Ketogenic Diet Attenuates NMDA-Induced Damage to Rat's Retinal Ganglion Cells in an Age-Dependent Manner

Abstract

Objective: This study was conducted to investigate neuroprotective effects of a high fat/low carbohydrate and protein diet (ketogenic diet, KD) in a model of N-methyl <smlcap>D</smlcap>-aspartate (NMDA)-induced retinal ganglion cell (RGC) damage in juvenile and young adult rats. Methods: Juvenile (30-35 days old) and young adult (56-70 days old) female Brown Norway rats were fed the KD for 21 days; rats exposed to a standard rodent diet (SRD) served as controls. The main constituents of the KD used in the present study were approximately 80% fats, 8% proteins, and less than 1% carbohydrates. On day 14 of exposure to the KD (or the SRD in the control group), each rat received a single intravitreal injection of NMDA; RGCs were then retrogradely labelled by hydroxystilbamidine on day 19 and collected on day 21 to assess the degree of damage induced by NMDA. Blood biomarkers to confirm the expected metabolic response to the KD (i.e. ketosis and hypoglycaemia) were also assessed. Results: Although both the juvenile and young adult rats developed comparable ketosis and hypoglycaemia when fed the KD, NMDA-induced loss in RGCs was significantly attenuated only in juvenile rats exposed to the KD in comparison with those fed the SRD; exposure to the KD had no protective effect in young adult rats. In summary, exposure to the KD had a neuroprotective effect in NMDA-induced RGC damage in juvenile rats, but not in young adult rats. Conclusion: These results support further exploration of metabolic interventions to treat optic neuropathies associated with neurodegeneration.