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Kinetic and density functional theory (DFT) studies
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carcinogen. This project produced the first comprehensive study reported from the Caribbean to quantify the levels of AA in foods indigenous to, as well as foods commonly consumed in the region, and provides vital data from a third world region, the Caribbean, to add to the AA food database.
The widest possible viewpoints and interactions of ideas are needed to transcend present limitation in our knowledge, and to catalyse progress in all areas that are relevant to the human diet. These include mechanisms of formation of acrylamide in food, distribution of acrylamide and its precursors in foods, analysis, impact of other biologically active dietary ingredients on the safety of acrylamide, toxicology, pharmacology and metabolism, epidemiology, and risk assessment.
Limited physico-chemical data are available on AA’s interactions within biological systems and, as such, in vivo and in vitro studies are being conducted to assess the potential of AA toxicity and carcinogenicity. AA reacts readily with, and has been widely used to selectively modify thiol groups of structural and functional proteins. For example, AA has been used to alkylate the thiol groups of various enzymes. However, the relationship of such reactions to AA’s toxicity and potential carcinogenicity is unknown.
The sulphur-containing amino acids, L-Cysteine (CySH) and Glutathione (GSH) are important thiols synthesised within the body, and they form part of the body’s natural defence mechanism by scavenging free radicals and helping to maintain the secondary structure of certain proteins. Captopril (CapSH) is important as a vasodilator in the treatment of congestive heart failure, where it protects nitric oxide (NO) from oxidation by scavenging free oxygen radicals. Captopril is also used to treat high blood pressure (hypertension), kidney problems caused by diabetes, and to improve survival after a heart attack. How AA reacts with these thiols, thus reducing or enhancing their ability to carry out their function within the body, is of great importance in understanding the mechanism and metabolism of AA.
The researchers reported a comprehensive study on the in vitro reaction rates of acrylamide with these three important thiols, CapSH, CySH, and GSH according to a Michael addition reaction scheme, and, assuming that the nucleophilicity of all three thiols is approximately the same, the rates of the reaction with AA were expected to decrease along the series: CySH > CapSH > GSH, reflecting the increasing molecular size of the thiols. However, this was not observed. Rather, the experimental reaction rate follows the order: CySH > GSH > CapSH. The reason for this unexpected trend was probed with the application of computational studies, where the density functional theory (DFT) calculations strongly support the experimental results through marked effects of solvation and hydrogen bonding on the activation energies, where the GSH-AA activated complex is computed at 8-10 kcal mol-1 higher than CapSH and CySH. This is consistent with diminished intra-molecular hydrogen bonding in GSH-AA owing to more inter-molecular interactions with the polar water solvent molecules. The activation parameters were used to generate a linear isokinetic (entropic-enthalpy compensation) plot, which supports AA reacting with all three thiols via the same mechanism.
The experimental kinetic data and supporting computational studies provide new insight into the mechanism of interaction of AA with these very important sulphur-containing amino acids, and the effect that water molecules can have on their relative rates of reaction.
Recognising Outstanding Researchers 2016