Forteo Trial on Idiopathic Osteoporosis in Premenopausal Women

Osteoporosis is a skeletal disorder characterized by reduced bone strength that predisposes to an increased risk of fracture. Osteoporosis affects postmenopausal women and elderly men and is very unusual in healthy individuals under age 50. Moreover, more than 90% of young men and premenopausal women with osteoporosis have a secondary cause of bone lose, such as an underlying disorder (e.g., hypogonadism) or a medication exposure (e.g., glucocorticoids, antiepileptic drugs), that either interfered with acquisition of peak bone mass or caused excessive bone loss thereafter. Idiopathic osteoporosis (IOP) is defined as osteoporosis that affects young, otherwise completely healthy individuals with intact gonadal function and no secondary cause of bone loss. First described by Fuller Albright in 1944, IOP is an uncommon condition with an estimated annual incidence of 0.4 cases per 100,0003. IOP predominantly affects Caucasians, who generally present in their mid-30s with one more low trauma fractures.

In the course of a previously conducted NIH-funded study of premenopausal women, the investigators demonstrated that women with IOP have low areal bone mineral density (aBMD) at the spine, hip and forearm compared to normal women. Additionally, using noninvasive high resolution imaging of the central and peripheral skeleton and detailed analyses of transiliac crest bone biopsies, the investigators identified several distinctive and consistent features of bone quality in premenopausal women with IOP: thin cortices, lower trabecular volumetric bone mineral density (vBMD), fewer trabecular plates, fewer and longer trabecular rods, decreased connectivity between rods and plates, lower mineralization density and lower estimated stiffness of cancellous bone. Bone remodeling and biochemical indices of mineral metabolism did not differ between IOP subjects and controls.

Although not every woman with IOP requires pharmacologic intervention, many have sustained multiple low-trauma fractures or have extremely low bone mineral density (BMD). There is currently no FDA-approved therapy for IOP in premenopausal women, therefore a safe and effective therapy is urgently needed. Bisphosphonates are one therapeutic option but the associated gains in BMD are primarily due to reduction in the remodeling space and increased mineralization of bone rather than improvements in microarchitecture, an important consideration as microarchitectural deficits are a consistent feature of IOP in premenopausal women, while remodeling activity is most commonly normal or low. Furthermore, potential teratogenic effects limit the safety of bisphosphonates in premenopausal women.

However, anabolic therapy with human recombinant parathyroid hormone (hPTH) 1-34 (or teriparatide (TPTD)), has been shown to improve bone mass and microarchitecture in postmenopausal women and is approved for men with primary or idiopathic osteoporosis, as well as men, premenopausal and postmenopausal women with glucocorticoid-induced osteoporosis. TPTD, on the other hand, increases bone formation and BMD, while improving microarchitecture and strength. Moreover, TPTD has been shown to increase BMD in men with IOP, in premenopausal women with glucocorticoid-induced osteoporosis (GIOP) and to prevent bone loss in premenopausal women with nafarelin-induced acute estrogen deficiency. Although there have been no studies evaluating TPTD in estrogen-replete premenopausal women with IOP, data from studies of hPTH(1-34) in postmenopausal women on estrogen are relevant to this proposal. These studies found increased aBMD at the LS and of lesser magnitude at the hip, as well as major reductions in vertebral fracture. Also important, BMD remained stable in postmenopausal women on estrogen followed for two years after TPTD discontinuation. Lane et al. reported similar results in postmenopausal women with GIOP on estrogen. These two studies suggest that in estrogen-replete premenopausal women with IOP, increases in bone mass resulting from TPTD will be sustained after the course of therapy is completed.

The major objective of this protocol is a therapeutic one, namely to establish the safety and efficacy of TPTD in premenopausal women with IOP in a phase 2 clinical trial. The investigators hypothesize that anabolic therapy with teriparatide will improve areal and vBMD in premenopausal women with IOP. The investigators also hypothesize that teriparatide will restore abnormal microarchitecture toward normal and improve other aspects of bone quality in premenopausal women with IOP. The primary aim of this research study will be to establish the efficacy and safety of 6 months of teriparatide versus placebo in premenopausal women with IOP. The secondary aim is to determine the extent to which 12 and 24 months of teriparatide improves areal and volumetric BMD, bone microarchitecture and stiffness compared to baseline measures in premenopausal women with IOP. This study will have high impact on clinical practice as it pertains to the management of premenopausal women with IOP.