Concentration Of Calcitriol Research Articles

The in vitro effect of calcitriol on parathyroid cell proliferation and apoptosis.

Calcitriol treatment is used to reduce parathyroid hormone levels in azotemic patients with secondary hyperparathyroidism (HPT). Whether long-term calcitriol administration reduces parathyroid gland size in patients with severe secondary hyperparathyroidism is not clear. The aim of the study was to evaluate in vitro the effect of calcitriol on parathyroid cell proliferation and apoptosis in normal parathyroid glands and in adenomatous and hyperplastic human parathyroid glands. Freshly harvested parathyroid glands from normal dogs and hyperplastic and adenomatous glands from patients with secondary (2 degrees) and primary (1 degree) HPT undergoing parathyroidectomy were studied. Flow cytometry was used to quantify the cell cycle and apoptosis of parathyroid cells. Apoptosis was also evaluated by DNA electrophoresis and light and electron microscopy. In normal dog parathyroid glands, culture with calcitriol (10(-10) to 10(-7) M) for 24 h produced a dose-dependent inhibitory effect on the progression of cells into the cell cycle and into apoptosis. When glands from patients with 2 degrees HPT were cultured for 24 h, only high calcitriol concentrations (10(-7) M) inhibited the progression through the cell cycle and the induction of apoptosis. In parathyroid adenomas (1 degrees HPT), even a high concentration of calcitriol (10(-7) M) had no significant effect on the cell cycle or apoptosis. The present study shows that in vitro, calcitriol inhibits in a dose-dependent manner in normal parathyroid glands both parathyroid cell proliferation and apoptosis. However, in secondary hyperplasia, only high concentrations of calcitriol inhibited cell proliferation and apoptosis. In 1 degree HPT, even high concentrations of calcitriol had no effect. Because calcitriol simultaneously inhibits both cell proliferation and apoptosis, a reduction in the parathyroid gland mass may not occur as a direct effect of calcitriol treatment.

Cell biology of parathyroid hyperplasia in uremia.

Marked parathyroid hyperplasia of heterogeneous degrees is often seen in chronic dialysis patients with severe secondary hyperparathyroidism. In uremia, parathyroid cell proliferation is initially stimulated by decreased concentration of calcium ions and calcitriol and also by direct effect of phosphate accumulation, leading to diffuse hyperplasia of the parathyroid. Then, small nodules caused by monoclonal cell proliferation form within diffuse hyperplasia, which progress to form nodular hyperplasia. Cells in nodular hyperplasia have a lower density of calcitriol receptor and calcium-sensing receptor than diffuse hyperplasia and are thus more resistant to medical therapy, including calcitriol pulse therapy. One of these nodules may grow more vigorously than the others and may finally occupy a large part of the enlarged gland. Genetic mutations and rearrangements of these cells in nodular hyperplasia remain to be fully elucidated in the near future to establish an effective method for the prevention of parathyroid hyperplasia in uremia.

Low serum calcidiol concentration in older adults with reduced muscular function.

To examine the association between muscular function and the serum concentrations of 25-hydroxyvitamin D (calcidiol) and 1,25-dihydroxyvitamin D (calcitriol). A randomized population survey. Baseline measurements of serum calcidiol and calcitriol concentrations and assessment of muscular function (hand grip strength, ability to climb stairs, outdoor activity, and fall occurrence). The Medical department, Aker University Hospital, Oslo, and subjects' homes. Two hundred forty-six recently hospitalized older patients and 103 randomly selected older people living at home. Serum concentration of calcidiol and calcitriol in relation to muscle function. Reduced muscle function was associated with low calcidiol levels. In both the hospital group and the home group, calcidiol concentrations correlated positively to arm muscle strength (r = .22, P < .001; r = .37, P < .001), ability to climb stairs (r = -.16, P < .05; r = -.42, P = < .001), physical activity (r = -.27, P < .001; r = -.31, P < .001), and the absence of fall occurrences (r = -.27, P < .001; r = -.31, P = .004). Calcitriol showed an association with physical activity in the hospital group (r = -.19, P < .05), and with fall last month in the home group (r = -.22, P < .05). Older people with reduced muscle function often had reduced levels of calcidiol serum concentration. Low levels of calcidiol were not associated with signs of general undernutrition, such as low body mass, or with reduced arm-muscle circumference or triceps skinfold thickness. This finding may suggest a physiological role for calcidiol in muscle function. Reduced muscle strength increased disability in our older subjects, which may be improved by vitamin D supplementation in vitamin D-deficient subjects.

1α,25-DIHYDROXYVITAMIN D3 (CALCITRIOL) INDUCES APOPTOSIS IN STIMULATED T CELLS THROUGH AN IL-2 DEPENDENT MECHANISM

The steroid hormone 1α,25-dihydroxyvitamin D3 (calcitriol) has been shown to inhibit PHA-induced T-cell proliferation. In the present work we show that calcitriol caused a concentration-dependent decrease in the viability of` PHA stimulated but not unstimulated T lymphocytes. Under microscopy, nonviable cells exhibit classic features of programmed cell death or apoptosis. In addition, the same concentration of calcitriol induces a blockage in the G1 phase of T cell cycle and decreased secretion of IL-2, which was correlated with the extent of apoptosis. Thus, addition of exogenous IL-2 reverted both the cell cycle block and the apoptotic cell death induced by calcitriol. This data indicates that calcitriol induced apoptotis in PHA-stimulated T cell, and suggests that this action is mediated through suppression of IL-2 secretion.

Molecular basis for the management of secondary hyperparathyroidism in chronic renal failure.

Recent clinical and experimental data suggest that the resistance of parathyroid cells to the physiological concentration of calcitriol plays an important role in the pathogenesis and the progression of secondary hyperparathyroidism in chronic renal failure. This resistance is due to the decreased density of the calcitriol receptor in parathyroid cells, which may result from impaired upregulation of calcitriol receptor. Since patients with larger parathyroid glands were more resistance to calcitriol pulse therapy than those with smaller glands and calcitriol receptor density inversely correlated with gland weight, the size of the parathyroid gland may serve as a marker for the degree of resistance to calcitriol. Furthermore, the possible role of phosphorus in the control of parathyroid function has been suggested recently. Thus, it is most important to prevent the progression of parathyroid hyperplasia in chronic renal failure by the early use of active vitamin D, calcitriol pulse therapy, and dietary phosphorus restriction.

Direct injections of calcitriol into enlarged parathyroid glands in chronic dialysis patients with severe parathyroid hyperfunction

Summary: Severe secondary hyperparathyroidism in chronic dialysis patients has been recently treated by supraphysiological concentration of calcitriol achieved through pulse therapy. However, there are many patients resistant to this therapy, who usually have larger parathyroid gland(s). to overcome this resistance, calcitriol was injected directly into the enlarged glands under ultrasonographic guidance. We injected 70–90% of the calculated gland volume of calcitriol solution (1 μg/mL) into the glands of 7 patients three times per week for 2 weeks. the parathyroid hormone (PTH) levels decreased significantly after 2 weeks of direct injections of calcitriol. Following a further 4 weeks of calcitriol pulse therapy, PTH levels remained suppressed and serum alkaline phosphatase activity and the volume of parathyroid glands also decreased. During the long‐term follow up, five patients remained well controlled with calcitriol pulse therapy, while two patients needed ethanol injections to control hyperparathyroidism. Although we could not completely rule out a toxic effect of the vehicle, direct injection of calcitriol into parathyroid glands may be another treatment option for chronic dialysis patients. Our data further support the important role of resistance of parathyroid cells to calcitriol in the pathogenesis of parathyroid hyper function in uraemic patients.

1,25-Dihydroxyvitamin D 3 receptors in peripheral blood mononuclear cells from patients with primary and secondary hyperparathyroidism

A decreased number of calcitriol (1,25(OH) 2D 3) receptors has been observed in parathyroid glands of uremic animals. In humans, studies carried out in surgically removed parathyroid glands have shown that calcitriol binding is higher in primary than in secondary hyperparathyroidism. Since specific receptors for calcitriol have been described in peripheral blood mononuclear cells (PBMC), we have investigated the specific uptake of 3H-labelled l,25(OH) 2D 3 in PBMC of 12 women with primary hyperparathyroidism (PHP), 8 women with hyperparathyroidism secondary to chronic renal failure (SH), 9 women with renal transplant (RT), and 23 healthy women. The median dissociation constant ( K d) was similar in all three groups of patients and in healthy women (mean ± S.D. (range): PHP, 1.2 ± 1.0 (0.2–4) × 10 −10 M; SH, 0.6 ± 0.4 (0.2–1.2) × 10 −10 M; RT, 1.1 ± 0.5 (0.4–1.9) × 10 −10 M; controls, 1.0 ± 0.6 (0.3–2.6) × 10 −10 M). However, the maximal binding capacity ( N max) was significantly enhanced in PHP (3.9 ± 1.9 (1.3–7.6) fmol/10 7 cells vs. 2.3 ± 0.9 (1.1–4.4) fmol/10 7 cells in controls; P = 0.0006) and decreased in SH (0.8 ± 0.5 (0.2–1.6) fmol/10 7 cells vs. 2.3 ± 0.9 (1.1–4.4) fmol/10 7 cells in controls; P = 0.0001), whereas no changes were seen in RT (2.3 ± 0.7 (1.2–3.3) fmol/10 7 cells vs. 2.3 ± 0.9 (1.1–4.4) fmol/10 7 cells in controls). In three patients with PHP who were subjected to parathyroidectomy, the calcitriol number came down to normal. Changes of calcitriol receptors in primary and secondary hyperparathyroidism could magnify the consequences of disturbances in serum concentration of calcitriol itself and might play an important role in the development of secondary hyperparathyroidism in uremia.

The effects of high phosphorus intake on calcium homeostasis.

Survey data confirm that the dietary pattern of many American women who are at high risk of developing osteoporosis is typically high in phosphorus and low in calcium. The imbalance between calcium and phosphorus intake may become more pronounced with continued changes in food preferences and the growing use of phosphorus-containing food additives. Recent studies in young women have shown that a high phosphorus diet moderately low in calcium results in a mild secondary hyperparathyroidism that persists over 4 weeks. Plasma levels of calcitriol did not change despite changes in PTH and serum ionized calcium. Studies on men have shown that dietary phosphorus at levels within the normal range of intakes can affect the renal production and serum concentration of calcitriol. High phosphorus intakes for ten days reduced their plasma calcitriol levels; a 70% reduction in phosphate intake significantly increased their plasma calcitriol. Thus, several lines of evidence indicate that prolonged high phosphorus intake may impair the usual homeostatic mechanisms that come into play when dietary calcium is limited. This, in turn, could impair achievement of maximal bone mass or accelerate bone loss. Although no clinical studies have linked high phosphorus intake with lower bone mass or higher rates of bone loss in humans, this relationship has been demonstrated in animal models. For example, young beagles fed high phosphorus, moderately low calcium diets showed a significant reduction in vertebral bone mass. Current dietary patterns of high phosphorus, low calcium consumption result in persistent changes in calcium regulating hormones that are not conducive to maximizing peak bone mass during growth or slowing the rate of aging bone loss. The net effect of the present dietary pattern on bone status, particularly in teenage and young adult women, needs to be determined. Optimal nutrition early in life, which may include higher calcium and lower phosphorus intakes, together with adequate exercise, may be the most cost-effective approach to the prevention of osteoporotic fractures.

Effect of dietary contents of cholecalciferol, 1 alpha,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol on blood concentrations of 25-hydroxycholecalciferol, 1 alpha,25-dihydroxycholecalciferol, total calcium and eggshell quality.

1. Withdrawal of cholecalciferol (D3) supplement from a layers diet drastically reduced blood 25-hydroxycholecalciferol (25-OH-D3), 1 alpha,25-dihydroxycholecalciferol (calcitriol) and egg specific gravity (SG) within two weeks, followed by a decrease in blood total calcium (Ca). 2. Doubling the D3 supplement in the control diet (27.5 micrograms or 1100 IU/kg) almost linearly increased the circulating concentration of 25-OH-D3 without raising the concentration of calcitriol, Ca, or egg SG. 3. Replacing D3 by the optimal concentration of calcitriol (5 micrograms/kg diet) improved egg SG after 21 weeks of treatment without increasing blood calcitriol or total Ca. 4. By itself, 24,25-dihydroxycholecalciferol [24,25-(OH)2D3] was unable to maintain normal blood levels of calcitriol, Ca or egg SG and, when added together with calcitriol in the diet, tended to elevate blood Ca but suppress the beneficial effect of calcitriol on shell quality, with little or no effect on blood calcitriol.

Increased serum concentrations of type I procollagen C-terminal propeptide and osteocalcin during a short course of calcitriol administration to adult male volunteers

To investigate bone collagen metabolism during vitamin D treatment, 15 healthy males (aged 28-45 years, median 34) were treated orally with calcitriol, 2 micrograms daily for 7 days and followed for a total of 2 weeks. The serum concentration of calcitriol rose markedly (median difference and 95% confidence limits: 49% (5-82), p less than 0.005) during treatment, whereas serum levels of calcidiol, and calcium remained unchanged. The serum level of procollagen type I C-terminal propeptide rose 15% (7-33, p less than 0.003), whereas no alterations were observed concerning serum procollagen type III N-terminal propeptide, and serum hyaluronan. The serum concentration of osteocalcin rose concomitantly (26% (12-45), p less than 0.003). All values returned to baseline levels within seven days after the treatment week. The serum levels of osteocalcin and procollagen type I C-terminal propeptide were positively correlated (rs = 0.71, p less than 0.004) during the study. Serum procollagen type I C-terminal propeptide and serum osteocalcin did not correlate with serum procollagen type III N-terminal propeptide or serum hyaluronan either at baseline or after treatment. It is concluded that a short course of calcitriol administration to healthy males stimulates the biosynthesis of bone-related matrix proteins. By contrast, connective tissue components of predominantly extraosseous origin are not affected.

T lymphocytes and their CD4 subset are direct targets for the inhibitory effect of calcitriol

We studied the direct effects of the hormone calcitriol on the activation and proliferation of pure T lymphocytes and their subsets. Calcitriol inhibited the proliferation of T lymphocytes stimulated in the absence of monocytes with phytohemagglutinin (PHA) and either a monocytic culture supernatant or a combination of monocyte-derived interleukin 1 and interleukin 6. This inhibition was not influenced by the concentration of the stimulating agents. The minimal effective concentration of calcitriol was 10 −10 M. In contrast, the interleukin 2 (10 U/ml)-driven growth of PHA-stimulated T lymphocytes was not significantly altered by calcitriol at 10 /t-8 M. The hormone had also no influence on the T lymphocyte proliferation induced by a combination of PHA and the anti-CD28 monoclonal antibody 9.3. Pure T lymphocytes, after incubation for 5 days with PHA and monocytic factors, expressed a high level of transferrin receptors. This phenomenon was strongly suppressed on both CD4 and CD8 subsets when 10 −8 M calcitriol had been present during the culture. Moreover, the proliferation of pure CD4 cells was directly inhibited by calcitriol in similar conditions as for unseparated T lymphocytes. We conclude that T lymphocytes and their CD4 subset are direct targets for the inhibitory effect of calcitriol.

Calcitriol synthesis is decreased in spontaneously hypertensive rats

To investigate the mechanisms of abnormal calcium metabolism, such as hypocalcemia, decreased intestinal calcium absorption and hypercalciuria in spontaneously hypertensive rats (SHR), we have measured the plasma concentration of calcitriol and its synthesis in 5-, 8-, 12-, 16-, and 20-week-old normotensive Wistar Kyoto rats (WKY) and SHR. Metabolic clearance rate (MCR) and production rate (PR) of calcitriol were measured by the constant isotope infusion method. Plasma concentration of calcitriol and PR of calcitriol were decreased in SHR after 12 weeks of age. MCR of calcitriol, however, was not different between WKY and SHR in any age group. Therefore, the decreased synthesis of calcitriol accounts for the lower plasma level of calcitriol in SHR after 12 weeks of age. Metabolic acidosis or decreased renal function could not account for the decreased synthesis of calcitriol, since the blood pH and pCO2 and creatinine clearance were similar between WKY and SHR at times when the calcitriol synthesis was reduced in SHR. Plasma concentration of ionized calcium was also lower in SHR after 12 weeks of age. Plasma concentration of calcitonin was significantly higher in 16-week-old SHR (41.6 +/- 1.5 pg/ml) than in age-matched WKY (30.5 +/- 1.7, P less than 0.001). The values, however, were not different between 8- and 12-week-old WKY and SHR. We believe that the decreased synthesis of calcitriol could be the pathogenetic factor for the development of abnormal calcium metabolism in SHR. Age of animals should be considered when studying the calcium metabolism in SHR.

Calcium and vitamin D metabolism in children with nephrotic syndrome

Although abnormalities of calcium and vitamin D metabolism are recognized in children with nephrotic syndrome, longitudinal observations are not available in these patients during periods of relapse and remission. We report observations in 58 children (mean age 10.1 years) with nephrotic syndrome and normal glomerular filtration rate. Hypocalcemia, modest hyperparathyroidism, and strikingly low calcidiol levels were identified during episodes of relapse. Most alterations were transient, and normalized on remission. The plasma concentration of calcitriol, the most active metabolite of vitamin D, was found to be normal in both relapse and remission. In the presence of hypocalcemia and hyperparathyroidism, however, normal plasma calcitriol levels in relapse may be inappropriately low and reflect a state of relative deficiency. Concurrent glucocorticoid therapy did not modify the results. A corollary of our observations is that children with relapsing or protracted nephrotic syndrome are at risk of developing metabolic bone disease, even without impairment of glomerular filtration rate.