Oxidation and cytotoxicity of 6-OHDA are mediated by reactive intermediates of COX-2 overexpressed in PC12 cells

The Tangential Dialogue Between Science and Medicine: A Case in Point

The road between a hypothesis about a disease or condition and its cure or palliation is never simply linear. There are many tantalizing tangents to be chased and many seemingly obvious truths with countless exceptions; this is usually a feature, not a bug, as they say in computer programming. In the tangents and exceptions are clues and alternative roads to science and medicine that can provide cures and palliative measures, sometimes for diseases or conditions other than the one being studied. The narrative that follows uses the author's scientific experience in childhood nervous system cancer to illustrate the importance of a robust, bidirectional interaction between the laboratory bench and the clinic bedside in the quest for solutions to problems of health, longevity, and quality of life.

Croix CM, Tyurina YY, Planas-Iglesias J, Jiang J, Huang Z, Amoscato AA, Tyurin VA, Kapralov AA, Cheikhi A, Maguire J, Klein-Seetharaman J, Bayır H, Kagan VE. Mitochondrial Redox Opto-Lipidomics Reveals Mono-Oxygenated Cardiolipins as Pro-Apoptotic Death Signals

While opto-genetics has proven to have tremendous value in revealing the functions of the macromolecular machinery in cells, it is not amenable to exploration of small molecules such as phospholipids (PLs). Here, we describe a redox opto-lipidomics approach based on a combination of high affinity light-sensitive ligands to specific PLs in mitochondria with LC-MS based redox lipidomics/bioinformatics analysis for the characterization of pro-apoptotic lipid signals. We identified the formation of mono-oxygenated derivatives of C18:2-containing cardiolipins (CLs) in mitochondria after the exposure of 10-nonylacridine orange bromide (NAO)-loaded cells to light. We ascertained that these signals emerge as an immediate opto-lipidomics response, but they decay long before the commencement of apoptotic cell death. We found that a protonophoric uncoupler caused depolarization of mitochondria and prevented the mitochondrial accumulation of NAO, inhibited the formation of C18:2-CL oxidation product,s and protected cells from death. Redox opto-lipidomics extends the power of opto-biologic protocols to studies of small PL molecules resilient to opto-genetic manipulations.

Human prostaglandin H synthase (hPHS)-1- and hPHS-2-dependent bioactivation, oxidative macromolecular damage, and cytotoxicity of dopamine, its precursor, and its metabolites

The dopamine (DA) precursor l-dihydroxyphenylalanine (L-DOPA) and metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine may serve as substrates for prostaglandin H synthase (PHS)-catalyzed bioactivation to free radical intermediates. We used CHO-K1 cells expressing human (h) PHS-1 or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. hPHS-1- and hPHS-2-expressing cells incubated with DA, L-DOPA, DOPAC, or HVA exhibited increased cytotoxicity compared to untransfected cells, and cytotoxicity was increased further by exogenous arachidonic acid (AA), which increased hPHS activity. Preincubation with catalase, which detoxifies reactive oxygen species, or acetylsalicylic acid, an inhibitor of hPHS-1 and -2, reduced the cytotoxicity caused by DA, L-DOPA, DOPAC, and HVA in hPHS-1 and -2 cells both with and without AA. Protein oxidation was increased in hPHS-1 and -2 cells exposed to DA or L-DOPA and further increased by AA addition. DNA oxidation was enhanced earlier and at lower substrate concentrations than protein oxidation in both hPHS-1 and -2 cells by DA, L-DOPA, DOPAC, and HVA and further enhanced by AA addition. hPHS-2 cells seemed more susceptible than hPHS-1 cells, whereas untransfected CHO-K1 cells were less susceptible. Thus, isozyme-specific, hPHS-dependent oxidative damage and cytotoxicity caused by neurotransmitters, their precursors, and their metabolites may contribute to neurodegeneration associated with aging.

Adaptive immune regulation of glial homeostasis as an immunization strategy for neurodegenerative diseases

Neurodegenerative diseases, notably Alzheimer's and Parkinson's diseases, are amongst the most devastating disorders afflicting the elderly. Currently, no curative treatments or treatments that interdict disease progression exist. Over the past decade, immunization strategies have been proposed to combat disease progression. Such strategies induce humoral immune responses against misfolded protein aggregates to facilitate their clearance. Robust adaptive immunity against misfolded proteins, however, accelerates disease progression, precipitated by induced effector T cell responses that lead to encephalitis and neuronal death. Since then, mechanisms that attenuate such adaptive neurotoxic immune responses have been sought. We propose that shifting the balance between effector and regulatory T cell activity can attenuate neurotoxic inflammatory events. This review summarizes advances in immune regulation to achieve a homeostatic glial response for therapeutic gain. Promising new ways to optimize immunization schemes and measure their clinical efficacy are also discussed.

Alpha-synuclein, lipids and Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease, after Alzheimer's disease, among the aging human population. The main symptoms of Parkinson's disease such as tremor and movement disabilities are the result of degeneration of dopaminergic neurons in substantia nigra pars compacta. The widely-accepted subcellular factor which underlies Parkinson's disease neuropathology is the presence of Lewy bodies with characteristic inclusions of aggregated alpha-synuclein. This small soluble protein has been implicated in a range of interactions with phospholipid membranes and free fatty acids. The precise biological function of this protein is, however, still under investigation. Here we review the evidence linking alpha-synuclein, lipid metabolism, fatty acid oxidation, mitochondrial damage and Parkinson's disease. We propose that association of alpha-synuclein with oxidized lipid metabolites can lead to mitochondrial dysfunction in turn leading to dopaminergic neuron death and thus to Parkinson's disease.

Neuroinflammation in Parkinson's disease

During the last two decades, a wealth of animal and human studies has implicated inflammation-derived oxidative stress and cytokine-dependent neurotoxicity in the progressive degeneration of the dopaminergic nigrostriatal pathway, the hallmark of Parkinson's disease (PD). In this review, we discuss the various hypotheses regarding the role of microglia and other immune cells in PD pathogenesis and progression, the inflammatory mechanisms implicated in disease progression from pre-clinical and clinical studies, the recent evidence that systemic inflammation can trigger microglia activation in PD-relevant central nervous system regions, the synergism between gene products linked to parkinsonian phenotypes (alpha-synuclein, parkin, Nurr1, and regulator of G-protein signaling-10) and neuroinflammation in promoting neurodegeneration of the nigrostriatal pathway, and the latest update on meta-analysis of epidemiological studies on the risk-lowering effects of anti-inflammatory drug regimens.

Innate and adaptive immunity for the pathobiology of Parkinson's disease

Innate and adaptive immunity affect the pathogenesis of Parkinson's disease (PD). In particular, activation of microglia influences degeneration of dopaminergic neurons. Cell-to-cell interactions and immune regulation critical for neuronal homeostasis also influence immune responses. The links between T cell immunity and nigrostriatal degeneration are supported by laboratory, animal model, and human pathologic investigations. Immune-associated biomarkers in spinal fluids and brain tissue of patients with idiopathic or familial forms of PD provide means to improve diagnosis and therapeutic monitoring. Relationships between oxidative stress, inflammation, and immune-mediated cell death pathways are examined in this review as they are linked to PD pathogenesis. Harnessing the immune system by drugs or by vaccination remain promising future therapeutic options.

Dopaminergic but not glutamatergic neurotransmission is increased in the striatum after selective cyclooxygenase-2 inhibition in normal and hemiparkinsonian rats

In the present work, we studied the effect of the selective cyclooxygenase-2 (COX-2) inhibitors, compound 11 g, celecoxib and selective COX-1 inhibitor SC-560 (intraperitoneally and acutely) on striatal glutamatergic and dopaminergic neurotransmission in normal and substantia nigra pars compacta (SNc)-lesioned rats using the microdialysis technique. We also investigated the effect of acute COX inhibition on the damaged SNc neurons. Our results indicate a significant increase in dopaminergic neurotransmission and a decrease in glutamatergic neurotransmission (P<0.05) only after selective COX-2 inhibition in the striatum of normal and hemiparkinsonian rats. Nonetheless, neither COX-1 nor COX-2 inhibitors showed any improvement in the damaged SNc neurons.

Cyclooxygenase-2 is involved in oxidative damage and alpha-synuclein accumulation in dopaminergic cells

Cyclooxygenase (COX) is the rate-limiting enzyme that catalyzes the formation of prostaglandins from arachidonic acid. The inducible isoform COX-2 is upregulated in the dopaminergic neurons of the substantia nigra of postmortem Parkinson's disease (PD) patients and in neurotoxin-induced Parkinsonism models. COX-2 has attracted significant attention as an important source of oxidative stress in dopaminergic neurons due to its potential to oxidize catechols including dopamine. However, the role of COX-2 in the pathogenesis of PD has not been fully evaluated. Here, we show that COX-2 induces dopamine oxidation, as evidenced by the findings that COX-2 can facilitate dopamine oxidation in a cell-free system and in COX-2-overexpressing SH-SY5Y cells, and that this can be completely abolished by the selective COX-2 inhibitor meloxicam. Increased COX-2 expression causes oxidative protein modification and alpha-synuclein accumulation in dopaminergic cells. These data suggest that an abnormal increase in COX-2 expression causes dopamine oxidation and contributes to the preferential vulnerability of dopaminergic cells as in PD.

Role of cyclooxygenase-2 in tetrahydrobiopterin-induced dopamine oxidation

Dopamine is considered one of the main contributing factors in the induction of oxidative stress and selective dopaminergic neurodegeneration in Parkinson's disease. We have previously reported that tetrahydrobiopterin (BH4) leads to dopamine oxidation and renders dopamine-producing cells vulnerable. In the present study, we found that BH4 selectively upregulates cyclooxygenase-2 (COX-2) expression in dopaminergic cells. BH4 caused an induction of COX-2 mRNA, and a critical regulatory motif for BH4-induced transcriptional activation of COX-2 is CRE/AP-1. COX-2 can oxidize dopamine and cause oxidative stress, which is evidenced by the findings that significant increase in dopamine-chrome formation and protein carbonyl contents by BH4-induced COX-2 up-regulation, and the increases are abolished by COX-2 selective inhibitor meloxicam. Increased COX-2 promotes dopaminergic neurodegeneration in both SH-SY5Y cells and rat mesencephalic neurons. These data suggest that BH4-induced COX-2 expression is responsible for dopamine oxidation, leading to the preferential vulnerability of dopaminergic cells in Parkinson's disease.

Non-steroidal anti-inflammatory drugs in Parkinson's disease

Parkinson's disease (PD) is known to be a chronic and progressive neurodegenerative disease caused by a selective degeneration of dopaminergic (DAergic) neurons in the substantia nigra pars compacta (SNc). A large body of experimental evidence indicates that the factors involved in the pathogenesis of this disease are several, occurring inside and outside the DAergic neuron. Recently, the role of the neuron-glia interaction and the inflammatory process, in particular, has been the object of intense study by the research community. It seems to represent a new therapeutic approach opportunity for this neurological disorder. Indeed, it has been demonstrated that the cyclooxygenase type 2 (COX-2) is up-regulated in SNc DAergic neurons in both PD patients and animal models of PD and, furthermore, non-steroidal anti-inflammatory drugs (NSAIDs) pre-treatment protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6 hydroxydopamine (6-OHDA)-induced nigro-striatal dopamine degeneration. Moreover, recent epidemiological studies have revealed that the risk of developing PD is reduced in humans who make therapeutical use of NSAIDs. Consequently, it is hypothesized that they might delay or prevent the onset of PD. However, whether or not these common drugs may also be of benefit to those individuals who already have Parkinson's disease has not as yet been shown. In this paper, evidence relating to the protective effects of aspirin or other NSAIDs on DAergic neurons in animal models of Parkinson's disease will be discussed. In addition, the pharmacological mechanisms by which these molecules can exert their neuroprotective effects will be reviewed. Finally, epidemiological data exploring the effectiveness of NSAIDs in the prevention of PD and their possible use as adjuvants in the therapy of this neurodegenerative disease will also be examined.