Hyperhomocysteinemia enhances the negative influence of Salmonella typhimurium LPS on vascular contractility and gene expression of receptor and regulatory proteins in rats

Abstract

The most severe manifestation of SARS-CoV-2 infection is the development of acute respiratory distress syndrome. A high blood level of homocysteine in patients is a prognostically unfavorable factor for the course of COVID-19 infection. The development of multiple organ failure in COVID-19 infection is aggravated by endotoxemia. The aim of the study was to investigate the effect of hyperhomocysteinemia and Salmonella Typhimurium lipopolysaccharide (LPS) on the rat aorta and renal artery contractility and the gene expression of receptor and regulatory proteins.

Methods. Hyperhomocysteinemia was modeled in rats by adding L-methionine to drinking water at a concentration of 5 g/L (0.5%) for 14 days. Endotoxemia was induced with a single injection of Salmonella Typhimurium LPS (Sigma, 5 mg/kg, intraperitoneally). The contractile force of isolated blood vessels was measured in the isometric mode. Gene expression was assessed with the PCR analysis.
Results. At 24 h after a single injection of LPS, the force of aortic contractile response to angiotensin II (ATII) increased 1.6 times and to arginine vasopressin (AVP) 1.5 times whereas the response to endothelin-1 (ET1) decreased by 37.5% compared to the respective values for control rats. Upon repeated administration of LPS, the blood vessels lost the sensitivity to vasoconstrictors. After methionine loading, the plasma level of total homocysteine increased more than three times. Homocysteinemia resulted in severe disorders in the neuroendocrine regulation of vascular contractility, including decreased sensitivity of the aorta and the renal artery to vasoconstrictor effects of ATII (41.2% and 61.5%, respectively), AVP (33.3% and 41.2%, respectively), serotonin (5HT, 16.7% and 44.4%, respectively) and ET1 (33.3% and 37.5%, respectively). The administration of LPS to rats on the background of a high plasma level of homocysteine further aggravated the disorders of vascular contractile activity. Administration of LPS was associated with lower expression of vasoconstrictor α1A- and α1D-adrenoceptors, and of vasodilator β1- and β2-adrenoceptors and with a higher expression of ETA and ETB receptors. Both LPS and hyperhomocysteinemia led to significant decreases in angiotensin-converting enzymes ACE and ACE2 mRNA, and in MasR and V1AR receptor mRNA. The methionine loading induced a decrease in the gene expression of inositol trisphosphate receptors IP3R2 and IP3R3, which indicated a disorder of calcium homeostasis in the blood vessels. The methionine loading was not fatal. In the group of animals after a single administration of LPS, the mortality rate was 7%, and in the group after the administration of LPS and methionine loading, the mortality rate was 50%.
Conclusion. Thus, hyperhomocysteinemia enhances LPS-induced disorders in the neuroendocrine regulation of vascular tone, aggravates the course of endotoxemia, and increases the mortality rate.