Characterizing kidney structures in health and diseases using eosin fluorescence from hematoxylin and eosin stained sections

For a long time, hematoxylin and eosin (H&E) staining has been widely used for the diagnosis of many diseases by assessing the histopathological changes in tissue sections. Eosin, one of the staining dyes in the H&E stain, is fluorescent in the fluorescein isothiocyanate (FITC) and Texas Red (TxR) fluorescent channels. In this study, the use of eosin fluorescence to visualize and quantify histopathological changes was elucidated in a glycerol-induced model of acute kidney injury (AKI) in mice. AKI was induced in BALB/c mice by intramuscularly injecting 10 mL/kg of 50% glycerol after 24 h of water deprivation and, after another 24 h, the kidneys were dissected out. After H&E staining, kidney tissue sections were examined under a fluorescent microscope using a double-channel filter cube (FITC and TxR). The H&E fluorescence pattern of normal kidney structures was characterized as the fluorescence patterns varied between different parts of the kidney and could be used for the structural identification of different parts of the kidney. Interestingly, in the injured kidney sections, a striking increase in the red fluorescence was noticed only in the damaged areas. In the damaged kidney sections, casts deposited inside tubules showed bright yellow fluorescence, whereas fibers showed strong green fluorescence. In vitro experiments were also performed in order to understand possible mechanisms underlying this phenomenon. It was concluded that eosin fluorescence can be used to quantify the degree of damage to kidney tissue which, in turn, may help in assessing the kidney-protective effects of unknown compounds and plant extracts.