Étude des dyslipoprotéinémies associées à l'hypercholestérolémie familiale et à la résistance à l'insuline : de la physiopathologie à l'approche clinique

Authors: Drouin-Chartier, Jean-Philippe
Advisor: Couture, PatrickLamarche, Benoît
Abstract: Familial hypercholesterolemia (FH), caused by mutation in the LDL-receptor (LDLR) gene, is amongst the most frequent primary dyslipoproteinemias worldwide. Extreme plasma concentrations of LDLcholesterol (LDL-C) is the main clinical feature of this disorder. The dyslipoproteinemia associated with insulin resistance (IR) is amongst the most frequent secondary dyslipidemias and is mainly characterized by postprandial hyperlipidemia. These two dyslipoproteinemias play major role in the pathogenesis of atherosclerosis and cardiovascular diseases. The general objective of this thesis was to study physiopathological mecanisms modulating phenotypic severity of dyslipoproteinemias associated with FH and IR as well as the impact of different clinical approaches in the management of these lipid disorders. With regard to the dyslipoproteinemia associated with FH, the association between plasma levels of proprotein convertase subtilisin/kexin type 9 (PCSK9) and the phenotypic severity of this dyslipoproteinemia, as evidenced by plasma levels of LDL-C, Lp(a), apo B (total and B-48), was evaluated. In patients with heterozygous FH, positive associations among plasma levels of PCSK9, LDL-C, Lp(a) and total apo B, but not apo B-48, were observed, independent of LDLR genotype. Next, cardioprotective mechanisms and determinants of the efficacy of lipoprotein apheresis (LA) were studied. LA is the gold-standard therapy for homozygous FH as it allows to delipidate plasma using extracorporeal system. Our work demonstrated that LA has only a limited impact on the whole blood expression of genes involved in lipid metabolism and cardiovascular health. We also described the differential impact of two different LA systems on plasma levels of apo B-containing lipoproteins and other molecules involved in cardiovascular health (e.g. inflammatory and adhesion markers). Finally, associations between pre-LA plasma TG levels, the LDLR genotype and LA efficacy was investigated for the first time in homozygous FH (HoFH) patients. These analyses suggest that receptor-negative and/or hypertriglyceridemic HoFH patients may benefit from more frequent LA to reduce their exposure to apoB-containing lipoproteins in comparison with receptor-defective HoFH patients. Regarding the dyslipoproteinemia associated with IR, our first objective was to characterize alterations in intestinal TG-rich lipoprotein (TRL) metabolism associated with this condition. We demonstrated that plasma levels of insulin and glucose are differentially associated with the intestinal expression of key genes involved in TRL synthesis and with the production rate of these lipoproteins. Plasma concentrations of C-reactive protein and PCSK9 were also found to be associated with the apoB-48-containing TRL production rate in IR men. These data suggest that intestinal TRL metabolism is altered by the progression of IR and/or the onset of insulin insufficiency, inflammation and PCSK9. The impact of inhibiting the intestinal cholesterol absorption with ezetimibe was subsequently investigated in order to gain further insight into lipid-lowering mechanisms of this drug in IR state. We demonstrated that ezetimibe increases the intestinal expression of the LDLR gene, supporting the concept that increased clearance of LDLs with ezetimibe occurs not only in the liver, but also in the intestine. The impact of two different dietary interventions on postprandial lipoprotein metabolism was finally studied. We first demonstrated that the substitution of omega-6 polyunsaturated fatty acids for saturated fatty acids has no impact on TRL apo-48 kinetics, but decreases the production rate and the pool size of LDLs apoB-100. We also demonstrated that the cheese matrix modulates the impact of dairy fat on postprandial lipemia. Indeed, firm cheese matrix attenuates postprandial lipid response in comparison with soft cheese matrix, independent of cheese milk-fat content. Using a translational approach, from physiopathology to clinical approach, this thesis allowed to develop new knowledge on dyslipoproteinemias associated with FH and IR. These data will allow us to have a more comprehensive understanding of the impact of different clinical approaches, from diet to drugs, in the management of these lipid disorders.
Document Type: Thèse de doctorat
Issue Date: 2018
Open Access Date: 25 July 2018
Permalink: http://hdl.handle.net/20.500.11794/30433
Grantor: Université Laval
Collection:Thèses et mémoires

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