Intravaginal Toxicity Studies of a Gel-Microemulsion Formulation of Spermicidal Vanadocenes in Rabbits

Abstract

Bis-cyclopentadienyl complexes of vanadium(IV) or vanadocenes are rapid and potent inhibitors of human sperm motility with potential as a new class of contraceptive agents. We investigated the toxicity potential of intravaginally administered gel-microemulsion formulation of two representative vanadocenes, vanadocene acetylacetonato monotriflate (VDACAC) and vanadocene dithiocarbamate (VDDTC), in the rabbit model. New Zealand White rabbits in subgroups of three were exposed intravaginally to a gel-microemulsion with and without 0.1 or 0.25% VDACAC and VDDTC for 10 consecutive days. The doses of vanadocenes used were nearly 500- to 1250-fold and 2000- to 5000-fold higher than their respective in vitro spermicidal EC50 values. Animals were euthanized on day 11 and vaginal tissues were evaluated for local toxicity by histopathology, cell proliferating activity by immunohistochemical detection of proliferating cell nuclear antigen (PCNA), and in situ apoptosis by the terminal deoxynucleotidyl transferase-mediated FITC-deoxyuridine triphosphate nick end-labeling (TUNEL) assay and confocal laser scanning microscopy (CLSM). Blood was analyzed for clinical chemistry profiles. Vanadium content in selected organs and body fluids was determined by atomic absorption spectroscopy. None of the rabbits given 0.1% VDACAC and VDDTC intravaginally developed epithelial ulceration, edema, leukocyte influx, or vascular congestion characteristic of inflammation. Only minimal to moderate irritation was observed at 0.25% VDACAC and VDDTC. A significant decrease in epithelial and stromal PCNA expression was observed in the 0.25% dose group. However, TUNEL assay and CLSM revealed no staining in the vaginal epithelium and only minimal nonspecific staining in the stroma. Repetitive intravaginal application of 0.1 or 0.25% VDACAC and VDDTC had no adverse effects on clinical chemistry profiles. Vanadium was not incorporated into rabbit tissues and body fluids at levels above 1 μg/g. Thus, intravaginal administration of VDACAC and VDDTC at concentrations nearly 500 and 2000 times higher than their respective in vitro spermicidal EC50 values did not induce marked vaginal irritation, mucosal toxicity, or systemic absorption of vanadium in the rabbit model. The lack of significant mucosal or systemic toxicity of intravaginal vanadocenes observed may have particular clinical utility as a new class of contraceptive agents.