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Biomedical subjects

G Dallner

Publications and source records attributed to G Dallner.

At least 55 records · Page 3Linked to original sources
PubMed1995

Coenzymes Q9 and Q10 in skeletal and cardiac muscle in tumour-bearing exercising rats.

Physical exercise increases metabolic rate, and induces both adaptational biogenesis of mitochondria in skeletal muscle and an increase in antioxidant capacity. The onset of experimental anorexia and cachexia can be delayed by voluntary exercise. As skeletal muscle is the main target for cancer cachexia, we determined the levels of coenzymes Q9 and Q10 in skeletal muscle from tumour-bearing exercising rats, and compared them to those of sedentary tumour-bearers and controls. Both tumour-bearing groups had increased levels of coenzymes Q9 and Q10 in the anterior tibial muscle (P < 0.05 for exercised animals). In the soleus muscle, only the tumour-bearing exercising animals demonstrated an increase in the levels of both coenzymes (P < 0.05). In cardiac muscle, the presence of tumour and exercise reduced the levels of coenzymes below that of sedentary controls. Exercise counteracted the anaemia in the tumour-bearing host (P < 0.05). In conclusion, the increase in antioxidant capacity in skeletal muscle indicates a defence mechanism in the tumour-bearing hosts which is augmented by physical exercise.

Animals↗
PubMed1995

ELISA procedures for the quantitation of glutathione transferases in the urine.

The proximal portion of the human kidney tubular system contains the alpha form, while the distal portion contains the pi form of glutathione transferase. These cytoplasmic proteins are released into the urine under pathological conditions, and an ELISA procedure has been developed for their quantitation. Optimal conditions with respect to concentrations of antibody and antigen and incubation times were determined. The procedure developed can detect as little as 0.5 ng enzyme per ml urine, even in the presence of high concentrations of other proteins. No cross reaction between these two isoenzymes or with a number of other proteins in the urine was observed. Antibodies interacted with these antigens in urine samples in the same manner as they interacted with the purified proteins. Storage of samples without loss of antigen required the presence of low concentrations of detergent, such as Tween 20, which both stabilized the enzymes and prevented their adsorption to the walls of the plastic tubes. The results indicate that increased urinary levels of these two enzyme proteins, as determined by the ELISA procedure, are useful markers for tubular damage.

Animals↗
PubMed1995

Changes in the levels of dolichol and dolichyl phosphate in a murine model of Niemann-Pick's type C disease.

The distributions of mevalonate pathway lipids in various organs of a mouse strain used as a model for Niemann-Pick's type C disease were analyzed. Extensive accumulation of cholesterol was observed in all tissues with the exception of the brain, where the content of this lipid was decreased. The changes in total dolichol contents of most organs varied from a 50% decrease in the lung to a twofold increase in kidney and heart. There was relative enrichment of longer-chain dolichols, but no increase in the relative amount of alpha-unsaturated polyprenols was observed. The levels of dolichyl phosphate in all organs were increased, and most of this lipid was associated with bound oligosaccharides or proteins. Ubiquinone levels were largely unchanged. Subfractionation studies revealed that heavy and light lysosomes exhibited a 10-fold increase in cholesterol level, the amount of dolichol was decreased in lysosomes and increased in microsomes, and there was an increase in the dolichyl phosphate levels of all three of these subfractions. These results indicate that in diseased mice cholesterol accumulation in various organs is paralleled by an increase in the dolichyl phosphate concentration, whereas dolichol transport from the endoplasmic reticulum to lysosomes is inhibited.

Animals↗
PubMed1995

Distribution of branch point prenyltransferases in regions of bovine brain.

Bovine brains contain large amounts of isoprenoid compounds and the enzymes involved in their biosynthesis were investigated. Ten different regions were dissected from fresh bovine brains and, in addition, fractions from cerebellum, spinal cord, and hypophysis were obtained. The cholesterol concentration was found to be approximately 8 mg/g in the cortex regions and three times higher in the pons, medulla oblongata, and white matter. Dolichol concentration varied between 8 and 40 micrograms/g in the different tissues, and ubiquinone was found at a lower level, which varied between 3 and 25 micrograms/g. Farnesylpyrophosphate synthase activity in cytosolic fractions from various regions exhibited only a twofold variation, whereas geranylgeranyl pyrophosphate synthase displayed larger differences, being particularly rich in the pons, medulla oblongata, white matter, and spinal cord. Squalene synthase activity was lowest in the thalamus and threefold higher in the pons. Determination of specific activity based on cholesterol content revealed that enzyme activities in various regions are not related to the actual lipid amount present. Both cis- and trans-prenyltransferases exhibited similarities in their regional distribution showing up to 20-fold differences in activity. Thus, it appears that the mevalonate pathway lipids and the various branch point enzymes involved in their syntheses vary greatly in different brain regions and are subjected to separate regulation.

Animals↗
PubMed1995

Enzymes of the mevalonate pathway in rat liver nodules induced by 2-acetylaminofluorene treatment.

Certain enzymes of the mevalonate pathway have been investigated in persistent liver nodules induced in the rat by 2-acetylaminofluorene. In these nodules the dolichol level was increased 5-fold, the ubiquinone-9 content elevated 6-fold and the amount of cholesterol unchanged. Microsomal beta-hydroxy-beta-methylglutaryl-coenzyme A reductase activity was greatly increased compared to control liver tissue, which was also the case for the cytosolic farnesyl pyrophosphate synthase. A significant elevation of all-transgeranylgeranyl pyrophosphate synthase activity in the cytosol was also observed. The branch-point enzyme of microsomal dolichol synthesis, i.e. cis-prenyltransferase, was decreased in the nodules; whereas the activity of squalene synthase, the terminal regulating enzyme of cholesterol synthesis, remained unchanged. The dolichol species in nodular tissue were redistributed towards the longer chain length species. One factor regulating the chain length of the polyisoprene products formed in vitro was shown to be the ratio of the concentrations of isopentenyl pyrophosphate:farnesyl pyrophosphate employed. Other regulatory factors in the terminal steps of this biosynthetic pathway appear to determine the amounts and nature of the final isoprenoid compounds formed in vivo. In contrast to the microsomal trans-prenyltransferase activity, which was unchanged, the activity of nonaprenyl-4-hydroxybenzoate transferase, an enzyme participating in ubiquinone synthesis, was greatly elevated. The alterations observed in the activities of enzymes in the mevalonate pathway can at least partially explain the increased levels of dolichol and ubiquinone and the unchanged level of cholesterol found in liver nodules. It is reasonable to propose that this modified mevalonate metabolism will render nodular cells resistant to certain toxic factors and prone to cell proliferation.

2-Acetylaminofluorene↗
PubMed1995

Uptake of dietary coenzyme Q supplement is limited in rats.

Coenzyme Q is an important mitochondrial redox component and the only endogenously produced lipid-soluble antioxidant. Its tissue concentration decreases with aging and in a number of diseases; dietary supplementation of this lipid would fulfill important functions by counteracting coenzyme Q depletion. To investigate possible uptake, rats were administered 12 mumol coenzyme Q10/100 g body wt once daily by gastric intubation. The appearance of coenzyme Q10 in various tissues and blood after 6 h, 4 d or 8 d was studied. The control group of rats received rapeseed-soybean oil (the vehicle in the experimental group). Lipids were extracted with petroleum ethermethanol, and the reduced and oxidized forms of coenzyme Q9 and Q10 were separated and quantified by reversed-phase HPLC. In the plasma, the total coenzyme Q concentration was doubled after 4 d of treatment. Coenzyme Q10 was also recovered in liver homogenates, where, as in the plasma, it was largely in the reduced form. Uptake into the spleen could be to a large extent accounted for by the blood content of this organ. No dietary coenzyme Q10 was recovered in the heart or kidney. The uptake in the whole body was 2-3% of the total dose. Coenzyme Q10 found in the liver was located mainly in the lysosomes. Dietary coenzyme Q10 did not influence the endogenous biosynthesis of coenzyme Q9. This is in contrast to dietary cholesterol, which down-regulates cholesterol biosynthesis. The dietary coenzyme Q10 level in the plasma decreased to approximately 50% after 4 d. These results suggest that dietary coenzyme Q10 may play a role primarily in the blood and that no appreciable uptake occurs into tissues.

Animals↗
PubMed1994

Effect of squalestatin 1 on the biosynthesis of the mevalonate pathway lipids.

The effects of squalestatin 1 on rat brain and liver homogenates and on Chinese hamster ovary tissue culture cells have been investigated. This compound effectively inhibits squalene biosynthesis in a highly selective manner. Cytoplasmic farnesyl pyrophosphate and geranylgeranyl pyrophosphate synthases are not affected, which is also the case for microsomal cis-prenyltransferase. In tissue culture cells, squalestatin 1 inhibits cholesterol biosynthesis completely, but does not alter dolichol synthesis or protein isoprenylation to a great extent. Incorporation of [3H]mevalonate into ubiquinone-9 and -10 increases 3-4-fold, probably as a result of increased synthesis of this lipid. Squalestatin 1 appears not only to be an effective inhibitor of cholesterol biosynthesis, but also to be more specific than other inhibitors used earlier in various in vitro and in vivo systems.

Animals↗
PubMed1994

The endoplasmic reticulum-Golgi system is a major site of plastoquinone synthesis in spinach leaves.

Plastoquinone biosynthesis was recently found to be enriched in the microsomal fraction of spinach leaves. Since it is generally assumed that this lipid may predominantly be synthesized in the chloroplast envelope we have prepared total microsomes, containing both endoplasmic reticulum and Golgi membranes, and chloroplast envelopes. Marker enzymes and lipid content showed no significant cross-contamination. Nonaprenyl-2-methylquinol transferase, participating in plastoquinone synthesis, was found in the microsomes but was absent from the chloroplast envelopes and thylakoid membranes. Nonaprenyl-4-hydroxybenzoate transferase activity, an enzyme of ubiquinone biosynthetic system, in microsomes exceeded more than 10 times that found in chloroplast envelopes. The result indicates that in plants plastoquinone is synthesized in the endoplasmic reticulum-Golgi system and transported to the chloroplasts.

Alkyl and Aryl Transferases↗
PubMed1994

Age-dependent changes in rat liver prenyltransferases.

Mevalonate pathway lipids including cholesterol, ubiquinone and dolichol, are of great importance for cellular function. Many of the enzymes of this pathway are thus strictly regulated. During development of the rat, the cellular levels of certain of these lipids vary. Prenyltransferases have been investigated and it is reported here that farnesyl pyrophosphate synthase activity in rat liver cytosol decreases after birth to a lower, steady level. This decrease is not paralleled by the level of synthase protein, which shows two maxima, one immediately after birth and the other 30 days later. cis-Prenyltransferase activity is low after birth, increases continuously up to day-54 and then decreases to a low level which was maintained throughout the remainder of the study (365 days). Squalene synthase exhibits high activity after birth, but decreases during the first 100 days thereafter, and subsequently remains at the low level thus reached. In contrast to these changes in the activities of the prenyltransferases, the level of cholesterol is constant and the dolichol concentration increases continuously throughout the entire period studied.

Aging↗
PubMed1994

Modulations in hepatic branch-point enzymes involved in isoprenoid biosynthesis upon dietary and drug treatments of rats.

Three branch-point enzymes of the mevalonate pathway, farnesyl pyrophosphate synthase, cis-prenyltransferase and squalene synthase were characterized in rat hepatic cytosol, microsomes and peroxisomes isolated from rats after treatment with peroxisome proliferators, inducers of the endoplasmic reticulum or modulators of lipid metabolism. Cholestyramine and phenobarbital induced primarily the cytosolic farnesyl pyrophosphate synthase, whereas clofibrate and phthalates elevated the corresponding peroxisomal activity. cis-Prenyltransferase activities in microsomes were induced 4-5-fold after clofibrate, phthalate and phenobarbital administration, but these same treatments affected the peroxisomal activity to only a limited extent. Squalene synthase activity in microsomes was completely abolished, but the peroxisomal activity was unaffected after administration of cholesterol. On the other hand, clofibrate and phthalate induced only the microsomal activities. Mevinolin treatment greatly increased peroxisomal and cytosolic farnesyl pyrophosphate synthase activities, but not the mitochondrial activity, and the cis-prenyltransferase activities were elevated in peroxisomes, but not in microsomes. These results demonstrate that the branch-point enzymes in cholesterol and dolichol biosynthesis at various cellular locations are regulated differentially and that the capacities of peroxisomes and the endoplasmic reticulum to participate in the synthesis of polyisoprenoid lipids is affected profoundly by treatment with different xenobiotics.

Animals↗
PubMed1994

Lipid peroxidation of microsomal and mitochondrial membranes extracted with n-pentane and reconstituted with ubiquinol, dolichol and cholesterol.

Microsomes and mitochondria prepared from rat liver were extracted with n-pentane, a procedure which does not denature enzyme proteins. Protein and phospholipid were not extracted, but 75-80% of the total dolichol, 80-100% of the ubiquinone and 85-95% of the cholesterol were removed from both organelles by this procedure. Enzymatic and non-enzymatic lipid peroxidation in microsomes and non-enzymatic peroxidation in mitochondria were strongly inhibited when ubiquinol was reinserted into n-pentane-extracted membranes. When reconstitution with dolichol was performed, lipid peroxidation was increased or unchanged, while cholesterol decreased this activity in a concentration-dependent manner. In reconstitution experiments ubiquinol and dolichol together were less inhibitory than ubiquinol alone, whereas cholesterol accentuated the inhibitory effect of ubiquinol. Reconstitution with dolichols of different lengths, dolichyl esters or with alpha-unsaturated polyprenols further demonstrated that dolichol is not an antioxidant. It appears that mevalonate pathway lipids influence lipid peroxidation in membranes by modifying the properties of the bilayer.

Animals↗
PubMed1994

Isoprenoid biosynthesis in rat liver mitochondria. Studies on farnesyl pyrophosphate synthase and trans-prenyltransferase.

Mevalonate pathway enzyme activities in rat liver mitochondria were investigated, and it was found that isopentenyl pyrophosphate can be utilized for the synthesis of all-trans-polyprenyl pyrophosphates in vitro. In this reaction sequence intermediate formation of farnesyl pyrophosphate (FPP) predominates, and the FPP synthase activity was studied in more detail. The mitochondrial activity constitutes 13% of the total hepatic capacity for FPP synthesis, exceeding the corresponding microsomal, nuclear, and peroxisomal activities by 10-fold. Mitochondrial FPP synthase exhibits trypsin sensitivity only after sonication of intact mitochondria and upon subfractionation the activity is found localized in the matrix. FPP synthase activities at different locations responded distinctly when rats were treated with a diet enriched in cholesterol or containing mevinolin or cholestyramine. With the high cholesterol diet, mitochondrial FPP synthase activity increased 2-fold, while the cytosolic activity was slightly decreased. Both mevinolin and cholestyramine treatment resulted in 3-fold increases in cytosolic FPP synthase activities, without altering the mitochondrial activity. FPP was utilized as substrate for trans-prenyltransferase activity in the inner mitochondrial membrane. The products formed in this reaction were identified as nona- and decaprenyl-PP, and the reaction was influenced by changes in both substrate and Mg2+ concentration, giving more decaprenyl-PP when the concentrations of these substances were increased. These results demonstrate that mitochondria utilize endogenously produced FPP for isoprenoid biosynthesis and that the biosynthetic steps in mitochondria are regulated independently from those occurring in other subcellular compartments.

Animals↗
PubMed1994

Effects of clofibrate, phthalates and probucol on ubiquinone levels.

Rats were exposed through their diet to clofibrate, di(2-ethylhexyl)phthalate or probucol for 6 weeks and the levels of ubiquinone (UQ), cholesterol and dolichol were monitored in liver, muscle, heart, brain and blood. The levels of UQ-9 and -10 were increased by clofibrate and, in particular by phthalate administration. With the latter agent this increase in liver was fourfold, in muscle was twofold and levels in the heart and blood increased by 20%, whereas there was no change in the brain. Probucol led to a moderate decrease in the level of UQ in liver, muscle and blood, but not in heart or brain. The extent of reduction of UQ was not modified by any of the treatments employed. Probucol did not have any effect on tissue or blood cholesterol levels, whereas clofibrate or phthalate elicited a variable response, including both increases and decreases depending on the tissue analyzed. Phthalate treatment increased the dolichol content to some extent in all tissues and in blood, but the level of this lipid was not modified upon clofibrate or probucol treatment. These results demonstrate that tissue and blood levels of UQ can be increased by exposure to appropriate chemical agents without elevating the concentration of cholesterol.

Animals↗
PubMed1994

Regulation of coenzyme Q biosynthesis.

The side-chain moiety of coenzyme Q is synthesized by a trans-prenyltransferase present in microsomes. Condensation of this moiety with the precursor ring takes place in the Golgi system. The enzymes involved, as well as the cytosolic geranylgeranyl-PP synthase, are regulated in an independent fashion. When the size of the farnesyl-PP pool is decreased or increased by employing appropriate inhibitors, the rate of CoQ synthesis is modified accordingly, indicating the dependence of trans-prenyltransferase activity on the level of intracellular substrate concentrations. Administration of peroxisome proliferators elevates CoQ concentrations not only in blood, but also in various tissues. Thus, it may be possible in the future to selectively increase CoQ concentrations in certain organs, without increasing the level of cholesterol.

Alkyl and Aryl Transferases↗
PubMed1994

Ubiquinone-10 protects neurons from virus-induced degeneration.

Cultured neurons from rat dorsal root ganglia and cerebral cortex were infected with Sendai virus, which gives a productive replication with lysis of most neurons, and with the RW strain of mumps virus, which undergoes defective replication causing degeneration of only 30-40% of the neurons within 5 days after initial infection. In Sendai virus-infected cells the amount of polyisoprenoid lipids was enhanced. In mumps virus-infected cultures there were transient reductions in the contents of cholesterol, dolichol, and ubiquinone-9 in the cultures, whereas the reduction in the ubiquinone-10 level was progressive, reaching 20% of its original value 21 days after infection. Treatment of mumps virus-infected cultures with ubiquinone-10 protected the neurons from degeneration, whereas no effects were observed on exposure to ubiquinone-9. Linolenic acid (18:3) and arachidonic acid (20:4), but not myristic acid (14:0) and palmitic acid (16:0), also had significant neuroprotective effects.

Animals↗
PubMed1994

Quantitation of glutathione transferase-pi in the urine by radioimmunoassay.

A radioimmunoassay procedure for the quantitation of glutathione transferase-pi was developed in order to determine the levels of this protein in human urine. The enzyme was isolated from human placenta with a purification factor of 366 (compared to the original high-speed supernatant fraction), and upon gel electrophoresis, only a single band was seen. Polyclonal antisera were subsequently raised in rabbits and found to be suitable for a radioimmunoassay. Glutathione transferase-pi was localized immunohistochemically to the cells of the distal tubules, the thin loop of Henle and the collecting ducts in the kidney. In contrast, the alpha-isoenzyme was localized exclusively in the proximal tubular epithelium. Samples of urine from healthy individuals contained about 6 ng of the pi-transferase/ml. The method proved to be specific for glutathione transferase-pi, and no cross-reaction with the alpha- or mu-transferase or with other proteins occasionally appearing in urine occurred. The protein was quite stable upon storage and insensitive to variations in the urine pH. Thus, it appears that glutathione transferase-pi can be conveniently quantitated by radioimmunoassay and changes in the concentration of this protein in human urine thus monitored.

Enzyme Stability↗
PubMed1994

Urinary pi-class glutathione transferase as an indicator of tubular damage in the human kidney.

Glutathione transferase-pi released from kidney tubular epithelial cells was analyzed in the urine of recipients of renal allografts. Urinary content of alpha-class glutathione transferase was also determined for comparison. Control urine from healthy individuals contained detectable levels of the pi-isoenzyme (6.6 +/- 0.46 ng/ml, mean +/- SEM) and this concentration was not increased in the urine of patients demonstrating cyclosporine A-induced nephrotoxicity (6.3 +/- 0.29 ng/ml), in contrast to the alpha-form. Acute rejection increased excretion of the pi-isoenzyme (19.0 +/- 2.0 ng/ml), but not of the alpha-glutathione transferase. Thus, while the serum creatinine level increases in connection with both cyclosporine A-induced nephrotoxicity and acute rejection, analyses of urinary glutathione transferases distinguish well between these conditions. Acute tubular necrosis and renal transplant infarction resulted in a rapid elevation in urinary levels of both alpha- and pi-transferase. The advantages of this approach are that release of the protein into the urine occurs rapidly after tubular damage, the assay is sensitive and specific and can also distinguish between certain pathological conditions. These studies thus indicate that the urinary level of glutathione transferase-pi can be used for monitoring certain pathological processes in the kidney. Quantitation of this enzyme complements the information obtained by measurement of glutathione transferase-alpha.

Adolescent↗