Birgit Niggemann

A standardized approach for iris color determination

Latanoprost, the phenyl-substituted prostaglandin F2α, has been found to be an effective agent for glaucoma therapy. This prostaglandin derivative exerts ocular hypotensive activity but is also associated with an untoward side effect, namely iris color changes. Latanoprost provoked iris color changes in cynomolgus monkeys and in multicenter clinical trials. Until now photographs were taken and compared with color plates to document these changes. The disadvantage of this method is obvious, i.e., the color luminance varies between measurements due to changes in the developer. Furthermore, subjective comparison of color changes relative to color plates rendered judgment subject to impression and opinion rather than to objective data. Therefore, a computerized method using a 3-CCD video camera attached to a slit lamp was developed. The signals were transferred to a computer and a single frame, which was “frozen” by means of a “grabber card.” Camera and the computer had previously been calibrated and color plates were measured to check the standard conditions. They were evaluated by a software program displaying average color (as red, green, and blue values) of the selected area. This method provides a fast and accurate way to quantify color changes in the iris of both experimental animals and clinical trials.

Measurement of hyper- and hypotension during repeated dose toxicity studies in either freely moving or physically restrained cynomolgus monkeys

INTRODUCTION The measurement of cardiovascular endpoints in standard toxicology studies remains a challenge as the routinely used non-invasive methods require physical restraint, causing an increase of sympathetic neural activity, leading to excitement and potentially hypertension in the experimental animals. In this study, a miniature telemetry blood pressure transmitter was used to evaluate if the acute hyper- and hypotension could be detected in free moving cynomolgus monkeys as well as physically restrained animals using positive control drugs. Furthermore, as a comparator, routine high definition oscillometry (HDO) was performed in restrained animals. METHODS Hemodynamic parameters were monitored continuously from conscious, freely moving animals following oral administration of vehicle (water) or 1 and 10mg/kg of etilefrine, and 1 and 4mg/kg of dihydralazine as positive control articles. A second dose session was performed to confirm the reproducibility of results and a third dose session combined with physical restraint procedures for blood collection and HDO measurements. RESULTS There was a dose-dependent, statistically significant increase in the systolic blood pressure following oral doses of etilefrine at all 3 dose sessions. This effect was less apparent during session 3, probably due to the physical restraint applied for the blood sampling and HDO measurement. No differences in the blood pressure were measured using HDO. On all three dose sessions following oral doses of dihydralazine the expected statistically significant decrease in the diastolic pressure could be clearly measured even when the telemetric data recordings were combined with physical restraint. DISCUSSION Due to the advantages of the minimally invasive telemetry technique compared to HDO and the possibility of prolonged measurement periods, it is an invaluable tool for blood pressure measurement in freely moving animals in toxicology studies.

Ophthalmological Investigations in Toxicity Studies

Abstract Because of the high similarity of the morphology of the eye in humans and nonhuman primates (NHPs), the NHP is a very good model to assess the toxicity of drugs to the eye. As a standard for all good laboratory practice (GLP) toxicity studies, the posterior part of the eye (retina, optic nerve, macula, and vessels) is examined by direct and/or indirect ophthalmoscopy, and the anterior and medium part of the eye is examined using a slit lamp. More specific investigations are necessary to provide more detailed information about the potential influence of the compounds to the eye. If the eye is identified as the target organ, additional investigations need to be performed. Fundus photographs can be taken to document fundus findings and the progression of these changes. Fluorescence angiography demonstrates vascular flow and abnormalities of the vascular trees within the fundus. Electroretinography is used to detect functional defects of the photoreceptors, neuronal cells, and glia cells. Intraocular pressure (IOP) measurements can be used to monitor drug-induced IOP changes. Corneal thickness is mainly determined in studies with local administration to the cornea. In addition, specular microscopy is able to evaluate the cornea endothelium. Scheimpflug photography is a technique to further evaluate the lens. Optical coherence tomography is an imaging technique demonstrating the tissue microstructure with resolution approaching that of light microscopy. This technique and laser scanning ophthalmoscope are used to investigate the structure of the posterior part of the eye.