Lactucaxanthin – a potential anti-diabetic carotenoid from lettuce (Lactuca sativa) inhibits α-amylase and α-glucosidase activity in vitro and in diabetic rats

Abstract

Intestinal and pancreatic α-amylase and α-glucosidase inhibitors offer an approach to lower the levels of post-prandial hyperglycemia through the control of dietary starch breakdown in digestion. This study hypothesized that lactucaxanthin (Lxn) in lettuce (Lactuca sativa) inhibits the activity of α-amylase and α-glucosidase. In this study, the interaction of Lxn with α-amylase and α-glucosidase in silico and its inhibitory effect on these enzymes were studied using in vitro and STZ-induced diabetic rat models. Lxn was isolated from lettuce with 96% purity confirmed by HPLC and LCMS. The in silico analysis showed that Lxn has a lower binding energy (-6.05 and -6.34 kcal mol) with α-amylase and α-glucosidase compared to their synthetic inhibitors, acarbose (-0.21 kcal mol) and miglitol (-2.78 kcal mol), respectively. In vitro α-amylase and α-glucosidase inhibition assays revealed that Lxn had IC values of 435.5 μg mL and 1.84 mg mL, but acarbose has values of 2.5 and 16.19 μg mL. The in vivo results showed an increased activity for α-amylase and α-glucosidase in the intestine (4.7 and 1.30 fold, p < 0.05) and pancreas (1.3 and 1.48 fold, p < 0.05) of STZ induced diabetic rats compared to normal rats. Whereas the activity decreased (p < 0.05) in the Lxn fed diabetic rats, except for the intestinal α-glucosidase activity (1.69 ± 0.12 PNP per min per mg protein). This was confirmed by the low blood glucose level (239.4 ± 18.2 mg dL) in diabetic rats fed Lxn compared to the diabetic group (572.2 ± 30.5 mg dL, p < 0.05). Lxn significantly inhibited (p < 0.05) the activity of α-amylase and α-glucosidase and could be of medical and nutritional relevance in the treatment of diabetes.

Alpha Glucosidase Inhibitory Activities of Plants with Focus on Common Vegetables

“…Aqueous radish sprout extract was also reported to cause 50% reduction of AG activity at the concentration of 60.7 ± 1.2 mg/mL [59]. Lactucaxanthin, a carotenoid extracted from lettuce, showed AG inhibition with an IC 50 value of 1.84 mg/mL, while acarbose showed a value of 16.19 µg/mL [60]. Cucurbits are another major vegetable crops that possess inhibitory activity against AG enzymes.…”

Nutrients and Oxidative Stress: Friend or Foe?

“…Data from a meta-analysis included a study from 1966 to 2014 that demonstrated that a high intake of fruit, particularly berries, and yellow, cruciferous, green leafy vegetables or their fibers, is negatively linked to type 2 diabetes [ 291 ]. As an example, lactucaxanthin (Lxn), a carotenoid in lettuce ( Lactuca sativa ), suppresses α -amylase and α -glucosidase activity both in vitro and in diabetic rats [ 292 ]. Such findings highlight the role of unique complexes of bioactive components in fruits and vegetables.…”

Anti-Diabetic Effects of Phenolic Extract from Rambutan Peels (Nephelium lappaceum) in High-Fat Diet and Streptozotocin-Induced Diabetic Mice

“…DM is the most common chronic disease characterized by elevated blood glucose levels [1]. Long-term exposure to high blood glucose levels results in production of reactive oxygen species.…”