APOA1 and non-proliferative diabetic retinopathy: In another study, the inflammation-regulating proteins α2-HS-glycoprotein (AHSG), α1-acid glycoprotein (AGP), apolipoprotein A-1 (APOA1), and haptoglobin (HP) were found to be differentially expressed in the serum from patients with NPDR and PDR as compared to healthy controls [10].