Solid lipid nanoparticles loaded with oleanolic and asiatic acid show antidiabetic potential in cell studies

Oleanolic acid and asiatic acid, two plant-derived triterpenes with documented antidiabetic, antioxidant and anti-inflammatory properties, have long been hampered by a practical problem: they dissolve poorly in water and are absorbed poorly by the body. Their findings, published in Discover Pharmaceutical Sciences, suggest that the nanoformulations can inhibit the starch-digesting enzyme α-amylase, lower glucose concentrations in the culture medium of liver cells, and do so with little apparent toxicity to three human cell lines, although the authors themselves caution that the work is strictly preliminary in vitro evidence.

The study built on the team’s earlier publication, in which they characterised the physicochemical properties, solubility, stability and drug release profiles of oleanolic acid- and asiatic acid-loaded solid lipid nanoparticles. In the new work, they extended that characterisation by asking whether the encapsulated compounds actually behave differently from their free forms in biological assays. Solid lipid nanoparticles are delivery vehicles made from physiologically acceptable lipids, in this case glyceryl behenate, stabilised with the non-ionic surfactant polysorbate 80. Because the hydrophobic core of the lipid matrix is compatible with non-polar compounds, triterpenes such as oleanolic acid and asiatic acid can be encapsulated efficiently. The formulations were produced by an emulsion solvent evaporation method involving high-speed homogenisation and sonication, followed by overnight solvent removal, and their particle size, polydispersity index and zeta potential were tracked over 60 days.

The first experimental question concerned α-amylase, a pancreatic enzyme that breaks down starch into simpler sugars. Using a validated colorimetric assay with porcine pancreatic α-amylase and potato starch, the researchers measured enzyme inhibition across five concentrations of each compound and formulation. Both the free compounds and their nanoparticle versions inhibited α-amylase. The half-maximal inhibitory concentration, or IC50, was 39.41 micromolar for free oleanolic acid and 42.26 micromolar for oleanolic acid-loaded nanoparticles, values the authors describe as comparable. For asiatic acid, the picture differed: free asiatic acid had an IC50 of 143.85 micromolar, while the asiatic acid-loaded nanoparticles achieved 112.75 micromolar, indicating that encapsulation improved the inhibitory activity of this compound. Acarbose, the positive control, was considerably more potent at 17.81 micromolar in the oleanolic acid assay series and 30.21 micromolar in the asiatic acid series. Importantly, statistical testing showed no significant difference between each nanoformulation and its corresponding free compound, meaning the encapsulation did not statistically change α-amylase inhibition, although the asiatic acid trend favoured the nanoparticle version.

Cytotoxicity was assessed with the MTT assay, a standard colorimetric test that estimates cell viability by measuring metabolic activity, on three human cell lines: HepG2 liver carcinoma cells, HEK293 embryonic kidney cells and Caco-2 colorectal adenocarcinoma cells. Cells were exposed to concentrations of the compounds and formulations up to 100 micrograms per millilitre for 24 hours. Viability remained above 85 percent across HEK293 and Caco-2 cells treated with the nanoparticle formulations, and above 90 percent for cells treated with the free compounds, in each case comparable to untreated controls. HepG2 cells likewise stayed above 85 percent viability across all treatments. Statistical comparisons found no significant differences in viability between the nanoformulations and their free compounds, and the cytotoxic effects were not concentration-dependent.

The most direct test of antidiabetic potential came from glucose quantification experiments in HepG2 cells, a human liver cell line commonly used to study glucose metabolism. The researchers induced a hyperglycaemia-like state by culturing the cells in medium containing 25 millimolar glucose, then treated them with 25 or 50 micrograms per millilitre of each compound or nanoformulation under two conditions: a non-fasting protocol, in which cells were treated continuously for 24 hours, and an intermittent fasting protocol, in which cells underwent an additional 8-hour starvation period before treatment. Glucose remaining in the treatment medium was measured with an Accu-Chek Active glucose meter, a device the authors note meets ISO 15197:2013 accuracy requirements. Because glucose disappearing from the medium is taken up by the cells, lower residual glucose indirectly indicates greater cellular glucose uptake, although the authors explicitly acknowledge that this method does not directly measure the amount of glucose entering the cells.

Under non-fasting conditions, the high-glucose control medium contained 21.1 millimoles per litre of glucose, far above the 1.85 millimoles per litre measured in the normal-glucose control. Metformin, the positive control, reduced the residual glucose to 17.3 millimoles per litre. Free oleanolic acid at 25 and 50 micrograms per millilitre lowered residual glucose to 19.3 and 18.6 millimoles per litre respectively, while the corresponding oleanolic acid nanoparticles achieved 19.7 and 17.1 millimoles per litre, the strongest effect among the oleanolic acid treatments. Asiatic acid results were more mixed: the 50 microgram per millilitre nanoparticle treatment reduced glucose to 18.9 millimoles per litre, a significant change, but free asiatic acid at 25 micrograms per millilitre actually increased residual glucose slightly, and the 25 microgram nanoparticle treatment showed a non-significant decrease. Under intermittent fasting conditions, metformin and nearly all treatments significantly reduced glucose levels, with the notable exception of asiatic acid nanoparticles at the lower dose, which slightly increased residual glucose. Oleanolic acid treatments showed a concentration-dependent pattern in the fasting condition, with the higher dose consistently outperforming the lower one.

To explore how the compounds might interact with their molecular targets, the team performed molecular docking against two carbohydrate-digesting enzymes: α-amylase, using the protein structure 3BAJ, and α-glucosidase, using the structure 5NN8. Both compounds and acarbose were docked at the active sites where the co-crystallised inhibitor normally binds, a strategy that validates the docking protocol. The results showed that asiatic acid bound more strongly than oleanolic acid to both enzymes, but acarbose, the approved drug, showed the strongest binding affinity of all. For α-amylase, asiatic acid achieved a binding free energy of minus 30.69 kilocalories per mole under the MMGBSA rescoring method, compared with minus 12.21 for oleanolic acid and minus 51.91 for acarbose. Molecular dynamics simulations over 100 nanoseconds confirmed that all protein-ligand complexes remained structurally stable, with root mean square deviation values below 2 angstroms and relatively low flexibility values, indicating that the compounds form stable interactions with the enzyme once bound.

An interesting tension emerges between the computational and experimental results. Docking predicted that asiatic acid binds α-amylase more strongly than oleanolic acid, yet the actual enzyme inhibition assay showed oleanolic acid to be the more potent inhibitor, with an IC50 roughly one-third that of asiatic acid. The authors address this discrepancy directly, noting that computational models capture only the three-dimensional geometry of molecular interactions and cannot fully account for solubility, kinetic factors or the cellular environment. They cite a previous study in which oleanolic acid showed weaker experimental α-amylase inhibition than acarbose despite a computationally stronger docking score, reinforcing the point that in silico predictions must be validated by biological experiments rather than treated as definitive evidence of activity.

The authors are careful to frame their conclusions within the limits of the study design. The glucose measurements were indirect, relying on residual glucose in the medium rather than direct quantification of uptake. The MTT assay, while widely used, has known limitations in sensitivity and susceptibility to chemical interference, and the authors recommend complementary assays such as lactate dehydrogenase release to build a fuller safety profile. The MMGBSA rescoring for α-glucosidase was not completed due to computational constraints. Most importantly, the entire study was conducted in vitro, with no animal or human data. The authors state explicitly that the results should not be interpreted as validation of the safety or therapeutic efficacy of the formulations, but rather as preliminary evidence signalling the need for future research, including in vivo studies of subchronic and systemic effects, pharmacokinetics and bioavailability.

Within those boundaries, the findings offer a coherent picture. Encapsulating oleanolic acid and asiatic acid in solid lipid nanoparticles did not compromise cell viability at the tested concentrations, preserved or modestly improved α-amylase inhibitory activity depending on the compound, and reduced glucose concentrations in the culture medium of hyperglycaemic liver cells under both fasting and non-fasting conditions, with oleanolic acid nanoparticles showing the most consistent glucose-lowering effect. The computational work supports the plausibility of enzyme binding without overstating its predictive power. Taken together, the study positions these lipid-based nanoformulations as candidates worth further investigation as delivery systems for lipophilic triterpenes with potential antidiabetic properties, while leaving open the fundamental questions of efficacy and safety that only properly controlled animal and eventually human studies can answer.

Subject of Research: In vitro evaluation of oleanolic acid- and asiatic acid-loaded solid lipid nanoparticles for alpha-amylase inhibition, glucose uptake and cytotoxicity

Article Title: Antidiabetic and cytotoxic effects of solid lipid nanoparticles loaded with oleanolic acid and asiatic acid and in silico evaluation

Article References: Oboh, M., Khan, R., Govender, L., Siwela, M., & Mkhwanazi, B. N. (2026). Antidiabetic and cytotoxic effects of solid lipid nanoparticles loaded with oleanolic acid and asiatic acid and in silico evaluation. Discover Pharmaceutical Sciences, 2(1), Article 17. https://doi.org/10.1007/s44395-026-00054-4

Image Credits: AI Generated

DOI: 10.1007/s44395-026-00054-4

Keywords: solid lipid nanoparticles, oleanolic acid, asiatic acid, alpha-amylase inhibition, type 2 diabetes, glucose uptake, cytotoxicity, molecular docking, HepG2 cells, triterpenes, drug delivery, in vitro study