Serum concentration of small dense low-density lipoprotein-cholesterol during oral glucose tolerance test and oral fat tolerance test

BackgroundSmall dense low-density lipoprotein (sdLDL) is well known as an atherogenic lipoprotein. We developed a new assay to measure serum concentration of sdLDL-cholesterol (sdLDLC). Using this assay, we reported a unique circadian rhythm of sdLDLC. We determined whether a glucose intake and/or a fat intake affects on serum sdLDLC concentration and determined the modulators of serum sdLDLC concentration.MethodsTen healthy volunteers were recruited to perform both a 75 g oral glucose tolerance test (OGTT) and an oral fat tolerance test (OFTT) to determine the effects of glucose and fat ingestion separately. Blood was measured for sdLDLC concentration and other valuables.ResultsSerum concentrations of total cholesterol, LDLC, remnant-like particles-cholesterol (RLPC), and apolipoprotein B significantly decreased during OGTT (p < 0.05). SdLDLC also decreased and was a minimum at 2 h after glucose ingestion and increased to the baseline by 3 h. The sdLDLC decrease was seen while serum insulin level was high. The change of sdLDLC during OGTT had greater inverse correlationship with that of serum insulin level (r = − 0.74, p < 0.01) than that of plasma glucose level (r = − 0.69, p = 0.04). After fat ingestion, triglyceride and RLPC increased remarkably (p < 0.01) but sdLDLC, LDLC, apolipoprotein B, and insulin did not change significantly.ConclusionsSerum concentration of sdLDLC was not affected by a fat intake but by a glucose intake. The change of sdLDLC was associated by that of serum insulin level, suggesting that insulin can be one of the key modulator of serum sdLDLC level as well as LDL metabolism.