gms | German Medical Science

Objective: Carnosine (b-alanyl-L-histidine) is a naturally occurring dipeptide that inhibits the growth of cells derived from glioblastoma. Previous work demonstrated that the anti-neoplastic effect is mimicked by its component L-histidine. Here we investigated whether the release of L-histidine is required for the anti-neoplastic effect.

Methods: Glioblastoma cells from 10 different cell lines and from cell cultures derived from 21 patients were cultivated in medium with different concentrations of carnosine or L-histidine and viability was analyzed using cell based assays. Carnosinase expression was determined by immunoblotting and qRT-PCR. In addition, the intracellular amounts of carnosine and L-histidine of cells from 10 lines and 5 primary cultures which were exposed to medium containing either L-histidine or carnosine were determined by Liquid Chromatography coupled to Mass Spectrometry.

Results: A 48 hour exposure to carnosine (50 mM) significantly reduced viability in all tumor cells as determined by the amount of ATP in cell lysates to an average of 73.6±20.5% compared to the untreated control, whereas L-histidine revealed a more pronounced effect (49.8±18.6% at 50 mM and 69.4±22.2% at 25 mM). Analyzing the intracellular release of L-histidine under the influence of carnosine, we observed a significantly enhanced (p<0.05) abundance of L-histidine in 9 of 10 cell lines and in 4 of 5 primary cell cultures. In the presence of 25 mM L-histidine, we detected a 37.4 fold higher abundance of L-histidine compared to carnosine (50 mM) treated cells. No correlation between the expression of carnosinases and the anti-neoplastic effect was observed. Furthermore, the aminopeptidase inhibitor bestatin (10 to 100 µM) did neither attenuate nor enhance the effect of carnosine. These observations clearly indicate that the release of L-histidine from carnosine is not required for the anti-neoplastic effect of the dipeptide.

Conclusion: Carnosine and L-histidine inhibited the viability of all 31 tested tumor cell cultures. Although L-histidine revealed a more pronounced effect than carnosine the intracellular release of L-histidine is not required for the anti-neoplastic effect of the dipeptide. As L-histidine and most likely its imidazole ring appear to be responsible for growth-inhibition it should be considered whether this observation can be used for the design of drugs that are able to deliver therapeutic amounts of imidazole groups to tumor cells.