RBP4 and diabetes mellitus: Candidate proteins which including alpha-1-antichymotrypsin, alpha-1-antitrypsin, apolipoprotein A-I (apoA-I), haptoglobin, retinol-binding protein 4, transthyretin, and zinc-alpha2-glycoprotein were shown to vary significantly between normal and prediabetes/diabetes in human patients (Riaz, 2015; Kim et al., 2019).