Chewing Behavior Attenuates the Tumor Progression-Enhancing Effects of Psychological Stress in a Breast Cancer Model Mouse

Abstract

We examined whether chewing behavior affects the tumor progression-enhancing impact of psychological stress. Human breast cancer cell line (MDA-MB-231) cells were inoculated into the mammary fat pads of athymic nude mice. The mice were assigned randomly to control, stress, and stress+chewing groups. Psychological stress was created by keeping mice in a transparent restraint cylinder for 45 min, three times a day, for 35 days after cell inoculation. Animals in the stress+chewing group were provided with a wooden stick for chewing on during the psychological stress period. Chewing behavior remarkably inhibited the tumor growth accelerated by the psychological stress. Immunohistochemical and Western blot findings revealed that chewing behavior during psychological stress markedly suppressed tumor angiogenesis and cell proliferation. In addition, chewing behavior decreased serum glucocorticoid levels and expressions of glucocorticoid and β2-adrenergic receptors in tumors. Chewing behavior decreased expressions of inducible nitric oxide synthase and 4-hydroxynonenal, and increased expression of superoxide dismutase 2 in tumors. Our findings suggest that chewing behavior could ameliorate the enhancing effects of psychological stress on the progression of breast cancer, at least partially, through modulating stress hormones and their receptors, and the subsequent signaling pathways involving reactive oxygen and nitrogen species.

Chewing Behavior Attenuates Lung-Metastasis-Promoting Effects of Chronic Stress in Breast-Cancer Lung-Metastasis Model Mice

“…Cells were maintained in a humidified incubator containing 5% CO 2 at 37 °C, and cultured with the Dulbecco’s modified Eagle’s medium, containing 10% fetal bovine serum. The antibiotics, 1% penicillin and streptomycin, were added to prevent bacterial contamination [ 24 ].…”

“…The restraint and chewing-procedure was performed as previously described [ 25 ]. Animals in the stress and stress-with-chewing groups were placed in a transparent tube (inner diameter: 3.5 cm), in which the mice were able to move back and forth but not turn around, as previously reported [ 24 ]. Animals were placed in the tube for 45 min, 3 times a day for 7 weeks.…”

“…The serum was obtained by centrifugation of the blood sample at 3000 rpm for 15 min at 4 °C. The corticosterone level in the serum was measured using an enzyme-linked immunosorbent assay kit (Assaypro, St. Charles, MO, USA), following the manufacturer’s instructions [ 24 ].…”

“…To determine the percentage of GR- and β2AR-positive cells in the metastatic nodules, 5 sections per animal ( n = 5) and 5 fields per section were randomly selected for evaluation. All measurements were conducted in a double-blind procedure, as previously reported [ 24 ].…”

“…Chewing behavior or active mastication could alleviate psychological-stress response [ 21 , 22 , 23 ]. We recently reported that chewing behavior can alleviate the promoting effects of chronic stress on the development and progression of breast cancer in model mice [ 24 ]. It is important to examine the impacts of chewing behavior on lung metastasis of breast-cancer cells under chronic stress conditions.…”