Metabolism of some radiolabeled essential fatty acids in isolated rat hepatocytes is affected by dietary ethanol.

The metabolism of the essential fatty acids [1-14C]20:4n-6, [1-14C]20:5n-3 and [1-14C]22:6n-3 was studied in rat hepatocytes fed ethanol in two different diets. Using a diet with a low lipid content ethanol (1) reduced the elongation of eicosapentaenoic acid, (2) reduced the esterification of docosahexaenoic acid (DHA) in phospholipids (PL), (3) increased the oxidation of DHA, (4) increased the ratio of esterification of DHA in phosphatidylethanolamine (PE) compared to phosphatidylcholine (PC) (PE/PC ratio), (5) altered the formation of PL molecular species, and (6) induced a decrease in the endogenous content of the hepatocytes of arachidonic acid and linoleic acid and an increase in oleic acid, 20:3n-9 and DHA. Using a high lipid diet, only the above-mentioned effect (4) was induced by ethanol, not the effects (1)-(3) and (5)-(6).

Phospholipid molecular species with eicosapentaenoic acid (20:5(n-3)) are less stable than species with arachidonic acid (20:4(n-6)) in isolated rat liver cells.

We have studied the incorporation of [1-14C]20:5(n-3) and [1-14C]20:4(n-6) in the molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in isolated rat liver cells. These two fatty acids are present in very different amounts in endogenous phospholipids, with 20:4 as one of the major fatty acids and 20:5 as a minor and very diet-dependent constituent. The main phospholipid species formed from 20:4(n-6) were 16:0-20:4 and 18:0-20:4. When formed, they were stable during incubations of liver cells for 2-3 h. The main species formed from 20:5(n-3) were 16:0-20:5 and 18:0-20:5. After formation, 16:0-20:5 and to a lesser degree 18:0-20:5 were, however, degraded during 1-2 h of incubation, especially in PC. Only small amounts of 22:5(n-3) and very little 22:6(n-3) were formed from 20:5(n-3) and small amounts of 22:4(n-6) were produced from 20:4(n-6). With 20:4(n-6) and 20:5(n-3) as substrates, 20:4-20:4 and 20:5-20:5 molecular species respectively were initially formed in PC and PE but both species were rapidly degraded.

Eicosapentaenoic- and arachidonic acid metabolism in isolated liver cells.

The oxidation and esterification of 14C labelled eicosapentaenoic acid (20:5,n-3) and arachidonic acid (20:4,n-6) in isolated liver cells has been studied. The bioconversion of C18 and C22 polyunsaturated fatty acids to 20:5(n-3) and 20:4(n-6) is also discussed. Adrenic acid (22:4,n-6) and docosahexaenoic acid (22:6,n-3) are retroconverted to 20:4(n-6) and 20:5(n-3) respectively by peroxisomal beta-oxidation. 20:4(n-6) and 20:5(n-3) are both mainly oxidized in the mitochondria. The peroxisomal contribution to the oxidation of 20:5,n-3 is however larger than with 18:2(n-6) and 18:1(n-9) which are predominantly oxidized by mitochondrial beta-oxidation. Isolated liver cells oxidize more 20:5(n-3) and esterify less than observed with 20:4(n-6) as substrate. In liver cells from essential fatty acid deficient animals 20:5(n-3) and 20:4(n-6) are both efficiently directed to the phospholipids. In hepatocytes from animals fed a diet rich in 18:2(n-6) and 18:3(n-3) arachidonic acid is still to a large extent esterified in the phospholipids while 20:5(n-3) only to a small extent is esterified in this lipid fraction. 18:2(n-6) is much more efficiently esterified in the phospholipids than is 18:3(n-3) which is also rapidly removed from the phospholipids. The delta 4 desaturase activity is increased in essential fatty acid deficiency similar to delta 6 desaturase. The competition between 18:3(n-3) and 18:2(n-6) for delta 6 desaturation in combination with a much higher dietary intake of 18:2(n-6) than of 18:3(n-3) may limit the conversion of dietary 18:3(n-3) to 20:5(n-3).(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple molecular forms of rat liver pantothenate kinase.

Pantothate kinase (E.C.2.7.1.33) was partially purified from rat liver and analyzed by preparative isoelectric focusing and cation-exchange high performance liquid chromatography. Two main peaks of catalytic activity were found in the focusing gel at isoelectric point of 5.7 (peak A) and 5.1 (peak B). Two major molecular forms of the enzyme was also demonstrated by high performance liquid chromatography. Both molecular forms of the enzyme were inhibited by 0.02 mmol/l CoASH and acetyl-CoA. CoA at 0.02 mmol/l inhibited the isoenzyme peak B only slightly (6%) compared to the isoenzyme peak A (80%). Acetyl-CoA at 0.02 mmol/l inhibited peak A and B with about equal strength (96% and 83% respectively). The relative amounts of these two molecular forms of pantothenate kinase in different organs might contribute to the regulation of CoA synthesis in mammalian cells.