ADA and non-proliferative diabetic retinopathy: Nevertheless, the activities of eN/CD73 (Fig. 2a), ADA (Fig. 2b) AK (Fig. 2c), and ALP (Fig. 2e), but not NTPDase/ADPase (Fig. 2d), were increased in VF from PDR patients, with the first two enzymes being also significantly upregulated in NPDR eyes.