Stroke, dementia, and drug delivery

Combined ligand and structure-based virtual screening approaches for identification of novel AChE inhibitors

The excessive activity of acetylcholinesterase enzyme (AChE) causes different neuronal problems, especially dementia and neuronal cell deaths. Food and Drug Administration (FDA) approved drugs donepezil, rivastigmine, tacrine and galantamine are AChE inhibitors and in the treatment of Alzheimer’s disease (AD) these drugs are currently prescribed. However, these inhibitors have various adverse side effects. Therefore, there is a great need for the novel selective AChE inhibitors with fewer adverse side effects for the effective treatment. In this study, combined ligand-based and structure-based virtual screening approaches were used to identify new hit compounds from small molecules library of National Cancer Institute (NCI) containing approximately 265,000 small molecules. In the present study, we developed a computational pipeline method to predict the binding affinities of the studied compounds at the specific target sites. For this purpose, a text mining study was carried out initially and compounds containing the keyword “indol” were considered. The therapeutic activity values against AD were screened using the binary quantitative structure activity relationship (QSAR) models. We then performed docking, molecular dynamics (MD) simulations and free energy analysis to clarify the interactions between selected ligands and enzyme. Thus, in this study we identified new promising hit compounds from a large database that may be used to inhibit the enzyme activity of AChE.

Exact location of sensorimotor cortex injury after photochemical modulation; evidence of stroke based on stereological and morphometric studies in mice

The integrity of the structural cerebral cortex is disrupted after stroke either at the macroscopic or microscopic levels. Therefore, many attempts have been gathered to circumvent stroke-associated problems in the brain tissue. The current study was aimed to design an animal model of photochemical stroke using rose bengal (RB) plus laser irradiation (L) after 10, 15, and 20 min (´) and evaluate its effect on the cerebral tissue using unbiased stereological quantitative methods and morphometric histological analysis. Photochemical stroke was induced by intraperitoneal injection of RB dye and further activation through the exposure of the right sensorimotor cortex with the green laser radiation (100 mW; 532 nm). Mice were randomly allocated into 4 groups (each in 15) as follows: control (10 μg/gbw RB), RB + 10'L, RB + 15'L, and RB + 20'L. Target irradiation site was adjusted to 2 mm lateral to the bregma. Vernier caliper morphometric evaluation, cresyl violet staining, and unbiased stereological assays including Cavalier's principle and point counting techniques were used to monitor the pathological changes and lesion volume on days 1, 3, and 7 after the ischemia induction. Our data showed that the mean diameter of the lesion site and lesion infarct volume in the group RB + 20'L) was significantly increased relative to the other groups (P < 0.05). Notably, the lesion volume and diameter in the group RB + 15'L was larger compared with the group RB + 10'L and control mice (P < 0.05). Data showed an increased acute inflammatory response such as hyperemia and edema 3 days after ischemic induction while the intensity of acute changes and lesion volume were reduced and replaced with necrotic and chronic pathological changes including astrogliosis on day 7. It is concluded that the laser irradiation of RB-injected mice at a distinct time period could induce the magnificent degenerative effects on the cerebral cortex which is similar to the stroke condition.

Microfluidic investigation of BDNF-enhanced neural stem cell chemotaxis in CXCL12 gradients

In vivo studies have suggested that gradients of CXCL12 (aka stromal cell-derived factor 1α) may be critical for neural stem cell (NSC) migration during brain development and neural tissue regeneration. However, traditional in vitro chemotaxis tools are limited by unstable concentration gradients and the inability to decouple cell migration directionality and speed. These limitations have restricted the reproducible and quantitative analysis of neuronal migration, which is required for mechanism-based studies. Using a microfluidic gradient generator, nestin and Sox-2 positive human embryonic NSC chemotaxis is quantified within a linear and stable CXCL12 gradient. While untreated NSCs are not able to chemotax within CXCL12 gradients, pre-treatment of the cells with brain-derived neurotrophic factor (BDNF) results in significant chemotactic, directional migration. BDNF pre-treatment has no effect on cell migration speed, which averages about 1 μm min(-1). Quantitative analysis determines that CXCL12 concentrations above 9.0 nM are above the minimum activation threshold, while concentrations below 14.7 nM are below the saturation threshold. Interestingly, although inhibitor studies with AMD 3100 revealed that CXCL12 chemotaxis requires receptor CXCR4 activation, BDNF pre-treatment is found to have no profound effects on the mRNA levels or surface presentation of CXCR4 or the putative CXCR7 scavenger receptor. The microfluidic study of NSC migration within stable chemokine concentration profiles provides quantitative analysis as well as new insight into the migratory mechanism underlying BDNF-induced chemotaxis towards CXCL12.

Controlled epi-cortical delivery of epidermal growth factor for the stimulation of endogenous neural stem cell proliferation in stroke-injured brain

One of the challenges in treating central nervous system (CNS) disorders with biomolecules is achieving local delivery while minimizing invasiveness. For the treatment of stroke, stimulation of endogenous neural stem/progenitor cells (NSPCs) by growth factors is a promising strategy for tissue regeneration. Epidermal growth factor (EGF) enhances proliferation of endogenous NSPCs in the subventricular zone (SVZ) when delivered directly to the ventricles of the brain; however, this strategy is highly invasive. We designed a biomaterials-based strategy to deliver molecules directly to the brain without tissue damage. EGF or poly(ethylene glycol)-modified EGF (PEG-EGF) was dispersed in a hyaluronan and methylcellulose (HAMC) hydrogel and placed epi-cortically on both uninjured and stroke-injured mouse brains. PEG-modification decreased the rate of EGF degradation by proteases, leading to a significant increase in protein accumulation at greater tissue depths than previously shown. Consequently, EGF and PEG-EGF increased NSPC proliferation in uninjured and stroke-injured brains; and in stroke-injured brains, PEG-EGF significantly increased NSPC stimulation. Our epi-cortical delivery system is a minimally-invasive method for local delivery to the brain, providing a new paradigm for local delivery to the brain.

Effect of oral resveratrol on the BDNF gene expression in the hippocampus of the rat brain

Resveratrol is a plant polyphenolic compound. Evidence indicates that resveratrol has beneficial effects against aging and neurodegenerative diseases. The goal of our study was in vivo examination of the effects of resveratrol on the abundance of mRNA encoding Brain Derived Neurotrophic Factor (BDNF) in the hippocampus of rat brain. Rats were administrated orally by different doses (2.5-20 mg/kg bwt) of resveratrol for 3, 10 and 30 days. Saline was used as control and 10% ethanol in saline was used as vehicle for resveratrol. Measurement of BDNF mRNA by Real-time RT-PCR showed that levels of the mRNA for BDNF were significantly and dose dependently elevated in the hippocampal tissues of rats. The findings suggest that the neuroprotective effects of resveratrol may be at least partly due to its inducing effects on the expression levels of the BDNF mRNA.

Transport of epidermal growth factor in the stroke-injured brain

Stroke is a neurological disorder that currently has no cure. Intrathecal delivery of growth factors, specifically recombinant human epidermal growth factor (rhEGF), stimulates endogenous neural precursor cells in the subventricular zone (SVZ) and promotes tissue regeneration in animal models of stroke. In this model, rhEGF is delivered with an invasive minipump/catheter system, which causes trauma to the brain. A less invasive strategy is to deliver rhEGF from the brain cortex; however, this requires the protein to diffuse through the brain, from the site of injection to the SVZ. Although this method of delivery has great potential, diffusion is limited by rapid removal from the extracellular space and hence for successful translation into the clinic strategies are needed to increase the diffusion distance. Using integrative optical imaging we investigate diffusion of rhEGF vs. poly(ethylene glycol)-modified rhEGF (PEG-rhEGF) in brain slices of both uninjured and stroke-injured animals. For the first time, we quantitatively show that PEG modification reduces the rate of growth factor elimination by over an order of magnitude. For rhEGF this corresponds to a two to threefold increase in predicted brain penetration distance, which we confirm with in vivo data.

Neuroprotection in experimental stroke with targeted neurotrophins

More than 30 neurotrophins have been identified, and many of them have neuroprotective effects in brain ischemia or injury. However, all the clinical trials with several neurotrophins for the treatment of acute ischemic stroke or neurodegenerative diseases have failed so far, primarily because of their poor blood-brain barrier (BBB) permeability. This article is an overview of recent progress in the research focused on BBB targeted neurotrophins using a chimeric peptide approach, in which antitransferrin receptor antibody was used as a BBB delivery vector, and neurotrophin peptide was conjugated to the antibody via the avidin/biotin technology. Vasoactive intestinal peptide was the first model chimeric peptide to show an enhanced CNS effect after noninvasive peripheral administration. Brain-derived neurotrophic factor (BDNF) chimeric peptide was neuroprotective in rats subjected to transient forebrain ischemia, permanent focal ischemia, or transient focal ischemia. Delayed treatments with the BDNF chimeric peptide showed an effective time window of 1-2 h after ischemia. Basic FGF chimeric peptide was highly effective in the reduction of infarct volume in the rat model of permanent focal ischemia, with lowest effective dose of 1 mug per rat. Future studies in this exciting area include genetically engineered fusion proteins or humanized antibodies for BBB drug targeting with less immunogenicity and reduced working burden in the chemical conjugation, the use of antihuman insulin receptor antibody for higher BBB delivery efficiency, and combination therapies using chimeric neurotrophins plus other neuroprotectants to achieve additive or synergistic effects.