Abstract
Purpose: :
To examine the effect of intravitreal bevacizumab on monkey and human eyes with particular focus on choroidal and retinal vessels
Methods: :
Five cynomolgus monkeys received an intravitreal injection of 1.25 mg bevacizumab with or without tritium labeling. The eyes were enucleated and prepared for light (left eyes) and electron microscopy (right eyes) on days 1, 4, 7 and 14. Control eyes from 6 monkeys remained untreated. Bevacizumab, GFAP, Vimentin, Iba1, CD32 and carbonic anhydrase were localized by immunocytochemistry. Bevacizumab was additionally localized by autoradiography. Thrombocytes and fibrin were stained by histochemistry. The diameter of the choriocapillaris was measured by morphometry. CNV membranes were extracted from AMD patients 1- 3 days after treatment with intravitreal bevacizumab and examined by electron microscopy.
Results: :
Bevacizumab has a very strong immunoreactivity and totally or partially filled the sectioned lumen of many blood vessels and coated red blood cells. Autoradiography showed localization of bevacizumab at the inner sites of retinal vessel walls. At the electron microscopical level, thrombocytes and granulocytes within the retinal vessels exhibited typical signs of activation such as pseudopodia, vacuoles and degranulation. Electron dense serotonin granules released from thrombocytes were present in the blood stream and endothelium of most vessels. As detected by electron microscopy, felt-like structures (several µm thick) were attached to the inner sides of retinal veins and interacted with blood and endothelial cells. Microthrombi were frequently observed, one retinal central vein was thrombotic. Müller cells, astrocytes, microglia were activated. The diameter of the choriocapillaries was significantly reduced in all treated eyes compared to the control. Activated thrombocytes were also present in CNVs from AMD patients.
Conclusions: :
Intravitreal bevacizumab accumulates locally at high concentration within the blood vessels. It attaches to the inner side of blood vessels and forms complexes, probably with other proteins of the plasma. These protein complexes form aggregates with blood cells, thrombocytes, neutrophils and endothelial cells. Through these aggregate formations, bevacizumab inhibits retinal and choroidal blood flow. It is likely that these immune complexes in combination with reduction of blood flow and VEGF removal reduce leakages from pathological vessels. The presence of serotonin in the bloodstream can explain the well-known hypertension induced by bevacizumab.
Keywords: age-related macular degeneration • drug toxicity/drug effects • choroid: neovascularization