The relationship between NADPH-dependent lipid peroxidation and degradation of cytochrome P-450 in adrenal cortex mitochondria

Immunolocalization of Glutathione-Peroxidase (GPx1) in the Rat Adrenal Cortex: Correlation between Steroidogenesis and Lipid Peroxidation

In order to confirm the relationship between glutathione-peroxidase (GPx1) and biological significance on steroidogenesis, we have studied the immunocytochemical localization of GPx1 in the rat adrenal cortical cells. GPx1 was observed not only in cytoplasm (cytosol GPx1) but in mitochondria (mitochondrial GPx1). The staining intensity was altered by the functional state of the adrenal cortical cells. Furthermore, cytosol- and mitochondrial-GPx1 was modified by lipoperoxidative damage in the adrenal cortical cells. Therefore, we proposed that the pattern of GPx1 staining should be a more sensitive and specific indicator of oxidative damage in cells. Thus, the staining pattern of GPx1 is thought to be a useful marker for lipid peroxidation in the adrenal cortical cells.

Antioxidant Protective Mechanisms against Reactive Oxygen Species (ROS) Generated by Mitochondrial P450 Systems in Steroidogenic Cells

Mitochondrial P450 type enzymes catalyze central steps in steroid biosynthesis, including cholesterol conversion to pregnenolone, 11beta and 18 hydroxylation in glucocorticoid and mineralocorticoid synthesis, C-27 hydroxylation of bile acids, and 1alpha and 24 hydroxylation of 25-OH-vitamin D. These monooxygenase reactions depend on electron transfer from NADPH via FAD adrenodoxin reductase and 2Fe-2S adrenodoxin. These systems can function as a futile NADPH oxidase, oxidizing NADPH in absence of substrate, and leak electrons via adrenodoxin and P450 to O(2), producing superoxide and other reactive oxygen species (ROS). The degree of uncoupling depends on the P450 and steroid substrate. Studies with purified proteins and overexpression in cultured cells show consistently that adrenodoxin, but not reductase, is responsible for ROS production that can lead to apoptosis. In the ovary and corpus luteum, antioxidant enzyme activities superoxide dismutase, catalase, and glutathione peroxidase parallel steroidogenesis. Antioxidant beta-carotene, alpha-tocopherol, and ascorbate can protect against oxidative damages of P450 systems. In testis Leydig cells, steroidogenesis is associated with aging of the steroidogenic capacity.

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.

Placental mitochondria as a source of oxidative stress in pre-eclampsia

Pre-eclampsia is a hypertensive disorder of human pregnancy that is a leading cause of premature delivery and fetal growth retardation. It is characterized by hypertension, reduced uteroplacental blood flow, proteinuria and oedema. Pre-eclampsia is associated with increased lipid peroxidation in the maternal circulation and in the placenta. Mitochondria are sources of oxygen radicals and are enriched with polyunsaturated fatty acids that are susceptible to peroxidation. Therefore, the mitochondria could be an important source of oxidative stress and lipid peroxidation. To study this, the level of lipid peroxidation in the mitochondrial fraction of placentae obtained from normally pregnant women (n=8) and women with pre-eclampsia (n=8) was examined. Placental tissues were homogenized and the mitochondrial fraction was isolated by ultracentrifugation. Mitochondrial lipid peroxides were estimated by malondialdehyde (MDA). NADPH and Fe++ were used to stimulate lipid peroxidation. Superoxide dismutase (SOD) was used to inhibit superoxide radicals and mannitol to inhibit hydroxyl radicals. The following results were found: (1) MDA levels were significantly greater in the mitochondrial fraction isolated from pre-eclamptic placentae than from normal placentae (27.4+/-3.0 versus 17.0+/-1.8 nmol/g tissue, mean+/-s.e., P<0.05); (2) the oxidative potential of the pre-eclamptic mitochondrial fraction was also higher than normal as evidenced by the significantly greater stimulation of lipid peroxidation by NADPH and Fe+ + (248+/-25 versus 164+/-35 nmol/g, P<0.05); (3) superoxide dismutase, but not mannitol, attenuated the lipid peroxidation induced by NADPH and Fe+ + demonstrating that superoxide is the radical responsible for mitochondrial lipid peroxidation in this system; and (4) the amount of mitochondrial protein was 47 per cent greater and the activity of the mitochondrial enzyme, citrate synthase, was 56 per cent greater in the pre-eclamptic placentae indicating an increase in the amount of mitochondria in the pre-eclamptic placentae. It is concluded that: (1) mitochondrial lipid peroxidation is increased in pre-eclampsia; (2) the amount of placental mitochondria is increased in pre-eclampsia; (3) placental mitochondria contribute to the abnormal increase in lipid peroxidation that occurs in pre-eclamptic placentae by both an increase in their amount and an increase in their susceptibility to oxidation; and (4) mitochondrial generation of superoxide could be an important source of oxidative stress in pre-eclampsia.

Inhibitory effect of free radicals derived from organic hydroperoxide on progesterone synthesis in human term placental mitochondria

Different natural and synthetic organic hydroperoxides have been found to stimulate TBARS formation in human term placental mitochondria. The levels of TBARS were lower than arising from NADPH-dependent lipid peroxidation. BHT, Mn2+ and DMPO counteracted TBARS formation in the presence of cumene hydroperoxide implicating involvement of free radicals in this process. On the other hand superoxide dismutase, catalase and EDTA while being inhibitory in NADPH-dependent lipid peroxidation did not inhibit cumene hydroperoxide-dependent TBARS formation. Amphenone B and SKF-525A, inhibitors of cytochrome P-450, strongly inhibit both NADPH- and cumene hydroperoxide-dependent lipid peroxidation. These data provide evidence that cytochrome P-450SCC is involved in both these processes. However NADPH-dependent lipid peroxidation and the cumene hydroperoxide have been found to inactivate placental mitochondrial cytochrome P-450SCC. The presence of cumene hydroperoxide resulted in a more rapid inactivation of cytochrome P-450SCC and consequently inhibited NADPH-dependent lipid peroxidation. It has been observed for the first time that progesterone biosynthesis can be inhibited by cumene hydroperoxide. Protective effect of Mn2+ and DMPO on progesterone biosynthesis indicates the importance of free radicals as transient products of cytochrome P-450SCC-dependent cumene hydroperoxide metabolism. In contrast to progesterone formation from cholesterol, the conversion of pregnenolone to progesterone was not affected by cumene hydroperoxide. This suggests that inhibition of progesterone synthesis from cholesterol by hydroperoxide may be ascribed to its effect on the desmolase activity of cytochrome P-450SCC in placental mitochondria. On the basis of the results obtained, we propose that the inhibition of progesterone biosynthesis by naturally occurring hydroperoxides may contribute to the development of preeclampsia.

SP-22 is a thioredoxin-dependent peroxide reductase in mitochondria

SP-22 is a mitochondrial antioxidant protein in bovine adrenal cortex. The protein is homologous to thioredoxin peroxidase and other antioxidant proteins. It protects radical-sensitive enzymes from oxidative damage by a radical-generating system (Fe2+/dithiothreitol) in the presence of a small amount of serum. In this study we purified a second mitochondrial protein with Mr 11,777, which cooperates with SP-22 to protect glutamine synthetase and other proteins from Fe2+/dithiothreitol-mediated damage. Without SP-22, the protein had no protecting activity. We determined amino acid and nucleotide sequences of the protein and its cDNA, respectively, and found that it was a protein of the thioredoxin family. The protein, designated as mt-Trx (mitochondrial thioredoxin), had a presequence composed of 59 amino acids that seemed to be a mitochondrial targeting signal. Mitochondrial extract prepared from adrenal cortex contained NADPH-dependent 5,5'dithiobis(2-nitrobenzoic acid) (Nbs2) reductase activity. The enzyme was thought to have thioredoxin reductase activity, since the Nbs2-reducing activity was stimulated by mt-Trx. We partially purified the Nbs2 reductase from bovine adrenocortical mitochondria. In the presence of the partially purified reductase, mt-Trx, and NADPH, SP-22 showed the activity to protect oxyhemoglobin against ascorbate-induced damage. Furthermore, with the three protein components (Nbs2 reductase, mt-Trx, and SP-22) NADPH was oxidized in the presence of hydrogen peroxide or tert-butyl hydroperoxide. The oxidation of NADPH was concomitant with the disappearance of an equimolar amount of hydrogen peroxide. Without any one of the protein components no hemoglobin-protecting and peroxide-dependent NADPH-oxidizing activities were observed. From these results we concluded that SP-22 is thioredoxin-dependent peroxide reductase or so-called thioredoxin peroxidase in mitochondria from the adrenal cortex.

The cDNA sequence encoding bovine SP-22, a new defence system against reactive oxygen species in mitochondria

We have isolated cDNA clones coding SP-22, an antioxidant protein in mitochondria, from a bovine adrenal medulla cDNA library constructed with (lambda)gt11. The largest clone contained the entire coding sequence for mature SP-22. Since the isolated cDNA clones lacked 5'- and 3'-ends, we determined the sequences of both ends by the "Rapid Amplification of cDNA Ends (RACE)" tecnique. The deduced amino acid sequence of the mature protein region was the same as that determined by protein sequencing. Since SP-22 had a mitochondrial targetting signal, its mitochondrial localization was confirmed.

Ferrous-iron induces lipid peroxidation with little damage to energy transduction in mitochondria

Addition of ferrous sulfate, but not ferric chloride, in micromolar concentrations to rat liver mitochondria induced high rates of consumption of oxygen. The oxygen consumed was several times in excess of the reducing capacity of ferrous-iron (O:Fe ratios 5-8). This occurred in the absence of NADPH or any exogenous oxidizable substrate. The reaction terminated on oxidation of ferrous ions. Malondialdehyde (MDA), measured as thiobarbituric acid-reacting material, was produced indicating peroxidation of lipids. The ratio of O2:MDA was about 4:1. Pretreatment of mitochondria with ferrous sulfate decreased the rate of oxidation (state 3) with glutamate (+ malate) as the substrate by about 40% but caused little damage to energy transduction process as represented by ratios of ADP:O and respiratory control, as well as calcium-stimulated oxygen uptake and energy-dependent uptake of [45Ca]-calcium. Addition of succinate or ubiquinone decreased ferrous iron-induced lipid peroxidation in intact mitochondria. In frozen-thawed mitochondria, addition of succinate enhanced lipid peroxidation whereas ubiquinone had little effect. These results suggest that ferrous-iron can cause peroxidation of mitochondrial lipids without affecting the energy transduction systems, and that succinate and ubiquinone can offer protection from damage due to such ferrous-iron released from the stores within the cells.

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.

Initiation of lipid peroxidation in submitochondrial particles: effect of respiratory inhibitors

Initiation of lipid peroxidation in the inner mitochondrial membrane was investigated using respiratory substrates and inhibitors and various iron chelates. An iron chelate was required for initiation of lipid peroxidation in the presence of either NADH or NADPH. The two nicotinamide nucleotides exhibited different activities in initiating lipid peroxidation with regard to concentration and to the effects of rotenone and rhein. Succinate and both nicotinamide nucleotides supported lipid peroxidation in the presence of thenoyl trifluoroacetone (TTFA), without a requirement for exogenously added iron. ADP stimulated lipid peroxidation in the case of NAD(P)H and TTFA, but inhibited it in the case of succinate and TTFA. Lipid peroxidation is thought to be enzymatically induced in both the NADH and the succinate dehydrogenase regions of the respiratory chain, and evidence is presented for a novel pathway of NADPH oxidation that may also be involved. Possible initiation mechanisms are discussed.

Cytochrome P-450 involvement in the NADPH-dependent lipid peroxidation in human placental mitochondria

The NADPH-dependent lipid peroxidation in human placental mitochondria has been found to be inhibited strongly by amphenone B, aminoglutethimide and carbon monoxide, inhibitors of cytochrome P-450-mediated reactions, but was hardly affected by respiratory chain inhibitors. Cytochrome c, an exogenous electron acceptor which is known to compete with cytochrome P-450 for the reducing equivalents, showed an inhibitory effect on NADPH-dependent lipid peroxidation. The observed NADPH-dependent superoxide generation was also strongly inhibited by amphenone B and aminoglutethimide. Moreover, the lipid peroxidation in placental mitochondria was demonstrated to be stimulated by xanthine/xanthine oxidase added as superoxide generating system. This peroxidation was not affected by amphenone B and aminoglutethimide. On the other hand, the superoxide dismutase was found to inhibit both the xanthine oxidase- and NADPH-dependent lipid peroxidation. These data provide evidence that cytochrome P-450 is involved in NADPH-dependent mitochondrial lipid peroxidation. It is suggested that superoxide liberated from cytochrome P-450, in combination with iron, may be responsible for initiation of NADPH-dependent lipid peroxidation in human placental mitochondria.

Coordinate modulation of murine hepatic xanthine oxidase activity and the cytochrome P-450 system by interferons

The role of xanthine oxidase (XO) in the interferon (IFN)-dependent modulation of the hepatic cytochrome P-450 system was assessed in SENCAR mice. Intraperitoneal administration of 10(4)-10(5) units of IFN-gamma resulted in dose-dependent increases in hepatic XO activities. XO activity was significantly elevated within 12 h of IFN-gamma treatment, and reached a maximum between 24-48 h, and returned to basal levels within 72-96 h. Although the kinetics of increase and decline of XO activity correlated with the loss and subsequent recovery of hepatic P-450 levels, there was no quantitative correlation between hepatic XO activity and P-450 content. Comparable results were obtained in mice pretreated with the P-450 inducer Aroclor 1254 3 days prior to IFN-gamma administration. The increases in XO activity following IFN-gamma treatment were the consequence of increases in xanthine dehydrogenase (XD), and the conversion of XD to XO. The ad libitum administration of allopurinol to IFN-gamma-treated mice reduced XO specific activity to approximately 4% of the basal activity of control mice, but did not prevent reductions in cytochrome P-450 levels or the activities of two P-450 dependent monooxygenases. Collectively, these data suggest that the reductions in the hepatic P-450 system noted after IFN administration are not a consequence of elevated XO activities.

Selective oxidation of mitochondrial glutathione in cultured rat adrenal cells and its relation to polycyclic aromatic hydrocarbon-induced cytotoxicity

Primary cultures of rat adrenal cells, as well as rat adrenals in vivo, are sensitive to the potent carcinogen 7,12-dimethylbenz[a]anthracene and its liver metabolite 7-hydroxymethyl-12-methylbenz[a]anthracene, whereas unmethylated polycyclic aromatic hydrocarbons like benzo[a]pyrene or benzo[a]anthracene are ineffective. The adrenocorticolytic potencies of the hydrocarbons are affected by adrenocorticotrophic hormone and various steroids, cytochrome P450 inhibitors, and antioxidants. In the present investigation digitonin was used to fractionate cultured rat adrenal cells. It was found that the mitochondria and cytosol of the cells contained 3-5 nmol/10(6) cells (approximately 15%) and 20-30 nmol/10(6) cells (approximately 85%) of the total soluble cellular glutathione equivalents, respectively. After exposing the cells to 7-hydroxymethyl-12-methylbenz[a]anthracene in the culture medium, a time- and concentration-dependent selective oxidation of mitochondrial glutathione was observed, whereas the effect on the cytosolic glutathione was negligible. Under the same conditions, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene were unable to alter the redox levels of the subcellular pools of glutathione. Omission of adrenocorticotrophic hormone lowered the oxidation of mitochondrial glutathione induced by 7-hydroxymethyl-12-methylbenz[a]anthracene about twofold. The results suggest that rat adrenal cells contain two separate pools of glutathione, one cytosolic and one mitochondrial, of which the latter is selectively influenced by 7-hydroxymethyl-12-methylbenz[a]anthracene. Moreover, it is concluded that rat adrenal cells offer a unique model system for general studies of the effects of a selective oxidation of mitochondrial glutathione on various cell functions. These effects may constitute early changes in cytotoxicity, preceding, e.g., membrane damage and loss of cytosolic components.

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 involvement of superoxide and iron ions in the NADPH-dependent lipid peroxidation in human placental mitochondria

Incubation of human term placental mitochondria with Fe2+ and a NADPH-generating system initiated high levels of lipid peroxidation, as measured by the production of malondialdehyde. Malondialdehyde formation was accompanied by a corresponding decrease of the unsaturated fatty acid content. This NADPH-dependent lipid peroxidation was strongly inhibited by superoxide dismutase and singlet oxygen scavengers, markedly stimulated by paraquat, but was not affected by hydroxyl radical scavengers. Catalase enhanced the production of malondialdehyde by placental mitochondria. The effects of catalase and hydroxyl radical scavengers suggest that the initiation of NADPH-dependent lipid peroxidation is not dependent upon the hydroxyl radical produced via an iron-catalyzed Fenton reaction. These studies provide evidence that hydrogen peroxide strongly inhibits NADPH-dependent mitochondrial lipid peroxidation. The inhibitory effect of superoxide dismutase and stimulatory effect of paraquat, which was abolished by the addition of superoxide dismutase, suggests that superoxide may promote NADPH-dependent lipid peroxidation in human placental mitochondria.

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.

Genetic differences in oxygen toxicity are correlated with cytochrome P-450 inducibility

Susceptibility to oxygen toxicity was studied in three inbred and two hybrid strains of mice. Because in vitro studies have shown that the cytochrome P-450 enzymes can produce oxygen radicals and H2O2, we tested the hypothesis that inducibility of these enzymes might play a role in oxygen toxicity. Mice responsive to hepatic microsomal enzyme induction by aromatic hydrocarbons [C3H/HeJ, C3H/HeN, C3H/HeJ X DBA/2J (designated C3D2F1/J), C3H/HeN X DBA/2J (designated C3D2F1/N)] were more sensitive to the toxic effects of 100% oxygen exposure than were genetically unresponsive mice (DBA/2J). DBA/2J mice survived significantly longer exposure periods with less lung damage. Lung and liver cytochrome P-450 levels increased 2-to 3-fold in C3H and F1 mice during 100% oxygen exposure (maximum levels at 72-96 hr) and subsequently fell prior to death. No increases were seen in cytochrome P-450 levels in DBA/2J mice. Metabolic pathways involving cytochrome P-450 enzymes may initiate or modulate oxidative damage due to oxygen radicals. The difference in responsiveness of mice to microsomal enzyme induction may imply genetic differences in susceptibility to oxidative stress, may help to explain species differences in susceptibility, and may have long-term implications in therapeutics and patient care if similar inherited differences exist in humans.

Utilization of intramitochondrial membrane cholesterol by cytochrome P-450-dependent cholesterol side-chain cleavage reaction in bovine adrenocortical mitochondria: steroidogenic and non-steroidogenic pools of cholesterol in the mitochondrial inner membranes

Inner and outer submitochondrial membranes were prepared after disruption of malate-treated bovine adrenocortical mitochondria. It was found that a part of the endogenous cholesterol in the inner membrane (approx. 50%) was rapidly utilized by the cholesterol side-chain cleavage reaction. The utilization of cholesterol in the outer membrane, on the other hand, was inefficient and slow in spite of the fact that cholesterol concentration is higher in the outer than in the inner membrane. When the inner membrane prepared from untreated mitochondria was incubated for 20 min in the presence of a reconstituted cytochrome P-450-reducing system, the inner membrane cholesterol was depleted by approximately 70%. The half-life of the depletion reaction was 2-3 min. In addition, when the outer membrane plus the soluble fraction from the untreated mitochondria were added as a source of cholesterol to the inner membrane fraction, a marginal increase in the production of steroids was observed. From these results it is concluded that a portion of the inner membrane cholesterol can be steroidogenic, whereas the rest of the cholesterol is non-steroidogenic.

Effect of Fe2+ -induced lipid peroxidation upon microsomal steroidogenic enzyme activities of porcine adrenal cortex

When porcine adrenocortical microsomes were treated with Fe2+, enhanced production of malondialdehyde was observed as a result of membrane lipid peroxidation. By treatment of the microsomes with Fe2+, the activity of delta 5-3 beta-hydroxysteroid dehydrogenase coupled with delta 5-delta 4 isomerase, concentration of cytochrome P-450 and the activity of the cytochrome-involving enzyme systems such as 17 alpha- and 21-hydroxylases were significantly reduced. 17 alpha-Hydroxylase activity was more effectively decreased by Fe2+ than that of 21-hydroxylase. On the other hand, activity of NADH- and NADPH-cytochrome c reductases remained unchanged or somewhat increased. Both the induction of lipid peroxidation and the decrease of the enzyme activities were prevented by alpha-tocopherol and N,N' -diphenyl-rho-phenylenediamine.

Enhanced production of ethylene from methional by iron chelates and heme containing proteins in the system consisting of quinone compounds and NADPH-cytochrome P-450 reductase

The addition of iron chelates or heme containing proteins to the systems consisting of NADPH-cytochrome P-450 reductase and quinone compounds, such as vitamin K3 (menadione), adriamycin, tetrahydropyranyladriamycin, daunomycin, aclacinomycin A, carbazilquinone, and mitomycin C, showed the enhanced production of ethylene from methional. In the vitamin K3 system, the effective iron chlates were Fe(II)-EDTA, Fe(II)-ADP, Fe(II)-bleomycin A2, and hemin, and the effective iron containing proteins were methemoglobin, myoglobin, ferredoxin, and partially purified cytochromes P-450, P-420, and b5, and the reversed effects were observed by horse radish peroxidase and sulfite reductase from yeast. In the system consisting of aclacinomycin A and methemoglobin, the ethylene production was potently inhibited by radical scavengers, such as Tiron, Tris, thiourea, and KI, and weakly inhibited by some other scavengers. In the system containing vitamin K3 and methemoglobin, the ethylene production was potently inhibited by catalase, but partially by superoxide dismutase, KCN, and NaN3. In this system, the absorption spectrum of methemoglobin was immediately changed to oxyform and quenched with time, and catalase protected the decrement of the spectrum. The addition of hydrogen peroxide or cumene hydroperoxide to methemoglobin also produced ethylene from methional.

Mode of action of butylated hydroxyanisole (BHA) and other phenols in preventing loss of 11 beta-hydroxylase activity in cultured bovine adrenocortical cells

When cultured bovine adrenocortical cells are incubated with cortisol, or other steroids that are pseudosubstrates for 11 beta-hydroxylase (cytochrome P-45011 beta), the activity of the enzyme decreases. In previous experiments, three substances were shown to protect 11 beta-hydroxylase against loss of enzymatic activity in the presence of pseudosubstrates:BHA (butylated hydroxyanisole,2(3)-tert-butyl-4-methoxyphenol), dimethyl sulfoxide (DMSO), and metyrapone. The present experiments examine the protective effects of several phenolic analogs of BHA in this system, and compare their activities to that of DMSO and metyrapone. When a variety of analogs of BHA were tested for their abilities to prevent loss of 11 beta-hydroxylase activity in cultured adrenocortical cells incubated with 50 microM cortisol for 24 hr, phenol itself was found to be about equipotent with BHA. Addition of methyl, methoxy and benzyl groups to phenol did not diminish protective activity of the compound, but addition of one and particularly two tert-butyl groups greatly diminished activity. Thus, BHT(2,6-di-t-butyl-4-methylphenol) was inactive, in contrast to BHA. The hydroxy group of phenol was essential since benzene and fluorobenzene were inactive. Compounds with multiple hydroxyl groups were not as active as phenol itself, with the exception of catechol. No products of phenol formed during incubations of cells with cortisol were detected by high performance liquid chromatography. Estimated EC50 values for protection of 11 beta-hydroxylase by phenols were about 100 microM, whereas the EC50 values for dimethyl sulfoxide and metyrapone were 10 mM and 300 nM respectively. On a semilogarithmic plot, the dose-response curves for all these compounds were approximately parallel. To aid in determining the mechanism of protection of 11 beta-hydroxylase, phenols and DMSO were tested for prevention of loss of 11 beta-hydroxylase activity at three different oxygen concentrations (2, 5, and 19% O2). Lowering the oxygen concentration itself resulted in a small diminution of the loss of 11 beta-hydroxylase. Phenols and dimethyl sulfoxide were more effective at low oxygen and less effective in air. Because the cytochrome P-450 inhibitor metyrapone was found previously to be very effective in protecting 11 beta-hydroxylase against loss of activity, we examined whether phenols and dimethyl sulfoxide may act by directly inhibiting 11 beta-hydroxylase activity. In a 1-hr incubation with cells, BHA, phenol, and dimethyl sulfoxide all inhibited 11 beta-hydroxylase, but at concentrations that ranged from 4- to greater than 100-fold higher than those required for protection.(ABSTRACT TRUNCATED AT 400 WORDS)