Polyunsaturated fatty acid deficiency reverses effects of alcohol on mitochondrial energy metabolism

Effect of physiological hyperthermia on mitochondrial fuel selection in skeletal muscle of birds and mammals

Both birds and mammals have important thermogenic capacities allowing them to maintain high body temperatures, i.e., 37 °C and 40 °C on average in mammals and birds, respectively. However, during periods of high locomotor activity, the energy released during muscular contraction can lead to muscle temperature reaching up to 43-44 °C. Mitochondria are responsible for producing the majority of ATP through cellular respiration and metabolizing different substrates, including carbohydrates and lipids, to generate ATP. A limited number of studies comparing avian and mammalian species showed preferential utilization of specific substrates for mitochondrial energy at different metabolic intensities, but authors always measured at body temperature. The present study evaluated mitochondrial respiration rates and OXPHOS coupling efficiencies at 37 °C, 40 °C and 43 °C associated with pyruvate/malate (carbohydrate metabolism) or palmitoyl-carnitine/malate (lipid metabolism) as substrates in pigeons (Columba livia) and rats (Rattus norvegicus), a well-known pair in scientific literature and for their similar body mass. The data show different hyperthermia-induced responses between the two species with (i) skeletal muscle mitochondria from rats being more sensitive to rising temperatures than in pigeons, and (ii) the two species having different substrate preferences during hyperthermia, with rats oxidizing preferentially carbohydrates and pigeons lipids. By analyzing the interplay between temperature and substrate utilization, we describe a means by which endotherms deal with extreme muscular temperatures to provide enough ATP to support energy demands.

High-fat diet promotes multiple binges-induced liver injury via promoting hepatic macrophage proinflammatory polarization

High-fat diet (HFD) and ethanol could synergistically induce liver damage, but the underlying mechanisms remain to be elucidated. M1-polarized macrophages have been demonstrated to be key players in ethanol-induced liver damage. The current study was designed to investigate whether hepatic steatosis could promote ethanol-induced liver injury by promoting liver macrophage M1 polarization. In the in vivo study, 12 weeks of HFD feeding induced a moderate increase in the F4/80 expression and protein levels of p-IKKα/β, p-IκBα, and p-p65, which was suppressed by single binge. In contrast, 8 weeks of HFD and multiple binges (two binges per week during the last 4 weeks) synergistically increased the F4/80 expression, mRNA levels of M1 polarization biomarkers including Ccl2, Tnfa, and Il1b, and protein levels of p65, p-p65, COX2, and Caspase 1. In the in vitro study, a nontoxic free fatty acids (FFAs) mixture (oleic acid/palmitic acid = 2: 1) induced a moderate increase of protein levels of p-p65 and NLRP3 in murine AML12 hepatocytes, which was inhibited by ethanol co-exposure. Ethanol alone induced proinflammatory polarization of murine J774A.1 macrophages evidenced by the enhanced secretion of TNF-α, increased mRNA levels of Ccl2, Tnfa, and Il1b, and upregulated protein levels of p65, p-p65, NLRP3, and Caspase 1, which was augmented by FFAs exposure. Collectively, these results suggest that HFD and multiple binges could synergistically induce liver damage by promoting the proinflammatory activation of macrophages in mice livers.

Dietary PUFAs drive diverse system-level changes in lipid metabolism

OBJECTIVE

Polyunsaturated fatty acid (PUFA) supplements have been trialled as a treatment for a number of conditions and produced a variety of results. This variety is ascribed to the supplements, that often comprise a mixture of fatty acids, and to different effects in different organs. In this study, we tested the hypothesis that the supplementation of individual PUFAs has system-level effects that are dependent on the molecular structure of the PUFA.

METHODS

We undertook a network analysis using Lipid Traffic Analysis to identify both local and system-level changes in lipid metabolism using publicly available lipidomics data from a mouse model of supplementation with FA(20:4n-6), FA(20:5n-3), and FA(22:6n-3); arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, respectively. Lipid Traffic Analysis is a new computational/bioinformatics tool that uses the spatial distribution of lipids to pinpoint changes or differences in control of metabolism, thereby suggesting mechanistic reasons for differences in observed lipid metabolism.

RESULTS

There was strong evidence for changes to lipid metabolism driven by and dependent on the structure of the supplemented PUFA. Phosphatidylcholine and triglycerides showed a change in the variety more than the total number of variables, whereas phosphatidylethanolamine and phosphatidylinositol showed considerable change in both which variables and the number of them, in a highly PUFA-dependent manner. There was also evidence for changes to the endogenous biosynthesis of fatty acids and to both the elongation and desaturation of fatty acids.

CONCLUSIONS

These results show that the full biological impact of PUFA supplementation is far wider than any single-organ effect and implies that supplementation and dosing with PUFAs require a system-level assessment.

Metabolomics Study of Serum from a Chronic Alcohol-Fed Rat Model Following Administration of Defatted Tenebrio molitor Larva Fermentation Extract

We have previously showed that defatted mealworm fermentation extract (MWF) attenuates alcoholic liver injury by regulating lipid, inflammatory, and antioxidant metabolism in chronic alcohol-fed rats. The current metabolomics study was performed to monitor biochemical events following the administration of MWF (daily for eight weeks) to a rat model of alcoholic liver injury by gas chromatography-tandem mass spectrometry (GC-MS/MS). The levels of 15 amino acids (AAs), 17 organic acids (OAs), and 19 free fatty acids (FFAs) were measured in serum. Analysis of variance (ANOVA), principal component analysis (PCA), and partial least squares discriminant analysis (PLS-DA) were used to compare the levels of 51 metabolites in serum. In particular, 3-hydroxybutyric acid (3-HB), pyroglutamic acid (PG), octadecanoic acid, and docosahexaenoic acid (DHA) were evaluated as high variable importance point (VIP) scores and PCA loading scores as determined by PLS-DA and PCA, and these were significantly higher in the MWF and silymarin groups than in the EtOH group. MWF showed a protective effect from alcohol-induced liver damage by elevating hepatic β-oxidation activity, and serum 3-HB levels were significantly higher in the MWF group than in the EtOH control group. Glycine levels were higher in the MWF group than in the EtOH group, and PG levels (related to glutathione production) were also elevated, indicating a reduction in alcohol-related oxidative stress. In addition, MWF is protected from alcohol-induced inflammation and steatosis by increasing serum DHA, palmitic, and octadecanoic acid levels as compared with the EtOH group. These results suggest that MWF might attenuate alcoholic liver disease, due to its anti-inflammatory and antioxidant effects by up-regulating hepatic β-oxidation activity and down-regulating liver FFA uptake.

Targeting n-3 Polyunsaturated Fatty Acids in Non-Alcoholic Fatty Liver Disease

BACKGROUND

Non-Alcoholic Fatty Liver Disease (NAFLD) is characterized by abnormal hepatic accumulation of triacylglycerides in the absence of alcohol consumption, in association with Oxidative Stress (OS), a pro-inflammatory state and Insulin Resistance (IR), which are attenuated by n-3 long-chain polyunsaturated Fatty Acids (FAs) C20-C22 (LCPUFAs) supplementation. Main causes of NAFLD comprise high caloric intake and a sedentary lifestyle, with high intakes of saturated FAs.

METHODS

The review includes several searches considering the effects of n-3 LCPUFAs in NAFLD in vivo and in vitro models, using the PubMed database from the National Library of Medicine- National Institutes of Health.

RESULT

The LCPUFAs eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n- 3, DHA) have a positive effect in diminishing liver steatosis, OS, and the levels of aspartate aminotransferase, alanine aminotransferase and pro-inflammatory cytokines, with improvement of insulin sensitivity and adiponectin levels. The molecular pathways described for n-3 LCPUFAs in cellular and animal models and humans include peroxisome proliferator-activated receptor-α activation favouring FA oxidation, diminution of lipogenesis due to sterol responsive element binding protein-1c downregulation and inflammation resolution. Besides, nuclear factor erythroid-2-related factor-2 activation is elicited by n-3 LCPUFA-derived oxidation products producing direct and indirect antioxidant responses, with concomitant anti-fibrogenic action.

CONCLUSION

The discussed effects of n-3 LCPUFA supplementation support its use in NAFLD, although having a limited value in NASH, a contention that may involve n-3 LCPUFA oxygenated derivatives. Clinical trials establishing optimal dosages, intervention times, type of patients and possible synergies with other natural products are needed in future studies.

Effects of membrane fatty acid composition on cellular metabolism and oxidative stress in dermal fibroblasts from small and large breed dogs

There is ample evidence that cell membrane architecture contributes to metabolism and aging in animals; however, the aspects of this architecture that determine the rate of metabolism and longevity are still being debated. The 'membrane pacemaker' hypothesis of metabolism and of aging, respectively, suggest that increased lipid unsaturation and large amounts of polyunsaturated fatty acids (PUFAs) in cell membranes increase the cellular metabolic rate as well as the vulnerability of the cell to oxidative damage, thus increasing organismal metabolic rate and decreasing longevity. Here, we tested these hypotheses by experimentally altering the membrane fatty acid composition of fibroblast cells derived from small and large breed dogs by incubating them in a medium enriched in the monounsaturated fatty acid (MUFA) oleic acid (OA, 18:1) to decrease the total saturation. We then measured cellular metabolic parameters and correlated these parameters with membrane fatty acid composition and oxidative stress. We found that cells from small dogs and OA-incubated cells had lower maximal oxygen consumption and basal oxygen consumption rates, respectively, which are traits associated with longer lifespans. Furthermore, although we did not find differences in oxidative stress, cells from small dogs and OA-treated cells exhibited reduced ATP coupling efficiency, suggesting that these cells are less prone to producing reactive oxygen species. Membrane fatty acid composition did not differ between cells from large and small dogs, but cells incubated with OA had more monounsaturated fatty acids and a higher number of double bonds overall despite a decrease in PUFAs. Our results suggest that increasing the monounsaturation of dog cell membranes may alter some metabolic parameters linked to increases in longevity.

Insulin resistance in clinical and experimental alcoholic liver disease

Alcoholic liver disease (ALD) is the number one cause of liver failure worldwide; its management costs billions of healthcare dollars annually. Since the advent of the obesity epidemic, insulin resistance (IR) and diabetes have become common clinical findings in patients with ALD; and the development of IR predicts the progression from simple steatosis to cirrhosis in ALD patients. Both clinical and experimental data implicate the impairment of several mediators of insulin signaling in ALD, and experimental data suggest that insulin-sensitizing therapies improve liver histology. This review explores the contribution of impaired insulin signaling in ALD and summarizes the current understanding of the synergistic relationship between alcohol and nutrient excess in promoting hepatic inflammation and disease.

Interactions of ethanol drinking withn-3 fatty acids in rats: potential consequences for the cardiovascular system

Moderate ethanol drinking (ED) andn-3 fatty acids have both been associated with low cardiac mortality. However, there are few data evaluating the interactions of ED withn-3. We recently reported that moderate ED results in increasedn-3 in cardiac patients. The main aim of the present study was, through a well-controlled experimental model, to confirm that chronic ED actually results in increasedn-3. Secondary aims were to examine the effects of chronic ED on cardiac mitochondria, cardiac function and experimental myocardial infarction. We studied the fatty acid profiles of plasma, cell membranes and cardiac mitochondria phospholipids in a rat model of chronic ED. In plasma and cell membranes, ED actually resulted in highern-3 (P = 0·005). In mitochondria phospholipids of ED rats,n-3 were also increased (P < 0·05) but quite modestly. Cardiac mitochondrial function and left ventricular function were not significantly different in ED and control rats, while infarct size after 30 min ischaemia and reperfusion was smaller (P < 0·0001) in ED rats. This is the first animal study confirming interaction of alcohol drinking withn-3. We found no harmful effect of chronic ED on the heart in that model but a significant cardioprotection. Further studies are warranted to investigate the mechanisms by which moderate ED alters the metabolism ofn-3 and whethern-3 are the mediators of the ED-induced cardioprotection.

Synergistic toxicity of ethanol and MDMA towards primary cultured rat hepatocytes

Ethanol is frequently consumed along with 3,4-methylenedioxymethamphetamine (MDMA; ecstasy). Since both compounds are hepatotoxic and are metabolized in the liver, an increased deleterious interaction resulting from the concomitant use of these two drugs seems plausible. Another important feature of MDMA-induced toxicity is hyperthermia, an effect known to be potentiated after continuous exposure to ethanol. Considering the potential deleterious interaction, the aim of the present study was to evaluate the hepatotoxic effects of ethanol and MDMA mixtures to primary cultured rat hepatocytes and to elucidate the mechanism(s) underlying this interaction. For this purpose, the toxicity induced by MDMA to primary cultured rat hepatocytes in absence or in presence of ethanol was evaluated, under normothermic (36.5 degrees C) and hyperthermic (40.5 degrees C) conditions. While MDMA and ethanol, by themselves, had discrete effects on the analysed parameters, which were slightly aggravated under hyperthermia, the simultaneous incubation of MDMA and ethanol for 24h, resulted in high cell death ratios accompanied by a significant disturbance of cellular redox status and decreased energy levels. Evaluation of apoptotic/necrotic features provided clear evidences that the cell death occurs preferentially through a necrotic pathway. All the evaluated parameters were dramatically aggravated when cells were incubated under hyperthermia. In conclusion, co-exposure of hepatocytes to ethanol and MDMA definitely results in a synergism of the hepatotoxic effects, through a disruption of the cellular redox status and enhanced cell death by a necrotic pathway in a temperature-dependent extent.

Mitochondrial adaptations to steatohepatitis induced by a methionine- and choline-deficient diet

Nonalcoholic fatty liver disease (NAFLD) has become common liver disease in Western countries. There is accumulating evidence that mitochondria play a key role in NAFLD. Nevertheless, the mitochondrial consequences of steatohepatitis are still unknown. The bioenergetic changes induced in a methionine- and choline-deficient diet (MCDD) model of steatohepatitis were studied in rats. Liver mitochondria from MCDD rats exhibited a higher rate of oxidative phosphorylation with various substrates, a rise in cytochrome oxidase (COX) activity, and an increased content in cytochrome aa3. This higher oxidative activity was associated with a low efficiency of the oxidative phosphorylation (ATP/O, i.e., number of ATP synthesized/natom O consumed). Addition of a low concentration of cyanide, a specific COX inhibitor, restored the efficiency of mitochondria from MCDD rats back to the control level. Furthermore, the relation between respiratory rate and protonmotive force (in the nonphosphorylating state) was shifted to the left in mitochondria from MCDD rats, with or without cyanide. These results indicated that, in MCDD rats, mitochondrial ATP synthesis efficiency was decreased in relation to both proton pump slipping at the COX level and increased proton leak although the relative contribution of each phenomenon could not be discriminated. MCDD mitochondria also showed a low reactive oxygen species production and a high lipid oxidation potential. We conclude that, in MCDD-fed rats, liver mitochondria exhibit an energy wastage that may contribute to limit steatosis and oxidative stress in this model of steatohepatitis.

Role of adiponectin in the protective action of dietary saturated fat against alcoholic fatty liver in mice

The protective effect of dietary saturated fatty acids against the development of alcoholic liver disease has long been known, but the underlying mechanism is not completely understood. We examined the involvement of the adipocyte hormone adiponectin. Circulating adiponectin levels were significantly elevated by chronic ethanol administration to mice consuming a diet high in saturated fat. The increase in circulating adiponectin was associated with the activation a set of hepatic signaling pathways mediated through AMP-activated protein kinase, PPAR-alpha, and PPAR-gamma coactivator alpha, which in turn led to markedly increased rates of fatty acid oxidation, prevention of hepatic steatosis, and alleviation of liver enzyme changes. Furthermore, treatment of rat 3T3-L1 adipocytes with saturated fatty acids (palmitic or stearic acids) in the presence of ethanol increased secretion of adiponectin and enhanced activity of a mouse adiponectin promoter. In conclusion, the protective action of saturated fat against the development of alcoholic fatty liver in mice is partially mediated through induction of adiponectin. The present findings suggest a novel paradigm for dietary fatty acids in the pathogenesis of alcoholic liver disease and provide a promising therapeutic strategy-nutritional modulation of adiponectin-in treating human alcoholic fatty liver disease.