High-dose cysteine administration does not increase synthesis of the antioxidant glutathione preterm infants

Parenteral Cysteine Supplementation in Preterm Infants: One Size Does Not Fit All

Due to their gastrointestinal immaturity or the severity of their pathology, many neonates require parenteral nutrition (PN). An amino acid (AA) solution is an important part of PN. Cysteine is a key AA for protein and taurine synthesis, as well as for glutathione synthesis, which is a cornerstone of antioxidant defenses. As cysteine could be synthesized from methionine, it is considered a nonessential AA. However, many studies suggest that cysteine is a conditionally essential AA in preterm infants due to limitations in their capacity for cysteine synthesis from methionine and the immaturity of their cellular cysteine uptake. This critical review discusses the endogenous synthesis of cysteine, its main biological functions and whether cysteine is a conditionally essential AA. The clinical evidence evaluating the effectiveness of the current methods of cysteine supplementation, between 1967 and 2023, is then reviewed. The current understanding of cysteine metabolism is applied to explain why these methods were not proven effective. To respond to the urgent need for changing the current methods of parenteral cysteine supplementation, glutathione addition to PN is presented as an innovative alternative with promising results in an animal model. At the end of this review, future directions for research in this field are proposed.

Parenteral Nutrition and Oxidant Load in Neonates

Neonates with preterm, gastrointestinal dysfunction and very low birth weights are often intolerant to oral feeding. In such infants, the provision of nutrients via parenteral nutrition (PN) becomes necessary for short-term survival, as well as long-term health. However, the elemental nutrients in PN can be a major source of oxidants due to interactions between nutrients, imbalances of anti- and pro-oxidants, and environmental conditions. Moreover, neonates fed PN are at greater risk of oxidative stress, not only from dietary sources, but also because of immature antioxidant defences. Various interventions can lower the oxidant load in PN, including the supplementation of PN with antioxidant vitamins, glutathione, additional arginine and additional cysteine; reduced levels of pro-oxidant nutrients such as iron; protection from light and oxygen; and proper storage temperature. This narrative review of published data provides insight to oxidant molecules generated in PN, nutrient sources of oxidants, and measures to minimize oxidant levels.

High particle counts in neonatal parenteral nutrition solutions with added cysteine: Relationship to crystal formation and effect of filtration on cysteine content

BACKGROUND

Parenteral nutrition(PN) solutions containing calcium gluconate and cysteine have elevated particle counts when analyzed using laser light obscuration (LO) as recommended by the United States Pharmacopeia. It is unclear whether increased particle formation in these solutions results in decreased availability of cysteine to neonatal patients due to filtration.

OBJECTIVE

The purpose of this study was to measure cysteine concentrations in neonatal PN solutions before and after filtration as well as analyze precipitates on filters.

METHODS

Solutions of PN containing amino acids with and without cysteine that were compounded with calcium chloride or calcium gluconate plus potassium phosphate were analyzed using LO. Concentrations of cysteine were measured before and after filtration. The effect on particle formation of magnesium sulfate (MgSO₄ ) and D70 was also evaluated.

RESULTS

Multiple additives including the specific calcium or D70 additive, cysteine, and MgSO₄ influenced particle formation of particles detected using LO. There was no significant decrease in cysteine concentration because of filtering and there was no difference in the amount of calcium on filters of various solutions after filtration regardless of LO particle counts. Scanning electron micrographic (SEM) analysis found no significant differences in crystal composition. Light microscopic and SEM examination did not show evidence of high particle counts on filters.

CONCLUSION

The increased particle counts detected in neonatal PN solutions containing cysteine added at the time of compounding does not appear to result in increased precipitate or crystal formation. It is not associated witha decrease in cysteine delivery to patients.

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.

Protein intakes to optimize outcomes for preterm infants

Proteins are key structural components of all human cells and are also involved in key physiologic processes through their roles as enzymes, hormones and transport proteins. Protein requirements are substantially higher in preterm infants than those born at term, yet inadequate protein intakes are a common problem on many neonatal units. Very preterm infants (VPT, <32 weeks) commonly receive parenteral amino acid solutions which are typically commenced on admission, and increased over the next few days. Several recent studies have explored differing parenteral amino acid intakes in the first few days, and recommendations have recently been updated. Parenteral nutrition intakes are decreased as enteral feeds are tolerated, but human milk alone will not meet protein needs in most VPT and supplementation or fortification will be required. This review paper considers basic protein and amino acid physiology in the newborn period, and the evidence base for current recommendations.

Thiol-Redox Regulation in Lung Development and Vascular Remodeling

Significance: Redox homeostasis is finely tuned and governed by distinct intracellular mechanisms. The dysregulation of this either by external or internal events is a fundamental pathophysiologic base for many pulmonary diseases. Recent Advances: Based on recent discoveries, it is increasingly clear that cellular redox state and oxidation of signaling molecules are critical modulators of lung disease and represent a final common pathway that leads to poor respiratory outcomes. Critical Issues: Based on the wide variety of stimuli that alter specific redox signaling pathways, improved understanding of the disease and patient-specific alterations are needed for the development of therapeutic targets. Further Directions: For the full comprehension of redox signaling in pulmonary disease, it is essential to recognize the role of reactive oxygen intermediates in modulating biological responses. This review summarizes current knowledge of redox signaling in pulmonary development and pulmonary vascular disease.

Calcium Chloride and Calcium Gluconate in Neonatal Parenteral Nutrition Solutions with Added Cysteine: Compatibility Studies Using Laser Light Obscuration Methodology

BACKGROUND

Parenteral nutrition (PN) solutions containing calcium gluconate (CaGlu) and cysteine have elevated particle counts when analyzed using laser light obscuration (LO) as recommended by the United States Pharmacopeia (USP). There are no compatibility studies for solutions compounded with cysteine and containing calcium chloride (CaCl₂ ) using LO. The purpose of this study was to conduct compatibility testing for neonatal PN solutions containing CaCl₂ and CaGlu with cysteine.

METHODS

Solutions of amino acids (2.5%), containing either CaCl₂ or CaGlu plus potassium phosphate, were compounded with 50 and 100 mg/dL cysteine. Solutions were analyzed for particle counts using LO. Maximum concentrations tested were 20 mmol/L calcium and 15 mmol/L phosphate. Three solutions containing CaCl₂ (144 total solutions) and 2 containing CaGlu (96 total solutions) and the same concentration of additives were compounded. If the average particle count of replicates exceeded USP guidelines, the solution was incompatible.

RESULTS

All solutions containing CaGlu had particle counts that exceeded USP guidelines for particle counts ≥10 μm (range, 86-580 particles/mL). For CaCl₂ , 90 of 144 solutions were compatible (range of particle counts for all solutions, 3-121 particles/mL). Maximum compatible concentrations of CaCl₂ and potassium phosphate were 15 mmol/L and 12.5 mmol/L, respectively, for solutions containing both 50 and 100 mg/dL cysteine.

CONCLUSION

This study found that neonatal PN solutions containing CaGlu with added cysteine have significantly higher particle counts, exceeding USP guidelines for compatibility, than those containing CaCl₂ .

Parenteral nutrition for preterm infants: Issues and strategy

Due to transient gut immaturity, most very preterm infants receive parenteral nutrition (PN) in the first few weeks of life. Yet providing enough protein and energy to sustain optimal growth in such infants remains a challenge. Extrauterine growth restriction is frequently observed in very preterm infants at the time of discharge from hospital, and has been found to be associated with later impaired neurodevelopment. A few recent randomized trials suggest that intensified PN can improve early growth; whether or not such early PN improves long-term neurological outcome is still unclear. Several other questions regarding what is optimal PN for very preterm infants remain unanswered. Amino acid mixtures designed for infants contain large amounts of branched-chain amino acids and taurine, but there is no consensus on the need for some nonessential amino acids such as glutamine, arginine, and cysteine. Whether excess growth in the first few weeks of life, at a time when very preterm infants receive PN, has an imprinting effect, increasing the risk of metabolic or vascular disease at adulthood continues to be debated. Even though uncertainty remains regarding the long-term effect of early PN, it appears reasonable to propose intensified initial PN. The aim of the current position paper is to review the evidence supporting such a strategy with regards to the early phase of nutrition, which is mainly covered by parenteral nutrition. More randomized trials are, however, needed to further support this type of approach and to demonstrate that this strategy improves short- and long-term outcome.

Characterizing thiol redox dynamics in the organogenesis stage rat embryo

Precise control of the glutathione (GSH): glutathione disulfide (GSSG) balance is vital for the developing embryo, but it is not yet well understood how GSH levels and the GSH redox state are regulated, maintained, and modulated over the course of mammalian embryonic development. In this study, we characterize and connect thiol redox dynamics, protein synthesis, volumetric growth and net cysteine fluxes over the course of early organogenesis (gestational day (GD) 10-GD11.13) in the rat embryo. Our results show that despite a significant exponential growth of conceptal volumes and protein mass, the GSH: GSSG redox balance is remarkably stable during early organogenesis, with distinct redox potentials for the visceral yolk sac (VYS) (- 218mV) and the embryo proper (EMB) (- 222mV). The yolk sac was found to play a key role in maintaining GSH levels and the GSH: GSSG redox balance in the developing embryo. Based on an overall cysteine (Cys) mass-balance, we show that until GD10.6, yolk sac supply of Cys, the rate-limiting precursor for GSH synthesis, is sufficient to sustain embryonic demands for its GSH synthesis and protein synthesis needs. After GD10.6, the EMB maintains the amino acid intake flux, resulting in a significant depletion of most thiols in the amniotic fluid and the yolk sac fluid. Cysteine, was found to be predominantly used for de novo protein synthesis in the developing embryo (approximately 90% of total Cys). Protein synthesis (rates) should thus be included in any quantitative assessment of GSH redox dynamics in the developing embryo. Our time-course dataset of thiol dynamics, developed exponential relationships for protein synthesis and volumetric growth, and yolk sac surface area-mediated protein influx, provide important quantitative insights in GSH redox dynamics during embryonic development and are a prerequisite to further develop quantitative 'systems biology' models for GSH metabolism in the developing embryo.

Aluminum Content of Neonatal Parenteral Nutrition Solutions

INTRODUCTION

Calcium chloride (CaCl₂) has been the only calcium additive available in the United States that has a low aluminum (Al) content. Calcium gluconate in glass vials (CaGluc-Gl) has a high Al content while calcium gluconate in plastic vials (CaGluc-Pl) has a low Al content. The purpose of this study was to measure Al concentrations in neonatal parenteral nutrition (PN) solutions prepared using various calcium additives.

METHODS

Samples of solutions compounded with CaCl₂ or CaGluc-Gl and sodium phosphate (NaPhos) as well as CaGluc-Pl and sodium glycerophosphate (NaGP) with and without cysteine were analyzed for Al content. Samples of the cysteine and calcium gluconate additives were also sent for analysis.

RESULTS

Solutions containing CaCl₂ and CaGlu-Pl had mean Al concentrations of 1.2-2.3 mcg/dL, while those with CaGlu-Gl had mean concentrations of 14.6-15.1 mcg/dL. Solutions made with NaGP were low in Al content. The measured Al content of 2 lots of the cysteine additive were 168 ± 23 mcg/L and 126 ± 5 mcg/L. The Al concentration equalled 2730 ± 20 mcg/L for the CaGlu-Gl additive and 310 ± 80 mcg/L for the CaGlu-Pl additive.

CONCLUSION

The study indicates that solutions containing CaCl₂ or CaGluc-Pl and NaPhos or NaGP are low in Al content. Using these options for calcium and phosphate additives can limit aluminum intake from neonatal PN to levels within the Food and Drug Administration guideline of ≤5 mcg/kg/d.

Calcium Chloride in Neonatal Parenteral Nutrition Solutions with and without Added Cysteine: Compatibility Studies Using Laser and Micro-Flow Imaging Methodology

BACKGROUND

Previous studies of compatibility of calcium chloride (CaCl2) and phosphates have not included particle counts in the range specified by the United States Pharmacopeia. Micro-flow imaging techniques have been shown to be comparable to light obscuration when determining particle count and size in pharmaceutical solutions.

OBJECTIVE

The purpose of this study was to do compatibility testing for parenteral nutrition (PN) solutions containing CaCl2 using dynamic light scattering and micro-flow imaging techniques.

METHODS

Solutions containing TrophAmine (Braun Medical Inc, Irvine, CA), CaCl2, and sodium phosphate (NaPhos) were compounded with and without cysteine. All solutions contained standard additives to neonatal PN solutions including dextrose, trace metals, and electrolytes. Control solutions contained no calcium or phosphate. Solutions were analyzed for particle size and particle count. Means of Z-average particle size and particle counts of controls were determined. Study solutions were compared to controls and United States Pharmacopeia (USP) Chapter 788 guidelines. The maximum amount of Phos that was compatible in solutions that contained at least 10 mmol/L of Ca in 2.5% amino acids (AA) was determined. Compatibility of these solutions was verified by performing analyses of 5 repeats of these solutions. Microscopic analyses of the repeats were also performed.

RESULTS

Amounts of CaCl2 and NaPhos that were compatible in solutions containing 1.5%, 2%, 2.5%, and 3% AA were determined. The maximum amount of NaPhos that could be added to TrophAmine solutions of > = 2.5% AA containing at least 10 mmol/L of CaCl2 was 7.5 mmol/L. Adding 50 mg/dL of cysteine increased the amount of NaPhos that could be added to solutions containing 10 mmol/L of CaCl2 to 10 mmol/L.

CONCLUSION

Calcium chloride can be added to neonatal PN solutions containing NaPhos in concentrations that can potentially provide an intravenous intake of adequate amounts of calcium and phosphorus.

Effect of High-Dose Cysteine Supplementation on Erythrocyte Glutathione: A Double-Blinded, Randomized Placebo-Controlled Pilot Study in Critically Ill Neonates

BACKGROUND

This study's objective was to determine if parenteral cysteine when compared with isonitrogenous noncysteine supplementation increases erythrocyte reduced glutathione (GSH) in neonates at high risk for inflammatory injury.

MATERIAL AND METHODS

Neonates with a score for neonatal acute physiology >10 requiring mechanical ventilation and parenteral nutrition (PN) were randomized in a double-blinded, placebo-controlled study to receive parenteral cysteine-HCl (CYS group) or additional PN amino acids (ISO group) at 121 mg/kg/d for ≥7 days. A 6-hour [(13)C2] glycine IV infusion was administered at study week 1 to determine the fractional synthetic rate of GSH (FSR-GSH).

RESULTS

Baseline characteristics were similar between the CYS (n = 17) and ISO groups (n = 21). Erythrocyte GSH and total glutathione concentrations, GSH:oxidized GSH (GSSG), and FSR-GSH after treatment were not different between groups. However, the CYS group had a larger individual positive change in GSH and total glutathione (infusion day - baseline) compared with the ISO group (P = .02 for each). After adjusting for treatment, a lower enrollment weight and rate of red blood cell transfusion were associated with a decreased change in total glutathione and GSH (P < .05 for each).

CONCLUSION

When compared with isonitrogenous noncysteine supplementation, high-dose cysteine supplementation for at least 1 week in critically ill neonates resulted in a larger and more positive individual change in GSH. Smaller infants and those who received transfused blood demonstrated less effective change in GSH with cysteine supplementation. The benefit of cysteine remains promising and deserves further investigation.

High-precision mass spectrometric analysis using stable isotopes in studies of children

The use of stable isotopes combined with mass spectrometry (MS) provides insight into metabolic processes within the body. Herein, an overview on the relevance of stable isotope methodology in pediatric research is presented. Applications for the use of stable isotopes with MS cover carbohydrate, fat, and amino acid metabolism as well as body composition, energy expenditure, and the synthesis of specific peptides and proteins, such as glutathione and albumin. The main focus of these studies is on the interactions between nutrients and the endogenous metabolism within the body and how these factors affect the health of a growing infant. Considering that the early imprinting of metabolic processes hugely impacts metabolism (and thus functional outcome) later in life, research in this area is important and is advancing rapidly. The major fluxes on a metabolic level are the synthesis and breakdown rates. They can be quantified using kinetic tracer analysis and mathematical modeling. Organic MS and isotope ratio mass spectrometry (IRMS) are the two most mature techniques for the isotopic analysis of compounds. Introduction of the samples is usually done by coupling gas chromatography (GC) to either IRMS or MS because it is the most robust technique for specific isotopic analysis of volatile compounds. In addition, liquid chromatography (LC) is now being used more often as a tool for sample introduction of both volatile and non-volatile compounds into IRMS or MS for (13)C isotopic analyses at natural abundances and for (13)C-labeled enriched compounds. The availability of samples is often limited in pediatric patients. Therefore, sample size restriction is important when developing new methods. Also, the availability of stable isotope-labeled substrates is necessary for measurements of the kinetics and concentrations in metabolic studies, which can be a limiting factor. During the last decade, the availability of these substrates has increased. Furthermore, improvements in the accuracy, precision, and sensitivity of existing techniques (such as GC/IRMS) and the development of new techniques (such as LC/IRMS) have opened up new avenues for tackling these limitations.

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.

Future applications of antioxidants in premature infants

PURPOSE OF REVIEW

This review will examine the unique susceptibility of premature infants to oxidative stress, the role of reactive oxygen species (ROS) in the pathogenesis of common disorders of the preterm infant, and potential for therapeutic interventions using enzymatic and/or nonenzymatic antioxidants.

RECENT FINDINGS

Oxidative stress is caused by an imbalance between the production of ROS and the ability to detoxify them with the help of antioxidants. The premature infant is especially susceptible to ROS-induced damage because of inadequate antioxidant stores at birth, as well as impaired upregulation in response to oxidant stress. Thus, the premature infant is at increased risk for the development of ROS-induced diseases of the newborn, such as bronchopulmonary dysplasia, retinopathy of prematurity, necrotizing enterocolitis, and periventricular leukomalacia.

SUMMARY

Potential therapies for ROS-induced disease include both enzymatic and nonenzymatic antioxidant preparations. More research is required to determine the beneficial effects of supplemental antioxidant therapy.

Amino acid composition in parenteral nutrition: what is the evidence?

PURPOSE OF REVIEW

Complete parenteral nutrition solutions contain mixed amino acid products providing all nine essential amino acids and a varying composition of nonessential amino acids. Relatively little rigorous comparative efficacy research on altered parenteral nutrition amino acid composition has been published in recent years.

RECENT FINDINGS

Limited data from randomized, double-blind, adequately powered clinical trials to define optimal doses of total or individual amino acids in parenteral nutrition are available. An exception is the growing number of studies on the efficacy of glutamine supplementation of parenteral nutrition or given as a single parenteral agent. Parenteral glutamine appears to confer benefit in selected patients; however, additional data to define optimal glutamine dosing and the patient subgroups who may most benefit from this amino acid are needed. Although some promising studies have been published, little data are available in the current era of nutrition support on the clinical efficacy of altered doses of arginine, branched chain amino acids, cysteine, or taurine supplementation of parenteral nutrition.

SUMMARY

Despite routine use of parenteral nutrition, surprisingly little clinical efficacy data are available to guide total or specific amino acid dosing in adult and pediatric patients requiring this therapy. This warrants increased attention by the research community and funding agencies to better define optimal amino acid administration strategies in patient subgroups requiring parenteral nutrition.

Maturation of the antioxidant system and the effects on preterm birth

The study of the interplay of the generation of reactive oxygen and nitrogen species with their related antioxidant enzymes at the maternal-placental-fetal interfaces during normal and abnormal pregnancy is in its 'infancy'. Our understanding of the role of antioxidant systems during fetal and neonatal development is constantly changing with research better defining the biological roles of these highly reactive species and the maintenance of optimal oxidant/antioxidant balance. The antioxidant enzyme system is upregulated during the last 15% of gestation, a timeframe when non-enzymatic antioxidants are also crossing the placenta in increasing concentrations. These developmental changes provide for the transition from the relative hypoxia of intrauterine development to the oxygen-rich extrauterine environment. Preterm birth is associated with an increased oxidant burden which places these infants at much higher risk of injury. This is especially true since studies have failed to reveal significant induction of antioxidants in response to the increased generation of these reactive species. Improved understanding of these relationships will be necessary for the development of rational treatments aimed at improving pregnancy outcomes and reducing the burden of oxidative stress to premature newborns.

Nutritional support for extremely low-birth weight infants: abandoning catabolism in the neonatal intensive care unit

PURPOSE OF REVIEW

Obviously, the ultimate goal in neonatology is to achieve a functional outcome in premature infants that is comparable to healthy term-born infants. As nutrition is one of the key factors for normal cell growth, providing the right amount and quality of nutrients could prove pivotal for normal development. However, many premature infants are catabolic during the first week of life, which has directly been linked to growth failure, disease, and suboptimal long-term outcome. This review describes the progress in research on parenteral nutrition for premature infants with a focus on amino acids and the influence of nutrition on later outcome.

RECENT FINDINGS

Although randomized clinical trials on early nutrition for premature infants remain relatively sparse, evidence is accumulating on its beneficial effects both on the short-term and long-term. However, some research also warns for adverse effects.

SUMMARY

Despite the fact that substantially improved nutritional therapies for preterm neonates have been implemented, still, some reluctance exists when it comes to providing high amounts of nutrition to the most immature infants. Pros and cons are outlined, as well as deficits in knowledge, when it comes to providing the optimal nutrient strategy in the first postnatal phase.

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.