Hyalinization of the pyloric stomach in CD-1 mice following oral (dietary) administration of the corticosteroid agonists mometasone furoate, budesonide, and flunisolide.

The purpose of this study was to compare the toxicity of three marketed corticosteroid receptor agonists (mometasone furoate, budesonide, or flunisolide) to the stomach of female CD-1 mice following oral administration via the diet for up to 52 weeks, with a 16-week recovery period (budesonide and flunisolide). A range of tissues was examined by light microscopy, accompanied by clinical pathology measurements to assess anticipated corticosteroid effects as a surrogate marker of systemic drug exposure. Microscopic changes seen in the stomach with each corticosteroid included pyloric hyalinization. This previously unreported finding was investigated using histochemical and immunohistochemical techniques and was found to consist of hyalinized collagen, in association with increased immunohistochemical signal for transglutaminase-2 and osteopontin. The significance of the osteopontin finding is unclear; however, the ability of transglutaminase-2 to facilitate the formation of degradation resistant protein bonds implies this protein may be involved in the pathogenesis of this change. Furthermore, published evidence that transglutaminase-2 may be induced by a corticosteroid agonist raises the possibility that pyloric stomach hyalinization may be a class effect of corticosteroids via the action of this enzyme.

Eosinophilic inclusions in rat Clara cells and the effect of an inhaled corticosteroid.

Large eosinophilic cytoplasmic inclusions (ECIs) are occasionally seen in untreated rat Clara cells. Following inhalation exposure to a corticosteroid, the number of ECIs was increased. This is the first histopathological description of rat ECIs and attempted characterization by immunohistochemistry, in situ hybridization, and electron microscopy. ECIs were strongly positive for surfactant protein D (SP-D) and weakly positive for Clara cell specific protein (CCSP). Clara cell cytoplasm was positive for CCSP mRNA regardless of ECIs, but not within ECIs. Corticosteroid treatment and ECI presence did not affect the immunohistochemistry and in situ hybridization staining intensities. Electron microscopy revealed large intracytoplasmic granules with an irregular limiting membrane. The ECI number was microscopically quantified in rats from three-, six-, and twenty-four-month studies. The mean ECI counts in treated rats increased from three- to fifty-four-fold with a positive dose-related trend, when compared with vehicle controls. Although the mechanism is unclear, SP-D and to a lesser extent CCSP accumulate in the ECIs. As human bronchial epithelium does not appear to contain structures analogous to the ECI, it is suggested that the observation of an increased number of ECIs in the treated rats is not likely to be relevant for human clinical risk assessment.

A cohort study of telomere and telomerase biology in cats.

OBJECTIVE: To investigate telomere lengths in tissues of domestic shorthair (DSH) cats of various ages, evaluate the relationship between telomere length and age of cats, and investigate telomerase activity in the somatic tissues of cats. SAMPLE POPULATION: Tissues obtained from 2 DSH cats and blood samples obtained from 30 DSH cats. PROCEDURE: DNA isolated from blood cells and somatic tissue samples was subjected to terminal restriction fragment (TRF) analysis to determine mean telomere repeat lengths. Protein samples were subjected to analysis by use of a telomeric repeat-amplification protocol to assess telomerase activity. RESULTS: MeanTRF values of cats ranged from 4.7 to 26.3 kilobase pairs, and there was significant telomeric attrition with increasing age of cat. Telomerase activity was not found in a wide range of normal tissues obtained from 2 cats. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of these results clearly indicates that telomeres are shorter in older cats, compared with young cats; therefore, telomeres are implicated in the aging process. The analysis of telomerase activity in normal somatic tissues of cats reveals a pattern of expression similar to that found in human tissues. IMPACT FOR HUMAN MEDICINE: Fundamental differences in the biological characteristics of telomeres and telomerase exist between humans and the other most widely studied species (ie, mice). The results reported here reveal similarities in telomere and telomerase biologic characteristics between DSH cats and humans. Hence, as well as developing our understanding of aging in cats, these data may be usefully extrapolated to aging in humans.

Telomere lengths in dogs decrease with increasing donor age.

In vitro and in vivo studies of human tissues have demonstrated telomeric attrition with age and have linked this attrition to cellular senescence and aging. Telomere studies in canine subjects have not thus far consistently uncovered the same pattern of telomere attrition that would be expected because of the end replication problem. In this report we describe the investigation of telomere lengths in a broad age range of dogs from three different breeds: the Labrador Retriever, Miniature Schnauzer and Beagle. Peripheral blood mononuclear cell-derived DNA samples were subjected to terminal restriction fragment (TRF) analysis and demonstrated a range of mean TRFs from 9.7 to 22.3 kbp. Telomeric attrition tended to be associated with increasing donor age (P = 0.06). Interbreed differences in mean TRF values were also noted (P = 0.006). These results warrant further investigation of possible interbreed differences, given that shorter telomeres may contribute to differing life expectancy between breeds.