Species variations in phospholipid class distribution of organs. II. Heart and skeletal muscle

Alkylglycerol enhances myogenesis and regulates ether-phospholipid metabolism in C2C12 myoblasts

1-O-Alkylglycerol (AKG), a lipid characteristic of marine organisms, possesses an ether-linked alkyl chain on its glycerol backbone. AKG exhibits various biological activities, including anti-cancer effects, promoting sperm motility, and stimulating immune response. Metabolically, AKG is converted into alkyl- and alkenyl-phospholipids (PLs), which are key components of the cell membrane and play essential roles in maintaining membrane homeostasis and cellular functions. However, the influence of AKG on myogenesis and ether-type PL metabolism in muscle cells remains unknown. This study evaluated the effects of AKG on myogenic differentiation and ether-PL metabolism in mouse C2C12 myoblasts. During differentiation, cells were treated with 10-20 μM 1-O-octadecyl-glycerol (batyl alcohol) and 1-O-hexadecyl-glycerol (chimyl alcohol). By day 7 of differentiation, myotube size had increased in cells treated with AKGs. Comparative tests using compounds with similar or partial structures, including monoacylglycerol and alkenylglycerol, demonstrated that this activity was linked to the structural features of AKG. Conversely, myotube growth was insufficient after treatment with 1-O-dodecyl-glycerol, which contains a shorter alkyl chain. Additionally, batyl alcohol treatment elevated the levels of ether-phosphatidylcholine (PC) molecular species, including e-PC38:4 and e-PC38:5, those are presumed to bind polyunsaturated fatty acids. Chimyl alcohol treatment also increased ether-PC species, including e-PC36:4 and e-PC36:5 while monoacylglycerol did not alter ether-PC levels. These findings suggest that AKG plays a crucial role in membrane dynamics during myogenesis through metabolic conversion to ether-PLs, providing novel insights into muscle homeostasis to contribute to developing nutritional strategies and preventing and treating muscle diseases.

Identification of the Active EPA/AA-Binding Ether-Type Phosphatidylcholine Derived from the Starfish Patiria pectinifera for C2C12 Myotube Growth

Concerns about nutritional approaches for promoting skeletal muscle mass and function have increased. This study assessed the effects of starfish-derived glycerophospholipids (PLs) (SPL), characterized by unique ether-linked subclasses, alkylacyl (Alk)- and alkenylacyl (Pls)-PL, on skeletal muscle function, focusing on myotube formation in C2C12 myoblasts. SPL was prepared via chloroform/methanol extraction from Patiria pectinifera, followed by silica gel chromatography fractionation. Myoblasts were induced to differentiate with or without SPL treatment. On day 7 of differentiation, 50 μg/mL of SPL treatment increased myotube diameter. The phosphatidylcholine (PC) fraction (SPC) also enhanced myotube growth at 30 μg/mL. LC-MS/MS analysis indicated the most abundant PC molecular species in SPC were Alk- and Pls-PC with eicosapentaenoic acid and arachidonic acid. Treatment with 1-O-hexadecyl-2-arachidonoyl-PC, 1-1(Z)-hexadecenyl-2-arachidonoyl-PC or 1-O-hexadecyl-2-eicosapentaenoyl-PC increased myotube diameter and myokine Il-15 mRNA expression. These results demonstrate a novel functionality of SPC and highlight the role of ether-type PC molecules in muscle function.

Application of partition coefficient methods to predict tissue:plasma affinities in common farm animals: Influence of ionisation state

Tissue affinities are conventionally determined from in vivo steady-state tissue and plasma or plasma-water chemical concentration data. In silico approaches were initially developed for preclinical species but standardly applied and tested in human physiologically-based kinetic (PBK) models. Recently, generic PBK models for farm animals have been made available and require partition coefficients as input parameters. In the current investigation, data for species-specific tissue compositions have been collected, and prediction of chemical distribution in various tissues of livestock species for cattle, chicken, sheep and swine have been performed. Overall, tissue composition was very similar across the four farm animal species. However, small differences were observed in moisture, fat and protein content in the various organs within each species. Such differences could be attributed to factors such as variations in age, breed, and weight of the animals and general conditions of the animal itself. With regards to the predictions of tissue:plasma partition coefficients, 80 %, 71 %, 77 % of the model predictions were within a factor 10 using the methods of Berezhkovskiy (2004), Rodgers and Rowland (2006) and Schmitt (2008). The method of Berezhkovskiy (2004) was often providing the most reliable predictions except for swine, where the method of Schmitt (2008) performed best. In addition, investigation of the impact of chemical classes on prediction performance, all methods had very similar reliability. Notwithstanding, no clear pattern regarding specific chemicals or tissues could be detected for the values predicted outside a 10-fold change in certain chemicals or specific tissues. This manuscript concludes with the need for future research, particularly focusing on lipophilicity and species differences in protein binding.

LPGAT1/LPLAT7 regulates acyl chain profiles at the sn-1 position of phospholipids in murine skeletal muscles

Skeletal muscle consists of both fast- and slow-twitch fibers. Phospholipids are important structural components of cellular membranes, and the diversity of their fatty acid composition affects membrane fluidity and permeability. Although some studies have shown that acyl chain species in phospholipids differ among various muscle fiber types, the mechanisms underlying these differences are unclear. To investigate this, we analyzed phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules in the murine extensor digitorum longus (EDL; fast-twitch) and soleus (slow-twitch) muscles. In the EDL muscle, the vast majority (93.6%) of PC molecules was palmitate-containing PC (16:0-PC), whereas in the soleus muscle, in addition to 16:0-PC, 27.9% of PC molecules was stearate-containing PC (18:0-PC). Most palmitate and stearate were bound at the sn-1 position of 16:0- and 18:0-PC, respectively, and 18:0-PC was found in type I and IIa fibers. The amount of 18:0-PE was higher in the soleus than in the EDL muscle. Peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) increased the amount of 18:0-PC in the EDL. Lysophosphatidylglycerol acyltransferase 1 (LPGAT1) was highly expressed in the soleus compared with that in the EDL muscle and was upregulated by PGC-1α. LPGAT1 knockout decreased the incorporation of stearate into PC and PE in vitro and ex vivo and the amount of 18:0-PC and 18:0-PE in murine skeletal muscle with an increase in the level of 16:0-PC and 16:0-PE. Moreover, knocking out LPGAT1 decreased the amount of stearate-containing-phosphatidylserine (18:0-PS), suggesting that LPGAT1 regulated the acyl chain profiles of phospholipids, namely PC, PE, and PS, in the skeletal muscle.

Net Conversion of Human-Edible Vitamins and Minerals in the U.S. Southern Great Plains Beef Production System

Beef is a good source of several vitamins and minerals but data on the net contribution to the human diet is lacking. The objective was to quantify the net nutrient contribution of the beef supply chain to provide vitamins and minerals to the human diet. Beef cattle production parameters for the beef supply chain were as described by Baber et al., 2018 with the red and organ meat yield from each production segment estimated using literature values of serially-harvested beef cattle. Nutrient concentration of feeds was acquired from feed composition tables in nutrient requirement texts, and the nutrient concentration of beef and organ meats was based on 2018 USDA Food and Nutrient Database for Dietary Studies. The nutrient absorption coefficients of feeds, red meat, and organs were acquired from the literature. The human-edible conversion ratio was >1.0 for phosphorus when only red meat yield was considered indicating that the beef supply chain produced more human-edible phosphorus than it consumed. When organ meats were included, riboflavin, niacin, choline, and phosphorus had conversion ratios >1.0. After adjusting for the absorption of nutrients, the beef supply chain was a net contributor of niacin and phosphorus in the human diet when accounting for red meat yield only, but when including organ meats, iron, riboflavin, and choline also had conversion ratios >1.0. The maximum proportion of corn in the corn grain plus distillers’ grains component of the feedlot diets for the absorbable conversion ratio to be ≥1 ranged from 8.34 to 100.00% when only red meat yield was considered and from 32.02 to 100.00% when red and organ meats were considered. In conclusion, the current beef production system in the Southern Great Plains produces more human-absorbable iron, phosphorus, riboflavin, niacin, and choline to the human diet than is consumed in the beef supply chain.

Bioactivity and health effects of ruminant meat lipids. Invited Review

Ruminant meat (RM) is an excellent source of high-quality protein, B vitamins and trace minerals and plays an important role in global food and nutrition security. However, nutritional guidelines commonly recommend reduced intake of RM mainly because of its high saturated fatty acid (SFA) content, and more recently because of its perceived negative environmental impacts. RM is, however, rich in heart healthy cis-monounsaturated fatty acids and can be an important source of long-chain omega-3 (n-3) fatty acids in populations with low fish consumption. In addition, RM is a source of bioactive phospholipids, as well as rumen-derived bioactive fatty acids including branched-chain, vaccenic and rumenic acids, which have been associated with several health benefits. However, the role of bioactive RM lipids in maintaining and improving consumers' health have been generally ignored in nutritional guidelines. The present review examines RM lipids in relation to human health, and evaluates the effectiveness of different feeding strategies and possibilities for future profile and content improvement.

Global Sensitivity Analysis of the Rodgers and Rowland Model for Prediction of Tissue: Plasma Partitioning Coefficients: Assessment of the Key Physiological and Physicochemical Factors That Determine Small-Molecule Tissue Distribution

In physiologically based pharmacokinetic (PBPK) modelling, the large number of input parameters, limited amount of available data and the structural model complexity generally hinder simultaneous estimation of uncertain and/or unknown parameters. These parameters are generally subject to estimation. However, the approaches taken for parameter estimation vary widely. Global sensitivity analyses are proposed as a method to systematically determine the most influential parameters that can be subject to estimation. Herein, a global sensitivity analysis was conducted to identify the key drug and physiological parameters influencing drug disposition in PBPK models and to potentially reduce the PBPK model dimensionality. The impact of these parameters was evaluated on the tissue-to-unbound plasma partition coefficients (Kpus) predicted by the Rodgers and Rowland model using Latin hypercube sampling combined to partial rank correlation coefficients (PRCC). For most drug classes, PRCC showed that LogP and fraction unbound in plasma (fu_p) were generally the most influential parameters for Kpu predictions. For strong bases, blood:plasma partitioning was one of the most influential parameter. Uncertainty in tissue composition parameters had a large impact on Kpu and Vss predictions for all classes. Among tissue composition parameters, changes in Kpu outputs were especially attributed to changes in tissue acidic phospholipid concentrations and extracellular protein tissue:plasma ratio values. In conclusion, this work demonstrates that for parameter estimation involving PBPK models and dimensionality reduction purposes, less influential parameters might be assigned fixed values depending on the parameter space, while influential parameters could be subject to parameters estimation.

Digestion of Ceramide 2-Aminoethylphosphonate, a Sphingolipid from the Jumbo Flying Squid Dosidicus gigas, in Mice

Ceramide 2-aminoethylphosphonate (CAEP), a sphingophosphonolipid containing a carbon-phosphorus bond, is frequently found in marine organisms and has a unique triene type of sphingoid base in its structure. CAEP has not been evaluated as a food ingredient, although it is generally contained in Mollusca organisms such as squids and shellfish, which are consumed worldwide. In this study, we aimed to elucidate the effects of CAEP as a food component by evaluating the digestion of CAEP extracted from the skin of the jumbo flying squid Dosidicus gigas. Our results revealed that dietary CAEP was digested to free sphingoid bases via ceramides by the mouse small intestinal mucosa. At pH 7.2, CAEP was hydrolyzed more rapidly than the major mammalian sphingolipid sphingomyelin; however, the hydrolysis of CAEP was similar to that of sphingomyelin at pH 9.0. Thus, the digestion of CAEP may be catalyzed by alkaline spingomyelinase and other enzymes. Our findings provide important insights into the digestion of the dietary sphingophosphonolipid CAEP in marine foods.

Disorders of phospholipid metabolism: an emerging class of mitochondrial disease due to defects in nuclear genes

The human nuclear and mitochondrial genomes co-exist within each cell. While the mitochondrial genome encodes for a limited number of proteins, transfer RNAs, and ribosomal RNAs, the vast majority of mitochondrial proteins are encoded in the nuclear genome. Of the multitude of mitochondrial disorders known to date, only a fifth are maternally inherited. The recent characterization of the mitochondrial proteome therefore serves as an important step toward delineating the nosology of a large spectrum of phenotypically heterogeneous diseases. Following the identification of the first nuclear gene defect to underlie a mitochondrial disorder, a plenitude of genetic variants that provoke mitochondrial pathophysiology have been molecularly elucidated and classified into six categories that impact: (1) oxidative phosphorylation (subunits and assembly factors); (2) mitochondrial DNA maintenance and expression; (3) mitochondrial protein import and assembly; (4) mitochondrial quality control (chaperones and proteases); (5) iron–sulfur cluster homeostasis; and (6) mitochondrial dynamics (fission and fusion). Here, we propose that an additional class of genetic variant be included in the classification schema to acknowledge the role of genetic defects in phospholipid biosynthesis, remodeling, and metabolism in mitochondrial pathophysiology. This seventh class includes a small but notable group of nuclear-encoded proteins whose dysfunction impacts normal mitochondrial phospholipid metabolism. The resulting human disorders present with a diverse array of pathologic consequences that reflect the variety of functions that phospholipids have in mitochondria and highlight the important role of proper membrane homeostasis in mitochondrial biology.

A Sequential Model of Host Cell Killing and Phagocytosis by Entamoeba histolytica

The protozoan parasite Entamoeba histolytica is responsible for invasive intestinal and extraintestinal amebiasis. The virulence of Entamoeba histolytica is strongly correlated with the parasite's capacity to effectively kill and phagocytose host cells. The process by which host cells are killed and phagocytosed follows a sequential model of adherence, cell killing, initiation of phagocytosis, and engulfment. This paper presents recent advances in the cytolytic and phagocytic processes of Entamoeba histolytica in context of the sequential model.

Tissue Distribution of Basic Drugs: Accounting for Enantiomeric, Compound and Regional Differences Amongst β-Blocking Drugs in Rat

The purpose of this research was to identify the major factors controlling the distribution of beta-blockers (acebutolol, betaxolol, bisoprolol, metoprolol, oxprenolol, pindolol, propranolol and timolol) in rats, across tissues, compounds and enantiomers. Tissue distribution was assessed at steady state by infusing cassette doses of beta-blockers into the jugular vein via an indwelling catheter at a constant rate. Blood was sampled via an indwelling catheter in the carotid artery, and 12 tissues excised at the end of dose infusion (4 or 8 h). Drug concentrations were quantified using a novel chiral LC-MS method and the tissue-to-plasma (Kp) and tissue-to-plasma water (Kpu) values were calculated for each tissue. Differences between Kp were observed between many enantiomeric pairs, and largely explained by enantiomeric differences in plasma protein binding. Across compounds, Kpu values were generally highest in lung and lowest in adipose, and were higher for the more lipophilic drugs betaxolol and propranolol. For any tissue, Kpu differences between the individual beta-blockers correlated well with the corresponding affinity for blood cells. For all compounds, regional tissue distribution correlated well with tissue acidic phospholipid concentrations, with phosphatidylserine appearing to have the strongest influence. This information may be used as the basis for predicting the tissue distribution of basic drugs.

Intermolecular interactions of lysobisphosphatidic acid with phosphatidylcholine in mixed bilayers

Lysobisphosphatidic acid (LBPA) can be regarded to represent a unique derivative of phosphatidylglycerol. This lipid is highly enriched in late endosomes where it can comprise up to 10-15 mol% of all lipids and in these membranes, LBPA appears to be segregated into microdomains. We studied the thermotropic behavior of pure dioleoyl-LBPA mono- and bilayers using Langmuir-lipid monolayers, electron microscopy, differential scanning calorimetry (DSC), and fluorescence spectroscopy. LBPA formed metastable, liquid-expanded monolayers at an air/buffer interface, and its compression isotherms lacked any indication for structural phase transitions. Neat LBPA formed multilamellar vesicles with no structural transitions or phase transitions between 10 and 80 degrees C at a pH range of 3.0-7.4. We then proceeded to study mixed LBPA/dipalmitoylphosphatidylcholine (DPPC) bilayers by DSC and fluorescence spectroscopy. Incorporating increasing amounts of LBPA (up to X(LBPA) (molar fraction)=0.10) decreased the co-operativity of the main transition for DPPC, and a decrease in the main phase transition as well as pretransition temperature of DPPC was observed yet with no effect on the enthalpy of this transition. In keeping with the DSC data for DPPC, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/LBPA mixed bilayers were more fluid, and no evidence for lateral phase segregation was observed. These results were confirmed using fluorescence microscopy of Langmuir-lipid films composed of POPC and LBPA up to X(LBPA)=0.50 with no evidence for lateral phase separation. As late endosomes are eminently acidic, we examined the effect of lowering pH on lateral organization of mixed PC/LBPA bilayers by DSC and fluorescence spectroscopy. Even at pH 3.0, we find no evidence of LBPA-induced microdomain formation at LBPA contents found in cellular organelles.

Lens lipids and maximum lifespan

Unlike in most organs, the lipid composition of lenses varies dramatically among species and with age. The focus of this study is to assess how these changes relate to lifespan. Studies on cataract suggest that the lens may serve as a window into the processes leading to accelerated mortality. As a first step toward elucidating cellular processes in the lens that may serve as markers for accelerated mortality, we examined the correlation between species-dependent and age-related lens lipid compositional differences and maximum life span. We included data from camels, which, even in old age, rarely develop cataracts although they live under adverse conditions. Camel lens lipids were mainly composed of sphingolipids (77%) and phosphatidylcholines (23%). Bovine lens lipid composition was comparable to a previous study, and both bovine lens sphingolipids, phosphatidylcholines and camel lens phosphatidylcholines content fit well (within the 95% confidence limits) in the curve obtained by plotting maximum life spans of other species with sphingolipids and phosphatidylcholines. Lifespan was directly related to lens sphingolipid content and indirectly related to lens phosphatidylcholine content. The camel lens sphingolipid value was significantly above the curve for other species. Except for the camel lens nucleus, lipid order and sphingolipid content were linearly related, p < 0.005 with a slope of 0.85+/-0.07, and intercept of 6.9+/-3.8. Lipid phase transition temperature and sphingolipid content were also linearly related, p = 0.01 with a slope of 0.20+/-0.07, and intercept of 21.7+/-5.3. Our data support the hypothesis that humans have adapted so that their lens membranes have a high sphingolipid content that confers resistance to oxidation, allowing these membranes to stay clear for a relatively longer time than is the case in many other species. Age-related changes in human lens lipid composition may serve as a marker for oxidative stress and may reflect systemic oxidative insult, providing a window into the health of an individual.

Nonradioactive analysis of phosphatidylinositides and other anionic phospholipids by anion-exchange high-performance liquid chromatography with suppressed conductivity detection

Phosphatidylinositol 4,5-biphosphate (PIP(2)) modulates the function of numerous ion transporters and channels, as well as cell signaling and cytoskeletal proteins. To study PIP(2) levels of cells without radiolabeling, we have developed a new method to quantify anionic phospholipid species. Phospholipids are extracted and deacylated to glycero-head groups, which are then separated by anion-exchange HPLC and detected by suppressed conductivity measurements. The major anionic head groups can be quantified in single runs with practical detection limits of about 100 pmol, and the D3 isoforms of phosphatidylinositol phosphate (PIP) and PIP(2) are detected as shoulder peaks. In HeLa, Hek 293 and COS cells, as well as intact heart, PIP(2) amounts to 0.5 to 1.5% of total anionic phospholipid (10 to 30 micromol/liter cell water or 0.15 to 0.45 nmol/mg protein). In cell cultures, overexpression of Type I PIP5-kinase specifically increases PIP(2), whereas overexpression of Type II PI4-kinase can increase both PIP and PIP(2). Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and the D3 isomers of PIP(2) are detected after treatment of cells with pervanadate; in yeast, overexpression of a phosphatidylinositol 3-kinase (VPS34) specifically increases phosphatidylinositol 3-phosphate (PI3P). Using isolated cardiac membranes, lipid kinase and lipid phosphatase activities can be monitored with the same methods. Upon addition of ATP, PIP increases while PIP(2) remains low; exogenous PIP(2) is rapidly degraded to PIP and phosphatidylinositol (PI). In summary, the HPLC methods described here can be used to probe multiple aspects of phosphatidylinositide (Ptide) metabolism without radiolabeling.

Prediction of pharmacokinetics prior to in vivo studies. 1. Mechanism-based prediction of volume of distribution

In drug discovery and nonclinical development the volume of distribution at steady state (V(ss)) of each novel drug candidate is commonly determined under in vivo conditions. Therefore, it is of interest to predict V(ss) without conducting in vivo studies. The traditional description of V(ss) corresponds to the sum of the products of each tissue:plasma partition coefficient (P(t:p)) and the respective tissue volume in addition to the plasma volume. Because data on volumes of tissues and plasma are available in the literature for mammals, the other input parameters needed to estimate V(ss) are the P(t:p)'s, which can potentially be predicted with established tissue composition-based equations. In vitro data on drug lipophilicity and plasma protein binding are the input parameters used in these equations. Such a mechanism-based approach would be particularly useful to provide first-cut estimates of V(ss) prior to any in vivo studies and to explore potential unexpected deviations between sets of predicted and in vivo V(ss) data, when the in vivo data become available during the drug development process. The objective of the present study was to use tissue composition-based equations to predict rat and human V(ss) prior to in vivo studies for 123 structurally unrelated compounds (acids, bases, and neutrals). The predicted data were compared with in vivo data obtained from the literature or at Roche. Overall, the average ratio of predicted-to-experimental rat and human V(ss) values was 1.06 (SD = 0.817, r = 0.78, n = 147). In fact, 80% of all predicted values were within a factor of two of the corresponding experimental values. The drugs can therefore be separated into two groups. The first group contains 98 drugs for which the predicted V(ss) were within a factor of two of those experimentally determined (average ratio of 1.01, SD = 0.39, r = 0.93, n = 118), and the second group includes 25 other drugs for which the predicted and experimental V(ss) differ by a factor larger than two (average ratio of 1.32, SD = 1.74, r = 0.42, n = 29). Thus, additional relevant distribution processes were neglected in predicting V(ss) of drugs of the second group. This was true especially in the case of some cationic-amphiphilic bases. The present study is the first attempt to develop and validate a mechanistic distribution model for predicting rat and human V(ss) of drugs prior to in vivo studies.

A priori prediction of tissue:plasma partition coefficients of drugs to facilitate the use of physiologically-based pharmacokinetic models in drug discovery

The tissue:plasma (P(t:p)) partition coefficients (PCs) are important drug-specific input parameters in physiologically based pharmacokinetic (PBPK) models used to estimate the disposition of drugs in biota. Until now the use of PBPK models in early stages of the drug discovery process was not possible, since the estimation of P(t:p) of new drug candidates by using conventional in vitro and/or in vivo methods is too time and cost intensive. The objectives of the study were (i) to develop and validate two mechanistic equations for predicting a priori the rabbit, rat and mouse P(t:p) of non-adipose and non-excretory tissues (bone, brain, heart, intestine, lung, muscle, skin, spleen) for 65 structurally unrelated drugs and (ii) to evaluate the adequacy of using P(t:p) of muscle as predictors for P(t:p) of other tissues. The first equation predicts P(t:p) at steady state, assuming a homogenous distribution and passive diffusion of drugs in tissues, from a ratio of solubility and macromolecular binding between tissues and plasma. The ratio of solubility was estimated from log vegetable oil:water PCs (K(vo:w)) of drugs and lipid and water levels in tissues and plasma, whereas the ratio of macromolecular binding for drugs was estimated from tissue interstitial fluid-to-plasma concentration ratios of albumin, globulins and lipoproteins. The second equation predicts P(t:p) of drugs residing predominantly in the interstitial space of tissues. Therefore, the fractional volume content of interstitial space in each tissue replaced drug solubilities in the first equation. Following the development of these equations, regression analyses between P(t:p) of muscle and those of the other tissues were examined. The average ratio of predicted-to-experimental P(t:p) values was 1.26 (SD = 1.40, r = 0.90, n = 269), and 85% of the 269 predicted values were within a factor of three of the corresponding literature values obtained under in vivo and in vitro conditions. For predicted and experimental P(t:p), linear relationships (r > 0.9 in most cases) were observed between muscle and other tissues, suggesting that P(t:p) of muscle is a good predictor for the P(t:p) of other tissues. The two previous equations could explain the mechanistic basis of these linear relationships. The practical aim of this study is a worthwhile goal for pharmacokinetic screening of new drug candidates.

Rapid separation and quantitation of combined neutral and polar lipid classes by high-performance liquid chromatography and evaporative light-scattering mass detection

Modifications are described for an innovative and widely used high-performance liquid chromatography technique that resolves a very broad spectrum of lipids for quantitation by evaporative light-scattering detection. Substitution of acetone for 2-propanol in a portion of the solvent gradient program yields consistent resolution of diacylglycerol and cholesterol without sacrificing baseline resolution of the remaining major lipid classes. Moreover, previously noted instabilities in triacylglycerol retention time are eliminated. The introduction of acetone also enables a 20% reduction in flow-rate without an increase in total run time. As a further modification of the mobile phase composition, acetic acid and ethanolamine are substituted for the serine-ethylamine combination that was originally shown to improve column performance. The combination of acetic acid and ethanolamine yields the same result but the increased volatility of these solutes over serine results in decreased baseline noise. Finally, 1,2-hexadecanediol is introduced as an internal standard that is well suited for this method. The chromatographic performance obtained with these modifications is demonstrated in compositional analyses of lipid extracts from rat liver, heart, kidney and brain.

HPTLC analysis of sphingomylein, ceramide and sphingosine in ischemic/reperfused rat heart

Since the sphingomylein-ceramide-sphingosine pathway, especially ceramide, has been shown to induce programmed cell death (apoptosis), and since apoptosis may be involved with ischemic/reperfused injury in the heart, it became desirable to quantitate the three components in ischemic/reperfused rat heart. One group of rat hearts (n = 6) was isolated and perfused with Krebs-Henseleit buffer using the Langendorff non-recirculating mode. The hearts were perfused for 10 min, made ischemic for 30 min and reperfused for 120 min. Hearts were collected and stored at - 70 degrees C before ischemia, after ischemia and after 30, 60 and 120 min of reperfusion. The hearts were homogenized, and lipids were extracted using the Folch method. The lipids were then chromatographed on Whatman silica gel 60 A high-performance thin-layered chromatography (HPTLC) plates. The plates were developed with iodine, photographed using Photoshop software and quantitated using NIH Imaging software. The results show a 50% decrease of sphingomylein during reperfusion with a corresponding increase in ceramide with sphingosine showing a smaller decrease as compared with the ceramide increase.

Palmitate incorporation into lipids pools of contracting red and white muscles

We compared the incorporation of the blood-borne [14C]-palmitate into selected lipid and phospholipid pools in rat muscles (soleus, red and white gastrocnemius), at rest and during contractions (15 and 60 tetani/min) in one leg (5 min) while the contralateral leg served as a control. [1-(14)C]-palmitate (20 microCi/rat) was administered into the carotid artery (t = 1 min). [14C]-palmitate deposition was greatest in soleus (100%) and lower in red (82%) and white gastrocnemius muscles (63%), respectively (p < 0.05). [14C] was deposited primarily into the tri-acylglycerol (approximately 50%) and phospholipid pools (approximately 30%) of soleus and red gastrocnemius muscles, and into the di-acylglycerol (approximately 30%), tri-acylglycerol (approximately 30%) and phospholipid pools (approximately 30%) in white gastrocnemius muscle. During contraction the concentrations of tri-acylglycerol were not changed. But, contraction increased [14C]-palmitate incorporation into soleus and red gastrocnemius muscles (600-700%) and into white gastrocnemius muscles (200%). Slightly more [14C] was directed from the phospholipids into the tri-acylglycerol pool during contraction. [14C]-palmitate deposition was also increased in the subclasses of phospholipids during contraction in red and white gastrocnemius. In conclusion, the deposition of [14C]palmitate into different lipid and phospholipid pools is quite rapid, and is dependent on contraction and the muscle fiber type.

Functional impairment of bronchoalveolar lavage phospholipids in early Pneumocystis carinii pneumonia in rats

Surfactant abnormalities may contribute to the impairment of gas exchange observed in Pneumocystis carinii pneumonia. Analysis of rat bronchoalveolar lavage (BAL) lipid extracts from normal controls, steroid controls, trimethaprim-sulfamethoxazole (TMP-SMX) controls, TMP-SMX/P. carinii pneumonia controls, and P. carinii pneumonia animals reveal similar total phospholipid and total protein levels. However, there was a marked reduction in phosphatidylglycerol (PG) from the BAL of P. carinii pneumonia rats as compared with control animals, with a decrease from 4.91 +/- 1.29 nmol/mg protein to 0.46 +/- 0.57 nmol/mg protein (p<0.05) and a decrease, as a percent of total phospholipids, from 7.7% +/- 0.88% to 0.91% +/- 0.59% (p<0.001). Furthermore, in vitro surface activities of BAL lipid extracts from control and P. carinii pneumonia rats revealed minimum surface tension increases from 9.38 +/- 1.71 mN/m in controls to 16.36 +/- 0.83 mN/m in P. carinii pneumonia rats (p<0.05) and likewise maximum surface tension increases from 22.14 +/- 4.34 mN/m to 38.57 +/- 2.07 mN/m (p<0.01). Of interest, the surface activity of PG-deficient P. carinii pneumonia BAL lipid extracts is completely restored to that of normal controls by the addition of exogenous PG. These findings suggest that a functionally abnormal surfactant occurs in P. carinii pneumonia and that this may account, in part, for the impairment of gas exchange observed in this disorder.

An approach for incorporating tissue composition data into physiologically based pharmacokinetic models

The objective of this study was to develop an approach for incorporating tissue composition data into physiologically based pharmacokinetic (PBPK) models in order to facilitate "built-in" calculation of tissue: air partition coefficients (PCs) of volatile organic chemicals. The approach involved characterizing tissue compartments within PBPK models as a mixture of neutral lipids, phospholipids, and water (instead of using the conventional description of them as "empty" boxes). This approach enabled automated calculation of the tissue solubility of chemicals from n-octanol and water solubility data, since these data approximate those of solubility in tissue lipids and water. Tissue solubility was divided by the saturable vapor concentration at 37 degrees C to estimate the tissue: air PCs within PBPK models, according to the method of Poulin and Krishnan (1995c). The highest and lowest lipid and water levels for human muscle, liver, and adipose tissues were obtained from the literature and incorporated within the tissue composition-based PBPK model to calculate the tissue: air PCs of dichloromethane (DCM) and simulate the pharmacokinetics of DCM in humans. The PC values predicted for human tissues were comparable to those estimated using rat tissues in cases where the relative levels of lipids and water were comparable in both species. These results suggest that the default assumption of using rat tissue: air PCs in human PBPK models may be acceptable for certain tissues (liver, adipose tissues), but questionable for others (e.g., muscle). The PBPK modeling exercise indicated that the interindividual differences in tissue dose arising from variations of tissue: air PCs may not be reflected sufficiently by venous blood concentrations. Overall, the present approach of incorporating tissue composition data into PBPK models would not only enhance the biological basis of these models but also provide a means of evaluating the impact of interindividual and interspecies differences in tissue composition on the tissue dose surrogates used in PBPK-based risk assessments.

An algorithm for predicting tissue: blood partition coefficients of organic chemicals from n-octanol: water partition coefficient data

The objectives of the present study were (1) to develop an algorithm to predict tissue:blood partition coefficients (PCs) of organic chemicals from n-octanol: water (Ko/w) PC data, and (2) to apply this algorithm to predict the rat tissue:blood PCs of some relatively hydrophilic organics, particularly ketones, alcohols, and acetate esters. The algorithm, developed by modifying a previously published one, involved predicting tissue:blood PCs of chemicals by dividing their partitioning into tissues by the sum of their partitioning into erythrocytes and plasma. The partitioning of a chemical into tissues, erythrocytes, and plasma was expressed as an additive function of its partitioning into neutral lipids, phospholipids, and water contained in them. The muscle, liver, and adipose tissue:blood PCs predicted with the present method were compared with the experimental values obtained from the literature for five ketones, eight alcohols, and eight acetate esters. The predicted muscle:blood and liver:blood PCs for the set of 21 hydrophilic organics were within a factor of 1.01 and 0.99 (on an average), respectively, of the experimental values. However, the predicted adipose tissue:blood PCs of the hydrophilic organics were greater than the experimental values by a factor of 4.13, which improved when vegetable oil:saline (Ko/s) PCs were used instead of Ko/w PCs (factor of 1.51). Overall, the use of the present algorithm should enable the prediction of tissue:blood PCs for organic chemicals for which Ko/w or Ko/s data are available.

Cardiolipin biosynthesis in the isolated heart

The pathway for the biosynthesis of new cardiolipin was investigated in the isolated perfused intact rat heart. Isolated rat hearts were perfused in the Langendorff mode for up to 60 min with Krebs-Henseleit buffer containing 0.1 microM [U-14C]glycerol. Analysis of radioactivity incorporated into phospholipids in the organic phase revealed an increase in radioactivity incorporated into phosphatidylglycerol, cardiolipin and other phospholipids with time of perfusion. This was associated with a loss of radioactivity from phosphatidic acid. In contrast, perfusion of hearts for up to 60 min with 0.1 mM [1,(3)-3H]glycerol in the perfusate revealed an increased radioactivity associated with phosphatidic acid as well as cardiolipin, phosphatidylglycerol and other phospholipids. Perfusion of hearts for up to 60 min with [32P]Pi in the perfusate revealed a time-dependent increase in radioactivity associated with all phospholipids. Perfusion of hearts for up to 60 min with 0.1 microM or 0.1 mM glycerol in the perfusate did not affect the concentration of phosphatidic acid, cardiolipin or phosphatidylglycerol. To determine the rate-limiting step of cardiolipin biosynthesis, hearts were pulsed for 5 min with 0.1 microM [1,(3)-3H]glycerol and chased for up to 60 min with 0.1 microM glycerol in the perfusate. Radioactivity was maximum at the start of the chase in phosphatidic acid (and 1,2-diacylglycerol), and was subsequently chased into phosphatidylinositol, phosphatidylglycerol and cardiolipin (and other phospholipids). Significant radioactivity in phosphatidylglycerol phosphate was not detected. Radioactivity in CDP-sn-1,2-diacylglycerol remained constant throughout the chase. The activities of the enzymes of the Kennedy pathway for cardiolipin biosynthesis in the heart were determined. On the basis of continuous-pulse and pulse-chase labelling studies it is postulated that the cardiac polyglycerophospholipids phosphatidylglycerol and cardiolipin are actively synthesized from newly synthesized phosphatidic acid via the Kennedy pathway. In addition, the results suggest that the rate-limiting step of cardiolipin biosynthesis in the intact heart is probably the conversion of phosphatidic acid into CDP-sn-1,2-diacylglycerol.

Phosphoinositides in giant barnacle muscle fibers: a quantitative analysis at rest and following electrical stimulation

Quantitative data are presented on the composition of the major phospholipids in isolated giant barnacle muscle fibers. It is shown, using internal perfusion techniques, that the high specific activity of labeling of polyphosphoinositides in vivo is attained by the activities of specific kinases. Electrical stimulation causes a reduction in the specific activity of labeling of PtdInsP2. This phospholipid, which is the immediate precursor for the release of InsP3, is found at a significant concentration (40 nmol/g wet weight) in single barnacle muscle fibers, sufficient to support a role as precursors of second messengers. The rapid catabolization of PtdInsP2 in the absence of external Ca2+ suggests that E-C coupling in barnacle muscle may be associated with a voltage-dependent, Ca(2+)-independent, activation of the breakdown of polyphosphoinositides.

Effects of lysophospholipids and diacylglycerols on the transfer of arachidonic acid to phospholipids and triacylglycerols in rat brain membranes

Brain membranes catalyze the acylation of lysophospholipids and diacylglycerols (DAG) to form the respective phospholipids and triacylglycerols (TAG). These acylation reactions were examined using brain plasma membrane-enriched fractions by measuring the incorporation of [14C]arachidonic acid into TAG and individual phospholipids under a variety of conditions. In the absence of added lipid substrates, the amount of [14C]arachidonic acid incorporated into TAG in the presence of ATP, Mg2+, and CoA was approx twice the amount incorporated into phosphatidylositol (PtdIns), and more than 10 times the amount incorporated into phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn) and phosphatidylserine (PtdSer). These results suggest the presence of endogenous DAG, lysoPtdIns, and the required enzymes in the membrane preparations for acylation reactions. The addition of DAG, lysoPtdCho or lysoPtdIns to the incubation system resulted in a 2-20-fold increase in the rate of incorporation of labeled arachidonic acid into TAG, PtdCho or PtdIns, respectively. LysoPtdEtn and lysoPtdSer were poor substrates for the synthesis of PtdEtn and PtdSer. On the other hand, the addition of lysoPtdSer stimulated the incorporation of [14C]arachidonic acid into TAG and into most phospholipids, especially phosphatidic acid, the synthesis of which was enhanced more than 10-fold. Exogenous lysoPtdCho and lysoPtdIns inhibited the incorporation of [14C]arachidonate into TAG in the presence of DAG, and DAG inhibited the incorporation of [14C]arachidonic acid into phospholipids in the presence of lysophospholipids. In general, [14C]palmitic acid was less effectively incorporated into lipids than arachidonic acid. These results suggest reciprocal regulatory effects of DAG and lysophospholipids on acyltransfer to phospholipids and triacylglycerol in brain membranes.

Comparative investigation of phospholipids and fatty acids of freshwater molluscs from the Volga river basin

1. Four Gastropoda species and two Bivalvia species from the Volga river basin were examined. 2. Distribution of phospholipids in the molluscs was studied by qualitative and quantitative micro thin-layer chromatography. 3. Major phospholipid classes, phosphatidylethanolamine and phosphatidylcholine, were found to contain plasmalogens. 4. One mollusc species notably contained 67 fatty acids including 25 saturated (both iso and anteiso), 24 monoenoic, five dienoic, four trienoic and eight polyenoic compounds identified by capillary gas chromatography; fatty acid contents in the other studied species were considerably lower. 5. Relatively high concentrations of nonmethylene-interrupted fatty acids were detected in certain examined species.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis of phosphatidylethanolamine and ethanolamine plasmalogen by the CDP-ethanolamine and decarboxylase pathways in rat heart, kidney and liver

Studies with mammalian cell lines have led to suggestions that mammalian tissues may derive all of their phosphatidylethanolamine (PE) from the decarboxylation of phosphatidylserine (PS), and also that the physiological significance of the CDP-ethanolamine pathway was the synthesis of ethanolamine plasmalogen. We have therefore investigated the biosynthesis of PE and ethanolamine plasmalogen via the CDP-ethanolamine and decarboxylation pathways in vivo in three rat tissues (heart, kidney and liver), which differ in ethanolamine plasmalogen content. In all three tissues [14C]ethanolamine was incorporated into both PE and ethanolamine plasmalogen, whereas [3H]serine was incorporated into only PS and PE fractions. When [14C]ethanolamine was introduced into the animals, the specific radioactivity of ethanolamine plasmalogen in the kidney was always greater than that of the PE fraction; in the heart the specific radioactivity of the ethanolamine plasmalogen fraction was similar to that of the PE fraction, whereas in the liver the specific radioactivity of the PE fraction was always greater than that of the ethanolamine plasmalogen fraction. The results obtained in this study indicate that: (1) the CDP-ethanolamine pathway is utilized for the synthesis of both PE and ethanolamine plasmalogen in all three tissues; (2) the decarboxylation pathway is utilized solely for the synthesis of PE; (3) serine plasmalogens are not formed by base-exchange reactions; (4) the relative utilization of the CDP-ethanolamine pathway for the synthesis of PE and ethanolamine plasmalogen varies among tissues. Our studies also revealed that the hypolipidaemic drug MDL 29350 is a potent inhibitor of PE N-methyltransferase activity in vitro and in vivo.

Separation and quantification of heart and liver phospholipid classes by high-performance liquid chromatography using a new light-scattering detector

This work describes a one-step separation of rat tissue phospholipid classes by high-performance liquid chromatography (HPLC) using a silica column and a new light-scattering detector (LSD). Complete separation of phosphatidylcholine, phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylserine, sphingomyelin, lysophosphatidylethanolamine, and lysophosphatidylcholine was obtained. Direct quantification was achieved after detector calibration for each phospholipid class. The detector response was shown to be linear within the ranges used. The LSD results agreed well with those obtained by phospholipid phosphorus assay. The present method was applied to rat heart and rat liver phospholipid analysis.

Phosphoinositides in frog skeletal muscle: a quantitative analysis

The contents of major phospholipids per g of wet wt. in frog skeletal muscle are: 5.3 mumol PC; 1.4 mumol PE; 1 mumol SM; 0.4 mumol PtdIns; 0.3 mumol CL; and 0.13 mumol PS. The quantities of polyphosphoinositides per g of wet wt. are: 181 nmol PtInsP; 28 nmol PtdInsP2; and 8 nmol lyso-PtdInsP2. The specific activity of labelling of the total muscle ATP attained by external incubation with [32P]Pi was found to be 57 dpm/nmol x g muscle wet wt. PtdInsP2, the highest labelled polyphosphoinositide, showed a specific activity of 64,000 dpm/nmol per g muscle wet wt., suggesting that high specific activity ATP may be compartmentalized in the local environment of the triads and used as a substrate by the PtdIns and PtInsP kinase in that region. PtdInsP2 which is the immediate precursor for the release of InsP3, is found at a significant concentration and strategically located for its postulated role as a substrate for the action of phosphoinositidase C. The presence of a novel endogenous polyphosphoinositide, lyso-PtdInsP2, in animal tissues is reported for the first time. Electrical stimulation leads towards a rapid catabolization of polyphosphoinositides revealed by reductions in the 3H- and 32P-labelling, suggesting that muscle excitation is associated with the activation of breaking down of polyphosphoinositides.

Amino acid sequence and circular dichroism of Indian cobra (Naja naja naja) venom acidic phospholipase A2

The full amino acid sequence of the acidic phospholipase A2 from Indian cobra (Naja naja naja) venom was determined and its tertiary structure examined by circular dichroism (CD). The sequence was aligned with other sequences of secreted phospholipase A2 from snakes of the genus Naja, using the progressive alignment method of Feng and Doolittle (J. Mol. Evol. (1987) 25, 351-360). The primary sequence of Naja naja naja phospholipases A2 shows up to 85% identity with the other acidic Naja phospholipase A2. CD studies indicate a 40-50% alpha-helical content in a tertiary structure which resists denaturation at high temperature, with or without chaotropic salts.

Changes in the phospholipid content in the left heart ventricle of male mice during repeated administration of isoprenaline

1. Male mice were injected 5 mg/kg isoprenaline (IPRO) daily and the heart weight, dry weight and phospholipid content in the left ventricle determined 24 hr after the last injection on days 1, 3, 5 and 10. 2. The phospholipid content sinks during the experiment, but the onset of the change is different in different phospholipids: for diphosphatidylglycerol it is clearly significant after 3 days, for phosphatidylcholine and phosphatidylethanolamine after 5 days and for sphingomyelin after 10 days; the relative amplitude of the change in this latter phospholipid was greatest of all. 3. If IPRO is given for 3 days and physiological saline for next 7 days, the content of some phospholipids (PE, SM and PG) continued to decrease. This suggests an important delayed effect of IPRO action.

Phospholipid content and fatty acid composition of human heart

Phospholipid content and fatty acid composition of human heart were determined on 36 biopsy specimens collected during open heart surgery. The main phospholipid classes, phosphatidylcholine (PC), phosphatidylethanolamine (PE), diphosphatidylglycerol (DPG), and sphingomyelin (SPH) were separated by HPLC, quantified, and converted to fatty acid methyl esters which were chromatographed on capillary GLC columns. Sex and age (mainly 40-70) of patients had no significant influence on the relative distribution of phospholipid classes and only a slight effect on fatty acid composition. Incorporation of trans 18:1 in phospholipid classes was low. cis and trans octadecenoic isomers seemed to be selectively incorporated, the delta 9 and delta 11 cis or trans isomers being predominant. Human and rat data were compared, and some species differences were noticed. In human PC, palmitic acid is higher and stearic acid much lower than in rat PC. Saturated dimethyl acetals (16:0 and 18:0) in PC and PE were greater for humans. Incorporation of 20:4 n-6 in human PE is higher than in rat PE.

Quantification, characterization and fatty acid composition of lysophosphatidic acid in different rat tissues

The amount and composition of lysophosphatidate present in different rat tissues have been estimated by an internal standard method in which a synthetic unnatural isomer (1-heptadecanoyl-rac-glycerol-3-phosphate) was added to the total lipid extracts, and the fatty acid composition of purified lysophosphatidate was determined. Lipids from tissues were extracted under acidic conditions, and the lysophosphatidate was purified by solvent partitions followed by thin-layer chromatography in multiple solvent systems. The purified lipid was shown to be 1-acyl-sn-glycerol-3-phosphate by chromatographic and chemical analysis, by its resistance to hydrolysis when treated with phospholipase A2 and also by its complete conversion to 1-acyl-sn-glycerol when treated with alkaline phosphatase. The fatty acid constituents of this lipid were determined by gas-liquid chromatography of the derived methyl esters. The concentrations (nmol/g of tissue) of lysophosphatidate in various tissues were: 86.2 +/- 4.2 in brain, 60.3 +/- 6.3 in liver, 46.4 +/- 6.5 in kidney, 30.6 +/- 5.0 in testis, 22.3 in heart and 19.3 in lung. Mostly (80%) saturated fatty acids were found to be present in this lyso lipid. A significantly high level of stearic acid was present in this lipid from all the tissues (50-60% in liver, kidney, brain and testis, and about 40% in heart and lung) compared to palmitic acid (10-15% in liver, kidney and brain and 25-30% in testis, heart and lung). The fatty acid compositions of phosphatidic acid, the putative product of lysophosphatidate acylation, from different tissues were also determined and palmitate was found to be the major saturated fatty acid.(ABSTRACT TRUNCATED AT 250 WORDS)