Lipopolysaccharide enhances oxidative modification of low density lipoprotein by copper ions, endothelial and smooth muscle cells

The effect of lipopolysaccharide (LPS, endotoxin) on low density lipoprotein (LDL) oxidative modification by copper ions, endothelial and smooth muscle cells was studied by determination of the level of lipid peroxidation products (thiobarbituric acid reactive substances or TBARS), the diene level and the electrophoretic mobility of the LDL particle. LPS 25-75 microg/ml induced a dose-dependent increase in LDL oxidation by copper ions, endothelial and smooth muscle cells. At 75 microg LPS/ml, the TBARS content was 1.9, 1.6, and 1.8-fold increased, respectively. The LDL degradation by J774 macrophage-like cells was concomitantly stimulated. Preincubation of the LDL particle with LPS induced a marked increase in the subsequent LDL oxidative modification either by copper ions or by endothelial and smooth muscle cells. In addition, pretreatment of endothelial and smooth muscle cells with LPS also induced an enhancement of LDL oxidative modification performed in the absence of LPS. This effect was accompanied by a parallel increase in superoxide anion release by the cells. These results point at one of the mechanisms involved in the described association between bacterial infection and acute myocardial infarction as well as coronary heart disease.

Verapamil enhances the uptake and the photocytotoxic effect of PII, but not that of tetra(4-sulfonatophenyl)porphine

The influence of the calcium channel blocker verapamil on the sensitivity of mouse fibrosarcoma cells of the line EMT-6 to treatment with Photofrin II (PII) or tetra(4-sulfonatophenyl)porphine (TPPS4) and light has been assessed. Cells were treated with 1.5 microg/ml PII or 75 microg/ml TPPS4 overnight in the absence or presence of 50 microg/ml verapamil and subsequently exposed to light. Verapamil increased the sensitivity of the EMT-6 cells to PII-induced photoinactivation by a factor of 2. In contrast, verapamil decreased the sensitivity of the cells to TPPS4-induced photoinactivation by 50-60%. Both sensitizers were found to be located to a large extent in lysosomes as revealed by fluorescence microscopy and by photochemical inactivation of the lysosomal marker enzyme beta-N-acetyl-D-glucosaminidase. Verapamil increased the uptake of PII by 30% and reduced the uptake of TPPS4 by 20%. Furthermore, verapamil enhanced the binding and uptake of LDL by about 40%. In conclusion, the effects of verapamil-induced sensitization of EMT-6 cells treated with PII or TPPS4 and light can to a large extent be attributed to the modulatory effects of verapamil on endocytosis.

Oxidized low density lipoprotein induces activation of the transcription factor NF kappa B in fibroblasts, endothelial and smooth muscle cells

The effect of cupric ions or endothelial cell-oxidized LDL on the transcription factor NF kappa B activation was investigated by electrophoretic mobility shift assay. Oxidized LDL induced NF kappa B activation in fibroblasts, endothelial and smooth muscle cells. The extent of NF kappa B activation was proportional to the degree of LDL oxidation, as assessed by the lipid peroxidation product and the conjugated diene level. A similar activation was observed with the lipid extract of copper-oxidized LDL, which indicates that lipid peroxidation products are involved in the activation mechanism. Furthermore, alpha-tocopherol, a lipophilic free radical scavenger, partially inhibited the stimulatory effect of Cu(2+)-oxidized LDL. Since NF kappa B is considered as an oxidative stress-responsive transcription factor, our study supports the evidence that the stress induced by oxidized LDL causes NF kappa B activation in different cell types, and that this effect can be ascribed to the lipid peroxidation products.

Familial isolated vitamin E deficiency. Extensive study of a large family with a 5-year therapeutic follow-up

A major neurological deterioration, beginning with ataxia, led to the diagnosis of familial vitamin E deficiency in a girl. Based upon vitamin E determinations, 4/8 members of the (consanguineous) sibship were considered to be homozygous. Homozygosity was also found for the alleles of six markers linked to the AVED locus, recently identified in similar Tunisian or Sicilian families on chromosome 8q. Measures of vitamin E in lipoprotein fractions and in liver biopsy after vitamin E oral load suggested that free diffusion of vitamin E between the different compartments was possible and even increased. However, a high-affinity ligand seemed to be lacking, either in the hepatic recycling of vitamin E or in both the hepatic and the other vitamin E compartments. The 5-year substitutive treatment was successful only in the pre- or paucisymptomatic patients. Serum vitamin E must be measured in any unexplained progressive ataxia.

Stimulation of cell-mediated low-density lipoprotein oxidative modification by oncostatin M

The effect of oncostatin M on low-density lipoprotein oxidative modification by human monocytes or murine endothelial cells was studied by determination of the lipid peroxidation products content and the electrophoretic mobility of the particle. In the range of concentrations from 10 to 30 ng/ml, oncostatin M induced a dose-dependent increase in LDL oxidation. The LDL degradation by J774 macrophage-like cells was also stimulated. Preincubation of cells with oncostatin M also enhanced the subsequent LDL modification. This effect was accompanied by a parallel increase in superoxide anion release by cells. Since oncostatin M is produced by immune cells, the described effect suggests a relationship between infection, inflammation and LDL oxidative modification.

Tumor necrosis factor enhances low density lipoprotein oxidative modification by monocytes and endothelial cells

The effect of tumor necrosis factor on the oxidative modification of LDL by U937 human monocytes or murine endothelial cells was studied by determination of the lipid peroxidation product content and the electrophoretic mobility of the particle. In the range of concentrations from 2.5 to 10 ng/ml, the cytokine induced a dose-dependent increase in cellular-induced oxidation of LDL. This effect was accompanied by a stimulation of LDL degradation by J774 macrophage-like cells. Concurrently, the TNF-treated cells secreted superoxide anion with a higher rate. Since LDL oxidation is believed to be an important feature in the formation of the atherosclerotic plaque, the described effects of TNF might be of importance in long-term exposure to this cytokine during inflammation.

1 Acyl-2 acetyl-sn-glycero-3 phosphocholine decreases the susceptibility of low-density lipoprotein to oxidative modification by copper ions, monocytes or endothelial cells

The effects of platelet-activating factor (PAF) and its analogue, 1 acyl-2 acetyl-sn-glycero-3 phosphocholine (1 acyl-2 acetyl-GPC), were investigated on the oxidative modification of low-density lipoprotein (LDL) by copper ions, U937 monocyte-like cells or endothelial cells, by determination of the lipid peroxidation end products (TBARS) content and measurement of the electrophoretic mobility of the particle. 1 Acyl-2 acetyl-GPC, in the concentration range 1-5 micrograms/ml, inhibited LDL oxidation in a dose-dependent manner in the three systems, whereas PAF had no effect. The protective effect of 1 acyl-2 acetyl-GPC was markedly more important when oxidative modification was performed with endothelial cells, leading to total inhibition at 5 micrograms/ml. At the same concentration, the TBARS production was inhibited by 60% and 20% with monocytes and copper ions, respectively. The degradation by J774 macrophage-like cells of LDL modified by copper ions, U937 monocyte-like cells or endothelial cells was also inhibited when modification was performed in the presence of 1 acyl-2 acetyl-GPC. Furthermore, preincubation of the LDL particle with 1 acyl-2 acetyl-GPC before modification protected the lipoprotein against oxidation, whereas preincubation of the cultured cells with the phospholipid had no effect. Thus 1 acyl-2 acetyl-GPC decreases the susceptibility of the LDL particle to oxidative modification, possibly by intercalation within the lipid phase of the particle. Since LDL oxidation is believed to play an important role in the initiation and progression of atherosclerosis, this inhibitory effect of 1 acyl-2 acetyl-GPC might be of importance in view of the fact that this phospholipid is produced concomitantly with PAF in some inflammatory cells.

Daflon as a cellular antioxidant and a membrane-stabilizing agent in human fibroblasts irradiated by ultraviolet A radiation

Daflon is a strong inhibitor of Cu(2+)-induced arachidonic acid peroxidation, as revealed by the inhibition of thiobarbituric acid-reactive substance formation in mixed liposomes of phosphatidylcholine and arachidonic acid. Diosmin, the major Daflon constituent, is a good complexant of Cu2+ ions but not of Fe2+ ions. The Cu2+ complex formation may thus explain part of the antioxidant effect. However, Daflon is also a good quencher of the singlet oxygen-induced arachidonic acid peroxidation that does not involve metal ions. When cultured human fibroblasts are incubated with the diosmin-hesperidin mixture constituting Daflon, the latter is as efficient as vitamin E in inhibiting the ultraviolet A-induced lipid peroxidation and plasma membrane damage measured by lactate dehydrogenase release.

Fractionation of charge-modified low density lipoproteins by fast protein liquid chromatography

We describe a methodology developed to separate different forms of charge-modified low density lipoproteins (LDL) using the fast protein liquid chromatography (FPLC) system from Pharmacia. Lipoproteins were isolated by sequential ultracentrifugation and introduced onto an anion-exchange column (Mono Q HR 5/5). The multistep NaCl gradient elution was optimized and the analytical variables were determined on copper-oxidized LDL. After oxidation by copper for various times (up to 48 h), five forms were obtained (fractions A, B, C, D, and E). Within-run and day-to-day reproducibility were better than 8.6% and 10%, respectively. Protein and cholesterol recovery after the chromatographic separation was good (greater than 82%) and the detection limit was about 1 microgram. The more negative forms of collected LDL were mainly characterized by an increase in the lipid peroxidation product content, a depletion of vitamin E, an alteration of apoB and increased degradation by macrophages. The proposed methodology was applied to the study of LDL modifications generated by human umbilical endothelial cells and the protective effect of antioxidants (vitamin E and probucol).

Could the interaction of neuroleptics with calmodulin be an "explanation" of the psychotropic effects?

Calmodulin is a protein with calcium-dependent binding sites. Binding of calcium ions induces changes in the conformation and activation of many enzymes such as adenylate cyclase, guanylate cyclase, ATPase. Neuroleptic drugs bind calmodulin. Trifluoperazine has a very high affinity for calmodulin. Tricyclic antidepressants and benzodiazepines also bind calmodulin. Binding of neuroleptics inhibits many biological phenomena such as lymphocyte endocytosis, platelets aggregation. When neuroleptics are administrated chronically, calmodulin could act in regulation of the receptors specially in the drug induced supersensitivity of striatum dopamine receptors. These experiments about the regulation of the receptors mediated by calmodulin have been performed ten years ago and their results were not confirmed later. Moreover, binding of calmodulin is not specific of neuroleptic drugs. The effects of neuroleptics on calmodulin, only observed in vitro or with animals, seem to be mainly related to structural properties of the drugs.

Teratogenic effect of the cholesterol synthesis inhibitor AY 9944 on rat embryos in vitro

AY 9944 [trans-1,4-bis(2-chlorobenzylaminomethyl) cyclohexane dihydrochloride] is an amphiphilic cationic molecule. This chemical is an established inhibitor of cholesterol synthesis and is teratogenic in rats. The mechanisms of this teratogenicity remain to be clarified. This study used cultured rat whole embryos to ascertain whether AY 9944 had a direct effect on embryos, or whether its action was indirect, via the maternal cholesterol metabolism. Four experimental conditions were investigated: (A) controls; (B) 10 day untreated embryos were cultured in serum of treated rats; (C) 10 day untreated embryos were cultured in serum containing added AY 9944 (0-1,000 micrograms/ml); and (D) 10 day embryos from females treated on day 4 of gestation were cultured in normal serum. In group B there was no growth retardation; some slight nonspecific abnormalities were not significant. In group C, direct addition of AY 9944 to culture medium retarded growth and differentiation in a dose-dependent manner. No malformation was observed, but histological examinations showed numerous areas of cell necrosis, especially in the CNS. In group D, not only was growth retardation observed, but also characteristic malformations of AY 9944 teratogenesis, including pituitary agenesis. These results show that AY 9944 teratogenicity is initiated prior to day 10.

UVB-induced photoperoxidation of lipids of human low and high density lipoproteins. A possible role of tryptophan residues

Ultraviolet radiation of the UVB region readily destroy tryptophan (Trp) residues of low (LDL) and high (HDL) density lipoproteins. The photooxidation of tryptophan residues is accompanied by the peroxidation of low and high density lipoproteins unsaturated fatty acids, as measured by the thiobarbituric acid assay. Moreover, low and high density lipoproteins are natural carriers of vitamin E and carotenoids. These two antioxidants are also rapidly bleached by UVB. The UVA radiation promotes neither tryptophan residue destruction nor lipid photoperoxidation. The redox cycling Cu2+ ions considerably increase lipid photoperoxidation. The synergistic action of photo and auto (Cu2(+)-induced) peroxidation induces marked post-irradiation modifications of apolipoproteins as illustrated by the degradation of most tryptophan residues after overnight incubation in the dark of pre-irradiated samples.

Cellular uptake and photosensitizing properties of anticancer porphyrins in cell membranes and low and high density lipoproteins

The mechanisms of the phototoxic effect of anticancer porphyrins used in the photodynamic therapy (PDT) of tumours are not yet completely understood. Irradiation of porphyrins gives rise to singlet oxygen which reacts with key residues of proteins, polyunsaturated fatty acids and cholesterol in membranes, leading to inactivation of various enzymes and transporters. Lipoproteins, mainly low density lipoproteins (LDL), are efficient carriers of anticancer porphyrins in blood and can deliver these photosensitizers to tissues through the apolipoprotein (apo) B/E specific LDL receptor pathway. In this review, we discuss some aspects of anticancer porphyrin transport, cellular uptake and photosensitizing properties in cell membranes and lipoproteins.

Modification of phospholipid polar head group with monomethylethanolamine and dimethylethanolamine decreases cholesteryl ester and triacylglycerol synthesis in cultured human fibroblasts

Modification of the phospholipid polar head group was achieved by supplementation of the growth medium of cultured human fibroblasts with the choline analogues monomethylethanolamine (ME) or dimethylethanolamine (DE) at a concentration of 80-200 micrograms/mL for 48 hr. The maximum concentration of phosphatidylmonomethylethanolamine (PME) or phosphatidyldimethylethanolamine (PDE) reached without affecting the phospholipid/protein ratio was about 45% of total phospholipids. Incorporation of oleic acid into cholesteryl esters and triacylglycerols was markedly inhibited after supplementation with ME or DE, and accounted for 60% and 40% of controls, respectively, at 200 micrograms/mL, whereas incorporation into phospholipids was not affected. AcylCoA:cholesterol acyltransferase (ACAT) and diacylglycerol acyltransferase (DGAT) activities measured on cell-free extracts appeared to be decreased also by phospholipid polar head group modification, whereas the overall phospholipid acyltransferase activity remained unchanged. The intracellular content of cholesteryl esters and triacylglycerols, determined by the isotopic equilibrium method with radioactive cholesterol and glycerol, was found to be diminished to 50-60% and 40-50% of controls, respectively, after supplementation with the choline analogues. The study showed that modification of the phospholipid polar head group affects the activity of membrane-bound enzymes involved in the metabolism of neutral lipids.

Cyclic AMP decreases LDL catabolism and cholesterol synthesis in the human hepatoma cell line HepG2

A 24h pretreatment of the human hepatoma cell line HepG2 with dibutyryl cyclic AMP in the presence of theophylline induced a dose dependent decrease in low density lipoprotein binding, uptake and degradation. This effect is most likely due to a reduction of the LDL receptor number. Sterol synthesis from sodium acetate is markedly inhibited, either in the presence or absence of LDL, whereas synthesis from mevalonic acid is unchanged. Cyclic AMP also induced a decrease in hydroxy methyl glutaryl coenzyme A reductase activity. These effects of cyclic AMP might be involved in some hormonal regulation of the LDL pathway and cholesterol metabolism in the liver.

Cholesterol prevents the teratogenic action of AY 9944: importance of the timing of cholesterol supplementation to rats

These studies were conducted to determine whether dietary cholesterol supplementation could prevent fetal malformations induced by the amphipathic drug AY 9944, which is well known as a cholesterol biosynthesis inhibitor, and to investigate whether the plasma maternal sterol level and the nature of the sterols found in treated Wistar rats could explain this prevention. Pituitary agenesis was the most constant element of holoprosencephaly when AY 9944 was administered on d 4 of gestation at two dosages, 50 or 75 mg/kg. The rate of malformed fetuses was dose related. A strong negative correlation was established between maternal plasma sterol levels on d 10 of gestation (day of pituitary gland formation) and the rate of fetal anomalies (r = -0.97, P less than 0.01). Supplementation of AY 9944-treated rats with cholesterol had an obvious preventive action on fetal malformations. When cholesterol was added to the diet the same day as AY 9944 treatment and maintained until d 15, the prevention of malformations was almost complete. When the supplementation was initiated later, the prevention of anomalies decreased. The nature of plasma maternal sterols shows that the cholesterol supplementation modifies significantly the ratio of cholesterol to 7-dehydrocholesterol in treated rats. Therefore, maternal plasma sterol perturbations may play a role in the teratogenic action of AY 9944.

Effect of dibutyryl cyclic AMP and theophylline on lipoprotein lipase secretion by human monocyte-derived macrophages

The effect of dibutyryl cyclic AMP and theophylline on lipoprotein lipase secretion was investigated after a 24 h pretreatment of human monocyte-derived macrophages. Both the effectors decreased in a dose-dependent manner the enzyme activity recovered in the culture medium. The decrease in lipoprotein lipase activity appeared to be related to reduced enzyme synthesis without apparent modification of its stability and half-life and was conversely associated with an increase of lysosomal acid hydrolase activities. This effect was reversible on removal of the nucleotide. The present findings suggest that cyclic AMP may play a role in lipoprotein lipase expression in human macrophages and therefore may participate in the regulation of lipoprotein uptake by these cells, which are strongly implicated in the atherogenic process.

Teratogenic effect of AY 9944 in rats: importance of the day of administration and maternal plasma cholesterol level

An inhibitor of cholesterol synthesis, AY 9944 (trans-1,4-bis(2-chlorobenzylaminomethyl) cyclohexane dihydrochloride) is teratogenic. A single dose of AY 9944 (50 mg/kg or 75 mg/kg) given to Wistar pregnant rats on the second, fourth, sixth, seventh, or eighth day of gestation induced malformations such as holoprosencephaly. They were often limited to isolated pituitary agenesis. The highest percentage of holoprosencephalic fetuses was found when AY 9944 was given on the fourth day of gestation. Whatever the dose and the day of administration, the lower the maternal plasma cholesterol level, the more frequent were holoprosencephalic fetuses. Therefore, it is suggested that the decrease in maternal plasma cholesterol level is at least one of the factors provoking holoprosencephaly.

Effects of phenothiazines on low density lipoprotein metabolism in cultured human fibroblasts

Treatment of cultured human fibroblasts with trifluoperazine or chlorpromazine resulted in a biphasic effect on low density lipoprotein (LDL) catabolism, depending upon the dose. At up to 10(-5) M, a marked increase in LDL binding, internalization and degradation was observed. This phenomenon took place within the first hours of incubation with the drugs, suggesting a direct effect on cell membrane physical characteristics, probably related to the lipophilic properties of phenothiazines. Concentrations above 2 X 10(-5) M resulted in a relative decrease in LDL binding and internalization, and in a dramatic decrease in LDL degradation, which may be related to an inhibition of calmodulin-dependent processes.

Incorporation of exogenous fatty acids into phospholipids by cultured hamster fibroblasts. Effect of SV40 transformation

In situ incorporation of two saturated (palmitic, 16:0; stearic, 18:0) and three unsaturated fatty acids (oleic, 18:1; linoleic, 18:2; arachidonic, 20:4) into the four major phospholipids, sphingomyelin, PC, PI and PE, was followed. Transformed cells incorporated unsaturated fatty acids more rapidly, whereas no significant differences were found concerning saturated fatty acids. In vitro determination of phospholipid acylation showed that incorporation of coenzyme A-activated forms of two saturated fatty acids (16:0 and 18:0) and one unsaturated fatty acid (18:1) into phospholipids was increased in transformed cells. Comparison of results obtained in situ and in vitro strongly suggests that incorporation of fatty acids into phospholipids in cultured cells is not limited by acyltransferase activities.

[A simple micromethod for sphingomyelinase determination (author's transl)]

A rapid and sensitive micromethod for routine determination of sphingomyelinase activity of leukocytes, fibroblasts and hair roots is described. This method makes use of the natural radioactive substrate of the enzyme. The product of the reaction is isolated by direct application of the incubation mixture on silica gel plates followed by ascending chromatography. The sensitivity of the method allows sphingomyelinase determination in less than 0.5 microgram of fibroblast proteins.

Effect of ethanol and prednisolone on growth rate and adherence of normal and SV 40 transformed hamster fibroblasts

Ethanol decreases the growth rate of normal cells, prednisolone increases it. These factors have no effect on the growth rate of transformed cells. Ethanol increases the detachment and mortality of transformed cells, prednisolone has an inverse effect. Both factors affect neither adherence nor mortality of normal cells.