[Incorporation of labelled glycerol, palmitic, linoleic and arachidonic acids in the hepatic lipids of the rat]

Evidence that lipid peroxidation products bind to DNA in liver cells

Three lines of evidence are presented indicating the association of lipid peroxidation products with DNA in liver cells, labeled with [3H]arachidonic acid, in the presence of Fe(2+)-DTPA: (1) the nuclear DNA isolated from treated cells had higher radioactivity, compared to controls and the radioactivity increased with longer incubation times, (2) lipid-DNA adducts with a characteristic fluorescence spectrum were formed during the incubation with Fe(2+)-DTPA; (3) the association of peroxidation products with DNA could be inhibited by vitamin E and BHT. Compared with control DNA, purified lipid-DNA adducts showed a decrease of hyperchromicity and melting point, and partial resistance to hydrolysis by DNase I. On the other hand, the repair test shows that the lipid-DNA adducts in cells were not repaired by 4 h after removal of Fe(2+)-DTPA. A decrease in cell viability and in the activity of O6-alkylguanine acceptor protein was also observed with increasing incubation time. These data suggest that the lipid-DNA association, an oxidative DNA damage, occurs in cells treated by Fe(2+)-DTPA and could result in cytotoxicity if not repaired.

Interaction of lipid peroxidation products with nuclear macromolecules

The interaction of lipid peroxidation products with nuclear macromolecules was investigated in rat liver nuclei labelled with [3H]arachidonic acid. Lipid peroxidation reactions were driven both non-enzymatically and enzymatically by the addition of ascorbate-Fe2+ or NADPH-ADP-Fe3+, respectively, to the incubation mixtures. The extent of peroxidation was evaluated by the formation of thiobarbituric acid chromophore and of radioactive hydrophilic peroxidation products. The results obtained show that: (1) nuclear membrane lipid peroxidation products formed during incubation interact with DNA and total nuclear proteins; (2) non-enzymatic lipid peroxidation processes induced a 40% larger association of peroxidation products to DNA compared to processes driven enzymatically, whereas the corresponding interaction with total nuclear proteins was similar in both peroxidation systems; (3) the radioactivity associated with histones decreased during incubation in the presence of ascorbate-Fe2+ or NADPH-ADP-Fe3+, and increased in control samples (no additions); (4) inhibition of lipid peroxidation by the iron chelator Desferrioxamine B prevented the association of peroxidation products to nuclear macromolecules; (5) the levels of radioactivity found in DNA after 180 min of incubation would represent the formation of 0.6-1.0 adducts per 10(6) DNA bases. The results obtained provide evidence for an interaction between lipid peroxidation products and chromatin in the interior of the cell nucleus.

Autoradiographic studies with fatty acids and some other lipids: a review

In this review, we have mainly included studies in which whole-body autoradiography was used. In lipid research, most studies have been done with fatty acids. These studies showed some common characteristics in the pattern of tissue distribution. A major uptake was seen in the brown fat, liver and adrenal cortex but also to some extent in other tissues with a high metabolic activity or high cell turn-over, e.g. the gastric and intestinal mucosa, diaphragm, kidney cortex and bone marrow. Low levels of radioactivity were generally found in the brain, testes, thymus, white fat, skeletal muscles, lungs and spleen. Most fatty acids showed some specific features, e.g the strong uptake of erucic, arachidonic and docosahexaenoic acid in myocardium and of eicosapentaenoic acid in the adrenal cortex. Studies with PGE1 and LTC3 showed that the liver and kidney and to a lesser degree the lungs were the major sites of metabolism. The distribution of free cholesterol and triolein emulsion labelled in the fatty acid moieties did show some similarities with respect to the general pattern found with most fatty acids. Specific for cholesterol was a very strong uptake in the adrenal cortex. There was also a significant uptake in the spleen whereas the uptake in the brown fat was not as marked as for most fatty acids. Specific for triolein was a marked uptake in the spleen and myocardium, in fed animals also in the white adipose tissue. These studies show that whole-body autoradiography can give much valuable information of the uptake and distribution of lipids that would be rather difficult to obtain with conventional methods. Combined with electron-microscopy, autoradiography can be used to study cellular and even subcellular distribution, and thus given further data on the metabolism of lipids in the body.

Interferon alters the composition and metabolism of lipids in the liver of suckling mice

Daily injection of suckling Swiss, C3H, and C57BL/6 mice with potent preparations of mouse interferon (IFN) alpha/beta resulted in a decrease in phospholipids and a decrease in the phospholipid-to-protein ratio in the liver. This decrease in polar lipids was accompanied by a marked accumulation of triglycerides without a pronounced change in free cholesterol. In contrast, a similar IFN treatment of adult mice did not change the content of liver phospholipids, although there was an increase in liver triglycerides. In suckling mice, after 10 days of IFN administration there was a marked decrease in the incorporation of 1(3)-[3H]glycerol into liver phospholipids, which was not observed in IFN-treated adult mice. Our findings suggest that IFN treatment results in the inhibition of some component of the system of phospholipid biosynthesis during the maturation of hepatocytes in suckling mice.

Comparative utilization in vivo of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose and [1-C14] palmitate in the rat

Female rats were injected i.v. with comparable trace amounts of [U-14C] glycerol, [2-3H] glycerol, [U-14C] glucose, or [1-14C] palmitate, and killed 30 min afterwards. The radioactivity remaining in plasma at that time was maximal in animals receiving [U-14C] glucose while the appearance of radioactive lipids was higher in the [U-14C] glycerol animals than in other groups receiving hydrosoluble substrates. The carcass, more than the liver, was the tissue where the greatest proportion of radioactivity was recovered, while the greatest percentage of radioactivity appeared in the liver in the form of lipids. The values of total radioactivity found in different tissues were very similar when using either labelled glucose or glycerol but the amount recovered as lipids was much greater in the latter. The maximal proportion of radioactive lipids appeared in the fatty-acid form in the liver, carcass, and lumbar fat pads when using [U-14C] glycerol as a hydrosoluble substrate, and the highest lipidic fraction appeared in adipose tissue as labelled, esterified fatty acids. In the spleen, heart, and kidney, most of the lipidic radioactivity from any of the hydrosoluble substrates appeared as glyceride glycerol. The highest proportion of radioactivity from [1-14C] palmitate appeared in the esterified fatty acid in adipose tissue, being followed in decreasing proportion by the heart, carcass, liver, kidney, and spleen. Thus at least in part, both labelled glucose and glycerol are used throughout different routes for their conversion in vivo to lipids. A certain proportion of glycerol is directly utilized by adipose tissue. The fatty acids esterification ability differs among the tissues and does not correspond directly with the reported activities of glycerokinase, suggesting that the alpha-glycerophosphate for esterification comes mainly from glucose and not from glycerol.

Effect of evisceration on the disposal of [14C] palmitate in the rat

The utilization in vivo of [1-(14)C] palmitate was studied in hepatectomized-nephrectomized rats and their sham-operated controls. After i.v. injection of the tracer, the [14C] lipids in plasma disappeared more slowly in eviscerated animals than in their controls. More label reappeared in plasma as esterified fatty acids in the latter group. At 30 min after the tracer, the amount of label found in the lipidic fraction of carcass and heart was much greater in eviscerated animals than in their controls although the percentile distribution of labelled lipidic fractions remained stable, a considerable proportion being present in the esterified fatty acid form. On the basis of these findings, the rapid increase in the plasma levels of FFA in eviscerated animals must be the result of augmented lipolytic activity more than reduced utilization of these metabolites.

Binding of products originating from the peroxidation of liver microsomal lipids to the non-lipid constituents of the microsomal membrane

The binding of products derived from the peroxidation of liver microsomal lipids to the non-lipid constituents of the microsomes was studied. To this end arachidonic acid labelled with tritium at the positions of the double bonds was given to rats and allowed to incorporate into the membrane lipids of the liver cell. When liver microsomes containing labelled arachidonic acid were incubated aerobically in the NADPH-dependent system, a marked production of malonic dialdehyde (MDA) occurred and, concomitantly, there was a consistent release of radioactivity from the microsomes into the incubation medium. The addition of EDTA to the incubation medium prevented, to a large extent, both the MDA formation and the release of radioactivity. Chromatographic studies showed that the bulk of the radioactivity released from the incubated microsomes is not MDA. In the incubated microsomes, the radioactivity decreased in total lipids, while it increased by about 15 times in the non-lipoidal residue. A similar increase in radioactivity was seen in microsomal protein, while no increase was observed in microsomal RNA (the radioactivity was negligible in both the incubated and the non-incubated samples). It seems therefore that products originating from lipoperoxidation of arachidonic acid covalently bind to the microsomal protein. In order to investigate whether alterations similar to those observed in the in vitro peroxidation of liver microsomes could be detected in the in vivo intoxication with carbon tetrachloride, rats given labelled arachidonic acid as above, were poisoned with CCl4. Sixty minutes after poisoning, the radioactivity present in the microsomal lipids was generally lower in the intoxicated rats than in the controls, while the labelling of the non-lipoidal residue and of the protein was higher in the CCl4-poisoned rats.

Phospholipid composition and [14C]glycerol incorporation into glycerolipids of toad retina and brain

The phospholipid composition as well as the in vivo [14C]glycerol uptake in lipids was found to be similar in the toad brain and retina. The choroid lipid labeling was markedly different. An in vitro time-course study of [14C]glycerol incorporation in toad retina lipids disclosed that under the conditions of these experiments: (1) retina is able to rapidly synthesize phosphatidic acid from the radioactive precursor; (2) the sequence phosphatidic acid-diacylglycerol-triacylglycerol operates; (3) a high rate of phosphatidylinositol de novo biosynthesis takes place; (4) phosphoglycerides of choline and of ethanolamine are also heavily labeled after a lag period; (5) in vivo labeling profiles resembled those obtained in vitro mainly regarding phosphatidylinositol biosynthesis; and (6) the presence of glycerol kinase in the CNS is suggested.