Interactions of the Gasotransmitters Contribute to Microvascular Tone (Dys)regulation in the Preterm Neonate

Background & Aims Hydrogen sulphide (H2S), nitric oxide (NO), and carbon monoxide (CO) are involved in transitional microvascular tone dysregulation in the preterm infant; however there is conflicting evidence on the interaction of these gasotransmitters, and their overall contribution to the microcirculation in newborns is not known. The aim of this study was to measure the levels of all 3 gasotransmitters, characterise their interrelationships and elucidate their combined effects on microvascular blood flow. Methods 90 preterm neonates were studied at 24h postnatal age. Microvascular studies were performed by laser Doppler. Arterial COHb levels (a measure of CO) were determined through co-oximetry. NO was measured as nitrate and nitrite in urine. H2S was measured as thiosulphate by liquid chromatography. Relationships between levels of the gasotransmitters and microvascular blood flow were assessed through partial correlation controlling for the influence of gestational age. Structural equation modelling was used to examine the combination of these effects on microvascular blood flow and derive a theoretical model of their interactions. Results No relationship was observed between NO and CO (p = 0.18, r = 0.18). A positive relationship between NO and H2S (p = 0.008, r = 0.28) and an inverse relationship between CO and H2S (p = 0.01, r = -0.33) exists. Structural equation modelling was used to examine the combination of these effects on microvascular blood flow. The model with the best fit is presented. Conclusions The relationships between NO and H2S, and CO and H2S may be of importance in the preterm newborn, particularly as NO levels in males are associated with higher H2S levels and higher microvascular blood flow and CO in females appears to convey protection against vascular dysregulation. Here we present a theoretical model of these interactions and their overall effects on microvascular flow in the preterm newborn, upon which future mechanistic studies may be based.The authors would like to acknowledge the parents of the neonates enrolled in the 2CANS study for their participation, the staff of the Kaleidoscope Neonatal Intensive Care Unit at the John Hunter Children’s Hospital, and Kimberly-Clark Australia for providing the diapers used in this stud

Reconstructing Curvilinear Networks using Path Classifiers and Integer Programming

We propose a novel Bayesian approach to automated delineation of curvilinear structures that form complex and potentially loopy networks. By representing the image data as a graph of potential paths, we first show how to weight these paths using discriminatively-trained classifiers that are both robust and generic enough to be applied to very different imaging modalities. We then present an Integer Programming approach to finding the optimal subset of paths, subject to structural and topological constraints that eliminate implausible solutions. Unlike earlier approaches that assume a tree topology for the networks, ours explicitly models the fact that the networks may contain loops, and can reconstruct both cyclic and acyclic ones. We demonstrate the effectiveness of our approach on a variety of challenging datasets including aerial images of road networks and micrographs of neural arbors, and show that it outperforms state-of-the-art techniques

Microvascular tone in the preterm neonate: gasotransmitter interactions may be the key

Abstract of an oral presentation that was presented at the 5th Congress of the European Academy of Paediatric Societies EAPS 17-21 October 2014, Barcelona, Spain

A role for H₂S in the microcirculation of newborns: the major metabolite of H₂S (Thiosulphate) is increased in preterm infants.

Excessive vasodilatation during the perinatal period is associated with cardiorespiratory instability in preterm neonates. Little evidence of the mechanisms controlling microvascular tone during circulatory transition exists. We hypothesised that hydrogen sulphide (H₂S), an important regulator of microvascular reactivity and central cardiac function in adults and animal models, may contribute to the vasodilatation observed in preterm newborns. Term and preterm neonates (24–43 weeks gestational age) were studied. Peripheral microvascular blood flow was assessed by laser Doppler. Thiosulphate, a urinary metabolite of H₂S, was determined by high performance liquid chromatography as a measure of 24 hr total body H₂S turnover for the first 3 days of postnatal life. H₂S turnover was greatest in very preterm infants and decreased with increasing gestational age (p = 0.0001). H₂S turnover was stable across the first 72 hrs of life in older neonates. In very preterm neonates, H₂S turnover increased significantly from day 1 to 3 (p = 0.0001); and males had higher H₂S turnover than females (p = 0.04). A significant relationship between microvascular blood flow and H₂S turnover was observed on day 2 of postnatal life (p = 0.0004). H₂S may play a role in maintaining microvascular tone in the perinatal period. Neonates at the greatest risk of microvascular dysfunction characterised by inappropriate peripheral vasodilatation - very preterm male neonates - are also the neonates with highest levels of total body H₂S turnover suggesting that overproduction of this gasotransmitter may contribute to microvascular dysfunction in preterms. Potentially, H₂S is a target to selectively control microvascular tone in the circulation of newborns

Microvascular circulatory dysregulation driven in part by cystathionine gamma-lyase: a new paradigm for cardiovascular compromise in the preterm newborn

Objective: H 2 S may explain the dysregulation of microvascular tone associated with poor outcome following preterm birth. In adult vasculature, H 2 S is predominantly produced by CSE. We hypothesized that vascular CSE activity contributes to microvascular tone regulation during circulatory transition. Methods: Preterm (GA62) and full-term (GA69) guinea pig fetuses and neonates were studied. Microvascular blood flow was assessed by laser Doppler flowmetry. Thiosulfate, primary urinary metabolite of H 2 S, was determined by high-performance liquid chromatography. Real-time H 2 S production was assessed using a microrespiration system in fetal and postnatal (10, 24 hours) skin and heart samples. CSE contribution was investigated by inhibition via propargylglycine. Results: In preterm animals, postnatal H 2 S production capacity in peripheral vasculature increased significantly and was significantly reduced by the inhibition of CSE. Urinary thiosulfate correlated with both microvascular blood flow and capacity of the vasculature to produce H 2 S. H 2 S produced via CSE did not correlate directly with microvascular blood flow. Conclusions: In preterm neonates, H 2 S production increases during fetal-to-neonatal transition and CSE contribution to total H 2 S increases postnatally. CSE-dependent mechanisms may therefore underpin the increase in H 2 S production over the first 72 hours of life in preterm human neonates, associated with both central and peripheral cardiovascular instability

Urinary thiosulphate levels over the first three days of life.

<p>H₂S turnover was stable across the first three days of life in term and preterm neonates. In very preterm neonates, levels rose significantly over the first 72 hours of life (median±IQR). ^a-b-cp<0.0001 significant difference across days in very preterm gestational age group (Friedman repeated measures ANOVA for non-parametric data).</p

Sex differences in thiosulphate levels in very preterm neonates in early postnatal life (median±IQR).

<p>H₂S turnover, measured as urinary thiosulphate excreted per day per kg body weight, was significantly higher in males than females on both day 1 (*p = 0.01) and day 2 (**p = 0.04) of postnatal life (Friedman repeated measures ANOVA for non-parametric data).</p

Clinical Characteristics of Neonates.

<p>Data presented as median (minimum-maximum) or number (%). APGAR Score – scores 7 and above are generally regarded as normal, 4 to 6 fairly low and 3 and below critically low; CRIB II Score – Clinical Risk Index for Babies II, higher scores reflect poorer physiological stability; CPAP – Continuous Positive Air Pressure respiratory support; Patent Ductus Arteriosus refers to a hemodynamically significant duct diagnosed in first 72 hrs; IVH – intraventricular hemorrhage greater than grade II (significant IVH); Mean Blood Pressure reported is that at 24 h postnatal age and was not assessed in term controls; Death is those infants that survived to 72 h postnatal age but died prior to discharge.</p><p>*significantly different from females of the same gestational age group p<0.05;</p>†<p>significantly different from preterm neonates, within sex.</p

Relationship between baseline microvascular blood flow at 24 hr and H₂S turnover on day 2 of postnatal life.

<p>H₂S turnover (measured as urinary thiosulphate) was significantly correlated with baseline microvascular blood flow in preterm male neonates 29–36 wk GA (Pearson correlation; p = 0.04, <i>r</i> = 0.43). No relationship was observed for females of the same gestational age, very preterm neonates (24–28 wk GA) or term neonates (37+wk GA).</p