A decreased n-6/n-3 ratio in the fat-1 mouse is associated with improved glucose tolerance

Changes Induced by Aging and Long-Term Exercise and/or DHA Supplementation in Muscle of Obese Female Mice

Obesity and aging promote chronic low-grade systemic inflammation. The aim of the study was to analyze the effects of long-term physical exercise and/or omega-3 fatty acid Docosahexaenoic acid (DHA) supplementation on genes or proteins related to muscle metabolism, inflammation, muscle damage/regeneration and myokine expression in aged and obese mice. Two-month-old C57BL/6J female mice received a control or a high-fat diet for 4 months. Then, the diet-induced obese (DIO) mice were distributed into four groups: DIO, DIO + DHA, DIO + EX (treadmill training) and DIO + DHA + EX up to 18 months. Mice fed a control diet were sacrificed at 2, 6 and 18 months. Aging increased the mRNA expression of Tnf-α and decreased the expression of genes related to glucose uptake (Glut1, Glut4), muscle atrophy (Murf1, Atrogin-1, Cas-9) and myokines (Metrnl, Il-6). In aged DIO mice, exercise restored several of these changes. It increased the expression of genes related to glucose uptake (Glut1, Glut4), fatty acid oxidation (Cpt1b, Acox), myokine expression (Fndc5, Il-6) and protein turnover, decreased Tnf-α expression and increased p-AKT/AKT ratio. No additional effects were observed when combining exercise and DHA. These data suggest the effectiveness of long-term training to prevent the deleterious effects of aging and obesity on muscle dysfunction.

Maternal Fat-1 Transgene Protects Offspring from Excess Weight Gain, Oxidative Stress, and Reduced Fatty Acid Oxidation in Response to High-Fat Diet

Overweight and obesity accompanies up to 70% of pregnancies and is a strong risk factor for offspring metabolic disease. Maternal obesity-associated inflammation and lipid profile are hypothesized as important contributors to excess offspring liver and skeletal muscle lipid deposition and oxidative stress. Here, we tested whether dams expressing the fat-1 transgene, which endogenously converts omega-6 (n-6) to omega-3 (n-3) polyunsaturated fatty acid, could protect wild-type (WT) offspring against high-fat diet induced weight gain, oxidative stress, and disrupted mitochondrial fatty acid oxidation. Despite similar body mass at weaning, offspring from fat-1 high-fat-fed dams gained less weight compared with offspring from WT high-fat-fed dams. In particular, WT males from fat-1 high-fat-fed dams were protected from post-weaning high-fat diet induced weight gain, reduced fatty acid oxidation, or excess oxidative stress compared with offspring of WT high-fat-fed dams. Adult offspring of WT high-fat-fed dams exhibited greater skeletal muscle triglycerides and reduced skeletal muscle antioxidant defense and redox balance compared with offspring of WT dams on control diet. Fat-1 offspring were protected from the reduced fatty acid oxidation and excess oxidative stress observed in offspring of WT high-fat-fed dams. These results indicate that a maternal fat-1 transgene has protective effects against offspring liver and skeletal muscle lipotoxicity resulting from a maternal high-fat diet, particularly in males. Altering maternal fatty acid composition, without changing maternal dietary composition or weight gain with high-fat feeding, may highlight important strategies for n-3-based prevention of developmental programming of obesity and its complications.

Endurance Training Counteracts the High-Fat Diet-Induced Profiling Changes of ω-3 Polyunsaturated Fatty Acids in Skeletal Muscle of Middle-Aged Rats

Purpose

To investigate the effects of endurance training on the content of ω-3 polyunsaturated fatty acids (PUFAs) and their distribution among lipid classes in skeletal muscle in middle aged, high-fat diet fed rats.

Method

Thirty 10-month old male Sprague Dawley (SD) rats were assigned to four groups. Two groups of rats remained sedentary and were fed chow diet (C group), or high-fat diet (H group), respectively. The other two groups of rats were subjected to endurance training while maintaining their chow diet (EC group), or high-fat diet (EH group). After 16 weeks endurance training and/or diet intervention, the content of ω-3 PUFAs and ω-3 PUFA-containing lipids in rat soleus muscle were analyzed by lipidomics.

Results

Rats fed a high-fat diet exhibited decreased overall amount of ω-3 PUFAs in soleus muscle, while endurance training preserved the total amount of ω-3 PUFAs. Both the endurance training and high-fat diet alone changed the profiles of ω-3 PUFAs in different lipid classes. Specifically, the amount of triacylglycerol (TG), lysophosphatidylcholine (LPC), phosphatidylcholine (PC), and phosphatidylglycerol (PG) containing ω-3 PUFAs in soleus muscle was increased by endurance training, but the amount of lysophosphatidylenthanol (LPE), lysophosphatidylinositol (LPI), lysophosphatidylserine (LPS), cardiolipin (CL), phosphatidic acid (PA), and phosphatidylinositol (PI) was decreased. The high-fat diet induced a decrease of ω-3 PUFAs in TG, LPE, LPS, CL, platelet activating factor (PAF), PC, phosphatidylethanolamine (PE), and phosphatidylserine (PS), and an increase in LPC, LPI, PA, and PG. In addition, the effects of the endurance training on ω-3 PUFAs in skeletal muscle was also evident in high-fat diets fed rats, which counteracts the profiling changes caused by high-fat diet feeding.

Conclusion

The beneficial effects of endurance training on skeletal muscle may be achieved to some extent through recovering the content of ω-3 PUFAs that has been decreased by high-fat diet feeding.

Defining lipid mediators of insulin resistance - controversies and challenges

Essential elements of all cells, lipids play important roles in energy production, signalling and as structural components. Despite these critical functions, excessive availability and intracellular accumulation of lipid is now recognised as a major factor contributing to many human diseases, including obesity and diabetes. In the context of these metabolic disorders, ectopic deposition of lipid has been proposed to have deleterious effects of insulin action. While this relationship has been recognised for some time now, there is currently no unifying mechanism to explain how lipids precipitate the development of insulin resistance. This review summarises the evidence linking specific lipid molecules to the induction of insulin resistance, describing some of the current controversies and challenges for future studies in this field.

Association of muscle lipidomic profile with high-fat diet-induced insulin resistance across five mouse strains

Different mouse strains exhibit variation in their inherent propensities to develop metabolic disease. We recently showed that C57BL6, 129X1, DBA/2 and FVB/N mice are all susceptible to high-fat diet-induced glucose intolerance, while BALB/c mice are relatively protected, despite changes in many factors linked with insulin resistance. One parameter strongly linked with insulin resistance is ectopic lipid accumulation, especially metabolically active ceramides and diacylglycerols (DAG). This study examined diet-induced changes in the skeletal muscle lipidome across these five mouse strains. High-fat feeding increased total muscle triacylglycerol (TAG) content, with elevations in similar triacylglycerol species observed for all strains. There were also generally consistent changes across strains in the abundance of different phospholipid (PL) classes and the fatty acid profile of phospholipid molecular species, with the exception being a strain-specific difference in phospholipid species containing two polyunsaturated fatty acyl chains in BALB/c mice (i.e. a diet-induced decrease in the other four strains, but no change in BALB/c mice). In contrast to TAG and PL, the high-fat diet had a minor influence on DAG and ceramide species across all strains. These results suggest that widespread alterations in muscle lipids are unlikely a major contributors to the favourable metabolic profile of BALB/c mice and rather there is a relatively conserved high-fat diet response in muscle of most mouse strains.

Efficient generation of sFat-1 transgenic rabbits rich in n-3 polyunsaturated fatty acids by intracytoplasmic sperm injection

N-3 polyunsaturated fatty acids (n-3 PUFAs) have their first double bond at the third carbon from the methyl end of the fatty-acid chain and had been proven to be beneficial to human health. However, mammals cannot produce n-3 PUFAs by themselves because they lack the n-3 fatty-acid desaturase (Fat-1) gene. Thus, the possibility of producing sFat-1 transgenic rabbits was explored in this study. The transgenic cassette of pPGK1-sFat-1-CMV-EGFP was constructed and transgenic rabbit embryos were produced by intracytoplasmic sperm injection (ICSI). When 123 EGFP-positive embryos at the 2-8-cell stage were transplanted into the oviduct of four oestrous-synchronised recipients, two of them became pregnant and gave birth to seven pups. However, transfer of embryos into the uterus of oestrous-synchronised recipients and oviduct or uterus of oocyte donor rabbits did not result in pregnancy. The integration of the sFat-1 gene was confirmed in six of the seven live pups by PCR and Southern blot. The expression of the sFat-1 gene in the six transgenic pups was also detected by reverse transcription polymerase chain reaction (RT-PCR). Gas chromatography-mass spectrometry analysis revealed that transgenic rabbits exhibited an ~15-fold decrease in the ratio of n-6:n-3 PUFAs in muscle compared with wild-type rabbits and non-transgenic rabbits. These results demonstrate that sFat-1 transgenic rabbits can be produced by ICSI and display a low ratio of n-6:n-3 PUFAs.

Insulin-Sensitizing Effects of Omega-3 Fatty Acids: Lost in Translation?

Omega-3 polyunsaturated fatty acids (n-3 PUFA) of marine origin, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have been long studied for their therapeutic potential in the context of type 2 diabetes, insulin resistance, and glucose homeostasis. Glaring discordance between observations in animal and human studies precludes, to date, any practical application of n-3 PUFA as nutritional therapeutics against insulin resistance in humans. Our objective in this review is to summarize current knowledge and provide an up-to-date commentary on the therapeutic value of EPA and DHA supplementation for improving insulin sensitivity in humans. We also sought to discuss potential mechanisms of n-3 PUFA action in target tissues, in specific skeletal muscle, based on our recent work, as well as in liver and adipose tissue. We conducted a literature search to include all preclinical and clinical studies performed within the last two years and to comment on representative studies published earlier. Recent studies support a growing consensus that there are beneficial effects of n-3 PUFA on insulin sensitivity in rodents. Observational studies in humans are encouraging, however, the vast majority of human intervention studies fail to demonstrate the benefit of n-3 PUFA in type 2 diabetes or insulin-resistant non-diabetic people. Nevertheless, there are still several unanswered questions regarding the potential impact of n-3 PUFA on metabolic function in humans.

Omega-3 Fatty Acids and Skeletal Muscle Health

Skeletal muscle is a plastic tissue capable of adapting and mal-adapting to physical activity and diet. The response of skeletal muscle to adaptive stimuli, such as exercise, can be modified by the prior nutritional status of the muscle. The influence of nutrition on skeletal muscle has the potential to substantially impact physical function and whole body metabolism. Animal and cell based models show that omega-3 fatty acids, in particular those of marine origin, can influence skeletal muscle metabolism. Furthermore, recent human studies demonstrate that omega-3 fatty acids of marine origin can influence the exercise and nutritional response of skeletal muscle. These studies show that the prior omega-3 status influences not only the metabolic response of muscle to nutrition, but also the functional response to a period of exercise training. Omega-3 fatty acids of marine origin therefore have the potential to alter the trajectory of a number of human diseases including the physical decline associated with aging. We explore the potential molecular mechanisms by which omega-3 fatty acids may act in skeletal muscle, considering the n-3/n-6 ratio, inflammation and lipidomic remodelling as possible mechanisms of action. Finally, we suggest some avenues for further research to clarify how omega-3 fatty acids may be exerting their biological action in skeletal muscle.

Dietary combination of sucrose and linoleic acid causes skeletal muscle metabolic abnormalities in Zucker fatty rats through specific modification of fatty acid composition

A dietary combination of sucrose and linoleic acid strongly contributes to the development of metabolic disorders in Zucker fatty rats. However, the underlying mechanisms of the metabolic disorders are poorly understood. We hypothesized that the metabolic disorders were triggered at a stage earlier than the 8 weeks we had previously reported. In this study, we investigated early molecular events induced by the sucrose and linoleic acid diet in Zucker fatty rats by comparison with other combinations of carbohydrate (sucrose or palatinose) and fat (linoleic acid or oleic acid). Skeletal muscle arachidonic acid levels were significantly increased in the sucrose and linoleic acid group compared to the other dietary groups at 4 weeks, while there were no obvious differences in the metabolic phenotype between the groups. Expression of genes related to arachidonic acid synthesis was induced in skeletal muscle but not in liver and adipose tissue in sucrose and linoleic acid group rats. In addition, the sucrose and linoleic acid group exhibited a rapid induction in endoplasmic reticulum stress and abnormal lipid metabolism in skeletal muscle. We concluded that the dietary combination of sucrose and linoleic acid primarily induces metabolic disorders in skeletal muscle through increases in arachidonic acid and endoplasmic reticulum stress, in advance of systemic metabolic disorders.

Endogenous ω-3 polyunsaturated fatty acid production confers resistance to obesity, dyslipidemia, and diabetes in mice

Despite the well-documented health benefits of ω-3 polyunsaturated fatty acids (PUFAs), their use in clinical management of hyperglycemia and obesity has shown little success. To better define the mechanisms of ω-3 PUFAs in regulating energy balance and insulin sensitivity, we deployed a transgenic mouse model capable of endogenously producing ω-3 PUFAs while reducing ω-6 PUFAs owing to the expression of a Caenorhabditis elegans fat-1 gene encoding an ω-3 fatty acid desaturase. When challenged with high-fat diets, fat-1 mice strongly resisted obesity, diabetes, hypercholesterolemia, and hepatic steatosis. Endogenous elevation of ω-3 PUFAs and reduction of ω-6 PUFAs did not alter the amount of food intake but led to increased energy expenditure in the fat-1 mice. The requirements for the levels of ω-3 PUFAs as well as the ω-6/ω-3 ratios in controlling blood glucose and obesity are much more stringent than those in lipid metabolism. These metabolic phenotypes were accompanied by attenuation of the inflammatory state because tissue levels of prostaglandin E2, leukotriene B4, monocyte chemoattractant protein-1, and TNF-α were significantly decreased. TNF-α-induced nuclear factor-κB signaling was almost completely abolished. Consistent with the reduction in chronic inflammation and a significant increase in peroxisome proliferator-activated receptor-γ activity in the fat-1 liver tissue, hepatic insulin signaling was sharply elevated. The activities of prolipogenic regulators, such as liver X receptor, stearoyl-CoA desaturase-1, and sterol regulatory element binding protein-1 were sharply decreased, whereas the activity of peroxisome proliferator-activated receptor-α, a nuclear receptor that facilitates lipid β-oxidation, was markedly increased. Thus, endogenous conversion of ω-6 to ω-3 PUFAs via fat-1 strongly protects against obesity, diabetes, inflammation, and dyslipidemia and may represent a novel therapeutic modality to treat these prevalent disorders.

Variable effects of 12 weeks of omega-3 supplementation on resting skeletal muscle metabolism

Omega-3 supplementation has been purported to improve the function of several organs in the body, including reports of increased resting metabolic rate (RMR) and reliance on fat oxidation. However, the potential for omega-3s to modulate human skeletal muscle metabolism has received little attention. This study examined the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplementation on whole-body RMR and the content of proteins involved in fat metabolism in human skeletal muscle. Recreationally active males supplemented with 3.0 g/day of EPA and DHA (n = 21) or olive oil (n = 9) for 12 weeks. Resting muscle biopsies were sampled in a subset of 10 subjects before (pre) and after (post) omega-3 supplementation. RMR significantly increased (5.3%, p = 0.040) following omega-3 supplementation (Pre, 1.33 ±0.05; Post, 1.40 ±0.04 kcal/min) with variable individual responses. When normalizing for body mass, this effect was lost (5.2%, p = 0.058). Omega-3s did not affect whole-body fat oxidation, and olive oil did not alter any parameter assessed. Omega-3 supplementation did not affect whole muscle, sarcolemmal, or mitochondrial FAT/CD36, FABPpm, FATP1 or FATP4 contents or mitochondrial electron chain and PDH proteins, but did increase the long form of UCP3 by 11%. In conclusion, supplementation with a high dose of omega-3s for 12 weeks increased RMR in a small and variable manner in a group of healthy young men. Omega-3 supplementation also had no effect on several proteins involved in skeletal muscle fat metabolism and did not cause mitochondrial biogenesis.

Docosahexaenoic acid prevents palmitate-induced activation of proteolytic systems in C2C12 myotubes

Saturated fatty acids like palmitate contribute to muscle atrophy in a number of conditions (e.g., type II diabetes) by altering insulin signaling. Akt is a key modulator of protein balance that inhibits the FoxO transcription factors (e.g., FoxO3) which selectively induce the expression of atrophy-inducing genes (atrogenes) in the ubiquitin-proteasome and autophagy-lysosome systems. Conversely, omega-3 polyunsaturated fatty acids have beneficial effects on insulin signaling and may preserve muscle mass. In an earlier report, the omega-3 fatty acid docosahexaenoic acid (DHA) protected myotubes from palmitate-induced atrophy; the mechanisms underlying the alterations in protein metabolism were not identified. This study investigated whether DHA prevents a palmitate-induced increase in proteolysis by restoring Akt/FoxO signaling. Palmitate increased the rate of protein degradation, while cotreatment with DHA prevented the response. Palmitate reduced the activation state of Akt and increased nuclear FoxO3 protein while decreasing its cytosolic level. Palmitate also increased the messenger RNAs (mRNAs) of two FoxO3 atrogene targets, the E3 ubiquitin ligase atrogin-1/MAFbx and the autophagy mediator Bnip3. DHA attenuated the effects of palmitate on Akt activation, FoxO3 localization and atrogene mRNAs. DHA, alone or in combination with palmitate and decreased the ratio of LC3B-II:LC3B-I protein as well as the rate of autophagosome formation, as indicated by reduced LC3B-II protein in the presence of 10 mmol/L methylamine, suggesting an independent effect of DHA on the macroautophagy pathway. These data indicate that palmitate induces myotube atrophy, at least in part, by activating multiple proteolytic systems and that DHA counters the catabolic effects of palmitate by restoring Akt/FoxO signaling.

The iFat1 transgene permits conditional endogenous n-3 PUFA enrichment both in vitro and in vivo

Fat-1 transgenic mice, which endogenously convert n-6 PUFA to n-3 PUFA, are a useful tool in health research; however with this model timing of n-3 PUFA enrichment cannot be directly controlled. To add such capability, the novel Cre-recombinase inducible fat-1 (iFat1) transgenic mouse has been developed. The aim of this study was to characterize the utility of the iFat1 transgene as a model of Cre-inducible endogenous n-3 PUFA enrichment. Functionality of the iFat1 transgene was screened both in vitro and in vivo. In the presence of Cre, the iFat1 transgene resulted in a balancing (p < 0.01) of the n-6/n-3 PUFA ratio within phospholipids in the human embryonic kidney 293T cell line. For in vivo analysis, iFat1 transgenic mice were crossed with the R26-Cre-ER^T2 (Tam-Cre) mouse line, a tamoxifen inducible Cre-expression model. Tam-Cre/iFat1 double hybrids were transiently treated with tamoxifen at 6–7 weeks, then terminated 3 weeks later. Tamoxifen treated mice had increased (p < 0.05) tissue n-3 PUFA and ≥two-fold reduction (p < 0.05) in the n-6/n-3 PUFA ratio of liver, kidney and muscle phospholipids relative to vehicle treated controls. Collectively these findings suggest that the iFat1 transgenic mouse may be a promising tool to help elucidate the temporal effects through which n-3 PUFA impacts health related outcomes.

Role of n-3 fatty acids in muscle loss and myosteatosis

Image-based methods such as computed tomography for assessing body composition enables quantification of muscle mass and muscle density and reveals that low muscle mass and myosteatosis (fat infiltration into muscle) are common in people with cancer. Myosteatosis and low muscle mass have emerged as independent risk factors for mortality in cancer; however, the characteristics and pathogenesis of these features have not been resolved. Muscle depletion is associated with low plasma eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) in cancer and supplementation with n-3 fatty acids has been shown to ameliorate muscle loss and myosteatosis in clinical studies, suggesting a relationship between n-3 fatty acids and muscle health. Since the mechanisms by which n-3 fatty acids alter body composition in cancer remain unknown, related literature from other conditions associated with myosteatosis, such as insulin resistance and obesity is considered. In these noncancer conditions, it has been reported that n-3 fatty acids act by increasing insulin sensitivity, reducing inflammatory mediators, and altering adipokine profiles and transcription factors; therefore, the plausibility of these mechanisms of action in the neoplastic state are considered. The aim of this review is to summarize what is known about the effects of n-3 fatty acids with regards to muscle condition and to discuss potential mechanisms for effects of n-3 fatty acids on muscle health.

Unesterified docosahexaenoic acid is protective in neuroinflammation

Docosahexaenoic acid (22:6n-3) is the major brain n-3 polyunsaturated fatty acid and it is possible that docosahexaenoic acid is anti-inflammatory in the brain as it is known to be in other tissues. Using a combination of models including the fat-1 transgenic mouse, chronic dietary n-3 polyunsaturated fatty acid modulation in transgenic and wild-type mice, and acute direct brain infusion, we demonstrated that unesterified docosahexaenoic acid attenuates neuroinflammation initiated by intracerebroventricular lipopolysaccharide. Hippocampal neuroinflammation was assessed by gene expression and immunohistochemistry. Furthermore, docosahexaenoic acid protected against lipopolysaccharide-induced neuronal loss. Acute intracerebroventricular infusion of unesterified docosahexaenoic acid or its 12/15-lipoxygenase product and precursor to protectins and resolvins, 17S-hydroperoxy-docosahexaenoic acid, mimics anti-neuroinflammatory aspects of chronically increased unesterified docosahexaenoic acid. LC-MS/MS revealed that neuroprotectin D1 and several other docosahexaenoic acid-derived specialized pro-resolving mediators are present in the hippocampus. Acute intracerebroventricular infusion of 17S-hydroperoxy-docosahexaenoic acid increases hippocampal neuroprotectin D1 levels concomitant to attenuating neuroinflammation. These results show that unesterified docosahexaenoic acid is protective in a lipopolysaccharide-initiated mouse model of acute neuroinflammation, at least in part, via its conversion to specialized pro-resolving mediators; these docosahexaenoic acid stores may provide novel targets for the prevention and treatment(s) of neurological disorders with a neuroinflammatory component. Our study shows that chronically increased brain unesterified DHA levels, but not solely phospholipid DHA levels, attenuate neuroinflammation. Similar attenuations occur with acute increases in brain unesterified DHA or 17S-HpDHA levels, highlighting the importance of an available pool of precursor unesterified DHA for the production of enzymatically derived specialized pro-resolving mediators that are critical in the regulation of neuroinflammation.

Transgenic increase in N-3/n-6 Fatty Acid ratio reduces maternal obesity-associated inflammation and limits adverse developmental programming in mice

Maternal and pediatric obesity has risen dramatically over recent years, and is a known predictor of adverse long-term metabolic outcomes in offspring. However, which particular aspects of obese pregnancy promote such outcomes is less clear. While maternal obesity increases both maternal and placental inflammation, it is still unknown whether this is a dominant mechanism in fetal metabolic programming. In this study, we utilized the Fat-1 transgenic mouse to test whether increasing the maternal n-3/n-6 tissue fatty acid ratio could reduce the consequences of maternal obesity-associated inflammation and thereby mitigate downstream developmental programming. Eight-week-old WT or hemizygous Fat-1 C57BL/6J female mice were placed on a high-fat diet (HFD) or control diet (CD) for 8 weeks prior to mating with WT chow-fed males. Only WT offspring from Fat-1 mothers were analyzed. WT-HFD mothers demonstrated increased markers of infiltrating adipose tissue macrophages (P<0.02), and a striking increase in 12 serum pro-inflammatory cytokines (P<0.05), while Fat1-HFD mothers remained similar to WT-CD mothers, despite equal weight gain. E18.5 Fetuses from WT-HFD mothers had larger placentas (P<0.02), as well as increased placenta and fetal liver TG deposition (P<0.01 and P<0.02, respectively) and increased placental LPL TG-hydrolase activity (P<0.02), which correlated with degree of maternal insulin resistance (r = 0.59, P<0.02). The placentas and fetal livers from Fat1-HFD mothers were protected from this excess placental growth and fetal-placental lipid deposition. Importantly, maternal protection from excess inflammation corresponded with improved metabolic outcomes in adult WT offspring. While the offspring from WT-HFD mothers weaned onto CD demonstrated increased weight gain (P<0.05), body and liver fat (P<0.05 and P<0.001, respectively), and whole body insulin resistance (P<0.05), these were prevented in WT offspring from Fat1-HFD mothers. Our results suggest that reducing excess maternal inflammation may be a promising target for preventing adverse fetal metabolic outcomes in pregnancies complicated by maternal obesity.

Polyunsaturated fatty acid derived signaling in reproduction and development: insights from Caenorhabditis elegans and Drosophila melanogaster

Polyunsaturated fatty acids (PUFAs) exhibit a diverse range of critical functions in biological systems. PUFAs modulate the biophysical properties of membranes and, along with their derivatives, the eicosanoids and endocannabinoids, form a wide array potent lipid signaling molecules. Much of our early understanding of PUFAs and PUFA-derived signaling stems from work in mammals; however, technological advances have made comprehensive lipid analysis possible in small genetic models such as Caenorhabditis elegans and Drosophila melanogaster. These models have a number of advantages, such as simple anatomy and genome-wide genetic screening techniques, which can broaden our understanding of fatty-acid-derived signaling in biological systems. Here we review what is known about PUFAs, eicosanoids, and endocannabinoids in the development and reproduction of C. elegans and D. melanogaster. Fatty acid signaling appears to be fundamental for multicellular organisms, and simple invertebrates often employ functionally similar pathways. In particular, studies in C. elegans and Drosophila are providing insight into the roles of PUFAs and PUFA-derived signaling in early developmental processes, such as meiosis, fertilization, and early embryonic cleavage.

Polyunsaturated fatty acids in inflammatory bowel diseases: a reappraisal of effects and therapeutic approaches

Recent epidemiological studies highlight the key role of the type of consumed unsaturated fatty acid and the development of ulcerative colitis (UC). We aimed to review the potential mechanisms behind the antiinflammatory effects of unsaturated fatty acids on intestinal inflammation, to discuss their potential limitations, and to propose a new reappraisal of polyunsaturated fatty acids (PUFAs) in the pathophysiology of inflammatory bowel disease (IBD). A literature search using PubMed was carried out to identify relevant studies (basic science, epidemiological studies, or clinical trials) with unsaturated fatty acids and IBD. Only articles published in English were included. IBD patients exhibit an altered lipid metabolism. While in vitro and in vivo studies have demonstrated the antiinflammatory properties of n-3 polyunsaturated fatty acids in experimental models IBD, results of clinical trials have been disappointing. In addition, the impact of fatty acid on innate immunity as an alternative therapeutic approach is explored. This may offer insight into therapeutic avenues for designing n-3 PUFA diet therapy for IBD.

Menhaden oil, but not safflower or soybean oil, aids in restoring the polyunsaturated fatty acid profile in the novel delta-6-desaturase null mouse

Background

Polyunsaturated fatty acids (PUFA) have diverse biological effects, from promoting inflammation to preventing cancer and heart disease. Growing evidence suggests that individual PUFA may have independent effects in health and disease. The individual roles of the two essential PUFA, linoleic acid (LA) and α-linolenic acid (ALA), have been difficult to discern from the actions of their highly unsaturated fatty acid (HUFA) downstream metabolites. This issue has recently been addressed through the development of the Δ-6 desaturase knock out (D6KO) mouse, which lacks the rate limiting Δ-6 desaturase enzyme and therefore cannot metabolize LA or ALA. However, a potential confounder in this model is the production of novel Δ-5 desaturase (D5D) derived fatty acids when D6KO mice are fed diets containing LA and ALA, but void of arachidonic acid.

Objective

The aim of the present study was to characterize how the D6KO model differentially responds to diets containing the essential n-6 and n-3 PUFA, and whether the direct provision of downstream HUFA can rescue the phenotype and prevent the production of D5D fatty acids.

Methodology

Liver and serum phospholipid (PL) fatty acid composition was examined in D6KO and wild type mice fed i) 10% safflower oil diet (SF, LA rich) ii) 10% soy diet (SO, LA+ALA) or iii) 3% menhaden oil +7% SF diet (MD, HUFA rich) for 28 days (n = 3-7/group).

Results

Novel D5D fatty acids were found in liver PL of D6KO fed SF or SO-fed mice, but differed in the type of D5D fatty acid depending on diet. Conversely, MD-fed D6KO mice had a liver PL fatty acid profile similar to wild-type mice.

Conclusions

Through careful consideration of the dietary fatty acid composition, and especially the HUFA content in order to prevent the synthesis of D5D fatty acids, the D6KO model has the potential to elucidate the independent biological and health effects of the parent n-6 and n-3 fatty acids, LA and ALA.

Fat-1 transgenic cattle as a model to study the function of ω-3 fatty acids

ω-3 polyunsaturated fatty acids have been shown to play an important role in health. Enriched with ω-3 polyunsaturated fatty acids modulate expression of a number of genes with such broad functions as cell proliferation, growth and apoptosis and cell signaling and transduction, these effects, seem to regulate coronary artery disease, hypertension, atherosclerosis, psychiatric disorders and various cancer. In this context, fat-1 transgenic cattle was designed to convert ω-6 to ω-3 fatty acids could form an ideal model to study the effect of ω-3 fatty acids on the above functions. This study focuses on the total genomic difference of gene expression between fat-1 transgenic cattle and wild-type using cDNA microarrays, several genes were found to be overexpressed or suppressed in transgenic cattle relative to wild-type, these discrepancy genes related with lipid metabolism, immunity, inflammation nervous development and fertility.