Fasting-Induced Changes in Serum Kynurenines Do Not Always Reflect Their Urinary Excretion

Area of Science:

• Metabolic research
• Physiology
• Nutritional science

Background:

• Fasting's impact on serum kynurenines (KYNs) is known, but urinary excretion effects are unclear.
• Kidney transporters suggest serum KYN changes may involve altered urinary elimination.
• Understanding KYN regulation is vital for physiological processes.

Purpose of the Study:

• To investigate the effect of an 8-day fast on serum and urinary kynurenine concentrations.
• To explore the relationship between serum and urinary kynurenine levels during fasting.

Main Methods:

• Thirteen participants completed an 8-day fasting period.
• Exercise tests were conducted at baseline and after 8 days of fasting.

Main Results:

• Fasting elevated serum 3-hydroxykynurenine (3-HK), anthranilic acid (AA), picolinic acid (PA), kynurenic acid (KYNA), and xanthurenic acid (XANA).
• Serum kynurenine (KYN) and quinolinic acid (QA) decreased; 3-hydroxyanthranilic acid (3-HAA) remained unchanged.
• Urinary KYN, 3-HK, XANA, and QA increased post-fasting, while AA and PA showed no change.

Conclusions:

• Fasting generally increases serum kynurenines, linked to enhanced urinary excretion, suggesting stimulated synthesis.
• Serum increases in AA and PA did not affect their urinary excretion.
• Decreased serum KYN and QA may be due to enhanced urinary excretion.