Vitamin D and other extracellular factors in the control of growth

Effects of two novel bisphosphonates on bone cells in vitro

Bisphosphonates are now widely used in the treatment of bone diseases, particularly where there is uncontrolled bone resorption, as they are known to be potent inhibitors of osteoclasis. It is still unclear whether the bisphosphonates act by inhibiting osteoclast maturation or by blocking the mechanism of bone resorption, and little is known of their effects on osteoblasts. Recent studies with 3-amino-1, hydroxypropylidene-1,1-bisphosphonic acid (APD) in the treatment of osteolytic metastases in breast cancer have suggested that APD may affect osteoblasts directly. We have now investigated the effects of two novel bisphosphonates, CGP 47072 and CGP 42446A on osteoclastogenesis in fetal rat calvariae cultured on collagen gels and on human osteoblasts (hOB) cultured as explants from bone taken from patients at surgery. We also compared the action of these new bisphosphonates with that of APD, which at concentrations of 2.5 x 10(-6) M to 2.5 x 10(-10) M inhibited osteoclast recruitment, even when this was stimulated by conditioned medium from MCF7 breast cancer cells. This bisphosphonate was particularly potent if cultured with calvaria taken at 19 days gestation, when more immature osteoclast precursors are present. If calvariae from 20 days gestation were used, which contain more mature cells, it produced less inhibition. In contrast, CGP 42446A (2.5 x 10(-6) M to 2.5 x 10(-8) M) was more effective in inhibiting osteoclast maturation in calvariae from 20 days gestation than in those from 19 days. CGP 47072 had a similar pattern of effects but was less potent than either of the other two compounds. APD or CGP 42446A at 10(-5) M significantly inhibited hOB numbers and DNA synthesis, but lower concentrations had little effect. CGP 47072 did not inhibit human osteoblast replication. It is unlikely that these effects are due to calcium chelation, as none of these compounds mimicked results obtained with EDTA, which was effective only at 2.5 x 10(-6) M in reducing osteoclast size and 10(-4) M in human osteoblast cultures. These results demonstrate that all three bisphosphonates are able to inhibit osteoclast formation at low concentrations. APD may be able to influence less mature osteoclast precursors and CGP 42446A and CGP 47072 may exert their effects on the fusion of more mature precursor cells on the bone surface. At these concentrations, however, there is little or no effect on osteoblasts.

Role of bone matrix in osteoclast recruitment in cultured fetal rat calvariae

In cultured 19 day fetal rat calvaria, osteoclasts first appear after 48 h, more rapidly than with other cultured embryonic long bone rudiments. This may be because the calvarial osteoclast precursors are more differentiated or intramembraneous bone is a more powerful stimulus for osteoclast maturation than endochondral bone. To investigate this further, 19 day calvariae were stripped of their endocranial membranes, devoiding them of osteoclast precursors, and cocultured with the membranes or with other sources of these cells, such as bone marrow, fetal liver, spleen, and blood. There was similar recruitment of mature osteoclasts onto the surface of the "stripped" calvariae from the endocranial membranes and from the hematopoietic tissues after 48 h culture. Intact 19 day fetal calvariae were cultured with human recombinant granulocyte-macrophage colony-stimulating factor (hrGM-CSF) or with 1,25-dihydroxyvitamin D3, [1,25-(OH)2D3], each thought to influence different stages of osteoclast maturation. They stimulated osteoclast recruitment, although 1,25-(OH)2D3 was effective only in the first 24 h of culture. They also increased osteoclast recruitment from fetal liver onto stripped calvariae. When intact bones were cultured with hrGM-CSF and 1,25-(OH)2D3 together, osteoclast number decreased but their area increased. Calvariae therefore appear to contain osteoclast precursors at earlier (GM-CSF-sensitive) and later [1,25-(OH)2D3-sensitive] stages. As recruitment onto stripped calvariae was similar whichever source of precursors was used, it is likely that calvarial bone matrix is an important influence on rapid osteoclast maturation in these bones in vitro.

Fat-soluble vitamin nutrition for dairy cattle

The need for supplementation of dairy cow diets with fat-soluble vitamins depends on the amount of vitamins naturally present in the diet, the availability of dietary vitamins, and the vitamin utilization rate of the animal. Fresh forage contains ample amounts of the vitamin A precursor beta-carotene as well as vitamin E. Irrespective of the dietary amount, however, the availability of vitamins A, D, and E, as well as beta-carotene, can be adversely influenced by poor fat digestion, as commonly occurs due to enteric disease in young calves. In addition, high-grain diets appear to increase the amount of ruminal vitamin destruction and may thus increase vitamin requirements. The vitamin utilization rate may be increased by inflammation as well as dietary and environmental factors. The factors influencing vitamin availability and utilization rate should be considered when formulating rations. Because the vitamin requirement is variable, blood concentrations of vitamins should be monitored when conditions such as poor fertility, weak calves, and poor immune response are present.