Preparation and Properties of Hydroxypropyl – β – Cyclodextrin Inclusion Complex of Chuanxiong Volatile Oil
Chuanxiong is the dried rhizome of Ligusticum chuanxiong Hort., a plant in the Umbelliferae family. It has a pungent, slightly bitter taste, and a warm nature. It has the effects of promoting blood circulation, dispelling wind and relieving pain, and is known as the “qi medicine in the blood”. It is used for chest pain, abdominal pain, wind dampness pain, and other symptoms such as chest obstruction, pain relief, menstrual disorders, abdominal pain, and wind dampness obstruction. Chuanxiong volatile oil (Chuanxiong oil) is one of the important effective components of Chuanxiong, with the main active ingredient being ligustilide. It has strong antispasmodic, anti asthmatic, and sedative effects and is effective in treating migraines and ischemic cerebrovascular diseases in clinical practice. However, the chemical properties of ligustilide are unstable and prone to various isomerization reactions such as dehydrogenation, oxidation, hydrolysis, and degradation. In addition, the low oil solubility and poor oral bioavailability of Ligusticum chuanxiong greatly limit its clinical application. In order to solve the problem of the stability and solubility of Chuanxiong oil, the reported preparation methods include soft capsules, dropping pills, nasal sprays, microemulsions, cyclodextrin inclusion, etc. Cyclodextrin inclusion is a commonly used formulation method, and hydroxypropyl – β – cyclodextrin (HP – β – CD) is one of the most widely used cyclodextrin derivatives and the first FDA approved injectable β – cyclodextrin (β – CD) derivative. HP – β – CD is a hydrophilic derivative obtained by the condensation of β – CD and epichlorohydrin. Due to the hydroxypropylation of β – CD, its intramolecular hydrogen bonds are disrupted, resulting in a significant increase in water solubility (75% W/W) of HP – β – CD. At the same time, the inclusion ability of β – CD is retained, greatly expanding the application range of the parent β – CD. It has the effect of improving drug solubility, stability, and bioavailability, reducing drug irritation or toxicity.

At present, most of the inclusion materials for volatile oils in traditional Chinese medicine are β – CD, and the inclusion complexes are generally prepared by saturated aqueous solution method, but the yield is low and the water solubility is poor. The inclusion complex is prepared using highly water-soluble HP – β – CD with high yield and good water solubility. Conventional preparation methods include aqueous solution method, grinding method, and ultrasonic method, all of which are carried out in the aqueous phase and require stirring, grinding, or ultrasonic treatment, resulting in low efficiency and difficulty in drying. Ao et al. prepared Chuanxiong oil HP – β – CD inclusion complex using anhydrous ethanol as the solvent and a rotary evaporator, replacing the traditional stirring process with rotation. However, anhydrous ethanol and rotation processes are difficult to apply in industrial production. Secondly, this study used ethyl acetate reflux to extract Chuanxiong oil, and calculated the inclusion rate based on the weight of the obtained Chuanxiong oil. However, the required amount of inclusion compound is large, and the extraction is incomplete, resulting in poor accuracy. In addition, the study did not characterize, evaluate the solubility and stability of the inclusion complex. This experiment is based on the feasibility and practicality of large-scale production, and intends to prepare Chuanxiong oil HP – β – CD inclusion complex using a single-phase method with 85-95% ethanol as the solvent. There is no need for stirring, grinding or other processes, and the complex can be directly recovered, concentrated and dried. This method is simple and easy to operate, with high yield and inclusion rate; The study determined the extraction and elution methods of the inclusion complex, accurately determined the inclusion rate using HPLC, optimized the inclusion process using orthogonal experimental design, characterized the inclusion complex, investigated its solubility and stability, and provided reference for the production and application of Chuanxiong oil preparations.

In this experiment, the single-phase method was used for encapsulation. Chuanxiong oil was added to an ethanol solution of HP – β – CD in one go without grinding, stirring, or ultrasonic treatment. The inclusion complex was directly recovered under reduced pressure and dried. This method is simple, practical, and has a high yield, making it suitable for industrial large-scale production.

The content determination of ligustilide and ligustilide A in Ligusticum chuanxiong oil cannot be determined by reference standards, which are unstable and difficult to calibrate and store. Therefore, our research group established a simple and feasible method for determining the content of ligustilide and ligustilide A in Ligusticum chuanxiong oil using butylphthalein as a reference standard in the early stage. This article examines the methodology of content determination and finds that specificity, linearity, precision, stability, and repeatability meet the requirements of quantitative analysis.

Regarding the determination of encapsulation efficiency, literature reports generally use the drug amount measured from the washed encapsulation material divided by the actual input amount as the encapsulation efficiency. Washing operations often involve rinsing the filtered cake with water or organic solvents during the preparation of the inclusion complex, or using organic solvents to extract the inclusion complex solution. Both methods can cause the inclusion complex to detach, resulting in a lower measured inclusion rate. In addition, there are also literature reports on the use of steam distillation to extract volatile oils from inclusion complexes. However, this method has incomplete quantitative extraction of volatile oils, resulting in low inclusion rates and poor reproducibility. This experiment conducted a comparative study, using 70% ethanol with high polarity to extract and determine the total drug amount of the inclusion complex, and then using petroleum ether with low polarity to extract and determine the unencapsulated drug amount. The difference between the total drug amount of the inclusion complex and the unencapsulated drug amount is the true drug amount of the inclusion complex. This method can more accurately determine the inclusion rate.

The solubility curve of HP – β – CD phase shows a linear increase within a certain concentration range, and the slope of ligustilide is greater than that of ligustilide A, indicating that HP – β – CD has a better solubilization effect on ligustilide. In addition, this experiment also investigated the phase solubility of Chuanxiong oil β – CD inclusion complex. Within the same experimental concentration range, its phase solubility curve showed nonlinear growth. The solubilization multiples of ligustilide and ligustilide A were 2.36 and 2.95, respectively, which were much lower than HP – β – CD, consistent with literature reports, indicating that HP – β – CD inclusion complex has significant advantages. Further experimental research is needed to investigate the bioavailability and pharmacological activity of Chuanxiong oil HP – β – CD inclusion complex.