The contrasting role of nasopharyngeal angiotensin converting enzyme 2 (ACE2) transcription in SARS-CoV-2 infection: A cross-sectional study of people tested for COVID-19 in British Columbia, Canada

Association Between ACE2 and Lung Diseases

Angiotensin-converting enzyme 2 (ACE2) is an important regulator of the Renin-Angiotensin System (RAS). Additionally, it has been identified as a functional receptor for the Coronavirus. Research indicates that ACE2 plays a role in the regulation of cardiovascular systems by modulating blood pressure and electrolyte balance. Its role in pulmonary diseases has also garnered significant attention due to the widespread prevalence of Coronavirus. There is solid evidence linking ACE2 to other pulmonary diseases, including chronic obstructive pulmonary disease, acute respiratory distress syndrome, allergic asthma, among others. However, the exact pathological and physiological mechanisms of ACE2 in these diseases remain elusive. Our research aims to review and explore the latest advancements in ACE2-related studies in pulmonary diseases. These findings have the potential to open new avenues for utilizing ACE2 as a potential biomarker for early diagnosis and monitoring of pulmonary diseases.

Lipid Nanoparticle-Based Inhibitors for SARS-CoV-2 Host Cell Infection

Purpose

The global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the lingering threat to public health has fueled the search for effective therapeutics to treat SARS-CoV-2. This study aimed to develop lipid nanoparticle (LNP) inhibitors of SARS-CoV-2 entry to reduce viral infection in the nose and upper airway.

Methods

Two types of LNP formulations were prepared following a microfluidic mixing method. The LNP-Trap consisted of DOPC, DSPC, cholesterol, and DSPE-PEG-COOH modified with various spike protein binding ligands, including ACE2 peptide, recombinant human ACE2 (rhACE2) or monoclonal antibody to spike protein (mAb). The LNP-Trim consisted of ionizing cationic DLin-MC3-DMA, DSPC, cholesterol, and DMG-PEG lipids encapsulating siACE2 or siTMPRSS2. Both formulations were assayed for biocompatibility and cell uptake in airway epithelial cells (Calu-3). Functional assessment of activity was performed using SARS-CoV-2 spike protein binding assays (LNP-Trap), host receptor knockdown (LNP-Trim), and SARS-CoV-2 pseudovirus neutralization assay (LNP-Trap and LNP-Trim). Localization and tissue distribution of fluorescently labeled LNP formulations were assessed in mice following intranasal administration.

Results

Both LNP formulations were biocompatible based on cell impedance and MTT cytotoxicity studies in Calu-3 cells at concentrations as high as 1 mg/mL. LNP-Trap formulations were able to bind spike protein and inhibit pseudovirus infection by 90% in Calu-3 cells. LNP-Trim formulations reduced ACE2 and TMPRSS2 at the mRNA (70% reduction) and protein level (50% reduction). The suppression of host targets in Calu-3 cells treated with LNP-Trim resulted in over 90% inhibition of pseudovirus infection. In vivo studies demonstrated substantial retention of LNP-Trap and LNP-Trim in the nasal cavity following nasal administration with minimal systemic exposure.

Conclusion

Both LNP-Trap and LNP-Trim formulations were able to safely and effectively inhibit SARS-CoV-2 pseudoviral infection in airway epithelial cells. These studies provide proof-of-principle for a localized treatment approach for SARS-CoV-2 in the upper airway.

Nasopharyngeal angiotensin converting enzyme 2 (ACE2) expression as a risk-factor for SARS-CoV-2 transmission in concurrent hospital associated outbreaks

BACKGROUND

Widespread human-to-human transmission of the severe acute respiratory syndrome coronavirus two (SARS-CoV-2) stems from a strong affinity for the cellular receptor angiotensin converting enzyme two (ACE2). We investigate the relationship between a patient's nasopharyngeal ACE2 transcription and secondary transmission within a series of concurrent hospital associated SARS-CoV-2 outbreaks in British Columbia, Canada.

METHODS

Epidemiological case data from the outbreak investigations was merged with public health laboratory records and viral lineage calls, from whole genome sequencing, to reconstruct the concurrent outbreaks using infection tracing transmission network analysis. ACE2 transcription and RNA viral load were measured by quantitative real-time polymerase chain reaction. The transmission network was resolved to calculate the number of potential secondary cases. Bivariate and multivariable analyses using Poisson and Negative Binomial regression models was performed to estimate the association between ACE2 transcription the number of SARS-CoV-2 secondary cases.

RESULTS

The infection tracing transmission network provided n = 76 potential transmission events across n = 103 cases. Bivariate comparisons found that on average ACE2 transcription did not differ between patients and healthcare workers (P = 0.86). High ACE2 transcription was observed in 98.6% of transmission events, either the primary or secondary case had above average ACE2. Multivariable analysis found that the association between ACE2 transcription (log2 fold-change) and the number of secondary transmission events differs between patients and healthcare workers. In health care workers Negative Binomial regression estimated that a one-unit change in ACE2 transcription decreases the number of secondary cases (β = -0.132 (95%CI: -0.255 to -0.0181) adjusting for RNA viral load. Conversely, in patients a one-unit change in ACE2 transcription increases the number of secondary cases (β = 0.187 (95% CI: 0.0101 to 0.370) adjusting for RNA viral load. Sensitivity analysis found no significant relationship between ACE2 and secondary transmission in health care workers and confirmed the positive association among patients.

CONCLUSION

Our study suggests that ACE2 transcription has a positive association with SARS-CoV-2 secondary transmission in admitted inpatients, but not health care workers in concurrent hospital associated outbreaks, and it should be further investigated as a risk-factor for viral transmission.

Hypercapnia increases ACE2 expression and pseudo-SARS-CoV-2 entry in bronchial epithelial cells by augmenting cellular cholesterol

Patients with chronic lung disease, obesity, and other co-morbid conditions are at increased risk of severe illness and death when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hypercapnia, the elevation of CO2 in blood and tissue, commonly occurs in patients with severe acute and chronic lung disease, including those with pulmonary infections, and is also associated with high mortality risk. We previously reported that hypercapnia increases viral replication and mortality of influenza A virus infection in mice. We have also shown that culture in elevated CO2 upregulates expression of cholesterol synthesis genes in primary human bronchial epithelial cells. Interestingly, factors that increase the cholesterol content of lipid rafts and lipid droplets, platforms for viral entry and assembly, enhance SARS-CoV-2 infection. In the current study, we investigated the effects of hypercapnia on ACE2 expression and entry of SARS-CoV-2 pseudovirus (p-SARS-CoV-2) into airway epithelial cells. We found that hypercapnia increased ACE2 expression and p-SARS-CoV-2 uptake by airway epithelium in mice, and in cultured VERO and human bronchial epithelial cells. Hypercapnia also increased total cellular and lipid raft-associated cholesterol in epithelial cells. Moreover, reducing cholesterol synthesis with inhibitors of sterol regulatory element binding protein 2 (SREBP2) or statins, and depletion of cellular cholesterol, each blocked the hypercapnia-induced increases in ACE2 expression and p-SARS-CoV-2 entry into epithelial cells. Cigarette smoke extract (CSE) also increased ACE2 expression, p-SARS-CoV-2 entry and cholesterol accumulation in epithelial cells, an effect not additive to that of hypercapnia, but also inhibited by statins. These findings reveal a mechanism that may account, in part, for poor clinical outcomes of SARS-CoV-2 infection in patients with advanced lung disease and hypercapnia, and in those who smoke cigarettes. Further, our results suggest the possibility that cholesterol-lowering therapies may be of particular benefit in patients with hypercapnia when exposed to or infected with SARS-CoV-2.

Polymorphisms within the SARS-CoV-2 Human Receptor Genes Associate with Variable Disease Outcomes across Ethnicities

The contribution of human genes to the variability of disease outcomes has been shown to be important across infectious diseases. Studies have shown mutations within specific human genes are associated with variable COVID-19 outcomes. We focused on the SARS-CoV-2 receptors/co-receptors to identify the role of specific polymorphisms within ACE2, TMPRSS2, NRP1 and CD147. Polymorphisms within ACE2 (rs2285666), TMPRSS2 (rs12329760), CD147 (rs8259) and NRP1 (rs10080) have been shown to associate with COVID-19 severity. Using cryopreserved samples from COVID-19-positive African, European and South Asian individuals within South Africa, we determined genotype frequencies. The genetic variant rs2285666 was associated with COVID-19 severity with an ethnic bias. African individuals with a CC genotype demonstrate more severe COVID-19 outcomes (OR = 7.5; 95% CI 1.164-80.89; p = 0.024) compared with those with a TT genotype. The expressions of ACE2 and SARS-CoV-2 viral load were measured using droplet digital PCR. Our results demonstrate rs2285666 and rs10080 were significantly associated with increased SARS-CoV-2 viral load and worse outcomes in certain ethnicities. This study demonstrates two important findings. Firstly, SARS-CoV-2 viral load is significantly lower in Africans compared with individuals of European and South Asian descent (p = 0.0002 and p < 0.0001). Secondly, SARS-CoV-2 viral load associates with specific SARS-CoV-2 receptor variants. A limited number of studies have examined the receptor/co-receptor genes within Africa. This study investigated genetic variants within the SARS-CoV-2 receptor/co-receptor genes and their association with COVID-19 severity and SARS-CoV-2 viral load across different ethnicities. We provide a genetic basis for differences in COVID-19 severity across ethnic groups in South Africa, further highlighting the importance of further investigation to determine potential therapeutic targets and to guide vaccination strategies that may prioritize specific genotypes.

Evaluation of the efficacy of tongue swab and saliva as samples for testing COVID-19 infection in symptomatic cases in comparison with nasopharyngeal swab

Introduction. COVID-19 caused by SARS CoV-2 continues to be a major health concern globally. Methods for detection of the disease are necessary for public health efforts to monitor the spread of this disease as well as for detecting the emergence of new variants.Gap statement. Collection of Nasopharyngeal swab (NPS), the gold standard sample for the detection of COVID-19 infection by RT-qPCR is invasive and requires the expertise of a trained medical provider. This highlights the need for validating less invasive samples that can be self-collected without the need for trained medical provider.Aim. To validate saliva and tongue swab as potential samples for the diagnosis of COVID-19.Methodology. Adult and paediatric cases who had acute influenza like illness were enrolled in the study. The study involved comparison of Nucleic Acid Amplification Tests (NAAT) results for the detection of COVID-19 obtained by using saliva and tongue swab with that of NPS.Result and Conclusion. The sensitivity and specificity of saliva as sample for COVID-19 detection were found to be 71 and 88% respectively whereas those of tongue swab as sample were 78 and 90 %. Further validation was based on the positive and negative predictive values, the likelihood ratio, agreement percentage and the kappa statistic. The findings of the study point towards tongue swab and saliva as suitable alternative samples for the diagnosis of COVID-19 with a slightly higher accuracy and agreement for tongue swab than saliva. However considering the fatality of COVID-19, they are better suited for mass screening of people than for diagnosis.

Association between soluble angiotensin-converting enzyme 2 in saliva and SARS-CoV-2 infection: a cross-sectional study

This study aimed to investigate the association between saliva soluble angiotensin-converting enzyme 2 (sACE2) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in children and adults. We selected a convenience sample of adults with post-acute SARS-CoV-2 infection and their household children living in quarantined family households of the metropolitan Barcelona region (Spain) during the spring 2020 pandemic national lockdown. Participants were tested for saliva sACE2 quantification by western blot and nasopharyngeal SARS-CoV-2 RT-PCR detection. A total of 161 saliva samples [82 (50.9%) from children; 79 (49.1%) from females] yielded valid western blot and RT-PCR results. Saliva sACE2 was detected in 79 (96.3%) children and 76 (96.2%) convalescent adults. Twenty (24.4%) children and 20 (25.3%) convalescent adults were positive for SARS-CoV-2 in nasopharynx by RT-PCR. SARS-CoV-2 RT-PCR-negative children had a significantly higher mean proportional level of saliva sACE2 (0.540 × 10^-3%) than RT-PCR-positive children (0.192 × 10^-3%, p < 0.001) and convalescent adults (0.173 × 10^-3%, p < 0.001). In conclusion, children negative for nasopharyngeal SARS-CoV-2 RT-PCR appear to exhibit a higher concentration of saliva sACE2 than SARS-CoV-2 RT-PCR-positive children and convalescent adults. Release of adequate levels of sACE2 in saliva could play a protective role against SARS-CoV-2.

An update on angiotensin-converting enzyme 2 structure/functions, polymorphism, and duplicitous nature in the pathophysiology of coronavirus disease 2019: Implications for vascular and coagulation disease associated with severe acute respiratory syndrome coronavirus infection

It has been known for many years that the angiotensin-converting enzyme 2 (ACE2) is a cell surface enzyme involved in the regulation of blood pressure. More recently, it was proven that the severe acute respiratory syndrome coronavirus (SARS-CoV-2) interacts with ACE2 to enter susceptible human cells. This functional duality of ACE2 tends to explain why this molecule plays such an important role in the clinical manifestations of coronavirus disease 2019 (COVID-19). At the very start of the pandemic, a publication from our Institute (entitled "ACE2 receptor polymorphism: susceptibility to SARS-CoV-2, hypertension, multi-organ failure, and COVID-19 disease outcome"), was one of the first reviews linking COVID-19 to the duplicitous nature of ACE2. However, even given that COVID-19 pathophysiology may be driven by an imbalance in the renin-angiotensin system (RAS), we were still far from understanding the complexity of the mechanisms which are controlled by ACE2 in different cell types. To gain insight into the physiopathology of SARS-CoV-2 infection, it is essential to consider the polymorphism and expression levels of the ACE2 gene (including its alternative isoforms). Over the past 2 years, an impressive amount of new results have come to shed light on the role of ACE2 in the pathophysiology of COVID-19, requiring us to update our analysis. Genetic linkage studies have been reported that highlight a relationship between ACE2 genetic variants and the risk of developing hypertension. Currently, many research efforts are being undertaken to understand the links between ACE2 polymorphism and the severity of COVID-19. In this review, we update the state of knowledge on the polymorphism of ACE2 and its consequences on the susceptibility of individuals to SARS-CoV-2. We also discuss the link between the increase of angiotensin II levels among SARS-CoV-2-infected patients and the development of a cytokine storm associated microvascular injury and obstructive thrombo-inflammatory syndrome, which represent the primary causes of severe forms of COVID-19 and lethality. Finally, we summarize the therapeutic strategies aimed at preventing the severe forms of COVID-19 that target ACE2. Changing paradigms may help improve patients' therapy.

A Review of Potential Therapeutic Strategies for COVID-19

Coronavirus disease 2019 is a rather heterogeneous disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The ongoing pandemic is a global threat with increasing death tolls worldwide. SARS-CoV-2 belongs to lineage B β-CoV, a subgroup of Sarbecovirus. These enveloped, large, positive-sense single-stranded RNA viruses are easily spread among individuals, mainly via the respiratory system and droplets. Although the disease has been gradually controlled in many countries, once social restrictions are relaxed the virus may rebound, leading to a more severe and uncontrollable situation again, as occurred in Shanghai, China, in 2022. The current global health threat calls for the urgent development of effective therapeutic options for the treatment and prevention of SARS-CoV-2 infection. This systematic overview of possible SARS-CoV-2 therapeutic strategies from 2019 to 2022 indicates three potential targets: virus entry, virus replication, and the immune system. The information provided in this review will aid the development of more potent and specific antiviral compounds.

Highly restricted SARS-CoV-2 receptor expression and resistance to infection by primary human monocytes and monocyte-derived macrophages

Severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV2), which causes the disease COVID-19, has caused an unprecedented global pandemic. Angiotensin-converting enzyme 2 (ACE2) is the major cellular receptor for SARS-CoV2 entry, which is facilitated by viral Spike priming by cellular TMPRSS2. Macrophages play an important role in innate viral defense and are also involved in aberrant immune activation that occurs in COVID-19, and thus direct macrophage infection might contribute to severity of SARS-CoV2 infection. Here, we demonstrate that monocytes and monocyte-derived macrophages (MDM) under in vitro conditions express low-to-undetectable levels of ACE2 and TMPRSS2 and minimal coexpression. Expression of these receptors remained low in MDM induced to different subtypes such as unpolarized, M1 and M2 polarized. Untreated, unpolarized, M1 polarized, and M2 polarized MDM were all resistant to infection with SARS-CoV2 pseudotyped virions. These findings suggest that direct infection of myeloid cells is unlikely to be a major mechanism of SARS-CoV2 pathogenesis. Summary sentence: Monocytes and macrophages express minimal ACE2 and TMPRSS2 and resist SARS-CoV-2 Spike-mediated infection, suggesting direct myeloid cell infection is unlikely a major contributor to pathogenesis.

Bimodal distribution pattern associated with the PCR cycle threshold (Ct) and implications in COVID-19 infections

SARS-CoV-2 is notable for its extremely high level of viral replication in respiratory epithelial cells, relative to other cell types. This may partially explain the high transmissibility and rapid global dissemination observed during the COVID-19 pandemic. Polymerase chain reaction (PCR) cycle threshold (Ct) number has been widely used as a proxy for viral load based on the inverse relationship between Ct number and amplifiable genome copies present in a sample. We examined two PCR platforms (Centers for Disease Control and Prevention 2019-nCoV Real-time RT-PCR, Integrated DNA Technologies; and TaqPath COVID-19 multi-plex combination kit, ThermoFisher Scientific) for their performance characteristics and Ct distribution patterns based on results generated from 208,947 clinical samples obtained between October 2020 and September 2021. From 14,231 positive tests, Ct values ranged from 8 to 39 and displayed a pronounced bimodal distribution. The bimodal distribution persisted when stratified by gender, age, and time period of sample collection during which different viral variants circulated. This finding may be a result of heterogeneity in disease progression or host response to infection irrespective of age, gender, or viral variants. Quantification of respiratory mucosal viral load may provide additional insight into transmission and clinical indicators helpful for infection control.

GDF15 and ACE2 stratify COVID-19 patients according to severity while ACE2 mutations increase infection susceptibility

Coronavirus disease 19 (COVID-19) is a persistent global pandemic with a very heterogeneous disease presentation ranging from a mild disease to dismal prognosis. Early detection of sensitivity and severity of COVID-19 is essential for the development of new treatments. In the present study, we measured the levels of circulating growth differentiation factor 15 (GDF15) and angiotensin-converting enzyme 2 (ACE2) in plasma of severity-stratified COVID-19 patients and uninfected control patients and characterized the in vitro effects and cohort frequency of ACE2 SNPs. Our results show that while circulating GDF15 and ACE2 stratify COVID-19 patients according to disease severity, ACE2 missense SNPs constitute a risk factor linked to infection susceptibility.

Performance of Immunoglobulin G Serology on Finger Prick Capillary Dried Blood Spot Samples to Detect a SARS-CoV-2 Antibody Response

We investigate the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested by a quantitative multiplex anti-immunoglobulin G (IgG) assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies after infection or vaccination. This cross-sectional study involved participants (n = 6,841) from several serological surveys conducted in nonhospitalized children and adults throughout 2020 and 2021 in British Columbia (BC), Canada. Analysis used paired DBS and serum samples from a subset of participants (n = 642) prior to vaccination to establish signal thresholds and calculate diagnostic accuracy by logistic regression. Discrimination of the logistic regression model was assessed by receiver operator curve (ROC) analysis in an n = 2,000 bootstrap of the paired sample (n = 642). The model was cross-validated in a subset of vaccinated persons (n = 90). Unpaired DBS samples (n = 6,723) were used to evaluate anti-IgG signal distributions. In comparison to paired serum, DBS samples from an unvaccinated population possessed a sensitivity of 79% (95% confidence interval [95% CI]: 58 to 91%) and specificity of 97% (95% CI: 95 to 98%). ROC analysis found that DBS samples accurately classify SARS-CoV-2 seroconversion at an 88% percent rate (area under the curve [AUC] = 88% [95% CI: 80 to 95%]). In coronavirus disease 2019 (COVID-19) vaccine dose one or two recipients, the sensitivity of DBS testing increased to 97% (95% CI: 83 to 99%) and 100% (95% CI: 88 to 100%). Modeling found that DBS testing possesses a high positive predictive value (98% [95% CI: 97 to 98%]) in a population with 75% seroprevalence. We demonstrate that DBS testing should be considered to reliably detect SARS-CoV-2 seropositivity from natural infection or vaccination.

IMPORTANCE Dried blood spot samples have comparable diagnostic accuracy to serum collected by venipuncture when tested by an electrochemiluminescent assay for antibodies and should be considered to reliably detect seropositivity following SARS-CoV-2 infection and/or vaccination.

COVID-19 Infection in Pregnancy: Obstetrical Risk Factors and Neonatal Outcomes-A Monocentric, Single-Cohort Study

The effects of coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 on pregnant women and neonates are mainly unknown, since limited data are available in the literature. We conducted a monocentric and cross-sectional study enrolling 122 un-vaccinated pregnant women with COVID-19 infection tested by RT-PCR nasopharyngeal swab. Only 4.1% of the patients had severe COVID-19 symptoms together with major respiratory symptoms and intensive care unit admission, whereas 35.25% of women had comorbidities and two-thirds of them were overweight or obese. COVID-19 was detected mainly in the third trimester (98.36%) and multiparous women (59.02%). The mode of delivery was influenced by mild-severe COVID-19 symptoms, with a higher number of urgent or emergent cesarean sections than spontaneous or operative vaginal births. Preterm births were associated with high BMI, mode of delivery (higher among cesarean sections), nulliparity, and severe COVID-19 symptoms. In cases of severe COVID-19 symptoms, there was a higher rate of respiratory distress syndrome among newborns. In the end, only the presence of a severe COVID-19 infection worsened the obstetrical and neonatal outcomes, with higher rates of urgent or emergent cesarean section, preterm births, and neonatal respiratory distress syndrome.

Nasopharyngeal Expression of Angiotensin-Converting Enzyme 2 and Transmembrane Serine Protease 2 in Children within SARS-CoV-2-Infected Family Clusters

Lower levels of angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2) in the nasal epithelium of children may be related to a lower incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, compared to adults. However, no direct evidence is available to support this hypothesis. In this study, we compared the transcript levels of ACE2 and TMPRSS2 in nasopharyngeal swab samples (n = 234) from children and adult family members within SARS-CoV-2-exposed families and assessed the association with SARS-CoV-2 infection status. Transcript levels for ACE2, but not TMPRSS2, were higher in adults than in children (n = 129 adults and 105 children; P < 0.05). The expression of the two genes was not significantly different between SARS-CoV-2 positive and SARS-CoV-2 negative patients within the same age groups. However, in families with one or more SARS-CoV-2 positive adult family members, expression of both genes was significantly higher in SARS-CoV-2 positive children than in SARS-CoV-2 negative children (P < 0.05). By multivariate analysis, ACE2 expression adjusted for age and sex was significantly associated with SARS-CoV-2 infection in the overall population (odds ratio [OR], 1.112 [95% confidence interval [CI], 1.012 to 1.229]; P < 0.05). The degree of this association was higher (OR, 1.172 [95% CI, 1.034 to 1.347]; P < 0.05) in the subgroup of families with only SARS-CoV-2 positive adult family members. Our results suggest that children with lower levels of nasal ACE2 and TMPRSS2 are more likely to remain SARS-CoV-2 negative despite being exposed to a SARS-CoV-2 positive adult family member.

IMPORTANCE ACE2 and TMPRSS2 are well established in the literature as SARS-CoV-2 entry factors. Recent data suggest that lower levels of nasal ACE2 in children may be associated with their lower incidence of coronavirus disease 2019 (COVID-19). In this study, using data from nasopharyngeal swab specimens from adult and pediatric members of families in which one or more members of the family had laboratory-confirmed SARS-CoV-2 infection, we show that children with lower levels of ACE2 and TMPRSS2 are more likely to remain SARS-CoV-2 negative despite being exposed to a SARS-CoV-2 positive adult family member. These results provide new insights into the roles of nasopharyngeal ACE2 and TMPRSS2 in acquiring SARS-CoV-2 infection, and they show that the differential expression of these genes in adults versus children may contribute to differential rates of SARS-CoV-2 infection in these populations.

Moderate exercise may prevent the development of severe forms of COVID-19, whereas high-intensity exercise may result in the opposite

Sedentary lifestyle increases the risk of hospitalization for COVID-19 independently of other factors. There is enough statistics to show that exercise prevents severe forms of COVID-19, but current recommendations do not set an upper limit for exercise intensity. The hypothesis presented in the paper states that intense exercise, through blood hypoxia, increases the expression of transmembrane angiotensin-converting enzyme 2 (tACE2) in the vascular endothelium, increasing the risk of developing serious forms of disease, especially in the untrained. On the other hand, moderate-intensity exercise increases the blood concentration of soluble angiotensin-converting enzyme 2 (ACE2) which has a protective role for SARS-CoV-2 infection and may prevent complications. The importance of this hypothesis consists in the revision of COVID-19 prophylaxis programs through physical exercises, with the possibility of administration of antioxidants to speed up the adaptation of vascular endothelial cells to exertion.

Which ones, when and why should renin-angiotensin system inhibitors work against COVID-19?

The article describes the possible pathophysiological origin of COVID-19 and the crucial role of renin-angiotensin system (RAS), providing several “converging” evidence in support of this hypothesis. SARS-CoV-2 has been shown to initially upregulate ACE2 systemic activity (early phase), which can subsequently induce compensatory responses leading to upregulation of both arms of the RAS (late phase) and consequently to critical, advanced and untreatable stages of COVID-19 disease. The main and initial actors of the process are ACE2 and ADAM17 zinc-metalloproteases, which, initially triggered by SARS-CoV-2 spike proteins, work together in increasing circulating Ang 1–7 and Ang 1–9 peptides and downstream (Mas and Angiotensin type 2 receptors) pathways with anti-inflammatory, hypotensive and antithrombotic activities. During the late phase of severe COVID-19, compensatory secretion of renin and ACE enzymes are subsequently upregulated, leading to inflammation, hypertension and thrombosis, which further sustain ACE2 and ADAM17 upregulation. Based on this hypothesis, COVID-19-phase-specific inhibition of different RAS enzymes is proposed as a pharmacological strategy against COVID-19 and vaccine-induced adverse effects. The aim is to prevent the establishment of positive feedback-loops, which can sustain hyperactivity of both arms of the RAS independently of viral trigger and, in some cases, may lead to Long-COVID syndrome.

A Review on Expression, Pathological Roles, and Inhibition of TMPRSS2, the Serine Protease Responsible for SARS-CoV-2 Spike Protein Activation

SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, uses the host cell membrane receptor angiotensin-converting enzyme 2 (ACE2) for anchoring its spike protein, and the subsequent membrane fusion process is facilitated by host membrane proteases. Recent studies have shown that transmembrane serine protease 2 (TMPRSS2), a protease known for similar role in previous coronavirus infections, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS), is responsible for the proteolytic cleavage of the SARS-CoV-2 spike protein, enabling host cell fusion of the virus. TMPRSS2 is known to be expressed in the epithelial cells of different sites including gastrointestinal, respiratory, and genitourinary system. The infection site of the SARS-CoV-2 correlates with the coexpression sites of ACE2 and TMPRSS2. Besides, age-, sex-, and comorbidity-associated variation in infection rate correlates with the expression rate of TMPRSS2 in those groups. These findings provide valid reasons for the assumption that inhibiting TMPRSS2 can have a beneficial effect in reducing the cellular entry of the virus, ultimately affecting the infection rate and case severity. Several drug development studies are going on to develop potential inhibitors of the protease, using both conventional and computational approaches. Complete understanding of the biological roles of TMPRSS2 is necessary before such therapies are applied.