Association between measured or calculated small dense low‐density lipoprotein cholesterol and oxidized low‐density lipoprotein in subjects with or without type 2 diabetes mellitus

BACKGROUND: Small dense low‐density lipoprotein (sdLDL) possesses atherogenic potential and is predicted to be susceptible to atherogenic modifications, which further increases its atherogenicity. However, studies on the association between measured or estimated sdLDL cholesterol (sdLDL‐C) levels and atherogenic modification in diverse population groups are lacking. METHODS: Surplus serum samples were collected from male subjects with type 2 diabetes mellitus (DM) under treatment (n = 300) and without DM (non‐DM; n = 150). sdLDL and oxidized LDL (oxLDL) levels were measured using the Lipoprint LDL subfractions kit (Quantimetrix Corporation) and the Mercodia oxidized LDL competitive enzyme‐linked immunosorbent assay kit (Mercodia), respectively. The estimated sdLDL‐Cs were calculated from two relevant equations. The effects of sdLDL‐C on oxLDL were assessed using multiple linear regression (MLR) models. RESULTS: The mean (±SD) of measured sdLDL‐C and oxLDL concentrations were 11.8 ± 10.0 mg/dl and 53.4 ± 14.2 U/L in the non‐DM group and 0.20 ± 0.81 mg/dl and 46.0 ± 15.3 U/L in the DM group, respectively. The effects of measured sdLDL‐Cs were significant (p = 0.031), whereas those of estimated sdLDL‐Cs were not (p = 0.060, p = 0.116) in the non‐DM group in the MLR models. The effects of sdLDL‐Cs in the DM group were not significant. CONCLUSION: In the general population, high level of sdLDL‐C appeared to be associated with high level of oxLDL. The equation for estimating sdLDL‐C developed from a general population should be applied with caution to a special population, such as patients with DM on treatment.