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J I Pedersen

Publications and source records attributed to J I Pedersen.

At least 73 records · Page 4Linked to original sources
PubMed1986

The effect of high-fat diets on microsomal lauric acid hydroxylation in rat liver.

A diet with 20% (w/w) fish oil or partially hydrogenated fish oil has been shown to stimulate omega-oxidation of lauric acid 2.5-fold with rat liver microsomal preparations after 1 week of feeding. A diet containing either 20% (w/w) soybean oil, partially hydrogenated soybean oil or rapeseed oil had no effect. The omega-oxidation was also stimulated by fasting (3.7-fold) and by clofibrate (13-fold). The stimulation of omega-oxidation with partially hydrogenated fish oil was at its highest level after 3 days of feeding, and was dose dependent in the dietary oil of range 5-25% (w/w). With various high-fat diets, a high correlation was found (r = 0.81) between peroxisomal beta-oxidation of palmitoyl-CoA and microsomal omega-oxidation of lauric acid.

Animals↗
PubMed1986

Conjugation of cholic acid with taurine and glycine by rat liver peroxisomes.

We have previously shown that rat liver peroxisomes catalyze conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid into cholic acid as the CoA-ester (1). In the present work it is shown that addition of taurine or glycine to the reaction mixture, choloyl-CoA is further converted to taurocholic or glycocholic acid, respectively. The identity of these products was verified by fast atom bombardment-mass spectrometry. The peroxisomal fraction catalyzed conjugation of cholic acid with taurine (22.3 nmol X mg-1 X h-1) or glycine (18.6 nmol X mg-1 X h-1) at rates twice those observed with the microsomal fraction. The results indicate that conjugation of newly formed bile acids may be an important function of liver peroxisomes.

Animals↗
PubMed1986

In vitro formation of bile acids from di- and trihydroxy-5 beta-cholestanoic acid in human liver peroxisomes.

The conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-[3H]cholestanoic acid into cholic acid and 3 alpha,7 alpha-dihydroxy-5 beta-[3H]cholestanoic acid into chenodeoxycholic acid has been studied in subcellular fractions of human liver. The products were separated from the substrates by high-pressure liquid chromatography and identified by combined gas chromatography-mass spectrometry. The highest rates of conversion were found in the light mitochondrial fraction. This fraction also contained the highest amount of the marker enzymes for peroxisomes. The maximal rates of cholic acid and chenodeoxycholic acid formation were 1.3 and 1.8 nmol/mg protein per h, respectively. The presence of KCN in the incubation medium stimulated the formation of bile acids. Peroxisomes were prepared from the light mitochondrial fraction by sucrose-gradient centrifugation. By use of different marker enzymes, it was confirmed that the major part of the activity for cholic acid formation in the light mitochondrial fraction was located in the peroxisomes. It is concluded that liver peroxisomes are important for the oxidative cleavage of the C27 steroid side chain in bile acid formation in man.

Acetylglucosaminidase↗
PubMed1986

Assay of 25-hydroxy vitamin D3-1 alpha-hydroxylase in pig kidney mitochondria using isotope dilution-mass spectrometry.

An assay of 1 alpha-hydroxylation of 25-hydroxy vitamin D3 in pig kidney mitochondria, based on selected ion monitoring, has been developed. Trideuterium-labeled 1,25-dihydroxy vitamin D3 was synthesized and used as internal standard. This standard was added immediately after incubation of 25-hydroxy vitamin D3 with the mitochondrial fraction. The incubation extracts were purified by high-performance liquid chromatography. After formation of the trimethylsilyl derivative, the product was quantitated by mass fragmentography using the ion at m/z 452 and m/z 455. With the use of this assay it was found that formation of 1,25-dihydroxy vitamin D3 was linear with the amount of mitochondrial protein and time of incubation. Substrate saturation was obtained at about 20 microM of 25-hydroxy vitamin D3. The maximal rate of conversion obtained under the conditions employed was about 0.1 pmol/mg protein X minute.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1986

Peroxisomal dysfunction in a boy with neurologic symptoms and amaurosis (Leber disease): clinical and biochemical findings similar to those observed in Zellweger syndrome.

A boy with psychomotor retardation and Leber congenital amaurosis, sensory hearing loss, and hepatomegaly is reported. Accumulation of bile acid precursors and very long chain fatty acids together with impaired biosynthesis of plasmalogens in cultured fibroblasts (similar to those in the cerebrohepatorenal syndrome of Zellweger) were detected, but the clinical picture was distinctly different. Defective oxidation of phytanic acid was measured in fibroblasts. The virtual lack of peroxisomes in a liver biopsy specimen lends further support to the contention that at least some patients with Leber congenital amaurosis may have one of the recently defined "peroxisomal disorders." The biochemical findings indicate the possibility of prenatal diagnosis.

Adrenoleukodystrophy↗
PubMed1986

Effect of alcohol consumption on serum concentration of 25-hydroxyvitamin D3, retinol, and retinol-binding protein.

The effect of chronic alcohol consumption on the concentration of 25-hydroxyvitamin D3, total retinol, and retinol-binding protein in serum was studied in chronic alcoholics (n = 12) and controls (n = 19). Ethanol intake during the last year was 178 +/- 116 and 3.7 +/- 4.5 g/day, respectively (p less than 0.002). Of the alcoholics, 58% had a concentration of 25-hydroxyvitamin D3 below lower limit of reference (20 ng/ml). Estimated dietary intake of vitamin D last year was not significantly different for the alcoholics and controls. Concentration of calcium in serum was significantly lower in alcoholics than in controls (p less than 0.05). The serum concentration of retinol and retinol-binding protein was similar in the two groups. These observations may be of relevance for some of the clinical findings related to bone disease among heavy alcohol consumers.

Adult↗
PubMed1986

Formation of chenodeoxycholic acid from 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid by rat liver peroxisomes.

The oxidation of the side chain of 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) into chenodeoxycholic acid has been studied in subcellular fractions of rat liver. The product was separated from the substrate by high pressure liquid chromatography and identified by gas-liquid chromatography-mass spectrometry. The highest specific rate of conversion was found in the heavy (M) and the light (L) mitochondrial fractions with the highest enrichment in the L fraction. Washing the M fraction reduced the side chain cleavage activity by 90%. The peroxisomal marker enzyme urate oxidase was reduced to the same extent. The activity found in the M fraction may thus be due to peroxisomal contamination. After centrifugation of the L fraction on a Nycodenz density gradient, the highest specific activity for side chain cleavage of DHCA (31 nmol X mg-1 X h-1) was found in the fraction with the highest peroxisomal marker enzyme activity. This fraction also catalyzed conversion of 3 alpha,7 alpha,12 alpha-5 beta-cholestanoic acid (THCA) into cholic acid at the highest rate (32 nmol X mg-1 X h-1). The peroxisomal oxidation of DHCA into chenodeoxycholic acid required the presence of ATP, CoA, Mg2+, and NAD in the incubation medium. The reaction was not inhibited by KCN. It is concluded that rat liver peroxisomes contain enzymes able to catalyze the cleavage of the side chain of both DHCA and THCA. The enzymes involved are similar to, but not necessarily identical to, those involved in the peroxisomal beta-oxidation of fatty acids.

Animals↗
PubMed1985

25-Hydroxylation of 1 alpha-hydroxyvitamin D-3 in rat and human liver.

1 alpha-Hydroxyvitamin D-3 25-hydroxylase activity was measured in subcellular fractions of rat and human liver. The formation of 1,25-dihydroxyvitamin D-3 was determined by high pressure liquid chromatography. In rat liver 1 alpha-hydroxyvitamin D-3 25-hydroxylase activities were found in the purified nuclei, the heavy mitochondrial fraction and the microsomal fraction. The enrichment of 25-hydroxylase activity was highest in the heavy mitochondrial fraction. With this fraction a minimum amount (about 0.5 mg) of protein was required before formation of 1,25-dihydroxyvitamin D-3 could be detected. Above this amount the reaction was linear with amount of protein up to at least 2 mg/ml. The reaction was also linear with time up to 60 min. An apparent Km value of 2 X 10(-5) M was found. The mitochondrial 25-hydroxylase was stimulated by addition of cytosolic protein or bovine serum albumin. The degree of stimulation was dependent on the amount of mitochondrial protein present in the incubation mixture. Maximal stimulation was seen with 0.2 mg/ml of either protein in the presence of 0.5 mg mitochondrial protein. The stimulating effect remained after heating the protein for 5 min at 100 degrees C. The cytosolic protein did not stimulate a reconstituted mitochondrial 1 alpha-hydroxyvitamin D-3 25-hydroxylase. The mitochondrial vitamin D-3 25-hydroxylase was inhibited both by cytosolic protein and by bovine serum albumin. Human liver revealed only one 1 alpha-hydroxyvitamin D-3 25-hydroxylase activity located to the heavy mitochondrial fraction. The results are in agreement with previous studies on the localization of vitamin D-3 25-hydroxylase in rat and human liver. The difference in localization of the 25-hydroxylase between rat and human liver implies that studies on the regulation of the microsomal 25-hydroxylase in rat liver may not be relevant to the situation in human liver.

Adult↗
PubMed1985

Binding protein for vitamin D and its metabolites in rat mesenteric lymph.

A protein with high affinity for vitamin D3 and 25-hydroxyvitamin D3 in rat mesenteric lymph has been studied. Mesenteric lymph was collected after duodenal instillation of radiolabeled vitamin D3 and 25-hydroxyvitamin D3. As previously described, approximately 10% of vitamin D3 (S. Dueland, J.I. Pedersen, P. Helgerud, and C.A. Drevon, J. Biol. Chem. 257: 146-150, 1982) and 95% of 25-hydroxyvitamin D3 (S. Dueland, J.I. Pedersen, P. Helgerud, and C.A. Drevon, Am. J. Physiol. 245 (Endocrinol. Metab. 8): E463-E467, 1983) recovered in mesenteric lymph were associated with the alpha-globulin fractions. The radioactive vitamin D3 recovered in the lymph fraction with d greater than 1.006 (free of chylomicrons) coeluted with purified rat serum binding protein for vitamin D and its metabolites (DBP) from an antirat DBP column. The results obtained by immunoblotting after sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that this protein in mesenteric lymph had molecular weight and immunological properties identical with purified serum DBP. Purified serum DBP labeled with 125I was injected intravenously and mesenteric lymph was collected. in lymph, suggesting that DBP may be transferred from blood to mesenteric lymph and that plasma and lymph DBP may have a similar origin.

Animals↗
PubMed1985

Defective peroxisomal cleavage of the C27-steroid side chain in the cerebro-hepato-renal syndrome of Zellweger.

Based on in vitro work with rat liver, we recently suggested that the peroxisomal fraction is most important for the oxidation of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid. The cerebro-hepato-renal syndrome of Zellweger is a fatal recessive autosomal disorder, the most characteristic histological feature of which is a virtual absence of peroxisomes in liver and kidneys. This disease offers a unique opportunity to evaluate the relative importance of peroxisomes in bile acid biosynthesis. A child with Zellweger syndrome was studied in the present work. In accordance with previous work, there was a considerable accumulation of THCA, 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid (24-OH-THCA), 3 alpha, 7 alpha, 12 alpha-trihydroxy-27-carboxymethyl-5 beta-cholestan-26-oic acid (C29-dicarboxylic acid), and 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid in serum. In addition, a tetrahydroxylated 5 beta-cholestanoic acid with all the hydroxyl groups in the steroid nucleus was found. 3H-Labeled 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol was administered intravenously together with 14C-labeled cholic acid. There was a rapid incorporation of 3H in THCA and a slow incorporation into cholic acid. The specific radioactivity of 3H in THCA was about one magnitude higher than that in cholic acid. The conversion was evaluated by following the increasing ratio between 3H and 14C in biliary cholic acid. The rate of incorporation of 3H in cholic acid was considerably less than previously reported in experiments with healthy subjects, and the maximal conversion of the triol into cholic acid was only 15-20%. About the same rate of conversion was found after oral administration of 3H-THCA. Both in the experiment with 3H-5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and with 3H-THCA, there was an efficient incorporation of 3H in the above unidentified tetrahydroxylated 5 beta-cholestanoic acid. There was only slow incorporation of radioactivity into 24-OH-THCA and into the C29-dicarboxylic acid. From the specific activity decay curve of 14C in cholic acid obtained after intravenous injection of 14C-cholic acid, the pool size of cholic acid was calculated to be 24 mg/m2 and the daily production rate to 9 mg/m2 per d. This corresponds to a reduction of approximately 85 and 90%, respectively, when compared with normal infants. It is concluded that liver peroxisomes are essential in the normal conversion of THCA to cholic acid. In the Zellweger syndrome this conversion is defective and as a consequence the accumulated THCA is either excreted as such or transformed into other metabolites by hydroxylation or side chain elongation. The accumulation of THCA, as well as the similar rate of conversion of 5 beta-cholestane-3 alpha,7 alpha.12 alpha-triol and THCA into cholic acid, support the contention that the 26-hydroxylase pathway with intermediate formation of THCA is the most important pathway for formation of cholic acid in man.

Bile↗
PubMed1985

In vivo and vitro studies on formation of bile acids in patients with Zellweger syndrome. Evidence that peroxisomes are of importance in the normal biosynthesis of both cholic and chenodeoxycholic acid.

The last step in bile acid formation involves conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid and 3 alpha,7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) into chenodeoxycholic acid. The peroxisomal fraction of rat and human liver has the highest capacity to catalyze these reactions. Infants with Zellweger syndrome lack liver peroxisomes, and accumulate 5 beta-cholestanoic acids in bile and serum. We recently showed that such an infant had reduced capacity to convert a cholic acid precursor, 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol into cholic acid. 7 alpha-Hydroxy-4-cholesten-3-one is a common precursor for both cholic acid and chenodeoxycholic acid. Intravenous administration of [3H]7 alpha-hydroxy-4-cholesten-3-one to an infant with Zellweger syndrome led to a rapid incorporation of 3H into biliary THCA but only 10% of 3H was incorporated into cholic acid after 48 h. The incorporation of 3H into DHCA was only 25% of that into THCA and the incorporation into chenodeoxycholic acid approximately 50% of that in cholic acid. The conversion of intravenously administered [3H]THCA into cholic acid in another infant with Zellweger syndrome was only 7%. There was a slow conversion of THCA into 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-C29-dicarboxylic acid. The pool size of both cholic- and chenodeoxycholic acid was markedly reduced. Preparations of liver from two patients with Zellweger syndrome had no capacity to catalyze conversion of THCA into cholic acid. There was, however, a small conversion of DHCA into chenodeoxycholic acid and into THCA. It is concluded that liver peroxisomes are important both for the conversion of THCA into cholic acid and DHCA into chenodeoxycholic acid.

Bile Acids and Salts↗
PubMed1985

Role of peroxisomes in the biosynthesis of bile acids.

Evidence is presented that peroxisomes are more important than other subcellular fractions in rat liver for the final reactions in the biosynthesis of cholic acid from cholesterol. The peroxisomal conversion of 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) into cholic acid was studied in detail and optimal assay conditions were defined. It was shown that the reaction involves intermediary formation of 3 alpha, 7 alpha, 12 alpha, 24-tetrahydroxy-5 beta-cholestanoic acid and that ATP, CoA, Mg++, NAD+ and FAD are necessary. With use of 18O2 and 2H2O it was further shown that the introduction of the 24-hydroxyl group in 3 alpha, 7 alpha, 12 alpha, 24 alpha-tetrahydroxy-5 beta-cholestanoic acid is the combined result of a desaturase and a hydratase. The reaction mechanism is thus analogous to that for beta-oxidation of fatty acids. The role of peroxisomes under conditions in vivo was studied in three patients with the rare inborn cerebro-hepato-renal syndrome of Zellweger. Apparently infants with this fatal disease have a complete lack of peroxisomes in the liver and kidneys. The patients were found to accumulate THCA and various polar metabolites of THCA in serum and bile. Administration of two 3H-labelled C27-precursors to bile acids (5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and 7 alpha-hydroxy-4-cholesten-3-one) resulted in a rapid conversion into THCA and a subsequent slow conversion into cholic acid. Administration of 3H-labelled THCA resulted in a slow conversion into cholic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile Acids and Salts↗
PubMed1984

Mechanism of peroxisomal 24-hydroxylation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid in rat liver.

We recently showed that the peroxisomal fraction of rat liver has a high capacity to catalyze conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid into cholic acid and that 3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestanoic acid is an intermediate in this conversion. With use of 2H2O and 18O2, evidence is presented here that the formation of 3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestanoic acid involves intermediary formation of a delta 24-unsaturate intermediate followed by hydration.

Animals↗
PubMed1984

Subcellular localization of vitamin D3 25-hydroxylase in human liver.

Vitamin D3 25-hydroxylase activity was measured in subcellular and submitochondrial fractions of human liver. Quantitation of 25-hydroxyvitamin D3 was based on high performance liquid chromatography. Vitamin D3 25-hydroxylase activity was detected in the mitochondrial fraction only. The mitochondrial 25-hydroxylase activity was linear with time up to 60 min and with mitochondrial protein up to 1 mg/ml. An apparent Km value of about 10(-5) M was found. Substrate satuation level was not reached. In the presence of 2.4 X 10(-4) M vitamin D3, the rate of 25-hydroxyvitamin D3 formation was 0.19 nmol X mg of protein-1 X h-1 After fractionation of the mitochondria, 86% of the 25-hydroxylase activity was recovered in the mitoplast fraction. The outer membrane fraction was devoid of activity. It is concluded that human liver contains only one detectable vitamin D3 25-hydroxylase enzyme localized to the mitochondrial inner membrane.

Cell Fractionation↗
PubMed1984

Urinary excretion of dicarboxylic acids from patients with the Zellweger syndrome. Importance of peroxisomes in beta-oxidation of dicarboxylic acids.

The urinary excretion of adipic acid, suberic acid and sebacic acid from two patients with the cerebrohepato-renal syndrome of Zellweger was studied. The patients had a complete lack of peroxisomes in the liver as judged by electron microscopy. In the non-ketotic state, the total excretion of free and conjugated adipic acid, suberic acid and sebacic acid was increased by about 100%, 200% and 350%, respectively, as compared to the corresponding excretion from six healthy infants of the same age. The excretion of free dicarboxylic acid was increased to a considerably lesser extent than the free + conjugated dicarboxylic acid. In view of the presence of adipic acid in urine of the Zellweger patients, it is concluded that peroxisomes are not obligatory for beta-oxidation of medium-chain dicarboxylic acids in vivo. The relative accumulation of suberic acid and sebacic acid as compared to adipic acid is, however, consistent with a relative block in the conversion of suberic acid and sebacic acid into adipic acid in patients with the Zellweger syndrome.

Dicarboxylic Acids↗
PubMed1984

Lymphatic absorption and transport of retinol and vitamin D-3 from rat intestine. Evidence for different pathways.

The lymphatic absorption and transport of retinol and vitamin D-3 from rat intestine has been studied. When rats were cannulated in the intestinal lymph duct and given an intraduodenal bolus of [3H]retinol and 14C-labelled vitamin D-3, 14C-labeled vitamin D-3 appeared later in the intestinal lymph than [3H]retinol and the rate of absorption of vitamin D-3 was still maximal at a time when that of retinol had declined. Both vitamins were absorbed via the lymphatic route in association with chylomicrons. Almost all the retinol was esterified, while vitamin D-3 appeared in the chylomicrons as free vitamin D-3. In vitro incubations and in vivo studies using hepatectomized and normal rats showed that the retinyl ester was a relatively nonexchangeable component of the chylomicrons and their remnants. Hence, all the vitamin A followed the remnants in their clearance from plasma. In contrast, significant amounts of vitamin D-3 were transferred from the chylomicrons to other plasma fractions. Therefore, only a fraction of this vitamin may be removed in association with the chylomicron remnants.

Animals↗
PubMed1983

25-Hydroxyvitamin D3-24-hydroxylase in rat kidney mitochondria.

Assay conditions for the measurement of 25-hydroxyvitamin D3-24-hydroxylase activity in rat kidney mitochondria have been worked out. The product, 24,25-dihydroxyvitamin D3 was quantitated either by high pressure liquid chromatography or by isotope dilution-mass spectrometry. By these procedures, the enzyme activity could be measured with saturating concentration (greater than 2.5 X 10(-6) M) of substrate. Pretreatment of the animals by aminophylline (Kulkowski, J. A., Chow, T., Martinez, J., and Ghazarian, J. G. (1979) Biochem. Biophys. Res. Commun. 90, 50-57) stimulated the 24-hydroxylase activity in vitro at least 2 to 3-fold. The identity of the product was verified by gas chromatography-mass spectrometry. The rates of the reaction varied between 1.5 and 5 pmol/mg of mitochondrial protein.min (at 25 degrees C), and the K'm was determined to be 4.2 X 10(-7) M. Malate, succinate, and isocitrate were all able to support the reaction. Low O2 tension, CO, KCN, and the uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited the reaction, while the respiratory inhibitor rotenone had no effect. Metyrapone inhibited the reaction with 50% inhibition at a concentration of 2.5 mumol/ml. The enzyme was found to be localized inside the inner mitochondrial membrane. The results indicate that in the rat the renal mitochondrial 25-hydroxyvitamin D3-24-hydroxylase is a cytochrome P-450 and that the reducing equivalents are primarily supplied by NADPH via the energy-dependent transhydrogenase.

24,25-Dihydroxyvitamin D 3↗