Paraoxonase enzyme protects retinal pigment epithelium from chlorpyrifos insult

Paraoxonase 2 Deficiency Causes Mitochondrial Dysfunction in Retinal Pigment Epithelial Cells and Retinal Degeneration in Mice

Although AMD is a complex disease, oxidative stress is a crucial contributor to its development, especially in view of the higher oxygen demand of the retina. Paraoxonase 2 (PON2) is a ubiquitously and constitutively expressed antioxidant protein that is found intracellularly associated with mitochondrial membranes and modulates mitochondrial ROS production and function. The contribution of PON2 to AMD has not been studied to date. In this study, we examined the role of PON2 in AMD utilizing both in vitro and in vivo models of AMD with emphasis on mitochondrial function. Mitochondrial localization and regulation of PON2 following oxidative stress were determined in human primary cultured retinal pigment epithelium (hRPE) cells. PON2 was knocked down in RPE cells using siRNA and mitochondrial bioenergetics were measured. To investigate the function of PON2 in the retina, WT and PON2-deficient mice were administered NaIO3 (20 mg/kg) intravenously; fundus imaging, optical coherence tomography (OCT), electroretinography (ERG) were conducted; and retinal thickness and cell death were measured and quantified. In hRPE, mitochondrial localization of PON2 increased markedly with stress. Moreover, a time-dependent regulation of PON2 was observed following oxidative stress, with an initial significant increase in expression followed by a significant decrease. Mitochondrial bioenergetic parameters (basal respiration, ATP production, spare respiratory capacity, and maximal respiration) showed a significant decrease with oxidative stress, which was further exacerbated in the absence of PON2. NaIO3 treatment caused significant retinal degeneration, retinal thinning, and reduced rod and cone function in PON2-deficient mice when compared to WT mice. The apoptotic cells and active caspase 3 significantly increased in PON2-deficient mice treated with NaIO3, when compared to WT mice. Our investigation demonstrates that deficiency of PON2 results in RPE mitochondrial dysfunction and a decline in retinal function. These findings imply that PON2 may have a beneficial role in retinal pathophysiology and is worthy of further investigation.

Retinal Toxicity Induced by Chemical Agents

Vision is an important sense for humans, and visual impairment/blindness has a huge impact in daily life. The retina is a nervous tissue that is essential for visual processing since it possesses light sensors (photoreceptors) and performs a pre-processing of visual information. Thus, retinal cell dysfunction or degeneration affects visual ability and several general aspects of the day-to-day of a person's lives. The retina has a blood-retinal barrier, which protects the tissue from a wide range of molecules or microorganisms. However, several agents, coming from systemic pathways, reach the retina and influence its function and survival. Pesticides are still used worldwide for agriculture, contaminating food with substances that could reach the retina. Natural products have also been used for therapeutic purposes and are another group of substances that can get to the retina. Finally, a wide number of medicines administered for different diseases can also affect the retina. The present review aimed to gather recent information about the hazard of these products to the retina, which could be used to encourage the search for more healthy, suitable, or less risky agents.

Aryl Hydrocarbon Receptor Activation Produces Heat Shock Protein 90 and 70 Overexpression, Prostaglandin E2/Wnt/β-Catenin Signaling Disruption, and Cell Proliferation in MCF-7 and MDA-MB-231 Cells after 24 h and 14 Days of Chlorpyrifos Treatment

The biocide chlorpyrifos (CPF) was described to increase breast cancer risk in humans, to produce breast cancer in animals, and to induce cell proliferation in MCF-7 and MDA-MB-231 cells after 1 and 14 days of treatment. The entire mechanisms related to these CPF actions remain unknown. CPF induced cell proliferation in MCF-7 and MDA-MB-231 cells after 1 and 14 days of treatment by AhR activation through the PGE2/Wnt/β-catenin pathway and HSP90 and HSP70 overexpression. Our results reveal new information on CPF toxic mechanisms induced in human breast cancer cell lines, which could assist in elucidating its involvement in breast cancer.

Antioxidant Potential of Ulexite in Zebrafish Brain: Assessment of Oxidative DNA Damage, Apoptosis, and Response of Antioxidant Defense System

In recent years, because of its significant biological roles, the usage of boron has been started in animal feeding. In this research, it was aimed to investigate the ulexite's action mechanism on the zebrafish brain with an evaluation of the oxidative parameters. The adult zebrafish were exposed to four ulexite doses (5, 10, 20, and 40 mg/l) in a static test apparatus for 96 h. For assessing the oxidative responses, multiple biochemical analyses were performed in brain tissues. The results indicated the supporting potential of low ulexite doses on the antioxidant system (< 40 mg/l) and that low-dose ulexite does not lead to oxidative stress in the zebrafish brain. Again, our results showed that low ulexite concentrations did not cause DNA damage or apoptosis. As a final result, in aquatic environments, ulexite (a boron compound) can be used in a safe manner, but it would be useful at higher concentrations to consider the damages of the cells that are probable to develop because of the oxidative stress.

Treatment of oxidative stress, apoptosis, and DNA injury with N-acetylcysteine at simulative pesticide toxicity in fish

Pesticide toxicities are common in aquatic ecosystems and affects aquatic livings negative. Therefore, it is important to strengthen the antioxidant system in aquatic organisms and to protect the organisms against these toxic chemicals. In this study, the simulative toxicity was established to the fish then the healing process was followed. For this purpose, rainbow trout Oncorhynchus mykiss exposed to cypermethrin and left to the recovery process with either N-acetyl cysteine (an antioxidant, 0.5 mM-1.0 mM concentrations) or no intervention (self-healing) for 96 h. In this context, paraoxonase (PON), arylesterase (AR), myeloperoxidase (MPO), antioxidant enzymes (SOD, CAT, GPx), acetylcholinesterase (AChE) activities as well as MDA, caspase-3 and 8-OHdG levels were measured in fish gills, liver and kidney tissues. In addition, trace element tests were performed in the tissues sampled for each group. At the result of pesticide exposure, SOD, CAT, GPx, PON, AR and AChE activities were increased but MDA, MPO, caspase-3 and 8-OHdG levels were decreased in N-acetyl cysteine (NAC) treated groups in all tissues compared to self-healing group (p < 0.05). When the element analysis of the samples was examined, tissue-based differences were observed significantly in all application groups (p < 0.05). Considering the results of the study, it was found that NAC administration at high concentration (1.0 Mm NAC) was more effective on pesticide toxicity. It was concluded that the most sensitive tissue was the kidney.

An updated review of protective effects of rosemary and its active constituents against natural and chemical toxicities

Natural and chemical toxic agents cause severe adverse effects on people's health in a variety of exposing ways. Herbal medications have taken into consideration as alternative safe treatments for toxicities. Rosmarinus officinalis also known as rosemary belongs to the Lamiaceae family. Rosemary and its constituents including carnosic acid, rosmarinic acid, and carnosol have a lot of benefits such as anti-inflammatory, antioxidant, anti-mutagenic, anti-bacterial, antiviral, antinociceptive, and neuroprotective activities. In this literate review, we focused on the protective effects of rosemary and its main compounds against natural and chemical toxicities in both in vitro and in vivo studies. The protective effects of rosemary and its components are mostly mediated through different mechanisms such as the inhibition of oxidative stress, reduction of inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-17 (IL-17), cyclooxygenase-2 (COX-2) and nuclear factor ĸB (NF-ĸB) as well as the modulation of apoptosis and mitogen-activated protein kinase (MAPK) signaling pathways.

Dysfunction in macula, retinal pigment epithelium and post retinal pathway in acute organophosphorus poisoning

CONTEXT

Organophosphorus (OP) insecticide poisoning is a significant health problem in South Asian countries. Although cholinergic receptors are present at the junction between photoreceptors and the retinal pigment epithelium (RPE), human studies of the effects of OP poisoning on the visual pathways are very few. This study aims to demonstrate the pattern of changes in retina and post retinal pathways in patients with acute OP poisoning using visual electrophysiological tests.

METHODS

This is an observational, cross-sectional study conducted at the Neurophysiology Unit, Teaching Hospital, Peradeniya, Sri Lanka. We tested 16 patients recovered from cholinergic phase, at least 24 h after deatropinization and within 8 weeks of OP ingestion. We assessed the functional integrity of the photoreceptors and ganglion cells of the macula by pattern electroretinography (PERG); RPE by electro-oculography (EOG); and post retinal pathways by pattern reversal visual evoked potentials (PR-VEP). Latencies and amplitudes of PR-VEP and PERG, light peak (LP), dark trough (DT) and Arden ratio of EOG were determined in patients and compared with 16 controls using the Mann-Whitney U test.

RESULTS

Of the 16 OP-poisoned patients (median age of 37 ± IQR 20 years), six (37.5%) had reduced Arden ratio with reference to the International Society of Clinical Electrophysiology of Vision cut-off value of 1.7. The median Arden ratio in patients (1.69 ± IQR 0.36) was significantly lower compared to controls (1.90 ± IQR 0.4). The median latencies and amplitudes of PR-VEP or PERG were not significantly different between patients and controls. However, three patients had prolonged P100 latencies in PR-VEP and one had prolonged P50 latency in PERG.

CONCLUSIONS

Acute OP poisoning seems to affect the functions of the RPE and the visual electrophysiological changes outlast the cholinergic phase. Limited evidence suggests that photoreceptors of the macula region and post retinal pathway might be affected in some patients.

WTAP and BIRC3 are involved in the posttranscriptional mechanisms that impact on the expression and activity of the human lactonase PON2

The activity of human paraoxonase 2 (PON2) is rapidly reduced in cells incubated with the bacterial quorormone 3-Oxo-dodecanoyl Homoserine Lactone (3OC12HSL), an observation that led to hypothesize a fast PON2 post-translational modification (PTM). Recently, we detected a 3OC12HSL-induced PTM in a cell-free system in which a crude extract from 3OC12HSL-treated HeLa cells was able to inactivate and ubiquitinate at position 144 a recombinant PON2. Here we show the occurrence of this and new PTMs on PON2 in HeLa cells. PTMs were found to gather nearby the two SNPs, A148G, and S311C, that are related to type-2 diabetes and its complications. Furthermore, we detected a PTM nearby a 12 amino acids region that is deleted in PON2 Isoform 2. An in vitro mutation analysis showed that the SNPs and the deletion are involved in PON2 activity and suggested a role of PTMs on its modulation, while a SAXS analysis pointed to Isoform 2 as being largely unstructured, compared to the wild type. Besides, we discovered a control of PON2 expression via a putative mRNA operon involving the Wilms tumor 1 associated protein (WTAP) and the E3 ubiquitin ligase (E3UbL) baculoviral IAP repeat-containing 3 (BIRC3).

Oxidized LDL, homocysteine, homocysteine thiolactone and advanced glycation end products act as pro-oxidant metabolites inducing cytokine release, macrophage infiltration and pro-angiogenic effect in ARPE-19 cells

Age-related Macular Degeneration (AMD) is one of the major vision-threatening diseases of the eye. Oxidative stress is one of the key factors in the onset and progression of AMD. In this study, metabolites associated with AMD pathology more so at the systemic level namely, oxidized LDL (oxLDL), homocysteine (Hcy), homocysteine thiolactone (HCTL), advanced glycation end product (AGE) were evaluated for their pro-oxidant nature in a localized ocular environment based on in vitro studies in human retinal pigment epithelial cells (ARPE-19 cells). Human ARPE-19 cells were treated with pro-oxidants 50 μg/mL oxLDL, 500 μM Hcy, 500 nM HCTL, 100 μg/mL AGE, 200 μM H₂O₂ and 200 μM H₂O₂ with and without pre-treatment of 5 mM N-acetyl cysteine (NAC). The cytokines IL-6, IL-8 and vascular endothelial growth factor (VEGF) secreted from ARPE-19 cells exposed to pro-oxidants were estimated by ELISA. In vitro angiogenesis assay was performed with conditioned media of the pro-oxidant treated ARPE-19 cells in Geltrex-Matrigel coated 96-well plate. The human acute monocytic leukemia cell line (THP-1) was differentiated into macrophages and its migration in response to conditioned media of ARPE-19 cells insulted with the pro-oxidants was studied by transwell migration assay. Western blot was performed to detect the protein expression of Bax, Bcl-2 and NF-κB to assess apoptotic changes. The compounds involved in the study showed a significant increase in reactive oxygen species (ROS) generation in ARPE-19 cells (oxLDL; Hcy; AGE: p < 0.001 and HCTL: p < 0.05). NAC pre-treatment significantly lowered the oxidative stress brought about by pro-oxidants as seen by lowered ROS and MDA levels in the cells. Treatment with pro-oxidants significantly increased the secretion of IL-6 (oxLDL: p < 0.05; Hcy, HCTL and AGE: p < 0.01) and IL-8 cytokines (oxLDL: p < 0.05; HCTL: p <. 001 and AGE: p < 0.01) in ARPE-19 cells. Serum samples of AMD patients (n = 23) revealed significantly higher IL-6 and IL-8 levels compared to control subjects (n = 23) (IL6: p < 0.01 and IL8: p < 0.05). The pro-oxidants also promoted VEGF secretion by ARPE-19 cells compared to untreated control (oxLDL: p < 0.001; Hcy: p < 0.01; HCTL and AGE: p < 0.05). In vitro angiogenesis assay showed that the conditioned media significantly increased the tube formation in RF/6A endothelial cells. Transwell migration assay revealed significant infiltration of macrophages in response to pro-oxidants. We further demonstrated that the pro-oxidants increased the Bax/Bcl-2 ratio and increased the NF-κB activation resulting in pro-apoptotic changes in ARPE-19 cells. Thus, oxLDL, Hcy, HCTL and AGE act as pro-oxidant metabolites in RPE that promote AMD through oxidative stress, inflammation, chemotaxis and neovascularization.

Therapeutic effect of N- acetyl cysteine as an antioxidant on rainbow trout's brain in cypermethrin toxicity

The aim of this study was to investigate the therapeutic effect of N-acetylcystein (NAC) against oxidative stress induced by Cypermethrin pesticide in rainbow trout (Oncorhynchus mykiss). The experiment was designed as 5 groups (A, B, C, D, and E). Group A was organized as control group and had no treatment. The other groups were treated with Cypermethrin for 14 days. At the end of this period, Groups B (1.0 mM NAC) and D (0.5 mM NAC) was performed with NAC for 96 h. Group C was not administered NAC, the recovery process was evaluated with this group. Group E was exposed to cypermethrin during 14 days and sampled. Acetylcholinesterase (AChE), malondialdehyde (MDA), glutathione peroxidase (GPx), superoxide dismutase (SOD), catalase (CAT), paraoxonase (PON), arylesterase (AR), myeloperoxidase (MPO) activities, oxidative DNA damage (8-hydroxy-2'-deoxyguanosine (8-OHdG)), caspase-3 levels, and trace elements contents analyses were performed in all fish brains. According to the results, MDA, MPO, 8-OHdG and caspase-3 levels were significantly decreased compared to the other groups (pesticide and recovery) (p < 0.05), AChE, SOD, CAT, GPx, PON, and AR activities increased (p < 0.05). In brain tissue, no statistically significant difference was observed in trace element analysis of all application groups. According to the obtained data, the positive effect of N-acetylcysteine on protein synthesis, detoxification, and diverse metabolic functions against cypermethrin toxicity has been more effective in 1.0 mM NAC. NAC has important therapeutic effect on pesticide-induced neurotoxicity for fish in terms of all data. It was concluded that NAC has an antioxidant effect against pesticide-induced oxidative stress and the selected biochemical markers are useful for such studies.

Ocular distribution of antioxidant enzyme paraoxonase & its alteration in cataractous lens & diabetic retina

Background & objectives:

The enzyme paraoxonase (PON), an antioxidant enzyme that has both arylesterase and thiolactonase activity, is well studied in cardiovascular diseases. Although a few studies have shown altered PON activity in ocular diseases such as age-related macular degeneration and diabetic retinopathy, but the tissue-wise expression of PON in its three gene forms has not been studied. This study was conducted to see the ocular distribution of PON for any altered expression in ocular pathologies such as in cataract and diabetes mellitus.

Methods:

Immunohistochemistry (IHC) of the ocular tissues was done for localizing all three forms of the PON in the human donor eyeballs. The PON arylesterase (PON-AREase) and thiolactonase (PON-HCTLase) activities were determined by spectrophotometry in kinetic mode, and the mRNA expression of the PON genes (PON1-3) was determined by reverse transcription-polymerase chain reaction.

Results:

IHC showed the presence of both PON1 and 2 in all the ocular tissues and PON3 was seen only in retina. The mRNA expression analysis showed that PON2 and PON3 were present in all the tissues, whereas PON1 was seen only in ciliary and retina. Both the PON-AREase and PON-HCTLase activities were detected in all ocular tissues and was in the order of lens>retina>choroid>ciliary body>iris. The expression and activity were studied in cataractous lens and in diabetic retina of the donor eyes. A significant decrease in PON-AREase activity was seen in cataractous lens (P<0.05) but not in diabetic retina, and there was an increase in PON- HCTLase activity (P<0.05) only in diabetic retina. Bioinformatic studies and in vitro experiments indicated that advanced glycation end products (AGE) such as carboxymethyl -lysine might decrease the PON- AREase activity of the PON.

Interpretation & conclusions:

Distribution of PON enzyme and its activity in ocular tissues is reported here. The study revealed maximal PON activity in lens and retina, which are prone to higher oxidative stress. Differential activities of PON were observed in the lens and retinal tissues from cataractous and diabetic patients, respectively.

Serum Paraoxonase activity in relation to lipid profile in Age-related Macular Degeneration patients

Age-related Macular Degeneration (AMD) is a multifactorial disease causing visual impairment in old age. Oxidative stress is one of the main contributors for the disease progression. Paraoxonase (PON), a HDL-resident antioxidant enzyme which removes oxidized low density lipoprotein (oxLDL), which is not studied much in AMD. This study assesses the PON activities in relation to the lipid status and genetic variants in AMD patients. In this prospective case-control study, a total of 48 AMD patients and 30 unrelated healthy controls were recruited. The serum oxLDL and Plasma Homocysteine (Hcy) levels were estimated by ELISA. Plasma Homocysteine thiolactone (HCTL) was estimated by HPLC. Serum PON activities were estimated by spectrophotometry. PON gene expression was assessed by qPCR and protein expression by western blot, immunofluorescence and FACS analysis. Two known single nucleotide polymorphisms (SNPs) in the coding region of PON1, Q192R and L55M variants were checked in the AMD patients and controls and their association with PON activity and lipid levels were determined. Serum paraoxonase (PONase) and thiolactonase (PON-HCTLase) activities were significantly elevated in AMD patients than in controls apart from elevated serum levels of total cholesterol (TC), triglycerides (TG), oxLDL. While serum LDL levels in AMD patients correlate positively with PON HCTLase activity, the serum high density lipoprotein (HDL) correlates with both PONase and PON-HCTLase activities. However, multiple regression analysis showed that, amongst the parameters, only serum TG was a significant risk factor for AMD, after adjusting for demographic parameters as well as cataract. PON2 was significantly increased at the level of gene expression (p = 0.03) as seen in circulating peripheral blood mononuclear cells (PBMC) of AMD patients possibly mediated by the transcription factor SP1, that showed 2-fold increase. PON1 and 2 protein expressions also showed significant increase in the PBMC of AMD patients. At serum level, PON1 protein was significantly increased in AMD patients. Cholesterol transporters such as CD36, SR-B1 and ABCA1 gene expressions were also found to be higher (1.5, 1.9 and 2.4-fold respectively) in AMD, though not statistically significant. While the wet AMD (CNV) was found to be associated with increase in oxLDL and serum PONase activity, the dry AMD was associated with increased HDL and serum PON-HCTLase activity. The genotype and allele frequencies of Q192R & L55M were not significantly different between AMD patients and controls. However, altered lipid status and PON activities were associated with the genotype in AMD patients. A higher enzyme activity was observed for the RR genotype of Q192R in the cohort, irrespective of case and control. Thus the PON genotype and phenotype seem to play a role in the pathogenesis of AMD.

Carnosic Acid Affords Mitochondrial Protection in Chlorpyrifos-Treated Sh-Sy5y Cells

Carnosic acid (CA; C20H28O4) is a phenolic diterpene found in rosemary (Rosmarinus officinalis L.) and exhibits protective properties, e.g., antioxidant, anti-inflammatory, antitumor, and antimicrobial activities. In this context, CA has been viewed as a neuroprotective agent due to its ability in rescuing neuronal cells from pro-oxidant and pro-apoptotic challenges. In the present work, we found that CA pretreatment at 1 µM for 12 h suppressed the mitochondria-related pro-oxidant and mitochondria-dependent pro-apoptotic effects of chlorpyrifos (CPF) in human neuroblastoma SH-SY5Y cells. CA prevented mitochondrial membrane potential disruption and decreased the levels of oxidative stress markers in mitochondrial membranes obtained from cells exposed to CPF. CA also inhibited cytochrome c release and activation of the caspases-9 and -3, as well as decreased DNA fragmentation, in CPF-treated cells. CA upregulated the content of glutathione (GSH) in mitochondria by a mechanism involving the activation of the phosphoinositide-3-kinase (PI3K)/Akt/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, since inhibition of PI3K/Akt or silencing of Nrf2 using siRNA strategy abolished the protection exerted by CA in SH-SY5Y cells. Therefore, CA protected mitochondria of SH-SY5Y cells through the activation of the PI3K/Akt/Nrf2 axis, causing upregulation of the mitochondrial GSH content and consequent antioxidant and anti-apoptotic effects.

DJ-1 interacts with and regulates paraoxonase-2, an enzyme critical for neuronal survival in response to oxidative stress

Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP⁺ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2.