Similar nature of inhibition of mitochondrial respiration of heart tissue and malignant cells by methylglyoxal. A vital clue to understand the biochemical basis of malignancy.

The effect of methylglyoxal on the oxygen consumption of mitochondria of heart and of several other organs of normal animals of different species has been tested. The results indicate that methylglyoxal (3.5 mM) strongly inhibits ADP-stimulated alpha-oxoglutarate and malate plus pyruvate-dependent respiration of exclusively heart mitochondria of normal animals of different species. Whereas, with the same substrates, but at a higher concentration of methylglyoxal (7.5 mM), the respiration of mitochondria of other organs of normal animals is not inhibited. Methylglyoxal also inhibits the respiration of slices of rat and toad hearts. But this inhibition is less pronounced. However, methylglyoxal (15 mM) fails to have any effect on perfused toad heart. Using rat heart mitochondria as a model, the effect of methylglyoxal on the oxygen consumption was also tested with different respiratory substrates, electron donors at different segments of the mitochondrial respiratory chain and site-specific inhibitors to identify the specific respiratory complex which might be involved in the inhibitory effect of methylglyoxal. The results strongly suggest that methylglyoxal inhibits the electron flow through complex I of rat heart mitochondrial respiratory chain. Moreover, lactaldehyde (0.6 mM), a catabolite of methylglyoxal, can exert a protective effect on the inhibition of rat heart mitochondrial respiration by methylglyoxal (2.5 mM). The effect of methylglyoxal on heart mitochondria as described in the present paper is strikingly similar to the results of our previous work with mitochondria of Ehrlich ascites carcinoma cells and leukemic leukocytes. We have recently proposed a new hypothesis on cancer which suggests that excessive ATP formation in cells may lead to malignancy. The above mentioned similarity apparently provides a solid experimental foundation for the proposed hypothesis which has been discussed.