Pro-osteogenic effects of green Rooibos (Aspalathus linearis) against different dietary backgrounds in male Wistar rats

Previous in vitro studies have demonstrated direct effects of Rooibos (Aspalathus linearis) on bone cell populations, notably osteoblasts and osteoclasts, but in vivo evidence of Rooibos effects on bone remain scant. Here, we compared the effects of a green (minimally oxidized) Rooibos extract (GRT) on the femora of male Wistar rats, against the background of a medium-fat/high-sugar (MF/HS) and a high-fat/high-fructose (HF/Fr) diet. Male Wistar rats were maintained for 17 weeks on one of three diets: control (CON), MF/HS (OB1) or HF/Fr (OB2) (n = 24 each). From weeks 11-17, n = 12 animals in each group received oral GRT supplementation (60 mg/kg body weight daily). Femoral bone mineral content and density (BMC, BMD) were analysed by densitometry; cortical and cancellous bone microarchitecture was assessed using micro-computed tomography (μCT); and osteoblast (N.Ob), osteoclast (N.Oc), adipocyte (N.Ad) and chondrocyte numbers (N.Ch) were quantified histomorphometrically. GRT supplementation did not affect femur weight, BMC or BMD, but improved trabecular measurements were observed in the CON-GRT group, compared to all other groups. GRT increased N.Ob/mm² and decreased N.Oc/mm² in the CON and OB2 dietary groups. Notably, GRT reversed the OB2 diet-associated increase in N.Oc/mm² in both cortical and cancellous bone. Although GRT had no effect on serum malondialdehyde (MDA) levels as a measure of systemic oxidative stress status, serum MDA levels were nevertheless positively correlated with cortical and cancellous N.Oc/mm² and negatively correlated with cortical N.Ob/mm². Overall, GRT supplementation had pro-osteogenic and anti-osteoclastogenic effects in vivo, indicating that green Rooibos should be further explored as a bone-supporting nutraceutical.