The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

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Nitric Oxide and Peroxynitrite in Health and Disease

Many lines of evidence suggest that mitochondria have a central role in ageing-related neurodegenerative diseases. Mitochondria are critical regulators of cell death, a key feature of neurodegeneration. Mutations in mitochondrial DNA and oxidative stress both contribute to ageing, which is the greatest risk factor for neurodegenerative diseases. In all major examples of these diseases there is strong evidence that mitochondrial dysfunction occurs early and acts causally in disease pathogenesis. Moreover, an impressive number of disease-specific proteins interact with mitochondria. Thus, therapies targeting basic mitochondrial processes, such as energy metabolism or free-radical generation, or specific interactions of disease-related proteins with mitochondria, hold great promise.

Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Mitochondrial Membrane Permeabilization in Cell Death

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell dea...

Ischemic Cell Death in Brain Neurons

Sepsis is a condition that results from a harmful or damaging host response to infection. Many of the components of the innate immune response that are normally concerned with host defences against infection can, under some circumstances, cause cell and tissue damage and hence multiple organ failure, the clinical hallmark of sepsis. Because of the high mortality of sepsis in the face of standard treatment, many efforts have been made to improve understanding of the dysregulation of the host response in sepsis. As a result, much has been learnt of the basic principles governing bacterial-host interactions, and new opportunities for therapeutic intervention have been revealed.

The immunopathogenesis of sepsis.

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(02)09459-X.pdf

Association between mitochondrial dysfunction and severity and outcome of septic shock

Within the CNS and under normal conditions, nitric oxide (.NO) appears to be an important physiological signalling molecule. Its ability to increase cyclic GMP concentration suggests that .NO is implicated in the regulation of important metabolic pathways in the brain. Under certain circumstances .NO synthesis may be excessive and .NO may become neurotoxic. Excessive glutamate-receptor stimulation may lead to neuronal death through a mechanism implicating synthesis of both .NO and superoxide (O2.-) and hence peroxynitrite (ONOO-) formation. In response to lipopolysaccharide and cytokines, glial cells may also be induced to synthesize large amounts of .NO, which may be deleterious to the neighbouring neurones and oligodendrocytes. The precise mechanism of .NO neurotoxicity is not fully understood. One possibility is that it may involve neuronal energy deficiency. This may occur by ONOO- interfering with key enzymes of the tricarboxylic acid cycle, the mitochondrial respiratory chain, mitochondrial calcium metabolism, or DNA damage with subsequent activation of the energy-consuming pathway involving poly(ADP-ribose) synthetase. Possible mechanisms whereby ONOO- impairs the mitochondrial respiratory chain and the relevance for neurotoxicity are discussed. The intracellular content of reduced glutathione also appears important in determining the sensitivity of cells to ONOO- production. It is concluded that neurotoxicity elicited by excessive .NO production may be mediated by mitochondrial dysfunction leading to an energy deficiency state.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1471-4159.1997.68062227.x

Nitric oxide-mediated mitochondrial damage in the brain: mechanisms and implications for neurodegenerative diseases

The effect of the neurotoxic nitric oxide derivative, the peroxynitrite anion (ONOO - ), on the activity of the mitochondrial respiratory chain complexes in cultured neurones and astrocytes was studied. A single exposure of the neurones to ONOO - (initial concentrations of 0.01 2.0 mM) caused, after a subsequent 24-h incubation, a dose-dependent decrease in succinate-cytochrome c reductase (60% at 0.5 mM) and in cytochrome c oxidase (52% at 0.5 mM) activities. NADH-ubiquinone-1 reductase was unaffected. In astrocytes, the activity of the mitochondrial complexes was not affected up to 2 mM ONOO - . Citrate synthase was unaffected in both cell types under all conditions studied. However, lactate dehydrogenase activity released to the culture medium was increased by ONOO - in a dose-dependent manner (40% at 0.5 mM ONOO - ) from the neurones but not from the astrocytes. Neuronal glutathione concentration decreased by 39% at 0.1 mM ONOO - , but astrocytic glutathione was not affected up to 2 mM ONOO - . In isolated brain mitochondria, only succinate-cytochrome c reductase activity was affected (22% decrease at 1 mM ONOO - ). We conclude that the acute exposure of ONOO - selectively damages neurones, whereas astrocytes remain unaffected. Intracellular glutathione appears to be an important factor for ameliorating ONOO - -mediated mitochondrial damage. This study supports the hypothesis that the neurotoxicity of nitric oxide is mediated through mitochondrial dysfunction

Effect of peroxynitrite on the mitochondrial respiratory chain: differential susceptibility of neurones and astrocytes in primary culture.

Nitric oxide, mitochondria and neurological disease.

The lysosomal storage disorder Gaucher disease (GD) is caused by autosomal recessive mutations in the glucocerebrosidase (GBA) gene. GBA encodes a lysosomal enzyme (GCase) that catalyses the metabolism of the sphingolipid glucosylceramide to ceramide and glucose. Deficiency of GCase activity results in accumulation of substrate in the lysosomes of several tissues, including brain. Mutations in GBA result in 3 clinical manifestations. Type 1 GD occurs in both children and adults and predominantly impacts on the non-neuronal organs, whereas types 2 and 3 have an onset in childhood and adolescence, respectively, and exhibit neurological deficits.1

Parkinson disease (PD) is primarily characterized by the motor symptoms of resting tremor, bradykinesia, rigidity, and postural instability. Pathological hallmarks include loss of dopaminergic neurons from the substantia nigra (SN) and the presence of cytoplasmic inclusions known as Lewy bodies in the surviving cells of affected brain regions.2

Typical parkinsonism is among the neurological complications of GD (including type 1).3, 4 The neuropathology of GD brains includes the typical hallmarks of PD, such as cortical and brainstem Lewy bodies.5 Heterozygote carriers of GBA mutations also have an increased frequency of PD, and these mutations are the most common genetic risk factor for developing the disease.6–8

Although the pathogenesis of PD is still unknown, the accumulation of α-synuclein and other ubiquitinated proteins in Lewy bodies has implicated protein mishandling as a putative cause. The proteasome and lysosomes are the 2 principal mechanisms for degrading cellular constituents. Autophagy utilizes lysosomes to degrade long-lived proteins, misfolded/aggregated proteins, and organelles such as mitochondria.9 Defective autophagy and/or lysosomal depletion have been implicated in PD.10–13 Cellular or animal models of GCase deficiency have caused α-synuclein accumulation.14–18 GCase has also been suggested to bind directly with α-synuclein in lysosomes19 and the GCase substrate glucosylceramide stabilizes soluble oligomeric α-synuclein species.18 These observations have led to the notion that GCase deficiency might contribute to the α-synuclein aggregation characteristic of PD pathology.

Despite the recognized association between GBA mutations and PD, it is unknown how heterozygous GBA mutations affect GCase activity in PD brains. In this paper, we provide the first report of the activity of GCase in several regions of PD brains from GBA mutation carriers and sporadic PD brains. GCase deficiency was greatest in the SN of PD brains with GBA mutations. This loss of activity was in part mediated by a decrease in GCase protein levels. GCase activity was also significantly decreased in the SN of sporadic PD brains.

/pdf/glucocerebrosidase-deficiency-in-substantia-nigra-of-4gjxwsa8nf.pdf

Simon J.R. Heales

Papers

Association between mitochondrial dysfunction and severity and outcome of septic shock

Nitric oxide-mediated mitochondrial damage in the brain: mechanisms and implications for neurodegenerative diseases

Effect of peroxynitrite on the mitochondrial respiratory chain: differential susceptibility of neurones and astrocytes in primary culture.

Nitric oxide, mitochondria and neurological disease.

Glucocerebrosidase deficiency in substantia nigra of parkinson disease brains