Letter: Iodoplatinate as a marker of quarternary ammonium compounds in electron microscopy

Effect of a Hydrophobic Phospholipid Lining of the Gastric Mucosa in Bioadhesion

PURPOSE

The role of a model hydrophobic phospholipid simulating lining of the gastric mucosa, as to adhesion of polymers with different surface functional groups and surface hydrophobicities, was evaluated using an in vitro gastric mucus model.

MATERIALS AND METHOD

Front-faced fluorescence measurement was used to determine adhesion of fluorescent polystyrene microspheres with different surface functional groups. Contact angle measurements and sticking bubble technique were used to measure relative surface hydrophobicity of the polymers.

RESULTS

Adhesion of fluorescent polystyrene microspheres using front-faced fluorescence measurement revealed the hydrophobic phospholipid lining of the in vitro gastric mucus model did not allow adhesion of microspheres with -COOH and -NH(2) functional groups, whereas it did allow adhesion of microspheres with hydrophobic attributes. In addition, in vitro adhesive force studies using diblock copolymers of polystyrene and polyacrylate showed that the in vitro adhesive force between the hydrophobic phospholipid lining of the in vitro gastric mucus model and the polymer increased when the surface hydrophobicity of the polymer increased.

CONCLUSION

The hydrophobic phospholipid acts as an adhesion barrier to hydrophilic bioadhesive polymers and polymers with surface functional groups of carboxylic acid and amine. The hydrophobic phospholipid lining of the gastric mucosa should be taken into considerations for screening and designing of a new gastric bioadhesive polymer.

Iodoplatinate visualization of phospholipids in rat incisor predentine and dentine, compared with malachite green aldehyde

The iodoplatinate (IP) reaction, a selective method for visualization of phospholipids, was applied to the predentine and dentine of rat incisors and compared with malachite green aldehyde (MG) fixation/staining. Spot tests indicated (1) that IP specifically stains phospholipids, but not amino acids, displaying as do phospholipids, quaternary ammonium groups; and (2) phosphatidylserine and sphingomyelin were also stained by MGA. Although this reagent is known to interact with phosphorus, phosphoproteins remained unstained. In the rat incisor, an IP-positive network including granules and thin filaments was seen in predentine in the inter-collagen spaces, in many cases closely associated with collagen fibres and their periodic striations. In dentine, positively stained needle-like structures were located along individual collagen fibres, or at the surface of groups of collagen fibres. This staining pattern was unchanged on sections of material pretreated with acetone, whereas the staining was abolished or markedly reduced when the samples were treated either with chloroform/methanol or phospholipase C prior to the IP reaction. Pretreatment of the samples with hyaluronidase promoted subsequent diffusion of the staining. A very similar staining pattern was observed with MGA, in accordance with earlier reports. The present findings validate the histochemical results reported previously on the distribution and potential role(s) of phospholipids in dentine biomineralization.

Demonstration of a phospholipid-rich zone in the human gastric epithelium damaged by Helicobacter pylori

BACKGROUND

Recently, a hydrophobic layer has been shown by the contact angle method in human gastric biopsy specimens. The aim of this study was to show the existence of a phospholipid-rich layer in the human gastric epithelium and to investigate the influence of Helicobacter pylori on these structures.

METHODS

Biopsy specimens from the gastric antrum were obtained during gastroscopy from patients with normal gastric mucosa as well as from patients with H. pylori-positive gastritis for electron microscopical and histological examination. Structures reacting with a phospholipid-selective stain, iodoplatinate were analyzed by electron microscopy and electron-dispersive x-ray microanalysis.

RESULTS

Both methods revealed the morphological existence of a phospholipid-rich zone covering the human gastric epithelial layer. Reaction products could be localized within the cells, at the epithelium closely associated with the surface, and in connection with the mucus. In infected tissue, H. pylori affects iodoplatinate-reactive material within the mucous layer and material covering the epithelium.

CONCLUSIONS

The phospholipid-rich zone in the apical region of surface mucous cells is likely to represent an important factor of the gastric protective system in humans. The destruction of this hydrophobic layer may result in a reduction of hydrophobicity giving access to gastric acid.

Morphological effects of aspirin and prostaglandin on the canine gastric mucosal surface. Analysis with a phospholipid-selective cytochemical stain

An iodoplatinate technique that selectively stains phospholipid was used to evaluate morphologically the effects of aspirin and 16,16-dimethyl prostaglandin E2 on canine gastric mucosa in an in vitro Ussing chamber system. The association between these morphological alterations and the changes in mucosal surface hydrophobicity as determined by contact angle analysis was also investigated. Prostaglandin (1 microgram/ml) did not alter aspirin-induced cell injury, although it reduced (45%) the detachment of damaged cells from the lamina propria. Mucus release appeared to be stimulated independently both by aspirin and prostaglandin treatment and by the blotting and drying procedure routinely performed before contact angle analysis. When an extracellular mucus gel coat was present, it contained numerous iodoplatinate-reactive vesicles and myelinated or lamellated structures. Iodoplatinate-reactive substances also appeared at the luminal surface of the mucus gel as a filamentous band. This band of reactivity was frequently seen after simultaneous treatment with prostaglandin and aspirin but only sporadically observed after aspirin treatment alone. The hydrophobic nature of the canine gastric mucosa under the above experimental conditions correlated well (r = 0.743, p less than 0.005) with the percentage of mucosal surface covered by this filamentous band, and less so with the density of iodoplatinate-reactive structures within the mucus gel. We conclude that phospholipid structures in the mucus gel may account for the hydrophobic nature of the gastric mucosal surface and the ability of damaging and "cytoprotective" agents to influence both surface wettability and barrier integrity.

Methods of heavy metal electron microscopic histochemistry applied to frog lung surfactant

Four heavy metal staining methods have been applied to frog lung surfactant. Among them, the iodoplatinate method is the only one that almost exclusively visualizes the phospholipid moiety being produced in the lamellated bodies of the pulmonary epithelial cells and forming the backbone of organized structures within the extracellular lining layer. The other three techniques-ruthenium red-osmium tetroxide, osmium tetroxide-ferrocyanide, acidic phosphotungstic acid in chromatic (Rambourg technique)--more or less give electron contrast to glycoproteins and to a lesser extent to the hydrophilic parts of phospholipids. They all show the extracellular lining layer to be a two component system: the content of the lamellar bodies form--when released--membranous configurations, similar to those observed in mammalian lungs; they unfold in an amorphous hypophase, which is apparently secreted by goblet cells of the pulmonary epithelium.

Ultrahistochemical investigations of dog lung surfactant with ruthenium red and iodoplatinate reactions

Dog lungs have been fixed by immersion and submitted to two histochemical procedures. An iodoplatinate reaction technique to demontrate choline phospholipids stains cell membranes, inclusion bodies of type II alveolar epithelial cells and tubular myelin figures of pulmonary surfactant, the latter as electron-dense lines measuring 5 nm. The ruthenium red procedure gives rise to an intense contrast of the free surface of alveolar epithelium. The 5 nm-lines of the pulmonary surfactant are seen as electron-lucent lines, but bordered by electron-dense rims. Though both techniques have limitations in their interpretation, which are discussed in this paper, they demonstrate the tubular myelin figures to be a highly organized mixture of phospholipids and glycoproteins.

Evidence for the cytoplasmic localization of betaine in leaf cells of Suaeda maritima

An attempt has been made to localize glycinebetaine in shoots of Suaeda maritima L. Dum. using a technique based on the formation of an iodoplatinate precipitate. Deposits were largely restricted to the cytoplasm of salt-grown plants and were analysed by transmission analytical electron microscopy. The results are considered to support the hypothesis that glycinebetaine acts as a cytoplasmic osmoticum to balance high vacuolar salt levels in certain halophytes.