Pharmacological Inhibition of MMP3 as a Potential Therapeutic Option for COVID-19 Associated Acute Respiratory Distress Syndrome

Abstract

The high mortality of coronavirus disease 2019 (COVID-19) patients is due to their progression to cytokine-associated organ injuries, primarily the acute respiratory distress syndrome (ARDS). The uncertainties in the molecular mechanisms leading to the switch from the early virus infection to the advanced stage ARDS is a major gridlock in therapeutic development to reduce mortality. Previous studies in our laboratory have identified matrix metalloprotease-3 (MMP3) as an important mediator of bacterial lipopolysaccharide (LPS)-induced ARDS, particularly in the exudative phase. Our studies have also reported elevated plasma MMP3 activity levels in the ARDS patients and that inhibition of MMP3 can reduce the severity of LPS-induced ARDS in mice. Given these observations, targeting MMP3 could be a potential option to treat COVID-19 patients with ARDS, and measurement of MMP3 activity in the plasma may serve as a biomarker for the early detection of ARDS in COVID-19 patients.

1. INTRODUCTION

Identification of therapeutic targets to inhibit the progress of coronavirus disease 2019 (COVID-19) to acute respiratory distress syndrome (ARDS) is critical. COVID-19 [1] has emerged as a worldwide health concern due to its high infection rate¹, prolonged asymptomatic incubation period, and high mortality [2, 3]. Several early trials for COVID-19 on medications such as hydroxychloroquine showed no benefits [4, 5]. COVID-19 is expected to infect several million people, and the advanced stage of COVID-19 is associated with acute respiratory distress syndrome (ARDS) and increased mortality [6]. According to the recent reports cited by the US Centers for Disease Control and Prevention (CDC), among all COVID-19 patients, ARDS develops between 3-17%. In contrast, ARDS develops between 20-42% of hospitalized patients and 67-85% of ICU patients [7-12]. Thus, targeting the mechanism of COVID-19 associated ARDS development is a key therapeutic strategy to decrease the high mortality rate. Further, the timely identification of patients at the highest risk of disease progression supports the use of early lung-protective strategies.

The exudative phase of ARDS is characterized by the outflow of plasma and cells from the circulation to the extravascular tissues setting up alveolar edema, mediated by inflammatory cytokines [13, 14]. Without therapeutic intervention, this process can cause irreversible damage to the lungs. Matrix metalloproteinases (MMPs) play an important role in innate immunity and inflammatory response, and various inflammatory lung diseases, such as ARDS, asthma, and pulmonary fibrosis, are characterized by an increase in the expression of one or more of the MMPs [15, 16]. MMP3, also known as stromelysin1, is a matricellular protease that not only degrades the extracellular matrix in the basement membrane but also promotes the cell-cell barrier disruption due to its enzymatic proteolysis of junctional proteins, particularly the tight junction proteins claudins and occludins [17]. The structure of MMP3 is shown in Fig. (1) [18]. Endothelial cells [19, 20], bronchial and alveolar epithelial cells and inflammatory cells [21] are reported to secrete MMP3 in the lungs, suggesting its potential role in the early stages of ARDS. Epithelial cells that line the bronchus and the alveoli, and endothelial cells that line the innermost later of the bllod vessels are the primary sites of infection and replication of the severe acute respiratory syndrome causing coronavirus-2 (SARS-CoV2) [22]. Notably, MMP3 inhibition reversed MMP3s association with inflammation via increased interleukin-1β and monocyte chemoattractant protein-3 expression [23]. In agreement with the finding that MMP3 is associated with inflammation and lung injury, studies from our laboratory have demonstrated that FoxO-regulated expression of MMP3 in endothelial cells promotes bacterial lipopolysaccharide (LPS)-induced endothelial-barrier disruption in vitro and lung injury and edema in vivo [19].

Fig. (1).

Structure of MMP3 (stromelysin1) showing the signal peptide, pro-domain, catalytic domain, hinge (linker) region, and hemopexin domain.

Increased endothelial MMP3 levels in our studies correlated with decreased expression of predominant endothelial tight junction protein claudin-5, whose decrease is associated with ARDS, suggesting the potential role of MMP3 in the promotion of vascular permeability [24]. Further, LPS-induced lung injury also correlated with increased expression of MMP3 in the bronchoalveolar lavage fluid (BALF) associated with increased neutrophil myeloperoxidase activity in the plasma, lung tissue, and BALF [19]. Another study from our group confirmed this further in human ARDS patients where significantly elevated MMP3 activity was observed in the plasma/serum samples of ARDS patients compared to the samples collected from the healthy control subjects [20]. The mechanisms by which MMP3 expression is regulated in inflammatory cells are currently unknown. Nevertheless, cotreatment with MMP3 inhibitor, UK356618, effectively reversed LPS-induced endothelial-barrier disruption in vitro and lung injury and edema in vivo [19], indicating the role of MMP3 in mediating pathological inflammation and tissue injury (Fig. 2). Although several compounds have been tested for their potency and selectivity for MMP3 inhibition (Table 1), UK356618 has demonstrated the highest efficacy and specificity for MMP3 [25].

Fig. (2).

MMP3 inhibition during the exudative phase of ARDS will reduce vascular injury and alveolar edema and prevent the disease progression to the irreversible stages of the disease.

Table 1.

MMP3 inhibitors and their specificity.

S.No.	MMP3 Inhibitor	Other MMPs Inhibited	References
1.	Actinonin	MMP-1/2/3/7/8/9/10/12/13	Mitchell et al., 2007 [33]
2.	PD166793	MMP-2/3/13	Paolocci et al., 2006 [34]
3.	MMP Inhibitor V	MMP-2/3/8/9/12/13	Okamoto et al., 2007 [35]
4.	MMP-3 Inhibitor VIII	MMP-3/12	Sindermann et al., 2008 [36]
5.	MMP-3 Inhibitor V	MMP-3 (Untested for other MMPs)	Johnson et al., 1999 [37]
6.	MMP-2/3 Inhibitor II	MMP-2/3	Jacobsen et al., 1999 [38]
7.	UK 370106	MMP-3 (Untested for other MMPs)	Matthews et al., 2008 [39]
8.	UK 356618	MMP-3 (Potent and highly specific)	Fray and Dickinson 2001 [25]

COVID-19 has been associated with upregulated proinflammatory cytokines in addition to hemodynamic instability, multi-system organ failure, and notably the development of ARDS [26]. In this process of excessive production of proinflammatory cytokines, macrophages are activated (macrophage activation syndrome) and cause secondary hemophagocytic lymphohistiocytosis, further disrupting immune homeostasis [26]. In this stage, COVID-19 patients are at a higher risk of fatality at the hands of their immune system, as an indirect effect of the virus, than the actual virus. This maladaptive immune response poses a key target to prevent ARDS if damage to the alveolar-capillary unit and infiltration of inflammatory cells to the extravascular tissues can be prevented. Based on our experimental models of LPS-induced ARDS, inhibiting the MMP3 activity appears to have the potential to restrict the damage to the alveolar epithelial and endothelial-barriers, thus limiting lung edema, injury, and inflammation [19].

Beyond the potential therapeutic benefits of targeting MMP3 in COVID-19, the measurement of MMP3 activity in COVID-19 patients may also have utility as a prognostic marker, which has been demonstrated in other disease states. Previous studies have determined that the cutoff value used for Kaplan Meier survival risk shows an association between MMP3 expression and severity of cardiovascular disease [27]. A recent study conducted in a cohort of male patients with and without acute coronary syndrome used MMP3 expression level to predict myocardial infarction (MI) [28]. In pulmonary fibrosis, a correlation between the expression of MMP3, endostatin, inflammatory cytokines in BALF, and lung functionality of idiopathic pulmonary fibrosis patients has been established [29]. Although a similar study has yet to be undertaken in ARDS or COVID-19 patients, our recent report on the elevated MMP3 activity in the serum/plasma samples of ARDS patients is an indication that MMP3 activity measurement may serve as an important prognosis marker for the disease severity of COVID-19 patients.

A correlation between MMP3 and the activity of plasminogen, an important precursor in breaking down clots, has also been reported suggesting its potential involvement in coagulopathy [30]. As such, investigating the effect of targeting MMP3 in hypercoagulopathic COVID-19 patients would be necessary; however, the administration of an MMP3 inhibitor via inhalation could avoid this potential pitfall [31, 32]. Given this compelling early evidence, the use of an MMP3 activity assay as a marker for COVID-19 associated ARDS prognosis deserves further investigation.