Effects of food, fasting, and exercise on plasma pyrophosphate levels and ENPP1 activity in healthy adults.

BACKGROUND

Inorganic pyrophosphate (PP) is highly regulated as it plays a critical role in the regulation of physiological mineralization. Dysregulation of plasma PP is associated with skeletal hypomineralization and pathogenic mineralization in soft connective tissue, arteries, and heart valves. There is no standard approach to measuring PP, making it difficult to establish PP as a biomarker of mineralization disorders. This study aims to determine the impact of time of day, meals, or exercise on plasma PP homeostasis using a highly sensitive PPi assay.

METHODS

In this single-center trial, a clinical laboratory improvement amendment (CLIA) validated modified sulfurylase-based adenosine 5-triphosphate (ATP) assay was used to measure PP levels throughout the day in 10 healthy adults under 3 conditions; normal diet (non-fasting), fasting, and normal diet with exercise. Serum ectonucleotide pyrophosphatase/phosphodiesterase 1 activity (ENPP1; an enzyme that produces PP) was also measured to determine whether these conditions influence PP levels through ENPP1 activity.

RESULTS

There is a circadian increase in mean PP levels under fasting and non-fasting conditions between 8 am and 6 pm, followed by a rapid return to baseline overnight. A circadian increase in ENPP1 activity was also measured under fasting but was lost under non-fasting conditions. Meals increased the individual variability of PP levels when compared to the same individual fasting. PP levels and ENPP1 activity exhibited a short-term increase after intense exercise. We found PP ranges from 1465 nM to 2969 nM (mean 2164 nM) after fasting overnight. Within this range, there was lower intra-subject variability in PP, suggesting that each individual has a uniquely regulated normal PP range.

CONCLUSION

Plasma levels of PP can be reliably measured after an overnight fast and show promise as a biomarker of mineralization disorders.