Diabetes mellitus is characterised by hyperglycaemia, lipidaemia and oxidative stress and predisposes affected individuals to long-term complications afflicting the eyes, skin, kidneys, nerves and blood vessels. Increased protein glycation and the subsequent build-up of tissue advanced glycation endproducts (AGEs) contribute towards the pathogenesis of diabetic complications. Protein glycation is accompanied by generation of free radicals through autoxidation of glucose and glycated proteins and via interaction of AGEs with their cell surface receptors (referred to as RAGE). Glycationderived free radicals can damage proteins, lipids and nucleic acids and contribute towards oxidative stress in diabetes. There is interest in compounds with anti-glycation activity as they may offer therapeutic potential in delaying or preventing the onset of diabetic complications. Although many different compounds are under study, only a few have successfully entered clinical trials but none have yet been approved for clinical use. Whilst the search for new synthetic inhibitors of glycation continues, little attention has been paid to anti-glycation compounds from natural sources. In the last few decades the traditional system of medicine has become a topic of global interest. Various studies have indicated that dietary supplementation with combined anti-glycation and antioxidant nutrients may be a safe and simple complement to traditional therapies targeting diabetic complications. Data for forty two plants/constituents studied for anti-glycation activity is presented in this review and some commonly used medicinal plants that possess anti-glycation activity are discussed in detail including their active ingredients, mechanism of action and therapeutic potential.

Protein glycation involves formation of early (Amadori) and late advanced glycation endproducts (AGEs) together with free radicals via autoxidation of glucose and Amadori products. Glycation and increased free radical activity underlie the pathogenesis of diabetic complications. This study investigated whether aged garlic has more potent antiglycation and antioxidant properties compared to fresh garlic extract in vitro in a cell-free system. Proteins were glycated by incubation with sugars (glucose, methylglyoxal or ribose) ±5–15 mg/mL of aged and fresh garlic extracts. Advanced glycation endproducts were measured using SDS-PAGE gels and by ELISA whereas Amadori products were assessed by the fructosamine method. Colorimetric methods were used to assess antioxidant activity, free radical scavenging capacity, protein-bound carbonyl groups, thiol groups and metal chelation activities in addition to phenolic, total flavonoid and flavonol content of aged and fresh garlic extracts. Aged garlic inhibited AGEs by 56.4% compared to 33.5% for an equivalent concentration of fresh garlic extract. Similarly, aged garlic had a higher total phenolic content (129 ± 1.8 mg/g) compared to fresh garlic extract (56 ± 1.2 mg/g). Aged garlic has more potent antiglycation and antioxidant properties compared to fresh garlic extract and is more suitable for use in future in vivo studies.