BONE REGENERATIVE EFFECTS OF ANTI-SCLEROSTIN ANTIBODY AFTER SPINAL CORD INJURY

描述 目前，美国有27万人患有脊髓损伤(SCI)。功能完整的脊髓损伤患者中，100%会出现局灶性骨质疏松，这是脊髓损伤后骨折风险增加100倍的根本原因。目前的骨丢失治疗，包括双磷酸盐(一种一线药物治疗)和运动只能减缓脊髓损伤后的骨丢失，但不能再生局灶性骨量。因此，脊髓损伤后需要新的骨再生疗法。最近，一种药理上的“抗硬化素”抗体(skerostin-Ab)已经被开发出来，它通过否定内源性硬化素(促进成骨细胞发育和骨形成的Wnt信号通路的负调节因子)而产生深刻的骨合成作用。仅用3周的治疗就能逆转卵巢切除引起的大鼠一年来的骨丢失，以及完全防止后肢卸载后的骨丢失，证明了硬化素-抗体的有效性。临床版本的硬化素-抗体(AMG785)也被证明在单剂治疗的85天内使脊柱和髋部骨密度增加3-5%。重要的是，在功能完全性脊髓损伤后，硬化素升高，这表明它在脊髓损伤引起的骨丢失中起作用；然而，还没有研究评估硬化素-抗体在脊髓损伤后的疗效。在将其推广到临床试验之前，检查硬化素抗体是否能够在临床前模型中再生骨是至关重要的。文献中很少有慢性脊髓损伤所致骨丢失的模型。目前的模型使用脊髓横断或年轻(非骨骼成熟)啮齿动物，限制了它们的临床相关性。相反，我们建立了一种中胸挫伤脊髓损伤模型(利用骨骼成熟的雄性啮齿动物)，该模型在损伤后表现出广泛的松质骨丢失。需要进一步发展这一模型来确定它是否表现出慢性皮质骨缺陷，这是脊髓损伤后临床骨丢失的一个特征。对于这一建议，我们将1)扩展我们现有的急性脊髓损伤骨丢失模型，以开发临床相关的慢性脊髓损伤所致骨丢失模型(解决现有模型的缺点)和2)确定硬化素-抗体在该模型中是否再生骨。为此，我们将在严重中胸挫伤(或假手术)后1、2和4个月评估：皮质和松质骨量(通过CT)、骨转换(通过组织形态计量学)、骨强度(通过机械强度测试)和硬化素表达，以确定脊髓损伤后皮质骨丢失的高峰时间。然后，我们将评估硬化素-抗体在皮质骨丢失高峰期给药时是否能再生骨。为了支持这一提议，我们通过退伍军人事务部合作研究和开发协议(CRADA)从安进公司获得了硬化素-抗体。我们的基本假设是：1)大鼠在脊髓损伤后将经历以早期松质骨丢失和延迟性皮质骨丢失为特征的进行性骨丢失；2)在慢性脊髓损伤所致骨丢失的啮齿动物模型中，硬化素-抗体可以再生骨并提高骨强度。为了验证这些假说，将评估以下具体目标：目的1：描述严重胸中挫伤后骨骼成熟雄性啮齿动物的急性和慢性骨缺失，以建立一种临床相关的慢性脊髓损伤骨丢失模型。目的：在表现出严重皮质和松质骨缺陷的慢性脊髓损伤啮齿动物模型中，确定skerostin-Ab是否能够再生后肢骨矿物质特征和骨强度。这项建议将扩展我们的急性脊髓损伤模型，显示严重的松质骨丢失，以开发临床相关的慢性脊髓损伤模型，显示皮质和松质骨丢失(解决现有模型的缺点)，并将提供有史以来第一个关于硬化素-抗体在脊髓损伤后骨再生能力的直接证据。这些发现将为未来的临床试验提供原则上的证据，这些临床试验旨在评估硬化素-抗体作为一种再生脊髓损伤退伍军人骨的手段的有效性。

DESCRIPTION 270,000 individuals currently have a spinal cord injury (SCI) in the US. 100% of those with functionally- complete SCIs experience sublesional osteoporosis, underlying the 100-fold greater bone fracture risk after SCI. Current bone loss treatments, including bisphosphonates (a frontline pharmacologic treatment) and exercise only slow bone loss after SCI, but do not regenerate sublesional bone mass. As such, need exists for novel bone regenerative therapies following SCI. Recently, a pharmacologic "anti-sclerostin" antibody (Sclerostin-Ab) has been developed that produces profound osteoanabolic effects by negating endogenous sclerostin (a negative regulator of the Wnt-signaling pathway that promotes osteoblast development and bone formation). The effectiveness of Sclerostin-Ab is demonstrated by its ability to reverse 1-year of ovariectomy- induced bone loss in rats with only 3 weeks of treatment and by its ability to completely prevent bone loss subsequent to hind limb unloading. A clinical version of Sclerostin-Ab (AMG 785) has also been shown to increase spine and hip BMD by 3-5% within 85 days of a single treatment dose. Importantly, sclerostin is elevated after functionally-complete SCI, suggesting that it plays a role in SCI-induced bone loss; however, no study has evaluated the efficacy of Sclerostin-Ab after SCI. It is essential to examine whether Sclerostin-Ab is able to regenerate bone in a pre-clinical model before promoting it to clinical trials in thi population. Few models of chronic SCI-induced bone loss exist within the literature. The current models utilize spinal cord transection or young (non-skeletally mature) rodents, limiting their clinical relevance. In contrast, we have developed a mid-thoracic contusion SCI model (utilizing skeletally-mature male rodents) that exhibits extensive cancellous bone loss acutely after injury. Further development of this model is required to determine whether it exhibits the chronic cortical bone deficits that are a hallmark characteristic of clinical bone loss after SCI. For thi proposal, we will 1) expand upon our current acute SCI bone loss model in order to develop a clinically-relevant model of chronic SCI-induced bone loss (addressing the weaknesses of the existing models) and 2) determine whether Sclerostin-Ab regenerates bone in this model. In order to do so, we will assess: cortical and cancellous bone mass (via ¿CT), bone turnover (via histomorphometry), bone strength (via mechanical strength tests), and sclerostin expression at 1, 2, and 4 months after severe mid-thoracic contusion SCI (or Sham surgery) in order to determine the time of peak cortical bone loss after SCI. We will then evaluate whether Sclerostin-Ab regenerates bone when administered at the time of peak cortical bone loss in this model. In support of this proposal, we have obtained Sclerostin-Ab from Amgen through a VA Cooperative Research and Development Agreement (CRADA). Our primary hypotheses are that 1) rats will experience progressive bone loss after SCI that is characterized by the early loss of cancellous bone and a delayed loss of cortical bone and 2) Sclerostin-Ab will regenerate bone and improve bone strength in a rodent model of chronic SCI-induced bone loss. In order to test these hypotheses, the following Specific Aims will be evaluated: AIM 1: Characterize the acute and chronic bone deficits in skeletally-mature male rodents after severe mid- thoracic contusion SCI in order to develop a clinically-relevant model of chronic SCI-induced bone loss. AIM 2: Determine whether Sclerostin-Ab is capable of regenerating hind limb bone mineral characteristics and bone strength in a rodent model of chronic SCI that exhibits severe cortical and cancellous bone deficits. This proposal will expand upon our acute SCI model that exhibits severe cancellous bone loss in order to develop a clinically-relevant chronic SCI model that exhibits cortical and cancellous bone loss (addressing the weaknesses of the existing models) and will provide the first-ever direct evidence regarding the ability of Sclerostin-Ab to regenerat bone after SCI. These findings will provide proof-of-principle for future clinical trials intended o assess the efficacy of Sclerostin-Ab as a means of regenerating bone in Veterans with SCI.