1α,25-Dihydroxyvitamin D Downregulates Adipocyte Impact on Breast Cancer Cell Migration and Adipokine Release.

Background/objectives: Excess adiposity is associated with a higher risk of breast cancer metastasis and mortality. Evidence suggests that dietary vitamin D inhibits breast cancer metastasis. However, the mechanistic link between vitamin D's regulation of adipocyte metabolism and metastasis has not been previously investigated. Therefore, the purpose of these experiments was to examine the effect of the active form of vitamin D, 1α,25-dihydroxyvitamin D (1,25(OH)₂D), on adipocyte release of bioactive compounds and whether the impact on adipocytes leads to inhibition of breast cancer cell migration, an important step of metastasis.

Methods: Differentiated 3T3-L1 adipocytes were treated with 1,25(OH)₂D for two days, followed by either harvesting the adipocytes or collecting adipocyte-conditioned media without 1,25(OH)₂D. A transwell migration assay was conducted with vehicle- or 1,25(OH)₂D-conditioned media. In order to explore the mechanism underlying effects on breast cancer metastatic capability, the mRNA expression of leptin, adiponectin, insulin-like growth factor (IGF-1), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1) was measured in adipocytes following either vehicle or 1,25(OH)₂D treatment.

Results: Conditioned media from 1,25(OH)₂D-treated adipocytes inhibited the migration of metastatic MDA-MB-231 breast cancer cells compared to conditioned media from vehicle-treated adipocytes. Treatment of adipocytes with 1,25(OH)₂D decreased mRNA expression of leptin, adiponectin, IGF-1, IL-6, and MCP-1. Consistent with mRNA expression, concentrations of leptin, adiponectin, IGF-1, and IL-6 in adipocyte-conditioned media were decreased with 1,25(OH)₂D treatment, although MCP-1 remained unchanged.

Conclusions: In summary, these results suggest that 1,25(OH)₂D alters adipocyte secretions to prevent breast cancer metastasis.