Exacerbated corneal inflammation and neovascularization in the HO-2 null mice is ameliorated by biliverdin.
Heme oxygenase (HO-1 and HO-2) represents an intrinsic cytoprotective and anti-inflammatory system based on its ability to modulate leukocyte migration and to inhibit expression of inflammatory cytokines and proteins. HO-2 deletion leads to unresolved corneal inflammation and chronic inflammatory complications including ulceration, perforation and neovascularization. We examined the consequences of HO-2 deletion on hemangiogenesis and lymphangiogenesis in the model of suture-induced inflammatory neovascularization. An 8.0 silk suture was placed at the corneal apex of wild type and HO-2 null mice. Neovascularization was assessed by vital microscopy and quantified by image analysis. Hemangiogenesis and lymphangiogenesis were determined by immunofluorescence staining using anti-CD31 and anti-LYVE-1 antibodies, respectively. Inflammation was quantified by histology and myeloperoxidase activity. The levels of HO-1 expression and inflammatory cytokines were determined by real time PCR and ELISA, respectively. Corneal sutures produced a consistent inflammatory response and a time-dependent neovascularization. The response in HO-2 null mice was associated with a greater increase compared to the wild type in the number of leukocytes (827,600+/-129,000 vs. 294,500+/-57,510; p<0.05), neovessels measured by vital microscopy (21.91+/-1.05 vs. 12.77+/-1.55 mm; p<0.001) 4 days after suture placement. Hemangiogenesis but not lymphangiogenesis was more pronounced in HO-2 null mice compared to wild type mice. Induction of HO-1 in sutured corneas was greatly attenuated in HO-2 null corneas and treatment with biliverdin diminished the exaggerated inflammatory and neovascular response in HO-2 null mice. The demonstration that the inflammatory responses, including expression of proinflammatory proteins, inflammatory cell influx and hemangiogenesis are exaggerated in HO-2 knockout mice strongly supports the notion that the HO system is critical for controlling the inflammatory and neovascular response in the cornea. Hence, pharmacological amplification of this system may constitute a novel therapeutic strategy for the treatment of corneal disorders associated with excessive inflammation and neovascularization.
Bellner
Lars
L
Department of Pharmacology, New York Medical College, Valhalla, NY 10595, USA.
Vitto
Marco
M
Patil
Kiran A
KA
Dunn
Michael W
MW
Regan
Raymond
R
Laniado-Schwartzman
Michal
M
D000818:Animals; D001664:Biliverdine / Q000627:therapeutic use*; D003315:Cornea / Q000201:enzymology; D016510:Corneal Neovascularization / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D018450:Disease Progression; D004353:Drug Evaluation, Preclinical; D005260:Female; D006419:Heme Oxygenase (Decyclizing) / Q000172:deficiency / Q000378:metabolism / Q000502:physiology; D051547:Heme Oxygenase-1 / Q000378:metabolism; D007634:Keratitis / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009195:Peroxidase / Q000378:metabolism
D009195:Peroxidase; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C105245:heme oxygenase-2; D001664:Biliverdine