Assessment of elastin maturation by radioimmunoassay of desmosine in the developing human lung

Effects of maternal food restriction on offspring lung extracellular matrix deposition and long term pulmonary function in an experimental rat model

Intrauterine growth restriction (IUGR) increases the risk of respiratory compromise throughout postnatal life. However, the molecular mechanism(s) underlying the respiratory compromise in offspring following IUGR is not known. We hypothesized that IUGR following maternal food restriction (MFR) would affect extracellular matrix deposition in the lung, explaining the long-term impairment in pulmonary function in the IUGR offspring. Using a well-established rat model of MFR during gestation to produce IUGR pups, we found that at postnatal day 21, and at 9 months (9M) of age the expression and abundance of elastin and alpha smooth muscle actin (αSMA), two key extracellular matrix proteins, were increased in IUGR lungs when compared to controls (P < 0.05, n = 6), as determined by both Western and immunohistochemistry analyses. Compared to controls, the MFR group showed no significant change in pulmonary resistance at baseline, but did have significantly decreased pulmonary compliance at 9M (P < 0.05 vs. control, n = 5). In addition, MFR lungs exhibited increased responsiveness to methacholine challenge. Furthermore, exposing cultured fetal rat lung fibroblasts to serum deprivation increased the expression of elastin and elastin-related genes, which was blocked by serum albumin supplementation, suggesting protein deficiency as the predominant mechanism for increased pulmonary elastin deposition in IUGR lungs. We conclude that accompanying the changes in lung function, consistent with bronchial hyperresponsiveness, expression of the key alveolar extracellular matrix proteins elastin and αSMA increased in the IUGR lung, thus providing a potential explanation for the compromised lung function in IUGR offspring.

PULMONARY ELASTIN SYNTHESIS AND DEPOSITION IN DEVELOPING AND MATURE SHEEP: EFFECTS OF INTRAUTERINE GROWTH RESTRICTION

Hypoxia and nutrient restriction during gestation restrict fetal growth and alter lung development. As elastin is intimately involved in lung development, our aim was to assess pulmonary elastin synthesis and deposition following intrauterine growth restriction (IUGR) induced by umbilicoplacental embolization (UPE). Pulmonary tropoelastin expression and elastin content were examined at 128 days (5 days UPE) and 140 days (20 days UPE) of the 147- days gestation and at 8 weeks and 2.3 years after birth (both approximately 27 days UPE) in sheep. UPE induced hypoxemia, hypoglycemia, and fetal growth restriction but did not affect pulmonary tropoelastin mRNA levels or elastin deposition at any age; furthermore, elastin content was unaltered apart from being lower at 140 days. The authors conclude that hypoxemia and undernutrition associated with IUGR do not affect elastin synthesis and deposition in fetal lungs; alterations in lung structure following IUGR must have other causes.

Progress in the methodological strategies for the detection in real samples of desmosine and isodesmosine, two biological markers of elastin degradation

Desmosines are crosslinking amino acids unique to mature elastin in humans. Owing to this unicity, they have been discussed as potentially attractive indicators of connective tissue disorders whose clinical manifestations are mostly the result of elastin degradation. This review covers advances in immunochemical, chromatographic, and electrophoretic procedures applied in the last 25 years to detect and quantitate these crosslinksin a variety of biological samples. Recent applications of CE with LIF detection (CE-LIF) for investigating the content of desmosines in different fluids will also be discussed.

Cyclopentenosine, major trifunctional crosslinking amino acid isolated from acid hydrolysate of elastin

A trifunctional crosslinking amino acid named cyclopentenosine (CP) was isolated from the hydrolysate of bovine nuchal ligament elastin. CP and its derivatives were identified by spectroscopic methods. CP was found to consist of a 2-cyclopenten-1-one structure and its imine-enamine tautomers with enantiomers in H(2)O. A model reaction for the formation of the CP crosslink using model compounds for allysine (propanal) and lysine (n-butylamine) demonstrated that CP is composed of 2-cyclopenten-1-one and alpha, beta, gamma, delta-unsaturated aldehyde derived from three allysine residues. An ion-paired high-performance liquid chromatographic method for the determination of CP was developed. Among various bovine tissues the nuchal ligament had the highest concentration of CP. The age-related changes in the concentration of CP were examined in the aorta from rat (short-lived species) and bovine (long-lived species). The CP content was very low in the newborn rat but increased markedly with growth. After maturity, the CP content remained nearly the same or slightly decreased. In bovine aorta, the CP content scarcely changed from 7 months to 16 years.

Comparative biochemistry of gestational and postnatal lung growth and development in the rat and human

We compared the ontogeny of collagen (hydroxyproline), elastin (desmosine), soluble protein, and DNA in the lungs of rate and humans during gestation and postnatal life. In humans, lung weight/body weight ratios declined faster during gestation than postnatally, whereas in rats lung weight/body weight ratio declined little during gestation and then suddenly on the first day of life. Lung weight/body weight ratios may be lower than expected around term in humans, and prediction data are given to assess human pulmonary hypoplasia. Rats and humans differed in water content of their lungs, with rats showing a sharper decline during gestation. In the human lung, collagen and elastin made their appearance at an early stage of gestation; elastin. In particular, increased rapidly during gestation, suggesting a role in intrauterine alveolar formation. In the rat, elastin accumulation is primarily a postnatal event, as is alveolar formation. Hydroxyproline concentrations increased with conceptual age and continued to increase rapidly postnatally between 4 and 7 weeks in the rat, but slowed in the human after 60 weeks of conceptual age. Desmosine concentrations level off at the end of the study period in rats, while these are still increasing, although slowly, in humans. Overall lung growth, as assessed by weight, was linear in humans, but phases of lung growth were apparent in the rat, including one of minimal growth in the immediate postnatal period.

Biochemical, clinical, and morphologic studies on lungs of infants with bronchopulmonary dysplasia

We correlated clinical, biochemical, and morphologic findings in the lungs of 48 infants dying of either bronchopulmonary dysplasia (BPD) or hyaline membrane disease (HMD) to obtain a better idea of the disease process. The infants ranged from 24 weeks of gestation to 1 1/2 postnatal years. The lungs of BPD and HMD infants had higher contents of DNA, alkalisoluble protein, hydroxyproline, and desmosine, as well as increased concentrations of DNA, hydroxyproline, and desmosine when compared with the lungs of 72 control infants. BPD was classified histologically into 4 groups: Group I was a phase of acute lung injury, Group II the proliferative phase; Group III the phase of early repair, and Group IV the phase of late repair. We saw a significant increase in hydroxyproline concentration in Groups II and III. The ratio of type I/III collagen decreased in BPD Groups II to IV. Desmosine was significantly higher only in Group III than in controls. When the pathological classification was related to biochemical and clinical features of BPD, the classification showed dependence on the number of days the infant survived postnatally and not on the gestational age of the infant. The number of days on assisted ventilation was a slightly better predictor of the disease classification than days on > 60% oxygen. A statistical model correctly predicted the pathologic classification 83% of the time.

Evaluation of amniotic fluid elastolytic activity: can it be a method of fetal lung maturity assessment? A comparison with Gluck's L/S test

Amniotic fluid elastolytic activity was assessed in a group of 120 women who delivered preterm infants and in 35 women who delivered at term. Amniotic fluid elastolytic activity decreases as pregnancy progresses. The lecithin-to-sphingomyelin (L/S) ratio in women's amniotic fluid was determined by the method developed by Gluck and associates [6] and elastolytic activity by that developed by Mehdi and associates. A significant negative correlation was found between the amniotic fluid L/S ratio and amniotic fluid elastolytic activity (r = -0.932; p < 0.001). The border value of elastolytic activity that indicates lung maturity (L/S ratio equal to or greater than 2) is 2.01 +/- 0.05 mmol/min ml. In the amniotic elastolytic activity test, it is the value that differentiates mature from immature lungs. The amniotic fluid elastolytic activity test is characterized by high sensitivity (91.43%) and specificity (91.67%), high positive prognostic value (76.19%) and low negative prognostic value (2.65%). The test parameters do not therefore differ greatly from those of the Gluck test. Moreover, the amniotic fluid elastolytic activity test is cheaper and takes less time to perform.

Biochemical and morphometric analyses in hypoplastic lungs

We report the results of biochemical and morphometric studies on lungs of infants with bilateral lung hypoplasia either with or without oligohydramnios (OH or NOH) in comparison with findings in normally grown lungs. The OH and NOH lungs were equally hypoplastic in terms of DNA content but OH lungs had a significantly lower disaturated phosphatidylcholine (DSPC) concentration than NOH or normal lungs, apart from a subgroup with gastrointestinal or airway obstruction. Hydroxyproline concentration in OH lungs was higher than that in NOH or normal lungs. Desmosine concentrations did not differ significantly between groups despite the obvious lack of elastin in the septal crests of the OH group on histology. Morphometry revealed low lung volume, low radial alveolar counts, low alveolar numbers, and low alveolar surface area in both OH and NOH groups. Alveoli and alveolar ducts constituted a higher proportion of lung volume in NOH than in OH lungs. The similarity of most morphometric indices in the two groups implies that maturation does not depend on quantitative elaboration of airways and alveoli. The finding of impaired epithelial maturation despite the high hydroxyproline concentration in the OH lungs suggests an abnormality in epithelial-mesenchymal interaction that is not present in the equally small lungs of the NOH group.

Role of elastase and lysyl oxidase activity in spontaneous rupture of internal elastic lamina in rats

Rupture of the internal elastic lamina may occur spontaneously with age in certain arteries of the rat and to various extents in different strains. This phenomenon may have some bearing on certain aspects of arterial pathology. For this study, we investigated biochemically the mechanisms of formation of interruptions in the internal elastic lamina (IIEL) by comparing aortas of Brown Norway (BN) rats, which develop numerous IIEL in the abdominal aorta, with those of Long-Evans (LE) rats, which develop none. We isolated aortic elastin from BN and LE rats and determined its amino acid composition and its susceptibility to different elastases. No differences were found between the two strains, but the quantity of elastin isolated per aorta was lower in the BN than in the LE rats. Elastase-like activity (ELA) of whole aortic extracts, measured with Suc(Ala)3NA as a substrate, was greater in the BN rats than in the LE rats of both sexes. The assay of ELA in endothelium, media, and adventitia extracted separately showed very low levels in the media compared to the endothelium and adventitia. The endothelium accounts for about one-half of the total aortic ELA, but a difference between the two strains was detected only in the adventitia. With 3H-insoluble elastins prepared from BN and LE aortas as substrates, elastinolytic activity (EA) was detected only in extracts of endothelium after prior exposure to trypsin. Extracts from BN endothelium on BN elastin were more active than were those from LE endothelium on LE elastin. The assay of lysyl oxidase activity in aortic extracts from the two strains with 3H-collagen from chick embryo calvaria as the substrate showed a lower activity in the BN than in the LE rats. Taken together, these results suggest that increased elastase activity and decreased lysyl oxidase activity may be involved in the formation of IIEL.

Isolation and characterization of new cross-linking amino acid "allodesmosine" from hydrolysate of elastin

A new pentafunctional cross-linking amino acid, termed allodesmosine, was isolated from bovine ligamentum nuchae elastin. This compound was a very hygroscopic, white amorphous solid with a faint yellow tinge, soluble in aqueous solvents but not dry methanol; it was characterized by UV, FAB mass and NMR spectroscopy. The compound was shown by UV and 1H-NMR to have a pyridinium ring structure similar to desmosine. Mass spectral analysis indicated a parent compound with a mass of 655. We postulated that it arose by condensation of a reduced aldol condensation product of allysine, allysine and lysine.

Pulmonary elastic fibers in normal human development and in pathological conditions

Normal human pulmonary elastic fiber development and development in some pathological conditions were examined using elastic stains by light microscopy, electron microscopy, and immunohistochemistry. In normal development elastic fibers, composed mainly of microfibrils, first appeared around primitive bronchioles at 10 weeks of gestation. As they matured, their appearance became more amorphous, and they extended into the peripheral alveolar walls. Development of elastic fibers was retarded in the hypoplastic lungs of the oligohydramnios syndrome, diaphragmatic hernia, and hydrops fetalis. Elastic development was also retarded in congenital pulmonary lymphangiectasia and in focal areas of lungs with pulmonary dysplasia. Distribution of well-developed elastic fibers was found around the dilated bronchioles and alveoli in cases of congenital cystic adenomatoid malformation and extralobar pulmonary sequestration. Elastic fibers were distributed irregularly and unevenly in the lungs of bronchopulmonary dysplasia and ventilated cases of Wilson Mikity syndrome. In addition, four very immature infants who had progressively deteriorating respiratory function showed an almost total lack of elastic fibers in their alveolar walls.

Fetal lung growth in congenital laryngeal atresia

Morphometric and biochemical indexes of lung growth were measured in 2 cases of uncomplicated laryngeal atresia at 27 and 30 weeks gestation and in 1 case of cryptophthalmos syndrome with anomalies including laryngeal atresia and renal agenesis. Findings were compared with those in normally formed fetuses and newborn infants. The cases of pure laryngeal atresia showed a marked increase in surface area and lung volume for age, associated with an increase in alveolar number and apparent advance in elastin maturation, but little increase in cell population as measured by lung DNA content. Alveolar walls were thin but there was no increase in disaturated phosphatidylcholine (DSPC) content. Similar features were observed in the case of cryptophthalmos in marked contrast to the lung hypoplasia expected to result from renal agenesis. The results give further support to the importance of lung liquid retention for normal fetal lung growth. Overdistention with lung liquid appears to promote alveolar development by redistribution of cells rather than increase in cell population.