Separation, quantitation and distribution of dolichol and dolichyl phosphate in rat and human tissues

Two procedures for quantitative determination of dolichol were studied and these were applied to analyze tissue and subcellular distribution. In the first procedure the dolichols were oxidized with Cr2O3 and reduced with NaB3H4. The radioactivity in the individual dolichols was measured using reversed-phase thin-layer chromatography. In the second procedure, dolichols were analyzed by high-pressure liquid chromatography. For determination of dolichyl phosphates the lipid extract was subjected to acid and alkaline hydrolysis, and after hydrolysis with acid phosphatase the distribution was determined by high-pressure liquid chromatography. Recovery was monitored by the addition of dolichol D15 and D23 phosphate to the homogenate. Rat spleen had the highest dolichol content (114 micrograms/g) followed by lower content in rat liver and brain. The distribution pattern was similar in all organs, with 18 and 19 isoprene residues as dominating components. Human organs contain considerably higher concentrations of dolichol, with the 19 and 20 isoprene residues as the main components. In rat liver, outer mitochondrial and Golgi membranes, lysosomes and plasma membranes contain considerable amounts of dolichol. A drastic increase in dolichol content was observed in rat liver hyperplastic nodules while human liver cirrhosis and hepatocarcinoma showed a marked decrease in dolichol. In the latter case, the distribution pattern was also changed. Of the total amount of dolichol present in the tissues, 2% was phosphorylated in human liver, 10% in human testis and 18% in rat liver. In rat liver mitochondria and in microsomes 4 and 31%, respectively, of the polyprenols were in activated form. The results demonstrated that dolichyl phosphate and dolichol concentrations were regulated by different mechanisms and that the two forms possessed an independent distribution.     

Frog liver dolichols: separation and quantitative determination related to seasonality

1. The liver of female frogs shows a significantly higher dolichol content in May (134 micrograms/g) than in November (90 micrograms/g). The male frog liver (134 micrograms/g May; 119 micrograms/g November) does not show any significant change. 2. The rat liver does not show any significant change in dolichol content from May to November (30 micrograms/g). 3. The dolichyl-phosphate level was the same in male and female frog livers and in the rat liver. 4. Data is given of the distribution of dolichols according to the number of their isoprene residues.     

The structure of brain polyisoprenols

Abstract— Long-chain polyisoprenols were isolated from brain in yields of 10-15 mg/kg tissue wet weight. On thin-layer chromatography, migrations were identical for brain polyisoprenols and pig liver dolichol which had been isolated as reference material. The IR, ¹H NMR and ¹³C (FT) NMR spectra of calf brain polyisoprenols were consistent with a molecular structure which had a saturated isoprenol unit followed by approximately 19 unsaturated isoprene units. About 3-4 isoprene units possessed trans double bonds. Using reversed phase thin-layer chromatography and pig liver dolichol as a reference, it was estimated that calf brain polyisoprenols had major structures of C95, C100 and C105 while rat brain polyisoprenols contained C90 and C95 as the major components. All data indicated that the brain polyisoprenols were very similar, chemically, to pig liver dolichols except for minor differences in molecular weight.     

Effect of alcohol on urinary and blood dolichols.

Alcohol appears to affect dolichol metabolism, as both serum and urinary dolichol concentrations were found to be significantly higher in alcoholics than in social drinkers. Furthermore, acute heavy drinking (5.5 g alcohol/kg body weight during 42 h) increased urinary dolichol excretion significantly, whereas moderate drinking (60 g/day for 10 days) had no effect. Increased urinary dolichol concentrations in alcoholics returned rapidly to normal with a half-life decay of 3 days, whereas increased serum dolichol concentrations did not change during a 7-day observation period. The mechanism behind alcohol-induced alterations in dolichol metabolism remains unclear, but based on our results, it seems likely that serum and urinary dolichols are regulated independently from each other.     

On the specificity of dolichol kinase and DolPMan synthase towards isoprenoid alcohols of different chain length in rat liver microsomal membrane.

1. A wide range of dolichols differing in the length of hydrocarbon chain (from 11 to 32 isoprene residues) were found to be phosphorylated in the presence of CTP in rat liver microsomes. 2. Fully unsaturated polyprenols of the same chain length as dolichols were poor substrates for dolichol kinase at low detergent (Nonidet P-40) concentration. At higher concentration of detergent, both dolichols and polyprenols were equally effective. 3. In the transfer of mannosyl residues from GDPMan, the dolichyl phosphates generated in rat liver microsomes were all good lipid acceptors, while fully unsaturated polyprenyl phosphates were not.     

High levels of brain dolichols in neuronal ceroid-lipofuscinosis and senescence

Dolichols as unesterified alcohols were identified as significant components of lipid extracts from storage cytosomes isolated post-mortem from the brains of patients with the infantile, late infantile, and juvenile types of neuronal ceroid-lipofuscinosis (NCL). Very small amounts of dolichols were present in the corresponding subcellular fractions of non-NCL brains. The nuclear fraction from NCL cerebral cortex contained the highest dolichol content expressed per milligram protein or lipid, whereas the crude mitochondrial fraction was the richest in normal brain. Highly significant elevations of dolichol levels were found in human cerebral cortex of patients with NCL and Alzheimer's disease compared with age-matched controls, but the levels were normal in Pick's disease. In human non-NCL cerebral cortex, dolichols increased from 16 micrograms/g at age 5 to over 200 at age 81. Rat cerebral cortex showed a similar progressive increase in dolichol content with age. The high dolichol values in NCL, Alzheimer's disease, and senescence appears to be related to the increase of lipofuscin in brain. This is the first time a uniform biochemical abnormality has been found in all childhood forms of NCL, but the enzyme defect is still unidentified. It may lie on pathways where dolichols and retinyl compounds are recycled in Golgi membranes and derived organelles during the biosynthesis of glycoproteins.     

Rat testicular dolichols: distribution and accumulation with age

Dolichols, linear isoprenoids essential in the biosynthesis of N-glycosylated glycoproteins, are abundant in testicular tissue. This study investigated the distribution of dolichols among testicular cell and subcellular fractions. In addition, the accumulation of dolichol within the rat testis as a function of age was investigated. Dolichol content expressed either as total dolichol/testicle or as dolichol/mg protein exhibited a marked and continuous increase between 14 and 60 days of age. The 4-, 6-, 9-, and 12-mo-old animals exhibited only minor increases in testicular dolichol content. Mean value for retired breeders was 279 ng dolichol/mg protein. Although previous studies have suggested that dolichol synthesis occurs primarily within the spermatogenic cell, elutriation-purified spermatogenic cell fractions showed very low concentrations of dolichol. Pachytene spermatocyte and round spermatid fractions contained 25.8 and 36.5 ng dolichol/mg protein, respectively. Washed epididymal sperm also had a very low dolichol content (18.8 ng dolichol/mg protein). Recovery studies during elutriation purification of spermatogenic cells showed that the majority of dolichol was contained within the Sertoli-rich tubular fragments. Microsomal fractions isolated from whole testis exhibited a small enrichment (1.6-fold) in dolichol content, whereas Golgi apparatus fractions exhibited a large (12-fold) enrichment over that of the initial homogenate. These studies suggest that, although dolichols may be synthesized within the spermatogenic cell, they accumulate within the Sertoli cell.     

Separation of dolichol and dolichyl-P in microsomal and lysosomal compartments of hepatocytes

The distribution, labeling and interrelationship of microsomal and lysosomal dolichol and dolichyl-P in rat liver was investigated. After membrane induction with phenobarbital, N-nitrosodiethylamine and diethylhexylphthalate, the amount of microsomal and lysosomal dolichols are modulated independently. Liposomal labeled dolichol injected into the portal vein appears only in lysosomes and even after 8 days is still limited to the lysosomes. After in vivo labeling with [3H]mevalonate, high initial labeling of dolichol and dolichyl-P is present in microsomes and the labeling in microsomes is greater than that in lysosomes even after 8 h. The results demonstrate compartmentalization of the intracellular dolichols in hepatocytes. These lipids may have independent roles at different membrane locations.     

Distribution and redox state of ubiquinones in rat and human tissues.

The distribution and redox state of ubiquinone in rat and human tissues have been investigated. A rapid extraction procedure and direct injection onto HPLC were employed. It was found in model experiments that in postmortem tissue neither oxidation nor reduction of ubiquinone occurs. In rat the highest concentrations of ubiquinone-9 were found in the heart, kidney, and liver (130-200 micrograms/g). In brain, spleen, and intestine one-third and in other tissues 10-20% of the total ubiquinone contained 10 isoprene units. In human tissues ubiquinone-10 was also present at highest concentrations in heart, kidney, and liver (60-110 micrograms/g), and in all tissues 2-5% of the total ubiquinone contained 9 isoprene units. High levels of reduction, 70-100%, could be observed in human tissues, with the exception of brain and lung. The extent of reduction displayed a similar pattern in rat, but was generally lower.     

The esterification of dolichol by rat liver microsomes.

The incubation of 1-[3H)dolichols with cell-free preparations from various rat tissues resulted in the formation of a labeled material which possessed the characteristics of synthetic dolichol palmitate. Rat liver microsomes were found to be a good source of the acyltransferase activity, and the properties of the reaction were investigated using microsomal preparations. The reaction did not require ATP, CoA, or Mg2+ and was stimulated by the addition of phosphatidylcholine. The esterification of dolichol appears to be similar to the esterification of retinol. The fact that the esterification of dolichol is not depressed even in the presence of a several-fold excess of retinol is evidence that the two reactions are catalyzed by different enzymes.     

Isolation and characterization of dolichols from Tetrahymena pyriformis

Dolichols of Tetrahymena pyriformis were isolated and characterized by TLC, HPLC and mass spectrometry. Four strains of Tetrahymena were studied and found to have relatively small amounts of dolichol, from 0.26 to 2.60 mg dolichol/kg wet weight. All four strains had approximately the same relative proportions of isoprenologs, dolichol-13 (2%), dolichol-14 (74%), dolichol-15 (23%), and dolichol-16 (less than 1%). Tetrahymena dolichols were found mainly in the mitochondrial subcellular fraction (86%). The pellicle fraction contained 9% and the microsomal fraction, 5% of the remaining dolichol. Free dolichol has also been found in the mitochondrial fraction of four other organisms. We were not able to demonstrate dolichyl esters in these organisms, but their presence is inferred, because reduced yields of dolichol were obtained if the lipid extracts were not saponified prior to HPLC assay.     

Time course of dolichol and dolichyl phosphate during chemical carcinogenesis in rat liver

Hyperplastic liver nodules were induced in rats by administration of an initiator (diethylnitrosamine or 3'-methyl-4-dimethylaminoazobenzene) and/or a promoter (phenobarbital) by the method reported by Tatematsu et al. (1983, Carcinogenesis 4, 381-386). The dolichol content in the liver and liver microsomes of the rats treated with the initiator were approx. 1.5-times higher than that of the control and rats treated with only the promoter. However, the composition of dolichols was not changed. The time course of the dolichyl phosphate concentration in the rat liver treated with both initiator and promoter showed a pattern different from that in the control liver, the initiator-treated liver or the promoter-treated liver. The main component of dolichyl phosphate in liver treated with both the initiator and promoter changed from that with 18 isoprene units to that with 19. It is suggested that the changes in liver dolichols and dolichyl phosphates may be related to the formation of hyperplastic liver nodules.     

The half-lives of dolichol and dolichyl phosphate in rat liver

Rat liver dolichol and dolichyl-P were labeled by injection of [³H]mevalonate into the portal vein and their rates of synthesis and breakdown determined. In the initial phase the radioactivity appeared in -unsaturated polyprenols. Subsequent saturation required 90 min. The half-lives of dolichols in microsomes were between 80 and 118 h, and shorter dolichols had shorter values of T_1/2. The half-lives of dolichols in lysosomes were between 115 and 137 h, while microsomal dolichyl-P exhibited a T_1/2 of 32 h. Injected dolichol was recovered in the lysomes of hepatocytes and exhibited a rate of breakdown which was slower than that of the endogenous compound. These results indicate differences in the catabolism of dolichol at different subcellular locations, as well as differences between the catabolism of dolichol and dolichyl-P.     

Esterification of dolichol in rat liver

In the various subcellular fractions of rat liver 45-75% of the total dolichol was esterified with a fatty acid. The esterification reaction was localized exclusively in the microsomes, and the transferase activity is 3-fold higher in the cation-insensitive smooth microsomes than in other microsomal subfractions. Although fatty acyl-CoAs tested served as substrates, palmitoyl-CoA was the most rapidly utilized. None of the phosphatidylcholine or phosphatidylethanolamine species tested could be utilized to esterify dolichol with a fatty acid, indicating the absence of transacylation. alpha-Saturated dolichols were esterified at a higher rate than their alpha-unsaturated counterparts. Albumin and low concentrations of Triton X-100 activated the esterification reaction, which was not dependent on mono- or divalent cations, ATP, or CoA. The sensitivity of the transferase activity to trypsin indicates localization of the enzyme(s) involved on the outer surface of microsomes (i.e. the cytoplasmic surface of the endoplasmic reticulum), as is also the case for enzymes of dolichol biosynthesis. Transferase activity was detected in all tissues examined but at a much lower level than in liver and testis. The patterns of fatty acids in dolichol esters of different organelles exhibited some specificity. Labeling in vivo indicated that esterification of dolichol may play a role in targeting this lipid from the endoplasmic reticulum to lysosomes.     

Separation of polyprenol and dolichol by monolithic silica capillary column chromatography

We attempted an analysis of naturally occurring polyprenol and dolichol using a monolithic silica capillary column in HPLC. First, the separation of the polyprenol mixture alone was performed using a 250 x 0.2 mm inner diameter (ID) octadecylsilyl (ODS)-monolithic silica capillary column. The resolution of the separation between octadecaprenol (prenol 18) and nonadecaprenol (prenol 19) exceeded by >or=2-fold the level recorded when using a conventional ODS-silica particle-packed column (250 x 4.6 mm ID) under the same elution conditions. Next, the mixture of the prenol type (polyprenol) and dolichol type (dihydropolyprenol) was subjected to this capillary HPLC system, and the separation of each homolog was successfully achieved. During the analysis of polyprenol fraction derived from Eucommia ulmoides leaves, dolichols were found as a single peak, including all-trans-polyprenol and cis-polyprenol previously identified. This sensitive high-resolution system is very useful for the analysis of compounds that are structurally close to polyprenols and dolichols and that have a low content.     

Blood dolichol in lysosomal diseases.

Highly elevated serum total dolichol (free dolichol + dolichyl ester) concentrations have recently been found in two lysosomal storage diseases, aspartylglucosaminuria (AGU) and mannosidosis. The present study demonstrates that the increase of serum dolichol in AGU patients is caused by an increase of serum free dolichol. In 15 patients the mean serum level of free dolichol (227 +/- 16 ng/mL) was 1.9 times higher (p < 0.001) than that in healthy controls (120 +/- 6 ng/mL), while the amounts of dolichol fatty acid esters were similar in the patients and controls (110 +/- 9 vs. 118 +/- 6 ng/mL). In contrast, 10 patients with neuronal ceroid-lipofuscinosis (NCL) (three with infantile, four with juvenile, and three with variant late infantile NCL) had significantly (p < 0.01) lower mean serum levels of both free (79 +/- 5 ng/mL) and total (159 +/- 6 ng/mL) dolichol than age-adjusted healthy controls (free, 100 +/- 6 ng/mL; total, 206 +/- 14 ng/mL). Decreased blood dolichol has not been reported earlier for any other disease. We conclude that the increased serum free dolichol in AGU reflects disturbed lysosomal function and that the decreased free and esterified dolichols in NCLs speak against their presumed primary lysosomal nature.     

Sugar availability modulates polyisoprenoid and phytosterol profiles in Arabidopsis thaliana hairy root culture

Sugars are recognized as signaling molecules regulating the biosynthesis of secondary metabolites in plants. Here, a modulatory effect of sugars on dolichol and phytosterol profiles was noted in the hairy roots of Arabidopsis thaliana. Arabidopsis roots contain a complex dolichol mixture comprising three groups (‘families’) of dolichols differing in the chain-length. These dolichols, especially the longest ones are accompanied by considerable amounts of polyprenols of the same length. The spectrum of polyisoprenoid alcohols, i.e. dolichols and polyprenols, was dependent on sugar type (glucose or sucrose) and its concentration in the medium. Among the long-chain dolichols Dol/Pren-20 (dolichol or prenol molecule composed of 20 isoprene residues) and Dol/Pren-23 were the main components at 0.5% and 2% glucose, respectively. Moreover, the ratio of polyprenols versus respective dolichols was also modulated by sugar in this group of polyisoprenoids, with polyprenols dominating at 3% sucrose and dolichols at 2% glucose. Glucose concentration affected the expression level of genes encoding cis-prenyltransferases, enzymes responsible for elongation of the polyisoprenoid chain. The most abundant phytosterols of the A. thaliana roots, β-sitosterol, stigmasterol and campesterol, were accompanied by corresponding stanols and traces of brassicasterol, stigmast-4,22-dien-3-one and stigmast-4-en-3-one. Similar to the polyisoprenoids, sterol profile responded to the sugar present in the medium, β-sitosterol dominating in roots grown on 3% or lower glucose concentrations and stigmasterol in 3% sucrose. These results indicate an involvement of sugar signaling in the regulation of cis-prenyltransferases and phytosterol pathway enzymes.     

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.     

The influence of dolichol, dolichol esters, and dolichyl phosphate on phospholipid polymorphism and fluidity in model membranes

The effect of dolichols, polyprenols, dolichol esterified with fatty acids, and dolichyl phosphate on the structure and fluidity of model membranes was studied using 31P NMR, small-angle x-ray scattering, differential scanning calorimetry, and freeze-fracture electron microscopy. These studies suggest that dolichol and dolichol derivatives destabilize unsaturated phosphatidylethanolamine containing bilayer structures and promote hexagonal II phase formation; high concentrations of dolichol induce lipid structures characterized by "isotropic" 31P NMR and particulate fracture faces; dolichol, contrary to cholesterol, has no effect on the thermotropic behavior of membranes consisting of phosphatidylcholine, while dolichyl-P incorporation abolishes the transition from the gel to liquid crystalline phase in 1,2-dimyristoyl-sn-glycero-3-phosphocholine; both dolichol and dolichyl-P increase the fatty acid fluidity in phosphatidylethanolamine mixtures; the effect of dolichol on bilayer structure and fluidity is more pronounced with increasing number of isoprene residues; dolichol esters are only soluble to a limited extent in the bilayer and segregates into domains at low concentrations; the results are consistent with a localization of dolichyl-P in which the phosphate group is oriented to the water interphase. The induction of hexagonal II phase by dolichyl-P may elicit the transmembrane movement of glycosylated lipid intermediate.     

Dolichol synthesis in liver slices of streptozotocin diabetic rats

The rate of dolichol synthesis in normal and diabetic liver slices in the presence or absence of insulin was investigated with radiolabeled acetate and mevalonate as substrates. Cholesterol and dolichol syntheses were found low in diabetic rat liver slices when incubated either with 1-14C-acetate or 2-3H-mevalonate. In the presence of insulin, cholesterol and dolichol synthesis in diabetic rat liver slices returned to normal in nine hours when incubated with 1-14C-acetate; however, with 2-3H-mevalonate, synthesis of cholesterol and dolichol normalized in about three hours. These studies show that dolichol synthesis in rat liver slices is dependent on insulin.