Pharmacological Application and Mechanism of Action of Honokiol Loaded Oral Solid Lipid Nanoparticles for the Treatment of Diabetic Neuropathy

Abstract

Honokiol is a phytochemical component with a variety of pharmacological properties. However, the major limitation of Honokiol is its poor solubility and low oral bioavailability. In this study, we formulated and characterized oral Honokiol-loaded solid lipid nanoparticles (Honokiol-SLNs) to enhance bioavailability and then evaluated their effectiveness in diabetic neuropathy (DN), experimental Type 1 diabetes (T1D), and diabetes-induced depression. The optimized formulation has a spherical morphology, a particle size (PS) of 121.31 nm, a polydispersity index (PDI) of 0.249, a zeta potential (ZP) of -20.8 mV, and an entrapment efficiency (%EE) of 88.6%. In vitro release data shows, Honokiol-SLNs displayed a sustained release profile at pH (7.4). The oral bioavailability of Honokiol-SLNs was remarkably greater (8-fold) than Honokiol-Pure suspension. The neuroprotective property of Honokiol- SLNs was initially demonstrated against hydrogen peroxide (H2O2)-stimulated PC12 (pheochromocytoma) cells. Furthermore, results of in vivo studies demonstrated that treatment with Honokiol-SLNs significantly suppressed oxidative stress by inhibition of nuclear factor kappa B (NF-κB) and upregulation of nuclear factor-erythroid 2- related factor 2 (Nrf2) signaling in the spinal cord. The expression of transient receptor potential melastatin 8(TRPM8) and transient receptor potential vanilloid 1 (TRPV1) was significantly downregulated. By regulating the expression level of cleaved caspase-3 it prevented apoptosis. The purpose of the second portion of the study was to learn more about the mechanism of action and protective effects of Honokiol-SLNs on pancreatic beta-cells (β-cells) in T1D. Male Swiss mice were induced with T1D by administering a 150 mg/kg intraperitoneal (i.p) injection of streptozotocin (STZ). Following the onset of hyperglycemia, they were given a daily dose of 5mg/kg Honokiol-SLNs for an experimental phase of 28 days. At the final stage of the examination, samples of pancreatic tissue and blood were taken to assess β-cell function, apoptosis, oxidative stress, and inflammation. Preliminary in vitro studies confirm that Honokiol-SLNs inhibit alpha-amylase (α-amylase) and alphaglucosidase (α-glucosidase), showing anti-diabetic activity. Results from in vivo animal studies showed that Honokiol-SLNs treatment significantly decreased fasting blood glucose levels, and improved food consumption, intake of water, and body weight in diabetic animals. The study revealed that Honokiol-SLNs have antioxidant properties by increasing the level of Nrf2, anti-inflammatory impact by reducing the xii level of NF-κB, and anti-apoptotic effects by decreasing the expression level of cleaved caspase-3 in the pancreas. Furthermore, the reduction in Annexin V/PIstained pancreatic cells suggests its potential to prevent apoptosis. The use of Honokiol-SLNs led to a reversal of pancreatic histopathological and spectroscopic changes, an intensification in antioxidant profile, a decrease in pro-inflammatory cytokines, and nitric oxide production. Pancreatic β-cells may be shielded, and their activity strengthened by Honokiol-SLNs, which reduce oxidative stress and promote anti-inflammatory, anti-apoptotic, and antioxidant properties. In the third part of the study, we explored the mechanism of action of Honokiol-SLNs in diabetes-induced depression. Diabetic patients have a greater incidence and susceptibility to depression than the population without diabetes. The underlying cause of depression linked to diabetes is unidentified, and treatment options are inadequate. This study investigated the antidepressant-like therapeutic effect of Honokiol-SLNs on diabetic mice induced by streptozotocin (STZ). We employed an in vitro model of HT-22 and BV-2 cell lines, as well as an in vivo mice model of STZ-induced diabetes, to explore the antioxidant and anti-neuroinflammatory features of Honokiol-SLNs. In a dose-reliant pattern, treatment with Honokiol-SLNs considerably diminished oxidative stress and H2O2-induced cytotoxicity. We investigated the influence of microglial activation, oxidative stress, and inflammatory status in the hippocampus and prefrontal cortex of diabetic mice. Treatment with Honokiol-SLNs proved an antidepressant-like property by greatly decreasing immobility time in the tail suspension test (TST) and forced swim test (FST). Evans's blue extravasation in the brain was greatly reduced by it. It successfully reversed the histopathological alterations in the prefrontal cortex and hippocampal regions brought on by STZ. It enhanced the expression of Nrf2, greatly enhancing the antioxidant defense mechanism. Similarly, it significantly reduced neuroinflammation in the hippocampus and prefrontal cortex by lowering the expression of NF-κB in addition, reduced generation of pro-inflammatory cytokines in the hippocampus and prefrontal cortex regions. Honokiol-SLNs significantly lowered serum cortisol levels. Honokiol-SLNs have significant neuroprotective potential in STZ-induced depression by modulating Nrf2-related oxidative stress, NF- κB-related inflammation, and inhibition of microglial activation. The result of the study concluded that Honokiol-SLNs exhibited significant therapeutic activity against diabetic neuropathy, T1D, and diabetes-induced depression because of enhanced oral bioavailability.