Prevalence of plasma small dense LDL is increased in obesity in a Thai population.

Sirikul Kulanuwat,Ian G Davies,Rungsunn Tungtrongchitr,David Billington

doi:10.1186/s12944-015-0034-1

Abstract

BackgroundPlasma low density lipoprotein (LDL) particles vary in size, density, electrical charge and chemical composition. An increased presence of small dense LDL (sdLDL), along with raised triglyceride concentrations and decreased high density lipoprotein (HDL) cholesterol concentrations is commonly known as the atherogenic triad and has been observed in some cases of obesity, principally in Europe and America. This study examines the prevalence of sdLDL in the plasma of an obese (BMI ≥ 25 kg/m2) Thai population.MethodsPlasma from fasted obese (n = 48) and non-obese (n = 16) Thai participants was subjected to density gradient ultracentrifugation in iodixanol to separate lipoproteins. Gradients were unloaded top-to-bottom into 20 fractions which were assayed for cholesterol, triglyceride, apo B and apo A-1 to identify lipoprotein types and subtypes.ResultsLDL cholesterol was subfractionated into LDL I + II (fractions 3–6, ρ = 1.021-1.033 g/ml) which was considered to represent large buoyant LDL (lbLDL), LDL III (fractions 7–9, ρ = 1.036-1.039 g/ml) which was considered to represent sdLDL, and, LDL IV (fractions 10–12, ρ = 1.044-1.051 g/ml) which was considered to represent very sdLDL. Concentrations of LDL III and IV were increased by 15-20% in obese participants whilst that of LDL I + II was concomitantly decreased by 10%. This was accompanied by a 50% increase in plasma triglyceride concentrations and 15% decrease in HDL cholesterol concentrations. Only 3/16 (19%) non-obese participants had a pattern B LDL cholesterol profile (peak density of >1.033 g/ml), whilst 28/48 (58%) obese participants were pattern B. When expressed as a fraction of the LDL concentration, total sdLDL (i.e. LDL III + IV) showed highly significant correlations to plasma triglyceride concentrations and the triglyceride/HDL cholesterol ratio.ConclusionsThe prevalence of sdLDL is increased in obesity in a Thai population such that they demonstrate a similar atherogenic triad to that previously observed in European and American populations.

Highlights

Plasma low density lipoprotein (LDL) particles vary in size, density, electrical charge and chemical composition
Both obese and non-obese participants had similar ages and plasma total cholesterol concentrations were similar in both groups whilst plasma triglyceride concentrations were significantly increased by approximately 50% in obese compared to non-obese participants (Table 1)
Under the conditions used in this study, LDL was identified as a broad peak of cholesterol (Figure 1a) and triglyceride (Figure 1b) between fractions 3–12 at a density of 1.021-1.051 g/ml

Summary

Introduction

Plasma low density lipoprotein (LDL) particles vary in size, density, electrical charge and chemical composition. This study examines the prevalence of sdLDL in the plasma of an obese (BMI ≥ 25 kg/m2) Thai population. Density gradient ultracentrifugation in high concentrations of salt (usually KBr) was originally used to identify and quantitate LDL subclasses in plasma. Using this method, four LDL subclasses were identified in the density range 1.019-1.060 g/ml; namely LDL-I (large buoyant, 1.019-1.023 g/ml), LDL-II (intermediate, 1.0241.034 g/ml), LDL-III (small dense, 1.034-1.044 g/ml) and LDL-IV (very small dense, 1.044-1.060 g/ml) [11,12]. Krauss and colleagues have simplified this to define two LDL phenotypes; so-called pattern A individuals

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Conclusion