Cysteine endopeptidase activity levels in normal human tissues, colorectal adenomas and carcinomas

We have assayed cysteine endopeptidase activities in 17 types of normal human tissue and in matched sets of colorectal mucosa, adenoma and carcinoma samples. Our data indicate that cathepsin B enzyme levels vary 70‐fold and cathepsin L enzyme levels vary 20‐fold from one normal tissue to another. Cathepsin B specific activity in normal tissues fell into 3 categories. High activity, with a mean of 156.7 ± 41.5 nmoles min−1 mg−1 protein, was measured in liver, thyroid, kidney and spleen; intermediate activity, with a mean of 60.2 ± 8.3 nmoles min−1 mg−1 protein, was measured in heart, colon, adrenal and lung; and low activity, with a mean of 18.4 ± 9.7 nmoles min−1 mg−1 protein, was measured in prostate, testis, nerve, stomach, pancreas, brain, skeletal muscle, skin and breast. Cathespin L specific activity fell into 2 categories. High activity, with a mean of 51.1 ± 4.9 nmoles min−1 mg−1 protein, was measured in thyroid, liver and kidney; and low activity, with a mean of 11.4 ± 5.5 nmoles min−1 mg−1 protein, was measured in spleen, colon, heart, adrenal, lung, testis, brain, nerve, skin, stomach, pancreas, skeletal muscle, prostate and breast. Our characterization of these enzyme levels provides a reference standard for normal cathepsin B and L activities in human tissues that should enhance the detection of their deregulation in disease states. For example, in studies of colorectal carcinoma and normal mucosa, we observed a significant tumor‐specific increase in cathepsin B and L activities with particularly high activity levels in earlier (Dukes′ A and B) compared to later (Dukes′ C and D) stages of colorectal cancer. In contrast, adenomas from colorectal cancer patients expressed normal levels of cathepsin B activity, providing evidence that the increase in expression of cathepsin B may be a sensitive marker for progression from the pre‐malignant to the malignant state in the development of colorectal cancer.