Arginase/NO axis signature in human monocytes exposed to autologous erythrocytes with reduced oxygen transport capacity.

Abstract

Background: Red blood cells have recently been recognized as more than mere oxygen transporters, with growing evidence pointing to their active role in influencing the functional behaviour of neighbouring immune cells. Through their capacity to shape local oxygen availability, they constitute a key microenvironmental factor capable of influencing monocyte behaviour and functional responses. However, the specific impact of haemoglobin-mediated oxygen transport on monocyte functional orientation through the NO/Arginase axis remains poorly understood, representing the central question addressed in the present study. Materials And Methods: This study was conducted on four experimental groups, in which monocytes isolated from anaemic donors characterized by reduced haemoglobin levels were treated with or without their intact autologous red blood cells (RBCs), in the presence or absence of LPS stimulation. The NO–arginase axis in monocytes was subsequently assessed by measuring iNOS activity through nitric oxide (NO) production using the Griess assay, and Arginase-1 activity through urea formation using a colorimetric urea-based assay, performed on both cell lysates and culture supernatants. Results: Exposure of human monocytes to red blood cells with reduced haemoglobin levels resulted in a significant increase in NO production and iNOS activity, while decreasing ARG1 activity. Consequently, the iNOS/ARG1 ratio was significantly elevated, indicating a shift toward the iNOS pathway. Conclusion: In conclusion, this study establishes that alterations in haemoglobin-mediated gas transport can influence the balance of NO–arginase in human monocytes.