Small molecule diketone flavorants diacetyl and 2,3-pentanedione promote neurotoxicity but inhibit amyloid β aggregation

We investigated the effects of the small molecule flavorants diacetyl, 2,3-pentanedione and acetoin on neuronal cell viability and beta amyloid aggregation and morphology. Two neuroblastoma cell lines, SH-SY5Y and Neuro 2a (N2a) were exposed to diacetyl, 2,3-pentanedione and acetoin, while Thioflavin T fluorescence kinetics and transmission electron microscopy were used to assess effects on A beta(1-42) fibril and aggregate formation and morphology respectively. Diacetyl was intrinsically toxic to both SH-SY5Y and N2a cells, with time and concentration-dependent reductions in cell viability occurring over 24 h and 48 h incubation periods. 2.3-Pentanedione evoked a similar concentration-dependent loss of cell viability in N2a cells at 48 h, but exhibited lessened toxicity in SH-SY5Y cells over 24 h, and minimal loss of cell viability by 48 h. Diacetyl inhibited A beta(1-42) aggregation kinetics, reduced aggregate and fibril density and rendered A beta(1-42) into amorphous small aggregates. 2,3-Pentanedione also reduced overall aggregate formation, but to a lesser extent than diacetyl and retaining the presence of a meshwork of A beta(1-42) aggregates and fibrils. Acetoin was innocuous to neuronal cells and did not alter A beta(1-42) fibril density or morphology. These findings highlight the intrinsic neurotoxicity of small molecule diketone flavorants. While providing further insight into their molecular interactions with amyloidogenic proteins, the neurotoxicity of such flavorants is a significant finding and warrants further investigation.