The modulation of protein kinase A and heat shock protein 70 is involved in the reversible increase of blood-brain tumor barrier permeability induced by papaverine

Blood-Brain Barrier Modulation to Improve Glioma Drug Delivery

The blood-brain barrier (BBB) is formed by brain microvascular endothelial cells that are sealed by tight junctions, making it a significant obstacle for most brain therapeutics. The poor BBB penetration of newly developed therapeutics has therefore played a major role in limiting their clinical success. A particularly challenging therapeutic target is glioma, which is the most frequently occurring malignant brain tumor. Thus, to enhance therapeutic uptake in tumors, researchers have been developing strategies to modulate BBB permeability. However, most conventional BBB opening strategies are difficult to apply in the clinical setting due to their broad, non-specific modulation of the BBB, which can result in damage to normal brain tissue. In this review, we have summarized strategies that could potentially be used to selectively and efficiently modulate the tumor BBB for more effective glioma treatment.

Strategies for Improved Intra-arterial Treatments Targeting Brain Tumors: a Systematic Review

Conventional treatments for brain tumors relying on surgery, radiation, and systemic chemotherapy are often associated with high recurrence and poor prognosis. In recent decades, intra-arterial administration of anti-cancer drugs has been considered a suitable alternative drug delivery route to intravenous and oral administration. Intra-arterial administration is believed to offer increasing drug responses by primary and metastatic brain tumors, and to be associated with better median overall survival. By directly injecting therapeutic agents into carotid or vertebral artery, intra-arterial administration rapidly increases intra-tumoral drug concentration but lowers systemic exposure. However, unexpected vascular or neural toxicity has questioned the therapeutic safety of intra-arterial drug administration and limits its widespread clinical application. Therefore, improving targeting and accuracy of intra-arterial administration has become a major research focus. This systematic review categorizes strategies for optimizing intra-arterial administration into five categories: (1) transient blood-brain barrier (BBB)/blood-tumor barrier (BTB) disruption, (2) regional cerebral hypoperfusion for peritumoral hemodynamic changes, (3) superselective endovascular intervention, (4) high-resolution imaging techniques, and (5) others such as cell and gene therapy. We summarize and discuss both preclinical and clinical research, focusing on advantages and disadvantages of different treatment strategies for a variety of cerebral tumor types.

MiR-34a regulates blood-tumor barrier function by targeting protein kinase Cε

It is shown for the first time that overexpression of miR-34a increases blood–tumor barrier permeability by targeting PKCε, which is activated by p-PKCε and directly regulates the expression of tight junction–related proteins.

MicroRNA-34a (miR-34a) functions to regulate protein expression at the posttranscriptional level by binding the 3′ UTR of target genes and regulates functions of vascular endothelial cells. However, the role of miR-34a in regulating blood–tumor barrier (BTB) permeability remains unknown. In this study, we show that miR-34a overexpression leads to significantly increased permeability of BTB, whereas miR-34a silencing reduces the permeability of the BTB. In addition, miR-34a overexpression significantly down-regulates the expression and distribution of tight junction–related proteins in glioma endothelial cells (GECs), paralleled by protein kinase Cε (PKCε) reduction. Moreover, luciferase reporter gene analysis shows that PKCε is the target gene of miR-34a. We also show that cotransfection of miR-34a and PKCε inversely coregulates BTB permeability and protein expression levels of tight junction–related proteins. Pretreatment of ψεRACK, a PKCε-specific activator, decreases BTB permeability in miR-34a–overexpressed GECs and up-regulates expression levels of tight junction proteins. In contrast, pretreatment of εV1-2, a specific PKCε inhibitor, gives opposite results. Collectively, our findings indicate that miR-34a regulates BTB function by targeting PKCε; after phosphorylation, PKCε is activated and contributes to regulation of the expression of tight junction–related proteins, ultimately altering BTB permeability.

Manipulation of olfactory tight junctions using papaverine to enhance intranasal delivery of gemcitabine to the brain

CONTEXT

Delivery of drugs from the nasal cavity to the brain is becoming more widely accepted, due to the non-invasive nature of this route and the ability to circumvent the blood brain barrier (BBB).

OBJECTIVE

Because of similarities in the proteins comprising the olfactory epithelial tight junction (TJ) proteins and those of the BBB, we sought to determine whether papaverine (PV), which is known to reversibly enhance BBB permeability, could increase the delivery of intranasally administered gemcitabine to the central nervous system in rats. Experimental methods: Included intranasal administration of gemcitabine, fluorescein isothiocyanate-dextran beads and PV, histopathology, immunostaining, RT-PCR, western blot analysis, immunofluorescence localization, spectrofluorometric analysis, in vivo brain microdialysis, HPLC analysis and in vitro gemcitabine recovery.

RESULTS AND DISCUSSION

PV transiently decreased the levels and altered immunolocalization of the TJ protein phosphorylated-occludin in the olfactory epithelium, while causing an approximately four-fold increase in gemcitabine concentration reaching the brain. The enhanced delivery was not accompanied by nasal epithelial damage or toxicity to distant organs.

CONCLUSIONS

The ability to transiently and safely increase drug delivery from the nose to the brain represents a non-invasive way to improve treatment of patients with brain disorders.

Green tea polyphenols alleviate early BBB damage during experimental focal cerebral ischemia through regulating tight junctions and PKCalpha signaling

Background

It has been supposed that green tea polyphenols (GTPs) have neuroprotective effects on brain damage after brain ischemia in animal experiments. Little is known regarding GTPs’ protective effects against the blood-brain barrier (BBB) disruption after ischemic stroke. We investigated the effects of GTPs on the expression of claudin-5, occludin, and ZO-1, and the corresponding cellular mechanisms involved in the early stage of cerebral ischemia.

Methods

Male Wistar rats were subjected to a middle cerebral artery occlusion (MCAO) for 0, 30, 60, and 120 min. GTPs (400 mg/kg/day) or vehicle was administered by intragastric gavage twice a day for 30 days prior to MCAO. At different time points, the expression of claudin-5, occludin, ZO-1, and PKCα signaling pathway in microvessel fragments of cerebral ischemic tissue were evaluated.

Results

GTPs reduced BBB permeability at 60 min and 120 min after ischemia as compared with the vehicle group. Transmission electron microscopy also revealed that GTPs could reverse the opening of tight junction (TJ) barrier at 60 min and 120 min after MACO. The decreased mRNA and protein expression levels of claudin-5, occludin, and ZO-1 in microvessel fragments of cerebral ischemic tissue were significantly prevented by treatment with GTPs at the same time points after ischemia in rats. Furthermore, GTPs could attenuate the increase in the expression levels of PKCα mRNA and protein caused by cerebral ischemia.

Conclusions

These results demonstrate that GTPs may act as a potential neuroprotective agent against BBB damage at the early stage of focal cerebral ischemia through the regulation of TJ and PKCα signaling.

Doxycycline-mediated protective effect against focal cerebral ischemia-reperfusion injury through the modulation of tight junctions and PKCδ signaling in rats

The strategy for the development of effective and safe neuroprotective agents has great potential to reduce cerebral ischemia-reperfusion injury and improve the functional outcome in stroke patients. Recently, doxycycline, a tetracycline antibiotic, has been shown to have neuroprotective efficiency in reduction of a variety of ischemia-reperfusion injuries as well as ischemic brain damage. We used the rat models of middle cerebral artery occlusion (MCAO) and reperfusion to investigate the effects of treatments with doxycycline against the blood-brain barrier (BBB) leakage at 3, 12, 72, and 120 h of reperfusion. Male Sprague-Dawley rats were subjected to MCAO for 2 h followed by reperfusion for 3, 12, 72, and 120 h and received either doxycycline (45 mg/kg) or saline. The results showed that the treatment of doxycycline significantly reduced the BBB leakage and cerebral infarct volume, which were proved by Evans blue assay and TTC staining. Real-time PCR, immunohistochemistry, and western blot assay verified that the administration of doxycycline significantly up-regulated the expression of tight junction claudin-5, occludin, and ZO-1 from 3 to 120 h after reperfusion. The results of real-time PCR, western blot, and gelatin zymography analyses revealed that the gene and protein expression and activities of matrix metalloproteinases (MMPs) MMP-2 and MMP-9 were significantly elevated in a different time-dependent manner after ischemia-reperfusion but significantly inhibited by doxycycline treatment. Moreover, doxycycline could also significantly down-regulate the expression of PKCδ mRNA and protein after ischemia-reperfusion. These results suggested that the protective effects of doxycycline against BBB damage induced by reperfusion might be related to the up-regulation of tight junction proteins and inhibition of MMP-2, MMP-9, and PKCδ.