Effect of ethane-1-hydroxy-1,1-diphosphonate (EHDP) administration on duodenal calcium transport

Effects of ethane-1-hydroxy-1,1-diphosphonate (EHDP) upon the kinetics of bone resorption and bone formation at the whole bone level in prelabelled chicks

Chicks chronically prelabelled with 45Ca, 3H-tetracycline, and 3H-proline were used to measure the weekly effect of EHDP (5 mg P/kg for 28 days) on bone turnover at the whole bone level in vivo. Direct measurements were made of cortical bone resorption (loss of 3H-tetracycline and 3H-collagen from whole femur, blood-bone ratio of 45Ca), skeletal collagen formation and bone mineralization (collagen and calcium mass per whole femur, respectively). Chicks were sacrificed after 5, 14, 21 and 28 days of EHDP administration. By five days of treatment, EHDP caused a greater inhibition of bone mineralization (86%) than bone resorption (30-39%) without affecting skeletal collagen mass. The blood-bone ratio of 45Ca decreased 34%, which was similar in degree to the inhibition of 3H-tetracycline loss (30%) and 3H-collagen loss (39%). Almost complete inhibition of bone resorption and bone mineralization occurred by 14 days of treatment without effects on skeletal collagen mass. No additional effect was seen at 21 and 28 days of EHDP treatment. In chicks, EHDP inhibits almost completely bone mineralization (bone formation) and cortical bone resorption without affecting skeletal collagen mass.

Regulation of Na-dependent phosphate influx across the mucosal border of duodenum by 1,25-dihydroxycholecalciferol

Animals teated with disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), at doses which decrease the renal production and/or the plasma levels of 1,25-dihydroxycholecalciferol [1,25(OH)2D3], display a reduced net absorption of phosphate. In this study we investigated whether EHDP-treatment and administration of 1,25(OH)2D3 to EHDP-treated animals affected the phosphate influx across the mucosal border of rabbit duodenum. The initial rate of phosphate influx into mucosal cells was measured in isolated intestine. In control, untreated rabbits, the phosphate influx shows a saturable, Na-dependent component and a diffusional, Na-independent uptake. In tissue from rabbits treated for 3 days with EHDP, the phosphate influx was found to be strongly reduced. EHDP-treatment decreased the Na-dependent, carrier mediated phosphate influx in duodenum. Administration of 1,25(OH)2D3 to EHDP-treated animals reversed the reduced phosphate influx. These effects were mainly apparent through changes in the J(mc)(max) of the phosphate influx, which was decreased from 211 +/- 38.7 nmol/cm2h in controls to 42.1 +/- 18.1 nmole/cm2 h in the EHDP-treated group and increased to 413 +/- 43.6 nmole/cm2 h by 1,25(OH)2D3. The treatment did not appear to affect the diffusional, Na-independent phosphate influx. EHDP-treatment did not affect the influx of alanine in this segment suggesting that EHDP-treatment affects only 1,25(OH)2D3-dependent transport mechanisms. The results suggest that 1,25(OH)2D3 modulates the number of carrier sites available at the mucosal membrane for Na-dependent phosphate entry.

Effect of ethane-1-hydroxy-1,1-diphosphonate and vitamin D on bone mineralization

Administration of large quantities of ethane-1-hydroxy-1,1-diphosphonate to growing chicks resulted in a decrease in percent bone ash and an increase in percent osteoid. The degree of inhibition of bone mineral accumulation was a function of both duration and quantity of ethane-1-hydroxy-1,1-diphosphonic acid administration. The inhibition of bone mineral accumulation could be partially corrected with administration of 1,25-dihydroxyvitamin D3. Administration of high levels of ethane-1-hydroxy-1,1-diphosphonate also resulted in inhibition of intestinal calcium absorption. This could be reversed or prevented by the administration of 1,25-dihydroxyvitamin D3.

Calcium containing lysosomes in the normal chick duodenum: a histochemical and analytical electron microscopic study

Absorptive cells of the normal chick duodenum contain numerous supranuclear vesicular/vacuolar structures. By routine transmission electron microscopy, such structures are membrane bound and demonstrate a granular content. These vesicles appear to move laterally and eventually coalesce with the lateral plasma membrane (exocytosis). The granular contents are resistant to high temperature microincineration, thus revealing their mineral-containing nature. The granular vesicular matrix also stains intensely with osmium pyroantimonate EGTA chelation of pyroantimonate-stained vesicles selectively extracts the granules indicating a high concentration of calcium. X-ray microanalysis also demonstrates a significant intravesicular calcium localization. When tissues were incubated for the presence of acid phosphatase, the supranuclear vesicles were markedly positive for this lysosomal enzyme. A possible role for these calcium-containing lysosomes in the transcellular flux of calcium ions across the intestinal absorptive cell is discussed.

A morphometric investigation of the duodenal mucosa of normal, vitamin D-deficient, and vitamin D-replete rats

Light and electron microscopy were utilized to determine differences in morphology and size in duodenal villi and microvilli from normal, vitamin D-deficient, and vitamin D-replete rats. An increase in villus diameter and surface area was observed in vitamin D-deficient rats. Administration of vitamin D reversed the increase in diameter but the height of villi increased resulting in longer, thinner villi without a significant change in surface area. A decrease in microvillus surface area seen in vitamin D-deficient animals was reversed by the administration of vitamin D.

Intestinal mitochondrial calcium uptake during adaptation to dietary calcium restriction

In order to evaluate the role of mitochondrial calcium uptake in intestinal calcium absorption, the effect of adaptation to dietary calcium deficiency on the in vitro uptake of calcium by isolated duodenal mitochondria was studied. Experiments were performed utilizing 28-day-old cockerels which had received a diet adequate in vitamin D3 and phosphate and containing either 0.08% or 1.20% calcium. Mitochondrial 45Ca uptake from chicks deprived of dietary calcium was not significantly different from controls. These results suggest that increased calcium uptake by intestinal mitochondria is not crucial for adaptation to a low calcium diet.

The alteration of osteoclast morphology by diphosphonates in bone organ culture

Two diphosphonates alter the morphology of the osteoclast, as they inhibit the calcium45 release from bones stimulated to resorb by lipopolysaccharide. Disodium dichloromethylene diphosphonate was more potent than disodium ethane-1-hydroxy-1, 1-diphosphonate in both inhibiting 45calium release and altering osteoclast morphology. Alteration in the morphology of osteoclasts is associated with little or no change in the morphology of the surrounding non-osteoclast cells. These results indicate a specific morphological effect of diphosphonates on osteoclasts.

Diphosphonate therapy in nephrocalcinosis

4 patients with nephrocalcinosis were treated with disodium ethane 1-hydroxy-1, 1-diphosphonate (EHDP) for a period of 13 months. No clinical side-effects were observed and growth proceeded normally. Radiographic changes of osteitis fibrosa cystica developed in 1 child and bone biopsy in 2 children showed defective osteoid mineralisation. It is suggested that EHDP prevented further crystal deposition in 3 children but did not prevent non-calcium stone formation in the 4th child. In view of this and the development of histological and radiographic evidence of osteomalacia and/or secondary hyperparathyroidism in these patients the value of EHDP remains dubious. On the other hand its use may be justified when rapidly increasing calcification is expected, as for example in hyperoxaluria.

Experimental renal osteodystrophy. The response to 25-hydroxycholecalciferol and dicholomethylene diphosphate therapy

Bone mineral and matrix maturation in chronically uremic, nonacidotic rats were investigated after 25-hydroxcholecalciferol (25OHD) and/or dichloromethylene diphosphonate (C12MDP) therapy utilizing bromoform-toluene density gradient fractionation and X-ray diffraction analyses. The bromoform-toluene density gradient analyses demonstrated that the progressive accumulation of less dense, more immature bone characteristic of progressive uremia was reversed by 25OHD and/or C12MDP therapy for a 2-wk period, and that after 4 wk of therapy the maturational profile of bones from chronically uremic animals treated with 250HD and/or C12MDP was comparable to that from nonuremic littermates. X-ray diffraction analysis revealed that by the 4th wk of therapy with 25OHD and C12MDP both the degree of crystallinity and the crystal size/perfection parameters in the uremic bones were comparable to those of nonuremic, pair-fed control littermates. Treatment for 4 wk with 25OHD resulted in enlarged and/or more perfect apatite crystallites, while C12MDP alone slightly inhibited crystal growth and/or perfection after 2 wk of treatment. Soft tissue calcification was diminished in uremic animals treated for 4 wk with C12MDP or a combined C2MDP/25OHD regimen, the latter being much more effective in this regard. The accumulated data in this study support the premise that the attendant accelerated bone resorption, soft tissue calcification, and abnormal mineralization and maturation of the skeletal tissue, well documented to characterize experimental ranal insufficiency, may be alleviated with therapeutic dosages of 25OHD and/or C12MDP.

Effect of 1,25-dihydroxycholecalciferol on ethanol mediated suppression of calcium absorption

Rats raised on laboratory diet and given 20% ethanol in water as a sole source of fluid for 12 days were given 0.2 mug of 1,25-dihydroxycholecalciferol 24 h before measuring duodenal calcium transport by an in vitro everted gut sac technique. This vitamin D metabolite did not reverse the ethanol-induced inhibitiom of transport capacity. Ultrastructural studies of intestinal epithelial cells from animals ingesting ethanol demonstrated changes in mitochondria and other subcellular organelles as well as accumulation of electron-dense, calcium-containing granules in microvilli and a paucity of granules in mitochondria. The results suggest that the inhibition is mediated at the intestinal level, affecting mechanisms which are probably independent of Vitamin D, and in part by an interference in transport of calcium from microvilli to other intracellular sites.