Abstract
Simple SummaryInsulin-regulated aminopeptidase (IRAP) is a well-known enzyme involved mainly in the regulation of the peptide hormones, oxytocin and vasopressin. However, this enzyme activity has hardly been analyzed in breast cancer patients. Additionally, the influence of both the hormonal status (pre or postmenopause) and the administration of neoadjuvant chemotherapy have rarely been studied. We show that there is a weak association between IRAP activity and the circulating levels of peptide hormones with variations depending on the hormonal status and the neoadjuvant treatment, and propose a role beyond oxytocin and vasopressin regulation that is related to the local mammary renin-angiotensin system and glucose transportation to the cells.Insulin-regulated aminopeptidase (IRAP) is the only enzyme known to cleave oxytocin and vasopressin; however, it is also the high-affinity binding site for angiotensin IV (AngIV) receptor type 4 (AT4) ligands and it is related to insulin-dependent glucose transporters through the translocation of the glucose transporter type 4 (GLUT4). Previous studies have demonstrated an association between IRAP activity and the number and size of mammary tumors in an animal model of breast cancer (BC). Also, a highly significant increase in IRAP activity has been found in BC tissue from women patients. Here, we found no changes in circulating IRAP in premenopausal (preMP) women, but it increased significantly in postmenopausal (postMP) women not treated with neoadjuvant chemotherapy (NACH). However, in women treated with NACH, IRAP activity increased in both preMP and postMP women. Two years of follow-up indicated lower levels of IRAP activity in untreated preMP women, but a return to control levels in untreated postMP women, while IRAP activity returned to control levels in women treated with NACH. Circulating oxytocin decreased in both preMP and postMP women during the follow-up period. Differences in Oxytocin appeared between preMP and postMP women treated with NACH, but not in women who were not treated with NACH. On the contrary, circulating vasopressin increased in untreated and treated preMP and postMP women, with most of the differences related to the hormonal status as well as the neoadjuvant treatment during the two year follow-up We propose that IRAP is involved in mechanisms related not only to oxytocin and/or vasopressin regulation, but also to the local mammary RAS through AngIV and its role in glucose transportation through the IRAP/GLUT4 system.
Highlights
Aminopeptidases are enzymes involved in the catabolism of peptidic hormones, which have important physiological functions and act through autocrine and/or paracrine means
In a previous work using an animal model of breast cancer (BC) induced by N-methyl-nitrosourea (NMU), we demonstrated a relationship between circulating Insulin-regulated aminopeptidase (IRAP) activity and the number and size of mammary tumors
In women not treated with neoadjuvant chemotherapy (NACH), no changes were found in IRAP specific activity in preMP women at the time of the surgery
Summary
Aminopeptidases are enzymes involved in the catabolism of peptidic hormones, which have important physiological functions and act through autocrine and/or paracrine means. Several aminopeptidases have been found to be involved in a number of breast cancer (BC) cell lines, in the animal model induced by nitrosourea and in human patients [1,2,3,4,5,6] These enzymes can be selectively modified in the affected tissue as a result of the specific microenvironment promoted by the tumoral cells. IRAP is known to be involved in other biological functions such as the presentation of antigens, the regulation of oxytocin and vasopressin levels and the translocation of the glucose transporter type 4 (GLUT4) [9,15,16,17,18]. The existence of GLUT4, including BC cells, has been shown in non-insulin-dependent tissues such as the mammary gland, and their role in cell cycle progression has been demonstrated [21,22]
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