Curcumin-Loaded Long-Circulation Liposomes Ameliorate Insulin Resistance in Type 2 Diabetic Mice

Abstract

Introduction: Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterised by insulin resistance, hyperglycaemia, and inflammation, with oxidative stress contributing to its progression. Curcumin (CUR), known for its anti-inflammatory, antioxidant, and insulin sensitising effects, has shown potential for the treatment of T2DM but is limited by low solubility and bioavailability. This study investigated long-circulating curcumin-loaded liposomes (CUR-LPs) to improve curcumin stability, solubility, and circulation and assessed their effect on insulin resistance in a murine model of T2DM.

Methods: CUR-LPs were prepared using the ethanol injection method and characterized for morphology, particle size, zeta potential, encapsulation efficiency, drug-loading capacity, and in vitro release. Cell viability was tested on murine L929 cells. In a T2DM murine model, after four weeks of CUR-LP treatment, inflammatory markers TNF-α and IL-6 were measured by real-time polymerase chain reaction, and liver tissues were analyzed for glutathione (GSH) and superoxide dismutase (SOD) via colorimetry.

Results: CUR-LPs were spherical, with an average diameter of (249 ± 2.3) nm and a zeta potential of (-33.5 ± 0.8) mV. They exhibited an encapsulation efficiency of (99.2 ± 0.5) %and a drug-loading capacity of (1.63 ± 0.02) %. CUR embedding in liposomes significantly maintained CUR release. In L929 cells, over 80% viability was maintained at 12 uM CUR concentration after 24 h. In HFD/STZ-induced T2DM mice, CUR-LPs improved blood glucose and insulin levels more efficiently than free CUR, and CUR-LPs also reduced hepatic inflammation (TNF-α, IL-6), enhanced hepatic GSH and SOD, and attenuated liver injury.

Conclusion: CUR-LPs improved glucose metabolism and insulin resistance in HFD/STZ-induced T2DM mice, which may be associated with a decrease in liver inflammation and oxidative stress.

Keywords: T2DM; curcumin; glucose metabolism; insulin resistance; liposomes; oxidative stress.

Figure 1

The transmission electron microscope images of CUR-LPs (×40000 Magnification, scale bar: 100 nm).

Figure 2

In vitro release of CUR from different preparations detected by dialysis method (n=3). The release medium was physiological saline containing 1.0% Tween 80 with pH adjusted to 7.0.

Figure 3

CCK-8 assays of CUR-LPs against L929 cells within 24 h (n=3).

Figure 4

Effect of CUR-LPs on body weight and fasting blood glucose level of T2DM mice. Normal diet: a normal diet group (0.9% sodium chloride, 5mg/kg, i.v., n=6), T2DM+Vehicle: a diabetic model control group (0.9% sodium chloride, 5mg/kg, i.v., T2DM, n=6), T2DM+Free CUR-L: a low-dose free curcumin treatment group (5mg/kg, i.g., n=6), T2DM+Free CUR-H: a high-dose free curcumin treatment group (50mg/kg, i.g., n=6), T2DM+Empty LPs: an empty liposome group (5mg/kg, i.v., n=6), T2DM+ CUR-LPs: a long-circulation liposomes loaded with CUR group (5mg/kg, i.v., n=6). (A) Description of the whole experimental process. (B) The body weight of T2DM mice treated with different ways. (C)The blood glucose level of T2DM mice treated with different ways. *p < 0.05 and **p < 0.01 vs T2DM+Vehicle.

Figure 5

Effect of CUR-LPs on insulin and HOMA-IR level of T2DM mice. (A)Evaluation of blood glucose levels in mice treated with different treatments. (B)The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated using the formula: HOMA-IR = [fasting plasma glucose (mmol/L) × fasting plasma insulin (mU/L)]/22.5. *p < 0.05, **p < 0.01 vs T2DM+Vehicle.

Figure 6

CUR-LPs attenuated liver inflammation and injury in T2DM mice. Mice with diabetes, induced by HFD/STZ, were treated with Free CUR, CUR-LPs, or Empty LPs. The expression of inflammatory cytokines TNF-α (A) and IL-6 (B) in the liver of HFD/STZ-induced T2DM mice were measured by RT-PCR. Liver tissues were fixed and sectioned for further analysis. (C and D) Hematoxylin and eosin staining was conducted for histochemical examination of liver tissue (original magnification 20×). *p < 0.05 and **p < 0.01, ***p < 0.001 vs T2DM+Vehicle.

Figure 7

CUR-LPs alleviated oxidative stress in T2DM mice. The levels of GSH (A) and SOD (B) in liver of mice treated with different methods were detected. *p < 0.05, ***p < 0.001 vs T2DM+Vehicle.