Inhibition of TNF-α-induced sickle RBC retention in retina by a VLA-4 antagonist

• Published in: Investigative ophthalmology & visual science Vol. 42; no. 6; pp. 1349 - 1355
• Main Authors: LUTTY, Gerard A, TAOMOTO, Makoto, JINGTAI CAO, MCLEOD, D. Scott, VANDERSLICE, Peter, MCINTYRE, Brad W, FABRY, Mary E, NAGEL, Ronald L
• Format: Journal Article
• Language: English
• Published: Rockville, MD Association for Research in Vision and Ophtalmology 01-05-2001
• Subjects: Anemia, Sickle Cell - blood; Anemias. Hemoglobinopathies; Animals; Antibodies, Monoclonal - pharmacology; Biological and medical sciences; Cell Adhesion - drug effects; Diseases of red blood cells; Endothelium, Vascular - drug effects; Erythrocytes, Abnormal - metabolism; Hematologic and hematopoietic diseases; Humans; Injections, Intraperitoneal; Integrin alpha4beta1; Integrins - antagonists & inhibitors; Integrins - immunology; Integrins - metabolism; Male; Medical sciences; Microscopy, Fluorescence; Peptides, Cyclic - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Lymphocyte Homing - antagonists & inhibitors; Receptors, Lymphocyte Homing - immunology; Receptors, Lymphocyte Homing - metabolism; Reticulocytes - drug effects; Retinal Vessels - metabolism; Tumor Necrosis Factor-alpha - pharmacology; Vascular Cell Adhesion Molecule-1 - metabolism; Hemoglobinopathy; VLA4; Retinopathy; Sickle cell anemia; Pathophysiology; Rat; Rodentia; Red blood cell; Retina; Hemopathy; Experimental study; Retention; Genetic disease; Eye disease; Vertebrata; Hemolytic anemia; Mammalia; Treatment; Animal; Antagonist; Inhibition; Tumor necrosis factor α
• ISSN: 0146-0404; 1552-5783

Patients with sickle cell disease have elevated circulating levels of cytokines including tumor necrosis factor (TNF) alpha. TNF-alpha stimulates expression by endothelial cells of adhesion molecules, including vascular cell adhesion molecule (VCAM) 1. Others have demonstrated that VLA-4 (alpha(4)beta(1)), a ligand for VCAM-1 or fibronectin, is present on a fraction of sickle reticulocytes. The intent of this study was to determine, using a rat model, if TNF-alpha increases retention of sickle erythrocytes in retina and if that retention can be inhibited.
TNF-alpha was given intraperitoneally to rats 5 hours before IV administration of FITC-labeled, density-separated sickle erythrocytes. After 5 minutes, rats were exsanguinated, and retinas were excised and incubated for ADPase activity, permitting the determination of the number and location of retained cells.
TNF-alpha caused a three- to fourfold increase in retention of sickle erythrocytes in retinal capillaries (P < 0.05) but not of normal human erythrocytes. Preincubation of sickle erythrocytes with TBC772, a peptide that blocks the binding of alpha(4)beta(1) and alpha(4)beta(7), or a monoclonal antibody against VLA-4 (19H8), significantly inhibited the TNF-alpha-induced retention (P < or = 0.02), whereas a control cyclic peptide and antibody had no effect. IV TBC772 also inhibited sickle erythrocyte retention (P = 0.01). Two intravenously administered anti-fibronectin antibodies inhibited sickle cell retention as well, but an anti-rat VCAM-1 antibody did not inhibit retention.
The authors conclude that TNF-alpha stimulates retention of sickle erythrocytes in the retinal vasculature. This increased retention can be blocked by a VLA-4 antagonist, suggesting that the cells retained after cytokine stimulation are reticulocytes. The counter-receptor for VLA-4 in this rat retina model appears to be fibronectin and not VCAM-1, based on data obtained using antibodies against these molecules.