Influence of dicarboxylic phosphatidylcholines on the stability and phase transition of phosphatidylcholine liposomes.

The effect of dicarboxylic phosphatidylcholines (glutaryl phosphatidylcholine) on the stability and phase transition of phosphatidylcholine liposomes is examined by using liposomes prepared with egg phosphatidylcholine or dipalmitoyl phosphatidylcholine and by varying the surface charge by addition of dicetyl phosphate. Light-scattering and osmotic behaviour studies showed that the stability of liposomes containing dicarboxylic phosphatidylcholine is influenced by the charge and the fatty acid saturation of the liposomes. Increasing the glutaryl phosphatidylcholine-to-phosphatidylcholine molar ratio in liposomes caused the formation of mixed glutaryl phosphatidylcholine/phosphatidylcholine micelles. The sensitivity of the lipid bilayers towards glutaryl phosphatidylcholine action increases with the fatty acid saturation of liposomes. Dipalmitoyl phosphatidylcholine liposomes are most sensitive to the dicarboxylic phosphatidylcholine effect. Dicetyl phosphate addition enhances the solubilization of liposomes prepared from saturated phospholipids. The effect of increasing concentrations of glutaryl phosphatidylcholine on the gel-to-liquid crystal thermal transition of dipalmitoyl phosphatidylcholine was observed. Glutaryl phosphatidylcholine modifies the thermal phase transition of the constituents of the liposome. The presence of dicetyl phosphate in liposomes affects the phase transition temperature of these liposomes. It is suggested that the formation of the mixed micelles is responsible for the phase transition modifications. These data show that the solubilization of liposomes by dicarboxylic phosphatidylcholines depends on the fatty acid composition of phosphatidylcholine and on the presence of dicetyl phosphate.

Influence of dicarboxylic phosphatidylcholines on phosphatidylcholine liposomes as revealed by gel chromatography and electron microscopy.

The effect of dicarboxylic phosphatidylcholines (glutarylphosphatidylcholine) on the structural changes of phosphatidylcholine liposomes is examined by using multilamellar liposomes prepared with egg phosphatidylcholine or dipalmitoylphosphatidylcholine and by varying the surface charge by addition of dicetyl phosphate. Investigations are performed by gel chromatography and electron microscopy. Glutarylphosphatidylcholine is in micellar form (rod-like micelles or globular micelles). The structures obtained depend on the fatty acid saturation of liposomes and on the charge of liposome (addition or not of dicetyl phosphate). With egg phosphatidylcholine/glutarylphosphatidylcholine dispersions, an aspect more similar to myelinic figures than liposomes is observed, while in the presence of dicetyl phosphate, liposomes similar to control egg phosphatidylcholine liposomes are obtained. Gel chromatography on Sepharose 4B and turbidity measurements prove that dicetyl phosphate increases the stability of egg phosphatidylcholine/glutarylphosphatidylcholine mixtures. On the other hand, in dipalmitoylphosphatidylcholine/glutarylphosphatidylcholine dispersions, incorporation of dicetyl phosphate destabilizes bilayer structure and the formation of mixed micelles occurs. Viscosity measurement shows, in the presence of dicetyl phosphate, an increased fluidity for dipalmitoylphosphatidylcholine/glutarylphosphatidylcholine dispersions, in agreement with the micellar organization. These data confirm that the disorganization of liposomal membranes by dicarboxylic phosphatidylcholine depends on the fatty acid composition of phosphatidylcholine and on the presence of dicetyl phosphate.

Effects of threonine-poor apolipoproteins on post-heparin plasma hepatic triacylglycerol lipase and lipoprotein lipase.

Whole-irradiated rabbit pre-heparin plasma had an important inhibitory effect on hepatic triacylglycerol lipase and lipoprotein lipase activities, whereas control rabbit pre-heparin plasma slightly inhibited hepatic triacylglycerol lipase activity at a high concentration and enhanced lipoprotein lipase activity. As some apolipoproteins were known to modulate these two lipolytic enzymes, the inhibitory effects of irradiated rabbit plasma were investigated in apolipoproteins. Three apolipoproteins, with isoelectric points of about 6.58, 6.44 and 6.12, characterized by their low content in threonine (threonine-poor apolipoproteins) were produced in high concentrations in rabbit VLDL and HDL after irradiation. The effects of these apolipoproteins on control rabbit post-heparin plasma hepatic triacylglycerol lipase and extrahepatic lipoprotein lipase were studied. Threonine-poor apolipoproteins substantially inhibited the hepatic triacylglycerol lipase activity and enhanced the apolipoprotein C-II-stimulated activity of lipoprotein lipase. The amounts of these apolipoproteins in triacylglycerol-rich lipoprotein particles may determine the lipolytic activity of lipoprotein lipase and hepatic triacylglycerol lipase in triacylglycerol hydrolysis. The existence of another inhibitor of lipoprotein lipase remains to be determined.

Affinity chromatography of arterial lysosomal cholesterol ester hydrolase.

The glycoproteic nature of rabbit aortic lysosomal cholesterol ester hydrolase has been demonstrated by affinity chromatography on Concanavalin A-Sepharose. After chromatography, the enzyme lacks synthesizing activity. This activity is restored by addition of deactivated lysosomes containing more endogenous cholesterol. On the other hand, a hypothesis for the activation role of bis(monoacylglyceryl) phosphate is suggested.

Ultraviolet-treated lipoproteins as a model system for the study of the biological effects of lipid peroxides on cultured cell. I. Chemical modifications of ultraviolet-treated low-density lipoproteins.

A new experimental model system constituted by ultraviolet-treated low-density lipoproteins (LDL) has been designed in order to investigate the biological effects of lipid peroxides entering the cell through the endocytotic pathway. This paper reports the chemical modifications of the lipid components and apolipoproteins of the ultraviolet-treated LDL. Human LDL were submitted to short ultraviolet radiations (254 nm, 0.5 mW/cm2, for variable periods of time) and compared to LDL peroxidized by iron. The lipid peroxidation was monitored by following the formation of the peroxidation products (conjugated dienes, thiobarbituric acid-reactive substances (TBARS) and fluorescent lipid-soluble products) and the change of the composition in polyunsaturated fatty acids, carotenes and vitamin E. Several parameters of the apo B-100 structure were investigated: molecular size (by SDS-PAGE) and TNBS-reactive amino groups (chemical determination by trinitrobenzene sulfonic acid). The most important feature was the absence of major modification of apo B-100 in ultraviolet-treated LDL: the molecular weight and the content in TNBS-reactive amino groups of apo B-100 were not modified. In contrast, iron-treated LDL exhibited a loss of the apo B-100 band and a decrease in the number of TNBS-reactive amino group. Both ultraviolet radiations and iron ions induced a significant decrease in the content of polyunsaturated fatty acids, carotenes and vitamin E together with a large formation of lipid peroxidation products. However, the time-course of the formation of conjugated dienes, TBARS and fluorescent lipid-soluble products was quite different using the two oxidative systems. These results demonstrate that ultraviolet radiations induced a strong peroxidation of the lipid content of LDL and no (or only minor) changes in the apolipoprotein moiety whereas iron-catalyzed peroxidation resulted in the formation fo lipid peroxidation products as well as apo B alterations.

Irradiation-induced free cholesterol accumulation in very-low-density lipoproteins. Role of lipoprotein lipase deficiency.

Irradiation of rabbits induced an accumulation of free cholesterol in VLDL fraction. In the present study, an attempt was made to explain the abnormal free cholesterol enhancement. The study demonstrated that lecithin:cholesterol acyltransferase activity was normal in irradiated rabbits. In addition, electron microscopy examination of HDL revealed no changes after irradiation: spherical particles were present. On the other hand, ACAT activity was increased while neutral and acidic cholesteryl esterases were strongly decreased. Moreover, HMG-CoA reductase was 3-fold reduced after irradiation. These results show that neither cholesterol esterification nor cholesterol ester hydrolysis nor cholesterol biosynthesis are responsible for this increase of free cholesterol in VLDL. In contrast, we have shown that extra-hepatic lipoprotein lipase was deficient in irradiated rabbit plasma although synthesis in the adipocytes is normal. To investigate a hypothetical deficiency of VLDL catabolism, we performed experiments with injection of heparin and with labeled VLDL. These experiments show that, in irradiated rabbits, VLDL were not catabolized, since the radioactivity was recovered only in the VLDL fraction. This impaired VLDL removal was compatible with the deficiency of extra-hepatic lipoprotein lipase activity.

Hydrolysis of fluorescent pyrenetriacylglycerols by lipases from human stomach and gastric juice.

Fluorescent triacylglycerols containing pyrenedecanoic (P10) and pyrenebutanoic (P4) acids were synthesized and their hydrolysis by lipases from human gastric juice and stomach homogenate was investigated. The existence in stomach homogenate of four different lipolytic enzymes hydrolyzing fluorescent triacylglycerols is suggested by the comparison of various enzymatic properties: acyl chain length specificity, heat inactivation and effect of detergents (Triton X-100 and taurocholate), serum albumin, diethyl-para-nitrophenyl phosphate (E600) and other inhibitors. (1) The acid pH4-lipase hydrolyzes P10-triacylglycerols but not P4-triacylglycerol and exhibited the characteristic properties of the lysosomal lipase: the maximal activating effect of detergents occurs at relatively high concentrations (the substrate/detergent optimal molar ratios were 1:5 and 1:25 for triacylglycerols/taurocholate and triacylglycerols/Triton X-100, respectively); its activity was strongly inhibited by para-chloromercuribenzoate (2.5 mmol/l), but was not significantly affected by serum albumin and E600 (10(-2) mmol/l). (2) The neutral pH7-lipase hydrolyzes P10-triacylglycerols but not P4-triacylglycerol. It is resistant to E600 and heat-stable, similarly to the acid pH4-lipase, but it is well discriminated from the acid enzyme by its substrate/detergent optimal molar ratios (1:2 and 1:3 for triacylglycerols/taurocholate and triacylglycerols/Triton X-100, respectively), whereas higher detergent concentrations, optimal for the acid lipase, are strongly inhibitory for the neutral enzyme. (3) The pH5-lipase present in gastric juice as well as in stomach homogenate exhibited properties obviously discriminating it from the other lipolytic enzymes from stomach homogenate: broad substrate specificity for P10- as well as P4-triacylglycerols, activation by low concentrations of amphiphiles (with optimal ratios triacylglycerols/taurocholate, triacylglycerols/taurocholate and triacylglycerols/phosphatidylcholine around 1:1, 1:3 and 1:0.1, respectively), heat-lability, strong activation by serum albumin and inhibition by E600 (10(-2) mmol/l). This pH5-lipase is the sole lipolytic enzyme present in gastric juice and is probably identical with the well-known 'gastric' lipase. (4) A pH7.5-enzyme is characterized by its specificity for P4-triacylglycerols, its heat-lability at 50 degrees C and its strong inhibition by E600 (10(-2) mmol/l).

Ultraviolet-treated lipoproteins as a model system for the study of the biological effects of lipid peroxides on cultured cells. II. Uptake and cytotoxicity of ultraviolet-treated LDL on lymphoid cell lines.

The 'cytotoxicity' of ultraviolet-treated low-density lipoproteins (LDL) has been investigated using cultured lymphoid cell lines from normal subjects and from a patient with receptor-negative familial hypercholesterolemia. The ultraviolet-treated LDL were taken up by control lymphoblasts through the classical apo B/E-receptor pathway, while they were slowly taken up by receptor-negative lymphoblasts by non-specific endocytosis. These LDL were found highly 'cytotoxic' on normal lymphoblasts as demonstrated by Trypan blue dye uptake, [3H]thymidine incorporation, lactate dehydrogenase release and by electron microscopy. The 'cytotoxicity' increased progressively with the concentration of ultraviolet-treated LDL in the culture medium and with the incubation time. In contrast, lymphoblasts from familial hypercholesterolemia were not sensitive to low doses of ultraviolet-treated LDL (up to 150 micrograms apo-B/ml). The comparison of cells from normals and familial hypercholesterolemia showed that the 'cytotoxic' effect occurred subsequently to the LDL uptake, either receptor-mediated or receptor-independent. Experiments combining short-time (5 h) pulse with ultraviolet-treated LDL (labelled with [3H]cholesteryl oleyl ether) and a relatively long-chase period (72 h) showed: (1) a relationship between the delay for the appearance of the 'cytotoxicity' and the amount of ultraviolet-treated LDL taken up by the cells; and (2) the existence of a minimal dose (threshold dose) for triggering the 'cytotoxic' effect. The use of 'hybrid' LDL, prepared by partial delipidation of non-treated LDL and reconstitution by re-incorporating the neutral lipid fractions isolated from ultraviolet-treated LDL, demonstrated that the 'cytotoxic' effect is mainly mediated by triacylglycerols and cholesteryl esters. Scanning electron microscopy showed that the most prominent morphological change resulting from the uptake of ultraviolet-treated LDL was the early blebbing of plasma membranes.

Triacylglycerol increase in plasma very low density lipoproteins in cyclophosphamide-treated rabbit: relationship with cholesteryl ester transfer activity.

We have studied the cholesteryl ester transfer between HDL and VLDL in cyclophosphamide-treated rabbits, in order to explain the abnormal cholesteryl ester partition between these two lipoprotein classes. The hypertriglyceridemia caused by treatment with the drug was associated with cholesteryl ester- and triacylglycerol-rich VLDL and with HDL poor in esterified cholesterol but relatively enriched in triacylglycerol. These two lipoprotein classes were characterized by their chemical composition and by gel filtration chromatography. VLDL particles were slightly larger in size, compared with controls. Different transfer combinations were envisaged between these abnormal lipoproteins and control ones. The transfer study involved the plasma fraction of d greater than 1.21 g/ml containing the cholesteryl ester transfer protein (CETP). It appeared that the chemical composition of lipoproteins was responsible for the level of cholesteryl ester transfer between lipoproteins. Actually, when the cholesteryl ester acceptor lipoproteins (VLDL) were enriched in triacylglycerol, the transfer was enhanced. Therefore, the effect of lipolysis on the transfer has also been explored. Lipoprotein lipase seemed to enhance the transfer of cholesteryl ester from HDL to VLDL when these lipoproteins were normal, but an important decline was obtained when triacylglycerol-rich VLDL were lipolyzed. This study defines the relationship between lipoprotein chemical composition and transfer activity of cholesteryl ester from HDL to VLDL.

Reduced Na(+)-K(+)-ATPase activity and plasma lysophosphatidylcholine concentrations in diabetic patients.

A fraction from normal human plasma inhibiting Na(+)-K(+)-ATPase has been recently identified as lysophosphatidylcholine (LPC). The aim of this study was to investigate the existence of a relationship between the activity of the cellular membrane Na(+)-K(+)-ATPase and plasma LPC in human diabetes. We studied 10 patients with insulin-dependent-diabetes mellitus (IDDM), 14 patients with non-insulin-dependent diabetes mellitus (NIDDM), and 10 sex- and age-matched control subjects. Plasma LPC concentrations were increased in both IDDM and NIDDM patients compared with control subjects. Na(+)-K(+)-ATPase activity was reduced in both groups of patients in erythrocyte and platelet membranes. There was a significant correlation between the concentrations of plasma LPC and Na(+)-K(+)-ATPase activity in both erythrocyte and platelet membranes (P < 0.01). To investigate the effect of LPC on the enzyme, Na(+)-K(+)-ATPase activity was determined in erythrocyte membranes obtained from six healthy subjects after in vitro incubation with increasing concentrations of LPC (1-10 microM). Enzymatic activity was significantly reduced by in vitro LPC at a concentration of 2.5 microM, with a further decrease at 5 microM. These data suggest that the decrease in Na(+)-K(+)-ATPase activity in diabetes might be due to increased LPC concentrations.

Influence of low density lipoprotein from insulin-dependent diabetic patients on platelet functions.

In the present work we studied in vitro the action of low density lipoproteins (LDL) isolated from normolipemic insulin-dependent diabetic (IDDM) patients on transmembrane cation transport, nitric oxide synthase (NOS) activity, and aggregating response to stimuli of platelets from healthy subjects to elucidate whether the modified interaction between circulating lipoproteins and cells might be one of the pathogenetic mechanisms of the increased platelet activation in IDDM. LDL were obtained by discontinuous gradient ultracentrifugation from 15 IDDM out-patients and 15 sex- and age-matched healthy subjects and used for incubation experiments with control platelets. Lipid composition and hydroperoxide concentrations were studied in LDL. Platelet aggregation responses to ADP, NOS activity, cytosolic Ca2+ concentrations, and platelet membrane Na+/K+-adenosine triphosphatase (Na+/K+-ATPase) and Ca2+-ATPase activities were measured after incubation. IDDM LDL showed an increased lysophosphatidylcholine content compared with that of control LDL. IDDM LDL significantly increased the platelet aggregating response to ADP, cytosolic Ca2+ concentrations, and plasma membrane Ca2+-ATPase activity and significantly reduced NOS activity and platelet membrane Na+/K+-ATPase activity compared with those of platelets incubated in buffer or cells incubated with control LDL. The effects exerted by IDDM LDL on platelet suspensions from healthy subjects mimic the alterations observed in platelets from diabetic subjects in basal conditions. Both the decreased activity of NOS and the higher cytoplasmic concentrations of Ca2+ might cause increased platelet activation, as observed in IDDM. In conclusion, the present study suggests a new mechanism with a potential role in the early development of atherosclerosis in diabetic patients, i.e. an altered interaction between circulating lipoproteins and platelets.

Cholesteryl ester transfer protein. Size of the functional unit determined by radiation inactivation.

Radiation inactivation was used to determine the functional Mr of cholesteryl ester transfer protein (CETP) in rabbit plasma from control and irradiated animals. This technique reveals the size of the functional unit required to carry out the transfer function. The functional Mr was calculated to be 70 000 +/- 3000 (mean +/- SD) for both control and irradiated rabbits. This result is in accordance with the Mr obtained by a completely different method, namely SDS-polyacrylamide gel electrophoresis of a partially purified (110-fold) rabbit CETP. The pI of this CETP was found by isoelectric focusing to be equal to 5.95. The results suggest that the functional unit of this enzyme is the monomer.

Effects of an antimitotic agent (cyclophosphamide) on plasma lipoproteins.

A cyclophosphamide injection to male New Zealand white rabbits induced a pronounced hypertriglyceridemia and a hypercholesterolemia whose concentration was maximal at 16 hr. Different doses were studied. In this hyperlipemia significant changes in plasma lipoprotein fractions appeared: the very low density lipoproteins increased and the high density lipoproteins decreased. Lipid composition showed that HDL cholesterol was very low comparatively to a high VLDL cholesterol. The apoprotein composition of VLDL from treated rabbits was studied and compared to that of normal rabbits. After electrophoresis in urea/polyacrylamide gels, two new apoproteins which resembled those observed in irradiated rabbits appeared. The molecular weight of these proteins was about 10,000, and they focused into three bands with isoelectric points of 6.72, 6.42 and 6.10. Total lipoprotein lipase activity in treated rabbits decreased; it was very low with 32.5 mg/kg. This lipolytic activity remains to be studied after separation of hepatic triacylglycerol lipase and lipoprotein lipase activities by chromatography.

Desialylated low density lipoproteins and atherosclerosis.

Oxidative modification of LDL is accompanied by a number of compositional and structural changes, now well known. In addition, other atherogenic modifications of LDL exist, such as desialylation. The present article summarizes the recent data related to desialylated LDL and to the presence of these LDL in blood plasma of patients with coronary atherosclerosis. In addition, this review examines the sensitivity of these LDL to peroxidative stress.

Increased susceptibility to lipid oxidation of low-density lipoproteins and erythrocyte membranes from diabetic patients.

The aim of the present study was to determine if low-density lipoproteins (LDLs) and red blood cell (RBC) membranes from diabetic patients present an increased susceptibility to lipoperoxidation, which might be related to the increased incidence of atherosclerosis in diabetes. LDLs and RBC membranes were isolated from 11 insulin-dependent (IDDM) and 18 non-insulin-dependent diabetic (NIDDM) patients and exposed to a peroxidative stress by incubation with phenylhydrazine. The susceptibility to peroxidation was determined by measuring the production of thiobarbituric acid-reactive substances (TBARS) after the incubation. The following parameters were also evaluated: plasma glucose, triglycerides (TG), phospholipids (PL), total and high-density lipoprotein (HDL) cholesterol, apolipoprotein (apo) A-I, apo B, hemoglobin A1c (HbA1c), LDL PL and cholesterol, LDL fatty acid composition, and RBC membrane PL and cholesterol. Although they were apparently normolipidemic, diabetic patients showed an increased susceptibility to peroxidation in LDLs and erythrocyte membranes as compared with control subjects. The amount of arachidonic acid in LDLs and the PL concentration of RBC membranes from diabetic patients were significantly higher than in normal subjects. The increased lipoperoxidability of both RBC membranes and LDLs might play a central role in the pathogenesis of the vascular complications of diabetes mellitus.

Effect of aluminium on lipid peroxidation of human high density lipoproteins.

We investigated the effect of aluminium (Al3+) on lipid peroxidation and physico-chemical properties of high density lipoproteins (HDL) isolated from human plasma. Our results demonstrated that Al3+ enhances lipid peroxidation of human HDL as shown by the significant increase in lipid hydroperoxides in Al-treated HDL with respect to control HDL. The oxidative effect was higher at acid pH (pH 5.5) with respect to pH 7.4. Moreover, a stimulating effect of Al3+ on iron-induced lipid peroxidation of HDL was demonstrated. The study of the effect of Al3+ on the physico-chemical properties of HDL, using the fluorescence polarization (Pf) of the probes TMA-DPH (1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene iodide) and DPH (1,6-diphenyl-1,3,5-hexatriene), showed a significant decrease of Pf in Al-treated HDL with respect to control. These results suggest that Al3+ induces a decrease of molecular order at the lipoprotein surface. Moreover, the study of tryptophan (Trp) fluorescence demonstrated that aluminium induces structural modifications of HDL apoproteins and on HDL physico-chemical properties. The effect of Al3+ on lipid peroxidation of HDL was observed at aluminium concentrations similar to those observed in the brain of patients affected by neurological diseases. Aluminium-induced oxidative damage of HDL could be involved in the development of neurological diseases.

Effect of aluminium ions on liposomal membranes as detected by Laurdan fluorescence.

We report here an investigation of the influence of aluminium on iron-induced peroxidation in brain model membranes. Laurdan fluorescence emission spectra and generalised polarisation measurements have been used to investigate how ferrous and aluminium ions can affect the phase components of phospholipid membranes. An increase in the generalised polarisation of oxidised liposomes with respect to controls has been observed, which reveals the presence of a less polar environment surrounding the probe that changes the properties of the bilayer. Aluminium has been shown to facilitate iron-mediated oxidation as detected from emission fluorescence spectra. However, no quantitative influence has been calculated relative to general polarisation and derived phase state determinations. The structural influence of aluminium on membranes may therefore be less significantly marked than initially expected.

Influence of the environment in space on the biochemical characteristics of human low density lipoproteins.

The purpose of this experiment was to study the efficiency of protective substances on the effects of cosmic radiation in space on low density lipoproteins. This environment induced modifications in LDL consisting of an increase of lipid peroxidation markers (hydroperoxides, thiobarbituric acid reactive substances). In contrast, apo B was not affected by cosmic radiation as shown by the stability of the trinitrobenzenesulfonic acid reactivity and the tryptophan content. Furthermore, oxidation of LDL was partially inhibited by the addition of cysteamine or/and probucol before the spaceflight experiment. The hydroperoxide formation was almost completely inhibited by cysteamine. It was concluded that antioxidants can exert a protective effect against peroxidative stress induced by the space environment.

Effect of nicotine and cotinine on the susceptibility to in vitro oxidation of LDL in healthy non smokers and smokers.

Cigarette smoke of which the major component is nicotine plays an important role in the development of cardiovascular diseases. To study the effect of in vitro incubation of LDL with nicotine and its metabolite, cotinine on a copper-induced peroxidation, we monitored the formation of conjugated dienes, hydroperoxides and thiobarbituric acid-reactive substances production. The LDL studied were taken from six non-smokers (aged 41.5 years) and six smokers who consumed at least ten cigarettes per day (40.7 years). LDL oxidation with CuSO4 showed that cigarette smoking promotes LDL susceptibility to peroxidative modification. During the peroxidation of LDL with nicotine (O to 5 mmol/1) and CuSO4 (5 micromol/l), the formation of hydroperoxides decreased when nicotine concentrations increased and the production of TBARS increased in a concomitant manner. The results showed that the presence of nicotine destabilized the production of hydroperoxides in LDL and increased the formation of secondary oxidation products. On the other hand, cotinine had no effect on LDL oxidative susceptibility in smokers and non-smokers.

Wavelength dependence of photoinduced peroxidation and cytotoxicity of human low density lipoproteins.

The relative abilities of UV-A, B and C radiations to initiate lipid peroxidation and apolipoprotein (apo) B modification of human purified low density lipoproteins have been compared. Ultraviolet-B and C (at 310 and 254 nm, respectively) exhibited similar efficacy as shown by the increase in lipid peroxidation markers (conjugated dienes, thiobarbituric acid reactive substances and fluorescent lipid soluble products) and in oxysterols, as well as by the decrease of the contents of natural antioxidants (tocopherols and carotenes) and in polyunsaturated fatty acids. In contrast, UV-A (at 360 nm) was found poorly effective and only at very high radiation intensities. Under all the conditions used, apoB was not affected by the UV radiations as shown by the stability of amino acid composition (except tryptophan level) and of trinitrobenzenesulfonic acid reactive amino group content. Similarly, the low density lipoprotein size was not altered. By comparison, low density lipoproteins oxidized by transition metal presented strong alterations of apoB and major changes of the apparent low density lipoprotein size. Finally, low density lipoproteins irradiated by UV-B. or C exhibited a much higher cytotoxicity on cultured cells than those irradiated by UV-A. Under the conditions used in this paper, the cytotoxic effect of the irradiated low density lipoproteins was positively correlated with their content in lipid peroxidation products and inversely correlated with their tocopherol content.