The influence of oxidation of membrane thiol groups on lysosomal proton permeability

Connection between oxidative stress and subcellular organelle in subarachnoid hemorrhage: Novel mechanisms and therapeutic implications

Spontaneous subarachnoid hemorrhage (SAH) is one of the most devastating forms of stroke, with limited treatment modalities and poor patient outcomes. Previous studies have proposed multiple prognostic factors; however, relative research on treatment has not yet yielded favorable clinical outcomes. Moreover, recent studies have suggested that early brain injury (EBI) occurring within 72 h after SAH may contribute to its poor clinical outcomes. Oxidative stress is recognized as one of the main mechanisms of EBI, which causes damage to various subcellular organelles, including the mitochondria, nucleus, endoplasmic reticulum (ER), and lysosomes. This could lead to significant impairment of numerous cellular functions, such as energy supply, protein synthesis, and autophagy, which may directly contribute to the development of EBI and poor long-term prognostic outcomes. In this review, the mechanisms underlying the connection between oxidative stress and subcellular organelles after SAH are discussed, and promising therapeutic options based on these mechanisms are summarized.

Merging the Multi-Target Effects of Phytochemicals in Neurodegeneration: From Oxidative Stress to Protein Aggregation and Inflammation

Wide experimental evidence has been provided in the last decade concerning the neuroprotective effects of phytochemicals in a variety of neurodegenerative disorders. Generally, the neuroprotective effects of bioactive compounds belonging to different phytochemical classes are attributed to antioxidant, anti-aggregation, and anti-inflammatory activity along with the restoration of mitochondrial homeostasis and targeting alterations of cell-clearing systems. Far from being independent, these multi-target effects represent interconnected events that are commonly implicated in the pathogenesis of most neurodegenerative diseases, independently of etiology, nosography, and the specific misfolded proteins being involved. Nonetheless, the increasing amount of data applying to a variety of neurodegenerative disorders joined with the multiple effects exerted by the wide variety of plant-derived neuroprotective agents may rather confound the reader. The present review is an attempt to provide a general guideline about the most relevant mechanisms through which naturally occurring agents may counteract neurodegeneration. With such an aim, we focus on some popular phytochemical classes and bioactive compounds as representative examples to design a sort of main highway aimed at deciphering the most relevant protective mechanisms which make phytochemicals potentially useful in counteracting neurodegeneration. In this frame, we emphasize the potential role of the cell-clearing machinery as a kernel in the antioxidant, anti-aggregation, anti-inflammatory, and mitochondrial protecting effects of phytochemicals.

Could Alzheimer's Disease Originate in the Periphery and If So How So?

The classical amyloid cascade model for Alzheimer's disease (AD) has been challenged by several findings. Here, an alternative molecular neurobiological model is proposed. It is shown that the presence of the APOE ε4 allele, altered miRNA expression and epigenetic dysregulation in the promoter region and exon 1 of TREM2, as well as ANK1 hypermethylation and altered levels of histone post-translational methylation leading to increased transcription of TNFA, could variously explain increased levels of peripheral and central inflammation found in AD. In particular, as a result of increased activity of triggering receptor expressed on myeloid cells 2 (TREM-2), the presence of the apolipoprotein E4 (ApoE4) isoform, and changes in ANK1 expression, with subsequent changes in miR-486 leading to altered levels of protein kinase B (Akt), mechanistic (previously mammalian) target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3), all of which play major roles in microglial activation, proliferation and survival, there is activation of microglia, leading to the subsequent (further) production of cytokines, chemokines, nitric oxide, prostaglandins, reactive oxygen species, inducible nitric oxide synthase and cyclooxygenase-2, and other mediators of inflammation and neurotoxicity. These changes are associated with the development of amyloid and tau pathology, mitochondrial dysfunction (including impaired activity of the electron transport chain, depleted basal mitochondrial potential and oxidative damage to key tricarboxylic acid enzymes), synaptic dysfunction, altered glycogen synthase kinase-3 (GSK-3) activity, mTOR activation, impairment of autophagy, compromised ubiquitin-proteasome system, iron dyshomeostasis, changes in APP translation, amyloid plaque formation, tau hyperphosphorylation and neurofibrillary tangle formation.

Redox control of protein degradation

Intracellular proteolysis is critical to maintain timely degradation of altered proteins including oxidized proteins. This review attempts to summarize the most relevant findings about oxidant protein modification, as well as the impact of reactive oxygen species on the proteolytic systems that regulate cell response to an oxidant environment: the ubiquitin-proteasome system (UPS), autophagy and the unfolded protein response (UPR). In the presence of an oxidant environment, these systems are critical to ensure proteostasis and cell survival. An example of altered degradation of oxidized proteins in pathology is provided for neurodegenerative diseases. Future work will determine if protein oxidation is a valid target to combat proteinopathies.

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Proteins undergo reversible and irreversible redox modifications.

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Oxidized proteins are cleared mainly through the 20S proteasome and autophagy.

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The proteolytic systems exhibit a dynamic crosstalk to adapt to redox alterations.

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Protein oxidation together with impaired degradation are linked to neurodegeneration.

Coenzyme Q10 depletion in medical and neuropsychiatric disorders: potential repercussions and therapeutic implications

Coenzyme Q10 (CoQ10) is an antioxidant, a membrane stabilizer, and a vital cofactor in the mitochondrial electron transport chain, enabling the generation of adenosine triphosphate. It additionally regulates gene expression and apoptosis; is an essential cofactor of uncoupling proteins; and has anti-inflammatory, redox modulatory, and neuroprotective effects. This paper reviews the known physiological role of CoQ10 in cellular metabolism, cell death, differentiation and gene regulation, and examines the potential repercussions of CoQ10 depletion including its role in illnesses such as Parkinson's disease, depression, myalgic encephalomyelitis/chronic fatigue syndrome, and fibromyalgia. CoQ10 depletion may play a role in the pathophysiology of these disorders by modulating cellular processes including hydrogen peroxide formation, gene regulation, cytoprotection, bioenegetic performance, and regulation of cellular metabolism. CoQ10 treatment improves quality of life in patients with Parkinson's disease and may play a role in delaying the progression of that disorder. Administration of CoQ10 has antidepressive effects. CoQ10 treatment significantly reduces fatigue and improves ergonomic performance during exercise and thus may have potential in alleviating the exercise intolerance and exhaustion displayed by people with myalgic encepholamyletis/chronic fatigue syndrome. Administration of CoQ10 improves hyperalgesia and quality of life in patients with fibromyalgia. The evidence base for the effectiveness of treatment with CoQ10 may be explained via its ability to ameliorate oxidative stress and protect mitochondria.

Autophagy, redox signaling, and ventricular remodeling

Autophagy is a catabolic process through which damaged or long-lived proteins, macromolecules, or organelles are recycled by using lysosomal degradation machinery. Although the occurrence of autophagy in several cardiac diseases including ischemic or dilated cardiomyopathy, heart failure, hypertrophy, and during ischemia/reperfusion injury have been reported, the exact role of autophagy in these diseases is not known. Emerging studies indicate that oxidative stress in cellular system could induce autophagy, and oxidatively modified macromolecules and organelles can be selectively removed by autophagy. Mild oxidative stress-induced autophagy could provide the first line of protection against major damage like apoptosis and necrosis. Cardiac-specific loss of Atg5, an autophagic gene involved in the formation of autophagosome, causes cardiac hypertrophy, left ventricular dilation, and contractile dysfunction. Recently, it was revealed that Atg4, another autophagic gene involved in the formation of autophagosomes, is controlled through redox regulation under the condition of starvation-induced autophagy. In this review, we discuss the function of autophagy in association with oxidative stress and redox signaling in the remodeling of cardiac myocardium. Further research is needed to explore the possibilities of redox regulation of other autophagic genes and the role of redox signaling-mediated autophagy in the heart.

Oxidative modifications, mitochondrial dysfunction, and impaired protein degradation in Parkinson's disease: how neurons are lost in the Bermuda triangle

While numerous hypotheses have been proposed to explain the molecular mechanisms underlying the pathogenesis of neurodegenerative diseases, the theory of oxidative stress has received considerable support. Although many correlations have been established and encouraging evidence has been obtained, conclusive proof of causation for the oxidative stress hypothesis is lacking and potential cures have not emerged. Therefore it is likely that other factors, possibly in coordination with oxidative stress, contribute to neuron death. Using Parkinson's disease (PD) as the paradigm, this review explores the hypothesis that oxidative modifications, mitochondrial functional disruption, and impairment of protein degradation constitute three interrelated molecular pathways that execute neuron death. These intertwined events are the consequence of environmental exposure, genetic factors, and endogenous risks and constitute a "Bermuda triangle" that may be considered the underlying cause of neurodegenerative pathogenesis.

Mechanism of Lysophosphatidylcholine-Induced Lysosome Destabilization

Lysosomal destabilization is critical for the organelle and living cells. Phospholipase A(2 )(PLA(2)) was shown to be able to destabilize lysosomes under some conditions. By what mechanism the enzyme affects lysosomal stability is not fully studied. In this study, we investigated the effects of lysophosphatidylcholine (lysoPC), a PLA(2)-produced lipid metabolite, on lysosomal ion permeability, osmotic sensitivity and stability. By measuring lysosomal beta-hexosaminidase free activity, membrane potential, proton leakage and their enzyme latency loss in hypotonic sucrose medium, we established that lysoPC could increase the lysosomal permeability to both potassium ions and protons and enhance lysosomal osmotic sensitivity. These changes in lysosomal membrane properties promoted entry of potassium ions into lysosomes via K(+)/H(+) exchange. The resultant osmotic imbalance across the membranes led to losses of lysosomal integrity. The enhancement of lysosomal osmotic sensitivity caused the lysosomes to become more liable to destabilization in osmotic shock. These results suggest that lysoPC may play a key role in PLA(2)-induced lysosomal destabilization.

The oxidative damage of butenolide to isolated erythrocyte membranes

Butenolide (CAS No. 16275-44-8), a mycotoxin produced by several Fusarium species, has been shown to be a potential risk factor for animal and human health. This study was undertaken to investigate the potential oxidative damage of butenolide to biomembranes in vitro using the erythrocyte membrane model. Following exposure of isolated rat erythrocyte membranes to butenolide, the extent of oxidative damage was assessed by measuring lipid peroxidation, -SH groups content, Ca2+/Mg2+-ATPase and Na+/K+-ATPase activities, and conformational changes in membrane proteins. It was observed that butenolide resulted in a significant lipid peroxidation, revealed by a concentration-dependent increase in the level of thiobarbituric acid reactive substances (TBARS). Similarly, this toxin induced a concentration-dependent decrease in the content of membrane total -SH groups, as well as free -SH groups. Membrane-bound enzymes were also impaired by the toxin, demonstrated by the marked inhibition of the activities of Na+/K+-ATPase and Ca2+/Mg2+-ATPase. Conformational changes in membrane proteins were determined using electron paramagnetic resonance (EPR) spin labeling. Butenolide caused an increase in the ratio of weakly to strongly immobilized components (W/S ratio) in a manner of concentration-dependent, indicating conformational changes in membrane proteins occurred. In conclusion, these findings indicate that butenolide is capable of inducing significant oxidative damage to membrane lipids and proteins.

Autophagy as a cell-repair mechanism: activation of chaperone-mediated autophagy during oxidative stress

Proper removal of oxidized proteins is an important determinant of success when evaluating the ability of cells to handle oxidative stress. The ubiquitin/proteasome system has been considered the main responsible mechanism for the removal of oxidized proteins, as it can discriminate between normal and altered proteins, and selectively target the latter ones for degradation. A possible role for lysosomes, the other major intracellular proteolytic system, in the removal of oxidized proteins has been often refused, mostly on the basis of the lack of selectivity of this system. Although most of the degradation of intracellular components in lysosomes (autophagy) takes place through "in bulk" sequestration of complete cytosolic regions, selective targeting of proteins to lysosomes for their degradation is also possible via what is known as chaperone-mediated autophagy (CMA). In this work, we review recent evidence supporting the participation of CMA in the clearance of oxidized proteins in the forefront of the cellular response to oxidative stress. The consequences of an impairment in CMA activity, observed during aging and in some age-related disorders, are also discussed.

Oxidative stress and autophagy

Organisms respond to oxidative injury by orchestrating a stress response to prevent further damage. An increase in the intracellular levels of antioxidant agents, and at the same time the removal of already damaged components, are both part of the oxidative stress response. Lysosomes have been classically considered one of the main targets of the reactive oxygen species. In fact, the destabilization of the lysosomal membrane during oxidizing conditions promotes the leakage of the enzymes contained in these organelles and contributes to cellular damage. However, recent evidence supports a protective role of the lysosomal system, which can eliminate altered intracellular components through autophagy, at least in the first stages of oxidative injury. Consequently, activation of the main intracellular proteolytic systems, the ubiquitin/proteasome, and also the lysosomal/autophagic system occurs during the oxidative stress response. The opposing roles for the lysosomal system under oxidizing conditions are discussed in this review.

Damage to the structure of erythrocyte plasma membranes in patients with type-2 hypercholesterolemia

BACKGROUND

Hypercholesterolemia may decrease the deformability of red blood cells which impairs their hemorheological behavior and promotes atherosclerosis. The study involved 60 hypercholesterolemic patients and 30 healthy individuals as the control group.

METHODS

The membrane fluidity of erythrocytes was estimated by a spin-label method (5-doxylstearic acid (5-DSA)). The ratio of weakly to strongly (W/S) immobilized residues of erythrocyte membrane-bond maleimide-tempo spin label was studied in oxidative damage to membrane protein. Damage to erythrocyte proteins was also indicated by means of Na(+) K(+) ATPase activity.

RESULTS

The membranes of hyperlipidemia (hlp) patients contain larger concentrations of cholesterol 2.16+/-0.24 than do those of the normolipemic individuals 0.31+/-0.24 (P<0.001). The level of Na(+) K(+) ATPase in the erythrocyte membrane from the control group was higher 103.4+/-1.3 (nmolPi/(mgproteinsh)) than in the patient group 93.6+/-3.2 (nmolPi/(mgproteinsh)) (P<0.001). The order parameter S 5-DSA in the control group was 0.745+/-0.009 and in hlp patients was 0.755+/-0.009 (P<0.001). The W/S ratio in the control group amounted to 2.00+/-0.09 and in the hlp patient group was 2.50+/-0.11 (P<0.001).

CONCLUSION

Type-2 hypercholesterolemia causes changes in the structure and fluidity of erythrocyte plasma membranes since the excess of cholesterol affects the normal rheology of blood through its interaction with erythrocytes. It also impairs the function and structure of plasma membrane proteins.