Effects of tumor necrosis factor-alpha and interleukin-6 on fluid-phase permeability and ammonia diffusion in CNS-derived endothelial cells

Proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) play an important role in the blood-brain barrier breakdown present in several neurological diseases including multiple sclerosis and AIDS. However, the specific effects of these cytokines on central nervous system-derived endothelial cells (CNS-EC) is not fully understood. In this study the effects of TNF-alpha and IL-6 were tested on different permeability mechanisms of CNS-EC.Central nervous system endothelial cells were isolated from human brain and retina and cultured in vitro in a transwell system. Fluid-phase endocytosis and transcytosis, absorptive-mediated endocytosis, and ammonia diffusion were measured with specific methods. Endothelial cells were studied with electron microscopy for the ultrastructural effects of cytokine stimulation.Fluid-phase endocytosis and transcytosis were significantly increased by TNF-alpha and IL-6. This effect was dose dependent and reversible. The ammonia diffusion rate was also significantly increased by TNF-alpha. Absorptive-mediated endocytosis was not enhanced by TNF-alpha. Ultrastructural analysis of cytokine-treated CNS-EC confirmed the alterations in permeability showing an increase in endocytotic activity and a decrease in tight junctions.The proinflammatory cytokines IL-6 and TNF-alpha induce specific changes in the morphology and permeability of CNS-EC. These alterations can be important in many diseases characterized by increased cytokine production.