Elevated serum levels of proinflammatory cytokines and biomarkers of matrix remodeling in never-treated patients with familial hypercholesterolemia

Abstract

Background

Familial hypercholesterolemia (FH) is a common inherited disorder of lipoprotein metabolism, whose origin involves mutations in the gene coding for the low-density lipoprotein receptor protein. Although FH is monogenic, wide variation occurs in the onset and severity of atherosclerosis in these patients.

Methods

Since data on levels of inflammatory proteins and/or active factors in FH patients who have never received lipid-lowering treatment are lacking, serum levels of MMP-3, active MMP-9 and TIMP-1 as well as pro-inflammatory cytokines (TNF-α, IL-18) were determined in never-treated homozygous FH Moroccan patients (n = 4) and compared to those of heterozygous FH subjects (n = 7) and of healthy control subjects (n = 5).

Results

When compared to controls, homozygous FH patients exhibited levels of active MMP-9 and TIMP-1 (p < 0.05), and of both high sensitive-CRP and IL-18 which were significantly elevated (p < 0.05 and p < 0.01, respectively). In heterozygous FH patients, intermediate values between FH homozygotes and healthy controls were observed for these markers, with the exception of MMP-9 activity whose levels were significantly elevated (p < 0.05). Multivariate analysis revealed a positive correlation between apolipoprotein B, TIMP-1 and IL-18 levels, and between hs-CRP and IL-18 (p < 0.01).

Conclusions

Although the sample size of this FH group was limited, our data suggest that nontreated homozygous FH patients, and to a lesser degree heterozygous FH patients, exhibit not only a markedly proinflammatory vascular state but also pronounced extracellular matrix remodeling, as reflected by elevated circulating levels of inflammatory cytokines and MMPs.

Introduction

Familial hypercholesterolemia (FH) is a common autosomal dominantly inherited disorder of lipid/cholesterol metabolism whose origins involve either mutations in the low-density lipoprotein (LDL) receptor gene or in the gene encoding apolipoprotein B or the in PCSK9 gene [1], [2], [3], [4]. As a result of the disruption of LDL receptor function, patients with FH display markedly elevated circulating levels of LDL cholesterol from birth, ranging from 7 to 15 mmol/l in heterozygous patients to up to move than 25 mmol/l in the homozygous state. As high levels of LDL-cholesterol are a major risk factor for cardiovascular disease (CAD), FH subjects exhibit a significantly increased risk of premature CAD, due to the formation of atherosclerotic lesions in childhood [5], [6].

Atherosclerosis is recognized as a chronic inflammatory disease of the arterial wall in which an inflammatory response is a key event that leads to the formation of atheromatous lesions [7]. Fragilisation of the fibrous cap of atherosclerotic plaques is intimately related to the presence of an inflammatory state which plays a crucial role in plaque rupture, the major pathophysiological event underlying acute coronary syndromes [8], [9], [10]. Expression of a spectrum of inflammatory factors, such as C-reactive protein (CRP) and proinflammatory cytokines including TNF-α and IL-18, constitutes a strong link between inflammation and atherogenesis in coronary artery disease [11]. Proinflammatory cytokines are responsible for vascular endothelial dysfunction and activation, leading for example to the overexpression of endothelial adhesion molecules [12], to enhanced uptake of oxidized LDL through increased expression of scavenger receptors in monocyte-derived macrophages [13], to plaque fragilisation [14] and to induction of cell proliferation in the arterial wall [15]. The matrix metalloproteinases (MMPs) and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs) constitute an additional group of biomarkers and of actors in the inflammatory process, and play a central role in subendothelial vascular extracellular matrix remodeling [16], [17], [18]. Experimental data have established that MMPs and TIMPs are involved in the development of atherosclerotic lesions and their fragilisation [16], [17], [18], [19]; moreover, we recently observed that asymptomatic hyperlipidemic subjects at high cardiovascular risk display elevated circulating levels of MMP-3, MMP-9 and TIMP-1 [20].

There is a paucity of information on the inflammatory state in untreated FH subjects, and more specifically on circulating levels of cytokines, MMPs and TIMPs [21], [22]. However, although the cause of FH is monogenic, wide variation exists in the onset and severity of atherosclerotic disease in these patients [23]. We hypothesized that comprehensive evaluation of the inflammatory state of never-treated FH patients might provide not only further insight into variation in disease severity but might also improve cardiovascular risk assessment. We therefore determined serum levels of several inflammatory markers, i.e. high sensitive CRP (hs-CRP), IL-18 and tumor necrosis factor (TNF)-α, and of matrix remodeling factors, i.e. MMP-3, MMP-9 and TIMP-1, in homozygous FH patients who had never received either lipid-lowering or anti-inflammatory treatment. We equally evaluated the potential relationships between these inflammatory molecules and the plasma lipid profile.