Effect of paraquat-induced oxidative stress on insulin regulation of insulin-like growth factor-binding protein-1 gene expression

Insulin Signaling Disruption and INF-γ Upregulation Induce Aβ1-42 and Hyperphosphorylated-Tau Proteins Synthesis and Cell Death after Paraquat Treatment of Primary Hippocampal Cells

Acute and long-term paraquat (PQ) exposure produces hippocampal neurodegeneration and cognition decline. Although some mechanisms involved in these effects were found, the rest are unknown. PQ treatment, for 1 and 14 days, upregulated interferon-gamma signaling, which reduced insulin levels and downregulated the insulin pathway through phosphorylated-c-Jun N-terminal-kinase upregulation, increasing glucose levels and the production of Aβ_1-42 and phosphorylated-tau, by beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) overexpression and phosphorylated-GSK3β (p-GSK3β; ser9) level reduction, respectively, which induced primary hippocampal neuronal loss. This novel information on the PQ mechanisms leading to hippocampal neurodegeneration could help reveal the PQ actions that lead to cognition dysfunction.

Protective Effect of Fenofibrate on Oxidative Stress-Induced Apoptosis in Retinal-Choroidal Vascular Endothelial Cells: Implication for Diabetic Retinopathy Treatment

Diabetic retinopathy (DR) is an important microvascular complication of diabetes and one of the leading causes of blindness in developed countries. Two large clinical studies showed that fenofibrate, a peroxisome proliferator-activated receptor type α (PPAR-α) agonist, reduces DR progression. We evaluated the protective effects of fenofibrate on retinal/choroidal vascular endothelial cells under oxidative stress and investigated the underlying mechanisms using RF/6A cells as the model system and paraquat (PQ) to induce oxidative stress. Pretreatment with fenofibrate suppressed reactive oxygen species (ROS) production, decreased cellular apoptosis, diminished the changes in the mitochondrial membrane potential, increased the mRNA levels of peroxiredoxin (Prx), thioredoxins (Trxs), B-cell lymphoma 2 (Bcl-2), and Bcl-xl, and reduced the level of B-cell lymphoma 2-associated X protein (Bax) in PQ-stimulated RF/6A cells. Western blot analysis revealed that fenofibrate repressed apoptosis through cytosolic and mitochondrial apoptosis signal-regulated kinase-1 (Ask)-Trx-related signaling pathways, including c-Jun amino-terminal kinase (JNK) phosphorylation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase-1 (PARP-1) cleavage. These protective effects of fenofibrate on RF/6A cells may be attributable to its anti-oxidative ability. Our research suggests that fenofibrate could serve as an effective adjunct therapy for ocular oxidative stress-related disorders, such as DR.

Herbicide Paraquat provokes the stress responses of HPA axis of laboratory mouse, Mus musculus

Paraquat (PQ) is a herbicide and well characterized pneumotoxicant which is also known to induce neurodegeneration in organisms. Aim of this study was to investigate the effect of PQ on hypothalamic - pituitary - adrenal (HPA) axis. PQ was administered i.p.10 mg/kg body weight once a week for 5 weeks in laboratory male mice. Results indicate that SOD activity decreased while catalase activity and nitrate-nitrite level increased significantly in the hypothalamus of PQ treated mice. The expression of both AVP and CRH mRNA in the hypothalamus as well as ir-AVP and ir-CRH increased in the PVN of PQ treated mice compared to control. Immunoreactivity of nNOS and Hsp70 including NF-κB mRNA expression increased in the PVN of PQ treated mice. As expected, serum corticosterone level was also elevated significantly in the herbicide PQ treated mice. From these findings it is concluded that paraquat treatment is capable of activating the HPA axis via upregulating transcription and translation of the hypothalamic neuropeptides AVP and CRH as well as serum corticosterone level. Increase in both oxidative and nitrosative stress in PQ treated mice might be the driver which also contributed to the activation of HPA axis. It seems that stress induced reactive species (ROS, RNS) might be also responsible for the induced expression of NF-κB mRNA and Hsp70 protein which are considered as the reliable markers of certain types of stressors including PQ toxicity.

Protective action of Omega-3 on paraquat intoxication in Drosophila melanogaster

Paraquat (PQ) (1,1'-dimethyl-4-4'-bipyridinium dichloride) is the second most widely used herbicide worldwide; however, in countries different sales and distribution remain restricted. Chronic exposure to PQ leads to several diseases related to oxidative stress and mitochondrial dysfunctions including myocardial failure, cancer, and neurodegeneration and subsequently death depending upon the dose level. The aim of this study was to examine if diet supplementation with eicosapentaenoic and docosahexaenoic acids (EPA and DHA, omega-3 long-chain fatty acids) serves a protective mechanism against neuromuscular dysfunctions mediated by PQ using Drosophila melanogaster as a model with focus on mitochondrial metabolism. PQ ingestion (170 mg/kg b.w. for 3 d) resulted in a decreased life span and climbing ability in D. melanogaster. In the brain, PQ increased thioflavin fluorescence and reduced either 4',6-diamidino-2-phenylindole dihydrochloride (DAPI) nuclei staining and neuronal nuclei protein (NeuN) positive neurons, indicating amyloid formation and neurodegenetation, respectively. In the thorax, PQ ingestion lowered citrate synthase activity and respiratory functions indicating a reduction in mitochondrial content. PQ elevated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) mRNA expression levels, indicative of high calcium influx from cytosol to mitochondrial matrix. In brain and thorax, PQ also increased hydrogen peroxide (H2O2) production and impaired acetylcholinesterase (AChE) activity. Concomitant EPA/DHA ingestion (0.31/0.19 mg/kg b.w.) protected D. melanogaster against PQ-induced toxicity preserving neuromuscular function and slowing down the rate of aging. In brain and thorax, these omega-3 fatty acids inhibited excess H2O2 production and restored AChE activity. EPA/DHA delayed amyloid deposition in the brain, and restored low citrate synthase activity and respiratory functions in the thorax. The effects in the thorax were attributed to stimulated mRNA expression level of genes involved either in mitochondrial dynamics or biogenesis promoted by EPA/DHA: dynamin-related protein (DRP1), mitochondrial assembly regulatory factor (MARF), mitochondrial dynamin like GTPase (OPA1), and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α). In conclusion, diet supplementation with EPA/DHA appears to protect D. melanogaster muscular and neuronal tissues against PQ intoxication.

On the methodological limitations of detecting oxidative stress: effects of paraquat on measures of oxidative status in greenfinches

Oxidative stress (OS) is widely believed to be responsible for generation of trade-offs in evolutionary ecology by means of constraining investment into a number of components of fitness. Yet the progress in understanding the true role of OS in ecology and evolution has remained elusive. Interpretation of current findings is particularly hampered by the scarcity of experiments demonstrating which of the many available parameters of oxidative status respond most sensitively to and are relevant for measuring OS. We addressed these questions in wild-caught captive greenfinches (Carduelis chloris) by experimental induction of OS by administration of the pro-oxidant compound paraquat with drinking water. Treatment induced 50% of mortality and a significant drop in body mass and an increase in oxidative DNA damage and glutathione levels in erythrocytes among the survivors of the high paraquat (0.2 g/L during 7 days) group. Three days after the end of the treatment, paraquat had no effect on peroxidation of lipids (plasma malondialdehyde), carbonylation of proteins (in erythrocytes), parameters of plasma antioxidant protection (TAC and OXY), uric acid or carotenoids. Our findings of an increase in one marker of damage and one marker of protection from the multitude of measured variables indicate that detection of OS is difficult even under most stringent experimental induction of oxidative insult. We hope that this study highlights the need for reconsideration of over-simplistic models of OS and draws attention to the limitations of detection of OS due to time-lagged and hormetic up-regulation of protective mechanisms. This study also underpins the diagnostic value of measurement of oxidative damage to DNA bases and assessment of erythrocyte glutathione levels.

Nrf2 deficiency improves glucose tolerance in mice fed a high-fat diet

Nrf2, a master regulator of intracellular redox homeostasis, is indicated to participate in fatty acid metabolism in liver. However, its role in diet-induced obesity remains controversial. In the current study, genetically engineered Nrf2-null, wild-type (WT), and Nrf2-activated, Keap1-knockdown (K1-KD) mice were fed either a control or a high-fat Western diet (HFD) for 12 weeks. The results indicate that the absence or enhancement of Nrf2 activity did not prevent diet-induced obesity, had limited effects on lipid metabolism, but affected blood glucose homeostasis. Whereas the Nrf2-null mice were resistant to HFD-induced glucose intolerance, the Nrf2-activated K1-KD mice exhibited prolonged elevation of circulating glucose during a glucose tolerance test even on the control diet. Feeding a HFD did not activate the Nrf2 signaling pathway in mouse livers. Fibroblast growth factor 21 (Fgf21) is a liver-derived anti-diabetic hormone that exerts glucose- and lipid-lowering effects. Fgf21 mRNA and protein were both elevated in livers of Nrf2-null mice, and Fgf21 protein was lower in K1-KD mice than WT mice. The inverse correlation between Nrf2 activity and hepatic expression of Fgf21 might explain the improved glucose tolerance in Nrf2-null mice. Furthermore, a more oxidative cellular environment in Nrf2-null mice could affect insulin signaling in liver. For example, mRNA of insulin-like growth factor binding protein 1, a gene repressed by insulin in hepatocytes, was markedly elevated in livers of Nrf2-null mice. In conclusion, genetic alteration of Nrf2 does not prevent diet-induced obesity in mice, but deficiency of Nrf2 improves glucose homeostasis, possibly through its effects on Fgf21 and/or insulin signaling.

Antioxidant N-acetyl-L-cysteine (NAC) supplementation reduces reactive oxygen species (ROS)-mediated hepatocellular tumor promotion of indole-3-carbinol (I3C) in rats

Indole-3-carbinol (I3C) has a liver tumor promoting activity in rats, and is also known as a cytochrome p450 1A (CYP1A) inducer. The generation of reactive oxygen species (ROS) resulting from CYP1A induction due to I3C, is probably involved in the tumor promotion. To clarify whether ROS generation contributes to I3C's induction of hepatocellular altered foci, partially hepatectomized rats were fed a diet containing 0.5% of I3C for 8 weeks with or without 0.3% N-acetyl-L-cysteine (NAC), an antioxidant, in their drinking water after N-diethylnitrosamine (DEN) initiation. Immunohistochemical analysis showed that the glutathione-S-transferase placental form (GST-P) positive foci promoted by I3C were suppressed by the administration of NAC. The mRNAs of members of the phase II nuclear factor, erythroid derived 2, like 2 (Nrf2) gene batteries, whose promoter region is called as antioxidant response element (ARE), were down-regulated in the DEN-I3C-NAC group compared to the DEN-I3C group, but Cyp1a1 was not suppressed in the DEN-I3C-NAC group compared to the DEN-I3C group. There was no marked difference in production of microsomal ROS and genomic 8-hydroxy-2'-deoxygunosine (8-OHdG) as an oxidative DNA marker between the DEN-I3C-NAC and DEN-I3C groups, while mapkapk3 and Myc were decreased by the NAC treatment. These results indicate that oxidative stress plays an important role for I3C's tumor promotion, and NAC suppresses induction of hepatocellular altered foci with suppressed cytoplasmic oxidative stress.