Topological and chronological features of the impairment of glucose metabolism induced by 1-methyl-4-phenylpyridinium ion (MPP+) in rat brain slices

Mild MPP+ exposure-induced glucose starvation enhances autophagosome synthesis and impairs its degradation

Parkinson's disease (PD) is a prevalent neurodegenerative disorder, mainly characterised by the progressive loss of dopaminergic neurons. MPP⁺ has been widely used as a PD-related neurotoxin, and their reports suggested the several hypotheses for neuronal cell death. However, most of these hypotheses come from the studies about the acute MPP⁺ exposure. We previously revealed that mild MPP⁺ exposure (10 and 200 μM), which induces gradual cell death, impairs autophagosome degradation at 48 h. In the present study, we further investigated the specific events of mild MPP⁺ exposure and revealed that mild MPP⁺ exposure causes the cell death through glucose starvation, but not acute toxic model (2.5 and 5 mM). At 36 h after mild MPP⁺ exposure, autophagosome synthesis was enhanced owing to glucose starvation and continued to enhance until 48 h, despite impaired autophagosome degradation. Inhibition of autophagosome synthesis reduced mild MPP⁺-induced cell death. In conclusion, we clarified that glucose starvation-enhanced autophagosome synthesis occurs at an earlier stage than impaired autophagosome degradation and is important in mild MPP⁺ toxicity.

Whole genome expression profile in neuroblastoma cells exposed to 1-methyl-4-phenylpyridine

Mitochondrial dysfunction and subsequent energy failure is a contributing factor to degeneration of the substantia nigra pars compacta associated with Parkinson's disease (PD). In this study, we investigate molecular events triggered by cell exposure to the mitochondrial toxin 1-methyl-4-phenylpyridine (MPP+) using whole genome-expression microarray, Western Blot and metabolic studies. The data show that MPP+ (500 μM) obstructs mitochondrial respiration/oxidative phosphorylation (OXPHOS) in mouse neuroblastoma Neuro-2a cells, juxtaposing accelerated glucose consumption and production of lactic acid. While additional glucose concentrations restored viability in the presence of MPP+ (500 μM), the loss of OXPHOS was sustained, suggesting that compensatory anaerobic metabolic systems were fulfilling required energy needs. Under these conditions, MPP+ initiated significant changes to the transcription of 439 genes of which 287 DAVID IDs were identified and subsequent functional annotation clusters identified. Prominent changes were as follows; MPP+ initiated loss of mRNA for mitochondrial encoded 3-hydroxybutyratedehydrogenase, type 2(Bdh2), tv1, NADH dehydrogenase 4,5 genes, cytochrome b and NADH dehydrogenase (ubiquinone) flavoprotein 3, concomitant to rise in a mitochondrial fission gene; ganglioside-induced differentiation-associated-protein 1 (GDAP1). The negative changes to OXPHOS components were accompanied by protective forces within the mitochondria espousing elevated ratio of anti/pro-apoptotic processes. These included a loss of apoptotic Bcl-2/adenovirus E1B 19-kDa-interacting protein (BNIP3) and family with sequence similarity 162, member A (FAM162a) and rise of heat shock protein 1 and Lon peptidase 1. There were no changes indicative of free radical damage (e.g. SOD, GSH-Px), rather MPP+ initiated significant elevation in G protein signaling components (which trigger catabolic processes) and anaerobic metabolic systems involving carboxylic acid/transamination reactions (e.g. glutamate oxaloacetate transaminase 1 (GOT1), glutamic pyruvate-alanine transaminase 2 (GPT2), cystathionase and redox proteins such as cytochrome b5 reductase 1 and ferredoxin reductase. Counter-intuitively, the data show reduction of mRNA in glycolytic processes [DAVID enrichment score 9.96 p value 1.90E-19], some corroborated by Western Blot, bringing in to question the sources of lactate observed in the presence of MPP+. Examining this aspect, the data show that diverse carboxylic acids (succinate, oxaloacetate and a-ketoglutarate) are capable of contributing to the lactate pool in addition to phosph(enolpyruvate) or pyruvate in the absence of glucose by this cell line. In conclusion, these findings show that MPP+ negatively affects the transcriptome involved with complex I, but initiated an elevation of G protein signaling and anaerobic metabolic systems involved with nitrogen/carboxylic acid metabolism. Future research will be required to elucidate the survival pathways that drive anaerobic substrate level phosphorylation, and define functional ramification to the loss of mitochondrial FAM162a and BNIP3 proteins.

The biochemical and cellular basis for nutraceutical strategies to attenuate neurodegeneration in Parkinson's disease

Future therapeutic intervention that could effectively decelerate the rate of degeneration within the substantia nigra pars compacta (SNc) could add years of mobility and reduce morbidity associated with Parkinson’s disease (PD). Neurodegenerative decline associated with PD is distinguished by extensive damage to SNc dopaminergic (DAergic) neurons and decay of the striatal tract. While genetic mutations or environmental toxins can precipitate pathology, progressive degenerative succession involves a gradual decline in DA neurotransmission/synaptic uptake, impaired oxidative glucose consumption, a rise in striatal lactate and chronic inflammation. Nutraceuticals play a fundamental role in energy metabolism and signaling transduction pathways that control neurotransmission and inflammation. However, the use of nutritional supplements to slow the progression of PD has met with considerable challenge and has thus far proven unsuccessful. This review re-examines precipitating factors and insults involved in PD and how nutraceuticals can affect each of these biological targets. Discussed are disease dynamics (Sections 1 and 2) and natural substances, vitamins and minerals that could impact disease processes (Section 3). Topics include nutritional influences on α-synuclein aggregation, ubiquitin proteasome function, mTOR signaling/lysosomal-autophagy, energy failure, faulty catecholamine trafficking, DA oxidation, synthesis of toxic DA-quinones, o-semiquinones, benzothiazolines, hyperhomocyseinemia, methylation, inflammation and irreversible oxidation of neuromelanin. In summary, it is clear that future research will be required to consider the multi-faceted nature of this disease and re-examine how and why the use of nutritional multi-vitamin-mineral and plant-based combinations could be used to slow the progression of PD, if possible.

Variable toxicological response to the loss of OXPHOS through 1-methyl-4-phenylpyridinium-induced mitochondrial damage and anoxia in diverse neural immortal cell lines

Immortal cell lines are used to investigate various aspects of neurodegeneration. These cells display high glycolytic turnover rate and produce an abundant amounts of lactate. Our previous studies indicate that these cells survive the loss of mitochondrial oxidative phosphorylation (OXPHOS) with ample glucose supply. In the current study, we investigate if cell type (w/variation in basal metabolic rate (MR)), can alter glucose utilization patterns which in turn may affect LC(50) for the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP(+)) in various cell lines. The data obtained indicate that cell lines MRs examined were generally consistent with the average of species adult body weight where mouse N-2A > rat-PC-12 > human SH-SY5Y. A higher MR was associated with accelerated utilization of glucose and earlier cell death with MPP(+): LC(50) mouse = 294 µM, rat = 695 µM, and human = 5.25 mM at 24 h. Cell death appears to be a function of the velocity by which glucose disappears, leading to the failure of glycolysis and subsequent halt of energy production. Similar effects were also observed at higher plating densities where the demand for glucose is amplified. A time-lapse study of MPP(+) toxicity (0-36 h) in N-2A cells indicates that an anaerobic shift occurs as early as 2 h (evidenced by a rise in lactate), followed by a descent in glucose concentrations at 4 h and exhaustion of glucose supplies at 22 h which was associated with the first detectable sign of cell death. It was also noted that MPP(+) toxicity was not associated with the generation of reactive oxygen species (O (2) (-) , H(2)0(2), and NO(2)) and was not attenuated by adding catalase or superoxide dismutase to the media. On the other hand, MPP(+) toxicity was reversed by providing additional supply of glucose, pyruvate ± mitochondrial monocarboxylate transporter blocker (α-cyano-4-HCA), or pyruvate ± pyruvate dehydrogenase inhibitor (octanoyl-CoA), suggesting that the exclusive anaerobic survival compensates for the loss of OXPHOS by MPP(+). To examine if neuroblastoma were capable of surviving the deprivation of O(2) for 24 h, a range of hypoxia to anoxia was established with various concentrations of dithionite. The data suggest that cell lines examined continue to thrive when incubated with high-glucose media (25 mM). In summary, vulnerability of immortal neuroblastoma cell lines to MPP(+) toxicity is dependent upon glucose concentrations within the media and cell MR, which indirectly dominates the velocity of glucose use and its end point disappearance, leading to cell death by ergogenic failure.