Exploring the Potent Combination of Quercetin–Boronic Acid, Epalrestat, and Urea Containing Nanoethosomal Keratolytic Gel for the Treatment of Diabetic Neuropathic Pain: In Vitro and In Vivo Studies

Transdermal penetration of therapeutic moieties from topical dosage forms always remains a challenge due to the presence of permeation impeding keratin which should be addressed. The purpose of the study was to formulate quercetin and 4-formyl phenyl boronic acid (QB complex) used for the preparation of nanoethosomal keratolytic gel (EF3-G). The QB complex was confirmed by Fourier transform infrared spectroscopy while skin permeation, viscosity, and epalrestat entrapment efficiency were used for the optimization of nanoethosomal gel. The keratolytic effect of the proposed nanoethosomal gel with urea (QB + EPL + U) was calculated in rat and snake skin. The spherical shape of nanoethosomes was confirmed by scanning electron microscopy. According to the findings of stability studies, viscosity decreases as temperature increases, proving their thermal stability. The negative charge of optimized EF3 with 0.7 PDI proved narrow particle size distribution with homogeneity. Optimized EF3 showed two folds increase of epalrestat permeation in highly keratinized snake skin as compared to rats' skin after 24 h. Antioxidant behaviors of EF3 (QB) > QB complex > quercetin > ascorbic acid proved reduction of oxidative stress in DPPH reduction analysis. Interestingly, the hot plate and cold allodynia test in the diabetic neuropathic rat model reduced 3-fold pain as compared to the diabetic control group which was further confirmed by in vivo biochemical studies even after the eight week. Conclusively, ureal keratolysis, primary dermal irritation index reduction, and improved loading of epalrestat render the nanoethosomal gel (EF3-G) ideal for the treatment of diabetic neuropathic pain.