Fish oil and krill oil differentially modify the liver and brain lipidome when fed to mice.

BACKGROUND: Marine food is an important source of omega-3 fatty acids with beneficial health effects. Oils from marine organisms have different fatty acid composition and differ in their molecular composition. Fish oil (FO) has a high content of eicosapentaenoic and docosahexaenoic acids mainly esterified to triacylglycerols, while in krill oil (KO) these fatty acids are mainly esterified to phospholipids. The aim was to study the effects of these oils on the lipid content and fatty acid distribution in the various lipid classes in liver and brain of mice. METHODS: Mice were fed either a high-fat diet (HF), a HF diet supplemented with FO or with KO (n = 6). After six weeks of feeding, liver and brain lipid extracts were analysed using a shotgun and TAG lipidomics approach. Student t-test was performed after log-transformation to compare differences between study groups. RESULTS: Six weeks of feeding resulted in significant changes in the relative abundance of many lipid classes compared to control mice. In both FO and KO fed mice, the triacylglycerol content in the liver was more than doubled. The fatty acid distribution was affected by the oils in both liver and brain with a decrease in the abundance of 18:2 and 20:4, and an increase in 20:5 and 22:6 in both study groups. 18:2 decreased in all lipid classes in the FO group but with only minor changes in the KO group. Differences between the feeding groups were particularly evident in some of the minor lipid classes that are associated with inflammation and insulin resistance. Ceramides and diacylglycerols were decreased and cholesteryl esters increased in the liver of the KO group, while plasmalogens were decreased in the FO group. In the brain, diacylglycerols were decreased, more by KO than FO, while ceramides and lactosylceramides were increased, more by FO than KO. CONCLUSION: The changes in the hepatic sphingolipids and 20:4 fatty acid levels were greater in the KO compared to the FO fed mice, and are consistent with a hypothesis that krill oil will have a stronger anti-inflammatory action and enhances insulin sensitivity more potently than fish oil.

PPARalpha is a key regulator of hepatic FGF21.

The metabolic regulator fibroblast growth factor 21 (FGF21) has antidiabetic properties in animal models of diabetes and obesity. Using quantitative RT-PCR, we here show that the hepatic gene expression of FGF21 is regulated by the peroxisome proliferator-activated receptor alpha (PPARalpha). Fasting or treatment of mice with the PPARalpha agonist Wy-14,643 induced FGF21 mRNA by 10-fold and 8-fold, respectively. In contrast, FGF21 mRNA was low in PPARalpha deficient mice, and fasting or treatment with Wy-14,643 did not induce FGF21. Obese ob/ob mice, known to have increased PPARalpha levels, displayed 12-fold increased hepatic FGF21 mRNA levels. The potential importance of PPARalpha for FGF21 expression also in human liver was shown by Wy-14,643 induction of FGF21 mRNA in human primary hepatocytes, and PPARalpha response elements were identified in both the human and mouse FGF21 promoters. Further studies on the mechanisms of regulation of FGF21 by PPARalpha in humans will be of great interest.

Impairment of mitochondrial anti-oxidant defence in SOD1-related motor neuron injury and amelioration by ebselen.

There is now compelling evidence of mitochondrial dysfunction in motor neuron disease (MND), but the molecular basis of these abnormalities is unknown. It is also unclear whether the observed mitochondrial dysfunction plays a central role in disease pathogenesis, and if so, whether its amelioration might present therapeutic opportunities. We adopted a candidate generation approach using proteomics to screen for changes in mitochondrial protein expression in a well-validated cell-culture model of superoxide dismutase 1 (SOD1) related familial MND (fMND). Changed proteins were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. Protein candidates included apoptotic regulators, anti-oxidants and components of the electron transport chain. Confirmatory Western blotting was performed, and validated protein expression changes were further investigated. Peroxiredoxin 3 (Prx3), a mitochondrial thioredoxin-dependent hydroperoxidase, is downregulated in the presence of mutant SOD1 in both our cell-culture model and in the spinal cord mitochondria of mutant SOD1 transgenic mice. We confirm the expression of Prx3 within the mitochondria of spinal motor neurons in mouse and humans by immunohistochemistry. Using quantitative real-time PCR (Q-PCR), we show that Prx3 is also downregulated in spinal motor neurons from patients with both sporadic (sMND) and SOD1-related fMND. In a disease characterized by oxidative stress, this represents a potentially important deficit in mitochondrial anti-oxidant defence. Recent evidence suggests that oxidative stress from aberrant copper chemistry may not play a major part in the pathogenesis of SOD1-related fMND. From the results of this study we propose disruption of mitochondrial anti-oxidant defence as an alternative mechanism whereby mutant SOD1 may generate oxidative stress within motor neurons. We further demonstrate that ebselen, an anti-oxidant drug already safely used in human studies and that acts as a Prx mimic, is able to ameliorate the toxicity of mutant SOD1 in our cell-culture model. We conclude by showing that ebselen is capable of inducing transcription of the anti-oxidant response element (ARE) and postulate that ebselen may act both by the transcriptional upregulation of anti-oxidant proteins, and directly as an anti-oxidant in its own right.

The human bile acid-CoA:amino acid N-acyltransferase functions in the conjugation of fatty acids to glycine.

Bile acid-CoA:amino acid N-acyltransferase (BACAT) catalyzes the conjugation of bile acids to glycine and taurine for excretion into bile. By use of site-directed mutagenesis and sequence comparisons, we have identified Cys-235, Asp-328, and His-362 as constituting a catalytic triad in human BACAT (hBACAT) and identifying BACAT as a member of the type I acyl-CoA thioesterase gene family. We therefore hypothesized that hBACAT may also hydrolyze fatty acyl-CoAs and/or conjugate fatty acids to glycine. We show here that recombinant hBACAT also can hydrolyze long- and very long-chain saturated acyl-CoAs (mainly C16:0-C26:0) and by mass spectrometry verified that hBACAT also conjugates fatty acids to glycine. Tissue expression studies showed strong expression of BACAT in liver, gallbladder, and the proximal and distal intestine. However, BACAT is also expressed in a variety of tissues unrelated to bile acid formation and transport, suggesting important functions also in the regulation of intracellular levels of very long-chain fatty acids. Green fluorescent protein localization experiments in human skin fibroblasts showed that the hBACAT enzyme is mainly cytosolic. Therefore, the cytosolic BACAT enzyme may play important roles in protection against toxicity by accumulation of unconjugated bile acids and non-esterified very long-chain fatty acids.