Dendrimer Donepezil Conjugates for Improved Brain Delivery and Better in Vivo Pharmacokinetics

In neurodegenerative disorders, crossing the blood-brain barrier to achieve higher brain uptake of drugs has attracted considerable interest of researchers in recent years. The present approach is designed with a hypothesis that polyamidoamine (PAMAM) dendrimer can be suitable for better brain delivery of donepezil (DZ) utilizing the conjugation strategy. Amine-terminated 4.0 G PAMAM dendrimers (utilizing ethylenediamine core) were synthesized and characterized by different spectroscopic methods (H-1 and C-13 NMR, UV-vis, Fourier transform infrared, electrospray ionization mass). The synthesized PAMAM dendrimer was then conjugated with DZ-ester and finally DZ (ester)-PAMAM conjugate (PDZ) was prepared. The chemical shifts of -CHO (delta = 9.92) and O-CH3 (delta = 3.153) in H-1 NMR spectrum confirmed the synthesis of PDZ. The percent drug conjugation of DZ was approximately 26%, and 16 DZ molecules were conjugated with each PAMAM molecule. The size and zeta-potential observed of PDZ conjugate were 122 +/- 1.88 nm and 0.434 +/- 0.322, respectively. In vitro release studies suggested that DZ release was in a sustained fashion until 120 h at physiological pH conditions. The in vitro acetylcholine esterase (AChE) inhibition activity of PDZ formulation was significantly higher (p < 0.05) than that of the DZ alone at 1 mu M dose. In the in vivo studies, the brain uptake of PDZ was quite higher than that of DZ following intravenous administration in Sprague-Dawley rats. The plasma drug concentration studies resulted into improved pharmacokinetic parameters. Half-life (t(1/2)), volume of distribution (V-d), and clearance were found to be 5.75 +/- 0.41 h(-1), 0.135 +/- 0.02 L, and 0.016 +/- 0.0021 L/h, respectively, in the case of PDZ formulation and 1.09 +/- 0.10 h(-1), 0.172 +/- 0.016 L, and 0.108 +/- 0.014 L/h, respectively, in the case of DZ solution. The improved half-life and 4-fold increase in brain uptake was observed in the case of the dendrimer-conjugated formulation, which suggested that the synthesized conjugates provide significantly higher DZ brain delivery. The prepared PDZ-conjugated formulation improved AChE inhibition in vitro and the brain delivery in vivo. This strategy may be explored further for better delivery of DZ to the brain.