Predicting the risk for cardiovascular disease with CRP and L5

Atherosclerosis is a complex, chronic, inflammatory process characterized by the accumulation of lipids on the inner surface of the blood vessel. It results in the formation of atherosclerotic plaque in arteries and can ultimately lead to infarction. Immune cells, especially blood monocytes-derived macrophages, play a major role in the inflammatory events that occur in the initiation and progression of atherosclerosis. Macrophages are recruited to the deposit site and start accumulating large amounts of lipids through the uptake of modified lipoproteins, which results in foam cell formation. This causes an amplification of the local inflammation process due to the secretion of pro-inflammatory cytokines, chemokines, and other matrix metalloproteinases. These secreted proteins then promote the development of plaque and provoke lesions within the vascular tissue.

Among numerous inflammatory biomarkers, C-reactive protein (CRP) is one of the most well validated markers and serves as an independent predictor in various stages of atherosclerosis. Atherosclerosis can remain asymptomatic for decades. By measuring elevations in baseline CRP levels using high-sensitivity assays, low - ( < 1 µg/ml ), moderate - ( 1-3 µg/ml ), and high - ( > 3 µg/ml ) risk groups can be predicted for future cardiovascular events, even in apparently healthy individuals. CRP belongs to the family of pentraxins and consists of five identical, non-covalently-linked 23 kDa subunits. It is primarily produced by hepatocytes under the stimulation of inflammatory cytokines such as IL-6. Recent evidence suggests that CRP is not only a marker but also a potential contributor to inflammatory disease. In the context of cardiovascular diseases, CRP has been shown to interact with the vascular endothelium and contributes to atherothrombosis by inducing effects such as: monocyte–endothelium adhesion, promoting low-density lipoprotein (LDL)-cholesterol accumulation in macrophages, increasing ROS production, decreasing endothelial nitric oxide production, triggering platelet aggregation, and rendering atherosclerotic plaque more fragile and prone to rupture.

L5 is a known atherogenic substance and the most electronegative circulating LDL. L5 has detrimental consequences on endothelial cells, notably apoptosis. Plasma L5 levels are elevated in patients with high cardiovascular risks such as hypercholesterolemia and type 2 diabetes mellitus. Interestingly, L5 and CRP are both ligands for the lectin-like oxidized LDL receptor-1 (LOX-1). This receptor is expressed at low levels in healthy endothelium but up-regulated in the presence of oxidized LDL or proinflammatory cytokines. Chu and colleagues from Kaohsiung Medical University Hospital in Taiwan demonstrated the existence of a positive feedback loop between L5, CRP, and LOX-1 receptor expression in human aortic endothelial cells (HAEC). By treating cells with L5, CRP expression and secretion was up-regulated in a dose- and time-dependent manner, whereas treatment with the less electronegative LDL subfraction (i.e. L1) had no effects. L5-induced CRP expression fell back to baseline level when LOX-1 was neutralized by using an inhibitory antibody indicating that the signaling pathway leading to CRP expression was initiated by L5 binding to LOX-1. In turn, incubation of HAEC with recombinant CRP stimulated LOX-1 expression. Using Enzo’s total ROS/Superoxide detection kit, they showed that L5 increased ROS production in live HAECs, which supports the idea that L5 induces oxidative stress as well as local endothelial cell inflammation and is therefore pro-atherogenic. The percentage of L5 in total LDL measured in hypercholesterolemic patients is significantly higher than in healthy individuals suggesting that L5 may be another candidate biomarker for identifying high-risk cardiovascular patients.

Statins (or HMG-CoA reductase inhibitors) are a class of drugs known to lower cholesterol levels by inhibiting the enzyme HMG-CoA reductase, which plays a central role in the production of cholesterol in the liver. Hypercholesterolemic patients treated with the medicament Atorvastatin have reduced total cholesterol and LDL-cholesterol levels. Interestingly, they also have reduced L5 percentage in total LDL. It is therefore conceivable that statin drug therapy may lower the risk of some cardiovascular diseases and provide vascular protection. This is achieved through the reduction of LDL-cholesterol levels as well as by targeting and reducing the level of circulating atherogenic L5, which in turn lowers endothelial CRP expression and ROS-initiated oxidative damage.

Enzo Life Sciences offers a comprehensive portfolio for studying inflammation and oxidative stress including live cells detection kit and high sensitivity ELISA kits, some of which are listed below:

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