Rat colonic mucosal cell sialic acid metabolism in azoxymethane-induced tumours.

Colonic tissue was examined from normal (control) rats and azoxymethane- (carcinogen-) treated animals. Tumour-bearing colons from azoxymethane-treated rats were divided into malignant and non-malignant areas. Mucosal cells were prepared from the three types of colonic tissue and then examined for DNA and protein content and for the activities of ten enzymes involved in sialic acid metabolism. Enzyme activities were related to either the protein or the DNA content of fractions. The DNA content of cell homogenates was significantly different between tumour and non-malignant tissue and between both these tissues and normal mucosa. The protein content of the 100000 X g membrane pellet and supernatant fraction did not vary significantly between normal and non-malignant material but both these tissues differed significantly from tumour tissue. Significant variation between normal control and tumour tissue was detected at all levels of sialic acid metabolism, including N-acetylhexosamine interconversion and phosphorylation, sialic acid formation and activation, CMP-NeuAc breakdown and transfer and sialic acid release from glycoconjugates. The results indicate that major changes at all levels of sialic acid metabolism are associated with malignancy in rat colonic mucosa. Some of these changes are apparent in non-malignant mucosa and may reflect a pre-malignant state.