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Transcellular metabolism of eicosanoids in circulation
21)0 EFA & Eicosanoids 1997 - Edinburgh
Wl
Wednesday 23 July
W2
The Second Hugh Sinclair Memorial Lecture
The First Ulf von Euler Memorial Lecture
Howard Sprecher, The Ohio State University, USA
Ryszard J Gryglewski, Jagiellonian University, Poland
THE ROLE PLAYED BY MICROSOMES AND PEROXISOMES IN REGULATING UNSATURATED FATTY ACID BIOSYNTHESIS
TRANSCELLULAR METABOLISM OF EICOSANOIDS CIRCULATION Ryszard J. Gryglewski, Chair of Pharmacology, Medical College of Jagiellonian University, Cracow, Poland
Howard Sprecher, Dept. Medical Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA The biosynthesis of 22-carbon fatty acids, with their first double bond at position 4 requires that after 24-carbon acids are made in the endoplasraic reticulum (ER), they must move to peroxisomes for one cycle of 13-oxidation. The chain-shortened acids then move back to the ER for use in membrane lipid synthesis. Twenty four carbon (n-6) and (n-3) acids were poor substrates for acylation into 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) by microsomes, suggesting that they move to peroxisomes. The preferred metabolic fate of [1J4C] and [3J4C]labeled acids, whose continued degradation requires only the enzymes of saturated fatty acid degradation, was 13-oxidation rather than esterification. Conversely, when an acid with its first double bond at position 4 was the substrate, or generated from a [3J4C]labeled precursor, its preferred metabolic fate was to move out of peroxisomes for esterification into 1-acyI-GPC in the ER. When a cycle of 13-oxidation requires NADPH-dependent 2,4-dienoyl-CoA reductase the substrate for this reaction always accumulated. The slow rate of this peroxisoraal reaction suggests that when an acid with its first double bond at position 4 is produced it is preferentially esterified rather than oxidized. Indeed, it was observed that there was an inverse relationship between rates of peroxisoraal degradation versus those for esterification into 1-acyl-GPC. When arachidonate was generated by peroxisomai degradation of 22-or 24-carbon (n-6) precursors its preferred metabolic fate was esterification rather than continued degradation. Peroxisomes contain A3'5,Az'a-dienoyl-CoA isomerase. Some arachidonate may be degraded via a pathway using this enzyme and the reductase. If this is the case, 6,9,12-18:3 a microsomal precursor of arachidonate, would be the product of the first cycle of degradation. It was further shown that the ER and peroxisomes can interact to produce linoleate from arachidonate. The ER pathways for unsaturated fatty acid biosynthesis now require that two acids in each pathway are desaturated at position 6 and three acids in each pathway must be chain elongated. Peroxisomal-ER interactions are not only required to make acids with a double bond at position 4, but they may provide the cell with a pathway for recycling unsaturated fatty acids.
IN
An idea of transcellular metabolism of eicosanoids emerged in 1976 out of a series of our papers on discovery of prostacyclin (PGI2) (Bunting, Gryglewski, Moncada, Vane). We found that rings of aorta of the indomethacin - treated rabbits still were capable to make PGI 2 provided that activated blood platelets were available to supply them with prostaglandin endoperoxide (PGH2). We hypothesized that in arterial circulation an inflow of PGH 2 from the shear-stress activated platelets to endothelial cells would trigger local generation of minute amounts of PGI 2 which prevent platelets from adhesion and formation of parietal microthrombi. Twenty years later Folco, Maclouf, Sala and others described an analogous transcellular metabolism between activated granulocytes (a source of leukotriene A4-LTA4) and endothelial cells (producers of LTC4) within coronary circulation of the rabbit. LTC 4 in Ioco pascendi brought about cardiac damage. Thus liable intermediates (PGH 2 or LTA4) from blood morphological elements when transferred to endothelial cells may give rise to either protective (PGI2) or suicidal (LTC4) eicosanoid mediators. Pharmacological modulation of transcellular metabolism of eicosanoids constitutes a potential therapeutical approach in the treatment of thrombosis, myocardial infarction, bronchial asthma or septic shock.
Wl
Wednesday 23 July
W2
The Second Hugh Sinclair Memorial Lecture
The First Ulf von Euler Memorial Lecture
Howard Sprecher, The Ohio State University, USA
Ryszard J Gryglewski, Jagiellonian University, Poland
THE ROLE PLAYED BY MICROSOMES AND PEROXISOMES IN REGULATING UNSATURATED FATTY ACID BIOSYNTHESIS
TRANSCELLULAR METABOLISM OF EICOSANOIDS CIRCULATION Ryszard J. Gryglewski, Chair of Pharmacology, Medical College of Jagiellonian University, Cracow, Poland
Howard Sprecher, Dept. Medical Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA The biosynthesis of 22-carbon fatty acids, with their first double bond at position 4 requires that after 24-carbon acids are made in the endoplasraic reticulum (ER), they must move to peroxisomes for one cycle of 13-oxidation. The chain-shortened acids then move back to the ER for use in membrane lipid synthesis. Twenty four carbon (n-6) and (n-3) acids were poor substrates for acylation into 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) by microsomes, suggesting that they move to peroxisomes. The preferred metabolic fate of [1J4C] and [3J4C]labeled acids, whose continued degradation requires only the enzymes of saturated fatty acid degradation, was 13-oxidation rather than esterification. Conversely, when an acid with its first double bond at position 4 was the substrate, or generated from a [3J4C]labeled precursor, its preferred metabolic fate was to move out of peroxisomes for esterification into 1-acyI-GPC in the ER. When a cycle of 13-oxidation requires NADPH-dependent 2,4-dienoyl-CoA reductase the substrate for this reaction always accumulated. The slow rate of this peroxisoraal reaction suggests that when an acid with its first double bond at position 4 is produced it is preferentially esterified rather than oxidized. Indeed, it was observed that there was an inverse relationship between rates of peroxisoraal degradation versus those for esterification into 1-acyl-GPC. When arachidonate was generated by peroxisomai degradation of 22-or 24-carbon (n-6) precursors its preferred metabolic fate was esterification rather than continued degradation. Peroxisomes contain A3'5,Az'a-dienoyl-CoA isomerase. Some arachidonate may be degraded via a pathway using this enzyme and the reductase. If this is the case, 6,9,12-18:3 a microsomal precursor of arachidonate, would be the product of the first cycle of degradation. It was further shown that the ER and peroxisomes can interact to produce linoleate from arachidonate. The ER pathways for unsaturated fatty acid biosynthesis now require that two acids in each pathway are desaturated at position 6 and three acids in each pathway must be chain elongated. Peroxisomal-ER interactions are not only required to make acids with a double bond at position 4, but they may provide the cell with a pathway for recycling unsaturated fatty acids.
IN
An idea of transcellular metabolism of eicosanoids emerged in 1976 out of a series of our papers on discovery of prostacyclin (PGI2) (Bunting, Gryglewski, Moncada, Vane). We found that rings of aorta of the indomethacin - treated rabbits still were capable to make PGI 2 provided that activated blood platelets were available to supply them with prostaglandin endoperoxide (PGH2). We hypothesized that in arterial circulation an inflow of PGH 2 from the shear-stress activated platelets to endothelial cells would trigger local generation of minute amounts of PGI 2 which prevent platelets from adhesion and formation of parietal microthrombi. Twenty years later Folco, Maclouf, Sala and others described an analogous transcellular metabolism between activated granulocytes (a source of leukotriene A4-LTA4) and endothelial cells (producers of LTC4) within coronary circulation of the rabbit. LTC 4 in Ioco pascendi brought about cardiac damage. Thus liable intermediates (PGH 2 or LTA4) from blood morphological elements when transferred to endothelial cells may give rise to either protective (PGI2) or suicidal (LTC4) eicosanoid mediators. Pharmacological modulation of transcellular metabolism of eicosanoids constitutes a potential therapeutical approach in the treatment of thrombosis, myocardial infarction, bronchial asthma or septic shock.