Abstract
Hyperglycaemia causes increased protein glycation and the formation of advanced glycation endproducts which underlie the complications of diabetes and ageing. Glycation is accompanied by metal-catalysed oxidation of glucose and Amadori products to form free radicals capable of protein fragmentation. Aged garlic extract is a potent antioxidant with established lipid-lowering effects attributed largely to a key ingredient called
S-allyl cysteine. This study investigated the ability of aged garlic extract and
S-allyl cysteine to inhibit advanced glycation
in vitro. Bovine serum albumin (BSA) was glycated in the presence of Cu
2+ ions and different concentrations of aged garlic extract and protein fragmentation was examined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Lysozyme was glycated by glucose or methylglyoxal in the presence of different concentrations of aged garlic extract or
S-allyl cysteine with subsequent analysis of glycation-derived crosslinking using SDS-PAGE. Amadori-rich protein was prepared by dialysing lysozyme that had been glycated by ribose for 24 h. This ribated lysozyme was reincubated and the effects of aged garlic extract,
S-allyl cysteine and pyridoxamine on glycation-induced crosslinking was monitored. Aged garlic extract inhibited metal-catalysed protein fragmentation. Both aged garlic extract and
S-allyl cysteine inhibited formation of glucose and methylglyoxal derived advanced glycation endproducts and showed potent Amadorin activity when compared to pyridoxamine.
S-allyl cysteine inhibited formation of carboxymethyllysine (CML), a non-crosslinked advanced glycation endproduct derived from oxidative processes. Further studies are required to assess whether aged garlic extract and
S-allyl cysteine can protect against the harmful effects of glycation and free radicals in diabetes and ageing.