Role of Glutamine Synthetase on Vascular Permeability in Gliomas

Background/Aim: This study aimed to investigate the effect and underlying mechanism of inhibiting glutamine synthetase (GS) on the vascular permeability of gliomas. Materials and Methods: C6 glioma rat models were randomly divided into control and L-methionine sulfoximine (MSO) treatment groups. MSO was intraperitoneally injected once every other day for a total of three injections in the MSO group. We assessed the effect of MSO on tumor vascular permeability by tail vein injection of Evans blue dye. GS activity, glutamate (Glu) concentration, glutamine (Gln) concentration, and arginine concentration in tumor tissues were measured using the corresponding kits. qPCR experiments were then conducted to examine the effect of glutamate concentration on N-methyl-D-aspartate (NMDA) receptor expression. Finally, the nitric oxide synthase (NOS) assay kit and the nitric oxide (NO) assay kit were employed to detect NOS activity and NO concentration changes, respectively. Results: Increased glioma tumor vascular permeability was observed after intraperitoneal injection of MSO; MSO acted as an inhibitor of GS, leading to a decrease in GS activity; increased glutamate levels caused activation of NMDA receptors and further activation of NOS; additionally, elevated NO levels were detected in association with an increase in arginine and NOS. Conclusion: Inhibiting GS results in increased vascular permeability in gliomas, which is associated with elevated NO levels and the vasodilatory effects of NO.