E2012, a gamma secretase modulator without affecting Notch processing, aimed at Alzheimer's disease by reduction of amyloid β-42, induced cataract following repeated doses in the rat. Cataract appeared first at week 10-11 of treatment as a posterior subcapsular area with granular/punctate opaque or shiny dots along the suture line, characterized histologically as lenticular fiber degeneration, which eventually coalesced to form a triangular or circular opacity. It was associated with prolonged and sustained elevation of lenticular desmosterol (24-dehydrocholesterol), the final precursor of cholesterol, and decrease in lenticular cholesterol. In vitro studies to investigate the effect of E2012 on cholesterol metabolism demonstrated that E2012 inhibits 3β-hydroxysterol Δ24-reductase (DHCR24) at the final step in the cholesterol biosynthesis. In vivo lenticular concentration of E2012 after 13-week repeated dose with cataract was well above those where inhibition was observed in vitro. There was no cataract formation at doses where desmosterol did not accumulate in the lens. The elevation of desmosterol and decreased cholesterol levels were also seen in the liver and plasma and preceded those in the lens. These results demonstrate that E2012 induces cataract in the rat by inhibiting DHCR24 at the final step of cholesterol synthesis with associated elevation in desmosterol within the lens, preceded by desmosterol changes that would serve as a predictive safety biomarker for lenticular opacity.

The Society of Toxicologic Pathology (STP) explored current institutional practices for selecting between non-blinded versus blinded histopathologic evaluation during Good Laboratory Practice (GLP)-compliant, regulatory-type animal toxicity studies using a multi-question survey and STP-wide discussion (held at the 2019 STP annual meeting). Survey responses were received from 107 individuals representing 83 institutions that collectively employ 589 toxicologic pathologists. Most responses came from industry (N = 46, mainly biopharmaceutical or contract research organizations) and consultants (N = 24). For GLP-compliant animal toxicity studies, histopathologic evaluation usually involves initial (primary) non-blinded analysis, with post hoc informal blinded re-examination at the study pathologist’s discretion to confirm subtle findings or establish thresholds. Initial blinded histopathologic evaluation sometimes is chosen by study pathologists to test formal hypotheses and/or by sponsors to address non-pathologist expectations about histopathology data objectivity. Current practice is that a blinded histopathologic evaluation is documented only if formal blinding (ie, using slides with coded labels) is employed, using simple statements without detailed methodology in the study protocol (or an amendment) and/or pathology report. Blinding is not an appropriate strategy for the initial histopathologic evaluation performed during pathology peer reviews of GLP-compliant animal toxicity studies. [Box: see text]

Malakoplakia is a rare form of chronic granulomatous inflammation in mammals, and usually affects the urinary tract in humans. In this report, we present a case of granulomatous nephritis consistent with malakoplakia in a 4-year-old male cynomolgus monkey. Gross examination showed that the kidney was markedly enlarged and adhered to the surrounding organs. Histology showed that there was diffuse interstitial infiltration of histiocytes with abundant foamy eosinophilic cytoplasm resembling von Hansemann cells, PAS-positive granular cytoplasm and occasional PAS- and iron-positive intracellular small inclusion bodies. Electron microscopy showed that these histiocytes contained abundant lysosomes and phagolysosomes but no obvious Michaelis-Gutmann bodies. Based on these findings, a diagnosis of granulomatous nephritis consistent with early malakoplakia was made. This is the first report in a monkey of a renal lesion consistent with malakoplakia.

Abstract. Vitamin A deficiency (VAD) caused by malnutrition and certain intestinal diseases induces visual impairments, including night blindness and photoreceptor cell dysfunction as indicated by reduced a-and b-waves in an electroretinogram (ERG). The effects of VAD on the inner retinal layer cells, including amacrine and ganglion cells, remain to be elucidated. The functions of these cells are reflected in oscillatory potentials (OPs), another component of the ERG. The present study investigated inner retinal layer cell function in VAD rats by analyzing OPs. In the present study, VAD was induced by feeding Brown Norway rats a vitamin A deficient diet for 10 weeks. A reduced body weight and peri-papillary opacification indicative of papilledema without histopathological alterations were observed, which are considered early symptoms of VAD. At this stage, the ERG revealed reduced OPs as well as a-and b-waves at various intensities of light stimulation. Further analysis indicated that the ratio of the alterations in OPs was more significant than those of a-and b-waves. After 5 weeks of recovery, these changes returned to control levels. These results suggest that OPs are the most sensitive and early marker of VAD-associated visual impairment in the ERG. IntroductionRetinoids, derivatives of vitamin A (Vit A), have essential roles in visual phototransduction. In the initial step of visual phototransduction, conversion of 11-cis retinal to all-trans (AT) retinal occurs in photoreceptor cells subjected to light exposure. Vitamin A deficiency (VAD) reduces this activity and subsequent downstream reactions in photoreceptor cells. As a result, patients with VAD exhibit visual abnormalities, including abnormal dark adaptation and night blindness, which may eventually progress to a severe visual impairment (1-3). Consistent with these clinical symptoms, electroretinogram (ERG) recordings in humans with VAD show decreases in amplitudes or loss of a-and b-waves, which reflect the function of photoreceptor and bipolar cells, respectively (1,3). A previous study reported that a reduced a-wave and a partial reduction of b-wave are induced by feeding albino rats a Vit A deficient diet for 8 weeks, with disintegration of the outer segments of photoreceptor cells (4). In contrast to the established effects of VAD on the a-and b-waves in ERG and histological alterations in photoreceptors, the effects of VAD on oscillatory potentials (OPs) remain to be elucidated. OPs, which are components of the ERG, are considered to be generated by the inner retinal layer cells, including amacrine and ganglion cells (5) and the reduction of OPs is known to be associated with reduced contrast sensitivity in diabetic patients (6). VAD has also been reported to reduce contrast sensitivity (7). Therefore, although, to the best of our knowledge, there are no studies indicating that VAD directly affects the formation of OPs or the function of inner retinal layer cells, it was hypothesized that OPs in ERG recordings may be affected during a state of ...

This article describes the Society of Toxicologic Pathology’s (STP) five recommended (“best”) practices for appropriate use of informed (non-blinded) versus masked (blinded) microscopic evaluation in animal toxicity studies intended for regulatory review. (1) Informed microscopic evaluation is the default approach for animal toxicity studies. (2) Masked microscopic evaluation has merit for confirming preliminary diagnoses for target organs and/or defining thresholds (“no observed adverse effect level” and similar values) identified during an initial informed evaluation, addressing focused hypotheses, or satisfying guidance or requests from regulatory agencies. (3) If used as the approach for an animal toxicity study to investigate a specific research question, masking of the initial microscopic evaluation should be limited to withholding only information about the group (control or test article-treated) and dose equivalents. (4) The decision regarding whether or not to perform a masked microscopic evaluation is best made by a toxicologic pathologist with relevant experience. (5) Pathology peer review, performed to verify the microscopic diagnoses and interpretations by the study pathologist, should use an informed evaluation approach. The STP maintains that implementing these five best practices has and will continue to consistently deliver robust microscopic data with high sensitivity for animal toxicity studies intended for regulatory review. Consequently, when conducting animal toxicity studies, the advantages of informed microscopic evaluation for maximizing sensitivity outweigh the perceived advantages of minimizing bias through masked microscopic examination.