ORCID
https://orcid.org/0000-0001-5446-9371
Date of Award
10-31-2023
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Biomarkers, a portmanteau of “biological markers”, are clinically relevant observations that can accurately and reproducibly indicate or predict patient outcomes. These objective measurements have vast clinical utility as they can aid clinicians with diagnoses, provide information about patient prognoses, and monitor changes in patient health statuses. While the discovery of several biomarkers are attributed to differential expression or concentration of genes or proteins within blood samples, biomarkers can be alternatively found in other bodily fluids or tissues depending on the associated condition. Recently, advances in urine proteomics have allowed for the identification of urine biomarkers that may eliminate the drawbacks associated with serum biomarkers. Identifying and evaluating urinary biomarkers has the potential to significantly increase patient comfort and accessibility to proper healthcare. To this end, our lab had previously investigated calprotectin (S100A8/A9) as a potential biomarker for tuberculosis (TB) as elevated serum concentrations were observed in patients with active forms of the disease. S100A8/A9 is a calcium-binding alarmin that mediates proinflammatory responses by binding to toll-like receptor 4 (TLR4) and the receptor for advanced glycation end products (RAGE). Comprising approximately 45% of the cytoplasmic proteins present in human neutrophils, it is a sensitive marker for neutrophil activation and has been associated with several inflammatory diseases. Severe COVID-19 cases are often characterized by cytokine storm, which is a dysregulated immune response involving the release of over 150 inflammatory cytokines. Studies published in the early period of the COVID-19 pandemic suggested that S100A8/A9 expression may be associated with cytokine storm and the formation of neutrophil subsets that were observed only in severe COVID-19 cases. Similar to our findings from initial TB studies, several non-US studies reported that S100A8/A9 serum levels were significantly elevated in patients with severe and fatal COVID-19 cases as compared to patients with mild forms of the disease. Because S100A8/A9 levels have been quantified in both serum and urine, we hypothesized that the trends observed in serum were mirrored in urine samples. In pursuit of evaluation of urine S100A8/A9 as a biomarker for COVID-19, I used protein quantification to demonstrate that urine S100A8/A9 cannot accurately indicate COVID-19 patient outcomes. In contrast, we found that serum S100A8/A9 levels mimicked results from non-US cohorts in their ability to distinguish COVID-19 disease severity. The lack of correlation between serum and urine S100A8/A9 levels suggested that previous findings of correlated S100A8/A9 values in patients with other conditions were likely disease-dependent. While the evaluation of urine S100A8/A9 as a marker for COVID-19 was unfavorable, we further delineated the utility of urine S100A8/A9 in the context of urinary tract infections (UTIs). While other studies accounted for patient UTI diagnosis as a confounding factor when determining the biomarker capacity of urine S100A8/A9 for kidney-related conditions, the utility of urine S100A8/A9 in diagnosing human UTIs was unexplored. We discovered that urine S100A8/A9 levels could predict both UTI diagnosis and clinically significant urine culture growth with a higher sensitivity than canonical markers for UTI, such as leukocyte esterase levels and white blood cell (WBC) presence. Collectively, this work highlights that S100A8/A9 is a promising target for the development of future, non-invasive diagnostic tools. In an attempt to address the challenges associated with the use of serum biomarkers, I have contributed to our understanding of the indicative and predictive capacity of S100A8/A9 in both serum and urine samples, and I have detailed a new potential utilization for urine S100A8/A9 in the context of urinary tract infections, which was previously unexplored.
Language
English (en)
Chair and Committee
Shabaana Khader
Committee Members
Gaya Amarasinghe
Recommended Citation
Mellett, Leah, "Evaluating the Utility of S100A8/A9 as a Non-Invasive Biomarker" (2023). Arts & Sciences Electronic Theses and Dissertations. 3184.
https://openscholarship.wustl.edu/art_sci_etds/3184