Abstract 5814: Lack of breast feeding may contribute to increased breast cancer risk by altering metabolism
Authors: Ormiston Kate , Kaul Kirti , Shinde Neelam , Zhang Allen , Bauer Morgan , Kim Hee Kyung , Ganju Ramesh K. , Majumder Sarmila , Ramaswamy Bhuvaneswari 
Published: June 2022

Abstract
Purpose: Epidemiological data links lack of breastfeeding with increased risk of breast cancer, particularly triple negative breast cancer (TNBC). The involution process is characterized by mammary tissue remodeling, including adipocyte repopulation and re-differentiation fueled by metabolic rewiring. Our mouse model mimicking short-term breast feeding that leads to abrupt involution (AI) revealed a chronic inflammatory state in the mammary gland (MG) (Basree, et al. Breast Cancer Research; 2019). As metabolic dysfunction is linked to increased BC risk, we sought to elucidate the effects of AI and gradual involution (GI) on MG energy metabolism and associated oxidative stress. In addition, we evaluated the impact of AI and GI on whole body glucose metabolism and insulin response/resistance.
Methods: FVB/n mice (8week old) were paired for breeding. At partum, dams were randomized to AI or GI cohort and standardized to 6 pups per dam. AI mice had pups removed on postpartum day 7 (d7) to mimic short-term breastfeeding. GI mice had 3 pups removed on day 28 and 31 each to mimic gradual weaning. MGs were harvested on d28, 56, and 120 postpartum. Prior to harvest, mice underwent an echoMRI and insulin tolerance test (ITT). At harvest, mice were fasted for 4 hours, and blood was collected for serum insulin measurement using Ultra-Sensitive Insulin ELISA. Lipid peroxidation (MDA) and DNA adduct formation (8-OHdG), which represent chronic oxidative stress, were measured in MG by ELISA. Whole MG RNA were subjected to affymetrix followed by gene set enrichment analyses (GSEA) and qPCR for target validation. MGs were also subjected to untargeted metabolomics analysis and Mitofuel flex assay to assess substrate dependence by Seahorse Bioanalyzer.
Results: GSEA and qPCR revealed enrichment of fatty acid oxidation (FAO) and mitochondrial oxidative phosphorylation (OXPHOS) pathways in AI MGs at d28, further validated by expression of genes (PGC-1α, Cpt-2, Srebp1c, and Chrebp). Metabolites associated with FAO were enriched in AI MGs at d28 and 56. Mitofuel flex assay indicated a significantly higher dependence on FAO in AI MGs. On d56, fasted blood glucose was significantly higher in AI mice with serum insulin and HOMA-IR trending to be higher than in GI mice. Level of 8-OHdG was elevated in AI MGs at d120. AI mice trended to be heavier, have greater body fat, and lower lean mass than GI Mice at d120. Body weight and percent body fat on d120 were positively correlated to MDA concentration in the mammary gland.
Conclusion: Our mouse models of AI and GI revealed early MG specific metabolic shift towards increased FAO and OXPHOS that persists over time in AI glands. Similarly, increased oxidative stress and its association with adiposity at d120 indicates continued effect of AI. This change in adiposity, altered systemic glucose metabolism and metabolic shift seen in AI mice may contribute to the higher risk of breast cancer.
[K.O. and K.K. are co-first authors.]
Citation Format: Kate Ormiston, Kirti Kaul, Neelam Shinde, Allen Zhang, Morgan Bauer, Hee Kyung Kim, Ramesh K. Ganju, Sarmila Majumder, Bhuvaneswari Ramaswamy. Lack of breast feeding may contribute to increased breast cancer risk by altering metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5814.