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Infantile Refsum's disease: biochemical findings suggesting multiple peroxisomal dysfunction.

Infantile Refsum's disease was diagnosed in three male patients, presenting with facial dysmorphia, retinitis pigmentosa, neurosensory hearing loss, hepatomegaly, osteopenia and delayed growth and psychomotor development. An elevated plasma phytanic acid concentration and a deficient phytanic acid oxidase activity in fibroblasts were found with an accumulation of very long chain fatty acids in plasma and fibroblasts. There were elevated pipecolic acid levels in plasma, urine and CSF, and abnormal bile acid metabolites in plasma. Deficient activity of acylCoA: dihydroxyacetone phosphate acyl transferase was found in thrombocytes and fibroblasts of these patients as well as an impaired de novo plasmalogen biosynthesis in fibroblasts. These biochemical abnormalities, previously described in the Zellweger syndrome, suggest multiple peroxisomal dysfunction in our patients.

Acyltransferases↗

Dyggve-Melchior-Clausen syndrome with increased pipecolic acid in plasma and urine.

A child with the Dyggve-Melchior-Clausen syndrome associated with elevated pipecolic acid levels in plasma and urine is described. Other studies of peroxisomal function, including phytanic acid, very long-chain fatty acids, and plasmalogen synthesis, were normal. This disorder may represent an incompletely characterized defect in peroxisomal metabolism.

Bone Diseases, Developmental↗

The role of peroxisomes in mammalian cellular metabolism.

Peroxisomes, which are widely distributed in mammalian tissues, carry out several important functions in cellular metabolism. Production of alkylglycerol-3-phosphate, a key intermediate in the synthesis of plasmalogens and other ether lipids, occurs in the peroxisome. A fatty acid beta-oxidation system with significant differences from mitochondrial beta-oxidation is also found in the peroxisomes; the acetyl-CoA produced is used for synthetic reactions. This pathway has a particularly important physiological role in the oxidation of very long chain fatty acids and the side chain of cholesterol. Peroxisomes also possess a number of oxidases that produce H2O2 which is decomposed by peroxisomal catalase. The function of this peroxisomal respiratory pathway is disposal of excess reducing equivalents, protection of the cell against H2O2 and possibly a role in thermogenesis in brown adipose tissue. Other peroxisomal functions include a role in gluconeogenesis and in purine and polyamine catabolism. Some enzymes of peroxisomes can be induced by dietary, hormonal and other physiological changes. The entire organelle proliferates under certain of these conditions.

Animals↗

Lipid characterization and 14C-acetate metabolism in catfish taste epithelium.

The catfish, Ictalurus punctatus is an important model system for the study of the biochemical mechanisms of taste reception. A detailed lipid analysis of epithelial tissue from the taste organ (barbel) of the catfish has been performed. Polar lipids account for 62 +/- 1% of the total, neutrals for 38 +/- 1%. Phosphatidyl-cholines, serines and ethanolamines are the major constituents of the polar fraction. Plasmalogen concentration is high relative to that of non-neural tissues. [14C]-Acetate is incorporated into cell lipid fractions after incubation of barbel tissue at 37 degrees C for 60 min. Percentage amounts of most lipids change with time during this in vitro incubation. The phospholipids are the most metabolically active fractions. This work yields information for continuing reconstitution experiments and indicates that the taste epithelium of this important model system is a metabolically active tissue capable of supporting lipid turnover/synthesis.

Acetates↗

Ischemia-reperfusion injury in the spinal cord of rabbits strongly enhances lipid peroxidation and modifies phospholipid profiles.

The effect of spinal cord ischemia (10, 20, and 40 min) and post-ischemic reperfusion (10, 30, and 60 min) on lipid peroxidation and phospholipids was investigated. Spinal cord ischemia was accompanied by lipolytic processes with significant changes in concentration of lipid peroxidation products (LPP). Reestablishment of the blood supply after 10 min ischemia was accompanied by significantly increased levels of thiobarbituric acid reactive substances (TBA-RS) after 10 and 30 min of reperfusion. Following 20 and 40 min ischemia a significant increase was observed at all reperfusion periods. Ischemia itself significantly reduced the concentration of phosphatidyl inositol (IP), phosphatidyl ethanolamine (EP) and ethanolamine plasmalogens (Epls). Significant changes were observed in concentration of phosphatidyl serine (SP) too, but only after 20 and 40 min of ischemia. The concentration of phosphatidic acid (PA) was significantly reduced only after 10 min of ischemia. The onset of reperfusion after ischemia was accompanied by a diverse pattern of changes in PA, IP, Epls and SP, while the concentration of EP remained at the above mentioned ischemic intervals.

Animals↗

Effects of storage conditions on rat brain ethanolamine glycerophospholipids, cerebrosides, and cholesterol.

The effects of storage on rat brain lipid composition were studied in terms of ethanolamine glycerophospholipid, cerebrosides, and cholesterol. Rat brains were stored at several combinations of temperature and time. Storage conditions were: 2 hr at room temperature, 12 hr of refrigeration, and a sequence of both of these conditions. Two-dimensional thin layer chromatography followed by colorimetric analyses of eluted lipids were used to determine molar ratios of phosphatidylethanolamine, ethanolamine plasmalogen, lysophosphatidylethanolamine, and cerebrosides. Cholesterol was also determined. These studies revealed small but significant increases in lysophosphatidylethanolamine in all three cases. A slight increase was also noted in the apparent molar proportion of cholesterol.

Animals↗

Alterations of phospholipids in ischemic canine myocardium during acute arrhythmia.

Myocardial ischemia was produced in the left ventricle of the canine heart by a Harris two-stage occlusion of the left anterior descending coronary artery. The lipid content in the ischemic myocardium was analyzed and compared with the control tissue. No significant change in total phospholipid and cholesterol was detected. A 2-fold elevation in the levels of the major lysophospoholipids was observed during acute ventricular arrhythmias at 24 hr after the onset of ischemia. Such increases were not caused by preferential hydrolysis of phospholipid plasmalogens from the parent phospholipids.

Animals↗

Polyunsaturated fatty acid changes suggesting a new enzymatic defect in Zellweger syndrome.

The fatty acid composition of red blood cells, fibroblasts, forebrain, liver and kidney were studied in a 3-month-old infant who died from Zellweger Syndrome, and the results were compared with those of age-matched controls. Besides a typical increase in the very long chain fatty acids 26:0 and 26:1 and a great reduction in the plasmalogen levels, confirming the diagnosis of Zellweger Syndrome, some striking changes in the polyunsaturated fatty acid patterns were discovered. The most important was a very drastic decrease in the values of 22:6 omega 3 and 22:5 omega 6, the two products of delta 4-desaturation. In the kidney, the level of 22:6 omega 3 fell below that of 26:0. Consequently, the ratio 26:0/22:6 omega 3 (and 26:1/22:6 omega 3) was most useful in emphasizing the fatty acid anomalies, especially in renal tissue, where the 26:0/22:6 omega 3 ratio increased to almost 200 times the normal values. Other significant, although less consistent fatty acid alterations were increases in 18:2 omega 6, 18:3 omega 6, 20:3 omega 6, 18:4 omega 3 and 20:4 omega 3, and a decrease in 20:4 omega 6 in some tissues. The existence is proposed of a new enzyme defect in peroxisomal disorders, involving the desaturase system of long chain polyunsaturated fatty acids.

Brain↗

Lipid alterations following impact spinal cord injury in the rat.

A computer-controlled impactor was used to produce a severe spinal cord injury in the rat thoracic spinal cord. Cords were rapidly frozen in situ at 5, 15, 30, and 60 min and 6, 12, and 24 h postinjury. Control cords were noninjured cords from animals having undergone a laminectomy and allowed to recover for 90 min postlaminectomy. The cords were assayed for alterations in lipid metabolism. Specifically, there were rapid increases in prostaglandin F2 alpha and thromboxane, with a peak increase in thromboxane levels at 30 min. Prostaglandin F2 alpha levels peaked at 15 min with levels remaining nearly constant for 12 h. There were no detectable changes in phospholipid levels, although diacylglycerol levels and free fatty acid levels were increased. Total free fatty acids were increased at 12 and 24 h postinjury by 2.3- and 3.2-fold over control levels, respectively. Arachidonic acid levels were not significantly elevated at early time points, however, these early time points correspond to elevated eicosanoid synthesis and this may account for the lack of early detectable increases in arachidonic acid. After 6 h postinjury, arachidonic acid levels were 20-fold greater than control levels and remained elevated at 24 h. There were minimal decreases in cholesterol and no decrease in either choline or ethanolamine plasmalogen levels. These results suggest a rapid turnover of arachidonic acid following spinal cord injury with a concomitant increase in vasoconstrictive eicosanoid synthesis. The lack of changes in major membrane constituents suggests the mechanisms may not involve general membrane degradation, but an over-stimulation of phospholipase A2-linked membrane receptors.

Animals↗

Membrane asymmetry in isolated canine cardiac sarcoplasmic reticulum: comparison with skeletal muscle sarcoplasmic reticulum.

Cardiac sarcoplasmic reticulum (CSR), isolated from dog hearts, was shown to be asymmetric in the distribution of phospholipids across the CSR bilayer. Phosphatidylethanolamine was mostly resident in the outer leaflet, phosphatidylcholine was equally distributed across both monolayers and phosphatidylserine was found primarily in the inner monolayer. This distribution of headgroups is similar to that found in fast skeletal muscle sarcoplasmic reticulum (SSR); however, the asymmetry in CSR is not as striking as that in SSR. Phospholipids retained by the CSR calcium pump protein (CaATPase) after detergent "stripping" were similar to those intimate to the SSR CaATPase, although the percentages of unsaturated phospholipids and plasmalogenic phospholipids are not as great as in the skeletal system. Lipids associated with the CSR CaATPase following DFDNB cross-linking showed a preference for retention of the aminophospholipids, again similar to the SSR CaATPase. Because the nonrandom distribution of membrane lipids modifies SSR function, it is likely these membrane lipids impact in situ the function of the CSR.

Animals↗

Postnatal development of phospholipids and their fatty acid profile in rat heart.

The aim of this study was to determine the concentration of phospholipids (PL), plasmalogen components of choline (PC) and ethanolamine (PE) phosphoglycerides (PLPC, PLPE) and fatty acid profile of PL and triacylglycerols (TAG) in developing rat left ventricular myocardium between postnatal day (d) 2 and 100. The steepest increase of total PL (TPL) concentration occurs between d2 and d5, followed by a further slower increase between d20 and d40. Similar developmental changes were observed in PC and PE. The PLPE concentration rises by d10, whereas PLPC does not change during the whole period investigated, except for the transient decline on d5. The concentration of diphosphatidylglycerol (DPG) increases by d60; the steepest rise occurs between d20 and d40. Phosphatidylinositol (PI) concentration rises only by d5. The concentration of phosphatidylserine (PS) decreases between d5 and d10 and then it does not change. Sphingomyelin (SM) concentration is maintained till d10, it declines on d20 and does not change thereafter. The proportion of saturated fatty acids (SFA) increases by d5 in PC, PE, PS and TAG, and by d10 in DPG and PI. After d20 the SFA proportion gradually decline in all lipids. Monounsaturated FA (MUFA) proportion decreases in PC, PE, PI and PS from d2 till d10, and in the weaning period it tends to rise again. In contrast, in DPG and TAG the proportion of MUFA declines during the whole postnatal period. N-6 polyunsaturated FA (PUFA) decrease in all PL by d20 and rise again thereafter; in TAG they decline between d2 and d10 and return to the initial level by d100. N-3 PUFA increase in all PL during the suckling period and decline after weaning; in TAG they increase only by d5 and then they decline. This remodeling of myocardial PL and TAG composition during postnatal development may affect membrane properties and contribute to developmental changes in the function of membrane proteins and cell signaling.

Animals↗

Exercise training-induced changes in sensitivity to endothelin-1 and aortic and cerebellum lipid profile in rats.

The purpose of this work was to study whether exercise training induces changes in the lipid profile of rat aorta and nervous system and in the in vitro intrinsic responsiveness of these tissues to endothel in-1 (ET-1) treatment. The exercise program performed successfully produced the characteristic metabolic alterations of the trained state. Exercise training induced a large and significant increase in the levels of both aortic ethanolamine plasmalogens (PlasEtn) and glucosylceramides. In contrast, a decrease of aortic ceramide and cholesterol levels was evoked by exercise training. ET-1 increased PlasEtn content only in sedentary animals. An exercise-induced increase in cerebellum levels of ceramides and ceramide monohexosides was found. The cerebellum ceramide content was increased by ET-1 more noticeably in sedentary rats than in trained animals. In contrast, cerebral cortex was observed to be largely insensitive to both exercise training and ET-1 treatment. It was concluded that exercise training (i) induces changes in both vascular and cerebellar lipid profiles, the former being much more pronounced than the latter, and (ii) diminishes the aortic and cerebellar sensitivity to ET-1 action.

Animals↗

Alterations in heart and kidney membrane phospholipids in hypertension as observed by 31P nuclear magnetic resonance.

Abnormalities of phospholipids in hypertension have previously been described in human erythrocyte, platelet, and plasma lipoproteins. Since the heart and kidney are adversely affected by hypertension, we investigated possible alterations in their membrane phospholipids, which could play a role in the derangement of intracellular ion balance widely observed in hypertension. The phospholipid compositions of heart and kidney from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were determined by using 31P nuclear magnetic resonance (NMR) spectroscopy. Absolute contents of all phospholipids in hypertensive hearts and kidneys were significantly higher than in normotensive hearts and kidneys. Expressed as a fraction of total phospholipid, cardiolipin (CL) and phosphatidylethanolamine plasmalogen (PEp) were significantly increased in SHR hearts compared to WKY hearts (CL and PEp were 7.95+/-0.22% and 13.16+/-0.35% in SHR vs. 7.01+/-0.20% and 11.19+/-0.42% in WKY rats, P< or =0.05), but phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were significantly decreased in SHR (PE and PC were 22.46+/-0.37% and 44.81+/-0.43% in SHR vs. 24.02+/-0.44% and 46.01+/-0.50% in WKY rats, P< or =0.05). In the phospholipids extracted from rat kidneys, the percentage of PE was significantly higher for SHR than for WKY rats (20.37+/-0.60% vs. 18.43+/-0.37%, P< or =0.05), while PEp and phosphatidylserine (PS) were significantly lower for SHR (PEp and PS were 10.22+/-0.36% and 8.42+/-0.28% in SHRs vs. 11.29+/-0.36% and 9.71+/-0.40% in WKY rats, P< or =0.05). The above alterations in phospholipid composition might contribute to the higher oxygen consumption in the hypertensive heart and abnormal intracellular ion concentrations and ion transport in the heart and the kidney in hypertension.

Animals↗

Lipid composition of Limulus photoreceptor membranes.

The lipid composition has been determined for rhabdomeric photoreceptor membranes of Limulus, and these data are compared with those from photoreceptor membranes of albino rats. The comparison is of interest because the membranes of these two photoreceptor cells regulate ionic transport differently during the response to illumination. 1. Phospholipid class composition of Limulus is similar, but not identical, to that of rats. The major differences are a greater percentage of sphingomyelin in Limulus and a greater percentage of phosphatidylethanolamine in the rat. 2. Ethanolamine plasmalogens, not observed in rat photoreceptor membranes, are present in Limulus photoreceptor fractions. 3. The level of cholesterol in Limulus is higher than that usually reported for vertebrate rod outer segments. 4. The predominant polyunsaturated fatty acids of Limulus photoreceptor membrane phospholipids are 20: 4(n-6) and 20: 5(n-3) with only traces of 22: 6(n-3). This is in sharp contrast with the large percentages of 22: 6(n-3) found in rat photoreceptors. 5. The fatty acid distributions of both membrane systems are highly unsaturated, but the ratio of (n-3) to (n-6) polyunsaturates is only 1.7 for Limulus as compared to 4.6 for rat.

Animals↗

2H-NMR studies on ether lipid-rich bacterial membranes: deuterium order profile of Clostridium butyricum.

Palmitic acid specifically deuterated at different carbon atoms, has been incorporated biosynthetically into the membrane lipids of Clostridium butyricum. The lipids of this organism are rich in plasmalogens and their glycerol acetals and exhibit an unusual fatty acyl and alkenyl chain distribution with saturated chains mainly at the sn-2 position and unsaturated chains at the sn-1 position. The ordering of the deuterated hydrocarbon chains in whole cells was measured with deuterium nuclear magnetic resonance and was compared to the order profiles of isolated cell membranes and membranes formed from the total phospholipid extract. The shape of the order profiles was similar for all three membranes, but the absolute values of the order profiles in whole cells and isolated membranes were lower than those of the liposomal lipids. The order profiles have the same characteristic shape as those found for the lamellar liquid-crystalline phases of synthetic diacylphospholipids.

Cell Membrane↗

A method for the quantitative determination of glycerolipids containing O-alkyl and O-alk-1-enyl moieties.

We have developed a spectrophotometric procedure, based on a combination of established methods, for the quantitative determination of aklyl and alk-1-enyl (plasmalogens) ether-linked glycerolipids. It depends upon the release of alkylglycerols and alk-1-enylglycerols from phospholipids by phosphlipase C (Bacillus cereus) followed by saponification or by Vitride reduction the phospholipids; aldehydes are subsequently formed and measured colorimetrically after reacting them with a fuchsin reagent. The total alkyl and alk-1-enyl content of glycerolipids is determined oxidation of the sample withperiodate to form aldehydes and alkylglycolic aldehydes. The O-alk-1-enyl lipid content is determined on a separate sample by measuring the aldehydes produced after acid hydrolysis. The quantity of O-alkyl lipids is calculated from the difference between the values obtained for the total ether-lipid content and that of the O-alk-1enyl lipid content. Alternately, direct determination of alk-1-enylglycerols and alkylglycerols can be made if these hydrolytic products are first separated by thin-layer chromatography.

Animals↗

Characterization of rabbit myocardial phospholipids with 31P nuclear magnetic resonance.

To reduce chemical modifications of phospholipids during extraction and analysis, we developed and evaluated a method for analyzing tissue phospholipids with 31P NMR. Our results indicate: (1) 31P NMR of chloroform/methanol tissue extracts is a convenient and rapid technique for characterizing myocardial phospholipids. (2) Normal rabbit myocardium contains little, if any, lysoglycerophospholipid. (3) Conventional extraction and chromatography of phospholipids may convert choline and ethanolamine plasmalogens to lysoglycerophospholipids by acid-catalyzed hydrolysis.

Animals↗

Specificity of lysophospholipase D.

The specificity of lysophospholipase D (1-alkyl-sn-glycero-3-phosphoethanolamine ethanolaminehydrolase, EC 3.1.4.39; also works on choline analogs) for 1-alkyl- and 1-acyl-linked substrates was examined using rat liver microsomes. The microsomes were treated with diisopropylphosphorofluoridate to inhibit the hydrolysis of acyl chains from the acyl-linked compounds (1-palmitoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-sn-glycero-3-phosphoethanolamine) and were treated with p-bromophenacyl bromide to block acylation of the compounds tested. In the presence of the inhibitors, 1-alkyl-sn-glycero-3-phosphocholine and 1-alkyl-sn-glycero-3-phosphoethanolamine were hydrolyzed extensively by lysophospholipase D but the corresponding 1-acyl-linked analogs were only negligibly hydrolyzed. Lysophospholipase D therefore appears to be specific for the ether-linked compounds. 1-Alk-1-'-enyl-sn-glycero-3-phosphoethanolamine (lyso plasmalogen) was also tested as a substrate, but a plasmalogenase in the rat liver microsomes rapidly hydrolyzed the compound and we were unable to determine whether it is a substrate for lysophospholipase D. Alkyl-linked substrates containing long-chain acyl groups at the 2-position are not hydrolyzed by the enzymes. We tested 1-alkyl-2-acetoyl-sn-glycero-3-phosphocholine and 1-alkyl-2-acetoyl-sn-glycero-3-phosphoethanolamine to determine if the less bulky, more hydrophilic acetate group would permit hydrolysis by lysophospholipase D; the derivatives did not appear to be attacked, except after hydrolysis of the acetate group. However, in the absence of inhibitors, the acetate groups were rapidly hydrolyzed by microsomal preparations.

Animals↗