Eicosatetraynoic and eicosatriynoic acids, lipoxygenase inhibitors, block meiosis via antioxidant action

ML355 Modulates Platelet Activation and Prevents ABT-737 Induced Apoptosis in Platelets

12-lipoxigenase (12-LOX) is implicated in regulation of platelet activation processes and can be a new promising target for antiplatelet therapy. However, investigations of 12-LOX were restricted by the lack of specific and potent 12-LOX inhibitors and by controversial data concerning the role of 12-LOX metabolites in platelet functions. A novel specific 12-LOX inhibitor ML355 was shown to inhibit platelet aggregation without adverse side effects on hemostasis; however, the molecular mechanisms of its action on platelets are poorly understood. Here, we showed that ML355 inhibited platelet activation induced by thrombin or thromboxane A2, but not by collagen-related peptide. ML355 blocked protein kinase B, phosphoinositide 3-kinase, and extracellular signal-regulated kinase, but not p38 kinase, spleen tyrosine kinase (Syk), or phospholipase Cγ2 phosphorylation in activated platelets. The main inhibitory effect of low doses of ML355 (1-20 μM) on thrombin activated platelets was mediated by the decrease in reactive oxygen species level, whereas high doses of ML355 (50 μM) caused cyclic adenosine monophosphate activation. ML355 did not affect the activity of nitric oxide-dependent soluble guanylyl cyclase, nor did it affect the relaxation of preconstricted aortic rings in mice. ML355 itself did not affect platelet viability, but at 50 μM dose blocked caspase-dependent apoptosis induced by B-cell lymphoma II inhibitor ABT-737. SIGNIFICANCE STATEMENT: The current paper provides novel and original data concerning molecular mechanisms of 12-LOX inhibitor ML355 action on platelets. These data reveal antiplatelet and protective effects of ML355 on platelets and may be of importance for both antiplatelet and anticancer therapy.

The capacity of oocytes for DNA repair

Female fertility and offspring health are critically dependent on the maintenance of an adequate supply of high-quality oocytes. Like somatic cells, oocytes are subject to a variety of different types of DNA damage arising from endogenous cellular processes and exposure to exogenous genotoxic stressors. While the repair of intentionally induced DNA double strand breaks in gametes during meiotic recombination is well characterised, less is known about the ability of oocytes to repair pathological DNA damage and the relative contribution of DNA repair to oocyte quality is not well defined. This review will discuss emerging data suggesting that oocytes are in fact capable of efficient DNA repair and that DNA repair may be an important mechanism for ensuring female fertility, as well as the transmission of high-quality genetic material to subsequent generations.

Mechanism of Protein Carbonylation in Glutathione-Depleted Rat Brain Slices

This study was conducted to further our understanding about the link between lipid peroxidation and protein carbonylation in rat brain slices incubated with the glutathione (GSH)-depletor diethyl maleate. Using this in vitro system of oxidative stress, we found that there is a significant lag between the appearance of carbonylated proteins and GSH depletion, which seems to be due to the removal of oxidized species early on in the incubation by the mitochondrial Lon protease. Upon acute GSH depletion, protein carbonyls accumulated mostly in mitochondria and to a lesser degree in other subcellular fractions that also contain high levels of polyunsaturated lipids. This result is consistent with our previous findings suggesting that lipid hydroperoxides mediate the oxidation of proteins in this system. However, these lipid hydroperoxides are not produced by oxidation of free arachidonic acid or other polyunsaturated free fatty acids by lipooxygenases or cyclooxygenases. Finally, γ-glutamyl semialdehyde and 2-amino-adipic semialdehyde were identified by HPLC as the carbonyl-containing amino acid residues, indicating that proteins are carbonylated by metal ion-catalyzed oxidation of lysine, arginine and proline residues. The present findings are important in the context of neurological disorders that exhibit increased lipid peroxidation and protein carbonylation, such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis.

Molecular Mechanisms Responsible for Increased Vulnerability of the Ageing Oocyte to Oxidative Damage

In their midthirties, women experience a decline in fertility, coupled to a pronounced increase in the risk of aneuploidy, miscarriage, and birth defects. Although the aetiology of such pathologies are complex, a causative relationship between the age-related decline in oocyte quality and oxidative stress (OS) is now well established. What remains less certain are the molecular mechanisms governing the increased vulnerability of the aged oocyte to oxidative damage. In this review, we explore the reduced capacity of the ageing oocyte to mitigate macromolecular damage arising from oxidative insults and highlight the dramatic consequences for oocyte quality and female fertility. Indeed, while oocytes are typically endowed with a comprehensive suite of molecular mechanisms to moderate oxidative damage and thus ensure the fidelity of the germline, there is increasing recognition that the efficacy of such protective mechanisms undergoes an age-related decline. For instance, impaired reactive oxygen species metabolism, decreased DNA repair, reduced sensitivity of the spindle assembly checkpoint, and decreased capacity for protein repair and degradation collectively render the aged oocyte acutely vulnerable to OS and limits their capacity to recover from exposure to such insults. We also highlight the inadequacies of our current armoury of assisted reproductive technologies to combat age-related female infertility, emphasising the need for further research into mechanisms underpinning the functional deterioration of the ageing oocyte.

The role of selenium in human conception and pregnancy

Selenium (Se) is a trace element essential for the appropriate course of vital processes in the human body. It is also a constituent of the active center of glutathione peroxidase that protects cellular membranes against the adverse effects of H2O2 lipid peroxides. Epidemiological surveys have demonstrated that selenium deficiency in the body may contribute to an increased risk for certain neoplasmic diseases (including colonic carcinoma, gastric carcinoma, pulmonary carcinoma and prostate carcinoma), as well as diseases of the cardiovascular, osseous and nervous systems. Apart from its cancer prevention and antioxidative activities, selenium protects the body against detrimental effects of heavy metals and determines the proper functioning of the immunological system. Furthermore, selenium plays a significant role in the undisturbed functioning of the reproductive system. Many studies have addressed correlations between its intake and fertility as well as disorders of procreation processes. Selenium deficiencies may lead to gestational complications, miscarriages and the damaging of the nervous and immune systems of the fetus. A low concentration of selenium in blood serum in the early stage of pregnancy has been proved to be a predictor of low birth weight of a newborn. A deficiency of this element may also cause infertility in men by causing a deterioration in the quality of semen and in sperm motility. For this reason, supplementation in the case of selenium deficiencies in the procreation period of both women and men is of utmost significance.

PKCδ and θ possibly mediate FSH-induced mouse oocyte maturation via NOX-ROS-TACE cascade signaling pathway

In mammals, gonadotropins stimulate oocyte maturation via the epidermal growth factor (EGF) network, and the protein kinase C (PKC) signaling pathway mediates this process. Tumor necrosis factor-α converting enzyme (TACE) is an important protein responding to PKC activation. However, the detailed signaling cascade between PKC and TACE in follicle-stimulating hormone (FSH)-induced oocyte maturation in vitro remains unclear. In this study, we found that rottlerin (mallotoxin, MTX), the inhibitor of PKC δ and θ, blocked FSH-induced maturation of mouse cumulus-oocyte complexes (COCs) in vitro. We further clarified the relationship between two molecules downstream of PKC δ and θ and TACE in COCs: nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) and its products, reactive oxygen species (ROS). We proved that the respective inhibitors of NOX, ROS and TACE could block FSH-stimulated oocyte maturation dose-dependently, but these inhibitory effects could be reversed partially by amphiregulin (Areg), an EGF family member. Notably, inhibition of PKC δ and θ prevented FSH-induced translocation of two cytosolic components of NOX, p47^phox and p67^phox, to the plasma membrane in cumulus cells. Moreover, FSH-induced TACE activity in cumulus cells was decreased markedly by inhibition of NOX and ROS. In conclusion, PKC δ and θ possibly mediate FSH-induced meiotic resumption in mouse COCs via NOX-ROS-TACE signaling pathway.

A moderate increase of hydrogen peroxide level is beneficial for spontaneous resumption of meiosis from diplotene arrest in rat oocytes cultured in vitro

Hydrogen peroxide (H₂O₂) acts as a signaling molecule and modulates various aspects of cell functions in a wide variety of cells including mammalian germ cells. We examined whether a decreased level of intra-oocyte cyclic 3′,5′-adenosine monophosphate (cAMP) leads to accumulation of H₂O₂, and if so, whether a moderate increase of H₂O₂ inactivates maturation promoting factor (MPF) during spontaneous resumption of meiosis in rat oocytes cultured in vitro. Removal of cumulus cells and culture of denuded oocytes in vitro significantly decreased oocyte cAMP level and led to spontaneous meiotic resumption from diplotene arrest. The reduced oocyte cAMP level was associated with an increased oocyte H₂O₂ level and reduced catalase activity. Exogenous supplementation of H₂O₂ induced meiotic resumption from diplotene arrest in a concentration- and time-dependent manner in oocytes treated with 0.1 mM of 3-isobutyl-1-methylxanthine, while dibutyryl-cAMP and 3-t-butyl-4-hydroxyanisole inhibited the stimulatory effect of exogenous H₂O₂. The increased intra-oocyte H₂O₂ level induced Thr-14/Tyr-15 phosphorylation of CDK1, while Thr-161 phosphorylated CDK1 and cyclin B1 levels were reduced significantly. These results suggest that a decreased level of intra-oocyte cAMP is associated with an increased level of H₂O₂. The increased level of H₂O₂ was associated with high phosphorylation of Thr-14/Tyr-15 and dephosphorylation of the Thr-161 residue of CDK1 and reduced the cyclin B1 level, which eventually inactivated MPF. The MPF inactivation triggered spontaneous resumption of meiosis from diplotene arrest in rat oocytes cultured in vitro.

Elevated blood plasma antioxidant status is favourable for achieving IVF/ICSI pregnancy

The aim of the study was to determine the roles of intrafollicular and systemic oxidative stress and antioxidant response in ovarian stimulation and intracytoplasmic sperm injection (ICSI) outcomes. For this purpose, 102 ICSI patients undergoing controlled ovarian stimulation were enrolled and samples were collected on the day of follicle puncture. Total peroxide (TPX) concentrations and total antioxidant response (TAR) were measured in follicular fluid and blood plasma, and an oxidative stress index (OSI) was calculated based on these two parameters. Urinary concentrations of 8-iso-prostaglandin F2a (F2IsoP) were measured. Elevated intrafollicular oxidative stress was positively correlated with ovarian stimulation outcome: less FSH per retrieved oocyte was used, more oocytes were collected and higher serum oestradiol concentrations were measured in patients with higher follicular OSI. However, high urinary F2IsoP related to lower embryo quality and F2IsoP was also elevated in smoking patients. Patients with endometriosis had lower follicular antioxidant status. Most importantly, higher systemic blood TAR was significantly favourable for achieving clinical pregnancy (P=0.03). In conclusion, the findings suggest clear associations between oxidative stress, antioxidant status and several aspects of ovarian stimulation and IVF/ICSI outcome, including pregnancy rate. Several oxygen-dependent biochemical reactions produce reactive oxygen species as by-products that may eventually lead to oxidative stress, which is detrimental to cells and tissues. Total antioxidant status, on the other hand, comprises several agents that balance the excess of these reactive oxygen species and reduce potential damage to the body. The aim of the current work was to study this balance in 102 patients participating in an ICSI programme and to examine the degree to which total peroxide content and antioxidant status influence infertility and pregnancy outcome. During the study, several tests were performed to characterize oxidative stress levels in ovarian follicular fluid, blood plasma and urine. We found a significantly higher oxidative stress environment in the ovary when compared with blood plasma. This suggests a prominent role of oxidative stress in the ovaries of these patients. The elevated oxidative stress levels were correlated to a higher number of oocytes that could be obtained via the procedure and to a lower amount of FSH needed to mature the oocytes, suggesting that oxidative stress, to some degree, is favourable for hormone stimulation outcome. A high level of lipid peroxidation products in the urine, another marker of oxidative stress, was observed in smokers and this marker was elevated in patients with embryos that had lower developmental potential. A higher overall antioxidant status in blood plasma was advantageous for achieving pregnancy.

Small molecule inhibitors of the Candida albicans budded-to-hyphal transition act through multiple signaling pathways

The ability of the pathogenic yeast Candida albicans to interconvert between budded and hyphal growth states, herein termed the budded-to-hyphal transition (BHT), is important for C. albicans development and virulence. The BHT is under the control of multiple cell signaling pathways that respond to external stimuli, including nutrient availability, high temperature, and pH. Previous studies identified 21 small molecules that could inhibit the C. albicans BHT in response to carbon limitation in Spider media. However, the studies herein show that the BHT inhibitors had varying efficacies in other hyphal-inducing media, reflecting their varying abilities to block signaling pathways associated with the different media. Chemical epistasis analyses suggest that most, but not all, of the BHT inhibitors were acting through either the Efg1 or Cph1 signaling pathways. Notably, the BHT inhibitor clozapine, a FDA-approved drug used to treat atypical schizophrenia by inhibiting G-protein-coupled dopamine receptors in the brain, and several of its functional analogs were shown to act at the level of the Gpr1 G-protein-coupled receptor. These studies are the first step in determining the target and mechanism of action of these BHT inhibitors, which may have therapeutic anti-fungal utility in the future.

Melatonin protects against clomiphene citrate-induced generation of hydrogen peroxide and morphological apoptotic changes in rat eggs

The present study was aimed to determine whether clomiphene citrate-induces generation of hydrogen peroxide in ovary, if so, whether melatonin could scavenge hydrogen peroxide and protect against clomiphene citrate-induced morphological apoptotic changes in rat eggs. For this purpose, forty five sexually immature female rats were given single intramuscular injection of 10 IU pregnant mare's serum gonadotropin for 48 h followed by single injections of 10 IU human chorionic gonadotropin and clomiphene citrate (10 mg/kg bw) with or without melatonin (20 mg/kg bw) for 16 h. The histology of ovary, ovulation rate, hydrogen peroxide concentration and catalase activity in ovary and morphological changes in ovulated eggs were analyzed. Co-administration of clomiphene citrate along with human chorionic gonadotropin significantly increased hydrogen peroxide concentration and inhibited catalase activity in ovary, inhibited ovulation rate and induced egg apoptosis. Supplementation of melatonin reduced hydrogen peroxide concentration and increased catalase activity in the ovary, delayed meiotic cell cycle progression in follicular oocytes as well as in ovulated eggs since extrusion of first polar body was still in progress even after ovulation and protected against clomiphene citrate-induced egg apoptosis. These results clearly suggest that the melatonin reduces oxidative stress by scavenging hydrogen peroxide produced in the ovary after clomiphene citrate treatment, slows down meiotic cell cycle progression in eggs and protects against clomiphene citrate-induced apoptosis in rat eggs.

Thermal tolerance of contractile function in oxidative skeletal muscle: no protection by antioxidants and reduced tolerance with eicosanoid enzyme inhibition

Mechanisms for the loss of muscle contractile function in hyperthermia are poorly understood. This study identified the critical temperature, resulting in a loss of contractile function in isolated diaphragm (thermal tolerance), and then tested the hypotheses 1) that increased reactive oxygen species (ROS) production contributes to the loss of contractile function at this temperature, and 2) eicosanoid metabolism plays an important role in preservation of contractile function in hyperthermia. Contractile function and passive force were measured in rat diaphragm bundles during and after 30 min of exposure to 40, 41, 42 or 43 degrees C. Between 40 and 42 degrees C, there were no effects of hyperthermia, but at 43 degrees C, a significant loss of active force and an increase in passive force were observed. Inhibition of ROS with the antioxidants, Tiron or Trolox, did not inhibit the loss of contractile force at 43 degrees C. Furthermore, treatment with dithiothreitol, a thiol (-SH) reducing agent, did not reverse the effects of hyperthermia. A variety of global lipoxygenase (LOX) inhibitors further depressed force during 43 degrees C and caused a significant loss of thermal tolerance at 42 degrees C. Cyclooxygenase (COX) inhibitors also caused a loss of thermal tolerance at 42 degrees C. Blockage of phospholipase with phospholipase A(2) inhibitors, bromoenol lactone or arachidonyltrifluoromethyl ketone failed to significantly prevent the loss of force at 43 degrees C. Overall, these data suggest that ROS do not play an apparent role in the loss of contractile function during severe hyperthermia in diaphragm. However, functional LOX and COX enzyme activities appear to be necessary for maintaining normal force production in hyperthermia.

Oxidative stress and antioxidants: exposure and impact on female fertility

BACKGROUND

Reproductive failure is a significant public health concern. Although relatively little is known about factors affecting fertility and early pregnancy loss, a growing body of literature suggests that environmental and lifestyle factors play an important role. There is sufficient evidence to hypothesize that diet, particularly its constituent antioxidants, and oxidative stress (OS) may influence the timing and maintenance of a viable pregnancy. We hypothesize that conditions leading to OS in the female affect time-to-pregnancy and early pregnancy loss.

METHODS

We review the epidemiology of female infertility related to antioxidant defenses and oxidation and examine potential sources of OS from the ovarian germ cell through the stages of human pregnancy and pregnancy complications related to infertility. Articles were identified through a search of the PubMed database.

RESULTS

Female OS is a likely mediator of conception and threshold levels for OS exist, dependent on anatomic location and stage of preconception.

CONCLUSIONS

Prospective pregnancy studies with dietary assessment and collection of biological samples prior to conception with endpoints of time-to-pregnancy and early pregnancy loss are needed.

Stress stimulates AMP-activated protein kinase and meiotic resumption in mouse oocytes

This study examined the effects of three different cellular stresses on oocyte maturation in meiotically arrested mouse oocytes. Cumulus-cell enclosed oocytes (CEO) or denuded oocytes (DO) from immature, eCG-primed mice were cultured for 17-18 h in dbcAMP-containing medium plus increasing concentrations of the metabolic poison, sodium arsenite, or the free radical-generating agent, menadione. Alternatively, oocytes were exposed to osmotic stress by pulsing with sorbitol and returned to control inhibitory conditions for the duration of culture. Arsenite and menadione each dose-dependently induced germinal vesicle breakdown (GVB) in both DO and CEO. DO, but not CEO, pulsed for 60 min with 500 mM sorbitol were stimulated to resume maturation. The lack of effect in CEO suggests that the cumulus cells may be playing a protective role in osmotic stress-induced GVB. The AMP-activated protein kinase (PRKA; formerly known as AMPK) inhibitors, compound C and araA, completely blocked the meiosis-stimulating effects of all the tested stresses. Western blots showed that acetyl-CoA carboxylase, an important substrate of PRKA, was phosphorylated before GVB, supporting a role for PRKA in stress-induced maturation. Together, these data show that a variety of stresses stimulate GVB in meiotically arrested mouse oocytes in vitro and suggest that this effect is mediated through activation of PRKA.

Small GTPase RhoA is required for ooplasmic segregation and spindle rotation, but not for spindle organization and chromosome separation during mouse oocyte maturation, fertilization, and early cleavage

RhoA, a small GTPase, plays versatile roles in many aspects of cell function such as stress fiber formation, cytokinesis, and cell polarization. In this study, we investigated the subcellular localization of RhoA and its possible roles during oocyte maturation and fertilization. RhoA was localized in the cytoplasm of eggs from the germinal vesicle (GV) stage to 2-cell stage, especially concentrating in the midbody of telophase spindle when oocyte extruded PB1 and PB2. The RhoA kinases (ROCKs) specific inhibitor Y-27632 blocked GV breakdown (GVBD) and first polar body extrusion, but did not affect apparatus formation and anaphase/telophase I entry. Anti-RhoA antibody microinjection into the oocytes showed similar results. RhoA inhibitor caused abnormal organization of microfilaments, failure of spindle rotation, PB2 extrusion as well as cleavage furrow formation, while sister chromatid separation was not affected. Microinjection of RhoA antibody also blocked PB2 emission. Our findings indicate that RhoA, by regulating microfilament organization, regulates several important events including GVBD, polar body emission, spindle rotation, and cleavage.

Hydrogen peroxide modulates meiotic cell cycle and induces morphological features characteristic of apoptosis in rat oocytes cultured in vitro

Hydrogen peroxide (H2O2) is known to induce cell cycle arrest and apoptosis in various somatic cell types cultured in vitro. We hypothesize that this reactive oxygen species (ROS) could modulate cell cycle and induce morphological features characteristics of apoptosis in oocytes cultured in vitro. To test this hypothesis, immature and mature oocytes were cultured in medium containing various doses of H2O2 with or without caspase-3 inhibitor for various times. The treatment of H2O2 induced germinal vesicle break down (GVBD) in all immature oocytes followed by initiation of shrinkage. Some of immature oocytes (but not mature oocytes) also showed membrane blebbing. On the other hand, H2O2 treatment inhibited first polar body emission in mature oocytes just prior to initiation of shrinkage. The cytoplasmic granulation and fragmentation into apoptotic bodies were observed in mature oocytes during later stages of H2O2 treatment. The shrinkage was induced by H2O2 in a dose- and time-dependent manner in both immature and mature oocytes. Although, H2O2-induced degeneration was observed in both immature and mature oocytes after 2.0 hrs of treatment, immature oocytes were more susceptible to undergo quick shrinkage, membrane blebbing and degeneration. Co-addition of caspase-3 inhibitor prevented shrinkage and degeneration of both immature and mature oocytes except membrane blebbing that was observed at higher doses of H2O2 after 1.0 hr of culture. Treatment of H2O2 induced bax protein expression (3 times), DNA fragmentation and caspase-3 activity (2.5 times) in oocytes undergoing morphological apoptotic changes. These findings clearly suggest that H2O2 induced GVBD in immature oocytes, inhibited first polar body extrusion in mature oocytes prior to initiation of morphological changes characteristic of apoptosis such as shrinkage, membrane blebbing and cytoplasmic fragmentation prior to degeneration.

Simulation of intrafollicular conditions prevents GVBD in bovine oocytes: A better alternative to affect their developmental capacity after two-step culture

To increase the developmental competence of bovine oocytes isolated from small, medium, and large follicles (2-3, 3-4, and 4-6 mm in diameter, respectively), we tried to modify the conditions for their in vitro culture. The first step involved conditions maintaining at least for 48 hr a reversible inhibition of the germinal vesicle breakdown (GVBD) and the second step stimulated the resumption of meiosis and completion of nuclear and cytoplasmic maturation during the subsequent 20-22 hr of culture. The effectiveness of this model depended mainly on the medium composition (reduced NaHCO3, substitution of serum with serum albumin, addition of antioxidants (curcumin), increased viscosity by agar, the reduction of oxygen concentration (within 6%-8%), the reduction of the proportion between the number of cumulus-oocyte complexes (COCs), and the reduction of the amount of a medium (within 6-7 mul per COC) to amplify the GVBD-inhibitory effect of oocyte surrounding granulosa cells. The COCs were incubated in clumps of 6-7 COCs. The effectiveness and reversibility of GVBD inhibition depended also on the duration of COCs isolation. The full reversibility of the GV block was controlled morphologically and also by measuring histone H1 and MAP kinase activities. The two-step versus one-step (24 hr) maturation technique was evaluated by the percentage of total and hatched blastocysts at day 9. When compared with one-step maturation, the two-step culture showed a slightly increased proportion of total and hatched blastocysts developed from growing follicles, mainly from the smallest category (13.9% vs. 7.1% and 9.2% vs. 3.3% for total blastocysts and hatched, respectively). However, the two-step culture of oocytes from large regressing follicles substantially reduced the blastocyst yield (9.7% vs. 39.1% and 4.9% vs. 26.7% for total blastocysts and hatched, respectively). The transfer of ten blastocysts (developed after two-step culture) to ten recipients resulted in seven pregnancies.

Lipoxygenase-dependent superoxide release in skeletal muscle

Superoxide anion radical (O2•−) is released from skeletal muscle at rest and is particularly elevated during conditions of heat stress (42°C). Previous studies have shown that in isolated rat diaphragm O2•−release is not dependent on mitochondrial electron transport, reduced NADP oxidase activity, or the integrity of membrane anion channels. This study hypothesized that O2•−release, as measured by cytochrome c reduction, is linked to metabolism of arachidonic acid. Phospholipase A2inhibition with manoalide significantly decreased O2•−release. In downstream pathways, neither the blockage of cyclooxygenase with indomethacin nor the inhibition of cytochrome P-450-dependent monooxygenase with SKF-525A decreased O2•−release. However, lipoxygenase (LOX) inhibition with general LOX blockers 5,8,11,14-eicosatetraynoic acid and cinnamyl-3,4-dihydroxy-α-cyanocinnamate greatly attenuated the signal. Furthermore, the specific 5-LOX inhibitor diethylcarbamazine also significantly decreased O2•−release. Immunohistochemistry localized 5- and 12-LOX to the cytosol and sarcolemma of muscle cells. Confocal studies, using the O2•−-sensitive fluorescent indicator hydroethidine, demonstrated that LOX inhibition had no significant influence on intracellular O2•−formation. When compared with the cytochrome c results, this indicates that intra- and extracellular O2•−must arise from different sources. These data show for the first time that arachidonic acid metabolism through LOX activity, is a major source of extracellular O2•−release in skeletal muscle.

Mechanisms of free-radical induction in relation to fenretinide-induced apoptosis of neuroblastoma

The mechanisms of fenretinide-induced cell death of neuroblastoma cells are complex, involving signaling pathways mediated by free radicals or reactive oxygen species (ROS). The aim of this study was to identify mechanisms generating ROS and apoptosis of neuroblastoma cells in response to fenretinide. Fenretinide-induced ROS or apoptosis of SH-SY5Y or HTLA 230 neuroblastoma cells were not blocked by Nitro l-argenine methyl ester (l-NAME), an inhibitor of nitric oxide synthase. Flavoprotein-dependent superoxide-producing enzymes such as NADPH oxidase were also not involved in fenretinide-induced apoptosis or ROS generation. Similarly, ketoconazole, a cytochrome P450 inhibitor, and inhibitors of cyclooxygenase (COX) were also ineffective. In contrast, inhibition of phospholipase A(2) or lipoxygenases (LOX) blocked the induction of ROS and apoptosis in response to fenretinide. Using specific inhibitors of LOX, blocking 12-LOX but not 5- or 15-LOX inhibited both fenretinide-induced ROS and apoptosis. The effects of eicosatriynoic acid, a specific 12-LOX inhibitor, were reversed by the addition of the 12-LOX products, 12 (S)-hydroperoxyeicosatetraenoic acid and 12 (S)-hydroxyeicosatetraenoic acid. The targeting of 12-LOX in neuroblastoma cells may thus be a novel pathway for the development of drugs inducing apoptosis of neuroblastoma with improved tumor specificity.

Effect of reactive oxygen species on NH4+ permeation in Xenopus laevis oocytes

To investigate the effects of reactive oxygen species (ROS) on NH4+ permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential (V(m)) and intracellular pH (pH(i)) induced by a 20 mM NH4Cl-containing solution. Under control conditions, NH4Cl exposure induced a large membrane depolarization (to V(m) = 4.0 +/- 1.5 mV; n = 21) and intracellular acidification [reaching a change in pH(i) (DeltapH(i)) of 0.59 +/- 0.06 pH units in 12 min]; the initial rate of cell acidification (dpH(i)/dt) was 0.06 +/- 0.01 pH units/min. Incubation of the oocytes in the presence of H2O2 or beta-amyloid protein had no marked effect on the NH4Cl-induced DeltapH(i). By contrast, in the presence of photoactivated rose bengal (RB), tert-butyl-hydroxyperoxide (t-BHP), or xanthine/xanthine oxidase (X/XO), the same experimental maneuver induced significantly greater DeltapH(i) and dpH(i)/dt. These increases in DeltapH(i) and dpH(i)/dt were prevented by the ROS scavengers histidine and desferrioxamine, suggesting involvement of the reactive species (1)DeltagO2 and.OH. Using the voltage-clamp technique to identify the mechanism underlying the ROS-measured effects, we found that RB induced a large increase in the oocyte membrane conductance (G(m)). This RB-induced G(m) increase was prevented by 1 mM diphenylamine-2-carboxylate (DPC) and by a low Na+ concentration in the bath. We conclude that RB, t-BHP, and X/XO enhance NH4+ influx into the oocyte via activation of a DPC-sensitive nonselective cation conductance pathway.

Endocrine-regulated and protein kinase C-dependent generation of superoxide by rat preovulatory follicles

The ovulatory LH surge results in follicular inflammation with an increase in cytokines and PGs. Reactive oxygen species (ROS) are also produced during inflammatory processes. To study ROS generation during the ovulatory cascade, preovulatory follicles were dissected from immature female rats primed with PMSG. Follicles were isolated, and ROS generation was assessed by luminol-amplified chemiluminescence. Immature rat granulosa cells were also subjected to luminometry after isolation from immature rats treated with diethylstilbestrol. Phorbol ester-stimulated ROS generation by follicular cells was completely suppressed by superoxide dismutase and the NADPH/NADH oxidase inhibitor diphenylene iodonium bisulfate, whereas catalase was without effect. Fractionation of granulosa cells with an antibody against leukocyte common antigen-1 showed that leukocyte-enriched cells produced more than 95% of the superoxide measured. In vivo treatment with LH produced a 5-fold increase in phorbol-stimulated superoxide production by isolated follicles. This response was maximal within 4 h and was blocked by indomethacin. In vivo administration of PGE(2) and PGF(2alpha) did not reverse the blockade by indomethacin; however, isolated follicles incubated with PGE(2) produced a time-dependent increase in phorbol-stimulated superoxide generation. Thus, a superoxide generator is present in the preovulatory follicle that is leukocytic in origin, hormone regulated, and activated by a protein kinase C-dependent pathway. The regulated generation of superoxide by preovulatory follicles may indicate a role for ROS in the periovulatory period.