Emerging Insights for Translational Pharmacokinetic and Pharmacokinetic-Pharmacodynamic Studies: Towards Prediction of Nose-to-Brain Transport in Humans.

To investigate the potential added value of intranasal drug administration, preclinical studies to date have typically used the area under the curve (AUC) in brain tissue or cerebrospinal fluid (CSF) compared to plasma following intranasal and intravenous administration to calculate measures of extent like drug targeting efficiencies (%DTE) and nose-to-brain transport percentages (%DTP). However, CSF does not necessarily provide direct information on the target site concentrations, while total brain concentrations are not specific to that end either as non-specific binding is not explicitly considered. Moreover, to predict nose-to-brain transport in humans, the use of descriptive analysis of preclinical data does not suffice. Therefore, nose-to-brain research should be performed translationally and focus on preclinical studies to obtain specific information on absorption from the nose, and distinguish between the different transport routes to the brain (absorption directly from the nose to the brain, absorption from the nose into the systemic circulation, and distribution between the systemic circulation and the brain), in terms of extent as well as rate. This can be accomplished by the use of unbound concentrations obtained from plasma and brain, with subsequent advanced mathematical modeling. To that end, brain extracellular fluid (ECF) is a preferred sampling site as it represents most closely the site of action for many targets. Furthermore, differences in nose characteristics between preclinical species and humans should be considered. Finally, pharmacodynamic measurements that can be obtained in both animals and humans should be included to further improve the prediction of the pharmacokinetic-pharmacodynamic relationship of intranasally administered CNS drugs in humans.

The exploration of rotenone as a toxin for inducing Parkinson's disease in rats, for application in BBB transport and PK-PD experiments.

INTRODUCTION: In search for a suitable rat model to study potentially affected blood-brain barrier (BBB) transport mechanisms in the course of Parkinsons disease (PD) progression, experiments were performed to characterise Parkinsons disease markers following subcutaneous (SC) and intracerebral (IC) infusion of the toxin rotenone in the rat. METHODS: Studies were performed using Male Lewis rats. SC infusion of rotenone (3 mg/kg/day) was performed via an osmotic minipump. IC infusion of rotenone occurred directly into the right medial forebrain bundle at three different dosages. At different times following rotenone infusion, behaviour, histopathology (tyrosine hydroxylase and alpha-synuclein immunocytochemistry), peripheral organ pathology (adrenals, heart, kidney, liver, lung, spleen and stomach) were assessed. In part of the SC and IC rats, BBB transport profiles of the permeability marker sodium fluorescein were determined using microdialysis. RESULTS: SC rotenone failed to produce dopaminergic lesions and led to extensive peripheral organ toxicity. BBB permeability for fluorescein following SC rotenone was changed, however due peripheral toxicity. In contrast, IC rotenone produced a progressive lesion of the nigrostrial dopaminergic pathway over 28 days with no associated peripheral toxicity. IC rotenone also exhibited a large increase in amphetamine induced rotational behaviour. In addition, a few IC rats showed alpha-synuclein immunoreactivity and aggregation. Following IC rotenone, no changes in BBB permeability were detected after 14 days. DISCUSSION: SC rotenone only produced peripheral toxicity. IC rotenone appeared to create a progressive lesion of the rat nigrostrial pathway, and may therefore be a more appropriate model of Parkinson's disease progression, compared with the most commonly used 6-OH-DA rat model.