Prostaglandin biosynthetic capacity of hepatomas with different growth rates

1. Prostaglandin synthesis from [14C]arachidonate by microsomal fractions was measured with preparations from rat liver and from hepatomas of different growth rates. The highest rates of synthesis were observed with microsomal preparations from the rapidly growing hepatoma HTC. 2. Assay of endogenous levels of prostaglandins E2, F2 alpha and thromboxane B2 also indicated high levels in solid tumors of the HTC line. 3. With HTC cells in culture it was necessary to incubate in the absence of serum in order to detect prostaglandin synthesis. 4. The data indicated that, while prostaglandin synthesis was elevated in HTC cells, the synthesis of prostaglandins by a series of hepatomas was not closely correlated with the growth rates of the tumors.     

Superoxide dismutase content and microsomal lipid composition of tumours with different growth rates

The content of cytosolic superoxide dismutase has been determined in Morris hepatomas 3924A (fast-growing) and 44 (slow-growing) and in ascites tumour cells (Novikoff hepatoma and Ehrlich-Lettré). The enzyme is decreased in all the tumours examined. The lowest amounts were found in the tumours with the fastest growth rates. Measurements of the lipid composition and fluidity of microsomal membranes isolated from Morris hepatomas show that also these parameters are changed in relation to the growth rate. The lipid to protein ratio and the degree of fatty acid unsaturation decrease gradually from rat liver to hepatoma 44 and 3924A microsomes. The different lipid composition is reflected also by differences in the physical environment of the bilayer, as indicated by data obtained with spin-labeled fatty acids. It is proposed that the changes in the membrane lipid composition and organization are consequent to the decrease in the protective effect of cytosolic superoxide dismutase against the O2- induced lipid peroxidation.     

Phospholipid fatty acid composition, vitamin E content and susceptibility to lipid peroxidation of duck spermatozoa

Recent studies on chicken semen have suggested that the lipid and fatty acid composition of spermatozoa may be important determinants of fertility. Phospholipid fatty acid composition, vitamin E content and in vitro susceptibility to lipid peroxidation of duck spermatozoa were investigated using GC-MS and HPLC based methods. The total phospholipid fraction of duck spermatozoa was characterized by high proportions of the n-6 polyunsaturated fatty acids arachidonic (20:4n-6), docosatetraenoic (22:4n-6) and docosapentaenoic (22:5n-6) acids but a substantial proportion of the n-3 fatty acid docosahexaenoic (22:6n-3) acid was also present. Palmitic (16:0) and stearic (18:0) fatty acids were the major saturates in sperm phospholipids. Among the phospholipid classes, phosphatidylserine (PS) had the highest degree of unsaturation due to very high proportions of 22:6n-3, 22:5n-6, 22:4n-6 and 20:4n-6, comprising together more than 75% of total fatty acids in this fraction. Phosphatidylethanolamine (PE) also contained high proportions of these four C(20-22) polyunsaturates, which together formed 60% of total fatty acids in this phospholipid. Spermatozoa and seminal plasma of duck semen were characterized by unexpectedly low content of vitamin E, being more than 4-fold lower than in chicken semen. In duck semen the major proportion of the vitamin E (>70%) was located in the spermatozoa. The very high proportion of 22:6n-3 in PS and PE fractions of duck sperm lipids and the comparatively low levels of vitamin E could predispose semen to lipid peroxidation. Nevertheless the in vitro susceptibilities to Fe2+-stimulated lipid peroxidation of duck and chicken spermatozoa were very similar. The results of the study suggest that increased superoxide dismutase and glutathione peroxidase activity and increased antioxidant activity of seminal plasma may compensate for the low levels of vitamin E to help protect the membranes of duck spermatozoa, which exhibit a high degree of unsaturation from oxidative stress.     

Importance of the polyunsaturated fatty acid to vitamin E ratio in the resistance of rat lung microsomes to lipid peroxidation

Rat lung microsomes and liposomes made from isolated lung microsomal lipids were found to be much more resistant to lipid peroxidation than those from liver in both enzymatic and nonenzymatic systems. The polyunsaturated fatty acid (PUFA) content of isolated lung microsomal lipids was 28% of total fatty acids, while liver was 54%. The vitamin E (α-tocopherol) content of isolated lung microsomal lipids was 2.13 nmol/μmol lipid phosphate and that of liver was 0.43. Individually, neither the lower PUFA content nor higher vitamin E levels could account for the resistance of lung microsomal lipids to peroxidation. Distearoyl-L-a-phosphatidylcholine and/or α-tocopherol were added to liver microsomal lipids to achieve different PUFA to vitamin E ratios at PUFA contents of 28% or 54%, and the resulting liposomes were subjected to an NADPH-dependent lipid peroxidation system utilizing cytochrome P450 reductase, EDTA-Fe⁺³, and ADP-Fe⁺³. Liposomes having PUFA to vitamin E ratios less than approximately 250 nmol PUFA/nmol vitamin E were resistant to peroxidation, whereas lipid peroxidation, as evidenced by malondialdehyde production, occurred in liposomes having higher ratios. When lipid peroxidation occurred, 40%–60% of the liposomal vitamin E was irreversibly oxidized. Irreversible oxidation did not occur in the absence of lipid peroxidation. These studies indicated that the low PUFA to vitamin E ratio in lung microsomes and isolated microsomal lipids was sufficient to account for the observed resistance to lipid peroxidation.     

Nephrotoxicity and its prevention by vitamin E in ferric nitrilotriacetate-promoted lipid peroxidation

Iron and aluminum complexes of nitrilotriacetic acid cause severe nephrotoxicity in Wistar rats. In addition, a high incidence of renal cell carcinoma is seen in ferric nitrilotriacetate-treated animals. The present study was performed to see if lipid peroxidation is involved in ferric nitrilotriacetate toxicity. Ferric nitrilotriacetate had more bleomycin-detectable 'free' iron than any ferric salt, while iron complexed with desferrioxamine or ferric chondroitin sulfate had none. The toxicity of ferric nitrilotriacetate in vivo was more pronounced in vitamin E-deficient rats. A thiobarbituric acid-reactive substance was present in the kidneys of vitamin E-deficient rats in amounts markedly elevated compared to vitamin E-sufficient, or vitamin E-supplemented rats. Non-complexed nitrilotriacetate or aluminum nitrilotriacetate did not produce any thiobarbituric acid-reactive substance in vitamin E-sufficient rats died by the 58th day of administration. We suggest that the iron-stimulated production of free radicals leading to lipid peroxidation is the major cause of ferric nitrilotriacetate-mediated renal toxicity. Vitamin E, a known scavenger of free radicals, is effective in protecting against this iron-induced toxicity.     

Exercise-induced lipid peroxidation and leakage of enzymes before and after vitamin E supplementation

1. The purpose of this study was to investigate the effects of vitamin E on serum levels of malondialdehyde following the acute exhaustive exercise in human, and to determine whether the magnitude of leakage of enzyme would be affected by vitamin E supplementation. 2. Increase of malondialdehyde after exercise before vitamin E supplementation was slight (but statistically significant), however after supplementation with vitamin E, malondialdehyde level after exercise was significantly decreased. 3. Leakage of enzyme was significantly increased after exercise before vitamin E supplementation, but it was lower following exercise after vitamin E supplementation. 4. Lipid peroxidation following a bout of acute heavy exercise can be inhibited by vitamin E supplementation.     

Supplementation with vitamin E but not with vitamin C lowers lipid peroxidation in vivo in mildly hypercholesterolemic men

Although the use of vitamin E supplements has been associated with a reduction in coronary events, assumed to be due to lowered lipid peroxidation, there are no previous long-term clinical trials into the effects of vitamin C or E supplementation on lipid peroxidation in vivo. Here, we have studied the long-term effects of vitamins C and E on plasma F₂-isoprostanes, a widely used marker of lipid peroxidation in vivo. As a study cohort, a subset of the “Antioxidant Supplementation in Atherosclerosis Prevention” (ASAP) study was used. ASAP is a double-masked placebo-controlled randomized clinical trial to study the long-term effect of vitamin C (500 mg of slow release ascorbate daily), vitamin E (200 mg of d-α-tocopheryl acetate daily), both vitamins (CellaVie^®), or placebo on lipid peroxidation, atherosclerotic progression, blood pressure and myocardial infarction (n = 520 at baseline). Lipid peroxidation measurements were carried out in 100 consecutive men at entry and repeated at 12 months. The plasma F₂-isoprostane concentration was lowered by 17.3% (95% CI 3.9–30.8%) in the vitamin E group (p = 0.006 for the change, as compared with the placebo group). On the contrary, vitamin C had no significant effect on plasma F₂-isoprostanes as compared with the placebo group. There was also no interaction in the effect between these vitamins. In conclusion, long-term oral supplementation of clinically healthy, but hypercholesterolemic men, who have normal vitamin C and E levels with a reasonable dose of vitamin E lowers lipid peroxidation in vivo, but a relatively high dose of vitamin C does not. This observation may provide a mechanism for the observed ability of vitamin E supplements to prevent atherosclerosis.     

Rat lung microsomal lipid peroxidation: effects of vitamin E and reduced glutathione

Lung microsomal membranes that contain the redox active components associated with the mixed-function oxidase system can be peroxidized in vitro. To investigate the characteristics of rat lung microsomal lipid peroxidation, we performed experiments using a variety of peroxidation initiators and microsomes obtained from normal and vitamin E-deficient rats. We found that lung microsomes obtained from normal rats are peroxidized much less than liver microsomes obtained from the same animals. Only initiation systems using very high concentrations of ferrous iron produced any significant peroxidation of normal rat lung microsomes. Lung microsomes obtained from vitamin E-deficient rats were found to be much more susceptible to peroxidation. Glutathione (GSH) was effective in inhibiting peroxidation when lung microsomes from normal rats were peroxidized. GSH was not effective in decreasing peroxidation when microsomes from vitamin E-deficient rats were peroxidized in the same system. We conclude that both GSH and vitamin E protect lung microsomal membranes from peroxidation. Glutathione protection appears to be related to the presence of a sulfhydryl group.     

Effect of retinol on the hemolysis and lipid peroxidation in vitamin E deficiency

A study on the effect of retinolin vitro on the hemolysis of vitamin E deficient rat red blood cells showed that retinol enhanced the lysis of the E deficient cells as compared to the lysis of normal cells. The lipid peroxidation present during hydrogen peroxide induced lysis of E deficient cells was however markedly inhibited in the presence of retinol without affecting the rate of lysis. In an actively peroxidising system of non-enzymatic lipid peroxidation of rat liver or brain homogenates and of brain lysosomes incubated with human erythrocytes, no lysis was obtained; incorporation of retinol in such systems resulted in lysis but no peroxidation. Hydrogen peroxide generating substances almost completely inhibited the lysis of normal human erythrocytes by retinol, but linoleic acid hydroperoxide and auto-oxidised liver or brain homogenates and ox-brain liposomes increased the lysis. It is concluded that vitamin E deficient erythrocyte hemolysis may be augmented by retinol, an anti-oxidant, having a lytic function without the peroxidation of stromal lipids     

The effect of vitamin E on lipid peroxidation in the copper-deficient rat

The present study was designed to determine whether the supplementation of vitamin E in the copper-deficient diet would ameliorate the severity of copper deficiency in fructose-fed rats. Lipid peroxidation was measured in the livers and hearts of rats fed a copper-deficient diet (0.6 microg Cu/g) containing 62% fructose with adequate vitamin E (0.1 g/kg diet) or supplemented with vitamin E (1.0 g/kg diet). Hepatic lipid peroxidation was significantly reduced by vitamin E supplementation compared with the unsupplemented adequate rats. In contrast, myocardial lipid peroxidation was unaffected by the level of vitamin E. Regardless of vitamin E supplementation, all copper-deficient rats exhibited severe signs of copper deficiency, and some of the vitamin E-supplemented rats died of this deficiency. These findings suggest that although vitamin E provided protection against peroxidation in the liver, it did not protect the animals against the severity of copper deficiency induced by fructose consumption.     

Electron paramagnetic resonance studies of iron-sulfur centers in mitochondria prepared from three Morris hepatomas with different growth rates

Iron-sulfur centers in mitochondria prepared from Morris hepatomas with different growth rates were compared with those in host liver and nontumor-bearing rat liver mitochondria by EPR measurements (< 77° K). In the slow growing hepatoma 16, EPR signals from iron-sulfur centers located in the NADH dehydrogenase region were specifically diminished. In the rapidly growing hepatoma 7777, EPR signals of all the iron-sulfur centers showed considerably diminished intensity. In hepatoma 7800 having an intermediate growth rate, all iron-sulfur centers showed no change. Those changes in iron-sulfur centers correlated with observed respiratory activities of Morris hepatoma mitochondria. No general correlation was obtained between these parameters and the growth rate of the tumors.     

Effect of vitamin E on lipid peroxidation in buffalo Bubalus bubalis L

Vitamin E significantly (P less than 0.01), inhibited lipid peroxidation as indicated by malonaldehyde (MDA) production and improved significantly (P less than 0.01) motility and percent live spermatazoa of B. bubalis semen. Bulls with higher MDA formation had lower sperm motility and percent live count. Variance due to bulls for all the three parameters were significant (P less than 0.05).     

GPX4 and vitamin E cooperatively protect hematopoietic stem and progenitor cells from lipid peroxidation and ferroptosis

Ferroptosis, a newly defined mode of regulated cell death caused by unbalanced lipid redox metabolism, is implicated in various tissue injuries and tumorigenesis. However, the role of ferroptosis in stem cells has not yet been investigated. Glutathione peroxidase 4 (GPX4) is a critical suppressor of lipid peroxidation and ferroptosis. Here, we study the function of GPX4 and ferroptosis in hematopoietic stem and progenitor cells (HSPCs) in mice with Gpx4 deficiency in the hematopoietic system. We find that Gpx4 deletion solely in the hematopoietic system has no significant effect on the number and function of HSPCs in mice. Notably, hematopoietic stem cells (HSCs) and hematopoietic progenitor cells lacking Gpx4 accumulated lipid peroxidation and underwent ferroptosis in vitro. α-Tocopherol, the main component of vitamin E, was shown to rescue the Gpx4-deficient HSPCs from ferroptosis in vitro. When Gpx4 knockout mice were fed a vitamin E-depleted diet, a reduced number of HSPCs and impaired function of HSCs were found. Furthermore, increased levels of lipid peroxidation and cell death indicated that HSPCs undergo ferroptosis. Collectively, we demonstrate that GPX4 and vitamin E cooperatively maintain lipid redox balance and prevent ferroptosis in HSPCs.Subject terms: Cell biology, Physiology, Stem-cell research     

Lipid peroxidation in hepatomas of different degrees of deviation

Lipid peroxidation rate in four different hepatomas is quite different and seems to be related to their degree of deviation, low deviation tumours displaying higher peroxidative ability. Moreover, the supernatant of the highly anaplastic Yoshida hepatoma is able to decrease the peroxidation rate in normal liver microsomes. This antioxidant ability is not dependent upon an increased level of glutathione. The concentration of reduced glutathione (GSH) declines strongly during incubation in conditions favouring lipid peroxidation. Unlike normal liver homogenates, this decline of GSH in hepatomas is not due to the transformation of GSH into oxidized glutathione (GSSG) but mostly to the increased activity of the γ-glutamyl-transpeptidase pathway.     

Supplementation with vitamin E but not with vitamin C lowers lipid peroxidation in vivo in mildly hypercholesterolemic men.

Although the use of vitamin E supplements has been associated with a reduction in coronary events, assumed to be due to lowered lipid peroxidation, there are no previous long-term clinical trials into the effects of vitamin C or E supplementation on lipid peroxidation in vivo. Here, we have studied the long-term effects of vitamins C and E on plasma F2-isoprostanes, a widely used marker of lipid peroxidation in vivo. As a study cohort, a subset of the "Antioxidant Supplementation in Atherosclerosis Prevention" (ASAP) study was used. ASAP is a double-masked placebo-controlled randomized clinical trial to study the long-term effect of vitamin C (500 mg of slow release ascorbate daily), vitamin E (200 mg of D-alpha-tocopheryl acetate daily), both vitamins (CellaVie), or placebo on lipid peroxidation, atherosclerotic progression, blood pressure and myocardial infarction (n = 520 at baseline). Lipid peroxidation measurements were carried out in 100 consecutive men at entry and repeated at 12 months. The plasma F2-isoprostane concentration was lowered by 17.3% (95% CI 3.9-30.8%) in the vitamin E group (p = 0.006 for the change, as compared with the placebo group). On the contrary, vitamin C had no significant effect on plasma F2-isoprostanes as compared with the placebo group. There was also no interaction in the effect between these vitamins. In conclusion, long-term oral supplementation of clinically healthy, but hypercholesterolemic men, who have normal vitamin C and E levels with a reasonable dose of vitamin E lowers lipid peroxidation in vivo, but a relatively high dose of vitamin C does not. This observation may provide a mechanism for the observed ability of vitamin E supplements to prevent atherosclerosis.     

Effect of oral methionine and vitamin E on blood lipid peroxidation in vitamin B6 deficient rats

Lipid peroxidation in blood of vitamin B6 deficient rats was significantly increased when compared to pair-fed controls. The observed increased lipid peroxidation in vitamin B6 deficiency was correlated with high levels of lipids, metal ions and low levels of antioxidants, alpha-tocopherol, ascorbic acid and reduced GSH. Supplementation of methionine or vitamin E along with the vitamin B6 deficient diet restored the levels of antioxidants to near normal and also protected against oxidative stress. However plasma TBARS level as well as total lipids were still elevated in M-B6 diet fed rats and normalized in E-B6-d rats.     

The content of lipid peroxidation products and the activity of antioxidant enzymes in the myocardium and liver of rats with various vitamin E allowances

After 2 month of feeding vitamin E-supplemented diet (100.6 and 0 mg/kg; group I-control, II and III, respectively) the concentration of lipid peroxidation products (diene conjugates, malondialdehyde, Schiff's bases) and activity of antioxidant enzymes (superoxide dismutase, glutathione peroxidase) was estimated in rat heart and liver. Although the content of alpha-tocopherol in organs of group II was significantly decreased, the concentration of peroxidation products and enzyme activities was unchanged. Moreover, these parameters were constant in rat liver of group III. The heart was more sensitive because in group III to vitamin E deficiency (the alpha-tocopherol level was dropped fourfold) the concentration of diene conjugates and malondialdehyde was increased and superoxide dismutase activity was decreased. Thus insufficiency of vitamin E may result in selective alterations of myocardial functions. In addition, vitamin E may be useful instrument for correction of free radical oxidation and antioxidant system activity in the heart.     

Vitamin E content and lipid peroxidation of blood in some chronic inflammatory diseases

Patients suffering from rheumatoid arthritis, spondylosis, coxarthrosis, ankylosing spondylitis, chronic active and chronic alcoholic hepatitis were studied. The plasma vitamin E content remained unchanged. The TBA-reactive plasma substances (malondialdehyde) content of plasma increased in all patients except those with ankylosing spondylitis. Catalase activity of plasma increased in patients of both sexes suffering from rheumatoid arthritis and spondylosis and coxarthrosis, but decreased in the two hepatitis groups. The glutathione-peroxidase activity of RBC (1:9 haemolysate) increased in female rheumatoid arthritis patients and decreased in those suffering from chronic alcoholic hepatitis. The results showed that chronic inflammatory processes affect the rate of lipid peroxidation and the activity of the biological antioxidant mechanism.     

Antioxidant effect of vitamin E and glutathione on lipid peroxidation in boar semen plasma

The protective effect of vitamin E and reduced glutathione (GSH) against lipid peroxidation in boar semen plasma was studied. The lipid peroxidation, measured by the test for thiobarbituric acid reactive substances (TBARS), doubled in the presence of the lipid peroxidation Fe²⁺-sodium ascorbate-inducing system. The ascorbate-induced TBARS were inhibited by about 62% through the water-soluble vitamin E analog (TROLOX) and about 57% by GSH. In the in vivo experiments, 7 wk of oraldl-α-tocopherol acetate (1000 IU/d/animal) administration caused a significant fall in the level of the semen plasma TBARS, from 2.2±0.09 to 1.2±0.13 nmol MDA/mL. The semen plasma superoxide dismutase (SOD) and GSSG tended to increase with the time of vitamin E administration, but the increment did not reach a significant level by the seventh week. The vitamin E supplementation significantly increased the number of spermatozoa per 1 cm³ of ejaculate. The protective role of vitamin E and GSH with respect to boar semen against fatty acid peroxidation and a positive influence of vitamin E supplementation on semen quality have been evidenced.