PAMAM dendrimers: blood-brain barrier transport and neuronal uptake after focal brain ischemia

Abstract

Drug delivery to the central nervous system is restricted by the blood-brain barrier (BBB). However, with the onset of stroke, the BBB becomes leaky, providing a window of opportunity to passively target the brain. Here, cationic poly(amido amine) (PAMAM) dendrimers of different generations were functionalized with poly(ethylene glycol) (PEG) to reduce cytotoxicity and prolong blood circulation half-life, aiming for a safe in vivo drug delivery system in a stroke scenario. Rhodamine B isothiocyanate (RITC) was covalently tethered to the dendrimer backbone and used as a small surrogate drug as well as for tracking purposes. The biocompatibility of PAMAM was markedly increased by PEGylation as a function of dendrimer generation and degree of functionalization. The PEGylated RITC-modified dendrimers did not affect the integrity of an in vitro BBB model. Additionally, the functionalized dendrimers remained safe when in contact with the bEnd.3 cells and rat primary astrocytes composing the in vitro BBB model after hypoxia induced by oxygen-glucose deprivation. Modification with PEG also decreased the interaction and uptake by endothelial cells of PAMAM, indicating that the transport across a leaky Version: Postprint (identical content as published paper) This is a self-archived document from i3S-Instituto de Investigação e Inovação em Saúde in the University of Porto Open Repository For Open Access to more of our publications, please visit http://repositorio-aberto.up.pt/ A01/00 BBB due to focal brain ischemia would be facilitated. Next, the functionalized dendrimers were tested in contact with red blood cells showing no haemolysis for the PEGylated PAMAM, in contrast to the unmodified dendrimer. Interestingly, the PEG-modified dendrimers reduced blood clotting, which may be an added beneficial function in the context of stroke. The optimized PAMAM formulation was intravenously administered in mice after inducing permanent focal brain ischemia. Twenty-four hours after administration, dendrimers could be detected in the brain, including in neurons of the ischemic cortex. Our results suggest that the proposed formulation has the potential for becoming a successful delivery vector for therapeutic application to the injured brain after stroke reaching the ischemic neurons. Graphical abstract (A) PEG-conjugated PAMAM dendrimers bound with RITC diffusing through a 'leaky' blood brain barrier upon focal cerebral ischemia. (B) Modified PAMAM dendrimer identified in neurons at the site of the brain ischemic injury.

Overcoming the Blood–Brain Barrier. Challenges and Tricks for CNS Drug Delivery

“…The most used DD is poly-amidoamine (PAMAM), which is water soluble and can encapsulate hydrophobe compounds. For example, cationic PAMAM DDs of different generations are used with PEGylation, as a safe in vivo drug delivery system in stroke patients [104].…”

Breaking Barriers: Bioinspired Strategies for Targeted Neuronal Delivery to the Central Nervous System

“…There are a wide range of different dendrimer families with great potential for gene delivery, drug delivery, and magnetic resonance and computed tomography imaging [73,74,[82][83][84]. Among them, the most explored dendrimers as delivery vectors for CNS applications have been the poly(amido amine) (PAMAM) dendrimers [80,85,86], but others, like poly(propylene imine) (PPI) [80,[87][88][89][90], poly(ether)-copoly(ester) (PEPE) [91], poly(l-lysine) based (PLL) [92], carbosilane [93], phosphorus [94], and poly(ether imine) (PETIM) [77,95], have also been reported.…”

“…Under pathological conditions, as, for example, in stroke, traumatic brain injury, multiple sclerosis, AD and brain tumors, the BBB undergoes significant changes [184,191,192]. As the BBB suffers a disruption caused by tight junction disassembly, this can be seen as a window of opportunity for therapeutic NP delivery through paracellular diffusion [86,193].…”

<p>Nanocarriers for Stroke Therapy: Advances and Obstacles in Translating Animal Studies</p>

“…91 In particular, it was shown that PEGylation improved the biocompatibility and reduced the clearance of polyamidoamine (PAMAM) dendrimers. 92 Some studies had applied strategies comparable to micelles to improve cell uptake of dendrimers and consequent gene transfection. One study had conjugated dexamethasone as the targeting device, while another had incorporated reducible residues to dendritic polymers for increased degradability.…”