glutathione reductase uses nadph to reduce gssg to gsh reaction Pathways Glutathione in Cellular Redox Homeostasis:

In addition, Astragaloside IV treatment increased the phosphorylation of PI3K and Akt to promote the restoration of NRF2 expression and nuclear translocation [220]

Therefore, sufficient GSH supply and active glutathione peroxidase are main defence resources of neurons under pro-oxidative conditions 23,24,25

Its also important to get it through natural sources

Lipotoxicity as a therapeutic target in obesity and diabetic cardiomyopathy

Mutations in gyrase and topoisomerase genes associated with fluoroquinolone resistance in Salmonella serovars from retail meats

If you've tried everything take your vet to the cat and also ask them about B12 How to Give Your Cat a B12 Shot Don't give your cat a B12 shot without consulting your vet first