What is the solubility of Congo red?
Congo red is water-soluble, yielding a red colloidal solution; its solubility is greater in organic solvents. However, the use of Congo red has long been abandoned, primarily because of its carcinogenic properties.
What is the history of Congo red?
See Article History. Congo red, first of the synthetic dyestuffs of the direct type, that is, not requiring application of a mordant (a substance such as tannin or alum used to fix the colour to cotton fibres). Introduced in 1884, Congo red belongs to a group of azo dyes derived from benzidine.
What is the metachromatic property of Congo red?
This property gives Congo red a metachromatic property as a dye, both in strongly acidic solutions and with strongly acidophilic tissue. Congo red has a propensity to aggregate in aqueous and organic solutions.
Is collagen refractile after Congo red?
Nonspecific red staining by Congo red can be seen with collagen, fibrin, or other protein deposits; collagen can be refractile but not usually green ± Congo red In contrast to fibrillar collagen, amyloid fibrils are only birefringent after Congo red
Is Congo red soluble in water?
It is an azo dye. Congo red is water-soluble, yielding a red colloidal solution; its solubility is greater in organic solvents. However, the use of Congo red has long been abandoned, primarily because of its carcinogenic properties.
Is Congo red hydrophilic?
Mounted in this carbohydrate-containing, hydrophilic medium, the Congo red molecules are oriented parallel to the surface of the amyloid filaments and the sign is linear positive, corresponding to an additive character of topo-optical staining reactions.
What kind of dye is Congo red?
azo dyesIntroduced in 1884, Congo red belongs to a group of azo dyes derived from benzidine. Congo red was formerly used to dye cotton but has been superseded by dyes more resistant to light and to washing.
Why is Congo red blue?
Congo red is also used as a pH indicator. The color transition is between pH 3.0 and 5.0. Below a pH of 3.0 (very acidic solutions), the indicator is blue.
Why is Congo red anionic?
Congo red (CR) is a benzidine-based anionic diazo dye that can cause allergic reactions and can be metabolized to benzidine, a carcinogenic product19. Depending on pH, various molecular structures of CR can be present in aqueous solution20, which hinders its elimination.
Why is Congo red called Congo red?
Conclusions: The Congo red stain was named "Congo" for marketing purposes by a German textile dyestuff company in 1885, reflecting geopolitical current events of that time.
What is Congo red soluble in?
Congo red is red-brown powder, soluble in hot water and the cold water 10 times of its weight; the color of the solution is yellow-red; soluble in ethanol and the solution is orange; slightly soluble in acetone, while almost insoluble in ether.
What is a Congo red stain?
Congo red stain is the gold standard for the demonstration of amyloid in tissue sections. It is used to evaluate the presence and extent of amyloidosis in different organs.
What does Congo red bind to?
amyloid fibrilsThe fact that Congo red binds to native, partially folded conformations and amyloid fibrils of several proteins shows that it must be used with caution as a diagnostic test for the presence of amyloid fibrils in vitro.
Why does Congo red turn black?
This is because these bacteria do not ferment any other sugars that may be necessary to release certain metabolites, which combine with Congo red to impart a black colour to the colonies indicating slime production.
How is Congo red made?
Congo Red is synthesised by coupling bis-diazotised benzidine with two molecules of napthionic acid. The blue dye so obtained is converted into its red disodium salt during its salting out with sodium chloride (Fig. 4.2).
Is Congo red light sensitive?
Congo red, despite having lower sensitivity, is the standard agent used to identify amyloid in tissues. While the apple-green birefringence seen under crossed polarized light is specific for amyloid material, staining with Congo red is technically difficult resulting in inconsistent staining.
What color is Congo red?
Congo red shows red-orange deposits under nonpolarized light; apple-green birefringence under polarized light required for specificity. –. Nonspecific red staining by Congo red can be seen with collagen, fibrin, or other protein deposits; collagen can be refractile but not usually green ± Congo red. –. In contrast to fibrillar collagen, amyloid ...
What is the most sensitive method of diagnosis for Congo red?
Fibrils are associated with electron-dense dot-like structures (P component) Fibrils found associated with sarcolemma and less frequently with vascular basal lamina. Transmission electron microscopy (TEM) is most sensitive and specific method of diagnosis, positive in cases where Congo red is negative or inconclusive.
What are the factors that affect the Congo red-amyloid reaction?
Two factors are important to the Congo red–amyloid reaction: the linearity of the dye molecule and the β-pleated sheet configuration. If the spatial configuration of either is altered, even though the chemical groupings are left intact, the reaction fails.
When was Congo red dye invented?
First introduced as a colorant for the cotton industry in 1884, Congo red is an acidic diazo dye that is comprised of two identical halves each composed of a phenyl ring bound to a naphthalene moiety by a diazo group.
What is Sirius red?
Sirius red technique ( Llewellyn 1970) This method, a modification of Sweat's, uses the direct cotton dye Sirius red F3B which, according to the authors, compares favorably with Congo red as a method for the detection of amyloid. The mechanism of staining is probably similar to that of Congo red.
What is a Congo red negative fibril?
These are two related yet distinct glomerular diseases characterized by deposition of Congo red–negative fibrils and characterized by a variety of light microscopic features and progressive clinical course. Fibrillary GN is defined as Congo red-negative fibrils < 30 nm in diameter, whereas immunotactoid GN is defined by glomerular deposition of hollow stacked microtubules > 30 nm in diameter. Both entities are relatively uncommon, accounting for less than 1% of native renal biopsies. Recurrence of these diseases is common after transplantation.
Is Congo red hydrogen bonding?
However, with Congo red there is probably also some hydrogen bonding. With both stains penetration of intact starch grains is poor and the stains can be used as a diagnosis of starch damage. Congo red is also a stain for amyloid deposits in animal tissues.
Is glomerulonephritis an Ig?
Fibrillary and immunotactoid glomerulonephritis are very uncommon non-amyloid ( Congo red negative) forms of Ig-associated kidney disease with abnormal tissue deposits from fibrils. Similar to LCDD, they usually present with a glomerulonephritis picture (hematuria and proteinuria, hypertension, and kidney impairment).
What is a Congo red negative fibril?
These are two related yet distinct glomerular diseases characterized by deposition of Congo red–negative fibrils and characterized by a variety of light microscopic features and progressive clinical course. Fibrillary GN is defined as Congo red-negative fibrils < 30 nm in diameter, whereas immunotactoid GN is defined by glomerular deposition of hollow stacked microtubules > 30 nm in diameter. Both entities are relatively uncommon, accounting for less than 1% of native renal biopsies. Recurrence of these diseases is common after transplantation.
Does Congo Red interfere with PrPC?
Based on earlier work that demonstrated that the amyloid binding dye Congo Red ( CR) could interfere with the conversion of PrPC to PrP Sc in cell based 118 and animal models 119 of prion disease structural analogues of CR, including tetracyclines and more specifically doxycycline were investigated for their therapeutic effect in prion disease, based on their lower toxicity and ability to cross the blood brain barrier. Initially in vitro studies using tetracycline demonstrated an ability to bind amyloid made from 106–126 and 82–146 fragments of the prion protein. In addition to binding to these fragments, tetracycline was also found to inhibit phosphate buffer induced fibrillization, increased sensitivity to protease digestion and reduced the in vitro toxicity of the 106–126 PrP peptide 120. The clinical relevance of these observations was further tested when it was shown that tetracycline and doxycycline could reduce the protease resistance of PrP Sc derived from the tissue of patients with type 1 or type 2 CJD, albeit with higher concentrations of tetracycline required to reduce the protease resistance of type 1 relative to type 2. Later studies also demonstrated that doxycycline and tetracycline treatment reduced the protease resistance of vCJD and BSE derived PrP Sc 121.
What is Congo red?
Congo red, first of the synthetic dyestuffs of the direct type, that is, not requiring application of a mordant ...
When was Congo red dye invented?
Introduced in 1884, Congo red belongs to a group of azo dyes derived from benzidine. Congo red was formerly used to dye cotton but has been superseded by dyes more resistant to light and to washing.
What is Congo red?
Congo red. More... Congo Red is the sodium salt of benzidinediazo-bis-1-naphthylamine-4-sulfonic acid; a diazo dye that is red in alkaline solution and blue in acid solution and used especially as an indicator and as a biological stain. Congo Red is an indicator dye that is blue-violet at pH 3.0 and red at pH 5.0.
Is Congo red or Congo rubin neurotoxic?
This neurotoxic effect can be inhibited completely by certain dyes. ... The most potent of these are Congo Red and Congo Rubin. ... Congo red also inhibits the neurotoxic effects of the human pancreatic amylodiogenic peptide amylin. It is postulated that these dyes, by interacting with the beta-pleated sheet structure of amylodiogenic peptides, prevent aggregation and hence neurotoxicity.
Is Congo red mutagenic?
Congo red, an azo dye derived from benzidine, and 2-azoxyfluorene, a derivative of 2-aminofluorene, were reduced during overnight incubation with a suspension of rat intestinal bacteria. HPLC and uv spectral analysis verified the presence of benzidine in the extracts of the Congo red incubations. ... Extracts of the Congo red incubations were mutagenic toward Salmonella typhimurium TA1538 in the presence of post-mitochondrial activating system, but Congo red was not mutagenic without this reductive pretreatment. ... The utility of the Ames test in screening for potential mutagens may be expanded by a reductive pretreatment utilizing cecal bacteria.
