Cathelicidin in Urinary Tract Diseases: Diagnostic, Prognostic and Therapeutic Potential of an Evolutionary Conserved Antimicrobial Protein

Despite being one of the most common infectious diseases, urinary tract infections (UTIs) still represent a challenge for clinicians to diagnose and treat, especially in the era of growing antibiotic resistance among uropathogenic bacteria. Recent studies investigating the pathophysiology of UTIs have discovered the prominent role of antimicrobial peptides in the urinary tract defense system. Cathelicidin is an evolutionary conserved antimicrobial peptide encoded by one single gene in humans. Except for being stored in neutrophil cytoplasmic granules, cathelicidin is produced by uroepithelial cells rapidly upon contact with a uropathogen, even before leukocytes invade the urinary tract. In addition to its bactericidal effect, cathelicidin acts as a chemoattractant for multiple immune cells and a potent inductor of numerous cytokine synthesis. Such a crucial role in the initial pathogenesis of a UTI makes cathelicidin a potential biomarker for an early UTI diagnosis. Indeed, multiple studies over the last two decades have proved the potential clinical utility of cathelicidin as a UTI diagnostic biomarker. Furthermore, since patients after the resolution of a UTI have been found to express a lower urinary cathelicidin level than healthy controls, decreased cathelicidin levels have been suggested as a risk factor for developing UTI recurrence. Therefore, measuring cathelicidin levels in urine might help in distinguishing patients with a higher risk for a recurrent UTI. Interestingly, except in UTIs, cathelicidin has also been evaluated in other urinary tract diseases and proposed as a biomarker for diagnosing severe vesicoureteral reflux (VUR) and for recognizing renal scar development in patients with VUR. Finally, a prominent role in UTI pathogenesis also makes cathelicidin an attractive therapeutic target for treating UTIs and, lately, different therapeutic agents up-regulating cathelicidin expression have been investigated in this matter. Therefore, the present review aims to summarize the current body of knowledge on the diagnostic, prognostic and therapeutic potential of cathelicidin in urinary tract diseases. For this purpose, three databases (Scopus, Medline and Web of Science) were extensively searched to cover all the published articles. This exhaustive review will update clinicians on the contemporary state of knowledge about the potential clinical utility of cathelicidin in urinary tract diseases and hopefully encourage further research, resulting in improvement in the current management of urinary tract diseases.