Morphometric analysis of the lung vasculature after extracorporeal membrane oxygenation treatment for pulmonary hypertension in newborns

Persistent pulmonary hypertension in the newborn (PPHN) is characterised by increased medial and adventitial thickness in the lung vasculature. This study describes morphometry of lung vasculature after extracorporeal membrane oxygenation (ECMO) in newborns with PPHN, due to meconium aspiration syndrome, sepsis or idiopathic persistent pulmonary hypertension of the newborn (i-PPHN). Three groups were studied: newborns with PPHN treated with ECMO (n=9), newborns with PPHN not treated with ECMO (n=12) and age-matched controls without PPHN (n=11). In pulmonary arteries with an external diameter of less than 150 m, arterial media, adventitia and total wall thickness, expressed as a percentage of the external diameter, and their cross-sectional areas were calculated. Newborns with PPHN, compared with controls, demonstrated increased percentage of media thickness, adventitia thickness and total wall thickness, and increased medial, adventitial and total wall cross-sectional area. Newborns treated with ECMO, compared with those not treated so, showed a decreased percentage of media thickness and medial cross-sectional area in arteries with an external diameter less than 75 m, and decreased percentage of media thickness and decreased medial, adventitial and total wall cross-sectional area in arteries with an external diameter of 75–150 m. ECMO for persistent PPHN, due to meconium aspiration syndrome, sepsis or i-PPHN, reduces the abnormal morphometry of small pulmonary arteries. The underlying mechanisms contributing to this improved morphometry are yet unknown.     

Expression of pulmonary vascular angiotensin-converting enzyme in primary and secondary plexiform pulmonary hypertension

The hypothesis for this study was that increased local expression of vascular angiotensin-converting enzyme (ACE) may contribute to the arterial remodelling which accompanies pulmonary hypertension, since angiotensin II (ANG II) is an important mediator of pulmonary vascular cell growth. The expression of ACE was studied by immunohistochemistry in paraffin-embedded lung sections from adults undergoing heart-lung transplantation for severe primary (n=6) and secondary (n=7) pulmonary arterial hypertension (PH), compared with age-matched controls (n=11). An antigen retrieval technique was used prior to incubating sections with the anti-ACE monoclonal antibody, CG2, or the endothelial marker, monoclonal anti-CD31. In control lungs, the highest level of ACE immunostaining was seen in the alveolar capillary endothelium, with less intense staining in small intra-acinar pulmonary arteries and relatively little staining in larger preacinar arteries. ACE immunostaining was virtually absent in lymphatics and veins. In both primary and secondary PH, there was an increase in ACE immunostaining in the endothelium of intra-acinar peripheral pulmonary arteries compared with control lungs, extending to the level of alveolar ducts, as confirmed by semi-quantitative analysis. The increase in endothelial ACE expression in the intra-acinar arteries of patients with primary and secondary PH is consistent with the hypothesis that locally increased production of ANG II may contribute to the process of pulmonary vascular remodelling.     

Adenosine triphosphate treatment for meconium aspiration-induced pulmonary hypertension in pigs

To investigate the pulmonary haemodynamic effects of meconium aspiration and subsequent adenosine triphosphate (ATP) treatment, 12 anaesthetized and ventilated pigs (wt 24-28 kg) received either ATP or an equal volume of saline into the right heart in doses of 0.02 to 0.80 lmol kg^-1 min^?1 after intratracheal administration of 2 mL kg^?1 of human meconium. Meconium instillation induced significant increases in pulmonary vascular pressures and total and postarterial resistances calculated from pulmonary artery occlusion studies, but did not affect the systemic haemodynamics, except for a fall in heart rate and increase in central venous pressure. Infusion of ATP at the lowest doses (0.02 and 0.08 µmol kg^?1 min^?1) selectively decreased the pulmonary arterial pressure and vascular resistance and at 0.32 and 0.80 µmol kg^?1 min^?1 reduced both the pulmonary and systemic resistances. In the lung circulation the increasing doses of ATP reduced preferably the arterial, but also the postarterial resistance. Withdrawal of ATP infusion led to a significant rebound effect especially in the postarterial segment of the lung circulation. Meconium aspiration thus induces an acute, predominantly postarterial obstruction in the lung circulation and infusion of ATP at low doses selectively dilates the pulmonary vascular bed and may help to preclude elevation of capillary pressures in meconium aspiration-induced pulmonary hypertension.     

Pulmonary endocrine cells in pulmonary arterial disease

Pulmonary endocrine cells containing bombesin or calcitonin have been identified in human lungs by the peroxidase-antiperoxidase method. The numbers of such cells were greatly increased in patients with plexogenic pulmonary arteriopathy whether that condition was associated with primary pulmonary hypertension or with pulmonary hypertension from intracardiac shunts. The numbers of endocrine cells tended to be increased, but to a lesser extent in patients with pulmonary hypertension and medial hypertrophy of the muscular pulmonary arteries in the absence of plexogenic arteriopathy. Increased numbers of endocrine cells comprised both greater numbers of solitary cells and a pronounced clustering, often of a disorganized nature.     

The Glu298Asp variant of the endothelial nitric oxide synthase gene is associated with an increased risk for abruptio placentae in pre-eclampsia

Attempts to define a pre-eclampsia susceptibility profile have been hampered by the wide clinical spectrum of the condition and the complex genetics underlying it. Genes that modulate blood pressure, fluid homeostasis and placental vascular development have been considered plausible candidates. Among these are the angiotensinogen (AGT) gene variant Met235Threo, which has been associated with pre-eclampsia and the endothelial nitric oxide synthase (eNOS) polymorphism Glu298Asp, which has been associated with both pre-eclampsia and abruptio placentae, a condition that often co-exists with pre-eclampsia. The aim of this study was to investigate a potential association between these gene variants and pre-eclampsia with and without abruptio placentae in a South African patient group. Fifty primigravidas with early onset, severe pre-eclampsia, 50 women presenting primarily with abruptio placentae (whether associated with pre-eclampsia or not) and a control panel of 50 healthy pregnant women constituted the study groups. The Met235Threo and Glu298Asp variants were characterised by polymerase chain reaction and restriction enzyme analysis. No association was demonstrated between the M235T variant of the AGT gene and pre-eclampsia or abruptio placentae. In contrast, the combined frequency of the eNOS variant genotypes (GT and TT) was significantly higher in the abruptio placentae group (49%) than the control group (21%) (p=0.006). Furthermore, in the pre-eclampsia patients who subsequently developed abruptio placentae, the eNOS GT genotype emerged as a major risk factor for the development of abruptio placentae (p<0.0001). These data suggest that the presence of a Glu298Asp eNOS variant may pre-dispose a pre-eclamptic woman to develop abruptio placentae or that it is a marker for predisposition.     

Arterial Changes in Crotalaria spectabilis-Induced Pulmonary Hypertension in Rats

Pulmonary hypertension has been induced in rats by feeding them the seeds of Crotalaria spectabilis for 34 days, when some were killed and others left to recover for 14, 31 or 54 days. By 34 days and after pulmonary arterial injection, right ventricular hypertrophy was demonstrated with an increase in pulmonary arterial medial muscle, a reduced number of small arteries and “ghost” arteries. With recovery, right ventricular hypertrophy had regressed by 31 days and by 54 days the arterial muscle was decreased. There was no increase in number of small arteries although “ghost” arteries had disappeared by 31 days. Similar features have recently been described in human primary pulmonary hypertension.     

New method for quantitating the medial component of pulmonary arteries. Factors affecting the measurements

The study objectives were to determine the effect of several factors related to tissue preparation on the relationship between medial area and size of the muscular pulmonary artery (defined in terms of total length of internal elastic lamina). This relationship took the form y = Axb that was linearized by plotting the square root of medial area against artery size. Complete distention of pulmonary arteries by an injection medium caused the internal elastic lamina to stretch by a factor of approximately 1.5. The relationship between medial area and artery size was unaffected by either the pressure method used for lung inflation/fixation or the tissue-embedding medium. Tissue shrinkage was considerable with paraffin embedding and negligible with glycol methacrylate. More arteries were considered measurable in glycol methacrylate-embedded tissue.     

In vitro effect of meconium on the physical surface properties and morphology of exogenous pulmonary surfactant.

The pathophysiology of meconium aspiration syndrome(MAS) is related to mechanical obstruction of the airways and to chemical pneumonitis. Meconium is also suggested to cause functional deterioration of pulmonary surfactant. Recent studies have reported that meconium inhibits the physical surface properties of pulmonary surfactant, and that administration of exogenous surfactant may provide therapeutic benefits in animal models or infants with respiratory distress due to MAS. To assess the effects of meconium on physical surface properties, especially the changes on the air-liquid interface and hypophase of pulmonary surfactant in vitro, we studied the following findings; a) the surface spreading rate(SSR) and the surface adsorption rate(SAR), b) the viscosity, c) the electron microscopic changes, on a series of mixtures with various concentrations of lyophilized human meconium and Surfactant-TA(SurfactenTM). The human meconium has significantly increased the surface tension of SSR and the viscosity of pulmonary surfactant, but had decreased the surface pressure of SAR of surfactant, and changed the electron microscopic findings of surfactant. We have concluded that these findings support the concept that meconium-induced surfactant dysfunction may play a role in the pathophysiology of MAS.     

Peptide-directed highly selective targeting of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary vasculature associated with elevated pulmonary vascular resistance. Despite recent advances in the treatment of PAH, with eight approved clinical therapies and additional therapies undergoing clinical trials, PAH remains a serious life-threatening condition. The lack of pulmonary vascular selectivity and associated systemic adverse effects of these therapies remain the main obstacles to successful treatment. Peptide-mediated drug delivery that specifically targets the vasculature of PAH lungs may offer a solution to the lack of drug selectivity. Herein, we show highly selective targeting of rat PAH lesions by a novel cyclic peptide, CARSKNKDC (CAR). Intravenous administration of CAR peptide resulted in intense accumulation of the peptide in monocrotaline-induced and SU5416/hypoxia-induced hypertensive lungs but not in healthy lungs or other organs of PAH rats. CAR homed to all layers of remodeled pulmonary arteries, ie, endothelium, neointima, medial smooth muscle, and adventitia, in the hypertensive lungs. CAR also homed to capillary vessels and accumulated in the interstitial space of the PAH lungs, manifesting its extravasation activity. These results demonstrated the remarkable ability of CAR to selectively target PAH lung vasculature and effectively penetrate and spread throughout the diseased lung tissue. These results suggest the clinical utility of CAR in the targeted delivery of therapeutic compounds and imaging probes to PAH lungs.     

Disseminated intravascular meconium in a newborn with meconium peritonitis.

A 3-day-old premature infant with meconium peritonitis, periventricular leukomalacia, and pulmonary hypertension died with respiratory insufficiency. An autopsy disclosed intravascular squamous cells in the lungs, brain, liver, pancreas, and kidneys. Numerous pulmonary capillaries and arterioles were occluded by squamous cells, accounting for pulmonary hypertension. Brain parenchyma surrounding occluded cerebral vessels showed infarct and gliosis. A mediastinal lymph node filled with squamous cells alluded to the mechanism by which these cells from the peritoneal cavity likely entered the bloodstream--namely, via diaphragmatic pores connecting with lymphatics. Thus, disseminated intravascular meconium rarely may complicate meconium peritonitis and have devastating consequences.     

Tumor-related thrombotic pulmonary microangiopathy: review of pathologic findings and pathophysiologic mechanisms

We report a middle-aged woman who died 2 days after presenting with dyspnea and severe pulmonary hypertension of unknown etiology. Her symptoms were highly suggestive of pulmonary embolism, but clinical evaluations for that disease yielded negative results. Autopsy revealed a Krukenberg tumor of the left ovary, representing metastatic gastric carcinoma from an occult primary lesion. Although the lungs exhibited no gross evidence of pulmonary emboli or neoplasia, microscopic examination revealed diffuse microscopic metastases in the pulmonary arterial vasculature. The pulmonary arteries exhibited fibrocellular intimal proliferation with smooth muscle colonization of the luminal neoplastic lesions and associated microthrombi. This disease entity, known as tumor-related thrombotic pulmonary microangiopathy, results in generalized microvascular obliteration and subsequent pulmonary hypertension. It is a rare condition that is distinct from ordinary pulmonary thromboembolism and primary pulmonary hypertension. Tumor-related thrombotic pulmonary microangiopathy should be considered diagnostically by the autopsy pathologist in cases of rapidly evolving pulmonary hypertension in a middle-aged or elderly individual, or respiratory failure of unknown cause, especially if there is a history of a visceral malignancy.     

Vascular remodeling process in reversibility of pulmonary arterial hypertension secondary to congenital heart disease

Pulmonary vascular remodeling process was analyzed using morphometry in lung biopsy specimens taken from 26 children, aged 6 to 160 months, who had congenital heart disease and significant pulmonary arterial hypertension. Reparative surgery was performed in 22 patients and palliative surgery was performed in four patients. One patient expired postoperatively and four others after hospital discharge. Vascular remodeling examination revealed a characteristic pathological picture: pronounced medial thickening with increased collagen content (fibrosis), without significant arterial intimal proliferation. At a mean follow-up of 44 months, 72% of the survivors were asymptomatic with no medication. Diagnosed by echocardiogram, 22% of these patients were shown to have pulmonary arterial hypertension. The characteristic pathological features described above occurred in 38% of the patients who either expired or had pulmonary hypertension postoperatively. These findings were an aid to identifying a high risk group in which the outcome does not meet expectations for the classical grade I and II changes. We concluded that the presence of isolated medial thickening does not ensure either survival or a normal postoperative pulmonary arterial pressure at late follow-up and that the collagen content can be a better reference for good outcome. Early intracardiac repair is recommended before the development of significant medial fibrosis.     

Pulmonary arterial dissections and ruptures: to be considered in patients with pulmonary arterial hypertension presenting with cardiogenic shock or sudden death

Four unusual cases of sudden death due to pulmonary arterial hypertension complicated by dissection and/or rupture of the main pulmonary artery are reported. The patients, 3 males and 1 female, ranged from 17 to 77 years old. Each had chronic pulmonary arterial hypertension, marked pulmonary arterial dilation and degenerative medial changes of the large elastic pulmonary arteries. The first patient had a partial thickness tear of the main pulmonary artery with local dissection without external rupture and died of shock. The other three patients died after external rupture of the main pulmonary artery, based on a full thickness tear in one case, a small dissection in another and extensive dissection in the third. In the setting of pulmonary arterial hypertension, dissection, rupture, or dissection and rupture of the pulmonary artery should be considered in the differential diagnosis when patients present in cardiogenic shock or with sudden death.     

The ultrastructure of the various forms of pulmonary arterial intimal fibrosis

Summary Intimal fibrosis of muscular pulmonary arteries may present in various forms and in varying degrees of severity according to the underlying condition. In patients with pulmonary hypertension, the type of intimal fibrosis is often significant with regard to prognosis and reversibility. For these reasons we have studied the ultrastructure of the thickened intimal layer in aged individuals, where intimal fibrosis occurs as a normal age change, and in patients with pulmonary hypertension associated with fibrosis of the lungs, mitral stenosis, chronic pulmonary thromboembolism and plexogenic pulmonary arteriopathy (either primary or secondary to congenital cardiac defects). In all these forms of intimal fibrosis, the cellular component of the subendothelial intimal layer was apparently almost exclusively the smooth muscle cell.These cells usually had a haphazard arrangement. In primary and secondary plexogenic pulmonary arteriopathy, however, there was a more regular circumferential arrangement. The ultrastructural evidence suggested that the intimal cells were derived from medial smooth muscle cells.     

The distribution of matrix metalloproteinases and tissue inhibitors of metalloproteinases in the lungs of congenital diaphragmatic hernia patients and age-matched controls

AIMS: In congenital diaphragmatic hernia (CDH), the pathogenesis of abnormal pulmonary morphology is still incompletely understood. Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are known to play an important role in the turnover of the extracellular matrix (ECM) during development and in remodelling of tissue. The aim of this study was to investigate differences in the expression of MMPs and TIMPs between CDH lungs and controls, against the background of the abnormal pulmonary vasculature in CDH. METHODS: We studied 12 lungs of term CDH patients who died < 24 h after birth and 11 normal age-matched control lungs, by immunohistochemistry with antibodies against human MMP-1, -2, -9, TIMP-1 and -2. RESULTS: There was a clear increase in the number of MMP-1-reactive capillaries and fibroblasts in CDH lungs compared with controls. In contrast, TIMP-2 reactivity in these structures was decreased in CDH lungs. The arterial endothelium and medial smooth muscle expressed MMP-2, -9 and TIMP-2 in both CDH and control lungs. In small arteries (< 100 microm in diameter), the positive surface area of MMP-2, -9 and TIMP-2 was significantly larger in CDH lungs than in controls. There was no difference in the distribution and expression of TIMP-1 between CDH lungs and normal controls. CONCLUSION: The differences in staining pattern of MMPs and TIMPs between normal and CDH lungs suggest that these enzymes might play a role in the abnormal remodelling of the interstitium and the pulmonary arteries in CDH lungs. This could contribute to our understanding of the abnormal lung morphology and the occurrence of pulmonary hypertension, which forms one of the major obstacles to the successful treatment of these patients.     

Hepatocyte growth factor improves the survival of rats with pulmonary arterial hypertension via the amelioration of pulmonary hemodynamics

Hepatocyte growth factor (HGF) is a multifunctional growth factor with mitogenic, anti-apoptotic and anti-fibrotic activities. In this study, we investigated the effect of administration of recombinant human HGF on pulmonary arterial hypertension. Pulmonary arterial hypertension was induced in rats by a single injection of monocrotaline (MCT) and recombinant human HGF (0.12 mg/day) was administered into the right ventricle cavity using osmotic pumps, which were implanted subcutaneously 21 days after MCT injection. Continuous intravenous delivery of recombinant human HGF for 14 days led to prolonged survival of animals suffering from severe MCT-induced pulmonary arterial hypertension. Although a bolus injection of recombinant human HGF did not affect pulmonary arterial pressure, a 14-day administration of recombinant human HGF attenuated the inflammatory cell infiltrate, matrix accumulation and vascular medial thickening. As a consequence, the pulmonary lumen was enlarged and the pulmonary arterial pressure was significantly reduced. Additionally, continuous administration of recombinant human HGF suppressed lung tissue expression of platelet-derived growth factor, which plays an important role in the development of pulmonary arterial hypertension. These results indicate that recombinant human HGF possibly has a great potential for improving symptoms and altering the clinical course of pulmonary arterial hypertension.     

Pulmonary hypoplasia in Down's syndrome

We studied the lungs of seven patients of various ages who had Down's syndrome, to determine whether they had abnormalities in pulmonary development. Six of the seven had hypoplastic lungs. Five had congenital heart disease, but pulmonary hypoplasia was of equal severity, irrespective of the presence or absence or the type of congenital heart disease. Three other patients with congenital heart disease but without Down's syndrome had lungs that were equally diminished in volume. However, these lungs lacked the structural abnormalities seen in Down's syndrome, which consisted of a diminished number of alveoli in relation to acini and enlarged alveoli and alveolar ducts. The patients with Down's syndrome also had a smaller total number of alveoli and a smaller alveolar surface area. We speculate that the smaller alveolar surface area is accompanied by loss of capillary surface area, which is responsible for the aggravation of pulmonary hypertension in Down's syndrome.     

MTHFD1 R653Q polymorphism is a maternal genetic risk factor for severe abruptio placentae

This study examined the relationship between folate/homocysteine-related genetic polymorphisms: MTHFD1 1958G --> A (R653Q), MTHFR 677C --> T (A222V), MTHFR 1298A --> C (E429A), and risk of severe abruptio placentae. We genotyped 62 women with a pregnancy history complicated by severe abruptio placentae and 184 control pregnancies. Analysis of the MTHFD1 1958G --> A (R653Q) polymorphism showed increased frequency of the 'QQ' homozygote genotype in pregnancies affected by severe abruptio placentae compared to control pregnancies (odds ratio 2.85 (1.47-5.53), P = 0.002). In contrast to previous reports, the MTHFR polymorphisms 677C --> T (A222V) and 1298A --> C (E429A) were not associated with abruptio placentae risk in our cohort, when analyzed either independently or in combination. We conclude that women who are 'QQ' homozygote for the MTHFD1 1258G --> A (R653Q) polymorphism are almost three times more likely to develop severe abruptio placentae during their pregnancy than women who are 'RQ' or 'RR.'     

Nodular regenerative hyperplasia of the liver associated with primary pulmonary hypertension

Nodular regenerative hyperplasia (NRH), a rare hyperplastic condition of the liver, is reported in two patients with primary pulmonary hypertension (PPH). The first patient was a 26-year-old man who died of PPH and showed multiple NRH without cirrhosis of the liver. The second patient was a 25-year-old man who had a PPH with pulmonary arterial thrombi and NRH of the liver. NRH has been described in association with immune disease, hematopoietic disorder, and diabetes mellitus, so that NRH with PPH is considered to be very rare. Histologic findings of the lungs show typically plexogenic pulmonary arteriopathy in both cases, and the livers of these patients are composed of multiple nodules that are histologically represented by slightly larger hepatocytes arranged in a cobblestone-like fashion, and are ultramicroscopically characterized by massive proliferation of mitochondria. The pathogenetic association of nodular regenerative hyperplasia with primary pulmonary hypertension will be discussed.     

Morphology of the internal elastic lamina in arteries from pulmonary hypertensive patients: a confocal laser microscopy study.

The development and progression of pulmonary hypertension lesions involve continuous remodeling of the arterial wall, including the extracellular matrix components. The integrity of the internal elastic lamina may represent a barrier to cell migration and formation of intimal proliferative lesions. Some patients with congenital cardiac shunts develop precocious intimal occlusive lesions,whereas others evolve with isolated medial hypertrophy. We studied the 2-D and 3-D morphology of the internal elastic lamina of peripheral pulmonary arteries to search for any difference regarding the type of histological lesion. Fifteen lung biopsies collected for diagnostic purposes from patients with congenital shunts and 6 control lungs (mean ages, 15.8 and 14.7 mo) were studied using the confocal laser scanning microscope, under predetermined conditions of laser intensity, brightness and contrast. We measured the thickness of the internal elastic lamina and determined the number of gaps and projections of elastic tissue towards the medial and intimal layers. The mean internal elastic lamina thickness was significantly higher in arteries from cases with isolated medial hypertrophy when compared with controls and to those with proliferative lesions (P <.05). The number of gaps of the internal elastic lamina was higher in arteries >100 micro m in diameter from the group with intimal lesions when compared to the cases presenting with isolated hypertrophy, but did not differ from the controls. There was a positive linear correlation between the external arterial diameter and the thickness of the internal elastic lamina (r =.74, P <.001) in cases presenting isolated medial hypertrophy. The increased thickness and smaller number of gaps of the internal elastic lamina may act as a barrier that prevents smooth muscle cell migration in patients with pulmonary hypertension without intimal proliferative lesions. On the other hand, a greater number of gaps does not represent, by itself, unrestrained migration, because controls also showed fenestrated laminae.