Abstract

Objective: Vascular smooth muscle cell (VSMC) dysfunction plays a role in diabetic macrovasculopathy. This dysfunction may be caused or exacerbated by expression of many of genes potently activated by the transcriptional factor nuclear factor κB (NF-κB). We have examined whether culture of VSMCs under high glucose conditions to stimulate the diabetic state can lead to the activation of NF-κB. Methods: NF-κB activation was assessed in VSMCs stably transfected with a cis-reporter plasmid containing the NF-κB binding sites. Results: Within 3-h incubation, high glucose (27.5 or 55 mmol/l) alone induced an increase in NF-κB activity in VSMCs; this increase was mimicked by mannitol given to deliver the same osmolar stress to the cells. High glucose or mannitol also enhanced TNFα-stimulated NF-κB activity. Incubation with high glucose for 48 h followed by stimulation with TNFα led to a marked potentiation of NF-κB activation compared with normoglycemic (5.5 mmol/l) VSMCs exposed to TNFα, while mannitol attenuated this effect. A 48-h incubation with high glucose substantially reduced glutathione (GSH) levels compared with normoglycemic VSMCs, whereas mannitol significantly increased GSH levels. An antioxidant N-acetyl-l-cysteine and a selective protein kinase C (PKC) inhibitor GF109203X significantly suppressed the TNFα-induced NF-κB activation, and abrogated potentiation of TNFα-induced NF-κB activity caused by high glucose (27.5 mmol/l). Conclusion: These results suggest that acutely high glucose causes alterations in osmolarity leading to activation of NF-κB, but that exposure to high glucose for more prolonged times causes changes in antioxidant defences and activation of PKC, which potentiates cytokine activation of NF-κB. Further definition of these pathways will help to delineate important signals mediating the aberrant behavior of VSMCs under hyperglycemic/diabetic conditions.