Renal and hepatic toxicity of a benzopyran-4-one in the Cynomolgus monkey.

The administration of PD 119819, a novel benzopyran-4-one brain dopamine autoreceptor agonist, to Cynomolgus monkeys was followed by deposition of needle-like drug crystals in the bile canaliculi, hepatocytes, proximal renal tubules and renal parenchyma. The crystals were associated with a granulomatous inflammation, and histological and biochemical evidence of hepatic and renal cell damage. Although metabolism differences may be the reason why primates, but not rodents, developed these changes, this form of crystallization appeared to be primarily a result of the insolubility of PD 119189 at alkaline pH.

Preclinical toxicity studies of an adenosine agonist, N-(2,2-diphenylethyl) adenosine.

N-(2,2-Diphenylethyl)adenosine (DPEA) has been identified as a potential antipsychotic agent acting via stimulation of adenosine receptors. The projected human therapeutic dose, based on animal studies, is 2-3 mg/kg. DPEA has been tested for potential toxicity in mice, rats, dogs and monkeys. Following single oral doses, median lethal dose values were approximately 10-fold greater in rats than in mice, although similar clinical signs including reduced activity, prostration, and necrosis of the tail were seen in both species. DPEA was well tolerated at daily doses up to 40 mg/kg in rats for 2 weeks. A no observed effect level (NOEL) was not identified in the dog or monkey studies. Reduced activity, dacryorrhea, ptosis, hypothermia, necrosis of the tail, and death occurred in rats given 120 and 160 mg/kg. Pathologic changes consisted of pancreatitis, gastric erosion/ulceration, lymphocyte depletion of the thymus, and pulmonary congestion and hemorrhage at 80 mg/kg or greater. In dogs, sporadic emesis was noted at 12.5 mg/kg and greater, and significant pathologic changes consisted of coronary arteritis associated with myocardial lesions and lymphocyte depletion at 25 and 50 mg/kg, pancreatic acinar necrosis at 50 mg/kg, and renal tubular degeneration at 12.5 mg/kg and greater. Emesis and depression were noted at 25 and 50 mg/kg in monkeys. Renal tubular dilatation and degeneration at 25 and 50 mg/kg were noted in the monkeys. These studies demonstrated that DPEA produced a range of adverse effects in common laboratory animal species.

Preclinical toxicology of the anticonvulsant calcium valproate.

The oral toxicity of the anticonvulsant calcium valproate with selected comparisons to valproic acid and sodium valproate was evaluated in mice, rats and Beagle dogs. Median lethal doses of the three forms of valproate in rodents ranged from 1100 to 3900 mg/kg. Clinical signs in acute studies and reductions in body weight or body weight gain and food consumption at high doses in rats and dogs during 2-, 13- and 52-week studies were considered to be central nervous system related. In the 13-week study in rats (calcium valproate at 200, 400, 800, 1200 and 1600 mg/kg and sodium valproate at 1200 mg/kg), reduced plasma globulin levels and low white blood cell counts due to suppressed neutrophil maturation were noted at doses of 800 mg/kg and higher. Platelet counts were reduced at 1200 and 1600 mg/kg. Testicular atrophy occurred at 1200 and 1600 mg/kg. In dogs given calcium valproate at 100, 200 and 400 mg/kg for 13 weeks, testicular atrophy was seen at 400 mg/kg and mild hepatocellular changes at all doses. In rats given calcium valproate at 125, 250 and 500 mg/kg for 1 year, reduced plasma protein and globulin levels and a dose-dependent increased incidence and severity of atrophic pancreatitis were noted at 250 and 500 mg/kg. Calcium valproate, given for 1 year to dogs at doses of 50, 100 and 200 mg/kg, was well tolerated. These studies indicated that calcium valproate has a toxicity profile similar to other forms of valproate.

Parkinson-like syndrome in nonhuman primates receiving a tetrahydropyridine derivative.

Antipsychotic drugs, while ameliorating symptoms in schizophrenia, evoke extrapyramidal effects which resemble parkinsonism. We studied the potential of 1- (4,4-bis(4-fluorophenyl)butyl)-4-(4-fluorophenoxy)-1,2,3,6-tetrahydropyr idine d-tartrate to induce extrapyramidal side effects in Rhesus monkeys. This agent shares neurochemical effects of known antipsychotic agents in its ability to antagonize cerebral dopamine action by competing for (3H)-Haloperidol binding of the dopamine receptors and inhibiting limbic and striatal adenylate cyclase in rat brain. The compound was administered orally to monkeys for 18 days, starting at 2 mg/kg and increasing to 20 mg/kg. Additional groups of monkeys received the drug for 29 consecutive days at 5 and 7.5 mg/kg/day. In both studies, extrapyramidal signs were associated with neuropathological changes in the brains of treated monkeys. The findings resemble those reported in Rhesus monkeys and in drug addicts after repeated intravenous administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The findings also suggest a structure/activity relationship of tetrahydropyridine analogs with neurologic and associated neuropathologic manifestations produced in monkeys. The experimental model is useful to study the pathogenesis and possibly therapeutic approaches for Parkinson's disease.

Histiocytic sarcoma in Wistar rats. A light microscopic, immunohistochemical, and ultrastructural study.

Histiocytic sarcoma, a recently described tumor entity in rats, was studied by light microscopy in 20 male and female Wistar rats. The tumors originated from subcutaneous tissues; metastasis involved primarily the liver with sinusoidal spread and the lungs with peribronchiolar distribution. The characteristic features of this tumor were the uniform population of tumor cells, palisading necrosis, and abundant multinucleated giant cells. Immunocytochemical and ultrastructural findings confirmed the histiocytic nature of the tumor cells.

Auricular chondritis in Wistar rats.

The macroscopic and microscopic features of auricular chondritis in Wistar rats are described. Histologic lesions are characterized by granulomatous inflammation, chondrolysis, and multinodular proliferative foci. The condition in Wistar rats is compared to auricular chondritis in other strains of rats.

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.

Morphologic features and incidence of spontaneous hyperplastic and neoplastic mammary gland lesions in Wistar rats.

A morphologic study of spontaneous proliferative lesions of the mammary gland was based on histologic examination of mammary glands from 1020 male and 1145 female albino Wistar rats aged 6 to 110 weeks. Three hundred and seventy-five mammary tumors representing an overall incidence of 33% were identified in the female groups, while the males had a total of five tumors which represented an incidence of 0.5%. Histologically, the most common types of tumors in females were: fibroadenoma (236), carcinoma (85), adenoma (40) and fibroma (8). Duct papilloma (1), lobular carcinoma (1), fibrosarcoma (1) and phyllodes tumor (1), were rare and constituted less than 2% of mammary neoplastic lesions. Mammary tumors were rare before one year of age, but increased with age thereafter. Nine percent of female rats studied also had proliferative non-neoplastic lesions that showed a mixture of benign ductular and/or lobular hyperplasia. One hundred and six of these lesions were identified, representing 22% of all grossly palpable nodules, thus stressing the importance of histologic examination of all gross mammary nodules for tumor evaluation.

Leukocyte and bone marrow effects of a thiomorpholine quinazosin antihypertensive agent.

PD-88823, a thiomorpholine analog of prazosin, induced a consistent dose-related suppression of granulopoiesis with subsequent neutropenia and leukopenia in rats and dogs. Rats treated at 600 mg kg-1 day-1 had neutrophil counts reduced by 44% in males and 30% in females after 13 weeks. A 4-week observation period after drug treatment resulted in a rebound in neutrophil counts to 123 and 215% of control values in males and females, respectively. White blood cell count reductions were less evident in dogs, probably because of the lower doses. In both species, the extent of bone marrow suppression was related to duration of treatment. No other hematologic changes were manifest in either species. The mechanism for bone marrow depression and subsequent granulocytopenia was not established. The lack of reported bone marrow effects by quinazosin analogs suggests that the thiomorpholine group of PD-88823 is involved in toxicity. This correlation may be important to safety considerations for future drug design.

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)

Morphologic and immunohistochemical features of two spontaneous peripheral nerve tumors in Wistar rats.

Morphologic features and S-100 protein immunoreactivity of a benign and malignant peripheral nerve sheath tumor were studied in two Wistar rats. Neoplasms that developed in untreated control rats from tumor bioassays were S-100 protein positive and had similar histopathologic features. Each peripheral nerve sheath tumor was encapsulated and composed of spindle cells arranged around small thin-walled blood vessels. Palisaded tumor cells were in the benign peripheral nerve sheath tumor while cells of the malignant peripheral nerve sheath tumor had cellular atypia and moderate numbers of mitoses. Ultrastructural examination of the malignant peripheral nerve sheath tumor revealed cells with external lamina and interdigitation of cytoplasmic processes. Intracytoplasmic concentric lamellae were seen; they were regularly spaced with a periodicity of about 15 nm. Such structures, indistinguishable from myelin sheaths, have not been commonly associated with peripheral nerve sheath tumors in man. Electron microscopy and immunohistochemistry were useful in the diagnosis of these tumors as Schwannomas and in differentiation from other spindle cell tumors.

Poxvirus infection in a colony of common marmosets (Callithrix jacchus).

An epizootic poxvirus infection occurred in a colony of 80 common marmosets (Callithrix jacchus) recently introduced to a laboratory facility. Over an 18-week period, 29 of the monkeys exhibited skin lesions that persisted for 4-6 weeks. Although eight marmosets died during the outbreak, their deaths were not attributed directly to the poxvirus infection. The skin lesions developed over the entire body surface including the soles and palms. Initially characterized as erythematous papules, they quickly changed to elevated coalescing lesions with extensive scab formation. Histopathologically, the lesions revealed moderate to marked acanthosis, and they progressed to full-thickness epidermal necrosis and ulceration. Intracytoplasmic inclusion bodies were observed occasionally within degenerate keratinocytes. These inclusions most probably constituted the intracytoplasmic aggregates of viral particles observed ultrastructurally and confirmed as members of the poxvirus group by negative staining of direct skin scrapings.

Chronic toxicity of the anticonvulsant zonisamide in beagle dogs.

The chronic toxicity of the new anticonvulsant drug zonisamide (1,2-benzisoxazole-3-methanesulfonamide) was evaluated in a detailed 52-week study in which dose levels of 0, 10, 30 and 75 mg/kg/day were administered orally in gelatin capsules to groups of five Beagle dogs per sex. Potential toxicity was based on the effects of zonisamide on body weight and food consumption; clinical and ophthalmic examinations; electrocardiography and heart rates; clinical biochemistry, hematology and urinalysis determinations; organ weights and gross and histopathologic evaluations; electron microscopy of high dose and control male dogs; and plasma zonisamide concentrations. Zonisamide was relatively well tolerated during the study. In animals given 75 mg/kg/day, early body weight losses occurred and therefore, from Weeks 2 and 3 until study termination, for males and females respectively, the high dose was given as two equal portions (i.e., 37.5 mg/kg each) approximately 3-4 hr apart. Clinical laboratory analyses in the dogs given 75 mg/kg revealed a small but statistically significant decrease in plasma albumin concentration and a small increase in alkaline phosphatase activity. In animals given 75 mg/kg, liver weights were increased and a brownish discoloration of the liver was noted grossly at necropsy. No significant light microscopic changes were evident; however, electron microscopic evaluation of the liver tissue from the 5 male dogs given 75 mg/kg revealed the presence of concentric lamellae of paired smooth membranes which were not seen in control animals. At the 10 and 30 mg/kg dose levels, plasma zonisamide concentrations reached steady-state and were proportional to dose, but at 75 mg/kg, plasma levels were disproportionately higher and never achieved steady-state. The results of this study indicated that at the high dose level of 75 mg/kg, chronic administration of zonisamide had a mild effect on the liver, particularly the endoplasmic reticulum.

Morphofunctional investigations on spontaneous pituitary tumors in Wistar rats.

Adenoma of the pituitary gland represents one of the commonest spontaneous tumors in strains of laboratory rats. In a retrospective survey of pituitary glands from 2165 albino Wistar rats, the total number of pituitary adenomas was 501, representing an overall incidence of 23% with females showing a higher incidence (32%) than males (13%). Pituitary adenoma was rare from 6-52 weeks of age and accounted for only 0.2% of the total incidence. The first pituitary tumors in this series were observed at 32 weeks in 2 female rats and at 40 weeks in a male rat. From 52-85 weeks of age, incidence remained low, and then increased progressively in animals that died from 85-110 weeks of age. In a series of 200 Wistar rats, detailed evaluation was completed for neoplastic and hyperplastic lesions of the pituitary gland. The immunocytochemical characteristics of the pituitary adenoma were investigated using markers for prolactin, growth hormone, and thyrotropic hormone. Positive immunoperoxidase staining revealed an incidence of 59% prolactinomas in both male and female rats. Forty-one percent of pituitary adenomas did not stain for prolactin, thyrotropic, or growth hormone and showed no specific morphologic differences from prolactinomas. The application of immunoperoxidase-staining techniques offers a useful tool for characterizing secretory activity of pituitary adenomas and evaluating histopathologic changes of the pituitary gland.