Anandamide (AEA), an endogenous
ligand of
cannabinoid CB1 and CB2 receptors, which also binds transient receptor potential vanilloid type 1 receptor (TRPV1), has been shown to display substantial selective cytotoxicity toward some
cancer cell lines in vitro, although the relevant data are not consistent. In the present study, we employed the MTT test to assess short-term cytotoxicity of AEA on C6 rat
glioma cell culture. When
anandamide was administered to the culture medium with foetal bovine serum (FBS), no cytotoxic effect was observed following 24 h exposure of the
glioma cells to micromolar concentrations of AEA. However, if no serum was present in the medium, micro-to-submicromolar concentrations of AEA induced dose-dependent cytotoxicity clearly detectable after 24 h. Control experiments made it possible to exclude significant interference of serum with the MTT test per se.
Bovine serum albumin mimicked the effect of FBS. We conclude that the apparent inhibition of short-term cytotoxicity of AEA toward C6 rat
glioma cells in vitro is caused by binding AEA to
serum proteins such as
albumin. Taking into account that blood serum or
albumin is practically always present in cell
culture media, we discuss implications of binding substances to
serum proteins for methodology and interpretation of in vitro cytotoxicity testing.