Dendrimer Brain Uptake and Targeted Therapy for Brain Injury in a Large Animal Model of Hypothermic Circulatory Arrest

Abstract

Treatment of brain injury following circulatory arrest is a challenging health issue with no viable therapeutic options. Based on studies in a clinically relevant large animal (canine) model of hypothermic circulatory arrest (HCA)-induced brain injury, neuroinflammation and excitotoxicity have been identified as key players in mediating the brain injury after HCA. Therapy with large doses of valproic acid (VPA) showed some neuroprotection but was associated with adverse side effects. For the first time in a large animal model, we explored whether systemically administered polyamidoamine (PAMAM) dendrimers could be effective in reaching target cells in the brain and deliver therapeutics. We showed that, upon systemic administration, hydroxyl-terminated PAMAM dendrimers are taken up in the brain of injured animals and selectively localize in the injured neurons and microglia in the brain. The biodistribution in other major organs was similar to that seen in small animal models. We studied systemic dendrimer–drug combination therapy with two clinically approved drugs, N-acetyl cysteine (NAC) (attenuating neuroinflammation) and valproic acid (attenuating excitotoxicity), building on positive outcomes in a rabbit model of perinatal brain injury. We prepared and characterized dendrimer-NAC (D-NAC) and dendrimer-VPA (D-VPA) conjugates in multigram quantities. A glutathione-sensitive linker to enable for fast intracellular release. In preliminary efficacy studies, combination therapy with D-NAC and D-VPA showed promise in this large animal model, producing 24 h neurological deficit score improvements comparable to high dose combination therapy with VPA and NAC, or free VPA, but at one-tenth the dose, while significantly reducing the adverse side effects. Since adverse side effects of drugs are exaggerated in HCA, the reduced side effects with dendrimer conjugates and suggestions of neuroprotection offer promise for these nanoscale drug delivery systems.

Nanoparticle transport across the blood brain barrier

“…105,107 In particular, a recent study 69 demonstrates that the administration of polyamidoamine (PAMAM) dendrimers could be taken up in the brain of injured animals and selectively localize in the injured neurons and microglia in the brain. Besides, these dendrimers were also able to deliver two clinically approved drugs, N-acetyl cysteine (attenuating neuroinflammation) and valproic acid (attenuating excitotoxicity), building on positive outcomes in a rabbit model of perinatal brain injury.…”

Nanoparticles for Brain-Specific Drug and Genetic Material delivery, Imaging and Diagnosis

“…Interestingly, dendrimer-Nacetylcysteine (NAC) conjugates may enable improved drug delivery and achieve the concentration of NAC in the brain required for neuroprotection. The administration of a hydroxil-functionalized G4 PAMAM-NAC dendrimer improved motor function and attenuated neurological injury in a model of hypothermic circulatory arrest [53].…”

“…The systemic administration of PAMAM dendrimers has shown minimal brain uptake in healthy animals. PAMAM dendrimers below generation 6 are rapidly cleared from systemic circulation by kidney filtration or by the RES, whereas PEGylated dendrimers or PAMAM dendrimers above generation 6 tend to circulate longer and be distributed to peripheral organs [52,53]. Only when BBB permeability is increased, as happens during neuroinflammation or meningitis, is the access of these dendrimers to the CNS favored.…”

“…Moreover, surface modification of dendrimers leads to a more efficient in vivo administration. Hydroxyl-functionalized generation-4 PAMAM dendrimers selectively localized in neurons and activated microglia in the injured brain and retina when administered intravenously to newborn rabbits [59], or to 6-12-month-old dogs [53]. One of the problems that arise following the functionalization of dendrimers to reduce toxicity is the observed decrease in diffusion and in cellular uptake of the dendrimers and their payload.…”

Nano-Engineered Biomaterials for Tissue Regeneration: What Has Been Achieved So Far?

“…Brain injury depends on the treatment, varying in degree with hypoxia-induced models or severance of specific neural circuits and cell populations (Orive et al, 2009). Primarily in brain injuries, nanotechnologies are used for sustained delivery of neurotrophic drugs or ECMmimetic scaffolds for localized cell populations (Orive et al, 2009;Mishra et al, 2014;Jo et al, 2015). Regenerative solutions for severe spinal injury and widespread degradation of neuronal cell populations in the brain are the most challenging tasks.…”