Genetic toxicity assessment: employing the best science for human safety evaluation part III: the comet assay as an alternative to in vitro clastogenicity tests for early drug candidate selection.

Early screening of drug candidates for genotoxicity typically includes an analysis for mutagenicity in bacteria and for clastogenicity in cultured mammalian cells. In addition, in recent years, an early assessment of photogenotoxicity potential has become increasingly important. Also, for screening purposes, expert computer systems can be used to identify structural alerts. In cases where structural alerts are identified, mutagenicity testing limited to bacteria can be conducted. The sequence of computer-aided analysis and limited testing using bacteria allows for screening a comparatively large number of drug candidates. In contrast, considerably more resources, in terms of supplies, technical time, and the amount of a test substance needed, are required when screening for clastogenic activity in mammalian cells. In addition, the relatively large percentage of false positive results for rodent carcinogenicity associated with clastogenicity assays is of considerable concern. As a consequence, mammalian cell-based alternatives to clastogenicity assays are needed for early screening of mammalian genotoxicity. The comet assay is a relatively fast, simple, and sensitive technique for the analysis of DNA damage in mammalian cells. This assay seems especially useful for screening purposes because false positives associated with excessive toxicity appear to occur less frequently, only relatively small amounts of a test compound are needed, and certain steps of the test procedure can be automated. Therefore, the in vitro comet assay is proposed as an alternative to cytogenetic assays in early genotoxicity/photogenotoxicity screening of drug candidates.     

Bone properties in patients with acromegaly: quantitative ultrasound of the heel.

Growth hormone (GH) deficiency and acromegaly serve as good models for investigating the effects of GH on bone remodeling. However, the results from various studies are rather conflicting. The aim of our study was to estimate the potential role of gender, disease activity, and duration on both calcaneus quantitative ultrasound (QUS) parameters and bone turnover markers in patients with acromegaly. Thirty-six acromegalic patients (17 men, 19 women) and 3 age- and gender-adjusted controls for every patient were included in the study. The disease was active in 22 patients, and was considered cured in 14 of them. In each subject, QUS of the heel and parameters of bone turnover (bone alkaline phosphatase, beta-crosslaps, and osteocalcin) were measured. The results demonstrated lower QUS values in acromegalic patients compared with the controls. When stratified by gender, the differences in QUS parameters were significant in men, but not in women. Male patients with active disease had significantly lower QUS values than those in remission. Such differences were not observed among women. Multiple regression model indicated strong association between disease activity and the QUS parameters. The group of patients with active disease had a higher level of serum beta-crosslaps, whereas osteocalcin concentration was significantly increased only in male patients with active disease. The results of our study suggest significantly lower QUS values and increased bone turnover in male patients with active acromegaly. The disease activity is the strongest predictor of the QUS parameters in acromegalic patients.     

Rat focal cerebral ischemia induced astrocyte proliferation and delayed neuronal death are attenuated by cyclin-dependent kinase inhibition.

Astroglial proliferation and delayed neuronal death are two common pathological processes in the ischemic brain. However, it is not clear if astrogliosis causes delayed neuronal death. In this study, we addressed this potential linkage by examining the relationship between attenuated astrocyte proliferation, induced by cyclin-dependent kinase (CDK) inhibition, and delayed neuronal death in rat ischemic hippocampus. Our results show that following middle cerebral artery occlusion (MCAO), astrocyte hypertrophy and proliferation were closely associated with delayed neuronal death. Importantly, administration of olomoucine, a selective CDK inhibitor, not only suppressed astroglial proliferation and glial scar formation, but also decreased neuronal cell death in the ischemic boundary zone and hippocampal CA1 region at days 1 and 30 after MCAO. These results indicate that reactive astrogliosis and delayed neuronal death, at least in rat hippocampus, are sequential pathological events following MCAO. Therefore, suppressing astroglial cell cycle progression in acute focal cerebral ischemia may be beneficial to neuronal survival. Our study also implies that cell cycle regulation should be considered as a promising future therapeutic intervention in treating those neurological diseases characterized by an excessive astrocyte proliferation.