. To investigate the clinical relevance of these findings in the context of transplantation, we treated recipients of lean or steatotic liver grafts with saline or CR2-Crry. There was a marked reduction in graft inflammation and injury and significantly improved 7-day survival in CR2-Crry-treated recipients of either lean or steatotic grafts. These data indicate that complement plays a key role in the enhanced susceptibility of steatotic livers to IRI and suggest that complement inhibition represents a potential strategy to reduce the donor shortage by allowing the more routine use of marginal steatotic donor livers.

Effects of n-3 polyunsaturated fatty acids from seal oils on nonalcoholic fatty liver disease associated with hyperlipidemia

AIM: To investigate the efficacy and safety of n-3 polyunsaturated fatty acids (PUFA) from seal oils for patients with nonalcoholic fatty liver disease (NAFLD) associated with hyperlipidemia.

METHODS: One hundred and forty-four patients with NAFLD associated with hyperlipidemia were included in the 24-wk, randomized, controlled trial. The patients were randomized into two groups. Group A (n = 72) received recommended diet and 2 g n-3 PUFA from seal oils, three times a day. Group B (n = 72) received recommended diet and 2 g placebo, three times a day. Primary endpoints were fatty liver assessed by symptom scores, liver alanine aminotransferase (ALT) and serum lipid levels after 8, 12, 16, and 24 wk. Hepatic fat infiltration was detected by ultrasonography at weeks 12 and 24 after treatment.

RESULTS: A total of 134 patients (66 in group A, 68 in group B) were included in the study except for 10 patients who were excluded from the study. After 24 wk of treatment, no change was observed in body weight, fasting blood glucose (FBG), renal function and blood cells of these patients. Total symptom scores, ALT and triglyceride (TG) levels decreased more significantly in group A than in group B (P < 0.05). As expected, there was a tendency toward improvement in aspartate aminotransferase (AST), γ-glutamyltranspeptidase (GGT), and total cholesterol (TCHO) and high-density lipoprotein (HDL) cholesterol levels (P < 0.05) after administration in the two groups. However, no significant differences were found between the two groups. The values of low-density lipoprotein (LDL) were significantly improved in group A (P < 0.05), but no significant change was found in group B at different time points and after a 24-wk treatment. After treatment, complete fatty liver regression was observed in 19.70% (13/66) of the patients, and an overall reduction was found in 53.03% (35/66) of the patients in group A. In contrast, in group B, only five patients (7.35%, 5/68) achieved complete fatty liver regression (P = 0.04), whereas 24 patients (35.29%, 24/68) had a certain improvement in fatty liver (P = 0.04). No serious adverse events occurred in all the patients who completed the treatment.

CONCLUSION: Our results indicate that n-3 PUFA from seal oils is safe and efficacious for patients with NAFLD associated with hyperlipidemia and can improve their total symptom scores, ALT, serum lipid levels and normalization of ultrasonographic evidence. Further study is needed to confirm these results.

Nutrition and nonalcoholic fatty liver disease in children

Nonalcoholic fatty liver disease (NAFLD) is an obesity-associated liver disease found in 3% to 9% of children in the United States. NAFLD represents a spectrum of liver disease and is frequently associated with features of the metabolic syndrome. Nutrition's role in NAFLD is complex. It does not appear that overweight children with NAFLD have an unusual diet compared with their overweight counterparts without NAFLD. It is more likely that they have increased genetic susceptibility to the general poor diet and state of positive calorie balance currently found in many children. The available treatment studies using nutrition counseling and increased physical activity are promising. We recommend initiating sustainable family-oriented lifestyle changes in all children with NAFLD.

Nutrition and nonalcoholic fatty liver disease in children

Nonalcoholic fatty liver disease (NAFLD) is an obesity-associated liver disease found in 3% to 9% of children in the United States. NAFLD represents a spectrum of liver disease and is frequently associated with features of the metabolic syndrome. Nutrition's role in NAFLD is complex. It does not appear that overweight children with NAFLD have an unusual diet compared with their overweight counterparts without NAFLD. It is more likely that they have increased genetic susceptibility to the general poor diet and state of positive calorie balance currently found in many children. The available treatment studies using nutrition counseling and increased physical activity are promising. We recommend initiating sustainable family-oriented lifestyle changes in all children with NAFLD.

Flaxseed oil prevents trans-10, cis-12-conjugated linoleic acid-induced insulin resistance in mice

Insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD) are found in 35 and 30 % of US adults, respectively. Trans-10, cis-12-conjugated linoleic acid (CLA) has been found to cause both these disorders in several animal models. We hypothesised that IR and NAFLD caused by CLA result from n-3 fatty acid deficiency. Pathogen-free C57BL/6N female mice (aged 8 weeks; n 10) were fed either a control diet or diets containing trans-10, cis-12-CLA (0.5 %) or CLA+flaxseed oil (FSO) (0.5 %+0.5 %) for 8 weeks. Weights of livers, concentration of circulating insulin, values of homeostatic model 1 (HOMA1) for IR and HOMA1 for beta cell function were higher by 160, 636, 985 and 968 % in the CLA group compared with those in the control group. FSO decreased fasting glucose by 20 % and liver weights by 37 % compared with those in the CLA group; it maintained circulating insulin, HOMA1-IR and HOMA1 for beta cell function at levels found in the control group. CLA supplementation decreased n-6 and n-3 wt% concentrations of liver lipids by 57 and 73 % and increased the n-6:n-3 ratio by 58 % compared with corresponding values in the control group. FSO increased n-6 and n-3 PUFA in liver lipids by 33 and 342 % and decreased the n-6:n-3 ratio by 70 % compared with corresponding values in the CLA group. The present results suggest that some adverse effects of CLA may be due to n-3 PUFA deficiency and that these can be corrected by a concomitant increase in the intake of alpha-linolenic acid, 18 : 3n-3.

Is liver fat detrimental to vessels?: intersections in the pathogenesis of NAFLD and atherosclerosis

NAFLD (non-alcoholic fatty liver disease) encompasses the spectrum of fatty liver disease in insulin-resistant individuals who often display T2DM (Type 2 diabetes mellitus) and obesity. The present review highlights the pathophysiological basis and clinical evidence for a possible causal linkage between NAFLD and CVD (cardiovascular disease). The role of traditional and non-traditional CVD risk factors in the pathophysiology of NAFLD is considered in the first part of the review, with the basic science shared by atherogenesis and hepatic steatogenesis discussed in depth in the second part. In conclusion, NAFLD is not an innocent bystander, but a major player in the development and progression of CVD. NAFLD and CVD also share similar molecular mechanisms and targeted treatment strategies. On the research side, studies should focus on interventions aimed at restoring energy homoeostasis in lipotoxic tissues and at improving hepatic (micro)vascular blood supply.

Fatty acids metabolic profile in high fat diet-induced non-alcoholic fatty liver disease in rats

AIM: To analyze fatty acid metabolic profile changes of fatty livers induced by a high fat diet and to determine it's role in non-alcoholic steatohepatitis (NASH).

METHODS: Sprague-Dawley rats were randomly divided into two groups: the control group (treated with normal diet, n = 7) and the model group (treated with high fat diet, n = 7). The rats were all killed at wk 16 to detect pathological changes in liver tissues. The metabolic profile changes of fatty acid in NASH and normal liver tissue samples were detected by ECF derivatization for GC/MS technology. Data were analyzed using SPSS 11.0 software package.

RESULTS: After a high fat diet for 16 wk, severe fatty livers (+++) were present in the high fat diet group with remarkable inflammation. A significant morphological difference was detected between the two groups. Total ion current (TIC) and principal component analysis (PCA) indicated that there were significantly different metabolic patterns in liver tissues between the two groups. Compared with the control group, all fatty acids were raised significantly except a 56% decrease in dodecanoic acid (P < 0.05). Octadecanoic acid, tetradecanoic acid, hexadecanoic acid, eicosanoic acid, 9-octadecenoic acid, 9, 12, 15-octadecatrienoic acid, 5, 8, 11, 14-eicosatetraenoic acid and 9, 12-octadecadienoic acid were raised 5.42, 4.10, 11.56, 5.86, 1.82 and 8.00, 2.44-folds, respectively. Moreover, ω-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio was raised.

CONCLUSION: Our results suggest that there are significant fatty acids metabolic profile changes in NASH. Excessive fatty acids accumulation in hepatic cells, ω-6/ω-3 ratio imbalance and dudecanoic acid decrease may pay a crucial role in steatohepatitis and hepatic injury.