Effects of parenteral cysteine and glutathione feeding in a baboon model of severe prematurity

Dose-Response Effects of Glutathione Supplement in Parenteral Nutrition on Pulmonary Oxidative Stress and Alveolarization in Newborn Guinea Pig

In premature infants, glutathione deficiency impairs the capacity to detoxify the peroxides resulting from O₂ metabolism and those contaminating the parenteral nutrition (PN) leading to increased oxidative stress, which is a major contributor to bronchopulmonary dysplasia (BPD) development. In animals, the supplementation of PN with glutathione prevented the induction of pulmonary oxidative stress and hypoalveolarization (characteristic of BPD). Hypothesis: the dose of glutathione that corrects the plasma glutathione deficiency is sufficient to prevent oxidative stress and preserve pulmonary integrity. Three-day-old guinea pigs received a PN, supplemented or not with GSSG (up to 1300 µg/kg/d), the stable form of glutathione in PN. Animals with no handling other than being orally fed constituted the control group. After 4 days, lungs were removed to determine the GSH, GSSG, redox potential and the alveolarization index. Total plasma glutathione was quantified. The effective dose to improve pulmonary GSH and prevent the loss of alveoli was 330 µg/kg/d. A 750 µg/kg/d dose corrected the low-plasma glutathione, high-pulmonary GSSG and oxidized redox potential. Therefore, the results suggest that, in a clinical setting, the dose that improves low-plasma glutathione could be effective in preventing BPD development.

High Branched-Chain Amino Acid Concentrations Are Found in Preterm Baboons Receiving Intravenous Amino Acid Solutions and Mimic Alterations Found in Preterm Infants

BACKGROUND

Parenteral amino acid (AA) nutrition administration after premature birth is necessary to ensure adequate growth and neurodevelopment. However, optimizing safety and efficacy remains a major challenge. This study investigated the effects of intravenous AA administration on plasma AA profiles in premature baboons and infants.

METHODS

Premature baboons were delivered by cesarean section at 125 days (67% gestation) and chronically ventilated. At 24 hours of life, a parenteral AA protocol comparable to the early and high AA regimens used in premature infants was initiated. Serial plasma AA concentrations were obtained on days of life (DOLs) 1, 3, and 7 and compared with concentrations at similar DOLs from preterm infants. Fetal baboon (165 ± 2 days; 89% gestation) and term baboon plasma AA concentrations were obtained for comparison.

RESULTS

Premature baboons receiving early and high parenteral AA supplementation exhibited significant differences in plasma AA concentrations compared with fetuses. In particular, concentrations of leucine, isoleucine, valine, and ornithine were elevated (fold increase: 2.14, 2.03, 1.95, and 16.5, respectively; P < 0.001) on DOL 3 vs fetuses. These alterations mimicked those found in preterm infants.

CONCLUSION

Early and high AA supplementation in extremely premature baboons significantly disrupted plasma AA concentrations. Elevated concentrations of branched-chain AAs and ornithine raise concerns for adverse neurodevelopmental outcomes. These results are consistent with those found in premature human infants and emphasize the need to optimize parenteral AA solutions for the unique metabolic requirements of premature infants. Improved technologies for rapid monitoring of AA concentrations during treatment are essential.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

Developmental regulation of antioxidant enzymes and their impact on neonatal lung disease

SIGNIFICANCE

Deficient antioxidant defenses and compromised ability to respond to oxidative stress burden the immature lung. Routine neonatal therapies can cause increased oxidative stress with subsequent injury to the premature lung. Novel therapeutic approaches to protect the premature lung are greatly needed.

RECENT ADVANCES

Live cell imaging with targeted redox probes allows for the measurement of subcellular oxidative stress and for comparisons of oxidative stress across development. Comprehension of subcellular and cell-type-specific responses to oxidative stress may influence the targeting of future antioxidant therapies.

CRITICAL ISSUES

Challenges remain in identifying the optimal cellular targets, degree of enzyme activity, and appropriate antioxidant therapy. Further, the efficacy of delivering exogenous antioxidants to specific cell types or subcellular compartments remains under investigation. Treatment with a nonselective antioxidant could unintentionally compromise cellular function or impact cellular defense mechanisms and homeostasis.

FUTURE DIRECTIONS

Genetic and/or biomarker screening may identify infants at the greatest risk for oxidative lung injury and guide the use of more selective antioxidant therapies. Novel approaches to the delivery of antioxidant enzymes may allow cell type- or cellular organelle-specific therapy. Improved comprehension of the antioxidant enzyme regulation across cell type, cell compartment, gender, and developmental stage is critical to the design and optimization of therapy.

The role of genetic polymorphisms in antioxidant enzymes and potential antioxidant therapies in neonatal lung disease

SIGNIFICANCE

Oxidative stress is involved in the development of newborn lung diseases, such as bronchopulmonary dysplasia and persistent pulmonary hypertension of the newborn. The activity of antioxidant enzymes (AOEs), which is impaired as a result of prematurity and oxidative injury, may be further affected by specific genetic polymorphisms or an unfavorable combination of more of them.

RECENT ADVANCES

Genetic polymorphisms of superoxide dismutase and catalase were recently demonstrated to be protective or risk factors for the main complications of prematurity. A lot of research focused on the potential of different antioxidant strategies in the prevention and treatment of lung diseases of the newborn, providing promising results in experimental models.

CRITICAL ISSUES

The effect of different genetic polymorphisms on protein synthesis and activity has been poorly detailed in the newborn, hindering to derive conclusive results from the observed associations with adverse outcomes. Therapeutic strategies that aimed at enhancing the activity of AOEs were poorly studied in clinical settings and partially failed to produce clinical benefits.

FUTURE DIRECTIONS

The clarification of the effects of genetic polymorphisms on the proteomics of the newborn is mandatory, as well as the assessment of a larger number of polymorphisms with a possible correlation with adverse outcome. Moreover, antioxidant treatments should be carefully translated to clinical settings, after further details on optimal doses, administration techniques, and adverse effects are provided. Finally, the study of genetic polymorphisms could help select a specific high-risk population, who may particularly benefit from targeted antioxidant strategies.

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.

Sulfur mustard analog, 2-chloroethyl ethyl sulfide-induced skin injury involves DNA damage and induction of inflammatory mediators, in part via oxidative stress, in SKH-1 hairless mouse skin

Bifunctional alkyalating agent, sulfur mustard (SM)-induced cutaneous injury is characterized by inflammation and delayed blistering. Our recent studies demonstrated that 2-chloroethyl ethyl sulfide (CEES), a monofunctional analog of SM that can be used in laboratory settings, induces oxidative stress. This could be the major cause of the activation of Akt/MAP kinase and AP1/NF-κB pathways that are linked to the inflammation and microvesication, and histopathological alterations in SKH-1 hairless mouse skin. To further establish a link between CEES-induced DNA damage and signaling pathways and inflammatory responses, skin samples from mice exposed to 2 mg or 4 mg CEES for 9-48 h were subjected to molecular analysis. Our results show a strong CEES-induced phosphorylation of H2A.X and an increase in cyclooxygenase-2 (COX-2), inducible NOS (iNOS), and matrix metalloproteinase-9 (MMP-9) levels, indicating the involvement of DNA damage and inflammation in CEES-induced skin injury in male and female mice. Since, our recent studies showed reduction in CEES-induced inflammatory responses by glutathione (GSH), we further assessed the role of oxidative stress in CEES-related DNA damage and the induction of inflammatory molecules. Oral GSH (300 mg/kg) administration 1h before CEES exposure attenuated the increase in both CEES-induced H2A.X phosphorylation (59%) as well as expression of COX-2 (68%), iNOS (53%) and MMP-9 (54%). Collectively, our results indicate that CEES-induced skin injury involves DNA damage and an induction of inflammatory mediators, at least in part via oxidative stress. This study could help in identifying countermeasures that alone or in combination, can target the unveiled pathways for reducing skin injury in humans by SM.

Animal models to study neonatal nutrition in humans

PURPOSE OF REVIEW

The impact of neonatal nutrition on the health status of the newborn and incidence of disease in later life is a topic of intense interest. Animal models are an invaluable tool to identify mechanisms that mediate the effect of nutrition on neonatal development and metabolic function. This review highlights recently developed animal models that are being used to study neonatal human nutrition.

RECENT FINDINGS

In recent years, mice, rats, and pigs have become the most frequently used animal models to study human neonatal nutrition. Techniques for rearing newborn mice, preterm rats, and preterm pigs have been developed. Neonatal mice have great potential for mechanistic and genomic research in postnatal nutrition and related diseases. The neonatal pig model is valuable to study acute and chronic effects of parenteral and enteral nutrition on whole-body metabolism as well as specific tissues. To date, a wealth of information from studies with neonatal pigs has been applied to humans.

SUMMARY

Further development of neonatal animal models related to nutrition is required for the advancement of research in early postnatal nutrition. Improvement of nutritional support during this critical period of development will enhance immediate clinical outcomes and possibly prevent diseases later in life.

Oral N-acetyl-l-cysteine is a safe and effective precursor of cysteine1

Relative bioavailability and toxicity of N-acetyl-l-Cys (NAC) were evaluated in 9-d chick growth assays. The bioavailability of NAC relative to Cys was determined by feeding young chicks a highly purified crystalline AA diet singly deficient in Cys. Bio-availability estimates were obtained using standard slope-ratio methodology. N-Acetyl-l-cysteine was shown to be as effective as Cys in supporting chick growth, and was assigned a relative bioavailability value of 100%. To assess toxicity, a nutritionally adequate corn-soybean meal diet was supplemented with graded concentrations of NAC (isomolar to 10, 20, 30, or 40 g/kg of Cys, as-fed). When NAC supplied 10 or 20 g/kg of Cys, chick growth performance was unaffected, but NAC supplying 30 or 40 g/kg of Cys reduced (P < 0.05) BW gain by 13 and 34%, respectively, relative to the unsupplemented control diet. Only plasma-free NAC was substantially increased (P < 0.05) because of excess dietary NAC; plasma-free Cys was unaltered. We concluded that dietary NAC is efficacious in supplying Cys in support of chick growth, and only large excesses of NAC are growth depressing. Hence, the human clinical benefits of oral NAC likely result from its ability to deliver Cys safely and effectively to the portal circulation.

Screening for Serum Total Homocysteine in Newborn Children

Background: Newborn screening for total homocysteine (tHcy) in blood may identify babies with vitamin B12 (B12) deficiency or homocystinuria, but data on the causes of increased tHcy in screening samples are sparse.

Methods: Serum concentrations of tHcy, cystathionine, methionine, folate, and B12 and the methylenetetrahydrofolate reductase (MTHFR) 677C&gt;T polymorphism were determined in 4992 capillary blood samples collected as part of the routine screening program in newborn children. Methylmalonic acid (MMA), gender (SRY genotyping), and the frequency of six cystathionine β-synthase (CBS) mutations were determined in 20–27% of the samples, including all samples with tHcy &gt;15 μmol/L (n = 127), B12 &lt;100 pmol/L (n = 159), or methionine &gt;40 μmol/L (n = 154).

Results: The median (5th–95th percentile) tHcy concentration was 6.8 (4.2–12.8) μmol/L. B12 status, as determined by serum concentrations of B12, tHcy, and MMA, was moderately better in boys than in girls. tHcy concentrations between 10 and 20 μmol/L were often associated with low B12, whereas tHcy &gt;20 μmol/L (n = 43) was nearly always explained by increased methionine. tHcy did not differ according to folate concentrations or MTHFR 677C&gt;T genotypes. None of the babies had definite CBS deficiencies, but heterozygosity led to low cystathionine, increased methionine, but normal tHcy concentrations.

Conclusion: Increased tHcy is a common but not specific finding in newborns. The metabolite and vitamin profiles will point to the cause of hyperhomocysteinemia. Screening for tHcy and related factors should be further evaluated in regions with high prevalence of homocystinuria and in babies at high risk of B12 deficiency.

Pulmonary antioxidant defenses in the preterm newborn with respiratory distress and bronchopulmonary dysplasia in evolution: implications for antioxidant therapy

Preterm neonates with respiratory distress are exposed not only to the relative hyperoxia ex utero, but also to life-saving mechanical ventilation with high inspired oxygen (O2) concentrations, which is considered a major risk factor for the development of bronchopulmonary dysplasia, also referred to as chronic lung disease of infancy. O2 toxicity is mediated through reactive oxygen species (ROS). ROS are constantly generated as byproducts of normal cellular metabolism, but their production is increased in various pathological states, and also upon exposure to exogenous oxidants, such as hyperoxia. Antioxidants, either enzymatic or nonenzymatic, protect the lung against the deleterious effects of ROS. Expression of various pulmonary antioxidants is developmentally regulated in many species so that the expression is increased toward term gestation, as if in anticipation of birth into an O2-rich extrauterine environment. Therefore, the lungs of prematurely born infants may be ill-adapted for protection against ROS. While premature birth interrupts normal lung development, the clinical condition necessitating the administration of high inhaled O2 concentrations may lead to permanent impairment of alveolar development. An understanding of the processes involved in lung growth, especially in alveolarization and vascularization, as well as in repair of injured lung tissue, may facilitate development of strategies to enhance these processes.

Effects of fasting on tissue contents of coenzyme A and related intermediates in rats

Exposure of rats and mice to hyperoxia decreases lung coenzyme A (CoASH) contents, with a decrease of 50% observed in adult male Fischer-344 rats exposed to >95% O(2) for 48 h. Decreases in lung CoASH levels are not accompanied by increases in contents of the mixed glutathione disulfide of CoA, as might be expected of a primary oxidative stress on CoASH status. Animals exposed to hyperoxia exhibit decreased food intake, and the present studies were to test the hypothesis that fasting would decrease lung CoASH contents, thereby suggesting a mechanism for the effects of hyperoxia. Adult male Fischer-344 rats were examined after 0, 24, or 48 h of fasting (n = 5, 6, and 6, respectively). Fasting for 24 or 48 h did not affect lung CoASH levels or lung weights, despite 6 and 12% losses in body weight. Lung glutathione concentrations (nanomoles per gram of tissue) and contents (nanomoles per whole organ) and glutathione disulfide contents were 10 to 20% lower in rats fasted for 48 h than in fed rats. Liver weights and glutathione and glutathione disulfide contents and concentrations were 30 to 70% lower in rats fasted for 24 or 48 h than in fed rats. Hepatic CoASH concentrations increased during fasting, but hepatic contents of CoASH remained remarkably constant. Liver protein contents (milligrams of protein per whole organ) decreased after 24 and 48 h of fasting, but protein concentrations (milligrams of protein per gram of tissue) were higher in rats fasted 48 h than in fed rats. Overall, glutathione, glutathione disulfide, and protein contents in liver and skeletal muscle decreased with fasting, but significant changes in CoASH contents were not observed. Diminished food intake in animals does not explain the effects of hyperoxia on lung CoASH contents. CoASH and derived thioesters participate in many cellular functions, and if depletion of lung CoASH during hyperoxia proves to be relevant to mechanisms of lung injury, support of mechanisms needed to sustain CoA levels could be helpful in prematurely born infants and in adults.

Practicalities of glutathione supplementation in nutritional support

New nutraceutical products for nutritional support and antioxidant therapy such as glutathione require practical advice and information on the indications, methods and routes of administration, dosing (therapeutic drug monitoring), stability and physicochemical compatibility. This review is based on recent clinical and experimental publications in which glutathione has been used as a drug.

Redox control of the transsulfuration and glutathione biosynthesis pathways

Intracellular reduction-oxidation status is increasingly recognized as a primary regulator of cellular growth and development. The relative reduction-oxidation state of the cell depends primarily on the precise balance between concentrations of reactive oxygen species and the cysteine-dependent antioxidant thiol buffers glutathione and thioredoxin, which by preferentially reacting with reactive oxygen species, protect other intracellular molecules from oxidative damage. The transsulfuration pathway constitutes the major route of cysteine biosynthesis, and may thus be central in controlling the intracellular reduction-oxidation state and the balance between self-renewal and differentiation programs. This review discusses new findings on reciprocal reduction-oxidation modulation of enzymes involved in the transsulfuration and glutathione biosynthesis pathways, as well as studies elucidating the impact of sulfur amino acid availability on these pathways.