Caloric Restriction Reverses Obesity-Induced Mammary Gland Inflammation in Mice

Obesity is a risk factor for the development of hormone receptor-positive breast cancer in post-menopausal women. Estrogen synthesis is catalyzed by aromatase. Recently, we identified an obesity-inflammation-aromatase axis in mouse models and women. In mouse models of obesity, inflammatory foci characterized by crown-like structures (CLS) consisting of dead adipocytes encircled by macrophages were found in the mammary gland (MG). CLS of the breast were found in most overweight and obese women. CLS were associated with adipocyte hypertrophy, activation of NF-κB, elevated levels of proinflammatory mediators and aromatase, and increased expression of the progesterone receptor (PR). Collectively, these findings provide a plausible explanation for the link between obesity, chronic inflammation, and post-menopausal breast cancer. Here we investigated whether caloric restriction (CR) reversed the inflammatory state and related molecular changes in the MG of obese mice. Obese ovariectomized C57BL/6J mice were subjected to 30% CR for 7 or 14 weeks. Findings in CR mice were compared with results in mice fed a high fat diet ad libitum or with control mice fed a low fat diet. CR was associated with more than a 75% decrease in mammary CLS/cm2. Reduced histological inflammation following CR was associated with decreased adipocyte diameter and MCP-1 levels, reduced NF-κB binding activity, and normalization of levels of proinflammatory mediators, aromatase and PR. In summary, obesity-related inflammation of the MG and elevated aromatase and PR levels were reversed with CR. Our results provide a rationale for determining whether weight loss can reverse breast inflammation associated with obesity in women.