Hemangiosarcoma in rodents: mode-of-action evaluation and human relevance

Although rarely occurring in humans, hemangiosarcomas (HS) have become important in evaluating the potential human risk of several chemicals, including industrial, agricultural, and pharmaceutical agents. Spontaneous HS arise frequently in mice, less commonly in rats, and frequently in numerous breeds of dogs. This review explores knowledge gaps and uncertainties related to the mode of action (MOA) for the induction of HS in rodents, and evaluates the potential relevance for human risk. For genotoxic chemicals (vinyl chloride and thorotrast), significant information is available concerning the MOA. In contrast, numerous chemicals produce HS in rodents by nongenotoxic, proliferative mechanisms. An overall framework is presented, including direct and indirect actions on endothelial cells, paracrine effects in local tissues, activation of bone marrow endothelial precursor cells, and tissue hypoxia. Numerous obstacles are identified in investigations into the MOA for mouse HS and the relevance of the mouse tumors to humans, including lack of identifiable precursor lesions, usually late occurrence of the tumors, and complexities of endothelial biology. This review proposes a working MOA for HS induced by nongenotoxic compounds that can guide future research in this area. Importantly, a common MOA appears to exist for the nongenotoxic induction of HS, where there appears to be a convergence of multiple initiating events (e.g., hemolysis, decreased respiration, adipocyte growth) leading to either dysregulated angiogenesis and/or erythropoiesis that results from hypoxia and macrophage activation. These later events lead to the release of angiogenic growth factors and cytokines that stimulate endothelial cell proliferation, which, if sustained, provide the milieu that can lead to HS formation.

Nonproliferative and Proliferative Lesions of the Rat and Mouse Endocrine System

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.asp) is a joint initiative among the Societies of Toxicological Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the endocrine organs (pituitary gland, pineal gland, thyroid gland, parathyroid glands, adrenal glands and pancreatic islets) of laboratory rats and mice, with color photomicrographs illustrating examples of the lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for endocrine lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Diet can prevent diabetes in the BB rat

When compared with laboratory chow, a defined, semipurified diet prevented diabetes, reduced the frequency of insulitis, increased thymus weight and total white blood cell count, and doubled thymus T-helper/T-suppressor cell ratios in diabetes-prone BB rats. These data show that the diabetic syndrome in BB rats may be prevented or delayed by changes in diet, which may occur through alteration of pathogenic defects in the immune system.

Sialodacryoadenitis virus-associated lesions in the lower respiratory tract of rats

Eight- to 10-week-old outbred Wistar rats were inoculated intranasally with 10(2.9) medium mouse lethal infective doses of sialodacryoadenitis (SDA) virus. Sham inoculated control rats and challenged rats were killed at 1 day intervals for the first 8 days, then on days 10, 12, 14, and 20. Typical lesions associated with SDA were seen microscopically in the salivary and lacrimal glands of inoculated rats. In addition, laryngitis, tracheitis, bronchitis, bronchiolitis, and multifocal alveolitis were present during the acute stages of the disease. Viral antigen was demonstrated in epithelial cells lining airways by immunofluorescence microscopy. SDA virus was recovered from the lower respiratory tract from days 2 to 6 post-inoculation (PI). Serum antibodies to SDA virus, but not to Sendai virus or Mycoplasma pulmonis were present in rats tested at day 20 PI. These findings demonstrate that during the acute stages of the disease, significant lesions do occur in the lower respiratory tract of SDA virus-infected rats.

Depletion of salivary gland epidermal growth factor by sialodacryoadenitis virus infection in the Wistar rat

Male and female Wistar rats 2 to 15 months of age were inoculated intranasally with sialoda-cryoadenitis (SDA) virus and killed at 8 to 21 days post-inoculation (PI). Submandibular glands were evaluated by light and electron microscopy, and levels of salivary gland epidermal growth factor (EGF) were quantitated by cytochemistry and competitive radioreceptor assay. Apical granules in the epithelial cells of the granular convoluted tubules (GCT) were selectively depleted during the acute and convalescent stages of the disease. In addition, levels of immunoreactive EGF were reduced in affected submandibular glands, especially at 8 to 14 days PI with SDA virus, but some evidence of EGF depletion was seen at up to 3 weeks PI. A corresponding transient depletion of EGF receptor reactive salivary EGF was seen between 1 and 3 weeks after experimental SDA infection. These studies suggest that a clinical (or subclinical) infection with SDA virus could have significant effects on experimental studies on EGF-dependent functions, including reproductive physiology and carcinogenesis.

Hyaline glomerulopathy in B6C3F1 mice

Hyaline glomerulopathy is a spontaneous disease of undetermined etiology that occurs sporadically in various strains of aging mice. In our laboratory, this disease was observed with unusual ultrastructural features as an incidental finding in 2 female B6C3F1 mice from 2 carcinogenicity bioassays. Microscopically, renal lesions were characterized by marked diffuse enlargement and prominent hyalinization of the glomeruli, equally affecting both kidneys. Affected glomeruli were PAS positive, but were negative for amyloid by the Congo red method. Immunocytochemical staining revealed weakly positive glomerular deposits with polyclonal anti-mouse IgG-IgM-IgA cocktail. Ultrastructurally, there were characteristic subendothelial osmiophilic deposits composed of loosely-packed linear structures in the glomeruli. Lamellae, which appeared as fibrils in perpendicular sections, were relatively uniform, measured 6.1-17.01 nm in diameter, and formed single or double-layered structures. The ultrastructural and immunocytochemical characteristics are suggestive of a spontaneous immune-mediated mechanism in a strain of mouse commonly used in toxicology studies.

Spontaneous fibro-osseous proliferative lesions in the sternums and femurs of B6C3F1 mice

Bone morphology associated with fibro-osseous proliferation in the femurs and sternums of 98 female B6C3F1 mice were compared morphologically and quantitatively to femurs and sternums from 100 male B6C3F1 and 79 CF1 mice (48 female and 31 male). In addition, sternal samples from five B6C3F1 mice per sex were collected and processed for electron microscopy. Fibro-osseous proliferation was present in female B6C3F1 mice, but not male B6C3F1 or female CF1 mice. In female B6C3F1 mice at 32 weeks of age, the marrow spaces in the region of the proximal and distal epiphyseal plate were lined by large osteoblasts and had large vascularized centers. At 58 weeks, metaphyseal fibrovascular proliferative areas containing multinucleated cells and new cancellous bone delineating the lesion were seen. At 84 weeks, fibro-osseous tissue occupied the outer third of the sternal marrow cavity and by 110 weeks, more than two thirds of the marrow cavity. Fibro-osseous proliferation was present in 100 and 94% of the examined sternums and femurs, respectively, of female B6C3F1 mice at 110 weeks of age, but not in male B6C3F1 or female CF1 mice. Ultrastructural examination of the sternal changes at 110 weeks showed numerous osteoblasts, irregular bony spicules, and fibrocyte-like cells. By morphometry, the normal marrow cavity in B6C3F1 females occupied 35% of a longitudinal section of the whole sternebra compared with 70% and 75% of the whole sternebra in B6C3F1 males and CF1 female, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

An outbreak of schistosomiasis in Atlantic brant geese, Branta bernicla hrota

A heavy infection with schistosomes of the genera Trichobilharzia and Dendritobilharzia was considered the cause of 90% mortality in a group of 40 wild-caught Atlantic brant geese (Branta bernicla hrota) that were maintained in captivity on a fresh-water pond in Aurora, Ontario. Numerous adult worms and eggs were disseminated in many organs throughout the body of all birds examined. The main pathological findings, attributed to both eggs and adults, included emaciation, thrombosis of the caudal mesenteric vein and its branches, fibrinohemorrhagic colitis, and in some birds, heptomegaly. Translocation of brant geese from their natural marine environment to a fresh-water pond may have caused them to be exposed to parasites which they would not normally encounter.

Intranasal nanoemulsion-based inactivated respiratory syncytial virus vaccines protect against viral challenge in cotton rats

Respiratory Syncytial Virus is a leading cause of bronchiolitis and pneumonia in infants, the elderly and individuals with compromised immune systems. Despite decades of research, there is currently no available vaccine for RSV. Our group has previously demonstrated that intranasal immunization of mice with RSV inactivated by and adjuvanted with W805EC nanoemulsion elicits robust humoral and cellular immune responses, resulting in protection against RSV infection. This protection was achieved without the induction of airway hyper-reactivity or a Th2-skewed immune response. The cotton rat Sigmodon hispidus has been used for years as an excellent small animal model of RSV disease. Thus, we extended these rodent studies to the more permissive cotton rat model. Intranasal immunization of the nanoemulsion-adjuvanted RSV vaccines induced high antibody titers and a robust Th1-skewed cellular response. Importantly, vaccination provided sterilizing cross-protective immunity against a heterologous RSV challenge and did not induce marked or severe histological effects or eosinophilia in the lung after viral challenge. Overall, these data demonstrate that nanoemulsion-formulated whole RSV vaccines are both safe and effective for immunization in multiple animal models.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Minipig

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the minipig used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Tyzzer's disease as a complication of canine distemper in a raccoon

Intercurrent canine distemper and Tyzzer's disease were diagnosed in a mature raccoon (Procyon lotor) submitted for necropsy. Clinical, gross and microscopic findings characteristic of canine distemper virus (CDV), included ataxia, dyspnea, suppurative conjunctivitis, interstitial pneumonitis and generalized lymphocytolysis. Inclusion bodies typical of CDV infection were present in many epithelial tissues. Acute multifocal hepatic necrosis and acute segmental necrotizing enteritis were attributed to the presence of Bacillus piliformis organisms in these lesions, confirmed by special stains and electron microscopy. This is apparently the first reported case of Tyzzer's disease in a raccoon.

Sequential changes in the harderian and exorbital lacrimal glands in Wistar rats infected with sialodacryoadenitis virus

A sequential light and electron microscopic study of the exorbital and Harderian lacrimal glands was done on 2.5- to 15-month-old Wistar rats exposed to sialodacryoadenitis (SDA) virus. Typical coronaviral particles were readily demonstrated in cytoplasmic vesicles of Harderian and exorbital glands examined at 6 days post-inoculation. Lesions were seen in a relatively high percentage of lacrimal glands in infected animals of all ages, with no obvious age-related variations in the incidence and extent of changes. Lesions frequently persisted for a longer interval post-exposure in lacrimal glands than in salivary glands. The persistence of lesions commonly seen in Harderian glands was attributed, at least in part, to the cytotoxic effects of porphyrin-containing secretions released during the acute necrotizing stages of the disease. The persistence of lesions in some lacrimal glands indicates that they are useful tissues for microscopic examination for the retrospective provisional diagnosis of SDA. Persistent lesions also indicate that normal functions of these glands may be compromised for up to several weeks following outbreaks of SDA.

Hemangiosarcoma in mice administered pregabalin: analysis of genotoxicity, tumor incidence, and tumor genetics

Pregabalin, (S)-3-(aminomethyl)-5-methylhexanoic acid, binds with high affinity to the α(2)δ subunit of voltage-gated calcium channels and exerts analgesic, anxiolytic, and antiseizure activities. Two-year carcinogenicity studies were completed in B6C3F1 and CD-1 mice and two separate studies in Wistar rats. Doses in mice were 200, 1000, and 5000 mg/kg/day, with systemic exposures (AUC(0-24 h)) up to 31 times the mean exposure in humans, given the maximum recommended clinical dose. In rats, doses were 50, 150, and 450 mg/kg/day in males and 100, 300, and 900 mg/kg/day in females; systemic exposures up to 24 times were achieved in clinical trials. In both strains of mice, pregabalin treatment was associated with an increased incidence of hemangiosarcoma primarily in liver, spleen, and bone marrow. The incidence of hemangiosarcoma was higher in B6C3F1 mice than in CD-1 mice, consistent with its spontaneous incidence. Pregabalin did not increase the incidence of any other tumor type in rats and was not genotoxic, based on an extensive battery of in vivo and in vitro tests in bacterial and mammalian systems. Thus, pregabalin is a single-species, single tumor-type, nongenotoxic mouse carcinogen. Hemangiosarcomas occurring in mice treated with pregabalin were genotypically distinct from hemangiosarcomas induced by genotoxic carcinogens in humans with respect to ras and p53 mutation patterns and were similar to spontaneous tumors. Furthermore, there was a strong association between pregabalin treatment and bone marrow changes in these studies in mice, suggesting a possible link between the effects observed in bone marrow and the increase in tumor incidence in pregabalin-treated mice.

Mode of action associated with development of hemangiosarcoma in mice given pregabalin and assessment of human relevance

Pregabalin increased the incidence of hemangiosarcomas in carcinogenicity studies of 2-year mice but was not tumorigenic in rats. Serum bicarbonate increased within 24 h of pregabalin administration in mice and rats. Rats compensated appropriately, but mice developed metabolic alkalosis and increased blood pH. Local tissue hypoxia and increased endothelial cell proliferation were also confirmed in mice alone. The combination of hypoxia and sustained increases in endothelial cell proliferation, angiogenic growth factors, dysregulated erythropoiesis, and macrophage activation is proposed as the key event in the mode of action (MOA) for hemangiosarcoma formation. Hemangiosarcomas occur spontaneously in untreated control mice but occur only rarely in humans. The International Programme on Chemical Safety and International Life Sciences Institute developed a Human Relevance Framework (HRF) analysis whereby presence or absence of key events can be used to assess human relevance. The HRF combines the MOA with an assessment of biologic plausibility in humans to assess human relevance. This manuscript compares the proposed MOA with Hill criteria, a component of the HRF, for strength, consistency, specificity, temporality, and dose response, with an assessment of key biomarkers in humans, species differences in response to disease conditions, and spontaneous incidence of hemangiosarcoma to evaluate human relevance. Lack of key biomarker events in the MOA in rats, monkeys, and humans supports a species-specific process and demonstrates that the tumor findings in mice are not relevant to humans at the clinical dose of pregabalin. Based on this collective dataset, clinical use of pregabalin would not pose an increased risk for hemangiosarcoma to humans.

Key components of the mode of action for hemangiosarcoma induction in pregabalin-treated mice: evidence of increased bicarbonate, dysregulated erythropoiesis, macrophage activation, and increased angiogenic growth factors in mice but not in rats

In carcinogenicity studies, pregabalin increased hemangiosarcoma incidence in mice but not in rats. Investigative studies, ranging in length from 24 h to 12 months, were conducted in mice (1000 or 5000 mg/kg) and rats (900 mg/kg) to evaluate a potential mode-of-action scheme for tumor formation. Three areas were evaluated: (1) hematopoiesis (because endothelial and hematopoietic cells arise from the same precursor and hemangiosarcomas are primarily located in mouse hematopoietic tissues), (2) angiogenic growth factors (because increased angiogenic growth factors may stimulate vascular tumors), and (3) pulmonary/blood gas parameters (because hypoxia is a known driver for endothelial cell proliferation). In mice, pregabalin rapidly increased platelet and megakaryocyte counts, activated platelets and bone marrow erythrophages, decreased the myeloid-to-erythroid (M:E) ratio (49%), and produced bone marrow and splenic congestion and extramedullary hematopoiesis (EMH). Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor immunohistochemical staining were also increased in mouse bone marrow and spleen and vascular endothelial growth factor receptor 2 immunolabeling was increased in liver. Serum bicarbonate was increased within 24 h of pregabalin administration, persisted over time, and was accompanied by decreased respiratory rate (up to 34%) and increased partial pressure of carbon dioxide (pCO(2)), resulting in sustained metabolic alkalosis and elevated blood pH in mice. In contrast, in rats, pregabalin decreased overall bone marrow cellularity, including decreased number of megakaryocytes (24%) with no evidence of erythrophages, no change in M:E ratio, no EMH, and no increase in angiogenic growth factors or blood pH. Persistent alterations in serum bicarbonate, respiratory function, and blood gas parameters in mice, without adequate compensatory mechanisms, has the potential to create chronic tissue hypoxia, an accepted driver of endothelial cell proliferation.

Hepatotumorigenicity and peroxisome proliferation induced by the hypolipidemic CI-924 in a two-year study in male and female B6C3F1 mice

The hepatic tumorigenicity of CI-924 (5,5'-(1,1'-biphenyl)-2,5-diylbis(oxy)(2,2-dimethylpentanoic acid)), a hypolipidemic agent, was evaluated in 50 B6C3F1 mice/sex/dose given drug in the diet at 0, 5, 25, and 75 mg/kg/day for 2 yr. Peroxisomal and drugmetabolizing enzyme determinations, as well as ultrastructural evaluations, were conducted in subsets of these same groups, because drugs of this class cause peroxisome proliferation and hepatic tumors in rodents. CI-924 elicited dose-dependent increases in the incidence of hepatocellular adenomas and carcinomas in both sexes that were statistically significant at 75 mg/kg. Stereologic evaluation revealed significant increases in hepatocellular peroxisome volume ratio, due to increased numbers of peroxisomes, in females at all doses and males at 75 mg/kg. Peroxisomal enzyme activity measurements revealed no change in catalase, but dose-dependent increases in carnitine acetyltransferase and cyanide-insensitive beta-oxidation in both sexes. Peroxisome proliferation, determined biochemically or ultrastructurally, was twice as great in females compared to males. Total cytochrome P-450 was increased in both sexes given 75 mg/kg. There were dose-dependent decreases in glutathione S-transferase in males and increased glutathione peroxidase in both sexes at 25 and 75 mg/kg. In conclusion, this study demonstrated that while CI-924 induced hepatic tumors in male and female B6C3F1 mice the associated peroxisome proliferation, while moderate in females, was only weak in the males after 2 yr of exposure.

A spontaneous corneal change in juvenile Wistar rats

Corneal changes were seen in a shipment of male and female Charles River Wistar (Crl:(WI)BR) albino rats aged 33 days. Seventeen weeks later, varying degrees of corneal roughness were observed ophthalmoscopically in 40 of 43 males and 26 of 29 females. Corneal lesions, described clinically as multiple punctate or particulate opacities, were most often bilateral and located paracentrally. Histologically, lesions were observed in only 21 of 40 males and in 15 of 26 females which had shown clinical changes. The lesions consisted of basophilic particulate material, which occasionally formed linear plaques, lining the basement membrane of the corneal epithelium. Ultrastructurally, irregularly distributed electron-dense deposits, occasionally assuming a concentric laminar appearance, were observed. X-ray microanalysis revealed that the granules consisted predominantly of calcium and phosphorus, with trace amounts of iron, zinc, sodium and aluminium. These mineral deposits in the corneas of Wistar rats were similar to those described in other species. Awareness of this spontaneously occurring disease in Wistar rats is of importance in relation to toxicological investigations in which the cornea may be a target organ.

Struvite urolithiasis in a B6C3F1 mouse

In a 2 year carcinogenicity bioassay using B6C3F1 mice, one male mouse developed clinical signs near termination of the study, comprising skin sores around the prepuce, penile prolapse and urine scalding. The predominant finding at necropsy was a markedly distended urinary bladder filled with numerous crystallized particles. Microscopically, there was subacute cystitis with marked hyperplasia of the transitional epithelium. X-ray diffraction analysis of the crystals showed a diffraction pattern characteristic of struvite (ammonium magnesium phosphate). The implications of the spontaneous occurrence of bladder stones in rodents on long-term toxicology studies are discussed.

Cutaneous herpesvirus infection in a mallard duck (Anas platyrhynchos)

Investigations of mortalities involving wild mallard ducks (Anas platyrhynchos) revealed the presence of a herpesvirus associated with skin lesions on the plantar surface of the foot web of one duck. Ultrastructurally, the paracrystalline arrays of viral core particles and unencapsidated nucleoids in the nucleus, and the enveloped viruses in cytoplasmic vacuoles are compatible with a herpesvirus. This appears to be the first report of cutaneous lesions in a mallard duck attributable to a herpesvirus. Whether this lesion is due to duck virus enteritis (DVE), suggesting that cutaneous shedding is possible, or due to another uncharacterized herpesvirus of ducks is unclear.

Toxicologic Pathology Forum: Opinion on Performing Good Laboratory Practice Histopathology Evaluation for Nonclinical Toxicity Studies in a Remote Location

Toxicologic/veterinary pathologists are working remotely from Good Laboratory Practice (GLP) test facilities (TFs) in increasing numbers, most commonly in home-office settings. A study pathologist (SP) generating data on GLP-compliant nonclinical studies must be keenly aware of applicable national GLP regulations and comply with TF and protocol requirements. This Toxicological Pathology Forum Opinion Piece will summarize primary areas of emphasis for the SP generating GLP data using glass slides. Peer review and digital review of whole slide images are out of scope for this opinion piece. Key GLP considerations for primary pathology on glass slides are discussed with respect to SP location and employment status, including pathologist qualifications, specimen management, facilities, equipment, archive, and quality assurance. Notable differences between national GLP regulations of the United States, the United Kingdom, Germany, the Netherlands, France, Ireland, Switzerland, Italy, and Israel are presented. With the understanding that each combination of location and employment is unique, the authors provide a general overview of considerations for successful remote GLP work.

Maple syrup urine disease in five hereford calves in ontario

Five newborn grade horned or polled Hereford calves in Ontario exhibited the clinical signs characteristic of hereditary neuraxial edema, namely, inability to rise, and hyperesthesia with extensor spasms upon tactile or auditory stimulation. Histologically, there was widespread spongy vacuolation in both white and gray matter in the brains of all five calves, especially in the midbrain, brain stem, and cerebellum. Amino acid analysis of formalin-fixed cerebral tissue of three calves demonstrated an amino acid composition consistent with a diagnosis of branched chain keto acid decarboxylase deficiency. This condition has been recently reported in Hereford calves in Australia; it is characterized by the delayed onset of neurological signs and severe lesions of status spongiosus, and has been considered analogous to maple syrup urine disease of children.

Nasal papillary adenoma in a goat

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