Does Activin Receptor Blockade by Bimagrumab (BYM338) Pose Detrimental Effects on Bone Healing in a Rat Fibula Osteotomy Model?

The Effect of Anti-Activin Receptor Type IIA and Type IIB Antibody on Muscle, Bone and Blood in Healthy and Osteosarcopenic Mice

BACKGROUND

Anti-Activin Receptor Type IIA and Type IIB antibody (αActRIIA/IIB ab) is a recently developed drug class that targets the activin receptor signalling pathway. Inhibition of receptor ligands (activins, myostatin, growth differentiation factor 11, etc.) can lead to skeletal muscle hypertrophy, bone formation, and increased haematopoiesis. Despite the αActRIIA/IIB ab, bimagrumab, having progressed to clinical trials, two crucial questions about αActRIIA/IIB ab therapy remain: Does αActRIIA/IIB ab influence bone metabolism and bone strength similarly to its generic classmates (activin receptor-based ligand traps)? Does αActRIIA/IIB ab affect red blood cell parameters, thereby increasing the risk of thromboembolism, similar to its generic classmates? Therefore, the aim of the present study was to investigate the therapeutic potential of αActRIIA/IIB ab in a mouse model of concurrent sarcopenia and osteopenia and to investigate the effect on bone and haematopoiesis in more detail.

METHODS

In C57BL/6JRj mice, combined sarcopenia and osteopenia were induced locally by injecting botulinum toxin A into the right hindlimb, resulting in acute muscle paresis. Immediately after immobilization, mice received twice-weekly intraperitoneal injections with αActRIIA/IIB ab (10 mg/kg) for 21 days, after which they were sacrificed. Muscle mass, skeletal muscle fibre size and Smad2 expression were analysed in the rectus femoris and gastrocnemius muscles. Bone mass and bone microstructure were analysed in the trabecular bone at the distal femoral metaphysis, while the cortical bone was analysed at the femoral mid-diaphysis. In a substudy, the effect on haematopoiesis was explored 2 and 7 days after a single αActRIIA/IIB ab (30 mg/kg) injection in C57BL/6JRj mice.

RESULTS

αActRIIA/IIB ab caused a large increase in muscle mass in both healthy (+21%) and immobilized (sarcopenic and osteopenic) (+12%) mice. Furthermore, αActRIIA/IIB ab increased trabecular bone (bone volume fraction) for both healthy (+65%) and immobilized (+44%) mice. For cortical bone, αActRIIA/IIB ab caused a small, but significant, increase in bone area (+6%) for immobilized mice, but not for healthy mice. Treatment with αActRIIA/IIB ab did not change red blood cell count, haemoglobin concentration or mean cell volume after either 2 or 7 days.

CONCLUSIONS

Treatment with αActRIIA/IIB ab caused a significant increase in both skeletal muscle mass and bone parameters in both healthy and immobilized mice, suggesting a potential in the treatment of concurrent osteopenia and sarcopenia. Interestingly, the bone anabolic effect of the treatment was much more pronounced on trabecular bone than on cortical bone. There was no pronounced effect of short-term treatment on haematopoiesis.

The Current Landscape of Pharmacotherapies for Sarcopenia

Sarcopenia is a skeletal muscle disorder characterized by progressive and generalized decline in muscle mass and function. Although it is mostly known as an age-related disorder, it can also occur secondary to systemic diseases such as malignancy or organ failure. It has demonstrated a significant relationship with adverse outcomes, e.g., falls, disabilities, and even mortality. Several breakthroughs have been made to find a pharmaceutical therapy for sarcopenia over the years, and some have come up with promising findings. Yet still no drug has been approved for its treatment. The key factor that makes finding an effective pharmacotherapy so challenging is the general paradigm of standalone/single diseases, traditionally adopted in medicine. Today, it is well known that sarcopenia is a complex disorder caused by multiple factors, e.g., imbalance in protein turnover, satellite cell and mitochondrial dysfunction, hormonal changes, low-grade inflammation, senescence, anorexia of aging, and behavioral factors such as low physical activity. Therefore, pharmaceuticals, either alone or combined, that exhibit multiple actions on these factors simultaneously will likely be the drug of choice to manage sarcopenia. Among various drug options explored throughout the years, testosterone still has the most cumulated evidence regarding its effects on muscle health and its safety. A mas receptor agonist, BIO101, stands out as a recent promising pharmaceutical. In addition to the conventional strategies (i.e., nutritional support and physical exercise), therapeutics with multiple targets of action or combination of multiple therapeutics with different targets/modes of action appear to promise greater benefit for the prevention and treatment of sarcopenia.

Association of activins, follistatins and inhibins with incident hip fracture in women with postmenopausal osteoporosis: a proof of concept, case-control study

PURPOSE

The activins-follistatins-inhibins (AFI) hormonal system is considered to regulate muscle and bone mass. We aimed to evaluate AFI in postmenopausal women with an incident hip fracture.

METHODS

In this post-hoc analysis of a hospital based case-control study, we evaluated circulating levels of the AFI system in postmenopausal women with a low-energy hip fracture admitted for fixation compared with postmenopausal women with osteoarthritis scheduled for arthroplasty.

RESULTS

Circulating levels of follistatin (p = 0.008), FSTL3 (p = 0.013), activin B and AB (both p < 0.001), as well as activin AB/follistatin and activin AB/FSTL3 ratios (p = 0.008 and p = 0.029, respectively) were higher in patients than controls in unadjusted models. Differences for activins B and AB remained after adjustment for age and BMI (p = 0.006 and p = 0.009, respectively) and for FRAX-based risk for hip fracture (p = 0.008 and p = 0.012, respectively) but were lost when 25OHD was added to the regression models.

CONCLUSIONS

Our data indicate no major changes in the AFI system in postmenopausal women at the time of hip fracture compared to postmenopausal women with osteoarthritis except for higher activin B and AB levels, whose significance, however, was lost when 25OHD was added to the adjustment models.

CLINICAL TRIALS

Clinical Trials identifier: NCT04206618.

Myostatin/Activin Receptor Ligands in Muscle and the Development Status of Attenuating Drugs

Muscle wasting disease indications are among the most debilitating and often deadly noncommunicable disease states. As a comorbidity, muscle wasting is associated with different neuromuscular diseases and myopathies, cancer, heart failure, chronic pulmonary and renal diseases, peripheral neuropathies, inflammatory disorders, and, of course, musculoskeletal injuries. Current treatment strategies are relatively ineffective and can at best only limit the rate of muscle degeneration. This includes nutritional supplementation and appetite stimulants as well as immunosuppressants capable of exacerbating muscle loss. Arguably, the most promising treatments in development attempt to disrupt myostatin and activin receptor signaling because these circulating factors are potent inhibitors of muscle growth and regulators of muscle progenitor cell differentiation. Indeed, several studies demonstrated the clinical potential of "inhibiting the inhibitors," increasing muscle cell protein synthesis, decreasing degradation, enhancing mitochondrial biogenesis, and preserving muscle function. Such changes can prevent muscle wasting in various disease animal models yet many drugs targeting this pathway failed during clinical trials, some from serious treatment-related adverse events and off-target interactions. More often, however, failures resulted from the inability to improve muscle function despite preserving muscle mass. Drugs still in development include antibodies and gene therapeutics, all with different targets and thus, safety, efficacy, and proposed use profiles. Each is unique in design and, if successful, could revolutionize the treatment of both acute and chronic muscle wasting. They could also be used in combination with other developing therapeutics for related muscle pathologies or even metabolic diseases.

Cytokine expressions of spinal cord injury treated by neurotropin and nafamostat mesylate

Background

Spinal cord injury (SCI) leads to severe physical disability and sensory dysfunction. Neurotropin (NTP) has been used clinically to alleviate neuropathic pain, while nafamostat mesylate (NM) used clinical on pancreatitis patients through inhibiting synthetic serine protease. Our previous studies showed that NTP and NM were able to repair SCI. However, the underlying mechanism has not been fully explored after treatment with these 2 different drugs.

Methods

The drugs NTP and NM were administered on a contusion SCI Wistar rat model. Cytokine array analysis was performed to describe the changes of 67 proteins after acute SCI. Hierarchical clustering and volcano plot analysis were conducted to clarify protein change profiles. The differently expressed proteins related to biological processes were analyzed by functional protein association networks, Gene Ontology and pathway analysis. Flow cytometric analysis was detected to reflect the activation of immune system after drug intervention, while withdrawal threshold and BBB score were detected to evaluated the mechanical allodynia and functional recovery after SCI.

Results

HGF, β-NGF, and activin were the 3 most upregulated proteins, while the receptor for RAGE, IL-1α, and TNF-α were the 3 most downregulated proteins after NTP treatment. Adiponectin, decorin and CTACK were the 3 most upregulated proteins, while RAGE, IL-1α, and IL-1β were the 3 most downregulated proteins in the NM group. Number of lymphocytes was decreased while BBB score was increased both in NTP and NM group. But only NTP could improve mechanical pain threshold after SCI.

Conclusions

The PI3K-Akt, Jak-STAT signaling pathway and apoptosis might participate in SCI restoration by NTP, while the MAPK and NOD-like receptor signaling pathway may participated in repairing SCI with NM. We concluded that NTP regulated the microenvironment via a neuroprotective effect and inhibition of inflammation to repair SCI, while NM healed SCI through an anti-inflammatory effect. Both NTP and NM could down-regulate the activation of immune system and improve the functional recovery while only NTP could improve the pathological neuralgia after SCI. Elucidating the molecular mechanisms of these 2 clinical drugs indicates that they their expected to be effective clinical treatment for SCI.

Monoclonal antibodies for treating osteoporosis

INTRODUCTION

Osteoporosis is the most widespread skeletal disease requiring innovative therapeutic strategies for its management. The understanding of receptor activator of nuclear factor kappa-B ligand (RANKL) and sclerostin's role in bone cell biology is completely changing the therapeutic landscape. RANKL supports osteoclast formation and activity and is mainly produced by cells of osteoblastic lineage. Sclerostin, an antagonist of the Wnt pathway, has a key role in bone formation and is mainly secreted by osteocytes. High levels of RANKL and sclerostin have been detected in osteoporosis, leading to the production of antibodies able to neutralize their activity.

AREAS COVERED

In this review, the authors give an overview and discuss the literature and data on denosumab and romosozumab to treat osteoporosis. Clinical studies indicate that long-term treatment with denosumab causes a continuous increase in bone mineral density with low incidence of adverse effects. Romosozumab treatment gives increases bone formation and improves bone mineral density (BMD) though further studies are needed to better evaluate the adverse effects.

EXPERT OPINION

Denosumab and romosozumab show promise in the treatment of osteoporosis. Furthermore, their different mechanisms of action compared to existing anti-osteoporotic drugs may permit alternative strategies for osteoporosis treatment down the line

Osteoporosis treatment: recent developments and ongoing challenges

Osteoporosis is an enormous and growing public health problem. Once considered an inevitable consequence of ageing, it is now eminently preventable and treatable. Ironically, despite tremendous therapeutic advances, there is an increasing treatment gap for patients at high fracture risk. In this Series paper, we trace the evolution of drug therapy for osteoporosis, which began in the 1940s with the demonstration by Fuller Albright that treatment with oestrogen could reverse the negative calcium balance that developed in women after menopause or oophorectomy. We note a watershed in osteoporosis drug discovery around the year 2000, when the approach to developing novel therapeutics shifted from one driven by discoveries in animal studies and clinical observations (eg, oestrogen, calcitonin, and teriparatide) or opportunistic repurposing of existing compounds (eg, bisphosphonates) to one driven by advances in fundamental bone biology (eg, denosumab) coupled with clues from patients with rare bone diseases (eg, romosozumab, odanacatib). Despite these remarkable advances, concerns about rare side-effects of anti-resorptive drugs, particularly bisphosphonates, and the absence of clear evidence in support of their long-term efficacy is leading many patients who could benefit from drug therapy to not take these drugs. As such, there remains an important clinical need to develop ways to enhance patient acceptance and compliance with these effective drugs, and to continue to develop new drugs that do not cause these side-effects and have prolonged anabolic effects on bone. Such changes could lead to a true reversal of this potentially devastating disease of ageing.

Soluble activin type IIB receptor improves fracture healing in a closed tibial fracture mouse model

Fractures still present a significant burden to patients due to pain and periods of unproductivity. Numerous growth factors have been identified to regulate bone remodeling. However, to date, only the bone morphogenetic proteins (BMPs) are used to enhance fracture healing in clinical settings. Activins are pleiotropic growth factors belonging to the TGF-β superfamily. We and others have recently shown that treatment with recombinant fusion proteins of activin receptors greatly increases bone mass in different animal models by trapping activins and other ligands thus inhibiting their signaling pathways. However, their effects on fracture healing are less known. Twelve-week old male C57Bl mice were subjected to a standardized, closed tibial fracture model. Animals were divided into control and treatment groups and were administered either PBS control or a soluble activin type IIB receptor (ActRIIB-Fc) intraperitoneally once a week for a duration of two or four weeks. There were no significant differences between the groups at two weeks but we observed a significant increase in callus mineralization in ActRIIB-Fc-treated animals by microcomputed tomography imaging at four weeks. Bone volume per tissue volume was 60%, trabecular number 55% and bone mineral density 60% higher in the 4-week calluses of the ActRIIB-Fc-treated mice (p<0.05 in all). Biomechanical strength of 4-week calluses was also significantly improved by ActRIIB-Fc treatment as stiffness increased by 64% and maximum force by 45% (p<0.05) compared to the PBS-injected controls. These results demonstrate that ActRIIB-Fc treatment significantly improves healing of closed long bone fractures. Our findings support the previous reports of activin receptors increasing bone mass but also demonstrate a novel approach for using ActRIIB-Fc to enhance fracture healing.