# Erythrocytes and Nanoparticles: New Therapeutic Systems
## 4 Innovative Application of RBC-Coated NPs versus Nano-RBCs  
Due to widespread antibiotic resistance, the application of nano- red blood cells (nano-RBCs) as antimicrobial drug carriers can be exploited by using enzyme-responsive properties. Loading antibiotics such as vancomycin [58] into gelatin NPs and coating them with RBC membranes has been shown to produce a nano system that can be activated by the gelatinase present at the site of bacterial infection. This enzyme was able to degrade carriers, leading to the release of the therapeutic agent only at the site of infection -thus killing bacteria and achieving a reduction in immune clearance thanks to the external shell. As explained above, introducing stimuli-responsive NPs onto RBC surfaces can induce specific cargo release. Additionally, by coating gold NPs (AuNPs) with RBCs-membrane, specific nano-RBCs for photothermal therapy can be produced. In this frame, RBC-coated AuNPs were injected into mice and irradiated with an infrared laser. A clear photothermal effect was observed together with the ablation of cancer cells within the irradiation zone [61]. In this way, creating a nano-RBC with the long blood circulation lifetime conferred by erythrocytes--together with the photothermal properties of AuNPs--allowed researchers to improve the treatment of tumors, thanks to the combined characteristics of the synthetic and natural carriers. Starting with one RBC, it is possible to obtain a great number of nano-RBCs through the classical hypotonic hemolysis, which leads to the formation of a ghost suspension. NERS are subsequently obtained by extrusion using a polycarbonate membrane filter pore and/or sonication (Figure 4). The final diameter of the produced vesicles is about 100 nm. If compared with NPs coated with RBC membrane, they seem to show interesting advantages, due to their smaller size. Other advantages include their biocompatibility, biodegradability, easy preparation, and lack of immune response after administration. The therapeutic agent can be encapsulated inside, but it cannot be loaded on the surface. Researchers employing nano-RBCs loaded with Fasudil (a therapeutic agent used for inhalation therapy in pulmonary arterial hypertension) have observed an increase in the half-life of drugs [33]. A recent study presented a design of nano-RBCs to deliver sodium tanshinone IIA sulfonate (STS) for the treatment of cardiovascular diseases [79], confirming the advantageous characteristics of this innovative carrier. The carrier preserved membrane proteins, thus avoiding the immune system, and showed an increased uptake from spleen and liver. It also improved the half-life time of the drug compared with the administration of the agent alone. Furthermore, the effectiveness of delivery was also influenced by the appropriate profile of drug release, showing a slower controlled release of the agent from nano-RBCs as opposed to the fast release of free STS. Figure 4: NERs synthesis using extrusion and sonication approaches. Another recent study concerned the treatment of lysosomal storage disease [80] caused by a deficiency of \(\beta\)-glucocerebrosidase lysosomal enzyme, through its loading into erythrocytes. This strategy opens interesting perspectives for enzyme replacement therapy. Alzheimer and Parkinson's are widespread neurodegenerative diseases which can probably be associated with hyperammonemia [81]. Researchers have shown that a promising solution could utilize the encapsulation of glutamate dehydrogenase or alanine aminotransferase into RBCs [82], which in turn could lead to a remarkable decrease in plasma ammonium concentration after administration. A further meaningful biomedical application of nano-RBCs concerns the improved treatment of widespread human malaria disease [83]. As is well known, malaria is caused by parasites of genus _Plasmodium_ belonging to species _P. vivax_, _P. ovale_, _P. malariae_, and _P. falciparum_. The female anopheles mosquito transmits the sporozoites of _Plasmodium_ parasites into the blood of the host.