SARS‐CoV‐2: Mechanism of infection and emerging technologies for future prospects

Association of soluble PD-L1 and NLR combination with 1-Year mortality in patients with COVID-19

PURPOSE

Understanding the relationship between patient immune characteristics, disease severity, and mortality represents a critical step in the fight against COVID-19. Elevated levels of programmed death ligand-1 (PD-L1) and Neutrophil-lymphocyte ratio (NLR) are linked to increased severity of acute COVID-19 in patients. This study aimed to investigate the association of the combination of sPD-L1 and NLR with 1-year Mortality in patients with COVID-19.

METHODS

A prospective study was conducted involving patients with COVID-19 in Karaganda, Kazakhstan. The level of sPD-L1 in the blood serum was evaluated by ELISA. The effect of biomarkers on the development of mortality was analyzed with multivariate regression.

RESULTS

The risk of mortality within one year HR was 2.46 if the plasma sPD-L1 value of more than 277.13 pg/ml, and for NLR more than 2.46 HR was 2.87. The model of combining sPD-L1 and NLR resulted in an improvement in the predictive accuracy of the Hazard Ratio 7.6 (95 % CI: 3.02-19.11).

CONCLUSION

The combination of two immune-mediated markers (sPD-L1 and NLR), which reflect the systemic inflammatory balance of activation and exhaustion, can complement each other and improve the assessment of the risk of death in patients with COVID-19.

The interplay of cells, polymers, and vascularization in three-dimensional lung models and their applications in COVID-19 research and therapy

Millions of people have been affected ever since the emergence of the corona virus disease of 2019 (COVID-19) outbreak, leading to an urgent need for antiviral drug and vaccine development. Current experimentation on traditional two-dimensional culture (2D) fails to accurately mimic the in vivo microenvironment for the disease, while in vivo animal model testing does not faithfully replicate human COVID-19 infection. Human-based three-dimensional (3D) cell culture models such as spheroids, organoids, and organ-on-a-chip present a promising solution to these challenges. In this report, we review the recent 3D in vitro lung models used in COVID-19 infection and drug screening studies and highlight the most common types of natural and synthetic polymers used to generate 3D lung models.

Combating the Progression of Novel Coronavirus SARS-CoV-2 Infectious Disease: Current State and Future Prospects in Molecular Diagnostics and Drug Discovery

A highly infectious and life-threatening virus was first reported in Wuhan, China, in late 2019, and it rapidly spread all over the world. This novel virus belongs to the coronavirus family and is associated with severe acute respiratory syndrome (SARS), causing respiratory disease known as COVID-19. In March 2020, WHO has declared the COVID-19 outbreak a global pandemic. Its morbidity and mortality rates are swiftly rising day by day, with the situation becoming more severe and fatal for the comorbid population. Many COVID-19 patients are asymptomatic, but they silently spread the infection. There is a need for proper screening of infected patients to prevent the epidemic transmission of disease and for early curative interventions to reduce the risk of developing severe complications from COVID-19. To date, the diagnostic assays are of two categories, molecular detection of viral genetic material by real-time RTpolymerase chain reaction and serological test, which relies on detecting antiviral antibodies. Unfortunately, there are no effective prophylactics and therapeutics available against COVID-19. However, a few drugs have shown promising antiviral activity against it, and these presently are being referred for clinical trials, albeit FDA has issued an Emergency Use Authorization (EUA) for the emergency use of a few drugs for SARSCoV- 2 infection. This review provides an insight into current progress, challenges and future prospects of laboratory detection methods of COVID-19, and highlights the clinical stage of the major evidence-based drugs/vaccines recommended against the novel SARS-CoV-2 pandemic virus.

Use of natural cysteine protease inhibitors in limiting SARS-Co-2 fusion into human respiratory cells

Specific antibodies that humans acquire as a result of disease or after vaccination are needed to effectively suppress infection with a specific variant of SARS CoV-2 virus. The S protein of the D614G variant of coronavirus is used as an antigen in known vaccines to date. It is known that COVID-19 disease resulting from infection with this coronavirus can often be very dangerous to the health and lives of patients. In contrast, vaccines produce antibodies against an older version of the protein S-D614G (January 2020) and therefore have difficulty recognizing new variants of the virus. In our project we propose to obtain specific and precise antibodies by means of so-called controlled infection against specific infectious variants of the SARS-CoV-2 virus “here and now”. Currently, several variants of this pathogen have already emerged that threaten the health and lives of patients. We propose to reduce this threat by partially, but not completely, blocking the fusion mechanism of the SARS-CoV-2 virus into human respiratory cells. According to our plan, this can be achieved by inhibiting cathepsin L activity in respiratory cells, after introducing natural and non-toxic cysteine protease inhibitors into this area. We obtain these inhibitors by our own method from natural, “human body friendly” natural resources. We hypothesize that blocking cathepsin L will reduce the number of infecting viruses in cells to such an extent that COVID-19 developing in infected individuals will not threaten their health and life. At the same time, the number of viruses will be sufficient for the body's own immune system to produce precise antibodies against a specific version of this pathogen.

Upregulation of PD-1 Expression and High sPD-L1 Levels Associated with COVID-19 Severity

COVID-19 has several mechanisms that can lead to lymphocyte depletion/exhaustion. The checkpoint inhibitor molecule programmed death protein 1 (PD-1) and its programmed death-ligand 1 (PDL-1) play an important role in inhibiting cellular activity as well as the depletion of these cells. In this study, we evaluated PD-1 expression in TCD4+, TCD8+, and CD19+ lymphocytes from SARS-CoV-2-infected patients. A decreased frequency of total lymphocytes and an increased PD-1 expression in TCD4+ and CD19+ lymphocytes were verified in severe/critical COVID-19 patients. In addition, we found a decreased frequency of total monocytes with an increased PD-1 expression on CD14+ monocytes in severe/critical patients in association with the time of infection. Moreover, we observed an increase in sPD-L1 circulant levels associated with the severity of the disease. Overall, these data indicate an important role of the PD-1/PDL-1 axis in COVID-19 and may provide a severity-associated biomarker and therapeutic target during SARS-CoV-2 infection.

(+)-Usnic acid and its salts, inhibitors of SARS-CoV-2, identified by using in silico methods and in vitro assay

The pandemic caused by severe acute respiratory Coronavirus-2 (SARS-CoV-2) has been ongoing for over two years, and treatment for COVID-19, other than monoclonal antibodies, is urgently required. Accordingly, we have investigated the inhibitors of SARS-CoV-2 protein targets by high-throughput virtual screening using a marine natural products database. Considering the calculated molecular properties and availability of the compounds, (+)-usnic acid was selected as a suitable hit. In the in vitro antiviral assay of (+)-usnic acid by the immunofluorescence method, IC₅₀ was 7.99 μM, which is similar to that of remdesivir used as a positive control. The generalized Born and surface area continuum solvation (MM/GBSA) method was performed to find the potent target of (+)-usnic acid, and the Mpro protein showed the most prominent value, -52.05 kcal/mol, among other SARS-CoV-2 protein targets. Thereafter, RMSD and protein-ligand interactions were profiled using molecular dynamics (MD) simulations. Sodium usnate (NaU) improved in vitro assay results with an IC₅₀ of 5.33 μM and a selectivity index (SI) of 9.38. Additionally, when (+)-usnic acid was assayed against SARS-CoV-2 variants, it showed enhanced efficacy toward beta variants with an IC₅₀ of 2.92 μM and SI of 11.1. We report the in vitro anti-SARS-CoV-2 efficacy of (+)-usnic acid in this study and propose that it has the potential to be developed as a COVID-19 treatment if its in vivo efficacy has been confirmed.

Nanoscale Technologies in the Fight against COVID-19: From Innovative Nanomaterials to Computer-Aided Discovery of Potential Antiviral Plant-Derived Drugs

The last few years have increasingly emphasized the need to develop new active antiviral products obtained from artificial synthesis processes using nanomaterials, but also derived from natural matrices. At the same time, advanced computational approaches have found themselves fundamental in the repurposing of active therapeutics or for reducing the very long developing phases of new drugs discovery, which represents a real limitation, especially in the case of pandemics. The first part of the review is focused on the most innovative nanomaterials promising both in the field of therapeutic agents, as well as measures to control virus spread (i.e., innovative antiviral textiles). The second part of the review aims to show how computer-aided technologies can allow us to identify, in a rapid and therefore constantly updated way, plant-derived molecules (i.e., those included in terpenoids) potentially able to efficiently interact with SARS-CoV-2 cell penetration pathways.

Nanoparticle-delivered TLR4 and RIG-I agonists enhance immune response to SARS-CoV-2 subunit vaccine

Despite success in vaccinating populations against SARS-CoV-2, concerns about immunity duration, continued efficacy against emerging variants, protection from infection and transmission, and worldwide vaccine availability remain. Molecular adjuvants targeting pattern recognition receptors (PRRs) on antigen-presenting cells (APCs) could improve and broaden the efficacy and durability of vaccine responses. Native SARS-CoV-2 infection stimulates various PRRs, including toll-like receptors (TLRs) and retinoic acid-inducible gene I (RIG-I)-like receptors. We hypothesized that targeting PRRs using molecular adjuvants on nanoparticles (NPs) along with a stabilized spike protein antigen could stimulate broad and efficient immune responses. Adjuvants targeting TLR4 (MPLA), TLR7/8 (R848), TLR9 (CpG), and RIG-I (PUUC) delivered on degradable polymer NPs were combined with the S1 subunit of spike protein and assessed in vitro with isogeneic mixed lymphocyte reactions (isoMLRs). For in vivo studies, the adjuvant-NPs were combined with stabilized spike protein or spike-conjugated NPs and assessed using a two-dose intranasal or intramuscular vaccination model in mice. Combination adjuvant-NPs simultaneously targeting TLR and RIG-I receptors (MPLA+PUUC, CpG+PUUC, and R848+PUUC) differentially induced T cell proliferation and increased proinflammatory cytokine secretion by APCs in vitro. When delivered intranasally, MPLA+PUUC NPs enhanced CD4+CD44+ activated memory T cell responses against spike protein in the lungs while MPLA NPs increased anti-spike IgA in the bronchoalveolar (BAL) fluid and IgG in the blood. Following intramuscular delivery, PUUC NPs induced strong humoral immune responses, characterized by increases in anti-spike IgG in the blood and germinal center B cell populations (GL7+ and BCL6+ B cells) in the draining lymph nodes (dLNs). MPLA+PUUC NPs further boosted spike protein-neutralizing antibody titers and T follicular helper cell populations in the dLNs. These results suggest that protein subunit vaccines with particle-delivered molecular adjuvants targeting TLR4 and RIG-I could lead to robust and unique route-specific adaptive immune responses against SARS-CoV-2.

Role of Diet and Nutrients in SARS-CoV-2 Infection: Incidence on Oxidative Stress, Inflammatory Status and Viral Production

Coronavirus illness (COVID-19) is an infectious pathology generated by intense severe respiratory syndrome coronavirus 2 (SARS-CoV-2). This infectious disease has emerged in 2019. The COVID-19-associated pandemic has considerably affected the way of life and the economy in the world. It is consequently crucial to find solutions allowing remedying or alleviating the effects of this infectious disease. Natural products have been in perpetual application from immemorial time given that they are attested to be efficient towards several illnesses without major side effects. Various studies have shown that plant extracts or purified molecules have a promising inhibiting impact towards coronavirus. In addition, it is substantial to understand the characteristics, susceptibility and impact of diet on patients infected with COVID-19. In this review, we recapitulate the influence of extracts or pure molecules from medicinal plants on COVID-19. We approach the possibilities of plant treatment/co-treatment and feeding applied to COVID-19. We also show coronavirus susceptibility and complications associated with nutrient deficiencies and then discuss the major food groups efficient on COVID-19 pathogenesis. Then, we covered emerging technologies using plant-based SARS-CoV-2 vaccine. We conclude by giving nutrient and plants curative therapy recommendations which are of potential interest in the COVID-19 infection and could pave the way for pharmacological treatments or co-treatments of COVID-19.

Transmembrane Protease Serine 2 Proteolytic Cleavage of the SARS-CoV-2 Spike Protein: A Mechanistic Quantum Mechanics/Molecular Mechanics Study to Inspire the Design of New Drugs To Fight the COVID-19 Pandemic

Despite the development of vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, there is an urgent need for efficient drugs to treat infected patients. An attractive drug target is the human transmembrane protease serine 2 (TMPRSS2) because of its vital role in the viral infection mechanism of SARS-CoV-2 by activation of the virus spike protein (S protein). Having in mind that the information derived from quantum mechanics/molecular mechanics (QM/MM) studies could be an important tool in the design of transition-state (TS) analogue inhibitors, we resorted to adiabatic QM/MM calculations to determine the mechanism of the first step (acylation) of proteolytic cleavage of the S protein with atomistic details. Acylation occurred in two stages: (i) proton transfer from Ser441 to His296 concerted with the nucleophilic attack of Ser441 to the substrate's P1-Arg and (ii) proton transfer from His296 to the P1'-Ser residue concerted with the cleavage of the ArgP1-SerP1' peptide bond, with a Gibbs activation energy of 17.1 and 15.8 kcal mol^-1, relative to the reactant. An oxyanion hole composed of two hydrogen bonds stabilized the rate-limiting TS by 8 kcal mol^-1. An analysis of the TMPRSS2 interactions with the high-energy, short-lived tetrahedral intermediate highlighted the limitations of current clinical inhibitors and pointed out specific ways to develop higher-affinity TS analogue inhibitors. The results support the development of more efficient drugs against SARS-CoV-2 using a human target, free from resistance development.

Ovarian granulosa cells from women with PCOS express low levels of SARS-CoV-2 receptors and co-factors

Purpose

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is global pandemic with more than 5 million deaths so far. Female reproductive tract organs express coronavirus-associated receptors and factors (SCARFs), suggesting they may be susceptible to SARS-CoV-2 infection; however, the susceptibility of ovary/follicle/oocyte to the same is still elusive. Co-morbidities like obesity, type-2 diabetes mellitus, cardiovascular disease, etc. increase the risk of SARS-CoV-2 infection. These features are common in women with polycystic ovary syndrome (PCOS), warranting further scope to study SCARFs expression in ovary of these women.

Materials and methods

SCARFs expression in ovary and ovarian tissues of women with PCOS and healthy women was explored by analyzing publically available microarray datasets. Transcript expressions of SCARFs were investigated in mural and cumulus granulosa cells (MGCs and CGCs) from control and PCOS women undergoing in vitro fertilization (IVF).

Results

Microarray data revealed that ovary expresses all genes necessary for SARS-CoV-2 infection. PCOS women mostly showed down-regulated/unchanged levels of SCARFs. MGCs and CGCs from PCOS women showed lower expression of receptors ACE2, BSG and DPP4 and protease CTSB than in controls. MGCs showed lower expression of protease CTSL in PCOS than in controls. Expression of TMPRSS2 was not detected in both cell types.

Conclusion

Human ovarian follicle may be susceptible to SARS-CoV-2 infection. Lower expression of SCARFs in PCOS indicates that the risk of SARS-CoV-2 infection to the ovary may be lesser in these women than controls. This knowledge may help in safe practices at IVF settings in the current pandemic.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00404-022-06567-4.

An in-silico study of the mutation-associated effects on the spike protein of SARS-CoV-2, Omicron variant

The emergence of Omicron (B.1.1.529), a new Variant of Concern in the COVID-19 pandemic, while accompanied by the ongoing Delta variant infection, has once again fueled fears of a new infection wave and global health concern. In the Omicron variant, the receptor-binding domain (RBD) of its spike glycoprotein is heavily mutated, a feature critical for the transmission rate of the virus by interacting with hACE2. In this study, we used a combination of conventional and advanced neural network-based in silico approaches to predict how these mutations would affect the spike protein. The results demonstrated a decrease in the electrostatic potentials of residues corresponding to receptor recognition sites, an increase in the alkalinity of the protein, a change in hydrophobicity, variations in functional residues, and an increase in the percentage of alpha-helix structure. Moreover, several mutations were found to modulate the immunologic properties of the potential epitopes predicted from the spike protein. Our next step was to predict the structural changes of the spike and their effect on its interaction with the hACE2. The results revealed that the RBD of the Omicron variant had a higher affinity than the reference. Moreover, all-atom molecular dynamics simulations concluded that the RBD of the Omicron variant exhibits a more dispersed interaction network since mutations resulted in an increased number of hydrophobic interactions and hydrogen bonds with hACE2.

SARS-CoV-2 Spike Protein Unlikely to Bind to Integrins via the Arg-Gly-Asp (RGD) Motif of the Receptor Binding Domain: Evidence From Structural Analysis and Microscale Accelerated Molecular Dynamics

The Receptor Binding Domain (RBD) of SARS-CoV-2 virus harbors a sequence of Arg-Gly-Asp tripeptide named RGD motif, which has also been identified in extracellular matrix proteins that bind integrins as well as other disintegrins and viruses. Accordingly, integrins have been proposed as host receptors for SARS-CoV-2. However, given that the microenvironment of the RGD motif imposes a structural hindrance to the protein-protein association, the validity of this hypothesis is still uncertain. Here, we used normal mode analysis, accelerated molecular dynamics microscale simulation, and protein-protein docking to investigate the putative role of RGD motif of SARS-CoV-2 RBD for interacting with integrins. We found, that neither RGD motif nor its microenvironment showed any significant conformational shift in the RBD structure. Highly populated clusters of RBD showed no capability to interact with the RGD binding site in integrins. The free energy landscape revealed that the RGD conformation within RBD could not acquire an optimal geometry to allow the interaction with integrins. In light of these results, and in the event where integrins are confirmed to be host receptors for SARS-CoV-2, we suggest a possible involvement of other residues to stabilize the interaction.

Two years of SARS-CoV-2 infection (2019-2021): structural biology, vaccination, and current global situation

The deadly SARS-CoV-2 virus has infected more than 259,502,031 confirmed cases with 5,183,003 deaths in 223 countries during the last 22 months (Dec 2019-Nov 2021), whereas approximately 7,702,859,718, vaccine doses have been administered (WHO: https://covid19.who.int/) as of the 24th of Nov 2021. Recent announcements of test trial completion of several new vaccines resulted in the launching of immunization for the common person around the globe highlighting a ray of hope to cope with this infection. Meanwhile, genetic variations in SARS-CoV-2 and third layer of infection spread in numerous countries emerged as a stronger prototype than the parental. New and parental SARS-CoV-2 strains appeared as a risk factor for other pre-existing diseases like cancer, diabetes, neurological disorders, kidney, liver, heart, and eye injury. This situation requires more attention and re-structuring of the currently developed vaccines and/or drugs against SARS-CoV-2 infection. Although a decline in COVID-19 infection has been reported globally, an increase in COVID-19 cases in the subcontinent and east Mediterranean area could be alarming. In this review, we have summarized the current information about the SARS-CoV-2 biology, its interaction and possible infection pathways within the host, epidemiology, risk factors, economic collapse, and possible vaccine and drug development.

Severe acute respiratory syndrome coronavirus-2: An era of struggle and discovery leading to the emergency use authorization of treatment and prevention measures based on computational analysis

Severe acute respiratory syndrome-Coronavirus-2 (SARS-CoV-2), a novel betacoronavirus, has surprised the world with its disease spread and mortality rate. SARS-CoV-2 is a positive-sense, enveloped RNA virus that can infect various organs of the body, potentially leading to multiple organ dysfunction and eventual death. While various medications have received emergency use authorizations (EUAs) for the treatment of Coronavirus disease-2019 (COVID-19), as of April 30, 2021, only one drug has been Food and Drug Administration (FDA)-approved: remdesivir. Currently, three vaccines have received EUAs in the United States, but none are FDA-approved. This shortage of treatments and prevention measures is extremely problematic. Thus computational approaches would provide important data about drug resistance and variants. Such data will be useful for the development of drugs and vaccines. This chapter is a synopsis of SARS-CoV-2 clinical presentation, COVID-19 symptomology, treatment, prevention mechanisms, and SARS-CoV-2 variants using computational analysis.

Small Extracellular Vesicles and COVID19-Using the "Trojan Horse" to Tackle the Giant

The COVID-19 pandemic is a global challenge, demanding researchers address different approaches in relation to prevention, diagnostics and therapeutics. Amongst the many tactics of tackling these therapeutic challenges, small extracellular vesicles (sEVs) or exosomes are emerging as a new frontier in the field of ameliorating viral infections. Exosomes are part of extracellular vesicles (EVs)-spherical biological structures with a lipid bilayer of a diameter of up to 5000 nm, which are released into the intercellular space by most types of eukaryotic cells, both in physiological and pathological states. EVs share structural similarities to viruses, such as small size, common mechanisms of biogenesis and mechanisms for cell entry. The role of EVs in promoting the viral spread by evading the immune response of the host, which is exhibited by retroviruses, indicates the potential for further investigation and possible manipulation of these processes when tackling the spread and treatment of COVID-19. The following paper introduces the topic of the use of exosomes in the treatment of viral infections, and presents the future prospects for the use of these EVs.

Cardiac Involvement in COVID-19 Patients: A Contemporary Review

Background: The widely variable clinical manifestations of SARS-CoV2 disease (COVID-19) range from asymptomatic infections to multiple organ failure and death. Among the organs affected is the heart. This does not only affect people who already have previous cardiovascular problems, but also healthy people. This is a reason not to overlook any symptoms or to perform targeted examinations, even if apparently unrelated to the heart, for quick recognition and timely therapy. Aim of the study: This review recapitulates the current state of knowledge on the potential mechanisms and manifestation of myocarditis in patients with COVID-19 infection. Methods: A web-based search of published data was performed for all relevant studies on patients diagnosed with a COVID-19-induced acute myocarditis, and a total of 50 reports were included. The analysis of the studies evaluated highlights a male predominance, with the average age of patients being 55 years. The most common presenting symptoms included fever, shortness of breath, cough, and chest pain. Among ECG changes, non-specific ST-segment and T-wave amplitude alterations and ventricular tachycardia episodes were reported. Finally, we wanted to use a general evaluation without distinguishing between various countries, taking into consideration only the peer or reviewer, regardless of the declared value of the journals that have been published. Results and critical findings: The most common presenting symptoms included fever, shortness of breath, cough, and chest pain. Among ECG changes, non-specific ST-segment and T-wave amplitude alterations and ventricular tachycardia episodes were reported. In most patients, elevated levels of cardiac and inflammatory biomarkers were measured. Left ventricular dysfunction and hypokinesis were commonly exhibited symptoms. Cardiac Magnetic Resonance Imaging (CMRI) confirmed the diagnosis of myocarditis with features of cardiac edema and cardiac injury. Nine patients underwent histopathological examination. Treatment with corticosteroids and immunoglobulins was the most applied strategy following the administration of antivirals. Discussion: Despite the exponentially growing knowledge on the management of COVID-19 infection, current available data on SARS-CoV2-correlated myocarditis are still limited, and several difficulties may be encountered in the differential diagnosis of acute myocarditis in the context of COVID-19 disease. Conclusions: While diagnostic criteria and evaluation strategies for myocarditis are well described, no guidelines for the diagnosis and treatment of myocarditis in COVID-19 patients have yet been established. Therefore, further research is needed to advance the understanding of this disease process and define the most appropriate strategic approach in these patients.

The human coronaviruses (HCoVs) and the molecular mechanisms of SARS-CoV-2 infection

In humans, coronaviruses can cause infections of the respiratory system, with damage of varying severity depending on the virus examined: ranging from mild-to-moderate upper respiratory tract diseases, such as the common cold, pneumonia, severe acute respiratory syndrome, kidney failure, and even death. Human coronaviruses known to date, common throughout the world, are seven. The most common-and least harmful-ones were discovered in the 1960s and cause a common cold. Others, more dangerous, identified in the early 2000s and cause more severe respiratory tract infections. Among these the SARS-CoV, isolated in 2003 and responsible for the severe acute respiratory syndrome (the so-called SARS), which appeared in China in November 2002, the coronavirus 2012 (2012-nCoV) cause of the Middle Eastern respiratory syndrome (MERS) from coronavirus, which exploded in June 2012 in Saudi Arabia, and actually SARS-CoV-2. On December 31, 2019, a new coronavirus strain was reported in Wuhan, China, identified as a new coronavirus beta strain ß-CoV from group 2B, with a genetic similarity of approximately 70% to SARS-CoV, the virus responsible of SARS. In the first half of February, the International Committee on Taxonomy of Viruses (ICTV), in charge of the designation and naming of the viruses (i.e., species, genus, family, etc.), thus definitively named the new coronavirus as SARS-CoV-2. This article highlights the main knowledge we have about the biomolecular and pathophysiologic mechanisms of SARS-CoV-2.