Management of Hypoparathyroidism: Present and Future.

CONTEXT: Conventional management of hypoparathyroidism has focused upon maintaining the serum calcium with oral calcium and active vitamin D, often requiring high doses and giving rise to concerns about long-term consequences including renal and brain calcifications. Replacement therapy with PTH has recently become available. This paper summarizes the results of the findings and recommendations of the Working Group on Management of Hypoparathyroidism. EVIDENCE ACQUISITION: Contributing authors reviewed the literature regarding physiology, pathophysiology, and nutritional aspects of hypoparathyroidism, management of acute hypocalcemia, clinical aspects of chronic management, and replacement therapy of hypoparathyroidism with PTH peptides. PubMed and other literature search engines were utilized. EVIDENCE SYNTHESIS: Under normal circumstances, interactions between PTH and active vitamin D along with the dynamics of calcium and phosphorus absorption, renal tubular handing of those ions, and skeletal responsiveness help to maintain calcium homeostasis and skeletal health. In the absence of PTH, the gastrointestinal tract, kidneys, and skeleton are all affected, leading to hypocalcemia, hyperphosphatemia, reduced bone remodeling, and an inability to conserve filtered calcium. Acute hypocalcemia can be a medical emergency presenting with neuromuscular irritability. The recent availability of recombinant human PTH (1-84) has given hope that management of hypoparathyroidism with the missing hormone in this disorder will provide better control and reduced needs for calcium and vitamin D. CONCLUSIONS: Hypoparathyroidism is associated with abnormal calcium and skeletal homeostasis. Control with calcium and active vitamin D can be a challenge. The availability of PTH (1-84) replacement therapy may usher new opportunities for better control with reduced supplementation requirements.

Vitamin D-resistant diseases.

Hereditary vitamin D receptor defects (HVDRDs) is a more appropriate and precise title for an inborn error of metabolism commonly known as pseudo-vitamin D deficiency or vitamin D dependency, type II. It is a rare autosomal recessive disorder, approximately 70 kindreds were described, but its main importance is elucidating the physiology of vitamin D and calcium homeostasis in humans. Patients usually develop the clinical and biochemical aberrations, identical to vitamin D deficiency, but with high serum levels of calcitriol, within the first year of life (i.e., muscle weakness, bone pain, deformities, and fractures). Defective calcium gut absorption leads to hypocalcemia, secondary hyperparathyroidism, hypophosphatemia, and defective mineralization of newly formed bone matrix. The disease is not cured by vitamin D replacement therapy, although some patients respond to very high doses of vitamin D or its metabolites. Cells derived from patients, mainly cultured skin fibroblasts, were used to assess steps in calcitriol action from cellular uptake to bioresponse and to elucidate the molecular aberrations in the vitamin D receptor (VDR). Point mutations in the VDR gene were identified in every patient examined, and the same defect was observed in the obligatory heterozygotes. The functional characterization of the patient's VDR reflected the localization of the mutation (18 different ones described to date), thus providing vital information about the structure-function relationship in the human VDR and the essentiality of the VDR as the mediator of vitamin D action.

Long-term safety of bisphosphonate therapy for osteoporosis: a review of the evidence.

This article reviews the long-term safety profile of bisphosphonates for the treatment and prevention of osteoporosis in postmenopausal women. Bisphosphonates inhibit osteoclastic resorption and reduce the rate of bone turnover, thereby reducing fracture risk. Placebo-controlled trials of oral amino-bisphosphonates of up to 4 years' duration and continuous treatment for up to 10 years in extensions of these trials (without continuous placebo comparison groups) have reported that bone quality remains normal, and suggest that the early reductions in fracture risk may be sustained for as long as treatment continues. Studies in animals using high doses of bisphosphonates have also reported normal quality bone with increased strength. The adverse experience profile (including upper gastrointestinal tolerability) of the oral bisphosphonates alendronic acid and risedronic acid has been similar to placebo in randomised trials with thousands of participants, whereas the incidence of flu-like symptoms was increased with the high doses used in oral monthly and intravenous ibandronic acid. Thus, the existing data are reassuring for long-term continued daily (or its weekly equivalent) administration of alendronic acid and risedronic acid, with no evidence of an adverse effect on bone health. For other dosing regimens, additional data are needed to evaluate their long-term safety.

Vitamin D sensitizes breast cancer cells to the action of H2O2: mitochondria as a convergence point in the death pathway.

Calcitriol, the hormonal form of vitamin D3, sensitizes breast cancer cells to reactive oxygen species (ROS)-dependent cytotoxicity induced by various anticancer modalities. This effect could be due to increased generation of ROS and/ or to increased sensitivity of the target cells to ROS. This work examined the effect of calcitriol on the damage inflicted on breast cancer cells by the direct action of ROS represented by H2O2. Treatment of MCF-7 cells with H2O2 resulted in activation of caspase 7 as well as induction of caspase-independent cell death. Both were enhanced by 48-72 h of pretreatment with calcitriol. This effect was not due to modulation of H2O2 degradation or to a specific effect on *OH-mediated cytotoxicity. The H2O2-induced drop in mitochondrial membrane potential and release of cytochrome c were enhanced by calcitriol. These findings indicate that calcitriol sensitizes breast cancer cells to ROS-induced death by affecting event(s) common to both caspase-dependent and -independent modes of cell death upstream to mitochondrial damage.

Meta-analysis of the efficacy of alendronate for the prevention of hip fractures in postmenopausal women.

Treatment with alendronate, a potent and specific inhibitor of bone resorption, is known to significantly reduce fracture risk among women with postmenopausal osteoporosis. The purpose of this meta-analysis was to assess the consistency of the effect of alendronate in reducing the risk of hip fracture among different studies and populations. Data from completed, randomized, treatment studies were pooled in a meta-analysis. The duration of the studies ranged from 1-4.5 years. The dose of alendronate ranged from 5-20 mg/day, with over 95% of patients receiving either 5 or 10 mg/day during the trials. In patients with a T-score of less than or equal to -2.0, or with a vertebral fracture, the effect on hip fracture risk consistently favored patients receiving alendronate therapy, with an overall reduction in risk of hip fracture of 45% [95% confidence interval (CI) 16% to 64%, P=0.007]. For patients who met the criteria of osteoporosis, as defined by the World Health Organization (WHO), the overall risk reduction was 55% (95% CI 29% to 72%, P=0.0008). In both analyses we performed a sensitivity analysis by removing one study at a time. The strength of the evidence was not dependent on any one study. We conclude that therapy with alendronate is associated with significant and clinically important reductions in the incidence of hip fracture in women with postmenopausal osteoporosis. The overall reduction is consistent among different patient populations.

The role of p38 MAP kinase in the synergistic cytotoxic action of calcitriol and TNF-alpha in human breast cancer cells.

Calcitriol, the hormonal form of Vitamin D, potentiates the activity of some agents of the anti-cancer immune system including tumor necrosis factor-alpha (TNF-alpha). Different signaling pathways activated by TNF-alpha may be targets for calcitriol action. Activation of p38 MAP kinase was shown to have both pro- and anti-apoptotic actions in TNF-alpha-induced programmed cell death depending on cell context. Treatment of MCF-7 breast cancer cells with TNF-alpha resulted in activation of p38 MAP kinase that persisted for at least 24h. Whereas calcitriol had no effect on the earlier phase of p38 MAP kinase activation (up to 1h), it inhibited the activation of this pathway between one and 24h after exposure to TNF-alpha. Both calcitriol and the p38 MAP kinase inhibitor SB203580 enhanced TNF-alpha-induced cytotoxicity and drop in mitochondrial membrane potential, but their combined effect was sub-additive. Taken together, these findings suggest that p38 MAP kinase plays an anti-apoptotic role in TNF-alpha-induced cytotoxicity in MCF-7 cells and that the synergistic interaction between TNF-alpha and calcitriol, leading to mitochondrial damage and subsequent cell death, is partially due to modulation of this signaling pathway.

Ten years' experience with alendronate for osteoporosis in postmenopausal women.

BACKGROUND: Antiresorptive agents are widely used to treat osteoporosis. We report the results of a multinational randomized, double-blind study, in which postmenopausal women with osteoporosis were treated with alendronate for up to 10 years. METHODS: The initial three-year phase of the study compared three daily doses of alendronate with placebo. Women in the original placebo group received alendronate in years 4 and 5 and then were discharged. Women in the original active-treatment groups continued to receive alendronate during the initial extension (years 4 and 5). In two further extensions (years 6 and 7, and 8 through 10), women who had received 5 mg or 10 mg of alendronate daily continued on the same treatment. Women in the discontinuation group received 20 mg of alendronate daily for two years and 5 mg daily in years 3, 4, and 5, followed by five years of placebo. Randomized group assignments and blinding were maintained throughout the 10 years. We report results for the 247 women who participated in all four phases of the study. RESULTS: Treatment with 10 mg of alendronate daily for 10 years produced mean increases in bone mineral density of 13.7 percent at the lumbar spine (95 percent confidence interval, 12.0 to 15.5 percent), 10.3 percent at the trochanter (95 percent confidence interval, 8.1 to 12.4 percent), 5.4 percent at the femoral neck (95 percent confidence interval, 3.5 to 7.4 percent), and 6.7 percent at the total proximal femur (95 percent confidence interval, 4.4 to 9.1 percent) as compared with base-line values; smaller gains occurred in the group given 5 mg daily. The discontinuation of alendronate resulted in a gradual loss of effect, as measured by bone density and biochemical markers of bone remodeling. Safety data, including fractures and stature, did not suggest that prolonged treatment resulted in any loss of benefit. CONCLUSIONS: The therapeutic effects of alendronate were sustained, and the drug was well tolerated over a 10-year period. The discontinuation of alendronate resulted in the gradual loss of its effects.

Vitamin D enhances caspase-dependent and -independent TNFalpha-induced breast cancer cell death: The role of reactive oxygen species and mitochondria.

Calcitriol, the hormonal form of vitamin D, potentiates the activity of some common anticancer drugs and agents of the anticancer immune system, including tumor necrosis factor alpha (TNFalpha). TNFalpha-induced cytotoxicity is due to both caspase-dependent and -independent pathways. Cotreatment with calcitriol enhanced both modes of TNFalpha-induced death in MCF-7 breast cancer cells. It increased caspase-3-like activity as assayed by the cleavage of poly-(ADP-ribose)polymerase and of the fluorogenic substrate ac-DEVD-AMC. It also enhanced TNFalpha-induced caspase-independent cytotoxicity in the presence of the pan-caspase inhibitor zD-2,6-dichlorobenzoyloxymethylketone. The antioxidants N-acetylcysteine, reduced glutathione, lipoic acid and ascorbic acid markedly reduced the enhancing effect of the hormone on TNFalpha-induced caspase activation. N-acetylcysteine and reduced glutathione also decreased caspase-independent cytotoxicity in the presence or absence of calcitriol, indicating that reactive oxygen species (ROS) have a key role in the cross talk between TNFalpha and calcitriol. Mitochondrial damage is common to both TNFalpha-induced caspase-dependent and -independent pathways and may underlie excessive production of ROS. Mitochondrial membrane potential (DeltaPsi) was assessed by the specific potential-sensitive fluorescent probe JC-1. The hormone augmented the drop in DeltaPsi and release of cytochrome c from mitochondria, induced by TNFalpha. The effect of calcitriol on DeltaPsi was mimicked by rotenone, which increased both the drop in DeltaPsi and caspase activation induced by TNFalpha. It is possible that the interaction of TNFalpha and calcitriol on the level of the mitochondria is the underlying mechanism responsible for the enhancement of TNFalpha-induced, ROS-mediated caspase-dependent and -independent cell death.

Vitamin D enhances mitogenesis mediated by keratinocyte growth factor receptor in keratinocytes.

The hormonally active vitamin D metabolite, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and keratinocyte growth factor (KGF) belong to the network of autocrine and paracrine mediators in the skin. Both were shown to modulate keratinocyte proliferation, to reverse epidermal atrophy, to increase wound healing, and to reduce chemotherapy-induced alopecia. The overlap between their activities may suggest that vitamin D exerts some of its actions by modulation of KGF activities in the skin. This notion was examined by using HaCaT keratinocytes cultured in serum-free medium in the absence of exogenous growth factors and in the presence of the EGF receptor tyrosine kinase inhibitor AG 1478 that blocks their autonomous proliferation. These cells could be stimulated to proliferate by different fibroblast growth factors (FGFs). The relative mitogenic efficacy of basic FGF, acidic FGF, or KGF was in correlation with their affinities for the KGF receptor (KGFR). Forty-eight hour co-treatment with 1,25(OH)(2)D(3) enhanced KGFR-mediated cell proliferation in a dose dependent manner. Both ERK1/2 and c-Jun N-terminal kinase (JNK) were activated by the FGFs. Treatment with 1,25(OH)(2)D(3) increased the activation of ERK but reduced the activation of JNK. Treatment with 1,25(OH)(2)D(3) increased the levels of KGFR in the presence but not in the absence of KGF, probably due to inhibition of ligand-induced receptor degradation. Inhibition of protein kinase C with bisindolylmaleimide did not interfere with the effect of 1,25(OH)(2)D(3) on KGFR-mediated ERK activation. Our results support the notion that the paracrine KGF-KGFR system in the skin can act in concert with the autocrine vitamin D system in keratinocytes to promote keratinocyte proliferation and survival under situations of stress and injury.

Changes in bone mineral density following discontinuation or continuation of alendronate therapy in glucocorticoid-treated patients: a retrospective, observational study.

OBJECTIVE: To evaluate the effects of discontinuing or continuing alendronate (ALN) therapy on bone mineral density (BMD) after patients on a long-term regimen of glucocorticoids (GCs) completed a 1-year treatment period with ALN. METHODS: Eligible patients were individuals with GC-induced osteoporosis who had received ALN (5 or 10 mg) for 1 year in a prior clinical trial and, at the end of the year, were still taking GCs at an average daily dose of > or =7.5 mg of prednisone or equivalent. Patients were contacted 3-5 years after completion of the prior ALN trial for followup measurements of the lumbar spine BMD and hip BMD, and retrospective information was collected about serious or drug-related adverse experiences and concomitant medication use. Some patients remained on GCs, and some remained on ALN, either alone or in combination with other drugs. The primary response parameter was the percentage change in lumbar spine BMD from the end of year 1 to the followup visit. Change in BMD at the hip was a secondary response parameter. RESULTS: Ninety (49.2%) of the eligible 183 patients participated in the retrospective study. The followup period, which began at the end of year 1 of the original clinical trial, ranged from 3.3 years to 4.6 years. The mean number of days of treatment with ALN was 507. Fifty patients were included in the analysis because they had received supraphysiologic doses of GCs (doses above the lowest tertile of GC use for the study population; that is, higher than approximately 6 mg/day), and they had not taken (defined as <6 months of use) other bone-affecting agents except ALN. Eleven of the 50 patients discontinued taking ALN (duration of use <90 days), 8 took ALN between 90 days and 300 days, and 31 continued to take ALN for >300 days after year 1 of the clinical trial. GC users who discontinued treatment with ALN (<90 days of therapy) had numerically greater decreases in BMD at the lumbar spine, femoral neck, and total hip from the end of year 1 (mean change -5.1%, -9.2%, and -6.6%, respectively), compared with patients who continued to take ALN for >300 days (mean change 0.1%, -0.9%, and 1.8%, respectively). CONCLUSION: Substantial loss of BMD in the lumbar spine and hip was seen in patients who discontinued treatment with ALN but who continued to take >6 mg/day of GCs. However, patients receiving GCs who remained on the ALN regimen appeared to benefit from continued ALN treatment, since BMD was maintained in this latter group.

Vitamin D protects keratinocytes from apoptosis induced by osmotic shock, oxidative stress, and tumor necrosis factor.

Calcitriol, the hormonal form of vitamin D, inhibited caspase-3-like activation in HaCaT keratinocytes exposed to hyperosmotic and oxidative stresses, heat shock, and the inflammatory cytokine TNF. The hormone also protected the cells from caspase-independent cell death induced by hyperosmotic and oxidative stresses. The protection against hyperosmotic stress is not affected by inhibitors of the EGF receptor, ERK or PI13 kinase pathways, neither is it due to reduced activity of the proapoptotic p38 MAP kinase. These results are in accordance with previous in vivo findings that vitamin D protects epidermal keratinocytes from apoptosis due to UV radiation or chemotherapy.