Functional residues on the enzyme active site of glyoxalase I from bovine brain

The butter flavorant, diacetyl, exacerbates β-amyloid cytotoxicity

Diacetyl (DA), an ubiquitous butter-flavoring agent, was found to influence several aspects of amyloid-β (Aβ) aggregation--one of the two primary pathologies associated with Alzheimer's disease. Thioflavin T fluorescence and circular dichroism spectroscopic measurements revealed that DA accelerates Aβ¹⁻⁴² aggregation into soluble and ultimately insoluble β-pleated sheet structures. DA was found to covalently bind to Arg⁵ of Aβ¹⁻⁴² through proteolytic digestion-mass spectrometric experiments. These biophysical and chemical effects translated into the potentiation of Aβ¹⁻⁴² cytotoxicity by DA toward SH-SY5Y cells in culture. DA easily traversed through a MDR1-MDCK cell monolayer, an in vitro model of the blood-brain barrier. Additionally, DA was found not only to be resistant to but also inhibitory toward glyoxalase I, the primary initiator of detoxification of amyloid-promoting reactive dicarbonyl species that are generated naturally in large amounts by neuronal tissue. In light of the chronic exposure of industry workers to DA, this study raises the troubling possibility of long-term neurological toxicity mediated by DA.

The butter flavorant, diacetyl, forms a covalent adduct with 2-deoxyguanosine, uncoils DNA, and leads to cell death

Diacetyl (DA), a natural butter flavorant, is a causative agent for the lung disease obliterative bronchiolitis. Mutagenic properties of 1,2-dicarbonyls have previously been empirically linked to their possible interaction with DNA nucleobases. This study for the first time identifies chemically the adduct of DA with 2-deoxyguanosine. Selective reactivity of DA with 5'-TTTGTTTTT-3' over 5'-TTTTTTTTT-3' indicated its propensity to modify specifically the guanosine residue. Treatment of plasmid DNA, pBR322, with DA induced changes in electrophoretic mobility that are typical of ternary structure disruption. Such DNA nucleobase interaction of DA translated into increased apoptosis in DA-treated SH-SY5Y cells in a dose-dependent manner (IC(50) = 0.114 ± 0.0421 mM). The traditional carbonyl scavengers metformin, 2-thiobarbituric acid, and d-penicillamine protected cells from DA toxicity in proportion to their rates of reaction with DA, with d-penicillamine causing a maximal increase in the IC(50) to 5.23 ± 0.0992 mM when co-incubated with DA.