gms | German Medical Science

Objective: Since previous experiments demonstrated that the anti-neoplastic effect of carnosine (beta-alanyl-L-histidine) is associated with enhanced expression of pyruvate dehydrogenase kinase 4 (PDK4), experiments were performed in order to analyse sequences and mechanisms involved in the transcriptional response.

Method: A reporter gene with the PDK4 5’-upstream sequence and the 5’-UTR (-3968/+319) controlling the secreted luciferase reporter gene from Gaussia princeps was transfected into cells from the glioblastoma cell line U87. Cells were cultivated in the absence and presence of carnosine, trichostatin A (TSA) and 5-azacytidine (5-aza) and reporter gene activity, PDK4 mRNA expression and viability were determined.

Results: In the transfection experiments neither carnosine nor the histone-deacetylase inhibitor TSA or the DNA methylation inhibitor 5’-aza enhanced reporter gene expression. However, endogenous expression of PDK4 under the influence of 0.8 µM TSA increased 4-fold within 24 hours which resembled the effect of carnosine on PDK4 expression in the presence of 20 mM carnosine. No effect on PDK4 expression was seen in the presence of 5-aza. In addition, we observed a reduced viability when cells were incubated in the presence of 0.8 µM TSA for 24 (81.3%), 48 (34.2%) and 72 hours (16.4%) that was even more prominent than that determined in the presence of 50 mM carnosine (24h: 80.4%; 48h: 66.3% and 72h: 51.5%).

Conclusions: The experiments demonstrate that the histone-deacetylase inhibitor TSA strongly affects glioblastoma cell viability that after 48 h and 72 h in 0.8 µM TSA is more strongly reduced than in the presence of 50 mM carnosine. In addition, both agents enhanced expression of endogenous PDK4. This coincidence may point towards the possibility that carnosine effects deacetylation, although much higher concentrations are necessary compared to TSA.