Osteoporosis is a debilitating skeletal side effect of androgen deprivation therapy based on gonadotropin-releasing hormone (GnRH) agonist in men. Tocotrienol from Bixa orellana (annatto) has been demonstrated to offer protection against osteoporosis by exerting anabolic effects on bone. Thus, it may prevent osteoporosis among GnRH agonist users.
This study aimed to determine the effectiveness of annatto-tocotrienol on the bone turnover markers and bone histomorphometry in a model of male osteoporosis induced by buserelin (a GnRH agonist).
Forty-six three-months-old male Sprague-Dawley rats (three months old; 300-350 g) were randomly divided into six groups. The baseline control group (n = 6) was sacrificed at the onset of the study. The normal control group (n = 8) received corn oil (the vehicle of tocotrienol) orally daily and normal saline (the vehicle of buserelin) subcutaneously daily. The buserelin control (n = 8) received corn oil orally daily and subcutaneous buserelin injection 75 μg/kg/day daily. The calcium control (n = 8) received 1% calcium in drinking water and subcutaneous buserelin injection 75 μg/kg/day. The remaining rats were treated with two different treatments, i.e., (1) oral annatto tocotrienol at 60 mg/kg/day plus subcutaneous buserelin injection 75 μg/kg/day (n = 8); (2) oral annatto tocotrienol at 100 mg/kg/day plus subcutaneous buserelin injection 75 μg/kg/day (n = 8). The rats were injected with calcein twice before being sacrificed to label the bones. The rats were euthanized, and their blood and right femur were harvested at the end of the treatment for bone turnover markers and bone histomorphometry examination.
Both serum osteocalcin and C-telopeptide of type 1 collagen were not significantly different between treated groups and buserelin control (P > 0.05). The buserelin control group had a significantly lower bone volume and higher eroded surface compared with the normal control group (P < 0.05). Both groups treated with annatto tocotrienol (60 mg/kg/day and 100 mg/kg/day) had significantly higher bone volume, trabecular thickness and osteoblast number, as well as a significantly lower single-labelled surface compared with the buserelin control (P < 0.05). Only rats treated with annatto tocotrienol 60 mg/kg/day had a significantly higher double-labelled surface compared with buserelin control (P < 0.05).
Annatto tocotrienol can prevent trabecular bone loss by increasing the mineralising surface and osteoblasts number. Thus, it has a potential role in preventing bone loss in men using GnRH agonist