Lesions in the Larynx of Wistar RccHan: WIST Rats

Difficulties in translating in vitro hazards of local acute irritants to relevant human risk: Learnings from Captan and Folpet

In order to assess the regulatory value of New Approach Methodologies (NAMs), authors should provide their opinion on the physiological and exposure relevance of observed in vitro effects for correlation with predicted in vivo effects. Further, peer-reviewers should be encouraged to request such information during review. This is critical to scientifically transition to animal-free, reliable, robust and -- most importantly -- relevant regulatory toxicology and risk assessment approaches. Recently published studies using NAMs for the fungicides Captan and Folpet illustrate the difficulties and limitations of applying NAMs to adequately assess the toxicological relevance of these substances.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

Inhalation toxicity of cyclic semi-volatile methylsiloxanes: Disentangling the conundrum of phase-specific adaptations from adverse outcomes

This paper compares the phase-specific inhalation toxicity of the cyclic semi-volatile methylsiloxanes (cVMSs) D4, D5 and D6. The objectives of this paper are to re-analyze information from acute to chronic inhalation studies on rats with these cVMSs to identify the unifying principles of phase-specific toxicity at the portal-of-entry and if they depend on acute, acute-on-chronic or chronic mechanisms. This re-analysis supports the hypothesis that concentrations must be high enough to exceed the vapor saturation at any given temperature for stabilizing the aerosol phase and evoking phase-specific effects at sites of the respiratory tract susceptible to the cVMSs-specific physicochemical properties amphiphilicity and surface tension. In summary, the portal-of-entry effects and related findings appear to be acute in nature and specific to liquid aerosol. The repeated inhalation exposure studies with D4 and D5 up to two years in duration did not reveal chronic aggravations of portal of entry outcomes. Findings at a pulmonary location where amphiphilic surfactant molecules are present appear to be caused by the acute adaptation to deposited dose. Such outcome should better be described as a high-dose liquid aerosol phenomenon imparted by the physicochemical properties "liquid" and "hydrophobic". This calls for a phase-specific human risk characterization of cVMSs.

Epithelial Alteration Associated With Recovery From Laryngeal Squamous Metaplasia in Rats: Kinetics of Recovery From a Test Item-Related Change

Squamous metaplasia is a nonspecific adaptive response to chronic irritation in the larynx and is often diagnosed as a test item-related change in rat inhalation studies. Investigating scientists are frequently asked to assess the adversity of laryngeal squamous metaplasia and to interpret its relevance to human risk. One factor in predicting relevance to human risk is the kinetics (degree and speed) of recovery following the cessation of exposure to the test item. Most reports describing recovery from squamous metaplasia in the rat larynx discuss the more severe end of the spectrum of metaplastic change (moderate to severe) and include relatively long (6 weeks or more) recovery periods. We conducted 2 studies to evaluate the toxicity and recovery from any potential effects of 4-(Chloro-2-methylphenoxy) butyric (MCPB) acid, a herbicide, when administered by inhalation to young male Sprague Dawley rats for 3 to 4 weeks. The studies resulted in minimal to moderate laryngeal squamous metaplasia for which we describe the kinetics of recovery over 1 to 4 weeks. We found that the microscopic change epithelial alteration, which is normally considered to be a precursor in the development of squamous metaplasia, can occur as a transitional stage between squamous and normal epithelium during recovery.