Background Resolving the coronavirus disease 2019 (COVID-19) pandemic requires diagnostic testing to determine which individuals are infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current gold standard is to perform reverse-transcription polymerase chain reaction (PCR) on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of approximately 100 copies of viral RNA per milliliter of transport media. However, LoDs of currently approved assays vary over 10,000-fold. Assays with higher LoDs will miss infected patients. However, the relative clinical sensitivity of these assays remains unknown. Methods Here we model the clinical sensitivities of assays based on their LoD. Cycle threshold (Ct) values were obtained from 4700 first-time positive patients using the Abbott RealTime SARS-CoV-2 Emergency Use Authorization test. We derived viral loads from Ct based on PCR principles and empiric analysis. A sliding scale relationship for predicting clinical sensitivity was developed from analysis of viral load distribution relative to assay LoD. Results Ct values were reliably repeatable over short time testing windows, providing support for use as a tool to estimate viral load. Viral load was found to be relatively evenly distributed across log10 bins of incremental viral load. Based on these data, each 10-fold increase in LoD is expected to lower assay sensitivity by approximately 13%. Conclusions The assay LoD meaningfully impacts clinical performance of SARS-CoV-2 tests. The highest LoDs on the market will miss a majority of infected patients. Assays should therefore be benchmarked against a universal standard to allow cross-comparison of SARS-CoV-2 detection methods.

Carbon monoxide (CO) has long been considered a toxic gas but is now a recognized bioactive gasotransmitter with potent immunomodulatory effects. Although inhaled CO is currently under investigation for use in patients with lung disease, this mode of administration can present clinical challenges. The capacity to deliver CO directly and safely to the gastrointestinal (GI) tract could transform the management of diseases affecting the GI mucosa such as inflammatory bowel disease or radiation injury. To address this unmet need, inspired by molecular gastronomy techniques, we have developed a family of gas-entrapping materials (GEMs) for delivery of CO to the GI tract. We show highly tunable and potent delivery of CO, achieving clinically relevant CO concentrations in vivo in rodent and swine models. To support the potential range of applications of foam GEMs, we evaluated the system in three distinct disease models. We show that a GEM containing CO dose-dependently reduced acetaminophen-induced hepatocellular injury, dampened colitis-associated inflammation and oxidative tissue injury, and mitigated radiation-induced gut epithelial damage in rodents. Collectively, foam GEMs have potential paradigm-shifting implications for the safe therapeutic use of CO across a range of indications.

Infection is a common complication of major trauma that causes significantly increased morbidity and mortality. The mechanisms however, linking tissue injury to increased susceptibility to infection remain poorly understood. To study this relationship, we present a novel murine model where a major liver crush injury is followed by bacterial inoculation into the lung. We find that such tissue trauma both impaired bacterial clearance and was associated with significant elevations in plasma heme levels. While neutrophil (PMN) recruitment to the lung in response to Staphylococcus aureus was unchanged after trauma, PMN cleared bacteria poorly. Moreover, PMN show >50% less expression of TLR2, which is responsible, in part, for bacterial recognition.Administration of heme effectively substituted for trauma. Last, day 1 trauma patients (n=9) showed similar elevations in free heme to that seen after murine liver injury and circulating PMN showed similar TLR2 reduction compared to volunteers (n=6). These findings correlate to high infection rates.

Highlights d Aerobic exercise increases circulating free heme due to skeletal muscle microtrauma d Hemopexin-null mice show higher heme levels but no difference in running capacity d Skeletal muscle lacking HO-1 has defective mitochondria and a fatigue-prone phenotype d HO-1 is required to maintain skeletal muscle health during aerobic training

Cellular protective mechanisms exist to ensure survival of the cells and are a fundamental feature of all cells that is necessary for adapting to changes in the environment. Indeed, evolution has ensured that each cell is equipped with multiple overlapping families of genes that safeguard against pathogens, injury, stress, and dysfunctional metabolic processes. Two of the better-known enzymatic systems, conserved through all species, include the heme oxygenases (HO-1/HO-2), and the ectonucleotidases (CD39/73). Each of these systems generates critical bioactive products that regulate the cellular response to a stressor. Absence of these molecules results in the cell being extremely predisposed to collapse and, in most cases, results in the death of the cell. Recent reports have begun to link these two metabolic pathways, and what were once exclusively stand-alone are now being found to be intimately interrelated and do so through their innate ability to generate bioactive products including adenosine, carbon monoxide, and bilirubin. These simple small molecules elicit profound cellular physiologic responses that impact a number of innate immune responses, and participate in the regulation of inflammation and tissue repair. Collectively these enzymes are linked not only because of the mitochondria being the source of their substrates, but perhaps more importantly, because of the impact of their products on specific cellular responses. This review will provide a synopsis of the current state of the field regarding how these systems are linked and how they are now being leveraged as therapeutic modalities in the clinic.

The urgent need for large-scale diagnostic testing for SARS-CoV-2 has prompted interest in sample-collection methods of sufficient sensitivity to replace nasopharynx (NP) sampling. Nasal-swab samples are an attractive alternative; however, previous studies have disagreed over how nasal sampling performs relative to NP sampling. Here, we compared nasal vs. NP specimens collected by healthcare workers in a cohort of individuals clinically suspected of COVID-19 as well as SARS-CoV-2 RT-PCR positive outpatients undergoing follow-up. We compared subjects being seen for initial evaluation vs. follow-up, two different nasal-swab collection protocols, and three different transport conditions, including traditional viral transport media (VTM) and dry swabs, on 307 total study participants. We compared categorical results and viral loads to those from standard NP swabs collected at the same time from the same patients. All testing was performed by RT-PCR on the Abbott SARS-CoV-2 RealTime EUA (limit of detection [LoD], 100 copies viral genomic RNA/mL transport medium). We found low concordance overall, with Cohen’s kappa of 0.49, with high concordance only for subjects with very high viral loads. We found medium concordance for testing at initial presentation (κ=0.68), and very low concordance for followup testing (κ=0.27). Finally, we show that previous reports of high concordance may have resulted from measurement using assays with sensitivity ≥1,000 copies/mL. These findings suggest nasal-swab testing be used for situations in which viral load is expected to be high, as we demonstrate that nasal-swab testing is likely to miss patients with low viral loads.

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Objective: Evidence indicates that bone marrow progenitor cells (BMPC) are a major contributor to neointima formation in transplant arteriosclerosis. HO-1 (heme oxygenase 1, Hmox1 ) and carbon monoxide (CO), a product of heme degradation by HO-1, ameliorate neointima formation by inhibiting proliferation of smooth muscle cells. We investigated the mechanism whereby HO-1 and CO modulate BMPC and mitigates neointima formation in transplant arteriosclerosis. Approach and Results: Using a murine model of aortic transplantation, bone marrow chimeric mice, and in vitro experiments, we report that CO does not inhibit mobilization of BMPC into the circulation or their homing to the vessel adventitia, but instead suppresses differentiation of BMPC into smooth muscle cells after they arrive in the adventitia. Specifically, the effect of CO on differentiation of BMPC into smooth muscle cell is mediated in part, by limiting PDGFR-β (platelet derived growth factor receptor-β) signaling. Hmox1 −/− BMPC exhibit a greater propensity to differentiate into smooth muscle cell in vitro, in part by regulating PDGFR-β + expression. Furthermore, wild-type mice transplanted with Hmox1 −/− bone marrow cells show augmented neointima formation after allografting versus control. CO exposure significantly ameliorated neointima formation, which remains more severe with Hmox1 −/− bone marrow cell versus air-treated mice receiving HO-1-expressing bone marrow cell, highlighting the importance of endogenous HO-1 in neointima formation. Conclusions: Host BMPC contribute to neointima formation in transplant arteriosclerosis and the protective effect afforded by HO-1/CO against neointima formation is mediated in part through the regulation of PDGFR-β expression. We propose that suppressing differentiation of BMPC is a major mechanism by which HO-1 and CO prevent neointima expansion after transplant.