The mammary gland undergoes extensive remodeling during pregnancy and lactation to mature into a milk‐secretory organ. This remodeling is accompanied by a series of alterations in gene expression that are fuelled by hormonal changes facilitating maturation of epithelial cells. Insulin, supplied by the maternal circulation, is thought to play a key role in this process. In this study, we examined whether mammary cells endogenously synthesize insulin during lactation. First, we stained rare specimens of human lactating breast tissue for insulin and found that some, but not all, mammary epithelial cells were positive for insulin. We subsequently confirmed this finding with FACS. We then detected the transcript for insulin in mammary cells accessed via freshly expressed breastmilk. Transcript levels were highly variable among the breastmilk samples tested, and were significantly higher than in mammary cells accessed from the resting breast (P<0.05). Insulin expression in breastmilk cells correlated with expression of various stem cell genes, such as ESRRB, and appeared to be associated with the stage of lactation. We have for the first time confirmed that the insulin in breastmilk is derived from both the pancreatic beta cells and mammary cells of the lactating epithelium. Furthermore, mammary‐derived insulin may provide developmental signals within the mammary gland as well as contribute to breastmilk insulin.

Mammary stem cells (MaSCs) are responsible for the normal expansion of the breast during pregnancy/lactation. MaSCs are also primary targets of malignant transformation, giving rise to invasive breast carcinomas, a subset of which display lactating features. We have recently reported expression of OCT4 and associated embryonic stem cell (ESC) genes in the normal lactating breast and breastmilk stem cells (hBSCs). This prompted us to examine OCT4 expression in breast cancers with lactating features and to compare it with that observed during normal lactation. Minimal OCT4 expression was found in the normal resting breast, whereas this significantly increased in the normal lactating breast. Further increase was found in breast tumours with lactating features. Comparison of normal hBSCs with OCT4‐overexpressing tumorigenic breast cell lines (OTBCs) showed that OTBCs had unbalanced expression of ESC genes. Similar to hBSCs, OTBCs differentiated into functional lactocytes synthesising milk proteins both in vitro and in vivo. These findings highlight ESC genes as potential regulators of the normal remodelling of the breast towards a milk‐secretory organ and of aberrant breast cell proliferation upon deregulation of their expression, suggesting a role in both normal lactation and breast oncogenesis.Grant Funding Source: Women and Infants Research Foundation; and Medela AG (Switzerland)

During pregnancy and lactation, mammary stem cells remodel the breast into a milk‐secretory organ by proliferating and subsequently differentiating into both myoepithelial cells and lactocytes. Thus, we reasoned that the lactating gland, which is the fully mature organ, can offer a more comprehensive view of the mammary cellular hierarchy and dynamics than the resting gland. To non‐invasively access cells from the human lactating breast, we used freshly expressed breastmilk from which cells were isolated and characterized ex vivo for expression of markers of various lineages and differentiation stages. These included markers of pluripotent and multipotent stem cells, epithelial and mammary‐specific markers, hematopoietic and mesenchymal markers. Rare specimens of human lactating breast tissues were used to examine the origin of the different cell types identified in breastmilk. The ex vivo and in situ analyses were coupled by in vitro studies, which showed that along with the more differentiated cells, breastmilk contains progenitor cells and stem cells, some of which display pluripotency. These findings reveal a novel cellular hierarchy in breastmilk, characteristic of the lactating breast. Importantly, the presence of stem cells in breastmilk raises the question of the role of these cells for the breastfed infant.Grant Funding Source: Women and Infants Research Foundation; Medela AG

BACKGROUND Nipple pain and insufficient milk supply are major causes of early weaning. We have found that persistent nipple pain was associated with strong infant sucking vacuums during breastfeeding. Several studies indicate that nipple pain and abnormal infant sucking have the potential to reduce milk transfer. We aimed to determine whether women with persistent nipple pain had low milk supply. SUBJECTS AND METHODS The 24-hour milk production and feeding characteristics of mothers with persistent nipple pain (n=21) were compared with those mothers without nipple pain (n=21). Milk productions were measured by test-weighing the infant before and after every feed from each breast over a 24-26-hour period. Comparisons were made using Student's t tests and linear mixed models as appropriate. RESULTS Lower milk productions were associated with longer meal durations for mothers with pain. There were no significant differences in the average 24-hour milk production or any feeding characteristics between the groups. However, four women with persistent nipple pain had milk production levels below 500 mL/day. CONCLUSIONS The majority of breastfeeding women experiencing persistent nipple pain were able to achieve normal milk production levels. Feeding duration and frequency were similar to those of women not experiencing pain. However, longer meal durations in the pain group were associated with lower levels of milk production. Further investigation is necessary to identify mothers most affected by maternal nipple pain.

Lactating breasts can increase their capacity to produce milk to meet the demand of the infants. The breast milk storage capacity (SC) is related to milk production (MP) in term mothers in established lactation. This study investigates the SC and MP in early lactation of preterm and term mothers.Nineteen breast expressing preterm and sixteen breastfeeding mothers collected milk samples and measured their milk production by either weighing the bottle with an electronic kitchen scale or the baby with BabyWeigh scales (Medela AG) at home before and after each breastfeed or breast expression over a 24‐h period between days 10 and 43 postpartum. The 24‐h MP and SC were calculated (Kent et al., 2003). 24‐h Milk production (ml) (mean±SD) Breast milk storage capacity (ml) (mean±SD) Left Right Left Right Preterm 398 ± 182 388 ± 198 142 ± 56 133 ± 68 Term 382 ± 142 431 ± 122 170 ± 66 174 ± 44 Mean MP and SC were not significantly different between breasts or between preterm and term mothers.The SC of both preterm and term mothers was positively related (p=0.0001) to the MP of their breasts.Despite premature delivery, SC and MP of preterm mothers’ breasts can reach to similar level as the term mothers’ breasts.Research Support: Medela AG, Switzerland.