Altered high density lipoprotein metabolism in patients with myeloproliferative disorders and hypocholesterolemia

Patients with the myeloproliferative disorders (MPD), myeloid metaplasia and polycythemia vera, have significantly reduced concentrations of plasma low density (LDL) and high density (HDL) lipoprotein cholesterol (C). We have previously demonstrated that increased catabolism of LDL was associated with the low LDL-C levels. In the present study we have determined the rates of synthesis and removal of apolipoprotein A-1 (apoA-1) in five subjects with MPD who had markedly reduced HDL-C concentrations (18.2 +/- 4.1 mg/dL). Their results were compared to those obtained in six subjects with hypertriglyceridemia (HTG) with similar levels of HDL-C (19.7 +/- 3.9 mg/dL) and five subjects with normal (N) HDL-C concentrations (49.6 +/- 7.4 mg/dL). The results demonstrated that the fractional catabolic rate (FCR) for apoA-1 was significantly increased in the MPD group v N (0.38 +/- 0.15 v 0.21 +/- 0.03 day-1, P less than 0.05) while the synthetic rates for apoA-1 were similar in the two groups. The FCR for apoA-1 in the HTG group (0.36 +/- 0.07 day-1) was nearly identical to that in the MPD group, in spite of the large differences in their plasma triglyceride concentrations (406.2 +/- 217.9 v 117.0 +/- 29.8 mg/dL, P less than 0.05). Compositional studies indicated that the HTG group had very cholesterol depleted HDL while the HDL particles in the MPD group appeared to have a normal cholesterol content. These studies indicate that subjects with MPD have striking increases in HDL catabolism that can account fully for their markedly reduced levels of HDL cholesterol. The pathophysiologic mechanisms that are the basis of this alteration remain to be determined.