Carnosine's inhibitory effect on glioblastoma cell growth is independent of its cleavage

The naturally occurring dipeptide carnosine (β-alanyl-L-histidine) inhibits the growth of tumor cells. As its component L-histidine mimics the effect, we investigated whether cleavage of carnosine is required for its antineoplastic effect. Using ten glioblastoma cell lines and cell cultures derived from 21 patients suffering from this malignant brain tumor, we determined cell viability under the influence of carnosine and L-histidine. Moreover, we determined expression of carnosinases, the intracellular release of L-histidine from carnosine, and whether inhibition of carnosine cleavage attenuates carnosine's antineoplastic effect. We observed a significantly higher response of the cells to L-histidine than to carnosine with regard to cell viability in all cultures. In addition, we detected protein and mRNA expression of carnosinases and a low but significant release of L-histidine in cells incubated in the presence of 50 mM carnosine (p < 0.05), which did not correlate with carnosine's effect on viability. Furthermore, the carnosinase 2 inhibitor bestatin did not attenuate carnosine's effect on viability. Interestingly, we measured a ~ 40-fold higher intracellular abundance of L-histidine in the presence of 25 mM extracellular L-histidine compared to the amount of L-histidine in the presence of 50 mM carnosine, both resulting in a comparable decrease in viability. In addition, we also examined the expression of pyruvate dehydrogenase kinase 4 mRNA, which was comparably influenced by L-histidine and carnosine, but did not correlate with effects on viability. In conclusion, we demonstrate that the antineoplastic effect of carnosine is independent of its cleavage.