Useful immunohistochemical markers of tumor differentiation.

Immunohistochemistry (IHC) has been somewhat underutilized in the practice of toxicological pathology but can be a valuable tool for the evaluation of rodent neoplasms, both in a diagnostic and an investigational role. Determining an exact tumor type using standard hematoxylin and eosin (H&E) staining of formalin-fixed tissues can be challenging, especially with metastatic and/or poorly differentiated tumors. Successful IHC is dependent on many factors, including species and tissue type, type and duration of fixation, quality fresh or frozen sectioning, and antibody specificity. The initial approach of most tumor diagnosis IHC applications is distinguishing epithelial from mesenchymal differentiation using vimentin and cytokeratin markers, although false-negative and/or false-positive results may occur. Experimentally, IHC can be employed to investigate the earliest changes in transformed tissues, identifying cellular changes not normally visible with H&E. Individual markers for proliferation, apoptosis, and specific tumor proteins can be used to help distinguish hyperplasia from neoplasia and determine specific tumor origin/type. IHC provides a relatively rapid and simple method to better determine the origin of neoplastic tissue or investigate the behavior or progression of a given neoplasm. Several experimental and diagnostic examples will be presented to illustrate the utility of IHC as a supplement to standard staining techniques.

Identification and localization of five CYP2Cs in murine extrahepatic tissues and their metabolism of arachidonic acid to regio- and stereoselective products.

The CYP2C subfamily has been extensively studied in humans with respect to the metabolism of clinically important drugs, and polymorphisms have been identified in these enzymes. In the present study, a murine model was used to determine the possible physiological functions and extrahepatic distribution of CYP2Cs. Using the reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and immununohistochemistry, this report demonstrates that the mouse CYP2Cs are extensively distributed in extrahepatic tissues and localized to heart muscle, lung Clara and ciliated cells, kidney collecting ducts, the X-zone of female adrenals, reproductive organs, white blood cells, and eyes (in the optic nerve, rods, and cones). RT-PCR, subcloning, and sequencing of the products indicate that each CYP2C has a unique tissue distribution. Four cDNA fragments representing potentially new CYP2Cs were identified, each with its own organ-specific pattern of expression. Using a bacterial cDNA expression system, we found that recombinant proteins for each of the five full-length murine CYP2Cs metabolize arachidonic acid to different regio- and stereospecific products, including epoxyeicosatrienoic acids and hydroxyeicosatetraenoic acids. Regio- and stereospecific metabolites of arachidonic acid have been reported to affect important physiological functions such as inflammation, neutrophil activation, ion transport, cellular proliferation, and vascular tone. Our results suggest that the presence of CYP2C enzymes in heart muscle, aorta, kidney, lung, adrenals, eyes, and reproductive organs could regulate important physiological and/or pathological processes in these tissues.