Age-dependent increase in serum levels of indoxyl sulphate and p-cresol sulphate is not related to their precursors: Tryptophan and tyrosine.

AIM: Retention of indoxyl sulphate and p-cresol sulphate is associated with many diseases. The aim of the present study was to examine serum levels of indoxyl sulphate and p-cresol sulphate, the dynamics of their changes according to age, and their precursors. METHODS: The study included 180 healthy individuals aged 20-90 years (n = 180), divided into subgroups by decade (n = 30 in each subgroup) and into subgroups of ≥65 years (n = 42) or <65 years (n = 138). Serum indoxyl sulphate and p-cresol sulphate, tryptophan, and tyrosine were measured using high-performance liquid chromatography-mass spectrometry. RESULTS: The 70-90 years age group had higher indoxyl sulphate than the 50-59 years age group (P = 0.033). The 70-90 years age group had higher p-cresol sulphate than the 20-29 years (P < 0.001), 30-39 years (P < 0.001), 40-49 years (P = 0.007) and 50-59 years (P = 0.001) age groups; the 60-69 years age group had higher p-cresol sulphate than the 20-29 years (P = 0.043) and 30-39 years (P = 0.011) age groups. Indoxyl sulphate and p-cresol sulphate serum levels were higher in those aged ≥65 years. Indoxyl sulphate and p-cresol sulphate serum levels correlated positively with age, but not with tryptophan and tyrosine, respectively. CONCLUSIONS: Healthy aging is associated with indoxyl sulphate and p-cresol sulphate serum level increases, which are not linked to tryptophan and tyrosine serum levels. Geriatr Gerontol Int 2017; 17: 1022-1026.