Introduction
The coronavirus disease-2019 (COVID-19), firstly originated in the city of Wuhan,
Hubei Province, People's Republic of China, is due to infection by the severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2) (Guo et al., 2020). SARS-CoV-2 has
shown high infectivity, and high mortality associated to respiratory failure from
acute respiratory distress syndrome (ARDS), becoming rapidly a worldwide health emergency
(Guo et al., 2020). In spite of the several efforts of researchers, the limited knowledge
on the disease progression and immunological profile, and the absence of medications
or vaccines proven to be effective for treatment or prevention of the SARS-CoV-2,
lead to the urgent need for efficient and safe therapies, and treatments to limit
acute inflammation associated with severe pneumonia and mortality (Mirastschijski
et al., 2020). Agents such as potent anti-inflammatory drugs, some antivirals including
Remdesevir and, recently, hyperimmune plasma, seem promising, whereas several studies
are currently ongoing to test and prove their effectiveness (Guo et al., 2020).
Indeed, approved safe therapies with potential ability to control infection and to
prevent respiratory complications may be preferential candidates (Zhou et al., 2020),
while the range of proposal drugs is rapidly growing (Scalise and Indiveri, 2020;
Ye et al., 2020). This approach may readily permit to identify and use safe drugs,
until knowledge on the viral biology will allow to identify specific SARS-CoV-2 drugs
and/or vaccines.
Alpha-1 Antitrypsin (AAT)
Alpha-1 antitrypsin (AAT) protein is one of the major serum proteins involved in anti-inflammatory
processes (de Serres and Blanco, 2014). AAT, mainly synthesized in the liver, is released
into the bloodstream. AAT is primarily known as a serine protease inhibitor (SERPIN)
targeting several enzymes involved in tissue damage/repair, whereas its activity is
very high in the lower respiratory tract where it provides over 90% of the defenses
against proteases, mainly neutrophil elastase (NE), protecting healthy tissues from
the digestive action of proteolytic enzymes. As an acute phase protein, AAT increases
4-6 fold during infections, inflammation, tissue injury, surgery and late pregnancy
(Sanford et al., 1999; Buttenschoen et al., 2001; Ziakas et al., 2011; de Serres and
Blanco, 2014).
Further, AAT displays immunomodulatory abilities. It inhibits pro-inflammatory cytokines,
while increasing anti-inflammatory mediators (Guttman et al., 2015). Specifically,
AAT functions have been linked to interleukin 6 (IL6) signaling (Yuan et al., 2018).
Also, AAT has shown anti-viral activities in in vitro and in vivo studies (Shapiro
et al., 2001; Munch et al., 2007; Wanner et al., 2012). In primary Rhesus monkey kidney
cells, AAT inhibited H1N1 influenza virus cell infection, whereas in infected mice
AAT decreased the mortality rates and inflammatory cytokines (Wanner et al., 2012).
In HIV infection, AAT suppressed viral production in chronically infected monocytes,
inhibited HIV-1 entry into a cell line designed to detect viral entry, and reduced
HIV-1 replication in human peripheral mononuclear cells (Shapiro et al., 2001; Munch
et al., 2007).
AAT is widely studied in clinical setting due to the existence of congenital genetic
defects that reduce its concentrations in the blood (Bornhorst et al., 2007). More
than 100 allelic variants of the gene coding for the AAT, called Serine Protease Inhibitor-A1
(SERPINA1) exist, whereas many of them are associated with reduced circulating protein
levels or altered protein activity (Bornhorst et al., 2007). Individuals with AAT
deficiency (AATD), in the presence or in the absence of concomitant factors such as
smoke, environmental pollutants, and age, have a very high risk of developing pathologies
of the respiratory system, such as pulmonary emphysema and chronic obstructive pulmonary
disease (COPD) associated to a progressive damage of lung parenchyma (Nuñez et al.,
2020).
Additionally, reduced levels of AAT or abnormal AAT proteins have been associated
with increased susceptibility to viral infections, such as hepatitis B, hepatitis
C, HIV-1, and HTLV-1 infections (Hashemi et al., 2005; Settin et al., 2006; da Silva
Ferreira et al., 2014, 2017), and the development of autoimmune and chronic inflammatory
diseases, such as diabetes mellitus and panniculitis (Hashemi et al., 2006; de Serres
and Blanco, 2014).
Alpha-1 Antitrypsin Therapy in COPD
Currently, AAT therapy, which is a FDA approved drug, is the only available pharmacological
treatment that can slow COPD progression in AATD patients (Griese and Scheuch, 2016;
Brantly et al., 2018). COPD is a respiratory disease characterized by persistent respiratory
symptoms with significant obstruction of airflow, and increased lung and systemic
inflammation (Bradford et al., 2017; Celli and Wedzicha, 2019).
The progression of COPD is associated with increased inflammation of the airway and
alveolar wall (Chen et al., 2016). Patients affected by COPD frequently present exacerbations,
often triggered by bacterial/viral respiratory infections or viruses, which lead to
disease progression through an exaggerated inflammatory response, therefore requiring
pharmacological treatments (Xiong et al., 2017). COPD exacerbations are characterized
by high neutrophil counts, and high levels of C-reactive protein (CRP), as well as
inflammatory cytokines including tumor necrosis factor α (TNFα), interleukin-1 (IL1),
interleukin-8 (IL8) and IL6 (Bradford et al., 2017; Xiong et al., 2017; Nuñez et al.,
2020).
Intravenous AAT therapy has been used for the treatment of individuals with AATD and
COPD since the late 1980s. Clinical AAT efficacy has been reported showing therapeutic
effect on FEV1 and CT lung densitometry in observational or registry studies (Chapman
et al., 2009, 2015). Further, AAT therapy impacts on several biological parameters
involved in COPD and its progression in AATD patients (Campos et al., 2019). AAT therapy
restores the serum protein levels to those of normal subjects, significantly reduces
protease activities and inflammation by downregulating several inflammatory markers
(Brantly et al., 2018; Campos et al., 2019).
The AAT multiple activities have suggested a potential therapeutic use of AAT for
the treatment of several inflammatory and autoimmune diseases beyond COPD, as well
as viral diseases including HIV-1 infection, whereby AAT infusion can decrease HIV
viral load (Forssmann et al., 2010; Lewis, 2012; Wanner et al., 2012). Therefore,
the research on the possible benefits of AAT therapy in other diseases is ongoing,
particularly in transplant and type-1 diabetes, as well as in rheumatologic diseases
(Lewis, 2012; Marcondes et al., 2016). In preclinical studies, beneficial effects
of AAT treatment have been observed in autoimmune disease models, such as rheumatoid
arthritis and systemic lupus erythematosus, whereas some clinical studies have investigated
AAT treatment in graft vs. host disease (GVHD) in organ transplantation and type 1
diabetes mellitus (Grimstein et al., 2011; Lewis, 2012; Wanner et al., 2012; Marcondes
et al., 2016).
Discussion
In COVID-19 patients, disease severity and high mortality are associated to respiratory
failure from ARDS and multiple organ dysfunctions due to an impressive cytokine storm,
with significant increased levels of several inflammatory mediators, including IL-6,
interferon gamma (INFγ), TNFα, interleukin 17 (IL-17), IL-8 (McElvaney et al., 2020;
Pedersen and Ho, 2020). Further, the neutrophil-to-lymphocyte ratio (NLR) in peripheral
blood, considered a systemic inflammatory biomarker, is increased in patients with
COVID-19 with severe disease compared to those with mild disease and healthy controls
(McElvaney et al., 2020). Because elevated levels of IL-6 have been associated to
poor prognosis and predictor of mortality, the use of IL6 antagonists has been early
proposed for the COVID-19 treatment. Recently, the treatment with the monoclonal antibody
Tocilizumab, which is currently used for the treatment of rheumatoid arthritis, has
been considered an attractive approach for the treatment of COVID-19 (Guaraldi et
al., 2020). Clinical trials to study the efficacy and safety of the Tocilizumab monoclonal
antibody are ongoing in several Countries, including Italy (Guaraldi et al., 2020).
Nevertheless, the validity of the treatment is debated (Arnaldez et al., 2020). In
fact, IL-6 is a crucial inflammatory cytokine for the development of antibodies and
the activation of T lymphocytes against infectious agents, and its inhibition could
even be deleterious, since it would lower the immune response against the SARS-CoV-
2 (Arnaldez et al., 2020).
To date AAT supplement therapy is largely used to avoid disease exacerbation in AATD
COPD patients (Brantly et al., 2018; Campos et al., 2019). In spite of several clinical
differences, COVID19 and COPD patients may present similar clinical outcome, such
as acute exacerbations, resulting in exaggerated inflammatory response and increased
NRL and IL6 levels (Chen et al., 2016; Wang et al., 2020). Interestingly, among common
comorbidities in COVID19, Wang et al. have shown that COPD is associated with a 5.9-fold
higher risk of progression in patients with COVID-19 (Wang et al., 2020). One explanation
could be that the expression of angiotensin-converting enzyme 2 (ACE2), which is the
host cell receptor for SARS-CoV-2 entry, is increased in COPD patients (Leung et al.,
2020).
The potential clinical utility of AAT treatment in COVID-19 patients is based on the
following considerations: (i) AAT acts as an efficient inhibitor of the host transmembrane
protease serine 2 (TMPRSS2) protein receptor (Azouz et al., 2020), which is essential
during the initial phase of the SARS-CoV-2 infection. Indeed, similar to other coronaviruses,
SARS-CoV-2 binds its envelope spike (S) protein ligand to the ACE2 receptor for entering
into cells (Azouz et al., 2020). The host TMPRSS2 receptor acts by processing the
viral S protein, allowing S protein–ACE2 interaction and infection of the host cell.
Consequently, the AAT treatment may limit the SARS-CoV-2 entry into host cells, which
represents the first step of the viral infection; (ii) despite AAT increase in COVID-19
patients, according to its role as an inflammatory acute phase protein, it has been
shown that the IL6:AAT ratio is higher in patients with the severe/critical disease
than in mild/stable disease (McElvaney et al., 2020). Moreover, in severe/critical
COVID-19 patients the increase and reduction of the IL-6:AAT ratio has been associated
with a poor outcome and clinical improvement, respectively (McElvaney et al., 2020).
Therefore, even though AAT levels are correctly risen in COVID-19 patients, AAT augmentation
may be useful to modulate the production and activity of key pro-inflammatory cytokines,
while preserving the production of the anti-inflammatory cytokine IL-10 (Guttman et
al., 2015); (iii) AATD is a largely under-recognized condition (De Serres et al.,
2003). AATD state by itself is not a disease, but a genetic background/predisposition
to the development of several diseases. One could speculate that individuals carrying
SERPINA1 deficient allelic variants may be at higher risk of SARS-CoV-2 infection
than those with wild type SERPINA1, as previously shown for retroviral infections
(Hashemi et al., 2005; Settin et al., 2006; da Silva Ferreira et al., 2014, 2017).
It is also possible to hypothesize that some SERPINA1 deficient allelic variants could
not allow AAT to be sufficiently increased or efficient to counteract SARS-CoV-2 infection,
leading to the progressive worsening of the COVID-19 disease. Of note, the Italian
register of the AATD reports a higher frequency of cases in northern Italy than in
central and southern Italy, with the highest incidence in Lombardy (47%), which is
the northern Italian region counting the highest mortality rate for COVID-19, reaching
up 85% cases (Luisetti et al., 2015; World Health Organization., 2020). This possible
association between AATD and COVID-19 deserves to be explored, and might reveal subtypes
of COVID-19 patients who could benefit from AAT supplementary therapy. In this view,
AAT treatment should be also useful to prevent severe outcome in AATD COVID-19 patients
presenting mild symptoms.
Based on these observations, it is reasonable to suggest that AAT treatment, used
to slow COPD progression, may be considered in COVID-19 patients. As AAT administration
is a FDA-approved drug with a confirmed safety profile, this novel therapeutic potential
makes AAT a promising candidate to counteract COVID-19 disease. The use of AAT in
the treatment of COVID-19 patients will allow to overcome the limits of the Tocilizumab
therapy, which could limit the immune response against SARS-CoV-2 (Arnaldez et al.,
2020). Furthermore, while treatment with Tocilizumab is limited to blocking only one
pro-inflammatory pathway (IL6/IL6-R), the administration of AAT could have a broader
immunomodulatory and “pro-resolving” effect, increasing the chances of clinical success.
In fact, from a biochemical point of view, AAT acts both extracellularly as a protease
inhibitor and as a ligand of some membrane receptors, inducing a signal, which modulates
the immune response (Guttman et al., 2015). AAT is able: (i) to polarize macrophage
cells toward a M2 phenotype, known to be anti-inflammatory and promoter of tissue
repair/regeneration programs (Guttman et al., 2016). This activity is significant,
since monocyte-macrophages are the main players in the initiation and maintenance
of the inflammatory cascade induced by SARS-CoV-2 (Guo et al., 2020); (ii) to neutralize
the elastase released by neutrophil granulocytes, also involved in the pathogenesis
of lung damage; (iii) to favor the differentiation of T lymphocytes toward the Treg
phenotype, endowed with immunosuppressive properties that could contribute the shutdown
of the cytokine storm (Baranovski et al., 2015).
Finally, engineered AAT (α1-PDX) converted to a furin inhibitor may be a promising
antiviral molecule for SARS-CoV-2 (Scott and Sheffield, 2020). The human serine proteinase
furin is a proprotein convertase, which processes different pathogens for entering
host cell (Shiryaev et al., 2007; Coutarda et al., 2020). Furin-mediated cleavage
of viral glycoproteins (gp) facilitates HIV-1, measles, and influenza viral infections
(Thomas, 2002). α1-PDX can block HIV-1 gp160 processing, which is required for cellular
invasion, whereas it reduces HIV-1 and measles infectivity in vitro. On this ground,
α1-PDX can be considered as a potential treatment strategy for COVID-19 (Anderson
et al., 1993; Watanabe et al., 1995; Bahbouhi et al., 2000).
In conclusion, due to the known roles of AAT and its current use in clinics (Chapman
et al., 2009, 2015; Forssmann et al., 2010; Lewis, 2012; Griese and Scheuch, 2016;
Marcondes et al., 2016; Brantly et al., 2018; Campos et al., 2019), AAT treatment
may represent a safe drug with potential activity in treating COVID-19 affected patients.
Safe protocols for treatments, including doses and timely infusions are currently
available for COPD patients (Chapman et al., 2009, 2015; Griese and Scheuch, 2016;
Brantly et al., 2018; Campos et al., 2019). AAT treatment via aerosol, used in COPD
treatment, could be administered in COVID-19 patients as well (Griese and Scheuch,
2016). AAT local instillation or aerosol in humid heat vaporization (40–41°C) in the
first phase of COVID-19 might be a powerful strategy for hampering SARS-CoV-2 entering
into the host cells by inhibiting host cell receptors, significantly decreasing viral
replication, risk of evolution to the more severe clinical pictures, reducing hospitalization
and death rate. As recently proposed for Remdesivir, local aerosolisation of AAT with
hot-wet humid water vaporization (WHV) at 40–41°C could significantly decrease viral
replication in hours or 2–3 days at most, in the early stages of respiratory disease
(Contini et al., 2020). The amount of product required may be minimal, plausibly reducing
disease evolution, patient pain and discomfort, the adverse effects of intravenous
administration and social cost.
We suggest that AAT treatment deserves the attention of clinicians for its potential
utility in the treatment of COVID-19. Further studies evaluating the levels and the
activity of AAT in COVID-19 patients presenting cytokine storm or affected by AATD
will lead to stratification of patients, assessing whether AAT treatment may be useful
as a therapy or to prevent severe outcomes.
Author Contributions
FM proposed the hypothesis. MD wrote the first draft. FM, CC, and MT corrected the
draft. FM, MD, CC, and MT wrote the final text. MT supervised the work and submitted
the manuscript.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial
or financial relationships that could be construed as a potential conflict of interest.