A sensitive method for the detection of GM1-ganglioside in rat adipocyte preparations based on its interaction with choleragen

Diagnostic techniques for rapid detection of Vibrio cholerae O1/O139

Cholera caused by the toxigenic Vibrio cholerae is still a major public health problem in many countries. This disease is mainly due to poor sanitation, hygiene and consumption of unsafe water. Several recent epidemics of cholera showed its increasing intensity, duration and severity of the illness. This indicates an urgent need for effective management and preventive measures in controlling the outbreaks and epidemics. In preventing and spread of epidemic cholera, rapid diagnostic tests (RDTs) are useful in screening suspected stool specimens, water/food samples. Several RDTs developed recently are considered as investigative tools in confirming cholera cases, as the culture techniques are difficult to establish and/or maintain. The usefulness of RDTs will be more at the point-of-care facilities as it helps to make appropriate decisions in the management of outbreaks or epidemiological surveillance by the public health authorities. Apart from RDTs, several other tests are available for the direct detection of either V. cholerae or its cholera toxin. Viable but non-culturable (VBNC) state of V. cholerae poses a great challenge in developing RDTs. The aim of this article is to provide an overview of current knowledge about RDT and other techniques with reference to their status and future potentials in detecting cholera/V. cholerae.

Analyzing T-Cell Plasma Membrane Lipids by Flow Cytometry

Plasma membrane lipid rafts are highly ordered membrane microdomains enriched for glycosphingolipids and cholesterol, which play an important role during T-cell antigen receptor (TCR) signaling. Our previous work has demonstrated that plasma membrane lipid composition is an important determinant of human CD4⁺ T-cell function and that defects in lipid raft expression contribute to CD4⁺ dysfunction in patients with autoimmunity. In this chapter we share three flow cytometry-based methods to quantitatively analyze plasma membrane lipid composition in primary human CD4⁺ T cells. We describe the quantification of glycosphingolipid expression using cholera toxin subunit B, cholesterol expression using filipin staining, and membrane "lipid order" using di-4-ANEPPDHQ. These methods can easily be adapted to analyze different cell types.

Obesity causes a shift in metabolic flow of gangliosides in adipose tissues

Obesity is associated with insulin resistance and a mild chronic inflammation in adipose tissues. Recent studies suggested that GM3 ganglioside mediates dysfunction in insulin signaling. However, it has not been determined the ganglioside profiling in adipose tissues of obese animals. Here, we for the first time examined semi-quantitative ganglioside profiles in the adipose tissues of high fat- and high sucrose-induced obese, diabetic C57BL/6J mice by TLC and HPLC/mass spectrometry. In control adipose tissues GM3 dominated with traces of GM1 and GD1a; obesity led to a dramatic increase in GM2, GM1, and GD1a with the GM3 content unchanged. Similar results were obtained in KK and KKAy mice. Adipocytes separated from stromal vascular cells including macrophages contained more of those gangliosides in KKAy mice than in KK mice. These results underscore those gangliosides in the pathophysiology of obesity-related diseases.

Lipids and glycosphingolipids in caveolae and surrounding plasma membrane of primary rat adipocytes

We have made a comprehensive and quantitative analysis of the lipid composition of caveolae from primary rat fat cells and compared the composition of plasma membrane inside and outside caveolae. We isolated caveolae from purified plasma membranes using ultrasonication in carbonate buffer to disrupt the membrane, or extraction with nonionic detergent, followed by density gradient ultracentrifugation. The carbonate-isolated caveolae fraction was further immunopurified using caveolin antibodies. Carbonate-isolated caveolae were enriched in cholesterol and sphingomyelin, and the concentration was three- and twofold higher, respectively, in caveolae compared to the surrounding plasma membrane. The concentration of glycerophospholipids was similar suggesting that glycerophospholipids constitute a constant core throughout the plasma membrane. The composition of detergent-insoluble fractions of the plasma membrane was very variable between preparations, but strongly enriched in sphingomyelin and depleted of glycerophospholipids compared to carbonate-isolated caveolae; indicating that detergent extraction is not a suitable technique for caveolae preparation. An average adipocyte caveola contained about 22 x 10(3) molecules of cholesterol, 7.5 x 10(3) of sphingomyelin and 23 x 10(3) of glycerophospholipid. The glycosphingolipid GD3 was highly enriched in caveolae, whereas GM3, GM1 and GD1a were present inside as well as outside the caveolae membrane. GD1b, GT1b, GM2, GQ1b, sulfatide and lactosylceramide sulfate were not detected in caveolae.

Ganglioside dependent return of TSH receptor function in a rat thyroid tumor with a TSH receptor defect

The 1-8 rat thyroid tumor line with a thyrotropin and cholera toxin receptor defect and a deficiency in higher order membrane gangliosides is shown to regain both receptor functions with the in vivo resynthesis or the in vitro reconstitution of higher order gangliosides. Reconstitution was achieved by exposing primary cell cultures of the tumor to preparations of gangliosides from thyroid cells with functional thyrotropin receptor activity.

Role of membrane gangliosides in the binding and action of bacterial toxins

Gangliosides are complex glycosphingolipids that contain from one to several residues of sialic acid. They are present in the plasma membrane of vertebrate cells with their oligosaccharide chains exposed to the external environment. They have been implicated as cell surface receptors and several bacterial toxins have been shown to interact with them. Cholera toxin, which mediates its effects on cells by activating adenylate cyclase, bind with high affinity and specificity to ganglioside GM1. Toxin-resistant cells which lack GM1 can be sensitized to cholera toxin by treating them with GM1. Cholera toxin specifically protects GM1 from cell surface labeling procedures and only GM1 is recovered when toxin-receptor complexes are isolated by immunoadsorption. These results clearly demonstrate that GM1 is the specific and only receptor for cholera toxin. Although cholera toxin binds to GM1 on the external side of the plasma membrane, it activates adenylate cyclase on the cytoplasmic side of the membrane by ADP-ribosylation of the regulatory component of the cyclase. GM1 in addition to functioning as a binding site for the toxin appears to facilitate its transmembrane movement. The heat-labile enterotoxin of E. coli is very similar to cholera toxin in both form and function and can also use GM1 as a cell surface receptor. The potent neurotoxin, tetanus toxin, has a high affinity for gangliosides GD1b and GT1b and binds to neurons which contain these gangliosides. It is not yet clear whether these gangliosides are the physiological receptors for tetanus toxin. By applying the techniques that established GM1 as the receptor for cholera toxin, the role of gangliosides as receptors for tetanus toxin as well as physiological effectors may be elucidated.

Mechanism of action of cholera toxin: effect of receptor density and multivalent binding on activation of adenylate cyclase

Choleragen (cholera toxin) activates adenylate cyclase in HeLa cells, which contain less than 15,000 toxin receptors per cell, in a time- and concentration-dependent manner. Activation is blocked by the addition of the oligosaccharide chain of the ganglioside GM1, the receptor for the toxin. When the cells are preincubated with choleragen at 4 degrees C and then incubated with oligosaccharide at 37 degrees C, adenylate cyclase is activated less than 10%. When the preincubation phase is above 18 degrees C, adenylate cyclase becomes activated and the amount of activation depends on the time of preincubation. This inhibitory effect of the oligosaccharide is also observed with human lymphocytes and rat glial C6 cells but not with Friend erythroleukemic and mouse neuroblastoma N18 cells. The latter two cell lines have large numbers ot toxin receptors, whereas the former two cell lines have few receptors. When the number of toxin receptors in HeLa and C6 cells is increased by treating the cells with GM1, activation of adenylate cyclase by choleragen is no longer blocked by the oligosaccharide. The oligosaccharide has a corresponding effect on the displacement of bound 125I-choleragen. When bound to cells at 4 degrees C, most of the radiotoxin is displaced from HeLa, C6, and lymphocytes but not from Friend, N18, or HeLa cells pretreated with GM1. In untreated HeLa cells, dissociation of toxin-receptor complexes by the oligosaccharide depends on the time and temperature of complex formation; above 18 degrees C, the toxin rapidly becomes stably bound to the cells. The inhibitory effect of GM1 oligosaccharide us reversible, as, once it is removed, the small amount of toxin that remains bound can activate adenylate cyclase. These results are consistent with a model in which choleragen, which is multivalent, must bind to several GM1 molecules on the cell surface in order to subsequently activate adenylate cyclase. Lateral mobility of toxin-receptor complexes may be required only to achieve multivalent binding in cells with few receptors.

A comparison of the ganglioside distributions of fat tissues in various animals by two-dimensional thin layer chromatography

The ganglioside distributions of various fat tissues from human, rabbit, rat, mouse, chicken and frog were compared with pig adipose gangliosides by two-dimensional thin layer chromatography. It was found that there is a remarkable species variation in ganglioside distribution, especially in the composition and relative concentration of complex gangliosides. Differing from pig adipose tissues, those of human, rabbit, rat, mouse, chicken, but not frog, contained GM3 as a most abundant ganglioside. The data for human, rabbit and chicken indicated a simple distribution of only NeuAc-type gangliosides, while those for rat and mouse indicated a rather complicated pattern containing both NeuAc- and NeuGc-type gangliosides. The ganglioside pattern of the frog fat body differed markedly from those of mammalian fat tissues because of the presence of three different, unusual monosialosylgangliosides as major components. In other respects, a substantial amount of disialosylgangliosides was commonly found in all animal fat tissues.