gms | German Medical Science

Objective: The naturally occurring dipeptide carnosine is known to inhibit growth of glioblastoma (GBM) cells. This effect is accompanied by a non-enzymatic reaction with glycolytic intermediates resulting in decreased activity of the pentose phosphate pathway. In addition, data from investigations with two GBM cell lines pointed towards the possibility that it might also interfere with mitochondrial metabolism in a GBM subtype specific manner. Here, we investigated this possibility using patient derived primary GBM cultures.

Methods: The GBM cell lines U87 and LN229 were incubated in medium supplemented either with glucose or pyruvate and a combination of carnosine (50 mM) and inhibitors (DNP and oligomycin) of oxidative phosphorylation (OxPhos). In addition, twelve patient-derived primary GBM cell cultures were cultivated in medium supplemented either with glucose or pyruvate and in the absence and presence of 50 mM carnosine. After 6 hours of incubation ATP in cell lysates as a measure of energy metabolism was determined.

Results: In the presence of glucose none of the OxPhos inhibitors had a significant effect on ATP production whereas in the presence of pyruvate, DNP reduced ATP production to 23.7±9.8% (LN229) and 2.3±1.1% (U87; both: p<0.0005). Oligomycin reduced ATP production in the presence of pyruvate to 13.7±8.7% (LN229) and 9.4±12.5% (U87; both: p<0.0005). This demonstrates that the GBM lines are independent from OxPhos in the presence of glucose but are able to use this pathway in case of glucose deprivation. Comparing the effect of carnosine in medium containing pyruvate we also observed a significant reduction of ATP production (LN229: 64.0±18.1%; p<0.0005; U87: 53.5±12.8%; p<0.005). As the inhibitors already severely inhibited OxPhos under the conditions employed no combinatorial effect together with the dipeptide was observed. More important, investigating the effect of carnosine in primary cultures 12 out of 11 cultures (7 significant) responded to the presence of carnosine in medium containing pyruvate (Range: 75% (p>0.0005) to 90% (p<0.05)).

Conclusion: In addition to its effect on glycolysis and the pentose phosphate pathway, the naturally occurring dipeptide carnosine also affects OxPhos in GBM cells. Further studies using the Seahorse technology to unravel the precise mechanisms behind this influence should be performed in order to exploit this observation as a starting point for the development of new strategies for the treatment of GBM.