Bone, metabolism

Bone metabolism comprises the processes of bone formation and bone resorption, the key actions by which skeletal mass, structure and quality are accrued and maintained throughout life. In the mature skeleton, anabolic and catabolic actions are mostly balanced due to the tight regulation of the activity of bone forming ( osteoblast) and bone resorbing ( osteoclast) cells through circulating osteotropic hormones and locally active cytokines. 

Bone Metabolism. Figure 1 Mechanisms of osteoclast activation. 

Bone Metabolism. Figure 2 The bone remodelling cycle. 

Bone Metabolism. Table 1 Current and future agents to modulate bone metabolism... 

Bone Metabolism. Figure 3 Chemical structure of pyrophosphate (a) and the bisphosphonates etidronate (b), clodronate (c), pamidronate (d), ibandronate (e). alendronate (f), risedronate (g), zoledronate (h). 

Bone Metabolism. Figure 4 The mevalonate pathway. Interferences by statins and N-containing bisphosphonates are shown. 

Heterotrimeric G-Proteins Adenylyl Cyclases Bone Metabolism... 

One of the cell types involved in bone metabolism. In concert with osteoblasts, their cellular counterpart, these cells maintain bone hemostasis and constant... 

Systemic regulators of osteoblast, osteocyte and osteoclast functions, and therefore of bone metabolism. The major bone-seeking hormones are parathyroid hormone (PIH), 1,25-dihydroxy vitamin D3 (calcitriol) and the various ex hormones. 

A major regulator of bone metabolism and calcium homeostasis, parathyroid hormone (PTH) is stimulated through a decrease in plasma ionised calcium and increases plasma calcium by activating osteoclasts. PTH also increases renal tubular calcium re-absorption as well as intestinal calcium absorption. Synthetic PTH (1-34) has been successfully used for the treatment of osteoporosis, where it leads to substantial increases in bone density and a 60-70% reduction in vertebral fractures. 

Many factors are involved in the regulation of bone metabolism, only a few of which will be mentioned here. Some stimulate osteoblasts (eg, parathytoid hormone and 1,25-dihydroxycholecalciferol) and others inhibit them (eg, corticosteroids). Parathyroid hormone and 1,25-dihydroxycholecalciferol also stimulate osteoclasts, whereas calcitonin and estrogens inhibit them. 

An overall osteoprotective effect is associated with soy diets, the major active component being the isoflavones although the contribution (if any) of soy protein has to be clarified. The spine, rather than the femur, appears to be the most consistently protected bone site. The average daily intake in Japanese women is around 50 mg/day and appears to be sufficient to have a long-term protective effect on the spine. In non-Asian, postmenopausal women, the demonstrated effective dose is 80-90 mg/day. In future clinical studies, investigating the effect of isoflavones on bone metabolism, larger scale, randomized, controlled, intervention trials for longer time periods (1-3 years) will be necessary with a standardized source of soy protein/isoflavones and... 

HORIUCHI T, ONOUCHI T, TAKAHASHi M, ITO H and ORIMO H (2000) Effect of soy protein on bone metabolism in postmenopausal Japanese women. Osteoporosis Int 11, 721—4. 

KHALIL D A, LUCAS E A, lUMA S, SMITH B J, PAYTON M E and ARJMANDI B H (2002) Soy prOteiu supplementation increases serum insulin-like growth factor-1 in young and old men but does not affect markers of bone metabolism. J Nutr 132, 2605-8. 

OMi N, AOi s, MURATA K and EZAWA I (1992) Evaluation of the effect of soybean milk and soybean milk peptide on bone metabolism in the rat model with bone strength in ovariectomized osteoporotic rats. JNutr Sci Vitaminol 40, 201-1E... 

RUSSELL G (2001) Introduction bone metabolism and its regulation. / . Eastell, R, Baumann, M, Hoyle, N R, Wieczorek, L Bone Markers Biochemical and Clinical Perspectives, London, Martin Dunitz Ltd, 1-26. 

UESUGi T, FUKUi Y and YAMORi Y (2002) Beneficial effects of soybean isoflavone snpplementation on bone metabolism and serum lipids in postmenopausal Japanese women a four-week study. JAm Coll Nutr 21, 97-102. 

LUCAS E A, WILD R D, HAMMOND L J, KHALIL D A, JUMA S, DAGGY B P, STOECKER B J and ARJMANDI B H (2002) Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women. J Clin Endocrinol Metab. 87 (4) 1527-32. 

Approximately 80% of patients with a GFR less than 20 to 30 mL/minute develop metabolic acidosis.38 Metabolic acidosis can increase protein catabolism and decrease albumin synthesis, which promote muscle wasting, and alter bone metabolism. Other consequences associated with metabolic acidosis in CKD include worsening cardiac disease, impaired glucose tolerance, altered growth hormone and thyroid function, and inflammation.38... 

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