Low HDL level is an independent risk factor for the development of several diseases such as type 2 diabetes and coronary heart disease [1,2]. The protective effects mediated by HDLs likely result from a variety of properties including apoptosis inhibition, stimulation of vaso-relaxation, and cholesterol extraction from tissues [2-4]. Both the quantity and the quality (size, composition, etc.) of HDL particles modulate their protective functions [5], and can be affected in sick individuals. For example, it has been reported earlier that alterations are found in HDLs isolated from patients with metabolic syndrome and this correlated with defective antiapoptotic properties [6]. A recent study shows that HDLs from type 2 diabetic patients have impaired vasoprotective effects [7*]. Specifically, these HDLs, in contrast to HDLs isolated from healthy individuals, were not able to increase nitric oxide production from endothelial cells and could not induce aortic ring relaxation. Additionally, a prospective study performed on women now reports that reduction in HDL particle size is independently associated with a higher risk of developing diabetes [8*]. Lipoprotein alterations may appear before diagnosis of diabetes and could therefore represent useful markers indicating an increased likelihood of disease development.
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