Distribution of gold nanoparticles into the brain: a systematic review and meta-analysis

Assessment of the potential cerebellar toxicity of gold nanoparticles on the structure and function of adult male albino rats

BACKGROUND

The regular use of gold nanoparticles (Au-NPs) may increase the likelihood of human exposure to these nanoparticles (NPs) and raises concerns about toxicity.

AIM

This study investigated the short-term impact of exposure to Au-NPs on inducing cerebellar pathology in rats, and whether the dose or duration of exposure was more important.

METHODOLOGY

The study used two concentrations of Au-NPs (25 and 50 particles per million) and 18 rats were randomly assigned to three groups. Assessments of the animals were done via behavioral, gene expression, histological, and immunohistochemistry analyses.

RESULTS

Both concentrations of Au-NPs caused cerebellar pathology, as assessed through the investigation test battery. The Au-NPs50 group displayed more injury and decreased mobility compared with the control and the Au-NPs25 group. The Au-NPs25 group showed an increase in supported rearing and significant up-regulation of the Rgc32 gene compared with the control. The Trkb gene was insignificantly up-regulated in both Au-NPs groups compared with the control.

CONCLUSION

The study indicates that exposure to Au-NPs can cause cerebellar pathology in rats and that the toxicity is more dependent on dose than the duration of exposure. These findings have significant implications for the safe use of Au-NPs in various applications.

The blood-brain barrier: structure, regulation, and drug delivery

Blood-brain barrier (BBB) is a natural protective membrane that prevents central nervous system (CNS) from toxins and pathogens in blood. However, the presence of BBB complicates the pharmacotherapy for CNS disorders as the most chemical drugs and biopharmaceuticals have been impeded to enter the brain. Insufficient drug delivery into the brain leads to low therapeutic efficacy as well as aggravated side effects due to the accumulation in other organs and tissues. Recent breakthrough in materials science and nanotechnology provides a library of advanced materials with customized structure and property serving as a powerful toolkit for targeted drug delivery. In-depth research in the field of anatomical and pathological study on brain and BBB further facilitates the development of brain-targeted strategies for enhanced BBB crossing. In this review, the physiological structure and different cells contributing to this barrier are summarized. Various emerging strategies for permeability regulation and BBB crossing including passive transcytosis, intranasal administration, ligands conjugation, membrane coating, stimuli-triggered BBB disruption, and other strategies to overcome BBB obstacle are highlighted. Versatile drug delivery systems ranging from organic, inorganic, and biologics-derived materials with their synthesis procedures and unique physio-chemical properties are summarized and analyzed. This review aims to provide an up-to-date and comprehensive guideline for researchers in diverse fields, offering perspectives on further development of brain-targeted drug delivery system.

Progress in research and development of temozolomide brain-targeted preparations: a review

Gliomas are a heterogeneous group of brain tumours with high malignancy, for which surgical resection remains the mainstay of treatment at present. However, the overall prognosis of gliomas remains poor because of their aggressiveness and high recurrence. Temozolomide (TMZ) has anti-proliferative and cytotoxic effects and is indicated for glioblastoma multiforme and recurrent mesenchymal astrocytoma. However, TMZ is disadvantaged by low efficacy and drug resistance, and therefore it is necessary to enhance the brain drug concentration of TMZ to improve its effectiveness and reduce the toxic and adverse effects from systemic administration. There have been many nano-formulations developed for the delivery of TMZ to gliomas that overcome the limitations of TMZ penetration to tumours and increase brain targeting. In this paper, we review the research progress of TMZ nano-formulations, and also discuss challenges and opportunities in the research and development of drug delivery systems, hoping that the data and information summarised herein could provide assistance for the clinical treatment of gliomas.

Treatment of Orthotopic U251 Human Glioblastoma Multiforme Tumors in NRG Mice by Convection-Enhanced Delivery of Gold Nanoparticles Labeled with the β-Particle-Emitting Radionuclide, 177Lu

In this study, we investigated convection-enhanced delivery (CED) of 23 ± 3 nm gold nanoparticles (AuNPs) labeled with the β-particle-emitting radionuclide ¹⁷⁷Lu (¹⁷⁷Lu-AuNPs) for treatment of orthotopic U251-Luc human glioblastoma multiforme (GBM) tumors in NRG mice. The cytotoxicity in vitro of ¹⁷⁷Lu-AuNPs (0.0-2.0 MBq, 4 × 10¹¹ AuNPs) on U251-Luc cells was also studied by a clonogenic survival assay, and DNA double-strand breaks (DSBs) caused by β-particle emissions of ¹⁷⁷Lu were measured by confocal immunofluorescence microscopy for γH2AX. NRG mice with U251-Luc tumors in the right cerebral hemisphere of the brain were treated by CED of 1.1 ± 0.2 MBq of ¹⁷⁷Lu-AuNPs (4 × 10¹¹ AuNPs). Control mice received unlabeled AuNPs or normal saline. Tumor retention of ¹⁷⁷Lu-AuNPs was assessed by single-photon emission computed tomography/computed tomography (SPECT/CT) imaging and biodistribution studies. Radiation doses were estimated for the tumor, brain, and other organs. The effectiveness for treating GBM tumors was determined by bioluminescence imaging (BLI) and T2-weighted magnetic resonance imaging (MRI) and by Kaplan-Meier median survival. Normal tissue toxicity was assessed by monitoring body weight and hematology and blood biochemistry analyses at 14 d post-treatment. ¹⁷⁷Lu-AuNPs (2.0 MBq, 4 × 10¹¹ AuNPs) decreased the clonogenic survival of U251-Luc cells to 0.005 ± 0.002 and increased DNA DSBs by 14.3-fold compared to cells treated with unlabeled AuNPs or normal saline. A high proportion of ¹⁷⁷Lu-AuNPs was retained in the U251-Luc tumor in NRG mice up to 21 d with minimal re-distribution to the brain or other organs. The radiation dose in the tumor was high (599 Gy). The dose in the normal right cerebral hemisphere of the brain excluding the tumor was 93-fold lower (6.4 Gy), and 2000-3000-fold lower doses were calculated for the contralateral left cerebral hemisphere (0.3 Gy) or cerebellum (0.2 Gy). The doses in peripheral organs were <0.1 Gy. BLI revealed almost complete tumor growth arrest in mice treated with ¹⁷⁷Lu-AuNPs, while tumors grew rapidly in control mice. MRI at 28 d post-treatment and histological staining showed no visible tumor in mice treated with ¹⁷⁷Lu-AuNPs but large GBM tumors in control mice. All control mice reached a humane endpoint requiring sacrifice within 39 d (normal saline) or 45 d post-treatment (unlabeled AuNPs), while 5/8 mice treated with ¹⁷⁷Lu-AuNPs survived up to 150 d. No normal tissue toxicity was observed in mice treated with ¹⁷⁷Lu-AuNPs. We conclude that CED of ¹⁷⁷Lu-AuNPs was highly effective for treating U251-Luc human GBM tumors in the brain in NRG mice at amounts that were non-toxic to normal tissues. These ¹⁷⁷Lu-AuNPs administered by CED hold promise for treating patients with GBM to prevent recurrence and improve long-term outcome.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.