Nanoliposomes of Spondias pinnata stem bark aqueous extract: in vitro antidiabetic activity and releasing profiles

Abstract

Nanoliposomes are amongst the most versatile lipid‐based carriers, which can encapsulate a range of compounds with different polarities. Decoctions, prepared from Spondias pinnata (L. f.) Kurz (wal ambarella) stem bark is used in Sri Lankan traditional medicine for the management of diabetes mellitus. Encapsulation of aqueous extract of stem bark (SAE) of S. pinnata in nanoliposomes could enhance its therapeutic potential by increasing bioavailability and providing controlled release. The present study investigates the in vitro anti-hyperglycaemic activity of SAE-encapsulated nanoliposomes (SAE-NLS) using α-amylase inhibitory, α-glucosidase inhibitory, glucose uptake, and glucose adsorption assays along with in vitro release profiles. Dried, powdered stem bark parts of S. pinnata were extracted using distilled water under ultrasonication to prepare SAE. SAE-NLS were synthesized from SAE, [phosphatidylcholine and cholesterol (20:1)] and an aqueous phase [phosphate buffer saline (pH 6.8) with Tween® 80 (0.1% v/v)], using a modified emulsification and ultrasonication methods. The synthesized SAE-NLS were characterized via size, zeta potential and FTIR data, encapsulation efficiency (EE) and loading capacity (LC) determination. The free polyphenol content was determined by the Folin-Ciocalteu method and was used in the estimation of EE. Further, the in vitro antidiabetic activity of SAE-NLS was screened using α- amylase, α-glucosidase inhibitory, glucose uptake and glucose adsorption activity assays. The Z-average particle diameter (389 nm), polydispersity index (0.37), and zeta potential (−27.27 mV) of SAE-NLS indicated moderate polydispersity. The free polyphenol content was determined by the Folin-Ciocalteu method. The highest EE (95.42±0.56%) and LC (0.02±0.00%) were observed when SAE was loaded at 3.0% w/v. The α-amylase inhibitory activity and α-glucosidase inhibitory activity (IC50) of SAE-NLS were 2.29±0.14 and 1.44±0.03 mgmL-1, respectively, while those for SAE were 0.05±0.01 and 0.08±0.00 mg mL-1, respectively. The glucose uptake (16.07±0.14%) at 10 mM glucose concentration and glucose adsorption (0.22±0.06 mmolg-1) of SAE-NLS at 50 mM were significantly higher (p<0.05) than those of reference standard metronidazole (5.81±1.27% and 0.05±0.01, respectively). The release of SAE from SAE-NLS was higher in simulated gastric fluid (60.63±0.27%) than in simulated intestinal fluid (24.11±0.94%) after 10 h. SAE-NLS showed higher α-glucosidase inhibitory and glucose adsorption activities than acarbose, and metronidazole, respectively. The results revealed that SAE-NLS are potential nanocarriers with potent in vitro antidiabetic activity providing controlled release.