A STUDY OF METASTATIC RENAL CALCIFICATION AT THE CELLULAR LEVEL

Comparison of 22-oxacalcitriol and 1,25(OH)2D3 on bone metabolism in young X-linked hypophosphatemic male mice

Using a mouse model (Hyp) of human hypophosphatemic vitamin D-resistant rickets [X-linked hypophosphatemia (XLH)], we compared the effects of 22-oxa-1,25-dihydroxyvitamin D3 (OCT) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on restoring defects in mineral and skeletal metabolism. Hyp/Y mice received OCT or 1,25(OH)2D3 at doses of 0.05-0.25 micron.kg-1.day-1 for 4 wk. OCT normalized serum calcium levels, whereas 1,25(OH)2D3 produced hypercalcemia in Hyp/Y. OCT and 1,25(OH)2D3 also normalized serum phosphate levels and increased urinary calcium levels. Additionally, OCT and 1,25(OH)2D3 reduced elevated urinary pyridinoline levels and suppressed urinary adenosine 3',5'-cyclic monophosphate levels to normal. Bone ash content was low in Hyp/Y, and OCT was more effective than 1,25(OH)2D3 in reversing this defect. Histomorphometric analysis of bone turnover, mineralization rate, and osteoid content demonstrated comparable responses with OCT and 1,25(OH)2D3, although the highest dose of 1,25(OH)2D3 resulted in increased osteoid content and delayed mineralization. OCT appears to be more effective and definitely less toxic than 1,25(OH)2D3 in reversing skeletal lesions in Hyp/Y mice and may prove to be the drug of choice in the treatment of childhood XLH.

Stimulation of undermineralized matrix formation by 1,25 dihydroxyvitamin D3 in long bones of rats

We previously reported that pharmacologic doses of 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) given for 2-3 days, inhibited osteoblastic collagen synthesis in young rats. In this study, we tested the effects of 5, 25, and 125 ng of 1,25(OH)2D3 injected subcutaneously into 6-week-old rats for 12 or 18 days. In rats given 125 ng, cortical bone of distal half femurs exhibited decreased calcium (Ca) content but dry weight and hydroxyproline (Hyp) content were no different from control. Trabecular bone Ca was not different from control but dry weight and Hyp were increased. When cortical and trabecular bone were combined, there was a decrease in Ca, an increase in Hyp, and a 50% decrease in Ca:Hyp. Fluorescent labels given after 8 days of treatment were either diffuse or absent in calcified sections from rats given 125 ng, indicating impaired mineralization. The 25 and 125 ng doses produced hypercalcemia with normal serum phosphate. There was a dose-related increase in serum immunoreactive bone gla protein (BGP) and serum 1,25(OH)2D3 and a decrease in serum 25(OH)D3. At the 5 ng dose, no adverse effects were seen on body growth. With 25 ng and 125 ng, growth was inhibited. Increased serum urea nitrogen and histologic evidence of nephrocalcinosis occurred at the 125 ng dose. When 125 ng was given for 12 days and then withdrawn for 6 days, systemic toxicity decreased and bone Hyp and Ca increased so that Ca:Hyp remained low and comparable to that of rats treated with 1,25(OH)2D3 continuously.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphate and the development of nephrocalcinosis in rats fed diets containing alpha protein

It has been suggested that nephrocalcinosis in rats fed diets containing alkali-treated soy protein may be due to a high availability of phosphate in the diet. In the present study, the development of nephrocalcinosis in rats fed a diet containing 20% alpha protein (an alkali-treated soy protein) was compared with that in rats fed the same diet supplemented with additional phosphate. Phosphate supplementation of the alpha protein diet produced a form of nephrocalcinosis that was morphologically different, at both the light- and electronmicroscopic level, from that obtained with the unsupplemented diet but was quite similar to that obtained with a phosphate-supplemented standard commercial laboratory diet. Levels of serum and urinary calcium and phosphorus and urinary cyclic AMP suggested that a phosphate-induced secondary hyperparathyroidism was present in the rats fed either of the phosphate-supplemented diets, but not in the rats fed the unsupplemented alpha protein diet. The results of this study suggest that nephrocalcinosis in rats fed a diet containing 20% alpha protein, without additional phosphate, is not typically phosphate-induced.

The ultrastructure of nephrocalcinosis induced in chicks by Cestrum diurnum leaves

Powdered Cestrum diurnum leaves, mixed with two diets differing in calcium and phosphorus contents, produced nephrocalcinosis in young chicks regardless of serum calcium elevation. The calcific deposits, found in both proximal and distal portions of cortical tubules, began either in the cytoplasm or in lysosomal bodies as a unilaminar spheroid structure containing apatite crystals. The ultrastructural characteristics of intraluminal concretions suggested that they were formed intracellularly but later were extruded into the lumen. The extent of calcific deposits increased with duration and with hypercalcemia. Although Cestrum contains an analog of 1,25-dihydroxycholecalciferol, neither mitochondria nor basal lamina contained calcific deposits described in nephrocalcinosis secondary to hypervitaminosis D.

Ultrastructural evaluation of the effects of 1,25-dihydroxyvitamin D3 on bone of thyroparathyroidectomized rats fed a low-calcium diet

Thyroparathyroidectomized rats fed a low-calcium-normal-phosphorus diet were administered 1 or 5 units of 1,25-dihydroxyvitamin D3-(1,25-[OH]2D3) or placebo daily for 7 days. 1,25-(OH)2D3 elevated serum and urine calcium and decreased serum phosphorus. Rats given 1 unit of 1,25-(OH)2D3 had increased numbers of osteoclasts in metaphyseal trabeculae, Ultrastructurally, osteoclasts, osteoblasts, and osteocytes in rats given 1 unit of 1,25-(OH)2D3, were similar to those in rats given placebo. In rats given 5 units of 1,25-(OH)2D3, osteoclasis was markedly increased. Osteoblasts were more numerous and interpreted to be active in matrix production and mineralization. Lamellated electron-dense bodies were observed adjacent to the plasma membranes of less active osteoblasts and were interpreted to be modified matrix. Most osteocytes in rats given 5 units of 1,25-(OH)2D3 were indistinguishable from osteocytes in rats given placebo. However,the pericellular space of some osteocytes in rats given 5 units of 1,25-(OH)2D3 contained electron-dense granular deposits that were interpreted to be calcium phosphate. It is concluded that 1,25-(OH)2D3 is able to significantly elevate serum calcium independent of dietary calcium, parathyroid hormone, and calcitonin primarily by increasing ostoeclasis with minimal dependence on osteocytic osteolysis.

Fluoride-induced mineralization within vacuoles in maturative ameloblasts of the rat

Dense crystalline deposits appeared within vacuoles in rat maturative ameloblasts as a result of repeated injections of sodium fluoride. The crystals assumed varied arrangements but were always observed within intracellular vacuoles. The crystals resemble those of normal enamel and resist microincineration. They are readily dissolved by decalcification and leave behind an organic framework which matches the outline of the crystals. An experimental model is presented which may be useful in further studies of calcium transport, enamel matrix absorption or digestion of cellular debris.

Bruch's membrane in pseudoxanthoma elasticum. Histochemical, ultrastructural, and x-ray microanalytical study of the membrane and angioid streak areas

In a case of pseudoxanthoma elasticum (PXE), Bruch's membrane was studied histochemically, ultrastructurally and by element analysis. Two kinds of calcifications were observed, one composed of hydroxyapatite and the other of CaHPO4. They were seen in the scar tissue of angioid streak areas and in the membrane outside these areas, respectively. Furthermore, a thready material was found in the membrane as well as an increased amount of acid mucopolysaccharides. The genesis of the calcifications and the pathogenesis of angioid streaks are discussed. The author is in favor of a malformed collagen as the basic defect in PXE.

Studies on the renal uptake of vitamin D3 in the mouse and the quail

The renal uptake of labelled vitamin D3 was studied in the mouse and the quail. Upon the administration of labelled vitamin D3 autoradiographic experiments showed a specific accumulation of radioactivity in the proximal tubuli of the mouse kidney. This was still obvious 18 days after the administration. In the quail, on the other hand, the uptake in the kidney did not exceed the level of the blood. In the mouse there was a slow increase in the amount of steriod in the kidney after the injection of vitamin D3, a maximum being reached 24 hours after the administration. The amount of steroid which accumulated in the kidney was largely proportional to the injected dose of the vitamin-from doses at 4.8 ng to 4.8 mug. Column chromatography showed that most of the renal vitamin D3, was present in a non-metabolized form. Cellular fractionation showed that most radioactivity in the kidney was present in the mitochondrial and microsomal fractions. Upon sonication of the fractions most radioactivity was still bound to these particles.

Hypophosphatasia-study on two autopsy cases

The autopsy findings of two cases of infantile hypophosphatasia are described and compared with those of 16 previously reported cases. Histochemical and biochemical tissue analysis for alkaline phosphatase showed a marked decrease in activity in liver, kidney, and bones. However, intestinal alkaline phosphatase possessed normal or slightly elevated activity. Nephrocalcinosis is a frequent complication and its development depends on hypercalcemia and length of survival of the patient. Electron microscopic findings are illustrated, and a mechanism for the development of nephrocalcinosis is proposed. For the first time, marked elevations of parathyroid hormone was detected. This finding, coupled with the extreme difficulty in locating the parathyroid glands in cases of hypophosphatasia, is enigmatic. Areas for furture investigation are suggested.

Morphology and function of Malpighian tubules and associated structures in the cockroach, Periplaneta americana

This paper describes the different regions of the Malpighian tubules and the associated structures (ampulla, midgut, ileum) in the cockroach, Periplaneta americana. There are about 150 tubules in each insect. Each tubule consists of at least three parts. The short distal region is thinner than the other parts and is highly contractile. The middle region comprises most of the tubule length and is composed of primary and stellate cells. Primary cells contain numerous refractile mineral concretions, while stellate cells have smaller nuclei, fewer organelles, simpler brush border, and numerous multivesicular bodies. Symbiont protozoa are sometimes present within the lumen of the middle region near where it opens into the proximal region of the tubule. The latter is a short region that drains the tubular fluid into one of the six ampullae. These are contractile diverticula of the intestine located at the midgut-hindgut junction. The ampulla is highly contractile, and consists of a layer of epithelial cells surrounding a cavity that opens into the gut via a narrow slit lined by cells of unusual morphology. The proximal region of the tubule and the ampulla resemble the midgut in that they have similar micromal origin and reabsorptive function for the proximal region of the tubule and for the ampulla. A number of inclusions found within the tubule cells are described, including peroxisomes and modified mitochondria. Current theories of fluid transport are evaluated with regard to physiological and morphological characteristics of Malpighian tubules. The possible role of long narrow channels such as those between microvilli and within basal folds is considered, as is the mechanism by which these structures are formed and maintained. Also discussed is the role of peroxisomes and symbionts in the excretory process.

Ouclar calcifications in primary hyperparathyroidism. Histochemical and ultrastructural study of a case. Comparison with ocular calcifications in idiopathic hypercalcaemia of infancy and in renal failure

In a case of primary hyperparathyroidism, ocular changes were observed as vacuoles in the basal cells of the corneal epithelium, and by staining procedures, calcium was found in the corneal and conjunctival epithelia, the corneal endothelium and in the sclera. By electron microscopy, needle-like crystals of calcium hydroxyapatite precursors were found intracellularly, also in keratocytes. The crystals in the epithelial cells were often confined to the nucleus. In a case of idiopathic hypercalcaemia of infancy, similar crystals were found intracellularly in the corneal epithelial and stromal cells, and in this case extracellular deposits, morphologically identical with extracellular deposits in conjunctival biopsies from patients with renal failure, were also seen. These extracellular aggregations were probably also composed of hydroxyapatite. The difference in morphology between intracellular and extracellular deposits is discussed in the light of the serum values of the mineral ions found in the three groups of cases.

The organic-inorganic relationship in calcified mitochondria

Experimentally induced calcification within mitochondria has been studied electron rnicroscopically. Cells investigated comprise hepatic cells damaged by CCl(4) intoxication, myocardial cells damaged by prolonged dihydrotachysterol (DHT) administration, and cells from skeletal muscle (gastrocnemius) damaged by DHT sensibilization and local injury. Cells from a human bowel carcinoma were studied too. Two types of intramitochondrial inorganic inclusion have been found. The first consists of clusters of apatite-like, needle-shaped crystals (crystalline aggregates), the second of clusters of very fine granules (granular aggregates). The former have been found mainly in mitochondria in apparently normal myocardial and muscular cells, the latter in mitochondria of degenerated hepatic, neoplastic, and myocardial cells. Crystalline aggregates are closely related to the membranes of cristae at first, but they later spread to occupy the whole mitochondrial matrix. Granular aggregates are initially found in the mitochondrial matrix near, but perhaps not touching, cristae; by growing they come into close contact with cristal membranes. Both types of aggregate show intrinsic electron opacity, which disappears after formic acid decalcification. Only the crystalline aggregates give an electron diffraction pattern of crystallinity. Uranium and lead staining of decalcified sections shows that both types of aggregate are intimately connected with an organic substrate. The substrate of crystalline aggregates consists of very thin, elongated structures shaped like the inorganic crystals. The substrate of granular aggregates consists of amorphous material gathered in clusters, with the same roundish shape and intercristal position as the inorganic granules. Both types of substrate are stained by phosphotungstic acid at low pH and by silver nitrate-methenamine after periodic acid oxidation. These results show that the organic content of the substrates includes glycoproteins; they have been confirmed by the periodic acid-Schiff (PAS) method under the optical microscope. These findings have been discussed in relation to the recent discovery of organic Ca(2+)-binding sites in mitochondria and to the general problems of soft tissue calcification.

The pathology of hypervitaminosis D in cattle

Experimental hypervitaminosis D was produced in cows by the daily feeding of 30 million U.S.P. units of vitamin D for varying periods of time. Cardiovascular mineralization was not present after 7 days, but was observed after 10 days and became extensive and widespread after 21 and 30 days. Pregnant cows developed more severe lesions than non-pregnant ones.

In the heart, the lesions were more severe on the left side, and consisted of subendocardial mineralization and hemorrhage. In the elastic arteries, the degree of mineralization was maximal proximally, and diminished in severity distally. In the muscular arteries, the mineral deposits when confined to the media were accompanied by a proliferative intimal reaction. The veins were less severely affected than the arteries.

Histochemically the mineral deposits contained abundant calcium and phosphorus. X-ray diffraction studies indicated the principal inorganic product of the vitamin D-induced mineralization was a carbonate hydroxyapatite, comparable in crystallochemical characteristics to that of bone.