Glyoxal: a proposed substitute for formalin in H&E and special stains

Histochemical and morphological evaluation of a glyoxal acid-free fixative

The application of most chemical fixatives, such as formalin, in the anatomic pathology laboratory requires safety training and hazardous chemical monitoring due to the toxicity and health risks associated with their use. Consequently, the use of formalin has been banned in most applications in Europe; the primary exception is its use in the histology laboratory in lieu of a suitable and safer alternative. Glyoxal based solutions, several of which are available commercially, are the most promising alternative fixatives, because they are based on a mechanism of fixation similar to that of formalin. Unlike formalin, however, glyoxal based solutions do not dissociate from water and therefore do not require ventilation measures such as a fume hood. A primary barrier to the adoption of commercially available glyoxal based solutions is their low pH, which can produce undesirable morphological and antigenic tissue alterations; however, a recently available neutral pH glyoxal product (glyoxal acid free) (GAF) has been developed to mitigate the challenges of low pH. We compared the morphology and histochemistry among tissues fixed in 10% neutral buffered formalin, a commercially available acidic glyoxal product (Prefer), and GAF. Tissues fixed in formalin and Prefer exhibited similar morphology and staining properties; tissues fixed with 2% GAF exhibited deleterious effects.

Glyoxal Fixation Is Optimal for Immunostaining of Brain Vessels, Pericytes and Blood-Brain Barrier Proteins

Brain vascular staining is very important for understanding cerebrovascular pathologies. 4% paraformaldehyde is considered the gold standard fixation technique for immunohistochemistry and it revolutionized the examination of proteins in fixed tissues. However, this fixation technique produces inconsistent immunohistochemical staining results due to antigen masking. Here, we test a new fixation protocol using 3% glyoxal and demonstrate that this method improves the staining of the brain vasculature, pericytes, and tight junction proteins compared to 4% paraformaldehyde. Use of this new fixation technique will provide more detailed information about vascular protein expressions, their distributions, and colocalizations with other proteins at the molecular level in the brain vasculature.

Different fixatives influence morphology, antigen preservation, and TUNEL staining in chicken (Gallus gallus) testis

The optimized fixative for testis is still controversial. This study investigated the effects of Modified Davidson's Fluid (mDF), 4% Paraformaldehyde (4% PFA), and Bouin's Fluid (BF) fixatives on chicken testes in normal/cadmium (Cd) feeding groups using hematoxylin and eosin (HE), immunohistochemistry (IHC), and Terminal Transferase dUTP Nick End Labeling (TUNEL) staining. Compared to the mDF, we established that the testes fixed with 4% PFA and BF in the normal group had severe shrinkage in tubular and interstitial compartments. Moreover, compared with 4% PFA, the number of GATA4-positive Sertoli cells/mm² reduced by 67.61% in mDF and 80.57% in BF for one seminiferous tubule. The TUNEL assay illustrated that more positive cells/mm² in mDF group (28.47 ± 11.38) than in 4% PFA (10.49 ± 7.89). In Cd-treated testes, mDF showed more morphological details than 4% PFA and BF. In contrast, the number of GATA4-positive Sertoli cells/mm² of 4% PFA was higher than that of mDF by 65.78% and BF by 64.80% in a seminiferous tubule. The number of TUNEL positive cells/mm² in mDF (272.60 ± 34.41) were higher than in 4% PFA (175.91 ± 19.87). These results suggest that mDF fixative is suitable for normal and Cd-treated testis fixation for HE and TUNEL staining in chicken, whereas 4% PFA fixative is better for IHC examination.