Cornelis J. Van der Schyf

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.

Multifunctional neuroprotective drugs targeting monoamine oxidase inhibition, iron chelation, adenosine receptors, and cholinergic and glutamatergic action for neurodegenerative diseases

A new paradigm is emerging in the targeting of multiple disease aetiologies that collectively lead to neurodegenerative disorders such as Parkinson’s disease, Alzheimer’s disease, post-stroke neurodegeneration and others. This paradigm challenges the widely held assumption that ‘silver bullet’ agents are superior to ‘dirty drugs’ when it comes to drug therapy. Accumulating evidence in the literature suggests that many neurodegenerative diseases have multiple mechanisms in their aetiologies, thus suggesting that a drug with at least two mechanisms of action targeted at multiple aetiologies of the same disease may offer more therapeutic benefit in certain disorders compared with a drug that only targets one disease aetiology. This review offers a synopsis of therapeutic strategies and novel investigative drugs developed in the authors’ own and other laboratories that modulate multiple disease targets associated with neurodegenerative diseases.

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.

Nicotine Exacerbates Brain Edema during In Vitro and In Vivo Focal Ischemic Conditions

We have previously shown that nicotine, the addictive component of tobacco products, alters the blood-brain barrier (BBB) Na+,K+,2Cl− cotransporter (NKCC) during in vitro hypoxia-aglycemia exposure. Attenuation of abluminal NKCC suggests that accumulation of ions in the brain extracellular fluid would result in an increase of fluid or cytotoxic edema in the brain during hypoxia-aglycemia or stroke conditions. To further investigate whether nicotine products have the potential to worsen stroke outcome by increasing edema formation, two separate models to mimic stroke conditions were utilized to decipher the effects of short-term and long-term administrations of nicotine products on brain edema following stroke. Oxygen glucose deprivation (OGD) was studied in rat hippocampal slices with short-term or long-term exposure to nicotine and cigarette smoke constituents. During short-term exposure, the presence of nicotine at a concentration mimicking heavy smokers increased water content of hippocampal slices during OGD. Furthermore, long-term 1-week administration of nicotine increased water content in hippocampal slices that could be attenuated with nicotine acetylcholine receptor (nAChR) antagonists, suggesting nicotine increase edema during OGD via nAChRs. A second model of focal ischemia, middle cerebral artery occlusion, showed an increase of infarct size during short-term exposure to nicotine and an increase of edema during both short-term and long-term administration of nicotine, compared with saline controls. These findings support the paradigm that nicotine products not only increase the incidence of stroke but also have the potential to worsen stroke outcome by increased edema formation.

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.

Effects of organophosphorus compounds on ATP production and mitochondrial integrity in cultured cells.

Recent studiesin vivo andin vitro suggested that mitochondrial dysfunction follows exposure to organophosphorus (OP) esters. As mitochondrial ATP production is important for cellular integrity, ATP production in the presence of OP neurotoxicants was examined in a human neuronal cell line (SH-SY5Y neuroblastoma cells) and primary dorsal root ganglia (DRG) cells isolated from chick embryos and subsequently cultured to achieve maturation with axons. These cell culture systems were chosen to evaluate toxic effects on the mitochondrial respiratory chain associated with exposure to OP compounds that do and do not cause OP-induced delayed neuropathy (OPIDN), a disorder preceded by inhibition of neurotoxic esterase (NTE). Concentration- and time-response studies were done in neuroblastoma cells exposed to phenyl saligenin phosphate (PSP) and mipafox, both compounds that readily induce delayed neuropathy in hens, or paraoxon, which does not. Phenylmethylsulfonyl fluoride (PMSF) was included as a non-neuropathic inhibitor of NTE. Purified neuronal cultures from 9 day-old chick embryo DRG were treated for 12 h with 1 μM PSP, mipafox, or paraoxon.In situ evaluation of ATP production measured by bioluminescence assay demonstrated decreased ATP concentrations both in neuroblastoma cells and chick DRG neurons treated with PSP. Mipafox decreased ATP production in DRG but not in SH-SY5Y cells. This low energy state was present at several levels of the mitochondrial respiratory chain, including Complexes I, II, III, and IV, although Complex I was the most severely affected. Paraoxon and PMSF were not effective at all complexes, and, when effective, required higher concentrations than needed for PSP. Results suggest that mitochondria are an important early target for OP compounds, with exposure resulting in depletion of ATP production. The targeting of neuronal, rather than Schwann cell mitochondria in DRG following exposure to PSP and mipafox was verified by loss of the mitochondrial-specific dye, tetramethylrhodamine, in these cells. No such loss was seen in paraoxon exposed neurons isolated from DRG or in Schwann cells treated with any of the test compounds.