Urinary Kim-1 Correlates with Interstitial Nephritis Activity in Patients with Microscopic Polyangiitis

Area of Science:

• Nephrology
• Immunology
• Rheumatology

Background:

• Microscopic polyangiitis (MPA) is a small vessel vasculitis within the anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) spectrum.
• Identifying reliable biomarkers for MPA risk stratification remains crucial for clinical practice.
• Kidney injury molecule-1 (Kim-1) is a potential biomarker for tubular damage.

Purpose of the Study:

• To investigate the potential of Kidney injury molecule-1 (Kim-1) as a biomarker in microscopic polyangiitis (MPA).
• To assess the correlation of urinary and tubular Kim-1 with disease activity and renal impairment in MPA patients.

Main Methods:

• Retrospective analysis of kidney biopsy tissues, urine, and blood samples from 52 MPA patients and 7 healthy controls.
• Assessment of global and renal disease activity using Birmingham vasculitis activity score (BVAS) and BVAS-renal (BVAS-R).
• Evaluation of correlations between urinary/tubular Kim-1, Mayo Clinic Chronicity Score (MCCS), and ANCA Kidney Risk Score (AKRiS).

Main Results:

• Urinary Kim-1 levels were significantly higher in MPA patients compared to controls.
• Urinary Kim-1 correlated with proteinuria and MCCS, while tubular Kim-1 associated with AKRiS.
• Higher tubular Kim-1 expression was linked to elevated BVAS-R, indicating renal involvement.
• Neither urinary nor tubular Kim-1 predicted MPA recurrence, unlike C-reactive protein (CRP).

Conclusions:

• Urinary Kim-1 serves as a biomarker reflecting histopathologic findings and renal impairment in MPA.
• Kim-1's utility lies in assessing chronic renal damage rather than predicting systemic disease activity or recurrence.
• Further research may elucidate Kim-1's role in MPA management and prognosis.