Alcian blue pyridine variant--a superior alternative to alcian blue 8GX: staining performance and stability

At least four distinct blue cationic phthalocyanine dyes sold as "alcian blue" raises the question: what is alcian blue?

We investigated physicochemical characteristics of dye lots sold as "alcian blue" using the Biological Stain Commission (BSC) precipitation test, differential scanning calorimetry, high performance liquid chromatography, thin layer chromatography and UV/visible spectroscopy. Four blue phthalocyanine dyes were detected in 11 commercial dye lots. These four included the original ingrain blue 1 CI 74000 dye and the dye sold with the name "alcian blue pyridine variant"; we discuss also the possible identity of the additional two dyes. A proposed extension to the BSC analytic scheme is presented that could distinguish three categories of commercial alcian blue dyes from each other and from the original alcian blue 8G.

Revised tests and standards for Biological Stain Commission certification of alcian blue dyes

Alcian blue dyes are copper phthalocyanines with a variety of cationic side chains; they are useful for staining carbohydrate polyanions while avoiding staining of nucleic acids. The properties of the original alcian blue and of similar dyes with published chemical structures are reviewed here. Variation among samples submitted to the Biological Stain Commission (BSC) for certification has led to the recognition of two types of commercially available alcian blue at this time. The designation "alcian blue 8G or equivalent" is reserved for dyes that resemble alcian blue 8GX manufactured in the 1960s (CI 74240; ingrain blue 1). These dyes react with alkali to form an insoluble pigment that cannot be re-dissolved in acid. The name "alcian blue variant" is for similar dyes that do not form insoluble pigments; an alkali-induced precipitate, if formed, re-dissolves with acidification. For certification by the BSC, both types of alcian blue must dissolve in 3% acetic acid to make a 1% solution (pH close to 2.5), which must provide selective coloration of intestinal mucus, cartilage and mast cells, but not of nuclei. After alcian blue staining and treatment with 0.03 M Na₂CO₃ or Li₂CO₃ to convert the bound dye to a pigment, the Feulgen stain for DNA is applied. Dyes to be certified as alcian blue 8G or the equivalent must resist extraction by the 5 M HCl used in the Feulgen reaction. Dyes to be certified as alcian blue variant are not required to be convertible to acid-insoluble pigments, but they must dissolve easily in water at pH 5.7 containing 0.5 M magnesium chloride and the dye must remain in solution for at least 24 h. A critical electrolyte concentration (CEC) staining test also is described; this must be passed for certification of an alcian blue variant. Successful CEC staining is also a desirable property of alcian blue 8G or equivalent, but not essential for certification of an otherwise satisfactory batch. The spectrophotometric criteria for alcian blue dyes also are revised; a wider range of absorption maximum (605-634 nm) is allowed. The dye powders used in published staining techniques with the original alcian blue 8G were 40-60% dye, but some modern alcian blue dyes have dye content as high as 90%. The BSC's assay for dye content is not a criterion for certification, but it should influence the amount of dye to include in a staining solution.

Synthesis, characterization and staining performance of peripherally and non-peripherally substituted metallo-phthalocyanines bearing 1,3-bis-(trimethylamino)-2-propoxy groups

In this study, water-soluble symmetrical phthalocyanines having cationic 1,3-bis-(trimethylamino)-2-propoxy groups at the peripheral and non-peripheral positions were synthesized and characterized.

Dibenzothiazoles as novel amyloid-imaging agents

Novel dibenzothiazole derivatives were synthesized and evaluated as amyloid-imaging agents. In vitro quantitative binding studies using AD brain tissue homogenates showed that the dibenzothiazole derivatives displayed high binding affinities with K(i) values in the nanomolar range (6.8-36 nM). These derivatives are relatively lipophilic with partition coefficients (logP oct) in the range of 1.25-3.05. Preliminary structure-activity relationship studies indicated dibenzothiazole derivatives bearing electron-donating groups exhibited higher binding affinities than those bearing electron-withdrawing groups. A lead compound was selected for its high binding affinity and radiolabeled with [(125)I] through direct radioiodination using sodium [(125)I] iodide in the presence of Chloramine T. The radioligand (4-[2,6']dibenzothiazolyl-2'-yl-2-[(125)I]-phenylamine) displayed moderate lipophilicity (logP oct, 2.70), very good brain uptake (3.71+/-0.63% ID/g at 2 min after iv injection in mice), and rapid washout from normal brains (0.78% and 0.43% ID/g at 30 and 60 min, respectively). These studies indicated that lipophilic dibenzothiazole derivatives represent a promising pharmacophore for the development of novel amyloid-imaging agents for potential application in Alzheimer's disease and related neurodegenerative disorders.

Cytochemical differences in bacterial glycocalyx

To examine new cytochemical aspects of the bacterial adhesion, a strain 41452/01 of the oral commensal Streptococcus sanguis and a wild strain of Staphylococcus aureus were grown with and without sucrose supplementation for 6 days. Osmiumtetraoxyde (OsO4), uranyl acetate (UA), ruthenium red (RR), cupromeronic blue (CB) staining with critical electrolytic concentrations (CECs), and the tannic acid-metal salt technique (TAMST) were applied for electron microscopy. Cytochemically, only RR-positive fimbriae in S. sanguis were visualized. By contrast, some types of fimbriae staining were observed in S. aureus glycocalyx: RR-positive, OsO4-positive, tannophilic and CB-positive with ceasing point at 0.3 M MgCl2. The CB staining with CEC, used for the first time for visualization of glycoproteins of bacterial glycocalyx, also reveals intacellular CB-positive substances-probably the monomeric molecules, that is, subunits forming the fimbriae via extracellular assembly. Thus, glycosylated components of the biofilm matrix can be reliably related to single cells. The visualization of intracellular components by CB with CEC enables clear distinction between S. aureus and other bacteria, which do not produce CB-positive substances. The small quantities of tannophilic substances found in S. aureus makes the use of TAMST for the same purpose difficult. The present work protocol enables, for the first time, a partial cytochemical differentiation of the bacterial glycocalyx.

Glycocalyx morphology of Candida albicans

In this study, we examine new cytochemical aspects of the fimbria-mediated adhesion of the oral facultative pathogen Candida albicans. A wild-type strain of the yeast was grown with and without sucrose supplementation for 8 days. Osmium tetroxide, uranyl acetate (UA), ruthenium red (RR), and cupromeronic blue (CB) staining with critical electrolytic concentrations (CECs) and tannic acid-metal salt technique (TAMST) were applied to specimens separately or in combination for transmission electron microscopy (TEM) examination. Cytochemically, two types of fimbriae of C. albicans were distinguished: RR-positive fimbriae of polyanionic glycoconjugates and CB-positive fimbriae with a ceasing point of 0.3 M MgCl2 where no staining of sulfated carboxyl-rich and/or phospho-glycoconjugates occurred. Additionally, CB-positive intercellular fibers were observed, which seemed to be involved in intercellular adhesion. The present protocol enables, for the first time, a partial cytochemical differentiation between at least two kinds of yeast fimbriae.