Mediation of cannabidiol anti-inflammation in the retina by equilibrative nucleoside transporter and A2A adenosine receptor.
OBJECTIVE
Cannabidiol (CBD), a nonpsychotropic, nontoxic compound has been shown to block diabetes- and endotoxin-induced retinal damage. However, the protective mechanism of this anti-inflammatory cannabinoid is not completely understood. The goal of this study is to determine the role of adenosine signaling in retinal inflammation and its potential modulation by CBD.


METHODS
The adenosine receptor (AR) subtypes expressed in rat retinal microglial cells were assessed by quantitative real-time RT-PCR. AR function was determined via in vitro and in vivo inflammatory models. Microglial cells or rats were treated with or without lipopolysaccharide (LPS) in the presence or absence of adenosine, adenosine receptor agonists/antagonists, or CBD. Adenosine uptake and tumor necrosis factor (TNF)-alpha release in cells or in retinas were determined.


RESULTS
The results showed that A(2A)ARs are abundantly expressed in rat retinal microglial cells. When the cells or rats were treated with LPS, activation of the A(2A)AR was the most efficient in mediating AR agonist- or CBD-induced TNF-alpha inhibition. CBD inhibited adenosine uptake via equilibrative nucleoside transporter 1 and synergistically enhanced adenosine's TNF-alpha suppression after treatment with LPS.


CONCLUSIONS
These results suggest that the activated A(2A)AR in the retinal microglial cells plays a major anti-inflammatory role in the retina and that CBD's anti-inflammatory effects are linked to the inhibition of adenosine uptake.
Liou
Gregory I
GI
Department of Ophthalmology, Medical College of Georgia, Augusta, Georgia 30912, USA. giliou@mcg.edu
Auchampach
John A
JA
Hillard
Cecilia J
CJ
Zhu
Gu
G
Yousufzai
Bilal
B
Mian
Salman
S
Khan
Sohail
S
Khalifa
Yousuf
Y
D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D002185:Cannabidiol / Q000494:pharmacology*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism; D033703:Nucleoside Transport Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D012160:Retina / Q000187:drug effects* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019779:Salmonella enterica; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000893:Anti-Inflammatory Agents; D008070:Lipopolysaccharides; D033703:Nucleoside Transport Proteins; D012333:RNA, Messenger; D043705:Receptor, Adenosine A2A; D014409:Tumor Necrosis Factor-alpha; D002185:Cannabidiol