Abstract
Purpose:
There is evidence that hydrogen sulfide (H2S) and endocannabinoids can protect the central nervous system against glutamate-induced excitotoxicity and oxidative stress. In the present study, we will compare the neuroprotective actions of H2S (using L-cysteine as a substrate) and endocannabinoids (using anandamide) against glutamate-induced excitotoxicity in the isolated bovine retinae.
Methods:
Isolated bovine neural retinae were pretreated with L-cysteine (10 nM - 1 µM) or anandamide (1 nM -100 nM) prior to insult with glutamate (2 mM), and retinal neuron survival was assessed using the methylthiazolydiphenyl-tetrazolium bromide (MTT) assay. For studies aimed at determining the involvement of the H2S biosynthesis pathway, glutamate-induced neurotoxic retinas were pretreated with enzyme inhibitors for H2S biosynthesis [aminooxyacetic acid (AOA, 30 µM), DL-propargylglycine (PAG, 1 mM), and ketobutyric acid (KBA, 1 mM)], prior to application of L-cysteine (100 nM).
Results:
In the presence of glutamate (2 mM), only 68% of neurons survived when compared to control. The H2S substrate L-cysteine (100 nM) significantly (P<0.001) reversed glutamate (2 mM)-induced neuron degeneration. Interestingly, the H2S biosynthetic enzyme inhibitors, AOA, PAG, and KBA did not alter the neuroprotective effects of L-cysteine. Anandamide (1 nM - 10 nM) also completely prevented the glutamate (2 mM)-induced damage.
Conclusions:
Both L-cysteine and anandamide can protect bovine neural retina from glutamate-induced excitotoxicity with the endocannabinoid displaying a higher potency. However, the neuroprotective effect of L-cysteine does not involve de novo intramural biosynthesis of H2S.<br />