These studies systematically assessed the impact of AD on BBB drug transport in a relevant animal model, and have demonstrated a reduction in the brain uptake of passively-absorbed molecules in this mouse model of AD.

Memantine (MEM) is prescribed in mono and combination therapies for treating the symptoms of moderate to severe Alzheimer's disease (AD). Despite MEM being widely prescribed with other AD and non-AD medicines, very little is known about its mechanism of transport across the blood-brain barrier (BBB), and whether the nature of this transport lends MEM to a potential for drug-drug interactions at the BBB. Therefore, the purpose of this study was to characterize the mechanisms facilitating MEM brain uptake in Swiss Outbred mice using an in situ transcardiac perfusion technique, and identify the putative transporter involved in MEM disposition into the brain. Following transcardiac perfusion of MEM with increasing concentrations, the brain uptake of MEM was observed to be saturable. Furthermore, MEM brain uptake was reduced (up to 55%) by various cationic transporter inhibitors (amantadine, quinine, tetraethylammonium, choline and carnitine) and was dependent on extracellular pH, while being independent of membrane depolarization and the presence of Na(+) in the perfusate. In addition, MEM brain uptake was observed to be sensitive to changes in intracellular pH, hence, likely to be driven by H(+)/MEM antiport mechanisms. Taken together, these findings implicate the involvement of an organic cation transporter regulated by proton antiport mechanisms in the transport of MEM across the mouse BBB, possibly the organic cation/carnitine transporter, OCTN1. These studies also clearly demonstrate the brain uptake of MEM is significantly reduced by other cationic compounds, highlighting the need to consider the possibility of drug interactions with MEM at the BBB, potentially leading to reduced brain uptake and, therefore, altered efficacy of MEM when used in patients on multidrug regimens.

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by β-amyloid plaques and hyperphosphorylated tau tangles in the brain. Alongside these pathological lesions, there have been multiple reports of physical and biochemical alterations to the blood-brain barrier (BBB) in people with AD, potentially impacting on the ability of systemically-administered drugs to reach the brain parenchyma. Though there has been much research into the identification of these BBB alterations during AD, there are very few studies that have assessed the impact of such BBB changes on the ability of therapeutic agents to traverse the BBB. Due to their increased age-associated risk of chronic disease, most people with AD are prescribed multiple concurrent medications. In people with AD, the altered nature of the BBB could impact upon the disposition and therefore pharmacological effects of a wide range of medicines. This review therefore evaluates the impact of BBB alterations in AD on CNS drug exposure, along with relevant examples of preclinical and clinical studies that address this current issue. This review highlights that the CNS exposure of drugs is likely to differ between people with AD and healthy individuals, warranting further clinical investigations and the consideration to tailor dosing regimens in people with this neurodegenerative disorder.

Understanding the effect of liposome size on tendency for accumulation in tumour tissue requires preparation of defined populations of different sized particles. However, controlling the size distributions without changing the lipid composition is difficult, and differences in compositions itself modify distribution behaviour. Here, a commercial microfluidic format as well as traditional methods was used to prepare doxorubicin-loaded liposomes of different size distributions but with the same lipid composition, and drug retention, biodistribution and localization in tumour tissues were evaluated. The small (∼50 nm diameter) liposomes prepared by microfluidics and large (∼75 nm diameter) liposomes displayed similar drug retention in in vitro release studies, and similar biodistribution patterns in tumour-bearing mice. However, the extent of extravasation was clearly dependent on size of the liposomes, with the small liposomes showing tissue distribution beyond the vascular area compared to the large liposomes. The use of microfluidics to prepare smaller size distribution liposomes compared to sonication methods is demonstrated, and allowed preparation of different size distribution drug carriers from the same lipid composition to enable new understanding of tissue distribution in compositionally consistent materials is demonstrated.

The shape-persistent nature and conformation of cylindrical polymer brushes (CPBs) present opportunities to explore the properties of anisotropic (i.e. non spherical) nanomaterials in biological settings. This study shows that CPBs with lengths of up to 1 μm are able to passively target tumours via the enhanced permeation and retention (EPR) effect. Moreover, large CPBs with higher aspect ratios (ARs) were able to penetrate tumours with similar efficiencies to much smaller systems with lower ARs.