Abstract
Magnolia spp. extracts are known for their use in traditional Korean, Chinese, and Japanese medicine in the treatment of gastrointestinal disorders, anxiety, and allergies. Among their main components with pharmacological activity, the most relevant are magnolol and honokiol, which also show antitumoral activity. The objectives of this work were to study some physicochemical properties of both substances and their stability under different conditions of temperature, pH, and oxidation. Additionally, liposomes of honokiol (the least stable compound) were formulated and characterized. Both compounds showed pH-dependent solubility, with different solubility–pH profiles. Magnolol showed a lower solubility than honokiol at acidic pH values, but a higher solubility at alkaline pH values. The partition coefficients were similar and relatively high for both compounds (log Po/w ≈ 4.5), indicating their lipophilic nature. Honokiol was less stable than magnolol, mainly at neutral and basic pH values. To improve the poor stability of honokiol, it was suitably loaded in liposomes. The obtained liposomes were small in size (175 nm), homogeneous (polydispersity index = 0.17), highly negatively charged (−11 mV), and able to incorporate high amounts of honokiol (entrapment efficiency = 93.4%). The encapsulation of honokiol in liposomes increased its stability only at alkaline pH values.
Highlights
Natural products have historically been used as remedies for the alleviation of diseases
A linear relationship was found between the magnolol and honokiol peak area and their concentrations in standards in the range of 0.1–100 μg/mL (magnolol: Peak area = 41.74 × Conc(μg/mL)—12.31; honokiol: Peak area = 69.97 × Conc(μg/mL)—7.43; r > 0.9992 for both relationships)
The results of this study showed that magnolol and honokiol are highly hydrophobic compounds with poor water solubility that limits their clinical applications
Summary
Natural products have historically been used as remedies for the alleviation of diseases. Natural bioactive compounds generally have better safety profiles, are well accepted by the patients, and are usually relatively inexpensive [1]. In this context, extracts from the bark of Magnolia species, such as M. officinalis and. The main substances responsible for the beneficial features of the Magnolia bark extract [16] are the neolignans magnolol and honokiol. The highest content of both substances is found in the roots of trees, and its concentration in the extracts varies widely depending on various environmental factors such as the area of origin, altitude of the cultivar, and age of the tree [19]
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