Patients with severe forms of COVID-19 often develop acute respiratory distress syndrome (ARDS) associated with high levels of proinflammatory cytokines and damage of lungs and other organs. A special feature in these patients is thrombotic events in the micro- and macro-vasculature. Owing to the lack of a specific and efficient treatment against COVID-19, lowering of this "cytokine storm" is a further proposed strategy.
Glycine is the major agonist of glycine receptors (GlyR), which are chloride channels that hyperpolarize cell membranes of inflammatory cells such as macrophages and neutrophils, turning them less sensitive to proinflammatory stimuli. In addition, glycine possesses a cytoprotective effect, improves endothelial function, and diminishes platelet aggregation.
In laboratory animals, in a rat model of endotoxic shock a 5% glycine-rich diet lowers mortality, reduces pulmonary neutrophilic inflammation and hepatic lesions, and avoids elevation of serum TNF-alpha. In animal models of ischemia-reperfusion injury, glycine protects the gut and lungs.
In in vitro studies, glycine diminishes the expression and release of TNF-alpha and IL-6 from adipose tissue, 3T3-L1 cells, and alveolar macrophages, probably through inhibition of phosphorylation of NF-kappaB. Finally, glycine diminishes platelet aggregation.
In human beings, glycine has been used for many years for the management of some ailments. In diabetic patients, oral glycine reduces glycosylated hemoglobin levels and serum TNF-alpha, and in patients with cystic fibrosis glycine improves the clinical and spirometric status, and tend to lower serum TNF-alpha, IL-6 and G-CSF.
Glycine is a white microcrystal powder soluble in water, with a sweet taste and relatively low cost.
This controlled, randomized, two-branches clinical trial will recruit participants of any sex, any age, with COVID-19 confirmed (or awaiting confirmation) by PCR, that are to initiate (or with \<48 h of) mechanical ventilation. After obtaining an informed consent, participants will be randomly assigned to two branches: 1) Experimental group, n=41 participants, that along with habitual management for their condition will receive 0.5 g/kg/day glycine divided in four doses every 6 h through nasogastric tube. 2) Control group, n=41 participants that will only receive habitual management. Pregnant women and subjects already participating in another study protocol will be excluded, and those with voluntary discharge or referenced to another institution will be discarded.
Blood samples for measurements of serum cytokines (Bio-Plex Human Cytokine 17-Plex, Bio-Rad) will be obtained at the beginning of the study and every 7 days thereafter.
The major outcome will be mortality. Secondary outcomes will be diminution of number of days under mechanical ventilation and evolution of PaO2/FiO2, proinflammatory and metabolic biomarkers, Sequence Organ Failure Assessment (SOFA), and Acute Physiology and Chronic Health Evaluation II (APACHE II).
Routine test such as arterial blood gases, blood chemistry, blood count, coagulation test, and ECG will also be analyzed by using the weighted average in certain time-periods (probably 7-days periods).
Group comparisons will be carried out by means of Fisher exact/chi-square tests and Student's t-/Mann-Whitney U-tests. Feasibility of multivariate analysis will be evaluated.
