Aspects of the haemolytic reaction induced by Kanagawa haemolysin of Vibrio parahaemolyticus

Electrochemical hematocrit determination in a direct current microfluidic device

Hematocrit (HCT) tests are widely performed to screen blood donors and to diagnose medical conditions. Current HCT test methods include conventional microhematocrit, Coulter counter, CuSO4 specific gravity, and conductivity-based point-of-care (POC) HCT devices, which can be either expensive, environmentally inadvisable, or complicated. In the present work, we introduce a new and simple microfluidic system for a POC HCT determination. HCT was determined by measuring current responses of blood under 100 V DC for 1 min in a microfluidic device containing a single microchannel with dimensions of 180 μm by 70 μm and 10 mm long. Current responses of red blood cell (RBC) suspensions in PBS or separately plasma at HCT concentrations of 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, and 70 vol% were measured to show feasibility of the microfluidic system for HCT determination. Key parameters affecting current responses included electrolysis bubbles and irreversible RBC adsorption; parameters were optimized via addition of nonionic surfactant Triton X-100 into sample solution and carbonizing electrode surfaces. The linear trend line of current responses over a range of RBC concentrations were obtained in both PBS and plasma. This work suggested that a simple microfluidic device could be a promising platform for a new POC HCT device.

Effect of a pore-forming protein derived from Flammulina velutipes on the Caco-2 intestinal epithelial cell monolayer

We have previously found a transepithelial electrical resistance (TEER)-decreasing protein derived from Flammulina velutipes, which was revealed to be identical to flammutoxin (FTX) that is known as a hemolytic pore-forming protein. This protein induced a rapid decrease in TEER and parallel increase in paracellular permeability in the intestinal epithelial Caco-2 cell monolayer without any cytotoxicity. An immunoblotting analysis revealed that the FTX-induced decrease in TEER was accompanied by the formation of a high-molecular-weight complex on the surface of Caco-2 cells. Intracellular Ca(2+) imaging showed that exposure to FTX caused a rapid Ca(2+) influx. It was observed by electron microscopy that FTX induced swelling of microvilli and expansion of the cellular surface. Staining with fluorescent phalloidin showed a marked change to filamentous actin in the FTX-treated cells. These results suggest that TEER reduction could sensitively detect small membrane pore formation by FTX in the intestinal epithelium which causes a morphological alteration and disruption of the paracellular barrier function.

Single channel evidence for innate pore-formation byVibrio parahaemolyticusthermostable direct haemolysin (TDH) in phospholipid bilayers

Vibrio parahaemolyticus thermostable direct haemolysin (TDH) is widely considered to be a pore-forming toxin. The protein has no significant homology to other known pore-forming toxins and its mechanism of action in vivo remains undefined. We demonstrate single channel pore-forming activity of V. parahaemolyticus TDH in planar lipid bilayers. Channel conductance ranged between 30-450 pS in 0.5 M KCl with a calculated cation selectivity (P(K)/P(Cl)) of 2.7. Channels were formed in NaCl and choline-Cl with and without cholesterol present and in the presence of neutral or negatively charged phospholipids. Zinc ions did not block pore formation. Whilst various techniques have previously suggested that TDH is a pore-forming toxin, the data in this study provide direct single channel evidence and indicate several features of pore formation in synthetic phospholipid membranes.

The Mechanism of Hemolysis by Surfactants: Effect of Solution Composition

The effect of ionic strength, solute size, and osmolarity of the suspending solution on surfactant-induced erythrocyte hemolysis was studied. Two possible mechanisms of hemolysis were considered: osmotic lysis (affected by solute particle size) and solubilization (not affected by solute particle size). It was found that the ionic strength of the solution has a major effect on the hemolysis process, depending on the surfactant nature and concentration. An increase in the ionic strength lowers the rate of hemolysis induced by DTAB, and enhances SDS-induced hemolysis. Changes in ionic strength have little effect on hemolysis induced by Triton X-100. To explain these effects, it was assumed that the changes in ionic strength differently affect the adsorption of cationic and anionic surfactants to the membrane. The change in the amount of adsorbed surfactant either influences the rate of osmotic hemolysis by changing the membrane permeability or induces a transition from the osmotic mechanism to solubilization. These phenomena were observed for isotonic as well as hypertonic solutions.

Enterotoxicity and cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin in in vitro systems

Vibrio parahaemolyticus is a marine bacterium known to be a common cause of seafood gastroenteritis worldwide. The thermostable direct hemolysin (TDH) has been proposed to be a major virulence factor of V. parahaemolyticus. TDH causes intestinal fluid secretion as well as cytotoxicity in a variety of cell types. In this study, we investigated the interplay between the hemolysin's enterotoxic and cytotoxic effects by using both human and rat cell monolayers. As revealed by microspectrofluorimetry, the toxin causes a dose-dependent increase in intracellular free calcium in both Caco-2 and IEC-6 cells. This effect was reversible only when low toxin concentrations were tested. The TDH-activated ion influx pathway is not selective for calcium but admits ions such sodium and manganese as well. Furthermore, in the same range of concentration, the hemolysin triggers a calcium-dependent chloride secretion. At high concentrations, TDH induces a dose-dependent but calcium-independent cell death as assessed by functional, biochemical, and morphological assays.

Vibrio parahaemolyticus thermostable direct hemolysin modulates cytoskeletal organization and calcium homeostasis in intestinal cultured cells

Vibrio parahaemolyticus is a marine bacterium known to be the leading cause of seafood gastroenteritis worldwide. A 46-kDa homodimer protein secreted by this microorganism, the thermostable direct hemolysin (TDH), is considered a major virulence factor involved in bacterial pathogenesis since a high percentage of strains of clinical origin are positive for TDH production. TDH is a pore-forming toxin, and its most extensively studied effect is the ability to cause hemolysis of erythrocytes from different mammalian species. Moreover, TDH induces in a variety of cells cytotoxic effects consisting mainly of cell degeneration which often leads to loss of viability. In this work, we examined the cellular changes induced by TDH in monolayers of IEC-6 cells (derived from the rat crypt small intestine), which represent a useful cell model for studying toxins from enteric bacteria. In experimental conditions allowing cell survival, TDH induces a rapid transient increase in intracellular calcium as well as a significant though reversible decreased rate of progression through the cell cycle. The morphological changes seem to be dependent on the organization of the microtubular network, which appears to be the preferential cytoskeletal element involved in the cellular response to the toxin.

Study of the haemolytic process and receptors of thermostable direct haemolysin from Vibrio parahaemolyticus

The haemolytic action of 125I-labelled thermostable direct haemolysin from Vibrio parahaemolyticus was studied on human and equine erythrocytes. In the first step, the haemolysin bound to the membranes of both erythrocyte species. This binding seemed temperature-independent. Then, for human erythrocytes, haemolysin produced cell disruption, and haemoglobin was released. Following this step, haemolysin was also released in a temperature-dependent manner. In contrast, equine erythrocytes were not disrupted, and no release of haemolysin occurred. The receptors of labelled haemolysin were analysed by assaying the lipid/toxin interaction on a nylon membrane and by binding on thin-layer chromatograms. the ganglioside asialo-GM2 was found to be the most potent receptor, but asialo-GM1 and lactocerebroside may also have been involved.

Nature of the cation leak induced in erythrocyte membranes by Kanagawa haemolysin of Vibrio parahaemolyticus

Vibrio parahaemolyticus is an important enteric pathogen that produces an exotoxin prepared as Kanagawa haemolysin (KH). Isotope flux techniques were used to analyse toxin action on the basal permeability of human erythrocytes. KH induced a cation leak that was (i) rapid in onset (lag phase < 1 min), (ii) 'pore-like' in terms of kinetic characteristics, and (iii) of high magnitude initially (first 10 min) and then subsequently lower (but still raised with reference to control cells). The susceptibilities of the induced flux pathway to washout in initial and later periods suggested a protracted binding time course for toxin action. Neuraminidase treatment of erythrocytes enhanced both haemolysis and flux induced by KH, suggesting that the affinity of the toxin for the membrane had increased, possibly as a result of additional toxin receptors being unmasked by this enzyme. These results show that KH elevates the basal permeability of human erythrocytes in a complex manner, a process that probably underlies the deleterious effects of this toxin on cellular function.

Changes to erythrocyte membrane cation permeability induced by a bacterial toxin

Vibrio parahaemolyticus secretes an exotoxin prepared as Kanagawa haemolysin (KH) which causes marked alterations to the function of epithelial, cardiac and other cell types, but whose cellular mode of action is poorly understood. Using human red cells as a model system with radiotracer flux techniques, we have shown that KH (1) markedly elevated the basal leak to K+, (2) raised Ca2+ influx, and as a consequence of this, (3) stimulated the Ca2+-activated K+ channel. These results suggest that an important deleterious effect of this toxin is to elevate cation permeability, which will have both direct and indirect actions on the behaviour of a variety of cell types in vivo.

Ca(2+)-independent cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin (TDH) on Intestine 407, a cell line derived from human embryonic intestine

The effects of Vibrio parahaemolyticus thermostable direct hemolysis on Intestine 407, a cell line derived from the intestine of human embryos, were investigated. The hemolysin was shown to be cytotoxic to Intestine 407. This cytotoxicity is accompanied by the damage of plasma membrane and lysosomes, as well as cellular degeneration in the form of large transparent blebs. Although an increase in cytosolic free Ca2+ due t the influx of extracellular Ca2+ was observed in cells treated with thermostable direct hemolysin, it was found to be irrelevant to any of the above effects. These results suggest that the effects of thermostable direct hemolysin observed in this study on Intestine 407 are not mediated by Ca(2+)-dependent pathways.