Studies on liver phosphatidyl cholines: I. Effects of fatty liver induction on phosphatidyl cholines from liver mitochondria and microsomes

[11C]choline uptake in regenerating liver after partial hepatectomy or CCl4-administration

To characterize [methyl-(11)C]choline ([(11)C]choline) as an oncologic PET radiopharmaceutical, [(11)C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl(4) insult as that of proliferating tissue with inflammation, was studied in rats. [(11)C]Choline, [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [2-(14)C]thymidine ([(14)C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl(4)-administration. [(11)C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [(14)C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl(4)-administration, though it significantly increased [(14)C]TdR uptake. There were no differences of [(11)C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [(18)F]FDG uptake was accelerated in the regenerating liver on either partial hepatectomy or CCl(4)-administration. The magnitude of the increase in [(18)F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [(11)C]choline. [(11)C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl(4)-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [(11)C]choline-PET.

Mass spectrometric detection of cross-linked fatty acids formed during radical-induced lesion of lipid membranes

A mass spectrometric method is described for the quantitative determination of dimers of polyunsaturated fatty acids (PUFA) formed in the hepatic endoplasmic reticulum of rats upon inhalation of tetrachloromethane. The results show that dimers account for a considerable fraction of microsomal PUFA which disappear during CCl4 metabolism. Cross-linking of the membrane lipids of the endoplasmic reticulum seems to be a significant process with respect to cell toxicity.

Fatty acids in liver microsomal lipids of rats exposed to hypoxia, tetrachloromethane, or both

Arachidonic and docosahexaenoic acid in hepatic microsomal lipids from male Sprague-Dawley rats are greatly lowered when the animals have been exposed to tetrachloromethane; at the same time, palmitic, oleic and linoleic acid are significantly increased. Hypoxia alone causes similar derangements, but to a lesser extent. These are largely corrected 18 h after exposure; the effects induced by tetrachloromethane are persistent. The increases in 16:0, 18:1 and 18:2 suggest that in both cases microsomal enzymes involved in fatty acid metabolism are inhibited, either reversibly or irreversibly. Reduction of oxygen partial pressure during tetrachloromethane exposure has little effect upon hepatotoxicity as judged by hepatic enzymes in serum; only the onset of their release into the bloodstream is earlier.

Fatty acid composition of liver lipids in rats fed brominated fatty acids

Feeding rats diets containing brominated corn oil or di- or tetrabromostearate as the monoglyceride produced changes in fatty acid composition of liver lipids. Those changes associated with the feeding of brominated corn oil or tetrabromostearate could be explained by the accumulation of triglyceride, and the changes associated with the feeding of dibromostearate could result from the proliferation of a membrane system. A unique response to the feeding of diets containing brominated corn oil is an increase in the level of gamma-linolenic acid.

Fatty acid composition of tissue phospholipids and prostaglandin excretion in hyperlipidemia induced in rats by implantation of the mammotropic pituitary tumor MtT-F4

A mammotropic pituitary tumor, MtT-F4, was implanted into male Fisher 344 rats for a period of 4 weeks. This tumor induced growth retardation, hyperlipidemia, hepatic hypertrophy and adrenal hyperplasia. Lipids were extracted from various tissues. In tumor-bearing rats, phospholipid concentration was found to be increased in plasma, spleen and testis. Distribution among the various phospholipid classes was similar to that of controls except in liver and heart, where phosphatidylcholine was increased at the expense of phosphatidylinositol and phosphatidylserine. The main difference was in the fatty acid composition of major phospholipids. The proportion of omega 6 fatty acids was lower and that of docosahexaenoic acid of the omega 3 series (22:6 omega 3) was higher in most tissues, especially in plasma, liver, heart and kidney. Concurrently, the urinary excretion of two endogenous metabolites of PGI2 (2,3-dinor-6-keto-PGF1 alpha and 6,15-diketo-13,14-dihydro-2,3-dinor-PGF1 alpha) was found to be increased significantly in tumor-bearing rats. The results raise the hypothesis that hormonal changes induced by the MtT-F4 tumor accelerate the conversion of arachidonic acid (20:4 omega 6) to prostaglandins. This effect, perhaps coupled with a diversion of linoleic acid (18:2 omega 6) towards other metabolic processes, would account for a partial depletion of membrane phospholipids in 18:2 omega 6 and for the reduced production of longer chain omega 6 unsaturated acids from 20:4 omega 6, creating a state of "relative essential fatty acid deficiency." As a result, the metabolism of omega 3 fatty acids is altered towards an enhanced production of 22:6 omega 3 which accumulates in the lipids of cell membranes to compensate for the depletion of unsaturated acids of the omega 6 series.

Subcellular distribution of phospholipids during liver damage induced by rare earths

After intravenous injection of praseodymium nitrate, female Wistar rats develop fatty livers. In contrast to the marked increase of triglycerides, the phospholipid content was only increased by 50%. The subcellular distribution of phospholipids showed that major changes occur in the microsomal fraction within the first 24 hrs. Among the individual phospholipids only phosphatidylcholine and phosphatidylethanolamine concentrations were elevated. Further subfractioning revealed that phospholipid concentration increased in the smooth endoplasmic reticulum, whereas it decreased in the rough endoplasmic reticulum. The individual phospholipids in the smooth endoplasmic reticulum increased to the same degree as did the total phospholipids. On the other hand, in the rough endoplasmic reticulum only the lecithin fraction decreased, while all other phospholipids remained unchanged. Cytochrome P450, cytochrome b5, and glucose 6-phosphatase activity were drastically reduced in the rough endoplasmic reticulum, while no changes could be observed in the smooth endoplasmic reticulum. In the serum, phospholipid concentration fell to half the normal value within the first 24 hrs after praseodymium intoxication.

Effect of low methionine, choline deficient diets upon major unsaturated phosphatidyl choline fractions of rat liver and plasma

To see how the metabolism of specific phosphatidyl choline fractions might be affected when only a limited source of methyl groups was available, rats were fed for 7 days a low methionine, choline-deficient diet or one supplemented with either choline or methionine. Prior to killing, they were injected with -14C-methyl methionine and liver and plasma phosphatidyl choline isolated and separated by argentation chromatography into 3 major unsaturated fractions. Fatty acid composition and radioactivity of the fractions were determined. Deficient rats had reduced total liver phosphatidyl choline when compared with the supplemented groups, but the proportions of 20:4 and 22:6 fatty acids in the total phosphatidyl choline were unchanged. Plasma phosphatidyl choline also was reduced sharply by the deficiency, as was its proportion of 20:4 fatty acid. Specific activities of the liver 22:6, 20:4, and 18:2 phosphatidyl choline fractions showed that deficient rats had less radioactivity in their 20:4 and 18:2 phosphatidyl choline than did the supplemented animals. Plasma phosphatidyl choline fractions presented a similar pattern. Feeding methionine or choline nearly doubled radioactive methyl group incorporation into the 20:4 phosphatidyl choline fraction of liver and plasma, while incorporation into the 22:6 phosphatidyl choline was reduced or unchanged. The results suggested that, in the rat, limited availability of methyl groups altered the metabolism of liver and plasma phosphatidyl choline fractions. Methionine, as a source of labile methyl groups, appears necessary for the normal synthesis of certain unsaturated phosphatidyl choline fractions (particularly 20:4 phosphatidyl choline). Transmethylation of phosphatidyl ethanolamine molecular species to the corresponding phosphatidyl choline species may be an important reaction in normal lipid metabolism and transport. Relative affinities for incorporation of the labeled methyl groups into the phosphatidyl choline fractions of either deficient or supplemented rats were: 22:6 less than 20:4 less than 18:2.

Reduced response to phenobarbital by the liver of rats fed a choline-deficient diet

1. The response of the liver to phenobarbital administration was compared in rats fed either laboratory chow, a semipurified choline-supplemented diet or a semipurified choline-deficient diet. 2. The liver contents of proteins, lipids and cytochrome P-450, as well as the activity of aminopyrine and ethylmorphine demethylases, were measured after 5 days of feeding and five daily injections of phenobarbital. Liver sections were examined electron microscopically. 3. In rats fed the choline-supplemented diet, phenobarbital administration caused increases in cellular constituents, enzyme activities and smooth endoplasmic reticulum membranes as great as those seen in rats fed laboratory chow. However, in rats fed the choline-deficient diet, the response of the liver to phenobarbital administration was severely reduced in comparison to that in rats fed the other diets. 4. It is concluded that dietary choline and an adequate synthesis of lecithins are necessary for the induction of microsomal mixed-function oxidases and the concomitant accumulation of smooth endoplasmic reticulum in hepatocytes.