2021 Volume 21 Issue 4 Pages 135-140
Plasma phosphate levels are maintained mainly by intestinal absorption, bone metabolism (bone formation and resorption), renal excretion and reabsorption, and tissue transfer to soft tissues such as liver and muscle. Plasma phosphate concentration forms a diurnal rhythm, and the mechanism of its formation is considered to be an important factor in defining the phosphate concentration during early morning fasting. The risk of death in CKD (Chronic kidney disease) and maintenance dialysis patients is known to be positively correlated with early morning fasting plasma phosphate concentration.
Recently, it was shown that the Nampt (nicotinamide phosphoribosyl transferase)/NAD (nicotinamide adenine dinucleotide) system regulates the expression levels of the sodium-dependent phosphate transporters NaPi-IIa (Npt2a), NaPi-IIc (Npt2c), and NaPi-IIb (Npt2b). This mechanism is involved in the formation of diurnal rhythms in plasma phosphate levels. In fact, the diurnal rhythm of plasma phosphate concentration is abolished in Nampt heterozygous mice.
In addition, liver-specific Nampt-deficient mice show abnormal diurnal rhythm formation, suggesting that the Nampt/NAD system may also be involved in the tissue transfer of phosphate. Further understanding of the formation of diurnal rhythms in plasma phosphate concentration is important for phosphate management in CKD and maintenance dialysis patients.
