Background
The renin-angiotensin system (RAS) regulates vascular tone and fluid-electrolyte homeostasis in a wide range of tissues [
1‐
4]. Angiotensin II (Ang II), formed by the activity of angiotensin-converting enzyme (ACE) on angiotensin I (Ang I), is the key effector peptide of the RAS and, via the angiotensin type I receptor (AT1R), mediates physiological effects, including vasoconstriction, inflammation, apoptosis, capillary leak, and fibroproliferation [
5‐
8]. ACE2 is a membrane-bound carboxypeptidase that hydrolyzes Ang II to the heptapeptide Angiotensin-(1–7) (Ang 1–7). ACE2 regulates RAS signaling, both directly by reducing Ang II/AT1R signaling and indirectly by activating the counterregulatory Ang 1–7/Mas receptor pathway [
9‐
12].
RAS signaling and ACE2 have been implicated in the pathogenesis of acute respiratory distress syndrome (ARDS). Mice deficient in ACE2 developed severe acute lung injury (ALI) following challenge with a variety of insults [
13,
14], which improved on repletion with recombinant ACE2 [
15]. The importance of ACE/Ang II signaling in human disease is suggested by increased levels of ACE and Ang II in patients with ARDS and patients with sepsis [
16‐
19], and it is further underlined by genetic studies of an insertion/deletion (I/D) polymorphism within the
ACE gene, with the D allele conferring higher ACE and Ang II levels in tissue and serum [
20]. A number of studies and meta-analyses [
20‐
23] suggest an association between the
ACE D allele and mortality in ARDS cohorts.
A recombinant version of the catalytic ectodomain of human ACE2 (rhACE2, GSK2586881) attenuated arterial hypoxemia in a piglet model of lipopolysaccharide-induced ALI [
24] and was well-tolerated when administered to healthy human volunteers [
25]. We postulated that the addition of exogenous ACE2 in patients with ARDS could attenuate lung injury without compromising systemic hemodynamics. We report the results of a prospective, placebo-controlled trial of GSK2586881 in mechanically ventilated patients with ARDS. The aim of the trial was to establish preliminary safety, pharmacokinetics (PK), and pharmacodynamics (PD) in critically ill patients and to explore the effects of GSK2586881 on relevant physiological measures of ARDS.
Discussion
The primary objective of this study was to assess the safety of GSK2586881 in patients with ARDS, and the study also included measurements of inflammatory biomarkers and exploratory endpoints relating to lung physiology and clinical efficacy. The study met its primary endpoint because there were no episodes of hypotension associated with infusion of GSK2586881. Most AEs were equally distributed between the treatment and placebo groups and were consistent with a critically ill population; however, some were reported more frequently in subjects receiving GSK2586881, including hypernatremia; pneumonia; dysphagia; and, in particular, rash. The occurrence of rash in patients taking ACE inhibitors has been reported [
30]. Rash sometimes accompanies infusions of therapeutic proteins as a result of formation of protein-protein or antibody-protein complexes that precipitate type II or III hypersensitivity reactions [
30]. Although no antibody responses to GSK2586881 were detected, given the small number of subjects in this trial, the possibility of immune-mediated rash cannot be ruled out. Although all pneumonia events occurred in the treatment arm, these occurred well after the last dose of study drug (ranging from 5 to 36 days), so a clear role for GSK2586881 in the increased reports of pneumonia is difficult to establish.
Despite the increased illness severity and dysregulated RAS signaling in the GSK2586881-treated group at baseline, infusion of GSK2586881 modulated RAS peptides as expected, resulting in a significant decrease in concentrations of Ang II, accompanied by similarly rapid increases in Ang 1–7 and Ang 1–5 concentrations. This is consistent with the PK data that suggested a good correlation between plasma concentrations of GSK2256881 and measured ACE2 activity (Additional file
1: Figure S4). Whereas infusion of GSK2586881 resulted in a mean decrease in Ang II, levels in some subjects remained higher than those reported in healthy volunteers [
25]. Increases in Ang 1–7 and Ang 1–5 peptide products were limited to the initial 30–60 minutes after infusion, perhaps reflecting high turnover of the initial Ang II substrate pool in the presence of high concentrations of rhACE2. This raises the possibility that continuous infusions of GSK2586881 that achieve lower plasma concentrations over a longer duration may be more effective as a result of more sustained production of Ang 1–7. Further dose regimen finding studies are required to explore these PK/PD relationships.
It is notable that 71% of patients had baseline concentrations of Ang II < 50 pg/ml, a level suggested to be of prognostic significance in some patient populations [
17,
31,
32]. This observation highlights the variability in RAS activation within heterogeneous cohorts of patients with ARDS and raises the possibility that RAS activation may be driving disease in only a subgroup of patients. Researchers in future studies could consider evaluating GSK2586881 only in patients with elevated Ang II and, in light of findings in animals, could further explore the impact of RAS modulation on pulmonary hemodynamics and markers of pulmonary vascular injury.
Treatment with GSK2586881 resulted in a reduction in IL-6 concentrations, although this did not reach statistical significance, owing to intersubject variability and baseline imbalances. The elevations in SP-D were unexpected and raise a number of questions about GSK2586881’s mechanism of action. SP-D is a large collectin family protein, with expression usually restricted to the lung [
33,
34]. Its presence in serum has been suggested to be an indicator of worsening alveolar capillary permeability. However, SP-D is also an anti-inflammatory [
33,
34] and antimicrobial protein [
35]; thus, the observed increases could be reflective of increased SP-D biosynthesis in the lung as a result of GSK2586881 treatment. These data highlight a need for further research on the potential mechanistic link between ACE2 and SP-D biology.
Although difficult to assess because of study limitations, it is possible that treatment with GSK2586881 worsened respiratory mechanics, with the change in compliance and ventilatory pressures possibly suggesting an increase in lung stiffness [
29,
36,
37]. Although most of the biomarkers measured suggested no change or reduced disease activity in GSK2586881-treated subjects, the increase in myeloperoxidase is difficult to explain on the basis of known ACE2 biology and previous effects in animals and humans, and it could reflect lung neutrophil accumulation and the potential for altered respiratory mechanics. Some of the analyses were impacted by missing data (e.g., subject withdrawal, extubation, technical issues, early mortality); therefore, the number of subjects supporting these comparisons was small, significantly increasing the possibility of systematic bias at later time points. There were baseline imbalances in severity of illness (based on SOFA score and serum IL-6 and Ang II levels) and case mix between treatment groups.
The lack of improvement in oxygenation in patients receiving GSK2586881 contrasts with effects reported in large animal models of ARDS, where IV rhACE2 rapidly improved arterial hypoxemia and pulmonary hemodynamics [
15,
38]. Although PaO
2/FiO
2 and other ventilatory parameters are important in the diagnosis of ARDS and in determining the severity of hypoxemia, they cannot be standardized clinically to the same extent as in animal studies, and they are influenced by numerous factors that were not adequately controlled for in this trial. These issues limit interpretation of the effects of GSK2586881 on oxygenation and ventilatory parameters.
Acknowledgements
The authors thank the patients and their families, as well as the following principal investigators and study coordinators and their institutions for their contributions to the study:
United States: Kelli Brooks (Duke University Medical Center, Durham, NC), Peter Morris (Wake Forest University School of Medicine, Winston-Salem, NC), Richard Wunderink (Northwestern Memorial Hospital, Chicago, IL), Evert Eriksson (Medical University of South Carolina, Charleston, SC), Juan Duchesne (Tulane University School of Medicine, New Orleans, LA), Hayley Gershengorn (Albert Einstein College of Medicine, Bronx, NY), Robert Hyzy (University of Michigan Medical Center, Ann Arbor, MI), Patrick Wright (Moses H. Cone Memorial Hospital, Greensboro, NC), Bharat Awsare (Thomas Jefferson University, Philadelphia, PA), Nathan Kessler (Oregon Health & Science University, Portland, OR), Katherine Markelz and Ana Campbell (University of Pennsylvania, Philadelphia, PA), Brian Morrissey (University of California, Davis School of Medicine, Sacramento, CA), Lori-Ann Kozikowski and Lesley De Souza (Baystate Medical Center, Springfield, MA).
Canada: Francois Lellouche (Institut Universitaire de Cardiologie et de Pneumologie de Québec, Sainte-Foy, PQ), John Muscedere (Kingston General Hospital, Kingston, ON), Yoanna Skrobik (McGill University Health Centre, Montreal, QC), Mélissa Joseph (Charles LeMoyne Hospital, Greenfield Park, QC)
The authors also acknowledge the contributions of the following GSK employees in the United States, United Kingdom, and Canada: Sandi VanBuren, Alina Goetz, Amanda Baines, Hina Abbas, Ann Barella, Kiran Ubhi, Adam Hughes, Thomas Mencken, and Thomas Lee. The authors acknowledge the assistance of Gillian Groeger of Fishawack Communications for assistance in producing the figures (funded by GSK).