A Pharmaco-Technical Investigation of Thymoquinone and Peat-Sourced Fulvic Acid Nanoemulgel: A Combination Therapy

Abstract

Thymoquinone has a multitude of pharmacological effects and has been researched for a wide variety of indications, but with limited clinical success. It is associated with pharmaco-technical caveats such as hydrophobicity, high degradation, and a low oral bioavailability. A prudent approach warrants its usage through an alternative dermal route in combination with functional excipients to harness its potential for treating dermal afflictions, such as psoriasis. Henceforth, the present study explores a nanoformulation approach for designing a fulvic acid (peat-sourced)-based thymoquinone nanoemulsion gel (FTQ-NEG) for an enhanced solubility and improved absorption. The excipients, surfactant/co-surfactant, and oil selected for the o/w nanoemulsion (FTQ-NE) are Tween 80/Transcutol-P and kalonji oil. The formulation methodology includes high-energy ultrasonication complemented with a three-dimensional/factorial Box-Behnken design for guided optimization. The surface morphology assessment through scanning/transmission electron microscopy and fluorescence microscopy revealed a 100 nm spherical, globule-like structure of the prepared nanoemulsion. Furthermore, the optimized FTQ-NE had a zeta potential of -2.83 ± 0.14 Mv, refractive index of 1.415 ± 0.036, viscosity of 138.5 ± 3.08 mp, and pH of 5.8 ± 0.16, respectively. The optimized FTQ-NE was then formulated as a gel using Carbopol 971^® (1%). The in vitro release analysis of the optimized FTQ-NEG showed a diffusion-dominant drug release (Higuchi model) for 48 h. The drug permeation flux observed for FTQ-NEG (3.64 μg/cm²/h) was much higher compared to that of the pure drug (1.77 mg/cm²/h). The results were further confirmed by confocal microscopy studies, which proved the improved penetration of thymoquinone through mice skin. Long-term stability studies of the purported formulation were also conducted and yielded satisfactory results.

Keywords: Box–Behnken design; enhanced stability; nanoemulsion; pseudo-ternary phase diagrams; thymoquinone; ultrasonication.

Figure 1

TQ solubility in various surfactants, co-surfactants, and oils.

Figure 2

Pseudo-ternary phase diagrams for various Smix ratios.

Figure 3

3D response surface depicting the interaction effect of the independent variables like oil, smix, sonication time on (a–c) particle size, (d–f) PDI, and(g–i) %transmittance.

Figure 4

(A) Dilution test, (B) filter paper test, and (C) cobalt chloride test.

Figure 5

Particle size, polydispersity index (A) (PDI), and zeta potential (B) of FTQ-NE.

Figure 6

Overlay of differential scanning calorimetry (DSC) (A) (thymoquinone), (B) (fulvic acid), (C) (mannitol), and (D) (FTQ-NE).

Figure 7

Overlay spectra showing the FTIR of (A) TQ, (B) FA, (C) mannitol, and (D) FTQ-NE.

Figure 8

Overlay of X-ray diffractograms.

Figure 9

(A) SEM, (B) TEM, and (C) fluorescent microscopy of the optimized FTQ-NE.

Figure 10

Texture analysis of the FTQ-NEG formulation (A) and placebo gel (B).

Figure 11

(A) In vitro drug release of TQ, FTQ-NE, and FTQ-NEG. (B) The ex vivo skin permeation release of the free drug TQ, FTQ-NEG, and FTQ-NE.

Figure 12

Confocal microscopic studies of mouse skin treated with (A) Rhodamine B hydroalcoholic solution, (B) drug solution with rhodamine dye, and (C) FTQ-NEG with rhodamine.