Background and Purpose Remote ischemic conditioning is cardioprotective in myocardial infarction and neuroprotective in mechanical occlusion models of stroke. However, there is no report on its therapeutic potential in a physiologically relevant embolic stroke model (eMCAO) in combination with intravenous (IV) tissue plasminogen activator (tPA). Methods We tested remote ischemic perconditioning therapy (RIPerC) at 2 hours after eMCAO in the mouse with and without IV tPA at 4 hours. We assessed cerebral blood flow (CBF) up to 6 hours, neurologic deficits, injury size and phosphorylation of Akt (Serine473; p-Akt) as a pro-survival signal in the ischemic hemisphere at 48 hours post stroke. Results RIPerC therapy alone improved the CBF and neurologic outcomes. tPA alone at 4 hours did not significantly improve the neurologic outcome even after successful thrombolysis. Individual treatments with RIPerC and IV tPA reduced the infarct size (25.7% and 23.8%, respectively). Combination therapy of RIPerC and tPA resulted in additive effects in further improving the neurologic outcome, and reducing the infarct size (50%). All the therapeutic treatments upregulated p-Akt in the ischemic hemisphere. Conclusions RIPerC is effective alone after eMCAO and has additive effects in combination with IV tPA. RIPerC may be a simple, safe and inexpensive combination therapy with IV tPA.

Large bone defects cannot form a callus and exhibit high complication rates even with the best treatment strategies available. Tissue engineering approaches often use scaffolds designed to match the properties of mature bone. However, natural fracture healing is most efficient when it recapitulates development, forming bone via a cartilage intermediate (endochondral ossification). Because mechanical forces are critical for proper endochondral bone development and fracture repair, we hypothesized that recapitulating developmental mechanical forces would be essential for large bone defect regeneration in rats. Here, we engineered mesenchymal condensations that mimic the cellular organization and lineage progression of the early limb bud in response to local transforming growth factor–β1 presentation from incorporated gelatin microspheres. We then controlled mechanical loading in vivo by dynamically tuning fixator compliance. Mechanical loading enhanced mesenchymal condensation–induced endochondral bone formation in vivo, restoring functional bone properties when load initiation was delayed to week 4 after defect formation. Live cell transplantation produced zonal human cartilage and primary spongiosa mimetic of the native growth plate, whereas condensation devitalization before transplantation abrogated bone formation. Mechanical loading induced regeneration comparable to high-dose bone morphogenetic protein-2 delivery, but without heterotopic bone formation and with order-of-magnitude greater mechanosensitivity. In vitro, mechanical loading promoted chondrogenesis and up-regulated pericellular matrix deposition and angiogenic gene expression. In vivo, mechanical loading regulated cartilage formation and neovascular invasion, dependent on load timing. This study establishes mechanical cues as key regulators of endochondral bone defect regeneration and provides a paradigm for recapitulating developmental programs for tissue engineering.

A microparticle-based growth factor delivery system was engineered to drive endochondral ossification within human bone marrow-derived mesenchymal stem cell (hMSC) aggregates. Compared with cell-only aggregates treated with exogenous growth factors, aggregates with incorporated transforming growth factor-β1- and BMP-2-loaded microparticles exhibited enhanced chondrogenesis and alkaline phosphatase activity and a greater degree of mineralization. This microparticle-incorporated system has potential as a readily implantable therapy for healing bone defects without the need for long-term in vitro chondrogenic priming.

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