Serum enzyme alterations in arginine-deficient, influenza-infected ferrets: a potential animal model of Reye's syndrome

Use of Ferrets in Toxicity Testing

A selective review of the literature is presented in order to introduce the reader to the extensive studies conducted in the ferret ( Mustela putorius furo) in such diverse fields as virology, gastroenterology, and teratology. Husbandry, anatomical variations, and the modeling of specific human disorders are discussed to indicate the increasing recognition of this species as a valuable asset in toxicity testing.

Influenza B virus model of Reye's syndrome in mice: the effect of aspirin

Aspirin is a possible cofactor with influenza B virus in Reye's syndrome. In an attempt to determine whether single or multiple doses of acetylsalicylic acid (ASA) alter mortality in an influenza B virus mouse model of Reye's syndrome, either ASA (300 to 667 mg/kg) or saline was given intraperitoneally to 3-week-old Balb/c mice. Two hours later, one median lethal dose (LD50) of influenza B/Lee virus was given intravenously. Mortality was not significantly increased by the single ASA dose. Blood ASA levels rose as high as 68 mg/dl. The average ASA blood levels in mice 12 hours after receiving the virus plus 667 mg/kg ASA was 22.6 mg/dl, which was significantly higher than the 3.4 mg/dl for mice who received saline plus ASA. No significant increase in mortality occurred in mice given 67 mg/kg ASA twice daily for 7 days and one LD50 dose of virus on day 4. We conclude that a single dose of ASA at up to half the median lethal dose or multiple doses of ASA do not significantly increase mortality in this influenza virus model of Reye's syndrome. However, influenza B virus infection appears to interfere with ASA metabolism.

Effects of influenza infection, aspirin, and an arginine-deficient diet on the inner ear in Reye's syndrome

The individual effects of an influenza B viral infection, aspirin, and an arginine-deficient diet on the inner ear were assessed in the ferret model for Reye's syndrome using both functional and morphological parameters. Auditory brainstem evoked responses recorded from inoculated ferrets revealed threshold elevations and increased latencies during the first 72 hours, but approximated those of control animals by 96 hours. Although there was a mild distention of Reissner's membrane, no pronounced structural alterations in sensory or supporting cells were observed in cochleas from inoculated ferrets. The administration of aspirin appeared to alter neither the functional nor the structural integrity of the cochlea. The presentation of an arginine-deficient diet, creating a hyperammonemic condition, led to both altered auditory evoked responses and vacuolization of cochlear tissues after treated animals had undergone seizures and coma. These data demonstrated that both influenza B and the arginine-deficient diet individually affected the hearing of treated animals. The individual agents did not alter the cochlea as severely as when they were presented in combination. These results suggest that hearing impairment in patients with Reye's syndrome may be a result of potentiation of certain metabolic-altering agents.

Altered auditory brainstem evoked responses in the ferret model for Reye's syndrome

The effects of influenza B, aspirin and hyperammonemia on the functional integrity of the cochlea were examined using the ferret model for Reye's syndrome. Auditory brainstem evoked responses (ABR) were recorded from treated ferrets and compared to those recorded from controls. Delayed latencies of all waves, as well as increased I-IV Interwave latencies were observed in recordings from treated ferrets. Importantly, the latencies of Wave I, nerve generator potential from the eighth nerve, and Wave IV, response potential from the brainstem nuclei, increased on Days 3 and 5 of the study. However, recorded ABR from treated ferrets on Day 10 showed that while the latencies of Wave IV were approximate to those of controls, Wave I remained delayed. These results suggest that systemic effects of influenza B, aspirin and hyperammonemia may lead acutely to both peripheral and central auditory dysfunction, and that the functional integrity of the central auditory system may recover more quickly than that of the peripheral system. Furthermore, these results suggest that such effects may lead to acute transient hearing impairment in patients with Reye's syndrome.

Inner ear changes in the ferret model for Reye's syndrome

The acute effects of influenza B, aspirin, and hyperammonemia on the inner ear were examined using the ferret model for Reye's syndrome. Histopathologic examination revealed varying degrees of vacuolization in both the sensory and nonsensory endolymphatic tissues of the cochlear and vestibular membranous labyrinth. The secretory epithelial cells of the stria vascularis and the vestibular dark cells appeared to be more severely affected, as demonstrated by the presence of an extensive number of intracytoplasmic vacuoles. The cells of the perilymphatic tissues appeared to be unaltered. Although all neuroepithelial regions of the inner ear appeared to be altered, an unexpected observation was that only the inner hair cells of the organ of Corti were pathologically affected. These results suggest that metabolic and virus-induced derangements may alter inner ear microhomeostasis in patients with Reye's syndrome and may potentially result in loss of hearing in such patients.

Free fatty acids in an animal model of Reye's syndrome

Recent studies have indicated that viral infections, aspirin treatment and hyperammonemia are associated with Reye's syndrome. It has also been reported that free fatty acids in serum and total lipids in the liver of Reye's syndrome patients are elevated during illness. The role of the lipid changes in the development of the disorder cannot be optimally studied in human patients, because infection and aspirin ingestion occur prior to the earliest symptoms of Reye's syndrome. Effects of influenza B infection, aspirin treatment and hyperammonemia on the level of free fatty acids, total lipids and triacylglycerols in serum and liver of an animal model of Reye's syndrome are reported here. Hyperammonemia was produced in young, male ferrets either by feeding them small amounts of an arginine-deficient diet after overnight fasting or by an intraperitoneal injection of jackbean urease. The ferret model resembled Reye's syndrome in developing increased levels of individual and total serum free fatty acids, liver triacylglycerol and total lipids. The results also indicate that influenza infection or aspirin treatment, or both, while increasing the severity of encephalopathy in the deficient ferrets, did not cause a significant change in the level of serum free fatty acids. Other results suggest that elevation of serum ammonia, serum free fatty acid or liver lipids, either singly or in various combinations, does not provide conditions that can explain the rapidly developing encephalopathy in the arginine-deficient ferrets.

Interactions of aspirin and other potential etiologic factors in an animal model of Reye syndrome

Recent studies of Reye syndrome (RS) patients have suggested aspirin treatment as a possible factor in the etiology of this often fatal childhood disorder. the relationship of aspirin treatment to other factors that have been strongly implicated (influenza, ammonia toxicity) cannot be examined directly in patients because aspirin treatment is usually initiated by family members in the prodromal period before RS is diagnosed. In this report we describe the use of an animal model for RS in examining the interactions of these several potential etiological factors. Hyperammonemia and coma were produced in young male ferrets by a brief feeding of an arginine-deficient diet. The effects of influenza infection or aspirin treatment (or both) of control and hyperammonemic ferrets on their serum levels of ammonia, glutamic-oxaloacetic transaminase (GOT;L-aspartate:2-oxoglutarate aminotransferase, EC 2.6.1.1), ornithine carbamoyltransferase (OCT; carbamoylphosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3), bilirubin, and salicylate were studied. Liver levels of lipids, proteins, and several urea-cycle enzymes were also determined in the comatose ferrets and compared with those of untreated controls and of controls treated with influenza or aspirin, or both. Synergism of these three factors (hyperammonemia, influenza infection, and aspirin treatment) in causing RS-like alterations in these parameters was observed.