Blood dolichols in a patient with abetalipoproteinaemia.

Dolichol and dolichyl derivatives have an important function as glycosyl carriers in the assembly of the N-asparaginyl-linked oligosaccharide core region of glycoproteins. Dolichols are synthesized through the cholesterol biosynthesis pathways in all mammalian organs and are present in all tissues, and are also associated with lipoproteins in the blood circulation. However, the origin and metabolic pathway of blood dolichols remain unknown. Abetalipoproteinaemia is a disorder of the secretion of very low-density lipoprotein (VLDL) from the liver and of chylomicrons from the intestine into the blood circulation. Therefore, examination of blood dolichols in this disorder may provide valuable information on their origin and metabolic pathway. Dolichols were exclusively associated with the high-density lipoprotein (HDL) fraction (80.7 +/- 6.3% of total dolichols) in control human blood. Serum from a patient also contained dolichols in the HDL fraction (82.8% of total dolichols). The total amount of dolichols was higher in the patient (207.0 ng/mL) than in the controls (106.2 +/- 22.7 ng/mL, n = 14). The compositions of dolichols were very similar to each other. These results indicated that, at least in the patient with abetalipoproteinaemia, the HDL-associated dolichols were possibly derived from the liver not through other lipoproteins but through dolichol transfer protein, or were possibly taken up and carried by HDL from peripheral tissues.