Alveolar Macrophage Distribution in a Mouse Model: The Importance of the Fixation Method.

Rodent lungs are routinely examined after intratracheal instillation (IT) of fixative. This study compares the histopathologic appearance of the lung after IT fixation with air inflation (AI) followed by immersion fixation. Lungs from mice chronically exposed to cigarette smoke were fixed either by IT or by AI. Increased numbers of macrophages with differing distributions were seen in both groups. Lungs fixed by IT had prominent, large macrophages floating in the alveolar lumina, as well as macrophage clusters and loose aggregates, often near terminal airways. Macrophages in lungs fixed by AI were randomly distributed throughout the lung, lying singly along alveolar walls, with large numbers visible in the interstitium. Clusters of macrophages were seen in the airways after AI but were fewer after IT fixation. The effects of intratracheal fixation on lung macrophages need to be considered carefully when assessing the significance of changes in macrophage appearance and distribution.

Temporal gene expression profiling indicates early up-regulation of interleukin-6 in isoproterenol-induced myocardial necrosis in rat.

Gene expression was evaluated in the myocardium of male Wistar rats after a single subcutaneous administration of 0.5 mg of isoproterenol, a beta-adrenergic agonist that causes acute tachycardia with subsequent myocardial necrosis. Histology of the heart, clinical chemistry, and hematology were evaluated at 9 time points (0.5 hours to 14 days postinjection). Myocardial gene expression was evaluated at 4 time points (1 hour to 3 days). Contraction bands and loss of cross-striation were identified on phosphotungstic acid-hematoxylin-stained sections 0.5 hours postdosing. Plasma troponin I elevation was detected at 0.5 hours, peaked at 3 hours, and returned to baseline values at 3 days postdosing. Interleukin 6 (Il6) expression spiked at 1 to 3 hours and was followed by a short-lived, time-dependent dysregulation of its downstream targets. Concurrently and consistent with the kinetics of the histologic findings, many pathways indicative of necrosis/apoptosis (p38 mitogen-activated protein kinase [MAPK] signaling, NF-kappaB signaling) and adaptation to hypertension (PPAR signaling) were overrepresented at 3 hours. The 1-day and 3-day time points indicated an adaptive response, with down-regulation of the fatty acid metabolism pathway, up-regulation of the fetal gene program, and superimposed inflammation and repair at 3 days. These results suggest early involvement of Il6 in isoproterenol-induced myocardial necrosis and emphasize the value of early time points in transcriptomic studies.

Toxicogenomics in predictive toxicology in drug development.

The goal of toxicology is the assessment of possible risk to man. An emerging technology with the potential to have a major impact on risk assessment is toxicogenomics. In this review, we provide an overview of the many possibilities for toxicogenomics including technology platforms, data interpretation, and regulatory perspective and we give examples of toxicogenomics investigations. Toxicogenomics is a powerful tool for compound classification, for mechanistic studies, and for the detection of toxicity markers. Thus, toxicogenomics helps in the extrapolation of findings across species and increases predictability. Biomarkers are valuable in the evaluation of compounds at earlier development phases, improving clinical candidate selection. Caution regarding the interpretation of the results is still necessary. Nevertheless, toxicogenomics will accelerate preclinical safety assessments and improve the prediction of toxic liabilities, as well as of potential risk accumulation for drug-drug or drug-disease interactions.