Forms of copper secreted by human mammary epithelial cells in response to lactational hormones

Abstract

Mammalian milk contains ceruloplasmin, but little is known about additional forms in which copper is provided the infant by this fluid. A human mammary epithelial cell line (PMC42) with the characteristics and hormone responsiveness of normal mammary cells (Michalczyk et al, J Histochem Cytochem 56: 389, 2008) was employed to begin to address this issue. Polarized PMC42 cell monolayers with tight junctions, grown in bicameral chambers with and without lactational hormones, were supplied with 64Cu‐labeled Cu attached to purified plasma proteins (albumin and alpha‐2‐macroglobulin) on the basal side. Apical secretions were collected at various times thereafter. Ultrafiltration and size exclusion chromatography (SEC) of the secretions indicated that 10‐30% of the 64Cu was attached to 3 components in the range of 1‐2 kDa. The rest was with major and minor components of ~160 and 800 kDa, respectively. The 800 and 1‐2 kDa components increased with hormone treatment. Stable Cu components of similar sizes were detected via SEC/HPLC directly coupled to ICP‐MS, but with domination of the low molecular weight forms. Ceruloplasmin was detected in the secretions by rocket immunoelectrophoresis. The results suggest that in addition to ceruloplasmin, several other forms of copper are secreted by mammary epithelial cells into the milk. Supported by PHS Grant No. RO1 HD 46949.