Zinc alpha 2 glycoprotein (ZAG): A potential novel pharmacological target in diabetic retinopathy

Zinc alpha 2 glycoprotein (ZAG) is a 41 KDa secretory soluble glycoprotein found in different body fluids likethe serum, saliva, sweat, breast milk, and urine. It is also found in tissues like the testis, epididymis, kidney, spleen, liver,lungs, heart, and brain. ZAG is an adipokine with multiple roles, including lipid mobilization, modulating glucosemetabolisms, improving insulin sensitivity, inhibiting tumor proliferation through RNAse activity, and suppressinginflammation. Low levels of zinc and ZAG are linked to metabolic syndrome and are also reported as potentialbiomarkers for diabetic nephropathy. Interestingly zinc has been found to regulate the binding of ZAG to fatty acids.Based on very few reports on the vitreous ZAG and based on its known functions, we speculate that ZAG has apotential role in diabetic retinopathy. In this article, we discuss the structural component of the protein, its secretionfrom various tissues, and its distribution in multiple tissues in normal and disease conditions, especially in diabetesand its complications.