Early transient hypoglycemia is associated with increased albumin nitration in the preterm infant

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

Biomarkers of oxidative and nitro-oxidative stress: conventional and novel approaches

The concept of oxidative stress (OS) that connects altered redox biology with various diseases was introduced 30 years ago and has generated intensive research over the past two decades. Whereas it is now commonly accepted that macromolecule oxidation in response to ROS is associated with a variety of pathologies, the emergence of NO as a key regulator of redox signalling has led to the discovery of the pathophysiological significance of reactive nitrogen species (RNS). RNS can elicit various modifications of macromolecules and lead to nitrative or nitro-OS. In order to investigate oxidative and nitro-OS in human and in live animal models, circulating biomarker assays have been developed. This article provides an overview of key biomarkers used to assess lipid peroxidation and NO/NO2 signalling, thereby stressing the necessity to analyse several OS biomarkers in relation to the overall (aerobic) metabolism and health condition of patients. In addition, the potential interest of heart rate variability as the non-invasive integrative biomarker of OS is discussed.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Real-time continuous glucose monitoring reduces the duration of hypoglycemia episodes: a randomized trial in very low birth weight neonates

OBJECTIVES

Hypoglycemia is frequent in very low birth weight (VLBW) neonates and compromises their neurological outcome. The aim of this study was to compare real-time continuous glucose monitoring system (RT-CGMS) to standard methods by intermittent capillary blood glucose testing in detecting and managing hypoglycemia.

STUDY DESIGN

Forty-eight VLBW neonates were enrolled in this prospective study. During their 3 first days of life, their glucose level was monitored either by RT-CGMS (CGM-group), or by intermittent capillary glucose testing (IGM-group) associated with a blind-CGMS to detect retrospectively missed hypoglycemia. Outcomes were the number and duration of hypoglycemic (≤ 50 mg/dl) episodes per patient detected by CGMS.

RESULTS

Forty-three monitorings were analyzed (IGM n = 21, CGM n = 22), with a median recording time of 72 hours. In the IGM group, blind-CGMS revealed a significantly higher number of hypoglycemia episodes than capillary blood glucose testing (1.2 ± 0.4 vs 0.4 ± 0.2 episode/patient, p<0.01). In the CGM-group, the use of RT-CGMS made it possible (i) to detect the same number of hypoglycemia episodes as blind-CGMS (1.2 ± 0.4 episode/patient), (ii) to adapt the glucose supply in neonates with hypoglycemia (increased supply during days 1 and 2), and (iii) to significantly reduce the duration of hypoglycemia episodes per patient (CGM 44[10-140] min versus IGM 95[15-520] min, p<0.05). Furthermore, it reduced the number of blood samples (CGM 16.9 ± 1.0 vs IGM 21.9 ± 1.0 blood sample/patient, p<0.001).

CONCLUSION

RT-CGMS played a beneficial role in managing hypoglycemia in VLBW neonates by adjusting the carbohydrate supply to the individual needs and by reducing the duration of hypoglycemia episodes. The clinical significance of the biological differences observed in our study need to be explored.

Prematurity Reduces Functional Adaptation to Intestinal Resection in Piglets

BACKGROUND

Necrotizing enterocolitis and congenital gastrointestinal malformations in infants often require intestinal resection, with a subsequent risk of short bowel syndrome (SBS). We hypothesized that immediate intestinal adaptation following resection of the distal intestine with placement of a jejunostomy differs between preterm and term neonates.

METHODS

Preterm or term piglets were born by cesarean section and fed enterally for 2 days. On day 2, piglets were subjected to 50% distal intestinal resection with placement of a jejunostomy. On the following 4-5 days, piglets received parenteral nutrition with gradually increasing doses of enteral nutrition (bovine colostrum). Intestinal tissue samples were collected at delivery and 2 and 6-7 days after birth for histological examination and assessment of digestive enzyme activities.

RESULTS

Preterm and term piglets showed similar increases in intestinal weight and digestive enzyme activities from birth to 2 days. On days 6-7 after birth, the remnant intestine showed a similar density (g/cm) and mucosal mass in term and preterm piglets, but villus height, crypt depth, enzyme activities (sucrase, maltase, dipeptidyl peptidase IV [DPPIV]), and hexose uptake capacity were significantly higher in term piglets (P < .05). Preterm piglets were more prone to develop hypoglycemia, respiratory distress syndrome, dehydration, and circulatory instability after surgery compared with term piglets.

CONCLUSION

Studies on intestinal adaptation after resection are feasible in both preterm and term piglets, but intensive clinical support is required when rearing preterm piglets with SBS. Physiological instability and immaturity of the intestine may explain the fact that immediate adaptation after resection is reduced in preterm vs term neonates.

Protein tyrosine nitration and thiol oxidation by peroxynitrite-strategies to prevent these oxidative modifications

The reaction product of nitric oxide and superoxide, peroxynitrite, is a potent biological oxidant. The most important oxidative protein modifications described for peroxynitrite are cysteine-thiol oxidation and tyrosine nitration. We have previously demonstrated that intrinsic heme-thiolate (P450)-dependent enzymatic catalysis increases the nitration of tyrosine 430 in prostacyclin synthase and results in loss of activity which contributes to endothelial dysfunction. We here report the sensitive peroxynitrite-dependent nitration of an over-expressed and partially purified human prostacyclin synthase (3.3 μM) with an EC₅₀ value of 5 μM. Microsomal thiols in these preparations effectively compete for peroxynitrite and block the nitration of other proteins up to 50 μM peroxynitrite. Purified, recombinant PGIS showed a half-maximal nitration by 10 μM 3-morpholino sydnonimine (Sin-1) which increased in the presence of bicarbonate, and was only marginally induced by freely diffusing NO₂-radicals generated by a peroxidase/nitrite/hydrogen peroxide system. Based on these observations, we would like to emphasize that prostacyclin synthase is among the most efficiently and sensitively nitrated proteins investigated by us so far. In the second part of the study, we identified two classes of peroxynitrite scavengers, blocking either peroxynitrite anion-mediated thiol oxidations or phenol/tyrosine nitrations by free radical mechanisms. Dithiopurines and dithiopyrimidines were highly effective in inhibiting both reaction types which could make this class of compounds interesting therapeutic tools. In the present work, we highlighted the impact of experimental conditions on the outcome of peroxynitrite-mediated nitrations. The limitations identified in this work need to be considered in the assessment of experimental data involving peroxynitrite.

Redox albuminomics: oxidized albumin in human diseases

SIGNIFICANCE

Albumin is the major contributor to colloid oncotic pressure and also serves as an important carrier protein of many endogenous and exogenous molecules throughout the body. In blood and extravascular fluids, albumin is susceptible to different oxidative modifications, especially thiol oxidation and carbonylation. Because of its metal-binding properties and the redox properties of its Cys34 thiol, albumin displays an important antioxidant activity. As albumin is the predominant protein in most body fluids, its Cys34 represents the largest fraction of free thiols within body fluids.

RECENT ADVANCES

Evidence that albumin oxidation takes place in vivo has been reported only recently. Different redox proteomic, mass spectrometric, and chromatographic techniques have shown albumin redox modifications in various human pathophysiological conditions. As a whole, most data here presented demonstrate that massive albumin oxidation occurs in vivo in different biological fluids and, to some extent, that this process is correlated to organ dysfunction.

CRITICAL ISSUES

Recent reports suggest that the albumin redox state may serve as a global biomarker for the redox state in the body in various human diseases. However, further study is required to elucidate the exact relationship between albumin oxidation and pathology. In addition, it is unknown if some albumin oxidized forms may also have diagnostic uses.

FUTURE DIRECTIONS

Application of specific redox proteomics techniques for the characterization of oxidized albumin forms in screening studies is required. A further challenge will be to analyze how these oxidative albumin modifications are related to real impact to the body.

Procedural pain and oxidative stress in premature neonates

Preterm neonates exposed to painful procedures in the neonatal intensive care unit exhibit increased pain scores and alterations in oxygenation and heart rate. It is unclear whether these physiological responses increase the risk of oxidative stress. Using a prospective study design, we examined the relationship between a tissue-damaging procedure (TDP; tape removal during discontinuation of an indwelling central arterial or venous catheter) and oxidative stress in 80 preterm neonates. Oxidative stress was quantified by measuring uric acid (UA) and malondialdehyde (MDA) concentration in plasma before and after neonates (n = 38) experienced a TDP compared to those not experiencing any TDP (control group, n = 42). Pain was measured before and during the TDP using the Premature Infant Pain Profile (PIPP). We found that pain scores were higher in the TDP group compared to the control group (median scores, 11 and 5, respectively; P < .001). UA significantly decreased over time in control neonates but remained stable in TDP neonates (132.76 to 123.23 μM versus 140.50 to 138.9 μM; P = .002). MDA levels decreased over time in control neonates but increased in TDP neonates (2.07 to 1.81 μM versus 2.07 to 2.21 μM, P = .01). We found significant positive correlations between PIPP scores and MDA. Our data suggest a significant relationship between procedural pain and oxidative stress in preterm neonates.

PERSPECTIVE

This article presents data describing a significant relationship between physiological markers of neonatal pain and oxidative stress. The method described in this paper can potentially be used to assess the direct cellular effects of procedural pain as well the effectiveness of interventions performed to decrease pain.