Glycaemic control boosts glucosylated nanocarrier crossing the BBB into the brain

Abstract

Recently, nanocarriers that transport bioactive substances to a target site in the body have attracted considerable attention and undergone rapid progression in terms of the state of the art. However, few nanocarriers can enter the brain via a systemic route through the blood-brain barrier (BBB) to efficiently reach neurons. Here we prepare a self-assembled supramolecular nanocarrier with a surface featuring properly configured glucose. The BBB crossing and brain accumulation of this nanocarrier are boosted by the rapid glycaemic increase after fasting and by the putative phenomenon of the highly expressed glucose transporter-1 (GLUT1) in brain capillary endothelial cells migrating from the luminal to the abluminal plasma membrane. The precisely controlled glucose density on the surface of the nanocarrier enables the regulation of its distribution within the brain, and thus is successfully optimized to increase the number of nanocarriers accumulating in neurons.There are only a few examples of nanocarriers that can transport bioactive substances across the blood-brain barrier. Here the authors show that by rapid glycaemic increase the accumulation of a glucosylated nanocarrier in the brain can be controlled.

Fig. 1

Characterization of the Gluc(6)-conjugated PIC micelle (Gluc(6)/m). a Scheme of Gluc(6)/m preparation via the assembly of oppositely charged block copolymers. b Size distribution of the 25%Gluc(6)/m determined by DLS. c TEM image of the 25%Gluc(6)/m. The scale bar indicates 50 nm

Fig. 2

Pharmacokinetic profiles of the polymeric micelles. a Biodistribution of micelles (Null/m and Gluc(6)/m) in mice under different feeding conditions at 48 h after the injection. Open and closed bars show free-feeding and glycaemic-controlled groups, respectively. Black, green, red and blue coloured bars indicate Null/m, 10%Gluc(6)/m, 25%Gluc(6)/m and 50%Gluc(6)/m, respectively. b Accumulation ratio in mice (glycaemic-controlled/free-feeding) of each micelle at 48 h calculated from the values shown in a. c Time course of micelle accumulation (Null/m, Gluc(6)/m and Gluc(3)/m) in the mouse brain under different feeding conditions. The arrow in c indicates when 20 wt% glucose was intraperitoneally injected. Open and closed circles denote the free-feeding and glycaemic-controlled groups, respectively. Black, green, red and blue coloured circles indicate Null/m, 10%Gluc(6)/m, 25%Gluc(6)/m and 50%Gluc(6)/m, respectively. An orange coloured circle shows 25%Gluc(3)/m (glycaemic-controlled). d In vivo inhibition study of the brain accumulation of the 25%Gluc(6)/m by phloretin. Red and grey bars show experiments conducted without and with phloretin, respectively. Experiments were performed using BALB/c mice (female, 6-week-old, n = 5). The data are expressed as the mean ± SEM for a, c, d and as the mean for b. *P < 0.05

Fig. 3

Real-time observation of the 25%Gluc(6)/m crossing the BBB. a Sequential images of mouse cerebrum observed using IVRT-CLSM. The 25%Gluc(6)/m (red) were intravenously injected to a mouse after a 24-h fast, followed by an intraperitoneal injection of 20 wt% glucose 30 min later. The scale bars indicate 50 μm. b Time course of blood glucose concentration (black squares) and the mean fluorescent intensities of the 25%Gluc(6)/m (red circles) in the region of interest (ROI) of the brain parenchyma indicated as white rectangles in a. The arrow indicates the time of intraperitoneal injection of the 20 wt% glucose. Blood glucose concentrations were expressed as the mean ± SEM. c Images of Gluc(6)/m (red) in the mouse cerebrum observed using intravital multiphoton microscopy 48 h after administration. Cross-sections at depths of 60 μm (d), 300 μm (e) and 500 μm (f) are also shown. The scale bars indicate 100 μm. g Distribution profiles of Gluc(6)/m from blood vessels to the brain parenchyma in the selected region (indicated by a white rectangle in d, e, f) at depths of 60 μm (black line), 300 μm (red line) and 500 μm (blue line). h Depth profiles of the mean fluorescent intensities from 0 to 700 μm in the brain parenchymal region

Fig. 4

Immunohistochemical analysis of the mouse brains after administration of polymeric micelles. Cerebral sections at 48 h after the administration of Null/m, 10%Gluc(6)/m, 25%Gluc(6)/m and 50%Gluc(6)/m (red). BCECs (a), neurons (b), microglia (c) and astrocytes (d) (green) are stained with anti-PECAM1, anti-Tuj1, anti-Iba1 and anti-GFAP antibodies, respectively. Nuclei (blue) are stained with DAPI. The scale bar indicates 20 μm (10 μm in insets)