Reduced photoreceptor damage after photodynamic therapy through blockade of nitric oxide synthase in a model of choroidal neovascularization.
OBJECTIVE
To investigate the role of nitric oxide synthase (NOS) in photoreceptor degeneration associated with photodynamic therapy (PDT) in a laser-induced model of choroidal neovascularization (CNV).


METHODS
PDT was performed in monkey and Brown Norway rats with laser-induced CNV. L-NAME, a NOS inhibitor, or saline was injected intraperitoneally in rats with CNV. An NO donor, or saline, was injected intravitreously into normal rats. Photoreceptor apoptosis was evaluated by TUNEL and electron microscopy. NOS, ED-1, and cleaved-caspase-3 (c-casp-3) expression were determined by immunohistochemistry. CNV lesions were examined by fluorescence angiography and choroidal flat mount.


RESULTS
TUNEL and electron microscopy showed photoreceptor apoptosis after PDT. In rats, there were significantly more TUNEL-positive cells in the photoreceptors 24 hours after PDT, whereas in the CNV lesions there were more TUNEL-positive cells 6 hours after PDT. C-casp-3 was detected in the CNV lesions but not in the photoreceptors after PDT. There was no difference in the numbers of ED-1-positive macrophages before and after PDT. However, inducible NOS (iNOS) was increased after PDT in macrophages. Intravitreous injection of the NO donor without PDT also induced substantial photoreceptor apoptosis. L-NAME-treated animals had significantly fewer TUNEL-positive cells in the photoreceptors than saline-treated animals after PDT (P < 0.05). There were no differences in CNV size and leakage between L-NAME- and saline-treated groups.


CONCLUSIONS
iNOS expression in macrophages contributes to PDT-induced photoreceptor degeneration. NOS inhibition reduces PDT-induced photoreceptor degeneration without compromising the treatment effect of PDT in an experimental model of CNV.
She
Haicheng
H
Angiogenesis and Laser Laboratories, Massachusetts Eye and Ear Infirmary, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.
Nakazawa
Toru
T
Matsubara
Akihisa
A
Hisatomi
Toshio
T
Young
Tara A
TA
Michaud
Norman
N
Connolly
Edward
E
Hafezi-Moghadam
Ali
A
Gragoudas
Evangelos S
ES
Miller
Joan W
JW
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D020256:Choroidal Neovascularization / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005451:Fluorescein Angiography; D019084:Fluorescent Antibody Technique, Indirect; D020287:In Situ Nick-End Labeling; D007274:Injections, Intraperitoneal; D008252:Macaca fascicularis; D008264:Macrophages / Q000201:enzymology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors*; D010778:Photochemotherapy; D020419:Photoreceptor Cells, Vertebrate / Q000201:enzymology / Q000648:ultrastructure*; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011166:Porphyrins / Q000627:therapeutic use; D051381:Rats; D011914:Rats, Inbred BN; D012162:Retinal Degeneration / Q000139:chemically induced / Q000201:enzymology / Q000473:pathology / Q000517:prevention & control*; D000077362:Verteporfin
D004791:Enzyme Inhibitors; D020030:Nitric Oxide Donors; D017319:Photosensitizing Agents; D011166:Porphyrins; D000077362:Verteporfin; D052247:Nitric Oxide Synthase Type II; D053148:Caspase 3; D019331:NG-Nitroarginine Methyl Ester