Ruminants can recycle nitrogen (N) and phosphorus (P), which are essential for vital body processes. Reduced N- and P-intake in ruminants is desirable for economic and ecologic reasons. Simultaneous modulation of mineral homoeostasis and bone metabolism occurs in young goats. This study aimed to investigate potential effects of dietary N- and/or P-restriction on molecular changes in bone metabolism. The twenty-eight young male goats were fed a control diet, an N-reduced diet, a P-reduced diet or a combined N- and P-reduced diet for 6–8 weeks. The N-restricted goats had lower plasma Ca concentration and higher plasma osteocalcin (OC) and CrossLaps concentrations. The P-restricted goats had reduced plasma inorganic phosphate (Pi) concentrations and increased plasma Ca concentrations. Due to the initiation of a signalling pathway that inhibits the fibroblast growth factor 23 (FGF23) expression, this was lower with P-restriction. Consequently, lower Pi concentrations were the main factor influencing the reduction in FGF23. The changes in mineral homoeostasis associated with P-restriction led to a reduction in OC, bone mineral content and mineral density. Simultaneously, bone resorption potentially increased with P-restriction as indicated by an increased receptor activator of NF-κB ligand/osteoprotegerin (OPG) ratio and an increase in OPG mRNA expression. Additionally, the increased mRNA expression of the calcitonin receptor during P-restriction points to a higher number of osteoclasts. This study demonstrates an impairment of bone remodelling processes in young goats by N- or P-restriction. With P-restriction, bone mineralisation rate was potentially reduced and bone quality impaired, while with N-restriction, bone remodelling increased.

Oestrogen and n-3 PUFA, especially EPA and DHA, have been reported to have beneficial effects on bone loss. Thus, the purpose of the present study was to investigate the synergistic bone-protective mechanism of combined treatments of EPA+DHA supplementation and oestrogen injection in ovariectomised rats. Rats were fed a modified American Institute of Nutrition-93G diet with 0 %, 1 % or 2 % n-3 PUFA (EPA+DHA) relative to the total energy intake for 12 weeks. Rats were surgically ovariectomised at week 8, and after a 1-week recovery period rats were injected with either 17β-oestradiol-3-benzoate (E2) or maize oil for the last 3 weeks. Combined use of n-3 PUFA and E2 synergistically increased femoral cortical bone volume, bone mineral content and the bone expression of runt-related transcription factor 2 (RUNX2), but decreased the bone expression of IL-1β. Both n-3 PUFA and E2 decreased the bone expressions of IL-7, TNF-α and PPAR-γ, and increased the bone expression of oestrogen receptor-α. n-3 PUFA in the presence of E2 and E2 alone significantly decreased the bone expressions of IL-1β and IL-6 and increased the bone expression of RUNX2. E2 significantly decreased the serum levels of bone turnover markers and the bone expression of receptor activator of NF-κB ligand, but decreased the bone expression of osteoprotegerin. The combined use of n-3 PUFA and E2 exerted synergistic bone-protective efficacy through up-regulation of RUNX2, an essential transcription factor for bone formation, as well as the suppression of bone-resorbing cytokine IL-1β.

Although several studies have confirmed the bone-protective properties of dried plum, its exact mechanisms of action remain unclear. Recent research has shown that osteocytes may control bone formation via the production of sclerostin and bone resorption via the receptor activator of NF-κB ligand (RANKL) and its inhibitor osteoprotegerin (OPG). To investigate the mechanism of action of dried plum in reversing bone loss, we measured serum levels of RANKL, OPG and sclerostin in osteopenic postmenopausal women (n 160). Participants were randomly assigned to the treatment group of either 100 g dried plum/d or 75 g dried apple/d (comparative control) for 1 year. All participants received 500 mg Ca plus 400 IU (10 μg) vitamin D daily. Bone mineral densities (BMD) of the lumbar spine, forearm, hip and whole body were assessed at baseline and at the end of the study using dual-energy X-ray absorptiometry. Blood samples were collected at baseline and after 12 months to assess bone biomarkers. Dried plum significantly increased the BMD of the ulna and spine in comparison with the control group. In comparison with corresponding baseline values, dried plum increased the RANKL levels by only +1·99 v. +18·33 % and increased the OPG levels by +4·87 v. − 2·15 % in the control group. Serum sclerostin levels were reduced by − 1·12 % in the dried plum group v. +3·78 % in the control group. Although percentage changes did not reach statistical significance (P≤ 0·05), these preliminary data may indicate that the positive effects of dried plum on bone are in part due to the suppression of RANKL production, the promotion of OPG and the inhibition of sclerostin.