Involvement of the endocannabinoid system in retinal damage after high intraocular pressure-induced ischemia in rats.
OBJECTIVE
To evaluate whether high intraocular pressure (IOP)-induced ischemia is associated with modifications in the retinal endocannabinoid metabolism and to ascertain whether drugs that interfere with the endocannabinoid system may prevent retinal damage due to ischemic insult.


METHODS
Anandamide (AEA) synthesis, transport, hydrolysis, and AEA endogenous levels were assessed by means of high-performance liquid chromatography in the retinas of rats undergoing 45 minutes of ischemia followed by 12 hours of reperfusion. Under these experimental conditions, binding to cannabinoid (CB1R) and vanilloid (TRPV1) receptor was assessed with rapid-filtration assays. AEA-hydrolase (FAAH, fatty acid amide hydrolase), CB1R and TRPV1 protein content was determined by enzyme-linked immunosorbent assay. Finally, to characterize the neuroprotective profile of drugs that interfere with the endocannabinoid system, cell counting in the retinal ganglion cell (RGC) layer and real-time polymerase chain reactions for Thy-1 mRNA expression were used.


RESULTS
In rat retina, ischemic insult followed by reperfusion resulted in enhanced FAAH activity and protein expression paralleled by a significant decrease in the endogenous AEA tone, whereas the AEA-membrane transporter or the AEA-synthase NAPE-PLD (N-acyl-phosphatidylethanolamine-hydrolyzing-phospholipase-d) were not affected. Retinal ischemia-reperfusion decreased the expression of cannabinoid (CB1) and vanilloid (TRPV1) receptors. Systemic administration of a specific FAAH inhibitor (e.g., URB597) reduced enzyme activity and minimized the retinal damage observed in ischemic-reperfused samples. Similarly, intravitreal injection of the AEA stable analogue, R(+)-methanandamide, reduced cell loss in the RGC layer, and this was prevented by systemic administration of a CB1 or TRPV1 selective antagonist (e.g., SR141716 and capsazepine, respectively).


CONCLUSIONS
The original observation that retinal ischemia-reperfusion reduces endogenous AEA via enhanced expression of FAAH supports the deduction that this is implicated in retinal cell loss caused by high IOP in the RGC layer.
Nucci
Carlo
C
Physiopathological Optics, Department of Biopathology and Diagnostic Imaging, University of Rome Tor Vergata, Rome, Italy.
Gasperi
Valeria
V
Tartaglione
Rosanna
R
Cerulli
Angelica
A
Terrinoni
Alessandro
A
Bari
Monica
M
De Simone
Chiara
C
Agrò
Alessandro Finazzi
AF
Morrone
Luigi Antonio
LA
Corasaniti
Maria Tiziana
MT
Bagetta
Giacinto
G
Maccarrone
Mauro
M
D000581:Amidohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D001549:Benzamides / Q000494:pharmacology; D063385:Cannabinoid Receptor Modulators / Q000502:physiology*; D002211:Capsaicin / Q000031:analogs & derivatives / Q000494:pharmacology; D002219:Carbamates / Q000494:pharmacology; D002452:Cell Count; D002851:Chromatography, High Pressure Liquid; D063388:Endocannabinoids; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006868:Hydrolysis; D007429:Intraocular Pressure; D008297:Male; D009798:Ocular Hypertension / Q000150:complications; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D015427:Reperfusion Injury / Q000209:etiology / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D012164:Retinal Diseases / Q000209:etiology / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D012165:Retinal Ganglion Cells / Q000473:pathology; D012171:Retinal Vessels / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077285:Rimonabant; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D018800:Thy-1 Antigens / Q000235:genetics; D000099252:Fatty Acid Amide Hydrolases
D000581:Amidohydrolases; D001095:Arachidonic Acids; D001549:Benzamides; D063385:Cannabinoid Receptor Modulators; D002211:Capsaicin; D002219:Carbamates; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011720:Pyrazoles; D012333:RNA, Messenger; D043884:Receptor, Cannabinoid, CB1; D000077285:Rimonabant; D050916:TRPV Cation Channels; D018800:Thy-1 Antigens; D000099252:Fatty Acid Amide Hydrolases; C493922:Trpv1 protein, rat; C500528:cyclohexyl carbamic acid 3'-carbamoylbiphenyl-3-yl ester; C071423:capsazepine; C078814:anandamide