Compact Magnetic Resonance Imaging Systems-Novel Cost-Effective Tools for Preclinical Drug Safety and Efficacy Evaluation

Pathology of Bioabsorbable Implants in Preclinical Studies

Bioabsorbable implants can be advantageous for certain surgical tissue bioengineering applications and implant-assisted tissue repair. They offer the obvious benefits of nonpermanence and eventual restoration of the native tissue’s biomechanical and immunological properties, while providing a structural scaffold for healing and a route for additional therapies (i.e., drug elution). They present unique developmental, imaging, and histopathological challenges in the conduct of preclinical animal studies and in interpretation of pathology data. The bioabsorption process is typically associated with a gradual decline (over months to years) in structural strength and integrity and may also be associated with cellular responses such as phagocytosis that may confound interpretation of efficacy and safety end points. Additionally, as these implants bioabsorb, they become increasingly difficult to isolate histologically and thus imaging modalities such as microCT become very valuable to determine the original location of the implants and to assess the remodeling response in tandem with histopathology. In this article, we will review different types of bioabsorbable implants and commonly used bioabsorbable materials; additionally, we will address some of the most common challenges and pitfalls confronting histologists and pathologists in collecting, handling, imaging, preparing tissues through histology, evaluating, and interpreting study data associated with bioabsorbable implants.

In Vivo Imaging With Confirmation by Histopathology for Increased Rigor and Reproducibility in Translational Research: A Review of Examples, Options, and Resources

Preclinical noninvasive imaging can be an indispensable tool for studying animal models of disease. In vivo imaging to assess anatomical, functional, and molecular features requires verification by a comparison to the macroscopic and microscopic morphological features, since all noninvasive in vivo imaging methods have much lower resolution than standard histopathology. Comprehensive pathological evaluation of the animal model is underutilized; yet, many institutions have veterinary or human pathologists with necessary comparative pathology expertise. By performing a rigorous comparison to gross or histopathology for image interpretation, these trained individuals can assist scientists with the development of the animal model, experimental design, and evaluation of the in vivo imaging data. These imaging and pathology corroboration studies undoubtedly increase scientific rigor and reproducibility in descriptive and hypothesis-driven research. A review of case examples including ultrasound, nuclear, optical, and MRI is provided to illustrate how a wide range of imaging modalities data can be confirmed by gross or microscopic pathology. This image confirmation and authentication will improve characterization of the model and may contribute to decreasing costs and number of animals used and to more rapid translation from preclinical animal model to the clinic.

Acute Histopathologic Findings Related to Needle Puncture Trauma during Subcutaneous Injection in the Sprague-Dawley Rat Model

It is important to detect injection site reactions during the nonclinical phases of drug development. However, differentiating between normal changes following needle trauma and changes due to the toxicity of injected drugs can be challenging. Therefore, we used the Sprague-Dawley rat model to evaluate the pathological findings expected following a single subcutaneous injection of normal saline. Rats were subcutaneously administered with normal saline, and the injection sites were examined microscopically. Inflammation was evident in most of the injection sites, mostly in minimal severity. Parakeratosis/epithelial crust was also seen in several sites, and necrosis was observed in a minority of the cases. These findings indicate that needle puncture trauma can present with some degree of inflammation and necrosis. Although limited to a specific time point and strain, this study shows that inflammation following subcutaneous injection can be attributed in part to the needle trauma and not necessarily to the drug itself.

Regulatory Forum Opinion Piece*: Imaging Applications in Toxicologic Pathology-Recommendations for Use in Regulated Nonclinical Toxicity Studies

Available imaging systems for use in preclinical toxicology studies increasingly show utility as important tools in the toxicologic pathologist's armamentarium, permit longitudinal evaluation of functional and morphological changes in tissues, and provide important information such as organ and lesion volume not obtained by conventional toxicology study parameters. Representative examples of practical imaging applications in toxicology research and preclinical studies are presented for ultrasound, positron emission tomography/single-photon emission computed tomography, optical, magnetic resonance imaging, and matrix-assisted laser desorption ionization-imaging mass spectrometry imaging. Some of the challenges for making imaging systems good laboratory practice-compliant for regulatory submission are presented. Use of imaging data on a case-by-case basis as part of safety evaluation in regulatory submissions is encouraged.