Elif Oztetik

A Tale of Plant Glutathione S-Transferases: Since 1970

Ubiquitously distributed multifunctional superfamily of Glutathione S-transferases (GST) generally constitute a dimeric enzymes and catalyse the conjugation of the thiol group of the glutathione (GSH) to diverse electrophilic centres on lipophilic molecules with the formation of rather less active end products. Besides their well investigated conjugation reaction for the detoxification of endogenous and xenobiotic compounds, they can also be involved in both GSH dependent peroxidation or isomerization reactions, and several other non-catalytic functions, like binding of non-substrate ligands, stress-induced signalling processes and preventing of apoptosis. Plant GSTs have been a focus of attention because of their roles in herbicide detoxification and today seven distinct classes of soluble (cytosolic) GSTs are presented as Phi, Tau, Theta, Zeta, Lambda, Dehydroascorbate reductases (DHARs) and Tetrachlorohydroquinone dehalogenase (TCHQD). While GSTs show overall sequence diversification within and between classes, they retain a high level of three-dimensional structure conservation over long evolutionary periods. In this review mainly the soluble plant GSTs will be considered by giving attention to their structures, subcellular localizations, genomic organizations, catalytic/noncatalytic functions, and comparisons given with respect to their mammalian counterparts where necessary.

Effects of urban air pollutants on elemental accumulation and identification of oxidative stress biomarkers in the transplanted lichen Pseudovernia furfuracea

Determining the origins of heavy metals, their accumulation, and their detoxification mechanisms constitutes a major problem in understanding environmental pollution in urban areas. The objective of this study was to detect the relative air quality in Eskisehir city center (Turkey) through the transplanted epiphytic lichen Pseudovernia furfuracea as a biomonitor of the concentrations of some heavy metals accumulated and to describe their toxic effects on lichen physiology during the study period of one year. The influence of heavy metal accumulations on macroelement levels were also examined. In addition to analysis of B, K, Ca, P, S, Al, Fe, Mg, Mn, Ni, Zn, Pb, and Cu, total soluble proteins and oxidative stress parameters through glutathione (GSH) contents and glutathione S-transferase (GST) activities were also determined. Results indicate that, although the heavy metal concentrations were found to be gradually increased from the unpolluted control zone to the city center, the concentrations of macroelements S and Ca were higher in the polluted area. However, B, K, Mg, and P elements were found to be higher in the unpolluted area than in the polluted zones. It seems that heavy metals induce oxidative stress in lichens; we found enhancement of GSH concentrations and GST activity. Most probably, the expected destruction in this organism was reduced by the intervention of antioxidant capacity. Therefore, this report confirms the fact that the epiphytic lichen P. furfuracea is a good model for biomonitoring atmospheric quality for a long-term transplantation study, and oxidative stress parameters stand out as a tool for an early environment assessment of other physiological parameters.

Biomarkers of ecotoxicological oxidative stress in an urban environment: using evergreen plant in industrial areas.

Plants react to air pollution by increased production of reactive oxygene species and oxidative stress, which triggers multiple defense mechanisms. In this study, some parameters that serve as biomarkers for antioxidative defense, such as glutathione S-transferase (GST) activity, glutathione (GSH), malondialdehyde, chlorophyll and total soluble protein contents, were investigated on the needles of Cedrus libani (A. Rich.) grown around two industrial areas in Eskisehir. The measurements revealed that metabolism in needles of C. libani trees is largely directed towards defence against ROS, due to effects of air pollution in the sampling areas. We observed significant increases in all parameters, except chlorophyll contents, which were strongly decreased. However, these sharp changes were also prominent not only between sampling sites and control site, but also among the areas investigated, suggesting the quantitative influence of the extent of pollution. Together with total soluble protein contents, the correlation between GST activities and GSH contents suggests that damage due to oxidative stress was most probably reduced due to the increased antioxidant capacity. Therefore, we can suggest C. libani as a good model for biomonitoring atmospheric quality with the oxidative stress parameters providing an effective measure for early environmental assessment due to their sensitivities of even low levels of pollution.

Early antioxidative defence responses in the aquatic worms (Limnodrilus sp.) in Porsuk Creek in Eskisehir (Turkey).

Certain oligochaeta specimens have been universally applied as bioindicators to reflect the organic and inorganic pollution in rivers and play a major role in the decomposition of pollutants. The aim of this study was to investigate the water quality in Porsuk Creek in Eskisehir (Turkey) through the specimens from two different species that belong to Limnodrilus genus, using their biomonitoring compatibilities for the accumulated trace element concentrations and to describe the applicability of antioxidative systems as biomarkers of pollution in Tubificinae. Therefore, some parameters that serve as biomarkers for antioxidative defence, total protein, glutathione (GSH) contents and glutathione S-transferase (GST) activities, were determined in Limnodrilus hoffmeisteri and Limnodrilus udekemianus. The study was completed with the chemical analysis of the trace elements from these specimens and also from the water samples. As a conclusion, the observed elevation in GSH levels and GST activities reflect the contribution of oxidative stress in toxicity mechanisms due to the accumulation of trace elements, and the study also suggests a general induction of detoxification metabolisms in the presence of several pollutants in benthic sediment–dwelling worms. According to the average value, the trace element levels for two species are as follows: Fe > Al > Zn > Mn > Pb > Cu > Ni > B > Cd = Cr = Hg. As Porsuk Creek is used for many purposes, such as irrigation, drinking water and fish production, discharges of all types of wastes should be under stringent control to avoid the unwanted health effects to its habitants and to humans.

Hepatic effects of yttrium oxide nanoflowers: in vitro risk evaluation

Yttrium oxide nanoflowers were prepared by a hydrothermal technique, and X-ray diffraction and scanning electron microscopy were used to determine their structures. The cytotoxic and genotoxic potentials of aqueous dispersions of the nanoflowers to cultured primary rat hepatocytes were examined at concentrations up to 500 mg L−1 for 72 h. Cell viability was determined by monitoring the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, release of lactate dehydrogenase, and uptake of neutral red. Genotoxicity was assessed by the liver micronucleus assay. Exposure to Y2O3 nanoflowers at concentrations lower than 100 mg L−1 did not lead to any cytotoxicity or genotoxicity. At higher concentrations (200, 400, and 500 mg L−1), cell viability decreased and induction of micronuclei increased (400 and 500 mg L−1).

New food for an old mouth: new enzyme for an ancient archaea.

As a multifunctional group of enzymes, glutathione S-transferases (GSTs) are capable of inactivation, degradation or excretion of wide range of compounds catalytically or non-catalytically. However, to date, no study has been addresses the presence of GSTs in archaea based on their enzymatic functions. In this study, beside glutathione (GSH) amount measurement, the determination of GST activity in halophilic archaeon called Haloarcula hispanica ATCC 33960 were aimed. According to the results, specific activity was determined as 19.68 nmol min⁻¹ mg⁻¹ protein and GSH content were found to be as 194 μg g⁻¹ K(m) and V(max) values for CDNB and GSH calculated from Lineweaver-Burk plot were 0.46 mM and 27.93 nmol min⁻¹ mg⁻¹, 0.13 mM and 22.03 nmol min⁻¹ mg⁻¹, respectively. Hanes-Woolf and Eadie-Hofstee plots for CDNB and GSH were also found to be in co-relation with the results obtained from Lineweaver-Burk plot. To the best of our knowledge, GST enzymes have not been identified in archaea yet, at least based on their catalytic activities. Therefore, it is the first report on this area.

Effects of tribenuron-methyl treatment on glutathione S-transferase (GST) activities in some wheat and barley varieties*

For efficient and profitable crop production, appropriate weed management is essential. Today, herbicides are an integral part of modern farming practice globally, as they assure the convenient method of weed control chemically. Glutathione S-transferases (GSTs, EC.2.5.1.18) are a superfamily of multifunctional enzymes that detoxify endo- and xeno-biotic compounds by conjugating glutathione (GSH) to a hydrophobic substrate. Plant GSTs have been a focus of attention because of their roles in herbicide detoxification and environmental safety. In this study, the application of herbicide called tribenuron-methyl to the cultivars of wheat (Triticum aestivum L. cv. Izgi-2001, Triticum aestivum L. cv. Alpu-2001) and barley plants (Hordeum vulgare L. cv. Bilgi-91, Hordeum vulgare L. cv. Kalayci-97) caused an increase in GST activities of both in roots and shoots. Total GSH and protein contents were also determined for all above-mentioned plants. As a conclusion, our results indicate that depending on the herbicide itself, treatment conditions and the origin of the plant, tribenuron-methyl had an effect on the parameters measured in this study, including the GST activities and synthesis of GSH. The maximum increase in enzyme activity was observed in herbicide-treated Triticum aestivum L. cv. Izgi-2001 roots: 192 % of control with a tribenuron-methyl concentration of 1.5 M. However, further investigations are needed to elucidate the presence of specific tribenuron-methyl GST isozymes in this plant.

Choosing the Right Antioxidant Supplement for Protecting Liver from Toxicity of Engineered Nanoparticles : A Comprehensive In Vitro Screening

With the rapid development of nanotechnology, more and more nanomaterials are being fabricated and manipulated to perform the particular function, such as adhesive, biosensors, cosmetics, drug delivery system and artificial organ and tissue. On the other hand, nanotoxicity has become the topic of concern in nanotechnology because of the serious toxicity potentials of engineered nanomaterials on the living organisms. Many in vivo and in vitro studies clearly indicated that nanoparticles (NPs) are closely associated with toxicity by increasing intracellular reactive oxygen species (ROS) levels. And antioxidant supplementation is considered as useful against nanotoxicity related oxidative damages. At this point, in this investigation we assessed the protective abilities of selected 22 antioxidant or antioxidant featured agents against engineered nanoparticle exposure (ZnO NPs) model. We performed all experiments in cultured primary rat hepatocytes since the liver is a target site for NPs toxicity. Cell viability was detected by [3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide] (MTT) assay and lactate dehydrogenase (LDH) release, while total antioxidant capacity (TAC) and total oxidative stress (TOS) levels were determined to evaluate the oxidative alterations. Our results showed that each agent provided hepatoprotection in different degree. Propolis, boric acid and ascorbic acid were found to be the most effective ones while astaxanthine, L-glutamine and taurine were found to be less effective against nanoparticle induced oxidative injuries. The results presented here can be considered as the first information and rationale strategy on determining hepatoprotective potentials of common antioxidants against NP exposure for choosing the right antioxidant supplement for protecting liver.