Quantitative disease progression model of α-1 proteinase inhibitor therapy on computed tomography lung density in patients with α-1 antitrypsin deficiency

Management of lung disease in alpha-1 antitrypsin deficiency: what we do and what we do not know

Management of lung disease in patients with alpha-1 antitrypsin deficiency (AATD) includes both non-pharmacological and pharmacological approaches. Lifestyle changes with avoidance of environmental pollutants, including tobacco smoke, improving exercise levels and nutritional status, all encompassed under a disease management program, are crucial pillars of AATD management. Non-pharmacological therapies follow conventional treatment guidelines for chronic obstructive pulmonary disease. Specific pharmacological treatment consists of administering exogenous alpha-1 antitrypsin (AAT) protein intravenously (augmentation therapy). This intervention raises AAT levels in serum and lung epithelial lining fluid, increases anti-elastase capacity, and decreases several inflammatory mediators in the lung. Radiologically, augmentation therapy reduces lung density loss over time, thus delaying disease progression. The effect of augmentation therapy on other lung-related outcomes, such as exacerbation frequency/length, quality of life, lung function decline, and mortality, are less clear and questions regarding dose optimization or route of administration are still debatable. This review discusses the rationale and available evidence for these interventions in AATD.

Safety of biweekly α1-antitrypsin treatment in the RAPID programme

α₁-antitrypsin (α₁-AT) deficiency is a hereditary disorder characterised by an abnormally low concentration of functional α₁-AT in blood and tissues [1]. The primary role of α₁-AT is to protect elastin-containing tissues, most notably the lung, against the destructive activity of proteolytic enzymes [2]. Patients with severe α₁-AT deficiency present with serum α₁-AT concentrations <11 μM and are prone to destruction of the lung tissue, often developing respiratory symptoms and emphysema in the fourth or fifth decade of life [3, 4].

Administration of 120 mg·kg⁻¹ α₁-antitrypsin on a biweekly basis was safe and well toleratedhttp://ow.ly/CVbz30lUBum

Intravenous Alpha-1 Antitrypsin Therapy for Alpha-1 Antitrypsin Deficiency: The Current State of the Evidence

Alpha-1 antitrypsin deficiency (AATD) is a largely monogenetic disorder associated with a high risk for the development of chronic obstructive pulmonary disease (COPD) and cirrhosis. Intravenous alpha-1 antitrypsin (AAT) therapy has been available for the treatment of individuals with AATD and COPD since the late 1980s. Initial Food and Drug Administration (FDA) approval was granted based on biochemical efficacy. Following its approval, the FDA, scientific community and third-party payers encouraged manufacturers of AAT therapy to determine its clinical efficacy. This task has proved challenging because AATD is a rare, orphan disorder comprised of individuals who are geographically dispersed and infrequently identified. In addition, robust clinical trial outcomes have been lacking until recently. This review provides an update on the evidence for the clinical efficacy of intravenous AAT therapy for patients with AATD-related emphysema.

Alpha-1 Antitrypsin Substitution for Extrapulmonary Conditions in Alpha-1 Antitrypsin Deficient Patients

Alpha-1 antitrypsin deficiency (AATD) is a genetic disorder which most commonly manifests as pulmonary emphysema. Accordingly, alpha-1 antitrypsin (AAT) augmentation therapy aims to reduce the progression of emphysema, as achieved by life-long weekly slow-drip infusions of plasma-derived affinity-purified human AAT. However, not all AATD patients will receive this therapy, due to either lack of medical coverage or low patient compliance. To circumvent these limitations, attempts are being made to develop lung-directed therapies, including inhaled AAT and locally-delivered AAT gene therapy. Lung transplantation is also an ultimate therapy option. Although less common, AATD patients also present with disease manifestations that extend beyond the lung, including vasculitis, diabetes and panniculitis, and appear to experience longer and more frequent hospitalization times and more frequent pneumonia bouts. In the past decade, new mechanism-based clinical indications for AAT therapy have surfaced, depicting a safe, anti-inflammatory, immunomodulatory and tissue-protective agent. Introduced to non-AATD individuals, AAT appears to provide relief from steroid-refractory graft-versus-host disease, from bacterial infections in cystic fibrosis and from autoimmune diabetes; preclinical studies show benefit also in multiple sclerosis, ulcerative colitis, rheumatoid arthritis, acute myocardial infarction and stroke, as well as ischemia-reperfusion injury and aberrant wound healing processes. While the current augmentation therapy is targeted towards treatment of emphysema, it is suggested that AATD patients may benefit from AAT augmentation therapy geared towards extrapulmonary pathologies as well. Thus, development of mechanism-based, context-specific AAT augmentation therapy protocols is encouraged. In the current review, we will discuss extrapulmonary manifestations of AATD and the potential of AAT augmentation therapy for these conditions.

Quantitative disease progression model of α-1 proteinase inhibitor therapy on computed tomography lung density in patients with α-1 antitrypsin deficiency

Aims

Early‐onset emphysema attributed to α‐1 antitrypsin deficiency (AATD) is frequently overlooked and undertreated. RAPID‐RCT/RAPID‐OLE, the largest clinical trials of purified human α‐1 proteinase inhibitor (A₁‐PI; 60 mg kg^–1 week^–1) therapy completed to date, demonstrated for the first time that A₁‐PI is clinically effective in slowing lung tissue loss in AATD. A posthoc pharmacometric analysis was undertaken to further explore dose, exposure and response.

Methods

A disease progression model was constructed, utilizing observed A₁‐PI exposure and lung density decline rates (measured by computed tomography) from RAPID‐RCT/RAPID‐OLE, to predict effects of population variability and higher doses on A₁‐PI exposure and clinical response. Dose–exposure and exposure–response relationships were characterized using nonlinear and linear mixed effects models, respectively. The dose–exposure model predicts summary exposures and not individual concentration kinetics; covariates included baseline serum A₁‐PI, forced expiratory volume in 1 s and body weight. The exposure–response model relates A₁‐PI exposure to lung density decline rate at varying exposure levels.

Results

A dose of 60 mg kg^–1 week^–1 achieved trough serum levels >11 μmol l^–1 (putative ‘protective threshold’) in ≥98% patients. Dose–exposure–response simulations revealed increasing separation between A₁‐PI and placebo in the proportions of patients achieving higher reductions in lung density decline rate; improvements in decline rates ≥0.5 g l^–1 year^–1 occurred more often in patients receiving A₁‐PI: 63 vs. 12%.

Conclusion

Weight‐based A₁‐PI dosing reliably raises serum levels above the 11 μmol l^–1 threshold. However, our exposure–response simulations question whether this is the maximal, clinically effective threshold for A₁‐PI therapy in AATD. The model suggested higher doses of A₁‐PI would yield greater clinical effects.