Effects of lipid peroxidation on adrenal microsomal monooxygenases

NADPH- and iron-dependent lipid peroxidation inhibit aromatase activity in human placental microsomes

During pregnancy placenta is the most significant source of lipid hydroperoxides and other reactive oxygen species (ROS). The increased production of lipid peroxides and other ROS is often linked to pre-eclampsia. It is already proved that placental endoplasmic reticulum may be an important place of lipid peroxides and superoxide radical production. In the present study we revealed that NADPH- and iron-dependent lipid peroxidation in human placental microsomes (HPM) inhibit placental aromatase--a key enzyme of estrogen biosynthesis in human placenta. We showed that significant inhibition of this enzyme is caused by small lipid peroxidation (TBARS (thiobarbituric acid-reactive substances)<4nmol/mg microsomal protein (m.p.)). More intensive lipid peroxidation (TBARS>9nmol/mg microsomal protein) diminishes aromatase activity to value being less than 5% of initial value. NADPH- and iron-dependent lipid peroxidation also causes disappearance of cytochrome P450 parallel to observed aromatase activity inhibition. EDTA, alpha-tocopherol, MgCl(2) and superoxide dismutase (SOD) prevent aromatase activity inhibition and cytochrome P450(AROM) degradation. Mannitol and catalase have not effect on TBARS synthesis, aromatase activity and cytochrome P450 degradation. In view of the above we postulate that the inhibition of aromatase activity observed is mainly a consequence of cytochrome P450(AROM) degradation induced by lipid radicals. The role of hydroxyl radical in cytochrome P450 degradation is negligible in our experimental conditions. The results presented here also suggest that the inhibition of aromatase activity can also take place in placenta at in vivo conditions.

Lipid peroxidation in the adrenal glands of male rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

This study was performed to determine whether TCDD (50 micrograms/kg; single oral dose) could induce adrenal microsomal lipid peroxidation, which might be correlated to decreased levels of cytochrome P-450 and 21-hydroxylase activity. The amount of malondialdehyde (MDA) formed was significantly higher than controls at days 1 through 5 following TCDD treatment. Microsomal cytochrome P-450 levels were depressed after lipid peroxidation at days 1, 3, and 5, and 21-hydroxylase activity decreased at day 5 after TCDD treatment. This study shows that TCDD stimulates adrenal microsomal lipid peroxidation which is associated with decreased cytochrome P-450 levels and 21-hydroxylase activity.

The influence of NADPH-dependent lipid peroxidation on the progesterone biosynthesis in human placental mitochondria

In an in vitro system consisting of human term placental mitochondria and an NADPH-generating system plus Fe2+, significant lipid peroxidation was observed along with a concomitant inhibition of progesterone biosynthesis. This inhibition could be markedly blocked by Mn2+, superoxide dismutase and dimethylfuran, inhibitors of NADPH-dependent lipid peroxidation. In addition, it has been found that malondialdehyde formation is accompanied by a corresponding decrease in placental mitochondrial cytochrome P-450 content. Inhibitors of lipid peroxidation also prevent the loss of cytochrome P-450, further demonstrating a direct relationship between NADPH-dependent lipid peroxidation and degradation of cytochrome P-450 in cell-free systems. These measurements provide the first evidence that the inhibition of progesterone biosynthesis by a NADPH-dependent lipid peroxidation in placental mitochondria is a consequence of cytochrome P-450 degradation due to lipid peroxidation.

alpha-Tocopherol depletion eliminates the regional differences in adrenal mitochondrial lipid peroxidation

Prior studies demonstrated far greater amounts of lipid peroxidation (LP) in mitochondria from the zona reticularis (inner zone) of the guinea pig adrenal cortex than in mitochondria from the outer zone (zona fasciculata + zona glomerulosa) of the gland. alpha-Tocopherol concentrations, by contrast, were greater in the outer zone. To determine if the differences in alpha-tocopherol content were responsible for the regional differences in LP, the effects of alpha-tocopherol deficiency on mitochondrial LP were investigated. Tocopherol deficiency had relatively little effect on ferrous ion- or ascorbic acid-induced LP in inner zone mitochondria. However, depletion of adrenal tocopherol substantially increased outer zone LP, eliminating the differences between the two zones. Fatty acid analyses revealed that mitochondria from tocopherol-deficient animals contained significantly less linoleic acid (C18:2) and arachidonic acid (C20:4) than those from controls, suggesting peroxidative losses in vivo. In mitochondria from control animals, subphysiological concentrations of ascorbic acid stimulated LP, but physiological levels did not. However, in tocopherol-depleted mitochondria, even physiological concentrations of ascorbic acid stimulated LP. The results indicate that the intra-adrenal distribution of alpha-tocopherol is responsible for the regional differences in mitochondrial LP and that alpha-tocopherol is a major determinant of ascorbic acid actions on adrenal LP. The data also provide evidence of adrenal LP in vivo in tocopherol-deficient animals.

Modulation of the effects of ascorbic acid on lipid peroxidation by tocopherol in adrenocortical mitochondria

Studies were done to evaluate the role of alpha-tocopherol in modulating the effects of ascorbic acid (AA) on lipid peroxidation (LP) by adrenocortical mitochondria. In control mitochondria from the inner (zona reticularis) or outer (zona fasciculata plus zona glomerulosa) zones of the guinea pig adrenal cortex, subphysiological concentrations of AA stimulated LP but higher levels had little or no effect. However, after depletion of adrenal tocopherol, even physiological concentrations of AA exerted prooxidant effects, stimulating LP. To assess the antioxidant potency of AA, its effects to inhibit ferrous ion (Fe2+)-induced LP were determined. Mitochondria from the outer zone contained far more alpha-tocopherol than those from the inner zone and were more sensitive to the antioxidant effects of AA. After tocopherol depletion, the antioxidant potency of AA in outer zone mitochondria decreased, but there was little change in the inner zone. The results indicate that the actions of AA are determined in part by mitochondrial tocopherol content, and, as a result, vary in the different zones of the adrenal cortex.

Relationship between mitochondrial lipid peroxidation and alpha-tocopherol levels in the guinea-pig adrenal cortex

Lipid peroxidation in mitochondria from the functionally distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea-pig adrenal cortex was investigated. Ferrous ion (Fe2+)-induced lipid peroxidation was far greater in inner than outer zone mitochondria. Ascorbic acid similarly initiated lipid peroxidation to a greater extent in inner zone mitochondrial preparations. Differences in the unsaturated fatty acid content of inner and outer zone mitochondria could not account for the regional differences in lipid peroxidation. Total fatty acid concentrations were greater in the outer than in the inner zone, and the relative amounts of each fatty acid were similar in the two zones. However, mitochondrial concentrations of alpha-tocopherol, an antioxidant known to inhibit lipid peroxidation, were approx. 5-times greater in the outer than inner zone. The results demonstrate that there are regional differences in mitochondrial lipid peroxidation in the adrenal cortex which may be attributable to differences in alpha-tocopherol content. Thus, alpha-tocopherol may serve to protect outer zone mitochondrial enzymes from the consequences of lipid peroxidation and thereby contribute to some of the functional differences between the zones of the adrenal cortex.

The effect of chronic adriamycin treatment on heart kidney and liver tissue of male and female rat

The influence of chronic adriamycin treatment on cellular defence mechanisms against free radicals has been determined in rats. To that end, the changes in vitamin E content, activity of superoxide dismutase, catalase and factors of the glutathione system were measured in heart, kidneys and liver after 24 and 52 days of treatment. Moreover, damage was assessed by measuring the activity of NADPH- and NADH-cytochrome c reductase. The results concerning the components of the oxidative defence systems in male rats showed reductions in the activity of superoxide dismutase and catalase in renal tissue and in factors of the glutathione system in liver tissue. In cardiac tissue an increased activity of catalase and elevated content of total glutathione were found. Vitamin E content was increased in liver and to a lesser extent, in kidneys. The activity of Se-dependent glutathione peroxidase sharply decreased only in liver. Major differences between male and female rats were not observed in renal and cardiac tissue, as far as protective factors were concerned. However, a decrease in catalase activity was detectable earlier in male kidneys. The protective factors in liver of female rats were far less susceptible to in vivo treatment with adriamycin, as compared to liver of male rats. Decreased activity of the cytochrome reductases was found in liver of male rats. In male renal tissue only cytochrome c reductase activity was significantly reduced. Male cardiac tissue showed no signs of biochemical damage, although from histological examination in a parallel study [J Natl Cancer Inst 76: 299-307 (1986)] lesions were evident. In female rats no damage was found in liver, kidneys and heart.

A role for dietary lipids and antioxidants in the activation of carcinogens

The ways in which dietary polyunsaturated fats and antioxidants affect the balance between activation and detoxification of environmental precarcinogens is discussed, with particular reference to the polycyclic aromatic hydrocarbon benzo(a)pyrene. The structure and composition of membranes and their susceptibility to peroxidation is dependent on the polyunsaturated fatty acid (PUFA) content of the cell and its antioxidant status, both of which are determined to a large degree by dietary intake of these compounds. An increase in the PUFA content of membranes stimulates the oxidation of precarcinogens to reactive intermediates by affecting the configuration and induction of membrane-bound enzymes (e.g., the mixed-function oxidase system and epoxide hydratase); providing increased availability of substrates (hydroperoxides) for peroxidases that cooxidise carcinogens (e.g., prostaglandin synthetase and P-450 peroxidase); and increasing the likelihood of direct activation reactions between peroxyl radicals and precarcinogens. Antioxidants, on the other hand, protect against lipid peroxidation, scavenge oxygen-derived free radicals and reactive carcinogenic species. In addition some synthetic antioxidants exert specific effects on enzymes, which results in increased detoxification and reduced rates of activation. The balance between dietary polyunsaturated fats, antioxidants and the initiation of carcinogenesis is discussed in relation to animal models of chemical carcinogenesis and the epidemiology of human cancer.

Regional differences in microsomal lipid peroxidation and antioxidant levels in the guinea pig adrenal cortex

Lipid peroxidation (LP) and antioxidant levels were studied in the chromatically distinct inner (zona reticularis) and outer (zona fasciculata + zona glomerulosa) zones of the guinea pig adrenal cortex. Ferrous ion (Fe2+) produced a concentration-dependent (10(-5) to 10(-3) M) stimulation of microsomal LP in both zones, but LP, as estimated by malonaldehyde production, was far greater in the inner zone. Although cytosolic ascorbic acid content was similar in the two zones, microsomal tocopherol levels were approx 4 times greater in the outer than inner zone. Subphysiological concentrations of ascorbic acid, like Fe2+, initiated LP to a greater extent in inner than outer zone microsomes; optimal stimulation of LP by ascorbic acid occurred at concentrations of 100-200 microM in both zones. Physiological concentrations of ascorbic acid (1-5 mM), by contrast, did not initiate LP and, in fact, markedly inhibited Fe2+-induced LP in both inner and outer zone microsomal preparations. Outer zone microsomes were more sensitive to the antioxidant effects of ascorbic acid than were inner zone preparations. Addition of alpha-tocopherol to inner zone microsomal suspensions inhibited Fe2+-induced LP. The results indicate that there are regional differences in adrenocortical LP which may be caused by differences in tocopherol content. alpha-Tocopherol may serve important antioxidant functions within the adrenal cortex, thereby contributing to the functional zonation of the gland.

Quantitative alterations in the metabolism of carbonyl compounds due to diet-induced lipid peroxidation in rats

Following the dietary induction of lipid peroxidation in rats (verified by the levels of malonaldehyde and glutathione peroxidase), the urinary carbonyl compounds were followed chromatographically. Through a headspace gas chromatographic procedure, increases of several aldehydes and furan derivatives were noticed. Liquid chromatography of the dinitrophenylhydrazone derivatives of urinary carbonyls provided a more definitive experiment, in which the increased-peroxidation animals could be compared to those maintained on a control diet. Several carbonyl metabolites, identified by mass spectrometry, were elevated following the lipid peroxidation induction.

Uptake of secondary autoxidation products of linoleic acid by the rat

Incorporation of secondary autoxidation products (SP) of linoleic acid into the rat body was investigated. Radioactive SP was administered orally to a group of 5 rats, and excretions of radioactive substances in feces, urine and respiration were measured and compared with excretions from rats fed linoleic acid and its hydroperoxides. The SP-fed group excreted 45% and the other groups about 10% of the administered radioactivity through feces. Urinary excretion accounted for 52% of activity ingested in the SP group and less than 30% in the other groups. The 14CO2 produced in each group was about 25% of the ingested activity. Incorporation of the radioactive substances of SP into tissues and organs was measured periodically after administration of a single dose. The radioactive substances accumulated in the liver between 12-24 hr after administration and accounted for 2.6% of the total amount given, the highest level of all tissues and organs. This accumulation led to an elevation of serum transaminase activities, an increase in hepatic lipid peroxide, as determined by thiobarbituric acid test, and a slight hypertrophy of liver (1.5-fold). Therefore, absorbed SP appeared to contribute to the deleterious condition of the liver.