Reoxygenation injury and antioxidant protection: a tale of two paradoxes

Antioxidant therapy for infertile couples: a comprehensive review of the current status and consideration of future prospects

Oxidative stress (OS) is established as a key factor in the etiology of both male and female infertility, arising from an imbalance between reactive oxygen species (ROS) production and the endogenous antioxidant (AOX) defenses. In men, OS adversely affects sperm function by inducing DNA damage, reducing motility, significantly impairing sperm vitality through plasma membrane peroxidation and loss of membrane integrity, and ultimately compromising overall sperm quality. In women, OS is implicated in various reproductive disorders, including polycystic ovary syndrome, endometriosis, and premature ovarian failure, leading to diminished oocyte quality, disrupted folliculogenesis, and poorer reproductive outcomes. Antioxidant therapy represents a promising intervention to mitigate the harmful effects of ROS on reproductive health in additions to its easy accessibility, safety, and low cost. Despite several findings suggesting improvements in fertility potential with AOX therapy, the data remains inconclusive regarding optimal dosage and combination, duration of treatment, and the specific patient populations most likely to benefit. In this review, we discuss the role of AOXs in the management of infertile couples, focusing on their biological mechanisms, potential adverse effects, therapeutic efficacy, and clinical applications in improving reproductive outcomes in both natural conception and medically assisted reproduction. Additionally, we highlight the current practice patterns and recommendations for AOX supplementation during the course of infertility treatment. Further, we provide an overview on the limitations of the current research on the topic and insights for future studies to establish standardized AOX regimens and to assess their long-term impact on key outcomes such as live birth rates and miscarriage rates.

On 'Oxygen free radicals and iron in relation to biology and medicine: Some problems and concepts' by Barry Halliwell and John M.C.Gutteridge

This commentary describes a highly-cited paper by John Gutteridge and myself that appeared in Arch. Biochem. Biophys. It is dedicated to the memory of John Gutteridge, my frequent co-author and a lifelong friend, who sadly passed away on July 5, 2021.

Commentary for "Oxygen free radicals and iron in relation to biology and medicine: Some problems and concepts"

This commentary describes a highly-cited paper by John Gutteridge and myself that appeared in Arch. Biochem. Biophys. It is dedicated to the memory of John Gutteridge, my frequent co-author and a lifelong friend, who sadly passed away on July 5, 2021.

Physiological basis of tolerance to complete submergence in rice involves genetic factors in addition to the SUB1 gene

Recurring floods in Asia cause poor crop establishment. Yields decline drastically when plants are completely submerged for a few days. Traditional rice cultivars predominate because they have acquired moderate tolerance to flooding but they carry the penalty of inherently lower grain yields. In contrast, modern high-yielding varieties are highly susceptible to flooding. Cultivars with tolerance to complete submergence were recently developed in the background of popular varieties by transferring the submergence tolerance gene SUBMERGENCE1 (SUB1) from the highly tolerant Indian landrace FR13A. The present study evaluated three pairs of Sub1 near-isogenic lines (NILs) together with FR13A and two of its submergence-tolerant derivatives under field conditions to assess the survival and growth processes occurring during submergence and recovery that are associated with SUB1. Under control conditions, the NILs showed similar growth and biomass accumulation, indicating that SUB1 had no apparent effects. Submergence substantially decreased biomass accumulation but with greater reduction in the genotypes lacking SUB1, particularly when submergence was prolonged for 17 days. When submerged, the lines lacking SUB1 showed greater elongation and lower or negative biomass accumulation. Sub1 lines maintained higher chlorophyll concentrations during submergence and lost less non-structural carbohydrates (NSC) after submergence. This indicates that the introgression of SUB1 resulted in better regulation of NSC during submergence and that high pre-submergence NSC is not essential for the submergence tolerance conferred by SUB1. During recovery, chlorophyll degradation was faster in genotypes lacking SUB1 and any surviving plants showed poorer and delayed emergence of tillers and leaves. Sub1 lines restored new leaf and tiller production faster. During submergence, FR13A showed not only slower leaf elongation but also accumulated extra biomass and was able to recover faster than Sub1 lines. This suggests the possibility of further improvements in submergence tolerance by incorporating additional traits present in FR13A or other similar landraces.

Investigation of oxidative balance in patients with dysmenorrhea by multiple serum markers

OBJECTIVE

To investigate the level of oxidative stress in patients with dysmenorrhea by multiple serum markers including malondialdehyde (MDA), nitrotyrosine (3-NT), deoxyguanosine (8-OHdG) and superoxide dismutase (SOD).

MATERIAL AND METHODS

Fifty-eight women, aged between 20 and 34, who had had regular menses for at least six previous cycles, were involved. The women were divided into two groups. The study group consisted of 33 patients with primary dysmenorrhea, and the control group consisted of 25 healthy women.

RESULTS

Demographic characteristics of patients were similar between the two groups. The serum MDA levels were 1.32±0.46 and 0.91±0.26 nmol/mL for the dysmenorrhea and control groups, respectively (p<0.001). The differences in plasma levels of 3-NT, SOD and serum 8-OhdG were similar in both groups (p>0.05). Also, no correlation was found between the severity of dysmenorrhea and the levels of oxidative markers.

CONCLUSION

Oxidative stress is slightly aggravated in patients with dysmenorrhea.

Aspects of plant behaviour under anoxia and post-anoxia

All plants are able to survive anoxic periods, but the degree of tolerance shows large variation. The main injuries related to anoxia are eventually due to changes in energy metabolism. Low energy charge values indicate a cessation of many ATP consuming processes. Sugar starvation, lactic acid fermentation and proton release from leaky vacuoles are responsible for cell death. Long-term anoxia tolerance is dependent on storage products in the vicinity of sinks, on an adequate control of glycolysis, synthesis of essential proteins, and stability of membranes and organelles. However, no fundamental differences between the metabolic pathways of tolerant and non-tolerant tissues are known. It is rather a question of minor changes and the regulation of anaerobic metabolism.

Re-exposure of anoxic tissues to air may even be more detrimental than anoxia itself. These injuries are mainly due to enhanced radical generation. Lipid peroxidation processes lead to membrane damage, disintegration, and leakage of solutes. Under natural conditions plants are equipped with radical-detoxifying systems (SOD, peroxidases and antioxidants). Natural detoxifying systems can be reduced in non-adapted plants under anoxia and they become more sensitive to post-anoxic damage. In addition, the rapid conversion of ethanol to extremely toxic acetaldehyde seems to be a cause of tissue injury and death.

Role of the interaction between puerarin and the erythrocyte membrane in puerarin-induced hemolysis

Adverse drug reactions (ADR), especially intravenous hemolysis, have largely limited the application of puerarin injections in clinics. This study investigated the underlying mechanisms of puerarin-induced hemolysis. Our results show that puerarin induced concentration-dependent and time-dependent hemolysis when human erythrocytes were incubated in saline solution with more than 2mM puerarin for over 2h. However, incubation in PBS or addition of 1mM of lidocaine to the saline solution completely abolished the hemolysis. Providing materials that could start ATP synthesis did not reverse the hemolysis, and puerarin did not affect Na(+)-K(+)-ATPase activity. In addition, puerarin (0.1-2mM) did not cause calcium influx or exhibited pro-oxidant activity in erythrocytes. Puerarin exhibited different influences on the membrane microviscosity of erythrocytes in saline and PBS. Moreover, 1mM lidocaine inhibited 8mM puerarin-induced reduction of membrane microviscosity in saline solution. SDS-PAGE analysis of membrane proteins revealed that 2mM puerarin treatment induced the appearance of several new protein bands but attenuated the expression of protein bands 2.1, 3, 4.1, 4.2 and 5. These results suggest that high concentrations of puerarin-induced hemolysis were associated with the changes of membrane lipids and of the composition of erythrocytes membrane proteins but not with ATP depletion, pro-oxidation and calcium influx. These changes could be related to the intercalation of amphiphilic puerarin at high concentration into the erythrocyte membrane in certain media, resulting in membrane disorganization and, eventually, cytolysis. Hence, in clinics, determining the optimal dose of puerarin is critical to avoid overdosing and ADR.

Assessment of reference ranges for blood Cu, Mn, Se and Zn in a selected Italian population

The reference ranges for blood Cu, Mn, Se and Zn of 215 adult subjects non-occupationally exposed and living in the Nuoro province (Sardinia, insular Italy) were assessed. Metals were determined by sector field inductively coupled plasma mass spectrometry after microwave-assisted acid digestion of blood. The blood reference ranges estimated as P5-P95 percentiles (geometric mean, GM) were 776-1495μg/L (1036μg/L) for Cu; 4.73-17.0μg/L (8.91μg/L) for Mn; 106-185μg/L (140μg/L) for Se and 4686-8585μg/L (6418μg/L) for Zn. These results were then stratified for sex, age, alcohol consumption, smoking habit and living area. The GM value of Cu was significantly higher in females (1127μg/L) than in males (957μg/L). Age, alcohol intake, smoking habit and residential area did not influence blood Cu. The GM of Mn was significantly higher in females (9.98μg/L) respect to males (8.01μg/L) and in drinkers (9.67μg/L) compared to non-drinkers (8.38μg/L). The other variables did not change the Mn data. Selenium concentrations did not differ significantly as a function of individuals factors. With reference to Zn, males had GM of 6804μg/L and females of 6031μg/L, and more blood Zn was found in subjects consuming alcohol (6618μg/L) respect to abstainers (6155μg/L). In addition, blood Zn was not affected by age, smoking habit and place of living.

Oxidative stress parameters in erythrocytes of post-reperfused patients with myocardial infarction

The effect of reperfusion of patients with myocardial infarction on the levels of some anti-oxidant enzymes, total thiols, malondialdehyde formation in erythrocytes and plasma ascorbate levels have been investigated. Significantly decreased activities of catalase and superoxide dismutase and decreased levels of total thiols in RBC's and ascorbic acid in plasma suggest that reperfusion of the infarcted myocardium leads to oxidative stress conditions wherein anti-oxidant mechanisms become less effective in coping with the oxidative insult. This view is further supported by the observation that in the post reperfused patients there is a highly significant enhancement in the levels of malondialdehyde.

Evaluation of antioxidant deficit in schizophrenia

AIM

Oxidative stress is a state in which there is disequilibrium between pro-oxidant processes and the antioxidant defense system in favor of the former and occurs as a consequence of increased production of free radicals or when the antioxidant defense system is inefficient or a combination of both events. A disturbance in the antioxidant defense system, including antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GSHPx), due to free radical-induced oxidative injury has also been implicated in various neuropsychiatric disorders. Hence the role of these antioxidant enzymes and the changes in their level in blood and correlation with oxidative stress and the overall mechanism of defense were studied in a common psychiatric illness, schizophrenia.

MATERIALS AND METHODS

Fifty subjects of either sex ranging in age from 18 to 60 years, divided into two age groups (< 40 years and >40 years), diagnosed for schizophrenia; and 50 age- and sex-matched normal subjects as controls were included in the study. Blood samples were collected for the determination of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GSHPx), and reduced glutathione (GSH).

RESULTS

Significantly lower levels of the two antioxidant enzymes were found in schizophrenics compared to normal controls, with an increased oxidative stress as indicated by high blood MDA levels. The condition worsened with advancing age, smoking, among literate masses, and in chronic schizophrenics; whereas gender did not show any effect.

CONCLUSION

It can be concluded that an imbalance in the antioxidant defense system, along with enzymatic antioxidants, occurs in schizophrenia due to the persistent oxidative stress. Modern life style perhaps also contributes to the condition.

Zinc, antioxidant systems and metallothionein in metal mediated-apoptosis: biochemical and cytochemical aspects

Copper, zinc and iron are essential metals for different physiological functions, even though their excess can lead to biological damage. This review provides a background of toxicity related to copper, iron and zinc excess, biological mechanisms of their homeostasis and their respective roles in the apoptotic process. The antioxidant action of metallothionein has been highlighted by summarizing the most important findings that confirm the role of zinc in cellular protection in relation to metallothionein expression and apoptotic processes. In particular, we show that a complex and efficient antioxidant system, the induction of metallothionein and the direct action of zinc have protective roles against oxidative damage and the resulting apoptosis induced by metals with redox proprieties. In addition, to emphasize the protective effects of Zn and Zn-MT in Cu and Fe-mediated oxidative stress-dependent apoptosis, some aspects of apoptotic cell death are shown. The most widely used cytochemical techniques also have been examined in order to critically evaluate the available data from a methodological point of view. The observations on the role of Zn and MT could potentially develop new applications for this metal and MT in biomedical research.

Mismatch recovery of regional cerebral blood flow and brain temperature during reperfusion after prolonged brain ischemia in gerbils

BACKGROUND

Recovery of cerebral reperfusion after stroke or cardiac arrest can take a long time. We aimed to identify differences in the postischemic recovery of physiologic parameters between short and prolonged brain ischemia.

METHODS

Eighteen Mongolian gerbils were assigned to one of three groups: 5-minute (G5), 15-minute (G15), or 30-minute (G30) ischemia. With the use of our original microspectroscopy system, global ischemic reperfusion was performed. We measured changes in regional cerebral blood flow (r-CBF), microvessel diameter, and brain temperature (BrT) simultaneously. We also monitored somatosensory evoked potentials (SEPs) to evaluate electrophysiologic response.

RESULTS

Both G5 and G15 showed concurrent recovery of r-CBF and BrT with hyperemia and hyperthermia, respectively, 10 to 15 minutes after reperfusion. The increase in BrT was <1 degree C and recovered to baseline within 60 minutes after reperfusion. In G30, recovery of r-CBF was significantly delayed relative to that of BrT. The increase in BrT was >2 degrees C, peaking approximately 15 minutes after reperfusion, and then maintained increases of >1 degree C for 120 minutes. SEPs in G5 and G15 showed concomitant recovery with that of r-CBF, whereas SEP recovery in G30 was delayed relative to that of r-CBF, eventually disappearing. All except one of the G30 gerbils died within 24 hours, but all in G5 and G15 survived.

CONCLUSIONS

These results suggest that mismatch recovery of r-CBF and BrT after prolonged ischemia initiates metabolic derangement in brain tissue, leading to the electrochemical dysfunction and mortality.

Thiol-based mechanisms of the thioredoxin and glutaredoxin systems: implications for diseases in the cardiovascular system

Reactive oxygen species (ROS) and the cellular thiol redox state are crucial mediators of multiple cell processes like growth, differentiation, and apoptosis. Excessive ROS production or oxidative stress is associated with several diseases, including cardiovascular disorders like ischemia-reperfusion. To prevent ROS-induced disorders, the heart is equipped with effective antioxidant systems. Key players in defense against oxidative stress are members of the thioredoxin-fold family of proteins. Of these, thioredoxins and glutaredoxins maintain a reduced intracellular redox state in mammalian cells by the reduction of protein thiols. The reversible oxidation of Cys-Gly-Pro-Cys or Cys-Pro(Ser)-Tyr-Cys active site cysteine residues is used in reversible electron transport. Thioredoxins and glutaredoxins belong to corresponding systems consisting of NADPH, thioredoxin reductase, and thioredoxin or NADPH, glutathione reductase, glutathione, and glutaredoxin, respectively. Thioredoxin as well as glutaredoxin activities appear to be very important for the progression and severity of several cardiovascular disorders. These proteins function not only as antioxidants, they inhibit or activate apoptotic signaling molecules like apoptosis signal-regulating kinase 1 and Ras or transcription factors like NF-kappaB. Thioredoxin activity is regulated by the endogenous inhibitor thioredoxin-binding protein 2 (TBP-2), indicating an important role of the balance between thioredoxin and TBP-2 levels in cardiovascular diseases. In this review, we will summarize cardioprotective effects of endogenous thioredoxin and glutaredoxin systems as well as the high potential in clinical applications of exogenously applied thioredoxin or glutaredoxin or the induction of endogenous thioredoxin and glutaredoxin systems.

Mitochondrial involvement in transhemispheric diaschisis following hypoxia-ischemia: Clomethiazole-mediated amelioration

Mitochondria play a central role in both the physiological and pathophysiological regulation of cell survival/death. Increasing evidence places mitochondrial dysfunction at the center of many neuropathological conditions. The present study investigates the extent of mitochondrial dysfunction in cortical, hippocampal and cerebellar tissues in a rat model of hypoxia-ischemia (HI). We hypothesized that; mitochondrial dysfunction in situ may be prevented by treatment with clomethiazole (CMZ), a GABA(A) receptor agonist. Assessment of mitochondrial FAD-linked respiration at both 1- and 3-day post-HI revealed a marked decrease in activity from ipsilateral cortical and hippocampal regions (P<0.001). In addition, small changes were seen in contralateral cortical and hippocampal tissues as well as in the cerebellum at 3-days (P<0.05). Assessment of the mitochondrial electron transport chain (complexes I-V), and mitochondrial markers of integrity (citrate synthase) and oxidative stress (aconitase) confirmed mitochondrial impairment in ipsilateral regions following HI. Complexes I, II-III, V and citrate synthase were also impaired in contralateral regions and cerebellum 3-days post-HI. Treatment with CMZ (414 mg/kg/day via minipumps) provided marked protection to all aspects of neuronal tissue assessed. Circulating cytokine (interleukin [IL]-1alpha, IL-1beta, tumor necrosis factor [TNF]-alpha, granulocyte macrophage colony-stimulating factor [GM-CSF], IL-4 and IL-10) levels were also assessed in these animals 3-days post-HI. Plasma IL-1alpha, IL-1beta, TNF-alpha and GM-CSF levels were significantly increased post-HI. Treatment with CMZ ameliorated the increases in IL-1alpha, IL-1beta, TNF-alpha and GM-CSF levels while increasing plasma IL-4 and IL-10 levels. This study provides evidence of the extent of mitochondrial damage following an HI-insult. In addition, we have shown that protection afforded by CMZ extends to preservation of mitochondrial function and integrity via anti-inflammatory mediated pathways.

The role of antioxidants in models of inflammation: Emphasis on l-arginine and arachidonic acid metabolism

Inflammatory processes are made up of a multitude of complex cascades. Under physiological conditions these processes aid in tissue repair. However, under pathophysiological environments, such as wound healing and hypoxia-ischaemia (HI), inflammatory mediators become imbalanced, resulting in tissue destruction. This review addresses the changes in reactive oxygen species (ROS), L-arginine and arachidonic acid metabolism in wound healing and HI and subsequent treatments with promising anti-oxidants. Even though these models may appear divergent, anti-oxidant treatments are nevertheless still having favourable effects. On the basis of recent findings, it is apparent that protection with anti-oxidants is not solely attributed to scavenging of ROS. In addition, the actions of anti-oxidants must be considered in light of the inflammatory process being assessed. To this end, there does not appear to be any universally applicable single mechanism to explain the actions of anti-oxidants.

Lipid peroxidation in diabetes mellitus

There is considerable evidence that hyperglycemia represents the main cause of complications of diabetes mellitus (DM), and oxidative stress resulting from increased generation of reactive oxygen species plays a crucial role in their pathogenesis. In fact, in the absence of an appropriate response from endogenous antioxidant mechanisms, the redox imbalance causes the activation of stress-sensitive intracellular signaling pathways. The latter play a key role in the development of late complications of DM, as well as in mediating insulin resistance (i.e., resistance to insulin-mediated glucose uptake by some cells) and impaired insulin secretion. This review, focused on lipid peroxidation in DM, will examine the mechanisms and clinical readouts of oxidative stress in this setting, the relationship between lipid peroxidation and antioxidant status in type 1 and type 2 DM, the effects of hyperglycemia and metabolic control on in vivo markers of lipid peroxidation (i.e., isoprostanes), and the association between isoprostane formation and platelet activation. Finally, possible targets of antioxidant therapy for diabetic vascular complications will be discussed.

Neuroprotective effects of (-)-epigallocatechin gallate following hypoxia-ischemia-induced brain damage: novel mechanisms of action

(-)-Epigallocatechin gallate (EGCG) is a potent antioxidant that is neuroprotective against ischemia-induced brain damage. However, the neuroprotective effects and possible mechanisms of action of EGCG after hypoxia-ischemia (HI) have not been investigated. Therefore, we used a modified "Levine" model of HI to determine the effects of EGCG. Wistar rats were treated with either 0.9% saline or 50 mg/kg EGCG daily for 1 day and 1 h before HI induction and for a further 2 days post-HI. At 26-days-old, both groups underwent permanent left common carotid artery occlusion and exposure to 8% oxygen/92% nitrogen atmosphere for 1 h. Histological assessment showed that EGCG significantly reduced infarct volume (38.0+/-16.4 mm(3)) in comparison to HI + saline (99.6+/-15.6 mm(3)). In addition, EGCG significantly reduced total (622.6+/-85.8 pmol L-[(3)H]citrulline/30 min/mg protein) and inducible nitric oxide synthase (iNOS) activity (143.2+/-77.3 pmol L-[(3)H]citrulline/30 min/mg protein) in comparison to HI+saline controls (996.6+/-113.6 and 329.7+/-59.6 pmol L-[(3)H]citrulline/30 min/mg protein for total NOS and iNOS activity, respectively). Western blot analysis demonstrated that iNOS protein expression was also reduced. In contrast, EGCG significantly increased endothelial and neuronal NOS protein expression compared with HI controls. EGCG also significantly preserved mitochondrial energetics (complex I-V) and citrate synthase activity. This study demonstrates that the neuroprotective effects of EGCG are, in part, due to modulation of NOS isoforms and preservation of mitochondrial complex activity and integrity. We therefore conclude that the in vivo neuroprotective effects of EGCG are not exclusively due to its antioxidant effects but involve more complex signal transduction mechanisms.

Neuroprotective effects of spermine following hypoxia‐ischemia‐induced brain damage: A mechanistic study

The polyamines (spermine, putrescine, and spermidine) can have neurotoxic or neuroprotective properties in models of neurodegeneration. However, assessment in a model of hypoxia-ischemia (HI) has not been defined. Furthermore, the putative mechanisms of neuroprotection have not been elucidated. Therefore, the present study examined the effects of the polyamines in a rat pup model of HI and determined effects on key enzymes involved in inflammation, namely, nitric oxide synthase (NOS) and arginase. In addition, effects on mitochondrial function were investigated. The polyamines or saline were administered i.p. at 10mg/kg/day for 6 days post-HI. Histological assessment 7 days post-HI revealed that only spermine significantly (P<0.01) reduced infarct size from 46.14 +/- 10.4 mm3 (HI + saline) to 4.9 +/- 2.7 mm3. NOS activity was significantly increased following spermine treatment in the left (ligated) hemisphere compared with nonintervention controls (P<0.01) and HI + saline (P<0.05). In contrast, spermine decreased arginase activity compared with HI + saline but was still significantly elevated in comparison to nonintervention controls (P<0.01). Assessment of mitochondrial function in the HI + saline group, revealed significant and extensive damage to complex-I (P<0.01) and IV (P<0.001) and loss of citrate synthase activity (P<0.05). No effect on complex II-III was observed. Spermine treatment significantly prevented all these effects. This study has therefore confirmed the neuroprotective effects of spermine in vivo. However, for the first time, we have shown that this effect may, in part, be due to increased NOS activity and preservation of mitochondrial function.

The role of reperfusion injury in photodynamic therapy with 5-aminolaevulinic acid--a study on normal rat colon

Reperfusion injury can occur when blood flow is restored after a transient period of ischaemia. The resulting cascade of reactive oxygen species damages tissue. This mechanism may contribute to the tissue damage produced by 5-aminolaevulinic acid-induced photodynamic therapy, if this treatment temporarily depletes oxygen in an area that is subsequently reoxygenated. This was investigated in the normal colon of female Wistar rats. All animals received 200 mg kg(-1) 5-aminolaevulinic acid intravenously 2 h prior to 25 J (100 mW) of 628 nm light, which was delivered continuously or fractionated (5 J/150 second dark interval/20 J). Animals were recovered following surgery, killed 3 days later and the photodynamic therapy lesion measured macroscopically. The effects of reperfusion injury were removed from the experiments either through the administration of free radical scavengers (superoxide dismutase (10 mg kg(-1)) and catalase (7.5 mg kg(-1)) in combination) or allopurinol (an inhibitor of xanthine oxidase (50 mg kg(-1))). Prior administration of the free radical scavengers and allopurinol abolished the macroscopic damage produced by 5-aminolaevulinic acid photodynamic therapy in this model, regardless of the light regime employed. As the specific inhibitor of xanthine oxidase (allopurinol) protected against photodynamic therapy damage, it is concluded that reperfusion injury is involved in the mechanism of photodynamic therapy in the rat colon.

Zinc in the retina

Experimental evidence exists to suggest that zinc can have positive and negative effects on the physiology of cells depending on the "local" concentration, localisation (extracellular vs. intracellular) and/or state (bound vs. free). The retina contains particularly high amounts of zinc suggesting a pivotal role in the tissue. There is also suggestive evidence that zinc deficiency in humans may result in abnormal dark adaptation and/or age-related macular degeneration. The purpose of this article is to provide an overview of various proposed functions for zinc, particularly in the retina. Endogenous chelatable zinc in the retina is localised mainly to the photoreceptors and retinal pigment epithelial cells. Moreover, the zinc localisation in the photoreceptors varies in dark and light, suggesting a role for zinc in a light-regulated process. Some zinc is also located to other areas of the retina but clearly defined zinc-enriched neurones could not be identified as has been shown to occur in certain areas of the brain. Neurones post-synaptic to zinc-enriched neurones in the brain have been suggested to be particularly vulnerable in ischaemia. The role of zinc in retinal ischaemia has been investigated to determine how it is involved in the process. It would appear that when zinc is administered in low concentrations it generally has a positive effect on an insulted retina as in ischaemia. However, higher concentrations of zinc exacerbates the influence of the insult and also acts as a toxin. Use of zinc supplements in diet must, therefore, be taken with caution.

Mitochondrial cytochrome c release and caspase-3-like protease activation during indomethacin-induced apoptosis in rat gastric mucosal cells

Indomethacin (IND), a nonsteroidal anti-inflammatory drug, has been known to cause gastric mucosal injury as a side effect. Using a rat gastric mucosal cell line, RGM1, we determined whether apoptosis is involved in IND-mediated gastropathy, and whether caspase activation and mitochondrial cytochrome c release play an important role in producing apoptosis of IND-treated RGM1 cells in the presence of serum. IND caused caspase-3-like protease activation followed by apoptosis in a dose- and time-dependent manner. Caspase-1-like protease activity did not change during IND-induced apoptosis. IND also increased mitochondrial cytochrome c release in a time-dependent fashion. Mitochondrial cytochrome c efflux occurred just before or at the same time as caspase-3-like protease activation, and preceded the increase in apoptotic cell numbers. Z-VAD-FMK, a caspase inhibitor, inhibited both the increase in caspase-3-like protease activity and apoptosis in IND-treated RGM1 cells but did not affect caspase-1-like protease activity or mitochondrial cytochrome c release. These observations suggest that the apoptosis of gastric mucosal cells could be involved in IND-induced gastropathy, that cytochrome c is released from mitochondria into the cytosol during the early phase of IND-mediated apoptosis, and that subsequent activation of caspase-3-like protease, but not caspase-1-like protease, is required for the execution of apoptosis.

The mitochondrial permeability transition pore and its role in cell death

This article reviews the involvement of the mitochondrial permeability transition pore in necrotic and apoptotic cell death. The pore is formed from a complex of the voltage-dependent anion channel (VDAC), the adenine nucleotide translocase and cyclophilin-D (CyP-D) at contact sites between the mitochondrial outer and inner membranes. In vitro, under pseudopathological conditions of oxidative stress, relatively high Ca2+ and low ATP, the complex flickers into an open-pore state allowing free diffusion of low-Mr solutes across the inner membrane. These conditions correspond to those that unfold during tissue ischaemia and reperfusion, suggesting that pore opening may be an important factor in the pathogenesis of necrotic cell death following ischaemia/reperfusion. Evidence that the pore does open during ischaemia/reperfusion is discussed. There are also strong indications that the VDAC-adenine nucleotide translocase-CyP-D complex can recruit a number of other proteins, including Bax, and that the complex is utilized in some capacity during apoptosis. The apoptotic pathway is amplified by the release of apoptogenic proteins from the mitochondrial intermembrane space, including cytochrome c, apoptosis-inducing factor and some procaspases. Current evidence that the pore complex is involved in outer-membrane rupture and release of these proteins during programmed cell death is reviewed, along with indications that transient pore opening may provoke 'accidental' apoptosis.

Oxidative stress and haematological changes in immobilized rats

Immobilization stress induces formation of reactive oxygen species (ROS) and leads to the oxidative injury in various tissues. In this study, the effects of immobilization stress on peripheral blood cells distribution, plasma level of thiobarbituric acid reactive substances (TBARS), and activities of antioxidant enzymes in erythrocytes were investigated in male Fischer rats. A significant increase in plasma TBARS was observed during and after the stress. Dramatic increases of neutrophils and monocytes imply that ROS formation resulted from their activation. Furthermore, the antioxidant activities of catalase and superoxide dismutase (SOD) in erythrocytes were dramatically increased during and after the stress, while a large fall in erythrocyte number was observed. These findings suggest that the activation of immune cells can be a source of the immobilization-induced ROS production, and that antioxidant enzymes in erythrocytes play an important role in preventing the ROS-induced injuries.

Nutritional regulation of glutathione in stroke

In contrast to cardiovascular disease, the impact of nutritional status on the prevention and outcome of stroke has received limited investigation. We present a mechanism based on animal studies, clinical data, and epidemiological data by which protein-energy status in the acute stroke and immediate postinjury periods may affect outcome by regulating reduced glutathione (GSH), a key component of antioxidant defense. As cysteine is the limiting amino acid for GSH synthesis, the GSH concentration of a number of nonneural tissues has been shown to be decreased by fasting, low-protein diets, or diets limiting in sulfur amino acids. The mechanism may also be relevant in brain since GSH in some brain regions is responsive to dietary sulfur amino acid supply and to the pro-cysteine drug, L-2-oxothiazolidine-4-carboxylate. The latter is an intracellular cysteine delivery system used to overcome the toxicity associated with cysteine supplementation. These findings may provide the mechanism to explain both the inverse correlation between dietary protein and stroke mortality and the documented association between suboptimal protein-energy status and diminished functional status following a stroke. Future investigations should examine the role of nutritional intervention in neuroprotective strategies aimed at improving stroke outcome. Pharmacological interventions such as L-2-oxothiazolidine-4-carboxylate should be investigated in animal models of stroke, as well as the impact of nutritional status on the response to these agents. Finally, micronutrient deficiencies that may accompany protein-energy malnutrition, such as selenium, should also be investigated for their role in antioxidant defense in cerebral ischemia.

Measurements of plasma glutaredoxin and thioredoxin in healthy volunteers and during open-heart surgery

Thioredoxin (Trx) and glutaredoxin (Grx) are both multifunctional redox-active proteins. In this study, Grx was identified in human plasma by immunoaffinity purification. The affinity-purified material from human plasma displayed a band of 12 kDa identical to recombinant human Grx by Western blotting and its glutathione-dependent reducing activity of beta-hydroxyethyl disulfide. Competitive enzyme-linked immunosorbent assays (ELISA) showed that plasma levels (mean +/- SD) of Grx and Trx in healthy volunteers (n = 41) were 456 +/- 284 ng/ml and 28.5 +/- 12.6 ng/ml, respectively. In cardiac surgical patients (n = 17), plasma Grx levels did not significantly change during cardiopulmonary bypass (CPB). In contrast, Trx levels in arterial plasma measured by sandwich ELISA and corrected for hemolysis were elevated during reperfusion of the postcardioplegic heart (p = .0001 at maximum), whereas by competitive ELISA Trx increased during surgical preparation for CPB, but decreased during CPB. When recombinant Trx was oxidized, immunoreactive Trx levels were decreased by competitive ELISA but not changed by sandwich ELISA. These results suggest that oxidized Trx is released into plasma during CPB. There was no significant difference in Trx and Grx levels between arterial and intracoronarial plasma samples, indicating no specific release by the post-cardioplegic heart. Trx and Grx may be important components in the plasma defense against oxidative stress.

Antioxidant systems and anoxia tolerance in a freshwater turtle Trachemys scripta elegans

The effects of anoxic submergence (20 h at 5 degrees C) and subsequent 24 h aerobic recovery on the antioxidant systems of six organs were examined in freshwater turtles, Trachemys scripta elegans. Both xanthine oxidase and xanthine dehydrogenase were detected in turtle tissues with xanthine oxidase composing 36-75% of the total activity. Turtle organs displayed high constitutive activities of catalase (CAT), superoxide dismutase (SOD), and alkyl hydroperoxide reductase (AHR). Measurements of lipid peroxidation damage products (conjugated dienes, lipid hydroperoxides, thiobarbituric acid reactive substances) showed minimal changes during anoxia or recovery suggesting that natural anoxic-aerobic transitions occur without the free radical damage that is seen during ischemia-reperfusion in mammals. Anoxia exposure led to selected decreases in enzyme activities in organs, consistent with a reduced potential for oxidative damage during anoxia: SOD decreased in liver by 30%, CAT decreased in heart by 31%, CAT and total glutathione peroxidase (GPOX) decreased in kidney (by 68 and 41%), and CAT and SOD decreased in brain (by 80 and 15%). AHR, however, increased 2 and 3.5 fold during anoxia in heart and kidney respectively. Most anoxia-induced changes were reversed during aerobic recovery although brain enzyme activities remained suppressed. Some specific changes occurred during the recovery period: SOD increased from controls in heart by 45%, AHR increased to 200 and 168% of control values in red and white muscle respectively, and total GPOX decreased from controls in heart and white muscle by 75 and 77% respectively. The results show that biochemical adaptation for natural anoxia tolerance in turtles includes well-developed antioxidant defenses that minimize or prevent damage by reactive oxygen species during the reoxygenation of organs after anoxic submergence.

Reduced levels of antioxidants in brains of apolipoprotein E-deficient mice following closed head injury

Recent animal model studies using apolipoprotein E (apoE)-deficient (knockout) mice revealed that these mice have memory deficits and neurochemical derangements and that they recover from closed head injury less adequately than control mice. In the present study, we examined the possibility that the diminished recovery of apoE-deficient mice from head injury is related to a reduction in their ability to counteract oxidative damage. Measurements of reducing agents by cyclic voltammetry revealed that cortical homogenates of apoE-deficient and control mice contain similar levels of these compounds whose oxidation potentials for the two groups of mice are at 400 +/- 40 mV and 900 +/- 50 mV. The responses of the apoE-deficient and control groups to closed head injury were both biphasic and were composed of initial reductions followed by subsequent increases in the levels of reducing antioxidant equivalents. However, the two groups differed markedly in the magnitude of their response. This difference was most pronounced with the 400-mV reducing compounds, such that at 4 h after injury their levels in injured control mice increased over twofold relative to the noninjured control mice, whereas the corresponding anodic current of the apoE-deficient mice recovered only to its original level and did not increase further even by 24 h after injury. In vitro studies using recombinant apoE allele E3 and beta very low density lipoprotein revealed that this lipoprotein can delay Cu(2+)-induced lipid peroxidation. This suggests that the inability of the apoE-deficient mice to respond to brain injury by a surge in brain reducing compounds may be related, at least in part to direct antioxidant activity of apoE.

Metabolic adaptations supporting anoxia tolerance in reptiles: recent advances

Animal survival during severe hypoxia and/or anoxia is enhanced by a variety of biochemical adaptations including adaptations of fermentative pathways of energy production and, most importantly, the ability to sharply reduce metabolic rate by 5-20 fold and enter a hypometabolic state. The biochemical regulation of metabolic arrest is proving to have common molecular principles that extend across phylogenetic lines and that are conserved in different types of arrested states (not only anaerobiosis but also estivation, hibernation, etc.). Our new studies with anoxia-tolerant vertebrates have identified a variety of regulatory mechanisms involved in both metabolic rate depression and in the aerobic recovery process using as models the freshwater turtle Trachemys scripta elegans and garter snakes Thamnophis sirtalis parietalis. Mechanisms include: 1) post-translational modification of cellular and functional proteins by reversible phosphorylation and changes in protein kinase (PKA, PKC) and/or phosphatase activities to regulate this, 2) reversible enzyme binding associations with subcellular structural elements, 3) differential gene expression and/or mRNA translation producing new mRNA variants and new protein products, 4) changes in protease activity, particularly the multicatalytic proteinase complex, and 5) both constitutive and anoxia-induced modifications to cellular antioxidant systems to deal with oxidative stress during the anoxic-aerobic transition of recovery.

Commentary: mannitol: molecule magnifique or a case of radical misinterpretation?

Reactive oxygen species are constantly formed in biological systems. When production exceeds antioxidant protection, oxidative stress leading to molecular damage occurs. The most reactive ROS in biological systems is the hydroxyl radical which damages adjacent molecules at diffusion controlled rates. The possibility of preventing such chemistry inside cells with therapeutic doses of mannitol at present seem remote.

Role of hydroxyl radical in the stimulation of arachidonic acid release caused by H2O2 in pulmonary smooth muscle cells: protective effect of anion channel blocker

We sought to investigate role of hydroxyl radical (OH.) in H2O2 caused stimulation of arachidonic acid (AA) release from rabbit pulmonary arterial smooth muscle cells, and to ascertain protective effect of the anion channel blocker DIDS in this phenomenon. Exposure of the smooth muscle cells to the oxidant H2O2 (1mM) stimulates iron release and enhances AA liberation from the cells. Pretreatment of the cells with either deferoxamine (DFO) or dimethyl thiourea (DMTU) markedly reduces AA release and prevents OH. production without causing any appreciable reduction of iron release caused by H2O2. Simultaneous treatment of either DFO or DMTU with H2O2 significantly reduces AA release, and also prevents OH. production without causing any significant reduction of iron release. In contrast, addition of either DFO or DMTU even 2 min after exposure of the cells to H2O2 does not cause any significant reduction of AA release, OH. production and iron release. Pretreatment of the cells with DIDS markedly reduces AA release caused by H2O2 without producing any discernible reduction of iron release, and OH. production.

Immobilization stress-induced antioxidant defense changes in rat plasma: effect of treatment with reduced glutathione

1. We examined immobilization stress-induced antioxidant defense changes in rat plasma and observed the antioxidant effect of reduced glutathione (GSH) administration on these changes. 2. Immobilization stress induced severe bleeding in the stomach and a significant increase in plasma levels of thiobarbituric acid receives substances (TBARS). 3. Immobilization stress induced a significant decrease in plasma iron-binding, iron-oxidizing protections and radical scavenging activity. 4. Plasma levels of ascorbic acid, ascorbyl radical and superoxide dismutase activity remained unchanged following immobilization stress. 5. Treatment with GSH showed a significant protective effect on stomach bleeding, on the increase in plasma TBARS, and on the decrease of iron-binding, iron-oxidizing protection and radical scavenging activity in plasma. 6. These results suggest that immobilization stress induces generation of reactive oxygen species and decreases the endogenous antioxidant defenses, which can be attenuated by extracellular administration of antioxidant GSH.

Platelet-aggregating effects of platelet-activating factor-like phospholipids formed by oxidation of phosphatidylcholines containing an sn-2-polyunsaturated fatty acyl group

Previously, we reported the formation of four kinds of phosphatidylcholines (PC) with a short-chain monocarboxylate, dicarboxylate, dicarboxylate semialdehyde or omega-hydroxymonocarboxylate group by oxidation of PCs containing polyunsaturated fatty acid (PUFA) in an FeSO4/ascorbate/EDTA system. In this study, we identified these novel phospholipids by GC-MS as oxidation products of two alkyl ether-linked PCs, 1-O-hexadecyl-2-docosahexaenoyl and 1-O-hexadecyl-2-arachidonoyl-sn-glycero-3- phosphocholine (GPC). The sn-2-acyl moieties of oxidatively fragmented PCs derived from PCs containing docosahexaenoate were one methylene unit shorter than those detected as major oxidation products of PCs containing arachidonate. The platelet-aggregations induced by the oxidized PCs were all inhibited by FR-900452, an antagonist of platelet activating factor (PAF). The PAF-like activity of oxidized 1-O-hexadecyl-2-docosahexaenoyl-GPC, which was equivalent of 1372 +/- 262 pmol 16:0-PAF/mumol starting PC, was 5 times that of oxidized 1-O-hexadecyl-2-arachidonoyl-GPC and 150 times that of oxidized 1-palmitoyl-2-docosahexaenoyl-GPC, suggesting that both an sn-1-alkyl ether linkage and an sn-2-acyl group with a short chain length are important structural requirements for induction of platelet aggregation. These possibilities were confirmed by experiments on the platelet-aggregating activities of synthetic PAF-like compounds. Quantitative measurements by GC-MS of PAF-like phospholipids formed by lipid peroxidation and the activities of synthetic PAF-like phospholipids, suggested that the activities of most oxidized PCs containing PUFA were ascribable to those of PCs with an sn-2-short-chain monocarboxylate group.

Chelatable iron and copper can be released from extracorporeally circulated blood during cardiopulmonary bypass

During cardiopulmonary bypass surgery blood is extracorporeally oxygenated and circulated before returning to the systemic arterial circulation. Blood undergoing extracorporeal dilution and circulation is exposed to non-physiological surfaces, which cause the activation of several regulatory cascades. Cells are also subjected to damaging shear stresses. Under such conditions neutrophils can be 'activated' to release reactive oxygen intermediates such as O2- and H2O2, and other cells can release proteolytic enzymes and metalloproteins. Collectively, these events can result in the release of micromolar quantities of redox active iron and copper. Bleomycin-detectable iron and phenanthroline-detectable copper were found in two out of four mock bypass experiments. However, there was no correlation between the presence of chelatable iron and copper and the activation of neutrophils measured as elastase.

Stress proteins and reperfusion stress in the liver

Blood reperfusion after temporary liver ischemia induces the expression of heat shock genes and the synthesis of heat shock proteins (hsps), in particular hsp 70. Induction requires a certain duration of ischemia, suggesting that cell damage before reperfusion is essential for activation of heat shock genes. The expression of the hsp 70 gene is preceded by activation of the cellular protooncogenes c-fos and c-jun. However, the product of these genes, which is transcription factor AP-1, seems unnecessary for activation of the hsp 70 gene, which does not require the integrity of protein synthesis. Hsp genes seem to behave as "early response genes," enabling the cell to respond to emergency situations.

Induction of manganese superoxide dismutase in cultured human trophoblast during in vitro differentiation

The antioxidant responses of human cell differentiation and membrane fusion are not known and may be important in understanding cellular response to injury in the human placenta. We studied the regulation of antioxidant enzymes in human trophoblasts which differentiate from mononucleated cellular trophoblasts to synctium in vivo and in culture. We characterized morphological and biochemical differentiation of cultured trophoblasts from term placenta in the presence or absence of serum, on different growth surfaces, and with a range of plating densities. Culture of cellular trophoblasts consistently and transiently induced the mRNAs of the mitochondrial antioxidant manganese superoxide dismutase (Mn SOD) but not the mRNAs for the antioxidant enzymes copper zinc SOD or catalase. Fibrin and type I collagen substrates modulated only the expression of the placental specific proteins, human chorionic gonadotropin, and human placental lactogen. Both Mn SOD induction and terminal differentiation, as reflected by human chorionic gonadotropin expression, were dependent on trophoblastic plating density. Increased levels of a smaller Mn SOD mRNA species correlated temporally with an increase in Mn SOD enzyme activity in cultured trophoblasts. These results demonstrate that Mn SOD gene expression and enzyme activity precede or are coordinately regulated with morphological and biochemical trophoblastic differentiation.

Development of a simple antioxidant screening assay using human skin fibroblasts

The purpose of this study was to develop a simple antioxidant screening assay for quantifying the protective effects of antioxidant enzymes, inhibitors and scavengers against extracellularly generated oxygen species on human skin fibroblast cytotoxicity. Different in vitro oxidative stresses have been studied: xanthine oxidase-hypoxanthine, flavin mononucleotide-NADH, and hydrogen peroxide. Cytotoxicity and protection were evaluated by two procedures: evaluation of the living cells using a colorimetric method (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide MTT), and ability of the viable cells to adherate and proliferate. Hypoxanthine-xanthine oxidase and H2O2 induced a dose dependent cytotoxicity only when we considered the delayed toxicity. The influence of the cell density was also investigated. The delayed toxicity was higher when cell density increased. One hundred percent protection against free radical cytotoxicity induced by the three systems were obtained with catalase (500 U/ml). When the oxidative stress used was H2O2 90-96% protection was obtained with deferoxamine an iron chelating agent that prevents iron catalysed radical reactions. Using the colorimetric method no significant protection was obtained when SOD was added before and during the stresses. Using the fibroblasts ability to proliferate SOD (10-150 micrograms/ml) reduced xanthine oxidase (20 U/l)-hypoxanthine (0.10-0.30 mM) or H2O2 (1-6 mM) cytotoxicity by 15-20%. SOD did not act as antioxidant when the applied stress was mediated by flavin. In this study we showed a paradoxical effect and the cytotoxicity of flavin-NADH system increased when we added SOD to the cell medium. This simple and reliable antioxidant screening assay required no costly or radioactive equipment.

Oxidative stress responses in Escherichia coli and Salmonella typhimurium

Oxidative stress is strongly implicated in a number of diseases, such as rheumatoid arthritis, inflammatory bowel disorders, and atherosclerosis, and its emerging as one of the most important causative agents of mutagenesis, tumorigenesis, and aging. Recent progress on the genetics and molecular biology of the cellular responses to oxidative stress, primarily in Escherichia coli and Salmonella typhimurium, is summarized. Bacteria respond to oxidative stress by invoking two distinct stress responses, the peroxide stimulon and the superoxide stimulon, depending on whether the stress is mediated by peroxides or the superoxide anion. The two stimulons each contain a set of more than 30 genes. The expression of a subset of genes in each stimulon is under the control of a positive regulatory element; these genes constitute the OxyR and SoxRS regulons. The schemes of regulation of the two regulons by their respective regulators are reviewed in detail, and the overlaps of these regulons with other stress responses such as the heat shock and SOS responses are discussed. The products of Oxy-R- and SoxRS-regulated genes, such as catalases and superoxide dismutases, are involved in the prevention of oxidative damage, whereas others, such as endonuclease IV, play a role in the repair of oxidative damage. The potential roles of these and other gene products in the defense against oxidative damage in DNA, proteins, and membranes are discussed in detail. A brief discussion of the similarities and differences between oxidative stress responses in bacteria and eukaryotic organisms concludes this review.

Hydroxyl radical formation from the auto-reduction of a ferric citrate complex

When a ferric citrate complex is prepared from citric acid and ferric chloride, and the pH value left unchanged, a reduction of the iron moiety takes place. Within several hours a substantial yield of ferrous ions can be detected in the solution. When placed in a phosphate buffer pH 7.0 with a suitable detector molecule, oxidative damage to the detector molecule can be observed. Thus, deoxyribose is degraded with the release of thiobarbituric acid-reactive material and benzoate is hydroxylated to form fluorescent dihydroxy products. Damage can be prevented by scavengers of the hydroxyl radical such as mannitol, formate the thiourea, by catalase and by the protein caeruloplasmin, suggesting that Fenton chemistry occurs leading to the formation of hydroxyl radicals.