Cardiovascular safety assessments in the conscious telemetered dog: utilisation of super-intervals to enhance statistical power.

INTRODUCTION: ICH S7A and S7B guidelines recommend the use of conscious animals for assessment of non-clinical cardiovascular safety of new chemical entities prior to testing in humans. Protocol design and data analysis techniques can affect the quality of the data produced and can therefore ultimately influence the clinical management of cardiovascular risk. It is therefore essential to have an understanding of the magnitude of changes detectable and the clinical relevance of these changes. This paper describes the utilisation of "super-intervals" to analyse and interpret data obtained from our conscious telemetered dog cardiovascular safety protocol and reports the statistical power achieved to detect changes in various cardiovascular parameters. METHODS: Cardiovascular data from 18 dog telemetry studies were used to calculate the statistical power to detect changes in cardiovascular parameters. Each study followed a test compound versus vehicle cross-over experimental design with 24h monitoring (n=4). 1 min mean raw data from each individual animal was compressed into 15 min mean data for each dose group for visualisation. Larger summary periods, or "super-intervals", were then selected to best represent any observed cardiovascular effects whilst taking into account the pharmacokinetic profile of the drug e.g. intervals of 1 to 6, 7 to 14 and 14 to 22h post-dose. RESULTS: With this methodology and study design we predict, using the median percentile that our studies have 80% power to detect the following changes: HR (+/-10bpm), LV +dP/dt max (+/-375mmHg/s), MBP (+/-5mmHg) and QTc (+/-4ms). DISCUSSION: Super-intervals are a simple way to handle the high degree of natural variability seen with any ambulatory cardiovascular assessment and, in our hands, result in highly statistically powered studies. The ability of this model to detect cardiovascular changes of small, but biologically relevant, magnitude enables confident decision making around the cardiovascular safety of new chemical entities.

Serum stimulation of lysyl hydroxylase activity in cultured human skin fibroblasts.

In the absence of ascorbic acid, confluent human skin fibroblasts incubated in 0.5% serum-supplemented medium had one-third of the level of lysyl hydroxylase activity of cells incubated in media containing high serum concentrations (5-20%). This difference appeared to be due to a decline in the enzyme activity following serum deficiency, and was largely abolished by addition of ascorbic acid to the medium. The effect of serum deficiency was slow, manifesting in 48 h at the earliest, and was completely reversed by replenishing the medium with serum. Prolyl hydroxylase activity was independent of serum concentration, both in the absence and in the presence of ascorbic acid in the culture medium.