Abstract
Emodin is a component in a Chinese herb, Rheum officinale Baill, traditionally used for diabetes and anticancer. Its poor solubility is one of the major challenges to pharmaceutical scientists. We previously reported on thermoreversible gel formulations based on poloxamer for the topical delivery of emodin. The present study was to understand the effect of poloxamer type on emodin solubility and its application in cellular activity screening. Various gel formulations composed of poloxamer 407 (P407), poloxamer 188 (P188) and PEG400 were prepared and evaluated. Major evaluation parameters were the gelation temperature (Tgel) and solubility of emodin. The emodin solubility increased with increasing poloxamer concentration and the Tgel was modulated by the proper combination of P407. In particular, this study showed that the amount of P407 in thermoreversible poloxamer gel (PG) was the dominant factor in enhancing solubility and P188 was effective at fixing gelation temperature in the desired range. A thermoreversible emodin PG was selected as the proper composition with the liquid state at room temperature and gel state at body temperature. The gel showed the solubility enhancement of emodin at least 100-fold compared to 10% ethanol or water. The thermoreversible formulation was applied for in vitro cellular activity screening in the human dermal fibroblast cell line and DLD-1 colon cancer cell line after dilution with cell culture media. The thermoreversible gel formulation remained as a clear solution in the microplate, which allowed reliable cellular activity screening. In contrast, emodin solution in ethanol or DMSO showed precipitation at the corresponding emodin concentration, complicating data interpretation. In conclusion, the gel formulation is proposed as a useful prototype topical formulation for testing emodin in vivo as well as in vitro.
Highlights
Emodin, 1,3,8-trihydroxy-6-methyl-anthraquinone (Figure 1), is an anthraquinone derivative from the roots of rhubarb (Rheum officinale Baill) [1]
We have prepared thermoreversible poloxamer gel (PG) containing emodin with high emodin solubility and the gelation temperature suited to physiological use
PG was applied for in vitro cellular activity screening in the HDF and DLD-1 colon cancer cell line to investigate the vehicle effect
Summary
1,3,8-trihydroxy-6-methyl-anthraquinone (Figure 1), is an anthraquinone derivative from the roots of rhubarb (Rheum officinale Baill) [1]. Improvement of emodin solubility is desirable for the evaluation of its pharmacological various approaches to improving solubility have been investigated, including physical or chemical and functional activity. 188 (P188) are the polymers frequently used for preparation of thermoreversible gels and enhancement of formulations poloxamer-based gels are being modified to achieve drug solubility,ofrespectively. For poloxamer-based gel is a very attractive formulation thermosensitive topical delivery. Poloxamer-based thermoreversible gel is a for delivery throughfor thetopical body delivery surface to reducethe metabolism andto improve solubilityand of verytopical attractive formulation through body surface reduce the metabolism emodin. Tgel emodin solubilityInby previous study, we In observed that study, poloxamers are capable enhancing are the water solubility of poorly quality by design.
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