Distribution, metabolism and function of dolichol and polyprenols

Characterization of dolichyl diphosphate phosphatase from rat liver

Dolichyl diphosphate phosphatase (DolPPase) has been characterized in rat liver. Subcellular distribution studies indicate that the enzyme is localized in the endoplasmic reticulum. The in vitro enzymatic activity is stimulated by EDTA, due to release of inhibition by trivalent cations found in the assay tubes. All di- and trivalent cations tested were inhibitory, with the trivalent ions Al3+ and Fe3+ showing greater than 70% inhibition at a concentration of 10 microM. The assay requires the presence of a detergent for optimal activity, with Triton X-100 giving maximum activity at 0.1%. The substrate specificity of DolPPase toward polyprenyl diphosphates has been determined and indicates that there is little preference of the enzyme for substrates of different chain length, and either stereochemical orientation or degree of saturation of the alpha-isoprene unit. Km values of 11-14 microM were obtained for all substrates tested. Preliminary studies on the transmembrane topology of the DolPPase using latency assays, indicate that the active site of the enzyme may reside on the cytoplasmic face of the endoplasmic reticulum.

Membrane properties of dolichol in different age groups of mice

Dolichol content and the effects of dolichol in vitro on synaptic plasma membrane (SPM) structure of different age groups of C57BL/6NNIA mice were examined. SPM of aged mice had higher amounts of dolichol as compared to younger animals. Age differences also were observed in dolichol isoprenologue distribution. In older animals, dolichol isoprenologue chain length was shifted towards shorter chain length values. The structure of SPM was determined by differential polarized phase fluorometry of 1,6-diphenyl-1,3,5-hexatriene (DPH). The SPM of old mice were more rigid, as indicated by higher limiting anisotropy, than those of young mice. Dolichol administered in vitro to SPM fluidized the membranes. However, dolichol administered in vitro fluidized SPM of younger mice significantly more than SPM of aged mice. The functional role of increased dolichol content in aged individuals is not known. Dolichol may act to regulate membrane fluidity of aged animals.

Age-associated changes in dolichol and dolichyl phosphate metabolism in the kidneys and liver of mice

The total amounts of cholesterol, dolichol and dolichyl phosphate (Dol-P) in kidneys and liver from 1- and 24-month-old mice were measured after saponification of the tissues. The cholesterol content of kidneys decreased by about 4-fold per g of tissue between the two ages, while the amount of cholesterol/g liver remained constant. The dolichol content of both tissues increased by about 2-fold. The amount of Dol-P in kidneys increased by 7-fold over 23 months, while the concentration in liver decreased some 6-fold. Metabolic labelling experiments using tritiated water demonstrated that the rate of synthesis of total dolichol (dolichol + Dol-P) in the kidneys did not change as a function of age. However, the kidneys of young mice incorporated 3-fold more radioactivity into dolichol than Dol-P, whereas this distribution was reversed in old mice. In liver, the rate of dolichol synthesis decreased 2-fold over 23 months. It was not possible to compare the rates of Dol-P biosynthesis between ages as Dol-P was undetectable in liver of old mice. The relative abundance of the 19 isoprene unit homologs of both dolichol and Dol-P decreased approx. 5% while the 17 isoprene unit homologs increased by a similar amount in both tissues of the old mice.

Effect of alcohol on blood dolichol concentration

Serum dolichol levels were studied in 95 active alcoholics and 16 abstinent alcoholics (at the time of blood sampling) and compared to those of 41 social drinkers. Active alcoholics had a significantly higher mean serum dolichol concentration (182.7 +/- 5.1 ng/ml, p less than 0.001 than either abstinent alcoholics (138.7 +/- 5.4 ng/ml) or social drinkers (142.1 +/- 4.1 ng/ml). During weekend (48 hr) heavy drinking (5.5 g of alcohol per kg b.w.) no significant changes were seen in mean serum dolichol concentrations in 10 healthy, nonalcoholic volunteers. Neither did moderate drinking for 10 days (60 g of alcohol daily)--preceded and followed by a period of abstinence--produce any significant changes in serum dolichol levels in 10 nonalcoholic subjects. During detoxification treatment of 12 alcoholics, mean serum dolichol concentration stayed constant for the first 7 days; on entering treatment it was 227.7 +/- 15.0 ng/ml, on the 3rd day 238.5 +/- 15.9 ng/ml, and on the 7th day of treatment 222.6 +/- 18.6 ng/ml. Our results show that as well as increasing urinary dolichol excretion, chronic alcohol abuse also produces increased serum dolichol concentrations. However, contrary to urinary dolichols, serum dolichol levels do not react significantly to heavy drinking lasting for 48 hr in nonalcoholic volunteers. Furthermore in alcoholics increased serum dolichol concentrations do not decrease as rapidly during abstinence as urinary dolichol concentrations do.

Significant increases in urinary dolichol levels in bacterial infections, malignancies and pregnancy but not in other clinical conditions

The effect of different clinical conditions on urinary dolichols was studied in 219 hospital patients and in 24 pregnant women. Significantly increased urinary dolichol levels were found in patients with severe bacterial infections (mean +/- SEM, 37.5 +/- 8.0 micrograms/mmol creatinine, P less than 0.001), in patients with haematological or metastatic (23.3. +/- 5.1, P less than 0.05) as well as localised (15.4 +/- 1.8, P less than 0.01) malignancies and in pregnant women (22.2 +/- 1.8, P less than 0.001) as compared to healthy controls (6.6 +/- 0.4). These results show that urinary excretion of dolichols may be increased, not only in alcoholics and patients with some rare neurodegenerative storage diseases, but also in patients suffering from various other diseases.

Increased dolichol content in glucocorticoid-sensitive human T-cell leukemia line grown in the presence of dexamethasone

Two cell lines, derived from human T-cell acute leukemia, one glucocorticoid sensitive (CEM-C7) and the other glucocorticoid resistant (CEM-C1) were grown in the presence of 1 x 10-7 M dexamethasone and were analyzed for their dolichol content. After 24 hrs of incubation, dolichols became significantly elevated in the sensitive but not in the resistant line. Lovastatin, the specific inhibitor of cholesterol synthesis did not affect dolichol levels in either of the two cell lines. The results raise the possibility that dolichol accumulation might be involved in the early stages of the glucocorticoid-induced apoptosis (directed cell killing).

Conditions for quantitation of dolichyl phosphate, dolichol, ubiquinone and cholesterol by HPLC

Conditions for the isolation and quantitation of dolichyl phosphate, dolichol, cholesterol, and ubiquinone by reversed phase high performance liquid chromatography were investigated. A simple and fast sample preparation procedure using prepacked mini columns was employed. The UV spectra of the fractions obtained were examined and, in the case of dolichol compounds, the maximum absorbance around 205 nm was shown to be linearly dependent on the number of double bonds present in the isoprenolog. The analytical procedure described shows a very broad range of linearity (five orders of magnitude) and detects single dolichyl phosphate isoprenologs in amounts as small as 0.1 ng. The lowest overall recovery, that for dolichyl phosphate, is 77%. Use of isoprenolog 23 and ergosterol as internal standards reduced the variation in the method to 2.5, 4.0 and 5.5% for cholesterol, dolichyl phosphate and dolichol, respectively. The method described was employed to study the lipid composition of rat organs and biological variations in these compositions.

Effects of moderate drinking and alcohol abstinence on urinary dolichol levels

Urinary dolichols were studied during a period of 10 days of moderate drinking (60 g of alcohol daily), preceded and followed by a period of abstinence, in 10 healthy volunteers. No significant changes were observed in dolichol levels during this time. Thus, moderate alcohol consumption does not affect urinary dolichols. Furthermore, to establish the time of abstinence needed for elevated urinary dolichol levels to return to normal, 17 alcoholic patients entering a detoxification unit and with initially increased urinary dolichols, were followed for seven days. Mean urinary dolichol level, which was clearly elevated in the beginning of detoxification, returned to normal by the 5th day of the treatment. Half-life decay for increased urinary dolichols was found to be about 3 days.

Extraction and quantitation of dolichol and dolichyl phosphate in soybean embryo tissue

A procedure for the quantitative extraction of both dolichol and dolichyl phosphate (Dol-P) in plant tissue (soybean embryos) into diethyl ether from an alkaline saponification mixture is described. A complete and quantitative separation of total dolichol and total Dol-P is then obtained based on their respective solubilities in diethyl ether and water. After separation dolichol and Dol-P can both be analyzed and quantitated directly by reverse-phase HPLC on C18 columns without additional purification. The two major homologs of dolichol and Dol-P are those with 17 and 18 isoprene units. The total dolichol and total Dol-P contents of dry embryos were 96.3 +/- 0.8 and 5.3 +/- 0.1 micrograms/g, respectively. The post-HPLC recoveries for dolichol and Dol-P were 101 +/- 2 and 84 +/- 3% respectively, using [1-14C]dolichol and Dol-P containing 20 isoprene units as recovery standards. Dol-P estimations could be carried out on material equivalent to as little as 65 mg embryo tissue.