Lipid peroxidation and phospholipase A2 activity in liposomes composed of unsaturated phospholipids: a structural basis for enzyme activation

Emerging roles of ferroptosis in infectious diseases

In living organisms, lipid peroxidation is a continuously occurring cellular process and therefore involved in various physiological and pathological contexts. Among the broad variety of lipids, polyunsaturated fatty acids (PUFA) constitute a major target of oxygenation either when released as mediators by phospholipases or when present in membranous phospholipids. The last decade has seen the characterization of an iron- and lipid peroxidation-dependent cell necrosis, namely, ferroptosis, that involves the accumulation of peroxidized PUFA-containing phospholipids. Further studies could link ferroptosis in a very large body of (physio)-pathological processes, including cancer, neurodegenerative, and metabolic diseases. In this review, we mostly focus on the emerging involvement of lipid peroxidation-driven ferroptosis in infectious diseases, and the immune consequences. We also discuss the putative ability of microbial virulence factors to exploit or to dampen ferroptosis regulatory pathways to their own benefit.

Addition of l-carnitine to the freezing extender improves post-thaw sperm quality of Okinawan native Agu pig

The objective of the present study was to establish whether the addition of l-carnitine (LC), which exhibits antioxidant activity, to the freezing extender improves the quality of cryopreserved Okinawan native Agu pig sperm. Ejaculated sperm frozen in an extender supplemented with 0, 1, 2.5, or 5 mM LC was thawed, and the integrities of mitochondria and the plasmalemma and other sperm characteristics were evaluated. The treatment with different concentrations of LC effectively improved sperm motility, mitochondrial and plasmalemmal integrities, and the proteolytic activity of acrosomal contents after freeze-thawing (P < 0.05). The proportion of post-thaw sperm possessing intact mitochondria and plasmalemma and higher proteolytic activity of acrosomal contents was markedly higher among sperm frozen in the presence of 2.5 mM LC than among sperm frozen in the extender without LC (P < 0.05). Furthermore, although the addition of LC to the freezing extender had no effect on disturbance of DNA damage and caspase activity, sperm treated with 2.5 mM LC during freezing exhibited significantly higher penetrability into matured oocytes in vitro than untreated sperm. Collectively, these results indicate that the addition of LC to the freezing extender effectively improved the post-thaw quality of Agu pig sperm by preventing mitochondrial dysfunction caused by oxidative stress during cryopreservation.

Host phospholipid peroxidation fuels ExoU-dependent cell necrosis and supports Pseudomonas aeruginosa-driven pathology

Regulated cell necrosis supports immune and anti-infectious strategies of the body; however, dysregulation of these processes drives pathological organ damage. Pseudomonas aeruginosa expresses a phospholipase, ExoU that triggers pathological host cell necrosis through a poorly characterized pathway. Here, we investigated the molecular and cellular mechanisms of ExoU-mediated necrosis. We show that cellular peroxidised phospholipids enhance ExoU phospholipase activity, which drives necrosis of immune and non-immune cells. Conversely, both the endogenous lipid peroxidation regulator GPX4 and the pharmacological inhibition of lipid peroxidation delay ExoU-dependent cell necrosis and improve bacterial elimination in vitro and in vivo. Our findings also pertain to the ExoU-related phospholipase from the bacterial pathogen Burkholderia thailandensis, suggesting that exploitation of peroxidised phospholipids might be a conserved virulence mechanism among various microbial phospholipases. Overall, our results identify an original lipid peroxidation-based virulence mechanism as a strong contributor of microbial phospholipase-driven pathology.

Does membrane curvature elastic energy play a role in mediating oxidative stress in lipid membranes?

The effects of oxidative stress on cells are associated with a wide range of pathologies. Oxidative stress is predominantly initiated by the action of reactive oxygen species and/or lipoxygenases on polyunsaturated fatty acid containing lipids. The downstream products are oxidised phospholipids, bioactive aldehydes and a range of Schiff base by-products between aldehydes and lipids, or other biomacromolecules. In this review we assess the impact of oxidative stress on lipid membranes, focusing on the changes that occur to the curvature preference (lipid spontaneous curvature) and elastic properties of membranes, since these biophysical properties modulate phospholipid homeostasis. Studies show that the lipid products of oxidative stress reduce stored curvature elastic energy in membranes. Based upon this observation, we hypothesize that the effects of oxidative stress on lipid membranes will be reduced by compounds that increase stored curvature elastic energy. We find a strong correlation appears across literature studies that we have reviewed, such that many compounds like vitamin E, Curcumin, Coenzyme Q10 and vitamin A show behaviour consistent with this hypothesis. Finally, we consider whether age-related changes in lipid composition represent the homeostatic response of cells to compensate for the accumulation of in vivo lipid oxidation products.

Antioxidant Synergy of Mitochondrial Phospholipase PNPLA8/iPLA2γ with Fatty Acid-Conducting SLC25 Gene Family Transporters

Patatin-like phospholipase domain-containing protein PNPLA8, also termed Ca²⁺-independent phospholipase A2γ (iPLA2γ), is addressed to the mitochondrial matrix (or peroxisomes), where it may manifest its unique activity to cleave phospholipid side-chains from both sn-1 and sn-2 positions, consequently releasing either saturated or unsaturated fatty acids (FAs), including oxidized FAs. Moreover, iPLA2γ is directly stimulated by H₂O₂ and, hence, is activated by redox signaling or oxidative stress. This redox activation permits the antioxidant synergy with mitochondrial uncoupling proteins (UCPs) or other SLC25 mitochondrial carrier family members by FA-mediated protonophoretic activity, termed mild uncoupling, that leads to diminishing of mitochondrial superoxide formation. This mechanism allows for the maintenance of the steady-state redox status of the cell. Besides the antioxidant role, we review the relations of iPLA2γ to lipid peroxidation since iPLA2γ is alternatively activated by cardiolipin hydroperoxides and hypothetically by structural alterations of lipid bilayer due to lipid peroxidation. Other iPLA2γ roles include the remodeling of mitochondrial (or peroxisomal) membranes and the generation of specific lipid second messengers. Thus, for example, during FA β-oxidation in pancreatic β-cells, H₂O₂-activated iPLA2γ supplies the GPR40 metabotropic FA receptor to amplify FA-stimulated insulin secretion. Cytoprotective roles of iPLA2γ in the heart and brain are also discussed.

Degree of Unsaturation and Backbone Orientation of Amphiphilic Macromolecules Influence Local Lipid Properties in Large Unilamellar Vesicles

Liposomes have become increasingly common in the delivery of bioactive agents due to their ability to encapsulate hydrophobic and hydrophilic drugs with excellent biocompatibility. While commercial liposome formulations improve bioavailability of otherwise quickly eliminated or insoluble drugs, tailoring formulation properties for specific uses has become a focus of liposome research. Here, we report the design, synthesis, and characterization of two series of amphiphilic macromolecules (AMs), consisting of acylated polyol backbones conjugated to poly(ethylene glycol) (PEG) that can serve as the sole additives to stabilize and control hydrophilic molecule release rates from distearoylphosphatidylcholine (DSPC)-based liposomes. As compared to DSPC alone, all AMs enable liposome formation and stabilize their colloidal properties at low incorporation ratios, and the AM's degree of unsaturation and hydrophobe conformation have profound impacts on stability duration. The AM's chemical structures, particularly hydrophobe unsaturation, also impact the rate of hydrophilic drug release. Course-grained molecular dynamics simulations were utilized to better understand the influence of AM structure on lipid properties and potential liposomal stabilization. Results indicate that both hydrophobic domain structure and PEG density can be utilized to fine-tune liposome properties for the desired application. Collectively, AMs demonstrate the potential to simultaneously stabilize and control the release profile of hydrophilic cargo.

Erythrocyte oxidative stress is associated with cell deformability in patients with retinal vein occlusion

Essentials Retinal vein occlusion (RVO), characterized by blood hyperviscosity, has an unclear pathogenesis. We aimed to find out if hemorheological profile is altered by oxidative stress in RVO patients. Red blood cell (RBC) oxidative stress is associated to whole blood viscosity and RBC deformability. Reactive oxygen species alter RBC membrane rigidity, playing a key role in RVO pathogenesis.

SUMMARY

Background Retinal vein occlusion (RVO) is characterized by vision loss resulting from hypoperfusion and hypoxia of the retina. RVO pathogenesis is not yet fully understood, although blood hyperviscosity has been observed. Erythrocyte deformability plays a key role in determining blood viscosity, and it is critical to microvascular perfusion and oxygen delivery. It has been shown that oxidative stress-induced erythrocyte membrane fluidity alterations are linked to the progression of cardiovascular diseases. Objectives To determine whether erythrocytes from RVO patients show signs of oxidative stress, and whether this condition can modify the hemorheologic profile in these patients. Patients and Methods We analyzed the entire hemorheologic profile and erythrocyte oxidative stress - reactive oxygen species (ROS) production and membrane lipid peroxidation - in 128 RVO patients and 128 healthy subjects, matched for age and sex. Fluorescence anisotropy was used to evaluate the fluidity of erythrocyte membranes. Results In RVO patients, erythrocyte oxidative stress was present and positively correlated with whole blood viscosity and erythrocyte deformability. Multivariate linear regression analysis after adjustment for age, cardiovascular risk factors, medications, leukocyte number and mean corpuscular volume indicated that erythrocyte-derived ROS and erythrocyte lipid peroxidation were significantly and positively correlated with erythrocyte membrane viscosity and deformability. Moreover, in vitro experiments demonstrated that ROS have a key role in erythrocyte membrane fluidity. Conclusions Our findings indicate that erythrocyte oxidative stress plays a key role in the pathogenesis of RVO, and pave the way to new therapeutic interventions.

Preventive effect of Desferal on sperm motility and morphology

Transition metal ions, mainly iron, are involved in the generation of highly reactive hydroxyl radicals, which are the most powerful inducers of oxidative damage to all biomolecules. The lipids in sperm membranes are highly susceptible to oxidation. Sperm lipid peroxidation (LPO) leads to decrease of motility and reduction of likelihood for sperm-oocyte fusion. The excess radical production may affect also the spermatozoa morphology. The aim of the present study was to investigate the effect of Desferal on the LPO, motility, and morphology of boar sperm subjected to oxidative stress. After collection, the ejaculates were equally separated and diluted in a commercial semen extender (experiment 1) or in physiological saline (experiment 2). The ejaculates of the 2 experiments were divided into aliquots, which were incubated with one of the following agents: FeSO4 (0.1mM), H2 O2 (0.5mM), or FeSO4  + H2 O2 (Fenton system), in the presence or absence of Desferal. The application of Desferal in the incubation medium had a protective effect against FeSO4  + H2 O2 -induced sperm damage, namely, decrease of LPO; decrease the quantity of immotile spermatozoa and decrease the number of morphological abnormalities, regardless of the used medium. In experiment 2, the presence of FeSO4 in the incubation medium induced LPO in the same range as the combination FeSO4  + H2 O2 , in which the effect was reduced by Desferal. Thus, the supplement of Desferal to media used for sperm storage and processing could be a useful tool for diminishing oxidative injury and improving the quality of the semen.

Absence of Dystrophin Disrupts Skeletal Muscle Signaling: Roles of Ca2+, Reactive Oxygen Species, and Nitric Oxide in the Development of Muscular Dystrophy

Dystrophin is a long rod-shaped protein that connects the subsarcolemmal cytoskeleton to a complex of proteins in the surface membrane (dystrophin protein complex, DPC), with further connections via laminin to other extracellular matrix proteins. Initially considered a structural complex that protected the sarcolemma from mechanical damage, the DPC is now known to serve as a scaffold for numerous signaling proteins. Absence or reduced expression of dystrophin or many of the DPC components cause the muscular dystrophies, a group of inherited diseases in which repeated bouts of muscle damage lead to atrophy and fibrosis, and eventually muscle degeneration. The normal function of dystrophin is poorly defined. In its absence a complex series of changes occur with multiple muscle proteins showing reduced or increased expression or being modified in various ways. In this review, we will consider the various proteins whose expression and function is changed in muscular dystrophies, focusing on Ca(2+)-permeable channels, nitric oxide synthase, NADPH oxidase, and caveolins. Excessive Ca(2+) entry, increased membrane permeability, disordered caveolar function, and increased levels of reactive oxygen species are early changes in the disease, and the hypotheses for these phenomena will be critically considered. The aim of the review is to define the early damage pathways in muscular dystrophy which might be appropriate targets for therapy designed to minimize the muscle degeneration and slow the progression of the disease.

Acquired deficiency of tafazzin in the adult heart: Impact on mitochondrial function and response to cardiac injury

The content and composition of cardiolipin (CL) is critical for preservation of mitochondrial oxidative phosphorylation (OXPHOS) and inner membrane integrity. Tafazzin (Taz) is an enzyme responsible for remodeling of immature CL containing mixed acyl groups into the mature tetralinoleyl form (C18:2)4-CL. We hypothesized that acquired defects in Taz in the mature heart would impact remodeling of CL and augment cardiac injury. The role of acquired Taz deficiency was studied using the inducible Taz knockdown (TazKD) mouse. Taz-specific shRNA is induced by doxycycline (DOX). One day of DOX intake decreased Taz mRNA in the heart to 20% vs. DOX-treated WT. Knockdown was initiated at an adult age and was stable during long term feeding. CL phenotype was assessed by (C18:2)4-CL content and was reduced 40% vs. WT at two months of DOX. TazKD showed increased production of reactive oxygen species and increased susceptibility to permeability transition pore opening at baseline. However, OXPHOS measured using the rate of oxygen consumption was unchanged in the setting of acquired Taz deficiency. Infarct size, measured in isolated buffer-perfused Langendorff hearts following 25min. Stop flow ischemia and 60min. Reperfusion was not altered in TazKD hearts. Thus, impaired Taz-function with onset at adult age does not enhance susceptibility to ischemia-reperfusion injury.

Effects of Echis pyramidum snake venom on hepatic and renal antioxidant enzymes and lipid peroxidation in rats

The effects of Echis pyramidum venom (EPV) (0.25, 0.50, and 1.00 mg/kg) on activities of superoxide dismutase (SOD) and catalase (CAT) and levels of thiobarbituric acid reactive substances (TBARS) and total thiols (T-SH) in liver and kidneys of rats were investigated. EPV significantly and dose dependently decreased the activities of SOD and CAT in livers. Although the kidney SOD and CAT activities were not affected by low and medium doses of EPV, the high dose significantly reduced the activities of these enzymes. Liver and kidney TBARS levels were not affected by the low and medium doses of EPV, whereas the high dose significantly increased the TBARS after 6 h postdosing. There was a significant depletion of T-SH in liver and kidneys of rats exposed to a high dose of EPV. The acute phase oxidative stress due to an EPV injection points toward the importance of an early antioxidant therapy for the management of snake bites.

Smoking dose modifies the association between C242T polymorphism and prevalence of metabolic syndrome in a Chinese population

BACKGROUND

The C242T polymorphism of the CYBA gene that encodes p22phox, a component of NADPH oxidase, has been found to modulate superoxide production. Oxidase is a major source of the superoxide anion that contributes to individual components of metabolic syndrome. We examined the relationship of the C242T polymorphism with the prevalence of metabolic syndrome in a Chinese population, taking account of consumed cigarette amounts.

METHODOLOGY/PRINCIPAL FINDINGS

In 870 participants, we collected biomarkers related to metabolic syndrome and detailed history of smoking and genotyped the C242T polymorphisms. After adjustment for covariates, the CT/TT genotypes were associated with a lower risk of metabolic syndrome (P = 0.0008). The odds of having metabolic syndrome in the CT/TT participants were 0.439 (95%CI: 0.265, 0.726), while for CC participants the odds were 1.110 (95%CI: 0.904, 1.362). There was significant (P = 0.014) interaction between the C242T polymorphism and smoking status in relation to the prevalence of metabolic syndrome. For smokers who smoke no less than 25 pack-years, those with CT/TT genotypes had lower risk of metabolic syndrome as compared with CC polymorphism carriers (P = 0.015). In the multiple regression analysis, the CT/TT genotypes were significantly associated with lower serum concentration of triglycerides both in all subjects and smokers; furthermore, the CT/TT genotypes were also related to smaller waist circumference in smokers.

CONCLUSIONS

Our study suggests that the C242T gene polymorphism is indeed related to the prevalence of metabolic syndrome and smoking dose might modify this association.

Lipid peroxidation modifies the picture of membranes from the "Fluid Mosaic Model" to the "Lipid Whisker Model"

The "Fluid Mosaic Model", described by Singer and Nicolson, explain both how a cell membrane preserves a critical barrier function while it concomitantly facilitates rapid lateral diffusion of proteins and lipids within the planar membrane surface. However, the lipid components of biological plasma membranes are not regularly distributed. They are thought to contain "rafts" - nano-domains enriched in sphingolipids and cholesterol that are distinct from surrounding membranes of unsaturated phospholipids. Cholesterol and fatty acids adjust the transport and diffusion of molecular oxygen in membranes. The presence of cholesterol and saturated phospholipids decreases oxygen permeability across the membrane. Alpha-tocopherol, the main antioxidant in biological membranes, partition into domains that are enriched in polyunsaturated phospholipids increasing the concentration of the vitamin in the place where it is most required. On the basis of these observations, it is possible to assume that non-raft domains enriched in phospholipids containing PUFAs and vitamin E will be more accessible by molecular oxygen than lipid raft domains enriched in sphingolipids and cholesterol. This situation will render some nano-domains more sensitive to lipid peroxidation than others. Phospholipid oxidation products are very likely to alter the properties of biological membranes, because their polarity and shape may differ considerably from the structures of their parent molecules. Addition of a polar oxygen atom to several peroxidized fatty acids reorients the acyl chain whereby it no longer remains buried within the membrane interior, but rather projects into the aqueous environment "Lipid Whisker Model". This exceptional conformational change facilitates direct physical access of the oxidized fatty acid moiety to cell surface scavenger receptors.

Ginsenoside-Rg1 Protects the Liver against Exhaustive Exercise-Induced Oxidative Stress in Rats

Despite regular exercise benefits, acute exhaustive exercise elicits oxidative damage in liver. The present study determined the hepatoprotective properties of ginsenoside-Rg1 against exhaustive exercise-induced oxidative stress in rats. Forty rats were assigned into vehicle and ginsenoside-Rg1 groups (0.1 mg/kg bodyweight). After 10-week treatment, ten rats from each group performed exhaustive swimming. Estimated oxidative damage markers, including thiobarbituric acid reactive substance (TBARS) (67%) and protein carbonyls (56%), were significantly (P < 0.01) elevated after exhaustive exercise but alleviated in ginsenoside-Rg1 pretreated rats. Furthermore, exhaustive exercise drastically decreased glutathione (GSH) content (∼79%) with concurrent decreased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities. However, these changes were attenuated in Rg1 group. Additionally, increased xanthine oxidase (XO) activity and nitric oxide (NO) levels after exercise were also inhibited by Rg1 pretreatment. For the first time, our findings provide strong evidence that ginsenoside-Rg1 can protect the liver against exhaustive exercise-induced oxidative damage.

Oxidizing substrate specificity of Mycobacterium tuberculosis alkyl hydroperoxide reductase E: kinetics and mechanisms of oxidation and overoxidation

Alkyl hydroperoxide reductase E (AhpE), a novel subgroup of the peroxiredoxin family, comprises Mycobacterium tuberculosis AhpE (MtAhpE) and AhpE-like proteins present in many bacteria and archaea, for which functional characterization is scarce. We previously reported that MtAhpE reacted ~10(3) times faster with peroxynitrite than with hydrogen peroxide, but the molecular reasons for that remained unknown. Herein, we investigated the oxidizing substrate specificity and the oxidative inactivation of the enzyme. In most cases, both peroxidatic thiol oxidation and sulfenic acid overoxidation followed a trend in which those peroxides with the lower leaving-group pK(a) reacted faster than others. These data are in agreement with the accepted mechanisms of thiol oxidation and support that overoxidation occurs through sulfenate anion reaction with the protonated peroxide. However, MtAhpE oxidation and overoxidation by fatty acid-derived hydroperoxides (~10(8) and 10(5) M(-1) s(-1), respectively, at pH 7.4 and 25°C) were much faster than expected according to the Brønsted relationship with leaving-group pK(a). A stoichiometric reduction of the arachidonic acid hydroperoxide 15-HpETE to its corresponding alcohol was confirmed. Interactions of fatty acid hydroperoxides with a hydrophobic groove present on the reduced MtAhpE surface could be the basis of their surprisingly fast reactivity.

Kinetic evaluation of cell membrane hydrolysis during apoptosis by human isoforms of secretory phospholipase A2

Some isoforms of secretory phospholipase A(2) (sPLA(2)) distinguish between healthy and damaged or apoptotic cells. This distinction reflects differences in membrane physical properties. Because various sPLA(2) isoforms respond differently to properties of artificial membranes such as surface charge, they should also behave differently as these properties evolve during a dynamic physiological process such as apoptosis. To test this idea, S49 lymphoma cell death was induced by glucocorticoid (6-48 h) or calcium ionophore. Rates of membrane hydrolysis catalyzed by various concentrations of snake venom and human groups IIa, V, and X sPLA(2) were compared after each treatment condition. The data were analyzed using a model that evaluates the adsorption of enzyme to the membrane surface and subsequent binding of substrate to the active site. Results were compared temporally to changes in membrane biophysics and composition. Under control conditions, membrane hydrolysis was confined to the few unhealthy cells present in each sample. Increased hydrolysis during apoptosis and necrosis appeared to reflect substrate access to adsorbed enzyme for the snake venom and group X isoforms corresponding to weakened lipid-lipid interactions in the membrane. In contrast, apoptosis promoted initial adsorption of human groups V and IIa concurrent with phosphatidylserine exposure on the membrane surface. However, this observation was inadequate to explain the behavior of the groups V and IIa enzymes toward necrotic cells where hydrolysis was reduced or absent. Thus, a combination of changes in cell membrane properties during apoptosis and necrosis capacitates the cell for hydrolysis differently by each isoform.

Reactive oxygen species and boar sperm function

Boar spermatozoa are very susceptible to reactive oxygen species (ROS), but ROS involvement in damage and/or capacitation is unclear. The impact of exposing fresh boar spermatozoa to an ROS-generating system (xanthine/xanthine oxidase; XA/XO) on sperm ROS content, membrane lipid peroxidation, phospholipase (PL) A activity, and motility, viability, and capacitation was contrasted to ROS content and sperm function after cryopreservation. Exposing boar sperm (n = 4-5 ejaculates) to the ROS-generating system for 30 min rapidly increased hydrogen peroxide (H2O2) and lipid peroxidation in all sperm, increased PLA in dead sperm, and did not affect intracellular O2- (flow cytometry of sperm labeled with 2',7'-dichlorodihydrofluorscein diacetate, BODIPY 581/591 C11, bis-BODIPY-FL C11, hydroethidine, respectively; counterstained for viability). Sperm viability remained high, but sperm became immotile. Cryopreservation decreased sperm motility, viability, and intracellular O2- significantly, but did not affect H2O2. As expected, more sperm incubated in capacitating media than Beltsville thawing solution buffer underwent acrosome reactions and protein tyrosine phosphorylation (four proteins, 58-174 kDa); which proteins were tyrosine phosphorylated was pH dependent. Pre-exposing sperm to the ROS-generating system increased the percentage of sperm that underwent acrosome reactions after incubation in capacitating conditions (P < 0.025), and decreased capacitation-dependent increases in two tyrosine-phosphorylated proteins (P < or = 0.035). In summary, H2O2 is the major free radical mediating direct ROS effects, but not cryopreservation changes, on boar sperm. Boar sperm motility, acrosome integrity, and lipid peroxidation are more sensitive indicators of oxidative stress than viability and PLA activity. ROS may stimulate the acrosome reaction in boar sperm through membrane lipid peroxidation and PLA activation.

Enhanced modification of cardiolipin during ischemia in the aged heart

Aging enhances cardiac injury during ischemia and reperfusion compared to the adult heart, including in the Fischer 344 rat model of aging (F344). In interfibrillar cardiac mitochondria obtained from the elderly F344 rat, the rate of oxidative phosphorylation and the activity of electron transport complex III is decreased, concomitant with an increase in the production of reactive oxygen species. In the isolated, perfused heart, 25 min of global ischemia results in additional damage to complex III. We proposed that ischemic damage superimposed upon the aging defect augments production of reactive oxygen species leading to greater oxidative damage in the aged heart. Cardiolipin is an oxidatively sensitive phospholipid located in the inner mitochondrial membrane. Oxidative damage to cardiolipin was assessed by characterization of the individual molecular species of cardiolipin via reverse phase HPLC and electrospray mass spectrometry (MS). The predominant molecular species of cardiolipin (95%) contains four linoleic acid residues (C18:2). Ischemia and reperfusion did not alter the content or composition of cardiolipin in the adult heart. Following ischemia and reperfusion in the aged heart, a new molecular species of cardiolipin was present with mass increased by 48 Da, suggesting the addition of three oxygen atoms. MS fragmentation localized the added mass to the C18:2 residues. Ischemia alone was sufficient to modify cardiolipin in the aged heart whereas cardiolipin in the adult heart remained unaltered. Thus, age-enhanced oxidative damage occurs within mitochondria in the heart during ischemia and reperfusion, especially during ischemia.

Mass-spectrometric characterization of phospholipids and their primary peroxidation products in rat cortical neurons during staurosporine-induced apoptosis

The molecular diversity of phospholipids is essential for their structural and signaling functions in cell membranes. In the current work, we present, the results of mass spectrometric characterization of individual molecular species in major classes of phospholipids -- phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylserine (PtdSer), phosphatidylinositol (PtdIns), sphingomyelin (CerPCho), and cardiolipin (Ptd(2)Gro) -- and their oxidation products during apoptosis induced in neurons by staurosporine (STS). The diversity of molecular species of phospholipids in rat cortical neurons followed the order Ptd(2)Gro > PtdEtn >> PtdCho >> PtdSer > PtdIns > CerPCho. The number of polyunsaturated oxidizable species decreased in the order Ptd(2)Gro >> PtdEtn > PtdCho > PtdSer > PtdIns > CerPCho. Thus a relatively minor class of phospholipids, Ptd(2)Gro, was represented in cortical neurons by the greatest variety of both total and peroxidizable molecular species. Quantitative fluorescence HPLC analysis employed to assess the oxidation of different classes of phospholipids in neuronal cells during intrinsic apoptosis induced by STS revealed that three anionic phospholipids -- Ptd(2)Gro >> PtdSer > PtdIns -- underwent robust oxidation. No significant oxidation in the most dominant phospholipid classes -- PtdCho and PtdEtn -- was detected. MS-studies revealed the presence of hydroxy-, hydroperoxy- as well as hydroxy-/hydroperoxy-species of Ptd(2)Gro, PtdSer, and PtdIns. Experiments in model systems where total cortex Ptd(2)Gro and PtdSer fractions were incubated in the presence of cytochrome c (cyt c) and H(2)O(2), confirmed that molecular identities of the products formed were similar to the ones generated during STS-induced neuronal apoptosis. The temporal sequence of biomarkers of STS-induced apoptosis and phospholipid peroxidation combined with recently demonstrated redox catalytic properties of cyt c realized through its interactions with Ptd(2)Gro and PtdSer suggest that cyt c acts as a catalyst of selective peroxidation of anionic phospholipids yielding Ptd(2)Gro and PtdSer peroxidation products. These oxidation products participate in mitochondrial membrane permeability transition and in PtdSer externalization leading to recognition and uptake of apoptotic cells by professional phagocytes.

Cardiolipin as an oxidative target in cardiac mitochondria in the aged rat

The aged heart sustains greater injury during ischemia (ISC) and reperfusion (REP) compared to the adult heart. In the Fischer 344 (F344) rat, aging decreases oxidative phosphorylation and complex III activity increasing the production of reactive oxygen species in interfibrillar mitochondria (IFM) located among the myofibrils. In the isolated, perfused 24 month old elderly F344 rat heart 25 min of stop-flow ISC causes additional damage to complex III, further decreasing the rate of oxidative phosphorylation. We did not observe further progressive mitochondrial damage during REP. We next asked if ISC or REP increased oxidative damage within mitochondria of the aged heart. Cardiolipin (CL) is a phospholipid unique to mitochondria consisting predominantly of four linoleic acid residues (C18:2). Following ISC and REP in the aged heart, there is a new CL species containing three oxygen atoms added to one linoleic residue. ISC alone was sufficient to generate this new oxidized molecular species of CL. Based upon oxidative damage to CL, complex III activity, and oxidative phosphorylation, mitochondrial damage thus occurs in the aged heart mainly during ISC, rather than during REP. Mitochondrial damage during ischemia sets the stage for mitochondrial-driven cardiomyocyte injury during reperfusion in the aged heart.

Effect of lipid peroxidation on the properties of lipid bilayers: a molecular dynamics study

Lipid peroxidation plays an important role in cell membrane damage. We investigated the effect of lipid peroxidation on the properties of 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphatidylcholine (PLPC) lipid bilayers using molecular dynamics simulations. We focused on four main oxidation products of linoleic acid with either a hydroperoxide or an aldehyde group: 9-trans, cis-hydroperoxide linoleic acid, 13-trans, cis-hydroperoxide linoleic acid, 9-oxo-nonanoic acid, and 12-oxo-9-dodecenoic acid. These oxidized chains replaced the sn-2 linoleate chain. The properties of PLPC lipid bilayers were characterized as a function of the concentration of oxidized lipids, with concentrations from 2.8% to 50% for each oxidation product. The introduction of oxidized functional groups in the lipid tail leads to an important conformational change in the lipids: the oxidized tails bend toward the water phase and the oxygen atoms form hydrogen bonds with water and the polar lipid headgroup. This conformational change leads to an increase in the average area per lipid and, correspondingly, to a decrease of the bilayer thickness and the deuterium order parameters for the lipid tails, especially evident at high concentrations of oxidized lipid. Water defects are observed in the bilayers more frequently as the concentration of the oxidized lipids is increased. The changes in the structural properties of the bilayer and the water permeability are associated with the tendency of the oxidized lipid tails to bend toward the water interface. Our results suggest that one mechanism of cell membrane damage is the increase in membrane permeability due to the presence of oxidized lipids.

Mitochondrial dysfunction early after traumatic brain injury in immature rats

Mitochondria play central roles in acute brain injury; however, little is known about mitochondrial function following traumatic brain injury (TBI) to the immature brain. We hypothesized that TBI would cause mitochondrial dysfunction early (<4 h) after injury. Immature rats underwent controlled cortical impact (CCI) or sham injury to the left cortex, and mitochondria were isolated from both hemispheres at 1 and 4 h after TBI. Rates of phosphorylating (State 3) and resting (State 4) respiration were measured with and without bovine serum albumin. The respiratory control ratio was calculated (State 3/State 4). Rates of mitochondrial H(2)O(2) production, pyruvate dehydrogenase complex enzyme activity, and cytochrome c content were measured. Mitochondrial State 4 rates (ipsilateral/contralateral ratios) were higher after TBI at 1 h, which was reversed with bovine serum albumin. Four hours after TBI, pyruvate dehydrogenase complex activity and cytochrome c content (ipsilateral/contralateral ratios) were lower in TBI mitochondria. These data demonstrate abnormal mitochondrial function early (<or=4 h) after TBI in the developing brain. Future studies directed at reversing mitochondrial abnormalities could guide neuroprotective interventions after pediatric TBI.

Time-course of lipid peroxidation in different organs of mice treated with Echis pyramidum snake venom

This study examined the effect of Echis pyramidum (EP) venom on time-course of lipid peroxidation in different vital organs of mice. Adult male Swiss albino mice were injected with EP venom (2 mg/kg, i.p.); control mice received vehicle alone (normal saline). Mice were killed at 1, 3, 6, 12, and 24 h post-envenomation. The liver, lung, kidney, heart, and brain (cerebrum and cerebellum) were collected for the estimation of malondialdehyde (MDA), an index of lipid peroxidation. The results of this study showed that a single injection of EP venom caused a significant lipid peroxidation in all the organs studied. The onset of lipid peroxidation was as early as 1 h and persisted for several hours, suggesting an important role of oxidative stress in the cytotoxicity of EP venom.

Activation of calcium-independent phospholipase A2 (iPLA2) in brain mitochondria and release of apoptogenic factors by BAX and truncated BID

Cleaved or truncated BID (tBID) is known to oligomerize both BAK and BAX. Previously, BAK and BAX lacing the C-terminal fragment (BAXDeltaC) were shown to induce modest cytochrome c (Cyt c) release from rat brain mitochondria when activated by tBID. We now show that tBID plus monomeric full-length BAX induce extensive release of Cyt c, Smac/DIABLO, and Omi/HtrA2 (but not endonuclease G and the apoptosis inducing factor) comparable to the release induced by alamethicin. This occurs independently of the permeability transition without overt changes in mitochondrial morphology. The mechanism of the release may involve formation of reactive oxygen species (ROS) and activation of calcium-independent phospholipase A(2) (iPLA(2)). Indeed, increased ROS production and activated iPLA(2) were observed prior to massive Cyt c release. Furthermore, the extent of inhibition of Cyt c release correlated with the degree of suppression of iPLA(2) by the inhibitors propranolol, dibucaine, 4-bromophenacyl bromide, and bromenol lactone. Consistent with a requirement for iPLA(2) in Cyt c release from brain mitochondria, synthetic liposomes composed of lipids mimicking the outer mitochondrial membrane (OMM) but lacing iPLA(2) failed to release 10 kDa fluorescent dextran (FD-10) in response to tBID plus BAX. We propose that tBID plus BAX activate ROS generation, which subsequently augments iPLA(2) activity leading to changes in the OMM that allow translocation of certain mitochondrial proteins from the intermembrane space.

p-Bromophenacyl bromide prevents cumene hydroperoxide-induced mitochondrial permeability transition by inhibiting pyridine nucleotide oxidation

Mitochondrial permeability transition is commonly characterized as a Ca2+ -dependent non-specific increase in inner membrane permeability that results in swelling of mitochondria and their de-energization. In the present study, the effect of different inhibitors of phospholipase A2--p-bromophenacyl bromide, dibucaine, and aristolochic acid--on hydroperoxide-induced permeability transitions in rat liver mitochondria was tested. p-Bromophenacyl bromide completely prevented the hydroperoxide-induced mitochondrial permeability transition while the effects of dibucaine or aristolochic acid were negligible. Organic hydroperoxides added to mitochondria undergo reduction to corresponding alcohols by mitochondrial glutathione peroxidase. This reduction occurs at the expense of GSH which, in turn, can be reduced by glutathione reductase via oxidation of mitochondrial pyridine nucleotides. The latter is considered a prerequisite step for mitochondrial permeability transition. Among all the inhibitors tested, only p-bromophenacyl bromide completely prevented hydroperoxide-induced oxidation of mitochondrial pyridine nucleotides. Interestingly, p-bromophenacyl bromide had no affect on mitochondrial glutathione peroxidase, but reacted with mitochondrial glutathione that prevented pyridine nucleotides from being oxidized. Our data suggest that p-bromophenacyl bromide prevents hydroperoxide-induced deterioration of mitochondria via interaction with glutathione rather than through inhibition of phospholipase A2.

Reproductive period affects lipid composition and quality of fresh and stored spermatozoa in Turkeys

Semen of Turkeys between 31 and 52 weeks of age was analyzed to investigate the cause of reduction in Turkey fertility at the end of the reproductive period. Sperm motility and viability, lipid concentration, fatty acid composition and lipid peroxides were evaluated on fresh spermatozoa or spermatozoa stored for 48h at 4 degrees C. Fertility of fresh semen was also evaluated. Fertility obtained with fresh semen decreased at 44-47 weeks of age. Ageing was also accompanied by a decrease in sperm viability (at 47 weeks) and later by a decrease in motility of spermatozoa (at 52 weeks). Polyunsaturated fatty acids (PUFAs) were the first lipids of fresh spermatozoa affected by age, especially n-3 and n-9 PUFAs. Changes in these PUFAs were followed by a 30% increase in lipid peroxidation at 47 and 52 weeks of age and a reduction in phospholipid content at 52 weeks. In vitro storage did not cause lipid peroxidation in sperm obtained during the first half of the reproductive period but malondialdehyde (MDA) levels significantly increased in sperm obtained during the second half of this period. In vitro storage also decreased phospholipid content of spermatozoa from 41 weeks of age, and viability and motility regardless of age. In conclusion, lipid alteration mainly originating from PUFAs peroxidation could partly explain the decrease in semen quality and fertility observed with ageing. In addition, lipid peroxidation was increased during in vitro storage of spermatozoa from older Turkeys.

Production of reactive oxygen species by spermatozoa undergoing cooling, freezing, and thawing

In the present study, we provide evidence for the production of reactive oxygen species (ROS) during cryopreservation of bovine spermatozoa. Cooling and thawing of spermatozoa cause an increase in the generation of superoxide radicals. Although nitric oxide production remains unaltered during sperm cooling from 22-4 degrees C, a sudden burst of nitric oxide radicals is observed during thawing. Increase in lipid peroxidation levels have been observed in frozen/thawed spermatozoa and appears to be associated with a reduction in sperm membrane fluidity as detected by spin labeling studies. The data presented provide strong evidence that oxygen free radicals are produced during freezing and thawing of bovine spermatozoa and suggest that these reactive oxygen species may be a cause for the decrease in sperm function following cryopreservation. Mol. Reprod. Dev. 59: 451-458, 2001.

Phospholipase A(2)s and lipid peroxidation

Lipid peroxidation of membrane phospholipids can proceed both enzymatically via the mammalian 15-lipoxygenase-1 or the NADPH-cytochrome P-450 reductase system and non-enzymatically. In some cells, such as reticulocytes, this process is biologically programmed, whereas in the majority of biological systems lipid peroxidation is a deleterious process that has to be repaired via a deacylation-reacylation cycle of phospholipid metabolism. Several reports in the literature pinpoint a stimulation by lipid peroxidation of the activity of secretory phospholipase A(2)s (mainly pancreatic and snake venom enzymes) which was originally interpreted as a repair function. However, recent experiments from our laboratory have demonstrated that in mixtures of lipoxygenated and native phospholipids the former are not preferably cleaved by either secretory or cytosolic phospholipase A(2)s. We propose that the platelet activating factor (PAF) acetylhydrolases of type II, which cleave preferentially peroxidised or lipoxygenated phospholipids, are competent for the phospholipid repair, irrespective of their role in PAF metabolism. A corresponding role of Ca(2+)-independent phospholipase A(2), which has been proposed to be involved in phospholipid remodelling in biomembranes, has not been addressed so far. Direct and indirect 15-lipoxygenation of phospholipids in biomembranes modulates cell signalling by several ways. The stimulation of phospholipase A(2)-mediated arachidonic acid release may constitute an alternative route of the arachidonic acid cascade. Thus, 15-lipoxygenase-mediated oxygenation of membrane phospholipids and its interaction with phospholipase A(2)s may play a crucial role in the pathogenesis of diseases, such as bronchial asthma and atherosclerosis.

Sho-saiko-to: Japanese herbal medicine for protection against hepatic fibrosis and carcinoma

Herbal medicines, which have been used in China for thousands of years, are now being manufactured in Japan, in standardized form in terms of quality and quantities of ingredients. The Chinese herbal medicine Sho-saiko-to is a mixture of seven herbal preparations, which is widely administered in Japan to patients with chronic hepatitis and cirrhosis. In a prospective study, this herbal medicine was found to play a chemopreventive role in the development of hepatocellular carcinoma in cirrhotic patients. However, little is known about the mechanism by which Sho-saiko-to protects against hepatic fibrosis and carcinoma. Several laboratories, including ours, have clearly demonstrated the preventive and therapeutic effects of Sho-saiko-to on experimental hepatic fibrosis, as well as its inhibitory effect on the activation of hepatic stellate cells, which are the major types of collagen-producing cells. We provided evidence that Sho-saiko-to functions as a potent anti-fibrosuppressant via the inhibition of oxidative stress in hepatocytes and hepatic stellate cells and that its active components are baicalin and baicalein. In addition, Sho-saiko-to has anti-carcinogenic properties in that it inhibits chemical hepatocarcinogenesis in animals, acts as a biological response modifier and suppresses the proliferation of hepatoma cells by inducing apoptosis and arrests the cell cycle. Among the active components of Sho-saiko-to, baicalin, baicalein and saikosaponin-a have the ability to inhibit cell proliferation. It should be noted that baicalin and baicalein are flavonoids with chemical structures very similar to silybinin, which shows anti-fibrogenic activities. This may provide valuable information on the search for novel anti-fibrogenic agents.

Effect of vitamin E on the response to ischemia-reperfusion of Langendorff heart preparations from hyperthyroid rats

Hyperthyroidism has been reported to decrease heart antioxidant capacity and increase its susceptibility to in vitro oxidative stress. This may affect the heart response to ischemia-reperfusion, a condition that increases free radical production. We compared the functional recovery from in vitro ischemia-reperfusion (Langendorff) of hearts from euthyroid (E), hyperthyroid (H, ten daily intraperitoneal injections of T3, 10 microg/100g body weight), vitamin E-treated (VE, ten daily intramuscular injections, 20 mg/100g body weight) and hyperthyroid vitamin E-treated (HVE) rats. We also determined lipid peroxidation, tissue antioxidant capacity and the tissue capability to face an oxidative stress in vitro. A significant tachycardia was displayed during reperfusion following 20 min ischemia by the hyperthyroid hearts, together with a low recovery of left ventricular developed pressure (LVDP) and left ventricular dP/dt(max). When H hearts were paced at 300 beats/min, the functional recovery (LVDP and dP/dt(max)) was close to 100% and significantly higher than in E paced hearts. At the end of the ischemia-reperfusion protocol, myocardium antioxidant capacity was significantly lower, whereas lipid peroxidation and the susceptibility to in vitro oxidative stress were higher in the T3 treated (H) than in euthyroid rats. The in vitro tachycardic response, the reduction in the antioxidant capacity and the increase in lipid peroxidation were prevented by treatment of hyperthyroid rats with vitamin E (HVE). These results suggest that the tachycardic response to reperfusion following chronic T3 pretreatment was associated with the reduced capability of the heart to face oxidative stresses in hyperthyroidism.

Role of group II secretory phospholipase A2 in atherosclerosis: 2. Potential involvement of biologically active oxidized phospholipids

Secretory nonpancreatic phospholipase A2 (group II sPLA2) is induced in inflammation and present in atherosclerotic lesions. In an accompanying publication we demonstrate that transgenic mice expressing group II sPLA2 developed severe atherosclerosis. The current study was undertaken to determine whether 1 mechanism by which group II sPLA2 might contribute to the progression of inflammation and atherosclerosis is by increasing the formation of biologically active oxidized phospholipids. In vivo measurements of bioactive lipids were performed, and in vitro studies tested the hypothesis that sPLA2 can increase the accumulation of bioactive phospholipids. We have shown previously that 3 oxidized phospholipids derived from the oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (PAPC) stimulated endothelial cells to bind monocytes, a process that is known to be an important step in atherogenesis. We now show that these 3 biologically active phospholipids are significantly increased in livers of sPLA2 transgenic mice fed a high-fat diet as compared with nontransgenic littermates. We present in vitro evidence for several mechanisms by which these phospholipids may be increased in sPLA2 transgenics. These studies demonstrated that polyunsaturated free fatty acids, which are liberated by sPLA2, increased the formation of bioactive phospholipids in LDL, resulting in increased ability to stimulate monocyte-endothelial interactions. Moreover, sPLA2-treated LDL was oxidized by cocultures of human aortic endothelial cells and smooth muscle cells more efficiently than untreated LDL. Analysis by electrospray ionization-mass spectrometry revealed that the bioactive phospholipids, compared with unoxidized PAPC, were less susceptible to hydrolysis by human recombinant group II sPLA2. In addition, HDL from the transgenic mice and human HDL treated with recombinant sPLA2 in vitro failed, in the coculture system, to protect against the formation of biologically active phospholipids in LDL. This lack of protection may in part relate to the decreased levels of paraoxonase seen in the HDL isolated from the transgenic animals. Taken together, these studies show that levels of biologically active oxidized phospholipids are increased in sPLA2 transgenic mice; they also suggest that this increase may be mediated by effects of sPLA2 on both LDL and HDL.

Mechanisms by which elevated intracellular calcium induces S49 cell membranes to become susceptible to the action of secretory phospholipase A2

Exposure of S49 lymphoma cells to exogenous group IIA or V secretory phospholipase A2 (sPLA2) caused an initial release of fatty acid followed by resistance to further hydrolysis by the enzyme. This refractoriness was overcome by exposing cells to palmitoyl lysolecithin. This effect was specific in terms of lysophospholipid structure. Induction of membrane susceptibility by lysolecithin involved an increase in cytosolic calcium and was duplicated by incubating the cells with calcium ionophores such as ionomycin. Lysolecithin also activated cytosolic phospholipase A2 (cPLA2). Inhibition of this enzyme attenuated the ability of lysolecithin (but not ionomycin) to induce susceptibility to sPLA2. Lysolecithin or ionomycin caused concurrent hydrolysis of both phosphatidylethanolamine and phosphatidylcholine implying that transbilayer movement of phosphatidylethanolamine occurred upon exposure to these agents but that susceptibility is not simply due to exposure of a preferred substrate (i.e. phosphatidylethanolamine) to the enzyme. Microvesicles were apparently released from the cells upon addition of lysolecithin or ionomycin. Both these vesicles and the remnant cell membranes were susceptible to sPLA2. Together these data suggest that lysolecithin induces susceptibility through both cPLA2-dependent and -independent pathways. Whereas elevated cytosolic calcium was required for both pathways, it was sufficient only for the cPLA2-independent pathway. This cPLA2-independent pathway involved changes in cell membrane structure associated with transbilayer phospholipid migration and microvesicle release.

Effect of nitric oxide releasers on some metabolic processes of rabbit spermatozoa

The authors investigated the possible effect of nitric oxide (NO) releasers (the free radical form of nitrogen monoxide, which control some functions of many cells) on rabbit spermatozoa. A significant (P < .01) increment was found in the percentage of the acrosome reaction in rabbit spermatozoa incubated for 30-60 min in presence of the NO releasers sodium nitroprusside (SNP) and N-acetyl-S-nitroso cysteine (NACysSNO), but not with S-nitroso cysteine (CysSNO). This effect was reverted or lowered when the NO scavenger HbO2 was included in the medium. The effects of SNP and NACysSNO on acrosome reaction do not appear to be related to glucose utilization, viability, or lipid peroxidation.

Suppressive effects of estradiol on dimethylnitrosamine-induced fibrosis of the liver in rats

As a model for the analysis of the fibrosuppressive role of estradiol, hepatic fibrosis was induced in male and female rats by the administration of a single dose of dimethylnitrosamine (DMN). The fibrotic response of the male liver after DMN treatment was significantly stronger than that of the female liver. In the male DMN model, estradiol reduced hepatic mRNA for type I and III procollagens and the tissue inhibitor of metalloproteinase-1 (TIMP-1), as well as deposition of type I and III collagen protein total hepatic collagen and malondialdehyde (MDA), a product of lipid peroxidation. Concomitant administration of a neutralizing antibody against rat estradiol enhanced fibrogenesis, as judged by the same parameters. Ovariectomy in the female model had a fibrogenic effect, inducing the hepatic expression of both types of procollagen and TIMP-1; in addition, the number of alpha-smooth muscle actin (alpha-SMA)-positive cells in the liver increased; estradiol replacement was fibrosuppressive in the castrated-female model. In rat hepatic stellate cells incubated in primary culture with estradiol, cell number, type I collagen production, and alpha-SMA expression were all reduced. These findings suggest that estradiol suppressed the induction of hepatic fibrosis, and may in part underlie the more rapid progression in males of hepatic fibrosis and its complications.

Effects of Sho-saiko-to, a Japanese herbal medicine, on hepatic fibrosis in rats

It has been shown that lipid peroxidation is associated with hepatic fibrosis and stellate cell activation. Sho-saiko-to (TJ-9) is an herbal medicine, which is commonly used to treat chronic hepatitis in Japan, although the mechanism by which TJ-9 protects against hepatic fibrosis is not known. As a result, we assayed the preventive and therapeutic effects of TJ-9 on experimental hepatic fibrosis, induced in rats by dimethylnitrosamine (DMN) or pig serum (PS), and on rat stellate cells and hepatocytes in primary culture, and assessed the antioxidative activities and the active components of TJ-9. Male Wistar rats were given a single intraperitoneal injection of 40 mg/kg DMN or 0.5 mL PS twice weekly for 10 weeks. In each model, rats were fed a basal diet throughout, or the same diet, which also contained 1.5% TJ-9, for 2 weeks before treatment or for the last 2 weeks of treatment. TJ-9 suppressed the induction of hepatic fibrosis, increased hepatic retinoids, and reduced the hepatic levels of collagen and malondialdehyde (MDA), a production of lipid peroxidation. Immunohistochemical examination showed that TJ-9 reduced the deposition of type I collagen and the number of alpha-smooth muscle actin (alpha-SMA) positive-stellate cells in the liver and inhibited, not only lipid peroxidation in cultured rat hepatocytes that were undergoing oxidative stress, but also the production of type I collagen, alpha-SMA expression, cell proliferation, and oxidative burst in cultured rat stellate cells. In addition, TJ-9 inhibited Fe2+/adenosine 5'-diphosphate-induced lipid peroxidation in rat liver mitochondria in a dose-dependent manner and showed radical scavenging activity. Among the active components of TJ-9, baicalin and baicalein were found to be mainly responsible for the antioxidative activity. These findings suggest that Sho-saiko-to (TJ-9) functions as a potent antifibrosuppressant by inhibition of lipid peroxidation in hepatocytes and stellate cells in vivo.

Retinyl palmitate reduces hepatic fibrosis in rats induced by dimethylnitrosamine or pig serum

BACKGROUND/AIMS

Lipid peroxidation has been found to be associated with Ito cell activation. Ito cells are the principal collagen-producing cells and the main storage sites of retinoids. However, the relationship between retinoids and hepatic fibrosis is complex. The aim of this study was to elucidate the role of retinoids as a fibrosuppressant: the effects of retinoids on hepatic fibrosis induced in rats by dimethylnitrosamine or pig serum, as well as on rat Ito cells in primary culture, were examined in order to assess the antioxidant activity of retinoids.

METHODS

Male Wistar rats were given a single injection of 40 mg/kg dimethylnitrosamine or 0.5 ml PS twice weekly for 10 weeks. In each model, rats were treated with retinyl palmitate for 2 weeks before hepatotoxin treatments or for the last 2 weeks of the treatments. The cumulative amount of retinyl palmitate administered in each experiment was 2, 10, or 20x10(4) IU/rat.

RESULTS

Retinyl palmitate treatment before or after administration of dimethylnitrosamine or pig serum suppressed the induction of hepatic fibrosis, restored hepatic retinyl palmitate levels, prevented increases in hepatic levels of collagen and malondialdehyde, a product of lipid peroxidation, and prevented increases in deposition of type III collagen and the number of alpha-smooth muscle actin (alpha-SMA) positive-Ito cells in the liver. Retinyl palmitate supplementation resulted in a dose-dependent reduction of alpha-SMA expression and an oxidative burst in cultured Ito cells. In addition, retinyl palmitate inhibited Fe2+/adenosine 5'-diphosphate-induced lipid peroxidation in rat liver mitochondria and showed radical scavenging activity.

CONCLUSIONS

These findings suggest that retinyl palmitate may suppress the induction of hepatic fibrosis, at least in part, by the inhibition of Ito cell activation through its antioxidant activity.

15-Lipoxygenation of phospholipids may precede the sn-2 cleavage by phospholipases A2: reaction specificities of secretory and cytosolic phospholipases A2 towards native and 15-lipoxygenated arachidonoyl phospholipids

Reticulocyte-type 15-lipoxygenase is known to dioxygenate phospholipids without preceding action of phospholipases A2 (PLA2). Therefore we studied the reaction of the secretory PLA2s (sPLA2) from pancreas and snake venom, and of the human cytosolic PLA2 (cPLA2) with 1-palmitoyl-2-arachidonoyl phosphatidylcholine (PAPC) and their 15-lipoxygenated species (PAPC-OOH and PAPC-OH) either alone or as equimolar mixtures. These PLA2s cleaved PAPC-O(O)H with higher (sPLA2) or similar rates (cPLA2) as compared with native PAPC. In mixtures, however, PAPC proved to be the preferred, albeit not exclusive substrate for all three PLA2s. Thus, partial 15-lipoxygenation of phospholipids may also trigger liberation of arachidonic acid.

Preferential hydrolysis of oxidized phosphatidylcholine in cholesterol-containing phosphatidylcholine liposome by phospholipase A2

Hydrolysis of 1-palmitoyl-2-linoleoyl-phosphatidylcholine (PLPC) hydroperoxide (PLPC-OOH) in PLPC liposomal membrane by Crotalus adamanteus venom phospholipase A2 (PLA2) was studied by measuring the decay of PLPC and PLPC-OOH and the formation of linoleate and linoleate hydroperoxide. We demonstrate that PLA2 has a preference to hydrolyze PLPC-OOH over PLPC when more than 25 mole % of cholesterol is incorporated into the PLPC liposomal membrane. Similar results were obtained for PLPC hydroxide (PLPC-OH). These results suggest that cholesterol displaces the hydrophilic hydroperoxyl and hydroxyl moieties of PLPC-O(O)H to the surface interface of the liposomal membrane where they are more accessible to PLA2 hydrolysis.

Oxidants as stimulators of signal transduction

Redox (oxidation-reduction) reactions regulate signal transduction. Oxidants such as superoxide, hydrogen peroxide, hydroxyl radicals, and lipid hydroperoxides (i.e., reactive oxygen species) are now realized as signaling molecules under subtoxic conditions. Nitric oxide is also an example of a redox mediator. Reactive oxygen species induce various biological processes such as gene expression by stimulating signal transduction components such as Ca(2+)-signaling and protein phosphorylation. Various oxidants increase cytosolic Ca2+; however, the exact origin of Ca2+ is controversial. Ca2+ may be released from the endoplasmic reticulum, extracellular space, or mitochondria in response to oxidant-influence on Ca2+ pumps, channels, and transporters. Alternatively, oxidants may release Ca2+ from Ca2+ binding proteins. Various oxidants stimulate tyrosine as well as serine/threonine phosphorylation, and direct stimulation of protein kinases and inhibition of protein phosphatases by oxidants have been proposed as mechanisms. The oxidant-stimulation of the effector molecules such as phospholipase A2 as well as the activation of oxidative stress-responsive transcription factors may also depend on the oxidant-mediated activation of Ca(2+)-signaling and/or protein phosphorylation. In addition to the stimulation of signal transduction by oxidants, the observations that ligand-receptor interactions produce reactive oxygen species and that antioxidants block receptor-mediated signal transduction led to a proposal that reactive oxygen species may be second messengers for transcription factor activation, apoptosis, bone resorption, cell growth, and chemotaxis. Physiological significance of the role of biological oxidants in the regulation of signal transduction as well as the mechanisms of the oxidant-stimulation of signal transduction are discussed.

Lipid peroxidation and changes in the ubiquinone content and the respiratory chain enzymes of submitochondrial particles

The relationship between, lipid peroxidation induced by ascorbate and adenosine ADP/Fe3+, and its effect on the respiratory chain activities of beef heart submitochondrial particles has been investigated. Lipid peroxidation, measured as thiobarbituric acid reactive substance formation, resulted in an inhibition of the NADH and succinate oxidase activities. Examination of several partial reactions of the respiratory chain revealed inactivation primarily of those involving endogenous ubiquinone, i.e., NADH- and succinate-ubiquinone1 and cytochrome c reductases. Ubiquinol-cytochrome c reductase, measured with reduced ubiquinone2 as electron donor, was unaffected. The amount of NADH- or succinate-reducible cytochrome b in the presence of cyanide was strongly decreased, but could be recovered by the addition of antimycin. There occurred a substantial decrease of the ubiquinone content in the course of lipid peroxidation, with a linear relationship between this decrease and the NADH and succinate oxidase activities. The results are consistent with the conclusion that the ubiquinone pool undergoes an oxidative modification during lipid peroxidation, to a form that can no longer function as a component of the respiratory chain. Lipid peroxidation also led to a partial inhibition of the succinate dehydrogenase and cytochrome c oxidase activities and a minor decrease of the cytochrome c and cytochrome a contents. Reduction of endogenous ubiquinone prevented lipid peroxidation as well as the concomitant modification of ubiquinone and inactivation of the respiratory chain. These observations suggest that the destruction of ubiquinone through lipid peroxidation is the primary cause of inactivation of the respiratory chain, and emphasize the antioxidant role of ubiquinol in preventing these effects. The possible implications of these findings for regulation of the cellular turnover of ubiquinone by the prevailing oxidative stress are discussed.

Sterol and steryl ester regulation of phospholipase A2 from the mosquito parasite Lagenidium giganteum

Lagenidium giganteum, a facultative parasite of mosquito larvae, cannot synthesize sterols, and requires an exogenous source of these lipids in order to enter its reproductive cycle. This parasite grows vegetatively in the absence of sterols, but requires cholesterol or structurally related compounds to produce motile zoospores, which are the only stage capable of infecting mosquitoes. Sterols structurally related to cholesterol and some steryl esters inhibited the activity of L. giganteum phospholipase A2 (PLA2), an enzyme that hydrolyzes fatty acids from the sn-2 position of glycerophospholipids. Sterols that induce reproduction inhibited L. giganteum PLA2 activity, while sterols and steroids that do not support sporulation had minimal effect. Most steryl esters had no effect on enzyme activity, but cholesteryl arachidonate (CA) was a potent inhibitor of parasite PLA2. Not all enzymes partly purified using a DEAE-Sephacel column were affected by these lipids, demonstrating selective inhibition of specific enzymes. Potency was enhanced by up to several orders of magnitude if epoxy fatty acids were esterified to the cholesterol nucleus. The steryl ester pool was dynamic during morphogenesis, and the fatty acid composition of the steryl esters did not mimic total cell or membrane (glycerophospholipid) fatty acid composition as L. giganteum proceeded through its growth cycle. Synthesis of CA and monoepoxy CA by the parasite was confirmed using electrospray mass spectrometry and collision-induced dissociation. Steryl derivatives selectively inhibited PLA2 enzymes from bovine pancreas, snake venom, and human cytoplasmic 85-kDa PLA2.

Bisallylic hydroxylation and epoxidation of polyunsaturated fatty acids by cytochrome P450

Polyunsaturated fatty acids can be oxygenated by cytochrome P450 to hydroxy and epoxy fatty acids. Two major classes of hydroxy fatty acids are formed by hydroxylation of the omega-side chain and by hydroxylation of bisallylic methylene carbons. Bisallylic cytochrome P450-hydroxylases transform linoleic acid to 11-hydroxylinoleic acid, arachidonic acid to 13-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid, 10-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid and 7-hydroxyeicosa-5Z,8Z,11Z,14Z-tetraenoic acid and eicosapentaenoic acid to 16-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid, 13-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid and 10-hydroxyeicosa-5Z,8Z,11Z,14Z,17Z-pent aenoic acid as major metabolites. The bisallylic hydroxy fatty acids are chemically unstable and decompose rapidly to cis-trans conjugated hydroxy fatty acids during acidic extractive isolation. Bisallylic hydroxylase activity appears to be augmented in microsomes induced by the synthetic glucocorticoid dexamethasone and by some other agents, but the P450 gene families of these hydroxylases have yet to be determined. The fatty acid epoxides, which are formed by cytochrome P450, are chemically stable, but are hydrolyzed to diols by soluble epoxide hydrolases. Epoxidation of polyunsaturated fatty acids is a prominent pathway of metabolism in the liver and the renal cortex and epoxy-genase activity appears to be under homeostatic control in the kidney. Many arachidonate epoxygenases have been identified belonging to the CYP2C gene subfamily. Epoxygenases have also been found in the central nervous system, endocrine organs, the heart and endothelial cells. Epoxides of arachidonic acid have been found to exert pharmacological effects on many cells.