Ornithine decarboxylase as a marker for colorectal adenomas
Sir I was interested to read the paper by Moorehead and colleagues (Br J Surg 1987; 74: 3645). In their discussion the authors state that the finding of diminished levels of ornithine decarboxylase in macroscopically normal rectal mucosa in patients with colorectal tumours is an unexpected finding.
No other cancers studied thus far. animal or human, have shown lower levels of ornithine decarboxylase when compared with normal tissue, as was reported in this paper. Human cancers studied thus far include astrocytomas, medulloblastomas, meningiomas, cutaneous epitheliomas, renal carcinomas, thyroid carcinomas, urinary bladder carcinomas, pancreatic cancers, gastric cancers, endometrial cancers and ovarian cancers.
Apart from the stlidy by Rozhin, cited in the discussion of this paper, there are four other studies specifically looking at ornithine decarboxylase in colorectal cancer. LaMuraglia' showed a 320 per cent increase in ornithine decarboxylase in cancers and polyps and Herrera-Ornelas2 showed an approximately two-fold increase in cancers and polyps compared with normal mucosa. In addition, LaMuraglia showed an increase in ornithine decarboxylase in non-involved mucosa taken from patients with colorectal cancer. With regard to the polyamines themselves, two studies show increased levels of polyamines in colorectal cancers compared with normal m ~c o s a ~' ~, and the study of Takenoshita shows raised levels of the polyamines in adjacent mucosa near to the colorectal cancers.
The results of Moorehead and colleagues thus conflict with all data published so far on the relationship of ornithine decarboxylase to neoplastic growth. Increased levels of ornithine decarboxylase and polyamines are required to sustain cells which exhibit an increased level of cellular proliferation.
With regard to the second paragraph of the discussion, concerning the regulation of ornithine decarboxylase activity, it should be noted that mammalian ornithine decarboxylase does not display allostericlike kinetics and is, remarkably, not susceptible to regulatory influences of small biomolecules. Regulation of ornithine decarboxylase is at the level of translation5.
Although a reference is cited concerning the method of ornithine decarboxylase assay, no details are given of the technique used by the authors. It was pointed out in the discussion that the warm ischaemia time may have reduced activity in tumour tissue removed, and I suspect this is the explanation for the authors' results.