Pore-forming toxins (PFTs) are the most common protein toxins found in nature and act by disrupting cells through the formation of pores in the cellular membrane. While PFTs have been identified as one of the major virulence mechanisms underlying toxins, such as bacterial infections, venomous injuries and biological weaponry, existing detoxification platforms, such as antisera, monoclonal antibodies, small-molecule inhibitors and molecularly imprinted polymers, can only act by specifically

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... ting the molecular structure of the toxin, and, therefore, must be customized for each application. In their article, Hu and coworkers describe nanosponges (85 nm in diameter) that consist of red blood cell (RBC) bilayer membrane vesicles fused onto poly(lactic-coglycolic acid) nanoparticles. In this way, the RBC membrane shell provides a biomimetic substrate to absorb PFTs regardless of their structure, while poly(lactic-co-glycolic acid) stabilizes the RBC membrane, prolonging circulation. As a proof of concept, nanosponges were mixed with staphylococcal a-hemolysin (a-toxin). Purified mouse RBCs were then added and hemolysis was quantified by measuring the absorbance of hemoglobin released into the supernatant. Compared with poly(lactic-co-glycolic acid) nanoparticles, liposomes and RBC membrane vesicle controls, the nanosponges were able to completely protect mouse RBCs from damage and SDS-PAGE ana lysis indicated that the nanosponges retained 90% of the toxin. While RBC membrane vesicle controls similarly retained 95% of the toxin, they were unable to protect mouse RBCs, probably because the vesicles fuse with the RBCs. Experiments were also repeated using streptolysin-O and melittin to confirm the platform's applicability to other PFTs. Next, to determine whether the nanosponges could detoxify a-toxin in the presence of cells, cellular toxicity was studied in human umbilical vein endothelial cells. The authors found that a-toxin toxicity was significantly reduced, both when premixed with nanosponges and when concurrently mixed with the nanosponges and human umbilical vein endothelial cells. This was also true for the other PFTs. Finally, in vivo, the authors demonstrated that the nanosponges were well tolerated by mice. The nanosponges were observed to neutralize a-toxin when an a-toxin/nanosponge mixture was subcutaneously injected into the flank of mice. More importantly, the authors reported that these nanosponges could efficiently detoxify systemic a-toxin. It is well established that a-toxin is extremely toxic in the circulation, resulting in coagulation, inflammation and endothelial dysfunction. However, even when a lethal dose of a-toxin was injected through the tail vein, administration of nanosponges was able to reduce the mortality rate to 11% versus the 100% mortality seen in a-toxin-treated control mice. Overall, Hu and coworkers successfully demonstrated the utility of a biocompatible and biodegradable detoxification platform that can act against a broad range of PFTs. Specifically, by targeting membrane perforation, which is one of the most common virulence mechanisms, the nanosponge platform distinguishes itself from the current paradigm in detoxification treatments, where toxin antagonists rely on structure-specific binding. It remains unclear what the exact fate of the nanosponge-sequestered toxins is; however, the reported nanosponges have tremendous clinical/therapeutic implications. Evaluation of: Hu CM, Fang RH, Copp J et al. A biomimetic nanosponge that absorbs poreforming toxins. Nat. Nanotechnol. 8(5), 336-340 (2013).