Monitoring of proteinuria in phase I studies in healthy male subjects

Abstract

Objective: The quantitative measurement of urinary marker proteins may improve the sensitivity of monitoring renal function in healthy male subjects in phase I studies. Little is known about the variability of physiological proteinuria in young, healthy male subjects. Thus, the biological and analytical variability of three marker proteins, i.e. albumin, α₁-microglobulin and N-acetyl-β-d-glucosaminidase (NAG), were investigated in this population.

Methods: Seven young, healthy male subjects participated in a prospective two-way cross-over study, and 139 in a retrospective study. Albumin and α₁-microglobulin were determined by immunological methods (radial immunodiffusion and/or kinetic nephelometry), and NAG by enzyme activity in a colorimetric assay.

Results: The inter-assay precision of NAG, albumin and α₁-microglobulin is good (<15%) if automated kinetic nephelometry is applied for albumin and α₁-microglobulin determination, but less impressive (<25%) with radial immunodiffusion. The highest frequency of detectable proteinuria and highest creatinine-adjusted protein levels are found in the second morning urine voided after a night's rest. The intra-individual biological variability of NAG excretion from day to day is low (CV: 15–25%), irrespective of outpatient or inpatient settings. By contrast, albumin and α₁-microglobulin excretion can differ by a factor of 2–3 from day to day, and higher levels are predominantly found in outpatient settings. The reference ranges for young, healthy male subjects are generally lower than published in cross-sectional studies in the total healthy population.

Conclusion: These findings and established reference ranges for young, healthy male subjects may assist in the evaluation of proteinuria in clinical pharmacological phase I trials.