Table 2.

Distribution and cellular localization of enzymes responsible for nitrosamine metabolism in human normal oral mucosa

Metabolic enzymeWestern blot dataa (n = 11)Enzyme distribution profile by IHC-normal oral mucosa (n = 7)
P450 1A211/11, 2.2-fold (0.47–1.05)Intense staining of the basal and spinous epithelial layers.
P450 2E111/11, 4.5-fold (0.15–0.67)Mild to moderate staining of the basal and peribasilar layers.
P450 2A611/11, 2.1-fold (0.54–1.12)Moderate to intense staining observed in basal and spinous layers.
P450 2A1311/11, 3.3-fold (0.23–0.76)Intense staining of the basal layer and moderate staining of spinous epithelial layer.
P450 3A411/11, 2.4-fold (0.44–1.05)Intense staining of basal and lower/middle spinous epithelial layers.
UGT1A, MRP1, BCRPbThese data have been previously reported (11). Notably, all oral mucosal specimens contained all three proteins as demonstrated by Western immunoblotting. IHC staining confirmed an intraepithelial localization.
  • aThe Western blot data are presented as the number of tissues that demonstrate presence of the specific protein; the fold difference between the highest and lowest normalized protein levels among the 11 tissues; and the ratio range of respective protein level relative to the housekeeping protein, β-actin.

  • bUGT1A increases water solubility and excretion by glucuronide attachment; MRP1 and BCRP are both ATP-dependent efflux transporters that function to remove Phase II enzyme conjugates such as glucuronides. Our reported study demonstrated expression of these enzymes in 11 human oral mucosal tissues by both Western blot and IHC staining (11).