Epithelial-Myoepithelial Carcinoma in a Canine Salivary Gland.

A 7-year-old male cavalier King Charles spaniel was presented with a cervical subcutaneous mass. The mass had a multilobular growth pattern and each individual lobule contained ductal epithelial cells and myoepithelial cells surrounding the ductal cells. Immunohistochemically, the ductal epithelial cells were positive for cytokeratin (CK) 7 and CAM5.2 and the myoepithelial cells were positive for α-smooth muscle actin and p63. Both types of cells were positive for CK14, a myoepithelial cell marker. Ultrastructurally, the ductal epithelial cells were attached by desmosomes and contained abundant intracytoplasmic tonofilaments. Some ductal epithelial cells contained myofilaments characteristic of myoepithelial cells. Based on these findings, a diagnosis of epithelial-myoepithelial carcinoma was made. It is presumed that the tumour originated from an intercalated duct in a parotid salivary gland.

Characterization of human neutrophil leukotriene B4 omega-hydroxylase as a system involving a unique cytochrome P-450 and NADPH-cytochrome P-450 reductase.

Leukotriene B4 (LTB4), a potent chemotactic agent, was catabolized to 20-hydroxyleukotriene B4 (20-OH-LTB4) by the 150,000 x g pellet (microsomal fraction) of human neutrophil sonicate. The reaction required molecular oxygen and NADPH, and was significantly inhibited by carbon monoxide, suggesting that a cytochrome P-450 is involved. The neutrophil microsomal fraction showed a carbon monoxide difference spectrum with a peak at 450 nm in the presence of NADPH or dithionite, indicating the presence of a cytochrome P-450. The addition of LTB4 to the microsomal fraction gave a type-I spectral change with a peak at around 390 nm and a trough at 422 nm, indicating a direct interaction of LTB4 with the cytochrome P-450. The dissociation constant of LTB4, determined from the difference spectra, is 0.40 microM, in agreement with the kinetically determined apparent Km value for LTB4 (0.30 microM). Such a spectral change was not observed with prostaglandins A1, E1 and F2 alpha or lauric acid, none of which inhibited the LTB4 omega-hydroxylation. The inhibition of the LTB4 omega-hydroxylation by carbon monoxide was effectively reversed by irradiation with monochromatic light of 450 nm wavelength. The photochemical action spectrum of the light reversal of the inhibition corresponded remarkably well with the carbon monoxide difference spectrum. These observations provide direct evidence that the oxygen-activating component of the LTB4 omega-hydroxylase system is a cytochrome P-450. Ferricytochrome c inhibited the hydroxylation of LTB4 and the inhibition was fortified by cytochrome oxidase. An antibody raised against rat liver NADPH-cytochrome-P-450 reductase inhibited both LTB4 omega-hydroxylase activity and the NADPH-cytochrome-c reductase activity of human neutrophil microsomal fraction. These observations indicate that NADPH-cytochrome-P-450 reductase acts as an electron carrier in LTB4 omega-hydroxylase. On the other hand, an antibody raised against rat liver microsomal cytochrome b5 inhibited the NADH-cytochrome-c reductase activity but not the LTB4 omega-hydroxylase activity of human neutrophil microsomal fraction, suggesting that cytochrome b5 does not participate in the LTB4-hydroxylating system. These characteristics indicate that the isoenzyme of cytochrome P-450 in human neutrophils, LTB4 omega-hydroxylase, is different from the ones reported to be involved in omega-hydroxylation reactions of prostaglandins and fatty acids.