A 60 Hz magnetic field does not affect the incidence of squamous cell carcinomas in SENCAR mice.

Two groups of SENCAR mice were treated with a single dose of carcinogen and then, for 23 weeks, with a chemical tumor promoter to induce skin tumors. During this period, one group was coexposed to a 2 mT power frequency (60 Hz) magnetic field, while the other was exposed to sham conditions. Application of the tumor promoter ceased after 23 weeks, but the exposure to sham conditions or magnetic fields continued for an additional 29 weeks. No difference was found between the two groups of mice in terms of the incidence of total tumors (P =.297) or squamous cell carcinomas (SSC) (P =.501). In summary, there was no evidence to support the hypotheses that 60 Hz magnetic fields (MF) can influence the development of either papillomas or SSC under our defined experimental conditions. The overall results add to previous animal studies that find no association between exposure to 60 Hz MF and the incidence of benign or malignant tumors.

Comparative study of the anti-human cytomegalovirus activities and toxicities of a tetrahydrofuran phosphonate analogue of guanosine and cidofovir.

Cidofovir is the first nucleoside monophosphate analogue currently being used for the treatment of human cytomegalovirus (HCMV) retinitis in individuals with AIDS. Unfortunately, the period of therapy with the use of this compound may be limited due to the possible emergence of serious irreversible nephrotoxic effects. New drugs with improved toxicity profiles are needed. The goal of this study was to investigate the anticytomegaloviral properties and drug-induced toxicity of a novel phosphonate analogue, namely, (-)-2-(R)-dihydroxyphosphinoyl-5-(S)-(guanin-9'-yl-methyl) tetrahydrofuran (compound 1), in comparison with those of cidofovir. The inhibitory activities of both compounds on HCMV propagation in vitro were similar against the AD 169 and Towne strains, with 50% inhibitory concentrations ranging from 0.02 to 0.17 microgram/ml for cidofovir and < 0.05 to 0.09 microgram/ml for compound 1. A clinical HCMV isolate that was resistant to ganciclovir and that had a known mutation within the UL54 DNA polymerase gene and a cidofovir-resistant laboratory strain derived from strain AD 169 remained sensitive to compound 1, whereas their susceptibilities to ganciclovir and cidofovir were reduced by 33- and 10-fold, respectively. Both compound 1 and cidofovir exhibited equal potencies in an experimentally induced murine cytomegalovirus (MCMV) infection in mice, with a prevention or prolongation of mean day to death at dosages of 1.0, 3.2, and 10.0 mg/kg of body weight/day. In cytotoxicity experiments, compound 1 was found to be generally more toxic than cidofovir in cell lines Hs68, HFF, and 3T3-L1 (which are permissive for HCMV or MCMV replication) but less toxic than cidofovir in MRC-5 cells (which are permissive for HCMV replication). Drug-induced toxic side effects were noticed for both compounds in rats and guinea pigs in a 5-day repeated-dose study. In guinea pigs, a greater weight loss was noticed with cidofovir than with compound 1 at dosages of 3.0 and 10.0 mg/kg/day. An opposite effect was detected in rats, which were treated with the compounds at relatively high dosages (up to 100 mg/kg/day). Compound 1 and cidofovir were nephrotoxic in both rats and guinea pigs, with the epithelium lining the proximal convoluted tubules in the renal cortex being the primary target site. The incidence and the severity of the lesions were found to be dose dependent. The lesions observed were characterized by cytoplasm degeneration and nuclear modifications such as karyomegaly, the presence of pseudoinclusions, apoptosis, and degenerative changes. In the guinea pig model, a greater incidence and severity of lesions were observed for cidofovir than for compound 1 (P < 0.001) with a drug regimen of 10 mg/kg/day.

Skin reservoir formation and bioavailability of dermally administered chemicals in hairless guinea pigs.

There is concern as to whether dermally applied chemicals that remain in the skin after exposure are bioavailable and should be included as part of the systemic dose; this study was conducted to investigate the temporal relationship between the skin depot and absorbed dose. Single doses of 14C-labelled phenanthrene, benzo[a]pyrene or di(2-ethylhexyl) phthalate were administered dermally to groups of four female, Hartley hairless guinea pigs which were housed individually in metabolism cages to collect urine and faeces for radioassay. The animals were sacrificed at 6 hr, 24 hr, 48 hr, 7 days or 14 days after dosing to harvest skin specimens for the determination of radioactivity by autoradiographic and liquid scintillation methods, and to determine the dose that remained in the body. It was found that for all three compounds the amount of chemical left in the skin decreased over time while the cumulative percent dose excreted in urine and faeces increased. The autoradiographic results were consistent with those obtained from the liquid scintillation method showing a gradual decrease in radioactivity grain accumulation over the time periods for the three compounds, with the highest grain density observed around hair follicles of the skin. The results of this study indicate that the chemicals left in the skin after surface washing eventually enter the systemic circulation and should be considered as part of the total dose absorbed, and that the hair follicle may play an important role in percutaneous penetration.

Early histopathologic and ultrastructural changes in the heart of Sprague-Dawley rats following administration of soman.

Male Sprague-Dawley rats were given atropine methylnitrate (20 mg/kg) and HI-6 (125 mg/kg) ip 10 min before a single injection of 130 micrograms soman/kg sc, and the heart was examined by light and electron microscopy 10, 25, 45, 90, and 180 min after the onset of seizures. Seizures appeared within 6-11 min after treatment. Control rats were given saline sc in place of soman. Early myocardial lesions consisting of hypercontraction and hyperextension of sarcomeres, focal myocytolysis, and contraction bands were detected in individual or groups of myocardial fibers. Hypercontraction was characterized by shortening of the sarcomere length, disappearance of the I and H bands, and thickening of the Z line. In contrast, hyperextended sarcomeres had thickened I and H bands. Myocytolysis was characterized by a progressively severe focal dissolution of myofilaments and edema of the affected sarcoplasmic area. Contraction bands appeared to result from the breakdown of markedly hypercontracted myofibril bundles. Due to the presence of a number of surviving myofilaments and the preservation of the sarcolemmal tube, distortion of the overall myocytic structure was minimal. Changes in the mitochondria and other intracellular organelles were also minimal and nonspecific. The close resemblance of morphologic findings to those induced by catecholamines supports the view that soman-induced myocardial damage is secondary to a treatment-related release of unphysiologic amounts of endogenous catecholamines.

A 60-Hz magnetic field increases the incidence of squamous cell carcinomas in mice previously exposed to chemical carcinogens.

The exposure of tumor-bearing SENCAR mice to a magnetic field of 2 mT at a frequency of 60 Hz for 52 weeks, was found to increase the rate of malignant conversion in chemically-induced dorsal skin papillomas. Detailed histopathology revealed the presence of squamous cell papillomas and squamous cell carcinomas in both sham and magnetic field exposed mice at week 52. However, of the nine mice assessed as having squamous cell carcinomas, eight came from the group exposed to magnetic fields, a difference which is statistically significant at P = 0.03.

Histomorphogenesis of soman-induced encephalocardiomyopathy in Sprague-Dawley rats.

Although myocardial damage caused by soman has been previously reported, its relation to brain damage is unclear. In order to clarify this relationship, we examined the histomorphogenesis of central nervous system (CNS) and myocardial lesions in Sprague-Dawley rats, given atropine methylnitrate (20 mg/kg) and HI-6 (125 mg/kg) ip 10 min before a single injection of 0 or 130 micrograms soman/kg (sc) and sacrificed 45 min and 1.5 hr, 3 hr, 24 hr, and 72 hr later. Bilaterally symmetrical CNS damage began with vacuolation of the neuropil and was followed by astrocytic degeneration and neuronal necrosis culminating in liquefaction necrosis and focal hemorrhage. The cerebral cortex, limbic system, thalamus, and substantia nigra were common target sites. Repair in affected sites was characterized by capillary endothelial cell proliferation, microgliosis, and reversal of microvacuolation. Myocardial damage began with myocytolysis and contraction bands and evolved into coagulative myocytolysis and replacement fibrosis with a transient recruitment of acute inflammatory cells. The left ventricle, especially its free wall and papillary muscles, was consistently affected. There was good correlation among seizures, CNS damage, and myocardial lesions at all times following treatment. The results support the view that CNS lesions are associated with protracted seizure activity and provide evidence that myocardial damage is neurogenic.

Experimental oral toxicity of domoic acid in cynomolgus monkeys (Macaca fascicularis) and rats. Preliminary investigations.

A recent outbreak of marine food poisoning in humans was attributed to the consumption of blue mussels (Mytilus edulis L.) contaminated with domoic acid (DA) that was produced by the diatom Nitzschia pungens. The clinical and morphological effects of single oral doses of extracts of mussels contaminated with DA or of DA isolated from toxic mussels were investigated in small groups (one to six) of cynomolgus monkeys (Macaca fascicularis; 0.5-10 mg DA/kg body weight) and of Sprague-Dawley rats (60 to 80 mg DA/kg body weight). Control animals were either given saline or were not treated. To test whether monosodium glutamate, present in the food consumed by some affected humans, and dimethylsulphoxide, suspected of being present in the plankton, enhanced the response, monosodium glutamate (at 0.25% of mussel extract bolus) or dimethylsulphoxide (at 1 g per bolus) were co-administered to two (one each) of the DA-treated monkeys. DA-treated monkeys developed transient excitation characterized by vomiting. DA-treated rats showed withdrawal followed by hyperexcitation and death (in one case). Mild to moderate central nervous system lesions consistent with neuroexcitation were present in both monkeys and rats. The addition of monosodium glutamate and dimethylsulphoxide had no significant effect on the appearance and severity of central nervous system clinical signs and lesions. The wide variations in the response of test animals to orally administered DA were attributed to the protective effect of vomiting, and to suspected incomplete or slow gastro-intestinal absorption of the toxic agent. The results reinforce the view that DA is an emetic and that under appropriate conditions may also inflict excitotoxic central nervous system damage.

Neuropathology of excitatory neurotoxins: the domoic acid model.

A novel type of intoxication in Canada in 1987 was traced to consumption of cultivated mussels contaminated with the excitotoxin domoic acid. Studies carried out in rats and monkeys revealed that parenterally administered domoic acid induces in rats neuroexcitatory phenomena culminating in seizures. Monkeys respond with gagging, emesis and less clearly evident seizure activity. CNS damage consisting of dendrotoxic and gliotoxic edema and nerve cell degeneration occurs in structures of the limbic system and the retina in both species. CNS lesion distribution similarities in animals treated with domoic acid or kainic acid suggest that these excitotoxins share a common pathogenesis mediated by glutamic acid, a putative endogenous excitatory neurotransmitter.

Acute parenteral neurotoxicity of domoic acid in cynomolgus monkeys (M. fascicularis)

To study the CNS effects of domoic acid (D.A.), 6 adult Cynomolgus monkeys (M. fascicularis) were dosed intraperitoneally (4 mg/kg) or intravenously (0.025-0.5 mg/kg) with D.A. obtained from cultured mussels contaminated with this neurotoxin. Clinical signs of neurotoxicity were preceded by a short presymptomatic period (2-3 min) and an even shorter prodromal period (0.5-1 min). The symptomatic period proper was characterized by persistent chewing with frothing, varying degrees of gagging, and vomit. Monkeys in the higher dose regimen exhibited additional signs including abnormal head and body positions, rigidity of movements and loss of balance, and tremors. The duration of the symptomatic period was dose dependent. Excitotoxic lesions consisting of vacuolation of the neuropil, astrocytic swelling, and neuronal shrinkage and hyperchromasia were detected in the area postrema, the hypothalamus, the hippocampus, and the inner layers of the retina in monkeys given D.A. at 0.5 mg/kg intravenously and 4 mg/kg intraperitoneally. It was concluded that D.A., administered intravenously, is neuroexcitatory and a powerful emetic at doses of 0.025 to 0.2 mg/kg. At higher doses (0.5 mg/kg intravenously and 4 mg/kg intraperitoneally), D.A. is strongly excitotoxic.

Acute neurotoxicity of domoic acid in the rat.

A recent outbreak of human food poisoning, characterized by severe gastrointestinal and neurologic abnormalities, with a fatal outcome in 3 patients, was attributed to the consumption of poisonous mussels containing domoic acid at an abnormally high concentration. The purpose of the present study was to determine if domoic acid, a glutamate analogue extracted from poisonous mussel, was neurotoxic to rats. Groups of female Sprague-Dawley rats were dosed once intraperitoneally with 0, 1, 2, 4, or 7.5 mg domoic acid/kg of body weight and observed for a maximum period of 24 hr. Clinically, control rats and rats in the 1 mg/kg group were unremarkable. Seventy-five percent of the animals in the 2 mg/kg group had equivocal transient behavioral signs. One that was given 2 mg/kg and all rats given in excess of 4 mg/kg of body weight developed unequivocal behavioral and neurologic signs culminating in partial seizures and status epilepticus. Histopathologically, severely affected rats developed selective encephalopathy characterized by neuronal degeneration and vacuolation of the neuropil in the limbic and the olfactory systems, and retinopathy characterized by neuronal hydropic degeneration of the inner nuclear layer and vacuolation of the external plexiform layer. The results of this study suggest that domoic acid is excitotoxic and causes a characteristic syndrome with clinical signs and histopathologic lesions similar to those reported for kainic acid.

Domoic acid poisoning and mussel-associated intoxication: preliminary investigations into the response of mice and rats to toxic mussel extract.

Consumption of cultivated blue mussels from Prince Edward Island was recently associated with episodes of gastro-intestinal and neurological distress. Extracts of the toxic mussels, tested in the mouse bioassay for paralytic shellfish poison, caused an atypical response characterized by scratching, convulsions and death. The present investigation shows that the domoic acid present in toxic mussels can produce in mice and rats signs identical to those induced by mussel extracts. These studies, preliminary in nature by virtue of the scarcity of domoic acid, gave ip no-effect levels in mice of 0.59 mg/kg body weight based on the behavioural response (scratching) and 2.4 mg/kg for death. These levels correspond to levels of 24 and 94 ppm in mussels. When administered orally doses of between 35 and 70 mg domoic acid/kg body weight were required to produce toxicity in mice and rats. This reduced toxicity is consistent with a lack of absorption from the gastro-intestinal tract: faecal excretion accounted for 102 +/- 17% and 98 +/- 12% (mean +/- SE) of the domoic acid administered to mice and rats, respectively. Since human intoxication occurred at an estimated 1-5 mg domoic acid/kg body weight, susceptible individuals appear to be more sensitive than rodents to the oral toxicity of domoic acid.

Alteration of neuronal cytoskeletal organization in dorsal root ganglia associated with pyridoxine neurotoxicity.

The pathogenesis of the sensory neurotoxicity arising from high doses of pyridoxine is obscure. Beagle dogs were fed 200 mg pyridoxine/kg per day and killed at 4, 10, 14 and 16 days. Dorsal root ganglia (DRG) and their processes were processed for electron microscopy and teased-fiber preparation following perfusion of anesthetized animals with heparinized saline and a fixative solution of 3% paraformaldehyde, 1% glutaraldehyde. Four days after initiation of treatment a striking accumulation of neurofilament (NF) in proximal unmyelinated axons of the DRG was observed. Domains of altered NF cytoskeleton consisting of well-demarcated zones of higher packing density and anomalous orientation were observed, mainly in the myelinated part of the DRG segment. In addition, aggregates of microtubules (MT) were noted. In the cyton the Golgi complexes were abundant and the Nissl bodies together with the NF appeared increased in numbers. At 10 days NF and MT aggregations were readily apparent in both perikarya and proximal cell processes. This phenomena was diminished in the 14- and 16-day-treated animals and retrogressive histological features appeared in the soma and in axons. Degeneration of NF with subsequent reduction in size of the axonal swellings and axonal breakdown with phagocytosis were prominent in central and peripheral processes of DRG. Cytons distended by NF were less prominent. Necrotizing changes, evidenced by disruption of the soma with the proliferation of satellite cells, were present. These results indicate that an early morphological correlate of pyridoxine neurotoxicity is the accumulation of NF with MT-NF dissociation in the unipolar process of the DRG in the absence of extensive vacuolization, and that the observed cytoskeletal disruption may be related to an increased rate of NF protein synthesis together with mechanical obstruction of transport phenomena.

Mode of inheritance of Samoyed hereditary glomerulopathy: an animal model for hereditary nephritis in humans.

The pedigree of a line of Samoyed dogs with Samoyed hereditary glomerulopathy (SHG) was investigated to determine the mode of inheritance. Sixty percent of males were affected with severe renal disease that progressed to renal failure before 15 months of age. In contrast, female carriers showed less severe involvement and their disease did not progress to renal failure. This pattern is consistent with the inheritance of an X-linked dominant gene. A similar mode of inheritance has been postulated in some families with hereditary nephritis. Further similarities between SHG in dogs and hereditary nephritis in humans have been demonstrated previously in clinical and renal morphologic studies. The present study supports the view that this line of Samoyed dogs would be an appropriate model for studying the human disease.

A short-term feeding study with deoxynivalenol (vomitoxin) using rats.

Groups of 25 male and 25 female Sprague-Dawley rats were fed diets containing 0, 0.25, 0.5, or 1.0 mg of deoxynivalenol (DON)/kg body wt for approximately 9 weeks. Each animal's body weight and feed consumption were measured weekly. Upon termination of the study, each animal's body, heart, liver, spleen, thymus, and kidneys were weighted. A hematological assessment and a 16-parameter serum evaluation were conducted and 8 animals from each group were randomly selected to receive tritiated thymidine iv to assess mitotic activity in the esophagus, jejunum, and spleen. A statistically significant, dose-related decrease in body weight gain was observed for all treated females, but only the males dosed at 1.0 mg/kg were found to have a treatment-related weight gain suppression. The reduced body weight was attributed to a reduced feed consumption. Reductions that were observed in absolute organ weights, were not apparent after adjusting for body weight suppression. No dose-related hematological findings were found. Serum chemistry changes included increased concentrations of chloride and decreased concentrations of CO2 and albumin, but only in the females. No histopathological lesions were attributed to DON treatment, but significant decreases in thymidine labeling occurred in the spleens and jejunums from the males dosed at 1.0 mg/kg.

Effects of the spermicide nonoxynol-9 on the pregnant uterus and the conceptus of rat.

In a series of experiments the embryotoxic potential of nonoxynol-9 (N-9) was investigated in adult female rats given a single per vaginam application of 5 mg/100 g (0.1 ml/100 g) of this spermicide on day 3 (pre-implantation period) or 7 (postimplantation period) of gestation. Control rats were given physiologic saline (0.1 ml/100 g) intravaginally. The vulvar labia were apposed for 24 h by metallic clips to prevent leakage of the solution. Groups of dams treated on pregnancy days 3 and 7 were killed by CO2 inhalation on gestational days 6, 9, 12 and 15, and 8, 9, 10, 12 and 15, resorption and total resorption of the conceptus, embryonal and placental resorption and total resorption of the conceptus, embryonal and placental necrosis, placentitis, endometritis, multicystic endometrium, and diffuse or segmental dilatation of the uterine horns. Generally, the incidence of these lesions varied with the length of time after N-9 was administered and it was consistently higher in the females treated on pregnancy day 3 than in those treated on day 7. Acute vaginitis waned with time after the application of N-9. It was concluded that under the conditions of this study, N-9 is embryocidal/fetocidal in the rat if administered during the first week of gestation. The impairment of embryonal/fetal development was attributed to the N-9-induced changes in the endometrium, the placenta and/or the embryo.