AW: [Histonet] Washing out formalin fixation (Lengthy)

From:"Gudrun Lang"

I think one reason for washing the fixed specimen in the "histo-beginning"
was to keep the following chemicals clean. Nowadays there's no problem to
get new alcohols in good quality for the infiltration-instruments. 
And I think, that washing wasn't excluded to formalin-fixation.
A positive effect of washing should also be the better stainability with
acid dyes. The "old" histologists certainly had good reasons (and plenty of
time) for this procedure, but today "time is more money".

Gudrun Lang
Biomed. Analytikerin
Akh Linz
Krankenhausstr. 9
4020 Linz
-----Ursprüngliche Nachricht-----
[] Im Auftrag von Mark
Gesendet: Sonntag, 09. März 2008 01:01
Betreff: Re: [Histonet] Washing out formalin fixation (Lengthy)

I just want to point out again that this works poorly and wastes water... I
don't want anyone to get too excited and ditch the HIER buffers.  Nobody
does this in the real world.  It all goes back to what René said, "It
(pretty much) doesn't work that way."

On Tue, Mar 4, 2008 at 7:56 AM, Bryan Hewlett  wrote:

> Hi Teri and everyone else on this thread,
> Washing out many of the effects of formaldehyde fixation on tissues with
> running water has been known for years (much longer than this old boy has
> been around).
> In modern terms, it is the essential underlying mechanism for so-called
> antigen retrieval (HIER).
> Formaldehyde fixes proteins by addition, with the formation of
> hydroxymethyl
> adducts on the reactive side chains of proteins.
> Once enough of these hydroxymethyl adducts are formed, and IF they are in
> close approximation to each other, they may slowly cross-link by the
> formation of methylene bridges.
> However, these adducts and initial cross-links are unstable and readily
> reversed by water and alcohol (see Kiernan (1999).
> It takes 24 hours at room temperature for all the hydroxymethyl adducts to
> form, i.e. maximal binding threshold (see Fox et al, 1985).
> If the tissue is then exposed to running water before all the adducts have
> formed (i.e. less than 24 hours), the reversal is very rapid.
> The shorter the time in formaldehyde, the more rapid the reversal.
> Even after the essential 24 hours fixation and also after a more lengthy 6
> days fixation, running water will still remove the adducts and hydrolyse
> the
> methylene bridges.
> There is at least one publication (Helander, 1994) that provides data
> regarding this effect.
> After 24 hours fixation, 50% reversal occurred in less than 24 hours, 90%
> reversal was obtained after 6 days washing and for 6 days fixation 90%
> reversal after 4 weeks washing.
> It should be noted that these reversal times were obtained at ambient
> temperatures and the times may be considerably reduced by elevated
> temperatures.
> This reversal effect is also obtained on tissue sections that have been
> processed to wax.
> However, because of the additional shrinkage and hydrophobicity of the
> processed proteins, the reversal is slowed somewhat until the proteins
> re-hydrate.
> The reversal effect can also be aided by the presence of other ions in the
> water (the purpose of HIER buffers).
> Back in the sixties, in order to successfully demonstrate Ig's by IF, we
> were reversing the fixation effects on paraffin sections by placing them
> in
> hypotonic buffers for 2 days at 37C.
> Today, since we are all in a great rush for results, we obviously drive
> the
> reversal at higher temperatures to speed things up!!
> References:
> Baker JR (1958), Principles of Biological Microtechnique, Methuen & Co.
> Ltd.
> Hopwood D. Fixatives and fixation: A review. Histochemical journal (1969);
> 1, p19-55
> Burnett MG. The mechanism of the formaldehyde clock reaction: Methylene
> glycol dehydration. J Chem. educ. (1982); 59, 160
> Fox CH et al. Formaldehyde fixation. J Histochem Cytochem (1985); 33,
> 845-853
> Helander KG. Kinetic studies of formaldehyde binding in tissue.
> Biotechnique
> and Histochemistry. (1994); 69, 177-179
> Kiernan J.A., Histological and Histochemical Methods: Theory and Practice,
> 3rd Edition, (1999). Oxford: Butterworth-Heinemann. ISBN # 0-7506-3106-6.
> Shi SR, Gu J. and Taylor CR. Antigen Retrieval Techniques:
> Immunohistochemistry and Molecular Morphology. (2000) Eaton Publishing.
> 1-881299-43-0.
> Sompuram SR, Vani K, Messana E and Bogen SA. A molecular mechanism of
> formalin fixation and antigen retrieval. Am J Clin Pathol (2004);121:
> 190-199
> Best regards,
> Bryan
> ----- Original Message -----
> From: "Johnson, Teri" 
> To: 
> Sent: Monday, March 03, 2008 2:33 PM
> Subject: [Histonet] Washing out formalin fixation
> Last week, a researcher here asked me what the chemical mechanism was of
> washing out the effects of formalin fixation on the tissues with running
> water. In other words, how does it work? Anybody here know?
> Teri Johnson, HT(ASCP)QIHC
> Managing Director Histology Facility
> Stowers Institute for Medical Research
> 1000 E. 50th St.
> Kansas City, MO 64110
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