Arginine Hydrochloride Reduce Rectal Mucosal Irritation of Sodium Aescinate: Molecular Docking, Physical Properties, Anti-Hemorrhoidal Activity, Safety and Topical Gel Formulations Investigation

Abstract

Background/Objectives: Sodium aescinate (SA) is commonly used topically due to its anti-inflammatory, anti-edematous, and anti-swelling properties. However, the clinical application of SA is limited by strong irritation, and cannot be used on the damaged skin and mucous membrane. This study aimed to investigate whether arginine hydrochloride (Arg·HCl) could reduce the rectal mucosal irritation of SA through the formation of a gel. Methods: Molecular docking was first used to explore potential interactions between SA and Arg·HCl. Gels for rectal administration were then formulated by combining SA with various ratios of Arg·HCl (from 1:0 to 1:10). In vitro tests, including pH, centrifuge stability, viscosity, and spreadability analysis, were conducted. The optimal gel formulation was determined based on rectal mucosal irritation tests and anti-inflammatory experiments. Additionally, the anti-hemorrhoidal characteristics and safety of the optimal gel in terms of acute toxicity and dermal sensitivity were evaluated. Results: The optimal SA to Arg·HCl ratio of 1:6 (F5-SA gel) was identified, significantly reducing rectal mucosal irritation while enhancing anti-inflammatory activity. The F5-SA gel demonstrated high efficacy against hemorrhoids, notably promoting anal ulcer healing. When administered rectally to rabbits at a dose of 132 mg·kg^-1·d^-1 (198 times the recommended therapeutic dose), no other obvious side effects were observed except a significant reduction in food intake on the day of administration. In addition, the gel did not induce dermal sensitivity. Conclusions: The F5-SA gel is a promising formulation that can reduce irritation and toxic side effects, and enhance the therapeutic effect to some extent, ultimately achieving a safer and more effective rectal delivery system for SA.

Keywords: arginine hydrochloride; gels; hemorrhoid; inflammation; rectal irritation; sodium aescinate.

Figure 1

Chemical structures of different geometrical isomers of SA.

Figure 2

The procedure of the SA gel formulation.

Figure 3

Predicted potential interactions between SA and Arg·HCl, showing an electrostatic map of SA’s surface, highlighting major areas of interaction. (a) SA A (skyblue: carbon atom, red: oxygen atom) and Arg·HCl (orange: carbon atom, blue: nitrogen atom); (b) SA B (green: carbon atom, red: oxygen atom) and Arg·HCl (cyan: carbon atom, blue: nitrogen atom); (c) SA C (yellow: carbon atom, red: oxygen atom) and Arg·HCl (magenta: carbon atom, blue: nitrogen atom); (d) SA D (pink: carbon atom and red: oxygen atom) and Arg·HCl (gray: carbon atom, blue: nitrogen atom).

Figure 3

Predicted potential interactions between SA and Arg·HCl, showing an electrostatic map of SA’s surface, highlighting major areas of interaction. (a) SA A (skyblue: carbon atom, red: oxygen atom) and Arg·HCl (orange: carbon atom, blue: nitrogen atom); (b) SA B (green: carbon atom, red: oxygen atom) and Arg·HCl (cyan: carbon atom, blue: nitrogen atom); (c) SA C (yellow: carbon atom, red: oxygen atom) and Arg·HCl (magenta: carbon atom, blue: nitrogen atom); (d) SA D (pink: carbon atom and red: oxygen atom) and Arg·HCl (gray: carbon atom, blue: nitrogen atom).

Figure 4

The organoleptic characteristics of the SA gels. F1~F6: six formulations with 2% SA and varying Arg·HCl ratios (SA:Arg·HCl = 1:0, 1:0.5, 1:1, 1:3, 1:6, and 1:10).

Figure 5

Histological sections of rectal mucosal stimulation for F1~F6 (HE staining ×100). (a) NS group; (b) SA gel matrix control group; (c) F1 group; (d) F2 group; (e) F3 group; (f) F4 group; (g) F5 group; (h) F6 group. Yellow arrows: hyperaemia; green arrows: mucosal surface shedding; red arrows: lymphocyte infiltration; black arrows: secretions.

Figure 6

Gross observation of rectal mucosa one week after discontinuation of treatment for F1~F6. (a) NS group; (b) SA gel matrix control group; (c) F1 group; (d) F2 group; (e) F3 group; (f) F4 group; (g) F5 group; (h) F6 group. Yellow arrows denote hyperemia.

Figure 7

Effects of F1~F6 SA gels on xylene-induced ear swelling. Results are presented as mean ± SD (n = 10). One-way ANOVA followed by Dunnett’s test where * p < 0.05, ** p < 0.01, in comparison to matrix control group. (* moderately significant, ** highly significant).

Figure 8

Effects of F1~F6 SA gels on histamine-induced capillary permeability. Results are presented as mean ± SD (n = 10). One-way ANOVA followed by Dunnett’s test where * p < 0.05, ** p < 0.01, in comparison to matrix control group. (* moderately significant, ** highly significant).

Figure 9

Effects of F5-SA gel on $\mathrm{r}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{a}\mathrm{n}\mathrm{a}\mathrm{l}$ swelling coefficient of hemorrhoidal rats induced by croton oil preparation. Results are presented as mean ± SD (n = 10). One-way ANOVA followed by Dunnett’s test where * p < 0.05, ** p < 0.01, in comparison to matrix control group. (* moderately significant, ** highly significant).

Figure 10

Effects of F5-SA gel on ulcer healing score of hemorrhoidal rabbits induced by acetic acid. Results are presented as mean ± SD (n = 10). One-way ANOVA followed by Dunnett’s test where * p < 0.05, ** p < 0.01, in comparison to matrix control group. (* moderately significant, ** highly significant). Day 0: before administration; Day 8: after 7 days of continuous administration.