Metabolism of pyrenedecanoic acid in Epstein-Barr virus-transformed lymphoid cell lines from normal subjects and from a patient with multisystemic lipid storage myopathy

A lymphoid cell line has been established from a patient with multisystemic lipid storage myopathy and showed a major triacylglycerol storage, whereas the content of other neutral lipids and phospholipids was in the normal range. The metabolism of the triacylglycerols has been investigated in this lymphoid cell line from multisystemic lipid storage myopathy as well as in control cells through pulse-chase experiments using 10-(1-pyrene)decanoic acid (P10), a fluorescent fatty acid derivative, as precursor. After 1 h incubation, the uptake of P10 was not significantly different in multisystemic lipid storage myopathy and control lymphoid cells. The amount of fluorescent lipids synthesized by the lymphoid cells was proportional to the concentration of P10 in the culture medium. After 24 h incubation, at any extracellular concentration of P10, the content of P10-labelled triacylglycerols was much higher in multisystemic lipid storage myopathy cells than in controls. Chase experiments showed an impairment in the rate of degradation of biosynthesized triacylglycerols in multisystemic lipid storage myopathy lymphoblasts compared to controls with time of chase (the ratio P10-triacylglycerols/P10-phospholipids increased in mutant cells while it decreased in normal cells). Elsewhere, no enzyme deficiency of the neutral triacylglycerol lipase activity, has been found in multisystemic lipid storage myopathy lymphoid cells.     

Independence of triacylglycerol-containing compartments in cultured fibroblasts from Wolman disease and multisystemic lipid storage myopathy

The functional relationship between the two subcellular compartments involved in catabolism of triglycerides, i.e. lysosomes and lipid-containing cytoplasmic vacuoles, has been investigated using cultured fibroblasts from patients affected with two different genetic lipid (triacylglycerol) storage disorders: Wolman disease and multisystemic lipid storage myopathy. As shown by metabolic studies in intact cultured cells, lysosomal degradation of exogenous labelled triacylglycerols (incorporated into lipoproteins and internalized via the apo B/E receptor pathway) was blocked in Wolman cells, whereas catabolism of endogenously biosynthesized triacylglycerols was in the normal range. In contrast, in fibroblasts from multisystemic lipid storage myopathy, the degradation of endogenous triacylglycerols was blocked, whereas that of exogenous triacylglycerols (i.e. from lipoproteins) was normal. This comparative study demonstrates that the lysosomal and cytoplasmic compartments are functionally independent. Enzymatic studies allows one to discriminate clearly between 3 lipases and 2 carboxylesterases the role of which is discussed.     

Characteristics of uptake of short chain fatty acids by luminal membrane vesicles from rabbit kidney

The mechanisms of renal transport of short chain fatty acids by luminal membrane vesicles prepared from pars convoluta or pars recta of rabbit proximal tubule were studied by a Millipore filtration technique and by a spectrophotometric method using a potential-sensitive carbocyanine dye. Both luminal membrane vesicle preparations take up propionate and butyrate by strictly Na+-dependent transport systems, although with different characteristics. The uptake of short chain fatty acids by membrane vesicles from the pars convoluta was insensitive to changes in membrane potential, which is indicative of electroneutral transport of these compounds. Furthermore, kinetic studies showed that the Na+-dependent, but electrically silent transport of propionate is saturable (Km = 10.9 +/- 1.1 mM and Vmax = 3.6 +/- 0.2 nmol/mg protein per 20 s) and is unaffected by the presence of L- and D-lactate, indicating that these monocarboxylic acids did not share the same common transport system. In the luminal membrane vesicles from the pars recta, the uptake of propionate and butyrate was mediated by an Na+-dependent electrogenic transport process, since addition of the organic compounds to these vesicle/dye suspensions depolarized the membrane vesicles and the renal uptake of propionate and butyrate was enhanced by K+ diffusion potential induced by valinomycin. Competition experiments revealed that in contrast to the transport of propionate by vesicles from the pars convoluta, the Na+-dependent electrogenic transport of short chain fatty acids in vesicles from the pars recta occurred via the same transport system that is responsible for the reabsorption of L- and D-lactate in this region of rabbit kidney proximal tubule.     

The elongation of exogenous fatty acids and the control of phospholipid acyl chain length in Micrococcus cryophilus.

The synthesis of fatty acids de novo from acetate and the elongation of exogenous satuated fatty acids (C12-C18) by the psychrophilic bacterium Micrococcus cryophilus (A.T.C.C. 15174) grown at 1 or 20 degrees C was investigated. M. cryophilus normally contains only C16 and C18 acyl chains in its phospholipids, and the C18/C16 ratio is altered by changes in growth temperature. The bacterium was shown to regulate strictly its phospholipid acyl chain length and to be capable of directly elongating myristate and palmitate, and possibly laurate, to a mixture of C16 and C18 acyl chains. Retroconversion of stearate into palmitate also occurred. Fatty acid elongation could be distinguished from fatty acid synthesis de novo by the greater sensitivity of fatty acid elongation to inhibition by NaAsO2 under conditions when the supply of ATP and reduced nicotinamide nucleotides was not limiting. It is suggested that phospholipid acyl chain length may be controlled by a membrane-bound elongase enzyme, which interconverts C16 and C18 fatty acids via a C14 intermediate; the activity of the enzyme could be regulated by membrane lipid fluidity.     

Glycolipids and fatty acids of two dog kidney cell lines.

Glycolipid and fatty acid compositions were studied in whole cells and plasma membranes from two dog kidney cell lines (Madin-Darby and SV40-transformed cells) grown in monolayer and suspension cultures. Glycolipids, which account for 5% or less of the total lipids in dog kidney cells, were substantially increased in plasma membranes relative to whole cells. Sialoglycolipids more complex than a Tay-Sachs-like ganglioside were not found in any whole-cell or plasma-membrane preparation of this study. Dog kidney cells transformed by SV40 virus contained primarily a less complex sialoglycolipid, haematoside. Neutral glycolipids comprised 26-43% of the total glycolipid content in Madin-Darby preparations, whereas in transformed cells and membranes neutral glycolipids constituted only 1-22% of the total glycolipid content. Ceramide trihexoside was found in Madin-Darby cultures, but not in transformed cultures. The values for short-chain fatty acids from neutral glycolipids and for saturated fatty acids were generally higher than the values for these fatty acids in calf serum.     

How fatty acids of different chain length enter and leave cells by free diffusion

Opposing views exist as to how unesterified fatty acids (FA) enter and leave cells. It is commonly believed that for short- and medium-chain FA free diffusion suffices whereas it is questioned whether proteins are required to facilitate transport of long-chain fatty acid (LCFA). Furthermore, it is unclear whether these proteins facilitate binding to the plasma membrane, trans-membrane movement, dissociation into the cytosol and/or transport in the cytosol. In this mini-review we approach the controversy from a different point of view by focusing on the membrane permeability constant (P) of FA with different chain length. We compare experimentally derived values of the P of short and medium-chain FA with values of apparent permeability coefficients for LCFA calculated from their dissociation rate constant (k(off)), flip-flop rate constant (k(flip)) and partition coefficient (Kp) in phospholipid bilayers. It was found that Overton's rule is valid as long as k(flip)相似文献   

Production of immunoglobulins by tumor cell lines from avian lymphoid leukosis.

Two avian lymphoma cell lines, 1104-X-5 and 1104-B, were examined for ability to produce immunoglobulin. They were found to produce and release the components of immunoglobulins related to IgG and IgM. The analysis of sucrose density gradient and gel electrophoresis suggested that these components might consist of light chains and fragments of heavy chains.     

CD36 mediates both cellular uptake of very long chain fatty acids and their intestinal absorption in mice

The intestine has an extraordinary capacity for fatty acid (FA) absorption. Numerous candidates for a protein-mediated mechanism of dietary FA absorption have been proposed, but firm evidence for this process has remained elusive. Here we show that the scavenger receptor CD36 is required both for the uptake of very long chain FAs (VLCFAs) in cultured cells and the absorption of dietary VLCFAs in mice. We found that the fraction of CD36-dependent saturated fatty acid association/absorption in these model systems is proportional to the FA chain length and specific for fatty acids and fatty alcohols containing very long saturated acyl chains. Moreover, intestinal VLCFA absorption is completely abolished in CD36-null mice fed a high fat diet, illustrating that the predominant mechanism for VLCFA absorption is CD36-dependent. Together, these findings represent the first direct evidence for protein-facilitated FA absorption in the intestine and identify a novel therapeutic target for the treatment of diseases characterized by elevated VLCFA levels.     

Constitutive uptake and degradation of fatty acids by Yersinia pestis.

Yersinia pestis was found to utilize palmitic acid as a primary carbon and energy source. No inhibition of growth by palmitic acid was observed. Comparison of palmitic acid uptake by cells pregrown either with or without palmitic acid demonstrated that fatty acid uptake was constitutive. High basal levels of two enzymes of beta-oxidation, beta-hydroxyacyl-coenzyme A dehydrogenase and thiolase, and the two enzymes of the glyoxylate shunt, isocitrate lyase and malate synthase, were found in cells grown in defined medium with glucose. Elevated levels of all four enzymes were found when cells were grown with acetate as a primary carbon and energy source, and even higher levels were observed when palmitic acid was provided as a primary carbon and energy source. High-pressure liquid chromatography was used to demonstrate that, in the presence of glucose, uniformly labeled [14C]palmitic acid was converted to intermediates of the tricarboxylic acid cycle and glyoxylate shunt. Pregrowth with palmitic acid was not required for this conversion. Strains lacking the 6- or the 47-megadalton plasmid did not take up [3H]palmitic acid but did possess levels of enzyme activity comparable to those observed in the wild-type strain.     

Influence of chain length and unsaturation on the effects of fatty acids on phosphoglyceride biosynthesis in isolated rat and pig hepatocytes.

Hepatocytes isolated from rat or pig by collagenase perfusion were incubated with [3H]glcyerol and different albumin-bount fatty acids. Among C22 fatty acids docosahexaenoic acid stimulated phosphatidylethanolamine synthesis in rat hepatocytes most effectively. Addition of docosahexaenoic acid plus either palmitic or stearic acid resulted almost in the same stimulation whereas combinations of this acid with lauric or myristic acid had no effect. Lauric acid and myristic acid alone inhibited phosphatidylethanolamine synthesis. The chain length specificity for monoenoic fatty acids was similar, the hexadecenoic and octadecenoic acids (both cis and trans) being most stimulatory. The addition of 0.2 mM ethanolamine markedly stimulated phosphatidylethanolamine synthesis, but most effects of fatty acids were similar in its presence or absence.     

Differential changes in lipid metabolism of myeloid and lymphoid cell lines induced by treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA)

Treatment of the myeloid cell lines, U-937 or HL-60, with 10 nM of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), for 24 h increased the rate of incorporation of [3H]glycerol into total chloroform extracts. A proportionally greater labeling of the non-polar lipid (NL) fraction compared to the polar, phospholipid (PL), fraction was observed. Chromatographic analysis showed a 6-fold increase in the labeling of triacylglycerols (TAG), a 2-fold increase in diacylglycerols, and no changes in monoacylglycerols. PL labeling showed a 3-fold increase in phosphatidylcholine (PC). The effect of TPA on TAG labeling was selectively observed in myeloid cell lines. No such a change was found in the lymphoid cell line. MOLT-3, which did respond to TPA with increased PC labeling. Incorporation of [3H]arachidonic acid (AA) into TAG by U-937 cells was selectively increased (2.5-fold) after treatment with TPA for 24 h. Treatment of U-937 cells with TPA in serum-free medium resulted in no increased labeling of TAG. These studies suggest that changes in TAG metabolism may be characteristic of myeloid differentiation and depend on the presence of serum factor(s).