Effects of l-Arginine Plus Vitamin C Supplementation on l-Arginine Metabolism in Adults with Long COVID: Secondary Analysis of a Randomized Clinical Trial.

Altered l-arginine metabolism has been described in patients with COVID-19 and has been associated with immune and vascular dysfunction. In the present investigation, we determined the serum concentrations of l-arginine, citrulline, ornithine, monomethyl-l-arginine (MMA), and symmetric and asymmetric dimethylarginine (SDMA, ADMA) in adults with long COVID at baseline and after 28-days of l-arginine plus vitamin C or placebo supplementation enrolled in a randomized clinical trial, compared with a group of adults without previous history of SARS-CoV-2-infection. l-arginine-derived markers of nitric oxide (NO) bioavailability (i.e., l-arginine/ADMA, l-arginine/citrulline+ornithine, and l-arginine/ornithine) were also assayed. Partial least squares discriminant analysis (PLS-DA) models were built to characterize systemic l-arginine metabolism and assess the effects of the supplementation. PLS-DA allowed discrimination of participants with long COVID from healthy controls with 80.2 ± 3.0% accuracy. Lower markers of NO bioavailability were found in participants with long COVID. After 28 days of l-arginine plus vitamin C supplementation, serum l-arginine concentrations and l-arginine/ADMA increased significantly compared with placebo. This supplement may therefore be proposed as a remedy to increase NO bioavailability in people with long COVID.

Development of a novel Ultra Performance Liquid Chromatography Tandem-Mass Spectrometry (UPLC-MS/MS) method to measure l-arginine metabolites in plasma.

INTRODUCTION: Arginine metabolism is involved in the regulation of several biological processes. Many liquid chromatography tandem-mass spectrometry methods for the determination of arginine and its metabolites have been developed but they are time consuming and imply long pre-analytical procedures. The purpose of this study was to develop a rapid method for the simultaneous determination of arginine, citrulline, ornithine, symmetric and asymmetric dimethylarginine and monomethylarginine in human plasma. MATERIALS AND METHODS: The pre-analytical procedure consisted in a simple deproteinization. The chromatographic separation was performed using hydrophilic interaction liquid chromatography. Analytes detection was performed with a triple quadrupole equipped with electrospray ion source operating in positive ion mode. Mass spectrometry experiments were conducted in multiple reaction monitoring mode. RESULTS AND CONCLUSIONS: Recovery ranged from 92.2 to 108.0%. The within-run imprecision and between-run imprecision ranged from 1.5 to 6.8 % and 3.8 to 11.9%, respectively. Carry over and matrix effect did not affect quantitative analysis. Extraction recovery was between 95 and 105 %. Stability after pre-analytical procedure was tested and all the metabolites were stable after 48 h at 4 °C. In conclusion, our novel method allow a rapid and easy determination of arginine and its metabolites both for research and clinical routine use.