Elena Bravo

Direct Interaction of Dietary Lipids Carried in Chylomicron Remnants with Cells of the Artery Wall: Implications for Atherosclerosis Development

The development of atherosclerotic lesions in the artery wall is a complex process involving the endothelium, lipid engorged macrophages (foam cells) and smooth muscle cells. In recent years it has become clear that chylomicron remnants, the lipoproteins which carry lipids of dietary origin in the blood, are strongly atherogenic, and there is increasing evidence to indicate that this is due to direct interaction of the remnant particles with cells of the artery wall. Chylomicron remnants have been demonstrated to inhibit endothelium dependent vasorelaxation and to activate signal transduction pathways associated with inflammation in cultured endothelial cells. They have also been shown to be taken up by smooth muscle cells and macrophages, and to cause the extensive lipid accumulation associated with foam cell formation, as well as influencing the expression of key genes regulating macrophage lipid uptake and metabolism. Furthermore, oxidative modification of the remnant particles is not required for many of these effects. Chylomicron remnants, therefore, have multiple direct effects on three major cell types of the arterial wall which are likely to promote the development of atherosclerotic lesions. These effects may be modulated by various lipids carried by the particles, including the type of fat (saturated or unsaturated or oxidised fat), micronutrients such as vitamins and carotenoids which have antioxidant properties, and orally administered lipophilic drugs. Delayed clearance of chylomicron remnants from the blood occurs in a number of dyslipidemias associated with premature atherosclerosis development, and the potentially atherogenic effects of the particles would clearly be enhanced in these circumstances. Thus, elucidation of the mechanisms involved will aid in the identification of new drug targets which may be particularly useful for these conditions.

Comparison of the hepatic uptake and processing of cholesterol from chylomicrons of different fatty acid composition in the rat in vivo

The effect of the fatty acid composition of chylomicrons on the uptake and processing of the cholesterol they carry was investigated in the rat in vivo. Rats kept on a standard low fat pellet diet and tube fed a single dose of palm, olive, corn or fish oil (rich in saturated, n-9 monounsaturated, n-6 polyunsaturated and n-3 polyunsaturated fatty acids, respectively) were used to prepare [3H]cholesterol-labelled chylomicrons of different fatty acid composition. These were then injected intravenously into rats (kept on the standard diet), and the clearance of radioactivity from the blood, distribution in the plasma lipoprotein density fractions, uptake by the liver and appearance in the bile were studied. [3H]Cholesterol from fish and corn oil chylomicrons was cleared from the blood more rapidly than that from palm and olive oil chylomicrons. After 180 min the proportion of the radioactivity present in the plasma in high density lipoprotein (HDL) was less when the chylomicrons were derived from palm oil as compared to any of the other oils. Approx. 40% of the administered label was recovered in the liver after 180 min in all experiments. The percentage of the injected radioactivity secreted into bile during 180 min was significantly higher with corn and fish oil chylomicrons than with palm oil chylomicrons, with chylomicrons from olive oil in an intermediate position, and these differences were most pronounced between 60 and 120 min after administration of the label. These studies clearly demonstrate that the fatty acid composition of chylomicrons has important effects on the hepatic uptake and processing of the cholesterol they carry, with enrichment with polyunsaturated fatty acids leading to an increased rate of uptake and more rapid removal from the body via the bile as compared to enrichment with saturated or monounsaturated fatty acids.

The Relationship between 1H- NMR mobile lipid intensity and cholesterol in two human tumor multidrug resistant cell lines (MCF-7 and LoVo)

The high resolution proton nuclear magnetic resonance (1H-NMR) spectra of two different cell lines exhibiting multidrug resistance (MDR) as demonstrated by the expression of the well-known energy-driven, membrane-bound 170 kDa P-glycoprotein pump known as Pgp were investigated. In particular, the mobile lipid (ML) profile, and the growth and biochemical characteristics of MCF-7 (human mammary carcinoma) and LoVo (human colon adenocarcinoma) sensitive and resistant tumor cells were compared. The results indicate that both MCF-7 and LoVo resistant cells have a higher ML intensity than their respective sensitive counterparts. However, since sensitive and resistant cells of each pair grow in the same manner, variations in growth characteristics do not appear to be the cause of the ML changes as has been suggested by other authors in non-resistant tumor cells. In order to investigate further the origin of the ML changes, lipid analyses were conducted in sensitive and resistant cell types. The results of these experiments show that resistant cells of both cell types have a greater amount of esterified cholesterol and saturated cholesteryl ester and triglyceride fatty acid than their sensitive counterparts. From a thorough analysis of the data obtained in this paper utilizing numerous techniques including biological, biophysical and biochemical ones, it is hypothesized that cholesterol and triglyceride play a pivotal role in inducing changes in NMR ML signals. The importance of these lipid variations in MDR is discussed in view of the controversy regarding the origin of ML signals and the paramount role played by the Pgp pump in resistance.

Induction of non-alcoholic fatty liver disease and insulin resistance by feeding a high-fat diet in rats: does coenzyme Q monomethyl ether have a modulatory effect?

OBJECTIVE The aim of this study was to investigate the development of non-alcoholic fatty liver disease (NAFLD) in response to a high-fat diet in rats and to test the hypothesis that dietary coenzyme Q monomethyl ether (CoQme) has antisteatogenic effects. METHODS Rats were fed a standard low-fat diet (control) for 18 wk or a diet containing 35% fat (57% metabolizable energy) for 10 wk, then divided into three groups for the following 8 wk. One group was given CoQ9me (30mg/kg body weight per day in 0.3mL olive oil: high fat+CoQ9me), the second olive oil (0.3mL/d) only (high fat + olive oil), and the third group received no supplements (high fat). RESULTS Insulin levels and the activity of alanine aminotransferase in the plasma were significantly increased in all high-fat diet groups, and the homeostasis model assessment of insulin resistance indicated insulin resistance. Triacylglycerol concentrations in whole plasma and in very low-density lipoprotein and low-density lipoprotein fractions were also raised. Liver histology showed lipid accumulation in animals fed the high-fat diets, and liver triacylglycerol levels were increased (2.5- to 3-fold) in all high-fat diet groups. These effects were not changed by the administration of CoQ9me. CONCLUSIONS Rats fed a diet with 57% energy from fat showed insulin resistance, hypertriglyceridemia, increased very low-density lipoprotein production, hepatic steatosis, and liver damage, and thus provide a good model for the early stages of NAFLD. Dietary CoQ9me, however, did not ameliorate the damaging effects of the high-fat diet.

Quantifying the use of bioresources for promoting their sharing in scientific research

An increasing portion of biomedical research relies on the use of biobanks and databases. Sharing of such resources is essential for optimizing knowledge production. A major obstacle for sharing bioresources is the lack of recognition for the efforts involved in establishing, maintaining and sharing them, due to, in particular, the absence of adequate tools. Increasing demands on biobanks and databases to improve access should be complemented with efforts of end-users to recognize and acknowledge these resources. An appropriate set of tools must be developed and implemented to measure this impact.To address this issue we propose to measure the use in research of such bioresources as a value of their impact, leading to create an indicator: Bioresource Research Impact Factor (BRIF). Key elements to be assessed are: defining obstacles to sharing samples and data, choosing adequate identifier for bioresources, identifying and weighing parameters to be considered in the metrics, analyzing the role of journal guidelines and policies for resource citing and referencing, assessing policies for resource access and sharing and their influence on bioresource use. This work allows us to propose a framework and foundations for the operational development of BRIF that still requires input from stakeholders within the biomedical community.

The lipolysis of chylomicrons derived from different dietary fats by lipoprotein lipase in vitro.

The lipolysis of chylomicrons derived from palm, olive, corn or fish oil (enriched in saturated, monounsaturated, n - 6 polyunsaturated and n - 3 polyunsaturated fatty acids, respectively) by rat post-heparin lipoprotein lipase in vitro was compared by measuring the release of [3H]oleate from their triacylglycerol. Chylomicrons derived from corn oil were lipolysed more rapidly than the other types in the first 20 min of the reaction, but after 120 min the total amount of triacylglycerol hydrolysed was similar with all types of chylomicrons used. The rate of lipolysis of the different types of chylomicrons also showed different dependencies on the substrate concentration. The highest Vmax values were obtained when the chylomicrons were derived from olive and corn oil and the lowest when they were derived from palm oil, while olive oil chylomicrons gave the highest Km and palm oil chylomicrons the lowest. These results indicate that differential metabolism of chylomicrons of different fatty acid composition by lipoprotein lipase may play a part in the differential rates of clearance from the blood of lipid of dietary origin demonstrated in earlier work from our laboratory.

Effect of Taurine Levels on Liver Lipid Metabolism: An In Vivo Study in the Rat

Abstract Previous studies using guinea pigs and cats have shown that liver lipid composition is affected by intrahepatic taurine levels. The purpose of the present study was to determine whether this sulfonated amino acid could also affect lipid metabolism in the rat, an animal capable of synthesizing substantial amounts of taurine and used extensively in studies on lipid metabolism. Wide variations in the hepatic taurine content were induced by administering either 1% taurine or 1% guanidinoethane sulfonate in the drinking water for 2 weeks. These treatments increased and decreased taurine liver content, respectively, but did not affect either food or water intakes, or growth rates. The plasma concentrations of the major lipid classes in treated animals did not show any significant alteration in comparison to control animals, except for nonesterified fatty acid levels that were significantly lowered by guanidinoethane sulfonate administration. Taurine supplementation did cause a significant decrease in total hepatic lipid content that was attributable to the reduction of free and esterified cholesterol, triglyceride, and phosphatidylethanolamine hepatic concentrations. This same treatment slightly increased both bile flow and secretion of taurine-conjugated primary bile salts. In particular, the proportion of tauro-β-muricholate significantly increased, whereas that of taurodeoxycholate greatly decreased. The administration of guanidinoethane sulfonate reduced both the bile flow and the secretion of taurine-conjugated bile salts and caused a significant alteration in the ratio between glycine- and taurine-conjugated bile salts. This did not occur after the treatment with taurine. Interestingly, we observed an inverse correlation between hepatic taurine levels and the proportion of either cholesteryl ester in hepatic lipids or taurochenodeoxycholate in biliary bile salts. These facts suggest that taurine hepatic levels influence mostly hepatic steroid metabolism, but they also affect the metabolism of other lipid classes.

High fat diet-induced non alcoholic fatty liver disease in rats is associated with hyperhomocysteinemia caused by down regulation of the transsulphuration pathway.

BackgroundHyperhomocysteinemia (HHcy) causes increased oxidative stress and is an independent risk factor for cardiovascular disease. Oxidative stress is now believed to be a major contributory factor in the development of non alcoholic fatty liver disease, the most common liver disorder worldwide. In this study, the changes which occur in homocysteine (Hcy) metabolism in high fat-diet induced non alcoholic fatty liver disease (NAFLD) in rats were investigated.Methods and resultsAfter feeding rats a standard low fat diet (control) or a high fat diet (57% metabolisable energy as fat) for 18 weeks, the concentration of homocysteine in the plasma was significantly raised while that of cysteine was lowered in the high fat as compared to the control diet fed animals. The hepatic activities of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGS), the enzymes responsible for the breakdown of homocysteine to cysteine via the transsulphuration pathway in the liver, were also significantly reduced in the high fat-fed group.ConclusionsThese results indicate that high fat diet-induced NAFLD in rats is associated with increased plasma Hcy levels caused by down-regulation of hepatic CBS and CGL activity. Thus, HHcy occurs at an early stage in high fat diet-induced NAFLD and is likely to contribute to the increased risk of cardiovascular disease associated with the condition.

Chylomicron remnant induction of lipid accumulation in J774 macrophages is associated with up-regulation of triacylglycerol synthesis which is not dependent on oxidation of the particles.

The influence of chylomicron remnants on lipid accumulation and synthesis and the activity and/or expression of mRNA for some of the key enzymes involved was investigated in the murine macrophage cell line J774. The effects of varying the polyunsaturated fatty acid (PUFA) composition and oxidation state of the remnants were also examined. Chylomicron remnants derived from corn oil (rich in n-6 PUFA) or fish oil (rich in n-3 PUFA) were prepared in vivo and oxidised by incubation with CuSO(4). The native and oxidised remnants caused a marked rise in intracellular triacylglycerol levels, but the rise induced by corn oil remnants (four- to sixfold) was greater than that observed with fish oil remnants (<2-fold). Triacylglycerol synthesis, as measured by the incorporation of [3H]oleate and [3H]glycerol into cellular triacylglycerol, was increased by all four remnant types tested, and corn oil remnants had a significantly greater effect than fish oil remnants. Oxidation of the remnants did not affect the results obtained. Although the incorporation of [3H]oleate into cholesteryl ester by the cells was not significantly changed by any of the four types of remnants tested, the activity and expression of mRNA for acyl Co-enzyme A: cholesterol acyltransferase (ACAT) was increased by corn oil, but not by fish or oxidised corn, remnants. Neutral cholesteryl ester hydrolase (nCEH) activity, however, was also raised by corn oil remnants. These studies indicate that chylomicron remnants induce the accumulation of triacylglycerol in J774 macrophages, and that increased synthesis of triacylglycerol plays a major role in this process. Furthermore, they demonstrate that these effects are enhanced when the remnants are enriched in n-6 PUFA as compared with n-3 PUFA, but not after oxidation of the particles, suggesting that the fatty acid composition of chylomicron remnants may be more important than their oxidation state in their ability to induce foam cell formation.

Hepatic uptake and metabolism of free cholesterol from different lipoprotein classes. An in vivo study in the rat.

Hepatic metabolism of [14C]cholesterol, vehiculated by LDL, HDL2 and HDL3 lipoprotein particles, has been studied in rats with a permanent biliary drainage. The lipoprotein fractions were infused individually by a jugular vein catheter and bile was collected for 180 min after the administration. At the end of this period, the animals were killed and the blood and livers were collected. The free cholesterol of the HDL2 fraction was secreted into bile, mainly as bile salt, preferentially to that associated with HDL3 and LDL fractions (11.7% vs. 2.3% and 0.3%, respectively). The free cholesterol of the HDL3 fraction, on the other hand, was taken up by liver more quickly and in a higher proportion than that associated with other lipoprotein fractions. The label incorporation in this lipoprotein fraction was secreted earlier and not transformed into bile. The contribution of LDL-vehiculated free cholesterol to bile secretion was small and the hepatic uptake amounted to no more than 12% of the injected label.