Fatty Livers Induced by Orotic Acid

Serum Orotidine: A Novel Biomarker of Increased CVD Risk in Type 2 Diabetes Discovered Through Metabolomics Studies

OBJECTIVE

To identify novel biomarkers of cardiovascular disease (CVD) risk in type 2 diabetes (T2D) via a hypothesis-free global metabolomics study, while taking into account renal function, an important confounder often overlooked in previous metabolomics studies of CVD.

RESEARCH DESIGN AND METHODS

We conducted a global serum metabolomics analysis using the Metabolon platform in a discovery set from the Joslin Kidney Study having a nested case-control design comprising 409 individuals with T2D. Logistic regression was applied to evaluate the association between incident CVD events and each of the 671 metabolites detected by the Metabolon platform, before and after adjustment for renal function and other CVD risk factors. Significant metabolites were followed up with absolute quantification assays in a validation set from the Joslin Heart Study including 599 individuals with T2D with and without clinical evidence of significant coronary heart disease (CHD).

RESULTS

In the discovery set, serum orotidine and 2-piperidinone were significantly associated with increased odds of incident CVD after adjustment for glomerular filtration rate (GFR) (odds ratio [OR] per SD increment 1.94 [95% CI 1.39-2.72], P = 0.0001, and 1.62 [1.26-2.08], P = 0.0001, respectively). Orotidine was also associated with increased odds of CHD in the validation set (OR 1.39 [1.11-1.75]), while 2-piperidinone did not replicate. Furthermore, orotidine, being inversely associated with GFR, mediated 60% of the effects of declining renal function on CVD risk. Addition of orotidine to established clinical predictors improved (P < 0.05) C statistics and discrimination indices for CVD risk (ΔAUC 0.053, rIDI 0.48, NRI 0.42) compared with the clinical predictors alone.

CONCLUSIONS

Through a robust metabolomics approach, with independent validation, we have discovered serum orotidine as a novel biomarker of increased odds of CVD in T2D, independent of renal function. Additionally, orotidine may be a biological mediator of the increased CVD risk associated with poor kidney function and may help improve CVD risk prediction in T2D.

Sheep’s milk cheeses as a source of bioactive compounds

Since ancient times, sheep`s milk cheeses have been a part of a human diet. Currently, their consumption is of great interest due to its nutritional and health values. The aim of the article was to review the chemical composition of sheep’s milk cheeses and its main bioactive ingredients in the context of nutritional and health values. Sheep’s milk cheeses are rich in functionally and physiologically active compounds such as: vitamins, minerals, fatty acids, terpenes, sialic acid, orotic acid and L-carnitine, which are largely originate from milk. Fermentation and maturation process additionally enrich them in other bioactive substances as: bioactive peptides, γ-aminobutyric acid (GABA) or biogenic amines. Studies show that sheep’s milk cheese consumption may be helpful in the prevention of civilization diseases, i.e. hypertension, obesity or cancer. However, due to the presence of biogenic amines, people with metabolic disorders should be careful of their intake.

Effects of Fatty Liver Induced by Excess Orotic Acid on B-Group Vitamin Concentrations of Liver, Blood, and Urine in Rats

Fatty liver is caused when rats are given orotic acid of the pyrimidine base in large quantities. The lack of B-group vitamins suppresses the biosynthesis of fatty acids. We investigated how orotic acid-induced fatty liver affects the concentrations of liver, blood, and urine B-group vitamins in rats. The vitamin B6 and B12 concentrations of liver, blood, and urine were not affected by orotic acid-induced fatty liver. Vitamin B2 was measured only in the urine, but was unchanged. The liver, blood, and urine concentrations of niacin and its metabolites fell dramatically. Niacin and its metabolites in the liver, blood, and urine were affected as expected. Although the concentrations of vitamin B1, pantothenic acid, folate, and biotin in liver and blood were decreased by orotic acid-induced fatty liver, these urinary excretion amounts showed a specific pattern toward increase. Generally, as for the typical urinary excretion of B-group vitamins, these are excreted when the body is saturated. However, the ability to sustain vitamin B1, pantothenic acid, folate, and biotin decreased in fatty liver, which is hypothesized as a specific phenomenon. This metabolic response might occur to prevent an abnormally increased biosynthesis of fatty acids by orotic acid.

Disruption of uridine homeostasis links liver pyrimidine metabolism to lipid accumulation

We report in this study an intrinsic link between pyrimidine metabolism and liver lipid accumulation utilizing a uridine phosphorylase 1 transgenic mouse model UPase1-TG. Hepatic microvesicular steatosis is induced by disruption of uridine homeostasis through transgenic overexpression of UPase1, an enzyme of the pyrimidine catabolism and salvage pathway. Microvesicular steatosis is also induced by the inhibition of dihydroorotate dehydrogenase (DHODH), an enzyme of the de novo pyrimidine biosynthesis pathway. Interestingly, uridine supplementation completely suppresses microvesicular steatosis in both scenarios. The effective concentration (EC(50)) for uridine to suppress microvesicular steatosis is approximately 20 µM in primary hepatocytes of UPase1-TG mice. We find that uridine does not have any effect on in vitro DHODH enzymatic activity. On the other hand, uridine supplementation alters the liver NAD(+)/NADH and NADP(+)/NADPH ratios and the acetylation profile of metabolic, oxidation-reduction, and antioxidation enzymes. Protein acetylation is emerging as a key regulatory mechanism for cellular metabolism. Therefore, we propose that uridine suppresses fatty liver by modulating the liver protein acetylation profile. Our findings reveal a novel link between uridine homeostasis, pyrimidine metabolism, and liver lipid metabolism.

Role of the AMPK/SREBP-1 pathway in the development of orotic acid-induced fatty liver

Orotic acid (OA), an intermediate in pyrimidine metabolism, has been used for a variety of purposes, such as dietary supplements. Although it is well documented that OA induces fatty liver in a species-specific manner, the precise molecular mechanisms remain unclear. The present study investigated the role of the adenosine monophosphate-activated protein kinase (AMPK)-sterol regulatory element-binding protein-1 (SREBP-1) pathway in the OA-induced fatty liver. Treatment with OA suppressed the phosphorylation of AMPK via proteasomal degradation of upstream kinase LKB1 and induced activation of SREBP-1 in both human hepatoma cell lines and primary rat hepatocytes. OA-induced SREBP-1 transcriptional activity was suppressed by cotreatment with aminoimidazole carboxamide ribonucleotide (AICAR) or metformin, or by overexpression of constitutively active AMPK (CA-AMPK) in the human hepatoma cell line. Importantly, in vivo data corroborated these results. Feeding 1% OA with diet decreased the phosphorylation of AMPK and increased the maturation of SREBP-1 and the expression of SREBP-responsive genes in the rat liver. OA-induced lipid accumulation was also completely inhibited by rapamycin. Mouse hepatocytes and mice were resistant to OA-induced lipogenesis because of little if any response in AMPK and downstream effectors. In conclusion, OA induces hepatic lipogenesis, mediated predominantly by the AMPK/SREBP-1 pathway in rat hepatocytes and human hepatoma cell lines.

Study on possible mechanism of orotic acid-induced fatty liver in rats

OBJECTIVE

The aim of this study was to investigate the possible mechanism of orotic acid-induced fatty liver in rats.

METHODS

Rats were randomly divided into two groups and fed an AIN-93 diet with 1% orotic acid or without orotic acid for 10 d. Hepatic lipid concentrations, such as triacylglycerol, total cholesterol, and phospholipids, were examined. To clarify the mechanism of orotic acid-induced fatty liver, hepatic enzyme activities and mRNA levels of key enzymes related in lipid metabolism and hepatic gene expression of transcription factors were determined.

RESULTS

Orotic acid administration significantly increased hepatic triacylglycerol concentration. The activity and mRNA level of fatty acid synthase were obviously upregulated by orotic acid treatment, whereas the activities and mRNA concentrations of carnitine palmitoyl transferase and microsomal triacylglycerol transfer protein were significantly depressed. Furthermore, orotic acid stimulated the mRNA expression of sterol regulatory element binding protein-1c but did not alter the mRNA concentration of peroxisome proliferator-activated receptor-α in the liver.

CONCLUSION

The stimulation of triacylglycerol synthesis induced by orotic acid is mainly caused by enhancement of sterol regulatory element binding protein-1c and its target gene involved in fatty acid biosynthesis. In contrast, the inhibition of fatty acid β-oxidation and very-low-density lipoprotein secretion were related to the observed lipid accumulation.

Dietary saponins of sea cucumber alleviate orotic acid-induced fatty liver in rats via PPARalpha and SREBP-1c signaling

Background

Nonalcoholic fatty liver disease is the most common chronic liver disease in the world, and is becoming increasingly prevalent. Saponins of sea cucumber (SSC) are proven to exhibit various biological activities. Therefore, the present study was undertaken to examine the effect of saponins extracted from sea cucumber (Pearsonothuria graeffei) on the preventive activity of fatty liver in rats.

Methods

Male Wistar rats were randomly divided into five groups, including normal control group, fatty liver model group, SSC-treated group with SSC at levels of 0.01%, 0.03% and 0.05%. Model rats were established by administration with 1% orotic acid (OA). After the experiment period, serum total cholesterol (TC), triglyceride (TG), and hepatic lipid concentrations were determined. To search for a possible mechanism, we examined the changes of key enzymes and transcriptional factors involved in hepatic lipids biosynthesis, fatty acid β-oxidation.

Results

Both 0.03% and 0.05% SSC treatment alleviated hepatic steatosis and reduced serum TG and TC concentration significantly in OA fed rats. Hepatic lipogenic enzymes, such as fatty acid synthase (FAS), malic enzyme (ME), and glucose-6-phosphate dehydrogenase (G6PDH) activities were inhibited by SSC treatment. SSC also decreased the gene expression of FAS, ME, G6PDH and sterol-regulatory element binding protein (SREBP-1c). Otherwise, the rats feeding with SSC showed increased carnitine palmitoyl transferase (CPT) activity in the liver. Hepatic peroxisome proliferator-activated receptor (PPARα), together with its target gene CPT and acyl-CoA oxidase (ACO) mRNA expression were also upregulated by SSC.

Conclusions

According to our study, the lipids-lowering effect of dietary SSC may be partly associated with the enhancement of β-oxidation via PPARα activation. In addition, the inhibited SREBP-1c- mediated lipogenesis caused by SSC may also contribute to alleviating fatty liver.

Effects of fatty liver induced by niacin-free diet with orotic acid on the metabolism of tryptophan to niacin in rats

The effects of dietary orotic acid on the metabolism of tryptophan to niacin in weaning rats was investigated. The rats were fed with a niacin-free, 20% casein diet containing 0% (control diet) or 1% orotic acid diet (test diet) for 29 d. Retardation of growth, development of fatty liver, and enlargement of liver were observed in the test group in comparison with the control group. The concentrations of NAD and NADP in liver significantly decreased, while these in blood did not decrease compared to the control group. The formation of the upper metabolites of tryptophan to niacin such as anthranilic acid, kynurenic acid, and 3-hydroxyanthranilic acid were not affected, but the quinolinic acid and beyond, such as nicotinamide, N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and N1-methyl-4-pyridone-3-carboxamide, were significantly reduced by the administration of orotic acid. Therefore, the conversion ratio of tryptophan to niacin significantly decreased in the test group in comparison with the control group.

Steatosis is not sufficient to cause an impaired regenerative response after partial hepatectomy in rats

BACKGROUND/AIMS

Fatty liver is known to be associated with increased mortality and morbidity after liver resection. The ability of fatty liver to regenerate after two-thirds partial hepatectomy was studied in three different models of steatosis in rats: obese Zucker rats, orotic acid-fed Wistar rats and Wistar rats fed a methionine-low, choline-deficient diet.

METHODS

Liver regeneration was assessed 24 h after partial hepatectomy by bromodeoxyuridine incorporation (immunohistochemistry), proliferating cell nuclear antigen, cyclin E and cyclin-dependent kinase 2 protein expression (Western blot analysis) and cyclin-dependent kinase 2 activity (kinase assays using histone H1 as a substrate).

RESULTS

No significant difference of proliferative response was found between orotic acid or methionine-low, choline-deficient diet-fed and control Wistar rats 24 h after partial hepatectomy. In contrast, hepatocyte proliferation in obese Zucker rats after partial hepatectomy was significantly reduced when compared with their lean controls.

CONCLUSIONS

Steatosis per se does not impair liver regeneration. The reduced liver regeneration observed in obese Zucker rats may not be due to fatty infiltration itself but to other factors such as leptin receptor dysfunction.

Supplementation of orotic acid to the casein, but not to egg protein, soy protein, or wheat gluten diets, increases serum ornithine carbamoyltransferase activity

Effects of dietary supplementation of orotic acid to a diet containing the casein protein were compared with diets containing egg protein, soy protein, or wheat gluten on lipid levels in the liver and serum and activities of ornithine carbamoyltransferase (OCT) and alanine aminotransferase in the serum of rats. We found that supplementation of orotic acid to each diet increased the contents of the liver total lipids, triacylglycerol, and phospholipids compared with those not supplemented. The contents of liver total lipids, triacylglycerol, cholesterol, and phospholipids in rats fed the casein diet were significantly higher than those of rats fed the other three diets when orotic acid was supplemented. The levels of triacylglycerol, cholesterol, and phospholipids in the serum of rats fed the casein diet were markedly decreased by addition of orotic acid. The supplementation of orotic acid significantly increased the activities of both serum OCT and alanine aminotransferase in rats fed the casein diet, but not in rats fed the other diets. In conclusion, liver lipid accumulation induced by dietary orotic acid depends on the type of dietary protein. The enhancement of serum OCT activity may result from liver lipid accumulation in rats fed the casein diet supplemented with orotic acid, demonstrating hepatic damage.

Association between hepatic triacylglycerol accumulation induced by administering orotic acid and enhanced phosphatidate phosphohydrolase activity in rats

Orotic acid is known to cause fatty liver, but it is unclear whether this is caused partly by stimulation of the enzymes for triacylglycerol (TG) synthesis. To understand the change of hepatic TG metabolism in fatty liver induced by orotic acid, we determined the liver tissue TG level and phosphatidate phosphohydrolase (PAP) activity over time in rats fed on a diet containing orotic acid (OA). A dietary lipid content of 10% was achieved by using n-6 fatty acid-rich corn oil in experiment 1, and n-6 fatty acid-rich safflower oil (SO) and n-3 fatty acid-rich fish oil (FO) with the same polyunsaturated fatty acid/monounsaturated fatty acid/saturated fatty acid (P/M/S) ratio in experiment 2. In experiment 1, an increase in the hepatic TG level due to OA intake was observed from day 5 onwards, the level rising approximately 6-fold by day 10. The activity of hepatic microsomal PAP, the rate-limiting enzyme in TG synthesis, increased markedly from day 5 onwards, concurrent with the liver diacylglycerol concentration. A strong correlation (r = 0.974) was observed between the hepatic TG level and microsome-bound PAP activity. In experiment 2, we investigated the effects of dietary fatty acid on OA-induced fatty liver. Compared with the n-6 fatty acid-rich vegetable oil diet, the relative increase in hepatic TG was smaller with the n-3 fatty acid-rich FO diet, and hepatic PAP activity fell markedly to the level for an OA-free diet. In addition, the hepatic TG accumulation and serum TG concentration were lower in the FO group than in the SO group. Nevertheless, because the hepatic TG level was low, it seems that the inhibition of liver PAP activity by FO possibly had a strong influence on the accumulation of TG in the liver. In conclusion, enhanced TG synthesis mediated by changes in liver PAP activity was involved in the hepatic TG accumulation induced by OA administration, this change being markedly suppressed by dietary n-3 fatty acids.

Diagnosis of fatty liver with MR imaging

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.

Effect of orotic acid on the generation of reactive oxygen and on lipid peroxidation in rat liver

The pyrimidine precursor orotic acid (OA) is a constituent of dairy products and therapeutic drugs. Several recent publications point towards a tumor promoting activity of OA in rat liver. An increased production of reactive oxygen has been discussed as a possible mechanism, leading to lipid peroxidation and DNA single strand breaks. In view of contradictory results, this postulated prooxidative action of OA was reexamined with new experimental techniques. Weanling Sprague-Dawley rats were fed 1% OA in different diets for 4-35 days. The NADPH-mediated lipid peroxidation in liver homogenate and microsomes was determined in vitro by analysis of low-level chemiluminescence (CL) and the strongly correlated formation of malondialdehyde (MDA). In no case did treatment with OA result in an increase of lipid peroxidation in vitro nor did such treatment enhance the generation of reactive oxygen as measured by lucigenin CL. In accordance, the total cytochrome P-450 content as well as the activity of individual P-450 isoenzymes were unchanged. Treatment with OA did not elevate the MDA content of fresh liver homogenate when butylated hydroxytoluene (BHT) was present in the test system. However, when the antioxidant was omitted, increased levels of thiobarbituric acid reactive material were found which correlated with the triglyceride content. This could explain some published data that have been taken as indication for a prooxidative action of OA. Evidence against an increased lipid peroxidation in vivo is given by the analysis of ethane exhalation. Furthermore, no increase in DNA single strand breaks by OA treatment could be observed by the alkaline elution technique. These results do not support the hypothesis of a prooxidative activity of OA. The observed reversible decrease of the GSH/GSSG ratio is assumed to result from the reduced size of the phosphopyridine nucleotide pool due to purine deficiency and an increased consumption of NADPH by the enhanced reductive degradation of pyrimidines.

Orotic acid in guinea pig milk: changes in concentration during lactation

The orotic acid concentration in guinea pig milk decreased rectilinearly beginning on d 1 through a lactation duration of 21 d. Concentration was 29 micrograms/ml on d 1 and 5 micrograms/ml on d 17. On d 18 to 21 it was less than 1 microgram/ml. The regression equation of orotic acid on day of lactation was: Y(micrograms orotic acid per milliliter milk) equals 32.3 - 1.6X (day of lactation) with a correlation coefficient of .94. Total orotic acid on a daily basis peaked on d 6 at 950 micrograms and declined to less than 5 micrograms by d 21. The rectilinear regression equation from d 6 to 21 was as follows: Y(micrograms orotic acid per milliliter milk) equals -1.64 + .68X (grams of milk production per day) with a correlation coefficient of .97. This may be used as a marker for persistency of lactation.

Effects on liver and serum lipids of dietary supplements of methionine and excess lysine given to previously-starved rats

The addition of lysine hydrochloride (50 g/kg) to a diet supplemented with methionine (3 g/kg) had no effect on liver lipids when rats (Wistar and Sprague-Dawley) were fed ad lib. for 14 d. However, refeeding a diet supplemented with methionine and excess lysine hydrochloride to previously-starved rats (Wistar) for 6, 7 or 9 d, but not 3 or 4 d, resulted in liver lipid accumulation, mainly triglycerides, which was prevented by the addition of arginine, citrulline, ornithine, adenine, allopurinol or maize oil, but not by guanine, cytosine, thymine or uracil. The addition of lysine hydrochloride to a methionine-supplemented diet resulted in reduced serum triglyceride levels after refeeding for 3 or 4 d and reduced serum cholesterol levels after refeeding for 3, 4 or 6 d. Serum lipids were unaffected by refeeding the diets for 7 or 9 d. Since hepatic lipid accumulation was preceded by the decline in the level of serum triglycerides, one of the factors responsible for lipid accumulation in the liver might be reduced transport of triglycerides from the liver into the blood. When adenine and allopurinol were added to the diet supplemented with methionine and lysine hydrochloride refed for 4 d, there was an increase in serum triglycerides. However, when this diet was refed for 7 d, with the addition of arginine, citrulline, guanine, pyrimidine bases, allopurinol or maize oil, no effects on serum cholesterol and triglyceride levels were observed.

Metabolism of orotic acid: lack of orotate phosphoribosyltransferase in rat intestinal mucosa

The main enzymes involved in orotic acid metabolism, orotate phosphoribosyltransferase and orotidine 5'-phosphate decarboxylase, are associated as a multienzyme complex (complex U) which is present in the liver of most vertebrate species. Orotic-acid-enriched diets produce increased pyrimidine synthesis which competes with purine synthesis for 5-phosphoribosyl diphosphate, resulting in decreased adenylate levels in liver cells. Inhibition of secretion of very low density lipoproteins and hepatic steatosis is then observed. In contrast, lipoproteins secretion by the intestine is not impaired and fat does not accumulate in enterocytes. The aim of this work was to investigate whether orotate is differently metabolized in gut and in liver thus explaining the lack of effect on the intestinal lipoproteins secretion. Complex U was found in appreciable amounts in rat, mouse and rabbit livers; the intestinal mucosa of the two last species contains a much lower level of multienzyme complex whereas in rat intestine its activity cannot be detected. Indeed, radioactive aspartate and orotate were not incorporated into intestinal cells RNA. The absence of orotate metabolisation by lack of orotate phosphoribosyltransferase and orotidine 5'-phosphate decarboxylase activity in rat intestine would explain why this organ, in contrast to the liver, is protected against disturbances of nucleotide metabolism and lipoproteins secretion induced by orotic-acid-supplemented diets.

Fatty liver of growing rats fed excess lysine and its prevention by adenine or allopurinol

Weanling male Sprague-Dawley rats were fed ad libitum 15% casein diets with and without 5.0% lysine-HCI, 0.25% adenine sulfate or 0.1% allopurinol for 2 weeks. Addition of lysine alone depressed 2-week growth from 94 to 65 g increased average daily urinary orotic acid excretion from 0.39 to 1.77 mg and increased the percentage of total liver lipids from 3.6 to 11.2. Adenine or allopurinol did not change growth but markedly enhanced lysine-induced orotic aciduria and completely prevented lysine-induced fatty livers. Reports by other show that adenine and allopurinol also prevent fatty livers or rats fed arginine-free diets or excess orotic acid. The authors conclude that lysine-induced orotic aciduria results from arginine deficiency caused by antagonism of arginine function by lysine, and that lysine-induced fatty liver probably results from a lesion identical to that produced by feeding excess orotic acid.

Subcellular localization of pyrimidine synthesis enzymes in bovine mammary tissue

Subcellular localization of enzymes of the pyrimidine biosynthetic pathway was determined in lactating bovine mammary tissue. Aspartate transcarbamylase was associated with a membrane portion of the microsomal cell fraction. Dihydroorotate dehydrogenase w3as in the mitochondrial fraction with no evidence for a cytosolic enzyme requiring pyridine nucleotides. Orotate phosphoribosyltransferase was in the cytosol of the cell. The significance of these findings to other mammalian cells and orotic acid accumulation in bovine milk is discussed.

Liver lipid alterations in rats fed arginine deficient diets

Arginine deficiency is associated with a marked increase in liver lipids in the rat. Triglyceride accumulation accounts for most of the fatty infiltration. Cholesterol concentration per gram of liver increased approximately 280% above control rats receiving dietary arginine. The percentage of phospholipids was significantly decreased in the arginine-deficient rat liver compared to controls. The fatty acid composition revealed a significant reduction in the reduction in the percentage of palmitic, palmitoleic, oleic, and linoleic acids. However, both stearic and arachidonic acids were increased approximately 250 and 160%, respectively, in arginine-deficient livers compared to controls. Arginine deficiency in the rat causes a marked alteration in lipid metabolism similar to that observed with orotic acid feeding. The similarities or arginine deficiency and orotic acid feeding are discussed.

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.

Sex difference in the development of fatty liver by orotic acid

Effects of orotic acid on liver lipid accumulation and incorporation of methionine [methyl-14C] into liver phosphatidylcholine and protein, and into serum beta-lipoprotein were studied. Male and female rats of Wistar strain were fed a semisynthetic diet supplemented with 1 per cent orotic acid for 7 days. Feeding of orotic acid induced a marked fatty liver in female rats, but not in males. In female rats, radioactivity in liver phosphatidylcholine was significantly decreased by orotic acid, and that in liver protein was slightly decreased. In male rats, incorporation of methionine [methyl-14C] into liver phosphatidylcholine and protein was unchanged between the control and the rats fed orotic acid. Radioactivity in serum beta-lipoprotein was decreased to a greater extent in female rats than in males. These results suggest that sex difference in the development of fatty liver may be due to the difference in the effect of orotic acid on liver phosphatidylcholine biosynthesis.

Vitamin E and stress. 8. Nutritional effects of dietary stress with silver in vitamin E-deficient chicks and rats

1. When chicks were given a fat-free casein–gelatin diet and, after 2 weeks of age, 0·15% silver acetate in the drinking water, they were found to have colourless exudates mainly in the pectoral region and partly in the peritoneal and pericardial spaces. Vitamin E and selenium, separately and together, failed to prevent this condition. Vitamin E was required together with methionine to prevent the condition. Methionine itself induced green staining of a few of the exudates.

2. When lard was added to the casein–gelatin diet and the chicks were also given Ag, some green exudates were found in addition to the colourless ones. Addition of vitamin E or Se or both prevented the green exudates, but raised the incidence of colourless exudates. Methionine enhanced the green exudate condition, but again when combined with vitamin E prevented both types of exudate.

3. A similar condition characterized by colourless exudates was induced by giving chicks diets based upon gelatin, yeast BPC, α-protein (with extra salts) or α-protein with gelatin. A torula yeast diet induced green exudates and haemorrhages.

4. All the basal diets, which were deficient in sulphur amino acids, produced dystrophy of the breast muscle. Four of these diets contained no fat. Some diets also induced dystrophy of the gizzard. Vitamin E and Se protected against both these lesions. Methionine was protective in all except the torula yeast diet.

5. Ethionine induced muscular dystrophy in chicks given a vitamin E-deficient diet adequate in sulphur amino acids. Additional methionine or vitamin E was protective, but cystine was not. Ethionine also produced a small incidence of green exudates and slight haemorrhages. This condition was prevented by vitamin E but not by methionine. The liver damage due to ethionine was not prevented by vitamin E, methionine or cystine.

6. Liver necrosis was induced in rats by giving them an 8·3% casein diet and Ag, 130–1000 ppm, in the drinking water or the diet. Necrosis was produced even in the absence of dietary fat. Vitamin E and DPPD (N,N′-diphenyl-p-phenylenediamine) prevented necrosis, but adenine sulphate (0·25%), methionine (0·15%) and IONOX 330 (2,4,6-tri-(3′,5′-di-tert.-butyl-4′-hydroxybenzyl) mesitylene) did not. Se, 0·05 ppm, protected against 130 ppm Ag, but 1000 ppm Ag overcame the protective effect of 1 ppm Se. Similarly, 3 ppm cyanocobalamin was partly protective against 130 ppm Ag, but not against the higher concentration. Gold chloride (1000 ppm Au) had a mildly necrotic effect against which vitamin E did not protect. Neither copper sulphate (500 ppm Cu) not arsanilic acid (70 ppm As) induced liver necrosis.

7. A high intake of Se (20 ppm as sodium selenate) was necrogenic in rats given a 10% casein diet; vitamin E and methionine did not protect. Vitamin E and cystine raised the low incidence of an exudative condition found in rats given 20 ppm Se. Methionine opposed this action of vitamin E.

8. It was concluded that exudative diathesis in chicks could be resolved into a simple exudative condition and a superimposed haemorrhagic condition. Ag is a pro-exudative factor. Vitamin E and Se are also pro-exudative for chicks given the casein–gelatin–lard–Ag treatment. Torula yeast, methionine, lard, Ag (with lard) and ethionine are all pro-haemorrhagic factors. Se and Ag have an antagonistic relationship in rats and chicks; in chicks, however, Se synergizes with Ag when the supply of methionine is limited.