The effect of PTH(1-34) on fracture healing during different loading conditions

Parathyroid hormone (PTH) and PTH(1-34) have been shown to promote bone healing in several animal studies. It is known that the mechanical environment is important in fracture healing. Furthermore, PTH and mechanical loading has been suggested to have synergistic effects on intact bone. The aim of the present study was to investigate whether the effect of PTH(1-34) on fracture healing in rats was influenced by reduced mechanical loading. For this purpose, we used female, 25-week-old ovariectomized rats. Animals were subjected to closed midshaft fracture of the right tibia 10 weeks after ovariectomy. Five days before fracture, half of the animals received Botulinum Toxin A injections in the muscles of the fractured leg to induce muscle paralysis (unloaded group), whereas the other half received saline injections (control group). For the following 8 weeks, half of the animals in each group received injections of hPTH(1-34) (20 µg/kg/day) and the other half received vehicle treatment. Fracture healing was assessed by radiology, dual-energy X-ray absorptiometry (DXA), histology, and bone strength analysis. We found that unloading reduced callus area significantly, whereas no effects of PTH(1-34) on callus area were seen in neither normally nor unloaded animals. PTH(1-34) increased callus bone mineral density (BMD) and bone mineral content (BMC) significantly, whereas unloading decreased callus BMD and BMC significantly. PTH(1-34) treatment increased bone volume of the callus in both unloaded and control animals. PTH(1-34) treatment increased ultimate force of the fracture by 63% in both control and unloaded animals and no interaction of the two interventions could be detected. PTH(1-34) was able to stimulate bone formation in normally loaded as well as unloaded intact bone. In conclusion, the study confirms the stimulatory effect of PTH(1-34) on fracture healing, and our data suggest that PTH(1-34) is able to promote fracture healing, as well as intact bone formation during conditions of reduced mechanical loading.

PTH(1-84) replacement therapy in hypoparathyroidism: a randomized controlled trial on pharmacokinetic and dynamic effects after 6 months of treatment

Untreated, hypoparathyroidism (hypoPT) is a state of hypocalcemia with inappropriately low plasma parathyroid hormone (PTH) levels and hyperphosphatemia. PTH administration normalizes plasma calcium and phosphate levels and reduces the doses of calcium and active vitamin D analogues needed. To develop an evidence-based clinical algorithm to monitor hypoPT patients treated with recombinant human PTH (rhPTH[1-84]) injected subcutaneously in the thigh, we performed a 24-hour monitoring study of pharmacokinetic and pharmacodynamic effects in a group of 38 patients who had completed a 6-month randomized study on effects of treatment with a fixed rhPTH(1-84) dose of 100 µg/d or similar placebo as an add-on to conventional treatment. PTH levels rose immediately, reaching a median peak level of 26.5 (interquartile range [IQR], 20.1-42.5) pmol/L 15 minutes following injection. Thereafter, levels gradually decreased until reaching predosing levels after 16 hours, with a plasma half-life of 2.2 (1.7-2.5) hours. rhPTH(1-84) changed the diurnal rhythms of ionized calcium levels and 1,25-dihydroxyvitamin D (1,25[OH]2 D) levels, with rising levels following injection. Ionized calcium peaked after 7.0 (5.0-10.0) hours. Asymptomatic hypercalcemia was present in 71% of the rhPTH(1-84)-treated patients. Compared with placebo, 24-hour urinary calcium, phosphate, and magnesium did not change, although the diurnal variation in renal excretion rates changed significantly in response to treatment. In conclusion, as a safety precaution, we recommend occasionally measuring calcium levels at approximately 7 hours after administration in order to reveal episodes of hypercalcemia. A 100-µg daily dose of rhPTH(1-84) appears to be too high in some patients, suggesting a need for a device allowing for individual dose adjustments.

EFFECT OF HORMONES ON THE TURNOVER OF POLYSACCHARIDES IN CONNECTIVE TISSUES

A number of hormones somehow modify the turnover of the polysaccharides in a variety of connective tissues. In hypophysectomized animals the turnover of chondroitin sulfate and hyaluronic acid is decreased; when such animals are given growth hormone the turnover of chondroitin sulfate is enhanced but that of hyaluronic acid is unaltered. The effect of parathyroid extracts may be of a dual nature: in some connective tissues there may be an increase in the rate at which chondroitin sulfate is catabolized, in other tissues its synthesis may be stimulated. Thyroxine effectively restores toward normal the depressed synthesis and breakdown of polysaccharides in hypothyroid animals. Estradiol, in addition to inhibiting the resorption of the metaphyses in rats, inhibits the synthesis of chondroitin sulfate in cartilage and aorta. Cortisone too inhibits the synthesis of chondroitin sulfates and hyaluronic acid; its effect on their catabolism is not as striking.

IMMUNOCHEMICAL IDENTIFICATION OF PARATHYROID HORMONE IN NON-PARATHYROID NEOPLASMS ASSOCIATED WITH HYPERCALCEMIA

1. Immunochemical cross-reactivity, but not identity, has been demonstrated between bovine parathyroid hormone and an antigen in biologically active extracts of human parathyroid tissue by quantitative C' fixation and C' fixation inhibition. 2. An antigen that fixes C' with rabbit antibody to bovine parathyroid hormone has been found in urea extracts of six human non-parathyroid neoplasms associated with a hypercalcemic syndrome mimicking primary hyperparathyroidism. Comparable extracts of control tissues and other tumors were serologically negative. 3. It is concluded that the tumor antigen is parathyroid hormone or a very closely related protein, and that its production by these neoplasms was the cause of the hypercalcemic syndrome in these six patients.

EQUILIBRATION BETWEEN TISSUE CALCIUM AND INJECTED RADIOCALCIUM IN THE RAT

The exchange of calcium in soft tissues was studied in normal and slightly hyperparathyroid, adult rats. Both chemical and radiocalcium assays were performed on a variety of tissues at periods from 10 min to 1 hr and also 1 to 4 days after Ca45 injections. Bone, brain, tendon, and muscle were found to exchange quite slowly, requiring from several hours to several days to equilibrate with the circulation. On the other hand, skin, lung, heart, liver, uterus, and kidney showed specific activities equal to or greater than that of the circulating blood within 10 min. Thereafter, the specific activities of these tissues fell rapidly, approximating the rapidly decreasing specific activity of serum. No significant alterations in these patterns were caused by parathyroid extract. The general significance of this rapid exchange of calcium in many soft tissues is discussed.