Cristina Manzoni

Mechanisms of Lipid-Lowering Agents

Lipid-lowering agents are used with the purpose of ameliorating hyperlipoproteinemias, in order to prevent arterial disease. Lipid-lowering drugs can be classified into absorbable agents and into nonabsorbable compounds, acting within the gastrointestinal lumen. Absorbable drugs (fibric acids, nicotinic acid, probucol, HMG-CoA reductase inhibitors) reduce plasma very-low-density lipoproteins (VLDL) and/or low-density lipoproteins (LDL) by a variety of mechanisms. Fibric acids, in particular, act by stimulating the catabolism of VLDL and also, as a consequence, improving LDL delipidation, thus favoring receptor uptake. Nicotinic acid and acipimox interfere with the biosynthesis of LDL and can also improve the clearance of VLDL/LDL. Probucol acts by a newly described mechanism, i.e. accelerating reverse transport of cholesteryl esters from high-density lipoproteins to lower-density lipoproteins. Finally, HMG-CoA reductase inhibitors, interfering with the biosynthesis of cholesterol, can induce an increased expression of liver high-affinity lipoprotein receptors. Nonabsorbable agents (anion-exchange resins, neomycin, beta-sitosterol) interrupt the recirculation of bile acids and/or reduce the absorption of cholesterol with the gut. They display a selective activity on hypercholesterolemia, again by increasing LDL receptor expression. The choice of one or more lipid-lowering agents will depend upon the patients phenotype, determining responsiveness to the pharmacological treatment.

Differential effects of beclobrate on lipid/lipoprotein distribution in normal and hypercholesterolemic rats.

Beclobrate, a new fibric acid derivative, displays remarkable lipid lowering activity in rodents. In order to evaluate changes in the distribution and liver handling of lipoproteins, beclobrate was tested in rats fed on a normal or hypercholesterolemic diet. On the normal diet, beclobrate lowered total plasma cholesterol by 22-33.4% (10-50 mg/kg); the cholesterol reduction occurred mainly in high density lipoproteins (HDL) (by 24-45% with the three tested doses). The metabolic clearance of 125I-labelled beta-very low density lipoproteins (beta-VLDL) injected into these animals almost doubled (0.20 1/h vs. 0.13 1/h in controls) after treatment with 20 mg/kg of beclobrate. In addition, beclobrate administration dramatically increased the activity of the high-affinity receptors for beta-VLDL in isolated liver membranes (Bmax: 208 +/- 17.6 vs. 146 +/- 2.6 ng/mg of protein for controls). On the hypercholesterolemic diet, beclobrate treatment (50 mg/kg) was associated with a 25% reduction in total cholesterol accompanied, however, by a 166% rise in HDL cholesterol. In these animals, the composition of VLDL, typically cholesterol-enriched, became close to normal. The increased HDL was characterized by a remarkable enrichment with particles containing apolipoprotein E (apo E), which is compatible with either an improved peripheral cholesterol removal or an enhanced direct secretion of apo E. The two models offer different opportunities for evaluating the mechanism of action of this new lipid lowering agent. Lipoprotein catabolism and receptor-mediated clearance were characteristically improved in normolipidemic rats whereas major effects on HDL metabolism could be demonstrated in hypercholesterolemic rats.

Internalisation and multiple phosphorylation of γ-Conglutin, the lupin seed glycaemia-lowering protein, in HepG2 cells

Lupin seed γ-Conglutin is a protein capable of reducing glycaemia in mammalians and increasing glucose uptake by model cells. This work investigated whether γ-Conglutin is internalised into the target cells and undergoes any covalent change during the process, as a first step to understanding its mechanism of action. To this purpose, γ-Conglutin-treated and untreated HepG2 cells were submitted to confocal and transmission electron microscopy. Immune-revelation of γ-Conglutin at various intervals revealed its accumulation inside the cytosol. In parallel, 2D-electrophoresis of the cell lysates and antibody reaction of the blotted maps showed the presence of the protein intact subunits inside the treated cells, whilest no trace of the protein was found in the control cells. However, γ-Conglutin-related spots with an unexpectedly low pI were also observed in the maps. These spots were excised, trypsin-treated and submitted to MS/MS spectrometric analysis. The presence of phosphorylated amino acids was detected. These findings, by showing that γ-Conglutin is internalised by HepG2 cells in an intact form and is modified by multiple phosphorylation, open the way to the understanding of the lupin γ-Conglutin insulin-mimetic activity.

Reduced platelet aggregability and increased vascular prostacyclin formation in a variant rat strain (IVA-SIV) with endogenous hypertriglyceridemia

The Ivanovas-Sieve (IVA-SIV) rat represents the only available animal model of endogenous hypertriglyceridemia, in the absence of obesity and/or overt diabetes. Since plasma lipids/lipoproteins can modulate platelet reactivity and eicosanoid metabolism, these were examined in two groups of Charles River (CR) and IVA-SIV rats of identical age. The IVA-SIV rats had 2-fold higher plasma triglycerides and a 55% higher number of circulating platelets; the number of platelets was significantly correlated with triglyceridemia. Platelet reactivity to ADP and to collagen was significantly reduced in these animals, whereas the formation of thromboxane B2 did not differ from that of the CR. After perfusion of platelet-rich plasma (PRP) through the aortas of animals of the two strains, platelet aggregability, already lower in the IVA-SIV, was reduced to a higher extent compared to the CR. Increased levels of the prostacyclin metabolite 6-keto-PGF1 alpha were identified in the perfusate from the aortas of IVA-SIV rats. Platelets from these animals also showed an increased sensitivity to Iloprost, a stable prostacyclin analogue, with an IC50 1.7-fold lower compared to CR rats. Spontaneous hypertriglyceridemia in the IVA-SIV model is not associated with platelet hyperresponsiveness, but rather with a reduced sensitivity to major aggregants.

Basic proteins and basic membranes adjusting blotting and staining conditions to immobilon CD

Abstract Transfer efficiency from polyacrylamide gels and binding to Immobilon P and CD were tested in different buffers with 125 I-labelled proteins. With a derivatized poly(vinylidene difluoride) membrane, a pH 8 medium was found to be superior to a more alkaline solution, for both acidic and basic proteins. New staining protocols were tried on Immobilon CD. Toluidine Blue and iodine vapour gave a negative and a positive stain, respectively, with a fair band-to-background contrast. Protein sequencing after both stains was not impaired by interfering peaks. Biuret solution stained the protein bands pale pink but, even after copper removal with a chelating agent, it completely prevented Edman degradation. The first two procedures compare favourably with a commercial kit for protein detection, Quick Stain, that provides comparable sensitivity but results in several spurious peaks on protein sequencing.

Comparative Evaluation of Olive Oil and of Corn Oil in the Prevention of Atherosclerosis

Regional cardiovascular morbidity and mortality data in the Western hemisphere shows a particularly low prevalence in the Mediterranean region1. In spite of the recent fall of cardiovascular disease in the US, mortality data are still about twice higher than those occurring in the Mediterranean nations2. The currently growing popularity of the so-called “Mediterranean diet”3 (characterized, among other things, by a moderately low intake of polyunsaturated fatty acids and by a high intake of monounsaturates from olive oil) is demonstrated by articles in a variety of lay publications4. There is, however, still no adequate basis to explain a direct influence of any nutrient intake on the low cardiovascular mortality in this region. Among: the different hypotheses, some have been stressed: low salt intake5, higher consumption of fiber-rich food6 or of red wine7.