Glucose protects cultured retinal cells from oxidative injury via the pentose phosphate pathway

Oxidative injury has been implicated in a range of common retinal neurodegenerative disorders. Protecting the retina from such an insult could therefore prove clinically beneficial. We sought to investigate whether glucose, acting via the pentose phosphate pathway (PPP), was able to counteract oxidative cytotoxicity to retinal cells in culture.

Mixed retinal neuron-glial cultures were prepared from Sprague-Dawley rat neonates and used at 7 days in vitro; neuron-only and Müller glial cell-only mono-cultures were subsequently prepared from these cultures. At appropriate stages, cultures were treated with t-butyl hydroperoxide (tbH; 10 nM-1 mM) in glucose/pyruvate-free DMEM to induce oxidative stress. Some cultures were co-treated with glucose. Additional compounds were co-applied to inhibit glycolysis, PPP, cystine uptake, glutathione biosynthesis and glutathione reductase (GR). The effect of glucose on stimulation of reactive oxygen species (ROS), as well as levels of glutathione and NADPH were also investigated.

Oxidative stress resulted in cytotoxicity to both retinal neurons and glial cells. Glucose was able to abrogate the toxicity to glial cells in mono-cultures and mixed cultures, but could only provide protection to neurons in the mixed cultures when glial cells were also present. Glucose was additionally shown to prevent stimulation of ROS and oxidative stress-induced depletions of glutathione and NADPH. Inhibition of PPP, cystine uptake or GR all diminished the protective response of glucose.

Glucose prevented oxidative stress to retinal cells via the PPP. Neurons were not subjected to glucose-induced protection except when glial cells were present, implying the passage of a transmissible mediator or other protective action between the two cell types.