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Inderjit Singh - One of the best experts on this subject based on the ideXlab platform.

  • Refsum disease: a defect in the a-oxidation of Phytanic Acid in peroxisomes
    2013
    Co-Authors: Inderjit Singh, Kalipada Pahan, Avtar K. Singh, Earnest Barbosat
    Abstract:

    Abstract The oxidation of Phytanic Acid to pristanic Acid was previously demonstrated to be deficient in monolayer cultures of skin fibroblasts (Hemdon et al. 1969. J. Clin. Invest. 48 1017-1032). However, identification of subcellular organelle with deficient enzyme activity has not been established. To define the subcellular organelle with deficient enzyme activity in the catabolism of Phytanic Acid, we measured the oxidation of [l-14C] Phytanic Acid to 14C02 and pristanic Acid in different subcellular organelles isolated from cultured skin fibroblasts from control and Refsum patients. The rates of oxidation of Phytanic Acid in peroxisomes, mitochondria, and endoplasmic reticulum were 37.1 * 2.65, 1.9 * 0.3, and 0.4 * 0.07 pmol/h per mg protein, respectively, from control fibroblasts. The Phytanic Acid oxidation activity in mitochondria (2.04 0.7 pmol/h per mg protein) and endoplasmic reticulum (0.43 * 0.2 pmol/h per mg protein) from Refsum fibroblasts was similar to control fibroblasts. However, Phytanic Acid oxidation in peroxisomes from Refsum fibroblasts was not detected at all the protein concentrations tested. On the other hand, the peroxisomes from Refsum fibroblasts had normal rates of activation and oxidation of palmitic and lignoceric Acids, suggesting that the peroxisomes isolated from Refsum fibroblasts were metabolically active. The phytanoyl-CoA ligase, the first enzyme in the a-oxidation pathway, had activity similar to that in peroxisomes from control (9.86 * 0.09 nmol/h per mg protein) and Refsum (10.25 f 0.31 nmol/h per mg protein) fibroblasts. 819 The data described here clearly demonstrate that pathognomonic accumulation of Phytanic Acid in patients with Refsum disease is due to the deficient activity of peroxisomal a-oxidation enzym

  • Phytanic Acid oxidation normal activation and transport yet defective alpha hydroxylation of Phytanic Acid in peroxisomes from refsum disease and rhizomelic chondrodysplasia punctata
    Journal of Lipid Research, 1996
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Inderjit Singh
    Abstract:

    In humans the oxidation of Phytanic Acid is a peroxisomal function. To understand the possible mechanisms for the pathognomic accumulation of Phytanic Acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chondrodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of Phytanic Acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP subjects. Activation of Phytanic Acid was normal in peroxisomes from both RD and RCDP. Transport of Phytanic Acid or phytanoyl-CoA in the absence or presence of fatty Acid activating cofactors (ATP, MgCl2, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of [(2,3)-3H]- or [1-14C]Phytanic Acid, or [1-14C]phytanoyl-CoA (substrate for the first step of alpha-oxidation) but normal oxidation of [1-14C] alpha-hydroxyPhytanic Acid (substrate for the second step of the alpha-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of Phytanic Acid in plasma and body fluids of RD is due to the deficiency of Phytanic Acid alpha-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of [1-14C]Phytanic Acid or phytanoyl-CoA or [(2,3)-3H]Phytanic Acid, the oxidation of [1-14C] alpha-hydroxyPhytanic Acid was also deficient, indicating that in RCDP the activities both of alpha-hydroxylation of Phytanic Acid and decarboxylation of alpha-hydroxyPhytanic Acid are deficient. These observations indicate that peroxisomal membrane functions (Phytanic Acid activation and transport) in Phytanic Acid metabolism are normal in both RD and RCDP. The defect in RD is in the alpha-hydroxylation of Phytanic Acid; whereas in RCDP both alpha-hydroxylation of Phytanic Acid as well as decarboxylation of alpha-hydroxyPhytanic Acid are deficient.

  • Phytanic Acid oxidation: normal activation and transport yet defective alpha-hydroxylation of Phytanic Acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata.
    Journal of lipid research, 1996
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Inderjit Singh
    Abstract:

    In humans the oxidation of Phytanic Acid is a per- oxisomal function. To understand the possible mechanisms for the pathognomic accumulation of Phytanic Acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chon- drodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of Phytanic Acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP sub- jects. Activation of Phytanic Acid was normal in peroxisomes from both RD and RCDP. Transport of Phytanic Acid or phytanoyl-CoA in the absence or presence of fatty Acid acti- vating cofactors (ATP, MgC12, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of ((2,3)JH)- or (1-14C)Phytanic Acid, or (l- Wlphytanoyl-CoA (substrate for the first step of a-oxidation) but normal oxidation of ( l-14C)a-hydroxyPhytanic Acid (sub- strate for the second step of the a-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of Phytanic Acid in plasma and body fluids of RD is due to the deficiency of Phytanic Acid a-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of ( 1-14ClPhytanic Acid or phytanoyl-CoA or ((2,3)sH)Phytanic Acid, the oxidation of ( l-W)a-hy- droxyPhytanic Acid was also deficient, indicating that in RCDP the activities both of a-hydroxylation of Phytanic Acid and decarboxylation of a-hydroxyPhytanic Acid are deficient. I These observations indicate that peroxisomal membrane functions (Phytanic Acid activation and transport) in Phytanic Acid metabolism are normal in both RD and RCDP. The defect in RD is in the a-hydroxylation of Phytanic Acid; whereas in RCDP both a-hydroxylation of Phytanic Acid as well as decarboxylation of a-hydroxyPhytanic Acid are defi- cient.-Pahan, K., M. Khan, and I. Singh. Phytanic Acid oxi- dation: normal activation and transport yet defective a-hy- droxylation of Phytanic Acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata. J. Lipid Res. 1996.37: 1137-1143.

  • Ketoconazole and other imidazole derivatives are potent inhibitors of peroxisomal Phytanic Acid α-oxidation
    FEBS letters, 1995
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Brian T. Smith, Inderjit Singh
    Abstract:

    The imidazole antimycotics like ketoconazole, clotrimazole, bifonazole, miconazole and CO, known as powerful inhibitors of cytochrome P-450, are potent inhibitors of peroxisomal Phytanic Acid α-oxidation to pristanic Acid suggesting the possible involvement of the cytochrome P-450 mono-oxygenase system in this oxidation. In contrast to the inhibition of the oxidation of [1-14C]Phytanic Acid, [1-14C]phytanoyl-CoA and [(2,3)-3H]Phytanic Acid, these drugs and CO have no effect on the oxidation of [1-14C]α-hydroxy Phytanic Acid indicating that these drugs and CO inhibit only the α-hydroxylation of Phytanic Acid. These studies using purified peroxisomes from liver and cultured human skin fibroblasts and Hep G2 cells clearly demonstrate that α-hydroxylation, an intermediate step in the α-oxidation of Phytanic Acid found to be impaired in Refsum Disease, is mediated by cytochrome P-450 containing enzyme.

  • Phytanic Acid oxidation: topographical localization of phytanoyl-CoA ligase and transport of Phytanic Acid into human peroxisomes
    Journal of lipid research, 1995
    Co-Authors: Kalipada Pahan, Inderjit Singh
    Abstract:

    To understand the possible role of phytanoyl-CoA li- gase, present in the membrane, in the oxidation of Phytanic Acid in the matrix of peroxisomes (Pahan, K. and I. Singh. 1993. FEES Lett. 333: 154-158) we examined the transport of Phytanic Acid/phytanoyl-CoA into peroxisomes and the topology of the active site of phytanoyl-CoA ligase in the peroxisomal mem- brane. The increase in lignoceroyl-CoA ligase as compared to no change in the activities of palmitoyl-CoA and phytanoyl-CoA li- gases when peroxisomes were disrupted with detergent or soni- cation and inhibition of the activities of both palmitoyl-CoA and phytanoyl-CoA ligase by impermeable inhibitor of acyl-CoA li- gases (mercury-dextran) and trypsin treatment in the intact peroxisomes. On the other hand, the lignoceroyl-CoA ligase ac- tivity was inhibited by mercury-dextran and trypsin only in the disrupted peroxisomes. Taken together, these studies support the conclusion that the enzymatic site of phytanoyl-CoA ligase is on the cytoplasmic surface of peroxisomal membrane. This implies that phytanoyl-CoA is synthesized on the cytoplasmic surface of peroxisomal membrane and is translocated through the mem- brane for its a-oxidation to pristanic Acid in the matrix of perox- isomes. llilll To delineate the transport for Phytanic Acid through the peroxisomal membrane, we examined cofactors and energy requirements for its transport into peroxisomes. The similar rates of transport of phytanoyl-CoA and Phytanic Acid under conditions favorable for fatty Acid activation (presence of ATP, CoASH, and MgC12) and the lack of transport of Phytanic Acid when ATP and/or CoASH were removed or replaced with their inactive analogues (ATP and/or CoASH) from assay medium clearly demonstrates that the transport of Phytanic Acid requires prior synthesis of phytanoyl-CoA by phytanoyl-CoA ligase. The prerequisite activation of Phytanic Acid to phytanoyl-CoA for its a-oxidation only in intact peroxisomes, and oxidation of free Phytanic Acid in digitonin-permealized peroxisomes or isolated matrix, suggests that phytanoyl-CoA ligase (in peroxisomal membrane) regulates the oxidation of Phytanic Acid in peroxi- somes by providing phytanoyl-CoA for its transport into peroxi- somes.-Pahan, K., and I. Singh. Phytanic Acid oxidation: topographical localization of phytanoyl-CoA ligase and trans- port of Phytanic Acid into human peroxisomes. J Lipid Res. 1995. 36: 986-997. Phytanic Acid (3,7,11,15-tetramethylhexadecanoic Acid), a highly branched isoprenoid-derived fatty Acid, accumu- lates in excessive amounts in the tissues and body fluids of patients with classical Refsum disease (1) and in pa- tients with defects in the biogenesis of peroxisomes (2, 3). Phytanic Acid is not synthesized de novo in humans but is taken exogenously. The ordinary human diet contains 50-100 mg of Phytanic Acid per day mainly as a consti- tuent of animal, dairy, and plant products. Due to the p- methyl group, Phytanic Acid cannot be @-oxidized; there- fore, a-oxidation is the only feasible route for its catabolism (1-4). Studies from our laboratory have demonstrated that in humans Phytanic Acid is a-oxidized to pristanic Acid in peroxisomes, but in rodents this process occurs in mitochondria (5, 6). In human skin fibroblasts the rate of Phytanic Acid oxidation in peroxi- somes was 26 and 130 times greater than that found in mitochondria and microsomes. Moreover, the excessive accumulation of Phytanic Acid and defective a-oxidation of Phytanic Acid in peroxisomes, but not mitochondria or microsomes, from cultured skin fibroblasts of patients with Refsum disease (7) and rhizomelic chondrodysplasia punctata (RCDP) (6) also support the conclusion that in humans the major site of a-oxidation of Phytanic Acid to pristanic Acid is the peroxisome. The oxidation of Phytanic Acid to pristanic Acid involves at least four steps: activation of Phytanic Acid to phytanoyl-CoA, a-hydroxylation to a-hydroxyPhytanic Acid, conversion to 2-ketoPhytanic Acid, and finally decar- boxylation to a 19-carbon homologue, pristanic Acid. The enzyme for activation of Phytanic Acid (phytanoyl-CoA li-

Kalipada Pahan - One of the best experts on this subject based on the ideXlab platform.

  • Refsum disease: a defect in the a-oxidation of Phytanic Acid in peroxisomes
    2013
    Co-Authors: Inderjit Singh, Kalipada Pahan, Avtar K. Singh, Earnest Barbosat
    Abstract:

    Abstract The oxidation of Phytanic Acid to pristanic Acid was previously demonstrated to be deficient in monolayer cultures of skin fibroblasts (Hemdon et al. 1969. J. Clin. Invest. 48 1017-1032). However, identification of subcellular organelle with deficient enzyme activity has not been established. To define the subcellular organelle with deficient enzyme activity in the catabolism of Phytanic Acid, we measured the oxidation of [l-14C] Phytanic Acid to 14C02 and pristanic Acid in different subcellular organelles isolated from cultured skin fibroblasts from control and Refsum patients. The rates of oxidation of Phytanic Acid in peroxisomes, mitochondria, and endoplasmic reticulum were 37.1 * 2.65, 1.9 * 0.3, and 0.4 * 0.07 pmol/h per mg protein, respectively, from control fibroblasts. The Phytanic Acid oxidation activity in mitochondria (2.04 0.7 pmol/h per mg protein) and endoplasmic reticulum (0.43 * 0.2 pmol/h per mg protein) from Refsum fibroblasts was similar to control fibroblasts. However, Phytanic Acid oxidation in peroxisomes from Refsum fibroblasts was not detected at all the protein concentrations tested. On the other hand, the peroxisomes from Refsum fibroblasts had normal rates of activation and oxidation of palmitic and lignoceric Acids, suggesting that the peroxisomes isolated from Refsum fibroblasts were metabolically active. The phytanoyl-CoA ligase, the first enzyme in the a-oxidation pathway, had activity similar to that in peroxisomes from control (9.86 * 0.09 nmol/h per mg protein) and Refsum (10.25 f 0.31 nmol/h per mg protein) fibroblasts. 819 The data described here clearly demonstrate that pathognomonic accumulation of Phytanic Acid in patients with Refsum disease is due to the deficient activity of peroxisomal a-oxidation enzym

  • Phytanic Acid oxidation normal activation and transport yet defective alpha hydroxylation of Phytanic Acid in peroxisomes from refsum disease and rhizomelic chondrodysplasia punctata
    Journal of Lipid Research, 1996
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Inderjit Singh
    Abstract:

    In humans the oxidation of Phytanic Acid is a peroxisomal function. To understand the possible mechanisms for the pathognomic accumulation of Phytanic Acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chondrodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of Phytanic Acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP subjects. Activation of Phytanic Acid was normal in peroxisomes from both RD and RCDP. Transport of Phytanic Acid or phytanoyl-CoA in the absence or presence of fatty Acid activating cofactors (ATP, MgCl2, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of [(2,3)-3H]- or [1-14C]Phytanic Acid, or [1-14C]phytanoyl-CoA (substrate for the first step of alpha-oxidation) but normal oxidation of [1-14C] alpha-hydroxyPhytanic Acid (substrate for the second step of the alpha-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of Phytanic Acid in plasma and body fluids of RD is due to the deficiency of Phytanic Acid alpha-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of [1-14C]Phytanic Acid or phytanoyl-CoA or [(2,3)-3H]Phytanic Acid, the oxidation of [1-14C] alpha-hydroxyPhytanic Acid was also deficient, indicating that in RCDP the activities both of alpha-hydroxylation of Phytanic Acid and decarboxylation of alpha-hydroxyPhytanic Acid are deficient. These observations indicate that peroxisomal membrane functions (Phytanic Acid activation and transport) in Phytanic Acid metabolism are normal in both RD and RCDP. The defect in RD is in the alpha-hydroxylation of Phytanic Acid; whereas in RCDP both alpha-hydroxylation of Phytanic Acid as well as decarboxylation of alpha-hydroxyPhytanic Acid are deficient.

  • Phytanic Acid oxidation: normal activation and transport yet defective alpha-hydroxylation of Phytanic Acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata.
    Journal of lipid research, 1996
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Inderjit Singh
    Abstract:

    In humans the oxidation of Phytanic Acid is a per- oxisomal function. To understand the possible mechanisms for the pathognomic accumulation of Phytanic Acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chon- drodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of Phytanic Acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP sub- jects. Activation of Phytanic Acid was normal in peroxisomes from both RD and RCDP. Transport of Phytanic Acid or phytanoyl-CoA in the absence or presence of fatty Acid acti- vating cofactors (ATP, MgC12, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of ((2,3)JH)- or (1-14C)Phytanic Acid, or (l- Wlphytanoyl-CoA (substrate for the first step of a-oxidation) but normal oxidation of ( l-14C)a-hydroxyPhytanic Acid (sub- strate for the second step of the a-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of Phytanic Acid in plasma and body fluids of RD is due to the deficiency of Phytanic Acid a-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of ( 1-14ClPhytanic Acid or phytanoyl-CoA or ((2,3)sH)Phytanic Acid, the oxidation of ( l-W)a-hy- droxyPhytanic Acid was also deficient, indicating that in RCDP the activities both of a-hydroxylation of Phytanic Acid and decarboxylation of a-hydroxyPhytanic Acid are deficient. I These observations indicate that peroxisomal membrane functions (Phytanic Acid activation and transport) in Phytanic Acid metabolism are normal in both RD and RCDP. The defect in RD is in the a-hydroxylation of Phytanic Acid; whereas in RCDP both a-hydroxylation of Phytanic Acid as well as decarboxylation of a-hydroxyPhytanic Acid are defi- cient.-Pahan, K., M. Khan, and I. Singh. Phytanic Acid oxi- dation: normal activation and transport yet defective a-hy- droxylation of Phytanic Acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata. J. Lipid Res. 1996.37: 1137-1143.

  • Ketoconazole and other imidazole derivatives are potent inhibitors of peroxisomal Phytanic Acid α-oxidation
    FEBS letters, 1995
    Co-Authors: Kalipada Pahan, Mushfiquddin Khan, Brian T. Smith, Inderjit Singh
    Abstract:

    The imidazole antimycotics like ketoconazole, clotrimazole, bifonazole, miconazole and CO, known as powerful inhibitors of cytochrome P-450, are potent inhibitors of peroxisomal Phytanic Acid α-oxidation to pristanic Acid suggesting the possible involvement of the cytochrome P-450 mono-oxygenase system in this oxidation. In contrast to the inhibition of the oxidation of [1-14C]Phytanic Acid, [1-14C]phytanoyl-CoA and [(2,3)-3H]Phytanic Acid, these drugs and CO have no effect on the oxidation of [1-14C]α-hydroxy Phytanic Acid indicating that these drugs and CO inhibit only the α-hydroxylation of Phytanic Acid. These studies using purified peroxisomes from liver and cultured human skin fibroblasts and Hep G2 cells clearly demonstrate that α-hydroxylation, an intermediate step in the α-oxidation of Phytanic Acid found to be impaired in Refsum Disease, is mediated by cytochrome P-450 containing enzyme.

  • Phytanic Acid oxidation: topographical localization of phytanoyl-CoA ligase and transport of Phytanic Acid into human peroxisomes
    Journal of lipid research, 1995
    Co-Authors: Kalipada Pahan, Inderjit Singh
    Abstract:

    To understand the possible role of phytanoyl-CoA li- gase, present in the membrane, in the oxidation of Phytanic Acid in the matrix of peroxisomes (Pahan, K. and I. Singh. 1993. FEES Lett. 333: 154-158) we examined the transport of Phytanic Acid/phytanoyl-CoA into peroxisomes and the topology of the active site of phytanoyl-CoA ligase in the peroxisomal mem- brane. The increase in lignoceroyl-CoA ligase as compared to no change in the activities of palmitoyl-CoA and phytanoyl-CoA li- gases when peroxisomes were disrupted with detergent or soni- cation and inhibition of the activities of both palmitoyl-CoA and phytanoyl-CoA ligase by impermeable inhibitor of acyl-CoA li- gases (mercury-dextran) and trypsin treatment in the intact peroxisomes. On the other hand, the lignoceroyl-CoA ligase ac- tivity was inhibited by mercury-dextran and trypsin only in the disrupted peroxisomes. Taken together, these studies support the conclusion that the enzymatic site of phytanoyl-CoA ligase is on the cytoplasmic surface of peroxisomal membrane. This implies that phytanoyl-CoA is synthesized on the cytoplasmic surface of peroxisomal membrane and is translocated through the mem- brane for its a-oxidation to pristanic Acid in the matrix of perox- isomes. llilll To delineate the transport for Phytanic Acid through the peroxisomal membrane, we examined cofactors and energy requirements for its transport into peroxisomes. The similar rates of transport of phytanoyl-CoA and Phytanic Acid under conditions favorable for fatty Acid activation (presence of ATP, CoASH, and MgC12) and the lack of transport of Phytanic Acid when ATP and/or CoASH were removed or replaced with their inactive analogues (ATP and/or CoASH) from assay medium clearly demonstrates that the transport of Phytanic Acid requires prior synthesis of phytanoyl-CoA by phytanoyl-CoA ligase. The prerequisite activation of Phytanic Acid to phytanoyl-CoA for its a-oxidation only in intact peroxisomes, and oxidation of free Phytanic Acid in digitonin-permealized peroxisomes or isolated matrix, suggests that phytanoyl-CoA ligase (in peroxisomal membrane) regulates the oxidation of Phytanic Acid in peroxi- somes by providing phytanoyl-CoA for its transport into peroxi- somes.-Pahan, K., and I. Singh. Phytanic Acid oxidation: topographical localization of phytanoyl-CoA ligase and trans- port of Phytanic Acid into human peroxisomes. J Lipid Res. 1995. 36: 986-997. Phytanic Acid (3,7,11,15-tetramethylhexadecanoic Acid), a highly branched isoprenoid-derived fatty Acid, accumu- lates in excessive amounts in the tissues and body fluids of patients with classical Refsum disease (1) and in pa- tients with defects in the biogenesis of peroxisomes (2, 3). Phytanic Acid is not synthesized de novo in humans but is taken exogenously. The ordinary human diet contains 50-100 mg of Phytanic Acid per day mainly as a consti- tuent of animal, dairy, and plant products. Due to the p- methyl group, Phytanic Acid cannot be @-oxidized; there- fore, a-oxidation is the only feasible route for its catabolism (1-4). Studies from our laboratory have demonstrated that in humans Phytanic Acid is a-oxidized to pristanic Acid in peroxisomes, but in rodents this process occurs in mitochondria (5, 6). In human skin fibroblasts the rate of Phytanic Acid oxidation in peroxi- somes was 26 and 130 times greater than that found in mitochondria and microsomes. Moreover, the excessive accumulation of Phytanic Acid and defective a-oxidation of Phytanic Acid in peroxisomes, but not mitochondria or microsomes, from cultured skin fibroblasts of patients with Refsum disease (7) and rhizomelic chondrodysplasia punctata (RCDP) (6) also support the conclusion that in humans the major site of a-oxidation of Phytanic Acid to pristanic Acid is the peroxisome. The oxidation of Phytanic Acid to pristanic Acid involves at least four steps: activation of Phytanic Acid to phytanoyl-CoA, a-hydroxylation to a-hydroxyPhytanic Acid, conversion to 2-ketoPhytanic Acid, and finally decar- boxylation to a 19-carbon homologue, pristanic Acid. The enzyme for activation of Phytanic Acid (phytanoyl-CoA li-

R. J. A. Wanders - One of the best experts on this subject based on the ideXlab platform.

  • peroxisomes refsum s disease and the α and ω oxidation of Phytanic Acid
    Biochemical Society Transactions, 2007
    Co-Authors: R. J. A. Wanders, J. C. Komen
    Abstract:

    In the present paper, we describe the current state of knowledge regarding the enzymology of the Phytanic Acid α-oxidation pathway. The product of Phytanic Acid α-oxidation, i.e. pristanic Acid, undergoes three cycles of β-oxidation in peroxisomes after which the products, including 4,8-dimethylnonanoyl-CoA, propionyl-CoA and acetyl-CoA, are exported from the peroxisome via one of two routes, including (i) the carnitine-dependent route, mediated by CRAT (carnitine acetyltransferase) and CROT (carnitine O-octanoyltransferase), and (ii) the free Acid route, mediated by one or more of the peroxisomal ACOTs (acyl-CoA thioesterases). We also describe our recent data on the ω-oxidation of Phytanic Acid, especially since pharmacological up-regulation of this pathway may form the basis of a new treatment strategy for ARD (adult Refsum9s disease). In patients suffering from ARD, Phytanic Acid accumulates in tissues and body fluids due to a defect in the α-oxidation system.

  • Phytanic Acid: production from phytol, its breakdown and role in human disease
    Cellular and Molecular Life Sciences, 2006
    Co-Authors: D. M. Brink, R. J. A. Wanders
    Abstract:

    Phytanic Acid is a branched-chain fatty Acid that accumulates in a variety of metabolic disorders. High levels of Phytanic Acid found in patients can exceed the millimolar range and lead to severe symptoms. Degradation of Phytanic Acid takes place by α-oxidation inside the peroxisome. A deficiency of its breakdown, leading to elevated levels, can result from either a general peroxisomal dysfunction or from a defect in one of the enzymes involved in α-oxidation. Research on Refsum disease, belonging to the latter group of disorders and characterized by a deficiency of the first enzyme of α-oxidation, has extended our knowledge of Phytanic Acid metabolism and pathology of the disease greatly over the past few decades. This review will centre on this research on Phytanic Acid: its origin, the mechanism by which its α-oxidation takes place, its role in human disease and the way it is produced from phytol.

  • Identification of the cytochrome P450 enzymes responsible for the ω‐hydroxylation of Phytanic Acid
    FEBS letters, 2006
    Co-Authors: J. C. Komen, R. J. A. Wanders
    Abstract:

    Patients suffering from Refsum disease have a defect in the α-oxidation pathway which results in the accumulation of Phytanic Acid in plasma and tissues. Our previous studies have shown that Phytanic Acid is also a substrate for the ω-oxidation pathway. With the use of specific inhibitors we now show that members of the cytochrome P450 (CYP450) family 4 class are responsible for Phytanic Acid ω-hydroxylation. Incubations with microsomes containing human recombinant CYP450s (Supersomes™) revealed that multiple CYP450 enzymes of the family 4 class are able to ω-hydroxylate Phytanic Acid with the following order of efficiency: CYP4F3A > CYP4F3B > CYP4F2 > CYP4A11.

  • Characterization of Phytanic Acid ω-hydroxylation in human liver microsomes
    Molecular genetics and metabolism, 2005
    Co-Authors: J. C. Komen, M Duran, R. J. A. Wanders
    Abstract:

    Abstract Phytanic Acid is a 3-methyl branched-chain fatty Acid which originates from dietary sources. Since the 3-methyl group blocks regular β-oxidation, it is broken down by peroxisomal α-oxidation. Adult Refsum disease patients accumulate Phytanic Acid as a result of an impairment in peroxisomal α-oxidation, caused by the deficient activity of the enzyme phytanoyl-CoA hydroxylase in the majority of patients. In this paper, we studied an alternative degradation route for Phytanic Acid, namely ω-oxidation. During ω-oxidation a fatty Acid is hydroxylated at its ω-end by a member of the cytochrome P450 multi-enzyme family. Subsequently, an alcohol dehydrogenase converts the formed hydroxyl group into an aldehyde, which is then converted into a carboxyl-group by an aldehyde dehydrogenase. In case of Phytanic Acid ω-hydroxylation would lead to the formation of phytanedioic Acid, which can be degraded by β-oxidation from the ω-end. Here, we show that Phytanic Acid indeed undergoes ω- and (ω-1)-hydroxylation in pooled human liver microsomes in an NADPH-dependent manner with a ratio of 15:1. Studies with imidazole antimycotics indicate that these reactions are catalyzed by one or more cytochrome P450 enzymes. Induction of the cytochrome P450 involved in Phytanic Acid ω-hydroxylation may increase the flux through the ω-oxidation pathway, causing increased clearance of Phytanic Acid in ARD patients. Hence, this alternative catabolic pathway is of potential therapeutic relevance.

  • Characterization of Phytanic Acid -hydroxylation in human liver microsomes
    2005
    Co-Authors: M Duran, R. J. A. Wanders
    Abstract:

    Phytanic Acid is a 3-methyl branched-chain fatty Acid which originates from dietary sources. Since the 3-methyl group blocks regular -oxidation, it is broken down by peroxisomal -oxidation. Adult Refsum disease patients accumulate Phytanic Acid as a result of an impairment in peroxisomal -oxidation, caused by the deWcient activity of the enzyme phytanoyl-CoA hydroxylase in the majority of patients. In this paper, we studied an alternative degradation route for Phytanic Acid, namely -oxidation. During -oxidation a fatty Acid is hydroxylated at its -end by a member of the cytochrome P450 multi-enzyme family. Subsequently, an alcohol dehydrogenase converts the formed hydroxyl group into an aldehyde, which is then converted into a carboxyl-group by an aldehyde dehydrogenase. In case of Phytanic Acid -hydroxylation would lead to the formation of phytanedioic Acid, which can be degraded by -oxidation from the -end. Here, we show that Phytanic Acid indeed undergoes - and (-1)-hydroxylation in pooled human liver microsomes in an NADPH-dependent manner with a ratio of 15:1. Studies with imidazole antimycotics indicate that these reactions are catalyzed by one or more cytochrome P450 enzymes. Induction of the cytochrome P450 involved in Phytanic Acid -hydroxylation may increase the Xux through the -oxidation pathway, causing increased clearance of Phytanic Acid in ARD patients. Hence, this alternative catabolic pathway is of potential therapeutic relevance.

Paul A. Watkins - One of the best experts on this subject based on the ideXlab platform.

  • Identification of differences in human and great ape Phytanic Acid metabolism that could influence gene expression profiles and physiological functions
    BMC Physiology, 2010
    Co-Authors: Paul A. Watkins, Ann B. Moser, Cicely B Toomer, Steven J Steinberg, Hugo W Moser, Mazen W Karaman, Krishna Ramaswamy, Kimberly D Siegmund, Oliver A Ryder, Joseph G Hacia
    Abstract:

    Background It has been proposed that anatomical differences in human and great ape guts arose in response to species-specific diets and energy demands. To investigate functional genomic consequences of these differences, we compared their physiological levels of Phytanic Acid, a branched chain fatty Acid that can be derived from the microbial degradation of chlorophyll in ruminant guts. Humans who accumulate large stores of Phytanic Acid commonly develop cerebellar ataxia, peripheral polyneuropathy, and retinitis pigmentosa in addition to other medical conditions. Furthermore, Phytanic Acid is an activator of the PPAR-alpha transcription factor that influences the expression of genes relevant to lipid metabolism. Results Despite their trace dietary Phytanic Acid intake, all great ape species had elevated red blood cell (RBC) Phytanic Acid levels relative to humans on diverse diets. Unlike humans, chimpanzees showed sexual dimorphism in RBC Phytanic Acid levels, which were higher in males relative to females. Cultured skin fibroblasts from all species had a robust capacity to degrade Phytanic Acid. We provide indirect evidence that great apes, in contrast to humans, derive significant amounts of Phytanic Acid from the hindgut fermentation of plant materials. This would represent a novel reduction of metabolic activity in humans relative to the great apes. Conclusion We identified differences in the physiological levels of Phytanic Acid in humans and great apes and propose this is causally related to their gut anatomies and microbiomes. Phytanic Acid levels could contribute to cross-species and sex-specific differences in human and great ape transcriptomes, especially those related to lipid metabolism. Based on the medical conditions caused by Phytanic Acid accumulation, we suggest that differences in Phytanic Acid metabolism could influence the functions of human and great ape nervous, cardiovascular, and skeletal systems.

  • Identification of differences in human and great ape Phytanic Acid metabolism that could influence gene expression profiles and physiological functions
    BMC physiology, 2010
    Co-Authors: Paul A. Watkins, Ann B. Moser, Cicely B Toomer, Steven J Steinberg, Hugo W Moser, Mazen W Karaman, Krishna Ramaswamy, Kimberly D Siegmund, D Rick Lee, John J Ely
    Abstract:

    It has been proposed that anatomical differences in human and great ape guts arose in response to species-specific diets and energy demands. To investigate functional genomic consequences of these differences, we compared their physiological levels of Phytanic Acid, a branched chain fatty Acid that can be derived from the microbial degradation of chlorophyll in ruminant guts. Humans who accumulate large stores of Phytanic Acid commonly develop cerebellar ataxia, peripheral polyneuropathy, and retinitis pigmentosa in addition to other medical conditions. Furthermore, Phytanic Acid is an activator of the PPAR-alpha transcription factor that influences the expression of genes relevant to lipid metabolism. Despite their trace dietary Phytanic Acid intake, all great ape species had elevated red blood cell (RBC) Phytanic Acid levels relative to humans on diverse diets. Unlike humans, chimpanzees showed sexual dimorphism in RBC Phytanic Acid levels, which were higher in males relative to females. Cultured skin fibroblasts from all species had a robust capacity to degrade Phytanic Acid. We provide indirect evidence that great apes, in contrast to humans, derive significant amounts of Phytanic Acid from the hindgut fermentation of plant materials. This would represent a novel reduction of metabolic activity in humans relative to the great apes. We identified differences in the physiological levels of Phytanic Acid in humans and great apes and propose this is causally related to their gut anatomies and microbiomes. Phytanic Acid levels could contribute to cross-species and sex-specific differences in human and great ape transcriptomes, especially those related to lipid metabolism. Based on the medical conditions caused by Phytanic Acid accumulation, we suggest that differences in Phytanic Acid metabolism could influence the functions of human and great ape nervous, cardiovascular, and skeletal systems.

  • Phytanic Acid α‐oxidation in Rat Liver Peroxisomes
    European journal of biochemistry, 1995
    Co-Authors: Stephanie J. Mihalik, Anne M. Rainville, Paul A. Watkins
    Abstract:

    Patients with generalized peroxisomal disorders, rhizomelic chondrodysplasia punctata, and Refsum disease are all unable to α-oxidize 3,7,11,15-tetramethylhexadecanoic (Phytanic) Acid. The exact cause of the oxidation defect in these patients is not well characterized, in part because there is only limited knowledge of the biochemical pathway. In 1969, the α-oxidation of Phytanic Acid was reported [Tsai, S.-C., Avigan, J. & Steinberg, D. (1969) Studies on the α-oxidation of Phytanic Acid by rat liver mitochondria, J. Biol. Chem. 244, 2682–2692] to involve the formation of an α-hydroxyPhytanic Acid intermediate prior to removal of the α carbon. Subsequently, most researchers have had difficulty detecting this intermediate. In the present study, cofactors known to form hydroxy intermediates by both monooxygen-ase and dioxygenase reaction mechanisms were incubated with purified rat liver peroxisomes and either [2,3-3H]Phytanic Acid or [1-14C]Phytanic Acid. Reaction products were separated by reverse-phase HPLC. A single reaction product, identified as α-hydroxyphytanoyl-CoA rather than the free fatty Acid, was detected when 2-oxoglutarate/Fe+2/ascorbate, cofactors associated with a dioxygenase reaction mechanism, were present. Concomitant with α-hydroxyphytanoyl-CoA production, there was an increased accumulation of formate and CO2. This increase in α-oxidation products is evidence that α-hydroxyphytanoyl-CoA is a true pathway intermediate and that the entire pathway functions in peroxisomes. In contrast, α-hydroxyphytanoyl-CoA was not formed in any quantity in mitochondria. These studies suggest that the α-hydroxylation step of Phytanic Acid oxidation, which has been shown to be defective in Refsum disease, is located in peroxisomes.

  • Phytanic Acid α oxidation in rat liver peroxisomes
    FEBS Journal, 1995
    Co-Authors: Stephanie J. Mihalik, Anne M. Rainville, Paul A. Watkins
    Abstract:

    Patients with generalized peroxisomal disorders, rhizomelic chondrodysplasia punctata, and Refsum disease are all unable to α-oxidize 3,7,11,15-tetramethylhexadecanoic (Phytanic) Acid. The exact cause of the oxidation defect in these patients is not well characterized, in part because there is only limited knowledge of the biochemical pathway. In 1969, the α-oxidation of Phytanic Acid was reported [Tsai, S.-C., Avigan, J. & Steinberg, D. (1969) Studies on the α-oxidation of Phytanic Acid by rat liver mitochondria, J. Biol. Chem. 244, 2682–2692] to involve the formation of an α-hydroxyPhytanic Acid intermediate prior to removal of the α carbon. Subsequently, most researchers have had difficulty detecting this intermediate. In the present study, cofactors known to form hydroxy intermediates by both monooxygen-ase and dioxygenase reaction mechanisms were incubated with purified rat liver peroxisomes and either [2,3-3H]Phytanic Acid or [1-14C]Phytanic Acid. Reaction products were separated by reverse-phase HPLC. A single reaction product, identified as α-hydroxyphytanoyl-CoA rather than the free fatty Acid, was detected when 2-oxoglutarate/Fe+2/ascorbate, cofactors associated with a dioxygenase reaction mechanism, were present. Concomitant with α-hydroxyphytanoyl-CoA production, there was an increased accumulation of formate and CO2. This increase in α-oxidation products is evidence that α-hydroxyphytanoyl-CoA is a true pathway intermediate and that the entire pathway functions in peroxisomes. In contrast, α-hydroxyphytanoyl-CoA was not formed in any quantity in mitochondria. These studies suggest that the α-hydroxylation step of Phytanic Acid oxidation, which has been shown to be defective in Refsum disease, is located in peroxisomes.

N M Verhoeven - One of the best experts on this subject based on the ideXlab platform.

  • Human metabolism of Phytanic Acid and pristanic Acid
    Progress in lipid research, 2001
    Co-Authors: N M Verhoeven, Cornelis Jakobs
    Abstract:

    Phytanic Acid is a methyl-branched fatty Acid present in the human diet. Due to its structure, degradation by beta-oxidation is impossible. Instead, Phytanic Acid is oxidized by alpha-oxidation, yielding pristanic Acid. Despite many efforts to elucidate the alpha-oxidation pathway, it remained unknown for more than 30 years. In recent years, the mechanism of alpha-oxidation as well as the enzymes involved in the process have been elucidated. The process was found to involve activation, followed by hydroxylase, lyase and dehydrogenase reactions. Part, if not all of the reactions were found to take place in peroxisomes. The final product of Phytanic Acid alpha-oxidation is pristanic Acid. This fatty Acid is degraded by peroxisomal beta-oxidation. After 3 steps of beta-oxidation in the peroxisome, the product is esterified to carnitine and shuttled to the mitochondrion for further oxidation. Several inborn errors with one or more deficiencies in the Phytanic Acid and pristanic degradation have been described. The clinical expressions of these disorders are heterogeneous, and vary between severe neonatal and often fatal symptoms and milder syndromes with late onset. Biochemically, these disorders are characterized by accumulation of Phytanic and/or pristanic Acid in tissues and body fluids. Several of the inborn errors involving Phytanic Acid and/or pristanic Acid metabolism have been characterized on the molecular level.

  • The metabolism of Phytanic Acid and pristanic Acid in man: A review
    Journal of Inherited Metabolic Disease, 1998
    Co-Authors: N M Verhoeven, R. J. A. Wanders, J.-m. Saudubray, C. Jakobs
    Abstract:

    The branched-chain fatty Acid Phytanic Acid is a constituent of the diet, present in diary products, meat and fish. Degradation of this fatty Acid in the human body is preceded by activation to phytanoyl-CoA and starts withone cycle of α-oxidation. Intermediates in this pathway are 2-hydroxy-phytanoyl-CoA and pristanal; the product is pristanic Acid. After activation, pristanic Acid is degraded by peroxisomal β-oxidation. Several disorders havebeen described in which Phytanic Acid accumulates, in some cases in combination with pristanic Acid. In classical Refsum disease, the enzyme that converts phytanoyl-CoA into 2-hydroxyphytanoyl-CoA – phytanoyl-CoA hydroxylase – is deficient, resulting in highly elevated levels of Phytanic Acid in blood and tissues. Also in rhizomelic chondrodysplasia punctata, Phytanic Acid accumulates, owing to a deficiency in the peroxisomal import of proteins with a peroxisomal targeting sequence type 2. In patients affected with generalized peroxisomal disorders, degradation of both Phytanic Acid and pristanic Acid is impaired owing to absence of functional peroxisomes. In bifunctional protein deficiency, the disturbed oxidation of pristanic Acid results in elevated levels of this fatty Acid and a secondary elevation of Phytanic Acid. In addition, several variant peroxisomal disorders with unknown aetiology have been described in which Phytanic Acid and/or pristanic Acid accumulate. This review describes the discovery of Phytanic Acid and pristanic Acid and the initial attempts to elucidate the origins and fates of these fatty Acids. The current knowledge on the α-oxidation and β-oxidation of these branched-chain fatty Acids is summarized. The disorders in which Phytanic Acid and/or pristanic Acid accumulate are described and some remarks are made on the pathogenic mechanisms of elevated levels of Phytanic Acid and pristanic Acid.

  • Studies on the oxidation of Phytanic Acid and pristanic Acid in human fibroblasts by acylcarnitine analysis
    Journal of inherited metabolic disease, 1998
    Co-Authors: N M Verhoeven, C.a.j.m. Jakobs, R. J. A. Wanders, H. J. Ten Brink, Charles R Roe
    Abstract:

    The alpha-oxidation of Phytanic Acid and the beta-oxidation of pristanitc Acid were investigated in cultured fibroblasts from controls and patients affected with different peroxisomal disorders using deuterated substrates. Formation of [omega-2H6]4,8-dimethylnonanoylcarnitine ([omega-2H6]C11-carnitine) from [omega-2H6]Phytanic Acid and [omega-2H6]pristanic Acid was used as marker for these processes. Analysis was performed by tandem mass spectrometry. In normal cells, formation of [omega-2H6]C11-carnitine from both [omega-2H6]Phytanic Acid and [omega-2H6]pristanic Acid was observed. When peroxisome-deficient fibroblasts were incubated with these substrates, [omega-2H6]C11-carnitine was not detectable or, in two cases, very low, which results from deficiencies in both peroxisomal alpha- and beta-oxidation. In cells with an isolated beta-oxidation defect at the level of the peroxisomal bifunctional protein, formation of [omega-2H6]C11-carnitine could also not be detected. Cells with an isolated defect in the alpha-oxidation of Phytanic Acid, obtained from patients affected with Refsum disease (McKusick 266500) or rhizomelic chondrodysplasia punctata (McKusick 215100), did not form [omega-2H6]C11-carnitine from [omega-2H6]Phytanic Acid. The observed formation of [omega-2H6]C11-carnitine from [omega-2H6]pristanic Acid in these cells is in accordance with a normal peroxisomal beta-oxidation in these disorders. This study shows that separate incubation of fibroblasts with [omega-2H6]Phytanic Acid and [omega-2H6]pristanic Acid, followed by acylcarnitine analysis in the medium by tandem mass spectrometry, can be used for screening cell lines for deficiencies in the peroxisomal alpha- and beta-oxidation pathways. Phytanic Acid (3,7,11,15-tetramethylhexadecanoic Acid) and pristanic Acid (2,6,10,14-tetramethylpentadecanoic Acid) are branched-chain fatty Acids that are constituents of the human diet. As Phytanic Acid possesses a beta-methyl group, it cannot be degraded by beta-oxidation. Instead, Phytanic Acid is first degraded by alpha-oxidation, yielding pristanic Acid, which is subsequently degraded by beta-oxidation (Figure 1). Phytanic Acid alpha-oxidation is thought to occur partly, and pristanic Acid beta-oxidation exclusively, in peroxisomes (see Wanders et al 1995 for review). Accumulation of Phytanic Acid and pristanic Acid is found in blood and tissues of patients affected with generalized peroxisomal disorders. In this type of disorder, no morphologically distinguishable peroxisomes are present in tissues, resulting in accumulation of metabolites that are normally metabolized in these organelles (see Wanders et al 1995 for review). The group of generalized peroxisomal disorders consists of three diseases, differing in clinical presentation. Patients suffering from the most severe disease, Zellweger syndrome (McKusick 214100), have symptoms from birth on and usually do not live beyond their first year of life. Neonatal adrenoleukodystrophy (N-ALD, McKusick 202370) has a milder presentation, whereas infantile Refsum disease (IRD, McKusick 266510) is the mildest form among the generalized peroxisomal disorders. Not only in these generalized peroxisomal disorders, but also in some isolated peroxisomal beta-oxidation defects, elevated levels of Phytanic Acid and pristanic Acid are found (ten Brink et al 1992a). The elevated Phytanic Acid levels are considered to be caused by product inhibition of alpha-oxidation by accumulating pristanic Acid. This is reflected in a highly elevated pristanic Acid to Phytanic Acid ratio in plasma from patients suffering from bifunctional protein deficiency or peroxisomal thiolase deficiency (ten Brink et al 1992a). Elevated Phytanic Acid concentrations are also found in plasma from patients affected with classical Refsum disease and rhizomelic chondrodysplasia punctata (RCDP). As pristanic Acid beta-oxidation is not disturbed in these disorders, pristanic Acid levels are normal (ten Brink et al 1992

  • Phytanic Acid alpha-oxidation in peroxisomal disorders: studies in cultured human fibroblasts.
    Biochimica et biophysica acta, 1997
    Co-Authors: N M Verhoeven, D S Schor, Christine Jakobs
    Abstract:

    We studied the alpha-oxidation of Phytanic Acid in human fibroblasts of controls and patients affected with classical Refsum disease, rhizomelic chondrodysplasia punctata, generalized peroxisomal disorders and peroxisomal bifunctional protein deficiency. Cultured fibroblasts were incubated with Phytanic Acid, after which medium and cells were collected separately. 2-HydroxyPhytanic Acid and pristanic Acid were measured in the medium and cells by stable isotope dilution gas chromatography mass spectrometry. In controls, 2-hydroxyPhytanic Acid and pristanic Acid could be detected in the medium after incubation with Phytanic Acid, proving that alpha-oxidation of Phytanic Acid via 2-hydroxyphytanoyl-CoA to pristanic Acid was active and intermediates were excreted into the medium. In cells from patients with a defective alpha-oxidation (Refsum disease, rhizomelic chondrodysplasia punctata and generalized peroxisomal disorders) 2-hydroxyPhytanic Acid and pristanic Acid were low or not detectable, showing that in these disorders the hydroxylation of phytanoyl-CoA to 2-hydroxyphytanoyl-CoA is deficient. In cells with a peroxisomal beta-oxidation defect, 2-hydroxyPhytanic Acid and pristanic Acid were formed in amounts comparable to those in the controls.

  • Stable isotope studies of Phytanic Acid alpha-oxidation: in vivo production of formic Acid.
    European journal of pediatrics, 1997
    Co-Authors: N M Verhoeven, D S Schor, Henri Brunengraber, Stephen F Previs, Christine Jakobs
    Abstract:

    The aim of this study was to test whether formate is formed during alpha-oxidation of Phytanic Acid in humans. To a healthy volunteer, [1-13C]Phytanic Acid was given as an oral substrate in a dose of 15 mg/kg body weight, after which plasma, urine and breath air samples were collected during 35 h. The plasma concentrations of [1-13C]-Phytanic Acid, 2-hydroxy[1-13C]Phytanic Acid, pristanic Acid and [13C]formate were analysed. The [1-13C]Phytanic Acid concentration increased within 5-7 h to 105 mumol/l, then decreased. Formation of 2-hydroxy[1-13C]Phytanic Acid increased during the first 11 h after which it decreased during the next 20 h. Pristanic Acid increased slightly during the test. In breath air, 13CO2 enrichment was measured, showing a cumulative output of ca. 30% of the ingested dose after 35 h. In both urine and plasma, enrichment of [13C]formate, higher than that of 13CO2 was demonstrated. These findings show that formate is a decarboxylation product in the alpha-oxidation of Phytanic Acid in vivo.