Changes with ageing in total dolichol and dolichol fractions in Drosophila.

Since it is unclear how the concentration of dolichol fractions change with ageing in mammals, we have examined the changes in another organism, Drosophila. Dolichol extracted from Drosophila melanogaster was found to consist of three fractions composed of 15, 16 and 17 isoprene units. The total dolichol content of female flies maintained at 25 degrees C increased with ageing between 0 and 64 days of adult age but the change was not significant. The total dolichol content of male flies decreased with ageing but the decrease was not significant. The relative amounts of the three different dolichol fractions in both male and female flies also failed to show any significant ageing-related change. The greatest amount of dolichol was found in the 16 isoprene unit fraction representing 67.2% of the total dolichol in male flies and 65.4% in female flies. Increased dietary dolichol had little or no influence on the life span of Drosophila when given either during the developmental or adult stages.

Transfer of liposomes containing dolichol into isolated hepatocytes.

Isolated rat hepatocytes were preincubated with egg lecithin liposomes containing [3H]dolichol and [3H]dolichyl ester, and the intracellular levels and distributions of these lipids were subsequently determined after incubation in a liposome-free medium. [3H]Dolichol was recovered initially mainly in microsomes, and no increase with time in the low level of this compound in the mitochondrial/lysosomal fraction could be observed. A small portion of the labeled dolichol was esterified in the endoplasmic reticulum and transferred to the lysosome-containing fraction. [3H]Dolichyl linoleate was initially localized in microsomes and supernatant, but later accumulated in the mitochondria/lysosomes. Dolichyl linoleate was found in the membrane of microsomes, in the membrane and lumen of lysosomes, and in the soluble cytoplasm. Exogenous dolichol recovered in microsomes was not phosphorylated to any significant extent. Liposomal phosphatidylcholine also showed preferential accumulation in microsomes after incubation with hepatocytes. These results indicate that exogenous or endogenously formed dolichyl esters are transferred from the endoplasmic reticulum to lysosomes, probably through the cytoplasm. It appears that fatty acids play a role in targeting these lipids to their intracellular locations.

Uptake and subcellular distribution of intraventricularly injected [1-3H]dolichol in rat brain.

The uptake of C95[1-3H]dolichol in the form of liposomes into rat brain after the intracerebral and intraperitoneal injection was investigated. Efficient, time-dependent uptake of dolichol into the brain was observed exclusively after the intraventricular injection. Within 24 h after the injection about 10% of the applied dolichol was found in the brain and 1.5% in liver. The distribution of dolichol in various parts of rat brain decreased in the order: cerebellum greater than midbrain greater than grey matter and brain stem greater than white matter. Seven days after the injection total radioactivity in the brain decreased and concomitantly a significant increase was observed in blood circulating and liver of the rat. The highest activity was found in grey matter and it remained a few times higher in comparison with that in white matter. About 80% of the dolichol taken up by the brain membrane was recovered in the following subcellular fractions: crude nuclear fraction greater than microsomes greater than mitochondria greater than synaptosomes greater than myelin. These results demonstrate for the first time that dolichol is actively taken up by the brain membrane exclusively after intraventricular injection of dolichol-phosphatidylcholine in the form of liposomes; this method may be useful in studies on the role of dolichol in brain function.

Uptake and modification of dietary polyprenols and dolichols in rat liver.

Short and long dolichols and polyprenols in free form or esterified with fatty acids were incorporated into liposomes and administered to rats through a gastric tube. The free alcohols were taken up by the liver to different extents. While uptake in other organs was less, it also involved the fatty acid esters. The use of systems other than liposomes did not increase the efficiency of uptake. Most of the administered lipids were recovered in the lysosomes. Exogenous dolichols and polyprenols were both partly esterified in the liver and, to some extent, also phosphorylated; a portion of the polyprenols was also alpha-saturated. These results indicate that various polyisoprenes are taken up, to a small extent, from the diet by tissues under normal conditions and in liver these dietary lipids undergo terminal modifications.

Intestinal absorption of dolichol from emulsions and liposomes in rats.

The intestinal absorption of dolichol from various dosage forms was investigated using the intestinal loop and everted sac methods in the rat. The in situ loop experiments showed that the absorption of dolichol from a triglyceride emulsion was dependent on the chain-length of the triglyceride; the absorption from a tri-n-butyrin emulsion in 1 h was 18.0% of the dose; and the absorption from an HCO-60 suspension was 4.3%. The liposomal preparation enhanced the absorption up to 39.1% of the dose. In in vitro experiments, 25.0% and 13.2% of dolichol were taken up by everted sacs of the jejunum and the ileum, respectively. On the other hand, phospholipids composing liposomes were not absorbed under these conditions. The above results suggest that the absorption mechanism from liposomal preparations may be as follows: dolichol is released from the liposomes into the aqueous phase adjacent to the surface of the intestine and is subsequently partitioned into the intestinal tissue.