APOA1 and diabetes mellitus: HDL dysfunction can also be caused by reduced HDL surface lipids, defective PON1 activity, and myeloperoxidase-promoted oxidative modification of apoA-I amino acid residues (such as tryptophan, tyrosine, methionine, and lysine) [102,103] Carbamylation, a non-enzymatic post-translational protein modification, is increased in people with diabetes.