Effects of the antihypercalcemic drugs gallium nitrate and pamidronate on hormone release of pathologic human parathyroid cells

The response of pre-osteoblasts and osteoclasts to gallium containing mesoporous bioactive glasses

Mesoporous bioactive glasses (MBGs) in the system SiO₂-CaO-P₂O₅-Ga₂O₃ have been synthesized by the evaporation induced self-assembly method and subsequent impregnation with Ga cations. Two different compositions have been prepared and the local environment of Ga(III) has been characterized using ²⁹Si, ⁷¹Ga and ³¹P NMR analysis, demonstrating that Ga(III) is efficiently incorporated as both, network former (GaO₄ units) and network modifier (GaO₆ units). In vitro bioactivity tests evidenced that Ga-containing MBGs retain their capability for nucleation and growth of an apatite-like layer in contact with a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Finally, in vitro cell culture tests evidenced that Ga incorporation results in a selective effect on osteoblasts and osteoclasts. Indeed, the presence of this element enhances the early differentiation towards osteoblast phenotype while disturbing osteoclastogenesis. Considering these results, Ga-doped MBGs might be proposed as bone substitutes, especially in osteoporosis scenarios.

STATEMENT OF SIGNIFCANCE

Osteoporosis is the most prevalent bone disease affecting millions of patients every year. However, there is a lack of bone grafts specifically designed for the treatment of bone defects occurred because of osteoporotic fractures. The consequence is that osteoporotic bone defects are commonly treated with the same biomaterials intended for high quality bone tissue. In this work we have prepared mesoporous bioactive glasses doped with gallium, demonstrating osteoinductive capability by promoting the differentiation of pre-osteoblast toward osteoblasts and partial inhibition of osteoclastogenesis. Through a deep study of the local environment of gallium within the mesoporous matrix, this work shows that gallium release is not required to produce this effect on osteoblasts and osteoclasts. In this sense, the presence of this element at the surface of the mesoporous bioactive glasses would be enough to locally promote bone formation while reducing bone resorption.

Negative association between serum parathyroid hormone levels and urinary perchlorate, nitrate, and thiocyanate concentrations in U.S. adults: the National Health and Nutrition Examination Survey 2005-2006

OBJECTIVES

Perchlorate, nitrate, and thiocyanate are well-known inhibitors of the sodium-iodide symporter and may disrupt thyroid function. This exploratory study investigated the association among urinary perchlorate, nitrate, and thiocyanate concentrations and parathyroid hormone (PTH) levels in the general U.S. population.

METHODS

We analyzed data on 4265 adults (aged 20 years and older) from the National Health and Nutrition Examination Survey in 2005 through 2006 to evaluate the relationship among urinary perchlorate, nitrate, and thiocyanate concentration and PTH levels and the presence of hyperparathyroidism cross-sectionally.

RESULTS

The geometric means and 95% confidence interval (95% CI) concentrations of urinary perchlorate, nitrate, and thiocyanate were 3.38 (3.15-3.62), 40363 (37512-43431), and 1129 (1029-1239) ng/mL, respectively. After adjusting for confounding variables and sample weights, creatinine-corrected urinary perchlorate was negatively associated with serum PTH levels in women (P = 0.001), and creatinine-corrected urinary nitrate and thiocyanate were negatively associated with serum PTH levels in both sex groups (P = 0.001 and P<0.001 for men, P = 0.018 and P<0.001 for women, respectively). Similar results were obtained from sensitivity analyses performed for exposure variables unadjusted for creatinine with urinary creatinine added as a separate covariate. There was a negative relationship between hyperparathyroidism and urinary nitrate and thiocyanate [odds ratio (95% CI) = 0.77 (0.60-0.98) and 0.69 (0.61-0.79), respectively].

CONCLUSIONS

A higher urinary concentration of perchlorate, nitrate, and thiocyanate is associated with lower serum PTH levels. Future studies are needed to determine the pathophysiological background of the observation.

Treatment of malignant hypercalcaemia

Hypercalcaemia is a common paraneoplastic syndrome caused by the production by tumours of several factors which affect bone resorption and/or tubular calcium reabsorption. Antihypercalcaemic therapy in cancer patients involves rehydration manoeuvres, as well as the use of a variety of available drugs which inhibit bone resorption, namely plicamycin, calcitonin, bisphosphonates and gallium nitrate. While plicamycin is currently out of use because of its considerable toxicity, bisphosphonates have become the standard therapy in hypercalcaemia of malignancy (HM). These compounds are potent inhibitors of bone resorption but they do not affect tubular calcium reabsorption, which limits their efficacy in humoral HM (HHM) cases. In these patients, gallium nitrate should be the therapy of choice. Among the available bisphosphonates, pamidronate administered in a single infusion of 90 mg, normalises serum calcium levels in > 90% of HM patients. A recently introduced bisphosphonate, zoledronate, is likely to replace pamidronate as a first-line therapy in these patients. The effectiveness of calcitonin in HM treatment is limited, although it seems to be useful at the outset in cases with severe symptomatic hypercalcaemia. Future treatment options of HM are likely to include new bone resorption inhibitors, for example, naturally-occurring osteoprotegerin, or alternate approaches aimed at reducing the tumour production of parathyroid hormone-related protein with noncalcaemic analogues of calcitriol or ras-isoprenylation inhibitors. The development of putative therapeutic agents targeted to inhibit distal calcium reabsorption should be valuable in the management of HHM cases.