Glutathione recycling and antioxidant enzyme activities in erythrocytes of term and preterm newborns at birth

The Silent Threat to Women's Fertility: Uncovering the Devastating Effects of Oxidative Stress

Oxidative stress (OS), which arises through an imbalance between the formation of reactive oxygen species (ROS) and antioxidant defenses, plays a key role in the pathophysiology of female infertility, with the latter constituting just one of a number of diseases linked to OS as a potential cause. The aim of the present article is to review the literature regarding the association between OS and female infertility. Among the reproductive diseases considered are endometriosis and polycystic ovary syndrome (PCOS), while environmental pollutants, lifestyle variables, and underlying medical conditions possibly resulting in OS are additionally examined. Current evidence points to OS likely contributing to the pathophysiology of the above reproductive disorders, with the amount of damage done by OS being influenced by such variables as duration and severity of exposure and the individual's age and genetic predisposition. Also discussed are the processes via which OS may affect female fertility, these including DNA damage and mitochondrial dysfunction. Finally, the last section of the manuscript contains an evaluation of treatment options, including antioxidants and lifestyle modification, capable of minimizing OS in infertile women. The prime message underlined by this review is the importance of considering OS in the diagnosis and treatment of female infertility. Further studies are, nevertheless required to identify the best treatment regimen and its ideal duration.

Bile acids profile and redox status in healthy infants

BACKGROUND

At birth, human neonates are more likely to develop cholestasis and oxidative stress due to immaturity or other causes. We aimed to search for a potential association between bile acids profile, redox status, and type of diet in healthy infants.

METHODS

A cross-sectional, exploratory study enrolled 2-month-old full-term infants (n = 32). We measured plasma bile acids (total and conjugated), and red blood cell (RBC) oxidative stress biomarkers. The type of diet (breastfeeding, mixed, formula) was used as an independent variable.

RESULTS

Plasma total bile acids medium value was 14.80 µmol/L (IQR: 9.25-18.00). The plasma-conjugated chenodeoxycholic acid percentage (CDCA%) correlated significantly and negatively with RBCs membrane-bound hemoglobin percentage (MBH%) (r = -0.635, p < 0.01) and with RBC-oxidized glutathione (r = -0.403, p < 0.05) levels. RBC oxidative stress biomarkers (especially MBH%) were predictors of conjugated CDCA%, and this predictive ability was enhanced when adjusted for the type of diet (MBH, r = 0.452, p < 0.001).

CONCLUSIONS

Our data suggest that the bile acid profile might play a role in the regulation of redox status (or vice versa) in early postnatal life. Eventually, the type of diet may have some impact on this process.

IMPACT

The conjugated CDCA% in plasma is negatively correlated with biomarkers of RBC oxidative stress in healthy infants. Specific biomarkers of RBC oxidative stress (e.g. MBH, GSH, GSSG) may be promising predictors of conjugated CDCA% in plasma. The type of diet may influence the predictive ability of hit RBC oxidative stress biomarkers (e.g. MBH, GSH, GSSG). Our findings suggest a link between plasma bile acids profile and the RBC redox status in healthy infants, eventually modulated by the type of diet. The recognition of this link may contribute to the development of preventive and therapeutic strategies for neonatal cholestasis.

Packed red blood cell transfusion in preterm infants

Premature infants commonly receive adult packed red blood cells (pRBCs) during their hospital stay. As adult erythrocytes differ substantially from those of preterm infants, transfusion of adult pRBCs into preterm infants can be considered inappropriate for the physiology of a preterm infant. An absence of standardisation of transfusion protocols makes it difficult to compare and interpret pertinent clinical data, as reflected by unclear associations between pRBC transfusion and complications related to prematurity, such as bronchopulmonary dysplasia, neurodevelopmental impairment, retinopathy of prematurity, or necrotising enterocolitis. The difficulty in interpreting clinical data is further increased by differences in study designs that either overestimate pRBC-associated complications of prematurity or have not yet been designed to directly link pRBC transfusions to their respective complications. Thus, neonatal transfusion practice has become an ongoing difficulty, in which differences in transfusion guidelines hinder the ability to generate comparable clinical data, and heterogeneity in clinical data prevents the implementation of standardised transfusion protocols. To overcome these issues, novel approaches with biochemical-clinical translational designs could enable clinicians to gather causal evidence instead of circumstantial correlation.

Altered central and blood glutathione in Alzheimer's disease and mild cognitive impairment: a meta-analysis

BACKGROUND

Increasing evidence implicates oxidative stress (OS) in Alzheimer disease (AD) and mild cognitive impairment (MCI). Depletion of the brain antioxidant glutathione (GSH) may be important in OS-mediated neurodegeneration, though studies of post-mortem brain GSH changes in AD have been inconclusive. Recent in vivo measurements of the brain and blood GSH may shed light on GSH changes earlier in the disease.

AIM

To quantitatively review in vivo GSH in AD and MCI compared to healthy controls (HC) using meta-analyses.

METHOD

Studies with in vivo brain or blood GSH levels in MCI or AD with a HC group were identified using MEDLINE, PsychInfo, and Embase (1947-June 2020). Standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated for outcomes using random effects models. Outcome measures included brain GSH (Meshcher-Garwood Point Resolved Spectroscopy (MEGA-PRESS) versus non-MEGA-PRESS) and blood GSH (intracellular versus extracellular) in AD and MCI. The Q statistic and Egger's test were used to assess heterogeneity and risk of publication bias, respectively.

RESULTS

For brain GSH, 4 AD (AD=135, HC=223) and 4 MCI (MCI=213, HC=211) studies were included. For blood GSH, 26 AD (AD=1203, HC=1135) and 7 MCI (MCI=434, HC=408) studies were included. Brain GSH overall did not differ in AD or MCI compared to HC; however, the subgroup of studies using MEGA-PRESS reported lower brain GSH in AD (SMD [95%CI] -1.45 [-1.83, -1.06], p<0.001) and MCI (-1.15 [-1.71, -0.59], z=4.0, p<0.001). AD had lower intracellular and extracellular blood GSH overall (-0.87 [-1. 30, -0.44], z=3.96, p<0.001). In a subgroup analysis, intracellular GSH was lower in MCI (-0.66 [-1.11, -0.21], p=0.025). Heterogeneity was observed throughout (I² >85%) and not fully accounted by subgroup analysis. Egger's test indicated risk of publication bias.

CONCLUSION

Blood intracellular GSH decrease is seen in MCI, while both intra- and extracellular decreases were seen in AD. Brain GSH is decreased in AD and MCI in subgroup analysis. Potential bias and heterogeneity suggest the need for measurement standardization and additional studies to explore sources of heterogeneity.

Oxidative stress biomarkers in the preterm infant

Oxidative stress (OS) plays a key role in the pathophysiology of preterm infants. Accurate assessment of OS remains an analytical challenge that has been partially addressed during the last few decades. A plethora of approaches have been developed to assess preterm biofluids to demonstrate a link postnatally with preterm OS, giving rise to a set of widely employed biomarkers. However, the vast number of different analytic methods and lack of standardization hampers reliable comparison of OS-related biomarkers. In this chapter, we discuss approaches for the study of OS in prematurity with respect to methodologic considerations, the metabolic source of different biomarkers and their role in clinical studies.

Oxidative stress and acid-base balance during the transition period of neonatal Holstein calves submitted to different calving times and obstetric assistance

During the neonatal period, constant adaptations to the extrauterine environment are required. These adaptations are made impossible or hindered when unexpected obstetrical events take place. This study aimed to identify clinical changes of vitality, metabolic and acid-base balance, and oxidative stress of newborn calves born to assisted dams that experienced different durations of calving. A prospective and observational study was conducted with 44 Holstein calves allocated to 3 groups according to the duration of calving: 2 h (n = 16), 2-4 h (n = 16), and >4 h (n = 12), and to 2 subgroups: spontaneous calving (n = 22) and assisted calving (n = 22). We observed that obstetric assistance was beneficial when calving lasted more than 4 h, because 100% of assisted calves had a high Apgar score (≥7) at 5 min, similar to that of spontaneously born calves after 2 h of calving. Rectal temperature of all calves remained within normal values, albeit with a reduction at 20 min of life. Calves born after a calving time >4 h had the highest rectal temperatures, especially those that required obstetrical assistance. There was a progressive increase in blood oxygenation with time, but calves in the >4 h group showed the highest partial pressure of carbon dioxide at birth, whereas calves in the 2 h and 2-4 h groups had lower values. A decrease in partial pressure of CO₂ was observed at 120 min in the 2-4 h and >4 h groups. In the 2-4 h group, calves with obstetrical assistance had higher oxidative stress (measured as thiobarbituric acid reactive substances, TBARS) at 120 min of life compared with that at birth. In spontaneously born calves, TBARS increased only after 240 min. In the >4 h group, TBARS increased progressively with time, regardless of obstetrical subgroup. Calves born spontaneously within the 2 h group had higher TBARS values at birth than calves in the >4 h group with obstetrical assistance. Calves in the >4 h group showed higher levels of glutathione peroxidase (an antioxidant enzyme) at birth than those in the remaining groups. Glutathione peroxidase decreased at 120 min in the >4 h group and at 240 min for the 2 h and 2-4 h groups. In conclusion, obstetric assistance did not improve neonatal vitality and blood oxygenation when calving lasted less than 2 h. Calves born after 2 h of calving showed decreased vitality, hypercapnia, hypoxemia, and increased antioxidant status (glutathione peroxidase).

Redox, acid-base and clinical analysis of preterm and term neonatal lambs

During pregnancy, fetal lambs are exposed to low oxygen tension. Thus, an effective antioxidant mechanism is partially developed which sensitizes fetus to oxidative stress. Consequently, term and preterm neonates are susceptible to molecular and cellular injury caused by oxygen species (ROS). This study aimed to evaluate the development of antioxidant enzymes and oxidative profile of preterm (135 days of pregnancy) and term (145 days of pregnancy) neonatal lambs, correlating with clinical analysis. Preterm lambs had significantly (P ≤ 0.05) lower score of vitality (4.00 ± 1.10), bradycardia (99 ± 34 bpm) and bradypnea (13 ± 10 mpm). However, both groups were normothermic and euglycemic. Preterm group had low blood pH (7.07 ± 0.10) and both groups had hypercapnia, more severe in preterm group (85.52 ± 18.65 mmHg). In addition, premature newborns had lower pO² (10.67 ± 5.65 mmHg) and SO² (6.17 ± 5.85%) values. No significant difference (P ≥ 0.05) on antioxidant enzymes and oxidative stress were verified among experimental groups, although glutathione peroxidase negatively correlated with Apgar score, heart rate, SO² and pO². Our data show that preterm neonates are less adapted to the odds of labor and to overcome the immediate changes of extra-uterine life. Furthermore, we verified an influence of glutathione peroxidase in controlling oxidative stress, which highlights mature enzymatic mechanisms of cell redox, even in premature lambs.

Vitamin E as an Antioxidant in Female Reproductive Health

Vitamin E was first discovered in 1922 as a substance necessary for reproduction. Following this discovery, vitamin E was extensively studied, and it has become widely known as a powerful lipid-soluble antioxidant. There has been increasing interest in the role of vitamin E as an antioxidant, as it has been discovered to lower body cholesterol levels and act as an anticancer agent. Numerous studies have reported that vitamin E exhibits anti-proliferative, anti-survival, pro-apoptotic, and anti-angiogenic effects in cancer, as well as anti-inflammatory activities. There are various reports on the benefits of vitamin E on health in general. However, despite it being initially discovered as a vitamin necessary for reproduction, to date, studies relating to its effects in this area are lacking. Hence, this paper was written with the intention of providing a review of the known roles of vitamin E as an antioxidant in female reproductive health.

Evaluation of dynamic thiol-disulfide homeostasis in very low-birth-weighted preterms

BACKGROUND

Thiols are organic compounds containing sulfhydryl groups which exert antioxidant effects via dynamic thiol-disulfide homeostasis. The shift towards disulfides indicates the presence of oxidative environment. Thiol-disulfide homeostasis has not been evaluated in neonates. We aimed to evaluate dynamic thiol-disulfide homeostasis in preterm infants.

METHODS

Preterm infants with birth weight less than 1500 g (25-32 weeks of gestation) were included. Infants with major congenital anomaly, perinatal asphyxia, twin to twin transfusion and infants who were mechanically ventilated and nil by mouth for more than 3 days or fed with formula, had intraventricular hemorrhage ≥ grade 2 or sepsis, received blood/blood product transfusion or inotrope treatment and developed bronchopulmonary dysplasia or retinopathy of prematurity (≥ stage 3), and died were excluded thereafter. Serum thiol-disulfide homeostasis was evaluated for three times: (Baseline, first week, third week). Serum native thiol, total thiol and disulfide were measured (µmol/Lt), disulfide:native thiol, disulfide:total thiol, and native thiol:total thiol ratios were calculated. Wilcoxon's test was used to analyze the significance of change in measurements. Baseline results were analyzed for gender and mode of delivery.

RESULTS

Eighty preterm infants [1255 (1080-1415) grams] were included. Baseline values were native thiol: 209.54 ± 41.83 µmol/L; total thiol: 251.70 ± 45.82 µmol/L; disulfide: 21.08 ± 7.43 µmol/Lt; disulfide:native thiol: 10.49 ± 4.62; disulfide:total thiol: 8.45 ± 2.93; native thiol:total thiol: 83.10 ± 5.87. Thiol levels increased in each measurement, disulfide and disulfide/thiol ratios increased in the first week, decreased in the third week, ratio of native/total thiol decreased in the first week, increased in the third week. No effect of gender or mode of delivery on baseline thiol-disulfide homeostasis was detected.

CONCLUSIONS

The shift in the thiol-disulfide equilibrium towards disulfides in the first week can be attributed to subjection of infants to many oxidative insults. Furthermore, the thiol predominance in the third week could be explained by the decrease in oxidative events and increase in feeding as a supply of antioxidants. This study, displaying the levels of the dynamic thiol-disulfide homeostasis in preterm infants without obvious risks for increased oxidative stress, may provide acceptable range for thiol-disulfide homeostasis in recovering preterm infants.

Oxidative Stress Biomarkers: Establishment of Reference Values for Isoprostanes, AOPP, and NPBI in Cord Blood

Oxidative stress (OS) is a common pathogenic factor involved in the onset of several diseases in humans, from immunologic disorders to malignancy, being a serious public health problem. In perinatal period, OS has been associated with adverse outcome of pregnancy and neonatal diseases. Dangerous effects of OS are mediated by increased production of free radicals (FRs) following various mechanisms, such as hypoxia, ischemia reperfusion, hyperoxia, inflammation, mitochondrial dysfunction, Fenton chemistry, and prostaglandin metabolism. FRs have short half-life, and their measurement in vivo is faced with many challenges. However, oxyradical derivatives are stable and thus may be measured and monitored repeatedly. The quantification of OS is based on the measurement of specific biomarkers in biologic fluids and tissues, which reflect induced oxidative damage to lipids, proteins, and DNA. Prostanoids, non–protein-bound iron (NPBI), and advanced oxidation protein products (AOPP) are actually considered truly specific and reliable for neonatal injury. Defining reference values for these biomarkers is necessary to investigate their role in neonatal diseases or also to evaluate the success of treatments. In this work, we wanted to define laboratory reference values for biomarkers of OS in a healthy population of term newborns.

Is it accurate to separate glucose-6-phosphate dehydrogenase activity in neonatal hyperbilirubinemia as deficient and normal?

BACKGROUND

The aim of this study was to investigate glucose 6-phosphate dehydrogenase (G6PD) activity in term and late preterm babies with severe neonatal hyperbilirubinemia and its relationship to the severity and treatment of this disorder, regardless of level of G6PD activity (deficient/normal).

METHODS

A total of 529 term and late preterm (≥35 weeks) infants (228 female, 301 male) who were diagnosed with severe hyperbilirubinemia were included in this study. In each case, serum was collected to evaluate blood group, direct Coombs' test, complete blood cell count, total and direct bilirubin, thyroid-stimulating hormone, and G6PD activity. A partial correlation analysis was carried out to assess the relationship between G6PD activity and total bilirubin levels.

RESULTS

A significant correlation was found between the severity of hyperbilirubinemia and G6PD activity in both males and females. Male neonates who had G6PD levels <12 U/g Hb required more phototherapy time than neonates who had G6PD levels ≥12 U/g Hb; and female neonates who had G6PD levels <16 U/g Hb required more phototherapy time than neonates who had G6PD levels ≥16 U/g Hb (p < 0.0001). When we analyzed only breastfed infants, a significant difference also emerged in both sexes. Decreased G6PD activity was associated with increased phototherapy time and the need for exchange transfusion.

CONCLUSION

Routine checks of G6PD level in hyperbilirubinemic neonates are very important in providing proper medical management to prevent bilirubin-induced neurological dysfunction. Appropriate identification of G6PD (<12 U/g Hb for male infants and <16 U/g Hb for female infants) raises awareness of the severity of the condition and the necessity for immediate care of severe hyperbilirubinemic infants.

Nitric oxide and antioxidant enzyme levels in blood of respiratory distress syndrome--Egyptian preterms and their mothers

BACKGROUND

The mechanisms of tissue injury in respiratory distress syndrome (RDS) have not been completely elucidated but the involvement of oxidative damage due to reactive oxygen species (ROS) is important in the pathogenesis of preterm labor and RDS.

OBJECTIVES

To assess the oxidative status in preterms with and without RDS and in their mothers.

PATIENTS AND METHODS

Measuring and comparing concentrations of serum nitric oxide (NO), and erythrocytic activities of some antioxidant enzymes in blood of 20 preterms with RDS and 20 preterms without and their mothers, respectively.

RESULTS

Our results confirm significant elevation of mean levels of serum NO and reduced mean levels of erythrocytic activities of antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT), in RDS preterms and their mothers compared with controls and their mothers. A significant positive correlations were found between maternal and preterm serum NO (r=0.3 & 0.6) and erythrocytic activity of SOD (r=0.5 & 0.4) for RDS and control groups, respectively. In addition, a significant negative correlations were found between NO and SOD in all groups.

CONCLUSIONS

The existence of oxygen metabolites and lipid peroxidation was significantly more obvious in RDS preterms and in their mothers than those without.

Oxidative injury in neonatal erythrocytes

Erythrocytes are continuously exposed to free radicals (FR) injury due to their high cellular oxygen concentration and heme iron. The autoxidation of oxyhaemoglobin to methaemoglobin, generating superoxide anion radical, represents the main source of FR in erythrocytes. The erythrocyte membrane is particularly sensitive to oxidative damage due to its high polyunsaturated fatty acid content, and hence, it represents an important system to evaluate the effect of oxidative stress (OS). Information on how red cells OS is triggered and mechanisms of erythrocytes oxidative pressure from plasma may provide a partial answer to questions about the causes of the anaemia of prematurity and about red cell involvement in hypoxia. The recent insights about the mechanism of oxidative injury of red cells and the evidence of relationships between erythrocyte, OS and hypoxia suggest that increased haemolysis is induced by severe hypoxia and acidosis in the perinatal period.

Biomarkers of oxidative stress in fetal and neonatal diseases

Oxidative stress (OS) is strongly involved in the pathogenesis of many fetal and newborn diseases. A low efficient antioxidant systems in preterm babies are not able to counteract the harmful effects of free radicals (FRs), leading to "FRs-related disease" of newborns promoting cellular, tissue and organ damages. The dangerous effects of FRs are linked to their property of being very unstable molecules and their ability to react with lipids, proteins, polysaccharides, nucleic acids, causing functional alterations within the cell, until cell death. OS is difficult to be measured in vivo, because FRs have a very short half-life. Actually, measurements of lipid peroxidation reach high specificity and sensitivity with the discovery of stable compounds, isoprostanes. Recent studies evaluating the damaging effects of FRs in the perinatal period, have observed a direct relation between the degree of OS and the severity of oxidative damage in the course of pregnancy and in perinatal period, with an interesting predictive role of OS biomarkers for diseases resulting from oxidative injury. The validation of a biomarker profile for early identification of newborns at high risk of OS, will pave the way to new clinical preventative or therapeutic approaches to reduce the prevalence of neonatal disability.

Maternal smoking does not influence vitamin A and E concentrations in mature breastmilk

OBJECTIVES

The aim of this study was to analyze the effects of maternal smoking on the total antioxidant status (TAS) and the concentrations of vitamins A and E in human breastmilk.

METHODOLOGY

The study group (n=20) comprised postpartum women who declared smoking more than five cigarettes per day (confirmed by urinalysis of the cotinine concentration). The control group included 25 nonsmoking postpartum women. Breastmilk samples were collected between day 30 and day 32 after delivery. TAS was determined by Rice-Evans and Miller method, whereas the amount of vitamins A and E was measured by high-performance liquid chromatography.

RESULTS

No significant differences were observed between breastmilk samples from smoking and nonsmoking mothers in terms of TAS and vitamin A and E concentrations. Additionally, no significant correlations were found between urinary cotinine and TAS (R=0.35, p=0.144) or vitamin A (R=0.14, p=0.571) and vitamin E (R=0.31, p=0.228) concentrations in breastmilk samples from smoking mothers.

CONCLUSIONS

Maternal smoking is not reflected by decreased TAS and vitamin A and E concentrations in mature milk.

The effects of oxidative stress on female reproduction: a review

Oxidative stress (OS), a state characterized by an imbalance between pro-oxidant molecules including reactive oxygen and nitrogen species, and antioxidant defenses, has been identified to play a key role in the pathogenesis of subfertility in both males and females. The adverse effects of OS on sperm quality and functions have been well documented. In females, on the other hand, the impact of OS on oocytes and reproductive functions remains unclear. This imbalance between pro-oxidants and antioxidants can lead to a number of reproductive diseases such as endometriosis, polycystic ovary syndrome (PCOS), and unexplained infertility. Pregnancy complications such as spontaneous abortion, recurrent pregnancy loss, and preeclampsia, can also develop in response to OS. Studies have shown that extremes of body weight and lifestyle factors such as cigarette smoking, alcohol use, and recreational drug use can promote excess free radical production, which could affect fertility. Exposures to environmental pollutants are of increasing concern, as they too have been found to trigger oxidative states, possibly contributing to female infertility. This article will review the currently available literature on the roles of reactive species and OS in both normal and abnormal reproductive physiological processes. Antioxidant supplementation may be effective in controlling the production of ROS and continues to be explored as a potential strategy to overcome reproductive disorders associated with infertility. However, investigations conducted to date have been through animal or in vitro studies, which have produced largely conflicting results. The impact of OS on assisted reproductive techniques (ART) will be addressed, in addition to the possible benefits of antioxidant supplementation of ART culture media to increase the likelihood for ART success. Future randomized controlled clinical trials on humans are necessary to elucidate the precise mechanisms through which OS affects female reproductive abilities, and will facilitate further explorations of the possible benefits of antioxidants to treat infertility.

Longitudinal study of vitamins A, E and lipid oxidative damage in human milk throughout lactation

BACKGROUND

Little is known about the intensity of oxidative damage in human milk resulting from maternal oxidative stress. The aim of our study was to explore the changes in Total Antioxidant Status (TAS) and concentrations of antioxidative vitamins and isoprostanes (markers of oxidative stress) in human colostrum and mature milk.

METHODS

The study included 49 postpartum women with normal, spontaneous full term delivery. The exclusion criteria included active and passive smoking, acute and chronic disorders, and pharmacotherapy other than vitamin supplementation. Colostrum samples were collected on the 3rd day after delivery and breast milk samples between the 30th and the 32nd day after delivery. TAS of colostrum/breast milk was determined by Rice-Evans and Miller method. The amount of vitamins A and E was measured by HPLC. Isoprostane concentrations in colostrum/mature milk and urine were determined immunoenzymatically.

RESULTS

No significant differences were observed in maternal dietary intakes of vitamins A and E determined prior to the colostrum and mature milk sampling. The TAS of mature milk was significantly higher compared to colostrum (P=0.002), while vitamin A and E concentrations were significantly lower (P=0.003 and P=0.001). Although the isoprostane concentration of mature milk was significantly higher than the colostrum concentration, this difference was not significant (P=0.129).

CONCLUSION

Human milk is a source of antioxidative vitamins and their concentrations decrease throughout the lactation, while their total antioxidative properties increase. The phase of lactation does not affect the degree of human milk's lipid oxidative damage.

Cord blood glutathione depletion in preterm infants: correlation with maternal cysteine depletion

BACKGROUND

Depletion of blood glutathione (GSH), a key antioxidant, is known to occur in preterm infants.

OBJECTIVE

Our aim was to determine: 1) whether GSH depletion is present at the time of birth; and 2) whether it is associated with insufficient availability of cysteine (cys), the limiting GSH precursor, or a decreased capacity to synthesize GSH.

METHODOLOGY

Sixteen mothers delivering very low birth weight infants (VLBW), and 16 mothers delivering healthy, full term neonates were enrolled. Immediately after birth, erythrocytes from umbilical vein, umbilical artery, and maternal blood were obtained to assess GSH [GSH] and cysteine [cys] concentrations, and the GSH synthesis rate was determined from the incorporation of labeled cysteine into GSH in isolated erythrocytes ex vivo, measured using gas chromatography mass spectrometry.

PRINCIPAL FINDINGS

Compared with mothers delivering at full term, mothers delivering prematurely had markedly lower erythrocyte [GSH] and [cys] and these were significantly depressed in VLBW infants, compared with term neonates. A strong correlation was found between maternal and fetal GSH and cysteine levels. The capacity to synthesize GSH was as high in VLBW as in term infants.

CONCLUSION

The current data demonstrate that: 1) GSH depletion is present at the time of birth in VLBW infants; 2) As VLBW neonates possess a fully active capacity to synthesize glutathione, the depletion may arise from inadequate cysteine availability, potentially due to maternal depletion. Further studies would be needed to determine whether maternal-fetal cysteine transfer is decreased in preterm infants, and, if so, whether cysteine supplementation of mothers at risk of delivering prematurely would strengthen antioxidant defense in preterm neonates.

Total antioxidant capacity and total oxidant status after surfactant treatment in preterm infants with respiratory distress syndrome

BACKGROUND

Oxidative damage is important in the pathogenesis of respiratory distress syndrome (RDS). However, data on the effect of surfactant therapy on oxidative stress in vivo are limited. We aimed to evaluate the oxidant/antioxidant status in preterm infants with RDS via measurement of total antioxidant capacity (TAC) and total oxidant status (TOS), to determine the effect of surfactant on oxidant/antioxidant balance and to assess the association between TAC, TOS and clinical outcomes of the patients.

METHODS

Sixty-nine infants with RDS were included. Blood samples for determining TAC and TOS were collected before and 48 h after surfactant treatment. TAC and TOS levels were analysed in serum. Patients were followed up until discharge or death.

RESULTS

Post-surfactant TAC levels were significantly higher than pre-surfactant TAC levels (P = 0.029). TAC/TOS ratio significantly increased after surfactant treatment (P = 0.018). Infants <28 weeks of gestational age had lower levels of baseline TAC than those ≥28 weeks of gestational age (P = 0.020), whereas TOS levels were similar. Baseline TAC/TOS ratio was lower in infants who died in the study period than those who survived (P = 0.023). After controlling gestational age, baseline TAC levels were significantly and inversely correlated with the duration of total respiratory support (r = -0.343; P = 0.009) and hospitalization (r = -0.341; P = 0.009). TAC or TOS levels were not associated with the development of bronchopulmonary dysplasia or other complications as determined during the investigation period.

CONCLUSIONS

Oxidant-antioxidant balance shifts in favour of the antioxidant system after surfactant treatment. Lower TAC/TOS ratio in preterm infants may be associated with increased mortality.

Potential utility of melatonin as an antioxidant during pregnancy and in the perinatal period

Reactive oxygen species (ROS) play a critical role in the pathogenesis of various diseases during pregnancy and the perinatal period. Newborns are more prone to oxidative stress than individuals later in life. During pregnancy, increased oxygen demand augments the rate of production of ROS and women, even during normal pregnancies, experience elevated oxidative stress compared with non-pregnant women. ROS generation is also increased in the placenta during preeclampsia. Melatonin is a highly effective direct free-radical scavenger, indirect antioxidant, and cytoprotective agent in human pregnancy and it appears to be essential for successful pregnancy. This suggests a role for melatonin in human reproduction and in neonatal pathologies (asphyxia, respiratory distress syndrome, sepsis, etc.). This review summarizes current knowledge concerning the role for melatonin in human pregnancy and in the newborn. Numerous studies agree that short-term melatonin therapy is highly effective in reducing complications during pregnancy and in the neonatal period. No significant toxicity or treatment-related side effects with long-term melatonin therapy in children and adults have been reported. Treatment with melatonin might result in a wide range of health benefits, including improved quality of life and reduced healthcare costs.

[Gender-dependent differences in glutathione (GSH) metabolism in very preterm infants]

BACKGROUND

Gender differences in mortality and morbidity are often reported in very preterm infants. In studies aiming to understand the underlying mechanisms, better protection against oxidative stress in baby girls has been suggested.

OBJECTIVES

Shortly after birth, we compared glutathione (GSH) metabolism in female and male preterm infants and its relationship with prenatal and postnatal parameters.

METHODS

We took the opportunity of a prospective randomised controlled trial evaluating the safety-efficacy balance of inhaled nitric oxide (Hamon and al., 2005) [12] to assess, in vivo, the antioxidant defences within the first 48 h of life in 240 premature infants less than 32 weeks gestational age (GA). We measured total plasmatic GSH level (nmol/L), intraerythrocyte glutathione peroxidase (GPX, μmol/min/g haemoglobin) and intraerythrocyte glutathione reductase (GR, μmol/min/g haemoglobin) from venous blood samples withdrawn through central lines.

RESULTS

Expressed as mean ± standard error of the mean: soon after birth (at 24h median), plasmatic GSH was not different between females (n=123) and males (n=117): 0.932 ± 0.016 vs 0.956 ± 0.012 nmol/L. However, at the same time, GPX, the enzyme involved in GSH synthesis, was at a significantly higher level in baby girls (p<0.001): 11.63 ± 0.25 vs 10.21 ± 0.24 μmol/min/g haemoglobin, as was GR, the enzyme responsible for GSH regeneration (p=0.02): 12.18 ± 0.23 vs 11.22 ± 0.21 μmol/min/g haemoglobin. We observed no significant correlation between GSH levels, GPX, or GR activities with prenatal steroids, GA, birth weight, severity of respiratory disease, and oxygen requirements for the entire population or between the two genders.

CONCLUSION

Whereas the level of glutathione, a key molecule in the defence against oxidative stress in humans, appears to be identical in preterm females and males soon after birth, the enzymes involved in its synthesis (GPX) and regeneration (GR) are higher in females.

SPECULATION

Study of the sequential progression of GSH, GPX, and GR with regard to prolonged oxidative stress exposure in preterm females and males is needed to better evaluate their potential clinical relevance.

Tailoring oxygen needs of extremely low birth weight infants in the delivery room

Fetal to neonatal transition poses an extraordinary challenge for the extremely low birth weight (ELBW) neonate. Indeed a significant number of ELBW neonates will need proactive resuscitation to achieve postnatal stabilization. Positive pressure ventilation and oxygenation are the most relevant interventions in the delivery room (DR). Oxygen needs during resuscitation still represent a conundrum for neonatologists. While hyperoxemia favors oxidative stress and subsequent organ injury, hypoxemia is associated with long-term neurodevelopmental impairment. It has been shown that ELBW neonates can be successfully resuscitated with lower concentrations of oxygen as had been done traditionally. Moreover, reducing oxygen load has resulted in achievement of arterial partial pressures of oxygen at admission closer to the physiologic range, less oxidative stress and less inflammation. The availability of reference ranges for arterial oxygen saturation (SpO(2)) for ELBW neonates in the first 10 min after birth has been an extraordinary step forward in our ability to individually titrate oxygen needs thus avoiding the risks of both hypo- and hyperoxemia. The optimal fraction of inspired oxygen (FiO(2)) to initiate resuscitation and the safest SpO(2) percentiles for ELBW neonates during the first minutes of life are still unknown and will need further research in the future. Until then, optimal ventilation at birth and individually tailoring FiO(2) according to the nomogram seem to be the most reasonable and safe approach.

Erythrocyte membrane AChE, Na(+), K(+)-ATPase and Mg(2+) ATPase activities in mothers and their premature neonates in relation to the mode of delivery

AIM

To investigate erythrocyte membrane AChE, Na(+), K(+)-ATPase and Mg(2+)-ATPase activities in mothers and their full-term or premature newborns in relation to the mode of delivery.

METHODS

Blood was obtained from mothers pre- and post-delivery and the umbilical cord (CB) of their full-term newborns: Group A₁ (n = 16) born with vaginal delivery (VD), Group B₁ (n = 14) full-terms with scheduled cesarean section (CS), Group A₂ (n = 12) prematures with VD, Group B₂ (n = 14) prematures with CS. Total Antioxidant Status (TAS) and common laboratory tests were measured with routine methods, and the membrane enzyme activities spectrophotometrically.

RESULTS

TAS was reduced in mothers post VD and in the CB whereas remained unaltered in CS mothers and their newborns. AChE and Na(+), K(+)-ATPase were increased in mothers post VD. AChE was lower in the CB of prematures than that of full-terms independently of the mode of delivery. Na(+), K(+)-ATPase activity was increased in the groups of mothers post VD and decreased in prematures. The enzyme was higher in prematures with CS than that with VD. Mg(2+)-ATPase activity was unchanged.

CONCLUSION

The increased maternal AChE and Na(+), K(+)-ATPase activities may be due to the low TAS determined post VD, whereas their decreased activities in prematures to their immaturity.

Plasma cortisol response to ACTH challenge in hypoxic newborn piglets resuscitated with 21% and 100% oxygen

Although the use of supplemental oxygen to resuscitate asphyxiated neonates remains controversial, the effects of hypoxia and reoxygenation (room air versus pure oxygen) on the hypothalamo-pituitary-adrenal axis are unknown. We aimed to evaluate the effect of hypoxia and reoxygenation with either 21% or 100% oxygen on plasma cortisol before and after an adrenocorticotrophin (ACTH) challenge in newborn piglets. Thirty-five piglets (aged 1-3 days, weighing 1.5-2.4 kg) were instrumented to measure heart rate, MAP, and cardiac output. After 2 h of normocapnic hypoxia (PaO2, 20-30 mmHg; pH, <6.95), piglets were resuscitated with 21% or 100% oxygen for 1 h and then 21% oxygen for 3 h. Sham-operated piglets had no hypoxia-reoxygenation (H-R). Serial plasma cortisol levels were determined after a blinded randomized administration of ACTH (4 microg/kg, i.v.) or saline at 2 h reoxygenation. The expression of steroidogenic factor 1 in the adrenals was studied. Cardiac output decreased with hypoxia and recovered with resuscitation. Piglets developed hypotension similarly in 21% and 100% H-R groups during reoxygenation (versus sham-operated group, P < 0.05). Both H-R groups had increased plasma cortisol levels (versus sham-operated group, P < 0.05) at 2 h of reoxygenation after hypoxia, with a further increase in levels in 21% H-R piglets at 4 h reoxygenation (versus 100% H-R piglets, P < 0.05). The response to ACTH was delayed in H-R groups, with the maximum increase at 120 min post-ACTH administration (versus 30-60 min post-ACTH for sham-operated piglets). Plasma cortisol levels increased significantly post-ACTH administration in 21% H-R and sham-operated piglets (115% +/-50% and 126% +/- 25% at 120 min, respectively, P < 0.05 vs. pre-ACTH baselines) but not in 100% H-R piglets (51% +/-14%), which had a lower expression of steroidogenic factor 1 than the other groups. Although the clinical significance of high cortisol levels and cortisol response to ACTH in H-R newborn piglets is uncertain, a preserved cortisol response may support using room air in neonatal resuscitation.

Oxygen toxicity: chemistry and biology of reactive oxygen species

Oxygen has a central role in the evolution of complex life on Earth mainly because of the biochemical symmetry of oxygenic photosynthesis and aerobic respiration that can maintain homeostasis within our planet biosphere. Oxygen can also produce toxic molecules, reactive oxygen species (ROS). ROS is a collective term that includes both oxygen radicals and certain oxidizing agents that are easily converted into radicals. They can be produced from both endogenous and exogenous substances. ROS play a dual role in biological systems, since they can be either harmful or beneficial to living systems. They can be considered a double-edged sword because on the one hand oxygen-dependent reactions and aerobic respiration have significant advantages but, on the other, overproduction of ROS has the potential to cause damage.

Glutathione synthesis rates in early postnatal life

Preterm infants have diminished antioxidant defenses. Glutathione (GSH), the main intracellular antioxidant, increases upon amino acid (AA) administration in preterm infants, without an accompanying rise of the fractional synthesis rate of GSH (FSRGSH) This study investigated the mechanism behind this increased GSH concentration by determining GSH synthesis in the first days after birth using stable isotope techniques in very low-birth-weight (VLBW) infants receiving i.v. AAs. Advanced oxidized protein products (AOPPs) were determined to quantify oxidative stress. Eighteen infants (birth weight 989 +/- 241 g, gestational age of 27/7 +/- 1/7 weeks) were studied either on postnatal day 1 or 2 (7 or 31 h postnatally, respectively). Concentration of GSH increased with postnatal age (1.45 +/- 0.48 mM versus 1.99 +/- 0.40 mM, p = 0.019). FSRGSH was not significantly different, but the absolute synthesis rate of GSH (ASRGSH) tended to be higher in the infants studied on day 2 [8.1 +/- 2.7 mg/(kg . d) versus 10.6 +/- 2.4 mg/(kg . d), p = 0.054]. AOPP concentrations were not different between groups. In conclusion, GSH concentration in VLBW infants increases significantly after birth. A concomitant increased synthesis rate was not found, suggesting that GSH consumption decreases upon AA administration.

Oxidative stress of the newborn in the pre- and postnatal period and the clinical utility of melatonin

Newborns, and especially those delivered preterm, are probably more prone to oxidative stress than individuals later in life. Also during pregnancy, increased oxygen demand augments the rate of production of reactive oxygen species (ROS) and women, even with normal pregnancies, experience elevated oxidative stress and lipid peroxidation compared with nonpregnant women. Also, there appears to be an increase in ROS generation in the placenta of pre-eclamptic women. In comparison with healthy adults, newborn infants have lower levels of plasma antioxidants such as vitamin E, beta-carotene, and sulphydryl groups, lower levels of plasma metal binding proteins including ceruloplasmin and transferrin, and reduced activity of erythrocyte superoxide dismutase. This review summarizes conditions of newborns where there is elevated oxidative stress. Included in this group of conditions is asphyxia, respiratory distress syndrome and sepsis and the review also summarizes the literature related to clinical trials of antioxidant therapies and of melatonin, a highly effective antioxidant and free radical scavenger. The authors document there is general agreement that short-term melatonin therapy may be highly effective and that it has a remarkably benign safety profile, even when neonates are treated with pharmacological doses. Significant complications with long-term melatonin therapy in children and adults also have not been reported. None of the animal studies of maternal melatonin treatment or in postnatal life have shown any treatment-related side effects. The authors conclude that treatment with melatonin might result in a wide range of health benefits, improved quality of life and reduced healthcare costs and may help reduce complications in the neonatal period.

Glutathione synthesis rates after amino acid administration directly after birth in preterm infants

BACKGROUND

The availability of glutathione, the main intracellular antioxidant, is compromised in preterm neonates. A possible explanation is the low availability of substrate for synthesis, because many neonatologists are reluctant to administer amino acids in the direct postnatal period for fear of intolerance.

OBJECTIVE

The objective of the study was to determine the effects of amino acid administration directly after birth on glutathione synthesis rates and markers of oxidative stress.

DESIGN

Premature infants (<1500 g) received from birth onward either dextrose (control group; n = 10) or dextrose plus 2.4 g amino acids . kg (- 1) . d(-1) (intervention group; n = 10). On postnatal day 2, [1-(13)C]glycine was administered to determine glutathione fractional synthesis rates (FSR(GSH)) and absolute synthesis rates (ASR(GSH)) in erythrocytes. In plasma, advanced oxidized protein products and dityrosine, both markers of oxidative stress, were measured. The results are expressed as means +/- SDs.

RESULTS

The FSR(GSH) was not different between groups: 44 +/- 6 and 48 +/- 9%/d in the control and intervention groups, respectively (P = 0.28). The concentration of erythrocyte glutathione was higher (P < 0.001) in the intervention group (2.28 +/- 0.35 mmol/L) than in the control group (1.73 +/- 0.37 mmol/L). ASR(GSH) values were 6.5 +/- 1.5 and 11.3 +/- 1.9 mg . kg(-1) . d(-1) in the control and intervention groups, respectively (P < 0.001). Advanced oxidized protein products and dityrosine concentrations were not significantly different between groups.

CONCLUSIONS

Amino acid administration directly after birth increases ASR(GSH) in preterm infants. Our data are consistent, however, with higher glutathione concentrations rather than a higher FSR(GSH). Greater availability of glutathione, nevertheless, did not decrease markers of oxidative stress.

Lower erythrocyte glutathione peroxidase activity in bronchopulmonary dysplasia in the first week of neonatal life

BACKGROUND

Bronchopulmonary dysplasia (BPD) is a major pulmonary complication in premature infants and is considered a free radical disorder. Erythrocyte catalase (CAT) and cellular glutathione peroxidase (c-GPx) are antioxidant enzymes that detoxify peroxides generated from dismutation of superoxide anion. The study goal was to measure enzyme activity for preterm infants during the first week of life.

METHODS

Blood samples were collected from umbilical arterial lines or the radial artery of 44 preterm infants (gestational age range: 25-30 weeks) on days 0, 2, and 5 after delivery. Erythrocyte CAT and c-GPx activities were evaluated, while clinical data were obtained and the correlations of enzyme activity and BPD status were examined.

RESULTS

There was no correlation between enzyme activity and gestational age or birth weight. Packed red cell transfusion did not affect enzyme activity and there was no difference in CAT activity between the patient groups. C-GPx activity from preterm infants with BPD was significantly lower than those of preterm infants without BPD on day 5.

CONCLUSIONS

Erythrocyte c-GPx may play an important role in the development of BPD. Lower c-GPx activity in early post-natal life might be a risk factor of BPD.

Erythrocyte anti-oxyenzyme activity in preterm infants with retinopathy of prematurity

BACKGROUND

Retinopathy of prematurity (ROP) is the main cause of visual impairment in premature infants and is considered to be a multifactorial disease. Because of the similarity between the human retina and the erythrocyte concerning their antioxidant mechanism, the aim of this study was to measure the erythrocyte anti-oxyenzyme activity of preterm infants.

METHODS

This prospective study was performed on a tertiary referral hospital. Blood samples were collected from umbilical arterial lines or the radial artery of 33 preterm infants within 24 h after delivery to evaluate erythrocyte anti-oxyenzyme activity. Clinical data and oxygen administration were obtained and the correlations of enzyme activity and ROP status were examined.

RESULTS

Gestational age, birth weight, 1-min Apgar score, and cellular glutathione peroxidase activity were significantly lower in preterm infants with ROP. There was no correlation between enzyme activity and gestational age, birth weight, or severity of ROP. There were no differences in cumulative oxygen and ventilator administration.

CONCLUSIONS

Gestational age and birth weight, 1-min Apgar score, and glutathione peroxidase activity are risk factors for ROP. Defective glutathione peroxidase activity may contribute to the initial phase of ROP.

GSH depletion, protein S-glutathionylation and mitochondrial transmembrane potential hyperpolarization are early events in initiation of cell death induced by a mixture of isothiazolinones in HL60 cells

We recently described that brief exposure of HL60 cells to a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (CMI) and 2-methyl-4-isothiazolin-3-one (MI) induces apoptosis at low concentrations (0.001-0.01%) and necrosis at higher concentrations (0.05-0.1%). In this study, we show that glutathione (GSH) depletion, reactive oxygen species generation, hyperpolarization of mitochondrial transmembrane potential (DeltaPsim) and formation of protein-GSH mixed disulphides (S-glutathionylation) are early molecular events that precede the induction of cell death by CMI/MI. When the cells exhibit common signs of apoptosis, they show activation of caspase-9, reduction of DeltaPsim and, more importantly, decreased protein S-glutathionylation. In contrast, necrosis is associated with severe mitochondrial damage and maximal protein S-glutathionylation. CMI/MI-induced cytotoxicity is also accompanied by decreased activity of GSH-related enzymes. Pre-incubation with L-buthionine-(S,R)-sulfoximine (BSO) clearly switches the mode of cell death from apoptosis to necrosis at 0.01% CMI/MI. Collectively, these results demonstrate that CMI/MI alters the redox status of HL60 cells, and the extent and kinetics of GSH depletion and S-glutathionylation appear to determine whether cells undergo apoptosis or necrosis. We hypothesize that S-glutathionylation of certain thiol groups accompanied by GSH depletion plays a critical role in the molecular mechanism of CMI/MI cytotoxicity.

Nonprotein-bound iron and plasma protein oxidative stress at birth

We previously reported plasma nonprotein-bound iron (NPBI) as a reliable early indicator of intrauterine oxidative stress (OS) and brain injury. We tested the hypothesis that albumin, an NPBI serum carrier, is the major target of NPBI-induced OS. Twenty-four babies were randomly selected from 384 newborns constituting the final cohort of a prospective study undertaken to evaluate the predictive role of NPBI in cord blood for neurodevelopmental outcome. Twelve were selected in the group with lowest NPBI levels (0-1.16 microM) and good neurodevelopmental outcome and 12 in the group with highest NPBI levels (>or=15.2 microM) and poor neurodevelopmental outcome. Protein carbonyl groups were identified in cord blood samples by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and Western blotting with anti-2,4-dinitrophenyl (DNP) antibodies. Two series of immunoreactive spots, corresponding to serum albumin and alpha-fetoprotein, were found only in the group with highest NPBI levels. We found an association between NPBI and carbonylated proteins in babies with highest NPBI levels. Since NPBI may produce hydroxyl radicals through the Fenton reaction, the major target of OS induced by NPBI is its carrier: albumin. Oxidation of albumin can be expected to decrease plasma antioxidant defenses and increase the likelihood of tissue damage due to OS in the newborns.

Biochemical and biological aspects of protein thiolation in cells and plasma

Protein thiolation is elicited by oxidation by different mechanisms and is involved in a variety of biological processes. Thiols, protein SH (PSH) and non-protein SH groups (NPSH, namely GSH), are in competition in all biological environments in the regulation of oxidant homeostasis because oxidants thiolate proteins, whereas GSH dethiolates them (e.g., GSSG + PSH --> GSSP + GSH). Although poorly investigated, the elimination of disulfides from thiolated proteins to regenerate critical PSH is important. These aspects are poorly known in cells, where glutaredoxin and peroxiredoxin operate as enzymes or potential chaperones to accelerate dethiolation. On the contrary, studies with plasma or albumin have highlighted the importance of protein conformation in dethiolation processes and have clarified the reason why homocysteine (thiol with potential toxicity) is preferentially bound to albumin as protein-thiol mixed disulfide with respect to other NPSH. Here we provide an overview of protein thiolation/dethiolation processes, with an emphasis on recent developments and future perspectives in this field.

The effects of age and hyperhomocysteinemia on the redox forms of plasma thiols

We assayed the redox forms of cysteine (reduced [CSH], oxidized [CSSC], and bound to protein [CS-SP]), cysteinylglycine (CGSH; cysteinylgycine disulfide [CGSSGC] and cysteinylglycine-protein mixed disulfide [CGS-SP]), glutathione (GSH; glutathione disulfide [GSSG] and glutathione-protein mixed disulfide [GS-SP]), homocysteine (Hcy; homocystine [HcyS] and homocystine-protein mixed disulfides [bHcy]), and protein sulfhydryls in the plasma of healthy subjects (divided into 8 groups ranging in age from birth to 70 years) and patients with mild hyperhomocysteinemia associated with cardiovascular disease (heart-transplant patients) or vascular atherosclerosis, with or without renal failure. In healthy individuals, levels of disulfides and protein-mixed disulfides were more abundant than those of thiols, and those of protein-thiol mixed disulfides were higher than disulfides. Concentrations of CSH, GSH, and CGSH in the various groups had profiles characterized by a maximum over time. The concentration of Hcy was unchanged up to the age of 30 years, after which it increased. CSSC concentration increased gradually with age, whereas concentrations of the other disulfides were essentially unchanged. By contrast, the concentrations of all protein-thiol mixed disulfides, especially those with CSH, increased gradually with age. Ranks of distribution of the reduced forms changed with age (at birth, CSH > CGSH > GSH > Hcy; in 1- to 2-year-olds, CSH > GSH > CGSH > Hcy; and in 51- to 70-year-olds, CSH > CGSH = GSH > Hcy), whereas those of disulfides and protein-thiol mixed disulfides were substantially unchanged (in all age groups, CSSC > CGSSGC > GSSG = HcyS and CS-SP > CGS-SP > bHcy > GS-SP). In patients with pathologic conditions, plasma levels of disulfide forms CSSC, HcyS, CS-SP, and bHcy were significantly increased, whereas other redox forms of thiols were unchanged or showed variations opposite (increasing or decreasing) to control values. Maximal increases in disulfides and protein-thiol mixed disulfides were associated with renal failure. Our data suggest that increases in plasma bHcy concentrations in subjects with pathologic conditions were more likely the result of activation of thiol-disulfide exchange reactions between free reduced Hcy and CS-SP than of a direct action of reactive oxygen species.