Alterazioni e modulazione farmacologica del profilo lipidico funzionale del siero in pazienti con malattie cardiovascolari e neurodegenerative

Circulating lipoproteins are currently considered to play a very important role in cardiovascular disease. In detail, High-density lipoproteins (HDL) are considered atheroprotective because their role to remove the excess of cholesterol from peripheral tissues by promoting the reverse cholesterol transport (RCT), in particular, by promoting cholesterol efflux from peripheral cells, especially from macrophage cells, which are the cells most involved in atherosclerotic plaque progression. Cholesterol efflux can occur by several pathways, including passive aqueous diffusion (AD) and active efflux, which is mainly mediated by two transporters, ATP-binding cassette G1 (ABCG1) and A1 (ABCA1). Low-density lipoproteins (LDL) are atherogenic because of their capacity to be loaded by macrophages, which may result in the formation of foam cells, a hallmark of atherosclerosis. In recent years, it has become clear that the function of lipoproteins may be more relevant to cardiovascular risk assessment than the quantification of their circulating levels. Another important factor modulating cholesterol homeostasis is Proprotein convertase subtilisin/kexin type 9 (PCSK9) which acts by degrading the hepatic low-density lipoprotein receptor (LDLR) increasing circulating LDL concentration. This underlines the importance of PCSK9 inhibitors (PCSK9-i) that by inhibiting the activity of PCSK9, reduce LDL-C levels and consequently cardiovascular (CV) risk. These three main components, namely the HDL capacity to promote cell cholesterol efflux (HDL-CEC) and the serum lipoproteins capacity to promote cholesterol accumulation in macrophages (CLC), and the PCSK9 activity, constitute the serum functional lipid profile. Based on these premises, the first aim of this study was to identify possible disturbances of the serum functional lipid profile in different clinical settings associated to a high cardiovascular risk, such Familial Hypercholesterolemia (FH) with Achilles Tendon Xanthoma presentation (ATX) and Abdominal aortic aneurysm (AAA), by measuring the HDL-CEC and the serum CLC. In this study, we also included the evaluation of the serum functional lipid profile in a neurodegenerative disease, the Alzheimer’s Disease (AD) clinical setting, which shares many risk factors with CV, of which dyslipidaemia is the most interesting for this work. In addition, another objective of this study was to evaluate whether the possible alteration of serum functional lipid profile in these different clinical settings may be related or not to plasma levels and/or lipoprotein composition and to CV risk parameters. Secondly, the project aimed to evaluate how a pharmacological intervention in FH under PCSK9-i may have a beneficial impact on serum functional lipid profile. Comparing FH presenting ATX and FH without ATX no significant differences were found in terms of plasma lipid profile. However, a significant increase in ABCA1-mediated HDL-CEC (+ 18.6 %) was observed in ATX compared to no ATX patients. Furthermore, in ATX-presenting patients, ABCG1-mediated HDL-CEC was lower (? 11 %) and serum CLC was higher (+ 14 %) compared to patients without ATX. Considering all the patients together, ABCG1 HDL-CEC and serum CLC correlated with ATX thickness inversely (p = 0.013) and directly (p < 0.0001), respectively. In AAA, ABCG1 HDL-CEC was lower (? 16 %; p < 0.001) and ABCA1 HDL-CEC was higher (+ 31.7 %; p < 0.0001) in AAA subjects compared to a control group, characterized by the same CV risk and no AAA. A stratification of the values suggests that smoking may partly contribute to these modifications. We found higher Lecithin:cholesterol acyltransferase (LCAT) (+ 23 %; p < 0.0001) and cholesteryl ester transfer protein (CETP) (+ 49 %; p < 0.0001) activity in AAA sera. HDL-CEC and CETP activity correlated with CLC only in AAA, suggesting the existence of a link between accelerated HDL function, intracellular cholesterol, and aneurysm formation. In AD subjects compared to a cognitive normal control group, we observed normal plasma lipids levels but significantly reduced unesterified cholesterol and unesterified/total cholesterol ratio. Cholesterol efflux capacity mediated by the transporters ABCA1 and ABCG1 was reduced in AD patients’ plasma, in agreement with the reduced content of small discoidal pre-? HDL in AD. LCAT activity and cholesterol esterification rate (CER), two measures of the efficiency of the esterification process, were reduced by 29 % and 16 %, respectively, in the plasma of AD patients. In another cohort of FH patients, that underwent 6-months treatment with PCSK9-i, total cholesterol and LDL-C significantly decreased (- 41.6 %, p < 0.0001 and - 56.7 %, p < 0.0001, respectively). Despite no changes in HDL-C levels between the groups, ABCG1 HDL-CEC significantly increased after treatment (+ 22.2 %, p < 0.0001) as well as HDL-CEC by AD (+ 7.8 %, p = 0.0008). Only a trend towards reduction of ABCA1 HDL-CEC was observed after treatment. PCSK9-i significantly decreased serum CLC (- 6.6 %, p = 0.0272). The latter effect was only partly related to the reduction of LDL-C levels (R2 = 0.091; p = 0.006). In conclusion, the results observed in the three clinical settings, all potentially associated with high cardiovascular risk, generally showed a dysregulation of lipoprotein function, notably a reduced ability of HDL to mediate cholesterol efflux through the ABCG1 transporter, independently HDL-C levels, and an increased ability of serum lipoproteins to promote cholesterol accumulation in macrophage cells, independently LDL-C levels. Accordingly, in FH after pharmacological intervention with PCSK9-i, we observed an increase in ABCG1 HDL-CEC and a reduction in serum CLC, suggesting a beneficial effect of pharmacological treatment on lipoprotein function, which could contribute to the reduction in CV risk associated with this therapy. Overall, these results contribute to the identification of novel functional parameters, to be used together with the traditional one to better define the CV risk in these populations. In addition, these parameters may represent in the future new pharmacological targets for the treatment of cardiovascular and neurodegenerative diseases.