Fasting
hypertriglyceridemia relates with
high-density lipoprotein (
HDL) cholesterol, but it is not known whether low
HDL cholesterol is associated with disturbances of
chylomicron metabolism. To clarify this issue this metabolism was studied in subjects with low
HDL cholesterol together with vascular reactivity and evaluation of no-flush
niacin treatment. Thirty men with HDL < 1.04 mmol/L and no other risk factors for
coronary artery disease (CAD) and 11 normal controls with HDL > 1.04 mmol/L were studied. The plasma kinetics of a
chylomicron-like
emulsion labeled with 14C-cholesterol
oleate (CO) and 3H-triolein (TG) was determined and the fractional clearance rate (FCR, min(-1)) was calculated. Vascular reactivity was evaluated using high-resolution ultrasonography. CO FCR was markedly reduced in the low HDL group compared to controls (3.6 x 10(-3) +/- 5.1 x 10(-3) min(-1) versus 12.2 x 10(-3) +/- 8.4 x 10(-3) min(-1), p < 0.001) but TG FCR was similar. Flow-mediated dilation (FMD) was diminished in low HDL (7.4 +/- 4.1 versus 12.8 +/- 4.6%, p < 0.001), whereas
nitrate-mediated dilation was similar. Twenty-two low HDL subjects with reduced FMD were randomized into two groups, one given 1.5 g/day
niacin and a placebo group. After 3-month treatment, plasma
lipids and
chylomicron kinetics were not changed by
niacin treatment but FMD improved to normal values (5.44 +/- 1.89 to 11.13 +/- 3.4%, p < 0.01). In conclusion, isolated low
HDL cholesterol subjects may also bear
chylomicron remnant accumulation and endothelial dysfunction, which highlight the importance of their preventive treatment.