Neutrophil gelatinase-associated lipocalin (NGAL) and matrix metalloproteinases (MMPs) as biomarkers of bladder cancer development and progression

Neutrophil gelatinase-associated lipocalin (NGAL), also called lipocalin-2, is a secreted protein belonging to the lipocalin family proteins and actively participates into the proliferation, differentiation, and development of human tissues, including tumours. It positively modulates the activity of the matrix metalloproteinases-9 (MMP-9) that are involved in the enzymatic remodelling of the extracellular matrix. MMP-9 regulates the degradation of extracellular matrix in processes such as angiogenesis, tumour growth, and metastasis. By forming the NGAL/MMP-9 complex, NGAL protects MMP-9 from proteolytic degradation, a fundamental mechanism in controlling the activity of the proteins, and enhances its enzymatic activities. As a secreted protein, NGAL is detectable in many biologic fluids, including urine, where several neoplastic cells and other tumor microenvironmental factors can be directly released from the cancer. Our in silico analysis suggested an active role of NGAL in tumour development of several cancer types. Validation of these findings is here described in bladder cancer as a good tumor model in which investigate the role of this protein because urine is in direct contact with the primary tumor. On these bases, the release of NGAL in both urine and serum samples from 89 bladder cancer patients was measured. Further investigations, aimed to emphasize the role of NGAL in cancer, were performed by analysing MMP-9 and NGAL/MMP-9 complex levels in the same subset of bladder cancer patients. Control experiments were performed in 119 cancer-free controls, previously enrolled in a case-control study. Urinary concentrations were standardized on creatinine level. The performance of these proteins as cancer biomarkers was evaluated through the receiver operating characteristic (ROC) analysis. In conclusion, the present study deepens the knowledge of the molecular mechanisms sustaining NGAL expression in tumor cells and its effects on cancer metastatic behaviour. Furthermore, NGAL/MMP-9 pathway is associated with an aggressive phenotype of transitional cell carcinoma of the bladder (TCC). The elevated negative predictive value of MMP-9 and NGAL/MMP-9 complex make them candidate markers of exclusion test for TCC. These findings suggest that these proteins may be integrated in the surveillance of bladder cancer, thus improving patients complaints and diminishing their discomfort.