Encapsulation of rhodanese and organic thiosulfonates by mouse erythrocytes

Erythrocytes as Carriers: From Drug Delivery to Biosensors

Drug delivery using natural biological carriers, especially erythrocytes, is a rapidly developing field. Such erythrocytes can act as carriers that prolong the drug's action due to its gradual release from the carrier; as bioreactors with encapsulated enzymes performing the necessary reactions, while remaining inaccessible to the immune system and plasma proteases; or as a tool for targeted drug delivery to target organs, primarily to cells of the reticuloendothelial system, liver and spleen. To date, erythrocytes have been studied as carriers for a wide range of drugs, such as enzymes, antibiotics, anti-inflammatory, antiviral drugs, etc., and for diagnostic purposes (e.g. magnetic resonance imaging). The review focuses only on drugs loaded inside erythrocytes, defines the main lines of research for erythrocytes with bioactive substances, as well as the advantages and limitations of their application. Particular attention is paid to in vivo studies, opening-up the potential for the clinical use of drugs encapsulated into erythrocytes.

Sealing Effects on the Storage Stability of the Cyanide Antidotal Candidate, Dimethyl Trisulfide

Background

Dimethyl trisulfide (DMTS) is a highly lipid-soluble cyanide (CN) antidote candidate molecule. In prior studies with various US FDA-approved co-solvents, surfactants, and their combinations, aqueous solutions containing 15% polysorbate 80 (Poly80) were found to effectively solubilize DMTS in formulations for intramuscular administration. However, DMTS formulated in 15% aqueous Poly80 solutions showed gradual losses over time when stored in vials with septum-based seals.

Objective

The present study tested whether storing DMTS formulations in hermetically sealed glass ampules could mitigate storage losses.

Methods

Samples consisted of 1-mL aliquots of a 50 mg/ml stock solution of DMTS in 15% aqueous Poly80. The control samples were stored using a vial-within-a-vial system—the inner and outer vials were sealed respectively, with a snap cap, and with a crimped septum. The hermetically sealed test samples were stored in fire-sealed glass ampules. The DMTS content was measured by HPLC–UV analysis at specific time points over a 100-day period.

Results

While the control samples exhibited systematic DMTS losses, no DMTS losses were observed from the test samples stored in hermetically sealed glass ampules over the 100-day testing period.

Conclusion

DMTS formulated in 15% aqueous Poly80 solution has excellent stability when stored in fire-sealed glass ampules and thus has the potential to be effectively stored as an intramuscular CN countermeasure for mass casualty scenarios.

Converting Red Blood Cells to Efficient Microreactors for Blood Detoxification

A simple method to convert red blood cells (RBCs) into efficient microreactors is reported. Triton X-100 is employed at finely tuned concentrations to render RBCs highly permeable to substrates, while low concentrations of glutaraldehyde are used to stabilize cells. The ability for blood detoxification of these microreactors is demonstrated.

Erythrocyte-mediated delivery of recombinant enzymes

The possibility to clone, express and purify recombinant enzymes have originated the opportunity to dispose of a virtually infinite array of proteins that could be used in the clinics to treat several inherited and acquired pathological conditions. However, the direct administration of these recombinant proteins faces some intrinsic difficulties, such as degradation by circulating proteases and/or inactivation by the patient immune system. The use of drug delivery systems may overcome these limitations. Concerning recombinant enzyme therapy, the present review will mainly focus on the exploitation of erythrocytes as a carrier system for enzymes removing potentially noxious metabolites from the circulation, either as limiting treatment strategy for auxotrophic tumours or as a detoxing approach for some intoxication type inherited metabolic disorders. Moreover, the possibility of using RBCs as a potential delivering system addressing the enzymes to the monocyte-macrophages of reticular endothelial system for the treatment of diseases associated with this cell lineage, e.g. lysosome storage diseases, will be briefly discussed.

Synthesis and antimicrobial properties of 4-acylaminobenzenethiosulfoacid S-esters

A series of esters of 4-acetyl, 4-trifluoroacetyl- and 4-(3-chloropropionyl)aminobenzenethiosulfoacids (twenty-four compounds) were synthesized and characterized by elemental analysis, ¹H NMR and IR spectroscopy. The antibacterial activity of the novel candidates has been screened using the agar diffusion or serial dilution methods against representative Gram-positive (Staphylococcus aureus, Bacillus subtilis, Bacillus mesentericus, Mycobacterium sp., Mycobacterium luteum), Gram-negative (Aeromonas sp., Burkholderia cepacia, Alcaligenes faecalis, Pseudomonas aeruginosa, Escherichia coli, Proteus vulgaris) bacteria and fungi (Candida albicans, Candida tenuis, Candida glabrata, Verticillium dahliae, Trichophyton gypseum, Aspergillus niger, Aspergillus fumigatus, Penicillium chrysogenum). Particular potency has been discovered against all tested pathogenic bacteria and fungi by compounds 1l and 3l at nanomolar concentrations. Some appropriate effect of thiosulfoesters structure upon their antimicrobial activity was determined.

Parenteral dosage form development and testing of dimethyl trisulfide, as an antidote candidate to combat cyanide intoxication

This study focused on the solubility enhancement and the in vivo antidotal efficacy testing of a new potential cyanide (CN) countermeasure, dimethyl trisulfide (DMTS). Various FDA approved cyclodextrins (HPβCD, RMβCD, HPγCD), cosolvents (ethanol, polyethylene glycols, propylene glycol), surfactants (cremophor EL, cremophor RH 40, sodium cholate, sodium deoxycholate, polysorbate 80) and their combinations were applied. Based on the solubility enhancing potential of the tested systems, polysorbate 80 was chosen for further in vivo efficacy studies. A composition comprising 15% polysorbate 80 and 50 mg/ml DMTS with the applied DMTS dose of 100 mg/kg provided a therapeutic antidotal protection of 3.4 × LD₅₀. For comparison, the present therapy of sodium thiosulfate (TS) with the dose of 100 mg/kg provided only 1.1 × LD₅₀ protection, and at the dose of 200 mg/kg, the LD₅₀ was enhanced by 1.3 times. No difference in the therapeutic protection by DMTS was detected when the concentration of polysorbate 80 was increased to 20% (3.2 × LD₅₀ protection). These data demonstrate the potential importance of DMTS as a CN countermeasure, and the formulation comprising polysorbate 80 provides the base of an injectable intramuscular dosage form that can later serve as a CN antidotal kit suitable for mass scenario.

Erythrocytes encapsulated with phenylalanine hydroxylase exhibit improved pharmacokinetics and lowered plasma phenylalanine levels in normal mice

Enzyme replacement therapy is often hampered by the rapid clearance and degradation of the administered enzyme, limiting its efficacy and requiring frequent dosing. Encapsulation of therapeutic molecules into red blood cells (RBCs) is a clinically proven approach to improve the pharmacokinetics and efficacy of biologics and small molecule drugs. Here we evaluated the ability of RBCs encapsulated with phenylalanine hydroxylase (PAH) to metabolize phenylalanine (Phe) from the blood and confer sustained enzymatic activity in the circulation. Significant quantities of PAH were successfully encapsulated within murine RBCs (PAH-RBCs) with minimal loss of endogenous hemoglobin. While intravenously administered free PAH enzyme was rapidly eliminated from the blood within a few hours, PAH-RBCs persisted in the circulation for at least 10days. A single injection of PAH-RBCs was able to decrease Phe levels by nearly 80% in normal mice. These results demonstrate the ability of enzyme-loaded RBCs to metabolize circulating amino acids and highlight the potential to treat disorders of amino acid metabolism.

Identification, solubility enhancement and in vivo testing of a cyanide antidote candidate

Present studies focused on the in vitro testing, the solubility enhancement and the in vivo testing of methyl propyl trisulfide (MPTS), a newly identified sulfur donor to treat cyanide (CN) intoxication. To enhance the solubility of the lipophilic MPTS, various FDA approved co-solvents, surfactants and their combinations were applied. The order of MPTS solubility in the given co-solvents was found to be the following: ethanol >> PEG 200 ≈ PEG400 ≈ PEG300 > PG. The maximum solubility of MPTS was found at 90% ethanol of 177.11 ± 12.17 mg/ml. The order of MPTS solubility in different surfactants is Cremophor EL>Cremophor RH40>polysorbate 80>sodium deoxycholate>sodium cholate. The maximum solubility of 40.99 mg/ml was achieved with 20% Cremophor EL. A synergistic solubilizing effect encountered with the combination of 20% Cremophor EL+75% ethanol lead to a 2900-fold increase (compared to water solubility) in solubility. The in vivo efficacy using intramuscular administration was determined on a therapeutic mice model and expressed as a ratio of CN LD50 with and without the test antidote(s) (APR). Intramuscular administration was shown to be effective and the therapeutic antidotal protection by MPTS alone and MPTS+thiosulfate (TS) was significantly higher than the present therapy of TS.

Cell-based drug-delivery platforms

Cell systems have recently emerged as biological drug carriers, as an interesting alternative to other systems such as micro- and nano-particles. Different cells, such as carrier erythrocytes, bacterial ghosts and genetically engineered stem and dendritic cells have been used. They provide sustained release and specific delivery of drugs, enzymatic systems and genetic material to certain organs and tissues. Cell systems have potential applications for the treatment of cancer, HIV, intracellular infections, cardiovascular diseases, Parkinson’s disease or in gene therapy. Carrier erythrocytes containing enzymes such us L-asparaginase, or drugs such as corticosteroids have been successfully used in humans. Bacterial ghosts have been widely used in the field of vaccines and also with drugs such as doxorubicin. Genetically engineered stem cells have been tested for cancer treatment and dendritic cells for immunotherapeutic vaccines. Although further research and more clinical trials are necessary, cell-based platforms are a promising strategy for drug delivery.

Sodium thiosulfonate salts: molecular and supramolecular structural features and solution radiolytic properties

Three sodium thiosulfonate salts, NaMeS(2)O(2)·H(2)O, NaPhS(2)O(2) and NaMeC(6)H(4)S(2)O(2) have been prepared by the direct reaction of the sodium sulfinate salts with elemental sulfur, a clean, benign route that produces no by-products. The structures of the phenyl (which crystallised as a hydrate, NaPhS(2)O(2)·1.5H(2)O) and p-tolyl compounds were determined by X-ray crystallography. For the p-tolyl derivative, NaMeC(6)H(4)S(2)O(2), the unexpected coordination of the pendant sulfur atom was found, a feature not reported previously for thiosulfonate salts, and observed only in two of the more common thiosulfate salts. Intermolecular CH/π interactions are postulated to contribute to the driving force of sulfur coordination, otherwise a different orientation of the aromatic rings would be expected. For NaPhS(2)O(2)·1.5H(2)O, the water ligands and thiosulfonate anions each contribute three oxygen atoms to form a NaO(6) coordination sphere. The thiosulfonate and water oxygens bridge to other sodium atoms forming a three-dimensional layer structure consisting of sheets of NaPhS(2)O(2)·1.5H(2)O with a hydrophilic interior layer, comprising the sodium ions, water ligands and -S(2)O(2)(-) groups, and a hydrophobic exterior formed by the phenyl substituent. The structure is further stabilised by an extensive H-bonding network between the ligated water and the non-coordinating thiosulfonate sulfur atom forming part of the hydrophilic layer and by weak intermolecular edge-to-face CH/π interactions between the sheets. Investigation of the radical chemistry of the three salts using pulse radiolysis indicated that oxidation of NaMeS(2)O(2)·H(2)O involves formation of a sulfur-centred radical rather than hydrogen abstraction from the methyl substituent, whereas oxidation of the aromatic ring is the preferred pathway for the phenyl and p-tolyl derivatives.

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.

Nano-intercalated rhodanese in cyanide antagonism

Present studies have focused on nano-intercalated rhodanese in combination with sulfur donors to prevent cyanide lethality in a prophylactic mice model for future development of an effective cyanide antidotal system. Our approach is based on the idea of converting cyanide to the less toxic thiocyanate before it reaches the target organs by utilizing sulfurtransferases (e.g., rhodanese) and sulfur donors in a close proximity by injecting them directly into the blood stream. The inorganic thiosulfate (TS) and the garlic component diallydisulfide (DADS) were compared as sulfur donors with the nano-intercalated rhodanese in vitro and in vivo. The in vivo and in vitro experiments showed that DADS is not a more efficient sulfur donor than TS. However, the utilization of external rhodanese significantly enhanced the in vivo efficacy of both sulfur donor-nitrite combinations, indicating the potential usefulness of enzyme nano-delivery systems in developing antidotal therapeutic agents.

Drug delivery by red blood cells: vascular carriers designed by mother nature

IMPORTANCE OF THE FIELD

Vascular delivery of several classes of therapeutic agents may benefit from carriage by red blood cells (RBC), for example, drugs that require delivery into phagocytic cells and those that must act within the vascular lumen. The fact that several protocols of infusion of RBC-encapsulated drugs are now being explored in patients illustrates a high biomedical importance for the field. AREAS COVERED BY THIS REVIEW: Two strategies for RBC drug delivery are discussed: encapsulation into isolated RBC ex vivo followed by infusion in compatible recipients and coupling therapeutics to the surface of RBC. Studies of pharmacokinetics and effects in animal models and in human studies of diverse therapeutic enzymes, antibiotics and other drugs encapsulated in RBC are described and critically analyzed. Coupling to RBC surface of compounds regulating immune response and complement, affinity ligands, polyethylene glycol alleviating immune response to donor RBC and fibrinolytic plasminogen activators are described. Also described is a new, translation-prone approach for RBC drug delivery by injection of therapeutics conjugated with fragments of antibodies providing safe anchoring of cargoes to circulating RBC, without need for ex vivo modification and infusion of RBC.

WHAT THE READER WILL GAIN

Readers will gain historical perspective, current status, challenges and perspectives of medical applications of RBC for drug delivery.

TAKE HOME MESSAGE

RBC represent naturally designed carriers for intravascular drug delivery, characterized by unique longevity in the bloodstream, biocompatibility and safe physiological mechanisms for metabolism. New approaches for encapsulating drugs into RBC and coupling to RBC surface provide promising avenues for safe and widely useful improvement of drug delivery in the vascular system.

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.

Applications of carrier erythrocytes in delivery of biopharmaceuticals

Carrier erythrocytes, resealed erythrocytes loaded by a drug or other therapeutic agents, have been exploited extensively in recent years for both temporally and spatially controlled delivery of a wide variety of drugs and other bioactive agents owing to their remarkable degree of biocompatibility, biodegradability and a series of other potential advantages. Biopharmaceuticals, therapeutically significant peptides and proteins, nucleic acid-based biologicals, antigens and vaccines, are among the recently focused pharmaceuticals for being delivered using carrier erythrocytes. In this article, the potential applications of erythrocytes in drug delivery have been reviewed with a particular stress on the studies and laboratory experiences on successful erythrocyte loading and characterization of the different classes of biopharmaceuticals.

Cyanide poisoning and its treatment

Cyanide is both widely available and easily accessible throughout the world. Although the compound is not frequently encountered, it has been used as a poison and contaminant in the past and is a potential terrorist agent. Cyanide has the ability to cause significant social disruption and demands special attention to public health preparedness. It can be obtained from a variety of sources, including industrial, medical, and even common household products. Another frequently encountered source of cyanide exposure is residential fires. Exposure to high concentrations of the chemical can result in death within seconds to minutes. Long-term effects from cyanide exposure can cause significant morbidity. The only treatment for cyanide toxicity approved for use in the United States is a kit consisting of amyl nitrite, sodium nitrite, and sodium thiosulfate. Future research aims to find a faster-acting, more effective, and better tolerated treatment for cyanide toxicity.

Drug, enzyme and peptide delivery using erythrocytes as carriers

Erythrocytes are potential biocompatible vectors for different bioactive substances, including drugs. These can be used successfully as biological carriers of drugs, enzymes and peptides. There are currently diverse methods that permit drug encapsulation in erythrocytes with an appropriate yield. The methods most commonly employed are based on a high-haematocrit dialysis procedure, mainly hypo-osmotic dialysis. Erythrocytes loaded with drugs and other substances allow for different release rates to be obtained. Encapsulation in erythrocytes significantly changes the pharmacokinetic properties of drugs in both animals and humans, enhancing liver and spleen uptake and targeting the reticulo-endothelial system (RES). Amongst other applications, erythrocytes have been used for drug-targeting the RES with aminoglycoside antibiotics; the selective transport to certain organs and tissues of certain antineoplastic drugs, such as methotrexate, doxorubicine, etoposide, carboplatin, etc.; the encapsulation of angiotensin-converting enzyme (ACE) inhibitors, systemic corticosteroids, the encapsulation of new prodrugs with increased duration of action, etc. Erythrocytes are also attractive systems in the sense of their potential ability to deliver proteins and therapeutic peptides. Thus, erythrocytes have been used for the transport of enzymes destined for the correction of metabolic alterations as l-asparaginase, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AlDH) among others. Erythrocytes have been used successfully as carriers of anti-HIV peptides, such as AZT, nucleoside analogues, antisense oligonucleotides, antineoplastic peptides, erythropoietin, interleukin 3, etc. Amongst other applications, mention may be made of paramagnetic erythrocytes, encapsulation of MRI contrast agents or the study of the metabolism of the red cell. Although erythrocytes have been applied with different uses in human medicine, their deployment is still very limited due to difficulties involving storage, its exposure to contamination and the absence of a validated industrial procedure for its preparation.

Stimulatory effect of sulphide on thiotaurine synthesis in three hydrothermal-vent species from the East Pacific Rise

Symbiotic associations between marine invertebrates and sulphur-oxidising bacteria are a common feature in communities from sulphide-rich environments, such as those flourishing in the vicinity of hydrothermal vents. While the bacterial endosymbionts provide the host with an undoubted nutritional advantage, their presence also requires specific adaptations for the transport and storage of sulphide, which is a potent toxin of aerobic respiration. Although different mechanisms such as the reversible binding of sulphide to serum binding proteins or its oxidation to less toxic forms have been described, many questions still remained unanswered. In the last decade, large amounts of thiotaurine, an unusual sulphur-amino acid, have been reported in sulphur-based symbioses from hydrothermal vents and cold seeps. Compounds such as thiotaurine are known to take part in trans-sulphuration reactions, so the involvement of thiotaurine in sulphide metabolism has been suggested. We present here an experimental study on thiotaurine biosynthesis in three sulphur-oxidising symbiont-bearing species from the East Pacific Rise: the vesicomyid Calyptogena magnifica, the mytilid Bathymodiolus thermophilus and the vestimentiferan Riftia pachyptila. In all three species, thiotaurine synthesis is stimulated in vitro by an input of sulphide, as well as by thiosulphate in B. thermophilus. Several distinct metabolic pathways seem to occur, however, since hypotaurine is the only precursor in the bivalves C. magnifica and B. thermophilus, whereas thiotaurine is also produced from taurine in R. pachyptila. Hypotaurine (NH(2)-CH(2)-CH(2)-SO(2)H) and thiotaurine (NH(2)-CH(2)-CH(2)-SO(2)SH) are two free sulphur amino acids whose chemical formulae differ by only one atom of sulphur. It appears that the extent of thiotaurine synthesis is strongly dependent on the initial equilibrium between these two amino acids, since the strongest thiotaurine synthesis rates are found in tissues with the lowest initial thiotaurine concentration. Moreover, the lack of any effect of sulphide in symbiont-free tissues and in gills of the methanotrophic mussel Bathymodiolus childressi reinforces the assumption that thiotaurine synthesis is a specific adaptation to the thiotrophic mode of life. While the precise function (i.e. transport and/or storage of sulphide) of hypotaurine and thiotaurine has yet to be established, our results strongly support a general role for these free amino acids in the metabolism of sulphide in hydrothermal-vent thiotrophic symbioses.

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

This investigation effort is focused on increasing organophosphate (OP) degradation by phosphotriesterase to antagonize OP intoxication. For these studies, sterically stabilized liposomes encapsulating recombinant phosphotriesterase were employed. This enzyme was obtained from Flavobacterium sp. and was expressed in Escherichia coli. It has a broad substrate specificity, which includes parathion, paraoxon, soman, sarin, diisopropylfluorophosphate, and other organophosphorous compounds. Paraoxon is rapidly hydrolyzed by phosphotriesterase to the less toxic 4-nitrophenol and diethylphosphate. This enzyme was isolated and purified over 1600-fold and subsequently encapsulated within sterically stabilized liposomes (SL). The properties of this encapsulated phosphotriesterase were investigated. When these liposomes containing phosphotriesterase were incubated with paraoxon, it readily degraded the paraoxon. Hydrolysis of paraoxon did not occur when these sterically stabilized liposomes contained no phosphotriesterase. These sterically stabilized liposomes (SL) containing phosphotriesterases (SL)* were employed as a carrier model to antagonize the toxic effects of paraoxon by hydrolyzing it to the less toxic 4-nitrophenol and diethylphosphate. This enzyme-SL complex (SL)* was administered intravenously to mice either alone or in combination with pralidoxime (2-PAM) and/or atropine intraperitoneally. These results indicate that this carrier model system provides a striking enhanced protective effects against the lethal effects of paraoxon. Moreover when these carrier liposomes were administered with 2-PAM and/or atropine, a dramatic enhanced protection was observed.