Butyrate metabolism in human colon carcinoma cells: implications concerning its growth-inhibitory effect

Butyrate and acetate are bacterial metabolites present in the large intestine lumen. Although butyrate is well known to inhibit the in vitro proliferation of human colon carcinoma cells in a process involving the hyperacetylation of specific nuclear histones, little is known about the possible link between butyrate metabolism and its growth-inhibitory effect. In a previous study (Leschelle et al., 2000, Eur J Biochem 267: 6435-6442), we showed that butyrate accumulates and is metabolized in HT-29 Glc(-/+) cells without increasing oxygen consumption. In the present study, using the same cell line incubated with (14)C-labeled butyrate, we determined that a minor part of (14)C from butyrate was recovered in nuclear histones. Unlike butyrate, acetate exerted no effect on cell growth but was a precursor for overall net histone acetylation. Although butyrate was able to increase the cellular AMP/ADP ratio, it did not affect the ATP cell content or the adenylate charge or the oxidation of endogenous L-glutamine. Butyrate oxidation was found to be markedly sensitive to the presence of other substrates with D-glucose decreasing this oxidation and L-malate stimulating it. Furthermore, in the presence of L-malate, the growth-inhibitory effect of butyrate was significantly weaker than in its absence. From these data, we conclude that the metabolism of butyrate downstream acetyl-CoA synthesis is not involved in the butyrate antiproliferative effect. The suggestion that butyrate metabolism in mitochondria is not used in these cells as a fuel but acts as a regulator of butyrate free concentrations (thus limiting its action upon cellular targets), is discussed.