α-Klotho is unstable in human urine

Area of Science:

• Biochemistry
• Clinical Chemistry
• Nephrology

Background:

• Alpha-Klotho (α-Klotho) is recognized as a significant biomarker in kidney and cardiovascular diseases.
• Urinary α-Klotho measurement is increasingly reported due to its primary expression in renal tissue.
• The reliability of urinary α-Klotho quantification remains unaddressed, necessitating investigation into its stability in urine.

Purpose of the Study:

• To investigate the stability of α-Klotho in fresh catheter and voided urine samples.
• To assess the impact of different storage conditions and additives on urinary α-Klotho integrity.
• To provide recommendations for reliable measurement of urinary α-Klotho.

Main Methods:

• Collected fresh catheter and voided urine samples.
• Measured α-Klotho concentrations under various conditions: short-term storage at 37°C, long-term storage at -20°C and -80°C, and after freeze-thaw cycles.
• Assessed the effect of protease inhibitors and albumin on α-Klotho stability.

Main Results:

• Storage of catheter urine at 37°C for 3 hours caused an 82% decrease in α-Klotho.
• Compared to fresh voided urine, α-Klotho decreased by 45% at -80°C and 82% at -20°C.
• An additional freeze-thaw cycle further reduced α-Klotho levels; protease inhibitors and albumin offered partial protection against degradation.

Conclusions:

• Urinary α-Klotho is highly unstable and susceptible to degradation under common laboratory conditions.
• Significant concentration decreases occur with short-term incubation at body temperature and prolonged cold storage.
• Future studies must detail sample handling and conservation methods and validate measurement reliability to ensure accurate urinary α-Klotho biomarker assessment.