Dipeptidyl Peptidase-IV Activity and Neuropeptide Y in the Mouth: The Relationship with Body Composition and the Impact of Carbohydrates

Abstract

Dipeptidyl peptidase-IV (DPP-IV) is an enzyme present in the saliva, and its interaction with satiety related hormones is poorly understood. The purpose of this study was to determine possible relationships between salivary DPP-IV activity and body composition. Further, the response of salivary DPP-IV activity to carbohydrates was investigated. We tested 111 people for plasma and saliva DPP-IV activity using a fluorometric assay and Neuropeptide Y (NPY) protein using an EIA. Body composition was determined via a DEXA scan. Relationships were determined using regression analysis. In the second part, we tested 35 people on four separate occasions, where the participants either swished and spit or ingested a commercially available sucrose or aspartame sweetened beverage. Saliva and plasma were collected before and after each condition and were processed as described above. Blood glucose was also measured. No relationship was found between salivary DPP-IV activity or NPY and any body composition measurement. For Part 2, no change in plasma DPP-IV occurred with any of the conditions, despite an increase in blood glucose with the sucrose-beverage ingestion condition (p<0.05). However, salivary DPP-IV activity was attenuated with all conditions, except aspartame-beverage swish and spit. Salivary NPY was not altered by the conditions. The unique finding from this study was that salivary DPP-IV activity was attenuated with sucrose or aspartame beverage, but plasma DPP-IV was unchanged. This result implies that satiety may be reduced when drinking sucrose or aspartame beverages.