A specific, sensitive, and rapid method for the determination of glutathione and its application in ocular tissues

Selenium Diminishes Docetaxel-Induced Cell Death, Oxidative Stress, and Inflammation in the Laryngotracheal Epithelium of the Mouse

Docetaxel (DOCX) kills tumor cells through the formation of microtubules, calcium ion influx, apoptosis, and inflammation. However, DOCX has adverse effect on normal tissues through the production of reactive oxygen species (ROS), despite the adverse effect was inhibited by antioxidants. We investigated the protective role of selenium against DOCX-induced apoptosis and mitochondrial oxidative injury in laryngotracheal epithelial (LARYN) cells of mice. Thirty-two mice were divided into four groups (n = 8). The first group was used as a control. The second and third groups were treated with sodium selenite (Na-Sel) and DOCX, respectively. The fourth group was the combined group of Na-Sel and DOCX. At the end of the experiment, LARYN mucosa and cells were obtained from the mice. In the LARYN cells, the cell viability level was low in DOCX group, although glutathione peroxidase activity and cell viability level were increased by the treatment of Na-Sel. Increased lipid peroxidation, intracellular ROS, mitochondrial membrane depolarization, cell death levels, TNF-α, IL-1β, IL-6, caspase -3, and -9 activities in the DOCX group of LARYN cells were diminished by the treatment of Na-Sel. In conclusion, DOCX increased mitochondrial ROS, cell death, and inflammation in the LARYN cells, although the increase was reduced in the cells by Na-Sel treatment. DOCX-induced adverse oxidant, inflammatory, and apoptotic effects in the tissue might be reduced by the Na-Sel treatment.

Protective effect of cabergoline on mitochondrial oxidative stress-induced apoptosis is mediated by modulations of TRPM2 in neutrophils of patients with endometriosis

Calcium ion (Ca²⁺) signaling in endometriosis (ENDO) is associated with increased neutrophil activation and oxidative stress. A Ca²⁺ signaling modulator and antioxidant actions of cabergoline (CBG) in some cells were recently reported. TRPM2 cation channel is activated by reactive oxygen species (ROS). Antioxidant action of CGB via inhibition of ROS may modulate the channel. We aimed to investigate the effect of CBG on TRPM2 inhibition in serum and neutrophils of patients with ENDO. The serum and neutrophil samples were grouped into healthy samples (no treatment), ENDO and ENDO + CBG treated groups (n = 10 in each). In some experiments, the neutrophils were also incubated with TRPM2 (ACA) and PARP-1 (PJ34) blockers. The values of intracellular ROS, Ca²⁺ concentration, mitochondrial membrane depolarization, lipid peroxidation, apoptosis, and caspase - 3, caspase - 9, PARP-1 and TRPM2 expressions were high in the neutrophils of patients with ENDO, although antioxidant levels (reduced glutathione, glutathione peroxidase, vitamin A, and vitamin E) were low in the neutrophils and serum from these patients. However, markers for apoptosis, oxidative stress, and mitochondrial dysfunction were reduced with CBG, ACA and PJ34 treatments, although the antioxidant levels were increased in the serum and neutrophils following treatment with CBG. Taken together, our current results suggest that CBG are useful antagonists against apoptosis and mitochondrial oxidative stress via inhibition of TRPM2 in neutrophils of patients with ENDO.

Mitochondrial oxidative stress-induced brain and hippocampus apoptosis decrease through modulation of caspase activity, Ca2+ influx and inflammatory cytokine molecular pathways in the docetaxel-treated mice by melatonin and selenium treatments

Docetaxel (DOCE) is widely used to treat several types of glioblastoma. Adverse effects DOCE seriously limit its clinical use in several tissues. Its side effects on brain cortex and hippocampus have not been clarified yet. Limited data indicated a protective effect of melatonin (MLT) and selenium (SELEN) on DOCE-induced apoptosis, Ca²⁺ influx and mitochondrial reactive oxygen species (ROS) in several tissues except brain and hippocampus. The purpose of this study is to discover the protective effect of MLT and SELEN on DOCE-induced brain and hippocampus oxidative toxicity in mice. MLT and SELEN pretreatments significantly ameliorated acute DOCE-induced mitochondrial ROS production in the hippocampus and brain tissues by reducing levels of lipid peroxidation, intracellular ROS production and mitochondrial membrane depolarization, while increasing levels of total antioxidant status, glutathione, glutathione peroxidase, MLT, α-tocopherol, γ-tocopherol, vitamin A, vitamin C and β-carotene in the tissues. Furthermore, MLT and SELEN pretreatments increased cell viability and TRPM2 channel activation in the hippocampus and brain followed by decreased activations of TNF-α, IL-1β, IL-6, and caspase -3 and - 9, suggesting a suppression of calcium ion influx, apoptosis and inflammation responses. However, modulator role of SELEN on the values in the tissues is more significant than in the MLT treatment. MLT and SELEN prevent DOCE-induced hippocampus and brain injury by inhibiting mitochondrial ROS and cellular apoptosis through regulating caspase -3 and - 9 activation signaling pathways. MLT and SELEN may serve as potential therapeutic targets against DOCE-induced toxicity in the hippocampus and brain.

Glutathione depletion induces ferroptosis, autophagy, and premature cell senescence in retinal pigment epithelial cells

Glutathione (GSH) protects against oxidative damage in many tissues, including retinal pigment epithelium (RPE). Oxidative stress-mediated senescence and death of RPE and subsequent death of photoreceptors have been observed in age-related macular degeneration (AMD). Although the consequences of GSH depletion have been described previously, questions remain regarding the molecular mechanisms. We herein examined the downstream effects of GSH depletion on stress-induced premature senescence (SIPS) and cell death in human RPE cells. Briefly, cultured ARPE-19 cells were depleted of GSH using: (1) incubation in cystine (Cys₂)-free culture medium; (2) treatment with buthionine sulphoximine (BSO, 1000 µM) to block de novo GSH synthesis for 24-48 h; or (3) treatment with erastin (10 µM for 12-24 h) to inhibit Cys₂/glutamate antiporter (system x_c^-). These treatments decreased cell viability and increased both soluble and lipid reactive oxygen species (ROS) generation but did not affect mitochondrial ROS or mitochondrial mass. Western blot analysis revealed decreased expression of ferroptotic modulator glutathione peroxidase 4 (GPX4). Increased autophagy was apparent, as reflected by increased LC3 expression, autophagic vacuoles, and autophagic flux. In addition, GSH depletion induced SIPS, as evidenced by increased percentage of the senescence-associated β-galactosidase-positive cells, increased senescence-associated heterochromatin foci (SAHF), as well as cell cycle arrest at the G1 phase. GSH depletion-dependent cell death was prevented by selective ferroptosis inhibitors (8 μM Fer-1 and 600 nM Lip-1), iron chelator DFO (80 μM), as well as autophagic inhibitors Baf-A1 (75 nM) and 3-MA (10 mM). Inhibiting autophagy with Baf-A1 (75 nM) or 3-MA (10 mM) promoted SIPS. In contrast, inducing autophagy with rapamycin (100 nM) attenuated SIPS. Our findings suggest that GSH depletion induces ferroptosis, autophagy, and SIPS. In addition, we found that autophagy is activated in the process of ferroptosis and reduces SIPS, suggesting an essential role of autophagy in ferroptosis and SIPS.

Drug transport in corneal epithelium and blood-retina barrier: emerging role of transporters in ocular pharmacokinetics

Corneal epithelium and blood-retina barrier (i.e. retinal capillaries and retinal pigment epithelium (RPE)) are the key membranes that regulate the access of xenobiotics into the ocular tissues. Corneal epithelium limits drug absorption from the lacrimal fluid into the anterior chamber after eyedrop administration, whereas blood-retina barrier restricts the entry of drugs from systemic circulation to the posterior eye segment. Like in general pharmacokinetics, the role of transporters has been considered to be quite limited as compared to the passive diffusion of drugs across the membranes. As the functional role of transporters is being revealed it has become evident that the transporters are widely important in pharmacokinetics. This review updates the current knowledge about the transporters in the corneal epithelium and blood-retina barrier and demonstrates that the information is far from complete. We also show that quite many ocular drugs are known to interact with transporters, but the studies about the expression and function of those transporters in the eye are still sparse. Therefore, the transporters probably have greater role in ocular pharmacokinetics than we currently realise.

Short-term ascorbic acid deficiency induced oxidative stress in the retinas of young Guinea pigs

We examined whether short-term ascorbic acid deficiency induces oxidative stress in the retinas of young guinea pigs. Four-week-old guinea pigs were given a scorbutic diet (20 g/animal/day) with and without adequate ascorbic acid (400 mg/animal/day) in drinking water for 3 weeks. The serum concentrations of the reduced form of ascorbic acid and the oxidized form of ascorbic acid in the deficient group were 14.1 and 4.1%, respectively, of those in the adequate group. The retinal contents of the reduced form of ascorbic acid and the oxidized form of ascorbic acid in the deficient group were 6.4 and 27.3%, respectively, of those in the adequate group. The retinal content of thiobarbituric acid-reactive substances, an index of lipid peroxidation, was 1.9-fold higher in the deficient group than in the adequate group. Retinal reduced glutathione and vitamin E contents in the deficient group were 70.1 and 69.4%, respectively, of those in the adequate group. This ascorbic acid deficiency did not affect serum thiobarbituric acid-reactive substances and reduced glutathione concentrations but increased serum vitamin E concentration. These results indicate that short-term ascorbic acid deficiency induces oxidative stress in the retinas of young guinea pigs without disrupting systemic antioxidant status.

Cu/Zn superoxide dismutase plays a role in angiogenesis

Endothelial cells produce oxygen radicals spontaneously and this process is augmented by hypoxia/reoxygenation. Cu/Zn superoxide dismutase (SOD-1) is an important enzyme in cellular oxygen metabolism. To determine whether alterations in SOD-1 activity affect angiogenesis we used transgenic SOD-1 (Tg-SOD) mice with elevated level of SOD-1. Angiogenesis induced subcutaneously by bFGF in Tg-SOD mice was 3-fold higher than in control non-transgenic (ntg) mice. Oral administration of disulfiram (DSF), an inhibitor of SOD-1, inhibited angiogenesis in Tg-SOD mice as well as in CD1 nude mice. Effects of DSF on cultured cells were also tested. Application of DSF to cultured bovine capillary endothelial (BCE) cells caused inhibition of DNA synthesis and induction of apoptosis. These effects were prevented by addition of antioxidants, further indicating involvement of reactive oxygen species. DSF also reduced the level of glutathione and the production of H(2)O(2) in BCE cells. Moreover, PC12-SOD cells with elevated SOD-1 were less sensitive to DSF treatment then control cells. These data indicate that the effects of DSF are mediated by inhibition of SOD-1 activity. Tumor development is known to largely depend on angiogenesis. We found that oral administration of DSF to mice caused significant inhibition of C6 glioma tumor development and marked reduction (by 10-19-fold) in metastatic growth of Lewis lung carcinoma. The data suggest a role for SOD-1 in angiogenesis, establish DSF as a potential inhibitor of angiogenesis and raise the possibility that attenuating SOD-1 activity may be important in treatment of angiogenesis-dependent pathologies.

Cataract development in diabetic sand rats treated with alpha-lipoic acid and its gamma-linolenic acid conjugate

BACKGROUND

Diabetes commonly leads to long-term complications such as cataract. This study investigated the effects of alpha-lipoic acid (LPA) and its gamma-linolenic acid (GLA) conjugate on cataract development in diabetic sand rats.

METHODS

Two separate experiments were conducted. In Experiment 1, sand rats were fed a "high-energy" diet (70% starch), an acute model of Type 2 diabetes, and injected with LPA. In Experiment 2, the animals received a "medium-energy" diet (59% starch), a chronic diabetic model, and were intubated with LPA or its GLA conjugate. Throughout the experiments, blood glucose levels and cataract development were measured. At the termination of the experiments, lens aldose reductase (AR) activity and lenticular reduced glutathione (GSH) levels were analyzed.

RESULTS

LPA injection significantly inhibited cataract development and reduced blood glucose levels in rats fed the "high-energy" diet. Lens AR activity tended to be lower, while lenticular GSH levels increased. In sand rats fed a "medium-energy" diet (59% starch), LPA intubation had no effect on blood glucose levels and cataract development but GSH levels were increased. In contrast, sand rats intubated with GLA conjugate showed the highest blood glucose levels and accelerated cataract development. The conjugate treatment also decreased lenticular GSH content.

CONCLUSIONS

The hypoglycemic effects of LPA are beneficial in the prevention of acute symptoms of Type 2 diabetes. It remains to be shown that the antioxidant activity of LPA is responsible for prevention or inhibition of cataract progression in sand rats.

5-(Pentafluorobenzoylamino)fluorescein: A selective substrate for the determination of glutathione concentration and glutathione S-transferase activity

5-(Pentafluorobenzoylamino)fluorescein (PFB-F), a new thiol-reactive molecule was synthesized to improve the detection limits and specificity of the assays for glutathione S-transferase (GST) activity and glutathione (GSH). A rapid assay method to measure GSH concentration or GST activity and the simultaneous analysis of multiple samples is possible because the glutathione adduct, GS-TFB-F, is separated from PFB-F by thin-layer chromatography (TLC) and can be quantitated by a fluorescence scanner. The detection limits for GSH and for GST activity using TLC were found to be as low as 10 pmol/microl and 1 ng/microl using equine liver GST, respectively. Determination of GSH concentration or GST activity in bovine pulmonary artery endothelial (BPAE) cell lysates gave a linear response for samples corresponding to 500-2500 cells. PFB-F could also measure GST activities of GST fusion proteins and prove to be a suitable substrate for determining the activities of human GST isozymes and other sources of mammalian GST. The selectivity of PFB-F with GSH was proven by comparing trace amount of the adducts that formed with cysteine and beta-galactosidase to that formed with GSH. The HPLC profile of a reaction mixture where cell lysate was used in place of purified GST, also shows only two main peaks, corresponding to GS-TFB-F and unreacted PFB-F. The selectivity of PFB-F for GSH was further confirmed by exposing BPAE cells to dl-buthionine-[S,R]-sulfoximine (BSO). Our results of GS-TFB-F determination indicate that 12-, 24-, or 36-h incubations with BSO caused 2-, 6-, or 7.6-fold reductions in GSH levels, respectively.

Cooperation between glutathione depletion and protein synthesis inhibition against naturally occurring neuronal death

It is generally agreed that naturally-occurring neuronal death in developing animals is dependent on the synthesis of proteins. Oxidative stress, as when intracellular concentrations of free radicals are raised or when cell constituents such as membrane lipids or protein thiols are oxidized, is also involved in various types of neuronal death. In the present report, we show that the number of naturally dying retinal cells in the chick embryo can be reduced by intraocular injections of cycloheximide, an inhibitor of protein synthesis. L-buthionine-[S,R]-sulfoximine, an inhibitor of glutathione synthesis, can either enhance or diminish the cell death, depending on the conditions of treatment. Moreover, when the two inhibitors are combined, L-buthionine-[S,R]-sulfoximine potentiates the neuroprotective effects of cycloheximide. Measurements of retinal glutathione concentration and protein synthesis show the specificity of the treatments: buthionine-sulfoximine diminishes glutathione concentrations but not protein synthesis whereas cycloheximide inhibits protein synthesis without decreasing glutathione concentrations. Naturally-occurring neuronal death thus seems to involve the synthesis of proteins, and is also influenced by oxidative phenomena. Our results extend previous data in tectal-lesioned embryos, and suggest that a moderate, non-lethal oxidative stress can enhance the resistance of ganglion cells that might otherwise have died (spontaneously or following axotomy) owing to insufficient retrograde trophic support.

Improved myeloperoxidase assay for quantitation of neutrophil influx in a rat model of endotoxin-induced uveitis

Previously described models of endotoxin-induced uveitis quantify neutrophil influx into the eye using biochemical or direct cell count methods that result in an underestimation of ocular leukocyte accumulation following the inflammatory stimulus. We have optimized the rat model of endotoxin-induced uveitis by first overcoming interference in the biochemical assay of myeloperoxidase due to endogenous ocular reductants and cellular constituents containing free thiol functional groups. This was accomplished by simultaneously 1) extensively diluting soluble, interfering substances and 2) blocking tissue sulfhydril functional groups during tissue homogenization. Uveitis was induced in rats by subplantar injection of endotoxin. Twenty-four hours later, eyes were enucleated, homogenized, fractionated, and myeloperoxidase activity of neutrophils sedimenting with the membranous pellet was extracted. Previously published extraction procedures yielded only 40% of total assayable myeloperoxidase activity. Optimal recovery of myeloperoxidase activity (>twofold increase) was achieved only with two sequential extractions using 50 mM phosphate buffer (pH 7.4) containing 10 mM N-ethylmaleimide, and subsequent solubilization of myeloperoxidase activity by extraction with 0.5% hexadecyltrimethylammonium bromide in 50 mM phosphate buffer (pH 6.0). This modified extraction procedure and optimized myeloperoxidase assay conditions (300 microM hydrogen peroxide and 1.5 mM o-dianisidine) were then used to enhance the uveitis model. Maximum ocular neutrophil accumulation was observed at endotoxin doses of 100-200 microg. Total ocular neutrophil infiltrations ranged from 250,000 to 800,000 cells/globe. This leukocyte influx was inhibited dose-dependently by topical ocular administration of dexamethasone, with half-maximal inhibition observed at a concentration of 0.01%, w/v. Further validated by the correlation of biochemical results with histological evaluation, the refined methodology described in this report has application in assessing the ophthalmic therapeutic potential of antiinflammatory agents.

Inhibition of glutathione synthesis can enhance cycloheximide-induced protection of developing neurons against axotomy

Developing neurons depend for survival on target-derived trophic substances. These are thought to block the expression of a genetic program of cell death. Nevertheless, it is known that less orderly events such as oxidative stress are involved in neuron death. In vivo, retinal ganglion cell death induced by axotomy can be reduced by antioxidants. In this study, we investigated the effects of inhibiting glutathione synthesis by means of buthionine sulfoximine to characterize the influence of endogenous glutathione-dependent antioxidant systems on ganglion cell death. Moreover, since protein synthesis inhibition by cycloheximide has been shown to enhance glutathione synthesis in vitro, we studied the effects on cell death of intraocular injections of buthionine sulfoximine, cycloheximide and combinations of the two inhibitors. Cycloheximide's protective action did not seem to involve an increase in glutathione synthesis. Surprisingly, buthionine sulfoximine injected before cycloheximide enhanced its protective effects, whereas it inhibited them when injected later. We interpret our results as an interaction between death-promoting effects of glutathione depletion through an elevation of free radical concentrations and cycloheximide-sensitive effects of oxidative stress through the synthesis of both death-inhibiting and death-promoting proteins.

Determination of glutathione, cysteine and N-acetylcysteine in rabbit eye tissues using high-performance liquid chromatography and post-column derivatization with 5,5'-dithiobis(2-nitrobenzoic acid)

A high-performance liquid chromatographic method to determine glutathione, cysteine and N-acetylcysteine in rabbit retina, vitreous and lens has been developed. The thiols are separated using a 25 x 0.46-cm octadecylsilane column with 0.5 M phosphate buffer, pH 3, as mobile phase. The detection, at 412 nm, involves a post-column derivatization with 5,5-dithiobis(2-nitrobenzoic acid) in presence of cationic micelles of hexadecyltrimethylammonium bromide that enhances the sensitivity. The detection limits are 0.21, 0.92 and 0.61 mumol/g wet sample for glutathione, cysteine and N-acetylcysteine, respectively.

A rapid HPLC method for the quantification of GSH and GSSG in ocular lens

Purpose. To develop a rapid and accurate method for the quantification of reduced glutathione (GSH) and oxidized glutathione (GSSG) using micro-quantities of ocular lens. Methods. The epithelium, cortex and nucleus of the lens were separated and also the whole lens was homogenized in 3% metaphosphoric acid. The homogenate was ultrafiltered by centrifugation at 10,000 g in an Amicon microconcentrator, molecular weight cut off 3,000 g. The method does not require prior derivatization of the glutathiones. The filtrate was analyzed on a Microsorb-MV by a high performance liquid chromatography (HPLC) column using an isocratic solvent system (3% methanol and 10 mM potassium phosphate, pH 3.0) and detection at 200 nm.

RESULTS

The GSH and GSSG were eluted from the HPLC column at retention times 5 and 10 min, respectively. The detection limit was 100 pmoles applied to the column. The recovery of GSH and GSSG added to the tissue samples was 97-100%.

CONCLUSIONS

A fast and sensitive HPLC-method for the quantification of picomole quantities of GSH and GSSG in ocular lens, which does not require prior derivatization, has been developed.