This disclosure relates to isotopically modified amino acids and their pharmaceutical or nutritional uses in stabilizing pharmaceutical protein-based formulations, proteins with long life span, and preventing or treating disease such as Alzheimer's disease. Specifically, the disclosure provides protein drugs having increased stability comprising an L-aspartate (L-Asp) residue or an L-asparagine (L-Asn) residue, wherein the L-Asp residue or the L-Asn residue comprises a deuterium atom.
