Influence of Choline-Based Ionogel on Transdermal Delivery of Vancomycin Hydrochloride

Abstract

Ionic liquids (ILs) have attracted considerable interest as new drug delivery solvents because of their superior transdermal absorption of large molecular weight drugs across the biological barrier and their capacity to solubilize hydrophobic compounds. It is difficult to administer hydrophilic peptide treatments with large molecular weights through the skin. Vancomycin hydrochloride (VH) is a glycopeptide antibiotic that cures bacterial infections. With a molecular weight of 1449 Da and a high water solubility of 50 mg/mL, VH is an impressive compound. This study aimed to quantify the amount of VH transdermal penetration by analyzing the influence of choline-based ILs. Choline geranate was used as an IL in this investigation, whereas oleic acid (OA) (unsaturated) and palmitic acid (PA) (saturated) were chosen as the two types of fatty acids. The molar ratio of choline bicarbonate (CB) to either OA (CO) or PA (CP) was 2:1. In an additional series of trials, choline geranate (CAGE) ILs were prepared by mixing CB and geranic acid in a 1:2 molar ratio. For NMR spectroscopy, powder X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared investigations, these formulations were characterized. Zeta potential indicated that all of the formulations had negative charges. The decreased irritation potential of CAGE, as shown by conductivity studies, makes it appropriate for skin application. To determine which formulation enhancers worked best, ex vivo skin permeation studies were carried out on both intact and tape-stripped skin. After 48 h, skin transport investigations showed that neat VH did not penetrate the excised porcine skin. Nevertheless, the CO and CP-based formulations greatly improved the skin penetration (6729 ± 437 μg/cm²) and retention (3892 ± 215 μg/g) of VH across the tape-stripped skin, whereas CAGE exhibited the most significant improvement (p < 0.05). Ionogel (CAGE-P) was finally fabricated by combining CAGE with 22.7% w/v Pluronic F-127 and 45.0% w/v PEG-400. The physical and rheological properties of VH-loaded CAGE-P gel were examined. The amount of VH permeated across the CAGE-P gel cotreated intact skin was 369 ± 41 μg/cm², but that penetrated tape-stripped skin was 7543 ± 585 μg/cm². The skin's barrier property underwent notable modifications (p < 0.05) following incubation with CAGE and CAGE-P gel formulations, as seen in the biophysical investigations conducted at various time intervals. Taken together, CAGE-Pluronic F-127 ionogel is promising and efficient as a topical formulation for the administration of VH in a localized and systemic manner.

Keywords: choline-geranate; dermal delivery; ionogel; oleic acid; palmitic acid; pluronic F-127; vancomycin hydrochloride.

1

Chemical structures of VH, choline/OA (CO), choline/PA (CP), and choline geranate (CAGE).

2

Representative spectra for characterization of neat or mixture of choline-based enhancers using ¹H NMR spectroscopy (a), XRD (b), FT-IR spectroscopy (c), and DSC thermograms (d). CBcholine bicarbonate; GAgeranic acid; PApalmitic acid; OAoleic acid; CPcholine/palmitic acid; COcholine/oleic acid; CAGE-ILcholine geranate ionic liquid.

3

Measurement of TEWL and TEER in intact (a,b) and tape-stripped skin (c,d). Ex vivo skin permeation profile and retention of vancomycin across and within the intact (e,f) and tape-stripped skin (g,h). Values represent mean ± SD (n = 4). “*” denotes that the value is significantly different at p < 0.05 compared to all the other groups at 48 h. “$” denotes that the value is significantly different at p < 0.05 compared to all the other groups at 12 h. “&” denotes that the value is significantly different at p < 0.05 compared to the CP group at 48 h. “@” denotes that the value is significantly different at p < 0.05 compared to the CP group at 48 h. “#” denotes that the value is significantly different at p < 0.05 compared to all the other groups, except CP. COcholine/oleic acid; CPcholine/palmitic acid; CAGE-ILcholine geranate ionic liquid.

4

Digital images captured for the sol-to-gel transformation of VH + CAGE-P ionogel formulation (a). Representative powder X-ray diffractograms (b), DSC thermograms (c), and FT-IR spectra (d) of neat VH, Pluronic F-127, CAGE-P ionogel, and VH + CAGE-P ionogel. Scanning electron microscopic images captured for VH + CAGE-P gel formulation (e). The scale bar represents 100 μm.

5

Experimental set-up for the measurement of the contact angle of ionogel on the skin using a goniometer (a). Measurement of contact angle with time (b). Rheological analysis of VH + CAGE-P ionogel formulation. Storage (G′) and loss (G″) moduli were determined in amplitude (c) and temperature sweep (d) studies. Change in viscosity with the increase in temperature (e) and varying shear rate (f). Data represents a mean of 3–4 repetitions. Refer to Table for formulation composition.

6

In vitro release profile of VH from different formulations. Data represent mean ± SD (n = 3). “*” indicates that the value is significantly different at p < 0.05 compared to other groups at 48 h.

7

Measurement of TEWL and TEER in intact (a) and tape-stripped skin (b). Ex vivo skin permeation profile (c) and retention (d) of vancomycin across and within the intact and tape-stripped skin. Values represent mean ± SD (n = 4). “$” denotes that the TEWL value is significantly different at p < 0.05 compared to 0 and 2 h. “@” depicts that, at 48 h, the TEWL and TEER results differ significantly compared to all other groups at p < 0.05. “*” represents that the value is significantly different at p < 0.05 compared to the other groups.

8

SEM images showing surface morphology for intact SC and viable epidermis (VE) treated with different formulations at different time points. The left panel shows the neat SC and VE, with their respective control groups, treated with phosphate-buffered saline (PBS, pH 7.4) at 0 h. SEM images were captured for SC (a–d) and VE (i–l) treated at 2 h, and SC (e–h) and VE (m–p) treated at 12 h. The yellow arrow indicates the presence of cracks or wide pores on the surface, which were more prominent for the CAGE and CAGE-P gel-treated groups. The green line indicates the representative measurement of pore size in micrometers. The scale bar indicates 50 μm.

9

Representative DSC thermograms (a,b) and FT-IR spectra (c,d) of intact (SC), and tape-stripped skin (VE), respectively. Both SC and VE were treated with different formulations for 2 h (black line) and 12 h (blue line), respectively. For control, in both cases, SC and VE were treated with PBS, pH 7.4.

10

TEWL and LDF values for intact (a) and tape-stripped (b) skin treated with VH-loaded in CAGE and CAGE-P gel formulations after 2 h of application. “@” and “*” denote that the value for CAGE-IL and CAGE-P gel is significantly different at p < 0.05 compared to untreated intact skin. “#” denotes that the value for CAGE-IL is significantly different at p < 0.05 compared to untreated tape-stripped skin. Values are represented as mean ± SD; n = 4. CAGE-ILcholine geranate ionic liquid; CAGE-P gelcholine geranate Pluronic ionogel.

11

Representative digital images were captured for the shaved dorsal skin without furrows of SD rats (a), tape-stripping with 3M scotch tape for the removal of the SC (b), and morphological appearance of skin after tape-stripping (c). H&E-stained images were captured for the intact skin (d), and intact skin, applied with VH + CAGE (e) and VH + CAGE-P gel formulations (f). H&E-stained images were captured for the tape-stripped skin (g), and tape-stripped skin, applied with VH + CAGE (h) and VH + CAGE-P gel formulations (i). Measurement of TEWL and LDF after 14 days for the tape-stripped skin that was applied with VH + CAGE-P gel formulation. “*” indicates that the value for VH + CAGE-P gel is significantly different at p < 0.05 compared to the intact skin (j). H&E-stained images were captured for the tape-stripped skin applied with VH + CAGE-P gel formulation after 14 days (k). The scale bar indicates 100 μm.