Cyst(e)ine requirements in enterally fed very low birth weight 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.

Enteral and parenteral nutrition considerations in pediatric patients

PURPOSE

Current clinical practice guidelines on management of enteral nutrition (EN) and parenteral nutrition (PN) in pediatric patients are reviewed.

SUMMARY

The provision of EN and PN in pediatric patients poses many unique considerations and challenges. Although indications for use of EN and PN are similar in adult and pediatric populations, recommended EN and PN practices differ for pediatric versus adult patients in areas such as selection of EN and PN formulations, timing of EN and PN initiation, advancement of nutrition support, and EN and PN goals. Additionally, provision of EN and PN to pediatric patients poses unique compounding and medication administration challenges. This article provides a review of current EN and PN best practices and special nutrition considerations for neonates, infants, and other pediatric patients.

CONCLUSION

The provision of EN and PN to pediatric patients presents many unique challenges. It is important for pharmacists to keep current with pediatric- and neonatal-specific guidelines on nutritional management of various disease states, as well as strategies to address compounding and medication administration challenges, in order to optimize EN and PN outcomes.

Neonatal Parenteral Nutrition Containing Calcium Chloride and Sodium Phosphate

Objective. The authors’ objectives were to determine mineral as well as Al intakes for ≤1000 g birth weight (ELBW) infants supported with parenteral nutrition (PN) solutions containing calcium chloride (CaCl) and sodium phosphate (NaPhos). Study design. This study was a prospective cohort study of 32 ELBW infants. Nutrient and Al intakes were recorded based on actual fluid intakes and concentrations of nutrients and Al in PN solutions. Growth velocities and peak alkaline phosphatase (AP) levels during the hospital stay were recorded. Result. Mean (±standard deviation) weight, length, and head circumference gains and AP were 13.7 ± 1.8 g/kg/d, 1.0 ± 0.2 cm/wk, 0.7 ± 0.1 cm/wk, and 636 ± 227 U/L, respectively. Al intake was 0.27 ± 0.07 µmol/kg/d (7.2 ± 1.8 µg/kg/d) in infants receiving PN with low Al content. This study documented average parenteral Ca and P intakes of 1.15 to 1.20 and 1.19 to 1.29 mmol/kg/d, (46-48 and 37-40 mg/kg/d), respectively, with PN fluid intakes of 90 to 100 mL/kg/d. Conclusion. AP and growth in ELBW infants receiving PN solutions containing CaCl are comparable to those reported in the literature for ELBW infants. Ca and P intakes approaching those reported for preterm infants receiving PN containing calcium gluconate can be provided with PN solutions containing CaCl. Fluid restriction is a significant factor limiting mineral intakes. Al intake can be limited to near FDA recommended intakes in PN solutions containing CaCl.

Working group reports: evaluation of the evidence to support practice guidelines for nutritional care of preterm infants-the Pre-B Project

The "Evaluation of the Evidence to Support Practice Guidelines for the Nutritional Care of Preterm Infants: The Pre-B Project" is the first phase in a process to present the current state of knowledge and to support the development of evidence-informed guidance for the nutritional care of preterm and high-risk newborn infants. The future systematic reviews that will ultimately provide the underpinning for guideline development will be conducted by the Academy of Nutrition and Dietetics' Evidence Analysis Library (EAL). To accomplish the objectives of this first phase, the Pre-B Project organizers established 4 working groups (WGs) to address the following themes: 1) nutrient specifications for preterm infants, 2) clinical and practical issues in enteral feeding of preterm infants, 3) gastrointestinal and surgical issues, and 4) current standards of infant feeding. Each WG was asked to 1) develop a series of topics relevant to their respective themes, 2) identify questions for which there is sufficient evidence to support a systematic review process conducted by the EAL, and 3) develop a research agenda to address priority gaps in our understanding of the role of nutrition in health and development of preterm/neonatal intensive care unit infants. This article is a summary of the reports from the 4 Pre-B WGs.

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.

Branched-chain amino acid requirements for enterally fed term neonates in the first month of life

BACKGROUND

Knowledge of essential amino acid requirements in infants is important because excessive intake of protein can lead to increased long-term morbidity such as obesity. A deficient intake may lead to suboptimal growth and impaired neurodevelopment. The current recommended branched-chain amino acid requirements in infants aged 0-1 mo are based on the amino acid content of human milk.

OBJECTIVE

We quantified the requirements for isoleucine, leucine, and valine for term neonates by using the indicator amino acid oxidation method with [1-(13)C]phenylalanine as the indicator.

DESIGN

Fully enterally fed term infants received randomly graded amounts of isoleucine (5-216 mg · kg(-1) · d(-1)), leucine (5-370 mg · kg(-1) · d(-1)), or valine (5-236 mg · kg(-1) · d(-1)) as part of an elemental formula. Data are expressed as means ± SDs.

RESULTS

Eighty-three Asian, term neonates (mean ± SD birth weight: 3.3 ± 0.4 kg; gestational age: 39.4 ± 1.3 wk) were studied at a postnatal age of 13 ± 5 d. Mean requirements for isoleucine, leucine, and valine (measured in boys only) were 105 mg · kg(-1) · d(-1) (r(2) = 0.61, P < 0.001), 140 mg · kg(-1) · d(-1) (r(2) = 0.26, P < 0.01), and 110 mg · kg(-1) · d(-1) (r(2) = 0.35, P = 0.001), respectively.

CONCLUSIONS

Current human milk-based recommendations for isoleucine and valine in term infants aged 0-1 mo are correct. However, the current recommendation for leucine (166 mg · kg(-1) · d(-1)) is higher than the mean requirement of 140 mg · kg(-1) · d(-1) that we determined in this study. This trial was registered at www.trialregister.nl as NTR1610.

New insights into the methodological issues of the indicator amino acid oxidation method in preterm neonates

BACKGROUND

We determined the effect of adaptation to the study diet on oxidation of the indicator amino acid and the required tracer washout time in preterms.

METHODS

Subjects received a study diet for 6 d that entailed a 50% reduction in leucine. Tracer studies using enterally infused [(13)C]bicarbonate and [1-(13)C]phenylalanine were performed on days 1, 2, 4, and 6. Breath samples containing (13)CO2 were collected during steady state and measured by infrared spectrometric analysis, and the fraction of (13)CO2 recovery from (13)C oxidation (F(13)CO2) was calculated.

RESULTS

Preterm infants (n = 11, birth weight 1.9 ± 0.1 kg, gestational age 32.6 ± 1.5 wk) received 166 mg/kg/d of leucine. Baseline enrichment changed significantly at day 1 of the study diet. F(13)CO2 did not change significantly between days 2 and 4 but was significantly lower at day 6. The tracer washout time was determined to be 7.5 h using a biphasic regression analysis.

CONCLUSION

One day of adaptation to a new diet is necessary to adapt to the (13)C enrichment of the study formula before starting infant requirement studies. Adaptation for a period of 5 d results in a protein-sparing response. The minimal time between two studies within the same subject is 7.5 h.

Methods to assess amino acid requirements in humans

PURPOSE OF REVIEW

There are now different stable isotopic methods to measure minimum daily human indispensable amino acid (IAA) requirements. There has been debate on the appropriateness of statistical methods used to define the nature of change in the response.

RECENT FINDINGS

Current isotopic methods measure daily amino acid oxidation and balance of the IAA under test, or of a selected indicator amino acid, to graded intakes of the test IAA. A key concern is how response curves of oxidation/balance are analyzed to find the inflection point (breakpoint) at which the intake requirement is identified. Evaluating the pattern of the response to identify a breakpoint by a two-phase regression appears best. The indicator amino acid oxidation method has also been shortened and developed into a noninvasive protocol suitable for different populations and age groups.

SUMMARY

The indicator amino acid oxidation and balance method might be considered the best approach currently available, but it is challenging. The short-term indicator oxidation method is noninvasive and nondemanding. IAA requirements, based on these methods, have implications for the quality of protein in the dietary intake of populations. Methods that assess the IAA requirements to support optimal body function also need to be developed.

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.

The addition of cysteine to the total sulphur amino acid requirement as methionine does not increase erythrocytes glutathione synthesis in the parenterally fed human neonate

Controversy exists as to whether the parenterally (PN) fed human neonate is capable of synthesizing adequate cysteine from methionine if the total dietary requirement for sulfur amino acid (SAA) is provided as methionine only. The goal of this study was to gather data on whether glutathione (GSH) synthesis is maximized at a methionine intake previously shown to be adequate for protein synthesis in the PN-fed human neonate. We measured GSH concentration, fractional, and absolute synthesis rate in five PN-fed human neonates. Each neonate underwent two isotope infusion studies of 7 h duration after a 2-d adaptation to the total SAA requirement (methionine only) and again after a further 2-d adaptation to the same methionine intake supplemented with cysteine at 10 mg x kg(-1) x d(-1). Cysteine supplementation did not significantly affect GSH synthesis. These data suggest that term infants are capable of synthesizing cysteine from methionine, not only for protein but also for GSH synthesis.

Initial nutritional management of the preterm infant

Postnatal nutrition has a large impact on long-term outcome of preterm infants. Evidence is accumulating showing even a relationship between nutrient supply in the first week of life and later cognitive development in extremely low birth weight infants. Since enteral nutrition is often not tolerated following birth, parenteral nutrition is necessary. Yet, optimal parenteral intakes of both energy and amino acids are not well established. Subsequently, many preterm infants fail to grow well, with long-term consequences. Early and high dose amino acid administration has been shown to be effective and safe in very low birth weight infants, but the effect of additional lipid administration needs to be defined.

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

OBJECTIVE

Our aim was to evaluate whether administration of additional cysteine is safe and stimulates glutathione synthesis in preterm infants in early life.

METHODS

We conducted a prospective, randomized, clinical trial with infants with birth weights of <1500 g (N = 20). The infants were assigned randomly to receive either a standard dose (45 mg/kg per day) or a high dose (81 mg/kg per day) of cysteine. Intakes of other amino acids were similar, providing a total protein intake of 2.4 g/kg per day in both groups. We recorded base requirements in the first 6 days of life. On postnatal day 2, we conducted a stable isotope study to determine glutathione concentrations and synthesis rates in erythrocytes.

RESULTS

Base requirements were higher in the high-dose cysteine group on days 3, 4, and 5. Despite an 80% increase in cysteine intake, plasma cystine concentrations did not increase. Glutathione concentrations and synthesis rates did not increase with additional cysteine administration.

CONCLUSIONS

Administration of a high dose of cysteine (81 mg/kg per day) to preterm infants seems clinically safe but does not stimulate glutathione synthesis, compared with a lower dose (45 mg/kg per day). Further research is required to determine whether there is significant benefit associated with cysteine supplementation.

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.

Cysteine, cystine or N-acetylcysteine supplementation in parenterally fed neonates

BACKGROUND

L-cysteine is thought to be a conditionally essential (i.e., essential under certain conditions) amino acid for neonates. It is a precursor of glutathione, an antioxidant that may reduce oxidation injury. The addition of cysteine to parenteral nutrition (PN) allows for the reduction of the amount of methionine in PN, thereby limiting hepatotoxicity, and acidifies the solution, thereby increasing calcium and phosphate solubility, and potentially improving bone mineralization.

OBJECTIVES

To determine the effects of supplementing parenteral nutrition with cysteine, cystine or its precursor N-acetylcysteine on neonatal growth and short and long-term outcomes.

SEARCH STRATEGY

The standard search method of the Cochrane Neonatal Review Group was used. MEDLINE (1966-December 2005), EMBASE (1974-December 2005), the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006) and recent abstracts (until December 2005) from the Society for Pediatric Research/American Pediatric Society, Eastern Society for Pediatric Research, and Society for Parenteral and Enteral Nutrition were searched.

SELECTION CRITERIA

All randomized (RCTs) and quasi-randomized trials that examined the effects of cysteine, cystine or N-acetylcysteine supplementation of neonatal PN were reviewed. Predetermined outcome variables included growth, nitrogen retention, mortality, morbidity secondary to oxidation injury, bone accretion, acidosis, liver disease, and cysteine levels.

DATA COLLECTION AND ANALYSIS

The standard methods of the Cochrane Collaboration and its Neonatal Review Group were used. Statistical analysis included relative risk, risk difference, and weighted mean difference (WMD).

MAIN RESULTS

Six trials fulfilled entry criteria. The majority of patients in these trials were preterm. Five small trials evaluated short-term cysteine supplementation of cysteine-free PN. One large multicenter RCT evaluated short-term N-acetylcysteine supplementation of cysteine-containing PN in extremely low birth weight infants (< or = 1000 grams).

PRIMARY OUTCOMES

Growth was not significantly affected by cysteine supplementation (evaluated in one quasi-randomized trial) or by N-acetylcysteine supplementation (evaluated in one RCT). Nitrogen retention was significantly increased by cysteine supplementation (studied in four trials) (WMD 31.8 mg/kg/day, 95% confidence interval +8.2, +55.4, n = 95, including 73 preterm infants).

SECONDARY OUTCOMES

Plasma levels of cysteine were significantly increased by cysteine supplementation but not by N-acetylcysteine supplementation. N-acetylcysteine supplementation did not significantly affect the risks of death by 36 postmenstrual weeks, bronchopulmonary dysplasia (BPD), death or BPD, retinopathy of prematurity (ROP), severe ROP, necrotizing enterocolitis requiring surgery, periventricular leukomalacia, intraventricular hemorrhage (IVH), or severe IVH. No data were available on other outcomes.

AUTHORS' CONCLUSIONS

Available evidence from RCTs shows that routine short-term cysteine chloride supplementation of cysteine-free PN in preterm infants improves nitrogen balance.However, there is insufficient evidence to assess the risks of cysteine supplementation, especially regarding metabolic acidosis, which has been reported during the first two weeks of cysteine chloride administration. Available evidence from a large RCT trial does not support routine N-acetylcysteine supplementation of cysteine-containing PN in extremely low birth weight infants. A large RCT would be required to assess whether routine prolonged cysteine supplementation of cysteine-free PN affects growth and short and long-term neonatal outcomes in very low birth weight infants.