NONSPECIFIC STEROIDAL ESTERASE-ACTIVITY AND DISTRIBUTION IN HUMAN ANDOTHER MAMMALIAN-TISSUES

An NADPH dependent arylamine carcinogen and fatty acid steroid ester m etabolizing esterase activity belonging to the B- or carboxylesterase class of non-specific esterase (EC 3.1.1.1) was measured by two differ ent methods: (i) a spectrophotometric assay using alpha naphthyl aceta te (ANA) as substrate and (ii) a radiometric method using the conversi on of beclomethasone-17,21-dipropionate to beclomethasone-17-monopropi onate as the end-point. The two methods were strongly correlated when assayed in human mononuclear leukocytes (r = 0.89, P < 0.0001) and hum an mammary tissue (r = 0.91, P < 0.0001). Hence it was concluded that the two substrates are metabolized at least in part by the same enzyme . This esterase activity was abundant in human monocytes, present in T -lymphocytes and equally divided between CD4 and CD8 T-lymphocyte subs ets. The same activity was expressed in human liver, colon, stomach, b reast and brain tissues. The distribution of this esterase in human ti ssues showed high activity in liver, intermediate activity in colon, s tomach and breast and low activity in brain tissue. The interorgan dis tribution observed in human tissues was closely mimicked when the este rase activity was assessed in liver, colon and brain tissues from thre e mouse strains and three rat strains. The non-specific steroidal este rase activity determined by ANA metabolism in human mammary tissue was shown to be reproducible when assayed as triplicate samples from each of 16 different women (intraclass correlation coefficient 67.3%, P < 0.03). The interindividual variation in mammary tissue was high (18.4- fold) and there was a positive correlation between the esterase activi ty and age (r = 0.58, P < 0.01), as well as a tendency toward bimodal distribution. To our knowledge, these data represent the first systema tic study of interorgan and interspecies comparisons of a non-specific steroidal esterase activity.