The acyl composition of mammalian phospholipids: an allometric analysis

Summer fades, deer change: Photoperiodic control of cellular seasonal acclimatization of skeletal muscle

We found major seasonal changes of polyunsaturated fatty acids (PUFAs) in muscular phospholipids (PL) in a large non-hibernating mammal, the red deer (Cervus elaphus). Dietary supply of essential linoleic acid (LA) and α-linolenic acid (ALA) had no, or only weak influence, respectively. We further found correlations of PL PUFA concentrations with the activity of key metabolic enzymes, independent of higher winter expression. Activity of the sarcoplasmic reticulum (SR) Ca++-ATPase increased with SR PL concentrations of n-6 PUFA, and of cytochrome c oxidase and citrate synthase, indicators of ATP-production, with concentrations of eicosapentaenoic acid in mitochondrial PL. All detected cyclic molecular changes were controlled by photoperiod and are likely of general relevance for mammals living in seasonal environments, including humans. During winter, these changes at the molecular level presumably compensate for Arrhenius effects in the colder peripheral body parts and thus enable a thrifty life at lower body temperature.

What do molecular laws of life mean for species: absolute restrictions or mere suggestions?

Evolutionary biologists are interested in finding universal patterns of covariation between macroscopic and molecular traits. Knowledge of such laws of life can be essential for understanding the course of evolutionary processes. Molecular parameters are presumably close to fundamental limits set to all organisms by laws of physics and chemistry. Thus, laws of life that include such parameters are hypothesized to be similar at both wide interspecific levels of variation and narrower levels of intraspecific and intraindividual variation in different species. In this Commentary, I discuss examples where the significance or direction of such molecular laws of life can be compared at different levels of biological variation: (1) the membrane pacemaker theory of metabolism, (2) the correlation between variation in metabolic rate and mitochondrial efficiency and (3) the allometric scaling of metabolism. All three examples reveal that covariations within species or individuals that include molecular parameters do not always follow patterns observed between species. I conclude that limits set by molecular laws of life can be circumvented (at least to some degree) by changes in other traits, and thus, they usually do not impose strict limitations on minor within-species evolutionary changes (i.e. microevolution). I also briefly discuss some of the most promising perspectives for future studies on the universality of molecular laws of life.

Role of ferroptosis in pregnancy related diseases and its therapeutic potential

Ferroptosis is a form of regulated cell death characterized by iron overload, overwhelming lipid peroxidation, and disruption of antioxidant systems. Emerging evidence suggests that ferroptosis is associated with pregnancy related diseases, such as spontaneous abortion, pre-eclampsia, gestational diabetes mellitus, intrahepatic cholestasis of pregnancy, and spontaneous preterm birth. According to these findings, inhibiting ferroptosis might be a potential option to treat pregnancy related diseases. This review summarizes the mechanisms and advances of ferroptosis, the pathogenic role of ferroptosis in pregnancy related diseases and the potential medicines for its treatment.

Fatty Acid Composition of M. Biceps Femoris of Edible Dormouse (Glis glis L.)

This study aimed to investigate the fatty acid (FA) composition of edible dormouse m. biceps femoris in both sexes. More than 20 FA were identified in the muscle, with the 18:1cis-9 (oleic acid) being the most abundant in both sexes, comprising more than 50% of total FA in muscle. The most dominated FA were monounsaturated (MUFA), followed by saturated FA (SFA) and polyunsaturated FA (PUFA), reaching 54.8%, 25.43% and 19.8% of total FA, respectively. Sums of PUFA and n-3 PUFA tended (p > 0.05) to be higher in males than in females. There were no significant differences between sexes on the FA composition. Nevertheless, the 18:2n-6 tended to differ between sexes (p = 0.063). Several long-chain PUFA (LC-PUFA) were detected in dormouse muscle, with the 20:4 n-6 (arachidonic acid, AA) and the 22:6 n-3 (docosahexaenoic acid, DHA) being the most abundant in both sexes. The relatively high stearoyl-CoA desaturase (SCD) indexes and the large concentration of 18:1cis-9 in dormouse muscle tissues might point to a low mobilization of the SCD products. Furthermore, finding the unusual FA 20:3 ∆5,∆11,∆14, suggests feeding on leaf and wood lipids of Coniferophytes. We demonstrated sexual size monomorphism in edible dormouse. The literature regarding the composition of dormouse meat is scarce and no studies reported the FA composition of muscle, thus, this work can contribute to increasing the knowledge on edible dormouse physiology and nutritional traits.

The Effect of Climate and Diet on Body Lipid Composition in the Oriental Hornet (Vespa orientalis)

Fatty acids (FA) are the primary metabolic fuel for many organisms and the fundamental component of membranes of all living organisms. FAs can be saturated (SFA), monounsaturated (MUFA), or polyunsaturated (PUFA). PUFA are not synthesized by most animals and are considered as essential nutrients. We examined the effect of climate on the saturation level of polar (mostly membranal) and neutral lipids in the body of the Oriental hornet (Vespa orientalis) from two extreme climatic zones: Mediterranean high elevation; and hot arid desert. In contrast to previous reports, the environmental temperature was shown to affect the hornet colonies’ thermal environments. The hornets nonetheless maintained their colony temperature within a narrow range. Analyses of the hornets’ unsaturation levels of polar and non-polar body lipids revealed caste differences: gynes and males contained less unsaturated lipids than workers. However, there were no differences in the respective castes between the two different climate zones tested. Experimentally manipulating the diet of queenless hornet colonies to a high Omega-3 diet (salmon) or a high Omega-6 diet (crickets) had only a minor effect on the worker-born males’ lipid composition. Although salmon-fed males had a higher Omega-3 content than cricket-fed ones, the proportion of these fatty acids was still low (below 1%). Cricket-fed males had significantly higher levels of Omega-6 than salmon-fed males. Our data show that the specific lipid composition of the hornet body is highly regulated and deficient in essential PUFA, even under different climates or high Omega-3 or Omega-6 PUFA diet. PUFA, especially Omega-3, is considered to have a beneficial effect on physiological processes. Our finding that these FA, when common in the diet, are almost absent in the body raises questions about how they affect animals’ physiology.

Omega-3 fatty acids accelerate fledging in an avian marine predator: a potential role of cognition

Consuming omega-3 fatty acids (n-3 LCPUFAs) during development improves cognition in mammals, but the effect remains untested in other taxa. In aquatic ecosystems, n-3 LCPUFAs are produced by phytoplankton and bioaccumulate in the food web. Alarmingly, the warming and acidification of aquatic systems caused by climate change impair n-3 LCPUFA production, with an anticipated decrease of 80% by the year 2100. We tested whether n-3 LCPUFA consumption affects the physiology, morphology, behaviour and cognition of the chicks of a top marine predator, the ring-billed gull. Using a colony with little access to n-3 LCPUFAs, we supplemented siblings from 22 fenced nests with contrasting treatments from hatching until fledging; one sibling received n-3 LCPUFA-rich fish oil and the other, a control sucrose solution without n-3 LCPUFAs. Halfway through the nestling period, half the chicks receiving fish oil were switched to the sucrose solution to test whether n-3 LCPUFA intake remains crucial past the main growth phase (chronic versus transient treatments). Upon fledging, n-3 LCPUFAs were elevated in the blood and brains of chicks receiving the chronic treatment, but were comparable to control levels among those receiving the transient treatment. Across the entire sample, chicks with elevated n-3 LCPUFAs in their tissues fledged earlier despite their morphology and activity levels being unrelated to fledging age. Fledging required chicks to escape fences encircling their nest. We therefore interpret fledging age as a possible indicator of cognition, with chicks with improved cognition fledging earlier. These results provide insight into whether declining dietary n-3 LCPUFAs will compromise top predators' problem-solving skills, and thus their ability to survive in a rapidly changing world.

Mammals to membranes: A reductionist story

This is the story of a series of reductionist studies that started with an attempt to explain what underpins the high-level of aerobic metabolism in mammals (i.e. associated with the evolution of endothermy) and almost forty years later had led to investigations into the role of membrane lipids in determining metabolism. Initial studies showed that the increase in aerobic metabolism in mammals was driven by a combination of increases in mitochondrial volume and membrane densities, organ size and changes in the molecular activity of enzymes. The increase in the capacity to produce energy was matched by an increase in energy use, notably driven by increases in H⁺, Na⁺ and K⁺ fluxes. In the case of increased Na⁺ flux, it was found this was matched by increases in Na⁺-dependent metabolism at the tissue level and increases in enzyme activity at a cellular level but not by an increase in the number of sodium pumps. To maintain Na⁺ gradient across cell membranes, increased Na⁺ flux is not controlled by an increase in sodium pump number but rather by an increase in sodium pump molecular activity (i.e. an increase the substrate turnover rate of each sodium pump) in tissues of endotherms. This increase in molecular activity is coupled to an increase in the level of highly unsaturated polyunsaturated fatty acids (PUFA) in membranes, a mechanism similar to that used by ectotherms to ameliorate decreasing activities of metabolic processes in the cold. Determination of how changes in membrane fatty acid composition can change the activities of proteins in membranes will be the next step in this story.

Coevolution of body size and metabolic rate in vertebrates: a life-history perspective

Despite many decades of research, the allometric scaling of metabolic rates (MRs) remains poorly understood. Here, we argue that scaling exponents of these allometries do not themselves mirror one universal law of nature but instead statistically approximate the non-linearity of the relationship between MR and body mass. This 'statistical' view must be replaced with the life-history perspective that 'allows' organisms to evolve myriad different life strategies with distinct physiological features. We posit that the hypoallometric allometry of MRs (mass scaling with an exponent smaller than 1) is an indirect outcome of the selective pressure of ecological mortality on allocation 'decisions' that divide resources among growth, reproduction, and the basic metabolic costs of repair and maintenance reflected in the standard or basal metabolic rate (SMR or BMR), which are customarily subjected to allometric analyses. Those 'decisions' form a wealth of life-history variation that can be defined based on the axis dictated by ecological mortality and the axis governed by the efficiency of energy use. We link this variation as well as hypoallometric scaling to the mechanistic determinants of MR, such as metabolically inert component proportions, internal organ relative size and activity, cell size and cell membrane composition, and muscle contributions to dramatic metabolic shifts between the resting and active states. The multitude of mechanisms determining MR leads us to conclude that the quest for a single-cause explanation of the mass scaling of MRs is futile. We argue that an explanation based on the theory of life-history evolution is the best way forward.

Conversion of dietary polyunsaturated fats between humans and rodents: A review of allometric scaling models

The purpose of this research was to explore various allometric scaling models for dietary nutrients to improve translational validity between preclinical experimental rodent models and humans, focusing on polyunsaturated fats. Currently, there is no authoritative document that provides standardized guidelines for which dietary designs can be based on to improve translational fidelity between species. This paper reviews the challenges of using a rodent model, the major allometric scaling models, the use of these mathematical models to extrapolate human equivalent doses, and then tests one of these models using data generated in mice, with comparisons of data generated in human clinical trials. Mice were fed diets containing micro- and macronutrient compositions that approximated the US diet based on energy distribution and were then supplemented with increasing levels of various n-3 and n-6 polyunsaturated fatty acids at human equivalent doses. Changes in plasma and erythrocyte fatty acid phospholipid compositions were determined and compared to corresponding data generated in humans. Our findings suggest that basing lipid composition on percent of energy may result in comparable outcomes between mice and humans and that extrapolation of non-energy producing nutrients between species might be done using differences in energy needs (based on food intake).

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.

Plant-based stearidonic acid as sustainable source of omega-3 fatty acid with functional outcomes on human health

Dietary omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFA) like eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) are known to be potent biological regulators with therapeutic and preventive effects on human health. Many global health organizations have recommended consuming marine based omega-3 sources for neonatal brain development and reducing the risk of various chronic diseases. However, due to concerns regarding the origin, sustainable supply and safety of the marine sources, alternative n-3 PUFA sources are being explored. Recently, plant-based omega-3 sources are gaining much importance because of their sustainable supply and dietary acceptance. α-linolenic acid (ALA, 18:3n-3) rich seed oils are the major omega-3 fatty acid source available for human consumption. But, efficiency of conversion of ALA to n-3 LC-PUFAs in humans is limited due to a rate-limiting step in the n-3 pathway catalyzed by Δ6-desaturase. Botanical stearidonic acid (SDA, 18:4n-3) rich oils are emerging as a sustainable omega-3 source with efficient conversion rate to n-3 LC-PUFA especially to EPA, as it bypasses the Δ6-desaturase rate limiting step. Several recent studies have identified the major plant sources of SDA and explored its potential health benefits and preventive roles in inflammation, cardiovascular disease (CVD) and cancer. This systematic review summarizes the current state of knowledge on the sources, nutraceutical roles, food-based applications and the future perspectives of botanical SDA.

Fundamentals about onset and progressive disease character of type 2 diabetes mellitus

ResearchGate is a world wide web for scientists and researchers to share papers, ask and answer questions, and find collaborators. As one of the more than 15 million members, the author uploads research output and reads and responds to some of the questions raised, which are related to type 2 diabetes. In that way, he noticed a serious gap of knowledge of this disease among medical professionals over recent decades. The main aim of the current study is to remedy this situation through providing a comprehensive review on recent developments in biochemistry and molecular biology, which can be helpful for the scientific understanding of the molecular nature of type 2 diabetes. To fill up the shortcomings in the curricula of medical education, and to familiarize the medical community with a new concept of the onset of type 2 diabetes, items are discussed like: Insulin resistance, glucose effectiveness, insulin sensitivity, cell membranes, membrane flexibility, unsaturation index (UI; number of carbon-carbon double bonds per 100 acyl chains of membrane phospholipids), slow-down principle, effects of temperature acclimation on phospholipid membrane composition, free fatty acids, energy transport, onset of type 2 diabetes, metformin, and exercise. Based on the reviewed data, a new model is presented with proposed steps in the development of type 2 diabetes, a disease arising as a result of a hypothetical hereditary anomaly, which causes hyperthermia in and around the mitochondria. Hyperthermia is counterbalanced by the slow-down principle, which lowers the amount of carbon-carbon double bonds of membrane phospholipid acyl chains. The accompanying reduction in the UI lowers membrane flexibility, promotes a redistribution of the lateral pressure in cell membranes, and thereby reduces the glucose transporter protein pore diameter of the transmembrane glucose transport channel of all Class I GLUT proteins. These events will set up a reduction in transmembrane glucose transport. So, a new blood glucose regulation system, effective in type 2 diabetes and its prediabetic phase, is based on variations in the acyl composition of phospholipids and operates independent of changes in insulin and glucose concentration. UI assessment is currently arising as a promising analytical technology for a membrane flexibility analysis. An increase in mitochondrial heat production plays a pivotal role in the existence of this regulation system.

The highly unnatural fatty acid profile of cells in culture

The fatty acid profile of cells in culture are unlike those of natural cells with twice the monounsaturated (MUFA) and half the polyunsaturated fatty acids (PUFA) level (Mol%). This is not due to cell lines primarily being derived from cancers but is due to limited access to lipid and an inability to make PUFA de novo as vertebrate cells. Classic culture methods use media with 10% serum (the only exogenous source of lipid). Fetal bovine serum (FBS), the serum of choice has a low level of lipid and cholesterol compared to other sera and at 10% of media provides 2-3% of the fatty acid and cholesterol, 1% of the PUFA and 0.3% of the essential fatty acid linoleic acid (18:2n-6) available to cells in the body. Since vertebrate cell lines cannot make PUFA they synthesise MUFA, offsetting their PUFA deficit and reducing their fatty acid diversity. Stem and primary cells in culture appear to be similarly affected, with a rapid loss of their natural fatty acid compositions. The unnatural lipid composition of cells in culture has substantial implications for examining natural stems cell in culture, and for investigations of cellular mechanisms using cell lines based on the pervasive influence of fats.

Docosahexaenoic acid varies in rat skeletal muscle membranes according to fibre type and provision of dietary fish oil

BACKGROUND

Dietary fish oil provides polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) and is associated with modified oxygen consumption, contractile fatigue and physiological responses to ischaemia or hypoxia in striated muscle. This study systematically investigated the membrane incorporation of fatty acids, with a focus on DHA, into skeletal muscle in relation to functional/metabolic differences and their responsiveness to fish oil doses.

METHODS

Male Sprague-Dawley rats were randomised to isoenergetic diets (10% fat by weight). Human Western-style diets were simulated with 5.5% tallow, 2.5% n-6 PUFA sunflower seed oil and 2% olive oil (Control). High-DHA tuna oil exchanged for olive oil provided a Low (0.32%) or moderate (Mod) (1.25%) fish oil diet. Membrane phospholipid fatty acid composition was analysed in samples of five skeletal muscles selected for maximum variation in muscle fibre-type.

RESULTS

Concentrations of DHA varied according to muscle fibre type, very strongly associated with fast oxidative glycolytic fibre population (r² = 0.93; P < 0.01). No relationship was evident between DHA and fast glycolytic or slow oxidative fibre populations. Fish oil diets increased membrane incorporation of DHA in all muscles, mainly at the expense of n-6 PUFA linoleic and arachidonic acid.

CONCLUSION

The exquisite responsiveness of all skeletal muscles to as little fish oil as the equivalent of 1-2 fish meals per week in a human diet and the selective relationship to fatigable muscle fibre-types supports an integral role for DHA in muscle physiology, and particularly in fatigue resistance of fast-twitch muscles.

SUMMARY

Skeletal muscle fibres vary according to structural, metabolic and neurological characteristics and ultimately influences contractile function. This study sort to determine if the composition of phospholipid polyunsaturated fatty acids (PUFA), incorporated in their membranes, might also differ according to fibre type and when omega-3 PUFA are made available in the diet. We systematically demonstrated that the omega-3 PUFA, docosahexaenoic acid (DHA), incorporated into skeletal muscle membranes well above its provision in the diet and without competitive influence of high omega-6 PUFA concentrations, typical to the Western-style human diet. Notably, incorporation preferentially occurred according to metabolic characteristics of each muscle, supporting the notion that DHA plays an integral role in fast oxidative glycolytic muscle fibres.

Valuable carcasses: postmortem preservation of fatty acid composition in heart tissue

In order to effectively conserve species, we must understand the structure and function of integral mechanisms at all levels of organismal organisation, from intracellular biochemistry to whole animal ecophysiology. The accuracy of biochemical analyses depend on the quality and integrity of the samples analysed. It is believed that tissue samples collected immediately postmortem provide the most reliable depiction of the living animal. Yet, euthanasia of threatened or protected species for the collection of tissue presents a number of ethical complications. Polyunsaturated fatty acids (PUFA) are essential to the cardiovascular system of all animals and the structure of PUFA can be degraded by peroxidation, potentially modifying the fatty acid composition of the tissue over postmortem time. Here, we assessed the composition of PUFA in cardiac tissue of bats (Carollia perspicillata) over the course of 12-h postmortem. We show that PUFA are resistant to naturally occurring postmortem degradation in heart tissue, with no difference in the overall composition of fatty acids across all time classes (0, 3, 6 or 12-h postmortem). Our results suggest that carcasses that would otherwise be discarded may actually be viable for the assessment of fatty acid composition in a number of tissues. We hope to spur further investigations into the viability of carcasses for other biochemical analyses as they may be an untapped resource available to biologists.

Honeybee caste lipidomics in relation to life-history stages and the long life of the queen

Honey bees have evolved a system in which fertilised eggs transit through the same developmental stages but can become either workers or queens. This difference is determined by their diet through development. Whereas workers live for weeks (normally 2-6 weeks), queens can live for years. Unfertilised eggs also develop through the same stages but result in a short living male caste (drones). Workers and drones are fed pollen throughout their late larval and adult life stages, while queens are fed exclusively on royal jelly and do not eat pollen. Pollen has high content of polyunsaturated fatty acids (PUFA) while royal jelly has a negligible amount of PUFA. To investigate the role of dietary PUFA lipids, and their oxidation in the longevity difference of honey bees, membrane fatty acid composition of the three castes was characterised at six different life-history stages (larvae, pupa, emergent, and different adult stages) through mass spectrometry. All castes were found to share a similar membrane phospholipid composition during early larval development. However, at pupation, drones and workers increased their level of PUFA, whilst queens increased their level of monounsaturated fatty acids. After emergence, worker bees further increased their level of PUFA by 5-fold across most phospholipid classes. In contrast, the membrane phospholipids of adult queens remained highly monounsaturated throughout their adult life. We postulate that this diet-induced increase in membrane PUFA results in more oxidative damage and is potentially responsible for the much shorter lifespans of worker bees compared to long-living queens.

The membrane pacemaker hypothesis: novel tests during the ontogeny of endothermy

The ‘membrane pacemaker’ hypothesis proposes a biochemical explanation for among-species variation in resting metabolism, based on the positive correlation between membrane docosahexaenoic acid (DHA) and metabolic rate. We tested this hypothesis using a novel model, altricial red-winged blackbird nestlings, predicting that the proportion of DHA in muscle and liver membranes should increase with the increasing metabolic rate of the nestling as it develops endothermy. We also used a dietary manipulation, supplementing the natural diet with fish oil (high DHA) or sunflower oil (high linoleic acid) to alter membrane composition and then assessed metabolic rate. In support of the membrane pacemaker hypothesis, DHA proportions increased in membranes from pectoralis muscle, muscle mitochondria, and liver during post-hatch development. By contrast, elevated dietary DHA had no effect on resting metabolic rate, despite causing significant changes to membrane lipid composition. During cold challenges, higher metabolic rates were achieved by birds that had lower DHA and higher linoleic acid in membrane phospholipids. Given the mixed support for this hypothesis, we conclude that correlations between membrane DHA and metabolic rate are likely spurious, and should be attributed to a still-unidentified confounding variable.

Effect of Selection for High Activity-Related Metabolism on Membrane Phospholipid Fatty Acid Composition in Bank Voles

Endothermy, high basal metabolic rates (BMRs), and high locomotor-related metabolism were important steps in the evolution of mammals. It has been proposed that the composition of membrane phospholipid fatty acids plays an important role in energy metabolism and exercise muscle physiology. In particular, the membrane pacemaker theory of metabolism suggests that an increase in cell membrane fatty acid unsaturation would result in an increase in BMR. We aimed to determine whether membrane phospholipid fatty acid composition of heart, liver, and gastrocnemius muscles differed between lines of bank voles selected for high swim-induced aerobic metabolism-which also evolved an increased BMR-and unselected control lines. Proportions of fatty acids significantly differed among the organs: liver was the least unsaturated, whereas the gastrocnemius muscles were most unsaturated. However, fatty acid proportions of the heart and liver did not differ significantly between selected and control lines. In gastrocnemius muscles, significant differences between selection directions were found: compared to control lines, membranes of selected voles were richer in saturated C18:0 and unsaturated C18:2n-6 and C18:3n-3, whereas the pattern was reversed for saturated C16:0 and unsaturated C20:4n-6. Neither unsaturation index nor other combined indexes of fatty acid proportions differed between lines. Thus, our results do not support the membrane pacemaker hypothesis. However, the differences between selected and control lines in gastrocnemius muscles reflect chain lengths rather than number of double bonds and are probably related to differences in locomotor activity per se rather than to differences in the basal or routine metabolic rate.

Of mice, pigs and humans: An analysis of mitochondrial phospholipids from mammals with very different maximal lifespans

The maximal lifespan (MLS) of mammals is inversely correlated with the peroxidation index, a measure of the proportion and level of unsaturation of polyunsaturated fatty acids (PUFA) in membranes. This relationship is likely related to the fact that PUFA are highly susceptible to damage by peroxidation. Previous comparative work has examined membrane composition at the level of fatty acids, and relatively little is known regarding the distribution of PUFA across phospholipid classes or phospholipid molecules. In addition, data for humans is extremely rare in this area. Here we present the first shotgun lipidomics analysis of mitochondrial membranes and the peroxidation index of skeletal muscle, liver, and brain in three mammals that span the range of mammalian longevity. The species compared were mice (MLS of 4 years), pigs (MLS of 27 years), and humans (MLS of 122 years). Mouse mitochondria contained highly unsaturated PUFA in all phospholipid classes. Human mitochondria had lower PUFA content and a lower degree of unsaturation of PUFA. Pig mitochondria shared characteristics of both mice and humans. We found that membrane susceptibility to peroxidation was primarily determined by a limited number of phospholipid molecules that differed between both tissues and species.

Perspectives on the membrane fatty acid unsaturation/pacemaker hypotheses of metabolism and aging

The membrane pacemaker hypotheses of metabolism and aging are distinct, but interrelated hypotheses positing that increases in unsaturation of lipids within membranes are correlated with increasing basal metabolic rate and decreasing longevity, respectively. The two hypotheses each have evidence that either supports or contradicts them, but consensus has failed to emerge. In this review, we identify sources of weakness of previous studies supporting and contradicting these hypotheses and suggest different methods and lines of inquiry. The link between fatty acyl composition of membranes and membrane-bound protein activity is a central tenet of the membrane pacemaker hypothesis of metabolism, but the mechanism by which unsaturation would change protein activity is not well defined and, whereas fatty acid desaturases have been put forward by some as the mechanism behind evolutionary differences in fatty acyl composition of phospholipids among organisms, there have been no studies to differentiate whether desaturases have been more affected by natural selection on aging and metabolic rate than have elongases or acyltransferases. Past analyses have been hampered by potentially incorrect estimates of the peroxidizability of lipids and longevity of study animals, and by the confounding effect of phylogeny. According to some authors, body mass may also be a confounding effect that should be taken into account, though this is not universally accepted. Further research on this subject should focus more on mechanisms and take weaknesses of past studies into account.

Membranes as a possible pacemaker of metabolism in cypriniform fish: does phylogeny matter?

The 'membrane pacemaker theory of metabolism' proposes that membranes set metabolic rate by modulating protein activity, and thus purports to explain membrane fatty acid allometry. This relationship has never been tested across species in ectotherms. After accounting for phylogeny, recent analyses have failed to support this theory based on correlations between muscle membrane composition and body mass across mammals. Therefore, the goal of this study was to seek phylogenetically corrected correlations between membrane composition, body mass and calcium-ATPase activity, using 12 species of closely related cypriniform fish (4-5500 g) covering a much narrower genetic scale than in previous tests. The results show that fish membrane unsaturation decreases with mass, but through different mechanisms from those in endotherms: 16:0 replacing 22:6 in muscle and 18:0 replacing 16:1, 18:1 and 18:2 in liver. This shows that allometric patterns differ between endotherms and ectotherms as well as between tissues. After accounting for phylogeny, however, almost all these relationships lose significance except for overall unsaturation. No relationship between calcium-ATPase activity and mass or phospholipid composition was detected. This study shows that membrane unsaturation of cypriniforms decreases with mass, but that genetic cues unrelated to size account for differences in the relative abundance of individual fatty acids. The membrane pacemaker concept accurately predicts general membrane properties such as unsaturation, but fails to explain finer scale allometric patterns. Future examinations of the membrane pacemaker hypothesis will have to take into account that allometric patterns vary between endotherms and ectotherms and between tissues of the same animal class.

An antioxidant-like action for non-peroxidisable phospholipids using ferrous iron as a peroxidation initiator

The degradation of phospholipids containing polyunsaturated fatty acids, termed peroxidation, poses a constant challenge to membranes lipid composition and function. Phospholipids with saturated (e.g. PC 16:0/16:0) and monounsaturated fatty acids (e.g. PC 16:0/18:1) are some of the most common phospholipids found in membranes and are generally not peroxidisable. The present experiments show that these non-peroxidisable phospholipids, when present in liposomes with peroxidisable phospholipids (i.e. those containing polyunsaturated fatty acids) such as PC 16:0/18:2 and Soy PC, produce an inhibitory effect on rates of peroxidation induced by ferrous-iron. This inhibitory effect acts to extend the duration of the lag phase by several-fold. If present in natural systems, this action could enhance the capacity of conventional antioxidant mechanisms in membranes. The results of this preliminary work suggest that non-peroxidisable phospholipids may exert an antioxidant-like action in membranes.

Impact of lipid oxidization on biophysical properties of model cell membranes

The oxidization of glycerophospholipids in cell membranes due to aging and environmental stresses may cause a variety of pathological and physiological consequences. A variety of oxidized phospholipid products (OxPl) are produced by the chemical oxidization of unsaturated hydrocarbon chains, which would significantly change the physicochemical properties of cell membranes. In this work, we constructed cell membrane models in the absence and presence of two stable oxidized lipid products and investigated their impact on physical properties of supported membranes using quartz crystal microbalance with dissipation (QCM-D) and high-energy X-ray reflectivity (XRR). Our experimental findings suggest that the lipid oxidization up to 20 mol % leads to the rupture of vesicles right after the adsorption. Our XRR analysis unravels the membrane thinning and the decrease in the lateral ordering of lipids, which can be explained by the decrease in the lateral packing of hydrocarbon chains. Further studies on mechanics of membranes incorporating oxidized lipids can be attributed to the decrease in the bending rigidity and the increase in the permeability.

Differences in the fatty-acid composition of rodent spermatozoa are associated to levels of sperm competition

Sperm competition is a prevalent phenomenon that drives the evolution of sperm function. High levels of sperm competition lead to increased metabolism to fuel higher sperm velocities. This enhanced metabolism can result in oxidative damage (including lipid peroxidation) and damage to the membrane. We hypothesized that in those species experiencing high levels of sperm competition there are changes in the fatty-acid composition of the sperm membrane that makes the membrane more resistant to oxidative damage. Given that polyunsaturated fatty acids (PUFAs) are the most prone to lipid peroxidation, we predicted that higher sperm competition leads to a reduction in the proportion of sperm PUFAs. In contrast, we predicted that levels of sperm competition should not affect the proportion of PUFAs in somatic cells. To test these predictions, we quantified the fatty-acid composition of sperm, testis and liver cells in four mouse species (genus Mus) that differ in their levels of sperm competition. Fatty-acid composition in testis and liver cells was not associated to sperm competition levels. However, in sperm cells, as predicted, an increase in sperm competition levels was associated with an increase in the proportion of saturated fatty-acids (the most resistant to lipid peroxidation) and by a concomitant decrease in the proportion of PUFAs. Two particular fatty acids were most responsible for this pattern (arachidonic acid and palmitic acid). Our findings thus indicate that sperm competition has a pervasive influence in the composition of sperm cells that ultimately may have important effects in sperm function.

Docosahexaenoic and arachidonic acid peroxidation: It's a within molecule cascade

Peroxidation is a well-known natural phenomenon associated with both health and disease. We compared the peroxidation kinetics of phosphatidylcholine (PC) molecules with different fatty acid compositions (i.e. 18:0, 18:1n-9, 18:2n-6, 20:4n-6 and 22:6n-3 at the sn-2 and 16:0 at sn-1 position) either as molecules free in solution or formed into liposomes. Fatty acid levels, oxygen consumption plus lipid hydroperoxide and malondialdehyde production were measured from the same incubations, at the same time during maximal elicitable peroxidation. PCs with highly peroxidizable fatty acids (i.e. 20:4n-6 and 22:6n-3) in the same incubation were found to be either fully peroxidized or intact. Rates of peroxidation of PCs with multiple bisallylic groups (i.e. 20:4n-6 and 22:6n-3) peroxidized at 2-3 times the rate per bisallylic bond than the same phospholipid with 18:2n-6. The results suggest that propagation of peroxidation (H-atom transfer) is firstly an intramolecular process that is several-fold faster than intermolecular peroxidation. PCs in solution peroxidized twice as fast as those in liposomes suggesting that only half of the phospholipids in liposomes were available to peroxidize i.e. the outer leaflet. Experiments on liposomes suggest that even after heavy peroxidation of the outer leaflet the inner leaflet is unaffected, indicating how cells may protect themselves from external peroxidation and maintain control over internal peroxidation. Intramolecular peroxidation may produce highly concentrated, localized sites of peroxidation product that together with internal control of peroxidation of the inner leaflet of membranes provide new insights into how cells control peroxidation at the membrane level.

Effects of metabolic rate and sperm competition on the fatty-acid composition of mammalian sperm

The sperm membrane is a key structure affecting sperm function and thus reproductive success. Spermatozoa are highly specialized and differentiated cells that undergo a long series of processes in the male and female reproductive tracts until they reach the site of fertilization. During this transit, the sperm membrane is prone to damage such as lipid peroxidation. The characteristics and performance of the sperm membrane are strongly determined by the fatty-acid composition of membrane phospholipids. Polyunsaturated fatty-acids (PUFAs) are the most prone to lipid peroxidation. Lipid peroxidation and other types of oxidative damage increase with higher metabolism and with higher levels of sperm competition due to the increased ATP production to fuel higher sperm velocities. Consequently, we hypothesized that, in order to avoid oxidative damage, and the ensuing impairment of sperm function, sperm cells exhibit a negative relationship between PUFA content and mass-specific metabolic rate (MSMR). We also hypothesized that higher sperm competition leads to a reduction in the proportion of sperm PUFAs. We performed a comparative study in mammals and found that high MSMR and high levels of sperm competition both promote a decrease in the proportion of PUFAs that are more prone to lipid peroxidation. The negative relationship between MSMR and these PUFAs in sperm cells is surprising, because a positive relationship is found in all other cell types so far investigated. Our results support the idea that the effects of MSMR and sperm competition on sperm function can operate at very different levels.

Body mass related variations in the polar lipid fatty acyl chain composition of the mammalian lung and alveolar surfactant

In nine mammalian species (mouse - cattle: 21.5 g-503 kg) lung total phospholipids (PL), alveolar surfactant phosphatidylcholine (PC) and sphingomyelin (SM) fatty acyl (FA) chain composition was tested relating to body mass (BM) and resting respiratory rate (RRR) associated adaptations. In PL, PC and SM oleic acid (C18:1 n9) provided negative correlations with RRR. Palmitic acid (C16:0) was strongly, positively correlated with RRR in the pulmonary PLs, and myristic (C14:0) acid correlated positively with RRR in the surfactant PCs. In pulmonary PLs negative allometry was found for myristic, palmitic, palmitoleic (C16:1 n7) and docosahexaenoic (C22:6 n3) acids and total saturation, while oleic (C18:1 n9), alpha-linolenic (C18:3 n3) and gondoic (C20:1 n9) acids, total n9 FA s and monounsaturation increased allometrically. In surfactant PC FA s palmitic acid provided negative, while oleic acid and monounsaturation positive allometry; the average FA chain length (ACL) was identical in all species. Surfactant SM FA composition was fully species independent for palmitic and arachidonic acids, total saturation, monounsaturation and ACL. The in vivo lipid peroxidation rate was species independent. The variability of lung PLs was consonant with the "membrane pacemakers theory", while surfactant PC composition was mostly related to RRR.

Dietary lipid quality and mitochondrial membrane composition in trout: responses of membrane enzymes and oxidative capacities

To examine whether membrane fatty acid (FA) composition has a greater impact upon specific components of oxidative phosphorylation or on overall properties of muscle mitochondria, rainbow trout (Oncorhynchus mykiss) were fed two diets differing only in FA composition. Diet 1 was enriched in 18:1n-9 and 18:2n-6 while Diet 2 was enriched in 22:6n-3. The FA composition of mitochondrial phospholipids was strongly affected by diet. 22:6n-3 levels were twice as high (49%) in mitochondrial phospholipids of fish fed Diet 2 than in those fed Diet 1. 18:2n-6 content of the phospholipids also followed the diets, whereas 18:1n-9 changed little. All n-6 FA, most notably 22:5n-6, were significantly higher in fish fed Diet 1. Nonetheless, total saturated FA, total monounsaturated FA and total polyunsaturated FA in mitochondrial phospholipids varied little. Despite a marked impact of diet on specific FA levels in mitochondrial phospholipids, only non-phosphorylating (state 4) rates were higher in fish fed Diet 2. Phosphorylating rates (state 3), oxygen consumption due to flux through the electron transport chain complexes as well as the corresponding spectrophotometric activities did not differ with diet. Body mass affected state 4 rates and cytochrome c oxidase and F 0 F 1 ATPase activities while complex I showed a diet-specific effect of body mass. Only the minor FA that were affected by body mass were correlated with functional properties. The regulated incorporation of dietary FA into phospholipids seems to allow fish to maintain critical membrane functions even when the lipid quality of their diets varies considerably, as is likely in their natural environment.

The extreme longevity of Arctica islandica is associated with increased peroxidation resistance in mitochondrial membranes

The deleterious reactive carbonyls released upon oxidation of polyunsaturated fatty acids in biological membranes are believed to foster cellular aging. Comparative studies in mammals and birds have shown that the susceptibility to peroxidation of membrane lipids peroxidation index (PI) is negatively correlated with longevity. Long-living marine molluscs are increasingly studied as longevity models, and the presence of different types of lipids in the membranes of these organisms raises questions on the existence of a PI-longevity relationship. We address this question by comparing the longest living metazoan species, the mud clam Arctica islandica (maximum reported longevity = 507 year) to four other sympatric bivalve molluscs greatly differing in longevity (28, 37, 92, and 106 year). We contrasted the acyl and alkenyl chain composition of phospholipids from the mitochondrial membranes of these species. The analysis was reproduced in parallel for a mix of other cell membranes to investigate whether a different PI-longevity relationship would be found. The mitochondrial membrane PI was found to have an exponential decrease with increasing longevity among species and is significantly lower for A. islandica. The PI of other cell membranes showed a linear decrease with increasing longevity among species and was also significantly lower for A. islandica. These results clearly demonstrate that the PI also decreases with increasing longevity in marine bivalves and that it decreases faster in the mitochondrial membrane than in other membranes in general. Furthermore, the particularly low PI values for A. islandica can partly explain this species' extreme longevity.

Negative allometry of docosahexaenoic acid in the fowl lung and pulmonary surfactant phospholipids

In a recent study (Comp. Biochem. Physiol. B. (2010)155: 301-308) we reported that the fatty acids (FA) of the avian (7 species) total lung phospholipids (PL) (i.e. lung parenchyma and surfactant together) provide allometric properties. To test whether this allometric scaling also occurs in either of the above components, in six gallinaceous species, in a body weight range from 150 g (Japanese quail, Coturnix coturnix japonica) to 19 kg (turkey, Meleagris gallopavo) the PL FA composition (mol%) was determined in the pulmonary surfactant, in native and in thoroughly lavaged lungs (referred to as lung parenchyma). In all three components docosahexaenoic acid (DHA) showed significant and negative allometric scaling (B = -0.056, -0.17 and -0.1, respectively). Surfactant PLs provided further negative allometry for palmitic acid and the opposite was found for palmitoleate and arachidonate. In the lung parenchymal PLs increasing body weight was matched with shorter chain FAs (average FA chain length) and competing n6 and n3 end-product fatty acids (positive allometry for arachidonic acid and negative for DHA). Negative allometric scaling was found for the tissue malondialdehyde concentration in the native and lavaged lungs (B = -0.1582 and -0.1594, respectively). In these tissues strong correlation was found between the MDA concentration and DHA proportion (r = 0.439 and 0.679, respectively), denoting the role of DHA in shaping the allometric properties and influencing the extent of in vivo lipid peroxidation of membrane lipids in fowl lungs.

Relationship between oxidizable fatty acid content and level of antioxidant glutathione peroxidases in marine fish

Biological membranes can be protected from lipid peroxidation by antioxidant enzymes including catalase (CAT) and selenium-dependent glutathione peroxidases 1 and 4 (GPx1 and GPx4). Unlike GPx1, GPx4 can directly detoxify lipid hydroperoxides in membranes without prior action of phospholipase A(2). We hypothesized that (1) GPx4 is enhanced in species that contain elevated levels of highly oxidizable polyunsaturated fatty acids (PUFA) and (2) activities of antioxidant enzymes are prioritized to meet species-specific oxidative stresses. In this study we examined (i) activities of the oxidative enzyme citrate synthase (CS) and antioxidant (CAT, GPx1 and GPx4) enzymes, (ii) GPx4 protein expression, and (iii) phospholipid composition in livers of five species of marine fish (Myxine glutinosa, Petromyzon marinus, Squalus acanthias, Fundulus heteroclitus and Myoxocephalus octodecemspinosus) that contain a range of PUFA. GPx4 activity was, on average, 5.8 times higher in F. heteroclitus and S. acanthias than in the other three marine fish species sampled. Similarly, activities of CAT and GPx1 were highest in S. acanthias and F. heteroclitus, respectively. GPx4 activity for all species correlates with membrane unsaturation, as well as oxidative activity as indicated by CS. These data support our hypothesis that GPx4 level in marine fish is a function, at least in part, of high PUFA content in these animals. GPx1 activity was also correlated with membrane unsaturation, indicating that marine species partition resources among glutathione-dependent defenses for protection from the initial oxidative insult (e.g. H(2)O(2)) and to repair damaged lipids within biological membranes.

Fatty acid composition of membrane bilayers: importance of diet polyunsaturated fat balance

In one of the most extensive analyses to date we show that the balance of diet n-3 and n-6 polyunsaturated fatty acids (PUFA) is the most important determinant of membrane composition in the rat under 'normal' conditions. Young adult male Sprague-Dawley rats were fed one of twelve moderate-fat diets (25% of total energy) for 8weeks. Diets differed only in fatty acid (FA) profiles, with saturate (SFA) content ranging 8-88% of total FAs, monounsaturate (MUFA) 6-65%, total PUFA 4-81%, n-6 PUFA 3-70% and n-3 PUFA 1-70%. Diet PUFA included only essential FAs 18:2n-6 and 18:3n-3. Balance between n-3 and n-6 PUFA is defined as the PUFA balance (n-3 PUFA as % of total PUFA) and ranged 1-86% in the diets. FA composition was measured for brain, heart, liver, skeletal muscle, erythrocytes and plasma phospholipids, as well as adipose tissue and plasma triglycerides. The conformer-regulator model was used (slope=1 indicates membrane composition completely conforming to diet). Extensive changes in diet SFA, MUFA and PUFA had minimal effect on membranes (average slopes 0.01, 0.07, 0.07 respectively), but considerable influence on adipose tissue and plasma triglycerides (average slopes 0.27, 0.53, 0.47 respectively). Diet balance between n-3 and n-6 PUFA had a biphasic influence on membrane composition. When n-3 PUFA<10% of total PUFA, membrane composition completely conformed to diet (average slope 0.95), while diet PUFA balance>10% had little influence (average slope 0.19). The modern human diet has an average PUFA balance ~10% and this will likely have significant health implications.

Relationship of electrophilic stress to aging

This review begins with the premise that an organism's life span is determined by the balance between two countervailing forces: (i) the sum of destabilizing effects and (ii) the sum of protective longevity-assurance processes. Against this backdrop, the role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses. Because most biological macromolecules contain nucleophilic centers, electrophiles are particularly reactive and toxic in a biological context. The majority of cellular electrophiles are generated from polyunsaturated fatty acids by a peroxidation chain reaction that is readily triggered by oxygen-centered radicals, but propagates without further input of reactive oxygen species (ROS). Thus, the formation of lipid-derived electrophiles such as 4-hydroxynon-2-enal (4-HNE) is proposed to be relatively insensitive to the level of initiating ROS, but to depend mainly on the availability of peroxidation-susceptible fatty acids. This is consistent with numerous observations that life span is inversely correlated to membrane peroxidizability, and with the hypothesis that 4-HNE may constitute the mechanistic link between high susceptibility of membrane lipids to peroxidation and shortened life span. Experimental interventions that directly alter membrane composition (and thus their peroxidizability) or modulate 4-HNE levels have the expected effects on life span, establishing that the connection is not only correlative but causal. Specific molecular mechanisms are considered, by which 4-HNE could (i) destabilize biological systems via nontargeted reactions with cellular macromolecules and (ii) modulate signaling pathways that control longevity-assurance mechanisms.

Molecular and structural antioxidant defenses against oxidative stress in animals

In this review, it is our aim 1) to describe the high diversity in molecular and structural antioxidant defenses against oxidative stress in animals, 2) to extend the traditional concept of antioxidant to other structural and functional factors affecting the "whole" organism, 3) to incorporate, when supportable by evidence, mechanisms into models of life-history trade-offs and maternal/epigenetic inheritance, 4) to highlight the importance of studying the biochemical integration of redox systems, and 5) to discuss the link between maximum life span and antioxidant defenses. The traditional concept of antioxidant defenses emphasizes the importance of the chemical nature of molecules with antioxidant properties. Research in the past 20 years shows that animals have also evolved a high diversity in structural defenses that should be incorporated in research on antioxidant responses to reactive species. Although there is a high diversity in antioxidant defenses, many of them are evolutionary conserved across animal taxa. In particular, enzymatic defenses and heat shock response mediated by proteins show a low degree of variation. Importantly, activation of an antioxidant response may be also energetically and nutrient demanding. So knowledge of antioxidant mechanisms could allow us to identify and to quantify any underlying costs, which can help explain life-history trade-offs. Moreover, the study of inheritance mechanisms of antioxidant mechanisms has clear potential to evaluate the contribution of epigenetic mechanisms to stress response phenotype variation.

Metabolic rate and membrane fatty acid composition in birds: a comparison between long-living parrots and short-living fowl

Both basal metabolic rate (BMR) and maximum lifespan potential (MLSP) vary with body size in mammals and birds and it has been suggested that these are mediated through size-related variation in membrane fatty acid composition. Whereas the physical properties of membrane fatty acids affect the activity of membrane proteins and, indirectly, an animal's BMR, it is the susceptibility of those fatty acids to peroxidation which influence MLSP. Although there is a correlation between body size and MLSP, there is considerable MLSP variation independent of body size. For example, among bird families, Galliformes (fowl) are relatively short-living and Psittaciformes (parrots) are unusually long-living, with some parrot species reaching maximum lifespans of more than 100 years. We determined BMR and tissue phospholipid fatty acid composition in seven tissues from three species of parrots with an average MLSP of 27 years and from two species of quails with an average MLSP of 5.5 years. We also characterised mitochondrial phospholipids in two of these tissues. Neither BMR nor membrane susceptibility to peroxidation corresponded with differences in MLSP among the birds we measured. We did find that (1) all birds had lower n-3 polyunsaturated fatty acid content in mitochondrial membranes compared to those of the corresponding tissue, and that (2) irrespective of reliance on flight for locomotion, both pectoral and leg muscle had an almost identical membrane fatty acid composition in all birds.

Allometric scaling of dietary linoleic acid on changes in tissue arachidonic acid using human equivalent diets in mice

Background

It is hypothesized that dietary linoleic acid (LA) promotes chronic and acute diseases in humans by enriching tissues with arachidonic acid (AA), its downstream metabolite, and dietary studies with rodents have been useful for validation. However, levels of LA in research diets of rodents, as published in the literature, are notoriously erratic making interspecies comparisons unreliable. Therefore, the ability to extrapolate the biological effects of dietary LA from experimental rodents to humans necessitates an allometric scaling model that is rooted within a human equivalent context.

Methods

To determine the physiological response of dietary LA on tissue AA, a mathematical model for extrapolating nutrients based on energy was used, as opposed to differences in body weight. C57BL/6J mice were divided into 9 groups fed a background diet equivalent to that of the US diet (% energy) with supplemental doses of LA or AA. Changes in the phospholipid fatty acid compositions were monitored in plasma and erythrocytes and compared to data from humans supplemented with equivalent doses of LA or AA.

Results

Increasing dietary LA had little effect on tissue AA, while supplementing diets with AA significantly increased tissue AA levels, importantly recapitulating results from human trials.

Conclusions

Thus, interspecies comparisons for dietary LA between rodents and humans can be achieved when rodents are provided human equivalent doses based on differences in metabolic activity as defined by energy consumption.

Nutritional ecology of essential fatty acids: an evolutionary perspective

There are four types of fatty acids but only two types are essential nutritional requirements for many animals. These are the omega-6 polyunsaturated fatty acids (n-6 PUFA) and the omega-3 polyunsaturated fatty acids (n-3 PUFA) and because they cannot be converted to one another they are separate essential dietary requirements. They are only required in small amounts in the diet and their biological importance stems largely from their role as constituents of membrane lipids. They are synthesised by plants and, as a generalisation, green leaves are the source of n-3 PUFA while seeds are the source of n-6 PUFA in the food chain. While the fatty acid composition of storage fats (triglycerides) is strongly influenced by dietary fatty acid composition, this is not the case for membrane fats. The fatty acid composition of membrane lipids is relatively unresponsive to dietary fatty acid composition, although n-3 PUFA and n-6 PUFA can substitute for each in membrane lipids to some extent. Membrane fatty acid composition appears to be regulated and specific for different species. The role of essential fats in the diet of animals on (1) basal metabolic rate, (2) thermoregulation, (3) maximum longevity, and (4) exercise performance is discussed.

Allometric scaling of fatty acyl chains in fowl liver, lung and kidney, but not in brain phospholipids

The phospholipid (PL) fatty acyl chain (FA) composition (mol%) was determined in the kidney, liver, lung and brain of 8 avian species ranging in body mass from 150g (Japanese quail, Coturnix coturnix japonica) to 19kg (turkey, Meleagris gallopavo). In all organs except the brain, docosahexaenoic acid (C22:6 n3, DHA) was found to show a negative allometric scaling (allometric exponent: B=-0.18; -0.20 and -0.24, for kidney, liver and lung, respectively). With minor inter-organ differences, smaller birds had more n3 FAs and longer FA chains in the renal, hepatic and pulmonary PLs. Comparing our results with literature data on avian skeletal muscle, liver mitochondria and kidney microsomes and divergent mammalian tissues, the present findings in the kidney, liver and lung PLs seem to be a part of a general relationship termed "membranes as metabolic pacemakers". Marked negative allometric scaling was found furthermore for the tissue malondialdehyde concentrations in all organs except the brain (B=-0.17; -0.13 and -0.05, respectively). In the liver and kidney a strong correlation was found between the tissue MDA and DHA levels, expressing the role of DHA in shaping the allometric properties of membrane lipids.

Effects of body lipid content on the resting metabolic rate and postprandial metabolic response in the southern catfish Silurus meridionalis

We assessed the effects of body lipid content on the resting metabolic rate and specific dynamic action (SDA) of the southern catfish Silurus meridionalis. Obese and lean fish were obtained by feeding the fish with two different feeds at 27.5 degrees C for 4 weeks prior to the experiment. The fish were fed with experimental diets with a meal size of 4% by body mass. A continuous-flow respirometer was used to determine the oxygen consumption rate at 2-h intervals until the postprandial oxygen consumption rate had returned to the preprandial level. The body lipid content of the obese fish was significantly greater than that of the lean fish. The metabolic parameters evaluated (resting metabolic rate, peak metabolic rate (R(peak)), factorial ratio, time to peak, duration, energy expended on SDA (SDA(E)), or SDA coefficient) were not significantly affected by body fat content in terms of the whole-body or mass-specific values. Increased body fat content did not decrease the resting metabolic rate in the southern catfish, which might be due to the higher levels of highly unsaturated fatty acids in these fish. The results also suggest that the body composition does not appear to affect the SDA response.

Are all n-3 polyunsaturated fatty acids created equal?

N-3 Polyunsaturated fatty acids have been shown to have potential beneficial effects for chronic diseases including cancer, insulin resistance and cardiovascular disease. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have been studied extensively, whereas substantive evidence for a biological role for the precursor, alpha-linolenic acid (ALA), is lacking. It is not enough to assume that ALA exerts effects through conversion to EPA and DHA, as the process is highly inefficient in humans. Thus, clarification of ALA's involvement in health and disease is essential, as it is the principle n-3 polyunsaturated fatty acid consumed in the North American diet and intakes of EPA and DHA are typically very low. There is evidence suggesting that ALA, EPA and DHA have specific and potentially independent effects on chronic disease. Therefore, this review will assess our current understanding of the differential effects of ALA, EPA and DHA on cancer, insulin resistance, and cardiovascular disease. Potential mechanisms of action will also be reviewed. Overall, a better understanding of the individual role for ALA, EPA and DHA is needed in order to make appropriate dietary recommendations regarding n-3 polyunsaturated fatty acid consumption.

High resistance to lipid peroxidation of bird heart mitochondria and microsomes: Effects of mass and maximum lifespan

The aim of this investigation was to study the connection between body size, fatty acid composition and sensitivity to lipid peroxidation of heart mitochondria and microsomes isolated from different size bird species: manon (Lonchura striata), quail (Coturnix coturnix var japonica), pigeon (Columba livia), duck (Cairina moschata) and goose (Anser anser), representing a 372-fold range of body mass. Fatty acids of total lipids were determined using gas chromatography and lipid peroxidation was evaluated with a chemiluminescence assay. The fatty acids present in heart organelles of the different bird species analyzed showed a small number of significant allometric trends. In mitochondria, from the individual fatty acid data, palmitoleic acid (C16:1 n7) increased allometrically (r=0.878), while stearic acid (C18:0) was negatively related to body mass (r=-0.903). Interestingly, none of the calculated fatty acid variables, the average fatty acid saturated, monounsaturated, polyunsaturated (PUFA) and the unsaturation index (UI) was established to show significant body size-related variations. In heart microsomes, the content of C18:0 was significantly smaller (r=-0.970) in the birds of greater size. A significant allometric increase in linoleic acid (C18:2 n6) (r=0.986), polyunsaturated (r=0.990) and UI (r=0.904) was observed in the larger birds. The total n6 fatty acids of heart mitochondria did not show significant differences when it was correlated to body mass of the birds. Moreover, positive allometric relationships were shown for microsomes. The total n3 fatty acids of heart mitochondria and microsomes indicated no significant correlations to body mass of birds. The C16:1 n7, C18:0 in mitochondria and C18:0, C18:2 n6, PUFA, UI and PUFA n6 in microsomes showed significant differences when they were correlated to maximum life span (MLSP) of birds. As light emission=chemiluminescence originated from heart organelles was not statistically significant, a lack of correlation between the sensitivity to lipid peroxidation and body size or maximum life span was obtained. These results indicate that the high resistance of bird hearts to the attack by free radicals is body size-independent and would be related to the preservation of cardiac function.