Inter-relationships between small, dense low-density lipoprotein (LDL), plasma triacylglycerol and LDL apoprotein B in an atherogenic lipoprotein phenotype in free-living subjects

A predominance of small, dense low-density lipoprotein (LDL) is a major com ponent of an atherogenic lipoprotein phenotype, and a common, but modifiabl e, source of increased risk for coronary heart disease in the free-living p opulation. While much of the atherogenicity of small, dense LDL is known to arise from its structural properties, the extent to which an increase in t he number of small, dense LDL particles (hyper-apoprotein B) contributes to this risk of coronary heart disease is currently unknown. This study repor ts a method for the recruitment of free-living individuals with an atheroge nic lipoprotein phenotype for a fish-oil intervention trial, and critically evaluates the relationship between LDL particle number and the predominanc e of small, dense LDL. In this group, volunteers were selected through loca l general practices on the basis of a moderately raised plasma triacylglyce rol (triglyceride) level (> 1.5 mmol/l) and a low concentration of high-den sity-lipoprotein cholesterol (< 1.1 mmol/l). The screening of LDL subclasse s revealed a predominance of small, dense LDL (LDL subclass pattern B) in 6 2% of the cohort. As expected, subjects with LDL subclass pattern B were ch aracterized by higher plasma triacylglycerol and lower hi,gh-density lipopr otein cholesterol (< 1.1 mmol/l) levels and, less predictably, by lower LDL cholesterol and apoprotein B levels (P < 0.05; LDL subclass A compared wit h subclass B). While hyper-apoprotein B was detected in only five subjects, the relative percentage of small, dense LDL-III in subjects with subclass B showed an inverse relationship with LDL apoprotein B (r = -0.57; P < 0.00 1), identifying a subset of individuals with plasma triacylglycerol above 2 .5 mmol/l and a low concentration of LDL almost exclusively in a small and dense form. These findings indicate that a predominance of small, dense LDL and hyper-apoprotein B do not always co-exist in free-living groups. Moreo ver, if coronary risk increases with increasing LDL particle number, these results imply that the risk arising from a predominance of small, dense LDL may actually be reduced in certain cases when plasma triacylglycerol excee ds 2.5 mmol/l.