Antagonism of paraoxon intoxication by recombinant phosphotriesterase encapsulated within sterically stabilized liposomes

Bioremediation and bioscavenging for elimination of organophosphorus threats: An approach using enzymatic advancements

Organophosphorus compounds (OP) are highly toxic pesticides and nerve agents widely used in agriculture and chemical warfare. The extensive use of these chemicals has severe environmental implications, such as contamination of soil, water bodies, and food chains, thus endangering ecosystems and biodiversity. Plants absorb pesticide residues, which then enter the food chain and accumulate in the body fat of both humans and animals. Numerous human cases of OP poisoning have been linked to both acute and long-term exposure to these toxic OP compounds. These compounds inhibit the action of the acetylcholinesterase enzyme (AChE) by phosphorylation, which prevents the breakdown of acetylcholine (ACh) neurotransmitter into choline and acetate. Thus, it becomes vital to cleanse the environment from these chemicals utilizing various physical, chemical, and biological methods. Biological methods encompassing bioremediation using immobilized microbes and enzymes have emerged as environment-friendly and cost-effective approaches for pesticide removal. Cell/enzyme immobilized systems offer higher stability, reusability, and ease of product recovery, making them ideal tools for OP bioremediation. Interestingly, enzymatic bioscavengers (stoichiometric, pseudo-catalytic, and catalytic) play a vital role in detoxifying pesticides from the human body. Catalytic bioscavenging enzymes such as Organophosphate Hydrolase, Organophosphorus acid anhydrolase, and Paraoxonase 1 show high degradation efficiency within the animal body as well as in the environment. Moreover, these enzymes can also be employed to decontaminate pesticides from food, ensuring food safety and thus minimizing human exposure. This review aims to provide insights to potential collaborators in research organizations, government bodies, and industries to bring advancements in the field of bioremediation and bioscavenging technologies for the mitigation of OP-induced health hazards.

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.

Therapeutic nanoreactors for detoxification of xenobiotics: Concepts, challenges and biotechnological trends with special emphasis to organophosphate bioscavenging

The introduction of enzyme nanoreactors in medicine is relatively new. However, this technology has already been experimentally successful in cancer treatments, struggle against toxicity of reactive oxygen species in inflammatory processes, detoxification of drugs and xenobiotics, and correction of metabolic and genetic defects by using encapsulated enzymes, acting in single or cascade reactions. Biomolecules, e.g. enzymes, antibodies, reactive proteins capable of inactivating toxicants in the body are called bioscavengers. In this review, we focus on enzyme-containing nanoreactors for in vivo detoxification of organophosphorous compounds (OP) to be used for prophylaxis and post-exposure treatment of OP poisoning. A particular attention is devoted to bioscavenger-containing injectable nanoreactors operating in the bloodstream. The nanoreactor concept implements single or multiple enzymes and cofactors co-encapsulated in polymeric semi-permeable nanocontainers. Thus, the detoxification processes take place in a confined space containing highly concentrated bioscavengers. The article deals with historical and theoretical backgrounds about enzymatic detoxification of OPs in nanoreactors, nanoreactor polymeric enveloppes, realizations and advantages over other approaches using bioscavengers.

Enhancing organophosphate hydrolase efficacy via protein engineering and immobilization strategies

Organophosphorus compounds (OPs), developed as pesticides and chemical warfare agents, are extremely toxic chemicals that pose a public health risk. Of the different detoxification strategies, organophosphate-hydrolyzing enzymes have attracted much attention, providing a potential route for detoxifying those exposed to OPs. Phosphotriesterase (PTE), also known as organophosphate hydrolase (OPH), is one such enzyme that has been extensively studied as a catalytic bioscavenger. In this review, we will discuss the protein engineering of PTE aimed toward improving the activity and stability of the enzyme. In order to make enzyme utilization in OP detoxification more favorable, enzyme immobilization provides an effective means to increase enzyme activity and stability. Here, we present several such strategies that enhance the storage and operational stability of PTE/OPH.

Enzymatic detoxification of organophosphorus pesticides and related toxicants

Millions of cases of pesticide intoxication occur yearly and represent a public health problem. In addition, pesticide poisoning is the preferred suicidal method in rural areas. The use of enzymes for the treatment of intoxication due to organophosphorus pesticides was proposed decades ago. Several enzymes are able to transform organophosphorus compounds such as pesticides and nerve agents. Some specific enzymatic treatments have been proposed, including direct enzyme injection, liposome and erythrocytes carriers, PEGylated preparations and extracorporeal enzymatic treatments. Nevertheless, no enzymatic treatments are currently available. In this work, the use of enzymes for treating of organophosphorus pesticide intoxication is critically reviewed and the remaining challenges are discussed.

Pralidoxime in carbaryl poisoning: an animal model

Introduction: Poisoning from organophosphates and carbamates is a significant cause of morbidity and mortality worldwide. Concerns have been expressed over the safety and efficacy of the use of oximes such as pralidoxime (2-PAM) in patients with carbamate poisoning in general, and more so with carbaryl poisoning specifically. The goal of the present study was to evaluate the role of 2-PAM in a mouse model of lethal carbaryl poisoning. Methods: Female ICR Swiss Albino mice weighing 25-30 g were acclimated to the laboratory and housed in standard conditions. One hundred and ten mice received an LD 50 dose of carbaryl subcutaneously. Ten minutes later, they were randomized by block randomization to one of eight treatment groups: normal saline control, atropine alone, 100 mg/kg 2-PAM with and without atropine, 50 mg/kg 2-PAM with and without atropine, and 25 mg/kg 2-PAM with and without atropine. All medications were given intraperitoneally and the atropine dose was constant at 4 mg/kg. The single objective endpoint was defined as survival to 24 hours. Fatalities were compared using a Chi squared or Fisher's exact test. Results: Following an LD50 of carbaryl, 60% of the animals died. Atropine alone statistically improved survival (15% lethality). High dose 2-PAM with and without atropine was numerically worse, but not statistically different from control. While the middle dose of 2-PAM was no different than control, the addition of atropine improved survival (10% fatality). Low-dose 2-PAM statistically improved survival (25% lethality). Atropine further reduced lethality to 10%. Conclusion: When appropriately dosed, 2-PAM alone protects against carbaryl poisoning in mice. Failure to demonstrate this benefit in other models may be the result of oxime overdose. Human & Experimental Toxicology (2007) 26, 125-129

Enzymatic reactions in confined environments

Within each biological cell, surface- and volume-confined enzymes control a highly complex network of chemical reactions. These reactions are efficient, timely, and spatially defined. Efforts to transfer such appealing features to in vitro systems have led to several successful examples of chemical reactions catalysed by isolated and immobilized enzymes. In most cases, these enzymes are either bound or adsorbed to an insoluble support, physically trapped in a macromolecular network, or encapsulated within compartments. Advanced applications of enzymatic cascade reactions with immobilized enzymes include enzymatic fuel cells and enzymatic nanoreactors, both for in vitro and possible in vivo applications. In this Review, we discuss some of the general principles of enzymatic reactions confined on surfaces, at interfaces, and inside small volumes. We also highlight the similarities and differences between the in vivo and in vitro cases and attempt to critically evaluate some of the necessary future steps to improve our fundamental understanding of these systems.

Enzyme therapeutics for systemic detoxification

Life relies on numerous biochemical processes working synergistically and correctly. Certain substances disrupt these processes, inducing living organism into an abnormal state termed intoxication. Managing intoxication usually requires interventions, which is referred as detoxification. Decades of development on detoxification reveals the potential of enzymes as ideal therapeutics and antidotes, because their high substrate specificity and catalytic efficiency are essential for clearing intoxicating substances without adverse effects. However, intrinsic shortcomings of enzymes including low stability and high immunogenicity are major hurdles, which could be overcome by delivering enzymes with specially designed nanocarriers. Extensive investigations on protein delivery indicate three types of enzyme-nanocarrier architectures that show more promise than others for systemic detoxification, including liposome-wrapped enzymes, polymer-enzyme conjugates, and polymer-encapsulated enzymes. This review highlights recent advances in these nano-architectures and discusses their applications in systemic detoxifications. Therapeutic potential of various enzymes as well as associated challenges in achieving effective delivery of therapeutic enzymes will also be discussed.

Confidence limit calculation for antidotal potency ratio derived from lethal dose 50

AIM: To describe confidence interval calculation for antidotal potency ratios using bootstrap method.

METHODS: We can easily adapt the nonparametric bootstrap method which was invented by Efron to construct confidence intervals in such situations like this. The bootstrap method is a resampling method in which the bootstrap samples are obtained by resampling from the original sample.

RESULTS: The described confidence interval calculation using bootstrap method does not require the sampling distribution antidotal potency ratio. This can serve as a substantial help for toxicologists, who are directed to employ the Dixon up-and-down method with the application of lower number of animals to determine lethal dose 50 values for characterizing the investigated toxic molecules and eventually for characterizing the antidotal protections by the test antidotal systems.

CONCLUSION: The described method can serve as a useful tool in various other applications. Simplicity of the method makes it easier to do the calculation using most of the programming software packages.

Nanogel scavengers for drugs: local anesthetic uptake by thermoresponsive nanogels

The use of functional nanogels based on poly(N-isopropylacrylamide) for effectively scavenging compounds (here, the model drug bupivacaine) is demonstrated using an in vitro cell-based assay. Nanogels containing higher loadings of acidic functional groups or more core-localized functional group distributions bound more bupivacaine, while nanogel size had no significant effect on drug binding. Increasing the dose of nanogel applied also facilitated more bupivacaine binding for all nanogel compositions tested. Binding was driven predominantly by acid-base interactions between the nanogels (anionic) and bupivacaine (cationic) at physiological pH, although both non-specific absorption and hydrophobic partitioning also contributed to drug scavenging. Nanogels exhibited minimal cytotoxicity to multiple cell types and were well tolerated in vivo via peritoneal injections, although larger nanogels caused limited splenic toxicity at higher concentrations. The cell-based assay described herein is found to facilitate more robust drug uptake measurements for nanogels than conventional centrifugation-based assays, in which nanogels can be compressed (and thus drug released) during the measurement.

Nano-intercalated organophosphorus-hydrolyzing enzymes in organophosphorus antagonism

A dendritic poly(2-alkyloxazoline)-based polymer was studied as a new carrier system for the organophosphorus-hydrolyzing recombinant enzymes, organophosphorus acid anhydrolase and organophosphorus hydrolase. Paraoxon (PO) and diisopropylfluorophosphate (DFP) were used as model organophosphorus compounds. Changes in plasma cholinesterase activity were monitored. The cholinesterase activity was proportional to the concentrations of DFP or PO. Plasma cholinesterase activity was higher in animals receiving enzyme and oxime before the organophosphates than in the oxime-only pretreated groups. These studies suggest that cholinesterase activity can serve as an indicator for the in vivo protection by the nano-intercalated organophosphorus acid anhydrolase or organophosphorus hydrolase against organophosphorus intoxications. These studies represent a practical application of polymeric nano-delivery systems as enzyme carriers in drug antidotal therapy.

Nanoencapsulated and microencapsulated enzymes in drug antidotal therapy

A catalytic bioscavenger for the therapeutic and prophylactic defense against recognized chemical threat agents has been a long-standing objective of civilian and military research. Among the toxic agents, organophosphate molecules and cyanide have been widely studied. In order to overcome the limitations of traditional antidotal therapies, isolated, purified, recombinant enzymes with bacterial origin possessing fast catalytic activity were used in in vitro and in vivo experiments. However, the fast degradation, excretion and adverse immunologic reaction against enzymes limit their in vivo use. Development of biodegradable, nontoxic carrier systems, microparticles, and nanoparticles—offering advantageous pharmacokinetic parameters was suggested. Present work deals with the perspectives of carrier systems, such as resealed and annealed erythrocytes and sterically stabilized liposomes. Dendritic polymers and polymer-conjugated enzymes, being in the focus of extensive research efforts nowadays, are also discussed.

Physicochemical characterization of stealth liposomes encapsulating an organophosphate hydrolyzing enzyme

The present studies were focused on the preparation and characterization of stericaly stabilized liposomes (SLs) encapsulating a recombinant organophosphorus hydrolyzing phosphotriesterase (OPH) enzyme for the antagonism of organophosphorus intoxication. Earlier results indicate that the liposomal carrier system provides an enhanced protective effect against the organophosphorus molecule paraoxon, presenting a more effective therapy with less toxicity than the most commonly used antidotes. Physicochemical characterization of the liposomal OPH delivery system is essential in order to get information on its in vitro stability and in vivo fate. Osmolarity, pH, viscosity, and encapsulation efficiency of the SL preparation and the surface potential of the vesicles were determined. The membrane rigidity and the impact of OPH enzyme on it was studied by electron-paramagnetic resonance spectroscopy, using spin probes. The in vitro stability of the liposomal preparations, the vesicle size distribution, and its alteration during a 3-week storage were followed by dynamic light-scattering measurements. Further, the stability of encapsulated and nonencapsulated OPH was compared in puffer and plasma.

Characterization of liposomal vesicles encapsulating rhodanese for cyanide antagonism

The major mechanism of removing cyanide from the body is its enzymatic conversion by a sulfurtransferase, e.g. rhodanese, to the less toxic thiocyanate in the presence of a sulfur donor. Earlier results demonstrated that externally administered encapsulated rhodanese significantly enhances the in vivo efficacy of the given sulfur donor. Present studies are focused on liposomal carrier systems encapsulating rhodanese. Physicochemical properties, e.g. membrane rigidity, size distribution, surface potential, osmolarity, and viscosity, were determined for various liposomal lipid compositions and hydrating buffers to establish in vitro stability and in vivo fate. Lipid composition was also optimized to achieve maximum encapsulation efficiency.

Current and Emerging Detoxification Therapies for Critical Care

Toxicity resulting from prescription drugs such as tricyclic antidepressants and cardioactive steroids, as well as drugs of abuse and exposure to environmental chemicals, represents a major need for detoxification treatments. Particles and colloids, antibody fragments (Fab), and indirect treatment methods such as macroemulsions, are currently being developed or employed as detoxification therapies. Colloids, particles, and protein fragments typically mitigate toxicity by binding to the toxin and reducing its concentration in vital organs. Indirect methods such as macroemulsions and sodium bicarbonate act directly on the affected organs, rather than the toxin. In this review, key design parameters (i.e. binding affinity, biocompatibility, pharmacokinetics) are discussed for each type of detoxification treatment. In addition, some of the latest research in each area is reviewed.

[Novel method for preparing vesicles from a monodisperse emulsion aimed at controlling the size and improving the entrapment yield]

A vesicle is a compartment composed of lipid bilayer of amphiphilic molecules. The vesicle is applied to carriers of drugs, cosmetics and functional food ingredients in industries. Vesicles are also applied as a model for artificial cell membrane and expected as micro- and nano-reactors. They are generally prepared by the hydration of dry lipid film, but there is no method to prepare vesicles of a controlled size and high entrapment yield of hydrophilic materials inside them. In this article, a microchannel (MC) emulsification method was applied to prepare vesicles aimed at controlling the size and improving the entrapment yield. Firstly, monodisperse water-in-oil (W/O) emulsions were prepared by the MC emulsification method. In this process, hydrophilic materials to be entrapped were contained inside the water droplets of the emulsions. Keeping the water droplets frozen, the emulsifier was replaced by a bilayer-forming lipid mixture, and then the oil phase was evaporated. After hydration of lipid layers surrounding the water droplets, vesicles were formed. We call this preparation "lipid-coated ice droplet hydration method". The final sizes of the prepared vesicles were comparable to the original emulsion droplet sizes. This means that the size of vesicles can be controlled by controlling the size of original water droplets of the W/O emulsions. Furthermore, calcein as a hydrophilic fluorescent marker and biopolymers, such as enzyme and polysaccharide, were entrapped into the internal water phases of vesicles. The method proposed in this study enables the formation of vesicles with a controlled size and high entrapment yields, potentially useful for expanding the application fields of vesicles as biocompatible carriers and micro- and nano-reactors for biochemical reactions.

Uptake of amitriptyline and nortriptyline with liposomes, proteins, and serum: implications for drug detoxification

Liposomes composed of DOPG and DMPC were studied for their ability to sequester amitriptyline and nortriptyline under physiological conditions. The liposomes reduced the free drug concentration in protein mixtures and in human serum, but the drug uptake efficiency of liposomes was reduced in the presence of plasma proteins, perhaps due to adsorption of proteins on the liposomes. The reduction was significantly more for the pure DOPG liposomes. The 50:50 DMPC:DOPG liposomes (0.72 mg lipid/mL) reduced the free amitriptyline concentration by 50-60% in the presence of 7% proteins (4% albumin (w/w), 2% fibrinogen (w/w), 1% globulins (w/w)). In human serum, the free drug reduction was 35-70% with the same 50:50 liposomes (0.72 mg lipid/mL). The liposomal systems were equally efficient at sequestering nortriptyline, which is a major metabolite of amitriptyline. The drug binding to liposomes in the presence of serum proteins is also quick and reversible and the likely mechanism of drug sequestration is adsorption of drug on the surface of liposomes. Accordingly, the drug uptake increases with increased charge and lipid loading. Even though the serum proteins reduced the effectiveness of the liposomes at sequestering the drug, the 50:50 DMPC:DOPG liposomes may be effective at treating amitriptyline overdose patients.

Injectable nanocarriers for biodetoxification

Hospitals routinely treat patients suffering from overdoses of drugs or other toxic chemicals as a result of illicit drug consumption, suicide attempts or accidental exposures. However, for many life-threatening situations, specific antidotes are not available and treatment is largely based on emptying the stomach, administering activated charcoal or other general measures of intoxication support. A promising strategy for managing such overdoses is to inject nanocarriers that can extract toxic agents from intoxicated tissues. To be effective, the nanocarriers must remain in the blood long enough to sequester the toxic components and/or their metabolites, and the toxin bound complex must also remain stable until it is removed from the bloodstream. Here, we discuss the principles that govern the use of injectable nanocarriers in biodetoxification and review the pharmacological performance of a number of different approaches.

Nano-enabled synthetic biology

Biological systems display a functional diversity, density and efficiency that make them a paradigm for synthetic systems. In natural systems, the cell is the elemental unit and efforts to emulate cells, their components, and organization have relied primarily on the use of bioorganic materials. Impressive advances have been made towards assembling simple genetic systems within cellular scale containers. These biological system assembly efforts are particularly instructive, as we gain command over the directed synthesis and assembly of synthetic nanoscale structures. Advances in nanoscale fabrication, assembly, and characterization are providing the tools and materials for characterizing and emulating the smallest scale features of biology. Further, they are revealing unique physical properties that emerge at the nanoscale. Realizing these properties in useful ways will require attention to the assembly of these nanoscale components. Attention to systems biology principles can lead to the practical development of nanoscale technologies with possible realization of synthetic systems with cell-like complexity. In turn, useful tools for interpreting biological complexity and for interfacing to biological processes will result.

Characterization and in vitro evaluation of spherulites as sequestering vesicles with potential application in drug detoxification

The aim of the present investigation was to prepare and characterize lecithin spherulites as parenteral drug sequestering agents with potential application in the treatment of drug overdose and chemical poisoning. The spherulites (approximately 200 nm) obtained by controlled hydration and shearing of lipid-alcohol mixtures, revealed unexpected differences in the physical properties of the bilayer when compared to liposomes. Differential scanning calorimetry, 31-phosphorus nuclear magnetic resonance, and pH-sensitive pyranine steady-state fluorescence studies indicated that although spherulites retained the typical bilayer conformation, the arrangement of the phospholipid molecules was perturbed relative to native liposome bilayer. The loosened packing of the phospholipids in bilayers was strongly supported by the relative ease with which spherulites lost the established pH-gradient. This permeability problem was overcome via incorporation of cholesterol in the bilayer. Subsequently, albumin/buffer components were encapsulated in these spherulites and the drug sequestration potential for detoxification application was examined. Citrate pH-gradient spherulites accumulated 75% of external haloperidol while those loaded with approximately 20% (w/w) albumin were able to take up 45% of haloperidol and 91-95% of taxanes (docetaxel and paclitaxel). In cytotoxicity studies, the competitive internalization of docetaxel by albumin-loaded spherulites resulted in an increase of the IC50 value for the free drug. Thus, the spherulite technology could be a versatile approach for actively sequestering toxins in the blood and for reducing the adverse effects by altering the pharmacokinetics and biodistribution of overdosed drugs.

Microbial degradation of organophosphorus compounds

Synthetic organophosphorus compounds are used as pesticides, plasticizers, air fuel ingredients and chemical warfare agents. Organophosphorus compounds are the most widely used insecticides, accounting for an estimated 34% of world-wide insecticide sales. Contamination of soil from pesticides as a result of their bulk handling at the farmyard or following application in the field or accidental release may lead occasionally to contamination of surface and ground water. Several reports suggest that a wide range of water and terrestrial ecosystems may be contaminated with organophosphorus compounds. These compounds possess high mammalian toxicity and it is therefore essential to remove them from the environments. In addition, about 200,000 metric tons of nerve (chemical warfare) agents have to be destroyed world-wide under Chemical Weapons Convention (1993). Bioremediation can offer an efficient and cheap option for decontamination of polluted ecosystems and destruction of nerve agents. The first micro-organism that could degrade organophosphorus compounds was isolated in 1973 and identified as Flavobacterium sp. Since then several bacterial and a few fungal species have been isolated which can degrade a wide range of organophosphorus compounds in liquid cultures and soil systems. The biochemistry of organophosphorus compound degradation by most of the bacteria seems to be identical, in which a structurally similar enzyme called organophosphate hydrolase or phosphotriesterase catalyzes the first step of the degradation. organophosphate hydrolase encoding gene opd (organophosphate degrading) gene has been isolated from geographically different regions and taxonomically different species. This gene has been sequenced, cloned in different organisms, and altered for better activity and stability. Recently, genes with similar function but different sequences have also been isolated and characterized. Engineered microorganisms have been tested for their ability to degrade different organophosphorus pollutants, including nerve agents. In this article, we review and propose pathways for degradation of some organophosphorus compounds by microorganisms. Isolation, characterization, utilization and manipulation of the major detoxifying enzymes and the molecular basis of degradation are discussed. The major achievements and technological advancements towards bioremediation of organophosphorus compounds, limitations of available technologies and future challenge are also discussed.

Sequestration of amitriptyline by liposomes

We study the uptake of amitriptyline, which is a common cause of overdose-related fatalities, in aqueous solutions by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes and liposomes composed of a mixture of DMPC and 1,2-dioleoyl-sn-glycero-3-[phospho-rac(1-glycerol)] (DOPG) lipids. The effect of drug concentration, liposomal charge, pH, salt, and protein presence on the drug uptake is investigated using two different methodologies, a precipitation and a centrifugation method. Furthermore, the time scale of the drug uptake is studied through qualitative observations at high pH and through conductivity measurements at neutral pH and found to be <5 s. The results of the quantitative studies show that the fractional drug uptake decreases with increasing drug concentration, and for a given concentration it increases with the pH and decreases in the presence of salt. We find that a larger amount of drug is sequestered by negatively charged liposomes (those containing DOPG) than liposomes with no net charge (DMPC). We speculate that the mechanism of drug uptake is due to both electrostatic interactions as well as hydrophobic effects. The fractional uptake by DMPC:DOPG in a 70:30 ratio is as high as 95% in water and about 90% in physiological buffer. The fractional uptake is also measured in presence of 2% (w/w) bovine serum albumin (BSA), which is approximately the protein concentration in the intercellular fluid. In presence of protein the fractional uptakes by 70:30 DMPC:DOPG liposomes and 50:50 DMPC:DOPG liposomes are 82 and 90%, respectively, at 125 muM drug amitriptyline. In the absence of liposomes, 67% of the drug is taken up by the protein in a 2% (w/w) BSA, 125 muM amitriptyline solution. Thus, addition of 50:50 DMPC:DOPG liposomes reduces the free drug concentration by a factor of about 3.5, making them attractive candidates for drug detoxification.

Enzymatic bioremediation: from enzyme discovery to applications

1. Enzymatic bioremediation is potentially a rapid method of removing environmental pesticide residues. Applications include the treatment of residues resulting from agricultural production and processing industries, such as the treatment of irrigation waters, surface-contaminated fruit and vegetables and spent dip liquors. 2. A specific application for some organophosphate-degrading enzymes involves detoxification of nerve agent stockpiles. Effective and affordable remediation requires highly specialized enzymes, so protein engineering techniques are being used to improve properties of various source enzymes to enhance catalytic rates, stability and substrate range. 3. Trials with an optimized organophosphate-degrading enzyme have shown the feasibility of such technology in various applications. 4. The enzymes developed for environmental remediation for specific pesticide classes also have applications as antidotes for high-dose pesticide poisonings and as prophylaxis for people at risk of high pesticide doses.

Contribution of the active-site metal cation to the catalytic activity and to the conformational stability of phosphotriesterase: temperature- and pH-dependence

Phosphotriesterase (PTE) detoxifies nerve agents and organophosphate pesticides. The two zinc cations of the PTE active centre can be substituted by other transition metal cations without loss of activity. Furthermore, metal-substituted PTEs display differences in catalytic properties. A prerequisite for engineering highly efficient mutants of PTE is to improve their thermostability. Isoelectric focusing, capillary electrophoresis and steady-state kinetics analysis were used to determine the contribution of the active-site cations Zn2+, Co2+ or Cd2+ to both the catalytic activity and the conformational stability of the corresponding PTE isoforms. The three isoforms have different pI values (7.2, 7.5 and 7.1) and showed non-superimposable electrophoretic titration curves. The overall structural alterations, causing changes in functional properties, were found to be related to the nature of the bound cation: ionic radius and ion electronegativity correlate with Km and kcat respectively. In addition, the pH-dependent activity profiles of isoforms were different. The temperature-dependent profiles of activity showed maximum activity at T < or =35 degrees C, followed by an activation phase near 45-48 degrees C and then inactivation which was completed at 60 degrees C. Analysis of thermal denaturation of the PTEs provided evidence that the activation phase resulted from a transient intermediate. Finally, at the optimum activity between pH 8 and 9.4, the thermostability of the different PTEs increased as the pH decreased, and the metal cation modulated stability (Zn2+-, Co2+- and Cd2+-PTE showed different T (m) values of 60.5-67 degrees C, 58-64 degrees C and 53-64 degrees C respectively). Requirements for optimum activity of PTE (displayed by Co2+-PTE) and maximum stability (displayed by Zn2+-PTE) were demonstrated.

Future applications of phosphotriesterases in the prophylaxis and treatment of organophosporus insecticide and nerve agent poisonings

Organophosphorus compounds (OPs) are being used as insecticides and warfare agents. OP insecticides represent an important problem of public health, causing around 200,000 deaths annually. The World Health Organization has pointed to the necessity to introduce new medical practices that improve the results of classical treatments. Many studies have shown that the administration of phosphotriesterases (enzymes that detoxify OPs through hydrolysis) is a promising treatment of persons poisoned with OPs. Such an enzyme-based treatment might introduce important improvements in the treatment of patients having ingested large amounts of OPs. Phosphotriesterases might also be suitable for prophylactic treatment of persons at risk to be severely exposed. The new experimental treatments do not exhibit the intrinsic neurotoxicity of the classical prophylaxis based on carbamates and antimuscarinic drugs. Experimental data suggest that might be time to initiate clinical trials in order to study the efficacy of phosphotriesterases in the therapy and prophylaxis of OP intoxication.

Study of the mechanism ofFlavobacteriumsp. for hydrolyzing organophosphate pesticides

The biotransformation by Flavobacterium sp. of the following organophosphate pesticides was experimentally and theoretically studied: phorate, tetrachlorvinphos, methyl-parathion, terbufos, trichloronate, ethoprophos, phosphamidon, fenitrothion, dimethoate and DEF. The Flavobacterium sp. ATCC 27551 strain bearing the organophosphate-degradation gene was used. Bacteria were incubated in the presence of each pesticide for a duration of 7 days. Parent pesticides were identified and quantified by means of a gas-chromatography mass spectrum system. Activity was considered as the amount (micromol) of each pesticide degraded by Flavobacterium sp. Also, structural parameters obtained by means of the CAChe program package for biomolecules, the reactivity index of phosphorus, of oxygen at the P = O function and of sulfur at the P = S function, and lipophilicity (log Poct) (ALOGPS v. 2.0) were obtained for each pesticide. Pesticides were hydrolyzed at the bond between phosphorous and the heteroatom, producing phosphoric acid and three metabolites. Enzymatic activity was significantly explained by the following multiple linear relationship: Enzymatic activity = 162.2 - 9.5(dihedral angle energy) - 25.0(Total energy) - 0.51(Molecular weight). Finally, a mechanism of Flavobacterium sp. to hydrolyze pesticides was proposed.

Enzymes inside lipid vesicles: preparation, reactivity and applications

There are a number of methods that can be used for the preparation of enzyme-containing lipid vesicles (liposomes) which are lipid dispersions that contain water-soluble enzymes in the trapped aqueous space. This has been shown by many investigations carried out with a variety of enzymes. A review of these studies is given and some of the main results are summarized. With respect to the vesicle-forming amphiphiles used, most preparations are based on phosphatidylcholine, either the natural mixtures obtained from soybean or egg yolk, or chemically defined compounds, such as DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) or POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). Charged enzyme-containing lipid vesicles are often prepared by adding a certain amount of a negatively charged amphiphile (typically dicetylphosphate) or a positively charged lipid (usually stearylamine). The presence of charges in the vesicle membrane may lead to an adsorption of the enzyme onto the interior or exterior site of the vesicle bilayers. If (i) the high enzyme encapsulation efficiencies; (ii) avoidance of the use of organic solvents during the entrapment procedure; (iii) relatively monodisperse spherical vesicles of about 100 nm diameter; and (iv) a high degree of unilamellarity are required, then the use of the so-called 'dehydration-rehydration method', followed by the 'extrusion technique' has shown to be superior over other procedures. In addition to many investigations in the field of cheese production--there are several studies on the (potential) medical and biomedical applications of enzyme-containing lipid vesicles (e.g. in the enzyme-replacement therapy or for immunoassays)--including a few in vivo studies. In many cases, the enzyme molecules are expected to be released from the vesicles at the target site, and the vesicles in these cases serve as the carrier system. For (potential) medical applications as enzyme carriers in the blood circulation, the preparation of sterically stabilized lipid vesicles has proven to be advantageous. Regarding the use of enzyme-containing vesicles as submicrometer-sized nanoreactors, substrates are added to the bulk phase. Upon permeation across the vesicle bilayer(s), the trapped enzymes inside the vesicles catalyze the conversion of the substrate molecules into products. Using physical (e.g. microwave irradiation) or chemical methods (e.g. addition of micelle-forming amphiphiles at sublytic concentration), the bilayer permeability can be controlled to a certain extent. A detailed molecular understanding of these (usually) submicrometer-sized bioreactor systems is still not there. There are only a few approaches towards a deeper understanding and modeling of the catalytic activity of the entrapped enzyme molecules upon externally added substrates. Using micrometer-sized vesicles (so-called 'giant vesicles') as simple models for the lipidic matrix of biological cells, enzyme molecules can be microinjected inside individual target vesicles, and the corresponding enzymatic reaction can be monitored by fluorescence microscopy using appropriate fluorogenic substrate molecules.

Biomedical application of immobilized enzymes

Reports on chemical immobilization of proteins and enzymes first appeared in the 1960s. Since then, immobilized proteins and enzymes have been widely used in the processing of variety of products and increasingly used in the field of medicine. Here, we present a review of recent developments in immobilized enzyme use in medicine. Generally speaking, the use of immobilized enzyme in medicine can be divided into two major categories: biosensors and bioreactors. A brief overview of the evolution of the biosensor and bioreactor technology, of currently existing applications of immobilized enzymes, of problems that researchers encountered, and of possible future developments will be presented.

In vitro studies on sterically stabilized liposomes (SL) as enzyme carriers in organophosphorus (OP) antagonism

This study describes a new approach for organophosphorous (OP) antidotal treatment by encapsulating an OP hydrolyzing enzyme, OPA anhydrolase (OPAA), within sterically stabilized liposomes. The recombinant OPAA enzyme was derived from Alteromonas strain JD6. It has broad substrate specificity to a wide range of OP compounds: DFP and the nerve agents, soman and sarin. Liposomes encapsulating OPAA (SL)* were made by mechanical dispersion method. Hydrolysis of DFP by (SL)* was measured by following an increase of fluoride ion concentration using a fluoride ion selective electrode. OPAA entrapped in the carrier liposomes rapidly hydrolyze DFP, with the rate of DFP hydrolysis directly proportional to the amount of (SL)* added to the solution. Liposomal carriers containing no enzyme did not hydrolyze DFP. The reaction was linear and the rate of hydrolysis was first order in the substrate. This enzyme carrier system serves as a biodegradable protective environment for the recombinant OP-metabolizing enzyme, OPAA, resulting in prolongation of enzymatic concentration in the body. These studies suggest that the protection of OP intoxication can be strikingly enhanced by adding OPAA encapsulated within (SL)* to pralidoxime and atropine.