Potential Therapeutic Strategies and Drugs That Target Vascular Permeability in Severe Infectious Diseases

Severe infection pathogenicity is induced by processes such as pathogen exposure, immune cell activation, inflammatory cytokine production, and vascular hyperpermeability. Highly effective drugs, such as antipathogenic agents, steroids, and antibodies that suppress cytokine function, have been developed to treat the first three processes. However, these drugs cannot completely suppress severe infectious diseases, such as coronavirus disease 2019 (COVID-19). Therefore, developing novel drugs that inhibit vascular hyperpermeability is crucial. This review summarizes the mechanisms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced vascular hyperpermeability and identifies inhibitors that increase endothelial cell (EC) junction-related proteins and determines their efficacy in COVID-19 and endotoxemia models. Analyzing the effects of SARS-CoV-2 on vascular permeability revealed that SARS-CoV-2 suppresses Claudin-5 (CLDN5) expression, which is responsible for adhesion between ECs, thereby increasing vascular permeability. Inhibiting CLDN5 function in mice induced vascular hyperpermeability and pulmonary edema. In contrast, Enhancing CLDN5 expression suppressed SARS-CoV-2-induced endothelial hyperpermeability, suggesting that SARS-CoV-2-induced vascular hyperpermeability contributes to pathological progression, which can be suppressed by upregulating EC junction proteins. Based on these results, we focused on Roundabout4 (Robo4), another EC-specific protein that stabilizes EC junctions. EC-specific Robo4 overexpression suppressed vascular hyperpermeability and mortality in lipopolysaccharide-treated mice. An ALK1 inhibitor (a molecule that increases Robo4 expression), suppressed vascular hyperpermeability and mortality in lipopolysaccharide- and SARS-CoV-2-treated mice. These results indicate that Robo4 expression-increasing drugs suppress vascular permeability and pathological phenotype in COVID-19 and endotoxemia models.

A Rare Mutation in SPLUNC1 Affects Bacterial Adherence and Invasion in Meningococcal Disease

Background

Neisseria meningitidis (Nm) is a nasopharyngeal commensal carried by healthy individuals. However, invasive infections occurs in a minority of individuals, with devastating consequences. There is evidence that common polymorphisms are associated with invasive meningococcal disease (IMD), but the contributions of rare variants other than those in the complement system have not been determined.

Methods

We identified familial cases of IMD in the UK meningococcal disease study and the European Union Life-Threatening Infectious Disease Study. Candidate genetic variants were identified by whole-exome sequencing of 2 patients with familial IMD. Candidate variants were further validated by in vitro assays.

Results

Exomes of 2 siblings with IMD identified a novel heterozygous missense mutation in BPIFA1/SPLUNC1. Sequencing of 186 other nonfamilial cases identified another unrelated IMD patient with the same mutation. SPLUNC1 is an innate immune defense protein expressed in the nasopharyngeal epithelia; however, its role in invasive infections is unknown. In vitro assays demonstrated that recombinant SPLUNC1 protein inhibits biofilm formation by Nm, and impedes Nm adhesion and invasion of human airway cells. The dominant negative mutant recombinant SPLUNC1 (p.G22E) showed reduced antibiofilm activity, increased meningococcal adhesion, and increased invasion of cells, compared with wild-type SPLUNC1.

Conclusions

A mutation in SPLUNC1 affecting mucosal attachment, biofilm formation, and invasion of mucosal epithelial cells is a new genetic cause of meningococcal disease.

Association Between Neutralizing Antibody Titers against Parechovirus A3 in Maternal and Cord Blood Pairs and Perinatal Factors

BACKGROUND

Parechovirus A3 (PeV-A3) is a pathogen that causes severe infectious diseases such as sepsis and meningoencephalitis in neonates and young infants. In this study, we aimed to measure the neutralizing antibody titer (NAT) against PeV-A3 in paired maternal and cord blood samples and to clarify the serum epidemiology of PeV-A3 and the association between the NAT and perinatal factors.

METHODS

NATs against PeV-A3 were measured in 1033 mothers (maternal and cord blood pairs; total of 2066 samples) who delivered their infant in Fukushima Prefecture between December 2013 and June 2014. RD-18S cells were used to measure NATs against PeV-A3. The association between NATs against PeV-A3 in maternal and cord blood and perinatal factors was determined using multivariate logistic regression analysis.

RESULTS

The median gestational age of the infants was 39 weeks 4 days (interquartile range, 38 weeks 4 days to 40 weeks 3 days). The NATs against PeV-A3 in maternal blood and in cord blood were almost the same. The proportion of samples assigned to the low-titer group (NAT ≤ 1:16) was approximately 70%, and the proportion of samples assigned to the high-titer group tended to increase with gestational age. The high-titer rate and geometric mean titers decreased with increased maternal age.

CONCLUSIONS

Cord blood indicates that neonates born at a lower gestational age and older mothers have a low NAT against PeV-A3. Thus, more attention should be paid to the onset of severe PeV-A3 disease in such neonates and young infants.