Origin and Fate of Erythropoietin in Human Milk

Abstract

Erythropoietin (Epo) is a normal constituent of human milk, but the origin and fate of this cytokine in milk are not known. Regarding its origin, we hypothesized that cells of the mammary gland secrete Epo into milk actively and, therefore, that concentrations in milk do not correlate with concentrations in serum. Regarding its fate, we hypothesized that Epo concentrations in milk change with time postpartum and that Epo in milk is protected from digestion in the neonatal gastrointestinal tract. To address these issues, we measured Epo concentrations in 103 milk samples (ELISA), 55 of which were paired with serum. Mammary duct epithelial cells were evaluated as a source of Epo by breast tissue immunohistochemistry and by cell culture. Circulating and milk Epo were compared by Western analysis to detect size differences, possibly reflecting differences in processing. Epo stability in simulated conditions of digestion was evaluated. We observed that milk Epo concentrations increase as a function of duration of breast-feeding and have a negative correlation with serum Epo or milk protein concentration. Mammary duct epithelial cells from breast biopsies of lactating women had marked immunoreactivity to Epo, but such activity was minimal to absent in nonlactating breast tissue. Further evidence that mammary duct epithelia produce Epo was obtained by observing Epo mRNA and protein expression in cultured human mammary epithelial cells. The molecular size of Epo in milk and serum is identical. Recombinant Epo added to human milk or commercial infant formulas was relatively stable in conditions that simulate gastric and small intestinal conditions of newborn infants; however, recombinant Epo added to D 5 W was not protected from digestion. We conclude that Epo concentrations in milk increase as a function of the duration of breast feeding, that Epo is actively secreted into human milk by mammary duct epithelia, and that the Epo within milk is largely protected from digestion. Abbreviations Epo, erythropoietin Epo-R, erythropoietin receptors GI, gastrointestinal HMEC, human mammary epithelial cells rEpo, recombinant erythropoietin Significant Epo concentrations have been measured in human milk (1), but the origin and fate of Epo in milk are not known. Specifically, it is not known whether Epo is secreted actively or passively into milk, whether any Epo-producing cells exist in breast tissue, whether maternal serum Epo concentrations correlate with milk Epo concentrations, or whether milk Epo is processed differently from circulating Epo, resulting in a difference in glycosylation. In addition, it is not known whether Epo concentrates in a particular partition (fore, mid, or hind milk) or phase (aqueous versus lipid) of milk. No information is available regarding the stability of rEpo added to commercially available infant formulas or whether routine storage conditions (freeze/thaw) or pasteurization procedures (heating) degrade Epo.A physiologic role for enteral Epo is likely, as Epo-R are present on mucosal cells of the ...

Functional Significance of Erythropoietin Receptor Expression in Breast Cancer

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“…More recently, estrogen-dependent EPO production was demonstrated in the female reproductive tract, specifically in the uterus (Yasuda et al, 1998) and oviduct (Masuda et al, 2000). Another study reported EPO expression in lactating breast (Juul et al, 2000). In our studies investigating nonhematopoietic functions of EpoR signaling, we asked whether breast cancer cells express EPO protein.…”

Erythropoietin and Its Receptor in Breast Cancer: Correlation with Steroid Receptors and Outcome

“…In concordance, vessels are always positive in EPOR immunostaining. It is interesting that, in other types of breast hyperplasia (lactation), EPO is also expressed in breast epithelial cells and secreted in milk (54).…”

Prognostic significance of erythropoietin expression in human endometrial carcinoma

“…The specificity of the Epo and EpoR antibodies has been confirmed in previous reports. 5,7,11 In addition, the specificity of EpoR and Epo immunoreactivity also was evaluated using the antibody absorption test. For example, the primary antibody was preincubated with blocking peptide for EpoR (Santa Cruz Biotechnologies) or rHuEpo (R & D Systems, Minneapolis, MN) (10:1 peptide-to-antibody ratio), which resulted in the complete elimination of immunohistochemical staining.…”

“…However, recently, other sites of Epo production have been reported, including brain astrocytes, 4 breast epithelial cells, [5][6][7] and human female reproductive organs, including the uterus. 8,9 EpoR is expressed by a variety of cell types as well, including endothelial cells, 10 neurons, 11 mammary epithelial cells, [5][6][7] and human endometrial cells, 9 suggesting a wider biologic role for Epo signaling unrelated to erythropoiesis. Epo also stimulates proliferation and migration of human endothelial cells 10 and promotes angiogenesis.…”