Increased nutrient availability in dense breast tissue of postmenopausal women in vivo

Childhood adiposity, serum metabolites and breast density in young women

BACKGROUND

Childhood adiposity is inversely associated with young adult percent dense breast volume (%DBV) and absolute dense breast volume (ADBV), which could contribute to its protective effect for breast cancer later in life. The objective of this study was to identify metabolites in childhood serum that may mediate the inverse association between childhood adiposity and young adult breast density.

METHODS

Longitudinal data from 182 female participants in the Dietary Intervention Study in Children (DISC) and the DISC 2006 (DISC06) Follow-Up Study were analyzed. Childhood adiposity was assessed by anthropometry at the DISC visit with serum available that occurred closest to menarche and expressed as a body mass index (BMI) z-score. Serum metabolites were measured by untargeted metabolomics using ultra-high-performance liquid chromatography-tandem mass spectrometry. %DBV and ADBV were measured by magnetic resonance imaging at the DISC06 visit when participants were 25-29 years old. Robust mixed effects linear regression was used to identify serum metabolites associated with childhood BMI z-scores and breast density, and the R package mediation was used to quantify mediation.

RESULTS

Of the 115 metabolites associated with BMI z-scores (FDR < 0.20), 4 were significantly associated with %DBV and 6 with ADBV before, though not after, adjustment for multiple comparisons. Mediation analysis identified 2 unnamed metabolites, X-16576 and X-24588, as potential mediators of the inverse association between childhood adiposity and dense breast volume. X-16576 mediated 14% (95% confidence interval (CI) = 0.002, 0.46; P = 0.04) of the association of childhood adiposity with %DBV and 11% (95% CI = 0.01, 0.26; P = 0.02) of its association with ADBV. X-24588 also mediated 7% (95% CI = 0.001, 0.18; P = 0.05) of the association of childhood adiposity with ADBV. None of the other metabolites examined contributed to mediation of the childhood adiposity-%DBV association, though there was some support for contributions of lysine, valine and 7-methylguanine to mediation of the inverse association of childhood adiposity with ADBV.

CONCLUSIONS

Additional large longitudinal studies are needed to identify metabolites and other biomarkers that mediate the inverse association of childhood adiposity with breast density and possibly breast cancer risk.

Platelet Activation In Situ in Breasts at High Risk of Cancer: Relationship with Mammographic Density and Estradiol

CONTEXT

High mammographic density in postmenopausal women is an independent risk factor for breast cancer by undetermined mechanisms. No preventive therapy for this risk group is available. Activated platelets release growth factors that modulate the microenvironment into a protumorigenic state. Estrogens may affect the risk of breast cancer and platelet function. Whether platelets are activated in situ in breast cancer or in normal breast tissue at high risk of breast cancer and the association to estradiol remains elusive.

OBJECTIVE

To investigate whether platelets are activated in situ in breast cancers and in dense breast tissue of postmenopausal women and explore correlations between estradiol, released platelet factors, and inflammatory proteins.

SETTING AND DESIGN

Sampling of in vivo proteins was performed using microdialysis in a total of 71 women: 10 with breast cancer, 42 healthy postmenopausal women with different breast densities, and 19 premenopausal women.

RESULTS

Our data demonstrate increased levels of coagulation factors in dense breast tissue similar to that found in breast cancers, indicating excessive platelet activation. Premenopausal breasts exhibited similar levels of coagulation factors as postmenopausal dense breasts. Out of 13 coagulations factors that were upregulated in dense breasts, 5 exhibited significant correlations with estradiol, both locally in the breast and systemically. In breast tissue, positive correlations between coagulation factors and key inflammatory proteins and matrix metalloproteinases were detected.

CONCLUSIONS

Breast density, not estradiol, is the major determinant of local platelet activation. Inactivation of platelets may be a therapeutic strategy for cancer prevention in postmenopausal women with dense breasts.

Lysine in Combination With Estradiol Promote Dissemination of Estrogen Receptor Positive Breast Cancer via Upregulation of U2AF1 and RPN2 Proteins

The majority of estrogen receptor positive (ER+) breast cancer (BC) maintain the ER at metastatic sites. Despite anti-estrogen therapy, almost 30% of ER+ BC patients relapse. Thus, new therapeutic targets for ER+ BC are needed. Amino acids (AAs) may affect the metastatic capacity by affecting inflammatory cells. Essential AAs (EAAs) cannot be produced by human cells and might therefore be targetable as therapeutics. Here we sampled extracellular EAAs in vivo by microdialysis in human BC. Mass spectrometry-based proteomics was used to identify proteins affected after EAA and estradiol (E2) exposure to BC cells. Proteins relevant for patient survival were identified, knocked down in BC cells, and metastatic capability was determined in vivo in the transgenic zebrafish model. We found that lysine was the most utilized EAA in human ER+BC in vivo. In zebrafish, lysine in presence of E2 increased neutrophil-dependent dissemination of ER+ BC cells via upregulation of U2AF1 and RPN2 proteins, which both correlated with poor prognosis of ER+ BC patients in clinical databases. Knockdown of U2AF1 and RPN2 decreased the expression of several cell-adhesion molecules resulting in diminished dissemination. Dietary lysine or its related metabolic pathways may be useful therapeutic targets in ER+ BC.

Postmenopausal Dense Breasts Maintain Premenopausal Levels of GH and Insulin-like Growth Factor Binding Proteins in Vivo

CONTEXT

Dense breast tissue is associated with 4 to 6 times higher risk of breast cancer by poorly understood mechanisms. No preventive therapy for this high-risk group is available. After menopause, breast density decreases due to involution of the mammary gland. In dense breast tissue, this process is haltered by undetermined biological actions. Growth hormone (GH) and insulin-like binding proteins (IGFBPs) play major roles in normal mammary gland development, but their roles in maintaining breast density are unknown.

OBJECTIVE

To reveal in vivo levels of GH, IGFBPs, and other pro-tumorigenic proteins in the extracellular microenvironment in breast cancer, in normal breast tissue with various breast density in postmenopausal women, and premenopausal breasts. We also sought to determine possible correlations between these determinants.

SETTING AND DESIGN

Microdialysis was used to collect extracellular in vivo proteins intratumorally from breast cancers before surgery and from normal human breast tissue from premenopausal women and postmenopausal women with mammographic dense or nondense breasts.

RESULTS

Estrogen receptor positive breast cancers exhibited increased extracellular GH (P < .01). Dense breasts of postmenopausal women exhibited similar levels of GH as premenopausal breasts and significantly higher levels than in nondense breasts (P < .001). Similar results were found for IGFBP-1, -2, -3, and -7 (P < .01) and for IGFBP-6 (P <.05). Strong positive correlations were revealed between GH and IGFBPs and pro-tumorigenic matrix metalloproteinases, urokinase-type plasminogen activator, Interleukin 6, Interleukin 8, and vascular endothelial growth factor in normal breast tissue.

CONCLUSIONS

GH pathways may be targetable for cancer prevention therapeutics in postmenopausal women with dense breast tissue.

Equal Pro-inflammatory Profiles of CCLs, CXCLs, and Matrix Metalloproteinases in the Extracellular Microenvironment In Vivo in Human Dense Breast Tissue and Breast Cancer

The inflammatory microenvironment affects breast cancer progression. Proteins that govern the inflammatory response are secreted into the extracellular space, but this compartment still needs to be characterized in human breast tissues in vivo. Dense breast tissue is a major risk factor for breast cancer by yet unknown mechanisms and no non-toxic prevention for these patients exists. Here, we used the minimal invasive technique of microdialysis for sampling of extracellular proteins in live tissues in situ in breast cancers of women before surgery and in healthy women having dense or non-dense breast tissue on mammography. Proteins were profiled using a proximity extension assay. Out of the 32 proteins assessed, 26 exhibited similar profiles in breast cancers and dense breast tissues; CCL-4, -7, -8, -11, -15, -16, -22, -23, and -25, CXCL-5, -8, -9, -16 as well as sIL-6R, IL-18, vascular endothelial growth factor, TGF-α, fibroblast growth factor 19, matrix metalloproteinase (MMP)-1, -2, -3, and urokinase-type plasminogen activator were all increased, whereas CCL-3, CX3CL1, hepatocyte growth factor, and MMP-9 were unaltered in the two tissues. CCL-19 and -24, CXCL-1 and -10, and IL-6 were increased in dense breast tissue only, whereas IL-18BP was increased in breast cancer only. Our results provide novel insights in the inflammatory microenvironment in human breast cancer in situ and define potential novel therapeutic targets. Additionally, we show previously unrecognized similarities of the pro-inflammatory microenvironment in dense breast tissue and breast cancer in vivo suggesting that anti-inflammatory breast cancer prevention trials for women with dense breast tissue may be feasible.