Serum angiotensin converting enzyme levels in patients with alpha 1-antitrypsin variants

Discovery of SERPINA3 as a candidate urinary biomarker of lupus nephritis activity

Objectives

We used an unbiased proteomics approach to identify candidate urine biomarkers (CUBMs) predictive of LN chronicity and pursued their validation in a larger cohort.

Methods

In this cross-sectional pilot study, we selected urine collected at kidney biopsy from 20 children with varying levels of LN damage (discovery cohort) and performed proteomic analysis using isobaric tags for relative and absolute quantification (iTRAQ). We identified differentially excreted proteins based on degree of LN chronicity and sought to distinguish markers exhibiting different relative expression patterns using hierarchically clustered log10-normalized relative abundance data with linked and distinct functions by biological network analyses. For each CUBM, we performed specific ELISAs on urine from a validation cohort (n = 41) and analysis of variance to detect differences between LN chronicity, with LN activity adjustment. We evaluated for CUBM expression in LN biopsies with immunohistochemistry.

Results

iTRAQ detected 112 proteins in urine from the discovery cohort, 51 quantifiable in all replicates. Simple analysis of variance revealed four differentially expressed, chronicity-correlated proteins (P-values < 0.05). Further correlation and network analyses led to selection of seven CUBMs for LN chronicity. In the validation cohort, none of the CUBMs distinguished LN chronicity degree; however, urine SERPINA3 demonstrated a moderate positive correlation with LN histological activity. Immunohistochemistry further demonstrated SERPINA3 staining in proximal tubular epithelial and endothelial cells.

Conclusion

We identified SERPINA3, a known inhibitor of neutrophil cathepsin G and angiotensin II production, as a potential urine biomarker to help quantify LN activity.

Analysis of systemic biomarkers in COPD patients

The finding that alphal-antitrypsin (AAT) deficiency, PiZZ, a well-established genetic risk factor for COPD, is related to high levels of circulating AAT polymers, prompted us to measure serum levels of such polymers and selected markers of inflammation in age- and gender-matched patients with stable COPD and control subjects with and without severe AAT deficiency, and to assess their relationship with each other and with the genetic AAT-variant. We found that COPD individuals (n= 20), independent of AAT-variant, had significantly higher serum levels of AAT and its polymers, MMP-9, sICAM-1, VEGF and sE-selectin than controls (n=30). Subjects with PiZZ COPD (n= 10) showed significantly elevated serum levels of AAT-polymers, sE-selectin and sICAM-1, while patients with PiMM COPD (n= 10) showed higher levels of MMP-9, VEGF, IL-8 and MCP-1 than controls. By using factor analysis we were able to split the analysed biomarkers into two independent components: the first containing MMP-9, MCP-1, IL-8 and VEGF and the second-AAT and its polymers and sE-selectin. The result from the binomial logistic regression showed that 95.2 percent of the control individuals and 94.7 percent of the COPD patients can be correctly classified on the basis of the measured serum biomarkers. These observations highlight the importance of the finding sets of biomolecules, which could offer new strategies for the diagnosis of COPD and may have value for monitoring progression of COPD.