Quantitative analysis of serum lipids with thin-layer chromatography

Standardization and validation of assay of selected omega-3 and omega-6 fatty acids from phospholipid fraction of red cell membrane using gas chromatography with flame ionization detector

Background

Docosahexaenoic acid (DHA) is an important structural component of human brain and retina. Evidence exists linking nutritional status of pregnant mothers and cognitive functions of their born infants. The DHANI (Maternal DHA Supplementation and Offspring Neurodevelopment in India) trial was implemented to evaluate the effect of maternal supplementation with DHA during pregnancy and for 6 months following delivery on motor and mental development of infants at 1 and 12 months. We describe here the standardization and validation of an assay for measurement of selected omega-3 and omega-6 fatty acids from the phospholipid fraction of red blood cells to assess their status in mothers at baseline, delivery and 6 months post-delivery and for infants in cord blood and at 1 and 12 months of age. The validated method has been used for the analysis of samples for DHANI.

Methods

Lipids were extracted from a pool of red blood cells, separated using thin layer chromatography. The phospholipid fraction was esterified, and fatty acids were separated by gas chromatography using a flame ionization detector.

Result

The method accuracy for DHA was between 97 - 98% and between 91 - 95% for arachidonic acid (AA) at three different concentrations. The intra-assay and inter-assay coefficient of variation for the fatty acids ranged from 1.19 to 5.7% and 0.78 to 13.0% respectively. Intraclass correlation (ICC), as a measure of reproducibility, ranged between 0.689 and 0.996. A good linearity was observed for all the fatty acids between concentrations of 0.2–4 μg/ml.

Conclusion

The standardized and validated method is suitable for implementation in large epidemiological studies for evaluation of fatty acids and in nutritional trials for assessment of fatty acid content of various lipid classes.

Serum proteins and lipids in mild form of calf bronchopneumonia: candidates for reliable biomarkers

Calf bronchopneumonia is complex multifactorial disease and for its accurate diagnosis and therapy, besides clinical examination, microbiologic, hematologic and biochemical analyses could be necessary. In general, additional analyses are not implemented, mainly because the disease biomarkers are not defined.

To establish which analysis might be useful for determining the severity of the disease, we analyzed 23 three-month old calves with mild clinical signs of bronchopneumonia and 15 age-matched healthy calves. Pasteurella multocida was isolated from deep nasal swabs of diseased calves. Peripheral blood erythrocyte and leukocyte count of bronchopneumonic and healthy calves showed no difference. Serum proteins, lipoproteins and lipids were analyzed with spectrophotometry, agarose gel electrophoresis, non-reducing SDS-PAGE, gel zymography, and thin-layer chromatography. The bronchopneumonic calves had an increased level of circulating immune complexes and α globulins, which contain some of the positive acute phase proteins. In diseased calves the increased concentration of total γ globulins (IgG), due to an increased concentration of anionic γ globulins (predominately IgG1), was detected. The increased concentration of anionic γ globulins followed by increased concentration of transferrin (negative acute phase protein) and HDL cholesterol, decreased concentration of LDL-cholesterol, unchanged activity of matrix metalloproteases and leukocyte counts might reflect the obvious absence of generalized inflammation. A positive correlation was found between the acquired results and the appearance of mild clinical signs. Therefore, we believe that the parameters analyzed in the peripheral blood could be applied as reliable disease markers to distinguish between severe (inflammatory) and mild forms of calf bronchopneumonia and to predict a better outcome for these calves.

Studies on the lipids of sheep red blood cells. I. Lipid composition in low and high potassium red cells

The lipid composition of whole red blood cells was investigated in five sheep with red cells containing a low concentration of potassium (LK) and in five sheep with red cells containing a high concentration of potassium (HK). No apparent differences within the limit of error of the experiment were detected in the lipid class composition between the HK and LK red cells. Cholesterol, the only nonpolar lipid detected in the tissue, was present in oneto-one molar ratio to the total phospholipids. Phosphatidyl ethanolamine and sphingomyelin accounted for 85% of the total phospholipids; phosphatidyl serine, phosphatidyl inositol, phosphatidic acid, and lysolecithin were present in lesser amounts. No lecithin was detected in any of the animals in this investigation. Plasmalogen compounds were found only in the ethanolamine lipids. The molar ratio of choline to noncholine phospholipids was also approximately one to one. It was concluded that the major lipid class distribution in the two types of red cells cannot be directly responsible for the differences observed in the cation concentrations in these cells in the two species of sheep.

Direct assessment of lipoprotein outflow from in vivo-labeled arterial tissue as determined in an in vitro perfusion system

The rate of cholesterol deposition during the atherosclerotic process is determined by the balance between the inflow and outflow of plasma lipoproteins in the arterial wall. Whereas the rate of inflow may be measured directly, the rate of outflow has most often been calculated indirectly from lipoprotein uptake by using the 2-compartment model. One objection against such calculations is that lipoprotein binding is not being considered. In the present study 2 different protocols were used to obtain a direct measure of the outflow of lipoproteins from atherosclerotic rabbit aortas. Thus, 3 rabbits with experimental atherosclerosis were given 125I-LDL intravenously and 3 were given [14C]cholesterol perorally. Twenty-four hours later the aortas were removed and the outflow of label was monitored during in vitro perfusion. Despite the different protocols, our results were consistent and indicated that fractional loss relative to whole tissue was approximately 0.01 pool/h, which is 1 order of magnitude lower than current estimates based on the 2-compartment model (0.04 to 0.4 pool/h). Furthermore, whereas as much as 2/3 to 3/4 of the tracer that had entered the arterial wall was effectively trapped, the remainder equilibrated at a faster rate (0.06 pool/h). In conclusion, it seems that tissue binding constitutes a prominent and possibly underrated mechanism of lipoprotein deposition, at least in the atherosclerotic rabbit aorta. Furthermore, this means that current estimates of lipoprotein exchange parameters based on the 2-compartment model (eg, fractional loss) may rest on invalid assumptions and should be regarded with caution.

Chromatographic methods in the analysis of cholesterol and related lipids

Methods using thin-layer chromatography, solid-phase extraction, gas chromatography, high-performance liquid chromatography and supercritical fluid chromatography are described for the analysis of single cholesterol, esterified and sulfated cholesterol, and for cholesterol in the context of other lipid components, like other sterols and lipid classes. In connection with these techniques several clinical applications are mentioned.

The effects of triiodothyronine, hydrocortisone and insulin on lipid synthesis by cultured fibroblasts preincubated in a serum-free medium

Studies of lipid metabolism in cell cultures are usually carried out after preincubation of cells in media containing lipoprotein-deficient or delipidated serum. The artifacts produced during delipidation prevent the standardization of assays and the study of the role of hormones on lipid metabolism. We studied the effects of triiodothyronine, hydrocortisone, insulin and their combination on cholesterol and fatty acid synthesis in cultured human skin fibroblasts preincubated for 24 h in an artificial medium (medium A) consisting of equal volumes of Dulbecco's modified Eagle's and Ham's F-12 media enriched with transferrin, biotin and calcium pantothenate. In cells preincubated in medium A the incorporation of acetate to cholesterol and the activity of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase were much lower than in cells preincubated in standard medium containing lipoprotein-deficient serum. Addition of the three hormones caused a marked stimulation of the incorporation of acetate to cholesterol (from 3.1 to 17.7 pmol/min per mg protein), an activity similar to that in cells preincubated in lipoprotein-deficient serum plus hormones. The stimulatory effect of the hormones on HMG-CoA reductase activity was smaller, from 11 to 26 pmol/min per mg protein compared to 83 pmol/min per mg protein in cells preincubated in lipoprotein-deficient serum plus hormones. Most of the stimulatory effect was due to insulin. The lack of coordinate response between these two parameters in cells preincubated in artificial medium could not be explained by (a) stimulation of a post-mevalonate step as measured by the incorporation of mevalonate to cholesterol; (b) the in vitro inactivation of HMG-CoA reductase by phosphorylation: incubation of fibroblast microsomes with Escherichia coli alkaline phosphatase resulted in a decrease in HMG-CoA reductase activity, in contrast to an increase in hepatic microsomes; (c) the presence of inhibitors of HMG-CoA reductase in the microsomal extract. In cells preincubated in medium A the incorporation of acetate to fatty acids and the activities of acetyl-CoA carboxylase and fatty acid synthetase were approximately equal to that of cells preincubated in standard medium containing lipoprotein-deficient serum. Hormones added to medium A caused a stimulation of incorporation of acetate to fatty acids (from 5.1 to 19.8 pmol/min per mg protein), the activity of acetyl-CoA carboxylase (from 494 to 820 pmol/min per mg protein) and of fatty acid synthetase (from 300 to 678 pmol/mg protein). These values were significantly higher than those obtained in cells preincubated with lipoprotein-deficient serum with or without hormones.(ABSTRACT TRUNCATED AT 400 WORDS)

A system for long-term perfusion of rabbit aorta in vitro

In an in vitro system for the perfusion of arterial tissue, the volume of the incubation chamber should be small, and the composition of the medium should be easily modified. The tissue should consist of media and intima only, and the interaction with the medium should occur via the intimal side. Consecutive sampling of the medium and the tissue should be possible. This paper describes a system with these characteristics. Scanning and transmission electron microscopy of the perfused tissue indicated that the endothelium was intact during the first day and that it still covered more than 95% of the surface after 3 days. On the 2nd day, the nonthrombogenic properties of the endothelium were maintained. The medial smooth muscle cells of the inner two-thirds of the preparation were viable during the perfusion, while the cells in the outer one-third were dead from the start. Still, the metabolic activity of the tissue was stable, at least during the 2nd day as assessed by the study of DNA, protein, and lipid synthesis, as well as by oxygen consumption. We conclude that the perfusion system presented here might be useful in the study of the interaction between cellular and humoral components of the blood and the arterial wall.

Studies on zonation in the epididymis of the guinea pig. I. Ultrastructural and biochemical analysis of the zone rich in large lipid droplets (zone II)

In the epididymis of the guinea pig, zone II exhibits striking histological features that distinguish it readily from the other six regions of the epididymis. At the light microscope level, the pseudostratified epithelium of zone II is characterized by tall principal cells that are densely packed with large, intensely staining granules or droplets ranging up to 8 mu in diameter. At the electron microscope level, the principal cells exhibit numerous large lipid droplets and abundant agranular endoplasmic reticulum, which is frequently arranged in concentric whorls around one or more of the droplets. Quantitative biochemical studies comparing zone II with zones I and III show that zone II contains 2.5 - 3-fold more cholesterol and a significantly greater amount of cholesterol ester than the other two zones. These data indicate that the epididymal duct of the guinea pig includes a clearly defined region of epithelial cells possessing ultrastructural and biochemical characteristics consistent with steroidogenic activity. The potential significance of these observations to the epididymal physiology of the guinea pig and epididymal physiology in general is discussed.

Fatty acid metabolism during hypothermic perfusion of the isolated dog kidney

Perfusion of isolated dog kidneys was performed at 8--12 degrees C using an albumin solution containing caprylic acid (about 6 mmol/l) and long-chain fatty acids (about 0.5 mmol/l). During 48 h the amounts of caprylic acid in the perfusate fell by about 3 mmol, whereas long-chain FFA increased by 0.2--0.3 mmol and small amounts of arachidonic acid appeared. [14C]palmitate or [14C]linoleate--when added--decreased by about 10% in the perfusate. The decrease was mainly due to exchange with kidney phospholipid fatty acids. Only about 0.4% was recovered as [14C]CO2. The amounts of total phospholipids in kidney tissue decreased by up to 10% during the perfusion (when 10% kidney weight gain was taken into account), whereas lysophospholipids, cholesterol, triglycerides and free fatty acids remained essentially unchanged. The distribution of fatty acids in the total phospholipid fraction was strikingly altered. The relative amounts of arachidonic acid increased, whereas all other major fatty acids decreased. Synthesis of arachidonic acid by chain elongation of perfusate [14C]linoleic acid could not be demonstrated, and no evidence was found for a significant increase of the total amounts of arachidonic acid. The possibility that arachidonic acid-containing phospholipids in the kidney are preferentially preserved during the hypothermic conditions is discussed.

Cholinesterase in the atherosclerotic intima and in fibroblast cultures

Cholinesterase activity was present in the atheromatous plaque of the rabbit's atherosclerotic aorta. Cholinesterase activity was significantly increased in rat fibroblast cultures grown in the presence of hypercholesterolemic serum. Cholesterol ester synthesis in these cultures was inhibited by neostigmine, a cholinesterase inhibitor.

Plasma lipid analysis by thin-layer chromatography with flame ionisation detection and quantitation

A method is presented whereby cholesterol, cholesterol ester, triacylglycerol, non-esterified fatty acid and polar lipid in plasma may be simultaneously quantitated. Following the addition of umbelliferyl palmitate as internal standard, plasma (0.1 ml) is extracted with chloroform/methanol (2 : 1, v/v). A portion of the extract is chromatographed on silica gel fused to a narrow cylindrical quartz rod. After chromatography the rod is traversed through a flame ionisation detector and the responses recorded and integrated. The procedure is shown to be sensitive, linear, reproducible and to compare well with conventional methods for the determination of plasma lipid classes.

Isolation and characterization of a larval lipoprotein from the hemolymph of Manduca sexta

1. The larval high density lipoprotein (HDL) from the hemolymph of Manduca sexta, isolated by density gradient centrifugation, contains 61% protein, 37% lipid and 2% carbohydrate. 2. The molecular weight of HDL is 6 x 10(5), with two apoproteins of 2.85 x 10(5) and 8.1 x 10(4) daltons. 3. The large apoprotein is destroyed by trypsin treatment of the particle, while the small one is not. 4. Calculations based upon size and composition show that this particle is very different in structure from mammalian lipoproteins. It is proposed that a portion of the apoprotein occupies the central core region.

Diagnosis of fat absorption with 14C-tripalmitate/3H-palmitic acid

In 44 normal subjects, in 89 patients with chronic pancreatitis, of whom 23 had elevated faecal fat, and in 19 patients with various diseases of the small gut investigations with 14C-tripalmitate and 3H-palmitic acid, dissolved in 1.0 g Indian corn oil/kg, were performed. Serum lipid activity of 14C and 3H was measured 4, 6, and 8 h later. Compared with absolute values of triglyceride absorption (percentage dose of 14C-lipid activity/l serum), relative values (14C/3H ratio of the serum lipids) led to a significantly better discrimination between the control group and patients, attributable to a much smaller normal range. Compared with fatty acid absorption, triglyceride absorption was lowered in all cases of pancreatic steatorrhoea, in most cases of chronic pancreatitis, and in some cases of intestinal malabsorption. While the proposed procedure seems to be sensitive and reliable in the detection of maldigestion, a distinction between maldigestion and malabsorption is apparently uncertain.

Physical and chemical characterization of vitellogenin from the hemolymph and eggs of the tobacco hornworm, Manduca sexta

1. Vitellogenin has been purified from mature eggs and the hemolymph of adult females of Manduca sexta by a combination of gel permeation chromatography and sodium bromide density gradient centrifugation. 2. It has a molecular weight of 2.6 x 10(5) and is a glycolipoprotein containing approx 11% lipids and 3% carbohydrates. 3. The carbohydrate moiety is comprised entirely of mannose and N-acetyl glucosamine. 4. Two polypeptide chains are present with molecular weights of 1.8 x 10(5) and 5.0 x 10(4). 5. Partial proteolytic hydrolysis of vitellogenin resulted in the degradation of the large polypeptide but did not affect the small one, suggesting that the small polypeptide is located in the interior of the particle. 6. The proteolytic hydrolysis products of the large polypeptide differed from one another by approx 12.5 x 10(3) daltons.

The effect of insulin and glucose on sterol synthesis in cultured rat arterial smooth muscle cells

The smooth muscle cell plays an important role in the process of atherogenesis, proliferating in the arterial intima and becoming filled with lipid during the course of the disease. In these experiments the effect of insulin and glucose on sterol synthesis in cultured rat arterial smooth muscle cells was studied. Arterial smooth muscle cells were cultured from pieces of intima and inner media of young rat aortas. The cells were grown in Petri dishes in culture medium with foetal calf serum and when confluent were exposed to insulin or glucose for 24 hours. Insulin in concentrations of 10 micromicron-100 millimicron per ml stimulated the incorporation of sodium [2-(14)C]acetate into non-saponifiable lipids and digitonin precipitable sterols. However, insulin had no effect on the incorporation of labelled mevalonate into cell sterols. Increasing concentrations of glucose in the medium up to 140 mM had had no effect on the incorporation of isotope into sterols, but higher concentrations of glucose caused cell damage and sterol synthesis was markedly depressed. These results may have relevance to the development of atherosclerosis in diabetes and obesity.

Diagnosis of familial hypercholesterolemia by measurement of sterol synthesis in cultured skin fibroblasts

The incorporation of radioactive acetate into the digitonin precipitable fraction (cholesterol) was measured in monolayers of primary cultures of skin fibroblasts. Mean incorporation was increased approximately 20-fold in 4 subjects homozygous for familial hypercholesterolemia (FH) and 4-fold in 6 heterozygotes derived from the immediate family of homozygotes. Incorporation was normal in 4 subjects with Type IV and V hyperlipoproteinemia. In cells that had been preincubated in lipid free medium, incorporation by cells from homozygotes was equal to controls, denoting a derangement in the feedback inhibition of cholesterol synthesis by medium lipids in paralleled the values obtained for sterol synthesis. The assay described could be useful in making an "etiologic" diagnosis of familial hypercholesterolemia and could possible identify variants of monogenic hyperbetalipoproteinemia.

Substrate incorporation into hepatic lipids and proteins in vitro in patients with pre-beta hyperlipoproteinemia

Fifty-three patients operated on for uncomplicated gallstone disease have been studied concerning the hepatic synthesis rate in vitro of glycerides and proteins. Thirteen of the patients had pre-beta hyperlipoproteinemia. Five of them and four normolipoproteinemic patients were fed a sucrose-enriched diet for two weeks prior to the operation. In the non-sucrose-fed hyperlipoproteinemic patients the liver concentration of triglycerides (TG) and the incorporation rate of precursors into TG were increased. A significant correlation was found between the synthesis rate of TG in liver tissue and the plasma TG concentration in these hyperlipoproteinemic patients. After sucrose feeding of patients with hyperlipoproteinemia the concentration of phosphoglycerides (PG) the incorporation rate of labelled precursors in PG were significantly lower than in normolipoproteinemic patients and in hyperlipoproteinemic patients on an ordinary diet. The incorporation rate of leucine into hepatic proteins and the hepatic protein concentration were the same in non-sucrose-fed controls, sucrose-fed, and non-sucrose-fed hyperlipoproteinemic patients. The results indicate an increased vulnerability of the hepatic PG and protein metabolism for dietary sucrose in patients with pre-beta hyperlipoproteinemia.

Effects of lipid removal on the molecular size and kinetic properties of bovine plasma arylesterase

A purified arylesterase preparation from bovine plasma was characterized to the extent that it has a partial specific volume of 0.91ml/g and an apparent z-average molecular weight of 440000. The relatively large magnitude of the former reflects the presence of phospholipids, cholesterol, triglycerides and beta-carotene, the last-named being responsible for the pronounced yellow colour of the preparation. Removal of the lipid material is accompanied by a decrease in the apparent z-average molecular weight to 120000, the size of the smallest species detected by high-speed sedimentation equilibrium being in the vicinity of 70000 daltons: denaturation of the lipid-free preparation with 6m-guanidine hydrochloride caused essentially complete breakdown into subunits of this size. In kinetic studies on the enzyme the maximal velocity for the hydrolysis of phenyl acetate was found to increase by 60% on addition of 1 mm-Ca(2+), with the K(m) showing a concomitant decrease from 6.6 to 2.1 mm. Removal of lipid had no detectable effect on V(max.) or K(m) in either the presence or the absence of Ca(2+). It is concluded that the bovine plasma arylesterase preparation is either a lipoprotein or an enzyme-lipoprotein complex with properties very similar to those of the alpha(1)-lipoprotein or high-density lipoprotein (HDL(2)) fraction of serum.