Teriparitide Update

Retreatment with teriparatide: our experience in three patients with severe secondary osteoporosis

Teriparatide is a drug for the treatment of osteoporosis which is licensed for use for up to 24 months. There is little experience with retreatment. The aim of this study was to evaluate, in three patients with severe secondary osteoporosis, the response to a second cycle of teriparatide regarding bone mineral density (BMD) and osteocalcin. Case 1 : A 62-year-old woman with multiple vertebral fractures has received corticoids for a long time. After starting teriparatide, her BMD and osteocalcin increased. She then received ibandronate for 3 years but her BMD declined. After a second treatment with teriparatide, her BMD increased again (18%). Case 2 : A 60-year-old woman with severe osteoporosis in lumbar spine (LS) (T-score - 4.5) had received corticoids for a long time and had celiac disease. After starting teriparatide, her BMD improved by 11.7%. She then received zoledronic acid for 15 months, but bone density decreased, so she was retreated with teriparatide. BMD had a slightly higher increase than after the first cycle (12.6%). Case 3 : A 60-year-old woman consulted for osteoporosis (LS T-score - 5.3), several fractures, and hyperthyroidism. She started teriparatide with improvement in BMD (39%). After 24 months, she received ibandronate for 1 year, but as her BMD declined, she was retreated with teriparatide. BMD showed an increase of 15%. The indication of a second cycle of treatment with teriparatide in three patients was effective in increasing BMD. Additional studies are needed to further identify the benefits and safety of retreatment with teriparatide.

Intermittent parathyroid hormone administration attenuates endothelial dysfunction in old rats

Aging is an independent risk factor for cardiovascular disease and is characterized by a decline in endothelial function. Parathyroid hormone (PTH) administration has been shown to increase endothelial nitric oxide synthase (eNOS) expression. The purpose of this investigation was to determine the effect of intermittent PTH administration on aortic endothelial function in old rodents. We hypothesized that intermittent PTH administration would improve endothelial function in older rodents. Old (24-mo-old) and young (4-mo-old) Fischer-344 rats were given 10 injections of PTH 1-34 (43 μg·kg^-1·day^-1) or phosphate-buffered saline (100 μl/day) over 15 days. Endothelium-dependent relaxation of aortic rings in response to acetylcholine (10^-9 to 10^-5 M) was significantly impaired in old control (OC) compared with young control (YC) as indicated by a reduced area under the curve (AUC, 100 ± 6.28 vs. 54.08 ± 8.3%; P < 0.05) and impaired maximal relaxation (E_max, 70.1 ± 4.48 vs. 92.9 ± 4.38%; P < 0.05). E_max was improved in old animals treated with PTH (OPTH) (OC, 70.1 ± 4.48 vs. OPTH, 85 ± 7.48%; P < 0.05) as well as AUC (OC, 54.08 ± 8.3 vs. OPTH, 82.5 ± 5.7%; P < 0.05) while logEC₅₀ was not different. Endothelial-independent relaxation in response to sodium nitroprusside was not different among groups. Aortic eNOS protein expression was significantly decreased in OC compared with YC (P < 0.05). PTH treatment restored eNOS expression in OPTH animals (P < 0.05). These data suggest that PTH may play a role in attenuating age-related impairments in aortic endothelial function.

NEW & NOTEWORTHY

We have demonstrated that intermittent parathyroid hormone administration can rescue age-related vascular dysfunction by improving endothelial-dependent dilation in the aorta of older rodents. This demonstrates a novel potential benefit of parathyroid hormone administration in aging.

Mechanisms of vasodilation to PTH 1-84, PTH 1-34, and PTHrP 1-34 in rat bone resistance arteries

Parathyroid hormone (PTH) augments bone metabolism and bone mass when given intermittently. Enhanced blood flow is requisite to support high tissue metabolism. The bone arteries are responsive to all three PTH analogs, which may serve to augment skeletal blood flow during intermittent PTH administration.

INTRODUCTION

PTH augments bone metabolism. Yet, mechanisms by which PTH regulates bone blood vessels are unknown. We deciphered (1) endothelium-dependent and endothelium-independent vasodilation to PTH 1-84, PTH 1-34, and PTHrP 1-34, (2) the signaling pathways (i.e., endothelial nitric oxide synthase [eNOS], cyclooxygenase [COX], protein kinase C [PKC], and protein kinase A [PKA]), and (3) receptor activation.

METHODS

Femoral principal nutrient arteries (PNAs) were given cumulative doses (10(-13)-10(-8) M) of PTH 1-84, PTH 1-34, and PTHrP 1-34 with and without signaling pathway blockade. Vasodilation was also determined following endothelial cell removal (i.e., denudation), PTH 1 receptor (PTH1R) inhibition and to sodium nitroprusside (SNP; a nitric oxide [NO] donor).

RESULTS

Vasodilation was lowest to PTH 1-34, and maximal dilation was highest to PTHrP 1-34. Inhibition of eNOS reduced vasodilation to PTH 1-84 (-80 %), PTH 1-34 (-66 %), and PTHrP 1-34 (-48 %), evidencing the contribution of NO. Vasodilation following denudation was eliminated (PTH 1-84 and PTHrP 1-34) and impaired (PTH 1-34, 17 % of maximum), highlighting the importance of endothelial cells for PTH signaling. Denuded and intact PNAs responded similarly to SNP. Both PKA and PKC inhibition diminished vasodilation in all three analogs to varying degrees. PTH1R blockade reduced vasodilation to 1, 12, and 12 % to PTH 1-84, PTH 1-34, and PTHrP 1-34, respectively.

CONCLUSIONS

Vasodilation of femoral PNAs to the PTH analogs occurred via activation of the endothelial cell PTH1R for NO-mediated events. PTH 1-84 and PTHrP 1-34 primarily stimulated PKA signaling, and PTH 1-34 equally stimulated PKA and PKC signaling.

The role of recombinant PTH in human fracture healing: a systematic review

OBJECTIVES

Human parathyroid hormone (PTH) is known to be efficacious in the treatment of osteoporosis and reduction of risk of vertebral and nonvertebral fractures; however, its role in the enhancement of human fracture healing is controversial. Our objective is to conduct a systematic literature review on the use of recombinant PTH in human fracture healing to (1) evaluate the evidence for recombinant PTH in human fracture healing and (2) assess whether there are notable differences between previous case reports and prospective trials.

DATA SOURCES

We performed a literature search in PubMed, EMBASE, Web of Science, and the Cochrane Database of Systematic Reviews for "teriparatide," "PTH (1-84)," "fracture," and "healing."

STUDY SELECTION

References of retrieved articles were screened for additional studies, and exclusion criteria were applied.

DATA EXTRACTION

Due to the limited publications on the subject, case reports and case series were included in our data analysis.

DATA SYNTHESIS

Due to the limited publications on the subject, our data are presented in simple tabular format.

CONCLUSIONS

Our literature review yielded 16 publications on the use of recombinant PTH in human fracture healing and 2 randomized controlled trial with 1 retrospective subgroup analysis. There continues to be anecdotal evidence for the use of recombinant PTH to enhance fracture healing. There are discrepancies in study design in the randomized controlled trials and the majority of case reports and, additional prospective studies are warranted.

Current perspectives on parathyroid hormone (PTH) and PTH-related protein (PTHrP) as bone anabolic therapies

Osteoporosis is characterized by low bone mineral density and/or poor bone microarchitecture leading to an increased risk of fractures. The skeletal alterations in osteoporosis are a consequence of a relative deficit of bone formation compared to bone resorption. Osteoporosis therapies have mostly relied on antiresorptive drugs. An alternative therapeutic approach for osteoporosis is currently available, based on the intermittent administration of parathyroid hormone (PTH). Bone anabolism caused by PTH therapy is mainly accounted for by the ability of PTH to increase osteoblastogenesis and osteoblast survival. PTH and PTH-related protein (PTHrP)-an abundant local factor in bone- interact with the common PTH type 1 receptor with similar affinities in osteoblasts. Studies mainly in osteoporosis rodent models and limited data in postmenopausal women suggest that N-terminal PTHrP peptides might be considered a promising bone anabolic therapy. In addition, putative osteogenic actions of PTHrP might be ascribed not only to its N-terminal domain but also to its PTH-unrelated C-terminal region. In this review, we discuss the underlying cellular and molecular mechanisms of the anabolic actions of PTH and the similar potential of PTH-related protein (PTHrP) to increase bone mass and improve bone regeneration.