Fractional exhaled Nitric Oxide (FeNO) level as a predictor of COVID-19 disease severity

Objective

To assess the feasibility of Fractional exhaled Nitric Oxide (FeNO) as a simple, non-invasive, cost-effective and portable biomarker and decision support tool for risk stratification of COVID-19 patients.

Methods

We conducted a single-center prospective cohort study of COVID-19 patients whose FeNO levels were measured upon ward admission by the Vivatmo-me handheld device. Demographics, COVID-19 symptoms, and relevant hospitalization details were retrieved from the hospital databases. The patients were divided into those discharged to recover at home and those who died during hospitalization or required admission to an intensive care unit, internal medicine ward, or dedicated facility (severe outcomes group).

Results

Fifty-six patients were enrolled. The only significant demographic difference between the severe outcomes patients (n = 14) and the home discharge patients (n = 42) was age (64.21 ± 13.97 vs. 53.98 ± 15.57 years, respectively, P = .04). The admission FeNO measurement was significantly lower in the former group compared with the latter group (15.86 ± 14.74 vs. 25.77 ± 13.79, parts per billion [PPB], respectively, P = .008). Time to severe outcome among patients with FeNO measurements ≤11.8 PPB was significantly shorter compared with patients whose FeNO measured >11.8 PPB (19.25 ± 2.96 vs. 24.41 ± 1.09 days, respectively, 95% confidence interval [CI] 1.06 to 4.25). An admission FeNO ≤11.8 PPB was a significant risk factor for severe outcomes (odds ratio = 12.8, 95% CI: 2.78 to 58.88, P = .001), with a receiver operating characteristics curve of 0.752.

Conclusions

FeNO measurements by the Vivatmo-me handheld device can serve as a biomarker and COVID-19 support tool for medical teams. These easy-to-use, portable, and noninvasive devices may serve as valuable ED bedside tools during a pandemic.

A transepithelial pathway delivers succinate to macrophages, thus perpetuating their pro-inflammatory metabolic state

The gut metabolite composition determined by the microbiota has paramount impact on gastrointestinal physiology. However, the role that bacterial metabolites play in communicating with host cells during inflammatory diseases is poorly understood. Here, we aim to identify the microbiota-determined output of the pro-inflammatory metabolite, succinate, and to elucidate the pathways that control transepithelial succinate absorption and subsequent succinate delivery to macrophages. We show a significant increase of succinate uptake into pro-inflammatory macrophages, which is controlled by Na+-dependent succinate transporters in macrophages and epithelial cells. Furthermore, we find that fecal and serum succinate concentrations were markedly augmented in inflammatory bowel diseases (IBDs) and corresponded to changes in succinate-metabolizing gut bacteria. Together, our results describe a succinate production and transport pathway that controls the absorption of succinate generated by distinct gut bacteria and its delivery into macrophages. In IBD, this mechanism fails to protect against the succinate surge, which may result in chronic inflammation.

Systemic Succinate Homeostasis and Local Succinate Signaling Affect Blood Pressure and Modify Risks for Calcium Oxalate Lithogenesis

BACKGROUND

In the kidney, low urinary citrate increases the risk for developing kidney stones, and elevation of luminal succinate in the juxtaglomerular apparatus increases renin secretion, causing hypertension. Although the association between stone formation and hypertension is well established, the molecular mechanism linking these pathophysiologies has been elusive.

METHODS

To investigate the relationship between succinate and citrate/oxalate levels, we assessed blood and urine levels of metabolites, renal protein expression, and BP (using 24-hour telemetric monitoring) in male mice lacking slc26a6 (a transporter that inhibits the succinate transporter NaDC-1 to control citrate absorption from the urinary lumen). We also explored the mechanism underlying this metabolic association, using coimmunoprecipitation, electrophysiologic measurements, and flux assays to study protein interaction and transport activity.

RESULTS

Compared with control mice, slc26a6^-/- mice (previously shown to have low urinary citrate and to develop calcium oxalate stones) had a 40% decrease in urinary excretion of succinate, a 35% increase in serum succinate, and elevated plasma renin. Slc26a6^-/- mice also showed activity-dependent hypertension that was unaffected by dietary salt intake. Structural modeling, confirmed by mutational analysis, identified slc26a6 and NaDC-1 residues that interact and mediate slc26a6's inhibition of NaDC-1. This interaction is regulated by the scaffolding protein IRBIT, which is released by stimulation of the succinate receptor SUCNR1 and interacts with the NaDC-1/slc26a6 complex to inhibit succinate transport by NaDC-1.

CONCLUSIONS

These findings reveal a succinate/citrate homeostatic pathway regulated by IRBIT that affects BP and biochemical risk of calcium oxalate stone formation, thus providing a potential molecular link between hypertension and lithogenesis.

Modulation of Cl- signaling and ion transport by recruitment of kinases and phosphatases mediated by the regulatory protein IRBIT

IRBIT is a multifunctional protein that controls the activity of various epithelial ion transporters including NBCe1-B. Interaction with IRBIT increases NBCe1-B activity and exposes two cryptic Cl^--sensing GXXXP sites that enable regulation of NBCe1-B by intracellular Cl^- (Cl^- _in). Here, phosphoproteomic analysis revealed that IRBIT controlled five phosphorylation sites in NBCe1-B that determined both the active conformation of the transporter and its regulation by Cl^- _in Mutational analysis suggested that the phosphorylation status of Ser²³², Ser²³³, and Ser²³⁵ was regulated by IRBIT and determined whether NBCe1 transporters are in active or inactive conformations. The absence of phosphorylation at Ser²³², Ser²³³, or Ser²³⁵ produced NBCe1-B in the conformations pSer²³³/pSer²³⁵, pSer²³²/pSer²³⁵, or pSer²³²/pSer²³³, respectively. The activity of the pSer²³³/pSer²³⁵ form was similar to that of IRBIT-activated NBCe1-B, but it was insensitive to inhibition by Cl^- _in The properties of the pSer²³²/pSer²³⁵ form were similar to those of wild-type NBCe1-B, whereas the pSer²³²/pSer²³³ form was partially active, further activated by IRBIT, but retained inhibition by Cl^- _in Furthermore, IRBIT recruited the phosphatase PP1 and the kinase SPAK to control phosphorylation of Ser⁶⁵, which affected Cl^- _in sensing by the ³²GXXXP³⁶ motif. IRBIT also recruited the phosphatase calcineurin and the kinase CaMKII to control phosphorylation of Ser¹², which affected Cl^- _in sensing by the ¹⁹⁴GXXXP¹⁹⁸ motif. Ser²³², Ser²³³, and Ser²³⁵ are conserved in all NBCe1 variants and affect their activity. These findings reveal how multiple kinase and phosphatase pathways use phosphorylation sites to fine-tune a transporter, which have important implications for epithelial fluid and HCO₃ ^- secretion.