Kara N. Goss

Estradiol Improves Right Ventricular Function In Rats With Severe Angioproliferative Pulmonary Hypertension: Effects Of Endogenous And Exogenous Sex Hormones

Estrogens are disease modifiers in PAH. Even though female patients exhibit better right ventricular (RV) function than men, estrogen effects on RV function (a major determinant of survival in PAH) are incompletely characterized. We sought to determine whether sex differences exist in RV function in the SuHx model of PAH, whether hormone depletion in females worsens RV function, and whether E2 repletion improves RV adaptation. Furthermore, we studied the contribution of ERs in mediating E2s RV effects. SuHx-induced pulmonary hypertension (SuHx-PH) was induced in male and female Sprague-Dawley rats as well as OVX females with or without concomitant E2 repletion (75 μg·kg(-1)·day(-1)). Female SuHx rats exhibited superior CI than SuHx males. OVX worsened SuHx-induced decreases in CI and SuHx-induced increases in RVH and inflammation (MCP-1 and IL-6). E2 repletion in OVX rats attenuated SuHx-induced increases in RV systolic pressure (RVSP), RVH, and pulmonary artery remodeling and improved CI and exercise capacity (V̇o2max). Furthermore, E2 repletion ameliorated SuHx-induced alterations in RV glutathione activation, proapoptotic signaling, cytoplasmic glycolysis, and proinflammatory cytokine expression. Expression of ERα in RV was decreased in SuHx-OVX but was restored upon E2 repletion. RV ERα expression was inversely correlated with RVSP and RVH and positively correlated with CO and apelin RNA levels. RV-protective E2 effects observed in females were recapitulated in male SuHx rats treated with E2 or with pharmacological ERα or ERβ agonists. Our data suggest significant RV-protective ER-mediated effects of E2 in a model of severe PH.

Neonatal hyperoxic lung injury favorably alters adult right ventricular remodeling response to chronic hypoxia exposure.

The development of pulmonary hypertension (PH) requires multiple pulmonary vascular insults, yet the role of early oxygen therapy as an initial pulmonary vascular insult remains poorly defined. Here, we employ a two-hit model of PH, utilizing postnatal hyperoxia followed by adult hypoxia exposure, to evaluate the role of early hyperoxic lung injury in the development of later PH. Sprague-Dawley pups were exposed to 90% oxygen during postnatal days 0-4 or 0-10 or to room air. All pups were then allowed to mature in room air. At 10 wk of age, a subset of rats from each group was exposed to 2 wk of hypoxia (Patm = 362 mmHg). Physiological, structural, and biochemical endpoints were assessed at 12 wk. Prolonged (10 days) postnatal hyperoxia was independently associated with elevated right ventricular (RV) systolic pressure, which worsened after hypoxia exposure later in life. These findings were only partially explained by decreases in lung microvascular density. Surprisingly, postnatal hyperoxia resulted in robust RV hypertrophy and more preserved RV function and exercise capacity following adult hypoxia compared with nonhyperoxic rats. Biochemically, RVs from animals exposed to postnatal hyperoxia and adult hypoxia demonstrated increased capillarization and a switch to a fetal gene pattern, suggesting an RV more adept to handle adult hypoxia following postnatal hyperoxia exposure. We concluded that, despite negative impacts on pulmonary artery pressures, postnatal hyperoxia exposure may render a more adaptive RV phenotype to tolerate late pulmonary vascular insults.

Postnatal Hyperoxia Exposure Durably Impairs Right Ventricular Function and Mitochondrial Biogenesis

&NA; Prematurity complicates 12% of births, and young adults with a history of prematurity are at risk to develop right ventricular (RV) hypertrophy and impairment. The long‐term risk for pulmonary vascular disease, as well as mechanisms of RV dysfunction and ventricular‐vascular uncoupling after prematurity, remain poorly defined. Using an established model of prematurity‐related lung disease, pups from timed‐pregnant Sprague Dawley rats were randomized to normoxia or hyperoxia (fraction of inspired oxygen, 0.85) exposure for the first 14 days of life. After aging to 1 year in standard conditions, rats underwent hemodynamic assessment followed by tissue harvest for biochemical and histological evaluation. Aged hyperoxia‐exposed rats developed significantly greater RV hypertrophy, associated with a 40% increase in RV systolic pressures. Although cardiac index was similar, hyperoxia‐exposed rats demonstrated a reduced RV ejection fraction and significant RV‐pulmonary vascular uncoupling. Hyperoxia‐exposed RV cardiomyocytes demonstrated evidence of mitochondrial dysregulation and mitochondrial DNA damage, suggesting potential mitochondrial dysfunction as a cause of RV dysfunction. Aged rats exposed to postnatal hyperoxia recapitulate many features of young adults born prematurely, including increased RV hypertrophy and decreased RV ejection fraction. Our data suggest that postnatal hyperoxia exposure results in mitochondrial dysregulation that persists into adulthood with eventual RV dysfunction. Further evaluation of long‐term mitochondrial function is warranted in both animal models of premature lung disease and in human adults who were born preterm.

Increased Cardiac Output and Preserved Gas Exchange Despite Decreased Alveolar Surface Area in Rats Exposed to Neonatal Hyperoxia and Adult Hypoxia

Despite data indicating that adult and adolescent survivors of chronic lung disease associated with extreme prematurity exhibit deficits in ventilatory control, airflow, and exercise tolerance (1–4), there remains a paucity of preclinical data examining the long-term effects of neonatal lung injury on adult cardiopulmonary structure and function. Although the consequences remain unclear, consistent with the inhibition of alveolar–capillary development and increased need for oxygen supplementation observed in infants with chronic lung disease (5, 6), survivors of extreme prematurity have persistent mild to moderate decreases in lung diffusing capacity (2, 7, 8). In addition, increasing preclinical and clinical evidence indicates that disrupted alveolar–capillary membrane development associated with premature chronic lung disease is associated with an increased risk for pulmonary hypertension (9–13). It is unknown, however, whether pulmonary hypertension persists in these infants or places them at increased risk of developing future pulmonary vascular disease. In adults with pulmonary arterial hypertension, decreased diffusing capacity is an independent predictor of disease-related mortality and cardiac dysfunction (14), which raises concerns about ongoing cardiopulmonary dysfunction in survivors of prematurity. Furthermore, a recently published study in young adults born prematurely demonstrated increased right ventricular (RV) mass and elevated risk for RV dysfunction that correlated with the severity of prematurity (15). However, in the absence of a clear assessment of how RV function interacts with alveolar–capillary membrane disease and gas exchange, it is difficult to draw conclusions regarding the significance of RV hypertrophy (RVH) or its relation to diffusing capacity. Using rodent models that closely resemble the pathological features of premature chronic lung disease, we recently demonstrated that briefly exposing the developing lung to hyperoxia was associated with alveolar simplification, reduced pulmonary arterial density, elevated RV systolic pressure (RVSP), and impaired gas exchange (16, 17). In addition, when adult rats were subsequently exposed to the secondary insult of hypoxia, previous exposure to neonatal hyperoxia significantly increased RVSP and RVH yet, surprisingly, maintained cardiac output, suggesting that animals exposed to neonatal hyperoxia respond to the secondary insult of hypoxia with a more adaptive RV phenotype. A better understanding of the mechanisms by which cardiopulmonary structure and function adapt to secondary insults may allow for the development of targeted therapeutics that promote optimal alveolar–capillary development and function after neonatal lung disease. Here, we sought to understand the role of diffusing capacity, as measured by the lung diffusion factor for carbon monoxide (DFCO), in characterizing the relative contributions of alveolar surface area versus cardiac output to alveolar gas exchange in a model of premature lung disease. We demonstrate, first, that neonatal hyperoxia, but not adult hypoxia, significantly reduces alveolar surface area; second, that although gas diffusion efficiency is impaired similarly by neonatal hyperoxia and adult hypoxia alone, there is no additive effect of the combination of both exposures; and third, that in response to hypoxia, animals previously exposed to neonatal hyperoxia exhibit increased cardiac output in the face of a decreased diffusing capacity. We interpret this increase in cardiac output as a compensatory measure aimed at maintaining gas exchange.

Impaired autonomic function in adolescents born preterm

Preterm birth temporarily disrupts autonomic nervous system (ANS) development, and the long‐term impacts of disrupted fetal development are unclear in children. Abnormal cardiac ANS function is associated with worse health outcomes, and has been identified as a risk factor for cardiovascular disease. We used heart rate variability (HRV) in the time domain (standard deviation of RR intervals, SDRR; and root means squared of successive differences, RMSSD) and frequency domain (high frequency, HF; and low frequency, LF) at rest, as well as heart rate recovery (HRR) following maximal exercise, to assess autonomic function in adolescent children born preterm. Adolescents born preterm (less than 36 weeks gestation at birth) in 2003 and 2004 and healthy age‐matched full‐term controls participated. Wilcoxon Rank Sum tests were used to compare variables between control and preterm groups. Twenty‐one adolescents born preterm and 20 term‐born controls enrolled in the study. Preterm‐born subjects had lower time‐domain HRV, including SDRR (69.1 ± 33.8 vs. 110.1 ± 33.0 msec, respectively, P = 0.008) and RMSSD (58.8 ± 38.2 vs. 101.5 ± 36.2 msec, respectively, P = 0.012), with higher LF variability in preterm subjects. HRR after maximal exercise was slower in preterm‐born subjects at 1 min (30 ± 12 vs. 39 ± 9 bpm, respectively, P = 0.013) and 2 min (52 ± 10 vs. 60 ± 10 bpm, respectively, P = 0.016). This study is the first report of autonomic dysfunction in adolescents born premature. Given prior association of impaired HRV with adult cardiovascular disease, additional investigations into the mechanisms of autonomic dysfunction in this population are warranted.

Early Pulmonary Vascular Disease in Young Adults Born Preterm

Rationale: Premature birth affects 10% of live births in the United States and is associated with alveolar simplification and altered pulmonary microvascular development. However, little is known about the long‐term impact prematurity has on the pulmonary vasculature. Objectives: Determine the long‐term effects of prematurity on right ventricular and pulmonary vascular hemodynamics. Methods: Preterm subjects (n = 11) were recruited from the Newborn Lung Project, a prospectively followed cohort at the University of Wisconsin‐Madison, born preterm with very low birth weight (≤1,500 g; average gestational age, 28 wk) between 1988 and 1991. Control subjects (n = 10) from the same birth years were recruited from the general population. All subjects had no known adult cardiopulmonary disease. Right heart catheterization was performed to assess right ventricular and pulmonary vascular hemodynamics at rest and during hypoxic and exercise stress. Measurements and Main Results: Preterm subjects had higher mean pulmonary arterial pressures (mPAPs), with 27% (3 of 11) meeting criteria for borderline pulmonary hypertension (mPAP, 19‐24 mm Hg) and 18% (2 of 11) meeting criteria for overt pulmonary hypertension (mPAP ≥ 25 mm Hg). Pulmonary vascular resistance and elastance were higher at rest and during exercise, suggesting a stiffer vascular bed. Preterm subjects were significantly less able to augment cardiac index or right ventricular stroke work during exercise. Among neonatal characteristics, total ventilatory support days was the strongest predictor of adult pulmonary pressure. Conclusions: Young adults born preterm demonstrate early pulmonary vascular disease, characterized by elevated pulmonary pressures, a stiffer pulmonary vascular bed, and right ventricular dysfunction, consistent with an increased risk of developing pulmonary hypertension.

Addressing the challenges of phenotyping pediatric pulmonary vascular disease

Pediatric pulmonary vascular disease (PVD) and pulmonary hypertension (PH) represent phenotypically and pathophysiologically diverse disease categories, contributing substantial morbidity and mortality to a complex array of pediatric conditions. Here, we review the multifactorial nature of pediatric PVD, with an emphasis on improved recognition, phenotyping, and endotyping strategies for pediatric PH. Novel tailored approaches to diagnosis and treatment in pediatric PVD, as well as the implications for long-term outcomes, are highlighted.

Sex-Specific Skeletal Muscle Fatigability and Decreased Mitochondrial Oxidative Capacity in Adult Rats Exposed to Postnatal Hyperoxia

Premature birth affects more than 10% of live births, and is characterized by relative hyperoxia exposure in an immature host. Long-term consequences of preterm birth include decreased aerobic capacity, decreased muscular strength and endurance, and increased prevalence of metabolic diseases such as type 2 diabetes mellitus. Postnatal hyperoxia exposure in rodents is a well-established model of chronic lung disease of prematurity, and also recapitulates the pulmonary vascular, cardiovascular, and renal phenotype of premature birth. The objective of this study was to evaluate whether postnatal hyperoxia exposure in rats could recapitulate the skeletal and metabolic phenotype of premature birth, and to characterize the subcellular metabolic changes associated with postnatal hyperoxia exposure, with a secondary aim to evaluate sex differences in this model. Compared to control rats, male rats exposed to 14 days of postnatal hyperoxia then aged to 1 year demonstrated higher skeletal muscle fatigability, lower muscle mitochondrial oxidative capacity, more mitochondrial damage, and higher glycolytic enzyme expression. These differences were not present in female rats with the same postnatal hyperoxia exposure. This study demonstrates detrimental mitochondrial and muscular outcomes in the adult male rat exposed to postnatal hyperoxia. Given that young adults born premature also demonstrate skeletal muscle dysfunction, future studies are merited to determine whether this dysfunction as well as reduced aerobic capacity is due to reduced mitochondrial oxidative capacity and metabolic dysfunction.

Altered Right Ventricular Mechanical Properties Are Afterload Dependent in a Rodent Model of Bronchopulmonary Dysplasia

Infants born premature are at increased risk for development of bronchopulmonary dysplasia (BPD), pulmonary hypertension (PH), and ultimately right ventricular (RV) dysfunction, which together carry a high risk of neonatal mortality. However, the role alveolar simplification and abnormal pulmonary microvascular development in BPD affects RV contractile properties is unknown. We used a rat model of BPD to examine the effect of hyperoxia-induced PH on RV contractile properties. We measured in vivo RV pressure as well as passive force, maximum Ca2+ activated force, calcium sensitivity of force (pCa50) and rate of force redevelopment (ktr) in RV skinned trabeculae isolated from hearts of 21-and 35-day old rats pre-exposed to 21% oxygen (normoxia) or 85% oxygen (hyperoxia) for 14 days after birth. Systolic and diastolic RV pressure were significantly higher at day 21 in hyperoxia exposed rats compared to normoxia control rats, but normalized by 35 days of age. Passive force, maximum Ca2+ activated force, and calcium sensitivity of force were elevated and cross-bridge cycling kinetics depressed in 21-day old hyperoxic trabeculae, whereas no differences between normoxic and hyperoxic trabeculae were seen at 35 days. Myofibrillar protein analysis revealed that 21-day old hyperoxic trabeculae had increased levels of beta-myosin heavy chain (β-MHC), atrial myosin light chain 1 (aMLC1; often referred to as essential light chain), and slow skeletal troponin I (ssTnI) compared to age matched normoxic trabeculae. On the other hand, 35-day old normoxic and hyperoxic trabeculae expressed similar level of α- and β-MHC, ventricular MLC1 and predominantly cTnI. These results suggest that neonatal exposure to hyperoxia increases RV afterload and affect both the steady state and dynamic contractile properties of the RV, likely as a result of hyperoxia-induced expression of β-MHC, delayed transition of slow skeletal TnI to cardiac TnI, and expression of atrial MLC1. These hyperoxia-induced changes in contractile properties are reversible and accompany the resolution of PH with further developmental age, underscoring the importance of reducing RV afterload to allow for normalization of RV function in both animal models and humans with BPD.

Hypoxic Pulmonary Hypertension

Elevation in pulmonary arterial pressure is a common occurrence in patients with chronic lung disease. Hypoxic pulmonary vasoconstriction, parenchymal lung disease, and inflammation contribute to increased pulmonary vascular tone and remodeling. Diagnosis of pulmonary vascular disease in patients with lung disease may be especially challenging due to the lack of specificity of common complaints of dyspnea and inaccuracy of echocardiographic estimates such as pulmonary arterial pressure in this group of patients. The presence of pulmonary hypertension (PH) in chronic lung disease is associated with increased morbidity and mortality, but the efficacy of pharmacologic treatment of PH in this population has not been established. This chapter will review the epidemiology and pathogenesis of PH associated with chronic lung disease and provide an approach to evaluation and management including the identification and selection of some patients who may benefit from currently available pulmonary vasodilator therapies.