Urinary HER2, TWEAK and VCAM-1 levels are associated with new-onset proteinuria in paediatric lupus nephritis

Abstract

Objective: Lupus nephritis is a key driver of morbidity and mortality in SLE. Detecting active nephritis on a background of pre-existing renal damage is difficult, leading to potential undertreatment and accumulating injury. An unmet need is a biomarker that distinguishes active lupus nephritis, particularly important in paediatrics where minimising invasive procedures is desirable.

Methods: This was a multicentre, prospective study of 113 paediatric patients with biopsy-proven lupus nephritis. Clinical data and urine were obtained every 3-4 months and patients averaged 2 years on study with seven time points. Urine was analysed for human epidermal growth factor receptor 2 (HER2), tumour necrosis factor-like weak inducer of apoptosis and vascular cell adhesion molecule-1 (VCAM-1) by ELISA. We defined active disease as either a rise in serum creatinine ≥0.3 mg/dL from baseline or a rise in renal Systemic Lupus Erythematosus Disease Activity Index score from the previous visit. These markers were also studied in patients with acute kidney injury, juvenile idiopathic arthritis (JIA), amplified pain syndrome and healthy controls.

Results: The rate of active disease was 56% over an average of 2 years of follow-up. HER2 and VCAM-1 were significantly elevated at time points with active disease defined by increased serum creatinine compared with time points with inactive disease or patients who never flared. All three biomarkers were associated with new-onset proteinuria and VCAM-1 was elevated at time points preceding new-onset proteinuria. These biomarkers were not increased in acute kidney injury or JIA.

Conclusion: All three biomarkers were associated with new onset proteinuria and increased VCAM-1 may predict impending proteinuria. These biomarkers provide potential non-invasive measures for monitoring that may be more sensitive to impending flare than conventional measures.

Keywords: autoimmune diseases; autoimmunity; lupus nephritis.

Figure 1

Urine biomarker study. (A) The sample sizes of the clinical subsets described in the manuscript are displayed. (B) HER2, TWEAK and VCAM-1 were measured by ELISA in the entire LN cohort and three control cohorts with RF+JIA (RF+), amplified pain (Pain) and healthy donors (Control). Significance after Bonferroni correction was set at 0.0083. VCAM-1 is significantly higher in LN compared with Pain and Control. The bars represent the mean and the error bars are SDs with each dot representing a single measure. AMPS, amplified pain syndrome; Cr, creatinine; HER2, human epidermal growth factor receptor 2; LN, lupus nephritis; RF+ JIA, rheumatoid factor-positive juvenile idiopathic arthritis; R-SLEDAI, renal Systemic Lupus Erythematosus Disease Activity Index; TWEAK, tumour necrosis factor-like weak inducer of apoptosis; VCAM-1, vascular cell adhesion molecule-1.

Figure 2

Urine biomarkers analysed according to disease characteristics. (A) Each separate component of the R-SLEDAI score was analysed cross-sectionally with respect to biomarker levels. Significance after Bonferroni correction was set at 0.0125. None of the biomarkers were statistically associated with pyuria but all three were associated with the other components of the R-SLEDAI. Individual p values are shown above the bars. (B) Biomarker levels were compared from visits at the time of a rise in R-SLEDAI or serum creatinine (Cr). Significance after Bonferroni correction was set at 0.0083. The comparator groups are patients who never flared (inactive) or non-flare time points across the entire cohort. Elevated HER2 levels were associated with time points with increased serum Cr compared with time points of patients who never had a flare. VCAM-1 levels were associated with time points with increased serum Cr compared with both patients who never had a flare and patients with inactive disease at time of urine collection. Furthermore, VCAM-1 levels were elevated in time points with R-SLEDAI rise when compared with time points of patients who never had a flare. The bars represent the mean and the error bars are SDs with each dot representing a single measure. HER2, human epidermal growth factor receptor 2; R-SLEDAI, renal Systemic Lupus Erythematosus Disease Activity Index; TWEAK, tumour necrosis factor-like weak inducer of apoptosis; VCAM-1, vascular cell adhesion molecule-1.

Figure 3

New-onset proteinuria. (A) We identified patient time points that had new-onset proteinuria, defined as the first visit with proteinuria (N=53). Biomarker levels were compared from those time points versus the biomarker levels from patients who never flared and time points without proteinuria. Significance after Bonferroni correction was set at 0.0167. All three biomarkers were significantly higher in the new-onset proteinuria time points. The bars represent the mean and the error bars are SDs with each dot representing a single measure. P values are indicated where significant. (B) ROC curves were used to display sensitivity and specificity. The area under the curve (AUC) and p values are displayed under each graph. HER2, human epidermal growth factor receptor 2; ROC, receiver operating characteristic; TWEAK, tumour necrosis factor-like weak inducer of apoptosis; VCAM-1, vascular cell adhesion molecule-1.

Figure 4

Previous time point analysis of urine biomarkers. We analysed the samples prior to visits where patients had a flare defined by rise in serum creatinine, new proteinuria or a rise in R-SLEDAI. Significance after Bonferroni correction was set at 0.0083. Non-significant p values are shown in grey. All three biomarkers were increased at time points prior to a rise in R-SLEDAI. The bars represent the mean and the error bars are SDs with each dot representing a single measure. HER2, human epidermal growth factor receptor 2; R-SLEDAI, renal Systemic Lupus Erythematosus Disease Activity Index; TWEAK, tumour necrosis factor-like weak inducer of apoptosis; VCAM-1, vascular cell adhesion molecule-1.