Pharmacokinetics and bioavailability of diisopropanolamine (DIPA) in rats following intravenous or dermal application

This study was conducted to determine the relative dermal bioavailability (absorption), distribution, metabolism, and excretion (ADME) of diisopropanolamine (DIPA), an alcohol amine used in a number of industrial and personal care products. Groups of 4 female Fischer 344 rats received either a single bolus i.v. dose of 19.0mg/kg (14)C-DIPA in water or a dermal application of 19.5mg/kg (14)C-DIPA in acetone to an area of 1cm(2) on the back and covered with a bandage. Time-course blood and excreta were collected and radioactivity determined. Urine was analyzed for DIPA and monoisopropanolamine (MIPA). Following i.v. administration, DIPA was rapidly cleared from the plasma and excreted into urine in a biexponential manner (t(1/2alpha), 0.4h; t(1/2beta), 2.9h). The levels of radioactivity in plasma dropped below the limit of detection 12h post-dosing. A total of 97+/-4% of the dose was actively excreted in urine by kidney, most ( approximately 71%) within 6h of dosing, virtually all as parent compound; renal clearance exceeded the glomerular filtration rate. Following dermal application, approximately 20% of the dose was absorbed in 48 h with the steady-state penetration rate of approximately 0.2%/h. Most (14.4%) of the applied radioactivity was excreted in urine at a relatively constant rate due to the presence of large amount of the (14)C-DIPA at the application site. Fecal elimination was <0.2% of the dose. The absorbed DIPA did not accumulate in tissues; only approximately 0.1% of the administered dose was found in liver and kidney. The absolute systemic dermal bioavailability (dose corrected AUC(dermal)/AUC(i.v.)) of (14)C-DIPA was 12%. The ADME of DIPA contrasts that of its diethanol analogue, diethanolamine, which displays a broad spectrum of toxicity in rats and mice. Toxicologically significant concentrations of DIPA are unlikely to be achieved in the systemic circulation and/or tissues as a result of repeated dermal application of products containing DIPA due to slow absorption from the skin, rapid unchanged elimination in urine, and majority of the products contain <or= 1% DIPA.

The determination of the ability of polyurethane foam to release toluene diisocyanate into air

A study was conducted to assess the ability of polyurethane foam to release toluene diisocyanate (TDI) into the air. The study was completed in two phases. In the first phase, three-day post-production foam samples were "extracted" using 37 degrees C, 30 percent relative humidity air for a total of three days. In the second phase, foam samples were "loaded" with TDI (approximately 1 ppm (w/w) in the foam) by passing air containing a controlled level of TDI vapor through the foam. The "loaded" foam was then aged for three days (to simulate minimum possible expected time between production and consumer contact) before being extracted for three days using 37 degrees C, 30 percent relative humidity air. In both phases of the study, the extracted TDI was quantified by trapping it from the air using glass-fiber filters coated with 1,(2-pyridyl)piperazine (PP) derivatizing agent (modified OSHA Method 42) then analyzing the TDI derivative formed using high-performance liquid chromatography with ultraviolet detection. Validation of the test system was conducted using diffusion-tube-generated TDI atmospheres. Results of the Phase 1 portion of the study showed no quantifiable TDI being extracted from the three-day post-production commercial foam samples at a limit of quantitation of approximately 0.1 ppb TDI in air. Results of the Phase 2 portion of the study showed no quantifiable TDI being extracted from the "loaded" foams at a limit of quantitation of 0.12 microgram TDI (less than 0.03% of the level of TDI loaded into the foams). In conclusion, the results from this study indicate that it is not likely that TDI would be released from three-day post-production polyurethane foams in amounts likely to produce air concentrations of concern.

Evaluation of the cost-effectiveness of various passive monitors and active monitors for industrial hygiene sampling

A framework for evaluating passive or active industrial hygiene air sampling monitors on a cost-effectiveness basis is described. Five passive monitors and one active monitor (charcoal tube with pump) were compared in several hypothetical scenarios. Using certain assumptions regarding method validation costs, sampling equipment costs, and labor costs, both a per sample cost and a total annual cost were calculated for each type of sampling monitor as a function of total samples taken per year. The results of this study indicate that even when the additional expense of full validation of the passive sampling monitor is required, these monitors are more cost-effective than active monitors. A specific type of passive monitor utilizing replaceable capsules is the most cost-effective when more than 500 samples per year are taken.

Craniocervical injuries in judicial hangings: an anthropologic analysis of six cases

Restoration projects and archaeologic excavations in two Canadian prisons resulted in the recovery of the skeletons of six felons executed by judicial hanging. Damage inflicted by hanging on various skeletal elements was observed. Among the injuries seen were fractures of the hyoid cornua, styloid processes, occipital bones, and cervical vertebral bodies (C2) and transverse processes (C1, C2, C3, and C5). Despite the general uniformity of the hanging technique, which involved a subaural knot, the trauma to the skeletal elements and the cause of death varied among individuals. Although some of this variation was probably due to minor differences in hanging practices, individual anatomic peculiarities of the victims likely also contributed.

Regulation of low density lipoprotein receptor and 3-hydroxy-3-methyl-glutaryl-CoA reductase activities are differentially affected in Niemann-Pick type C and type D fibroblasts

Defective regulation of intracellular cholesterol metabolism has been investigated in cultured fibroblasts from two subtypes of Niemann-Pick type II disease: the panethnic Niemann-Pick type C (NPC) and the Nova Scotia type D (NPD). Cell extracts from NPC and NPD fibroblasts cultured in lipoprotein-deficient medium exhibited activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase that were two-fold greater than in normal cells. Addition of serum resulted in only a 15% decrease in HMG-CoA reductase activity within 6 h in these cells, compared with a decrease of 80% in normal fibroblasts. The initial rate of return to maximal values for the first 6 h after removal of serum was similar in all three cell types; thereafter, the rate was faster in the mutant fibroblasts. Binding and internalization of 125I-labeled low density lipoprotein (LDL) was not decreased within 12 h of incubation of NPC fibroblasts with serum, while a decrease of 50% was observed for both NPD and normal fibroblasts over this time period. Northern blot analysis also indicated a slower decrease in steady-state LDL receptor mRNA in NPC relative to normal and NPD cells. In all three cell types, inhibition of HMG-CoA reductase with mevinolin had no effect on serum-stimulated cholesterol esterification, while inhibition of acyl-CoA:cholesterol acyltransferase with Sandoz 58-035 did not influence HMG-CoA reductase activity, indicating that defects in these regulatory mechanisms are independent.(ABSTRACT TRUNCATED AT 250 WORDS)

Limited metabolic interaction of serine with ethanolamine and choline in the turnover of phosphatidylserine, phosphatidylethanolamine and plasmalogens in cultured glioma cells

Modulation of choline phosphoglyceride turnover has been investigated extensively but less is known about regulation of serine and ethanolamine phosphoglyceride synthesis and turnover. We investigated incorporation and interactions of [3H(G)]L-serine, [1,2-14C]ethanolamine and [methyl-3H]choline in cultured glioma cells. Exogenous serine did not compete with ethanolamine or choline incorporation and did not chase labeled headgroup from ethanolamine phosphoglycerides (PE); serine displaced headgroup of prelabeled phosphatidylserine (PtdSer) resulting in less labeled PtdSer for decarboxylation. In contrast, exogenous ethanolamine markedly chased labeled headgroup of non-plasmenylethanolamine phosphoglycerides (NP-PE) with less effect on plasmalogen (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) whether headgroup was derived from [3H]serine or [14C]ethanolamine. Label in chase medium was mainly ethanolamine to 12 h; phosphoethanolamine was present with longer chase (12-48 h). Choline did not compete with serine incorporation and had little chase effect on PtdSer and PE. Choline and ethanolamine competitively interacted with preference for choline. These data suggest that (1) PtdSer synthesis in cultured glioma cells may involve more than headgroup exchange; (2) PE turnover with metabolite release to medium may involve both phospholipase D and phospholipase C; (3) acceleration of PE turnover by exogenous ethanolamine primarily involves NP-PE with lesser involvement of plasmalogen; and (4) in contrast to lack of interaction between serine and other headgroup precursors, choline and ethanolamine compete primarily at uptake.

Dissociation of phosphorylation and translocation of a myristoylated protein kinase C substrate (MARCKS protein) in C6 glioma and N1E-115 neuroblastoma cells

An 80-kDa protein labeled with [3H]myristic acid in C6 glioma and N1E-115 neuroblastoma cells has been identified as the myristoylated alanine-rich C kinase substrate (MARCKS protein) on the basis of its calmodulin-binding, acidic nature, heat stability, and immunochemical properties. When C6 cells preincubated with [3H]myristate were treated with 200 nM 4 beta-12-O-tetradecanoylphorbol 13-acetate (beta-TPA), labeled MARCKS was rapidly increased in the soluble digitonin fraction (maximal, fivefold at 10 min) with a concomitant decrease in the Triton X-100-soluble membrane fraction. However, phosphorylation of this protein was increased in the presence of beta-TPA to a similar extent in both fractions (maximal, fourfold at 30 min). In contrast, beta-TPA-stimulated phosphorylation of MARCKS in N1E-115 cells was confined to the membrane fraction only and no change in the distribution of the myristoylated protein was noted relative to alpha-TPA controls. These results indicate that although phosphorylation of MARCKS by protein kinase C occurs in both cell lines, it is not directly associated with translocation from membrane to cytosol, which occurs in C6 cells only. The cell-specific translocation of MARCKS appears to correlate with previously demonstrated differential effects of phorbol esters on stimulation of phosphatidylcholine turnover in these two cell lines.

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

Polyunsaturated fatty acid incorporation into plasmalogens in plasma membrane of glioma cells is preceded temporally by acylation in microsomes

Plasmalogens (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) are major phospholipids in many tissues and cells, particularly of neural origin. Using cultured C6 glioma cells and subcellular fractions isolated on Percoll gradients we investigated selectivity for esterification of several polyunsaturated fatty acids (PUFA) in the sn-2 position of plasmalogens compared to [1-14C]hexadecanol, representative of de novo synthesis of the ether-linked sn-1 position. In whole cells at a final concentration of 105 microM PUFA, 2-4 nmol plasmalogen/mg protein was labeled in 4 h and 10-14 nmol in 24 h, representing 8-15% and 35-50%, respectively, of initial plasmalogen mass. Incorporation of label from hexadecanol was lower than PUFA incorporation (20:5(n-3) greater than 20:4(n-6) greater than 18:3(n-3) much greater than 18:2(n-6)) suggesting deacylation-reacylation at the sn-2 position. Plasmalogens accounted for 50% of total cell ethanolamine phospholipids and 75% in plasma membrane. Using a novel, improved method for extraction of subcellular fractions containing Percoll, plasma membrane also was enriched in plasmalogen relative to microsomes (107.4 +/- 5.2 vs. 40.0 +/- 2.9 nmol/mg protein). Selectivity for esterification at the sn-2 position of plasmalogens with respect to chain length and unsaturation of the fatty acyl chain was similar in both subcellular fractions and reflected that of whole cells. Labeling of plasma membrane with PUFA and fatty alcohol lagged behind that of microsomes. Chase experiments in cells prelabeled with [1-14C]18:3(n-3) for 2 h showed no significant reduction of label in plasmalogen of any subcellular fraction although accumulation of label in the microsomal fraction was slowed initially. Reduction of plasmalogen label (40-50%) did occur in microsomes and plasma membrane when cells prelabeled for 24 h were switched to chase medium with or without chase fatty acid. Our data suggest that esterification of PUFA to plasmalogen may occur at the endoplasmic reticulum with subsequent translocation to plasma membrane resulting in accumulation of relatively stable pools of plasmalogen that are not readily accessible for deacylation-reacylation exchange with newly appearing PUFA. Alternatively, deacylation-reacylation may occur in a more stable phospholipid pool within the plasma membrane but would involve a slower process than at the endoplasmic reticulum.

Cultured fibroblasts from patients with Niemann-Pick disease type C and type D exhibit distinct defects in cholesterol esterification

The Niemann-Pick group of diseases can be broadly classified into two types based on clinical and biochemical characteristics. Type I is characterized by a primary deficiency of lysosomal sphingomyelinase while Type II may have a defect in the regulation of intracellular cholesterol metabolism. We have studied cholesterol esterification in cultured fibroblasts from patients with two phenotypes of Type II disease: an Acadian population of southwestern Nova Scotia (Canada) with a form of the disease known as Niemann-Pick type D (NPD) and a group of panethnic origin with Niemann-Pick type C (NPC). Addition of whole serum to normal fibroblasts grown initially in lipoprotein-deficient serum caused a rapid (within 6 h) increase in cholesterol esterification, reaching maximum values at around 24 h, while NPC fibroblasts showed little increase (less than 10% of normal). In contrast, cholesterol esterification in NPD fibroblasts increased slowly during the first 6-12 h and reached 50% of normal values by 24 h. 25-Hydroxycholesterol, a non-lipoprotein stimulator of cholesterol esterification, caused a similar stimulation of cholesterol esterification in NPC, NPD and normal cells. This was inhibited by addition of serum in mutant but not in normal cells. Within 24 h of serum addition, free cholesterol accumulated in all cell types with NPC greater than NPD greater than normal. These observations indicate that (a) regulation of cholesterol esterification in response to serum lipoproteins (but not 25-hydroxycholesterol) is abnormal in both NPC and NPD fibroblasts, and (b) the biochemical phenotypes of fibroblasts from NPC and NPD patients are distinct.

Niemann-Pick type II fibroblasts exhibit impaired cholesterol esterification in response to sphingomyelin hydrolysis

Fibroblasts from patients with Niemann-Pick Type II disease, including the panethnic type C (NPC) and Nova Scotia Acadian type D (NPD) forms, exhibit reduced or delayed stimulation of cholesterol esterification by low density lipoprotein (LDL). Based on recent evidence that cholesterol esterification can also be stimulated by cell surface sphingomyelin hydrolysis, we have compared the response of normal, NPC and NPD fibroblasts to treatment with exogenous sphingomyelinase (SMase). Staphylococcus aureus SMase (greater than 0.05 U/ml) hydrolyzed over 90% of endogenous sphingomyelin within 1 h and increased incorporation of [3H]oleic acid into cholesterol-[3H]oleate after an initial lag in all three cell types. However, normal levels of cholesterol esterification were not observed for NP Type II fibroblasts: four NPD cell lines exhibited an average of 32% of normal response while cholesterol esterification was only 20% in two well-characterized NPC lines. A third NPC line exhibited normal response to SMase despite greater than 90% impairment of LDL-stimulated cholesterol esterification. Incubation of fibroblasts with LDL followed by SMase produced a synergistic response, particularly in NPC cells where there was little response to either treatment alone. Chloroquine abolished LDL-stimulated cholesterol esterification in normal fibroblasts but had no effect on the response to SMase, indicating that lysosomal enzymes may not be involved in SMase-mediated cholesterol esterification. These results suggest that intracellular processing of cholesterol derived from either LDL or release from the plasma membrane (by sphingomyelin hydrolysis) is affected in Niemann-Pick Type II cells and that these pathways can complement one another in the stimulation of cholesterol esterification.

Alternate pathways in the desaturation and chain elongation of linolenic acid, 18:3(n-3), in cultured glioma cells

Cultured C6 glioma cells rapidly incorporate and metabolize the essential fatty acids, 18:2(n-6) and 18:3(n-3), to 20- and 22-carbon polyunsaturated fatty acids. Using several deuterated fatty acid substrates we have obtained data that suggest alternate pathways, one possibly involving delta 8-desaturation, may exist in glioma cells for formation of 20:5(n-3) and 22:6(n-3) from 18:3(n-3). With 18:3(n-3)-6,6,7,7-d4 practically no 18:4(n-3)-6,7-d2 or 20:4(n-3)-8,9-d2 was detected whereas 20:3(n-3)-8,8,9,9-d4 accounted for 3.4% and delta 5,11,14,17-20:4-8,8,9,9-d4 for 21.1% of the total deuterated fatty acids recovered in phospholipids after a 16 h incubation; 20:5(n-3)-8,9-d2, 22:5(n-3)-10,11-d2, and 22:6(n-3)-10,11-d2 accounted for 42.4%, 13.2%, and 2.8% of deuterated acyl chains, respectively. When added exogneously, 20:3-8,8,9,9,-d4 was extensively converted to delta 5,11,14,17-20:4(n-3)-8,8,9,9-d4 (45%) and 20:5(n-3)-8,9-d2 (24%); a small amount (4%) of 18:3(n-3)-d4 also was detected. Both 20:4(n-3)-8,9-d2 and 18:4(n-3)-12,13,15,16-d4 were also converted to 20:5(n-3) and 22:6(n-3) with 8 and 0% of the respective original deuterated substrate remaining after 16 h. A possible pathway for 18:3(n-3) metabolism in glioma cells is described whereby an initial chain elongation step is followed by successive delta 5 and delta 8 desaturation reactions resulting in 20:5(n-3) formation and accounting for the ordered removal of deuterium atoms. Alternatively, extremely effective retroconversion may occur to chain shorten 20:3(n-3)-d4 to 18:3(n-3)-d4 followed by rapid conversion through the classical desaturation and chain elongation sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of phosphatidylcholine and phosphatidylethanolamine biosynthesis by cytochalasin B in cultured glioma cells: potential regulation of biosynthesis by Ca(2+)-dependent mechanisms

The major route of phosphatidylcholine (PtdCho) biosynthesis in mammalian cells is the sequence: choline (Cho)----phosphocholine (PCho)----cytidinediphosphate choline (CDP-Cho)----PtdCho. Recently, we have found that intermediates of this pathway are not freely diffusible in cultured rat glioma (C6) cells but are channeled towards PtdCho biosynthesis (George et al. (1989). Biochim. Biophys. Acta. 1004, 283-291). Channeling of intermediates in other mammalian systems is thought to be mediated through adsorption of enzymes to membranes and cytoskeletal elements to form multienzyme complexes. In this study, agents which perturb the structure and function of cytoskeletal elements were tested for effects on phospholipid metabolism in glioma cells. The filament-disrupting agent cytochalasin B (CB), but not other cytochalasins or the microtubule depolymerizer colchicine inhibited PtdCho and phosphatidylethanolamine (PtdEtn) biosynthesis as judged by dose-dependent reduction of labeling from [3H]Cho and [14C]ethanolamine (Etn). 32Pi pulse-labeling indicated that CB selectively decreased PtdCho and PtdEtn biosynthesis without affecting synthesis of other phospholipids. Synthesis of water-soluble intermediates of PtdCho metabolism was unaffected but the conversion of phosphoethanolamine to CDP-ethanolamine was reduced by CB. Effects of CB on phospholipid biosynthesis were not due to inhibition of glucose uptake as shown by experiments with 2-deoxyglucose, glucose-starved cells and other cytochalasins. Experiments with Ca(2+)-EGTA buffers and digitonin-permeabilized cells, and the Ca(2+)-channel blocker verapamil suggest that effects of CB on PtdCho and PtdEtn biosynthesis are due to alteration of intracellular Ca2+. Taken together, these results suggest that CB acts at sites distinct from glucose transport and cellular microfilaments to specifically inhibit PtdCho and PtdEtn biosynthesis by mechanisms dependent on intracellular Ca2+.

Channeling of intermediates in the CDP-choline pathway of phosphatidylcholine biosynthesis in cultured glioma cells is dependent on intracellular Ca2+

The major route of phosphatidylcholine (Ptd-choline) biosynthesis in mammalian cells is the CDP-choline pathway which involves stepwise conversion of choline to phosphocholine (P-choline), cytidine diphosphate choline (CDP-choline), and Ptd-choline. Our previous studies with electropermeabilized (EP) rat glioma (C6) cells have indicated that the intermediates of this pathway are not freely diffusible in the cell but are channeled toward synthesis of Ptd-choline (George, T.P., Morash, S.C., Cook, H.W., Byers, D.M., Palmer, F. B. St.C., and Spence, M.W. (1989) Biochim. Biophys. Acta 1004, 283-291). In this study, Ca(2+)-[ethylene-bis(oxyethylenenitrilo)]tetraacetic acid buffers were used to investigate the role of intracellular free Ca2+ levels in functional organization of this pathway in EP glioma cells. In EP cells reduction of free Ca2+ in the medium from 1.8 mM to less than 200 nM resulted in 2-3-fold stimulation of exogenous [3H]choline and [14C]P-choline incorporation into Ptd-choline whereas incorporation of exogenous CDP-[14C]choline was augmented 100-fold; there was no uptake or incorporation of labeled P-choline or CDP-choline in intact cells. In EP cells incubated at 1.8 mM Ca2+ the water-soluble products of choline metabolism (choline, P-choline, CDP-choline, and glycerophosphocholine) were retained at 37 degrees C; in contrast, in the presence of 100 nM Ca2+ there was uniform leakage of these metabolites. Experiments with hemicholinium-3, an inhibitor of choline transport, and EP cells at 100 nM Ca2+ show that linkage of choline transport and Ptd-choline biosynthesis is also dependent on Ca2+. These results suggest that channeling of intermediates in the CDP-choline pathway of Ptd-choline biosynthesis in glioma cells is mediated by intracellular Ca2+ levels that may coordinately regulate the steps involved in conversion of choline to Ptd-choline.

Regulation of eukaryotic phospholipid metabolism

Phospholipids have diverse and critical roles in cellular metabolism and function. Questions about the mechanisms of regulation of phospholipid synthesis are being investigated with a variety of systems and approaches. For example, the yeast Saccharomyces cerevisiae is an organism in which both biochemical and genetic analyses are used. Biochemical approaches have yielded considerable information on the regulatory properties of enzymes of phospholipid biosynthesis. Studies of the activity of purified phosphatidylserine synthase have suggested how that enzyme is influenced by membrane phospholipids in the cell. The enzyme that regulates mammalian phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyltransferase, is also influenced by phospholipids. In addition, the activity of this enzyme often correlates with its translocation to membranes. The location of such enzymes in the cell is of particular interest in light of the possibility that the enzymatic reactions may be efficiently coupled in vivo. Techniques to render cultured cells permeable to phosphorylated molecules indicated that the enzymes of phosphatidylcholine biosynthesis may exist in an organized compartment so that the precursors of phosphatidylcholine are efficiently channeled through the pathway. To ask how phospholipids are transported in the cell, a combined biochemical and genetic approach has been used. These studies have revealed that the phosphatidylinositol/phosphatidylcholine transfer protein, considered to mediate intracellular phospholipid transfer, is a critical component of the secretory pathway for proteins. These results have allowed formulation of a number of new questions on the regulation of phospholipid metabolism and its relationship to general membrane processes.

Fabry disease in a large Nova Scotia kindred: carrier detection using leucocyte alpha-galactosidase activity and an NcoI polymorphism detected by an alpha-galactosidase cDNA clone

Fabry disease is an X linked recessive disorder of glycosphingolipid metabolism resulting from a deficiency of the lysosomal hydrolase alpha-galactosidase (alpha-gal). Measurement of the enzyme activity, however, is not an accurate method for identification of female carriers among at risk relatives of affected males. The alpha-gal cDNA and gene have been cloned previously and found to provide useful probes for the molecular analysis of affected families but these clones have not been available to us. Thus, to analyse Fabry disease in Nova Scotia, especially within a large kindred known to contain 30 affected males and 50 possible carrier females, we isolated an independent cDNA for alpha-gal. Using this clone as a probe, the mutation in the Nova Scotia kindred was shown not to be a major DNA alteration, but was found to be linked to the rarer allele (frequency 0.20) of the polymorphic NcoI site located 3' to the gene. Affected males from two Nova Scotia families who cannot be associated with the kindred by history were also found to have the rarer NcoI allele, which suggests they are, in fact, part of the kindred. The coupling of the mutation to an infrequent marker also helped carrier identification in the kindred where all of 17 obligate carriers examined, including six who were not identified as carriers by enzyme assays, were found to be heterozygous for the RFLP. Thus, DNA analysis can be used for presymptomatic and prenatal diagnosis in most portions of the Nova Scotia kindred affected with Fabry disease.

Serine utilization as a precursor of phosphatidylserine and alkenyl-(plasmenyl)-, alkyl-, and acylethanolamine phosphoglycerides in cultured glioma cells

In several tissues and cell lines, serine utilized for phosphatidylserine (PS) synthesis is an eventual precursor of the base moiety of ethanolamine phosphoglycerides (PE). We investigated the biosynthesis and decarboxylation of PS in cultured C6 glioma cells, with particular attention to 1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine (plasmenylethanolamine) biosynthesis. Incorporation of [3H]serine into PS reached a maximum within 4-8 h, and label in nonplasmenylethanolamine phosphoglyceride (NP-PE) and plasmenylethanolamine was maximal by 12-24 h and 48 h, respectively. After 8 h, label in PS decreased even though 40-60% of initial label remained in the culture medium. Serial additions of fresh [3H]serine restored PS synthesis to higher levels of labeled PS accumulation followed by a subsequent decrease in 4-8 h. High performance liquid chromatographic analyses confirmed that medium serine was depleted by 8 h, and thereafter metabolites, including acetate and formate, accounted for radioactivity in the medium. The rapid but transient appearance of labeled glycine and ATP inside the cells indicated conversion of serine by hydroxymethyltransferase. 78-85% of label from serine was in headgroup of PS or of PE formed by decarboxylation. A precursor-product relationship was suggested for label from [3H]serine appearing in the headgroup of diacyl, alkylacyl, and alkenylacyl subclasses of PE. By 48 h, a constant specific activity, ratio of approximately 1:1 was reached between plasmenylethanolamine and NP-PE, similar to the molar distribution of these lipids. In contrast, equilibrium was not achieved in cells incubated with [1,2-14C]ethanolamine; plasmenylethanolamine had 2-fold greater specific activity than labeled NP-PE by 72-96 h. These observations indicate that in cultured glioma cells 1) serine serves as a precursor of the head group of PS and of both plasmenyl and non-plasmenyl species of PE; 2) exchange of headgroup between NP-PE and plasmenylethanolamine may involve different donor pools of PE depending on whether the headgroup originates with exogenous serine or ethanolamine; 3) serine is rapidly converted to other metabolites, which limits exogenous serine as a direct phospholipid precursor.

The role of sphingomyelin in phosphatidylcholine metabolism in cultured human fibroblasts from control and sphingomyelin lipidosis patients and in Chinese hamster ovary cells

Human fibroblasts in culture take up exogenous [choline-Me-3H,32P]sphingomyelin (SM) from the medium and incorporate it into cellular SM and phosphatidylcholine [Spence, Clarke & Cook (1983) J. Biol. Chem. 258, 8595-8600]. The ratio of [3H]choline/[32P]Pi is similar in SM and phosphatidylcholine, indicating that the phosphocholine (P-Cho) moiety is transferred intact. Similar results are obtained with Niemann-Pick (NP) cells which are deficient in lysosomal sphingomyelinase activity, suggesting that the P-Cho transfer may not be mediated by the lysosomal sphingomyelinase and that alternative pathways of sphingomyelin catabolism are present in cultured cells. In this study we have shown that: (1) the P-Cho pool in control and NP cells incubated with exogenous labelled SM has a specific radioactivity intermediate between that of SM and PtdCho; (2) expansion of the intracellular P-Cho pool by incubation with exogenous choline reduces the incorporation of [3H]choline from SM into PtdCho; and (3) incorporation of P-Cho from SM into PtdCho is decreased at the non-permissive temperature in Chinese hamster ovary cells with a temperature-sensitive mutation in the cytidylyltransferase reaction. These results suggest that incorporation of P-Cho from SM into PtdCho involves a reaction sequence in which P-Cho is hydrolysed from SM by a sphingomyelinase, followed by incorporation of P-Cho into PtdCho via the cytidine pathway of biosynthesis (SM----P-Cho----CDP-Cho----PtdCho). The appreciable incorporation of P-Cho from SM into PtdCho in sphingomyelinase-deficient NP cells suggests a more substantial or effective lysosomal sphingomyelinase activity in intact cells than is measured in vitro, and/or a significant contribution by other sphingomyelinase activities in these cells.

Incorporation of polyunsaturated fatty acids into plasmalogens, compared to other phospholipids of cultured glioma cells, is more dependent on chain length than on selectivity between (n - 3) and (n - 6) families

In several tissues and cells, polyunsaturated fatty acids (PUFA) are esterified to plasmalogens (1-O-alk-1'-enyl-2-acyl-sn-glycero-3 phosphoethanolamine). Some studies have implicated selectivity for (n - 3) fatty acids, particularly of 20- and 22-carbons, over the (n - 6) family of fatty acids. We have investigated selectivity for esterification of both families of PUFA to plasmalogens in cultured C6 glioma cells. By 24 h, approx. 40% of cell-associated label from [1-14C]18:3(n - 3) was incorporated into plasmalogens and that label consisted almost exclusively of desaturation and chain elongation products [80% 20:5(n - 3) and 15% 22:5(n - 3)]. Relative incorporation of label from PUFA into plasmalogens was 20:5(n - 3) greater than 20:4(n - 6) greater than 18:3(n - 3) much greater than 18:2(n - 6); incorporation of unaltered 18-carbon chains was highly restricted. Cells incubated with [1-14C]18:3(n - 3) and 20-150 microM competing unlabeled fatty acids showed 20:5(n - 3) greater than 20:4(n - 6) greater than or equal to 22:4(n - 6) greater than 18:3(n - 3) as inhibitors of plasmalogen labeling. Chase experiments in cells prelabeled with [1-14C]18:3(n - 3) for 2 h showed limited reduction of label in plasmalogen. Reduction of plasmalogen label did occur when (n - 3) or (n - 6) fatty acids were added to cells prelabeled for 48 h, accounting for losses of 20-35% compared to controls. Accordingly, little selectivity occurs in esterification of plasmalogens from mixtures of (n - 3) and (n - 6) fatty acyl chains. Subsequent remodeling of (n - 3) acyl chains occurs, but is more dependent on acyl chain length than on selectivity between (n - 3) and (n - 6) families. Our data are consistent with a stable plasmalogen pool enriched in PUFA, but not specifically with (n - 3) fatty acids.

Phosphoinositide metabolism in cultured glioma and neuroblastoma cells: subcellular distribution of enzymes indicate incomplete turnover at the plasma membrane

The hypothesis that the small portion of cellular phosphoinositide participating in signal transduction might be preferentially recycled within the plasma membrane was tested in rat glioma (C6) and murine neuroblastoma (N1E-115) cells. Percoll density gradient centrifugation was used to isolate a purified plasma membrane fraction and the subcellular distribution of all enzymes mediating phosphoinositide turnover was assessed. A small but significant proportion of PtdInsP2-specific phosphodiesterase was located in the plasma membrane but only two of the five enzymes required to replace PtdInsP2 (diacylglycerol kinase and PtdInsP kinase) also were present. CTP:phosphatidate cytidylyltransferase and CMP-phosphatidate:inositol phosphatidyltransferase were located exclusively in a microsomal fraction containing enriched levels of endoplasmic reticulum markers. Thus, diacylglycerol from agonist-stimulated cleavage of PtdInsP2, or phosphatidic acid formed from it, must be transferred to the endoplasmic reticulum for conversion to PtdIns. Plasma membrane also lacked PtdIns kinase. If the soluble PtdIns kinase has access to membrane-bound substrate, PtdIns may be phosphorylated to PtdInsP before or during transport to the plasma membrane. Phosphorylation by the predominantly plasma membrane PtdInsP kinase to form PtdInsP2 completes the cycle. PtdInsP phosphatase was present in all membrane fractions suggesting that PtdInsP can be returned to the PtdIns pool in plasma membrane and elsewhere. PtdInsP2 phosphatase was almost exclusively in the cytosol suggesting that reversible interchange between PtdInsP and PtdInsP2 in the plasma membrane may be modulated by the ability of this phosphatase to act on PtdInsP2 in the membrane. Thus, PtdIns resynthesis in the plasma membrane of these cells does not occur and is not required for phosphoinositide-mediated signal transduction.

Measurement of organic vapors at sub-TLV concentrations using fast gas chromatography

Gas chromatography usually is considered too slow a method to be useful for real-time or near real-time monitoring. If the chromatographic system is optimized for speed, however, it is possible to reduce retention times significantly. Recently, a fast gas chromatograph (GC) was described that allows many simple separations to be completed in 10 sec or less. The system features a gas-cooled, electrically heated, capillary cold trap that focuses the sample as an extremely narrow band at the front of the column. In this study the fast GC was used to measure the concentrations of benzene, toluene, and xylene in test atmospheres generated in the laboratory. The measurements then were compared to simultaneous measurements made with a conventional GC. At concentrations ranging from the threshold limit value (TLV) to one-tenth of the TLV, the fast GC decreased retention times by a factor of 10- to 100-fold relative to the conventional GC, with no loss of precision or accuracy. These results indicate that it may be feasible to develop a high-speed monitoring system based on a GC design similar to the one in this study.

Defective activity of acyl-CoA:cholesterol O-acyltransferase in Niemann-Pick type C and type D fibroblasts

The activity of acyl-CoA:cholesterol acyltransferase (ACAT; EC 2.3.1.26) was measured in fibroblast homogenates from Niemann-Pick Type C (NPC) and Type D (NPD) patients to determine whether these cells exhibit similar defects in the regulation of cholesterol esterification. ACAT activity in normal cells cultured in the absence of serum lipoproteins responded rapidly (within 6 h) to the addition of serum and reached peak levels at 12-24 h, whereas little stimulation of activity in NPC cells was observed. In contrast, ACAT activity in NPD fibroblasts (cell lines from four different patients) began to increase between 6 and 12 h after serum addition, reaching levels up to 50% of normal values at 24 h. ACAT activity in NPC and NPD cell extracts could not be stimulated by preincubation with normal cell homogenates, nor was complementation between NPC and NPD homogenates observed. Addition of 25-hydroxycholesterol to fibroblasts cultured in delipidated serum increased ACAT activity for all three cell types, although stimulation in NPD cells was less than that observed in NPC cells. ACAT activity of deoxycholate-solubilized homogenates reconstituted into phosphatidylcholine vesicles was independent of the presence of serum lipoproteins during culture and dependent on cholesterol present in the vesicles for all cell types. However, ACAT activities of mutant fibroblasts in vesicles plus cholesterol were significantly (about 40%) lower than control levels. These results suggest that the metabolic lesions in NPC and NPD cells are biochemically distinct and that both may involve factors in addition to the availability of cholesterol substrate for the ACAT enzyme.

Phosphatidylcholine biosynthesis in cultured glioma cells: evidence for channeling of intermediates

The major pathway of choline (Cho) incorporation into phosphatidylcholine (PtdCho) in mammalian cells is sequential conversion of Cho to phosphocholine (PCho), cytidinediphosphate choline (CDP-Cho) and PtdCho. In intact cells, this sequence is usually demonstrated using radiolabeled Cho since PCho and CDP-Cho do not enter the cell intact. We have studied the incorporation of radiolabeled Cho, PCho and CDP-Cho into rat glioma (C6) cells following electropermeabilization. C6 cells were permeable as judged by [U-14C]sucrose and Erythrosin B uptake and more rapid incorporation of [1,2,3-3H]glycerol into cell lipids, and viable as assessed by uptake and incorporation of [methyl-3H]Cho, [1-14C]oleate and [1,2,3-3H]glycerol into complex lipids. Despite rapid incorporation of [methyl-3H]Cho into PtdCho in permeabilized cells, there was no incorporation of [methyl-14C]PCho or CDP-[methyl-14C]Cho into PtdCho. PCho (300 microM) and CDP-Cho (300 microM) failed to significantly reduce incorporation of 28 microM [methyl-3H]Cho into PtdCho. Radioactivity in PtdCho of cells prelabeled with [methyl-3H]Cho prior to permeabilization could be chased with 4 mM Cho but not with 4 mM PCho or 4 mM CDP-Cho. The water-soluble products of Cho metabolism--PCho, CDP-Cho and glycerophosphocholine--were retained at 37 degrees C in permeabilized cells compared with controls while there was uniform leakage from permeabilized cells at 4 degrees C. Hemicholinium-3, an inhibitor of high-affinity Cho transport, decreased [methyl-3H]Cho incorporation into PtdCho in permeabilized cells, as in controls, suggesting that even in permeabilized cells, Cho incorporation into PtdCho is linked to the transport system. We propose that individual steps of the cytidine pathway of PtdCho biosynthesis are functionally linked and that reaction intermediates are not freely diffusible within the cell but are channeled to PtdCho biosynthesis.

Lysophosphatidylcholine as an intermediate in phosphatidylcholine metabolism and glycerophosphocholine synthesis in cultured cells: an evaluation of the roles of 1-acyl- and 2-acyl-lysophosphatidylcholine

Previous studies in our laboratory have shown that the principal pathway of phosphatidylcholine (PtdCho) degradation in cultured mouse N1E-115 neuroblastoma, C6 rat glioma, primary rat brain glia and human fibroblasts is PtdCho----lysophosphatidylcholine (lysoPtdCho)----glycerophosphocholine (GroPCho)----glycerophosphate plus choline (Morash, S.C. et al. (1988) Biochim. Biophys. Acta 961, 194-202). GroPCho is the first quantitatively major degradation product in this pathway, and could be formed by phospholipases A1 or A2, followed by lysophospholipase, or by a co-ordinated attack releasing both fatty acids by phospholipase B. The quality and quantities of lysoPtdCho present in cells reflect the nature of the initial hydrolysis step (A1 or A2), specificities of the lysophospholipases, and activities of acyltransferases that form PtdCho from lysoPtdCho. The present study was undertaken to elucidate the relative importance of these pathways by examining the fate of exogenous 1-acyl and 2-acyl-lysoPtdCho incubated with N1E-115 and C6 cells in culture. By fatty acid composition, endogenous lysoPtdCho was found to be mainly 1-acyl in both cell types based on a predominance of saturated acyl species; this suggested either preferential further deacylation or reacylation of 2-acyl-lysoPtdCho, or that 2-acyl-lysoPtdCho was not formed. Exogenous 1- and 2-acyl-lysoPtdCho specifically radiolabelled with choline and/or fatty acid were incubated either singly or as equimolar mixtures with cells. Cell association was rapid and not reversible by washing and both species were taken up at similar rates. The 2-acyl species was acylated to PtdCho faster than the 1-acyl species in both cell lines. Acylation of both lyso species was higher in C6 compared to N1E-115 cells. Hydrolysis of lysoPtdCho to GroPCho was higher in N1E-115 cells and with 1-acyl-lysoPtdCho. Transacylation between two molecules of lysoPtdCho was a minor pathway. These results document the variety and relative importance of reactions of lysoPtdCho metabolism; under similar conditions, 1- and 2-acyl-lysoPtdCho are handled differently. Both species turn over actively, but only the 1-acyl species accumulates while 2-acyl-lysoPtdCho is likely to be reacylated to form PtdCho.

Differences in the metabolism of inositol and phosphoinositides by cultured cells of neuronal and glial origin

Phosphoinositide and inositol metabolism was compared in glioma (C6), neuroblastoma (N1E-115) and neuroblastoma X glioma hybrid (NG 108-15) cells. All cell lines had similar proportions of phosphatidylinositol (PI), phosphatidylinositol 4-phosphate (PIP), and phosphatidylinositol 4,5-bisphosphate (PIP2). Neuroblastoma and hybrid cells had almost identical phospholipid and phosphoinositide compositions and similar activities for the enzymes metabolizing polyphosphoinositides (PI kinase, PIP phosphatase, PIP kinase, PIP2 phosphatase, PIP2 phosphodiesterase). Glioma cells differed by having greater proportions of ethanolamine plasmalogen and sphingomyelin, lower PIP kinase, 3-5-fold higher PIP phosphatase activity and 10-15-fold greater PIP2 phosphodiesterase activity. Higher PIP phosphatase and PIP2 diesterase activities appear to be characteristic of cells of glial origin, since similar activities were found in primary cultures of astroglia. Glioma cells also metabolize inositol differently. In pulse and pulse-chase experiments, glioma cells transported inositol into a much larger water-soluble intracellular pool and maintained a concentration gradient 30-times greater than neuroblastoma cells. Label in intracellular inositol was less than in phosphoinositides in neuroblastoma and exchanged rapidly with extracellular inositol. In glioma, labeling of intracellular inositol greatly exceeded that of phosphoinositides. As a consequence, radioactivity in prelabeled phosphoinositides could not be effectively chased from glioma cells by excess unlabeled inositol. Such differences between cells of neuronal and glial origin suggest different and possibly supportive roles for these two cell types in maintaining functions regulated through phosphoinositide-linked signalling systems in the central nervous system.

Cell-specific fatty acylation of proteins in cultured cells of neuronal and glial origin

Distinct sets of cellular proteins were labeled with [3H]myristic and [3H]palmitic acids in primary (rat neurons and astroglia) and continuous (murine N1E-115 neuroblastoma and rat C6 glioma) cell cultures derived from the nervous system. Both soluble and membrane proteins were modified by myristate in a hydroxylamine-stable (amide) linkage, while palmitoylated proteins were ester-linked and almost exclusively membrane bound. Chain elongation of both labeled fatty acids prior to acylation was observed, but no protein amide-linked [3H]myristate originating from [3H]palmitate was detected. Fatty acylation profiles differed considerably among most of the cell lines, except for rat astroglial and glioma cells in which myristoylated proteins appeared to be almost identical based on SDS gel electrophoresis. An unidentified 47 kDa myristoylated protein was labeled to a significantly greater extent in astroglial than in glioma cells; the expression of this protein could be related to transformation or development in cells of glial origin.

A new Zn2+-stimulated sphingomyelinase in fetal bovine serum

Fetal bovine serum contains a Zn2+-dependent sphingomyelinase with optimal activity at pH 5.5 in vitro. Activity could be demonstrated with a liposomal sphingomyelin substrate suspension but was stimulated up to 15-fold by Triton X-100. Under a variety of conditions tested, phosphatidylcholine, lysophosphatidylcholine, glycerophosphocholine, and p-nitrophenyl phosphate were not substrates for this activity. Several inhibitors of serum alkaline and acid phosphatases had no effect on the activity. The enzyme resembles the acid lysosomal sphingomyelinase in pH optimum and inhibition by AMP but differs in inhibition by EDTA, stimulation by Zn2+, and heat lability at 55 degrees C. It resembles the neutral, Mg2+-stimulated enzyme in inhibition by EDTA and heat lability but differs in metal ion requirement and pH optima. Of the sera tested, activity was highest in fetal bovine serum, with fetal bovine greater than newborn bovine greater than horse greater than human; more than 95% of the activity is in the lipoprotein-free infranatant of serum (d greater than 1.21). This activity appears to be a hitherto undescribed sphingomyelinase. Its biological functions are not known but may subserve a special role in sphingomyelin catabolism in the circulation, in blood vessel walls, or in the tissue(s) of origin.

Dideoxycytidine, an anti-HIV drug, selectively inhibits growth but not phosphatidylcholine metabolism in neuroblastoma and glioma cells

Dideoxycytidine (ddCyd), an inhibitor of AIDS-related HIV, has been examined for effects on cell proliferation and phosphatidylcholine synthesis in tumor lines of nervous system origin. Uptake and metabolism of [3H]ddCyd, observed in all cells, was greatest in one human neuroblastoma line, HTB-10. Growth of the HTB-10 line was markedly inhibited by 40 microM ddCyd, whereas growth of C6 glioma and N1E-115 or HTB-11 neuroblastoma cells was unaltered. Phosphatidylcholine synthesis in the presence or absence of stimulation by phorbol ester was not specifically altered by ddCyd. Thus, ddCyd was incorporated and inhibited growth in a cell-specific manner but had little effect on cytidine-dependent phospholipid synthesis. This suggests that some cells derived from the nervous system may be more susceptible than others with respect to the positive and negative effects of ddCyd as a potential antiviral drug.

Alterations of phospholipid metabolism by phorbol esters and fatty acids occur by different intracellular mechanisms in cultured glioma, neuroblastoma, and hybrid cells

Differences between the influences of phorbol esters (such as 4 beta-12-O-tetradecanoylphorbol 13-acetate) and of fatty acids (such as oleic acid) on the synthesis and turnover of phosphatidylcholine (PtdCho) and other phospholipids have been studied in glioma (C6), neuroblastoma (N1E-115), and hybrid (NG108-15) cells in culture using [methyl-3H]choline, [32P]Pi, [1,2-14C]ethanolamine, or 1-14C-labeled fatty acids as lipid precursors. 100-500 microM oleic acid stimulated PtdCho synthesis 3- to 5-fold in all three cell lines, but had little influence on chase of choline label following a 24-h pulse. Phorbol ester (50-200 nM) stimulated PtdCho synthesis 1.5- to 3-fold in C6 cells, was without effect in N1E-115 cells, and had intermediate effects on NG108-15 cells. Phorbol ester stimulated both uptake of extracellular choline and synthesis of PtdCho, whereas fatty acid stimulated only synthesis. Release of radioactivity from 24-h pulse-labeled PtdCho to the medium was enhanced by phorbol ester in C6 cells. Incorporation of [32P]Pi, primarily into PtdCho, was stimulated, whereas utilization of [1,2-14C]ethanolamine or 1-14C-fatty acid was little altered by phorbol ester. C6 cells "down-regulated" with phorbol ester lost the stimulatory response of subsequent treatment with phorbol esters on PtdCho synthesis, but the response to fatty acid was enhanced. Fatty acid had little influence on the relative binding of phorbol ester or "translocation" of phorbol ester binding sites. Accordingly, metabolism of phospholipids in these cultured cells of neural origin is markedly influenced by cell type, phospholipid class, condition of incubation medium, and nature of stimulator. Phorbol esters and fatty acids appear to enhance phospholipid synthesis and turnover by distinct intracellular mechanisms.

Sodium channel activation does not alter lipid metabolism in cultured neuroblastoma cells

The interaction of voltage-sensitive Na+-channels and membrane lipid metabolism was examined by incubating cultured neuroblastoma cells with neurotoxins which alter the voltage-dependent relationship between the closed and open conformation of the channel protein. Guanidinium flux rate, a measure of Na+-channel activation, was increased 10-fold by the combined action of veratridine (100 microM) and scorpion venom (28 micrograms/ml). This response was completely blocked by tetrodotoxin (1 microM). Under the same experimental conditions, the toxins did not increase the efflux of [3H]arachidonic acid from prelabeled cell membrane lipids or stimulate uptake of exogenous [3H]arachidonic acid. In addition, altering membrane fatty acid composition by incubating cells for 24 hr in a medium containing 50 microM arachidonic or oleic acid did not alter guanidinium flux rates relative to that of control cultures. When cells were pulsed with 32Pi for 60 min and stimulated by veratridine plus scorpion venom for an additional 30 min, uptake of 32Pi into phosphatidylinositol was reduced; stimulating cells with bradykinin, a receptor agonist which activates the inositol cycle, promoted a 3.8 fold increase. Polyphosphoinositide turnover was not affected by Na+-channel activation, but was stimulated by bradykinin. These results suggest that voltage-sensitive Na+-channel activation in cultured neuroblastoma cells can function independent of membrane phospholipid and fatty acid metabolism.

Isolation of plasma membranes from cultured glioma cells and application to evaluation of membrane sphingomyelin turnover

A rapid and reliable method for the isolation of plasma membranes and microsomes of high purity and yield from cultured glioma cells is described. The procedure involves disruption by N2 cavitation, preliminary separation by centrifugation in Tricine buffer, and final separation on a gradient formed from 40% Percoll at pH 9.3. Enzyme and chemical markers indicated greater than 60% yield with six- to eightfold enrichment for plasma membranes and greater than 25% yield with three- to fourfold enrichment for a microsomal fraction consisting mainly of endoplasmic reticulum. The final fractions were obtained with high reproducibility in less than 1 h from the time of cell harvesting. Application of this procedure to human fibroblasts in culture is assessed. The isolation procedure was applied to investigations of synthesis and turnover of sphingomyelin and phosphatidylcholine in plasma membranes of glioma cells following incubation for 4-24 h with [methyl-3H]choline. These studies indicated that radioactivity from phosphatidylcholine synthesized in microsomes from exogenous choline may serve as a precursor of the head-group of sphingomyelin accumulating in the plasma membrane.

Phosphatidylcholine metabolism in cultured cells: catabolism via glycerophosphocholine

The catabolism of phosphatidylcholine (PtdCho) has been studied in cultured murine neuroblastoma (N1E-115), C6 glioma, rat brain primary glia, and human fibroblast cells. Cells were pulse labelled for 96 h with [methyl-3H]choline followed by a chase for up to 24 h in medium containing 4 mM choline. Measurement of the radioactivity and mass of choline-containing compounds in these cells indicated that the major degradative pathway is PtdCho----lysophosphatidylcholine (lysoPtdCho)----glycerophosphocholine (GroPCho)----choline. At all times during the chase, PtdCho, sphingomyelin and lysoPtdCho comprised 72-92% of the cell-associated radioactivity; the remaining 10-30% was water-soluble and was chiefly GroPCho (30-80%) in all cell lines. In fibroblasts, however, phosphocholine (PCho) was also a major labelled water-soluble component (33-54%). The specific activity of GroPCho closely parallelled that of PtdCho in fibroblasts, but decreased faster than PtdCho in C6 and N1E-115 cells. We postulate that this may be due to distinct pools of PtdCho in the cell with differing rates of turnover. The changes in specific activity of PCho suggest that the major portion is formed by synthesis rather than as a degradative product. However, the inability to reduce the specific activity of this fraction to that of the intracellular choline suggests that a portion may be derived from either PtdCho or GroPCho.

Compartmentation of phosphorylated precursors of phospholipid biosynthesis in cultured neuroblastoma cells

The continuous turnover of membrane phospholipids requires a steady supply of biosynthetic precursors. We evaluated the effects of decreasing extracellular Na+ concentration on phospholipid metabolism in cultured neuroblastoma (N1E 115) cells. Incubating cultures with 145 to 0 mM NaCl caused a concentration-dependent inhibition of [32P]phosphate uptake into the water-soluble intracellular pool and incorporation into phospholipid. Phospholipid classes were differentially affected; [32P]phosphate incorporated into phosphati-dylethanolamine (PE) and phosphatidylcholine (PC) was consistently less than into phosphatidylinositol (PI) and phosphatidylserine (PS). This could not be attributed to decreased phospholipid synthesis since under identical conditions, there was no effect on arachidonic acid or ethanolamine incorporation, and choline utilization for PC synthesis was increased. The effect of Na+ was highly specific since reducing phosphate uptake to a similar extent by incubating cultures in a phosphate-deficient medium containing Na+ did not alter the relative distribution of [32P]phosphate in phospholipid. Of several cations tested only Li+ could partially (50%) replace Na+. Incubation in the presence of ouabain or amiloride had no effect on [32P]phosphate incorporation into phospholipid. The differential effects of low Na+ on [32P]phosphate incorporation into PI relative to PC and PE suggests preferential compartmentation of [32P]phosphate into ATP in pools used for phosphatidic acid synthesis and relatively less in ATP pools used for synthesis of phosphocholine and phosphoethanolamine, precursors of PC and PE, respectively. This suggestion of heterogeneous and distinct pools of ATP for phospholipid biosynthesis, and of potential modulation by Na+ ion, has important implications for understanding intracellular regulation of metabolism.

Interaction of (n-3) and (n-6) fatty acids in desaturation and chain elongation of essential fatty acids in cultured glioma cells

Recent research in various biological systems has revived interest in interactions between the (n-6) and (n-3) essential fatty acids. We have utilized cultured glioma cells to show that linolenic acid, 18:3(n-3), is rapidly desaturated and chain elongated; 20:5(n-3) is the major product and accumulates almost exclusively in phospholipids. We examined effects of various (n-6), (n-3), (n-9) and (n-7) fatty acids at 40 microM concentration on desaturation and chain elongation processes using [1-14C]18:3(n-3) as substrate. In general, monoenoic fatty acids were without effect. The (n-6) fatty acids (18:2, 18:3, 20:3, 20:4 and 22:4) had little effect on total product formed. There was a shift of labeled product to triacylglycerol, and in phospholipids, slightly enhanced conversion of 20:5 to 22:5 was evident. In contrast, 22:6(n-3) was inhibitory, whereas 20:3(n-3) and 20:5(n-3) had much less effect. At concentrations less than 75 microM, all acids were inhibitory. Most products were esterified to phosphatidylcholine, but phosphatidylethanolamine also contained a major portion of 20:5 and 22:5. We provide a condensed overview of how the (n-6) and (n-3) fatty acids interact to modify relative rates of desaturation and chain elongation, depending on the essential fatty acid precursor. Thus, the balance between these dietary acids can markedly influence enzymes providing crucial membrane components and substrates for biologically active oxygenated derivatives.

Studies of the modulation of essential fatty acid metabolism by fatty acids in cultured neuroblastoma and glioma cells

In cultured neuroblastoma cells (N1E-115), the metabolism of the essential fatty acid, linoleic acid (18:2 (n-6)), to arachidonic acid (20:4(n-6)) can be altered by other fatty acids in a manner supporting a concerted action of the modulating fatty acid on the desaturation and chain elongation enzymes. In further examination of mechanisms involved, cultured glioma (C-6) or neuroblastoma-glioma hybrids (NG-108-15) cells showed similar patterns of activation by some fatty acids (e.g., 20:3(n-6) and 20:4(n-6)), and inhibition (e.g., 18:3(n-3) or 22:6(n-3)) or no effect (e.g., 18:1(n-9), 20:3(n-3)) by others. In contrast, only inhibition by 20:4(n-6) was seen in cultured HeLa cells, suggesting that the intracellular interactions may not be universal in all cell lines. For fatty acids that activate 20:4(n-6) formation, the lag observed when substrate and activator were administered simultaneously was eliminated by preincubation with activator. Maximal activation occurred within 4 h for neuroblastoma and 2 h for glioma; in each cell line activation declined steadily for 10 h after removal of the activator. Inhibition of protein synthesis did not alter activation. As 98% of the fatty acid incorporated was esterified to triacylglycerol or phospholipid and only the triacylglycerol mass expanded, several manipulations to potentially alter the flow of acyl chains between these lipid pools were evaluated using dual-label and pulse-chase experiments. Results suggested that competition between 18:2(n-6) utilization for esterification to phospholipid and the desaturation-chain elongation sequence as well as a more direct and specific interaction of certain fatty acids with the enzymes may influence 20:4(n-6) formation. A model to explain these observations is discussed.

Prevalence of major mental retardation and associated disabilities in the Canadian Maritime Provinces

A cross-sectional survey of the prevalence of major mental retardation in 7- to 10-year-olds in the three Canadian Maritime provinces was carried out in 1980. Case ascertainment from multiple sources was considered to be virtually complete and resulted in a study group of 307 children, for whom 72% of the parents consented to personal data collection. The overall regional prevalence of major mental retardation was 3.65/1,000. Variation in county prevalence rate (based on parental residence at the time of birth) was associated, by regression analysis, with maternal age, areas of greater population concentrations, and number of physicians per capita. These associations were still present when children with Down syndrome were excluded from the analysis. Speech and behavior disorders and epilepsy were the major associated disabilities.

Turnover of phospholipid fatty acyl chains in cultured neuroblastoma cells: involvement of deacylation-reacylation and de novo synthesis in plasma membranes

Cultured neuroblastoma cells (NIE-115) rapidly incorporated the essential fatty acid, linoleic acid (18:2 (n = 6), into membrane phospholipids. Fatty acid label appeared rapidly (2-10 min) in plasma membrane phospholipids without evidence of an initial lag. Specific activity (nmol fatty acid/mumol phospholipid) was 1.5-2-fold higher in microsomes than in plasma membrane. In these membrane fractions phosphatidylcholine had at least 2-fold higher specific activity than other phospholipids. With 32P as radioactive precursor, the specific activity of phosphatidylinositol was 2-fold higher compared to other phospholipids in both plasma membrane and microsomes. Thus a differential turnover of fatty acyl and head group moieties of both phospholipids was suggested. This was confirmed in dual-label (3H fatty acid and 32P), pulse-chase studies that showed a relatively rapid loss of fatty acyl chains compared to the head group of phosphatidylcholine; the opposite occurred with phosphatidylinositol. A high loss of fatty acyl chain relative to phosphorus indicated involvement of deacylation-reacylation in fatty acyl chain turnover. The patterns of label loss in pulse-chase experiments at 37 and 10 degrees C indicated some independent synthesis and modification of plasma membrane phospholipids at the plasma membrane. Lysophosphatidylcholine acyltransferase and choline phosphotransferase activities were demonstrated in isolated plasma membrane in vitro. Thus, studies with intact cells and with isolated membrane fractions suggested that neuroblastoma plasma membranes possess enzyme activities capable of altering phospholipid fatty acyl chain composition by deacylation-reacylation and de novo synthesis at the plasma membrane itself.

Causal origins of major mental handicap in the Canadian Maritime provinces

From a retrospective epidemiological survey, the prevalence of major mental handicap among seven- to 10-year-old children in the Maritime region of Canada in 1980 was estimated to be 36.5 per 10,000 children. Based on information obtained for 221 of the 307 children ascertained by the survey, prenatal origins dominated (58 per cent), followed by perinatal (10 per cent) and postnatal (4 per cent). No specific cause could be determined for 27 per cent of the children, but 41 per cent of this group had epilepsy and/or cerebral palsy in addition to major mental handicap. Significant differences were found in the causal spectrum between the Maritime region of Canada and regions studied in other developed countries. The results of this survey have implications for planning prevention programs, and for epidemiological surveillance and monitoring of adverse reproductive outcomes.

Acid and alkaline ceramidases of rat tissues

Ceramidase (N-acylsphingosine deacylase) was measured in rat tissue homogenates with N-[1-14C]oleoyl- and N-[9,10-3H]palmitoyl-sphingosine. Two activities were observed with pH optima of approximately 5 and 8. The activity at pH 8 exceeded that at pH 5 in all tissues and tissue areas examined, and both activities decreased in the following order: kidney greater than brain stem greater than cerebrum greater than cerebellum greater than liver greater than spleen greater than cardiac muscle greater than lung greater than psoas muscle. The distribution of activity is not as tissue specific as that of neutral Mg2+-stimulated sphingomyelinase which is enriched in cells of neural origin and thus suggests a less specialized role for the alkaline ceramidase.

Triacylglycerol as a precursor in phospholipid biosynthesis in cultured neuroblastoma cells: studies with labeled glucose, fatty acid, and triacylglycerol

Neuroblastoma cells rapidly incorporate exogenous fatty acids into cellular triacylglycerol and relationships between triacylglycerol and phospholipid biosynthesis have been indicated by the relative time course of labeling of these lipids. To evaluate this further, neuroblastoma cells were labeled using potential precursors of phospholipid including radiolabeled triacyglycerol, glycerol, glucose, and fatty acid. With [2-3H]glycerol or a mixture of [2-3H]glycerol trioleate and glycerol tri[1-14C]oleate, phospholipids were labeled at very low levels (less than 0.1 and less than 0.5%, respectively). With [6-3H]glucose, labeling of lipids (0.5-3.5%) was greatest in medium containing 19 mM fructose, whereas labeling with [1-14C]18:2(n-6) was similar in media containing either 19 mM fructose or 25 mM glucose. Labeling of the glycerol moiety of triacylglycerol with [6-3H]glucose increased with 40-200 microM 18:2(n-6) present and occurred predominantly in 2 h. Some [6-3H]glucose label was in fatty acyl chains (chiefly 16:0) of triacylglycerol by 16 h, but was unaffected by exogenous 18:2(n-6). Triacylglycerol was the only lipid to increase in mass (threefold with 200 microM 18:2(n-6)). During the chase of cells pulsed with [6-3H]glucose, label in triacylglycerol declined within 0.5 h, whereas in phospholipid it increased transiently up to 2 h and then declined. Changes were inversely proportional to 18:2(n-6) levels in the chase medium and labeled acyl chains moved in parallel with the glycerol moiety. Thus, a major portion of acyl chain transfer from triacylglycerol was accompanied by glycerol.(ABSTRACT TRUNCATED AT 250 WORDS)

Catabolism of exogenous and endogenous sphingomyelin and phosphatidylcholine by homogenates and subcellular fractions of cultured neuroblastoma cells. Effects of anesthetics

Cultured murine neuroblastoma cells contain a neutral, Mg2+-stimulated sphingomyelinase and an alkaline phosphatidylcholine-hydrolyzing activity that are enriched in the plasma membrane fraction. The reaction products of sphingomyelin catabolism are phosphocholine and ceramide and those of phosphatidylcholine, glycerophosphocholine and fatty acid. These reactions were studied with endogenous as well as exogenous liposomal substrates. With both exogenous and endogenous substrates, the sphingomyelinase activity was stimulated two- to threefold by Mg2+ and a further three- to fourfold by volatile anesthetic agents. Stimulation was concentration-dependent and corresponded to anesthetic potency: methoxyflurane greater than halothane greater than enflurane. Greater than 80% of the plasma membrane sphingomyelin was hydrolyzed within 2 h in the presence of Mg2+ and anesthetic. In contrast, the activity with exogenous and endogenous phosphatidylcholine was unaffected by Mg2+ or Ca2+ and was markedly inhibited (50-80%) by anesthetic agents. The degree of inhibition was concentration-dependent and corresponded to anesthetic potency. The quantitative importance of choline-containing lipids in cell membranes, the relatively exclusive localization of the neutral Mg2+-stimulated sphingomyelinase in cells of neural origin, the totally different type of hydrolytic attack on phosphatidylcholine, and the reciprocal effects of anesthetics on the hydrolysis of these two lipids strongly suggest important roles for these activities in cell membranes in general and in the neuron in particular.