Early NT-proBNP is able to predict spontaneous closure of patent ductus arteriosus in preterm neonates, but not the need of its treatment.

The objective of this study was to establish the potential utility of N-terminal pro-brain natriuretic peptide (NT-proBNP) in the management of patent ductus arteriosus (PDA). This was a monocentric prospective blind study that was conducted in a referral neonatal intensive care unit. The patients were very low-birth-weight/gestational-age neonates. Babies with cardiac congenital anomaly other than PDA, life-threatening congenital malformation, severe asphyxia at birth, persistent pulmonary hypertension, and death within the first week of life were excluded. Plasma NT-proBNP concentrations were determined on days 2, 4, and 7 of life. Echocardiography was performed on days 4 and 7. Results were blinded to clinicians. Only echographic results were available upon request. Thirty-one infants were included. NT-proBNP levels were significantly correlated to ductal size and to left atrial-to-aortic diameter ratio. The median NT-proBNP on both days 2 and 4 was significantly higher in neonates with later treated or persistent PDA. A level above 10.000 pg/mL at 48 h of age yielded a 100% positive and a 87% negative predictive value to exclude spontaneous ductal closure. However, no NT-proBNP threshold could predict which PDA would be judged necessary to treat. It was concluded that early low NT-proBNP values can be used as a reliable independent marker to predict spontaneous ductal closure in preterm neonates. Yet, high NT-proBNP levels should not be used to guide the decision to treat PDA, the risk being of treating many bystanding PDAs.

Hydration of lysozyme as observed by infrared spectrometry.

Infrared spectra of a film of lysozyme 3 mum thick, immersed in an atmosphere displaying a relative humidity, or hygrometry, which spans the whole range from 0 to 1 at room temperature, are recorded. The evolution of the spectra with this relative humidity is quantitatively analyzed on the basis of a newly proposed method. It allows the precise measurement of the quantity of water that remains embedded inside the dried sample at each stage of hydration, and the definition, in terms of chemical reactions of the three hydration mechanisms that correspond to the three hydration spectra on which all experimental spectra can be decomposed. With respect to preceding similar studies, some refinements are introduced that allow improvement of the interpretation, but that also raise some new questions, which mainly concern the structure of the hydrogen-bond network around the carbonyl peptide groups.

Hydration of hyaluronan polysaccharide observed by IR spectrometry. II. Definition and quantitative analysis of elementary hydration spectra and water uptake.

We recorded a series of spectra of sodium hyaluronan (HA) films that were in equilibrium with their surrounding humid atmosphere. The hygrometry of this atmosphere extended from 0 to 0.97% relative humidity. We performed a quantitative analysis of the corresponding series of hydration spectra that are the difference spectra of the film at a defined hygrometry minus the spectrum of the dried film (hygrometry = 0). The principle of this analysis is to use this series of hydration spectra to define a limited number (four) of "elementary hydration spectra" over which we can decompose all hydration spectra with good accuracy. This decomposition, combined with the measurements of the numbers of H(2)O molecules at the origin in these elementary hydration spectra of the three characteristic vibrational bands of H(2)O, allowed us to calculate the hydration number under different relative humidity conditions. This number compares well with that determined by thermogravimetry. Furthermore, the decomposition defines for each hygrometry value which chemical mechanisms represented by elementary hydration spectra are active. This analysis is pursued by determining for the elementary hydration spectra the number of hydrogen bonds established by each of the four alcohol groups found in each disaccharide repeat unit before performing the same analysis for amide and carboxylate groups. These results are later utilized to discuss the structure of HA at various stages of hydration.

Hydration of hyaluronan polysaccharide observed by IR spectrometry. III. Structure and mechanism of hydration.

The results of the analysis of hydration spectra of Na(+) hyaluronan (HA) performed in a companion study are translated in terms of chemical mechanisms. We find that dried HA is characterized by chains having ordered parts of at least 6 disaccharide repeat units that extend over 60 A. The order is mainly due to C3O3H...O5 and C4O4H...O5 hydrogen bonds that hinder rotations around beta(1-4) and beta(1-3) glycoside bonds. Along one chain there are two-thirds of the N-H amide groups and carboxyl groups that are directly hydrogen bonded, with no water intermediate, to form N-H...(-)O-C=O hydrogen bonds, which are collateral to C3O3H...O5 hydrogen bonds. The existence of these N-H...(-)O-C=O bonds is somewhat in opposition to literature descriptions. In this dry state a "water wire" of 4-5 H(2)O molecules, which are anchored on C=O carboxyl groups and hydrating the Na(+) CO(-) ionic group, establishes hydrogen bonds on other hydrophilic groups of the same chain or other chains and remains embedded in HA, even at 104 degrees C. Hydration occurs at low hygrometry around the remaining one-third of the N-H...(-)O-C=O pairs that are not hydrogen bonded. Each of these N-H and (-)O-C=O groups is hydrated by a nanodroplet of some 25 H(2)O molecules that finds other sites for binding and hydrates 2 disaccharide repeat units. At higher hygrometry bigger nanodroplets hydrate all hydrophilic sites.

Hydration of polysaccharide hyaluronan observed by IR spectrometry. I. Preliminary experiments and band assignments.

This article is the first one in a series dedicated to the study of hyaluronan as observed by IR spectrometry. The goal is to determine its hydration mechanism and the structural changes this mechanism implies. Hyaluronan is a natural polysaccharide that is widely used in biomedical applications and cosmetics. Its macroscopic properties are significantly dependent on its degree of hydration. In this article we record the IR spectrum of a several micron thick dried film and deduce that four or five residual H(2)O molecules remain around each disaccharide repeat unit in the dried film. We then compare the spectra of sodium hyaluronan and its acid form to assign vibrational bands linked to the carboxylate group. We proceed with a qualitative analysis of the spectral changes induced by changes of temperature and hygroscopicity, two independent parameters that act by modifying the hydrogen bond network of the sample. This enables us to assign most of the vibrational bands of the hydrophilic groups and to distinguish the bands that are due to these hydrophilic groups when they are or are not hydrogen bonded. It constitutes a prerequisite for the quantitative analysis of hydration spectra that will be described in the following articles of this series.

Bovine serum albumin observed by infrared spectrometry. I. Methodology, structural investigation, and water uptake.

The results of preliminary infrared (IR) spectrometry experiments on bovine serum albumin (BSA) films are presented. An analysis of spectral variations due to raising the temperature and deuteration of N--H groups leads to the assignment of most IR bands of BSA. From this analysis we furthermore deduce that at 115 degrees C only hydrogen bonds established by N&bond;H groups on the still present H(2)O molecules, which are so strongly bound to the protein that they do not evaporate, are weakened, some of which are broken. These N--H...OH(2) groups represent some 5% of all N--H groups in the dried protein. Spectral changes due to hydration by water vapor are also analyzed and a precise method to measure the water-vapor pressure of the atmosphere surrounding the BSA film, or equivalently the relative humidity, is described. Various procedures to measure the number of H(2)O molecules embedded in BSA are then presented and evaluated. One of them is selected as the best one for proteins, because it matches previous measurements based on gravimetric methods. This procedure is subsequently used in a study that is devoted to the determination of the various hydrogen-bond configurations, or interaction configurations, which are adopted by H(2)O molecules during the various steps of hydration of BSA. This first analysis of hydration spectra allows the completion of the assignment of IR bands. The various spectral components of the amide I band, which are interchanged during the hydration process, cannot be assigned to various secondary structures, as is usually proposed. It suggests that this usual assignment should be used with care, especially by taking into account the state of hydration, when one wishes to obtain structural information from it.

Bovine serum albumin observed by infrared spectrometry. II. Hydration mechanisms and interaction configurations of embedded H(2)O molecules.

The hydration mechanism of bovine serum albumin (BSA) is studied, and we analyze (de)hydration spectra displayed previously. We first determine the three elementary (de)hydration spectra on which all these (de)hydration spectra can be decomposed. They correspond to three different hydration mechanisms for the protein, which we define after a quantitative analysis performed in a second step. The first mechanism, which involves ionization of carboxylic COOH groups, occurs at low hydration levels and rapidly reaches a plateau when the hygroscopy is increased. It is a mechanism that involves a single H(2)O molecule and consequently requires somewhat severe steric conditions. The second mechanism occurs at all hydration levels and, because it involves more H(2)O molecules, requires less severe steric conditions. It consists of the simultaneous hydration of one amide N--H group and one carbonyl-amide C=O group by four H(2)O molecules and one carboxyl COO(-) group by eight H(2)O molecules. The third mechanism is simpler and consists of the introduction of H(2)O molecules into the hydrogen-bond network of the hydrated protein. It becomes important at a high hydration level, when the presence of an appreciable number of H(2)O molecules makes this hydrogen-bond network well developed. This analysis also shows that 80 H(2)O molecules remain embedded in one dried protein made of 604 peptide units. They are held by hydrogen bonds established by N--H groups and at the same time they establish two hydrogen bonds on two carbonyl-amide C=O groups. The proportion of free N--H groups can be determined together with that of carbonyl-amide C=O groups accepting no hydrogen bonds and that of carbonyl-amide C=O groups accepting two hydrogen bonds. The proportion of N--H groups establishing one hydrogen bond directly on a carbonyl-amide C=O group is 65%, which is the proportion of peptide units found in alpha helices in BSA.