Werner J. Geldenhuys

Oxidative stress and Alzheimer’s disease: dietary polyphenols as potential therapeutic agents

Oxidative stress has been strongly implicated in the pathophysiology of neurodegenerative disorders such as Alzheimer’s disease (AD). In recent years, antioxidants – especially those of dietary origin – have been suggested as possible agents useful for the prevention and treatment of AD. This article reviews the role of oxidative stress and the contribution of free radicals in the development of AD, and also discusses the use of antioxidants as a therapeutic strategy in the amelioration of this illness. The antioxidant potential of polyphenolic compounds obtained from dietary sources, such as anthocyanins from berries, catechins and theaflavins from tea, curcumin from turmeric, resveratrol from grapes and peanuts, the dihydrochalcones aspalathin and nothofagin from rooibos and the xanthone mangiferin from honeybush, are discussed in this review. The neuroprotective effects of these phytochemicals in preclinical models of AD are highlighted. Finally, innovative concepts, novel hypotheses, current challenges and future directions in the use of dietary polyphenols for the treatment of AD are discussed.

Brain Iron Toxicity: Differential Responses of Astrocytes, Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain’s highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron.

Multifunctional drugs with different CNS targets for neuropsychiatric disorders

The multiple disease etiologies that lead to neuropsychiatric disorders, such as Parkinsons and Alzheimers disease, amyotrophic lateral sclerosis, Huntington disease, schizophrenia, depressive illness and stroke, offer significant challenges to drug discovery efforts aimed at preventing or even reversing the progression of these disorders. Transcriptomic tools and proteomic profiling have clearly indicated that such diseases are multifactorial in origin. Further, they are thought to be initiated by a cascade of molecular events that involve several neurotransmitter systems. In response to this complexity, a new paradigm has recently emerged that challenges the widely held assumption that ‘silver bullet’ agents are superior to ‘dirty drugs’ in therapeutic approaches aimed at the prevention or treatment of neuropsychiatric diseases. A similar pattern of drug development has occurred in strategies for the treatment of cancer, AIDS and cardiovascular diseases. In this review, we offer an overview of therapeutic strategies and novel investigative drugs discovered or developed in our own and other laboratories, that address multiple CNS etiological targets associated with an array of neuropsychiatric disorders.

NGP1-01, a lipophilic polycyclic cage amine, is neuroprotective in focal ischemia

NGP1-01, a member of the pentacycloundecylamine cage compound family, was recently shown to exhibit both NMDA receptor channel blocking and L-type calcium channel antagonism activity. In the present study, focal ischemia was induced in mice by permanent middle cerebral artery occlusion (MCAO) to test for potential neuroprotective properties of the compound. In female CD-1 mice injected 30 min before MCAO, NGP1-01 (20 mg/kg) reduced infarct area by 42.6% (P < 0.05) compared to vehicle-treated controls as visualized by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Concomitantly, NGP1-01 reduced brain swelling by 78.3% (P < 0.001), compared to vehicle (DMSO) treated controls. These data identify NGP1-01 and related compounds as potential lead structures to develop neuroprotective compounds based on a dual mechanism of action.

The serotonin 5-HT6 receptor: a viable drug target for treating cognitive deficits in Alzheimer’s disease

The serotonin 6 receptor is attracting attention as an etiological contributor in cognition deficits in diseases such as Alzheimer’s disease, anxiety/depression and schizophrenia. In this review, we discuss the role of this recently discovered G protein-coupled receptor in cognition and memory, particularly in Alzheimer’s disease. A surge in publications that describe the development of ligands for this receptor have recently come to light, underscoring the emerging interest in this receptor as a drug target. We also explore the current status of structure–activity relationship studies that have focused on the design of novel antagonists for the serotonin 6 receptor.

Optimizing the use of open-source software applications in drug discovery

Drug discovery is a time consuming and costly process. Recently, a trend towards the use of in silico computational chemistry and molecular modeling for computer-aided drug design has gained significant momentum. This review investigates the application of free and/or open-source software in the drug discovery process. Among the reviewed software programs are applications programmed in JAVA, Perl and Python, as well as resources including software libraries. These programs might be useful for cheminformatics approaches to drug discovery, including QSAR studies, energy minimization and docking studies in drug design endeavors. Furthermore, this review explores options for integrating available computer modeling open-source software applications in drug discovery programs.

Voltage-gated Calcium Channels Provide an Alternate Route for Iron Uptake in Neuronal Cell Cultures

Recent studies suggest that iron enters cardiomyocytes via the L-type voltage-gated calcium channel (VGCC). The neuronal VGCC may also provide iron entry. As with calcium, extraneous iron is associated with the pathology and progression of neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. VGCCs, ubiquitously expressed, may be an important route of excessive entry for both iron and calcium, contributing to cell toxicity or death. We evaluated the uptake of 45Ca2+ and 55Fe2+ into NGF-treated rat PC12, and murine N-2α cells. Iron not only competed with calcium for entry into these cells, but iron uptake (similar to calcium uptake) was inhibited by nimodipine, a specific L-type VGCC blocker, and enhanced by FPL 64176, an L-VGCC activator, in a dose-dependent manner. Taken together, these data suggest that voltage-gated calcium channels are an alternate route for iron entry into neuronal cells under conditions that promote cellular iron overload toxicity.

Brain-targeted delivery of Tempol-loaded nanoparticles for neurological disorders.

Brain-targeted Tempol-loaded poly-(lactide-co-glycolide) (PLGA) nanoparticles (NPs) conjugated with a transferrin antibody (OX 26) were developed using the nanoprecipitation method. These NPs may have utility in treating neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease. Central to these diseases is an increased production of reactive oxygen and nitrogen species which may take part in the development of these conditions. As proof of principle, the NPs were loaded with Tempol, a free radical scavenger that has been shown to be protective against oxidative insults. To enhance the delivery of NPs to the central nervous system (CNS), we conjugated the transferrin receptor antibody covalently to PLGA NPs using the NHS-PEG3500-Maleimide crosslinker. The NPs showed a particle size suitable for blood brain barrier (BBB) permeation (particle size 80–110 nm) and demonstrated a sustained drug release behavior. A high cellular uptake of antibody-conjugated NPs was demonstrated in RG2 rat glioma cells. The ability of the Tempol-loaded NPs to prevent cell death by resveratrol in RG2 cells was determined using the MTT assay. The conjugated NPs containing Tempol were more effective in preventing cell viability by resveratrol when compared with unconjugated NPs or free Tempol in solution. Our findings suggest that transferrin-conjugated NPs containing antioxidants may be useful in the treatment of neurodegenerative diseases.

Primary cilia regulates the directional migration and barrier integrity of endothelial cells through the modulation of Hsp27 dependent actin cytoskeletal organization

Cilia are mechanosensing organelles that communicate extracellular signals into intracellular responses. Altered functions of primary cilia play a key role in the development of various diseases including polycystic kidney disease. Here, we show that endothelial cells from the oak ridge polycystic kidney (Tg737orpk/orpk) mouse, with impaired cilia assembly, exhibit a reduction in the actin stress fibers and focal adhesions compared to wild‐type (WT). In contrast, endothelial cells from polycystin‐1 deficient mice (pkd1null/null), with impaired cilia function, display robust stress fibers, and focal adhesion assembly. We found that the Tg737orpk/orpk cells exhibit impaired directional migration and endothelial cell monolayer permeability compared to the WT and pkd1null/null cells. Finally, we found that the expression of heat shock protein 27 (hsp27) and the phosphorylation of focal adhesion kinase (FAK) are downregulated in the Tg737orpk/orpk cells and overexpression of hsp27 restored both FAK phosphorylation and cell migration. Taken together, these results demonstrate that disruption of the primary cilia structure or function compromises the endothelium through the suppression of hsp27 dependent actin organization and focal adhesion formation, which may contribute to the vascular dysfunction in ciliopathies. J. Cell. Physiol. 227: 70–76, 2012.

Polycyclic Cage Structures as Lipophilic Scaffolds for Neuroactive Drugs

Polycyclic cage scaffolds have been successfully used in the development of numerous lead compounds demonstrating activity in the central nervous system (CNS). Several neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, schizophrenia, and stroke, as well as drug abuse, can be modulated with polycyclic cage derivatives. These cage moieties, including adamantane and pentacycloundecane derivatives, improve the pharmacokinetic and pharmacodynamic properties of conjugated parent drugs and serve as an important scaffold in the design of therapeutically active agents for the treatment of neurological disorders. In this Minireview, we focus on the recent developments in the field of polycyclic cage compounds, as well as the relationship between the lipophilic character of these cage‐derived drugs and the ability of such compounds to target and reach the CNS and improve the pharmacodynamic properties of compounds conjugated to it.