[Histonet] cyclic dextrins?

[John Kiernan]

I can't really recommend a fixative because I have never tried to stain for any type of dextrin in tissues and have never seen a published method for doing so. That doesn't mean there isn't one. In your original post you said the specimens were already fixed in formalin (presumably aqueous); they may well not contain any cyclodextrin. 

If you must start from scratch, the first place to look is in a library. Mowry's 1953 paper in Am. J. Path. should be worth looking at, even though dextran is not the same as dextrin. Do a cited reference search with Scopus or Web of Science (the best two) or with Google Scholar (also good, and freely available to all). Find publications that cite R.Mowry 1953, and follow up the ones with likely-looking titles. Another valuable resource is www.jhc.org where anyone can search the whole of the Journal of Histochemistry and Cytochemistry (since it began, in the early 1950s) and download (free) the full text of any papers published more than about a year ago. Perhaps you'll find that nobody has wanted to stain cyclodextrin in tissue before. In that case you will have the opportunity to devise a new technique.

John Kiernan
Anatomy, UWO
London, Canada
---
----- Original Message -----
From: Cynthia Swanson <CSwanson <@t> biotechnics-inc.com>
Date: Tuesday, October 23, 2007 9:33
Subject: RE: [Histonet] cyclic dextrins?
To: John Kiernan <jkiernan <@t> uwo.ca>
Cc: histonet <@t> lists.utsouthwestern.edu

> Thank you for a very informative post. Would you please 
> recommend a
> non-aqueous fixative?
> 
>  
> 
> Cyndi
> 
>  
> 
> ________________________________
> 
>  
> 
> What are the "cyclic dextrins" that you are asked to stain in 
> "formalinfixed tissue"? Are they cyclodextrins, dextrins or 
> dextrans?  
> 
>  
> 
> If the fixative was mostly water, dextrins (and dextrans if present)
> have probably all been dissolved out. These oligo- and polysaccharides
> are soluble in water. Unlike proteins, they do not react with
> formaldehyde to form insoluble products. Read on.
> 
>  
> 
> Cyclodextrins are made by the action of a bacterial amylase on starch.
> The long chain of 1-->4-linked  glucose units is broken 
> down to shorter
> chains (6, 7 or 8 units), with the ends of each chain joined 1--
> >4 to
> make a ring. There are three types of cyclodextrin: alpha (smallest,
> with 6 glucose units), beta (7), and gamma (8 units). In three
> dimensions the ring is a shell or cage, with hydrophilic -OH 
> groups of
> glucose units on the outside and a hydrophobic interior. A hydrophobic
> organic molecule can be enclosed within a cyclodextrin molecule 
> withoutchemical change. The complex, known as a clathrate, is 
> soluble in water;
> this provides a way to make an aqueous solution of an otherwise
> insoluble hydrophobic substance. 
> 
>  
> 
> The ordinary non-cyclic dextrins (3 types) are produced by 
> either dry
> heating (toast) or acid hydrolysis of starch. Properties vary with
> method of production. They are soluble in water and precipitated by
> addition of alcohol. The information in this and the previous 
> paragraphis from the Merck Index (which gives some references) 
> and from an old
> biochemistry textbook for medical students (West & Todd, 1956). 
> 
>  
> 
> I do not have any authoritative statement about the solubilities 
> of the
> three cyclodextrins in liquids other than water. They may, like simple
> dextrins, be insoluble in alcohols. You can be sure they won't 
> dissolve in xylene or paraffin. 
> 
>  
> 
> Dextrins must not be confused with dextrans, which are bacterial
> polysaccharides composed of glucose units linked 1-->6 (in 
> contrast to
> the 1-->4 of plants and animals). Dextrans are the protein substitutes
> in traditional artificial plasma expanders (Rheomacrodex when I was
> young; is it still used?) and they can end up in the renal tubules.
> According to Lillie's big book, which cites a paper by Bob Mowry 
> (Am. J.
> Path. 29:523, 1953), water must be avoided at all stages prior to
> staining dextran. That means a non-aqueous fixative and floating out
> paraffin sections on 95% alcohol, not water. The reagents for staining
> (periodic acid-Schiff) should be made up in alcohol rather than 
> water. 
> 
>  
> 
> Mowry's and Lillie's simple rules probably apply also to the
> histochemical detection of cyclo- and other dextrins: Non-aqueous
> fixative --> wax --> flatten on warm alcohol  --> dewax 
> with xylene and
> then -->  alcoholic PAS method. Does this help?  
> Please reply to all.
> 
>  
> 
> John Kiernan
> 
> Anatomy, UWO
> 
> London, Canada
> ---
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>