Scientific and Regulatory Policy Committee Best Practices: Recommended ("Best") Practices for Informed (Non-blinded) Versus Masked (Blinded) Microscopic Evaluation in Animal Toxicity Studies

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.

Inhibition of endothelin A receptor by a novel, selective receptor antagonist enhances morphine-induced analgesia: Possible functional interaction of dimerized endothelin A and μ-opioid receptors

BACKGROUND

The misuse of opioids has led to an epidemic in recent times. The endothelin A receptor (ETAR) has recently attracted attention as a novel therapeutic target to enhance opioid analgesia. We hypothesized that endothelin A receptors may affect pain mechanisms by heterodimerization with μ opioid receptors. We examined the mechanisms of ETAR-mediated pain and the potential therapeutic effects of an ETAR antagonist, Compound-E, as an agent for analgesia.

METHODS

Real-time in vitro effect of Compound-E on morphine response was assessed in HEK293 cells expressing both endothelin A and μ opioid receptors through CellKey™ and cADDis cAMP assays. Endothelin A/μ opioid receptor dimerization was assessed by immunoprecipitation and live cell imaging. The in vivo effect of Compound-E was evaluated using a morphine analgesia mouse model that observed escape response behavior, body temperature, and locomotor activity.

RESULTS

In CellKey™ and cAMP assays, pretreatment of cells with endothelin-1 attenuated morphine-induced responses. These responses were improved by Compound-E, but not by BQ-123 nor by bosentan, an ETAR and endothelin B receptor antagonist. Dimerization of ETARs and μ opioid receptors was confirmed by Western blot and total internal reflection fluorescence microscopy in live cells. In vivo, Compound-E potentiated and prolonged the analgesic effects of morphine, enhanced hypothermia, and increased locomotor activity compared to morphine alone.

CONCLUSION

The results suggest that attenuation by endothelin-1 of morphine analgesia may be caused by dimerization of Endothelin A/μ opioid receptors. The novel ETAR antagonist Compound-E could be an effective adjunct to reduce opioid use.

Opinion on Current Use of Non-Blinded Versus Blinded Histopathologic Evaluation in Animal Toxicity Studies

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].

Histopathologic Characterization of Mifepristone-induced Ovarian Toxicity in Cynomolgus Monkeys

Mifepristone, which is an orally active synthetic steroid with antiprogesterone activity, is known as an ovarian toxicant. Because the available data regarding the histopathologic characteristics of ovarian toxicity in nonhuman primates are limited, the present study was undertaken in order to investigate detailed histopathologic changes accompanying mifepristone-induced ovarian toxicity and its relationship to changes in menstrual cycle and circulating sex steroid hormone. Twenty mg/kg of mifepristone was orally administered daily to 4 cynomolgus monkeys for 2 months. Mifepristone inhibited the cyclic increases in circulating estradiol-17β and progesterone levels with associated absence of menstruation. Histopathologically, the ovary in the treated animals showed follicular phase without changes in the percentage of atretic antral follicles, and reduced endometrial thickness was noted in the uterus. These changes indicated that a certain degree of antral follicle development had been retained in spite of the menstrual cycle having been arrested in mifepristone-treated animals. Our investigation suggested that it is important to perform detailed histopathologic examination of reproductive organs with precise knowledge of the characteristics of each menstrual stage to detect ovarian toxicity in nonhuman primates. Monitoring menstrual signs and circulating sex steroid hormone levels provides additional evidence for the investigation of the mechanism of ovarian toxicity.

The effects of ethylene glycol monomethyl ether on female reproductive system in juvenile rats

Ethylene glycol monomethyl ether (EGME), which is widely used in various industrial products, is known for adverse effects on the reproductive system in adult rats. However, the effects of EGME on reproductive development in juvenile rats have not been demonstrated. In order to investigate the effects of EGME on the female reproductive system and pubertal development in juvenile rats, EGME was administered to female Sprague Dawley rats from postnatal day 21 to 41 at a dose level of 0, 50, 100, or 300 mg/kg. The animals were examined for general condition, body weight, vaginal opening (VO), estrous cyclicity, and histopathology of reproductive organs. EGME treatment resulted in a prolonged estrous cycle interval characterized by persistent diestrus at 50 mg/kg without effects on body weight, timing of VO, or histology of the reproductive organs. EGME at 100 mg/kg induced decreases in body weight gain, a delay of VO, and irregular estrous cycle with absence of corpora lutea and hypertrophy of uterine epithelium indicating disturbance of the ovulatory process associated with hormonal effect. At 300 mg/kg, there was significant delay of puberty due to severe growth retardation. The present results revealed that irregular estrous cycle is a first indicator of the effects of EGME on the female reproductive system in juvenile rats, with delayed pubertal onset and ovulatory process disturbance at a higher dose.

Wif1 and Ifitm3 gene expression preferentially altered in the colon mucosa of benzo[a]pyrene pre-treated mice following exposure to dextran sulfate sodium

Benzo[a]pyrene (BP) is highly mutagenic and yet does not lead to tumor development in the murine colon. We recently reported the generation of colonic tumors one week after treatment with BP followed by dextran sulfate sodium (DSS), a colitis-inducer. In this BP/DSS model, male CD2F1 mice were treated orally with BP at 125 mg/kg/day for 5 days, followed by 4% DSS in drinking water for one week. There has been no report so far on the molecular mechanisms involved in tumor development in this model. In the present study, we performed global gene expression analysis on the colonic mucosae obtained from BP-exposed mice one week after treatment with DSS and those treated with the vehicle, BP, or DSS alone. Global gene expression analysis revealed that there were 563 genes preferentially altered (≥2-fold vs vehicle group) in the colonic mucosae exposed to both BP and DSS. Furthermore, comparative gene expression analysis combined with Ingenuity Pathway Analysis™ identified 2 genes associated with Wnt/β-catenin signaling pathway that were preferentially up-regulated (≥2-fold vs vehicle group) when BP and DSS were treated in combination in the distal part (site of predilection for tumor induction) of the colonic mucosae, especially in colonic tumors: WNT inhibitory factor 1 (Wif1; 14.6-fold increase) and interferon induced membrane protein 3 (Ifitm3; 5.7-fold increase). In colonic tumors, expression of Wif1 and Ifitm3 proteins were both confirmed by western blot analysis. These findings suggest that these genes are associated with rapid induction of colonic tumors in mice after exposure to BP/DSS, providing insights into the mechanisms of the BP/DSS short-term colon carcinogenesis.

Oscillatory potentials in electroretinogram as an early marker of visual abnormalities in vitamin A deficiency

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.

Brunner's gland lesions in rats induced by a vascular endothelial growth factor receptor inhibitor

Vascular endothelial growth factor (VEGF) receptor tyrosine kinase (RTK) inhibitors are reported to cause reversible mucosal hyperplasia (adenosis) in the duodenum of rats; however, the pathogenesis is not fully elucidated. Using lenvatinib, a VEGF RTK inhibitor, we characterized the histologic time course of this duodenal change in rats. At 4 weeks, there was degeneration and necrosis of Brunner's gland epithelium accompanied by neutrophil infiltration around the affected glands. At 13 weeks, the inflammation was more extensive, and Brunner's gland epithelium was attenuated and flattened and was accompanied by reactive hyperplasia of duodenal epithelium. At 26 weeks, the changes became more severe and chronic and characterized by marked cystic dilation, which extended to the external muscular layer. These dilated glands exhibited morphological characteristics of duodenal crypt epithelium, suggestive of replacement of disappeared Brunner's glands by regenerative duodenal crypt epithelial cells. Similar changes were not present in similar time course studies in dog and monkey studies, suggesting that this is a rodent- or species-specific change. Based on the temporal progression of Brunner's gland lesion, we identify degeneration and necrosis of the Brunner's glands as the primary change leading to inflammation, cystic dilatation, and regeneration with cells that are morphologically suggestive of duodenal crypt epithelium.

Granulomatous nephritis consistent with malakoplakia in a cynomolgus monkey

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.