Novel in situ gelling vaginal sponges of sildenafil citrate-based cubosomes for uterine targeting

Abstract

Sildenafil citrate (SIL), a type 5-specific phosphodiesterase inhibitor, demonstrates valuable results in the management of infertility in women; however, the absence of vaginal dosage form in addition to the associated oral adverse effects minimize its clinical performance. The present study is concerned with SIL uterine targeting following intravaginal administration via optimization of cubosomal in situ gelling sponges (CIS). An emulsification method was employed for preparation of cubosomal dispersions incorporating glyceryl monooleate as a lipid phase and poloxamer 407 as a surfactant with or without polyvinyl alcohol as a stabilizer. Cubosomes were estimated regarding entrapment efficiency (EE%), particle size, and in vitro drug release. Chitosan (2% w/w) was incorporated into the optimum formulation and then lyophilized into small sponges. For the CIS, in vivo histopathological and pharmacokinetic studies were conducted on female Wistar rats and compared with intravaginal free SIL sponges (FIS) and oral SIL solution. SIL-loaded cubosomes showed EE% ranging between 32.15 and 72.01%, particle size in the range of 150.81-446.02 nm and sustained drug release over 8 h. Histopathological study revealed a significant enlargement in endometrial thickness with congestion and dilatation of endometrial blood vessels in intravaginal CIS compared to intravaginal FIS and oral-treated groups. The pharmacokinetic study demonstrated higher AUC_0-∞ and C_max with oral administration compared to intravaginal CIS or intravaginal FIS indicating potential involvement of first uterine pass effect after intravaginal administration. Finally, intravaginal CIS could be considered as a promising platform for SIL uterine targeting with minimized systemic exposure and side effects.

Keywords: Sildenafil citrate; cubosomes; in-situ gelling sponges; pharmacokinetic study; uterine targeting.

Figure 1.

Response surface plot for the effect of P-407 (X1) and PVA (X2) concentrations on (a) EE%, (b) particle size, (c) Q8h, and (d) desirability of the prepared cubosomal dispersions.

Figure 2.

Transmission electron micrograph of the optimized cubosomal formulation (OCF).

Figure 3.

Histopathological characteristics of uterus, ovary and vagina from different studied groups after two weeks of SIL treatment. Hematoxylin and Eosin (H & E) staining. a–d: uterus of female Wistar rats. Magnification ×100. (a) Uterus of normal group showing endometrium lined by simple columnar epithelium (S), normal endometrial gland (G) and blood vessels (arrow). (b) Uterus of rat in oral-treated group showing increased height of endometrial epithelium, activity of endometrial glands (arrow), and increased vascularity of uterus (Bv). (c) Uterus of rat in intravaginal CIS-treated group showing a massive increase in the endometrial epithelium (S), endometrial glands (G) and number of blood vessels as well as the blood flow (Bv). d- uterus of rat in intravaginal FIS-treated group showing the endometrial epithelium (S) and endometrial glands (G) similar to normal group with minor increase in number of blood vessels (arrow). (e–h): uterus of female Wistar rats. Periodic acid Schiff (PAS) staining. Magnification ×100. (e) Uterus of normal group showing moderate reaction in the endometrial glands (arrow). (f) Uterus of rat in oral-treated group showing increased activity of endometrial glands (arrow). Note, increased vascularity of uterus (Bv). (g) Uterus of rat in intravaginal CIS-treated group showing a massive increase in the endometrial vascularity (Bv). Note, strong reaction in the endometrial glands (arrow). (h) Uterus of rat in intravaginal FIS-treated group showing normal endometrial vascularity (Bv) with moderate reaction in the endometrial glands (arrow). (i–l) Ovary of female Wistar rats. Magnification ×100. (i) Ovary of rat in normal group showing normal ovarian tissue with growing follicles (F) and normal ovarian blood vessels (Bv). (j) Ovary of rat in oral-treated group showing increased vascularity of ovarian tissue (Bv) and growing follicles (F). (k) Ovary of rat in intravaginal CIS-treated group showing a massive increase in the ovarian tissue vascularity (Bv) and growing follicles (F). (l) Ovary of rat in intravaginal FIS-treated group showing a slight increase in the ovarian tissue vascularity (Bv) and growing follicles (F). (m–p): Vagina of female Wistar rats. (m) Vagina of normal group showing normal vaginal epithelium (stratified squamous epithelium less keratinized (S)) and normal vaginal blood vessels (arrow). (n) Vagina of oral-treated group showing increased height of vaginal epithelium (S) and increased vascularity of vaginal tissue (arrow). (o)- vagina of intravaginal CIS-treated group showing a massive increase in height of vaginal epithelium (S) and increased vascularity of vaginal tissue (Bv). (p) Vagina of rat in intravaginal FIS-treated group showing increased height of vaginal epithelium (S) and minor changes in vascularity of vaginal tissue (arrow).