A solvent system for delipidation of plasma or serum without protein precipitation

Relation of cellular phospholipid composition to oligodendroglial differentiation in C-6 glial cells

The relation of the polar head group composition of cellular phospholipids to a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Induction of the oligodendroglial enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), was determined after alteration of the polar head group composition of phospholipids by exposure of the cells to choline analogues, especially N,N'-dimethylethanolamine. To accomplish the phospholipid alteration, cells were grown in the presence of the analogue in medium free of exogenous lipid, i.e., first for 24 h in 10% delipidated serum and then for 48 h in serum-free medium. The 48-h exposure to serum-free medium resulted in untreated C-6 cells in a several fold increase in CNP activity, but in cells treated with 2.5 mM N,N'-dimethylethanolamine, total inhibition of this induction was observed. A graded, concentration-dependent inhibitory effect of the analogue on the induction of CNP was defined. The effect of the analogue was relatively specific, e.g., the activity of another plasma membrane enzyme of C-6 cells, (Na+ + K+)-activated ATPase, was not affected. Morever, there was no evidence of a toxic effect of the analogue; thus, total protein synthesis and cell growth were not altered, and the induction of CNP in serum-free medium recurred after removal of the analogue. N,N'-Dimethylethanolamine was shown to be incorporated into cellular phospholipids, primarily at the expense of phosphatidylcholine. The data define an important role for the polar head group composition of membrane phospholipids in oligodendroglial differentiation in this model system.

Synergistic stimulation of alkaline phosphatase activity in bovine aortic endothelial cells grown in the presence of retinoids and glucocorticoids

Low concentrations of retinol (10 nM-10 microM) and dexamethasone (0.1 nM-1.0 microM) elevated activity of alkaline phosphatase (E.C. 3.1.3.1) in bovine endothelial cells in culture. The effect was apparent after 48 hr of growth in the presence of either of the two compounds, prior to any growth stimulatory effects. A synergistic stimulation of alkaline phosphatase was achieved in the presence of both retinol and dexamethasone implying different mechanisms of induction. Retinoic acid and retinyl acetate also elevated alkaline phosphatase but the retinol analogue reduced in the side chain (perhydroretinol) was inactive. The ability of steroids to elevate alkaline phosphatase activity was associated with the structure commonly required for glucocorticoid activity; however, competitors for the steroid receptor binding failed to prevent the elevation by dexamethasone or the synergism in the presence of retinol and dexamethasone.

Quantitative determination of human plasma apolipoprotein A-I by a noncompetitive enzyme-linked immunosorbent assay

A noncompetitive enzyme-linked immunosorbent assay (ELISA) for human plasma apolipoprotein A-I (ApoA-I) was developed. Microtiter plates were coated with purified antibodies to ApoA-I and blocked. Plasma samples from normolipidemic and hypertriglyceridemic subjects were added and ApoA-I was allowed to bind to coating antibodies. After washing, the amount of ApoA-I bound to microtiter plates was estimated with horseradish peroxidase-labeled antibodies to ApoA-I. A single step delipidization procedure was included to expose masked antigenic sites of ApoA-I in plasma. The average concentration of ApoA-I in plasma of normolipidemic subjects was 1.37 g/l. Recovery of ApoA-I added to plasma varied from 93-107%. Intra- and inter-assay coefficients of variations were 4 and 8%, respectively. The assay was also used for quantifying ApoA-I in lipoprotein density classes. There was a good correlation between this assay and electroimmunoassay (r = 0.84-0.92). The described sandwich ELISA is a specific, precise, sensitive and relatively simple method for measuring ApoA-I levels in human plasma.

Selenium deficiency in cultured adrenocortical cells: restoration of glutathione peroxidase and resistance to hydroperoxides on addition of selenium

Cultured bovine adrenocortical cells were previously shown to be functionally deficient in selenium and vitamin E when grown in medium supplemented with fetal bovine serum. In the present experiments, the lack of significant bioavailable amounts of selenium in the medium was demonstrated by the finding of only low levels of glutathione peroxidase in the cultured cells (0.008 U/mg protein compared with 0.045 U/mg protein in fresh adrenocortical tissue). When 20 nM selenium as selenite was added to the cultured adrenocortical cells, glutathione peroxidase activity increased continuously over 72 h, with a total increase of about eightfold over this period. Over the same time-course, the highest concentration of cumene hydroperoxide tolerated by the cells without cell death increased progressively from 10 microM to 50 microM. Addition of 1 microM alpha-tocopherol also increased the amount of cumene hydroperoxide tolerated to 50 microM. Cell death was measured by cloning efficiency after removal of cumene hydroperoxide. Addition of either selenium or alpha-tocopherol had little effect on the growth rate of the cells over six passages, even when residual vitamin E was removed from the serum by extraction with ether and residual low molecular weight selenium compounds were removed by dialysis. It is concluded that combined deficiency of selenium and vitamin E, at least in the presence of other components of fetal bovine serum, has little effect on the ability of the cells to survive under normal conditions, as evidenced by continued long-term proliferation. However, the low levels of glutathione peroxidase resulting from selenium deficiency cause an increase susceptibility to peroxide-mediated toxicity. The combined deficiency of selenium and vitamin E impairs the ability of cells to survive under adverse conditions, as well as altering mitochondrial functions, as previously demonstrated.

A comparative study of the effects of acipimox and clofibrate in type III and type IV hyperlipoproteinemia

Acipimox, an analogue of nicotinic acid, is a hypolipidemic drug with antilipolytic activity. Ten patients with type III and 10 with type IV hyperlipoproteinemia participated in a comparative open cross-over study of the effect of acipimox (750 mg/day) and clofibrate (2 g/day) on lipoproteins, apoliproproteins and postheparin lipase activities during 6 weeks. During acipimox treatment 2 type III patients complained of flushing, resulting in one drop-out. In the type III patients serum cholesterol decreased 30% (P less than 0.01) during treatment with acipimox and 24% (P less than 0.01) with clofibrate, and serum triglycerides 48% (P less than 0.01) and 34% (P less than 0.01), respectively. In the type IV patients serum cholesterol remained unchanged and serum triglycerides decreased 34% (P less than 0.05) and 35% (P less than 0.01), respectively. HDL cholesterol increased during treatment with both drugs in both groups between 6 and 15% (P less than 0.05) mainly due to a rise in HDL3 cholesterol (d greater than 1.100 g/ml). LDL cholesterol increased significantly during treatment with clofibrate, but not with acipimox. There were no or slight changes in the apoproteins A and B. Postheparin lipoprotein lipase increased during clofibrate treatment and hepatic lipase decreased during acipimox treatment. We concluded that acipimox in a dose of 750 mg/day has a similar hypolipidemic effect as 2 g clofibrate daily in type III and IV hyperlipoproteinemia.

Acylated proteins in Acholeplasma laidlawii

The covalent modification of membrane proteins by long-chain fatty acids was determined in two strains of Acholeplasma laidlawii by one-dimensional gel electrophoresis of radiolabeled membranes. Of the more than 50 membrane polypeptides detected, approximately 30 were labeled with [3H]palmitate, whereas covalent binding of [3H]oleate to membrane proteins could not be demonstrated. We suggest that in these wall-less bacteria, membrane protein acylation with saturated fatty acids may serve to ensure the structural integrity of the membrane.

A solvent partition method for microscale ganglioside purification

A simple and rapid method for the purification of gangliosides from the total lipid extract of plasma, cells, or tissue is described. The novel component of the method is the partition of the dried total lipid extract in the three-component solvent system consisting of diisopropyl ether, 1-butanol, and 50 mM aqueous NaCl (6/4/5, v/v/v). Gangliosides partition nearly quantitatively into the lower aqueous phase, and other lipids into the upper organic phase, resulting from the mixture of these three solvents. The ganglioside-containing aqueous phase is then freed of salts and other low-molecular-weight impurities by gel filtration. The thin-layer chromatographic patterns of total gangliosides thus obtained are clear and distinct, even when small samples with very low ganglioside concentrations (e.g., 1-ml samples of plasma) are processed by this method. Thus, this new ganglioside purification method is especially applicable to comparative qualitative studies of gangliosides requiring the analysis of multiple small samples.

Immunonephelometric quantitation of the apolipoprotein C-III in human plasma

A quantitative assay, based on endpoint immunonephelometry, was developed for human apolipoprotein C-III (Apo C-III) in plasma and lipoprotein fractions. The standard curve was constructed either with purified Apo C-III2 as a primary standard or with plasma as a secondary standard. It was linear between 50 and 400 ng Apo C-III per sample, corresponding to 1 microliter undiluted plasma. The intra- and interassay coefficients of variation (CV values) were 2.2 and 6.3%, respectively. The Apo C-III immunoreactivity was not influenced by detergents, denaturants nor by delipidation. The use of a non-ionic detergent (Apovax, 0.1 g/l) avoided the need for organic solvent extraction for plasma containing up to 4 g of triglycerides/l by reducing the sample turbidity. As measured in 126 normolipidemic subjects, the plasma Apo C-III concentration was 0.118 +/- 0.028 g/l (mean +/- SD). Apo C-III concentrations were only slightly elevated in patients with Fredrickson type IIa hyperlipoproteinaemia. The Apo C-III levels were nearly 3 times higher in type I, IIb, III and IV patients, while subjects with type V hyperlipaemia had about a 5-fold increase in Apo C-III compared to the healthy. The plasma Apo C-III values were strongly correlated with the plasma triglyceride concentrations (r = 0.80, n = 201). The Apo C-III distribution among the various lipoprotein fractions showed a higher proportion of Apo C-III in VLDL in hypertriglyceridaemic subjects compared to normolipaemic subjects.

Enzyme linked immunosorbent assay for human apolipoprotein C-III

A sandwich enzyme linked immunosorbent assay (ELISA) for apolipoprotein C-III was developed. Anti apolipoprotein C-III immunoglobulins were used both for coating of microtitre plates and for the preparation of an anti apolipoprotein C-III horse-radish peroxidase conjugate. Under optimized assay conditions, the sensitivity lies around 0.3 ng apolipoprotein C-III with a working range of 1 to 6 ng. Standard curves are parallel for purified apolipoprotein C-III, for untreated plasma and for lipoprotein fractions. Delipidation did not affect the content of apolipoprotein C-III in plasma. The assay was evaluated by comparison with an immunonephelometric assay for apolipoprotein C-III, yielding a correlation coefficient of 0.982 (n = 79). The mean intra- and interassay CV for the whole working range of the assay were 3.6% and 4.2% respectively.

Isolation of high-density lipoproteins by immunoaffinity column chromatography from hog plasma

High density lipoprotein (HDL) was isolated from hog plasma by a simple immunoaffinity column chromatography procedure using immobilized anti-apolipoprotein AI. The composition of HDL isolated by immunoaffinity chromatography was nearly identical to that of a control sample that was isolated by an alternate method utilizing ultracentrifugation and gel chromatography. The HDL isolated by immunoaffinity chromatography had a larger number of polypeptide components that the control as indicated by acrylamide gel electrophoresis in the presence of urea. When the HDL isolated by immunoaffinity chromatography was applied to a heparin-agarose column the amount of protein retained was approximately twice that of the control. These findings indicate that the ultracentrifugation procedure probably induced the loss of apolipoprotein E containing components from the HDL complex.

Dolichol and phosphorylated dolichol content of tissues in ceroid-lipofuscinosis

Concentrations of free dolichol, total non-phosphorylated dolichol, and total phosphorylated dolichol were measured in autopsy specimens of brain and liver from ceroid-lipofuscinosis (CL) and control cases. Levels of non-phosphorylated dolichol, mainly as free dolichol, were increased approximately two-fold in late-infantile CL brain. No increase was observed for CL liver. In late-infantile and juvenile CL brain, the increase in phosphorylated dolichol was at least ten-fold, but no significant difference was found for CL liver. A substantial part of the increase in phosphorylated dolichol in CL brain appeared to be due to lipid-linked oligosaccharides. The results suggest that CL might involve a defect in the metabolism of dolichol-linked oligosaccharides.

The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures

A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids.

Description of analytical problems arising from elevated serum solids

There has always been a problem with the collection of data and interpretation of the results obtained from any biological fluid in which the solids content was increased to a great extent. Of these solids, the triglycerides of the lipids may cause a plasma (serum) to vary in appearance from opalescent to milky. This condition of the specimen and the concomitant turbidity upon its addition to reagents creates the well-documented optical aberrations of spectrophotometric measurements. In addition, the lipids, in conjunction with the proteins, can act as diluents when they are elevated, thereby decreasing what might be termed the residual true plasma volume. Thus the water content of an aliquot sampled for a particular analytical procedure is diminished, and by that means a situation is created in which a short sample is drawn. This dilution effect by the solids results in a lowering of the assay values obtained for the measured constituents of such a serum sample. An associated phenomenon of high concentrations of solids, especially proteins, is the increase in viscosity of a specimen, a condition that also causes an error of short sampling when certain peristaltic pumping devices are used. This review considers several aspects of problems encountered when dealing with a number of circumstances that are critical to the measurement of analytes in severely hyperlipemic and/or hyperproteinemic specimens. These include the problems of short sampling; the potential amelioration of the problem by corrective mathematics, extraction of the lipids, or ultracentrifugation of the true plasma from the lipids; the important need to include most analytes into our considerations; the difference in reference base values for the calculation of concentrations of lipids of serum versus other analytes; the concept of the use of ratios when the reference base values differ, numerator analyte from denominator analyte; and the problems of using serum blanks when necessary corrective action for the solids volume is neglected. Thus, in the final analysis, problems with underestimated volumes of samples used for many spectrophotometric determinations are considered here along with the other difficulties encountered when the need to measure analytes in serums with extremely high solids content presents.

Cholesterol and phospholipids in cultured skin fibroblasts from patients with dystonia

Cultured skin fibroblasts from patients with hereditary (recessive) torsion dystonia or adult-onset sporadic dystonia and from healthy volunteers were compared with respect to total cellular cholesterol, total phospholipid, and phospholipid composition. Differences that could be attributed specifically to dystonia were not detected. The data suggest that the reported cell membrane abnormality in recessive torsion dystonia does not involve a generalized defect in cholesterol or phospholipid metabolism.

Cholesterol synthesis in cultured skin fibroblasts from patients with Huntington's disease

In view of the proposed membrane defect in Huntington's disease, cultured skin fibroblasts from healthy volunteers and patients with Huntington's disease were compared with respect to their ability to carry out de novo synthesis of cholesterol. At confluency, values for incorporation of [14C]acetate and 3H2O into cholesterol, and activities of HMG-CoA reductase (the rate-limiting enzyme in the cholesterol biosynthetic pathway), did not differ significantly in the Huntington's disease cells compared to the controls. Determinations of total cellular cholesterol gave similar ratios of cholesterol/protein and cholesterol/phospholipid in the Huntington's disease and control fibroblasts. The data suggest that the proposed generalized cell membrane abnormality in Huntington's disease cannot be attributed to a defect in the cholesterol biosynthetic pathway.

Compactin (ML-236B) reduces the content of filipin-cholesterol complexes in the plasma membrane of chronic lymphocytic leukemia cells

The polyene antibiotic filipin was used to visualize the presence and distribution of cholesterol in the plasma membrane of glutaraldehyde-fixed human chronic lymphocytic leukemia (CLL) cells. Both compactin (ML-236B), a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and 25-hydroxycholesterol reduced the content of filipin-cholesterol complexes in the plasma membrane of CLL cells grown in media supplemented with either 15% delipidized horse serum or 15% normal (whole) horse serum. The reduction due to compactin was reversed by the concomitant addition of mevalonolactone. The ability of compactin to reduce the relative cholesterol content (as judged by filipin labeling) in CLL cells grown in lipoprotein-containing (normal) serum suggest that either CLL cells are different from other cells in that they predominantly utilize endogenously synthesized cholesterol for incorporation into the plasma membrane, or that a separate pool of endogenously synthesized cholesterol provides cholesterol for the plasma membrane.

A possible regulatory role of squalene epoxidase in Chinese hamster ovary cells

Growth of Chinese Hamster Ovary (CHO) cells in the presence of 20% lipid depleted serum (LDS) for only 2 hr results in an increase in the synthesis of [14C]sterols from [14C]mevalonate and from [14C]squalene compared with cells grown under normal growth conditions in the presence of 10% fetal calf serum (FCS). This enhanced sterol synthesis increases with time of exposure of the cells to LDS. However, exposing these cells for time periods up to 42.5 hr to a growth medium containing 20% LDS did not result in enhanced [14C]sterol synthesis from [14C]2,3-oxidosqualene. Incubation of these cells with [14C]mevalonate resulted in the accumulation of [14C]squalene regardless of the presence of either LDS or FCS. These results suggest that squalene epoxidase is a regulatory enzyme in the cholesterol biosynthetic pathway in CHO.

Serum apolipoprotein A-I, A-II and B levels and their discriminative values in relatives of patients with coronary artery disease

Serum cholesterol, triglyceride, high density lipoprotein cholesterol (HDL-C) and apolipoprotein (apo) A-I, A-II and B concentrations were measured in 109 first-degree relatives of patients with angiographically defined coronary artery disease (CAD). Age- and sex-matched healthy factory employees were chosen as a control group. Male relatives of the CAD patients had significantly higher serum triglyceride and apoB levels, and significantly lower serum HDL-C and apoA-I levels than the controls. Female relatives of the CAD patients also showed similar differences in serum HDL-C, apoA-I and apoB levels. Discriminant analysis indicated that apolipoproteins were better discriminators than lipids in both patients with CAD and their relatives. In univariate analysis, the best discriminator was apoB between male relatives and the controls, and apoA-I between female relatives and the controls. The percentage of exact classification achieved using three variables (serum cholesterol, triglyceride and HDL-C) was 74% in male relatives and 70% in female relatives. By adding variables of apoA-I and apoB, the percentage of correctly classified subjects was increased to 82% and 80%, respectively. These results indicate that serum apolipoprotein abnormalities are prevalent in relatives of the CAD patients. These abnormalities may explain the familial aggregation of CAD.

Serum-stimulated cyclic-AMP production in S49 lymphoma cells grown in serum-free medium

Growth of S49 lymphoma cells with horse serum leads to an increase in cellular cAMP phosphodiesterase activity and a resultant loss of hormone- and cholera-toxin-stimulated cAMP accumulation. We now show that the serum requires protein synthesis to produce these effects. Further, we show that acute addition of serum to wild-type S49 cells, grown in serum-free medium, rapidly (under 2 min) and transiently (under 30 min) stimulates cellular cAMP, 10-fold over basal levels. This 'acute' effect of serum was not observed in UNC S49 cells, suggesting that a functional Ns, the guanine nucleotide regulatory component that mediates stimulation of adenylate cyclase, is required for the serum-mediated stimulation of cellular cAMP. Serum added acutely to wild-type S49 cells also augmented cAMP accumulation in response to isoproterenol and forskolin. The half-maximally effective concentrations of horse serum that acutely stimulated or more slowly decreased the cAMP accumulation were approx. 0.2% and 2.0%, respectively. Preliminary attempts to characterize further the serum factor indicate that it has a high (250 000-300 000) molecular weight and is insensitive to boiling; chromatography on Sepharose CL-6B yields a 100-fold purification. Thus, the serum contains one or more components that activate adenylate cyclase, increase cellular cAMP levels and ultimately induce cAMP phosphodiesterase in S49 lymphoma cells.

Cholesteryl ester transfer activity. Localization and role in distribution of cholesteryl ester among lipoproteins in man

The cholesteryl ester exchange/transfer protein is involved in the transport of cholesteryl ester from high density lipoproteins (HDL) to very low density lipoproteins (VLDL) and low density lipoproteins (LDL). Localization of cholesteryl ester transfer activity (CETA) in plasma was studied by measuring CETA in various delipidated fractions from a single step density ultracentrifugation gradient of plasma. CETA was measured in an in vitro system by calculating the exchange of cholesteryl ester in a standard mixture of [3H]CE-HDL and LDL. The method used for the delipidation of plasmas and fractions to be tested was critical. Optimal results were obtained by delipidation with diisopropylether-butanol (60: 40, v/v) at O degrees C. The bulk of CETA was detected in HDL3 (1.125 less than d less than 1.210 g/ml) when the lipoproteins were separated by single-step density gradient ultracentrifugation and in the 'lipoprotein-free' fraction (d greater than 1.250 g/ml) when the lipoproteins were separated by flotation ultracentrifugation including two washes. To determine whether CETA plays a role in the distribution of cholesteryl ester among the various lipoproteins, it was measured in whole plasma from normal and hyperlipidemic subjects. Plasma was delipidated before the assay in order to prevent bias due to variation of cholesterol content. CETA was higher in delipidated plasma of hyperlipidemic subjects (117.3 +/- 36.5 nmol CE/ml/h) than in delipidated plasma of normolipidemic controls (68.7 +/- 17.6 nmol CE/ml/h) (P less than 0.005). A positive correlation (r = 0.80, P less than 0.005) was found between CETA and (VLDL + LDL) cholesterol levels. A negative correlation (r = 0.57, P less than 0.05) existed between CETA and HDL cholesterol. This correlation was found both in the group as a whole and within the normal and the hyperlipidemic groups separately. The activity of the cholesteryl ester transfer appears to be a regulatory factor in the distribution of cholesteryl ester over the various lipoproteins.

[Dissociation of human serum low density lipoproteins in several immunologically distinct subunits. Isolation and characterization of a B-III subunit]

Low density lipoproteins (d = 1.030-1.055) were partially delipidated with ethyl-ether (LDLe). These LDLe exhibit a spontaneous dissociation several days after delipidation. Four different immunoprecipitation complexes (B-I to B-IV) are observed when using two dimensional immunoelectrophoresis against anti LDLe immunserum. The various subunits of LDLe have different behaviour upon electrophoresis. On disc gel electrophoresis containing urea three bands can be seen; all are phospholipoproteins. The apolipoprotein moiety of LDL and LDLe have the same apparent molecular weight around 550 000. With time several subunits appear in LDLe, the majority of them have a molecular weight around 370 000, 260 000 and 125 000. One of the components from dissociated LDLe containing the immunodeterminant B-III, has been separated by chromatography on heparin-agarose. This LDLe-B-III has the same phospholipid/protein ratio as total LDLe and a protein moiety with an apparent molecular weight of 110 000. This part of apolipoprotein B has no affinity for heparin. Immunocompetition studies by the ELISA technique indicated that sialic acid, one of terminal residues of LDL glycoprotein, is involved in the immunological recognition of LDL and of its derivatives by anti LDL and anti LDLe antisera.

Serum factors and the maturation of Trypanosoma congolense infections in Glossina morsitans

Removal of certain components from pig or cow blood greatly reduces the maturation rate of Trypanosoma congolense infections in Glossina morsitans fed on such diets. In particular, delipidation of serum has the same effect as complete removal of dietary serum with few midgut infections reaching maturity. The addition of gamma-globulin to red cells partially restores the ability of immature infections to transform suggesting that serum lipids or other serum factors are not acting directly on midgut trypanosome metabolism but indirectly through interactions between dietary constituents and the flies' metabolic processes. As susceptibility to T. congolense infection is known to be maternally inherited in G. morsitans, it is suggested that serum factors act through the flies' symbionts to induce maturation in midgut infections.

Acinar cell carcinoma of rat pancreas: mechanism of deregulation of cholesterol metabolism

The mechanism of deregulation of cholesterol metabolism was studied in fast and slow growing nude mouse tumors and cancer cells in culture derived from azaserine-induced rat pancreatic acinar cell carcinoma. The tumors showed a loss of feedback control of the de novo synthesis of cholesterol, probably due to a loss of low density lipoprotein (LDL) receptors on plasma membranes or to a defect in the binding and internalization of LDL in the cancer cells. The hexosemonophosphate shunt pathway is stimulated in the cancer cells, presumably because of an increased demand for NADPH in cholesterol synthesis and for ribose phosphate in DNA synthesis. The uncontrolled de novo synthesis of cholesterol is one of the factors responsible for the high rate of cell proliferation in the tumors.

Characterization of serine palmitoyltransferase activity in Chinese hamster ovary cells

Serine palmitoyltransferase (palmitoyl-CoA: L-serine C-palmitoyltransferase (decarboxylating) EC 2.3.1.50) catalyzes the first unique and regulatory reaction of sphingolipid biosynthesis. Its activity was demonstrated in Chinese hamster ovary cells (CHO-K1) by measuring the incorporation of radiolabel from L-[3H]serine into 3-ketosphinganine, which was found to be the predominant chloroform-soluble product under optimal assay conditions. Most of the total activity (14.8 +/- 4.2 pmol/min per 10(6) cells, measured with sonicated cells) was recovered in particulate fractions, with the highest percentage (54%) and specific activity (102 pmol/min per mg) in the high-speed (airfuge) pellet. The greatest activity was obtained with palmitoyl-CoA; however, other fatty acyl-CoA thioesters were also utilized. Serine palmitoyltransferase required pyridoxal 5'-phosphate for activity, but was apparently fully saturated with this coenzyme when assayed with sonicated cells. Regardless of whether the CHO cells were grown in culture medium containing whole serum with or without sphinganine addition, lipoprotein-depleted serum, lipid-extracted serum, low-density lipoproteins, or no serum, the activities of this enzyme were identical. This finding was confirmed using human fibroblasts. Hence, these results establish that CHO cells, and probably others, are engaged in long-chain base synthesis de novo and that serine palmitoyltransferase activity is not regulated by the availability of such compounds in the culture media.

Characterization of rabbit surfactant-associated proteins

In the present study, the apolipoproteins associated with a purified surfactant fraction isolated from lung lavage of adult rabbits were characterized. Surfactant purity was assessed by the glycerophospholipid composition and by electron microscopic examination. The purified surfactant was delipidated and the apolipoproteins were analyzed by two-dimensional polyacrylamide gel electrophoresis. By use of this technique at least eight proteins or families of proteins were found to be associated with surfactant. Four of these apolipoproteins were families of proteins of 55-70, 29-36, 26-28 and 22-23 kilodaltons (kDa). All of these apolipoprotein families had acidic isoelectric points (pI less than or equal to 5.6), and were specifically bound to a Con A-Sepharose matrix, indicative that these apolipoprotein families are modified by oligosaccharide side-chains. The finding that neuraminidase treatment degraded the 29-36 kDa family is suggestive that this apolipoprotein family contains sialic acid residues. Three major proteins of 66, 43-45 and 35 kDa and a minor protein of 86 kDa were also observed. These proteins had isoelectric points in the more neutral range (pI 6.0-6.5). The 66 kDa protein (pI 6.4) had the same apparent molecular weight and isoelectric point as the major protein of delipidated rabbit serum and as purified rabbit albumin, which suggests that this protein is albumin. These findings are indicative that the apolipoproteins of surfactant are more numerous and complex than previously reported.

Altered sterol synthesis and its relationship to fluid-phase endocytosis in a macrophage cell line P388D1

In a previous study glucocorticoids have been shown to depress the rate of fluid-phase endocytosis in a macrophage cell line, P388D1. This effect was observed when either fluorescein-labeled dextran or horseradish peroxidase (HRP) was used to measure endocytosis. In this report the relationship between cholesterol synthesis and endocytosis was examined in light of the ability of glucocorticoids to inhibit cholesterol biosynthesis. Two known inhibitors of cholesterol biosynthesis, ML-236B and 25-hydroxycholesterol (25-OH), were compared with dexamethasone (dex) for the ability to suppress endocytosis in cells grown in media supplemented with either 10% whole or delipidized neonatal bovine serum (NBS). In 10% whole serum all inhibitors reduced the uptake of HRP after 12 h incubation. Dexamethasone (1 microM) suppressed endocytosis by 30% whereas 25-OH (2.5 microM) and ML-236B (11.6 microM) inhibited by 38 and 52%, respectively. Supplementation of the growth medium with mevalonolactone (3.4 mM) prevented the inhibition of endocytosis by ML-236B. In contrast, mevalonolactone supplementation did not prevent either dex or 25-OH from suppressing endocytosis. The same pattern of results was obtained when cultures were grown in delipidized NBS. After 4 h all inhibitors caused a decrease in amount of [14C]acetate incorporated into both nonsaponifiable lipids and digitonin precipitable sterols. Although dex inhibited cholesterol biosynthesis, total cellular cholesterol was unaffected by dex treatment after 24 h incubation. It is suggested that in addition to suppressing mevalonate synthesis, 25-OH, and by analogy dex, may act at some metabolic site(s) distal to the formation of mevalonate.

Analysis of the coordinate expression of 3-hydroxy-3-methylglutaryl coenzyme A synthase and reductase activities in Chinese hamster ovary fibroblasts

Decreased activities of both 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase and HMG CoA reductase are observed in the presence of sterol in the Chinese hamster ovary (CHO) fibroblast. In three different genotypes of CHO cell mutants resistant to 25-hydroxycholesterol both enzyme activities exhibit a decreased response to 25-hydroxycholesterol compared to wild-type cells. Permanently repressed levels of both HMG CoA synthase and HMG CoA reductase activities are observed in another CHO mutant, phenotypically a mevalonate auxotroph. Mevinolin, a competitive inhibitor of HMG CoA reductase, has no effect on HMG CoA synthase activity measured in vitro. Incubation of CHO cells with sublethal concentrations of mevinolin produces an inhibition of the conversion of [14C]acetate to cholesterol and results in elevated levels of both HMG CoA synthase and HMG CoA reductase activities. Studies of CHO cells in sterol-free medium supplemented with cycloheximide indicate that continuous protein synthesis is not required for the maximal expression of HMG CoA synthase activity and provide an explanation for the lack of temporal similarity between HMG CoA synthase and reductase activities after derepression. These results support the hypothesis of a common mode of regulation for HMG CoA synthase and HMG CoA reductase activities in CHO fibroblasts.

Vitamin A augments collagen production by corneal endothelial cells

When isolated confluent corneal endothelial cells were cultured in delipidized serum, a marked reduction in collagen production was observed. Supplementation of such cultures with vitamin A as either retinol or retinoic acid at concentrations of 10(-6)-10(-7) M was capable of significantly increasing collagen production. In addition, when cultured in normal (non-delipidized) serum, both retinol and retinoic acid were capable of further increasing collagen production by corneal endothelial cells. Such augmentation of collagen production was relatively specific as total protein synthesis was not altered to the same extent, nor was it merely a reflection of changes in total cell number, as such cell numbers were similar in all treatment groups.

A glial progenitor cell that develops in vitro into an astrocyte or an oligodendrocyte depending on culture medium

We have identified a cell type in 7-day-old rat optic nerve that differentiates into a fibrous astrocyte if cultured in the presence of fetal calf serum and into an oligodendrocyte if cultured in the absence of serum. In certain culture conditions some of these cells acquire a mixed phenotype, displaying properties of both astrocytes and oligodendrocytes. These observations suggest that fibrous astrocytes and oligodendrocytes develop from a common progenitor cell and provide a striking example of developmental plasticity and environmental influence in the differentiation of CNS glial cells.

Evaluation of four reagents for delipidation of serum

Four reagents, Aerosil 380, Freon 113, Dextran sulfate 500-S, and a mixed organic solvent were tested for their abilities to produce optically clear, pooled human serum. Aerosil-380, a silicon dioxide, removed 95% of serum cholesterol and triglycerides, and 80% of the free fatty acids. A mixed organic solvent (n-butanol:diisopropyl ether) was equally effective, but also removed nearly all endogenous alkaline phosphatase and lactate dehydrogenase. Freon-113 and Dextran sulfate 500-S removed about half of the serum cholesterol and triglycerides. The serum content of several non-lipid components was unaffected by Aerosil-380, Freon-113, and Dextran sulfate treatments; however, the mixed organic solvent removed 69% of the endogenous calcium. Light scattering data revealed that treatment with all reagents except the mixed organic solvent resulted in optically-clear serum products.

The coordination of sterol and phospholipid synthesis in cultured myogenic cells. Effect of cholesterol synthesis inhibition on the synthesis of phosphatidylcholine

The coordination of biosynthesis of cholesterol and phosphatidylcholine has been investigated in a myoblast cell line L6, grown in lipid-depleted medium. The addition of 25-hydroxycholesterol or compactin to this medium inhibits cholesterol synthesis by over 95%. The rate of [3H]choline incorporation into phosphatidylcholine begins to decline after 6 h and eventually falls to 45% of control. Measurements of choline flux through the CDPcholine pathway and of the pool sizes of choline-containing intermediates indicate that the formation of CDPcholine is the rate-limiting step in phosphatidylcholine synthesis in L6. The rate of CDPcholine synthesis was measured in vivo by pulse-chase experiments. Culturing cells with 25-hydroxycholesterol or compactin results in an inhibition of this step, which parallels the inhibition of incorporation of [3H]choline into phosphatidylcholine. The specific activities of the enzymes of phosphatidylcholine synthesis were assayed under optimal substrate conditions. Growth in the presence of sterol-synthesis inhibitors for 24 h has a significant, but variable, effect on the activity of microsomal and cytosolic cholinephosphate cytidylytransferase. Inhibition is seen in approximately one-half of the preparations and ranges up to 60%. The degree of inhibition of the enzyme in vitro correlates with an elevation of cytosolic triacylglycerol and phospholipid levels, and is not eliminated by the inclusion of excess stimulatory phospholipids in the assay. The pool sizes of the substrates, cholinephosphate and CTP, are unaffected by cholesterol synthesis inhibition. In contrast to the effects on cholinephosphate cytidylytransferase, the microsomal enzymes glycerol-3-phosphate acyltransferase and choline phosphotransferase are stimulated 2-fold or more. Choline kinase specific activity was inhibited 2-fold after 24 h of treatment with 25-hydroxycholesterol; however, no effect on this step was observed in vivo. These results indicate that the coordination of cholesterol and phosphatidylcholine synthesis involves regulation at the cytidylytransferase-catalyzed step.

Determination of human apolipoprotein C-II by electroimmunoassay. Studies on standardization and determination before and after physical training

1. Human VLDL and HDL were fractionated by sequential ultracentrifugation until free of contaminant plasma proteins. 2. Column chromatofocusing method was used to isolate apolipoprotein C-II from apoVLDL and apo HDL. C-apoprotein peak was rechromatofocused and the second peak was the apo C-II (pI 4.7, homogeneous band on SDS slab gel). 3. New Zealand white rabbits were immunized with apo C-II. Antiserum gave a single precipitate are of identity between whole serum, apoVLDL, apoHDL and apo C-II. 4. Apo C-II concentration was measured by electroimmunoassay method. During standardization 1% Triton X-100 improved the rocket shapes and contours. Total delipidation did not affect the assay system and so the antigenic determinants of apo C-II are all available to antiserum. The lowest concentration of apo C-II possible to determine with this method was 70 ng/sample well. 5. There was no difference between the apo C-II values before (39.8 +/- 7.1 mg/l, n = 19) and after (41.6 +/- 6.4 mg/l, n = 19) moderate physical training among normolipemic subjects. 6. Specific immunoprecipitation technique was also used to determine apo C-II content in standard pool serum.