Variable Lipid Content Research Articles

Stable isotope analysis: modelling lipid normalization for muscle and eggs from arctic mammals and birds

Summary1. Lipids are more depleted in 13C than proteins. Variable lipid contents in tissues affect therefore the measurements of stable carbon isotope ratios. Model based (also called mathematical) normalization has been suggested to correct δ13C values using the ratio of carbon to nitrogen (C/N) as a proxy for lipid content. This approach has not been thoroughly validated for terrestrial animals and it is not clear to what extent it is generally applicable or species/tissue specific.2. Ratios of stable carbon isotopes (δ13C) were obtained for muscle samples of 22 mainly terrestrial arctic mammal and bird species and for egg samples of 32 bird species from nine sites in the circumpolar Arctic. We used linear and nonlinear equations to model the difference in δ13C between samples from which lipids had been extracted chemically and bulk tissue samples. Models were compared on the basis of a model selection criterion (AIC) and of prediction error as estimated by cross‐validation.3. For muscle samples, a linear and a nonlinear equation performed equally well. The observed values were also well predicted by a previously published general equation for aquatic organisms. For egg samples, a nonlinear equation fitted separately to waterfowl and non waterfowl bird species fitted the data best. Prediction errors were, however, larger than for muscle samples.4. The generality of the inferred normalization equations was assessed by applying them to a second data set from a similar ecosystem, but produced in the frame of another study. The predicted lean δ13C values were within 0·5‰ of the observed values for 73% of the muscle samples, but only for 27% of the egg samples.5. Based on our results, we recommend model based normalization of δ13C values as an economic way to deal with varying lipid contents in muscle samples of mammals and birds. For egg samples, on the contrary, model based predictions had large errors. Therefore, we recommend chemical lipid extraction in order to estimate lipid‐free δ13C values for egg content.

Zooplankton, lipids and stable isotopes: importance of seasonal, latitudinal, and taxonomic differences

We found considerable seasonal, latitudinal, and taxonomic differences in zooplankton lipid content and concurrent δ13C values of zooplankton. We collected cladoceran as well as cyclopoid and calanoid copepod zooplankton from boreal and subarctic lakes throughout a year, allowing us to study zooplankton likely subjected to different isotopic fractionation processes and with highly variable lipid contents. Considerable seasonal variation was observed in the difference between bulk and lipid-extracted zooplankton δ13C values, indicating that seasonally changing lipid content introduced notable variation in zooplankton δ13C values. The difference between bulk and lipid-extracted material was most amplified in lipid-rich subarctic zooplankton in winter, δ13C difference being >5 units. Significant differences were also observed among zooplankton taxa, with copepods showing a greater lipid impact on δ13C than cladocerans. Published lipid correction models failed to produce satisfying fits to our data, and considerable variation was left even after recalibrating the model parameters. This was likely due to taxonomic differences in lipid effects on δ13C values. We therefore produced separate mass balance-based lipid correction models for cladocerans and also cyclopoid and calanoid copepods. We conclude that arithmetic lipid correction models perform well with zooplankton samples, but taxonomic differences need to be considered.

PRELIMINARY INVESTIGATION INTO THE GEOGRAPHICAL ORIGIN DIFFERENTIATION OF SAFFRON (CROCUS SATIVUS L.) BY MULTI-ELEMENT (HCN) STABLE ISOTOPE ANALYSIS

ISHS III International Symposium on Saffron: Forthcoming Challenges in Cultivation, Research and Economics PRELIMINARY INVESTIGATION INTO THE GEOGRAPHICAL ORIGIN DIFFERENTIATION OF SAFFRON (CROCUS SATIVUS L.) BY MULTI-ELEMENT (HCN) STABLE ISOTOPE ANALYSIS

Lipid corrections in carbon and nitrogen stable isotope analyses: comparison of chemical extraction and modelling methods

1. Lipids have more negative delta(13)C values relative to other major biochemical compounds in plant and animal tissues. Although variable lipid content in biological tissues alters results and conclusions of delta(13)C analyses in aquatic food web and migration studies, no standard correction protocol exists. 2. We compared chemical extraction and mathematical correction methods for freshwater and marine fishes and aquatic invertebrates to better understand impacts of correction approaches on carbon (delta(13)C) and nitrogen (delta(15)N) stable isotope data. 3. Fish and aquatic invertebrate tissue delta(13)C values increased significantly following extraction for almost all species and tissue types relative to nonextracted samples. In contrast, delta(15)N was affected for muscle and whole body samples from only a few freshwater and marine species and had a limited effect for the entire data set. 4. Lipid normalization models, using C : N as a proxy for lipid content, predicted lipid-corrected delta(13)C for paired data sets more closely with parameters specific to the tissue type and species to which they were applied. 5. We present species- and tissue-specific models based on bulk C : N as a reliable alternative to chemical extraction corrections. By analysing a subset of samples before and after lipid extraction, models can be applied to the species and tissues of interest that will improve estimates of dietary sources using stable isotopes.

Effect of isoenergetic diets with different protein and lipid content on the growth performance and heat increment of rainbow trout

The heat increment of feeding (HiE) is the metabolic cost associated with feeding, typically measured in fish as the increase in oxygen consumption (MO2) over some estimate of standard metabolic rate (SMR). The present study sought to accurately measure HiE using a variety of different methods in order to remove the influence of routine fish activity and excitement which could overestimate HiE. Protein handling makes up a large component of HiE. Thus, there is an expectation that variations in dietary protein content could influence HiE. Therefore, growth performance parameters were assessed in juvenile rainbow trout fed daily to satiation one of three isoenergetic diets with equivalent carbohydrate content (12%) but variable protein (P) and lipid (L) content [theoretical protein:lipid levels were: 55%:10% (HP:LL); 45%:15% (MP:ML) and 35%:20% (LP:HL)]. The estimated dietary digestible protein (DP) to digestible energy (DE) ratios of 19.8, 24.8 and 29.8 g/MJ bracketed the recommended levels of 22–25 g/MJ for juvenile rainbow trout. HiE values for the same groups of fish that were maintained on the test diets after the growth trial were subsequently assessed following a single meal (by gavage) of 2% of their body mass so that the growth performance parameters could be compared with the HiE estimates. Some growth performance parameters (i.e., specific growth rate, feed efficiency and dry feed intake) did not vary significantly among fish fed the diets, whereas percent protein deposition was inversely related to dietary protein content and the dietary DP to DE ratio. The dissimilar diet treatments did not result in differences in values for SMR, RMR, peak MO2 or time-to-peak MO2 or in estimates for HiE. The mean SMR from all fish combined across treatments was 50.4±3.4 mg O2/kg/h. MO2 increased significantly above SMR by 4-h postprandial and peaked at 116.2±7.7 mg O2/kg/h, representing an increase of 131%. The metabolic cost of the diets (as a % of DE) was low, and best estimates ranged between 4.0 and 4.8%.

Variation among females in egg lipid content and developmental success of echinoderms from McMurdo Sound, Antarctica

Egg lipid and protein content of different females of Antarctic echinoderms in McMurdo Sound, Antarctica, were measured to assess variation among females and developmental success. Egg triacylglycerol content of the Antarctic sea urchin Sterechinus neumayeri, when less than 70 ng, correlated with embryos that failed to develop past the 4-day-old blastula stage. In contrast asteroids (Odontaster meridionalis, O. validus, Acodontaster hodgsoni) all produced eggs that developed normally, even with variable egg lipid content. This difference might be related to dietary sources for more herbivorous sea urchins compared to more omnivorous and predatory asteroids. Low egg lipid content, with resulting poor embryonic survivorship, suggests that herbivorous sea urchins may be under unusual levels of nutritional stress in McMurdo Sound during the time frame studied (2004–2005). This nutritional stress might be related to the presence of large icebergs, known to have reduced primary production in the Ross Sea area.

Depth related trends in proximate composition of demersal fishes in the eastern North Pacific

The proximate chemistry of the white muscle and liver of 18 species of demersal fish from the eastern North Pacific was studied to determine trends with depth, locomotory mode and buoyancy mechanism, foraging strategy and to elucidate energetic strategies. Data for 24 species from shallow water were taken from the literature and included for analysis of muscle water content. Benthopelagic species, primarily gadiforms, have significantly larger lipid-rich livers than benthic species. The benthopelagic species may use this lipid to add buoyancy, but it is also used as energy storage. Buoyancy mechanism was directly related to proximate composition. Fishes using gasbladders had normal muscle composition. The two species of benthopelagic fishes without gasbladders have either very high muscle lipid content ( Anoplopoma fimbria) or gelatinous muscle ( Alepocephalus tenobrosus) to aid in achieving neutral buoyancy. The macrourid, Albatrossia pectoralis, has a very small gasbladder and also has gelatinous muscle. Both of these benthopelagic fishes with gelatinous muscle feed on pelagic organisms. Gelatinous muscle was also found in two flatfishes that inhabit the oxygen minimum zone. For these fishes, high water content may serve to lower metabolic costs while maintaining large body size. Scavengers such as Coryphaenoides armatus and Coryphaenoides acrolepis have lipid rich livers and others such as A. fimbria and Pachycara sp. have high and variable muscle lipid content. Thus foraging mode also acts to influence proximate composition. Several depth-related trends in proximate composition were found. White muscle water content increased significantly with depth, and all four gelatinous species occurred at bathyal depths. This adds evidence in support of the hypothesis that decreasing light levels shorten reactive distances and relax the selective pressure for high locomotory capacity. In addition significant declines in liver protein content were observed, suggesting that the rates of metabolism in this organ also decline with depth. There was little evidence for food availability affecting proximate composition. There were no significant changes in either muscle or liver lipid or caloric density with depth. Total lipid stores actually increased significantly, but they were driven primarily by the abyssal scavenger C. armatus suggesting that foraging strategy rather than depth may be the most important factor determining total lipid stores.

Production of butter fat rich intrans10-C18:1 for use in biomedical studies in rodents

Trans fatty acids are suspected to be detrimental to health, particularly to cardiovascular function. Trans fatty acids include a wide range of fatty acids, with isomers of C18:1, conjugated and non-conjugated C18:2 as major components. A vaccenic acid (trans11-C18:1) + rumenic acid (cis9,trans11-CLA)-rich butter has been shown previously to exhibit health beneficial effects, but less is known concerning another trans-C18:1 present in hydrogenated vegetable oil-based products and sometimes in milk fat, the trans10-isomer. The present experiment was conducted to produce butters from milk of variable fatty acid composition for use in biomedical studies with rodents, with the overall aim of evaluating the specific effect of trans10-C18:1 and trans11-C18:1 + cis9,trans11-CLA on cardiovascular function. Milks from lactating dairy cows fed two types of maize-based diets supplemented (5% of dry matter)--or not--with sunflower oil were collected, and used to manufacture butters either rich in trans10-C18:1 (14% of total fatty acids, 64.5% of fat content) or rich in trans11-C18:1 + cis9,trans11-CLA (7.4 and 3.1% of total fatty acids, respectively, 68.5% of fat content), or with standard fatty acid composition (70% of fat content). Additionally, total saturated fatty acid percentage was reduced by more than one third in the enriched butters compared with the standard butter. An understanding of the role of nutrition on milk fatty acid composition in cows allows for the production of dairy products of variable lipid content and composition for use in biomedical studies in animal models and human subjects.

Evaluation and comparison of the CEM rapid extraction method with official standard methods for the determination of lipid content in fillets of farmed Atlantic salmon ( Salmo salar)

The CEM rapid extraction method for lipid content determination was compared with official standard methods and was found to give accurate results for individual samples, taking approximately 8 min per sample. The study involved the lipid analysis of 47 white muscle samples from six fillets of farmed Atlantic salmon, using both the CEM and the Soxhlet method, in order to evaluate the performance of the former. Nine samples from each fillet with variable lipid content, ranging from 2.0% to 25.4%, were analysed. The comparison of the CEM with the Soxhlet method showed that the CEM lipid values were significantly linearly correlated ( r 2=0.993, P<0.001), but were consistently lower than those of the standard by a factor of 0.37%. This difference was found to be more distinct in samples with lipid content below 10%. It is concluded that the CEM method is an effective rapid analysis method for the determination of lipid content in salmon fillets under commercial conditions for the routine monitoring of muscle lipid. For research purposes, it may be necessary to add a correction factor (0.59% for levels below 10% lipid and 0.27% above 10%) if direct comparisons with Soxhlet results are required.

Effect of dietary lipid content on circadian rhythm of feeding activity in European sea bass

In fish, dietary digestible energy (DE) content is a major factor controlling feed intake. It was therefore of interest to determine how circadian rhythm of feeding activity is influenced by the dietary DE levels. To that end, groups of European sea bass were fed on demand by means of self feeders, under light–dark and constant light conditions, with a fixed or an unlimited amount of feed with variable lipid contents. Daily total feed intake, but not the feeding rhythm, was adjusted in relation to the DE content of the diet regardless of the lighting conditions. We conclude that a satiation mechanism was likely responsible for the regulation of feed intake in relation to the dietary fat content but was not acting in itself on the mechanisms that drive the free-running rhythms of feeding activity. These results are giving additional evidence that a true endogenous clock is driving feeding activity rhythms in fish.

Modulation of Lipoprotein B Binding to the LDL Receptor by Exogenous Lipids and Apolipoproteins CI, CII, CIII, and E

We have recently shown that apo B-containing lipoproteins isolated by immunoaffinity chromatography bind to the LDL receptor with an affinity dependent on their apo E or apo CIII content. However, these lipoproteins--LpB:E, LpB:CIII, and LpB:CIII:E--isolated from whole plasma have variable lipid and apolipoprotein contents, and it is difficult to consider each parameter separately, particularly because an increase in the apo CIII content is always associated with an increase in the content of other C apolipoproteins. Therefore, we used affinity-purified LpB free of other apolipoproteins. Lipid content of LpB was increased by incubation with a lipid emulsion, and this triglyceride-enriched LpB was named TG-LpB. Free apo CI, apo CII, apo CIII, and apo E were added to LpB and TG-LpB and their associations to the lipoprotein were assessed by gel filtration, nondenaturing electrophoresis, and immunoblotting. Molar ratios of 6 (apo E), 30 (apo CII), 20 (apo CIII), and 30 (apo CI) for 1 apo B were obtained. The association of apo CII to LpB and TG-LpB induced modifications to the LpB structure and a redistribution of lipids and apolipoproteins on the lipoprotein particles. The binding of these LpBs and TG-LpBs with and without added apo CI, CII, CIII, and E was tested at 4 degrees C on the LDL receptors of HeLa cells. The increased content of lipids reduced TG-LpB binding to the LDL receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Study on the composition-structure relationship of lipophorins

High density lipophorin (HDLp is the main lipoprotein found in resting insect hemolymph. It has, in general, two molecules of apolipoproteins: apoLp-I (250 kDa) and apoLp-II (80 kDa) and a variable lipid content which ranges from 35% to 59% (w/w). Diacylglycerols (DG), phospholipids (PL), and hydrocarbons (HC) are the main lipid components, whereas cholesterol and triacylglycerols are minor components. DG content varies from 7 to 30%, PL from 11 to 24%, and HC from 0 to 15%. In order to determine the relationship between the lipid composition and the arrangement of lipid and protein components in the lipoprotein particle, a density-composition structural model was designed. The model was established by means of 12 sets of data on lipophorin density-composition relationships, and model validity was determined throughout lipoprotein space- and surface-filling conditions. Despite the differences among the lipid compositions of lipophorins, it is concluded that there are several unifying structural restrictions that govern the molecular organization of lipophorins. Quantitative treatment of the model indicates that lipophorin structure is consistent with the following. 1) Spherical particles with a protein-rich outer layer of approximately 20-21 A thickness, comprised of proteins, phospholipids, cholesterol, and small amounts of DG, and a lipid-rich core composed of HC, TG, and almost all the lipophorin DG. 2) Apolipophorins have a lipid-embedded localization within the lipoprotein particle. They might represent one of the few examples of proteins containing beta-shift structure, exerting strong hydrophobic interaction and having a lipid-embedded localization.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a simple and rapid radioimmunoassay for melatonin in plasma with highly variable lipid content

Development of a simple and rapid radioimmunoassay for melatonin in plasma with highly variable lipid content

Properties of discoidal complexes of human apolipoprotein A-I with phosphatidylcholines containing various fatty acid chains

In this study we demonstrate that apolipoprotein A-I determined the common size classes of discoidal particles formed with numerous phosphatidylcholines, and with ether analogs of phosphatidylcholines. We show furthermore, that the nature of the lipids dictates the distribution of particles among the different size classes. These experiments were performed with discoidal complexes containing various phospholipids (phosphatidylcholines with saturated and unsaturated fatty acid chains of different lengths and the ether analog of 1-palmitoyl-2-oleoylphosphatidylcholine), cholesterol, and human apolipoprotein A-I, prepared by the sodium cholate dialysis method, and fractionated by Bio-Gel A-5m gel-filtration chromatography. The complex preparations were analyzed in terms of their average composition, spectral properties of the apolipoprotein, and the dynamic behavior of the lipid domains. Nondenaturing gradient gel electrophoresis was used to analyze the size classes of particles present in the complex preparations. Starting with reaction mixtures containing around 100:1, phospholipid/apolipoprotein A-I molar ratios, complexes were isolated with molar ratios from 40:1 to 100:1. In most complexes apolipoprotein A-I had high levels of α-helical structure (65–77% α-helix), and tryptophan residues in a nonpolar environment. The lipid domains of complexes exhibited the dynamic behavior expected of the main phospholipid components. In the average size range from 90 to 100 Å diameters, discrete particle classes with 80, 87, 102, 108, or 112 Å Stokes diameters were observed for all the complexes containing different phospholipids. These discrete, recurring particle sizes are attributed to distinct apolipoprotein A-I conformations and variable lipid content.

On Density of Chum Salmon (Oncorhynchus keta) Eggs in Shallow Matrix Substrate Incubators

Eyed chum salmon (Oncorhynchus keta) eggs were loaded at seven equidistant densities ranging from 10 760 to 75 350 eggs/m2 of gravel into Netarts-type shallow matrix substrate incubators. Egg density did not affect fry survival but altered emergence timing which influenced fry quality. Fry emergence was most premature in the 32 290 and 43 060 eggs/m2 treatments. Early migrants had higher development index values, more variable lipid contents, and lower water contents than peak and late migrants. Results are discussed in relation to economic and biological optimization of hatchery incubation.Key words: Oncorhynchus keta, egg density, gravel incubators, fry survival, fry quality

Current methods for apolipoprotein evaluation in normal and dyslipoproteinemic plasma.

The apolipoprotein quantitation has become a prominent feature in clinical chemistry. Since Apo-Lp vary in size, serum concentration and hydrophobicity, a general rule for their quantitation cannot be elaborated. In addition, the various Apo-Lp are distributed among lipoproteins of different densities, which exhibit variable size and lipid content. As a consequence, the antigenic determinants may be exposed with a variable degree. In pathological conditions, where dyslipoproteinemia is prominent, these distributions are frequently different than in the normal situation, and consequently the immunochemical quantitation requires sophisticated pretreatments of the sample. Storage, as well as influences brought about by temperature and chemical agents lead to a distortion of the native state and thus influence the accuracy of the results. In order to prevent these problems, delipidation of sera is necessary if Apo-LpA and Apo-LpC are quantified. ApoB, ApoE and Apo(a), on the other hand, tend to reach an irreversible aggregation upon delipidation. In this connection, the use of hydrolytic enzymes may help in rendering them in an uniform particle size and morphology. Despite all types of immunochemical methods, polyacrylamide gel electrophoresis and IEF were proved to be useful in the apolipoprotein quantitation. On the basis of the current knowledge, the quantitation of ApoAI, AII, B, Lp(a) as well as the ApoE isoforms are of clinical importance and are well suited to discriminate normals from patients with atherosclerosis and myocardial infarction. In addition, these apolipoproteins can be used in diagnosing secondary dyslipoproteinemias.

Some properties of plastidic cytochrome b-563.

Abstract Plastidic Cytochrome b-563 Cytochrome b-563 from spinach chloroplasts was isolated in a homogeneous and enzymatically active form. It has a low, but variable lipid content and a molecular weight of about 18,000 daltons.

Effect of Prepartum Milk Removal on Quantitative Morphology of Bovine Lactogenesis

The effect of prepartum milking on bovine mammary histology and milk composition was studied in five Holstein cows. One udder half was milked twice daily starting 10 days before the estimated calving date. One udder half was not milked until 2 days postpartum when all quarters were milked and two tissue samples per quarter were taken for morphological analyses. Lactose, casein, and fat concentrations differed from prepartum-milked to postpartum-milked quarters (.82, −1.44, and 3.29%). Quarters milked prepartum were more developed: mature epithelium 24.8%, immature epithelium −8.9%, total epithelium 15.6%, stroma −24.8%, and alveolar lumen 8.5%. Most alveolar cells in prepartum-milked halves had prominent rounded basal nuclei, hypertrophied secretory vesicles, and a mixed array of lipid droplets. Cells within alveoli were morphologically similar. Secretory epithelial cells from postpartum-milked glands had irregular randomly located nuclei, indistinct Golgi, variable lipid content, and less cytoplasm. These differences demonstrate the importance of prepartum-product removal on secretory cell development and subsequent milk production.

Seasonal variations in the total lipid content of Chorismus antarcticus (Pfeffer) (Crustacea: Decapoda) at South Georgia

The Antarctic benthic prawn Chorismus antarcticus (Pfeffer) was sampled regularly for a year and its total lipid content measured. Immature and transitional prawns had very variable lipid contents but similar mean values (2.92 and 2.91 % fresh wt, respectively); the variation was, in part, due to fluctuations in lipid reserves associated with ecdysis. Maturation of the testes involved the synthesis of ≈ 1.8 mg lipid, and female prawns synthesized an average of 50 % of their own lipid content for the gonad. Fecundity did not appear to be limited by the demand for egg lipid and synchrony in the breeding cycle was probably related to the planktonic feeding of the newly-hatched larvae. Eggs showed an unusual increase in total lipid content during the early stages of embryonic development, followed by the more normal decrease; larvae probably hatch with some reserve lipid. Available data on lipid contents of Antarctic crustaceans are briefly reviewed. The high lipid contents observed in herbivorous Antarctic planktonic crustaceans are due to the patterns of feeding imposed by the strongly seasonal nature of primary production in Antarctic waters, rather than low temperature per se. There is no evidence from the benthos of any systematic elevation of lipid content in polar species, although there is an indication of an increased lipid content in the muscle of polar crustaceans.

Isolation and Some Molecular Properties of Plastidic Algal Cytochrome b-559

Abstract Cytochrome b-559, Algae, Spinach Cytochrome b-559, an integral protein of diloroplast thylakoids, was prepared in a homogeneous form from the alga Bumilleriopsis filiformis. The protein is easily denatured and can be solubilized by treatment of isolated thylakoids with high concentrations of urea and detergents in addition to weak sonification. The reduced form exhibits absorption maxima at 559, 530 and 429 nm. By comparative determination, a molecular weight of 17 000 was found for the protein from Bumilleriopsis, whereas that for spinach has 37 000 daltons. Both proteins have a low, but variable lipid content which is not a necessary part of the enzymatically active cytochrome b-559. The purified cytochrome exhibits a low midpoint the preparation a transient “high-potential” form (reducible by hydroquinone) was also solubilized.