The role of lipid peroxidation and biological antioxidants in the function of the adrenal cortex. Part 1: A background review

Practical approaches for evaluating adrenal toxicity in nonclinical safety assessment

The adrenal gland has characteristic morphological and biochemical features that render it particularly susceptible to the actions of xenobiotics. As is the case with other endocrine organs, the adrenal gland is under the control of upstream organs (hypothalamic-pituitary system) in vivo, often making it difficult to elucidate the mode of toxicity of a test article. It is very important, especially for pharmaceuticals, to determine whether a test article-related change is caused by a direct effect or other associated factors. In addition, antemortem data, including clinical signs, body weight, food consumption and clinical pathology, and postmortem data, including gross pathology, organ weight and histopathologic examination of the adrenal glands and other related organs, should be carefully monitored and evaluated. During evaluation, the following should also be taken into account: (1) species, sex and age of animals used, (2) metabolic activation by a cytochrome P450 enzyme(s) and (3) physicochemical properties and the metabolic pathway of the test article. In this review, we describe the following crucial points for toxicologic pathologists to consider when evaluating adrenal toxicity: functional anatomy, blood supply, hormone production in each compartment, steroid biosynthesis, potential medulla-cortex interaction, and species and gender differences in anatomical features and other features of the adrenal gland which could affect vulnerability to toxic effects. Finally practical approaches for evaluating adrenal toxicity in nonclinical safety studies are discussed.

Effects of dietary concentrations of methionine on growth performance and oxidative status of broiler chickens with different hatching weight

1. A study was conducted to evaluate the effects of two hatching weight (HW) levels and two dietary concentrations of methionine on the growth performance and oxidative status of broilers. Male Arbor Acres chickens were divided into two groups on their HW (low and high HW, H and L). Each HW group was then distributed into two subgroups, of similar HW, receiving either low or high dietary concentrations of methionine (4.9 g methionine/kg, LM; 5.9 g methionine/kg, HM). Thus, all day-old birds were distributed into 4 treatments (H-LM, H-HM, L-LM, L-HM) × 6 replicates × 10 birds for 21 d. 2. Broilers with high HW were heavier than those with low HW during the 21 d assay, which appeared to result from increased body weight gain rather than improved feed conversion efficiency. A higher dietary concentration of methionine (5.9 g/kg) improved growth performance of broilers with low HW in terms of body weight gain and feed conversion ratio. 3. Broilers with different HW had similar antioxidant status both in serum and liver. 4. Broilers given a diet containing 5.9 g/kg methionine had enhanced serum superoxide dismutase (SOD) activity and decreased hepatic malondialdehyde (MDA) content at day 7. 5. Broilers given a diet containing 5.9 g/kg methionine had a higher hepatic reduced glutathione (GSH):glutathione disulphide (GSSG) ratio than those given a diet containing 4.9 g/kg methionine at day 21. High dietary methionine concentration reduced hepatic GSH content and glutathione peroxidase (GPX) activity of broilers with high HW at day 7 and at day 21, respectively, but increased hepatic GSH content of broilers with low HW at day 7. 6. Although broilers with different HW had similar oxidative status as indicated by several parameters in blood and liver, HW can have positive effects on the subsequent growth performance of broilers, and a higher dietary methionine concentration (5.9 g/kg) can improve growth performance and antioxidant status in broilers exhibiting low HW.

Impairment of spermatogenesis in rats by mercuric chloride: involvement of low 17β-estradiol level in induction of acute oxidative stress

Mercuric chloride (HgCl(2)) has been shown to affect the male reproductive organs, and oxidative stress has been linked with hypospermatogenesis and with male infertility. However, the specific mode of impairment of spermatogenesis during HgCl(2) exposure has not yet been clarified fully. Because of the involvement of 17β-estradiol (E2) in the male reproductive tract and its putative role on spermatogenesis, the present study aimed to investigate the possibility that HgCl(2)-induced oxidative stress-mediated modulation of the E2 level exerts adverse effects on testicular steroidogenic and gametogenic activities. HgCl(2) treatment at 50 and 100 ppm for 90 days by continuous oral administration in the drink water resulted in significant dose-dependent fashion decrease in serum and testicular E(2) levels and an increase in testicular testosterone levels in dose-dependent manner, without statistical alteration in serum testosterone level among HgCl(2) exposed groups compared to the control. Cauda epididymal sperm count and motility were decreased significantly (p < 0.01), in a dose-dependent manner, in the HgCl(2)-treated groups, and qualitative examination revealed inhibition of spermatogenesis and the preferential loss of maturing and elongated spermatids. The seminiferous tubules were dilated in treated animals. When compared to the control, increase in lipid peroxidation due to toxic effects of HgCl2 was accompanied by significant reduction (p < 0.01) in antioxidant enzymes activities, superoxide dismutase, catalase, and glutathione peroxidase of testes, implicating the presence of oxidative tissue damage. Furthermore, these tissue injuries caused functional impairment as evidenced with testicular elevated activity of lactate dehydrogenase. Unless oxidative stress can lead to cancer development, testis' tumor markers as beta human chorionic gonadotropin and alpha-fetoprotein levels have shown no significant differences in the HgCl(2)-exposed group compared with respect to the control. Large quantities of metal accumulated in the testis tissue are in agreement with the testis-activity failure verified in this tissue. These findings suggest that a decrease in E2 level after mercury exposure may render testis more susceptible to oxidative damage leading to its functional inactivation, thus providing new dimension to mechanisms underlying heavy metal-induced male infertility.

Overexpression of glutamate-cysteine ligase protects human COV434 granulosa tumour cells against oxidative and gamma-radiation-induced cell death

Ionizing radiation is toxic to ovarian follicles and can cause infertility. Generation of reactive oxygen species (ROS) has been implicated in the toxicity of ionizing radiation in several cell types. We have shown that depletion of the antioxidant glutathione (GSH) sensitizes follicles and granulosa cells to toxicant-induced apoptosis and that supplementation of GSH is protective. The rate-limiting reaction in GSH biosynthesis is catalysed by glutamate-cysteine ligase (GCL), which consists of a catalytic subunit (GCLC) and a regulatory subunit (GCLM). We hypothesized that overexpression of Gclc or Gclm to increase GSH synthesis would protect granulosa cells against oxidant- and radiation-induced cell death. The COV434 line of human granulosa tumour cells was stably transfected with vectors designed for the constitutive expression of Gclc, Gclm, both Gclc and Gclm or empty vector. GCL protein and enzymatic activity and total GSH levels were significantly increased in the GCL subunit-transfected cells. GCL-transfected cells were resistant to cell killing by treatment with hydrogen peroxide compared to control cells. Cell viability declined less in all the GCL subunit-transfected cell lines 1-8 h after 0.5 mM hydrogen peroxide treatment than in control cells. We next examined the effects of GCL overexpression on responses to ionizing radiation. ROS were measured using a redox-sensitive fluorogenic dye in cells irradiated with 0, 1 or 5 Gy of gamma-rays. There was a dose-dependent increase in ROS within 30 min in all cell lines, an effect that was significantly attenuated in Gcl-transfected cells. Apoptosis, assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labelling and activated caspase-3 immunoblotting, was significantly decreased in irradiated Gclc-transfected cells compared to irradiated control cells. Suppression of GSH synthesis in Gclc-transfected cells reversed resistance to radiation. These findings show that overexpression of GCL in granulosa cells can augment GSH synthesis and ameliorate various sequelae associated with exposure to oxidative stress and irradiation.

The reported active metabolite of methoxychlor, 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane, inhibits testosterone formation by cultured Leydig cells from neonatal rats

Methoxychlor (MC) is an insecticide that is presently used on agricultural crops, especially after the ban on the use of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) in the United States. Following administration in vivo, MC is converted to 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), which is thought to be the active agent. However, both MC and HPTE have been reported to have weak estrogenic and antiandrogenic activities, and they are thought to exert their potential adverse (endocrine disruptive) effects through the estrogen and androgen receptors, respectively. In a recent study, HPTE was shown to inhibit both basal and hCG-stimulated testosterone production by cultured Leydig cells from immature and adult rats, and these effects were reported to be mediated through the estrogen receptor. Because fetal Leydig cells represent a separate population from adult Leydig cells and many of the reported adverse actions of endocrine disruptors are thought to have their effects during gestational exposure, the present studies examined the effects of HPTE on testosterone formation by cultured fetal Leydig cells from neonatal rats to determine whether these cells are sensitive to HPTE. Our studies demonstrated that HPTE inhibited both basal and hCG-stimulated testosterone formation in a dose-dependent manner. Significant declines in testosterone were observed at about 100nM HPTE, and this effect was detected as early as 1h after exposure. The main effects of HPTE appeared to be localized to the cholesterol side-chain cleavage step which converts cholesterol to pregnenolone. In addition, this effect did not appear to be mediated through the estrogen receptor as a weak estrogen or the androgen receptor as an antiandrogen, which are the currently proposed modes of action of MC and HPTE.

Prostaglandin F2alpha potentiates the calcium dependent activation of mitochondrial metabolism in luteal cells

Cytoplasmic Ca2+ signals are transferred to the mitochondria and activate the Krebs cycle. We have compared the efficiency of this process for two Ca2+ mobilising agonists, PGF2alpha and ATP (acting at metabotropic P2 receptors) in rat luteal cells. [Ca2+]c, [Ca2+]m and mitochondrial NAD(P)H were monitored by means of microspectrofluorimetry and confocal microscopy. While both agonists caused similar elevations of [Ca2+]c, changes in NAD(P)H were larger in response to PGF2alpha than to ATP. PGF2alpha more effectively increased NAD(P)H level also in mouse luteal cells. PGF2alpha caused a faster rate of rise of NAD(P)H fluorescence than ATP when reoxidation was prevented with rotenone, suggesting a faster rate of NAD(P)+ reduction. The NAD(P)H response to both agonists was dependent on the mobilisation of stored Ca2+. We found no difference in the efficacy of transmission of the [Ca2+]c signal to mitochondria in response to PGF2alpha and ATP. Raising [Ca2+]c with ionomycin increased the NAD(P)H signal, which was further raised by PGF2alpha but not by ATP. These data suggest that PGF2alpha potentiates the Ca2+-induced stimulation of mitochondrial metabolism by a Ca2+-independent mechanism and shows that agonists may modulate mitochondrial function differentially through a novel process beyond the simple transfer of Ca2+ from ER to mitochondria.

The inhibitory effects of polychlorinated biphenyl Aroclor 1254 on Leydig cell LH receptors, steroidogenic enzymes and antioxidant enzymes in adult rats

Polychlorinated biphenyls (PCBs) are global pollutants of major concern to human and animal reproductive health. The present study has examined the impact of Aroclor 1254 exposure on oxidative stress and testicular Leydig cell function. Adult albino male rats of the Wistar strain were dosed for 30 days with daily intraperitoneal injections of 2 mg/kg Aroclor 1254 or vehicle (corn oil). One day after the last treatment, animals were euthanized and blood collected for the assay of serum testosterone and estradiol. Testes were removed and Leydig cells were isolated for the assay of luteinizing hormone (LH) receptors, steroidogenic enzymes cytochrome P450 side chain cleavage enzyme (P450 scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and 17beta-hydroxysteroid dehydrogenase (17beta-HSD). Cellular antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR), and glutathione-S-transferase (GST) were also assayed. Lipid peroxidation (LPO) and reactive oxygen species (ROS) were quantified. Results showed that Aroclor 1254 exposure lowered serum testosterone and estradiol levels. Leydig cell LH receptor density, activities of the steroidogenic enzymes P450 scc, 3beta-HSD, 17beta-HSD, antioxidant enzymes SOD, CAT, GPX, GR, and GST were significantly diminished whereas, LPO and ROS significantly elevated. Taken together, these results suggest that inefficient LH receptors, steroidogenic enzymes and antioxidant enzymes are possible mechanisms by which Aroclor 1254 treatment disrupts Leydig cell steroidogenesis.

The effects of the reported active metabolite of methoxychlor, 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane, on testosterone formation by cultured Leydig cells from young adult rats

Methoxychlor (MC) is an insecticide that is currently used on a variety of agricultural crops, especially following the ban of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT) use in the United States. Following in vivo administration, MC is converted to 2,2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), which is proposed to be the active agent. Both MC and HPTE have been demonstrated to exhibit weak estrogenic and antiandrogenic activities, and they are thought to exert their effects through estrogen or androgen receptors, respectively. A recent study reported that HPTE inhibited both basal and hCG-stimulated testosterone formation by immature and adult cultured rat Leydig cells and that this effect was mediated through the estrogen receptor. In the current studies, we examined the effects of HPTE on basal and hCG-stimulated testosterone formation by cultured Leydig cells from young adult rats. In addition, we evaluated whether the effects of HPTE on rat Leydig cell testosterone biosynthesis were mediated through the estrogen receptor as an estrogen agonist or the androgen receptor as an antiandrogen. The current studies demonstrated that HPTE inhibited both basal and hCG-stimulated testosterone formation in a dose-dependent manner with significant declines in testosterone being observed at approximately 100 nM. The effects of HPTE were localized to the cholesterol side-chain cleavage step; however, these effects were not mediated through the classic estrogen receptor or by its acting as an antiandrogen, the currently recognized modes of action of MC and HPTE.

Effect of supplementation with methionine and different fat sources on the glutathione redox system of growing chickens

The effect of supplementary methionine and fats of different saturation levels on the glutathione redox system of growing broiler cockerels was studied. The diet of three groups of chicks was supplemented with corn germ oil, beef tallow and fish oil at the levels of 30 g/kg and 50 g/kg of feed, respectively. The diet of further three groups was supplemented with methionine (5 g/kg of feed) in addition to the different fat sources. Control chicks were fed with a compound feed without methionine and fat supplementation. Reduced glutathione (GSH) and glutathione disulphide (GSSG) content as well as glutathione peroxidase activity in the liver were determined and GSH/GSSG ratio was calculated at day old and then at one and three weeks of age. Our results indicate that supplementary methionine stimulates both the synthesis of the glutathione redox system and glutathione peroxidase activity in growing chickens in the first period of postnatal life, when the risk of lipid peroxidation is high due to feeding unsaturated fats in the diet.

Selenium deficiency impairs corticosterone and leptin responses to adrenocorticotropin in the rat

Selenium deficiency causes oxidative stress and impairs steroidogenesis in vitro. Leptin is closely related to the hypothalamo-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis at the central level while corticosteroids have been shown to stimulate leptin secretion in most studies. We hypothesized that oxidative stress impairs adrenal steroidogenesis and decreases leptin production in vivo. The goal of this study was to investigate in rats the effects of selenium deficiency and oxidative stress on adrenal function and on leptin concentrations. Weanling rats were fed a selenium-deficient (Se-) or selenium-sufficient (Se+) diet for 4-10 weeks. Selenium deficiency caused a marked decrease in liver (> or = 99%) and adrenal (> or = 81%) glutathione peroxidase (GPx) activities. Selenium deficiency did not affect basal and short-term adrenocorticotropin (ACTH) stimulated corticosterone or leptin concentrations. In contrast, after long-term ACTH stimulation, selenium deficiency caused a doubling in adrenal isoprostane content and blunted the increase in corticosterone and leptin concentrations observed in Se+ animals. Plasma leptin concentrations were 50% lower in Se- compared to Se+ animals following long-term ACTH. Our results suggest that oxidative stress causes a decrease in circulating corticosterone in response to ACTH, and, as a consequence, a decrease in plasma leptin concentrations.

Localization of glutamate cysteine ligase subunit mRNA within the rat ovary and relationship to follicular apoptosis

Ovarian levels of the antioxidant tripeptide glutathione (GSH) increase following gonadotropin administration, suggesting that GSH synthesis in the ovary may be associated with follicular growth. In situ hybridization with (35)S-labeled riboprobes was used to localize ovarian mRNA expression of the catalytic and modulatory subunits of glutamate cysteine ligase (Gclc and Gclm), the rate-limiting enzyme in GSH synthesis, during each stage of the rat estrous cycle. Gclm was highly expressed in the granulosa cells and oocytes of healthy, growing follicles, not in atretic follicles. Gclc was also highly expressed in follicles; however, unlike Gclm, Gclc was also expressed in corpora lutea and interstitial cells. In a subsequent experiment, the hypothesis that GSH synthesis occurs in healthy, but not in apoptotic, follicles was tested. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) was used to detect apoptotic cells in the ovaries, and in situ hybridization for Gclm and Gclc was performed in adjacent sections of the same ovaries. TUNEL staining was found to be significantly associated with absence of Gclm hybridization in granulosa cells and oocytes and with lack of strong Gclc hybridization in granulosa cells. These results suggest that follicular apoptosis may be associated with down-regulation of Gclm and Gclc transcription in granulosa cells and oocytes.

Plasma antioxidant status and cell injury after severe physical exercise

Strenuous exercise leads to an increase in metabolic rate, increased production of reactive oxygen species, and compromised antioxidant defense systems. To study the effects of oxidative stress during strenuous exercise, a homogeneous group of 31 male subjects participated in a 6-month, 5 days/week training schedule involving two extreme marches of 50 km and 80 km at sea level, separated by 2 weeks of regular training. Each participant carried 35 kg of extra weight. Blood samples were drawn immediately before and after each march. Twenty-nine subjects completed the 50-km march, and only 16 completed the 80-km march. Plasma levels of reduced ascorbic acid, total ascorbate, and dehydroascorbate did not undergo significant changes during either march. However, the 50- and 80-km marches led to 25% and 37% increases, respectively, in plasma levels of uric acid; due presumably to increases in the metabolic rate and consequent pyrimidine nucleotide metabolism. Both marches led to an approximately 10-fold increase leakage of creatine phosphokinase into the plasma. Likewise, plasma levels of aspartate transaminase, a characteristic marker of liver injury, increased approximately 4-fold. Plasma levels of bilirubin, creatine, urea, and glucose also increased. Plasma protein carbonyl content, a marker of protein oxidative damage, decreased significantly during each march. These results are discussed with respect to the consideration that elevation of the respiration rate during exercise leads to production of more reactive oxygen species than the antioxidant systems can scavenge. Plausible explanations for leakage of molecules into the plasma are discussed.

Effect of local interaction of reactive oxygen species with prostaglandin F(2alpha) on the release of progesterone in ovine corpora lutea in vivo

Prostaglandin (PG) F(2alpha) is implicated in the process of luteal regression in many species, and has been shown to increase the generation of reactive oxygen species. In this study, the role of reactive oxygen species in the local regulatory mechanisms of functional luteolysis in the ewe was examined. In Experiment 1, we studied local effects of hydrogen peroxide (H(2)O(2)) and its interaction with PGF(2alpha) on P secretion in ovine corpus luteum (CL) in vivo. For this purpose, a microdialysis system (MDS) was used, where only the cells surrounding the capillary membrane in the microenvironment of the CL are exposed to these factors, and the P secretory ability of the CL is maintained as if intact. The study used a multiple CL model to implant the MDS, enabling us to examine in parallel several experimental infusions into the MDS implanted in different CLs (one MDS line per CL) developed after superovulation in one ewe. On Day 8 after GnRH treatment, the MDS were implanted into multiple CL in both ovaries of six ewes. A 4-h infusion with PGF(2alpha) (10(-6)M) at 8-12 h slightly increased P release during infusion, while a 4-h infusion with H(2)O(2) (10(-3)M) at 20-24 h decreased P release at 27-38 h. A pre-infusion with PGF(2alpha) for 4h at 8-12h, followed by infusion of H(2)O(2) at 20-24 h rapidly decreased the P release at 20-40 h (P<0.05); this decrease occurred 7h earlier than in the CL treated with H(2)O(2) alone. In Experiment 2, by utilizing the MDS we also applied free radical scavengers to examine their possible weakening effect on the inhibition of P secretion in the microenvironment within the regressing CL induced by PGF(2alpha) treatment. On Day 8 after estrus, the MDS were implanted into the CL (single CL model, two MDS lines per CL). Infusion of free radical scavengers, superoxide dismutase (SOD;50mg/ml)+catalase (CAT; 10mg/ml), at 0-28 h first increased P release until 12 h (P<0.05), and consequently delayed the decrease in P release until 30 h after administration of PGF(2alpha) i.m. (P<0.05). The present results support the concept that the leading pathway from PGF(2alpha) induces an increase of reactive oxygen species in luteolysis in the ewe.

Identification of two novel ACTH-responsive genes encoding manganese-dependent superoxide dismutase (SOD2) and the zinc finger protein TIS11b [tetradecanoyl phorbol acetate (TPA)-inducible sequence 11b]

ACTH is the major trophic factor regulating and maintaining adrenocortical function, affecting such diverse processes as steroidogenesis, cell proliferation, cell migration, and cell survival. We used differential display RT-PCR to identify genes that are rapidly induced by ACTH in the bovine adrenal cortex. Of 42 PCR products differentially amplified from primary cultures of bovine adrenocortical cells treated with 10 nM ACTH, six identified mRNAs that were confirmed by Northern blot analysis to be induced by ACTH. Four of these amplicons encoded noninformative repetitive sequences. Of the other two sequenced amplicons, one encoded a partial sequence for mitochondrial manganese-dependent superoxide dismutase (SOD2), an enzyme that is likely to protect adrenocortical cells from the cytotoxic effects of radical oxygen species generated during steroid biosynthesis. The second was identified as TIS11b (phorbol-12-myristate-13-acetate-inducible sequence 11b)/ERF-1/cMG, a member of the CCCH double-zinc finger protein family. SOD2 induction by ACTH was independent of extracellular steroid concentration or oxidative stress. SOD2 and TIS11b mRNA expressions were rapidly induced by ACTH, reaching a maximal level after 8 h and 3 h of treatment, respectively. These ACTH effects were mimicked by forskolin but appeared independent of cortisol secretion. Upon ACTH treatment, induction of TIS11b expression closely followed the previously characterized peak of vascular endothelial growth factor (VEGF) expression. Transfection of a TIS11b expression plasmid into 3T3 fibroblasts induced a decrease in the expression of a reporter gene placed upstream of the VEGF 3'-untranslated region, indicating that TIS11b may be an important regulator of VEGF expression through interaction with its 3'-untranslated region.

Changes in circulatory antioxidant status in horses during prolonged exercise

Prolonged low-medium intensity exercise is associated with increased oxidative stress in humans. We hypothesized that competitive equine endurance racing would induce changes in circulatory antioxidants and produce systemic oxidative stress. Forty horses competing in a 140-km endurance race in warm conditions [shade temperature 15-19 degrees C; 62-88% relative humidity (%RH)] were sampled before (Pre), immediately after exercise (End) and at approximately 16 h into recovery (+16 h). Plasma ascorbic acid concentration was not different between Pre [11.1 (median); 4.6-20.3 micromol/L (range)] and End [9.7; 3.0-38.9 (range) micromol/L] but was significantly decreased at +16 h (5.5; 2.8-15.5 micromol/L; P < 0.05). Total red cell hemolysate glutathione (TGSH) concentration was significantly reduced by exercise (Pre 1261; 883-1532 micromol/L; End 1065; 757-1334 micromol/L; P < 0.05) and at +16 h recovery (1032; 752-1362 micromol/L; P < 0.05). Glutathione redox ratio was unchanged by exercise but was significantly decreased at +16 h compared with that at both Pre and End (P < 0.05). The concentration of total barbituric acid reactive substances (TBARS) in plasma was increased compared with that at Pre (309; 66-1048 nmol/L), both at End (408; 170-1196 nmol/L; P < 0.05) and +16 h (380; 99-1161 nmol/L; P < 0.05). alpha-Tocopherol was unchanged by exercise or recovery. Mean race speed was 16.5 +/- 1.6 km/h and ranged from 13.9 to 19.7 km/h. Mean speed during competition in horses that completed the full 140 km (n = 28) was significantly correlated with end of exercise ascorbic acid (r = 0.622; P = 0.0004). Although there were increases in creatine phosphokinase (CK), aspartate aminotransferase (AST) and TBARS and a loss of TGSH, this study failed to demonstrate evidence of classical oxidative stress.

Mutations in aldosterone synthase gene of Milan hypertensive rats: phenotypic consequences

Using in vitro and in vivo methods, we have demonstrated increased sensitivity of adrenocortical steroidogenesis to ACTH in Milan hypertensive (MHS) compared with normotensive (MNS) rats and have investigated whether this is caused by mutations of steroidogenic enzymes. Genes encoding aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) in MHS and MNS have been cloned and sequenced. Nucleotide 752 (G) in exon 4 of MHS CYP11B2 differs from that of MNS (A); CYP11B1 sequences were identical. The nucleotide 752 mutation caused a Q251R substitution in the amino acid sequence of MHS CYP11B2. The phenotype of MHS CYP11B2 alleles, when expressed in COS-1 cells, differed from that of MNS alleles. The relative activities of the three reactions catalyzed by CYP11B2 (11beta-hydroxylation of deoxycorticosterone, 18-hydroxylation of corticosterone, and dehydrogenation of 18-hydroxycorticosterone) were estimated after incubation of transfected cells with [(14)C]deoxycorticosterone and analysis of radioactivity associated with deoxycorticosterone, corticosterone, 18 hydroxycorticosterone, and aldosterone. Both 11- and 18-hydroxylase activities were lower (19 and 12%, respectively; P < 0.01 and P < 0.05) in cells transfected with MHS compared with MNS alleles, whereas 18-oxidase activity was 42% higher (P < 0.01). To assess the significance of the CYP11B2 mutation in vivo, DNA from F2 hybrid MHS x MNS rats was genotyped. MHS alleles were associated with lower urine volumes in both sexes, lower ventricle weights in male rats, but no difference in systolic or diastolic blood pressures between the sexes. We conclude that a mutation in CYP11B2 may affect aldosterone secretion in MHS; however, under normal environmental circumstances, we were unable to demonstrate any influence of this mutation on blood pressure.

Oxidative stress in athletes during extreme endurance exercise

Despite the many known health benefits of exercise, there is a body of evidence suggesting that endurance exercise is associated with oxidative stress. To determine whether extreme endurance exercise induces lipid peroxidation, 11 athletes (3 females, 8 males) were studied during a 50 km ultramarathon (trial 1) and during a sedentary protocol (trial 2) 1 month later. The evening before each trial, with dinner, subjects consumed 75 mg each d(3)-RRR and d(6)-all rac-alpha-tocopheryl acetates. Blood was obtained at baseline, 30 min pre-race, mid-race, post-race, 1 h post-race, 24 h post-race, and at corresponding times during trial 2. All 11 subjects completed the race; average run time was 391 +/- 23 min. Plasma F(2)-isoprostanes increased from 75 +/- 7 pg/ml at pre-race to 131 +/- 17 (p <.02) at post-race, then returned to baseline at 24 h post-race; F(2)-isoprostanes were unchanged during trial 2. Deuterated alpha-tocopherol disappearance rates were faster (2.8 x 10(-4) +/- 0.2 x 10(-4)) during the race compared to the sedentary trial (2.3 x 10(-4) +/- 0.2 x 10(-4); p <.03). These data suggest that extreme endurance exercise results in the generation of lipid peroxidation with a concomitant increase in vitamin E disappearance.

Gonadotropin regulation of glutathione synthesis in the rat ovary

Glutathione (GSH), an antioxidant and conjugator of electrophilic toxicants, prevents toxicant-mediated destruction of ovarian follicles and oocytes. Ovarian GSH has previously been shown to change with estrous cycle stage in rats, suggesting that the gonadotropin hormones may regulate ovarian GSH synthesis. The present studies tested the hypotheses that [1] estrous cycle-related changes in ovarian GSH result from cyclic changes in protein and mRNA expression of the rate-limiting enzyme in GSH synthesis, glutamate cysteine ligase (GCL, also called gamma-glutamylcysteine synthetase), and [2] that these changes result from gonadotropin-mediated regulation of GCL subunit expression. In the first experiment, ovaries were harvested from cycling adult female rats on each stage of the estrous cycle. In the second experiment immature female rats were injected with pregnant mare's serum gonadotropin (PMSG) to stimulate follicular development or with vehicle and killed 8, 24, or 48 h later. In both experiments the ovaries were harvested for [1] total GSH assay, [2] Western analysis for GCL catalytic (GCLc) and regulatory (GCLm) subunit protein levels, or [3] Northern analysis for Gclc and Gclm mRNA levels. Ovarian GSH concentrations and Gclc and Gclm mRNA levels, but not GCL subunit protein levels, varied significantly with estrous cycle stage. PMSG administration significantly increased ovarian GSH concentrations 24 and 48 h later. GCLm protein levels increased significantly at 24 h and 48 h following PMSG. GCLc protein levels did not increase significantly following PMSG. Gcl subunit mRNA levels were not significantly increased at any time point by the planned ANOVA; however, an increase in Gelc at 48 h was identified by t-testing. These results support the hypothesis that gonadotropins regulate ovarian GSH synthesis by modulating GCL subunit expression.

Differential effects of octylphenol, 17beta-estradiol, endosulfan, or bisphenol A on the steroidogenic competence of cultured adult rat Leydig cells

In the current studies, we evaluated the effects of 4-tert-octylphenol (OP), endosulfan, bisphenol A (BPA), and 17beta-estradiol on basal or hCG-stimulated testosterone formation by cultured Leydig cells from young adult male rats. Exposure of Leydig cells to increasing concentrations of OP (1 to 2000 nM), 17beta-estradiol (1 to 1000 nM), endosulfan (1 to 1000 nM) or BPA (1 to 1000 nM), alone or with 10 mIU/mL hCG for 4 or 24 h, did not lower ambient testosterone levels, although cells exposed to higher OP concentrations + hCG for 24 h often had modest declines in testosterone (10 to 20%). Of interest, exposure to the highest concentration OP (2000 nM) alone for 4 or 24 h increased testosterone levels (approximately 2-fold in 4-h exposed cells). Whether prior exposure to OP + hCG for 24 h affects the subsequent conversion of steroid substrates to testosterone over 4 h was evaluated. Progressive declines in 1 microM 22(R) hydroxycholesterol, 1 microM pregnenolone, or 1 microM progesterone conversion to testosterone was observed beginning at 100 to 500 nM OP exposure (maximal declines of 40 to 12% of controls were observed); however, the conversion of 1 microM androstenedione to testosterone was not affected by OP. These results suggested that 24-h exposure to OP + hCG has no effect on 17beta-hydroxysteroid dehydrogenase, which converts androstenedione to testosterone, but that it inhibits the 17alpha-hydroxylase/C17-20 lyase step, which converts progesterone to androstenedione. In addition, potentially, OP could inhibit cholesterol side/chain cleavage activity, which converts cholesterol to pregnenolone, and/or 3beta-hydroxysteroid dehydrogenase, which converts pregnenolone to progesterone. Of interest, exposure to increasing concentrations of 17beta-estradiol (1 to 1000 nM), endosulfan (1 to 1000 nM), or BPA (1 to 1000 nM) + hCG for 24 h had no effect on subsequent conversion of 22(R)hydroxycholesterol to testosterone. Furthermore, the inhibiting effects of OP + hCG exposure on subsequent conversion of progesterone to testosterone was unaffected by concomitant exposure to the pure estrogen antagonist, ICI 182,780, or the antioxidants, ascorbate or dimethyl sulfoxide, suggesting that the actions of OP are not mediated through binding to estrogen receptor alpha or beta or by free radical induced damage to steroidogenic enzymes, respectively. These results demonstrate that direct exposure of adult Leydig cells to OP may have subtle effects on their ability to produce testosterone, which may not be detected by measuring ambient androgen levels. In addition, the effects of OP on Leydig cell testosterone formation appear to be different from those of the native estrogen, 17beta-estradiol, and from other reported weak xenoestrogens such as endosulfan and BPA.

Role of exercise and ascorbate on plasma antioxidant capacity in thoroughbred race horses

During exercise, the oxygen consumption and the production of free radicals increase and can lead to oxidative stress with a deleterious effect on cellular structures involved in physical activity. To evaluate the oxidative stress produced by exercise and the role of ascorbate as an antioxidant, venous blood samples were obtained from 44 thoroughbred racehorses, before and after a 1000+/-200-m race at maximum velocity. Fourteen of these horses were treated intravenously with 5 g of ascorbate before running. Antioxidant capacity (PAOC), endogenous and exogenous ascorbate concentration, total antioxidant reactivity (TAR), urate concentration, creatine kinase activity, protein concentration and thiobarbiturate reactive substances (TBAR) as oxidative stress indicators were measured in the plasma of some of these horses. PAOC, TAR and TBAR increased after the race, while plasma ascorbate and urate concentrations remained unchanged. Total plasma protein (TPP) concentrations increased in line with antioxidant capacity. As predicted, both the plasma ascorbate concentration and PAOC increased immediately after ascorbate administration, but was not modified after the race, such as TBAR. However, in both groups plasma creatine kinase activity increased after the race. These results would suggest that the administration of ascorbate could nullify the oxidative stress produced by exercise in thoroughbred racehorses, but could not prevent muscular damage.

Modulation of steroidogenesis by selenium in a novel adrenal cell line developed using targeted tumorigenesis

Glutathione peroxidase (GPx-1) is a selenoenzyme that metabolizes H(2)O(2), a source of potentially toxic free radicals. Steroidogenesis is markedly inhibited by H(2)O(2) in vitro.

OBJECTIVE

to study the effects of selenium deficiency on GPx activity and adrenal steroidogenesis in a novel adrenal cell line developed using targeted tumorigenesis.

METHODS

AN4Rppc7 cells were grown for 7 days in serum-free medium. 8-Br-cAMP-stimulated concentrations of steroid hormones were measured by RIA. StAR (Steroid Acute Reactive Protein) mRNA was measured by Northern blot.

RESULTS

selenium deficiency caused a 99% There was a 51%, progesterone, corticosterone and aldosterone production, respectively (p<0.05 by ANOVA). StAR mRNA was not affected by selenium.

CONCLUSIONS

selenium deficiency causes a marked decrease in GPx activity. Decreased steroid hormone production occurs for selenium concentrations equal or lower than 5 nM. The absence of changes in StAR mRNA content suggests that selenium deficiency does not affect cholesterol access to the mitochondria.

Inhibitory effects of stress-activated nitric oxide on antioxidant enzymes and testicular steroidogenesis

The messenger role of nitric oxide (NO) in immobilization stress-induced inhibition of testicular steroidogenesis has been previously suggested. In accord with this, here, we show that the intratesticular injection of isosorbide dinitrate (ISDN; 2x2.5 mg/testis), an NO donor, mimicked the action of stress on serum testosterone concentrations and hCG-stimulated testosterone production in rat testicular tissue. When added in vitro, ISDN inhibited testicular 3beta-hydroxysteroid dehydrogenase and 17alpha-hydroxylase/lyase. Immobilization stress and injections of ISDN also decreased the activity of catalase, glutathione peroxidase, glutathione transferase, and glutathione reductase in the interstitial compartment of testis. When stressed rats were treated concomitantly with bilateral intratesticular injections of N(omega)-nitro-L-arginine methyl ester, a non-selective NOS inhibitor (2x600 microg/testis), the activities of antioxidative enzymes, as well as serum testosterone concentration, were partially normalized. These results indicate that stress-induced stimulation of the testicular NO signalling pathway leads to inhibition of both steroidogenic and antioxidant enzymes.

Octylphenol inhibits testosterone biosynthesis by cultured precursor and immature Leydig cells from rat testes

4-tert-octyphenol (OP) is a surfactant additive widely used in the manufacture of a variety of detergents and plastic products. OP has been reported to mimic the actions of estrogen in many cellular systems. The present studies evaluated the direct effects of OP on human chorionic gonadotropin (hCG)-stimulated testosterone biosynthesis by cultured precursor and immature Leydig cells from 23-day old (prepubertal) rats. Exposure to increasing OP concentrations (1 to 2000 nM) progressively decreased hCG-stimulated testosterone formation in both precursor and immature Leydig cells at higher OP concentrations (100 or 500 to 2000 nM). Testosterone levels were reduced approximately 30 to 70% below control at the highest concentration in both cell types. Similar reductions in testosterone associated with OP exposure were observed in cells stimulated with 1 mM 8-Br-cAMP, suggesting that the main actions of OP occur after the generation of cAMP. Increasing concentrations of 17beta-estradiol (1 to 1000 nM) had no effect on hCG-stimulated testosterone formation in both precursor and immature Leydig cells and the inclusion of 100 nM ICI 182,780, a pure estrogen antagonist, in precursor and immature Leydig cells exposed to OP and hCG, did not alter the inhibition by higher OP concentrations of testosterone formation in both cell types. These results suggest that OP is a hormonally active agent, but that some of its actions are distinct from those of 17beta-estradiol and are not mediated through the estrogen receptor alpha or beta pathway. To further localize the potential site(s) of action of OP, cultured precursor and immature Leydig cells were exposed to increasing concentrations of OP and hCG for 24 h. Next, fresh media containing 1 microM 22(R)-hydroxycholesterol, 1 microM pregnenolone, 1 microM progesterone, or 1 microM androstenedione was added, and the conversion of each substrate to testosterone was determined after incubation for 4 h. The conversion of androstenedione to testosterone was unaffected by exposure to OP, suggesting that the 17beta-hydroxysteroid dehydrogenase step is not inhibited. However, the conversion of 22(R)-hydroxycholesterol, pregnenolone and progesterone all were inhibited by prior exposure to OP and hCG. This finding suggests that the 17alpha-hydroxylase/c17-20-lyase step, which converts progesterone to androstenedione, is inhibited by OP, and that the cholesterol side-chain cleavage and 3beta-hydroxysteroid dehydrogenase -isomerase steps, which convert cholesterol to pregnenolone and pregnenolone to progesterone, respectively, are other potential sites of OP action. Because concomitant exposure to the antioxidants alpha-tocopherol or ascorbate did not alter the inhibition of testosterone formation by higher OP concentrations, it does not appear that OP is acting as a pseudosubstrate for the generation of free radicals, which can damage P450 enzymes.

Experimental pancreatitis induced by synthetic prooxidant tert-butyl hydroperoxide

The purpose of this study was to verify whether injection of tert-butyl hydroperoxide (Bu(t)OOH, a well-known prooxidant agent) into the bile-pancreatic duct can induce acute pancreatitis. A rapid blockade of the secretion was observed in the majority of the animals after 3 hours of observation. After 6 hours, the secretion reached a very low level, significantly different compared with controls. In groups of rats injected with Bu(t)OOH, pancreatic weight gain was observed compared with the rats injected with physiologic saline. Histology of pancreata removed 3 hours after injection of Bu(t)OOH showed acinar cell vacuolization, interstitial edema, focal necrosis of pancreatic acini, fat-tissue necrosis, and leukocyte infiltration of the organ. These changes were considerably greater after the 6-hour observation period. Electron-microscopic inspection revealed profound morphologic changes 3 hours after Bu(t)OOH injection. The control rats receiving physiologic saline alone had well-preserved pancreatic tissue structure. In conclusion, injection of the prooxidant agent, tert-butyl hydroperoxide, into common bile-pancreatic duct induces acute necrotizing pancreatitis, which indicates the crucial role of free radical reactions in pathogenesis of this disease.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Biphasic effects of octylphenol on testosterone biosynthesis by cultured Leydig cells from neonatal rats

The present studies evaluated the suitability of using cultured dispersed testicular cells from neonatal rats as a source for fetal Leydig cells and the use of these cells to examine direct toxic effects of environmental/occupational chemicals on androgen biosynthesis. For the current studies, the direct actions of octylphenol (OP), a surfactant additive widely used in the manufacture of various detergents, on testosterone biosynthesis by cultured rat neonatal Leydig cells were examined. Octylphenol is considered a xenoestrogen and has been reported to mimic the actions of estrogen in many cellular systems. Following exposure of cultured cells for 24 h to varying concentrations of OP (1 to 2000 nM) together with 10 mlU/mL human chorionic gonadotropin (hCG), the lower concentrations of OP (1 and 10 nM) consistently enhanced testosterone levels (approximately 10 to 70% above control), whereas higher OP concentrations (100 to 2000 nM) progressively decreased testosterone from peak levels to approximately 40 to 80% below control at the highest OP concentration. Interestingly, increasing concentrations of 17beta-estradiol (1 to 1000 nM) were without effect on testosterone biosynthesis under the same conditions, and the biphasic pattern of testosterone biosynthesis elicited by increasing OP concentrations was unaffected by concomitant treatment with 10 or 100 nM ICI 182,780, which is considered a pure estrogen antagonist. Therefore, the actions of OP on testosterone biosynthesis by cultured neonatal Leydig cells do not appear to be mediated through the classic estrogen receptor alpha or beta pathway. Although the increase in testosterone levels after exposure to lower OP concentrations and to 0.1 and 1.0 mM 8-Br-cAMP was attenuated, suggesting that lower OP concentrations may alter cellular cAMP levels, because hCG-stimulated cAMP levels were unaffected by any of the OP concentrations evaluated, it appears that its main site(s) of action occurs after the generation of cAMP. In addition, because pretreatment of cells with increasing OP concentrations and hCG had no effect on the conversion of steroid precursors (22(R)-hydroxycholesterol, pregnenolone, progesterone, or androstenedione) to testosterone, it seems that the main actions of OP under the present conditions occur before the mitochondrial cholesterol side-chain cleavage step. Furthermore, because concomitant treatment of cells with various antioxidants (alpha-tocopherol, butylated hydroxyanisole, or ascorbic acid) did not alter the biphasic pattern of testosterone response to increasing concentrations of OP and hCG, it seems that OP is not acting as an anti- or pro-oxidant in producing these effects. It will be important to determine whether this dose-sensitive response to OP is observed in vivo, and whether the maturational status of Leydig cells influences their pattern of response to OP and similar chemicals.

Superoxide Dismutase in Human Adrenal and its Disorders: A Correlation with Development and Neoplastic Changes

In adrenal glands, oxidative free radicals are synthesized in the course of hormonal production, and enzyme superoxide dismutase (SOD) is considered to scavenge these harmful superoxide radicals and, subsequently, to protect the cells. We studied immunohistochemical localization of Mn (manganese)-SOD and Cu,Zn (copper-zinc)-SOD in human adrenal and its disorders from fetus to adult obtained from autopsy or surgery in order to examine the possible biological significance of these two enzymes. In fetal adrenal (n = 4), Cu,Zn-SOD and Mn-SOD were detected only in the fetal cortex. In adrenal glands from children (n = 21) to adults (n = 15), Mn-SOD immunoreactivity was exclusively detected in adrenal medulla, whereas Cu,Zn-SOD immunoreactivity was present only in adrenocortical parenchymal cells, weakly in the zona glomerulosa, and markedly in the zona reticularis. There were no differences in relative immunointensity and/or patterns of immunolocalization of these two SODs among different age groups. Both Cu,Zn-SOD and Mn-SOD immunoreactivity were detected in compact tumor cells of adrenocortical adenoma (n = 16). Marked immunoreactivity of both Cu,Zn-SOD and Mn-SOD was detected in adrenocortical carcinoma (n = 11) and pheochromocytoma (n = 5). These results indicate that Cu,Zn-SOD and Mu-SOD may play different roles as a scavenger or antioxidants in normal human adrenal glands, i.e., Cu,Zn-SOD as a scavenger of toxic superoxide radicals generated during steroidogenesis and Mn-SOD during catecholamine production. Cu,Zn-SOD and Mn-SOD immunoreactivities detected in adrenal neoplasms are also considered to represent altered expression of these enzymes associated with neoplastic transformation, as reported in other human malignancies.

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.

Antioxidant capacity is correlated with steroidogenic status of the corpus luteum during the bovine estrous cycle

The reactions of steroid hormone biosynthesis are accompanied by formation of oxygen radicals. We determined the levels of some antioxidants and antioxidative enzymes at different developmental stages of bovine corpora lutea to examine their correlation with steroidogenic status. Plasma progesterone concentrations of estrous cycle synchronized cows increased until day 16, and then decreased rapidly during luteal regression. The levels of steroidogenic cytochrome P450scc and adrenodoxin paralleled the changes in plasma progesterone. Among the antioxidative enzymes examined, the SOD and catalase activities showed patterns most similar to plasma progesterone. Catalase and SOD activities increased 6-8 fold from day 6 to 16 of the estrous cycle and then decreased during the luteal regression. Ascorbate and beta-carotene showed low but significant correlation with P450scc and plasma progesterone levels. The profiles of two lipophilic antioxidants in corpora lutea were very different. beta-carotene concentration increased by approximately 6 fold from day 6 to 16, and decreased in regressive tissue. alpha-tocopherol showed a 3 fold increase between days 6 and 9 followed by a rapid decrease. Thus, at the peak of steroidogenesis at mid-luteal phase alpha-tocopherol levels decreased, but beta-carotene levels increased. The correlation between the levels of some antioxidant enzymes and compounds with progesterone levels indicates that antioxidative mechanisms are activated to cope with steroidogenesis dependent oxyradical formation in the bovine corpus luteum.

Evidence of ultracytochemical mitochondria-derived hydrogen peroxide activity in myocardial cells from broiler chickens with an ascites syndrome

The location of the cytotoxic reactive oxygen metabolite hydrogen peroxide was investigated ultracytochemically in broiler chickens which had been reared at sea level and had spontaneous hypoxia-induced ascites syndrome. In the ascitic birds the activity was located within the mitochondrial matrices of the cardiomyocytes, whereas in flock-mate control birds it was membrane-bound. Little or no activity was present in negative control material, which was prepared by detoxification with catalase, by extraction with acetone, by the omission of NADH and by the replacement of NADH by NADPH. The study demonstrated that there was probably hydrogen peroxide activity in the mitochondria of the ascitic birds.

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.

Alteration of the adrenal antioxidant defense system during aging in rats

The goal of this study was to determine to what extent aging affects the antioxidant defense system of the rat adrenal and to evaluate the impact of any change in this system on the recognized age-related decline in steroidogenic capacity of adrenocortical cells. The studies were conducted on young (2-5 mo) and aging (12-27 mo) Sprague-Dawley rats and involved procedures measuring steroidogenesis; oxidative damage to tissue; non enzymatic antioxidants such as vitamin C, E, and glutathione; and tissue antioxidant enzyme (Mn and CuZn superoxide dismutases, catalase, and glutathione peroxidase) activity and expression (mRNA, protein mass, and location). Some measurements were made also on rats maintained on vitamin E-deficient diets. The data show that adrenals from young animals are especially well protected against oxidative events; i.e., these adrenals show the least endogenous lipid peroxidation and the highest level of resistance to prooxidant-induced damage (of various tissues measured) and show exceedingly high levels of tissue antioxidants. Aging, on the other hand, results in oxidative changes in adrenal tissue that are generally linked in time to a reduction in efficiency of the normally protective antioxidant defense system and to the decline in corticosterone production. We speculate that these events are causally related, i.e., that the age-related reduction in oxidative mechanisms in adrenal tissues leads to oxidative damage of membrane or cytosolic factors important to cholesterol transport, and, as a consequence of this damage, cholesterol cannot reach appropriate mitochondrial cholesterol side chain cleavage sites, and corticosterone production fails.

The effect of peroxides on the vascular endothelium of isolated pig aorta in vitro

The effect of peroxide on endothelial cells (perfused pig aorta) was examined using an in vitro perfusion model. Hydrogen peroxide was added to the perfusion medium (pig serum together with a buffer solution) which was expected to lead to an increased oxidation of lipids and lipoproteins. Oxidation processes of this type play a decisive role in the pathogenesis and progression of arteriosclerosis. The aim of the present investigation was to demonstrate by introducing hydrogen peroxide (H2O2) in varying concentrations (0.5-1.5%), the destructive impact of peroxides on the endothelium, while these cells are believed to play a key role in the pathogenesis of arteriosclerosis. The extent of endothelial cell impairment was assessed by means of silver staining visualisation of endothelial cell borders as well as light- and scanning-electronmicroscopic investigation. It was discovered that the endothelial cells show increasing impairment after 10 h of perfusion due to the effect of peroxide (hydrogen peroxide).

Essential fatty acid metabolism and requirements for LBW infants

Humans are unable to synthesize linoleic acid (LA) (18:2 omega-6) and alpha-linolenic acid (LNA) (18:3 omega-3). Most formulas provide ample LA, yet infants are at risk for omega-3 deficiency unless they are fed human milk. Neonates born at 30 weeks received human milk or were randomized to three formulas: formula A, based on corn oil, similar to old commercial formula; formula B, based on soy oil supplied LNA; or formula C, a product similar to B with added marine oil to provide docosahexaenoic acid (22:6 omega-3). The fatty acids of plasma and red blood cells had marked diet-induced differences. The rod photo-receptor tests demonstrated higher threshold and decreased sensitivity in the omega-3-deficient infants. Visual acuity also showed improved function of the brain cortex in the human milk and group C infants at follow-up at 57 weeks. These results suggest that omega-3 fatty acids are needed for optimal development of visual function.

Lipid peroxidation and antioxidative vitamins under extreme endurance stress

The aim of this study was to examine whether extreme endurance stress of trained athletes can influence lipid peroxidation and muscle enzymes. A randomized and placebo-controlled study was carried out on 24 trained long-distance runners who were substituted with alpha-tocopherol (400 I.U. d-1) and ascorbic acid (200 mg d-1) during 4.5 weeks prior to a marathon race. The serum concentrations of retinol, ascorbic acid, beta-carotene, alpha-tocopherol, malondialdehyde (TBARS) and uric acid as well as glutathione peroxidase (GSH Px) and catalase were measured 4.5 weeks before (A), immediately before (B), immediately after (C) and 24 h after (D) the course. After competition (C) TBARS serum concentrations of the athletes (n = 22) decreased in both groups (P < 0.0001). The ascorbic acid serum concentration increased significantly in the supplemented group from (A) to (B) (P < 0.01), from (B) to (C) (P < 0.001) and in the placebo group a significant increase from (B) to (C) (P < 0.01) was observed. The alpha-tocopherol serum concentration increased significantly in the supplemented group from (A) to (B) (P < 0.001) and from (B) to (C) (P < 0.05). The enzymes glutathione peroxidase (GSH Px) and catalase measured in erythrocytes as well as the serum selenium levels did not show significant differences at any time. A significant increase of CK concentration was observed from (C) to (D) in the supplemented group (P < 0.01) and in the placebo group (P < 0.001). The increase of CK serum concentration is remarkably lower in the supplemented group compared with the placebo group (P < 0.01). It is concluded that endurance training coupled with antioxidant vitamin supplementation reduces blood CK increase under exercise stress.

A model for studying regulation of aldosterone secretion: freshly isolated cells or cultured cells?

Practically all studies relating to zona glomerulosa function have been performed either with freshly isolated cells or with cells used after 2 or 3 days in culture. This study compares the step-by-step response (binding, second messenger production and aldosterone response) of isolated glomerulosa cells vs cells maintained in primary culture to the main stimuli of aldosterone secretion. One day in culture induces a decrease of 77 and 65% in the basal level of corticosterone and aldosterone secretions, compared to that observed in freshly isolated cells. In these conditions, the cells become more sensitive to most of their stimuli, but not all: e.g. important differences are noted in the dose-response of aldosterone secretion to adrenocorticotropin (ACTH), which is often shifted to a lower concentration sensitivity in cultured cells. For example, 0.1 nM ACTH stimulates steroid secretion by three-fold in isolated cells while 1 pM ACTH already induces a 25 and nine-fold increase, respectively, in corticosterone and aldosterone output in cultured cells. Moreover, some stimuli such as isoproterenol do not have any effect in isolated cells but do stimulate steroid secretion in cultured cells. In contrast, other stimuli, such as serotonin or DA (via DA2 receptors) act preferentially in freshly isolated cells. The main observation derived from this study is that glomerulosa cells, under appropriate conditions, are able to respond to their main secretagogues even after 4 days in culture. At this time, glomerulosa cells maintain their ultrastructural characteristics and functional properties and, aside from a few exceptions, demonstrate higher sensitivity to their known stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood superoxide dismutase and plasma malondialdehyde among workers exposed to asbestos

Blood superoxide dismutase (SOD) and plasma malondialdehyde (MDA) (an indicator of lipid peroxidation [LPO]) were determined in 97 randomly selected asbestos exposed workers (age range: 25-60 years, mean duration of exposures 19.8 +/- 8.3 years) and in 42 healthy male controls. MDA, SOD, and MDA/SOD ratio in asbestos exposed workers were significantly higher than in controls. Among both the controls and exposed workers neither age nor smoking was related to SOD or MDA levels. SOD was significantly positively correlated with MDA among the exposed workers. Such correlation was not observed among the controls. SOD but not MDA was significantly positively correlated with the duration of exposure to asbestos. Mean levels of SOD or MDA in exposed workers with radiographic signs of lung fibrosis or pleural thickening did not differ significantly from those without such signs. The results confirm the possible involvement of LPO and development of anti-oxidant mechanism(s) of prolonged exposure to asbestos in humans. However, SOD seems not to be the essential anti-asbestos-induced LPO. Relation between these factors and lung fibrosis is still unclear.

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.

Testosterone lowers aromatase activity in cultured human genital skin fibroblasts

The cytochrome P-450-dependent aromatase pathway utilizes the androgens testosterone (T) and androstenedione, as substrates for estrogen formation. In addition, androgens have been shown to influence the level of aromatase activity in various tissues. In cultured human skin fibroblasts, incubation with T for 14 h resulted in a dose-dependent decline in aromatase activity, the concentration of T producing a half-maximal decline being 6 nM. In the presence of T (50 nM), aromatase activity declined in a time-dependent fashion with maximal reduction occurring by 9 h. When aromatase kinetics were determined after preincubation of cells with T, there was a significant decline in the calculated Vmax with no significant change in the apparent Km, suggesting that incubation of cells with T reduced the number of active enzyme sites. Aromatase activity was unaffected by preincubation of cells with the synthetic androgen methyltrienolone. In addition, the decline in aromatase activity following preincubation with T was observed in cells derived from patients with complete androgen insensitivity demonstrating that the effect of T was not mediated by androgen receptors. Furthermore, new protein synthesis was not necessary for the T-mediated effect as the presence of cycloheximide (50 micrograms/ml) did not prevent it. When cells were incubated at low oxygen tension, the inhibition of aromatase activity by T was diminished. Testosterone is rapidly metabolized in genital skin fibroblasts to dihydrotestosterone, androstanedione, androsterone, 3 alpha-androstanediol, 3 beta-androstanediol and estradiol. To determine if a metabolite of T might be responsible for the repression of aromatase activity, aromatase activity was determined in cells following preincubation with various metabolites of T. Preincubation of cells with androstenedione, androstanedione or 3 alpha-androstanediol produced a small but significant decline in aromatase activity, whereas preincubation of cells with dihydrotestosterone, androsterone, or 3 beta-androstanediol did not have a significant effect. Aromatase activity was also unaffected by preincubation of cells with estradiol or diethylstilbestrol. When aromatase activity was assayed in microsomal preparations from cells preincubated with T, activity was reduced. Although cells preincubated with 50 nM [3H]T contained between 0.25 and 0.51 pmol of residual steroid/mg microsomal protein, the amount of [1-3H]androstenedione and T was insufficient to account for the observed decline in aromatase activity on the basis of competitive inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism and toxicity of xenobiotics in the adrenal cortex, with particular reference to 7,12-dimethylbenz(a)anthracene

The adrenal cortex contains high amounts of detoxifying enzymes, as well as generators and protectors of reactive oxygen species. The high content of cytochrome P-450 enzymes in the adrenal cortex together with its remarkable tendency to accumulate hydrophobic substances probably contributes to the extraordinary vulnerability of the gland to a number of xenobiotics. The best studied adrenocorticolytic compounds are the potent carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) and its liver metabolite 7-hydroxymethyl-12-methylbenz(a)anthracene (7-OHM-12-MBA). Adrenocorticolysis generated by these agents in vivo as well as in vitro demonstrates high regioselective requirements and is strongly influenced by the presence of ACTH, steroids, cytochrome P-450 inhibitors and antioxidants. Furthermore, 7-OHM-12-MBA has been demonstrated to uniquely generate selective and massive oxidation of mitochondrial glutathione in cultured rat adrenal cells. The DMBA-induced adrenocorticolysis is thoroughly discussed in this review with particular emphasis on the metabolism of DMBA and the influence of various effectors. A working hypothesis involving a possible peroxidative mechanism is also presented.

Oxidative stress. Biochemistry and human disease

The early involvement of free radicals in the evolution of life may explain their ubiquitous presence and vital physiological role. Imbalance between protection against free radicals and their generation, explains the likely association of various diseases with toxic oxygen species. An elaborate defence system against oxygen-free radicals exists. The effects of oxidative stress are manifold. Direct demonstration of oxygen radicals in intact biological systems is difficult. Frequently, effect-related measurements are used in this respect. The clinical conditions adult respiratory distress syndrome and multiple organ failure, reflex sympathetic dystrophy and sugar cataract are discussed and the role of oxygen radicals in the aetiology of these diseases are described.

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.

Effect of 7-hydroxymethyl-12-methylbenz[a]anthracene and 1,3-bis-(2-chloroethyl)-1-nitrosourea on enzyme activities and oxidation of glutathione in cultured rat adrenal cells

1. The activities of enzymes participating in the regeneration of reduced glutathione (GSH), and their subcellular distribution were studied in cultured rat adrenal cells. 2. It has previously been shown that the adrenocorticolytic agent 7-hydroxymethyl-12-methylbenz[a]anthracene (7-hydroxymethyl-12-MBA) causes a drastic and selective oxidation of mitochondrial GSH in rat adrenal cells. Treatment of the adrenal cells with 7-hydroxymethyl-12-MBA, resulted in a minor decrease in the content of cytochrome c oxidase, nicotinamide nucleotide transhydrogenase, isocitrate dehydrogenase and cytosolic GSH reductase, whereas the activity of lactate dehydrogenase and citrate synthase was unaffected. None of these effects were considered to be responsible for the massive oxidation of mitochondrial GSH induced by 7-hydroxymethyl-12-MBA. 3. 1,3-Bis-(2-chloroethyl)-1-nitrosourea (BCNU) was used to obtain rat adrenal cells cultures with inactivated cytosolic and mitochondrial GSH reductase. The oxidation of mitochondrial GSH, induced by 7-hydroxymethyl-12-MBA, was not dramatically enhanced by the inactivation of GSH reductase, indicating that this enzyme was not rate-limiting in the regeneration of GSH. 4. Fractionation of rat adrenal cells with increasing concentrations of digitonin resulted in an earlier release of citrate synthase in cells treated with 7-hydroxymethyl-12-MBA compared with controls. These results may indicate damage to mitochondrial membranes as a result of 7-hydroxymethyl-12-MBA treatment.

Steroid and xenobiotic effects on the adrenal cortex: mediation by oxidative and other mechanisms

Because steroids reach high concentrations within the adrenal cortex, effects of the direct interaction of steroids and cytochrome P450 enzymes are possible and may involve oxidative damage. Steroid pseudosubstrate effects studied in cultured adrenocortical cells show that these effects are probably not mediated by steroid receptors. Release of oxidants during pseudosubstrate interaction with cytochrome P450s may be responsible for loss of enzymatic activity observed; enzyme activity can be protected by cytochrome P450 inhibitors, antioxidants, and lowered oxygen concentration. There may be pathological effects of pseudosubstrates in the adrenal cortex. Cytochrome P450/pseudosubstrate effects could be involved in the aging and death of adrenocortical cells in vivo, and necrosis of the adrenal cortex due to excessive ACTH stimulation or due to the action of adrenolytic chemicals could result from damage by oxygen radicals originating from cytochrome P450s. The possible mechanism of damage to the adrenal cortex by the xenobiotics dimethylbenzanthracene, TCDD, 3-methylcholanthrene, and o', p'-DDD are reviewed.

Glucocorticoid enhancement of glucocorticoid production by cultured ovine adrenocortical cells

The present study examines the effect of chronic treatment with glucocorticoids on the steroidogenic activity of ovine adrenocortical cells in vitro. Cells cultured in the presence of 10(-9) to 10(-5) M dexamethasone produced more glucocorticosteroids in response to ACTH1-24, forskolin or 8 BrcAMP than did control cells. Such an enhancing effect required more than 5 h of treatment and was maximal at 30 h; it was both concentration-dependent and steroid-specific. The maximal secretion of corticosteroids was observed when cells were exposed to 10(-7) M dexamethasone; with higher concentrations the response to ACTH1-24 decreased steadily; the ED50 was 2.8 +/- 0.8 nM. Cortisol and corticosterone enhanced ACTH1-24-induced steroidogenesis to the same extent as dexamethasone, but at concentrations roughly 100-fold higher than for dexamethasone. Testosterone and 17 beta-oestradiol had no enhancing effect. Dexamethasone not only enhanced the maximal steroidogenic response to ACTH1-24 but also decreased its ED50 3-fold. Treatment of cultures with the antiglucocorticoid RU 38486 resulted in a dose-dependent, time-dependent, decrease in ACTH1-24-induced corticosteroid output. Moreover, RU 38486 antagonized the enhancing effect of dexamethasone. The production of corticosteroids by dexamethasone-treated cells incubated in the presence of 22(R)-hydroxycholesterol or of exogenous pregnenolone was similar to that of control cells. The enhancing effect of dexamethasone was also observed when cultures were performed in the absence of insulin and/or in serum-free media. These data suggest that chronic exposure to glucocorticoids is necessary for the full steroidogenic activity of ovine adrenocortical cells. Moreover, they indicate that glucocorticoids exert their effect at least at two different levels in the cell: (i) on the adenylate cyclase system and (ii) at step(s) beyond cAMP but before pregnenolone formation.