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Biomedical subjects

H Fleisch

Publications and source records attributed to H Fleisch.

At least 109 records · Page 6Linked to original sources
PubMed1985

Extrarenal handling of phosphate: effect of thyroparathyroidectomy, 1,25-dihydroxycholecalciferol, and dietary calcium.

It is known that 1,25-dihydroxycholecalciferol [1,25(OH)2D3] mobilizes inorganic phosphate (Pi) from gut and bone, thus increasing the entry of Pi into the extracellular space (ECS). In this work, we have investigated whether 1,25(OH)2D3 could also facilitate the net exit of Pi out of this pool into certain soft tissue and/or bone compartments in thyroparathyroidectomized (TPTX) rats. Sham-operated, TPTX, and TPTX rats treated with 1,25(OH)2D3 (26 pmol/day ip for 1 wk) were infused with a known amount of Pi over a given time. The amount of Pi excreted in the urine in excess of base-line values and the rise of the phosphatemia ([Pi]p) were measured. The difference between these two parameters corresponded to the net retention of infused Pi in the whole animal (RAPi) for a given rise in [Pi]p. The results show that RAPi was markedly diminished in TPTX as compared with sham-operated animals. This decrease could be corrected by 1,25(OH)2D3 treatment. Chronic reduction in the level of calcemia in TPTX 1,25(OH)2D3-supplemented rats as induced by decreasing dietary Ca intake also diminished RAPi. These effects could not be ascribed to the known actions of the experimental maneuvers on the renal excretion of Pi. Since infusions were chosen to obtain similar rises in [Pi]p and started from same levels of [Pi]p in animals of the same weight, the differences in RAPi were not due to variation of Pi retention in the ECS.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Renal transport of bisphosphonates: accumulation by renal cortical slices enhanced by calcium phosphate ions.

Bisphosphonates have been recognized as useful therapeutic agents in metabolic bone disease. Earlier studies showed a net renal secretion of 1-hydroxy-ethylidene-1,1-bisphosphonate (HEBP). They suggested a renal cellular uptake of this compound. We further studied this concept by investigating the uptake in vitro of 14C-HEBP by rat renal cortex slices. HEBP was accumulated against a concentration gradient, a process that was dependent on time, temperature, and substrate concentration. Unlike that of 3H-p-aminohippurate, the uptake was not affected by change in medium Na+ or glucose and acetate concentration, or by anoxia and various metabolic inhibitors. It was, however, markedly increased by raising the medium calcium and inorganic phosphate concentration. Equilibrium dialysis with renal cortex homogenates suggests that HEBP binds to a cytosolic macromolecule through a process that exhibits saturability and calcium dependency. In conclusion, the results suggest that the bisphosphonate HEBP can penetrate kidney cells by a process that does not appear to be energy dependent, but is markedly influenced by the extracellular calcium-phosphate concentration.

Animals↗
PubMed1984

Calcification inhibitors in rat and human serum and plasma.

Rat and human serum and plasma were shown to contain considerable amounts of calcium phosphate precipitation inhibitors. Two general classes of inhibiting molecules were observed for both species: high molecular weight (approx. 30 000-200 000) and low molecular weight (less than 1000). The high molecular weight components eluted from a Bio-Gel P-200 column in two peaks, one at approx. 158 000 and a broader peak at approx. 43 000. The identity of these inhibitors is unknown at present. Low molecular weight inhibitors include magnesium, pyrophosphate, and citrate ions and at least one unidentified component that coelutes with pyrophosphate and citrate on a Bio-Gel P-4 column. Quantitatively, most of the inhibitor activity resides in the high molecular weight components and it is possible that it is this activity which is responsible for maintaining the metastability of the circulating fluids. The role of the low molecular weight components may be to regulate calcification at sites inaccessible to high molecular weight molecules.

Animals↗
PubMed1984

Influence of macrophage products on the release of plasminogen activator, collagenase, beta-glucuronidase and prostaglandin E2 by articular chondrocytes.

We describe the effects of products of mononuclear phagocytes on the secretory activity of chondrocytes. The primary confluent cultures of rabbit articular chondrocytes were exposed to standard medium alone or enriched with conditioned medium obtained from cultures of rabbit peritoneal macrophages, the mouse macrophage cell line P388D1 or human blood mononuclear cells. Four markers of release were assessed, the neutral proteinases plasminogen activator and collagenase, the acid hydrolase beta-glucuronidase and prostaglandin E2, and the kinetics of their changes were monitored. Chondrocytes that were cultured in standard medium secreted large amounts of plasminogen activator, some beta-glucuronidase, but no collagenase, and released only minor amounts of prostaglandin E2. The addition of conditioned medium from rabbit macrophages induced a rapid release of large quantities of prostaglandin E2 and an abundant secretion of collagenase, while abolishing or strongly decreasing plasminogen activator secretion. In addition, beta-glucuronidase secretion was markedly enhanced. The decrease in secretion of plasminogen activator appeared to reflect a diminished production, since no evidence was found for the generation of inhibitors or for an accelerated extracellular breakdown of the enzyme. Conditioned media of the mouse and human mononuclear cells influenced the secretory activities of rabbit articular chondrocytes in a similar way, suggesting that the factor (or factors) acting on chondrocytes is produced by a variety of macrophages, and that its action is not species-restricted. The time course and concentration-dependence of the effects observed indicate that the secretion of plasminogen activator and collagenase are influenced in a strictly reciprocal fashion by the macrophage products. The release of prostaglandin E2 paralleled that of collagenase.

Animals↗
PubMed1984

Interleukin 2-independent stimulation of rabbit chondrocyte collagenase and prostaglandin E2 production by an interleukin 1-like factor.

In the present study, interleukin 1 (IL 1)-containing media from different sources, namely a murine macrophage cell line (P388D1), rabbit peritoneal macrophages, and human peripheral blood mononuclear cells, were compared for their effect on thymocyte proliferation and on collagenase and PGE2 secretion by chondrocytes. A high correlation was found between the enhancement of thymocyte proliferation and the induction of collagenase and PGE2 secretion by chondrocytes. Furthermore, a highly purified IL 1-like factor, namely mononuclear cell factor (MCF) was also active on chondrocytes. The addition of highly purified IL 2 to rabbit chondrocytes had no effect on collagenase and PGE2 secretion induced by IL 1-containing media. Our findings suggest that the factor which induced collagenase and PGE2 secretion by rabbit chondrocytes was an IL 1-like factor. Thus, collagenase secretion by chondrocytes may be used as an IL 2-insensitive assay for the detection of IL 1-like factors.

Animals↗
PubMed1984

The subcellular distribution of [14C]dichloromethylenebisphosphonate and [14C]1-hydroxyethylidene-1,1-bisphosphonate in cultured calvaria cells.

Rat calvaria cells were cultured for 6 days in the presence or absence of [14C]dichloromethylenebisphosphonate [( 14C]Cl2MBP) or [14C]1-hydroxyethylidene-1, 1-bisphosphonate [( 14C]HEBP), after which cell organelles were separated by differential centrifugation. The distribution of protein, glutamate dehydrogenase, acid phosphatase, and 5'-nucleotidase was similar for cells treated or not treated with Cl2MBP. About 70-80% of the [14C]Cl2MBP and [14C]HEBP was found to be present in the supernatant. This was the only fraction that showed a ratio higher than 1 for the relative specific radioactivity, indicating that the bisphosphonates accumulated mainly in the cytosol. Rapid separation of particulate components and soluble cytoplasm of cells treated with [14C]Cl2MBP confirmed this finding, showing that it is unlikely that the result was due to leakage from the organelles. The uptake of [14C]Cl2MBP into cells was similar in different cell types. The binding of both bisphosphonates to macromolecules in the medium was 0.1-0.2% and 1-4% in the cells. This binding is not due to metabolic activity of the cells. About 15-20% of [14C]HEBP and [14C]Cl2MBP was modified by the living cells.

Acid Phosphatase↗
PubMed1984

Comparative study of deflazacort, a new synthetic corticosteroid, and dexamethasone on the synthesis of collagen in different rat bone cell populations and rabbit articular chondrocytes.

Deflazacort is a new synthetic glucocorticoid which is an oxazoline derivative of prednisolone. In previous studies, it was shown that deflazacort, depending on the test model used, not only showed considerably more antiinflammatory potency than prednisolone in animals but also caused less deleterious effects on bone mineral metabolism than equivalent amounts of other glucocorticoids in man. In this study, we have compared the effects of deflazacort with those of dexamethasone on the synthesis of collagen in various rat bone cell populations and chondrocytes. Three bone cell populations were prepared by sequential time-dependent collagenase treatment of 1-day-old rat calvaria. Each cell population was further purified on a Percoll gradient (10-90%) yielding three populations of which two are different in alkaline and acid phosphatase and response to parathyroid hormone. A 3-day treatment of bone cell populations with deflazacort and dexamethasone (10(-11)-10(-5) M) revealed that both glucocorticoids, although at different concentrations, inhibited collagen synthesis. 21-desacetyl-deflazacort (5 beta, 11 beta, 16 beta)-11,21-dihydroxy-2'-methyl-5-H-pregna-1-enol [17,16-d]oxazole-3,20-dione), the presumably active form of the steroid, which is formed in vivo after administration, produced nearly identical results as its precursor. Glucocorticoid concentrations at which inhibition was initially observed were 10(-9) M and 10(-7) M for dexamethasone and deflazacort respectively. Inhibition of collagen synthesis was significantly impaired only in cells isolated from bone during early tissue digestion, and not in those obtained during extensive collagenase treatment. Chondrocytes isolated from articular cartilage of 3-month-old rabbits and grown in primary cultures did not respond to either steroid.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Phosphatase↗
PubMed1984

Differential response of bone cells isolated by sequential digestion to dichloromethylenebisphonate in culture.

Dichloromethylenebisphosphonate (Cl2-MBP), a compound structurally related to inorganic pyrophosphate but resistant to hydrolysis of endogenous phosphatase to yield inorganic phosphate, inhibits bone resorption and soft tissue mineralization in vivo. Previously, we have shown that bone cells isolated from rat calvaria respond profoundly to the exposure of Cl2MBP. To determine whether the cellular effects evoked by Cl2MBP are confined to a particular bone cell type, calvaria from 1 day postnatal rats were subjected to a sequential time-dependent enzyme digestion, yielding five bone cell populations marked by differences in PTH response, alkaline phosphatase activity and collagen, as well as hyaluronic acid synthesis. Culturing these bone cell populations with Cl2MBP revealed that previously observed results found with mixed bone cells (inhibition of cell proliferation, diminution of hyaluronic acid synthesis, and increase in alkaline phosphatase) were limited to cell populations which, according to the isolation scheme, stem from the outer tissue layer(s) of the calvaria. Collagen synthesis, however, was found to be equally increased regardless of cell type. These present results indicate that the action of Cl2MBP on bone may be cell specific.

Acid Phosphatase↗
PubMed1984

Measurement of inhibitors of calcium phosphate precipitation in plasma ultrafiltrate.

Two methods are described to measure quantitatively the inhibitory activity of calcium phosphate precipitation in undiluted plasma ultrafiltrates. The first, called the "seed test," is based on the determination of the amount of apatite needed to induce the precipitation of calcium phosphate from the ultrafiltrate that previously had been brought to a constant [Ca X Pi] supersaturation. The second, called the "supersaturation test," is based on the determination of the minimum [Ca X Pi] product necessary to induce the precipitation of calcium phosphate, care being taken to eliminate the influence of chelators. With both techniques pyrophosphate was found to be the most effective inhibitor, magnesium and citrate being less active. At the physiological concentrations present in plasma ultrafiltrate, magnesium represented the greatest part of the activity in the seed test, while pyrophosphate was the most important in the supersaturation test. However, the three known inhibitors represented only part of the total inhibitory activity. In a pilot study, patients with renal failure showed an increase in inhibitory activity both in the known and unknown fractions.

Adult↗
PubMed1984

Determination of calcium phosphate inhibitor activity. Critical assessment of the methodology.

A method is described which determines the amount of calcium phosphate inhibitor activity in solutions with ionic compositions similar to that of undiluted plasma or serum. Constant supersaturations were obtained for the inhibitor analysis by equilibrating an aliquot of sample with dicalcium phosphate dihydrate (DCPD) and it was shown that the ion activity product of the equilibrated solutions was similar to the solubility product of DCPD. The amount of inhibitor activity in solution is assessed by determining the amount of hydroxylapatite seed needed for a predetermined rate of crystal growth. It was shown that the Langmuir adsorption isotherm is an appropriate model for describing the inhibitor data and provides a convenient linear-regression means for computing inhibitor activities. When tested at its normal physiological concentrations in plasma, albumin was the most important of the known calcium phosphate inhibitors.

Animals↗
PubMed1984

Abnormal hyperphosphatemic response to fasting in X-linked hypophosphatemic mice.

It has been proposed that renal inorganic phosphate (Pi) transport adaptation is a prerequisite for the hyperphosphatemic effect of fasting in animals previously fed low Pi diet (LPD). To test the validity of this proposal we have used X-linked hypophosphatemic (HYP) mice, since these animals are unable to adapt their renal Pi transport to LPD. HYP and control mice were pair-fed either high Pi diet (HPD) or LPD for 9 days. Then the influence of 24-hour fasting on plasma and urine Pi was studied. In the HPD condition, fasting led to a decrease in plasma Pi concentration, [Pi]P1, in both control and HYP mice. In the LPD condition fasting markedly increased [Pi]P1 from 1.61 +/- 0.13 mmol/l (mean +/- SEM, n = 8) to 2.33 +/- 0.05 mmol/l (n = 8, p less than 0.001) in control mice. In sharp contrast, in HYP mice fed LPD [Pi]P1 tended to decrease from 1.17 +/- 0.10 (n = 7) to 0.91 +/- 0.12 mmol/l (n = 7). As estimated from 24-hour urinary Pi excretion the mobilization of Pi from body stores was not different in HYP as compared to control mice fed either LPD or HPD. In conclusion, the results of this study support the hypothesis that the renal Pi transport adaptation to dietary Pi restriction is indeed the prerequisite for a hyperphosphatemic response to fasting. They also suggest that the mobilization of Pi from body stores during fasting with LPD is normal in HYP mice, even after Pi restriction.

Animals↗
PubMed1983

The effect of bisphosphonates on glycolysis in cultured calvaria cells and their homogenate.

Rat calvaria cells previously cultured for 7 days in the presence of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) or dichloromethylenebisphosphonate (Cl2MBP), showed a decrease in the glycolytic pathway. When glycolysis was analyzed under anaerobic conditions, this effect was not observed. The inhibition by the bisphosphonates occurred to a similar degree regardless of whether lactate production was measured in whole cells or in cell homogenates. Bisphosphonates added directly to the homogenate had no inhibitory effect. Thus, the effect is not a direct one and is unlikely to be due to a soluble mediator in the cytoplasm.

Aerobiosis↗
PubMed1983

Structure-activity relationships of various bisphosphonates.

A variety of bisphosphonates with aliphatic side chains of increasing length, as well as 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (AHPrBP, formerly APD), dichloromethylene-bisphosphonate (Cl2MBP, formerly Cl2MDP), and dibromomethylene bisphosphonate (Br2MBP, formerly Br2MDP), were compared in vitro and in vivo to find (a) a possible relationship between structure and activity in order to give some indication about their mechanism(s) of action on bone and (b) the most efficient and safe compound having an effect on bone resorption. Some relationship was found between inhibition of calcium phosphate precipitation in vitro and of mineralization in vivo. No correlation existed, however, between any parameter measured and bone resorption. The number of calvaria cells in culture was decreased by compounds with a chain length greater than 5-C, by AHPrBP, Cl2MBP, and Br2MBP. Lactate production by these cells in vitro was increased by the long chain bisphosphonates and AHPrBP, and was decreased by Cl2MBP. No good correlation existed between the inhibition of bone resorption measured in vitro on calvaria and that seen in vivo on rat tibiae metaphyses. The latter was inhibited the most efficiently by the bisphosphonates longer than 5-C and by AHPrBP; these were 10 times more effective than Cl2MBP. Taking into account all factors, 1-hydroxypentylidene-1,1-bisphosphonate and AHPrBP seem to be the most active compounds to inhibit bone resorption.

Alkaline Phosphatase↗
PubMed1983

Unilateral nephrectomy and 1,25-dihydroxyvitamin D3.

Several renal functions respond to nephron loss by a compensatory adaptation. Whether the production of 1,25(OH)2D3 also adapts to a renal mass reduction is still a matter of controversy. In the present study we have investigated in rats the influence of unilateral nephrectomy, in both the acute (48 hr) and chronic (2 to 6 weeks) state, on plasma 1,25(OH)2D3 level measured by competitive protein binding assay. In the acute state no difference in plasma 1,25(OH)2D3 level between sham-operated (SHAM) and unilateral-nephrectomized (UNI-NX) rats was found. The presence of the thyroparathyroid glands was not required for maintaining plasma 1,25(OH)2D3 at a normal level 48 hr after UNI-NX. In the chronic state in rats fed at 1.1% Ca diet, plasma 1,25(OH)2D3 (means +/- SEM) was 94 +/- 4 in SHAM and 98 +/- 8 pM in UNI-NX. In rats fed a 0.1% Ca diet it was 252 +/- 16 in SHAM and 239 +/- 20 pM in UNI-NX. Analysis of 3H-1,25(OH)2D3 plasma decay curve indicated that in UNI-NX under a high calcium diet the normalization of plasma 1,25(OH)2D3 appears to be entirely due to an increase in production, whereas under a low calcium diet part of it may also result from a moderate decrease in the elimination rate. In conclusion, this study indicates that unilateral nephrectomy does not affect the level of plasma 1,25(OH)2D3 even under a calcium restriction challenge. This compensatory adaptation appears to be independent of parathyroid hormone.

Animals↗