Segmental defect healing in the presence or absence of recombinant human BMP2: Novel insights from a rat model.

This study defined and compared the course of native, impaired and growth factor-stimulated bone regeneration in a rat femoral defect model. A mid-diaphyseal defect with rigid internal fixation was surgically created in the right femur of male Fischer rats and serially analyzed over 36 weeks. Native bone regeneration was modeled using a sub-critical, 1 mm size defect, which healed uneventfully. Critical size defects of 5 mm were used to analyze impaired bone regeneration. In a third group, the 5 mm defects were filled with 11 µg of recombinant human bone morphogenetic protein 2 (rhBMP2) impregnated onto an absorbable collagen sponge, modeling its clinical use. Native bone regeneration was characterized by endochondral ossification with progressive remodeling to ultimately resemble intact femora. An endochondral response was also observed under conditions of impaired bone regeneration, but by week 8 medullary capping occurred with fibrofatty consolidation of the tissue within the defect, resembling an atrophic non-union. rhBMP2 treatment was associated with prolonged inflammatory cytokine expression and rapid intramembranous bone formation occurring with reduced expression of cartilage-associated collagens. Between weeks 4 and 36, rhBMP2-treated bones demonstrated decreased trabecular number and increased trabecular separation, which resulted in inferior mechanical properties compared with bones that healed naturally. Clinical Significance: Recombinant human bone morphogenetic protein 2 (rhBMP2) is used clinically to promote healing of long bones. Our data suggest that it drives intramembraneous ossification producing an inferior regenerate that deteriorates with time. Clinical outcomes would be improved by technologies favoring endochondral regenerative ossification.

IL-1Ra gene transfer potentiates BMP2-mediated bone healing by redirecting osteogenesis toward endochondral ossification.

An estimated 100,000 patients each year in the United States suffer severe disability from bone defects that fail to heal, a condition where bone-regenerative therapies could provide substantial clinical benefits. Although recombinant human bone morphogenetic protein-2 (rhBMP2) is an osteogenic growth factor that is clinically approved for this purpose, it is only effective when used at exceedingly high doses that incur substantial costs, induce severe inflammation, produce adverse side effects, and form morphologically abnormal bone. Using a validated rat femoral segmental defect model, we show that bone formed in response to clinically relevant doses of rhBMP2 is accompanied by elevated expression of interleukin-1 (IL-1). Local delivery of cDNA encoding the IL-1 receptor antagonist (IL-1Ra) achieved bridging of segmental, critical size defects in bone with a 90% lower dose of rhBMP2. Unlike use of high-dose rhBMP2, bone formation in the presence of IL-1Ra occurred via the native process of endochondral ossification, resulting in improved quality without sacrificing the mechanical properties of the regenerated bone. Our results demonstrate that local immunomodulation may permit effective use of growth factors at lower doses to recapitulate more precisely the native biology of healing, leading to higher-quality tissue regeneration.

Comparison of replicating and nonreplicating vaccines against SARS-CoV-2.

Most gene-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are nonreplicating vectors. They deliver the gene or messenger RNA to the cell to express the spike protein but do not replicate to amplify antigen production. This study tested the utility of replication in a vaccine by comparing replication-defective adenovirus (RD-Ad) and replicating single-cycle adenovirus (SC-Ad) vaccines that express the SARS-CoV-2 spike protein. SC-Ad produced 100 times more spike protein than RD-Ad and generated significantly higher antibodies against the spike protein than RD-Ad after single immunization of Ad-permissive hamsters. SC-Ad-generated antibodies climbed over 14 weeks after single immunization and persisted for more than 10 months. When the hamsters were challenged 10.5 months after single immunization, a single intranasal or intramuscular immunization with SC-Ad-Spike reduced SARS-CoV-2 viral loads and damage in the lungs and preserved body weight better than vaccination with RD-Ad-Spike. This demonstrates the utility of harnessing replication in vaccines to amplify protection against infectious diseases.

Malignant Hyperthermia Susceptibility and Fitness for Duty.

INTRODUCTION: Malignant hyperthermia (MH) is an inherited hypermetabolic condition characterized by uncontrolled calcium release from the sarcoplasmic reticulum of skeletal muscle, usually from exposure to inhaled general anesthetics and/or the depolarizing neuromuscular blocking agent succinylcholine. Multiple case reports now reveal that crises may be precipitated by environmental factors such as exercise or high ambient temperatures. Common signs of an MH crisis include life-threatening hyperthermia, metabolic acidosis, muscle rigidity, and tachycardia. Treatment consists of stopping triggering agents, administering dantrolene, and actively cooling the patient. MH is a medically disqualifying condition for service in the U.S. Armed Forces. However, patients with MH-causative mutations may never have experienced an MH episode. If they previously have had an event concerning for MH, details are often sparse and a formal evaluation is absent. MATERIALS AND METHODS: We present 2 case reports with military service implications, one as a formal applicant to the service academies and the other as the father of an active duty Navy chief. Both patients experienced prior MH-like reactions to anesthesia but had not undergone testing with a caffeine-halothane contracture test (CHCT) or genetic analysis. Both patients underwent skeletal muscle biopsies of the left vastus lateralis with nontriggering anesthetics at Children's National Medical Center in Washington, DC, and MH diagnostic CHCT at the Uniformed Services University of the Health Sciences (USUHS) in Bethesda, Maryland. The CHCT was performed according to the North American MH Registry Protocol. With USUHS Institutional Review Board approval, ryanodine receptor type 1 gene (RYR1) and L-type calcium channel α-1 subunit gene (CACNA1S) sequencing was performed on the remaining muscle at USUHS. RESULTS: Each subject was CHCT positive, confirming a diagnosis of MH. One was found to have a known MH-causative gene mutation. The applicant to the service academy was therefore determined unfit for military service. The active duty son of the MH-positive patient underwent muscle biopsy and CHCT in order to continue his military career. CONCLUSION: A personal or familial history concerning for MH raises important questions on fitness for duty in the U.S. Armed Forces. Department of Defense regulation uniformly defines MH as a disqualifying condition; however, screening for a history of anesthetic complications during accession into the military is inconsistent. Medical standards across the services are also variable in the context of a familial history of MH. These case reports highlight the need for clinicians to seek expert consultation about how to proceed with MH-related issues. They also stress the importance of applying current understanding of heritable conditions to our fitness for duty determinations. Further investigation is also recommended to establish an MH-susceptible individual's propensity for exercise or heat-related injury outside the operating room. Department of Defense policy may thereafter be updated to reflect a quantitative assessment of MH's relative risk during inherently strenuous military operations.