The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells

Endothelium dysfunction and thrombosis in COVID-19 with type 2 diabetes

SARS-CoV-2 can directly or indirectly damage endothelial cells. Endothelial injury, especially phosphatidylserine (PS) exposure on the outer membrane of cells, can more easily promote thrombosis. Type 2 diabetes(T2D) patients were more susceptible to COVID-19, they had more severe symptoms, higher risk of thrombotic complications, and longer duration of post-COVID-19 sequelae. This review provided a detailed overview of the mechanisms underlying endothelial dysfunction in T2D patients with COVID-19 (including long COVID), which may be influenced by hyperglycemia, hypoxia, and pro-inflammatory environments. The mechanisms of thrombosis in T2D patients with COVID-19 are also explored, particularly the effects of increased numbers of PS-exposing particles, blood cells, and endothelial cells on hypercoagulability. Given the high risk of thrombosis in T2D patients with COVID-19, early antithrombotic therapy can both minimize the impact of the disease on patients and maximize the chances of improvement, thereby alleviating patient suffering. We provided detailed guidance on antithrombotic drugs and dosages for mild, moderate, and severe patients, emphasizing that the optimal timing of thromboprophylaxis is a critical factor in influencing prognosis. Considering the potential interactions between antidiabetic, anticoagulant, and antiviral drugs, we proposed practical and comprehensive management recommendations to supplement the incomplete efficacy of vaccines in the diabetic population, reduce the incidence of post-COVID-19 sequelae, and improve patient quality of life.

Streptococcal arginine deiminase regulates endothelial inflammation, mTOR pathway and autophagy

Endothelial cells (EC) are active participants in the inflammation process. During the infection, the change in endothelium properties provides the leukocyte infiltrate formation and restrains pathogen dissemination due to coagulation control. Pathogenic microbes are able to change the endothelium properties and functions in order to invade the bloodstream and disseminate in the host organism. Arginine deiminase (ADI), a bacterial arginine-hydrolyzing enzyme, which causes the amino acid deficiency, important for endothelium biology. Previous research implicates altered metabolism of arginine in the development of endothelial dysfunction and inflammation. It was shown that arginine deficiency, as well as overabundance affects the balance of mechanical target of rapamycin (mTOR)/S6 kinase (S6K) pathway, arginase and endothelial nitric oxide synthase (eNOS) resulted in reactive oxygen species (ROS) production and EC activation. ADI creating a deficiency of arginine can interfere cellular arginine-dependent processes. Thus, this study was aimed at investigation of the influence of streptococcal ADI on the metabolism and inflammations of human umbilical vein endothelial cells (HUVEC). The action of ADI was studied by comparing the effect Streptococcus pyogenes M49-16 paternal strain expressing ADI and its isogenic mutant M49-16delArcA with the inactivated gene ArcA. Based on comparison of the parental and mutant strain effects, it can be concluded, that ADI suppressed mTOR signaling pathway and enhanced autophagy. The processes failed to return to the basic level with arginine supplement. Our study also demonstrates that ADI suppressed endothelial proliferation, disrupted actin cytoskeleton structure, increased phospho-NF-κB p65, CD62P, CD106, CD54, CD142 inflammatory molecules expression, IL-6 production and lymphocytes-endothelial adhesion. In spite of the ADI-mediated decrease in arginine concentration in the cell-conditioned medium, the enzyme enhanced the production of nitric oxide in endothelial cells. Arginine supplementation rescued proliferation, actin cytoskeleton structure, brought NO production to baseline and prevented EC activation. Additional evidence for the important role of arginine bioavailability in the EC biology was obtained. The results allow us to consider bacterial ADI as a pathogenicity factor that can potentially affect the functions of endothelium.

Beneficial Effects of L-Arginine in Patients Hospitalized for COVID-19: New Insights from a Randomized Clinical Trial

We have recently demonstrated in a double-blind randomized trial the beneficial effects of L-Arginine in patients hospitalized for COVID-19. We hypothesize that one of the mechanisms underlying the favorable effects of L-Arginine is its action on inflammatory cytokines. To verify our hypothesis, we measured longitudinal plasma levels of pro-inflammatory and anti-inflammatory cytokines implied in the pathophysiology of COVID-19 in patients randomized to receive oral L-Arginine or placebo. The study was successfully completed by 169 patients. Patients in the L-Arginine arm had a reduced respiratory support evaluated at 10 and 20 days; moreover, the time to hospital discharge was significantly shorter in the L-Arginine group. The assessment of circulating cytokines revealed that L-Arginine significantly reduced the circulating levels of pro-inflammatory IL-2, IL-6, and IFN-γ and increased the levels of the anti-inflammatory IL-10. Taken together, these findings indicate that adding L-Arginine to standard therapy in COVID-19 patients markedly reduces the need of respiratory support and the duration of in-hospital stay; moreover, L-Arginine significantly regulates circulating levels of pro-inflammatory and anti-inflammatory cytokines.

Effects of tofacitinib therapy on arginine and methionine metabolites in association with vascular pathophysiology in rheumatoid arthritis: A metabolomic approach

Introduction

Rheumatoid arthritis (RA) has been associated with changes in lipid, arginine and NO metabolism with increased cardiovascular (CV) risk. The aim of this study is to evaluate the effect of tofacitinib, a Janus kinase (JAK) inhibitor, on arginine and methionine metabolism in correlation with inflammation, functional and pathological vascular changes during one-year treatment of patients with RA.

Materials and methods

Thirty RA patients with active disease were treated with either 5 mg bid or 10 mg bid tofacitinib for 12 months. We determined DAS28, CRP, IgM rheumatoid factor (RF) and anti-cyclic citrullinated peptide (CCP) levels. We assessed brachial artery flow-mediated vasodilation (FMD), carotid intima-media thickness (IMT) and pulse-wave velocity (PWV) by ultrasound at baseline and after 6 and 12 months. We also determined plasma L-arginine, L-citrulline, L-ornithine, inducible nitric oxide synthase (iNOS), asymmetric (ADMA) and symmetric dimethylarginine (SDMA), L-N-monomethyl-arginine (L-NMMA), cysteine, homocysteine, and methionine levels at these time points.

Results

Twenty-six patients (13 on each arm) completed the study. CRP, ESR and DAS28 decreased significantly during one-year treatment with tofacitinib. Arginine and ADMA showed a negative univariate correlation with CRP but not with FMD, PWV or IMT. Tofacitinib at 10 mg bid significantly increased L-arginine, L-ornithine, iNOS and methionine levels after 12 months. ADMA and SDMA levels did not change in our study. Methionine showed negative correlation with FMD at baseline and positive correlation with PWV after 12 months. No change was observed in FMD and PWV but a significant increase was measured in IMT at 6 and 12 months. Multivariate analysis indicated variable correlations of L-arginine, L-citrulline, ADMA, L-NMMA, homocysteine and methionine with DAS28, CRP, ESR and RF but not with anti-CCP after one-year treatment. With respect to vascular pathophysiology, only PWV and methionine correlated with each other.

Conclusion

One-year tofacitinib treatment suppressed systemic inflammation and improved functional status in RA. FMD, PWV have not been affected by one-year tofacitinib treatment., while IMT increased further despite treatment. Increased arginine and methionine might contribute to the anti-inflammatory effects of tofacitinib. Increased arginine availability with no changing ADMA may protect FMD and PWV from deterioration. The increase of IMT in the anti-inflammatory environment cannot be explained by arginine or methionine metabolism in this study.