Role of cytoprotectants and nitric oxide inhibition in nonsteroidal anti-inflammatory drug-induced gastroduodenal injury in the rat.

BACKGROUND AND PURPOSE: Nonsteroidal anti-inflammatory drugs (NSAIDs) induce gastroduodenal injury and ulceration. The pathogenesis is uncertain, although reductions in cytoprotective prostaglandins and nitric oxide (NO) have been proposed. The effects of several cytoprotective agents on inhibition of gastroduodenal ulcerogenesis induced by CI-987, a novel NSAID, were evaluated in Wistar rats. METHODS: Male Wistar rats were given CI-987 orally (p.o.) at a dosage of 300 or 450 mg/kg of body weight or subcutaneously (s.c.) (3 x 50 mg/kg), alone or with misoprostol pretreatment (2 x 1 mg/kg, p.o.). In a second experiment, rats were pre-treated with 2 ml of gelusil p.o., 500 mg of sucralfate/kg, p.o., 100 mg of ranitidine/kg s.c., or 200 mg of N omega-nitro-L-arginine methyl ester (L-NAME)/kg, s.c.. Duodenal injury was induced by administration of 450 mg of CI-987/kg, p.o., 3 x 50 mg of CI-987/kg, s.c., or 300 mg of cysteamine/kg, s.c. Animals were euthanized within 24 to 48 hours, and the gastrointestinal tract was examined for evidence of gross or microscopic change. RESULTS: The L-NAME significantly reduced the incidence and severity of gastroduodenal injury induced by CI-987 and cysteamine. Prostaglandin ameliorated duodenal lesions induced by CI-987 given s.c., and Gelusil, ranitidine, and sucralfate were without effect on duodenal lesions induced by NSAID. CONCLUSIONS: Preemptive blockade of NO synthase is important in preventing NSAID-induced duodenal injury in rats. Inhibition of cytoprotective prostaglandins and enhanced acid-induced damage are unlikely to be primary mechanisms underlying NSAID-induced duodenal injury in rats.

Coronary arteriopathy in monkeys following administration of CI-1020, an endothelin A receptor antagonist.

A selective non-peptide endothelin A (ETA) receptor antagonist, CI-1020, was administered to cynomolgus monkeys intravenously (i.v.) for 2 or 4 wk and orally for 4 wk. Groups consisting of 3 animals of each sex received CI-1020 at 1, 5, and 10 mg/kg/hr (i.v.) or orally at 250, 500, and 750 mg/kg body weight for 4 wk. Control animals received the vehicle only. In a separate experiment, 1 male was infused with 10 mg/kg/hr for 2 wk, and Monastral blue dye was administered i.v. to facilitate localization of lesions to the vascular walls. One female was administered saline and the dye and served as a control. One female at 1 mg/kg/hr was found dead at week 2, and 1 female at 5 mg/kg/hr was euthanatized during week 4 as a result of severe thigh swelling at the catheter site. Macroscopically, extramural coronary arteries appeared thickened and nodular in the 4-wk i.v. study in the female found dead at 1 mg/kg/hr, in 1 male and 1 female at 5 mg/kg/hr, and in 2 females at 10 mg/kg/hr. Histologically, Monastral blue pigment trapped in the walls of coronary arteries with arteriopathy was observed in the male treated with CI-1020 at 10 mg/kg/hr for 2 wk. Extramural coronary arteriopathy occurred at all doses in the 4-wk i.v. study, with higher incidence occurring in females than in males (7 of 9 treated females compared with 3 of 9 treated males). In the oral study, 1 female at 500 mg/kg/day and 1 male and 2 females at 750 mg/kg/day had coronary arteriopathy. Histological changes after 2 wk of treatment were characterized by intimal thickening, fragmentation of the internal elastic lamina, necrosis and edema of the media, and mixed inflammatory-cell infiltrates in the intima, media, and adventitia. After 4 wk of i.v. administration, arteriopathy was characterized by segmental disruption of the elastic lamina and intimal and medial fibrosis with complete replacement of smooth muscle with fibrous tissue. The adventitia was thickened as a result of fibrosis and mixed or mononuclear inflammatory-cell infiltrates. CI-1020 concentrations were higher in males (1.57 to 29 micrograms/ml) than in females (0.974 to 24.4 micrograms/ml) in the i.v. study. Transient systemic exposure with high maximum plasma concentration (Cmax) (120-352 micrograms/ml) in the oral study was insufficient to provoke arterial changes of the same magnitude as those noted with continuous i.v. administration. The regeneration of the media by fibrous tissue and the disruption of the elastic lamina may weaken the arterial wall and increase the susceptibility of the artery to the development of aneurysm.

Arteriopathy induced by an adenosine agonist-antihypertensive in monkeys.

An adenosine agonist, designated chemically as (R)-N-(2,3-dihydro-1H-inden-1-yl) adenosine or CI-947, was administered orally to 2 males and 2 female cynomolgus monkeys each at 5, 10, 20, and 50 mg/kg of body weight for 2 wk. One male and 1 female given 50 mg/kg were euthanatized on days 10 and 8, respectively, because of poor clinical condition. Emesis was present at 10, 20, and 50 mg/kg. Decreased heart rate and QT prolongation were present at 50 mg/kg. Extramural coronary arterial lesions consisting of medial necrosis with cellular debris and mixed inflammatory cell response in the intima, media, and adventitia were present in 1 male at 20 mg/kg and 1 male at 50 mg/kg at study termination. Similar arterial lesions were present in the small and large intestines and testis of the male at 50 mg/kg. Colonic mucosal erosions with mixed inflammatory cell infiltrates in the lamina propria were seen in this male and in all CI-947 treated females at 10, 20, and 50 mg/kg. Myocardial degeneration and necrosis of myocardial fibers with mononuclear cell infiltrates in the interstititum were noted in the left ventricle of 1 female at 20 mg/kg and in all animals at 50 mg/kg. Renal cortical tubular dilatation with increases in serum creatinine and/or blood urea nitrogen were noted in a control female and animals at 10 and 50 mg/kg. Plasma CI-947 concentration increased with increasing dose. Coronary vascular injury in the monkey was similar to the arterial lesion in CI-947-treated dogs and may relate to the pharmacologic/hemodynamic effects induced by CI-947. When compared with the dog, the monkey appears to be less sensitive to development of arteriopathy, as indicated by lower incidence, at similar systemic exposure levels.

Renal toxicity of a nondopaminergic antipsychotic agent, trimethyl imidazopyrazolopyrimidine, in rats.

A nondopaminergic antipsychotic agent, 5-ethyl-1,3,8-trimethyl-1H-imidazo]1,2-c]pyrazolo[3,4-e]pyrimidine (TIPP; PD 112488), has been tested for potential toxicity in rats. As part of a preclinical safety evaluation, 10 Wistar rats per sex were administered TIPP as a dietary admixture, receiving doses of 0, 5, 10, 20, 25, 50, 100, and 200 mg/kg for 2 wk. In addition, 3 groups of 6 male Wistar rats were administered TIPP (PD 114877 and PD 117498, acid hydrolysis products of TIPP) at 100 mg/kg by gavage for 5 days. All animals given 200 mg/kg were euthanatized in moribund condition or found dead after 1 wk of treatment. Clinical evidence of renal toxicity was noted and included emaciation, hematuria, urinary incontinence, and enlarged kidneys at doses of 10 mg/kg and higher. Plasma urea levels were higher than those of controls in all TIPP-treated groups. Significant pathologic changes of the urothelium were evident at all doses and were characterized by necrotizing pyelitis and cystitis. Necrosis and inflammation of the urothelium resulted in secondary hydronephrosis. No renal toxicity was noted with the acid hydrolysis products. The urothelial changes with oral administration of TIPP in rats is species-specific, and the specificity may be related to the metabolism and excretion of the drug.

Toxicity of CI-949, a novel anti-allergy agent.

The toxicity of CI-949, an effective inhibitor of allergic mediator release in pharmacology models, was evaluated in rodents and dogs. Median lethal doses at 24-hr postdose ranged from 343 to 453 mg/kg in mice and 806 to 2058 mg/kg in rats. Delayed toxicity was observed at 300 mg/kg and greater in mice and at 500 mg/kg and greater in rats. Mortality and clinical intolerance occurred in rats at 200 and 400 mg/kg in the subacute studies, and at 100 and 150 mg/kg in the 13-week study. In rats, dose-dependent lymphoid tissue atrophy and depletion or necrosis of lymphocytes in lymphoid tissues were seen in deaths and moribund terminations. Although doses up to 60 mg/kg administrated for 2 weeks to dogs were well tolerated, 60 and 120 mg/kg in the 13-week dog study were poorly tolerated. Cutaneous sores, mucocutaneous purulent discharge, emesis, diarrhea, and weight loss were identified at these lethal doses. Histopathologic changes in dogs included myocardial, vascular and soft tissue inflammation, and gastric ulceration at 60 and 120 mg/kg, and thymic atrophy at 20 mg/kg and greater. Doses of 10 and 50 mg/kg were no-effect doses in 13-week repeated dose studies in dogs and rats, respectively. These results were used to support initial human clinical trials of CI-949.

Characterization of cardiac alterations in nonsedated cynomolgus monkeys.

Spontaneous variations in ECG and continuous Holter monitor recordings of a colony of 31 male and 31 female cynomolgus monkeys were characterized. Electrocardiograms recorded for approximately 1 minute on 2 occasions in nonsedated monkeys were analyzed, and intervals (PR, QRS, and QT), amplitudes (P, Q, R, and T), and heart rate were determined from lead II of these tracings. In addition, Holter monitor recorders were placed on monkeys by use of carrying jackets for 16 to 24 hours of continuous recording twice during the study, and tapes were analyzed. Mean heart rate and intervals and amplitudes were similar for males and females on the first and the second recordings. Mean heart rate for males and females was 232 and 226 beats/min (bpm), respectively. The PR, QRS, and QT interval measurements, 77, 29, and 165 milliseconds, respectively, were recorded for males and 81, 30, and 162 milliseconds, respectively, were recorded for females. The P, Q, R, and T wave amplitudes were 0.16, 0.11, 0.64, and 0.28, mV respectively, for males and were 0.17, 0.10, 0.79 and 0.24 mV, respectively, for females. In addition, ventricular ectopic beats were observed in ECG from 5 females, but not in ECG from the males. Single ventricular ectopic beats were observed in 3 females for either the first or second tracing. One monkey had ectopic beats in both tracings, but in both instances, the number of ectopic beats was low (3 singles in the first and 1 in the second tracing).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.