Rapid-releasing of HI-6 via brain-targeted mesoporous silica nanoparticles for nerve agent detoxification

A mix & act liposomes of phospholipase A2-phosphatidylserine for acute brain detoxification by blood‒brain barrier selective-opening

In the treatment of central nervous system disease, the blood-brain barrier (BBB) is a major obstruction to drug delivery that must be overcome. In this study, we propose a brain-targeted delivery strategy based on selective opening of the BBB. This strategy allows some simple bare nanoparticles to enter the brain when mixed with special opening material; however, the BBB still maintains the ability to completely block molecules from passing through. Based on the screening of BBB opening and matrix delivery materials, we determined that phospholipase A2-catalyzed 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine liposomes can efficiently carry drugs into the brain immediately. At an effective dose, this delivery system is safe, especially with its effect on the BBB being reversible. This mix & act delivery system has a simple structure and rapid preparation, making it a strong potential candidate for drug delivery across the BBB.

A Pralidoxime Nanocomplex Formulation Targeting Transferrin Receptors for Reactivation of Brain Acetylcholinesterase After Exposure of Mice to an Anticholinesterase Organophosphate

Introduction

Organophosphates are among the deadliest of known chemicals based on their ability to inactivate acetylcholinesterase in neuromuscular junctions and synapses of the central and peripheral nervous systems. The consequent accumulation of acetylcholine can produce severe acute toxicities and death. Oxime antidotes act by reactivating acetylcholinesterase with the only such reactivator approved for use in the United States being 2-pyridine aldoxime methyl chloride (a.k.a., pralidoxime or 2-PAM). However, this compound does not cross the blood-brain barrier readily and so is limited in its ability to reactivate acetylcholinesterase in the brain.

Methods

We have developed a novel formulation of 2-PAM by encapsulating it within a nanocomplex designed to cross the blood-brain barrier via transferrin receptor-mediated transcytosis. This nanocomplex (termed scL-2PAM) has been subjected to head-to-head comparisons with unencapsulated 2-PAM in mice exposed to paraoxon, an organophosphate with anticholinesterase activity.

Results and Discussion

In mice exposed to a sublethal dose of paraoxon, scL-2PAM reduced the extent and duration of cholinergic symptoms more effectively than did unencapsulated 2-PAM. The scL-2PAM formulation was also more effective than unencapsulated 2-PAM in rescuing mice from death after exposure to otherwise-lethal levels of paraoxon. Improved survival rates in paraoxon-exposed mice were accompanied by a higher degree of reactivation of brain acetylcholinesterase.

Conclusion

Our data indicate that scL-2PAM is superior to the currently used form of 2-PAM in terms of both mitigating paraoxon toxicity in mice and reactivating acetylcholinesterase in their brains.

BODIPY-labelled acetylcholinesterase reactivators can be encapsulated into ferritin nanovehicles for enhanced bioavailability in the CNS

The BODIPY-labelled oxime reactivator was prepared and used to study its biodistribution into central nervous system. The newly synthesized oxime was found to be weak inhibitor of acetylcholinesterase and strong inhibitor of butyrylcholinesterase. Its reactivation ability for organophosphate inhibited acetylcholinesterase was found similar to a parent oxime. The BODIPY-labelled oxime was further encapsulated into recombinant human H-ferritin and evaluated in vitro and in vivo. The oxime or encapsulated oxime were found to be bioaccumulated primarily in liver and kidneys of mice, but some amount was distributed also to the brain, where it was detectable even after 24 h. The BODIPY-labelled oxime encapsulated to human H-ferritin showed better CNS bioaccumulation and tissue retention at 8 and 24 h time points compared to free oxime, although the fluorescence results might be biased due to BODIPY metabolites identified in tissue homogenates. Taken together, the study demonstrates the first utilization of recombinant ferritins for changing the unfavourable pharmacokinetics of oxime reactivators and brings promising results for follow-up studies.

Strategies for enhanced bioavailability of oxime reactivators in the central nervous system

Oxime reactivators of acetylcholinesterase are commonly used to treat highly toxic organophosphate poisoning. They are effective nucleophiles that can restore the catalytic activity of acetylcholinesterase; however, their main limitation is the difficulty in crossing the blood-brain barrier (BBB) because of their strongly hydrophilic nature. Various approaches to overcome this limitation and enhance the bioavailability of oxime reactivators in the CNS have been evaluated; these include structural modifications, conjugation with molecules that have transporters in the BBB, bypassing the BBB through intranasal delivery, and inhibition of BBB efflux transporters. A promising approach is the use of nanoparticles (NPs) as the delivery systems. Studies using mesoporous silica nanomaterials, poly (L-lysine)-graft-poly(ethylene oxide) NPs, metallic organic frameworks, poly(lactic-co-glycolic acid) NPs, human serum albumin NPs, liposomes, solid lipid NPs, and cucurbiturils, have shown promising results. Some NPs are considered as nanoreactors for organophosphate detoxification; these combine bioscavengers with encapsulated oximes. This study provides an overview and critical discussion of the strategies used to enhance the bioavailability of oxime reactivators in the central nervous system.

Brain-targeted nanoreactors prevent the development of organophosphate-induced delayed neurological damage

BACKGROUND

Organophosphate (OP)-induced delayed neurological damage is attributed to permanent neuropathological lesions caused by irreversible OP-neurocyte interactions, without potent brain-targeted etiological antidotes to date. The development of alternative therapies to achieve intracerebral OP detoxification is urgently needed.

METHODS

We designed a brain-targeted nanoreactor by integrating enzyme immobilization and biomimetic membrane camouflaging protocols with careful characterization, and then examined its blood-brain barrier (BBB) permeability both in vitro and in vivo. Subsequently, the oxidative stress parameters, neuroinflammatory factors, apoptotic proteins and histopathological changes were measured and neurobehavioral tests were performed.

RESULTS

The well-characterized nanoreactors exerted favourable BBB penetration capability both in vitro and in vivo, significantly inhibiting OP-induced intracerebral damage. At the cellular and tissue levels, nanoreactors obviously blocked oxidative stress, cellular apoptosis, inflammatory reactions and brain histopathological damage. Furthermore, nanoreactors radically prevented the occurrence of OP-induced delayed cognitive deficits and psychiatric abnormality.

CONCLUSION

The nanoreactors significantly prevented the development of OP-induced delayed neurological damage, suggesting a potential brain-targeted etiological strategy to attenuate OP-related delayed neurological and neurobehavioral disorders.

Modulation of engineered nanomaterial interactions with organ barriers for enhanced drug transport

The biomedical use of nanoparticles (NPs) has been the focus of intense research for over a decade. As most NPs are explored as carriers to alter the biodistribution, pharmacokinetics and bioavailability of associated drugs, the delivery of these NPs to the tissues of interest remains an important topic. To date, the majority of NP delivery studies have used tumor models as their tool of interest, and the limitations concerning tumor targeting of systemically administered NPs have been well studied. In recent years, the focus has also shifted to other organs, each presenting their own unique delivery challenges to overcome. In this review, we discuss the recent advances in leveraging NPs to overcome four major biological barriers including the lung mucus, the gastrointestinal mucus, the placental barrier, and the blood-brain barrier. We define the specific properties of these biological barriers, discuss the challenges related to NP transport across them, and provide an overview of recent advances in the field. We discuss the strengths and shortcomings of different strategies to facilitate NP transport across the barriers and highlight some key findings that can stimulate further advances in this field.

An in vitro nerve agent brain poisoning transwell model for convenient and accurate antidote evaluation

Nerve agent (NA) can inhibit acetylcholinesterase (AChE) causing seriously injury at extremely low doses. However, the cruel reality is that the lack of effective cerebral antidotes for treatment of NA poisoning. There is an urgent requirement for the large-scale evaluation and screening of antidotes. An effective NA antidote should include two characteristics: a) to permeate the blood-brain barrier (BBB); 2) to reactivate the inhibited AChE in brain. Existing methods for evaluating reactivators in vitro can only examine the reactivation effect, while the current Transwell model can only evaluate the drug penetration performance for crossing the barrier. In this work, brain microvascular endothelial cells (RBMECs) were inoculated to establish a Transwell model. AChE, NAs and antidotes of reactivators were added into the different chambers to simulate central poisoning and peripheral drug administration. This method can evaluate the reactivation ability and brain penetration ability of compounds at same time, which is a rapidly and accurately way for drug preliminary screening. In addition to small-molecule drugs, a liposomal nanoantidote loaded with the reactivator Asoxime chloride (HI-6)was prepared. This nanoantidote show high reactivation rate against the NA (sarin), evaluated by both this modified model in vitro and animal test, gaining the consistence results.

A fast-acting brain-targeted nano-delivery system with ultra-simple structure for brain emergency poisoning rescue

Treatment for acute brain conditions remains a major challenge owing to the unavailability of antidotes, especially for organophosphorus compounds, exposure to which leads to rapid death. Despite recent advances in brain-targeted nano delivery systems (BTNDS), the traditional ones which have been developed will likely not lead to the quick release of an antidote, which is essential to counteract fast neurotoxic effects. Herein, we present a BTNDS using thermosensitive liposomes, without the need for functionalization, to obtain a platform for brain-targeted delivery, which has a simple structure and thus can be easily synthesized and scaled-up. The brain-targeting effect of BTNDS was amplified by phospholipase A2 (PLA2), an inflammatory biomarker. The combination of PLA2 and BTNDS significantly improved brain targeting, leading to an excellent emergency rescue effect - 83- and 4.8-fold better cerebral AChE reactivation response and survival time, respectively. These findings provide a promising strategy to generate a facile, druggable, and effective BTNDS.

Transdermal Delivery of 2-PAM as a Tool to Increase the Effectiveness of Traditional Treatment of Organophosphate Poisoning

For the first time, the efficacy of post-exposure treatment of organophosphate (OP) poisoning was increased by transdermal delivery of acetylcholinesterase (AChE) reactivator pyridine-2-aldoxime methochloride (2-PAM) as a preventive countermeasure. By selecting the optimal ratio of components, classical transfersomes (based on soybean phosphatidylcholine and Tween 20) and modified transfersomes (based on soybean phosphatidylcholine, Tween 20 and pyrrolidinium cationic surfactants with different hydrocarbon tail lengths) were obtained for 2-PAM encapsulation. Transfersomes modified with tetradecylpyrrolidinium bromide showed the best results in encapsulation efficiency and sustained release of 2-PAM from vesicles. Using Franz cells, it was found that the incorporation of surfactants into PC liposomes results in a more prolonged release of 2-PAM through the rat skin. Transfersomes containing 2-PAM, after exhaustive physical and chemical characterization, were embedded in a gel based on Carbopol^® 940. A significantly high degree of erythrocyte AChE reactivation (23 ± 7%) was shown for 2-PAM in unmodified transfersomes in vivo. Preliminary transdermal administration of 2-PAM 24 h before emergency post-exposure treatment of OP poisoning leads to an increase in the survival rate of rats from 55% to 90%.

Oxime Therapy for Brain AChE Reactivation and Neuroprotection after Organophosphate Poisoning

One of the main problems in the treatment of poisoning with organophosphorus (OPs) inhibitors of acetylcholinesterase (AChE) is low ability of existing reactivators of AChE that are used as antidotes to cross the blood-brain barrier (BBB). In this work, modified cationic liposomes were developed that can penetrate through the BBB and deliver the reactivator of AChE pralidoxime chloride (2-PAM) into the brain. Liposomes were obtained on the basis of phosphatidylcholine and imidazolium surfactants. To obtain the composition optimized in terms of charge, stability, and toxicity, the molar ratio of surfactant/lipid was varied. For the systems, physicochemical parameters, release profiles of the substrates (rhodamine B, 2-PAM), hemolytic activity and ability to cause hemagglutination were evaluated. Screening of liposome penetration through the BBB, analysis of 2-PAM pharmacokinetics, and in vivo AChE reactivation showed that modified liposomes readily pass into the brain and reactivate brain AChE in rats poisoned with paraoxon (POX) by 25%. For the first time, an assessment was made of the ability of imidazolium liposomes loaded with 2-PAM to reduce the death of neurons in the brains of mice. It was shown that intravenous administration of liposomal 2-PAM can significantly reduce POX-induced neuronal death in the hippocampus.

Cation-Exchangeable Pralidoxime Chloride@bio-MOF-1 as a Treatment for Nerve Agent Poisoning and Sulfur Mustard Skin Poisoning in Animals

A 2-PAM@bio-MOF-1 composite was prepared by cationic exchange of counter N,N-dimethylammonium cations in the pores of the anionic, biocompatible metal-organic framework (bio-MOF-1) with pralidoxime chloride (2-PAM-Cl) by impregnation. In vitro drug release measurements revealed that the release rate of 2-PAM from 2-PAM@bio-MOF-1 in simulated body fluid (SBF) was more than four-fold higher than that in deionized water, indicating that the presence of endogenous cations in SBF triggered the release of 2-PAM through cation exchange. The release of 2-PAM was rapid within the first 10 h but was much slower over the period of 10-50 h. At room temperature, the maximum release rate of 2-PAM was 88.5% (15 mg of 2-PAM@bio-MOF-1 in 1 mL of SBF), indicating that the drug was efficiently released from the composite MOF in SBF. In simulated gastric fluid, 64.3% of 2-PAM was released from bio-MOF-1 into the simulated gastric fluid after 50h. This suggested that 2-PAM@bio-MOF-1 might be effective for enabling the slow release of 2-PAM in the human body. Indeed, the maximum reactivation rate of acetylcholinesterase in sarin-poisoned mice reached 82.5%. In addition, 2-PAM@bio-MOF-1 demonstrated the ability to adsorb and remove sulfur mustard (HD) in solution and from the skin of guinea pigs.

Engineering mesoporous silica nanoparticles for drug delivery: where are we after two decades?

The present review details a chronological description of the events that took place during the development of mesoporous materials, their different synthetic routes and their use as drug delivery systems. The outstanding textural properties of these materials quickly inspired their translation to the nanoscale dimension leading to mesoporous silica nanoparticles (MSNs). The different aspects of introducing pharmaceutical agents into the pores of these nanocarriers, together with their possible biodistribution and clearance routes, would be described here. The development of smart nanocarriers that are able to release a high local concentration of the therapeutic cargo on-demand after the application of certain stimuli would be reviewed here, together with their ability to deliver the therapeutic cargo to precise locations in the body. The huge progress in the design and development of MSNs for biomedical applications, including the potential treatment of different diseases, during the last 20 years will be collated here, together with the required work that still needs to be done to achieve the clinical translation of these materials. This review was conceived to stand out from past reports since it aims to tell the story of the development of mesoporous materials and their use as drug delivery systems by some of the story makers, who could be considered to be among the pioneers in this area.

Antibody-Targeted Liposomes for Enhanced Targeting of the Blood-Brain Barrier

The blood-brain barrier (BBB) hinders therapeutic delivery to the central nervous system (CNS), thereby impeding the development of therapies for brain injury and disease. Receptor-mediated transcytosis (RMT) systems are a promising way to shuttle a targeted therapeutic into the brain. Here, we developed and evaluated an RMT antibody-targeted liposomal system. A previously identified antibody, scFv46.1, that binds to the human and murine BBB and can pass through the murine BBB by transcytosis after intravenous injection was used to decorate the surface of liposomes. Using an in vitro BBB model, we demonstrated the cellular uptake of scFv46.1-modified liposomes (46.1-Lipo). Next, the biodistribution and brain uptake capacity of 46.1-targeted liposomes were assessed after intravenous administration. Our results showed that 46.1-Lipo can lead to increased brain accumulation through targeting of the brain vasculature. Initial rate pharmacokinetic experiments and biodistribution analyses indicated that 46.1-Lipo loaded with pralidoxime exhibited a 10-fold increase in brain accumulation compared with a mock-targeted liposomal group, and this increased accumulation was brain-specific. These studies indicate the potential of this 46.1-Lipo system as a synthetic vehicle for the targeted transport of therapeutic molecules into the CNS.

Loading and Sustained Release of Pralidoxime Chloride from Swellable MIL-88B(Fe) and Its Therapeutic Performance on Mice Poisoned by Neurotoxic Agents

Maintaining a long-term continuous and stable reactivator blood concentration to treat organophosphorus nerve agent poisoning using acetylcholinesterase (AChE) reactivator pralidoxime chloride (2-PAM) is very important yet difficult. Because the flexible framework of MIL-88B(Fe) nanoparticles (NPs) can swell in polar solvents, pralidoxime chloride (2-PAM) was loaded in MIL-88B(Fe) NPs (size: ca. 500 nm) by stirring and incubation in deionized water to obtain 2-PAM@MIL-88B(Fe), which had a maximum drug loading capacity of 12.6 wt %. The as-prepared composite was characterized by IR, powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM), ζ-potential, Brunauer-Emmett-Teller (BET), and thermogravimetry/differential thermal analysis (TG/DTA). The results showed that under constant conditions, the maximum drug release rates of 2-PAM@MIL-88B(Fe) in absolute ethanol, phosphate-buffered saline (PBS) solution (pH = 7.4), and PBS solution (pH = 4) at 150 h were 51.7, 80.6, and 67.1%, respectively. This was because the composite showed different swelling behaviors in different solvents. In PBS solution with pH = 2, the 2-PAM@MIL-88B(Fe) framework collapsed after 53 h and released 100% of 2-PAM. For mice after intragastric poisoning with sarin (a neurotoxic agent), an atropine-assisted 2-PAM@MIL-88B(Fe) treatment experiment revealed that 2-PAM@MIL-88B(Fe) continuously released 2-PAM for more than 72 h so that poisoned AChE was continuously and steadily reactivated. The reactivation rate of AChE was 56.7% after 72 h. This composite is expected to provide a prolonged, stable therapeutic drug for the mid- and late-stage treatment of neurotoxic agent poisoning.

TRPV4 Regulates Soman-Induced Status Epilepticus and Secondary Brain Injury via NMDA Receptor and NLRP3 Inflammasome

Nerve agents are used in civil wars and terrorist attacks, posing a threat to public safety. Acute exposure to nerve agents such as soman (GD) causes serious brain damage, leading to death due to intense seizures induced by acetylcholinesterase inhibition and neuronal injury resulting from increased excitatory amino-acid levels and neuroinflammation. However, data on the anticonvulsant and neuroprotective efficacies of currently-used countermeasures are limited. Here, we evaluated the potential effects of transient receptor vanilloid 4 (TRPV4) in the treatment of soman-induced status epilepticus (SE) and secondary brain injury. We demonstrated that TRPV4 expression was markedly up-regulated in rat hippocampus after soman-induced seizures. Administration of the TRPV4 antagonist GSK2193874 prior to soman exposure significantly decreased the mortality rate in rats and reduced SE intensity. TRPV4-knockout mice also showed lower incidence of seizures and higher survival rates than wild-type mice following soman exposure. Further in vivo and in vitro experiments demonstrated that blocking TRPV4 prevented NMDA receptor-mediated glutamate excitotoxicity. The protein levels of the NLRP3 inflammasome complex and its downstream cytokines IL-1β and IL-18 increased in soman-exposed rat hippocampus. However, TRPV4 inhibition or deletion markedly reversed the activation of the NLRP3 inflammasome pathway. In conclusion, our study suggests that the blockade of TRPV4 protects against soman exposure and reduces brain injury following SE by decreasing NMDA receptor-mediated excitotoxicity and NLRP3-mediated neuroinflammation. To our knowledge, this is the first study regarding the "dual-switch" function of TRPV4 in the treatment of soman intoxication.

Brain-targeted delivery of obidoxime, using aptamer-modified liposomes, for detoxification of organophosphorus compounds

Effective intracerebral delivery acetylcholinesterase (AChE) reactivator is key for the acute organophosphorus (OPs) poison treatment. However, the blood-brain barrier (BBB) restricts the transport of these drugs from blood into the brain. Herein, we developed transferrin receptor (TfR) aptamer-functionalized liposomes (Apt-LP) that could deliver AChE reactivator (obidoxime) across the BBB to act against paraoxon (POX) poisoning. The aptamer had strong affinity for TfR and was modified with 3'-inverted deoxythymidine (dT) to improve serum stability. The uptake of Apt-LP by bEnd.3 cells was significantly higher than that of non-targeting liposomes. The ability of Apt-LP to penetrate intact BBB was confirmed in in vitro BBB mice model and in vivo biodistribution studies. Treatment of POX-poisoned mice with Apt-LP-LuH-6 reactivated 18% of the brain AChE activity and prevented brain damage to some extent. Taken together, these results showed that Apt-LP may be used as a promising brain-targeted drug delivery system against OPs toxicity.

Biomedical potentialities of cationic geminis as modulating agents of liposome in drug delivery across biological barriers and cellular uptake

Hydroxyethyl bearing gemini surfactants, alkanediyl-α,ω-bis(N-hexadecyl-N-2-hydroxyethyl-N-methylammonium bromide), 16-s-16(OH), were used to augment phosphatidylcholine based liposomes to achieve higher stability and enhanced cellular uptake and penetration. The developed liposomes were loaded with rhodamine B, doxorubicin hydrochloride, pralidoxime chloride to investigate release properties, cytotoxicity in vitro, as well as ability to cross the blood-brain barrier. At molar ratio of 35:1 (lipid:surfactant) the formulation was found to be of low toxicity, stable for two months, and able to deliver rhodamine B beyond the blood-brain barrier in rats. In vivo, pharmacokinetics of free and formulated 2-PAM in plasma and brain were evaluated, liposomal 2-PAM was found to reactivate 27% of brain acetylcholinesterase, which is, to our knowledge, the first example of such high degree of reactivation after intravenous administration of liposomal drug.

A protein nanocomposite for ultra-fast, efficient and non-irritating skin decontamination of nerve agents

In recent assassinations reported in London and Malaysia, nerve agents were used to cause death, by skin poisoning. Skin decontamination is the ultimate and most important defense against nerve agent poisoning, because no effective antidote currently exists. However, almost no existing material can achieve effective and rapid decontamination without irritating the skin. This study links proteins that exhibit no decontamination ability with polymers to form a nanocomposite. This creates a nanospace on the surface of the protein that attracts and traps organic molecules, effectively adsorbing the nerve agent Soman within several seconds, without irritating the skin. Analysis of the different components of proteins and polymers reveals that the decontamination efficiency is considerably affected by the thickness of the coated polymer. Moreover, the thickness of the layer is predominantly determined by the size and species of the core and the crosslinking method. Further in vivo experiments on rats poisoned with Soman verify the efficiency and safety of the nanocomposite. These results could be used to design and synthesize more multi-functional and effective decontamination materials.

A brief survey on the advanced brain drug administration by nanoscale carriers: With a particular focus on AChE reactivators

Obviously, delivery of the medications to the brain is more difficult than other tissues due to the existence of a strong obstacle, which is called blood-brain barrier (BBB). Because of the lipophilic nature of this barrier, it would be a complex (and in many cases impossible) process to cross the medications with hydrophilic behavior from BBB and deliver them to the brain. Thus, novel intricate drug-carriers in nano scales have been recently developed and suitably applied for this purpose. One of the most important categories of these hydrophilic medications, are reactivators for acetyl cholinesterase (AChE) enzyme that facilitates the breakdown of acetylcholine (as a neurotransmitter). The AChE function is inhibited by organophosphorus (OP) nerve agents that are extremely used in military conflicts. In this review, the abilities of the nanosized drug delivery systems to perform as suitable vehicles for AChE reactivators are comprehensively discussed.

Nanomaterials meet zebrafish: Toxicity evaluation and drug delivery applications

With the rapid development of engineered nanomaterials for various applications, in vivo toxicological studies for evaluating the potential hazardous effects of nanomaterials on environmental and human safety are in urgent need. Zebrafish has long been considered as the "gold standard" for biosafety assessments of chemicals and pollutants due to its high fecundity, cost-effectiveness, well-characterized developmental stages, optical transparency, and so forth. Thus, zebrafish holds great potential for high-throughput nanotoxicity screening. In this review, we summarize the in vivo toxicological profiles of different nanomaterials, including Ag nanoparticles (NPs), CuO NPs, silica NPs, polymeric NPs, quantum dots, nanoscale metal-organic frameworks, etc, in zebrafish and focus on how the physicochemical properties (e.g., size, surface charge, and surface chemistry) of these nanomaterials influence their biosafety. In addition, we also report the recent advances of the in vivo delivery of nanopharmaceuticals using zebrafish as the model organism for therapeutic assessment, biodistribution tracking, and the controlled release of loaded drugs. Limitations and special considerations of zebrafish model are also discussed. Overall, zebrafish is expected to serve as a high-throughput screening platform for nanotoxicity and drug delivery assessment, which may instruct the design of safe nanomaterials and more effective nanomedicines.

Current approaches to enhancing oxime reactivator delivery into the brain

The misuse of organophosphate compounds still represents a current threat worldwide. Treatment of poisoning with organophosphates (OPs) remains unsatisfactorily resolved despite the extensive investment in research in academia. There are no universal, effective and centrally-active acetylcholinesterase (AChE) reactivators to countermeasure OP intoxication. One major obstacle is to overcome the blood-brain barrier (BBB). The central compartment is readily accessible by the OPs which are lipophilic bullets that can easily cross the BBB, whereas first-line therapeutics, namely oxime-based AChE reactivators and atropine, do not cross or do so rather slowly. The limitation of oxime-based AChE reactivators can be ascribed to their chemical nature, bearing a positive charge which is essential either for their AChE affinity or their reactivating potency. The aim of this article is to review the methods for targeting the brain by oxime reactivators that have been developed so far. Approaches using prodrugs, lipophilicity enhancement, or sugar-based oximes have been rather unsuccessful. However, other strategies have been more promising, such as the use of nanoparticles or co-administration of the reactivator with efflux transporter inhibitors. Encouraging results have also been associated with intranasal delivery, but research in this field is still at the beginning. Further research of auspicious approaches is inevitable.

Combination delivery of two oxime-loaded lipid nanoparticles: Time-dependent additive action for prolonged rat brain protection

A novel approach for brain protection against poisoning by organophosphorus agents is developed based on the combination treatment of dual delivery of two oximes. Pralidoxime chloride (2-PAM) and a novel reactivator, 6-(5-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)pentyl)-3-hydroxy picolinaldehyde oxime (3-HPA), have been loaded in solid-lipid nanoparticles (SLNs) to offer distinct release profile and systemic half-life for both oximes. To increase the therapeutic time window of both oximes, SLNs with two different compartments were designed to load each respective drug. Oxime-loaded SLNs of hydrodynamic diameter between 100 and 160 nm and negative zeta potential (-30 to -25 mV) were stable for a period of 10 months at 4 °C. SLNs displayed longer circulation time in the bloodstream compared to free 3-HPA and free 2-PAM. Oxime-loaded SLNs were suitable for intravenous (iv) administration. Paraoxon-poisoned rats (0.8 × LD₅₀) were treated with 3-HPA-loaded SLNs and 2-PAM+3-HPA-loaded SLNs at the dose of 3-HPA and 2-PAM of 5 mg/kg. Brain AChE reactivation up to 30% was slowly achieved in 5 h after administration of 3-HPA-SLNs. For combination therapy with two oximes, a time-dependent additivity and increased reactivation up to 35% were observed.

Mixed cationic liposomes for brain delivery of drugs by the intranasal route: The acetylcholinesterase reactivator 2-PAM as encapsulated drug model

New mixed cationic liposomes based on L-α-phosphatidylcholine and dihexadecylmethylhydroxyethylammonium bromide (DHDHAB) were designed to overcome the BBB crossing by using the intranasal route. Synthesis and self-assembly of DHDHAB were performed. A low critical association concentration (0.01 mM), good solubilization properties toward hydrophobic dye Orange OT and antimicrobial activity against gram-positive bacteria Staphylococcus aureus (MIC=7.8 μg mL^-1) and Bacillus cereus (MIC=7.8 μg mL^-1), low hemolytic activities against human red blood cells (less than 10%) were achieved. Conditions for preparation of cationic vesicles and mixed liposomes with excellent colloidal stability at room temperature were determined. The intranasal administration of rhodamine B-loaded cationic liposomes was shown to increase bioavailability into the brain in comparison to the intravenous injection. The cholinesterase reactivator, 2-PAM, was used as model drug for the loading in cationic liposomes. 2-PAM-loaded cationic liposomes displayed high encapsulation efficiency (∼ 90%) and hydrodynamic diameter close to 100 nm. Intranasally administered 2-PAM-loaded cationic liposomes were effective against paraoxon-induced acetylcholinesterase inhibition in the brain. 2-PAM-loaded liposomes reactivated 12 ± 1% of brain acetylcholinesterase. This promising result opens the possibility to use marketed positively charged oximes in medical countermeasures against organophosphorus poisoning for reactivation of central acetylcholinesterase by implementing a non-invasive approach, via the "nose-brain" pathway.

A Transferrin-Conjugated Hollow Nanoplatform for Redox-Controlled and Targeted Chemotherapy of Tumor with Reduced Inflammatory Reactions

Purpose: In this study, we report the design, development and evaluation of a hollow drug delivery nanoplatform for cancer therapy in vitro and in vivo. This composite nanosystem was prepared by modifying hollow mesoporous silica nanoparticles (HMSNs) with transferrin (Tf) targeting moieties via redox-liable linkage, and was capable of delivering therapeutic cargos (doxorubicin) specifically to the tumor site and subsequently releasing them in an on-demand manner. Moreover, the Tf corona could simultaneously reduce the inflammatory response after intravenous administration in vivo. Methods: Nanostructural morphology of the drug delivery system was observed by scanning electron microscope and transmission electron microscope. The preparation process was monitored primarily using Fourier-transform infrared spectroscopy, dynamic light scattering, nitrogen adsorption/desorption isotherm, and thermogravimetric analysis. The release profile in solution was monitored by fluorescence spectroscopy. In vitro drug delivery efficacy was evaluated on MDA-MB-231 breast cancer cell line using confocal laser scanning microscopy, MTT assay and flow cytometry. In vitro inflammatory response was evaluated on RAW264.7 macrophage cells. In vivo therapeutic experiments were carried out using in situ mouse breast cancer models. Results: The experimental results evidently demonstrate that the developed nanocarrier could effectively deliver anticancer drugs to the tumor site in a targeted manner and release them in response to the elevated glutathione level inside tumor cells, resulting in improved anticancer efficacy both in vitro and in vivo. Moreover, the Tf conjugation significantly ameliorated the inflammatory reaction triggered by the administration of the nanocarrier. Conclusions: This manuscript demonstrated that the Tf-conjugated HMSNs could enhance the delivery efficiency of anticancer drugs, while simultaneously alleviating the adverse side effects. The current study presents a promising integrated delivery system toward effective and safe cancer treatment.

Mixed shell mesoporous silica nanoparticles for controlled drug encapsulation and delivery

Aim: Smart mesoporous silica nanoparticles (MSNs) with mixed polymeric shell (MS-MSNs) were prepared to realize controlled encapsulation and responsive delivery of anticancer drugs. Materials & methods: Two kinds of polymers, including nonthermoresponsive poly(ethylene glycol) and thermoresponsive poly(N-isopropyl acrylamide), were grafted onto the outlets of the MSNs through acidic liable Schiff base bonds. Results: Poly(N-isopropyl acrylamide) chains could control the release rate of drugs through phase transition, while poly(ethylene glycol) chains could maintain the colloid stability of MSNs. Drugs can be released through the gradual hydrolysis of Schiff base bonds in tumor acidic environment. Conclusion: The MS-MSNs gave consideration to both the responsiveness and stability of carriers, and could realize the release of drugs as much as possible in tumor tissues.

Nanoparticle-Delivered 2-PAM for Rat Brain Protection against Paraoxon Central Toxicity

Solid lipid nanoparticles (SLNs) are among the most promising nanocarriers to target the blood-brain barrier (BBB) for drug delivery to the central nervous system (CNS). Encapsulation of the acetylcholinesterase reactivator, pralidoxime chloride (2-PAM), in SLNs appears to be a suitable strategy for protection against poisoning by organophosphorus agents (OPs) and postexposure treatment. 2-PAM-loaded SLNs were developed for brain targeting and delivery via intravenous (iv) administration. 2-PAM-SLNs displayed a high 2-PAM encapsulation efficiency (∼90%) and loading capacity (maximum 30.8 ± 1%). Drug-loaded particles had a mean hydrodynamic diameter close to 100 nm and high negative zeta potential (-54 to -15 mV). These properties contribute to improve long-term stability of 2-PAM-SLNs when stored both at room temperature (22 °C) and at 4 °C, as well as to longer circulation time in the bloodstream compared to free 2-PAM. Paraoxon-poisoned rats (2 × LD₅₀) were treated with 2-PAM-loaded SLNs at a dose of 2-PAM of 5 mg/kg. 2-PAM-SLNs reactivated 15% of brain AChE activity. Our results confirm the potential use of SLNs loaded with positively charged oximes as a medical countermeasure both for protection against OPs poisoning and for postexposure treatment.

Cholinesterase reactivators and bioscavengers for pre- and post-exposure treatments of organophosphorus poisoning

Organophosphorus agents (OPs) irreversibly inhibit acetylcholinesterase (AChE) causing a major cholinergic syndrome. The medical counter-measures of OP poisoning have not evolved for the last 30 years with carbamates for pretreatment, pyridinium oximes-based AChE reactivators, antimuscarinic drugs and neuroprotective benzodiazepines for post-exposure treatment. These drugs ensure protection of peripheral nervous system and mitigate acute effects of OP lethal doses. However, they have significant limitations. Pyridostigmine and oximes do not protect/reactivate central AChE. Oximes poorly reactivate AChE inhibited by phosphoramidates. In addition, current neuroprotectants do not protect the central nervous system shortly after the onset of seizures when brain damage becomes irreversible. New therapeutic approaches for pre- and post-exposure treatments involve detoxification of OP molecules before they reach their molecular targets by administrating catalytic bioscavengers, among them phosphotriesterases are the most promising. Novel generation of broad spectrum reactivators are designed for crossing the blood-brain barrier and reactivate central AChE. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Antibody-conjugated mesoporous silica nanoparticles for brain microvessel endothelial cell targeting

Size and bioconjugation effects of Ri7 antibody conjugated mesoporous silica nanoparticles (MSNs) influence in vitro and in vivo targeting ability to BMECs.

Synthesis of a core/satellite-like multifunctional nanocarrier for pH- and NIR-triggered intracellular chemothermal therapy and tumor imaging

A core/satellite-like multifunctional system was developed for synergistic chemothermal therapy and tumor imaging based on the AuNRs capped mesoporous silica nanocarrier with UCNP core.