Atrioventricular valvular angiectasis in Sprague-Dawley rats

Subendothelial heart valve angiectasis has been reported in cows, dogs, pigs, rats, mice, and in human fetuses and newborns. We observed a high incidence (62 in 208 animals examined) of spontaneous angiectasis on the atrioventricular (AV) valves in 10- to 40-week-old Sprague-Dawley rats. The angiectasis was observed predominately on the septal cusp of the right AV valve and located near the AV ostium in 57 of 62 animals. Of the remaining 5 valvular angiectases, 2 were present on the parietal cusp of the right AV valve and 3 were on the left AV valve. The angiectases were single or multiple, ranging from 40 to 300 microm in diameter and were characterized by light microscopy as blood-filled dilatations lined by endothelium. Spontaneously occurring abnormalities in normal laboratory animals, such as the spontaneous valvular angiectasis reported here, need to be differentiated from drug-related lesions.

BMS-189453, a novel retinoid receptor antagonist, is a potent testicular toxin

BMS-189453 is a synthetic retinoid that acts as an antagonist at retinoic acid receptors alpha, beta, and gamma. In Sprague Dawley rats at daily oral doses of 15, 60, or 240 mg/kg for 1 month, BMS-189453 produced increases in leukocyte counts, alkaline phosphatase and alanine aminotransferase levels, and marked testicular degeneration and atrophy at all doses. Significant overt signs of toxicity and deaths occurred at 240 mg/kg, whereas body-weight and food-consumption decreases occurred at 60 and 240 mg/kg. When BMS-189453 was administered to male rats at daily doses ranging from 12.5 to 100 mg/kg for 1 week, only minimal testicular changes occurred at all doses, shortly after the dosing period. However, after a 1-month drug-free observation period, marked testicular atrophy was evident at all doses. BMS-189453 was then administered at doses of 2, 10, or 50 mg/kg to male rats for 1, 3, or 7 consecutive days. Dose- and duration-dependent testicular toxicity that occurred after a 1-month observation period did not recover, and, in some cases, was more severe 4 months after the last dose. In rabbits administered BMS-189453 at oral doses of 2, 10, or 50 mg/kg for 1 week, testicular degeneration and atrophy were evident in the high-dose group at 1 month following treatment. These studies indicate that retinoid antagonists can selectively produce progressive and prolonged testicular toxicity after single or repeated oral doses that are otherwise well tolerated.

Didanosine (ddl) and stavudine (d4T): absence of peripheral neurotoxicity in rabbits

Some 20 male New Zealand White rabbits (five/group) were given either didanosine (ddl) or stavudine (d4T) at 750 and 1500 mg/kg body weight/day by oral intubation for 24 wk. An additional group was given 300 mg/kg body weight/day zidovudine (AZT) as a negative control. After 13 weeks the high dose of ddl was lowered from 1500 to 1000 mg/kg body weight/day following the death of one rabbit and continued inappetence in the dose group. The rabbits were observed daily, plasma drug levels were monitored, and electrophysiological measurements of peripheral nerve conduction were performed during the study. Additionally, body weight and food intake were recorded, and clinicopathological parameters were evaluated. Sections of selected peripheral nerves, and dorsal and ventral spinal nerve roots were examined by light and transmission electron microscopy. Although peripheral neuropathy has been reported in rabbits with the nucleoside analogue zalcitabine (ddC), based on clinical observations, electrophysiological measurements, and light and electron microscopy, no evidence of peripheral neurotoxicity was observed in rabbits given either ddl of d4T.

Etoposide- and BMY-40481-induced sensory neuropathy in mice

The effects of high toxic doses of the anticancer drugs, etoposide and its phosphate derivative, BMY-40481, on the nervous system of female CD-1 mice were examined by light microscopy (LM) and transmission electron microscopy. Mice were euthanatized 4 wk following a single iv injection of either 0, 50, 100, or 150 mg/kg of BMY-40481 or 44 or 88 mg/kg of etoposide. Mice treated with 100 or 150 mg/kg of BMY-40481 or 88 mg/kg of etoposide had clinical symptomology of progressive ataxia, impaired righting reflex, and splaying and paresis of fore- and hindlimbs at day 8. Similar, dose-related LM changes were observed with both drugs at all doses and consisted of degeneration of dorsal root ganglion cells and axonal degeneration of their distal and proximal processes in peripheral nerves, dorsal spinal roots, and dorsal funiculi of spinal cord. Axonal degeneration was characterized by LM as shrinkage, swelling, and fragmentation of axon cylinders accompanied by secondary demyelination. Degenerative changes in ganglion cell bodies included eccentric nuclei, cytoplasmic vacuolation, central chromatolysis, and peripheral clumping of Nissl's bodies. Ultrastructurally, ganglion cell bodies had focally extensive dilation of the rough endoplasmic reticulum, mitochondrial swelling, increased numbers of phagolysosomes and prominent aggregations of microfilaments (globular filamentous bodies). Ultrastructural axonal changes occurred primarily in large, myelinated fibers and consisted of axonal swelling or loss, thinning of myelin sheaths, and a decrease in the number of organelles. This is the first report of etoposide-related sensory neuropathy in laboratory rats, a model that my be useful for the study of etoposide-related peripheral neuropathy in humans.

Comparison of in vitro biological properties and mouse toxicities of three thymidine analogs active against human immunodeficiency virus

Three analogs of thymidine, D4T [2',3'-didehydro-2',3'-dideoxythymidine; 1-(2,3-dideoxy-beta-D-glyceropent-2-enofuranosyl)thymine], FddT (3'-fluoro-3'-deoxythymidine), and AZT (3'-azido-3'-deoxythymidine), were compared in biological tests designed to assess their potential utility as anti-human immunodeficiency virus (HIV) agents. The in vitro potencies of these compounds against HIV infection in CEM cells were measured, with FddT and AZT being more potent than D4T. The cytotoxicities of D4T, FddT, and AZT for CEM cells were comparable. The triphosphates of these three derivatives inhibited purified HIV reverse transcriptase, and their affinities for this polymerase were found to be 1 or 2 orders of magnitude greater than that for the normal substrate, dTTP. D4T was less toxic than FddT or AZT for cultured human and mouse bone marrow cells (granulocyte-macrophage CFU). The three compounds had similar toxicities for human progenitor erythrocyte burst-forming units. In a 30-day mouse toxicity study, AZT and FddT produced a similar spectrum of hematopoietic toxicities. These toxic effects occurred at much lower doses of FddT than of AZT. At the higher doses of FddT, a significant incidence of lethality occurred. By contrast, D4T was considerably less toxic than both AZT and FddT in this study. The dose-limiting toxicity of D4T in mice was hepatotoxicity. The very different phosphorylation patterns of D4T, its lower toxicity, and its comparable potency relative to FddT and AZT suggest that the potential of D4T as an anti-HIV agent should be further explored.

Cardiac, renal, and pulmonary toxicity of several mitomycin derivatives in rats

The potential cardiotoxicity, nephrotoxicity, and pulmonary toxicity of several mitomycin (MMC) derivatives, BMY-25067 (N-7-[2-(4-nitrophenyldithio)ethyl]MMC), BMY-26107 (N-7-[2-(4-aminophenyldithio)ethyl]MMC), BMY-26605 (N-7 acetyl-MMC), BMY-25690 (7-N-(dimethylaminomethylene)-10-[1-morpholinomethyleneamino)carbo nyl- oxy]MMC), BMY-26646 (N-7-[2-(4-fluorophenyldithio)ethyl]MCC), and BMY-25551 (7-(2-hydroxyethyl)mitosane), were evaluated in rats. Groups of 10 male Sprague-Dawley rats were given single intravenous doses of the test compounds and were then observed for 10 weeks. Doses represented 67 and 33% of the respective mouse LD10 (corrected for body size on a mg/m2 basis) of each test compound. BMY-25282 (7-N-(dimethylaminomethylene)MMC), a mitomycin derivative that produces cardiac, renal, and arterial lesions, was used as a reference drug. Hematologic and blood chemical parameters were monitored at 3 days and at 3, 6, and 10 weeks after drug administration. Heart, kidney, and lung were examined histopathologically. Drug-related cardiac changes with late onset were seen histopathologically in rats treated with BMY-26605, BMY-25282, BMY-25551, and BMY-25690 (in order of decreasing severity). Drug-related renal changes, consisting of tubular degeneration and glomerulopathy, were seen in rats treated with BMY-25690, BMY-26107, BMY-25282, BMY-25551, BMY-26605, and BMY-25067 (in order of decreasing severity). Pulmonary arterial lesions were noted inconsistently in rats treated with BMY-26605, BMY-25282, and BMY-25551. Neither cardiac, renal, nor pulmonary changes were seen in rats administered BMY-26646, and only minor drug-related renal changes were seen in rats treated with BMY-25067.

Effects of cis-diamminedichloroplatinum(II) on rabbit kidney in vivo and on rabbit renal proximal tubule cells in culture

The nephrotoxic potential of cis-diamminedichloroplatinum(II) (CDDP) in rabbits, as well as its effect on cell viability, cellular synthetic activity, and specific enzyme activities in rabbit renal proximal tubule cells, was investigated. Male New Zealand White rabbits were given a single i.v. dose of either 2.5 or 5.0 mg/kg CDDP via the ear vein and sacrificed 5 days later. No drug-induced changes were observed in the kidneys of rabbits given 2.5 mg/kg CDDP. However, histopathological examination of kidneys from rabbits administered 5.0 mg/kg CDDP revealed marked tubular degeneration and necrosis, with the majority of lesions being situated in the outer zone of the cortex. This is in contrast to the effect of CDDP in the kidney of the rat where the necrosis is reported to be predominantly localized to the pars recta of the proximal tubule in the outer stripe of the medulla. The results from the in vitro experiments indicated that the viability of cells after a 6-h exposure to CDDP at concentrations up to 100 microM was greater than 95%. However, a dose-dependent decrease in cell viability was obtained after 24 h exposure with a TD50 (50% viability) of approximately 90 microM. In addition, the results after 24 h exposure to CDDP also indicated that Na+, K+-ATPase, a basolateral membrane marker enzyme, and alkaline phosphatase, a brush-border marker enzyme, were inhibited by 35-40% and 20%, respectively. No effect on succinic dehydrogenase, a mitochondrial marker enzyme, was obtained. Inhibition of all three marker enzymes was minimal at 6 h posttreatment. On the other hand, inhibition of DNA, RNA, and protein syntheses was evident as early as 6 h posttreatment with DNA (48-77%) and RNA (36-77%) syntheses being inhibited to a greater extent than protein synthesis (14-33%). These results demonstrate that inhibition of renal synthetic activity by CDDP, rather than its effect on enzyme activity, precedes the onset of cell lethality and may therefore be an important event in the initiation of CDDP-induced nephrotoxicity.

Cutaneous neoplasms in dogs associated with canine oral papillomavirus vaccine

A spectrum of proliferative cutaneous lesions occurred in 12 dogs at the injection site of live canine oral papillomavirus (COP) vaccine, suggesting a viral etiology for the masses. Lesions included epidermal hyperplasia, epidermal cysts, squamous papilloma, basal cell epithelioma, and squamous cell carcinoma. Peroxidase-antiperoxidase staining of tumor sections revealed nuclei which stained for group-specific papillomavirus antigen in five of 12 masses. Electron microscopic examination of tumor sections did not reveal virions. In transmission studies, macerated tumor tissue did not produce oral papillomas on the scarified mucosa of puppies; this procedure did protect the puppies from development of lesions when challenged with infectious papilloma material. These findings are evidence that COP can induce hyperplastic and neoplastic lesions in sites other than oral, pharyngeal, and ocular mucosa.

Single-dose and multiple-dose intravenous toxicity studies of BMY-25282 in rats

Single-dose and multiple-dose (daily X 5 and weekly X 5) intravenous toxicity studies in rats were conducted to determine the possible acute and delayed toxicity of BMY-25282 (7-N-(dimethylaminomethylene) mitomycin C), a potential anticancer drug. Rats in the single-dose study received either 0.05, 0.25, or 0.50 mg/kg (0.3, 1.5, or 3.0 mg/m2) of BMY-25282; rats in the daily X 5 multiple-dose study received doses of 0.005, 0.025, or 0.050 mg/kg (0.03, 0.15, and 0.3 mg/m2) of BMY-25282 once each day for 5 days; and rats in the weekly X 5 multiple-dose study received 0.05 mg/kg of BMY-25282. All doses were in 0.1% Pluronic F-68 diluent. Acute toxicities included gastrointestinal epithelial necrosis, myelosuppression, and splenic lymphoid depletion in the high and intermediate dose groups in the single-dose study and myelosuppression in the high dose group of the daily X 5 multiple-dose study. One death in a high dose male of the single-dose study was attributed to acute gastrointestinal and lymphoid toxicity. Between the interim necropsy on Day 5 or 9 and termination of the 9-week dose-free observation period, 9/20 rats of the high and intermediate dose groups of the single-dose study and 4/10 high dose rats in the daily X 5 multiple-dose study died, primarily due to hydrothorax and congestive heart failure caused by delayed, drug-related myocardial degeneration. The most prominent drug-related histopathologic changes observed in rats of both the single-dose study and the daily X 5 studies were myocardial degeneration (cardiomyopathy), glomerulopathy with tubular degeneration, and necrotizing arteritis. These three changes, observed at 0.5 and 0.25 mg/kg in the single-dose study and at 0.05 mg/kg/day in the multiple-dose (daily X 5) study, were delayed in onset and irreversible. Drug-related tubular degeneration and slight glomerulopathy were observed in male BMY-25282-treated rats in the weekly X 5 study, but cardiotoxicity, pulmonary arteritis, hydrothorax, and lethality were not observed. The diluent, Pluronic F-68, was not associated with any morphologic or clinico-pathologic changes. A single-dose of 0.05 mg/kg or 5 daily doses of 0.025 and 0.005 mg/kg of BMY-25282 were considered nontoxic doses in rats. A cumulative dose of 0.25 mg/kg, which caused cardiotoxicity in the daily X 5 study, was not cardiotoxic in the weekly X 5 study. These results indicate that the delayed cardiotoxicity of BMY-25282 is schedule dependent.

Testicular toxicity of N-methyltetrazolethiol cephalosporin analogs in the juvenile rat

The testicular toxicity of 10 antibiotics was evaluated in juvenile rats. Three of the antibiotics, cefbuperazone, cefamandole, and cefoperazone, contain the N-methyltetrazolethiol group as the 3-substituent; ampicillin, cefazolin, cephalothin, cefoxitin, piperacillin, and ceforanide do not contain this moiety. Testicular degeneration, partially irreversible in nature, was observed with those antibiotics which contain the N-methyltetrazolethiol substituent. Further, free N-methyltetrazolethiol also produced testicular degeneration in the juvenile rat. This substituent is most likely responsible for the testicular toxicity observed with cefbuperazone, cefamandole, and cefoperazone in the juvenile rat. The implications of these findings to man are undetermined.

Comparative nephrotoxicity of carboplatin and cisplatin in combination with tobramycin

The nephrotoxic potentials of cisplatin and carboplatin, alone and in combination with the aminoglycoside antibiotic tobramycin, were compared in male rats. Sixty (60) male Sprague-Dawley rats were divided into six groups of ten rats each and received the following treatments: Group I, saline; group II, cisplatin (5 mg/kg); group III, cisplatin (5 mg/kg) + tobramycin (50 mg/kg); group IV, carboplatin alone (50 mg/kg); group V, carboplatin (50 mg/kg) + tobramycin (50 mg/kg); and group VI, tobramycin alone (50 mg/kg). Carboplatin and cisplatin were each administered as a single i.v. injection on day 1. Tobramycin was administered i.-m. once daily on days 1-5. All rats were euthanatized on day 6. Smaller body weight gains occurred in groups II-V than in saline controls. Serum urea nitrogen (BUN) levels recorded on day 6 were elevated in group III. BUN values of all other groups were normal. Histopathologic examination of kidneys revealed acute tubular injury in rats treated with cisplatin, whether alone or in combination with tobramycin, and in carboplatin/tobramycin-treated rats. Carboplatin and tobramycin, when administered separately, were not nephrotoxic. The combination of cisplatin and tobramycin proved to be the most nephrotoxic treatment.

Pain on injection and muscle irritation: a comparison of animal models for assessing parenteral antibiotics

Pain on injection due to parenteral administration of cephaloridine, cephalothin, and cefoxitin with or without 1% lidocaine was examined in a rat paw-lick model and the results compared with those obtained in a rabbit intramuscular model of irritation. In both animal models, cephaloridine caused similar or a slightly greater response than sterile water. Conversely, cefoxitin and cephalothin caused a much greater reaction than water in both models. The only major difference in the rankings by the two models was with formulations in which an anesthetic agent was incorporated into the diluent. As expected, the presence of a local anesthetic masked pain on injection but not muscle damage. The rat paw-lick model is an alternative to the traditional rabbit muscle irritation model for rapidly assessing both pain on injection and muscle irritation of parenteral formulations.