Flaxseed and Soy Protein Isolate, Alone and in Combination, Differ in their Effect on Bone Mass, Biomechanical Strength, and Uterus in Ovariectomized Nude Mice with MCF-7 Human Breast Tumor Xenografts.

Key Findings

Combining soy protein isolate (SPI) and flaxseed (FS) may exert beneficial effects on tumors, its influence on other estrogen-sensitive tissues, such as uterus and bone, is unclear. The objective of this study was to investigate the effects of FS, alone or in combination with SPI, on both bone and other estrogen-sensitive tissues in a postmenopausal breast cancer mouse model. SPI, FS, and their combination, induced different effects on bone and uterus in a preclinical mouse model of breast cancer. While SPI induced adverse tumor stimulatory effects, it produced beneficial effects on the femur. FS, either alone or in combination with SPI, does not induce adverse effects on MCF-7 tumors, but enhances femur biomechanical strength. FS does not induce estrogenic effects on the uterus; however, when combined with SPI, uterus weight was significantly increased. Since uterus weight was the only parameter measured, the potential implications of this effect should be further investigated by analyzing other uterine histological parameters.

ABSTRACT

In our previous study, flaxseed (FS) reduced while soy protein isolate (SPI) stimulated MCF-7 breast tumor growth in ovariectomized mice. In addition, combining SPI and FS resulted in a negation of SPI-induced tumor growth. In this study, the effects of SPI, FS, and their combination were further examined on mouse bone and uterus to further ensure overall safety of the breast cancer treatments. Ovariectomized mice with established MCF-7 xenografts were fed either a basal diet (control), or a basal diet supplemented with 10% FS, 20% SPI, or SPI + FS for 25 wk.  Mouse bones were analyzed for mineral and biomechanical strength properties, and uterus weight was measured. The SPI group had a higher femur bone mineral density and biomechanical strength parameters (yield load, stiffness, and peak load) compared to control, while the FS group significantly increased femur stiffness and peak load. The SPI + FS group did not affect femur mineral, but significantly reduced whole femur area and length and increased femur yield load, stiffness, and peak load. Uterus weight was significantly increased by the SPI + FS group, while SPI alone induced an intermediate effect. In conclusion, all dietary treatments induced beneficial effects on bone in a preclinical mouse model of postmenopausal breast cancer. Although the SPI + FS and SPI groups exerted stimulatory effects on uterus weight, other histological parameters need to be measured to determine the overall safety of these breast cancer treatments on the uterus.