Building global development strategies for cf therapeutics during a transitional cftr modulator era.

As CFTR modulator therapy transforms the landscape of cystic fibrosis (CF) care, its lack of uniform access across the globe combined with the shift towards a new standard of care creates unique challenges for the development of future CF therapies. The advancement of a full and promising CF therapeutics pipeline remains a necessary priority to ensure maximal clinical benefits for all people with CF. It is through collaboration across the global CF community that we can optimize the evaluation and approval process of new therapies. To this end, we must identify areas for which harmonization is lacking and for which efficiencies can be gained to promote ethical, feasible, and credible study designs amidst the changing CF care landscape. This article summarizes the counsel from core advisors across multiple international regions and clinical trial networks, developed during a one-day workshop in October 2019. The goal of the workshop was to identify, in consideration of the highly transitional era of CFTR modulator availability, the drug development areas for which global alignment is currently uncertain, and paths forward that will enable advancement of CF therapeutic development.

Pulmonary edema in 6 children with Down syndrome during travel to moderate altitudes.

OBJECTIVE: Children with Down syndrome (DS) are living longer and are increasingly participating in recreational activities. When a child with DS was diagnosed with high-altitude pulmonary edema (HAPE), this study was undertaken to determine whether and under what circumstances children with DS develop HAPE. DESIGN: A retrospective review of the medical records of Children's Hospital, Denver, Colorado was performed for children with a discharge diagnosis of HAPE. Diagnostic criteria for HAPE included the presence of crackles or frothy sputum production on examination, hypoxemia, chest radiograph findings consistent with pulmonary edema, and rapid clinical improvement after descent or oxygen therapy. RESULTS: A total of 52 patients with HAPE were found of whom 6 also had DS. The age range of the children with DS was 2 to 14 years. HAPE developed at altitudes ranging from 1738 to 3252 m. Four children developed HAPE within 24 hours of arrival to altitude. Three children had chronic pulmonary hypertension, and 4 had either an existing cardiac defect with left-to-right shunt or previously had a defect with left-to-right shunt that had been repaired. One child had Eisenmenger syndrome with chronic right-to-left shunting of blood. Five children had preexisting illnesses before travel to altitude. CONCLUSION: Children with DS often have medical problems such as chronic pulmonary hypertension, frequent infections, and pulmonary vascular overperfusion and injury from existing or previous cardiac defects. These problems all may be viewed as risk factors for HAPE and thus result in the rapid development of HAPE at low altitudes. Care should be taken when traveling to even moderate altitudes with children with DS.

Viral respiratory infection increases susceptibility of young rats to hypoxia-induced pulmonary edema.

Recent clinical observations of a high incidence of preexisting respiratory infections in pediatric cases of high-altitude pulmonary edema prompted us to ask whether such infections would increase the susceptibility to hypoxia-induced pulmonary edema in young rats. We infected weanling rats with Sendai virus, thus causing a mild respiratory infection. Within 7 days of infection, Sendai virus was essentially undetectable by using viral culture and immunohistochemical techniques. Animals at day 7 of Sendai virus infection were then exposed to normobaric hypoxia (fraction of inspired O2 = 0.1) for 24 h and examined for increases in gravimetric lung water and in vascular permeability, as well as for histological evidence of increased lung water. Bronchoalveolar lavage was performed on a separate series of animals. Compared with control groups, infected hypoxic animals showed significant increases in perivascular cuffing, gravimetric lung water, and lung protein leak. In addition, infected hypoxic animals had increases in lavage fluid cell counts and protein content compared with controls. We conclude that young rats, exposed to moderate hypoxia while recovering from a mild viral respiratory infection, may demonstrate evidence of early pulmonary edema formation, a finding of potential relevance to human high-altitude pulmonary edema.

Smooth muscle cell heterogeneity in pulmonary and systemic vessels. Importance in vascular disease.

Experimental evidence is rapidly accumulating which demonstrates that the arterial media in both pulmonary and systemic vessels is not composed of a phenotypically homogeneous population of smooth muscle cells (SMCs) but rather of heterogeneous subpopulations of cells with unique developmental lineages. In vivo and in vitro observations strongly suggest that marked differences in the phenotype, growth, and matrix-producing capabilities of phenotypically distinct SMC subpopulations exist and that these differences are intrinsic to the cell type. These data also suggest that differential proliferative and matrix-producing capabilities of distinct SMC subpopulations govern, at least in part, the pattern of abnormal cell proliferation and matrix protein synthesis observed in the pathogenesis of vascular disease. Within the pulmonary circulation, the observation that the isolated medial SMC subpopulations exhibit differential proliferative responses to hypoxic exposure is important, since this in vitro cell-model system can now be used to better understand the mechanisms that regulate increased responsiveness of specific medial cell subpopulations to low oxygen concentrations. Our data also support the idea that protein kinase C is likely to be one important determinant of differential cell growth responses to hypoxia. The data also suggest differential involvement of specific arterial SMC subpopulations in the elastogenic responses of the vessel wall to injury. We believe that a better understanding of the mechanisms contributing to the unique behavior of specific arterial cell subpopulations will provide important future directions for therapies aimed at preventing abnormal cell replication and matrix protein synthesis in vascular disease.

Inflammatory processes may predispose children to high-altitude pulmonary edema.

We investigated retrospectively whether the preexistence of inflammation-producing illnesses such as viral respiratory tract infections contributed to the development of high-attitude pulmonary edema in children. We found that the large majority of native low-attitude children, but not adults, who had this form of edema after traveling to high altitude also had evidence of a preexisting illness. We speculate that the release of inflammatory mediators associated with these illnesses may be tolerated at sea level but may predispose children to increased capillary permeability when superimposed on hypoxia and, possibly, cold and exercise.

Expression and localization of tropoelastin mRNA in the developing bovine pulmonary artery is dependent on vascular cell phenotype.

During vascular development, the expression of tropoelastin (TE) messenger ribonucleic acid (mRNA) has been shown to be time dependent and to form complex patterns along the longitudinal and radial arterial axes. The factors contributing to these patterns of TE expression are not known, but it has been suggested that they reflect phenotypic changes in developing smooth muscle cells (SMC). In order to examine a possible correlation between the developmental state of the SMC and TE expression during lung vascular development, we localized and assessed relative TE mRNA expression in the developing bovine main pulmonary artery (PA), and correlated the observed patterns of TE expression to changes in SMC phenotype as determined by the expression of various developmentally related SMC proteins. Further, because TE expression can be modulated by physical forces such as pressure, fetal PA TE expression was evaluated with regard to changes in fetal arterial pressure. We found that expression of TE mRNA exhibited a biphasic pattern during fetal development. In early gestation, expression was noted throughout the entire PA wall; at midgestation, expression was markedly decreased in the outer wall but maintained in the inner vascular media; at late gestation, reexpression was observed throughout the entire PA wall, albeit in a heterogeneous pattern. Immunohistochemical studies showed that the decrease in SMC TE expression during midgestation coincided with the acquisition of SMC-specific proteins such as smooth muscle myosin heavy chains and desmin. The reexpression of TE late in gestation occurred in these "differentiated" SMC and was temporally associated with a large increase in arterial pressure shown to occur in late gestation. In addition, we identified an SMC population defined by its immunoreactivity to the muscle-specific cytoskeletal protein meta-vinculin that did not express TE mRNA either during fetal PA development or postnatally when PA hypertension was induced. We conclude that both the developmental state of the SMC and hemodynamic forces correlate with the pattern of PA TE mRNA expression during pulmonary vascular development. Further, a subpopulation of SMC defined by meta-vinculin expression exists in the fetal and neonatal bovine vascular wall and does not express detectable levels of TE mRNA regardless of vascular pressure.

Persistence, re-expression, and induction of pulmonary arterial fibronectin, tropoelastin, and type I procollagen mRNA expression in neonatal hypoxic pulmonary hypertension.

Changes in the structure and function of muscular pulmonary arteries are crucial for normal adaptation to extrauterine life and rapid changes in matrix protein gene expression are likely necessary for this adaptation. We hypothesized that pathological stimuli imposed at the time of birth would alter developmental changes in matrix protein gene expression thereby affecting the normal post-uterine changes in pulmonary hemodynamics. We used in situ hybridization to examine the normal developmental expression of three extracellular matrix protein mRNAs, fibronectin, tropoelastin, and alpha 1 (I) procollagen, in muscular pulmonary arteries of both fetal and neonatal calves and assessed the impact of severe hypoxia-induced pulmonary hypertension on their expression. Morphometric techniques were used to assess whether changes in matrix protein mRNA levels were related to changes in matrix fiber accumulation. Exposure to chronic hypoxia postnatally resulted in the persistence, reexpression, and induction of fibronectin, tropoelastin, and alpha 1 (I) procollagen mRNAs, respectively, in muscular pulmonary arteries. In each case the hybridization signal was localized primarily to the adventitial layer of the vessel. Morphometric analysis showed that the increased hybridization signals seen correlated with an increase in both vascular elastin and collagen fiber volumes in the adventitial layer. We conclude that the change in expression of matrix genes in the pulmonary artery wall during exposure to chronic hypoxia is an important adaptive response to changes in hemodynamic factors and/or oxygen tension. The unchecked increase in matrix protein expression seen likely contributes to the pathological pulmonary arterial structural remodeling and loss of vasoreactivity that occurs during the development of severe neonatal pulmonary hypertension.

Persistence of the fetal pattern of tropoelastin gene expression in severe neonatal bovine pulmonary hypertension.

Neonatal hypoxic pulmonary hypertension causes increases and spatial changes in tropoelastin expression in pulmonary arteries. However, it is not clear if this is due to recruitment of quiescent smooth muscle cells (SMC) into an elastin-producing phenotype or persistence of the fetal pattern of tropoelastin gene expression. We evaluated the distribution and relative concentration of tropoelastin mRNA in intralobar pulmonary arteries from late gestation fetuses and in animals exposed to hypobaric hypoxia (430 mmHg) from birth for 1, 3, 7, or 14 d, as well as in age-matched and adult room air-breathing controls. In situ hybridization demonstrated that tropoelastin mRNA was distributed throughout the entire radius of the pulmonary vessel wall in the fetus and newborn calf. By 15 d of age, only cells in the inner third of the media expressed tropoelastin mRNA, and by adulthood no tropoelastin mRNA was detected in the vessel wall. These findings demonstrated that tropoelastin expression shuts off in a spatially specific pattern, moving from the abluminal to the luminal side of the medial in the neonatal pulmonary artery when pressures and resistance are falling. In the aorta of 15-d-old calves, tropoelastin mRNA expression was seen equally throughout the media, indicating tissue-specific regulation of elastin in the neonatal period. In contrast, intralobar pulmonary arteries from calves exposed to hypoxia, which prevented the normal postnatal decline in pulmonary artery pressure, maintained the fetal pattern and levels of tropoelastin mRNA expression at all time points. Thus, rather than causing a recruitment of SMC into an elastin-producing phenotype, neonatal pulmonary hypertension caused a persistence of the fetal pattern of tropoelastin expression in medial SMC. Cell-free translation showed that the same tropoelastin isoforms were made by mRNA from control and hypertensive calves and, unlike the ligamentum nuchae, did not change during the transition from fetal to neonatal life. We conclude that pulmonary hypertension in the neonate perturbs the normal postpartum repression of tropoelastin expression resulting in a persistence of the fetal spacial and isoform patterns of tropoelastin gene expression.

Progressive loss of vasodilator responsive component of pulmonary hypertension in neonatal calves exposed to 4,570 m.

Severe neonatal pulmonary hypertension (PH) may have both reversible (vasoconstrictive) and "fixed" (vasodilator unresponsive) components. To assess when and to what degree vasodilator unresponsive PH developed in the neonate, pulmonary arterial pressures (PAP) and cardiac outputs (CO) were measured, and total pulmonary resistances (TPR) were calculated in neonatal calves exposed to chronic hypoxia (CH) (barometric pressure of 430 mmHg = 4,570 m) for 1, 3, 7, and 14 days under both normoxic (barometric pressure of 640 mmHg = 1,500 m) and hypoxic conditions with and without an infusion of the vasodilator acetylcholine (ACh). Studies were done at 4 h and at 2, 4, 8, and 15 days of life in both control and CH animals. The fixed component of PH was defined as that PAP or TPR above the control baseline value which remained in CH animals after an infusion ACh at 1,500 m. Small pulmonary arteries were also examined histologically in an attempt to correlate relative changes in the reversible and fixed elements of PH with alterations in vessel structure. Chronic exposure to 4,570 m altitude prevented the normal postnatal fall in PAP and TPR observed in control animals. Instead, PAP, TPR, and the structure of small pulmonary arteries initially remained similar to those of the 4-h-old newborn. By 7 days exposure to 4,570 m, a significant element of fixed PH developed, which increased dramatically between the 7- and 14-day exposure periods and appeared to correlate with a narrowed pulmonary artery lumen and increased medial and adventitial thickness.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional and structural adaptation of the yak pulmonary circulation to residence at high altitude.

The high-altitude (HA) native yak (Bos grunniens) has successfully adapted to chronic hypoxia (CH) despite being in the same genus as domestic cows, which are known for their great hypoxic pulmonary vasoconstrictor responses (HPVRs), muscular pulmonary arteries, and development of severe pulmonary hypertension on exposure to CH. To determine possible mechanisms by which the pulmonary circulation may adapt to CH, yak pulmonary vascular reactivity to both vasoconstrictor and vasodilator stimuli and yak pulmonary artery structure were assessed. Hypoxia caused a small but significant HPVR, and norepinephrine infusion caused a greater rise in pulmonary arterial pressure (Ppa) than did hypoxia. Acetylcholine, an endothelium-dependent vasodilator, had no effect on Ppa but lowered pulmonary resistance (Rp) by causing an increase in cardiac output. Sodium nitroprusside, an endothelium-independent vasodilator, decreased both Ppa and Rp significantly. Yak small pulmonary arteries had a 4.1 +/- 0.1% medial thickness, with vessels < or = 100 microns devoid of smooth muscle. Yak pulmonary artery endothelial cells were much longer, wider, and rounder in appearance than those of domestic cows. Thus the yak has successfully adapted to HA conditions by maintaining both a blunted HPVR and thin-walled pulmonary vessels. Differences in both endothelial cell morphology and response to acetylcholine between the yak and those reported in the domestic cow suggest the adaptation to HA may include changes not only in the amount of pulmonary vascular smooth muscle but in endothelial cell function and structure as well.

Hypoxia-induced inhibition of tropoelastin synthesis by neonatal calf pulmonary artery smooth muscle cells.

Animals chronically exposed to hypoxia develop characteristic structural changes in the pulmonary arterial vasculature including cell hypertrophy, hyperplasia, and increased deposition of extracellular matrix proteins. The medial smooth muscle cells' (SMC) increase in tropoelastin mRNA expression and elastin deposition as determined by in situ hybridization and histologic examination appears to contribute significantly to this increase in matrix protein accumulation. The primary stimulus for the increased tropoelastin production, which persists in vitro, is unknown but mechanical forces and hypoxia seem to play a role. In order to determine the direct effects of hypoxia on tropoelastin production by pulmonary artery SMC, cultured neonatal bovine pulmonary artery SMC were exposed to 3%, 10%, and 21% O2 concentrations for 48, 72, and 120 h and soluble tropoelastin was measured by direct immunoassay. Tropoelastin mRNA levels were also determined by Northern and slot blot analysis after 48 h of incubation under hypoxic conditions. SMC cultured in 3% and 10% O2 for 120 h showed dose-dependent decreases (11-fold and 2-fold, respectively) in measured tropoelastin levels compared with SMC cultured in 21% O2 conditions. This decrease was not due to cell damage or accumulation of toxic metabolites while under hypoxic conditions nor to a change in tropoelastin partitioning between the cell and media. Tropoelastin mRNA levels were also decreased under hypoxic conditions. Secreted, cell layer, and total protein synthesis determined by L-[3H]leucine incorporation again showed a dose-dependent decrease under hypoxic conditions but not to the same extent as tropoelastin production.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular adaptation during chronic neonatal hypoxic pulmonary hypertension.

Newborn animals develop more severe hypoxic pulmonary hypertension than do adults, their vascular changes are greater, and both the hypertension and vascular changes occur more rapidly. We hypothesize that this differential developmentally controlled response may arise from either a difference in the type or quantity of endogenously secreted mediators in response to a given injury or a difference in the replicative and/or matrix-producing response of the vascular cells to physical or chemical stimuli. We investigated the effect of chronic hypoxia (14 days) on the proliferative and matrix-producing phenotype of the neonatal (14-day-old) pulmonary artery smooth muscle cell (SMC) and examined the heterogeneity and potential mechanisms responsible for this response. In situ hybridization studies demonstrated a remarkable change in the distribution of cells hybridizing with a tropoelastin cRNA probe after 14 days of hypoxia. Studies also demonstrated a population of SMC that did not hybridize with the elastin or collagen probes, indicating that the pulmonary artery contains SMC of multiple phenotypes and that the response to hypoxic and hemodynamic stress is not uniform for the various types. Bromodeoxyuridine labeling experiments indicated a large increase in DNA synthesis in hypertensive vessels, which, again, was not uniform either across or along the arterial wall. In vitro experiments with neonatal SMC suggested that hypoxia alone could not be responsible for the proliferative or matrix changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Unilateral pulmonary hypertension as a result of chronic high flow to one lung.

The patient presented is a 27-month-old male with complex congenital heart disease consisting of severe left ventricular outflow tract obstruction and ventricular septal defect who had undergone a pulmonary trunk-to-aorta graft and a pulmonary artery banding procedure as a neonate. Sometime after this repair, but at least 15 months prior to presentation to this institution for placement of an aortic homograft, the pulmonary trunk band apparently slipped and migrated over the right pulmonary artery, severely limiting blood flow to the right lung and increasing flow to the left. Severe pulmonary hypertension developed, with a main pulmonary artery pressure of 94/53 mm Hg. We present clinical and radiographic evidence that the resulting chronic high blood flow and pressure in the left lung ultimately resulted in hypoperfusion of that lung, presumably secondary to chronic vascular changes with greatly increased vascular resistance. Upon surgical repair and removal of the constrictive band from the previously banded right PA, blood flow was increased to the low resistance right lung causing right-sided unilateral pulmonary edema, ventilation/perfusion mismatching, and severe hypoxemia. Perfusion studies documented that less than 10% of blood was directed to the left lung, with greater than 90% to the right. Perfusion studies 9 months postoperatively continued to demonstrate minimal blood flow to the left lung. Discussion focuses on the effects of mechanical forces and the interaction with hypoxia in causing pulmonary vascular remodeling.