Effect of increasing the level of omega-3 fatty acids on rat skeletal muscle sarcoplasmic reticulum

Resting metabolic rate and skeletal muscle SERCA and Na+ /K+ ATPase activities are not affected by fish oil supplementation in healthy older adults

Omega-3 polyunsaturated fatty acids (PUFAs) have unique properties purported to influence several aspects of metabolism, including energy expenditure and protein function. Supplementing with n-3 PUFAs may increase whole-body resting metabolic rate (RMR), by enhancing Na+ /K+ ATPase (NKA) activity and reducing the efficiency of sarcoplasmic reticulum (SR) Ca2+ ATPase (SERCA) activity by inducing a Ca2+ leak-pump cycle. The purpose of this study was to examine the effects of fish oil (FO) on RMR, substrate oxidation, and skeletal muscle SERCA and NKA pump function in healthy older individuals. Subjects (n = 16 females; n = 8 males; 65 ± 1 years) were randomly assigned into groups supplemented with either olive oil (OO) (5 g/day) or FO (5 g/day) containing 2 g/day eicosapentaenoic acid and 1 g/day docosahexaenoic acid for 12 weeks. Participants visited the laboratory for RMR and substrate oxidation measurements after an overnight fast at weeks 0 and 12. Skeletal muscle biopsies were taken during weeks 0 and 12 for analysis of NKA and SERCA function and protein content. There was a main effect of time with decrease in RMR (5%) and fat oxidation (18%) in both the supplementation groups. The kinetic parameters of SERCA and NKA maximal activity, as well as the expression of SR and NKA proteins, were not affected after OO and FO supplementation. In conclusion, these results suggest that FO supplementation is not effective in altering RMR, substrate oxidation, and skeletal muscle SERCA and NKA protein levels and activities, in healthy older men and women.

Sarcoplasmic reticulum Ca2+-ATPase (SERCA) activity during the transition to endothermy in an altricial bird

Sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) is a transmembrane pump critical to muscle calcium cycling during contraction, and SERCA has also been proposed as the basis for a non-shivering thermogenesis mechanism in birds. Despite its potential importance to both shivering and non-shivering thermogenesis, the activity of this transporter has rarely been studied in altricial birds, and never during the developmental transition from ectothermy to endothermy. Here, we describe SERCA activity in the pectoralis muscle and heart ventricle of red-winged blackbird (Agelaius phoeniceus) nestlings, fledglings and adults. Additionally, using a diet manipulation, we tested the hypothesis that muscle SERCA activity is affected by dietary fatty acid composition, as has been shown in some previous studies. In blackbird hearts, SERCA activity increased throughout development and into adulthood, conspicuously jumping higher just prior to fledging. In pectoralis muscle, SERCA activity increased throughout the nestling period, but then declined after fledging, an effect we attribute to remodeling of the muscle from a primarily heat-generating organ to a primarily force-generating organ. SERCA activity of the pectoralis muscle was correlated with the proportion of linoleic acid in muscle phospholipids when including all ages in the control group. However, in diet-manipulated birds, there was no consistent relationship between SERCA activity and muscle membrane fatty acid composition at any tested age (5-9 days old). It is unclear whether SERCA might be affected by developmental changes in fatty acid composition at younger ages.

Saturation of SERCA's lipid annulus may protect against its thermal inactivation

The sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) pumps are integral membrane proteins that catalyze the active transport of Ca²⁺ into the sarcoplasmic reticulum, thereby eliciting muscle relaxation. SERCA pumps are highly susceptible to oxidative damage, and cytoprotection of SERCA dampens thermal inactivation and is a viable therapeutic strategy in combating diseases where SERCA activity is impaired, such as muscular dystrophy. Here, we sought to determine whether increasing the percent of saturated fatty acids (SFA) within SERCA's lipid annulus through diet could protect SERCA pumps from thermal inactivation. Female Wistar rats were fed either a semi-purified control diet (AIN93G, 7% soybean oil by weight) or a modified AIN93G diet containing high SFA (20% lard by weight) for 17 weeks. Soleus muscles were extracted and SERCA lipid annulus and activity under thermal stress were analyzed. Our results show that SERCA's lipid annulus is abundant with short-chain (12-14 carbon) fatty acids, which corresponds well with SERCA's predicted bilayer thickness of 21 Å. Under control-fed conditions, SERCA's lipid annulus was already highly saturated (79%), and high-fat feeding did not increase this any further. High-fat feeding did not mitigate the reductions in SERCA activity seen with thermal stress; however, correlational analyses revealed significant and strong associations between % SFA and thermal stability of SERCA activity with greater %SFA being associated with lower thermal inactivation and greater % polyunsaturation and unsaturation index being associated with increased thermal inactivation. Altogether, these findings show that SERCA's lipid annulus may influence its susceptibility to oxidative damage, which could have implications in muscular dystrophy and age-related muscle wasting.

Dietary docosahexaenoic acid supplementation reduces SERCA Ca2+ transport efficiency in rat skeletal muscle

Docosahexaenoic acid (DHA) can reduce the efficiency and increase the energy consumption of Na(+)/K(+)-ATPase pump and mitochondrial electron transport chain by promoting Na(+) and H(+) membrane permeability, respectively. In skeletal muscle, the sarco(endo) plasmic reticulum Ca(2+)-ATPase (SERCA) pumps are major contributors to resting metabolic rate. Whether DHA can affect SERCA efficiency remains unknown. Here, we examined the hypothesis that dietary supplementation with DHA would reduce Ca(2+) transport efficiency of the SERCA pumps in skeletal muscle. Total lipids were extracted from enriched sarcoplasmic reticulum (SR) membranes that were isolated from red vastus lateralis skeletal muscles of rats that were either fed a standard chow diet supplemented with soybean oil or supplemented with DHA for 8 weeks. The fatty acid composition of total SR membrane lipids and the major phospholipid species were determined using electrospray ionization mass spectrometry (ESI-MS). After 8 weeks of DHA supplementation, total SR DHA content was significantly elevated (control, 4.1 ± 1.0% vs. DHA, 9.9 ± 1.7%; weight percent of total fatty acids) while total arachidonic acid was reduced (control, 13.5 ± 0.4% vs. DHA-fed, 9.4 ± 0.2). Similar changes in these fatty acids were observed in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, altogether indicating successful incorporation of DHA into the SR membranes post-diet. As hypothesized, DHA supplementation reduced SERCA Ca(2+) transport efficiency (control, 0.018 ± 0.0002 vs. DHA-fed, 0.014 ± 0.0009) possibly through enhanced SR Ca(2+) permeability (ionophore ratio: control, 2.8 ± 0.2 vs. DHA-fed, 2.2 ± 0.3). Collectively, our results suggest that DHA may promote skeletal muscle-based metabolism and thermogenesis through its influence on SERCA.

Pathophysiological effects of dietary essential fatty acid balance on neural systems

Dietary fatty acid balance has been revealed to affect neural functions as well as chronic diseases such as cancer, cerebro- and cardiovascular diseases, and allergic hyper-reactivity. In this review, we focused on the pathophysiological effects of n-6 and n-3 fatty acids on brain functions. Long-term n-3 fatty acid deficiency in the presence of n-6 fatty acids has been shown to affect learning behavior, drug sensitivity and retinal functions. Some membrane enzymes and ion channel functions have been shown in experimental animals to be regulated by membrane fatty acid modifications. We also summarized the effects of these fatty acids in diets on human psychotic aspects and brain diseases. Although biochemical mechanisms remain to be elucidated, investigations on the effect of dietary fatty acids on neural networks may provide an important clue to clarify complex brain functions.

Involvement of phospholipid molecular species in controlling structural order of vertebrate brain synaptic membranes during thermal evolution

Fluorescence anisotropy parameter of [p-(6-phenyl)-1,3,5-hexatrienyl]phenyl-propionic acid (DPH-PA) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) embedded in synaptic plasma membranes prepared from brains of cold (5 degrees C) and warm (22 degrees C) adapted fish (Cyprinus carpio L.), rat (Rattus norvegicus) and bird (Branta canadensis), was studied. Fatty acid composition of total lipids as well as molecular species composition of diacyl phosphatidylcholines and phosphatidylethanolamines was also determined. The amount of long-chain polyunsaturated fatty acids decreased with increasing body temperature. There was a near-complete compensation of membrane structural order for environmental/body temperature over the evolutionary scale as seen by DPH-PA. Using TMA-DPH, the compensation was partial with rat and bird. Since DPH-PA and TMA-DPH differ in their charges, it is proposed, that the former reported membrane regions rich in cationic or zwitterionic (neutral) phospholipids and the latter, membrane regions rich in negatively charged phospholipids in the synaptic plasma membranes. Many different molecular species (20-25) of diacyl phosphatidylcholines and diacyl phosphatidylethanolamines were identified. The level of 16:0/22:6 phosphatidylcholine decreased while disaturated phosphatidylcholines increased with increase of environmental/body temperature from the fish through the bird. Level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines also decreased with an increase in environmental/body temperature. Experiments using vesicles made of mixed synthetic phosphatidylcholine vesicles (16:0/16:0, 16:0/18:1, 16:0/22:6 in various proportions) showed that increase in disaturated phosphatidylcholine species does not explain the observed complete adjustment of membrane structural order in synaptic plasma membranes. Change in level of 1-monoenoic, 2-polyenoic phosphatidylethanolamines might be one of the factors involved in controlling the biophysical properties of the membrane according to the temperature.

Molecular architecture and biophysical properties of phospholipids during thermal adaptation in fish: an experimental and model study

Phospholipids from livers of carps (Cyprinus carpio L.) adapted to winter (5 degrees C) and summer (25 degrees C) temperatures were isolated, and the fatty acid composition of total phospholipids, as well as molecular species composition of diacyl phosphatidylcholines and ethanolamines, were determined. Order parameter of 5-doxyl stearic acid and steady-state fluorescence anisotropy of different anthroyloxy fatty acids--[2-, 12(N-9-anthroyloxy)stearic acid and 16(N-9-anthroyloxy)palmitic acid--embedded in native and synthetic (16:0/16:0, 16:0/22:6, 18:0/22:6, 18:1/22:6, 20:4/20:4, 22:6/22:6 phosphatidylcholines and 16:0/18:1, 18:1/22:6 phosphatidylethanolamines) phospholipid vesicles was also determined between -30 and 30 degrees C and 5 and 30 degrees C, respectively. There is an accumulation of 1-monoenoic, 2-polyenoic diacyl phosphatidylcholine and ethanolamine with a concomitant reduction of 1-stearoyl,2-docosahexaenoyl species in the cold-adapted state. Despite a 30% accumulation of long-chain polyunsaturated fatty acids in phospholipids in cold, there is only a 5 degrees C downshift in the solid-gel to liquid-crystalline phase transition temperature (-8 vs. -13 degrees C). Vesicles from total phospholipids of cold-adapted fish proved to be more disordered in all segments than from the warm-adapted ones when assayed using 2,12-(N-9-anthroyloxy)stearic and 16-(N-9-anthroyloxy)palmitic acid. Vesicles made from purified phosphatidylcholines showed the same pattern, but they were more disordered than the corresponding total phospholipids. This could be modelled using mixed phospholipid vesicles made of synthetic 16:0/22:6 phosphatidylcholine (75%) and either 18:1/22:6 phosphatidylethanolamine (25%) vs. 16:0/18:1 phosphatidylethanolamine (25%) and comparison of the anisotropy parameters of 100% 16:0/22:6 and 100% 18:1/22:6 phosphatidylcholine vesicles. Mixing either 16:0/18:1 (25%) or 18:1/22:6 (25%) phosphatidylethanolamines to 18:0/22:6 (75%) phosphatidylcholine shifted down or up, respectively, the transition temperature of vesicles compared to 100% 18:0/22:6 vesicles assayed by electron spin resonance spectroscopy using 5-doxylstearic acid. It is concluded that it is not the gross amount of long-chain polyunsaturated fatty acids in phospholipids, but rather their specific combination with cis delta 9 monounsaturated fatty acids in the position sn-1, especially in phosphatidylethanolamines, that is important in determining the physical properties of biomembranes in relation to adaptational temperature.

The effects of phospholipid unsaturation and alcohol perturbation at the protein/lipid interface probed using fluorophore lifetime heterogeneity

The influence of phospholipid unsaturation and perturbation by alcohols, on the membrane protein/lipid interface, was probed using the fluorescence decay properties of 1,6-diphenyl-1,3,5-hexatriene (DPH) and DPH attached to the sn-2 chain of phosphatidylcholine (DPH-PC), in lipid bilayers and microsomal membranes. With microsomal membranes it was found that it was appropriate to describe the fluorescence decay of DPH-PC as a range of decay rates, accomplished by fitting the data to a bimodal fluorescence lifetime distribution. The major lifetime center had a broad distributional width, indicative of excited state fluorophore heterogeneity. The effect was attributable to protein, and by inference, the protein/lipid interface, since in vesicles made from total microsomal lipids (i.e., without protein) the fluorescence decay was homogeneous. Upon addition of ethanol or hexanol the width of the lifetime distribution of the major lifetime center increased, indicating increased environmental heterogeneity. It was confirmed that the effect was manifest at the protein/lipid interface, and not due to lipid-reorganizational factors, since it could also be obtained using a simple lipid bilayer vesicle system with apocytochrome c as a model membrane protein, and DPH instead of DPH-PC. Environmental heterogeneity was also found to increase with increased phosphatidylcholine (sn-2) unsaturation. The environmental heterogeneity at the protein/lipid interface could arise from a combination of varying polarities of amino acid side chains and of water that may intercalate in packing defects on the hydrophobic surface of the protein. Therefore the results could be explained on the basis of an increased degree of hydration at the protein/lipid interface. Such an effect offers a route whereby acyl chain perturbation and increased unsaturation might influence protein conformation and hence function.

Effect of fish oil and vitamin E on ethanol-induced changes in membrane ATPases

We evaluated whether fish oil or vitamin E administration affected ethanol-induced changes in membrane ATPases. Male Wistar rats (225-250 g) were fed, through a gastric tube a liquid diet containing fish oil (25% of calories) and ethanol for one month. Another group of animals was given supplemental vitamin E (300 u/kg). In the pair-fed control animals, ethanol-derived calories were replaced with dextrose. The blood ethanol levels were maintained between 150 and 350 mg/dL. At sacrifice, the red cells were immediately washed with ice-cold saline, membranes were prepared and ATPases measured. These was no difference in the Na+K+ ATPase, Ca2+ ATPase and Mg2+ ATPase activities between the fish oil-dextrose and corn oil-dextrose groups. A decrease in Ca2+ ATPase and an increase in Na+K+ ATPase was seen with ethanol feeding; these change are similar to those seen in corn oil-ethanol fed rats. In contrast, Vitamin E administration prevented the ethanol-induced changes in ATPase. This observation provides support for the role of lipid peroxidation in alcohol-induced changes in cell membrane ATPase activities.

Effect of n-3 and n-6 fatty acids on hepatic microsomal lipid metabolism: a time course study

The present study examines the time dependent effects of n-6 and n-3 polyunsaturated fatty acids on liver microsomal lipid metabolism in FVB mice fed a diet supplemented with a mixture of free fatty acids (mainly 18:3n-6 and 20:5n-3) at 25 mg/g diet. Significant changes in the fatty acid composition of total liver and microsomal lipids were observed after 7 days on the diets. Thereafter, some animals remained on the same diet while others were fed a diet supplemented with hydrogenated coconut oil (HCO). With the exception of 20:5n-3 which showed a slower recovery, establishment of the HCO pattern was rapid indicating that the diet-induced changes could be easily reversed. The unsaturation index, the cholesterol/phospholipid ratio and the microviscosity of the microsomal membranes were not affected by these dietary manipulations. Unsaturated fatty acid supplementation reduced the activity of delta 9 desaturase by 50%. Feeding the HCO diet to mice previously fed the EPA/GLA diet led to a progressive increase in delta 9 desaturase activity, reaching 80% of the day zero values after 14 days. The monoene content of hepatic total lipids reflected, in most cases, the changes in enzyme activity. This study shows that a low dose of a n-3 and n-6 free fatty acid mixture increases the quantities of members of the n-3 family, without loss of n-6 fatty acids in microsomal membranes and modifies the activity of delta 9 desaturase without altering the microsome physicochemical parameters.

Chronic ethanol ingestion modifies liver microsomal phosphatidylserine inducing resistance to hydrolysis by exogenous phospholipase A2

Chronic ethanol ingestion leads to the acquisition of a tolerance to membrane lipid disordering, a lowered partition coefficient to hydrophobic compounds and a resistance to the hydrolysis of the phospholipids by exogenous phospholipase A2. Anionic phospholipids have been implicated as being responsible for the resistance to lipid disordering and a number of modifications to these phospholipids are known to occur as a result of chronic ethanol-ingestion. In this study the basis of the resistance to phospholipase A2 in hepatic microsomes was investigated. It was found that chronic ethanol-induced modifications to each of the major phospholipid classes was responsible to some extent for the resistance to phospholipase A2, however, PS was particularly potent considering it is a compositionally minor constituent. The effect was interpreted as a reduced ability to activate the phospholipase A2 since PS acts as an essential activator of phospholipase A2 (along with PI). Fatty acid analysis revealed that the chronic ethanol-treatment resulted in a elevated level of docosahexaenoate with a parallel reduction in arachidonate in phosphatidylserine. Lipid packing and organization is important in the regulating the level of exogenous phospholipase A2 activity but the activity was not found to correlate with lipid order of different phosphatidylserine species. It is concluded that subtle differences in the molecular species arrangement or disposition around the enzyme may be responsible for the altered phospholipase A2 interaction with the membrane induced by chronic ethanol-treatment. One implication of this study is that other anionic phospholipid dependent membrane proteins, of which there are many known examples, may also be modified as a result of chronic ethanol-ingestion.