2023 Volume 72 Issue 1 Pages 33-42
Urinary hyaline casts are the most frequently encountered type of casts and are found in small numbers in healthy individuals. Although the detection of hyaline casts in urine has recently been reported to be useful for the estimation of various pathological conditions, the mechanism of formation and components of hyaline casts are not fully understood. In this study, we investigated various in vitro conditions for hyaline cast formation and used laser microdissection to identify the constituents of hyaline casts. The number of hyaline casts was significantly increased under the following conditions: (1) acidic pH, (2) increased protein concentration, (3) concentrated urine, and (4) 24 hours of stagnation. Interestingly, the generated hyaline casts were formed as a mold. Proteins were identified by mass spectrometry in hyaline and waxy casts collected by laser microdissection. Seventy-eight different proteins were detected in both types of cast. The number of proteins significantly detected in the hyaline casts was 18, the same number of proteins detected in both casts was 41, and the number of proteins significantly detected in the waxy casts was 19. Importantly, the most predominant protein in the hyaline casts was uromodulin. On the basis of the identified protein information, the proteins required for hyaline cast composition were examined, and the addition of transferrin enabled the generation of hyaline casts similar to those found in clinical specimens. These results provide the basis for the mechanism of hyaline cast appearance and may be useful in understanding the relationship between hyaline casts and pathophysiology.
