Cholera toxin B-mediated targeting of lipid vesicles containing ganglioside GM1 to mucosal epithelial cells

Microgels Sopping Up Toxins-GM1a-Functionalized Microgels as Scavengers for Cholera Toxin

Vibrio cholerae is a Gram-negative bacterium that causes secretory diarrhea and constitutes a major health threat in the industrialized world and even more in developing countries. Its main virulence factor is the cholera toxin, which is internalized by intestinal epithelial cells after binding to the glycosphingolipid receptor GM1a on their apical surface. A potential future solution to dampen complications of cholera infection is by scavenging the cholera toxin by presenting competitive binding motifs to diminish the in vivo toxicity of V. cholerae. Here, we generate GM1a-functionalized and biocompatible microgels with diameters of 20 μm using drop-based microfluidics. The microgels are designed to exhibit a mesoporous and widely meshed network structure, allowing diffusion of the toxin protein deep into the microgel scavengers. Flow cytometry demonstrates strong and multivalent binding at high capacity of these microgels to the binding domain of the cholera toxin. Cell culture-based assays reveal the ability of these microgels to scavenge and retain the cholera toxin in direct binding competition to colorectal cells. This ability is evidenced by suppressed cyclic adenosine monophosphate production as well as reduced vacuole formation in mucus-forming colorectal HT-29 cells. Therefore, glycan-functionalized microgels show great potential as a non-antibiotic treatment for toxin-mediated infectious disorders.

Hypoglossal Motor Neuron Death Via Intralingual CTB-saporin (CTB-SAP) Injections Mimic Aspects of Amyotrophic Lateral Sclerosis (ALS) Related to Dysphagia

Amyotrophic lateral sclerosis (ALS) is a devastating disease leading to degeneration of motor neurons and skeletal muscles, including those required for swallowing. Tongue weakness is one of the earliest signs of bulbar dysfunction in ALS, which is attributed to degeneration of motor neurons in the hypoglossal nucleus in the brainstem, the axons of which directly innervate the tongue. Despite its fundamental importance, dysphagia (difficulty swallowing) and strategies to preserve swallowing function have seldom been studied in ALS models. It is difficult to study dysphagia in ALS models since the amount and rate at which hypoglossal motor neuron death occurs cannot be controlled, and degeneration is not limited to the hypoglossal nucleus. Here, we report a novel experimental model using intralingual injections of cholera toxin B conjugated to saporin (CTB-SAP) to study the impact of only hypoglossal motor neuron death without the many complications that are present in ALS models. Hypoglossal motor neuron survival, swallowing function, and hypoglossal motor output were assessed in Sprague-Dawley rats after intralingual injection of either CTB-SAP (25 g) or unconjugated CTB and SAP (controls) into the genioglossus muscle. CTB-SAP treated rats exhibited significant (p ≤ 0.05) deficits vs. controls in: (1) lick rate (6.0 ± 0.1 vs. 6.6 ± 0.1 Hz; (2) hypoglossal motor output (0.3 ± 0.05 vs. 0.6 ± 0.10 mV); and (3) hypoglossal motor neuron survival (398 ± 34 vs. 1018 ± 41 neurons). Thus, this novel, inducible model of hypoglossal motor neuron death mimics the dysphagia phenotype that is observed in ALS rodent models, and will allow us to study strategies to preserve swallowing function.

Phrenic long-term facilitation following intrapleural CTB-SAP-induced respiratory motor neuron death

Amyotrophic lateral sclerosis (ALS) is a devastating disease leading to progressive motor neuron degeneration and death by ventilatory failure. In a rat model of ALS (SOD1^G93A), phrenic long-term facilitation (pLTF) following acute intermittent hypoxia (AIH) is enhanced greater than expected at disease end-stage but the mechanism is unknown. We suggest that one trigger for this enhancement is motor neuron death itself. Intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB-SAP) selectively kill respiratory motor neurons and mimic motor neuron death observed in SOD1^G93A rats. This CTB-SAP model allows us to study the impact of respiratory motor neuron death on breathing without many complications attendant to ALS. Here, we tested the hypothesis that phrenic motor neuron death is sufficient to enhance pLTF. pLTF was assessed in anesthetized, paralyzed and ventilated Sprague Dawley rats 7 and 28 days following bilateral intrapleural injections of: 1) CTB-SAP (25 μg), or 2) un-conjugated CTB and SAP (control). CTB-SAP enhanced pLTF at 7 (CTB-SAP: 162 ± 18%, n = 8 vs. Control: 63 ± 3%; n = 8; p < 0.05), but not 28 days post-injection (CTB-SAP: 64 ± 10%, n = 10 vs. Control: 60 ± 13; n = 8; p > 0.05). Thus, pLTF at 7 (not 28) days post-CTB-SAP closely resembles pLTF in end-stage ALS rats, suggesting that processes unique to the early period of motor neuron death enhance pLTF. This project increases our understanding of respiratory plasticity and its implications for breathing in motor neuron disease.

Respiratory function after selective respiratory motor neuron death from intrapleural CTB-saporin injections

Amyotrophic lateral sclerosis (ALS) causes progressive motor neuron degeneration, paralysis and death by ventilatory failure. In rodent ALS models: 1) breathing capacity is preserved until late in disease progression despite major respiratory motor neuron death, suggesting unknown forms of compensatory respiratory plasticity; and 2) spinal microglia become activated in association with motor neuron cell death. Here, we report a novel experimental model to study the impact of respiratory motor neuron death on compensatory responses without many complications attendant to spontaneous motor neuron disease. In specific, we used intrapleural injections of cholera toxin B fragment conjugated to saporin (CTB-SAP) to selectively kill motor neurons with access to the pleural space. Motor neuron survival, CD11b labeling (microglia), ventilatory capacity and phrenic motor output were assessed in rats 3-28days after intrapleural injections of: 1) CTB-SAP (25 and 50μg), or 2) unconjugated CTB and SAP (i.e. control; (CTB+SAP). CTB-SAP elicited dose-dependent phrenic and intercostal motor neuron death; 7days post-25μg CTB-SAP, motor neuron survival approximated that in end-stage ALS rats (phrenic: 36±7%; intercostal: 56±10% of controls; n=9; p<0.05). CTB-SAP caused minimal cell death in other brainstem or spinal cord regions.

CTB-SAP

1) increased CD11b fractional area in the phrenic motor nucleus, indicating microglial activation; 2) decreased breathing during maximal chemoreceptor stimulation; and 3) diminished phrenic motor output in anesthetized rats (7days post-25μg,

CTB-SAP

0.3±0.07V; CTB+SAP: 1.5±0.3; n=9; p<0.05). Intrapleural CTB-SAP represents a novel, inducible model of respiratory motor neuron death and provides an opportunity to study compensation for respiratory motor neuron loss.

Platelets recognize brain-specific glycolipid structures, respond to neurovascular damage and promote neuroinflammation

Platelets respond to vascular damage and contribute to inflammation, but their role in the neurodegenerative diseases is unknown. We found that the systemic administration of brain lipid rafts induced a massive platelet activation and degranulation resulting in a life-threatening anaphylactic-like response in mice. Platelets were engaged by the sialated glycosphingolipids (gangliosides) integrated in the rigid structures of astroglial and neuronal lipid rafts. The brain-abundant gangliosides GT1b and GQ1b were specifically recognized by the platelets and this recognition involved multiple receptors with P-selectin (CD62P) playing the central role. During the neuroinflammation, platelets accumulated in the central nervous system parenchyma, acquired an activated phenotype and secreted proinflammatory factors, thereby triggering immune response cascades. This study determines a new role of platelets which directly recognize a neuronal damage and communicate with the cells of the immune system in the pathogenesis of neurodegenerative diseases.

Lessons from nature: "Pathogen-Mimetic" systems for mucosal nano-medicines

Mucosal surfaces establish an interface with external environments that provide a protective barrier with the capacity to selectively absorb and secrete materials important for homeostasis of the organism. In man, mucosal surfaces such as those in the gastrointestinal tract, respiratory tree and genitourinary system also represent significant barrier to the successful administration of certain pharmaceutical agents and the delivery of newly designed nano-scale therapeutic systems. This review examines morphological, physiological and biochemical aspects of these mucosal barriers and presents currently understood mechanisms used by a variety of virulence factors used by pathogenic bacteria to overcome various aspects of these mucosal barriers. Such information emphasizes the impediments that biologically active materials must overcome for absorption across these mucosal surfaces and provides a template for strategies to overcome these barriers for the successful delivery of nano-scale bioactive materials, also known as nano-medicines.

Trends and developments in liposome drug delivery systems

Since the discovery of liposomes or lipid vesicles derived from self-forming enclosed lipid bilayers upon hydration, liposome drug delivery systems have played a significant role in formulation of potent drugs to improve therapeutics. Currently, most of these liposome formulations are designed to reduce toxicity and to some extent increase accumulation at the target site(s) in a number of clinical applications. The current pharmaceutical preparations of liposome-based therapeutics stem from our understanding of lipid-drug interactions and liposome disposition mechanisms including the inhibition of rapid clearance of liposomes by controlling size, charge, and surface hydration. The insight gained from clinical use of liposome drug delivery systems can now be integrated to design liposomes targeted to tissues and cells with or without expression of target recognition molecules on liposome membranes. Enhanced safety and heightened efficacy have been achieved for a wide range of drug classes, including antitumor agents, antivirals, antifungals, antimicrobials, vaccines, and gene therapeutics. Additional refinements of biomembrane sensors and liposome delivery systems that are effective in the presence of other membrane-bound proteins in vivo may permit selective delivery of therapeutic compounds to selected intracellular target areas.

Characterization of calcitonin-containing liposome formulations for intranasal delivery

Calcitonin-containing liposome formulations were characterized to obtain information for evaluation of their feasibility in intranasal delivery. The parameters of liposomal charge characteristics, charge inducing agent concentration, calcitonin concentration and pH of the medium on the loading efficiency and leakage behaviour, and the chemical stability of calcitonin in liposomes were investigated. Results showed that the loading efficiency of calcitonin increased with increasing the added concentration of calcitonin. The magnitude of the loading efficiency due to the liposomal charge of negative, positive and neutral characteristics was in the order of negatively charged liposome > neutral liposome > positively charge liposome. The increase of molar ratio of phosphatidylserine in liposomes showed an increase of loading efficiency; while, the increase of molar ratios of stearylamine showed a decrease of loading efficiency. The loading efficiency at pH 7.4 was greater than that at pH 4.3. The leakage of positively charged liposomes was greater than that of neutral and negatively charged liposomes. The leakage at pH 4.3 was faster than that at pH 7.4. The leakage of positively charged liposomes increased as temperature increased. The chemical stability of calcitonin in both solution and liposomes demonstrated a pseudo-first-order kinetic degradation. Less degradation was observed at pH 3.4 and 4 degrees C. The degradation rate of calcitonin in solution, or in positively charged, negatively charged, and neutral liposomes, exhibited no significant difference. The particle size of the calcitonin-containing liposomes after storage for 1 month at pH 4.3 and 4 degrees C showed little change.

Charge-dependent interaction of self-emulsifying oil formulations with Caco-2 cells monolayers: binding, effects on barrier function and cytotoxicity

A positively charged self-emulsifying oil formulation (SEOF), aimed to enhance oral bioavailability of drugs poorly soluble in water, was recently developed. In the present study the Caco-2 cell model was used for the investigation of the charge-dependent interactions of this SEOF with human intestinal epithelial cells. The positively charged emulsions affected the barrier properties of the cell monolayer at high concentrations and reduced the cell viability. However, at the dilution with aqueous phase used in the present study (1:2000), the positively charged SEOF did not induce any detectable cytotoxic effect. The binding of the fluorescent dye DiIC(18)(3) was much higher from the positively charged SEOF, compared to the negatively charged formulation, suggesting an increased closer adhesion of the droplets to the cell surface due to the electrostatic attraction. No transepithelial transport of this compound across Caco-2 cell monolayers was observed with any SEOF formulation.

Caveolae: an alternative membrane transport compartment

Caveolae are omega-shaped invaginations of the plasma membrane with a diameter of 50-100 nm. Caveolae invaginations can detach from the plasma membrane to form discrete functional caveolae vesicles within the cell cytoplasm. Caveolae are most prominent in adipocytes, fibroblasts, muscle cells (skeletal, smooth and cardiac), capillary endothelium and type I pneumocytes, although other cell types also display these structures but at a lower numerical density. The key structural and functional protein for caveolae is caveolin. At the plasma membrane caveolae serve to compartmentalize and integrate a wide range of signal transduction processes. Caveolae also serve transport functions including that of the vesicular internalisation of small molecules by the process of potocytosis, and the endocytic and transcytotic movements of macromolecules. Opportunities exist for basic and applied investigators working within the pharmaceutical sciences to exploit caveolae membrane interactions with the aim to develop novel cellular or transcellular drug delivery strategies.

A ganglioside-based assay for cholera toxin using an array biosensor

A rapid assay for cholera toxin (CT) has been developed using a fluorescence-based biosensor. This sensor was capable of analyzing six samples simultaneously for CT in 20 min with few manipulations required by the operator. The biochemical assays utilized a ganglioside-"capture" format: ganglioside GM1, utilized for capture of analyte, was immobilized in discrete locations on the surface of the optical waveguide. Binding of CT to immobilized GM1 was demonstrated with direct assays (using fluorescently labeled CT) and "sandwich" immunoassays (using fluorescently labeled tracer antibodies). Limits of detection for CT were 200 ng/ml in direct assays and 40 ng/ml and 1 microg/ml in sandwich-type assays performed using rabbit and goat tracer antibodies. Binding of CT to other glycolipid capture reagents was also observed. While significant CT binding was observed to loci patterned with GD1b, Gb3, and Gb4, CT did not bind significantly to immobilized GT1b at the concentrations tested. This is the first description of such a non-antibody-based recognition system in a multi-specific planar array sensor.

Formulation of HIV-envelope protein with lipid vesicles expressing ganglioside GM1 associated to cholera toxin B enhances mucosal immune responses

Taking advantage of the ability of pentameric cholera toxin B subunit (CTB) to bind selectively to GM1, we developed recently a CTB-mediated GM1 lipid vesicle delivery system to target drugs and proteins to mucosal tissues [1]. In this report, we present the use of such a strategy to deliver an HIV envelope protein (HIV-env) to mucosal tissues via intranasal route. Intranasal administration of a recombinant HIV envelope protein formulated in CTB-associated GM1 lipid vesicles enhanced mucosal IgA antibody responses detected in the nasal and gut tissues, compared to that of control animals immunized with antigen formulated in GM1-free vesicles with CTB or formulated in alum-associated vesicles with CTB. We found a nearly 2- to 3-fold enhancement in IgA antibody titers detected both in nasal and gut tissues using the CTB-GM1 lipid vesicle delivery system, compared to using the GM1-free lipid vesicle system. Intranasal administration of HIV-env formulated in the CTB-associated GM1 vesicles also induced a significant level of serum IgG and cellular immune responses against HIV-env. IgG isotype analysis indicates that CTB in GM1 vesicle delivery system enhanced both IgG1 and IgG2a while CTB in alum formulation enhanced only IgG1. However, IgA and IgG antibody responses against CTB were similar for GM1 vesicles regardless of whether HIV-env was present in the vaccine formulation. Collectively, these data indicate that delivery of HIV-env to mucosal epithelial cells with CTB-associated GM1 lipid vesicles enhanced mucosal and systemic immune responses against the HIV-envelope protein. It is possible that both the CTB-mediated targeted delivery of antigen-loaded GM1 lipid vesicles and mucosal adjuvanticity of CTB may be involved in enhancing the immune responses.