Red Rooibos Tea Stimulates Osteoblast Mineralization in a Dose-Dependent Manner

Abstract

Most studies show a positive association between higher tea intake and bone mineral density (BMD), while associations with fracture are inconclusive. Although a few studies have investigated the potential effects of rooibos tea on the bone cell metabolism, only 1 or 2 doses were tested or specific flavonoids were evaluated in isolation. A dose-response study is needed to comprehensively identify whether a level that modulates bone cell activity is associated with dietary or supplemental levels of red rooibos (RR) tea. We investigated if RR tea stimulates mineralization in a dose-dependent manner. Mineralization was induced in Saos-2 cells in the presence of RR tea (0.1–10 µg/mL of polyphenols) or control (dH2O) for 5 days. Cell activity, mRNA, protein expression and activity of key regulators of mineralization were measured. A positive dose-dependent relationship was observed between RR tea concentration and mineralization accompanied with similar trends in cell activity. With high concentrations of tea, protein expression of enzymes directly regulating mineralization (ALP and NPP1) were unchanged but ALP activity was significantly elevated. Osteopontin (OPN) was significantly downregulated midway through mineralization while sclerostin (SOST) was upregulated in response to higher concentrations of RR tea. In conclusion, RR tea stimulated osteoblast mineralization in a dose-dependent manner and were accompanied with downregulation of OPN, increased ALP activity, and increased cell activity.

Black Tea Exhibits a Dose-Dependent Response in Saos-2 Cell Mineralization

“…Cellular viability was measured through cellular activity using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay after 24 and 48 h of cell exposure to BT (0.1, 0.5, 0.75, 1, 2, 5, or 10 μ g GAE/mL) or control vehicle. 17 , 18 After 24 h, Saos-2 cells displayed a significantly higher cellular activity ( P < .05) at concentrations 2–10 μ g GAE/mL. There was a dose-dependent response of BT doses at 24 h (CON, 0.1, 0.5, 0.75, 1, 2, 5, 10 μ g GAE/mL).…”

“…Expression of proteins of interest (alkaline phosphatase [ALP], osteopontin [OPN], ectonucleotide pyrophosphatase/ phosphodiesterase-1 [NPP1]) was determined at day 3 of mineralization through immunoblotting using a previously established protocol. 17 was 1:10000 (ab205718) in 5% BSA/TBST (ALP and NPP1) or 5% milk/TBST (OPN) (Abcam, Cambridge, UK). Protein signals were detected with the ChemiDoc Imaging System (Bio-Rad, Mississauga, ON, Canada) and densitometry analysis was performed using Image Studio Lite software (LICOR Biosciences, Lincoln, NE, USA).…”

“…Expression of proteins of interest (alkaline phosphatase [ALP], osteopontin [OPN], ectonucleotide pyrophosphatase/phosphodiesterase-1 [NPP1]) was determined at day 3 of mineralization through immunoblotting using a previously established protocol. 17 Differences in the protocol included use of either a 0.2 μ m polyvinylidene difluoride membrane (ALP and NPP1) or nitrocellulose membrane (OPN). Primary antibodies included ALP: 1:1000 (ab108337), 5% BSA/TBST; NPP1: 1:1000 (ab217368), 5% BSA/TBST; OPN: 1:1000 (ab33046), and 5% milk/TBST.…”

Black and Green Tea as Well as Specialty Teas Increase Osteoblast Mineralization with Varying Effectiveness

“…The effects of tea and its specific polyphenols on both osteoblasts and osteoclasts have been studied using cell models. [11][12][13][14][15][16][17][18][19] The majority of studies using osteoblasts have studied the effects of green or black teas and have consistently shown increases in mineralization in response to tea. More specifically black, green, and rooibos (red and green) teas have been shown to increase mineralization at concentrations likely attainable through diet.…”

“…More specifically black, green, and rooibos (red and green) teas have been shown to increase mineralization at concentrations likely attainable through diet. [11][12][13] As well, individual polyphenols and extracts derived from black, green, and rooibos teas have been studied and demonstrate a capacity to increase mineralization; however, the concentrations required to demonstrate these effects are usually at a level that would require supplementation. [14][15][16] While studies in osteoclasts are limited, previously published studies have shown that black, green, or green rooibos teas elicit a decrease in activity.…”