Optical coherence tomography for assessment of microbicide safety in a small animal model

Abstract

Sensitive imaging techniques for small animals are needed to assess drug toxicity in preclinical studies. Optical coherence tomography (OCT) provides a noninvasive tool for high-resolution, depth-resolved visualization of drug-induced changes in tissue morphology. In a mouse model, we utilize OCT to assess vaginal tissue integrity following the application of topical microbicides (drugs used to prevent infection). Mice are challenged with herpes simplex virus-2 (HSV-2) to determine the correlation of tissue damage as quantified by OCT to increased susceptibility. The microbicide benzalkonium chloride (BZK) (0.02, 0.2, or 2%) or phosphate buffered saline control is administered intravaginally. In vivo OCT imaging and collection of tissue samples are performed after treatment. A quantitative OCT scoring system is applied to assess epithelial damage, and the results are compared with those of histology. A separate group of mice are treated similarly then challenged with HSV-2. Epithelial morphology quantified noninvasively by OCT and histology are dose-dependent (p<0.0001). The OCT scoring system detected a significant increase in epithelial damage with increasing BZK concentration (p<0.0001). These results paralleled an increase in HSV-2 susceptibility (p<0.005). OCT can be used as a noninvasive tool to assess topical drug toxicity in a small animal model with potential to predict increased susceptibility to vaginal infection.

Colposcopic imaging using visible-light optical coherence tomography

“…3,6 Vincent et al 4 detected N-9-induced vaginal epithelial thinning and injury in human subjects from OCT B-scans, which could not otherwise be identified by conventional colposcopy. More recently, Bell et al 16 applied fiber-based endoscopic OCT to safe assessment of vaginal microbicide, which involved measurement of epithelial and stromal thicknesses of mouse vagina.…”

“…First, the imaging systems only achieved moderate resolution. Both axial and lateral resolutions were tens of micrometers, 3,4,6,16 which may not be ideal to resolve the mucosal and epithelial interface clearly and to evaluate epithelial integrity. Second, the imaging systems only provided cross-sectional B-scans of vaginal epithelial morphology.…”

In Vivo Rectal Mucosal Barrier Function Imaging in a Large-Animal Model by Using Confocal Endomicroscopy: Implications for Injury Assessment and Use in HIV Prevention Studies

“…5) indicated that this protective layer was affected. An interesting finding was that injury could be induced using even the very low concentration of 0.01%, a dose several times smaller than found in many products and one which is much smaller than doses found to result in partial denuding of the superficial vaginal epithelium (33)(34)(35). This is likely due to the fact the rectal epithelium only comprises a single layer of columnar cells.…”

“…The effects of BZK on epithelium are known (32)(33)(34)(35). Since BZK results in superficial denuding of epithelium, it provided a means to induce structural injury similar to that expected with either mechanical or chemical injury.…”

“…Localized injury to the rectal mucosa was accomplished through topical application of BZK, an agent that has been used in contraceptive gels and lubricants (28,29), as a topical antimicrobial in the vagina (30), and as a positive control in microbicide safety studies (31)(32)(33); it is known to result in epithelial disruption in a predictable manner with concentrations in the range of 0.02 to 2% in previous studies (24,34,35). A 16-in.…”