Plasma amino acid profiles are associated with biomarkers of breast cancer risk in premenopausal Japanese women

Recently, profiles of plasma amino acids have been utilized to detect diseases including breast cancer. However, there is a possibility that the amino acid status may be associated with the risk of breast cancer. We investigated the relationship of plasma levels of amino acids with levels of sex hormones and insulin-like growth factor (IGF)-1, which are relevant to the etiology of premenopausal breast cancer, in normal premenopausal women. Participants were 350 Japanese women who had regular menstrual cycles less than 40-day long. Fasting plasma samples were assayed for estradiol, testosterone, dehydroepiandrosterone sulfate, sex-hormone-binding globulin (SHBG), and IGF-1. A total of 20 amino acids in plasma were quantified by liquid chromatography-mass spectrometry. Information on lifestyle and reproductive factors was obtained using a self-administered questionnaire. The plasma arginine level was significantly inversely correlated with plasma levels of total and free estradiol and IGF-1 after adjusting for age, body mass index, and phase of the menstrual cycle. Plasma leucine and tyrosine levels were significantly positively correlated with the free testosterone level. The ratio of plasma asparagine to the total amino acids was significantly positively correlated with SHBG level. Plasma levels of some specific amino acids, such as arginine, leucine, tyrosine, and asparagine, were associated with the levels of sex hormones, SHBG, or IGF-1 in premenopausal women. However, the present cross-sectional study cannot provide a cause-effect relation. The implication of amino acids in the etiology of breast cancer needs to be addressed in future studies.