Salivary a-amylase exhibits antiproliferative effects in primary cell cultures of rat mammary epithelial cells and human breast cancer cells

Background: Breast cancer is one of the most diagnosed cancers in females, frequently with fatal outcome, so that new strategies for modulating cell proliferation in the mammary tissue are urgently needed. There is some, as yet inconclusive evidence that a-amylase may constitute a novel candidate for affecting cellular growth. Methods: The present investigation aimed to examine if salivary a-amylase, an enzyme well known for the metabolism of starch and recently introduced as a stress marker, is able to exert antiproliferative effects on the growth of mammary gland epithelial cells. For this purpose, primary epithelial cultures of breast tissue from two different inbred rat strains, Fischer 344 (F344) and Lewis, as well as breast tumor cells of human origin were used. Treatment with human salivary a-amylase was performed once daily for 2 days followed by cell counting (trypan blue assay) to determine alterations in cell numbers. Cell senescence after a-amylase treatment was assessed by b-galactosidase assay. Endogenous a-amylase was detected in cells from F344 and Lewis by immunofluorescence. Results: Salivary a-amylase treatment in vitro significantly decreased the proliferation of primary cells from F344 and Lewis rats in a concentration-dependent manner. Noticeably, the sensitivity towards a-amylase was significantly higher in Lewis cells with stronger impact on cell growth after 5 and 50 U/ml compared to F344 cells. An antiproliferative effect of a-amylase was also determined in mammary tumor cells of human origin, but this effect varied depending on the donor, age, and type of the cells. Conclusions: The results presented here indicate for the first time that salivary a-amylase affects cell growth in rat mammary epithelial cells and in breast tumor cells of human origin. Thus, a-amylase may be considered a novel, promising target for balancing cellular growth, which may provide an interesting tool for tumor prophylaxis and treatment.