DPP8 and Reticulocytopenia: Identification of DPP-IV inhibitor selective over dipeptidyl peptidase8 (DPP8), dipeptidyl peptidase9 (DPP9), and dipeptidyl peptidase II (DPP II) is important to avoid multiorgan toxicities (DPP8 and 9 non-selective) and reticulocytopenia in rats (DPP II non-selective).[19] In fact, sitagliptin behaved as a pure competitive type of inhibitor as its IC50 values on human plasma DPP-IV increase linearly with substrate (H-Gly-Pro-AMC) concentrations[13] and is highly selective over a variety of proline-specific proteases including DPP8, DPP89, and DPP II (Unpublished observations).