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Cannabidiol protects retinal neurons by preserving glutamine synthetase activity in diabetes.

El-Remessy AB, Khalifa Y, Ola S, Ibrahim AS, Liou GI - Mol. Vis. (2010)

Bottom Line: Diabetes causes significant increases in retinal oxidative and nitrative stress compared with controls.These effects were associated with Müller cell activation and dysfunction as well as with impaired GS activity and tyrosine nitration of GS.Cannabidiol treatment reversed these effects.

View Article: PubMed Central - PubMed

Affiliation: Clinical and Experimental Therapeutics, University of Georgia, Augusta, GA 30912, USA. aelremessy@mcg.edu

ABSTRACT

Purpose: We have previously shown that non-psychotropic cannabidiol (CBD) protects retinal neurons in diabetic rats by inhibiting reactive oxygen species and blocking tyrosine nitration. Tyrosine nitration may inhibit glutamine synthetase (GS), causing glutamate accumulation and leading to further neuronal cell death. We propose to test the hypothesis that diabetes-induced glutamate accumulation in the retina is associated with tyrosine nitration of GS and that CBD treatment inhibits this process.

Methods: Sprague Dawley rats were made diabetic by streptozotocin injection and received either vehicle or CBD (10 mg/kg/2 days). After eight weeks, retinal cell death, Müller cell activation, GS tyrosine nitration, and GS activity were determined.

Results: Diabetes causes significant increases in retinal oxidative and nitrative stress compared with controls. These effects were associated with Müller cell activation and dysfunction as well as with impaired GS activity and tyrosine nitration of GS. Cannabidiol treatment reversed these effects. Retinal neuronal death was indicated by numerous terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL)-labeled cells in diabetic rats compared with untreated controls or CBD-treated rats.

Conclusions: These results suggest that diabetes-induced tyrosine nitration impairs GS activity and that CBD preserves GS activity and retinal neurons by blocking tyrosine nitration.

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Related in: MedlinePlus

Cannabidiol (CBD) restores diabetes-impaired glutamine synthetase (GS) activity. Glutamine synthetase activity measured by the ability of the sample to convert 14C-glutamate to 14C-glutamine demonstrated significant inhibition of GS activity in diabetic rat retinas compared with controls. The GS activity was restored by treating the diabetic animals with CBD (10 mg/kg/2days, i.p.; n=4–5 retinas/group, *p<0.05, versus control [standard error of mean]).
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f4: Cannabidiol (CBD) restores diabetes-impaired glutamine synthetase (GS) activity. Glutamine synthetase activity measured by the ability of the sample to convert 14C-glutamate to 14C-glutamine demonstrated significant inhibition of GS activity in diabetic rat retinas compared with controls. The GS activity was restored by treating the diabetic animals with CBD (10 mg/kg/2days, i.p.; n=4–5 retinas/group, *p<0.05, versus control [standard error of mean]).

Mentions: Diabetes-induced peroxynitrite formation and its subsequent alteration of protein function via tyrosine nitration are well documented [30]. Recent studies have demonstrated that GS is a susceptible target for tyrosine nitration [21]. Therefore, we evaluated the specific tyrosine nitration levels of GS and the extent to which its activity can be altered in diabetic rat retinas. As shown in Figure 3, diabetes caused significant tyrosine nitration (2.3-fold) of GS that was significantly reduced by treatment with CBD. We next evaluated the effects of tyrosine nitration on GS activity. Indeed, diabetes-induced GS tyrosine nitration was positively correlated with a significant inhibition (40%) of GS activity (Figure 4), and treatment with CBD restored this activity in the diabetic animals. These results suggest a causal role of tyrosine nitration in impairing the function of GS, which can lead to the accumulation of glutamate and possibly cause neurotoxicity.


Cannabidiol protects retinal neurons by preserving glutamine synthetase activity in diabetes.

El-Remessy AB, Khalifa Y, Ola S, Ibrahim AS, Liou GI - Mol. Vis. (2010)

Cannabidiol (CBD) restores diabetes-impaired glutamine synthetase (GS) activity. Glutamine synthetase activity measured by the ability of the sample to convert 14C-glutamate to 14C-glutamine demonstrated significant inhibition of GS activity in diabetic rat retinas compared with controls. The GS activity was restored by treating the diabetic animals with CBD (10 mg/kg/2days, i.p.; n=4–5 retinas/group, *p<0.05, versus control [standard error of mean]).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2925907&req=5

f4: Cannabidiol (CBD) restores diabetes-impaired glutamine synthetase (GS) activity. Glutamine synthetase activity measured by the ability of the sample to convert 14C-glutamate to 14C-glutamine demonstrated significant inhibition of GS activity in diabetic rat retinas compared with controls. The GS activity was restored by treating the diabetic animals with CBD (10 mg/kg/2days, i.p.; n=4–5 retinas/group, *p<0.05, versus control [standard error of mean]).
Mentions: Diabetes-induced peroxynitrite formation and its subsequent alteration of protein function via tyrosine nitration are well documented [30]. Recent studies have demonstrated that GS is a susceptible target for tyrosine nitration [21]. Therefore, we evaluated the specific tyrosine nitration levels of GS and the extent to which its activity can be altered in diabetic rat retinas. As shown in Figure 3, diabetes caused significant tyrosine nitration (2.3-fold) of GS that was significantly reduced by treatment with CBD. We next evaluated the effects of tyrosine nitration on GS activity. Indeed, diabetes-induced GS tyrosine nitration was positively correlated with a significant inhibition (40%) of GS activity (Figure 4), and treatment with CBD restored this activity in the diabetic animals. These results suggest a causal role of tyrosine nitration in impairing the function of GS, which can lead to the accumulation of glutamate and possibly cause neurotoxicity.

Bottom Line: Diabetes causes significant increases in retinal oxidative and nitrative stress compared with controls.These effects were associated with Müller cell activation and dysfunction as well as with impaired GS activity and tyrosine nitration of GS.Cannabidiol treatment reversed these effects.

View Article: PubMed Central - PubMed

Affiliation: Clinical and Experimental Therapeutics, University of Georgia, Augusta, GA 30912, USA. aelremessy@mcg.edu

ABSTRACT

Purpose: We have previously shown that non-psychotropic cannabidiol (CBD) protects retinal neurons in diabetic rats by inhibiting reactive oxygen species and blocking tyrosine nitration. Tyrosine nitration may inhibit glutamine synthetase (GS), causing glutamate accumulation and leading to further neuronal cell death. We propose to test the hypothesis that diabetes-induced glutamate accumulation in the retina is associated with tyrosine nitration of GS and that CBD treatment inhibits this process.

Methods: Sprague Dawley rats were made diabetic by streptozotocin injection and received either vehicle or CBD (10 mg/kg/2 days). After eight weeks, retinal cell death, Müller cell activation, GS tyrosine nitration, and GS activity were determined.

Results: Diabetes causes significant increases in retinal oxidative and nitrative stress compared with controls. These effects were associated with Müller cell activation and dysfunction as well as with impaired GS activity and tyrosine nitration of GS. Cannabidiol treatment reversed these effects. Retinal neuronal death was indicated by numerous terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL)-labeled cells in diabetic rats compared with untreated controls or CBD-treated rats.

Conclusions: These results suggest that diabetes-induced tyrosine nitration impairs GS activity and that CBD preserves GS activity and retinal neurons by blocking tyrosine nitration.

Show MeSH
Related in: MedlinePlus