Effect of reactive oxygen species on lysosomal membrane integrity. A study on a lysosomal fraction

Endolysosomal trapping of therapeutics and endosomal escape strategies

Internalizing therapeutic molecules or genes into cells and safely delivering them to the target tissue where they can perform the intended tasks is one of the key characteristics of the smart gene/drug delivery vector. Despite much research in this field, endosomal escape continues to be a significant obstacle to the development of effective gene/drug delivery systems. In this review, we discuss in depth the several types of endocytic pathways involved in the endolysosomal trapping of therapeutic agents. In addition, we describe numerous mechanisms involved in nanoparticle endosomal escape. Furthermore, many other techniques are employed to increase endosomal escape to minimize entrapment of therapeutic compounds within endolysosomes, which have been reviewed at length in this study.

Hsp70.1 carbonylation induces lysosomal cell death for lifestyle-related diseases

Alzheimer's disease, type 2 diabetes, and non-alcoholic steatohepatitis (NASH) constitute increasingly prevalent disorders. Individuals with type 2 diabetes are well-known to be susceptible to Alzheimer's disease. Although the pathogenesis of each disorder is multifactorial and the causal relation remains poorly understood, reactive oxygen species (ROS)-induced lipid and protein oxidation conceivably plays a common role. Lipid peroxidation product was recently reported to be a key factor also for non-alcoholic steatohepatitis, because of inducing hepatocyte degeneration/death. Here, we focus on implication of the representative lipid-peroxidation product 'hydroxynonenal' for the cell degeneration/death of brain, pancreas, and liver. Since Hsp70.1 has dual roles as a chaperone and lysosomal membrane stabilizer, hydroxynonenal-mediated oxidative injury (carbonylation) of Hsp70.1 was highlighted. After intake of high-fat diets, oxidation of free fatty acids in mitochondria generates ROS which enhance oxidation of ω-6 polyunsaturated fatty acids (PUFA) involved within biomembranes and generate hydroxynonenal. In addition, hydroxynonenal is generated during cooking deep-fried foods with vegetable oils especially containing linoleic acids. These intrinsic and exogenous hydroxynonenal synergically causes an increase in its serum and organ levels to induce Hsp70.1 oxidation. As it is amphiphilic; being water-soluble but displays strong lipophilic characteristics, hydroxynonenal can diffuse within the cells and react with targets like senile and/or atheromatous plaques outside the cells. Hydroxynonenal can deepen and expand lysosomal injuries by facilitating 'calpain-mediated cleavage of the carbonylated Hsp70.1'. Despite the unique anatomical, physiological, and biochemical characteristics of each organ for its specific disease, there should be a common cascade of the cell degeneration/death which is caused by hydroxynonenal. This review aims to implicate hydroxynonenal-mediated Hsp70.1 carbonylation for lysosomal membrane permeabilization/rupture and the resultant cathepsin leakage for inducing cell degeneration/death. Given the tremendous number of worldwide people suffering various lifestyle-related diseases, it is valuable to consider how ω-6 PUFA-rich vegetable oils is implicated for the organ disorder.

Risperidone Toxicity on Human Blood Lymphocytes in Nano molar Concentrations

Risperidone is an atypical antipsychotic drug used for the pharmacotherapy of psychiatric disorders. Some reports indicate that risperidone is toxic to various systems of the body, including the immune system. This study evaluated the toxicity effect of risperidone on human blood lymphocytes. To achieve this aim, lymphocytes were isolated using Ficoll paque plus. The results showed that risperidone (12, 24 and 48 nM) causes toxicity in human blood lymphocytes by increasing the level of intracellular reactive oxygen species (ROS), damage to lysosomal membrane, the collapse of the mitochondrial membrane potential (MMP), and increased extracellular oxidized glutathione (GSSG). Also, exposure of human blood lymphocytes to risperidone is associated with a decrease in intracellular glutathione (GSH) levels. Finally, it could be concluded that oxidative stress is one of the mechanisms of risperidone-induced toxicity in human blood lymphocytes.

Bone Metastases of Glioblastoma: A Case Report and Review of the Literature

Background

Glioblastoma (GBM) is the most common primary intracranial tumor and originates from the small pool of adult neural stem and progenitor cells (NSPCs). According to the World Health Organization (WHO) classification of brain tumors, gliomas are classified into grades I–IV, and GBM is defined as the highest grade (IV). GBM can be disseminated by cerebrospinal fluid (CSF), but extracranial metastasis is rare. Additionally, the pathway and mechanism involved remain unclear.

Case Presentation

We report a rare case of left temporal lobe GBM with multiple bone metastases and soft tissue metastasis. This 49-year-old right-handed man who was diagnosed with GBM underwent surgery on May 9, 2017, followed by radiochemotherapy in June 2017. On August 13, 2019, local relapse was found. Then, the patient received a second surgery but not radiochemotherapy. In November 2019, the patient was reported to be suffering from low back pain for nearly 1 month. On December 6, 2019, magnetic resonance imaging (MRI) of the thoracolumbar vertebrae and abdominal computed tomography (CT) confirmed metastases on the ninth posterior rib on the right, the third anterior rib on the left, and the T7 and T10 vertebrae and their appendages. CT-guided rib space-occupying puncture biopsy was performed, and GBM was identified by pathology.

Conclusion

We should pay attention to extracranial metastasis of GBM. Timely detection and early treatment improve overall quality of patients’ life. The extracranial metastasis in this patient may have occurred through the spinal nerve root or intercostal nerve. Further clinical observations are required to clarify the pathway and mechanism involved.

Thymoquinone Suppresses the Proliferation, Migration and Invasiveness through Regulating ROS, Autophagic Flux and miR-877-5p in Human Bladder Carcinoma Cells

Bladder carcinoma is among the top 10 most frequently diagnosed cancer types in the world. As a phytochemical active metabolic, thymoquinone (TQ) is extracted from seeds of Nigella sativa, possessing various biological properties in a wide range of diseases. Moreover, the outstanding anti-cancer effect of TQ is attracting increasing attentions. In certain circumstances, moderate autophagy is regarded to facilitate the adaptation of malignant cells to different stressors. Conversely, closely linked with the mitochondrial membrane potential (MMP) loss, the upregulation of intracellular reactive oxygen species (ROS) is reported to activate the cell apoptosis in many cancer types. Furthermore, the vital effects of microRNAs in the pathological processes of cancer cells have also been confirmed by previous studies. The present research confirms that TQ restrains the viability, proliferation, migration and invasion through activating caspase-dependent apoptosis in bladder carcinoma cells, which is mediated by TQ induced ROS increase in bladder carcinoma cells. Furthermore, TQ is proved to block the fusion of autophagosomes and lysosomes, causing the accumulation of autophagosomes and subsequent cell apoptosis. In addition, TQ is also found to initiate the miR-877-5p/PD-L1 axis, which suppresses the epithelial mesenchymal transition (EMT) and invasion of bladder carcinoma cells. Taken together, TQ induces the apoptosis through upregulating ROS level and impairing autophagic flux, and inhibiting the EMT and cell invasion via activating the miR-877-5p/PD-L1 axis in bladder carcinoma cells.

Impact of ROS Generated by Chemical, Physical, and Plasma Techniques on Cancer Attenuation

For the last few decades, while significant improvements have been achieved in cancer therapy, this family of diseases is still considered one of the deadliest threats to human health. Thus, there is an urgent need to find novel strategies in order to tackle this vital medical issue. One of the most pivotal causes of cancer initiation is the presence of reactive oxygen species (ROS) inside the body. Interestingly, on the other hand, high doses of ROS possess the capability to damage malignant cells. Moreover, several important intracellular mechanisms occur during the production of ROS. For these reasons, inducing ROS inside the biological system by utilizing external physical or chemical methods is a promising approach to inhibit the growth of cancer cells. Beside conventional technologies, cold atmospheric plasmas are now receiving much attention as an emerging therapeutic tool for cancer treatment due to their unique biophysical behavior, including the ability to generate considerable amounts of ROS. This review summarizes the important mechanisms of ROS generated by chemical, physical, and plasma approaches. We also emphasize the biological effects and cancer inhibition capabilities of ROS.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

Oxidative stress and the homeodynamics of iron metabolism

Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress.

Urinary proteins induce lysosomal membrane permeabilization and lysosomal dysfunction in renal tubular epithelial cells

Lysosomal membrane permeabilization (LMP) has been shown to cause the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol and initiate a cell death pathway. Whether proteinuria triggers LMP in renal tubular epithelial cells (TECs) to accelerate the progression of renal tubulointerstitial injury remains unclear. In the present study, we evaluated TEC injury as well as changes in lysosomal number, volume, activity, and membrane integrity after urinary protein overload in vivo and in vitro. Our results revealed that neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 levels were significantly increased in the urine of patients with minimal change nephrotic syndrome (MCNS) and the culture supernatant of HK-2 cells treated by urinary proteins extracted from MCNS patients. Urinary protein overload also induced apoptotic cell death in HK-2 cells. Importantly, we found that lysosomal volume and number were markedly increased in TECs of patients with MCNS and HK-2 cells overloaded with urinary proteins. However, lysosome function, as assessed by proteolytic degradation of DQ-ovalbumin and cathepsin-B and cathepsin-L activities, was decreased in HK-2 cells overloaded with urinary proteins. Furthermore, urinary protein overload led to a diffuse cytoplasmic immunostaining pattern of cathepsin-B and irregular immunostaining of lysosome-associated membrane protein-1, accompanying a reduction in intracellular acidic components, which could be improved by pretreatment with antioxidant. Taken together, our results indicate that overloading of urinary proteins caused LMP and lysosomal dysfunction at least partly via oxidative stress in TECs.

The role of lysosomes in iron metabolism and recycling

Iron is the most abundant transition metal in the earth's crust. It cycles easily between ferric (oxidized; Fe(III)) and ferrous (reduced; Fe(II)) and readily forms complexes with oxygen, making this metal a central player in respiration and related redox processes. However, 'loose' iron, not within heme or iron-sulfur cluster proteins, can be destructively redox-active, causing damage to almost all cellular components, killing both cells and organisms. This may explain why iron is so carefully handled by aerobic organisms. Iron uptake from the environment is carefully limited and carried out by specialized iron transport mechanisms. One reason that iron uptake is tightly controlled is that most organisms and cells cannot efficiently excrete excess iron. When even small amounts of intracellular free iron occur, most of it is safely stored in a non-redox-active form in ferritins. Within nucleated cells, iron is constantly being recycled from aged iron-rich organelles such as mitochondria and used for construction of new organelles. Much of this recycling occurs within the lysosome, an acidic digestive organelle. Because of this, most lysosomes contain relatively large amounts of redox-active iron and are therefore unusually susceptible to oxidant-mediated destabilization or rupture. In many cell types, iron transit through the lysosomal compartment can be remarkably brisk. However, conditions adversely affecting lysosomal iron handling (or oxidant stress) can contribute to a variety of acute and chronic diseases. These considerations make normal and abnormal lysosomal handling of iron central to the understanding and, perhaps, therapy of a wide range of diseases.

Iron and oxidative stress in cold-initiated necrotic death of rat hepatocyte

Iron chelators and antioxidants have been shown to prevent hypothermia-induced apoptosis in hepatocytes. This study examined whether iron chelation and antioxidants could also prevent hypothermia-induced necrosis. Isolated rat hepatocytes were incubated at 4 degrees C for 6 hours and then rewarmed at 37 degrees C for 18 hours with or without the iron chelator deferoxamine and a selection of antioxidants. There was no evidence of increased cell death or adenosine triphosphate depletion during hypothermic incubation. After hypothermia and rewarming, the majority of rat hepatocytes died of necrosis as indicated by the absence of DNA fragmentation, caspase 3 activity, and apoptotic bodies. Cell death was significantly reduced if deferoxamine or a selection of antioxidants were present during hypothermia and rewarming. Deferoxamine was more effective in preventing cell death when added prior to hypothermia, indicating cell death processes were likely initiated during hypothermia.

Oxidative stress causes a decline in lysosomal integrity during hypothermic incubation of rat hepatocytes

Oxidative stress during cold preservation has been identified as a significant cause of cell injury but the process by which injury occurs is poorly understood. We examined loss of lysosomal integrity as a possible cause of cell injury during extended cold storage of isolated rat hepatocytes. After 21 h of hypothermia, there was a marked decline in lysosomal integrity, which was correlated with an increase in lipid peroxidation. When lipid peroxidation was prevented with the antioxidant Trolox (a vitamin E analog) or the iron chelator desferrioxamine, lysosomal integrity was preserved. In contrast, increasing lysosomal iron with ferric chloride caused an increase in lipid peroxidation and decreased lysosomal integrity. Loss of lysosomal integrity during cold preservation in this experimental model was consistent with iron-initiated oxidative stress. The progressive loss of lysosomal integrity during hypothermic incubation has the potential to affect liver function after transplantation.

Resolving vesicle fusion from lysis to monitor calcium-triggered lysosomal exocytosis in astrocytes

Optical imaging of individual vesicle exocytosis is providing new insights into the mechanism and regulation of secretion by cells. To study calcium-triggered secretion from astrocytes, we used acridine orange (AO) to label vesicles. Although AO is often used for imaging exocytosis, we found that imaging vesicles labeled with AO can result in their photolysis. Here, we define experimental and analytical approaches that permit us to distinguish unambiguously between fusion, leakage, and lysis of individual vesicles. We have used this approach to demonstrate that lysosomes undergo calcium-triggered exocytosis in astrocytes.

ROS stress in cancer cells and therapeutic implications

Reactive oxygen species (ROS) are constantly generated and eliminated in the biological system, and play important roles in a variety of normal biochemical functions and abnormal pathological processes. Growing evidence suggests that cancer cells exhibit increased intrinsic ROS stress, due in part to oncogenic stimulation, increased metabolic activity, and mitochondrial malfunction. Since the mitochondrial respiratory chain (electron transport complexes) is a major source of ROS generation in the cells, the vulnerability of the mitochondrial DNA to ROS-mediated damage appears to be a mechanism to amplify ROS stress in cancer cells. The escalated ROS generation in cancer cells serves as an endogenous source of DNA-damaging agents that promote genetic instability and development of drug resistance. Malfunction of mitochondria also alters cellular apoptotic response to anticancer agents. Despite the negative impacts of increased ROS in cancer cells, it is possible to exploit this biochemical feature and develop novel therapeutic strategies to preferentially kill cancer cells through ROS-mediated mechanisms. This article reviews ROS stress in cancer cells, its underlying mechanisms and relationship with mitochondrial malfunction and alteration in drug sensitivity, and suggests new therapeutic strategies that take advantage of increased ROS in cancer cells to enhance therapeutic activity and selectivity.

The effect of Pycnogenol on fluoride induced rat kidney lysosomal damage in vitro

Pycnogenol (PYC) is a procyanidin-rich extract of the bark of French maritime pine (Pinus pinaster) with a potent ability to scavenge free radicals. Lysosome-rich fractions from rat renal cortices were incubated with varying amounts of PYC and challenged with noxious doses of fl uoride. Controls were also included. The release of N-acetyl-beta-D-glucosaminidase (NAG) isozymes in the supernatant was estimated by spectrophotometric methods. The protein content of the renal cortex was also determined. Our results show that fluoride in unhealthy doses can cause a concentration dependent release of N-acetyl-beta-D-glucosaminidase (NAG) isozymes from the renal lysosomes. This may be related to its known ability to initiate free radical formation or direct damaging effects on the lysosomal membrane. As a blend of bio flavonoids pycnogenol has a potent ability to scavenge free radicals. In our study PYC was effective in preventing fluoride induced release of NAG isozymes from the renal lysosomes.

Phorbol ester induces elevated oxidative activity and alkalization in a subset of lysosomes

BACKGROUND

Lysosomes are acidic organelles that play multiple roles in various cellular oxidative activities such as the oxidative burst during cytotoxic killing. It remains to be determined how lysosomal lumen oxidative activity and pH interact and are regulated. Here, I report the use of fluorescent probes to measure oxidative activity and pH of lysosomes in live macrophages upon treatment with the tumor promotor phorbol 12-myristate 13-acetate (PMA), and providing new insight on regulation mechanism of oxidative activity and pH.

RESULTS

The substrate used to measure oxidative activity was bovine serum albumin covalently coupled to dihydro-2',4,5,6,7,7'-hexafluorofluorescein (OxyBURST Green H2HFF BSA). During pulse-chase procedures with live macrophages, this reduced dye was internalized through an endocytic pathway and accumulated in the lysosomes. Oxidation of this compound, which results in fluorescence increases, depends on the redox potential in the lysosomal lumen. By using low-light level fluorescence microscopy, I determined that phorbol ester treatment results in increased oxidative activity and pH elevation in different subsets of lysosomes. Furthermore, lysosomes with stronger oxidative activity tend to exclude an acidotropic lysosomal indicator, and thus exhibit higher alkalinity.

CONCLUSION

Results indicate that there is a regulatory mechanism between lysosomal oxidative activity and pH. Activation of lysosomal Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase by phorbol ester may result in increase of intralysosomal O2- and H2O2, concurrent with pH elevation due to consumption of H+ and generation of OH-. Furthermore, effect of phorbol ester on elevated oxidative activity and pH is heterogeneous among total lysosomal population. Higher oxidative activity and/or pH are only observed in subsets of lysosomes.

Superoxide dismutase: an emerging target for cancer therapeutics

Superoxide dismutase (SOD) is a critical enzyme responsible for the elimination of superoxide radicals and is considered to be a key anti-oxidant in aerobic cells. Cellular consumption of oxygen is essential for oxidative phosphorylation during ATP generation in the mitochondria, yet this cellular metabolism also leads to the production of reactive oxygen species (ROS), including the superoxide radical (O(2)(*)(-)) and hydrogen peroxide (H(2)O(2)). Accumulation of ROS results in cellular oxidative stress and, if not corrected, can lead to the damage of important biomolecules such as membrane lipids, proteins and DNA. Prolonged accumulation of high levels of free radicals in cells may cause irreversible cellular injury and ultimately result in cell death. Since SOD is the key enzyme in the first metabolic step of superoxide elimination, deficiency in SOD or inhibition of the enzyme activity may cause severe accumulation of O(2)(*)(-) in cells and lead to cell death. Thus, inhibition of SOD may provide a novel way to kill cancer cells. Due to dysfunction in the regulation of cell growth, cancer cells are active in energy metabolism, and thus produce high levels of O(2)(*)(-) and other ROS and are under constant oxidative stress. This may render the malignant cells more dependent on SOD to eliminate the toxic superoxide radicals and thus potentially more sensitive to SOD inhibitors. It is a plausible hypothesis that inhibition of SOD may preferentially kill malignant cells through a free radical-mediated mechanism. This article will review evidence that suggests SOD as an emerging therapeutic target for cancer treatment. The relevant clinical implications and potential risk will also be discussed.

Congenital disorders sharing oxidative stress and cancer proneness as phenotypic hallmarks: prospects for joint research in pharmacology

In spite of very distinct genotypic assets, a number of congenital conditions include oxidative stress as a phenotypic hallmark. These disorders include Fanconi's anaemia, ataxia telangiectasia, xeroderma pigmentosum and Bloom's syndrome, as well as two frequent congenital conditions: Down's syndrome and cystic fibrosis. Cancer proneness is a clinical feature shared by these disorders, while other manifestations include early ageing, neurological symptoms or congenital malformations. The onset of oxidative stress has been related to excess formation, or defective detoxification, of reactive oxygen species (ROS). This can arise from either the abnormal expression or inducibility of ROS-detoxifying enzymes, or by defective absorption of nutrient antioxidants. Resulting oxidative injury has been characterized through: (i) DNA, protein or lipid oxidative damage; (ii) excess ROS formation (in vitro and ex vivo); (iii) sensitivity to oxygen-related toxicity; (iv) improvement of cellular defects by either hypoxia or antioxidants; and (v) circumstantial evidence for in vivo oxidative stress (as e.g. clastogenic factors). Investigations conducted so far have been confined to individual disorders. Comparative studies of selected indicators for oxidative stress could provide further insights into the pathogenesis of each individual condition. Such a unified approach may have wide-ranging consequences for studies of ageing and cancer.

A pre-embedding technique for immunocytochemical visualization of cathepsin D in cultured cells subjected to oxidative stress

We describe a pre-embedding immunocytochemical method for visualization of the lysosomal enzyme cathepsin D in cultured cells. The protein was demonstrated at both light and electron microscopic levels by neutral-pH silver enhancement of ultrasmall (0.8-nm) gold particles conjugated to the antibodies. The best morphological preservation and the highest labeling density were achieved by initial fixation for 20 min at 4C in 4% paraformaldehyde (PFA) and 0. 05% glutaraldehyde (GA) in 0.15 M sodium cacodylate buffer, followed by permeabilization in sodium borohydride. Three cell types were used: human foreskin fibroblasts, histocytic lymphoma (J-774) cells, and primary rat heart myocytes. In all three, cathepsin D was demonstrated in lysosome-like structures. The rat heart myocytes were also exposed to the redox cycling substance naphthazarin (5, 8-dihydroxy-1,4-naphthoquinone) to induce oxidative stress. This was done for such a short period of time that the cells initially did not show any signs of morphological damage and retained normal plasma membrane stability, although an early and clear redistribution of cathepsin D from membrane-bound structures to the cytosol was apparent. This redistribution was followed by cell degeneration and, eventually, by cell death.

Lysosomal heterogeneity between and within cells with respect to resistance against oxidative stress

The prevailing opinion on lysosomal endurance is that, as long as the cells are still alive, these organelles are generally quite stable and, thus, do not induce cell damage by leaking their numerous powerful hydrolytic enzymes to the cytosol. We suggest that this opinion is basically wrong and consider that many lysosomes are quite vulnerable, especially to oxidative stress. Moreover, we suggest that cellular degeneration, including apoptosis as well as necrosis, follows upon lysosomal disruption. We have found differing stability of lysosomal membranes to oxidative stress, not only among different cell types, but also between cells of the same type and between lysosomes of individual cells. We suggest that cellular resistance to oxidative stress is mainly a function of three parameters: (i) the capacity to degrade hydrogen peroxide before it reaches, and may diffuse into, the acidic vacuolar compartment; (ii) the resistance to reactive oxygen species of lysosomal membranes; and (iii) the intralysosomal amounts of redox-active, low molecular weight iron. Iron-catalysed intralysosomal reactions, if pronounced enough, result in peroxidation and destabilization of the lysosomal membrane. Owing to differences in the cellular synthesis of hydrogen peroxide-degrading enzymes, degree of autophagocytotic degradation of iron-containing metalloproteins, lysosomal localization within the cytoplasm and intralysosomal iron chelation, the above three parameters may vary between both different and similar cells and between lysosomes of individual cells as well, explaining their observed variability with respect to resistance against oxidative stress.

The direct cause of photodamage-induced lysosomal destabilization

Whether membrane lipid photoperoxidation is the immediate cause for lysosomal lysis is still unclear. In this study, we investigated the direct causal factor of photoinduced lysosomal destabilization in a K+-containing solution. Methylene blue (MB)-mediated photodamage caused lysosomal membrane lipid peroxidation and loss of membrane fluidity. Compared with unirradiated lysosomes, the photodamaged lysosomes significantly lost enzyme latency in an isotonic K+-containing solution during a 20-min period of incubation. It indicates an increase in lysosomal K+ permeability. The inward K+ permeation of photodamaged lysosomes was further proved by a K+-induced elevation of internal membrane potential. In addition, the photodamaged lysosomes displayed an increased osmotic sensitivity, showing that MB-mediated photodamage promotes lysosomal osmotic fragility. Although these photoinduced alterations occurred, the lysosomes were relatively stable in an isotonic sucrose medium. In contrast, the organelle destabilized in a photodamage-dependent fashion in an isotonic K+-containing solution. The results indicate that membrane lipid peroxidation does not definitely destabilize lysosomes. The direct cause for the lysosomal destabilization is photoinduced osmotic imbalance across its membrane via an increased K+ uptake, while the increase in osmotic sensitivity favors the destabilization of photodamaged lysosomes.

Does an acidic pH explain why low density lipoprotein is oxidised in atherosclerotic lesions?

The oxidation of low density lipoprotein (LDL) within atherosclerotic lesions may be involved in atherogenesis. LDL oxidation by cells in the presence of iron is faster at acidic pH. In addition, LDL oxidation by iron alone or iron cysteine in the absence of cells is much faster at acidic pH, even at mildly acidic pH (pH 6.5). The effect of pH on LDL oxidation by copper ions is more complex, in that acidity slows down the initial oxidation, as measured by conjugated dienes, hydroperoxides and thiobarbituric acid-reactive substances, but can increase the later stages of LDL oxidation as measured by increased macrophage uptake. Extensive LDL oxidation by cells in atherosclerotic lesions probably requires a source of iron or copper as catalysts for the oxidation. Iron in plasma is carried by the protein transferrin. Lowering the pH releases some of the iron from transferrin so that it can catalyse LDL oxidation. Copper is carried in plasma on caeruloplasmin and becomes more effective in catalysing LDL oxidation when the caeruloplasmin is preincubated at acidic pH, or even at pH 7.0. These effects can be seen with concentrations of caeruloplasmin and transferrin below those present in plasma. By analogy to other inflammatory and ischaemic sites, atherosclerotic lesions may well have an acidic extracellular pH, particularly within clusters of macrophages where the oxidative stress may also be high. This localised acidic pH may help to explain why atherosclerotic lesions are one of the few sites in the body where extensive LDL oxidation occurs.

Inhibition of HIV-1 replication by hydroxychloroquine: mechanism of action and comparison with zidovudine

We have previously described the inhibition of human immunodeficiency virus serotype 1 (HIV-1) using the antimalarial hydroxychloroquine (HCQ), a weak base that inhibits the posttranslational modification of glycoprotein 120 (gp 120) in T cells and monocytes. The mechanism of inhibition of gp 120 production was presumed to be the ability of HCQ to increase endosomal pH and therefore alter enzymes required for gp120 production. To further clarify this action, we have determined the effect of HCQ and its enantiomers on endosomal pH. Pretreatment of cells with HCQ and the levo- and dextro-enantiomers at concentrations demonstrated to suppress anti-HIV-1 activity increased endosomal pH to levels similar to increases seen with chloroquine and ammonium chloride, two other weak bases, and decreased gp 120 production. The dextro- and levo-enantiomers suppressed HIV-1 replication to a similar extent and were no more toxic than racemic HCQ. We next compared the anti-HIV-1 effect of HCQ with zidovudine (ZDV) in both newly and chronically HIV-1-infected T-cell and monocytic cell lines (63 and 63HIV). HCQ suppressed HIV-1 replication in a dose-dependent manner in both recently and chronically infected T-cell and monocytic cell lines. In contrast, ZDV pretreatment had potent anti-HIV-1 activity in the newly infected T and monocytic cells but not in chronically infected cells. An additive effect of HCQ with ZDV was observed in the newly infected T and monocytic cells but not in the chronically infected cells. Although the anti-HIV-1 effect of HCQ was less than that of ZDV, HCQ may still be potentially useful either as an alternative HIV-1 treatment or in combination with other anti-HIV-1 agents, especially in patients who have rheumatic manifestations of HIV-1 infection.

Analytical and numerical techniques for the evaluation of free radical damage in cultured cells using scanning laser microscopy

Scanning laser microscopy (SLM) was used to develop an assay to visualize the generation of intracellular reactive oxygen species (ROS) and to evaluate the effect of the lipophilic antioxidant U-87,663 on ROS formation. Cultured N18 neuroglioma cells were challenged by extracellular addition of cumene hydroperoxide, and subsequent intracellular generation of ROS was characterized by measuring the fluorescence intensity of the ROS indicator 2',7'-dichlorofluorescein (DCF). The kinetics of the reaction between ROS and the indicator DCF, or the antioxidant U-87,663, can be most accurately assessed if results from individual cell clusters are analyzed independently. It is possible and necessary to account for the these experimental and analytical properties in order to characterize the properties of the antioxidant activity precisely. We determined that the temporal increase in DCF fluorescence was consistent with the reaction of DCF with free radicals generated from cumene hydroperoxide, as was the loss of fluorescence from U-87,663. The rate constants for the free radical reactions revealed that ROS reaction with DCF is 10 times faster than with U-87,663. These differences in reaction rates combined with differences in the cellular distribution of the ROS indicator DCF, the antioxidant U-87,663, and the bulk of the ROS prevented detection of any protection of U-87,663 may offer.

Loss of lysosomal integrity caused by the decrease of proton translocation in methylene blue-mediated photosensitization

Loss of lysosomal integrity is a critical event for killing tumor cells in the photodynamic therapy of cancers. To elucidate the mechanism of photodamage induced lysosomal disintegration, we investigated the role of losing lysosomal proton translocation in latency loss of photosensitized lysosomes. Isolated rat liver lysosomes were light exposed in the presence of Methylene blue. Through monitoring lysosomal delta pH with Acridine orange and measuring its membrane potential with 3,3'-dipropylthiadicarbocyanine iodide, loss of Mg-ATP dependent proton translocation and decrease in electrogenicity of the proton pump were observed after lysosomes were photosensitized. When normal lysosomes were incubated for 60 min in K+ contained medium, percentage free activity of lysosomal enzyme beta-galactosidase increased, i.e. lysosomal latency decreased. In the presence of Mg-ATP, the latency loss of incubated lysosomes reduced. Addition of n-ethylmaleimide, a potent inhibitor of lysosomal H(+)-ATPase, abolished the effect of Mg-ATP on lysosomal latency. It suggests a role of proton translocation in protecting lysosomal integrity. Under the same conditions, Methylene blue photosensitized lysosomes increasingly lost latency of beta-hexosaminidase and beta-galactosidase with light exposure, presumably due to the photodamage induced loss of proton pumping. In contrast, the photosensitization did not decrease lysosomal latency in the absence of Mg-ATP, implying that lysosomal integrity might not be impaired via other photodamage effects under the conditions of this study. These results indicate that lysosomal integrity can be photodestructed via the loss of proton translocation.

Renal oxidant injury and oxidant response induced by mercury

The role of oxidative stress in mercuric chloride (HgCl2)-induced nephrotoxicity is uncertain and controversial. We demonstrate that I.L.C-PK1 cells, exposed to HgCl2, generate massive amounts of hydrogen peroxide, the latter completely quenched by the hydrogen peroxide scavenger, pyruvate. HgCl2 exerts a dose-dependent cytotoxicity which is attenuated by pyruvate and catalase. Cellular generation of hydrogen peroxide arises, at least in part, from mitochondria since mitochondrial rates of generation of hydrogen peroxide increase in response to HgCl2; HgCl2 also provokes a shift in absorbance spectra in rhodamine 123 loaded-mitochondria and stimulates mitochondrial state 4 respiration. HgCl2, applied for one hour, impairs cellular vitality as demonstrated by the MTT assay, an assay dependent in part on mitochondrial function. HgCl2 impairs function in other organelles such as lysosomes that maintain a transmembrane proton gradient; these latter effects are partially attenuated by pyruvate. We complement these in vitro findings with in vivo evidence demonstrating that HgCl2 stimulates renal generation of hydrogen peroxide. The functional significance of such generation of hydrogen peroxide was evaluated in rats deficient in selenium and vitamin E, a nutrient deficiency that impairs the scavenging of hydrogen peroxide and promotes the toxicity of this oxidant. In these rats serum creatinine values were significantly higher on sequential days following the administration of HgCl2. To probe the renal response to oxidative stress induced by HgCl2, we examined hydrogen peroxide-scavenging enzymes and redox-sensitive genes. Catalase activity was unaltered whereas glutathione peroxidase activity was decreased, effects that may contribute to the net renal generation of hydrogen peroxide. The redox sensitive enzyme, heme oxygenase, was markedly up-regulated in the kidney in response to HgCl2. HgCl2 also induced members of the bcl family, bcl2 and bclx, genes that protect against apoptosis and oxidant injury. In another model of oxidant-induced renal injury, the glycerol model, bcl2 mRNA was not induced at 6 and 24 hours after the administration of glycerol. In summary, we demonstrate that HgCl2 potently stimulates renal generation of hydrogen peroxide in vitro and in vivo and such generation of peroxide contributes to renal dysfunction in vitro and in vivo. We also demonstrate that in response to HgCl2, redox sensitive genes are expressed including heme oxygenase and members of the bcl family.

Association of lowered plasma carotenoids with protection against cecal coccidiosis by diets high in n-3 fatty acids

A series of four experiments was run to assess the effectiveness of diets containing high amounts of n-3 fatty acids in reducing the pathological effects of cecal coccidiosis in chickens caused by Eimeria tenella. To determine whether the dietary effects were related to development of oxidative stress, plasma samples were analyzed for tocopherols and carotenoids. Plasma vitamin E (alpha-tocopherol) values were not consistent between experiments. Total plasma carotenoids, however, were significantly decreased by 2.5 to 20% diet supplementation with fish oil in several experiments. These decreases coincided with significant reductions in lesion scores. Under the experimental conditions, total plasma carotenoid concentrations may serve as a sensitive indicator for oxidative stress, which may be a factor in reducing cecal lesions in E. tenella infections.