Physiological role of erythrocyte nitric oxide

Oxygen debt as a predictor of high-flow nasal cannula therapy failure in SARS-CoV-2 patients with acute respiratory failure: A retrospective cohort study

BACKGROUND

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is known for its rapid progression to acute hypoxemic respiratory failure (AHRF). The increased use of oxygen therapy during the pandemic and the progression of AHRF have highlighted the need to promptly determine the need for orotracheal intubation (OTI).

OBJETIVE

To determine the validity of quantitative measurement of oxygen debt (DEOx) according to arterial gases compared to the use of iROX in patients with high-flow nasal cannula (HFNC) therapy requirement, presenting with acute respiratory failure as a consequence of SARS-CoV-2 infection. In addition, we aimed to identify the factors associated with the need for orotracheal intubation (OTI).

METHODS

A retrospective observational cohort study of a database collected from patients with SARS-CoV-2 infection admitted to intensive care units with AHRF and had received HFNC upon admission during the Covid-19 pandemic (March 23, 2020 through August 02, 2021). The variables of interest were factors determining the predictive ability of DEOx and iROX. We used a multiple logarithmic regression model to correct for confounding and mixed-effects variables, and validated for OTI in patients treated with HFNC.

RESULTS

From a total of 373 patients treated with HFNC, 317 patients (84.9%) required invasive mechanical ventilation. APACHE II (AOR 1.44; 95% CI: 1.14-1.83, p 0,032), vasopressor use (AOR 27.7; 95% CI: 1.83 - 420,63, p 0,017), and DEOx (AOR 1.26; 95% CI: 1.10 - 1.44, p 0,001) were associated with the need for intubation. The predictive model between iROX and DEOx evidenced an AUC of 0.535 vs. 0.606, respectively, with a DEOx cut off point of 7.14 (±10.16, p < 0.01). DEOx as an independent factor of OTI presents an OR 2,48 with cut point 4.5 mlO2/kg (AUC 0.780, CI 95%, 0.753 - 0.808, p < 0.01).

CONCLUSIONS

DEOx is a valuable measurment to identify the need for OTI in patients with SARS-CoV-2 who were under management with HFNC with a predictive value superior to iROX, being a reproducible and valid quantitative method for the need OTI that can be implemented in other critically illconditions. Further studies are required to characterize the usefulness of DEOx more precisely.

Resuscitation After Hemorrhagic Shock in the Microcirculation: Targeting Optimal Oxygen Delivery in the Design of Artificial Blood Substitutes

Microcirculatory preservation is essential for patient recovery from hemorrhagic shock. In hemorrhagic shock, microcirculatory flow and pressure are greatly reduced, creating an oxygen debt that may eventually become irreversible. During shock, tissues become hypoxic, cellular respiration turns to anaerobic metabolism, and the microcirculation rapidly begins to fail. This condition requires immediate fluid resuscitation to promote tissue reperfusion. The choice of fluid for resuscitation is whole blood; however, this may not be readily available and, on a larger scale, may be globally insufficient. Thus, extensive research on viable alternatives to blood has been undertaken in an effort to develop a clinically deployable blood substitute. This has not, as of yet, achieved fruition, in part due to an incomplete understanding of the complexities of the function of blood in the microcirculation. Hemodynamic resuscitation is acknowledged to be contingent on a number of factors other than volume expansion. The circulation of whole blood is carefully regulated to optimize oxygen delivery to the tissues via shear stress modulation through blood viscosity, inherent oxygen-carrying capacity, cell-free layer variation, and myogenic response, among other variables. Although plasma expanders can address a number of these issues, hemoglobin-based oxygen carriers (HBOCs) introduce a method of replenishing the intrinsic oxygen-carrying capacity of blood. There continue to be a number of issues related to HBOCs, but recent advances in the next-generation HBOCs show promise in the preservation of microcirculatory function and limiting toxicities. The development of HBOCs is now focused on viscosity and the degree of microvascular shear stress achieved in order to optimize vasoactive and oxygen delivery responses by leveraging the restoration and maintenance of physiological responses to blood flow in the microcirculation. Blood substitutes with higher viscous properties tend to improve oxygen delivery compared to those with lower viscosities. This review details current concepts in blood substitutes, particularly as they relate to trauma/hemorrhagic shock, with a specific focus on their complex interactions in the microcirculation.

Rho-kinase is a negative regulator of red blood cell eNOS under basal conditions

BACKGROUND

Rho-kinase, an effector of the small GTPase RhoA, is known to be a novel inhibitory regulator of eNOS in endothelial cells under basal conditions and disease states. However, although RBC possesses active RhoA/Rho-kinase pathway, Rho-kinase mediated eNOS regulation has not been investigated in RBC, so far.

OBJECTIVE

The aim of the present study is to investigate whether eNOS activity is regulated by Rho-kinase under basal conditions and to evaluate whether inhibition of this enzyme causes eNOS activation and intracellular NO production in RBC.

METHODS

RBC packeds were isolated from healthy volunteers and resuspended in Hepes solution at a hematocrit of 0.01 l/l. Intracellular NO and Ca+2 levels and eNOS activation measured by flow cytometry in response to Rho-kinase inhibitors, fasudil and Y-27632, in the absence and presence of NOS, and PI3K inhibitors.

RESULTS

Rho-kinase inhibitors fasudil and Y-27632 found to increase intracellular NO concentrations. These inhibitors also cause enhancement of intracellular Ca+2 and serine 1177 phosphorylated eNOS levels. Besides, although these responses have shown to be suppressed by NOS enzyme, PI3K inhibition had no effect on this mechanism.

CONCLUSIONS

The results of the present study demonstrated that RBC eNOS enzyme activity is regulated by inhibitory Rho-kinase pathway under basal conditions and inhibition of this pathway enhances the activity of eNOS in RBC. This activation is mediated by both intracellular Ca+2 and Serine 1177 phosphorylated eNOS increment, with no contribution of AKT activation, in RBC. The mechanism we described here gives first evidences about Rho-kinase mediated eNOS regulation in RBC under basal conditions. This pathway could also be more important under disease states.

Iron Dysregulation and Dormant Microbes as Causative Agents for Impaired Blood Rheology and Pathological Clotting in Alzheimer's Type Dementia

Alzheimer’s disease and other similar dementias are debilitating neurodegenerative disorders whose etiology and pathogenesis remain largely unknown, even after decades of research. With the anticipated increase in prevalence of Alzheimer’s type dementias among the more susceptible aging population, the need for disease-modifying treatments is urgent. While various hypotheses have been put forward over the last few decades, we suggest that Alzheimer’s type dementias are triggered by external environmental factors, co-expressing in individuals with specific genetic susceptibilities. These external stressors are defined in the Iron Dysregulation and Dormant Microbes (IDDM) hypothesis, previously put forward. This hypothesis is consistent with current literature in which serum ferritin levels of individuals diagnosed with Alzheimer’s disease are significantly higher compared those of age- and gender-matched controls. While iron dysregulation contributes to oxidative stress, it also causes microbial reactivation and virulence of the so-called dormant blood (and tissue) microbiome. Dysbiosis (changes in the microbiome) or previous infections can contribute to the dormant blood microbiome (atopobiosis¹), and also directly promotes systemic inflammation via the amyloidogenic formation and shedding of potent inflammagens such as lipopolysaccharides. The simultaneous iron dysregulation and microbial aberrations affect the hematological system, promoting fibrin amylodiogenesis, and pathological clotting. Systemic inflammation and oxidative stress can contribute to blood brain barrier permeability and the ensuing neuro-inflammation, characteristic of Alzheimer’s type dementias. While large inter-individual variability exists, especially concerning disease pathogenesis, the IDDM hypothesis acknowledges primary causative factors which can be targeted for early diagnosis and/or for prevention of disease progression.

Extracellular ATP activates eNOS and increases intracellular NO generation in Red Blood Cells

BACKGROUND

It has been well documented that ATP activates NOS enzymes and causes increased NO production in several cell types. Although RBC known to possesses eNOS enzyme activity, it has not been investigated whether RBC eNOS could be induced by extracellular ATP.

OBJECTIVE

The aim of the present study is to evaluate extracellular ATP mediated eNOS activation and NO production in RBC.

METHODS

RBC packed were isolated from healthy volunteers and re-suspended in Hepes solution at a hematocrit of 0.01 l/l. Intracellular NO and Ca+2 levels and eNOS activation measured by flow cytometry in response to P2X receptor agonist, Bz-ATP, in the absence and presence of NOS, P2 receptors and PI3K inhibitors.

RESULTS

P2X receptor agonist Bz-ATP found to increase intracellular NO, Ca+2 and serine 1177 phosphorylated eNOS levels and these responses have shown to be suppressed by NOS enzyme, P2 receptors and PI3K inhibitors.

CONCLUSIONS

The results of the study clearly demonstrated extracellular ATP induced NO generation in RBC through intracellular Ca+2 and PI3K/Akt pathways. The mechanism we described here might be important at basal conditions and also in conditions with increased ATP release.