MOLECULAR, CELLULAR, AND DEVELOPMENTAL BIOLOGY Epigallocatechin-3-gallate prevents lipid peroxidation and enhances antioxidant defense system via modulating hepatic nuclear transcription factors in heat-stressed quails K. Sahin,*1 C. Orhan,* M. Tuzcu,† S. Ali,‡ N. Sahin,* and A. Hayirli§ *Department of Animal Nutrition and Nutritional Disorders, Faculty of Veterinary Medicine, and †Department of Biology, Faculty of Science, Firat University, Elazig 23119, Turkey; ‡Department of Biochemistry, Faculty of Science, Jamia Hamdard University, Hamdard Nagar, New Delhi 110062, India; and §Department of Animal Nutrition and Nutritional Disorders, Faculty of Veterinary Medicine, Atatürk University, Erzurum 25240, Turkey ABSTRACT Epigallocatechin-3-gallate (EGCG), a polyphenol derived from green tea, exerts antioxidant effects. Oxidative stress is one of the consequences of heat stress (HS), which also depresses performance in poultry. This experiment was conducted to elucidate the action mode of EGCG in alleviation of oxidative stress in heat-stressed quail (Coturnix coturnix japonica). A total of 180 five-week-old female Japanese quails were reared either at 22°C for 24 h/d (thermoneutral, TN) or 34°C for 8 h/d (HS) for 12 wk. Birds in both environments were randomly fed 1 of 3 diets: basal diet and basal diet added with 200 or 400 mg of EGCG/kg of diet. Each of the 2 × 3 factorially arranged groups was replicated in 10 cages, each containing 3 quails. Performance variables [feed intake (FI) and egg production (EP)], oxidative stress biomarkers [malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px)] and hepatic transcription factors [nuclear factor κ-light-chainenhancer of activated B cells (NF-κB) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2)] were analyzed using 2-way ANOVA. Exposure to HS caused reductions in FI by 9.7% and EP by 14.4%, increased hepatic MDA level by 84.8%, and decreased hepatic SOD,
CAT, and GSH-Px activities by 25.8, 52.3, and 45.5%, respectively (P < 0.0001 for all). The hepatic NF-κB expression was greater (156 vs. 82%) and Nrf2 expression was lower (84 vs. 118%) for quails reared under the HS environment than for those reared under the TN environment (P < 0.0001 for both). In response to increasing supplemental EGCG level, there were linear increases in FI from 29.6 to 30.9 g/d and EP from 84.3 to 90.1%/d, linear decreases in hepatic MDA level from 2.82 to 1.72 nmol/g and Nrf2 expression from 77.5 to 123.3%, and linear increases in hepatic SOD (146.4 to 182.2), CAT (36.2 to 47.1), and GSH-Px (13.5 to 18.5) activities (U/mg of protein) and NF-κB expression (149.7 to 87.3%) (P < 0.0001 for all). Two-way treatment interactions revealed that the degree of restorations in all response variables was more notable under the HS environment than under the TN environment as supplemental EGCG level was increased. Moreover, levels of oxidative biomarkers were strongly correlated with expressions of hepatic nuclear transcription factors. In conclusion, supplemental EGCG alleviates oxidative stress through modulating the hepatic nuclear transcription factors in heat-stressed quails.
Key words: epigallocatechin-3-gallate, oxidative stress biomarker, nuclear transcription factor, heat stress, Japanese quail 2010 Poultry Science 89:2251–2258 doi:10.3382/ps.2010-00749
INTRODUCTION Heat stress (HS) is one of the important obstacles in poultry operations. High ambient temperature does not only compromise welfare and health status (Mashaly et al., 2004) but also adversely affects survival (Bog©2010 Poultry Science Association Inc. Received March 4, 2010. Accepted July 13, 2010. 1 Corresponding author:
[email protected]
in et al., 1996), performance (Wolfenson et al., 1979; Yalçin et al., 2001), and product quality (Smith, 1974; Sandercock et al., 2001). Moreover, HS causes oxidative stress, reflected by increased reactive oxygen species production (Halliwell and Gutteridge, 1989), and decreases serum vitamin (Sahin et al., 2002c) and mineral concentrations (Sahin et al., 2002a,b, 2009) that play a role in the antioxidant defense system. Oxidative stress impairs the cell membrane and mitochondrial integrity (Meng et al., 2008) and causes cell damage through lip-
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id peroxidation (Halliwell and Gutteridge, 1989), which can be minimized by supplementation of antioxidant vitamins (Puthpongsiriporn et al., 2001; Sahin et al., 2001; Franchini et al., 2002) or natural substances that possess antioxidant potential (Sahin et al., 2008; Tuzcu et al., 2008). Epigallocatechin-3-gallate (EGCG) is a major component of polyphenols in green tea and exerts numerous biological effects that are pertinent to human medicine, which include antioxidant, antimicrobial, antiproliferative, antimutagenic, and antiaging activities (Mukhtar and Ahmad, 2000; Trevisanato and Kim, 2000). The antioxidant effect of EGCG is attributed to possessing high reductive powers to quench singlet molecular oxygen and peroxyl radicals (Jovanovic et al., 1994; Valcic et al., 1999; Nagle et al., 2006). Transcription factors are proteins that regulate the transfer of genetic information from DNA to mRNA via acting downstream of signaling cascades in response to biological and environmental stimuli (Latchman, 1997). Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) is one of the transcription factors responsible for controlling the DNA transcription and is involved in cellular responses to several stimuli including free radicals (Gilmore, 2006). This complex protein acts as the first responder because it is normally present in the cytosol in an inactive form and enters the nucleus in response to a stimulus to activate the expression of specific genes (Nelson et al., 2004; Gilmore, 2006). Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is another transcription factor and is known as a master regulator of the antioxidant response (Li and Kong, 2009; Nguyen et al., 2009). Under the thermoneutral (TN) condition, Nrf2 is bound to another protein called kelch-like ECH-associated protein 1 (Keap1) in the cytosol (Itoh et al., 1999). Disruption of cysteine residues in Keap1 due to oxidative stress results in accumulation of Nrf2 in the cytosol (Yamamoto et al., 2008). Then, unbound Nrf2 is translocated into the nucleus where its binds to the antioxidant response element in the promoter region of many antioxidative genes to initiate their transcriptions (Itoh et al., 1997). In a previous experiment, we demonstrated a preventive effect of EGCG against HS in quails (Tuzcu et al., 2008). Antioxidants are shown to modulate the transcription system (Farombi et al., 2008; Jung et al., 2009). However, the action mode of EGCG in poultry species is largely unknown. This study was performed to elucidate the mechanism by which supplemental EGCG alleviates performance and oxidative stress in Japanese quails (Coturnix coturnix japonica) exposed to HS.
MATERIALS AND METHODS Birds, Grouping, and Management One hundred eighty 5-wk-old female Japanese quails were used in accordance with animal welfare regula-
tions at the Veterinary Control and Research Institute of Elazig, Turkey. The quails were kept in temperaturecontrolled rooms at either 22°C for 24 h/d (TN) or 34°C for 8 h (0900 and 1700 h) followed by 22°C for 16 h/d (HS) during the experimental period. The quails were then fed 1 of 3 diets: basal diet and basal diet supplemented with 200 or 400 mg of EGCG (Teavigo, DSM Co., Istanbul, Turkey) per kilogram of diet (Table 1). The product contained 94% natural EGCG isolated from green tea leaves. Each of the 2 × 3 factorially arranged groups was replicated in 10 cages with a 20 × 20 cm dimension, each consisting of 3 quails. The quails were exposed to a 17-h daily photoperiod and had free choice of feed and water throughout the experimental period (12 wk).
Data and Sample Collection Feed intake was measured weekly and egg production was recorded daily during the experimental period. At the end of the experiment, 1 bird from each cage (10 birds per group) was killed by cervical dislocation. The liver was removed and chopped into small pieces on ice for determination of the oxidative stress biomarkers, such as malondialdehyde (MDA) and antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) as well as nuclear transcription factors, such NF-κB and Nrf2.
Laboratory Analysis Dietary Nutrients. The diets were analyzed for contents of CP (method 988.05), Ca (method 968.08), and phosphorus (method 965.17) according to procedures described by the Association of Official Analytical Chemists (AOAC, 1990). Energy and amino acid (methionine and lysine) contents were calculated from tabular values listed for the feedstuffs (Jurgens, 1996). Oxidative Stress Biomarkers. A 10% (wt/vol) liver homogenate was prepared in 10 mM phosphate buffer (pH 7.4). The homogenate was centrifuged at 13,000 × g for 10 min at 4°C. The supernatant was collected and stored at −80°C. The hepatic MDA level was measured (Barim and Karatepe, 2010) using the fully automatic high-performance liquid chromatograph (Shimadzu, Kyoto, Japan) equipped with a pump (LC-20AD), a UV-visible detector (SPD-20A), an inertsil ODS-3 C18 column (250 × 4.6 mm, 5 m), a column oven (CTO10ASVP), an autosampler (SIL-20A), a degasser unit (DGU-20A5), and a computer system with LC Solution Software (Shimadzu). Total SOD activity was attained based on the amount of enzyme required to inhibit the rate of formazan dye formation by 50% (Spitz and Oberley, 1989). The CAT activity was estimated based on the amount of enzyme required to decompose 1 mmol of hydrogen peroxide to water and oxygen (Cohen et al., 1970). The GSH-Px activity assessment was based on the amount of enzyme required to oxidize
EPIGALLOCATECHIN-3-GALLATE SUPPLEMENTATION TO HEAT-STRESSED QUAILS Table 1. Ingredient and nutrient composition of the basal
diet1
Item
Amount
Ingredient, % Corn Soybean meal, 44% CP Soy oil Salt dl-Methionine Limestone Dicalcium phosphate Vitamin and mineral premix2 Nutrient composition ME,3 kcal/kg CP, % Ca, % P, % Methionine,3 % Lysine,3 %
53.76 29.27 4.85 0.31 0.20 9.50 1.76 0.35 2,830 17.95 3.96 0.63 0.42 1.05
1Epigallocatechin-3-gallate (EGCG; 0, 200, or 400 mg EGCG per kg of diet; DSM, Istanbul, Turkey) was added to the basal diet at the expense of corn. 2Per kilogram contained: vitamin A, 8,000 IU; vitamin D , 3,000 IU; 3 vitamin E, 25 IU; menadione, 1.5 mg; vitamin B12, 0.02 mg; biotin, 0.1 mg; folacin, 1 mg; niacin, 50 mg; pantothenic acid, 15 mg; pyridoxine, 4 mg; riboflavin, 10 mg; thiamin, 3 mg; copper (copper sulfate), 10.00 mg; iodine (ethylenediamine dihydriodide), 1.00 mg; iron (ferrous sulfate monohydrate), 50.00 mg; manganese (manganese sulfate monohydrate), 60.00 mg; zinc (zinc sulfate monohydrate), 60.00 mg; and selenium (sodium selenite), 0.42 mg. 3Calculated value according to tabular values listed for the feed ingredients (Jurgens, 1996).
1 mmol of NADPH (Lawrence and Burk, 1976). The enzyme activities were expressed as units per milligram of protein. Transcription Factors. Accurately weighed liver tissue was homogenized in 1:10 (wt/vol) in 10 mM TrisHCl buffer at pH 7.4, containing 0.1 mM NaCl, 0.1 mM phenylmethylsulfonyl fluoride, and 5 µM soybean (soluble powder; Sigma, St. Louis, MO) as trypsin inhibitor. Tissue homogenate was centrifuged at 15,000 × g at 4°C for 30 min, and the supernatant was transferred into fresh tubes. Sodium dodecyl sulfate-PAGE sample buffer containing 2% β-mercaptoethanol was added to the supernatant. Equal amounts of protein (20 µg) were electrophoresed and subsequently transferred to a nitrocellulose membrane (Schleicher and Schuell Inc., Keene, NH). Nitrocellulose blots were washed twice for 5 min in PBS and blocked with 1% BSA in PBS for 1 h before the application of primary antibody. Chicken antibodies against NF-κB (ab16502) and Nrf2 (ab31163) (Abcam, Cambridge, UK) were diluted (1:1,000) in the same buffer containing 0.05% Tween-20. The nitrocellulose membrane was incubated overnight at 4°C with protein antibody. The blots were washed and incubated with horseradish peroxidase-conjugated goat antimouse IgG (Abcam). Specific binding was detected using diaminobenzidine and hydrogen peroxide as substrates. Protein loading was controlled using a monoclonal mouse antibody against β-actin antibody (A5316; Sigma). Samples were analyzed in quadruplicates and protein levels were determined densitometrically using an image analysis system (Image J, National Institute
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of Health, Bethesda, MD) as described by Lowry et al. (1951).
Statistics Data on performance parameters, oxidative stress biomarkers, and nuclear transcription factors were analyzed by 2-way ANOVA using the PROC GLM procedure (SAS, 2002). The linear model to test the effect of treatments on response variables was as follows: yij = µ + Ei + Sj + (E × S)ij + eij, where y = response variable; µ = population mean; E = environmental temperature; S = EGCG supplementation; and e = residual error [N (σ, µ; 0, 1)]. The model also included polynomial contrast to determine changes in response variables as supplemental EGCG level was increased. Correlations among performance parameters, oxidative stress biomarkers, and nuclear transcription factors were determined using the CORR procedure (SAS, 2002). Statistical significance was considered at P ≤ 0.05.
RESULTS Performance Exposure to HS for 8 h per day adversely affected performance parameters. Quails reared under the TN environment consumed more feed (31.8 vs. 28.7 g/d, SE = 0.2) and produced more egg (94.2 vs. 80.6%/d, SE = 0.8) than quails exposed to HS (P < 0.0001 for both). Overall, there were 4.3 and 6.9% increases in feed intake and egg production, respectively, in response to increasing dietary EGCG supplementation (linear effect; P < 0.0001 for both). The mean feed intake (SE = 0.2) was 29.6, 30.2, and 30.9 g/d and egg production (SE = 0.9) was 84.3, 87.8, and 90.1%/d for quails supplemented with 0, 200, and 400 mg of EGCG/kg of diet, respectively. These increases were greater in the HS environment than in the TN environment (environmental temperature × EGCG level interaction effects on feed intake, P < 0.0001; Figure 1A and egg production, P < 0.007; Figure 1B).
Hepatic Oxidative Stress Biomarkers Quails subjected to HS had greater MDA level (2.92 vs. 1.58 nmol/g, SE = 0.05) and lower SOD (140 vs. 190, SE = 1.2), CAT (27 vs. 57, SE = 0.9), and GSH-Px (12 vs. 21, SE = 0.3) activities (U/mg of protein) than quails not subjected to HS (P < 0.0001 for all). Overall MDA level decreased linearly by 39% and activities of SOD, CAT, and GSH-Px increased linearly by 24, 30, and 17%, respectively, with increasing supplemental EGCG level (P < 0.0001 for all). The mean MDA level (SE = 0.06) was 2.82, 2.21, and 1.72 nmol/g; the mean SOD activity (SE = 1.5) was 146.4, 168.4, and 182.2 U/mg of protein; the mean CAT activity (SE = 1.1) was 36.2, 42.8, and 47.1 U/mg of protein; and
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the mean GSH-Px activity (SE = 0.3) was 13.5, 17.0, and 18.5 U/mg of protein for quails supplemented with 0, 200, and 400 mg of EGCG/kg of diet, respectively. Decrease in MDA level (P < 0.0001; Figure 2A) and increases in SOD (P < 0.0001; Figure 2B), CAT (P < 0.01; Figure 2C), and GHS-Px (P < 0.04; Figure 2D) in response to increasing dietary EGCG supplementation were more notable in the HS environment than in the TN environment (environmental temperature × EGCG level interaction effects).
Hepatic Nuclear Transcription Factors Hepatic NF-κB was expressed at a greater rate (156 vs. 82%, SE = 2.2) and Nrf2 was expressed at a lesser rate (84 vs. 118%, SE = 2.9) in quails exposed to HS than in quails not exposed to HS (P < 0.0001 for both). With increasing dietary EGCG supplementation, NF-κB expression was inhibited by 42%, whereas Nrf2 expression was enhanced by 59% (linear effect, P < 0.0001 for both). The mean NF-κB expression (SE = 2.7) was 149.7, 119.6, and 87.3% and the mean Nrf2 expression (SE = 3.5) was 77.5, 102.9, and 123.3% for quails supplemented with 0, 200, and 400 mg of EGCG/ kg of diet, respectively. Decreases in NF-κB expression (P < 0.0001; Figure 3A) and increases in Nrf2 expression (P < 0.03; Figure 3B) in response to increasing supplemental EGCG level were greater in the TN environment than in the HS environment (environmental temperature × EGCG level interaction effects).
mental EGCG increased feed intake (Figure 1A) and egg production (Figure 1B), which was more noticeable in the HS environment than in the TN environment similar to our previous findings (Tuzcu et al., 2008). Ambient environmental temperature causes oxidative stress and tissue damage via lipid peroxidation (Mujahid et al., 2007; Tan et al., 2010). This is reflected by elevated hepatic MDA level (Figure 2A). Epigallocatechin-3-gallate is a powerful free-radical scavenger and protects membrane stability (Terao et al., 1994; Salah et al., 1995). Epigallocatechin-3-gallate supplementation was shown to reduce muscle and liver TBA reactive substances, another indicator of lipid peroxidation in broiler-induced oxidative stress by glucocorticoid administration (Eid et al., 2003) and serum and liver MDA level in quail-induced oxidative stress by exposure to HS (Tuzcu et al., 2008). Living organisms facilitate the antioxidant defense system through increasing activities of detoxifying enzymes [SOD (Figure 2B), CAT (Figure 2C), and GSH-Px (Figure 2D)] to reduce harmful effects of reactive oxygen molecules produced due to HS (Tan et al., 2010). Antioxidant effects of EGCG have also been shown in oxidative stress induced by UV radiation in human skin (Katiyar et al., 2001) and hu-
Correlations Among Oxidative Stress Biomarkers and Hepatic Nuclear Transcription Factors There was an autocorrelation among response variables (P < 0.01; Table 2). Performance variables were positively correlated with hepatic antioxidant enzymes’ activities and negatively correlated with hepatic MDA level. Hepatic MDA level was negatively correlated with activities of all antioxidant enzymes and expression of Nrf2 and positively correlated with expression of NFκB. Activities of antioxidant enzymes were negatively correlated with expression of NF-κB and positively correlated with expression of Nrf2.
DISCUSSION Poultry species are less heat-tolerant than mammalian specie due to a limited heat dissipation capacity associated with lacking sweat glands and having firm feathers and high body temperature (Yahav et al., 2004). Birds consume less to reduce metabolic heat production (Shane, 1988), resulting in depressed growth rate, egg production, and worsened feed efficiency (Geraert et al., 1996; Yalçin et al., 2001). In agreement with literature, HS caused depressions in feed intake (Figure 1A) and egg production (Figure 1B). Moreover, supple-
Figure 1. Effects of environmental temperature [–□– = thermoneutral (22°C for 24 h/d) and –■– = heat stress (34°C for 8 h/d followed by 22°C for 16 h/d)] and dietary epigallocatechin-3-gallate (EGCG) supplementation on performance. Environmental temperature × supplemental EGCG interaction effect on feed intake (P < 0.0001; pooled SEM = 0.3; panel A) and egg production (P < 0.007; pooled SEM = 1.3; panel B) was significant.
EPIGALLOCATECHIN-3-GALLATE SUPPLEMENTATION TO HEAT-STRESSED QUAILS
man fibroblasts exposed to hydrogen peroxide (Wei et al., 1999; Meng et al., 2008). The antioxidant power of polyphenols (i.e., proanthocyanidins, catechins, epicatechin, and procyanidin) found in grape seeds is reported to be 20 times greater than vitamin E and 50 times greater than vitamin C (Shi et al., 2003). Supplemental EGCG decreased hepatic MDA level (Figure 2A) and increased activities of these enzymes (Figure 2B, C, and D) at a greater rate in heat-stressed quails than in quails reared under the TN environment. Moreover, the adverse effect of HS on the antioxidant defense system is further exacerbated by causing marginal deficiencies of minerals (i.e., Fe, Zn, Cu, and Se; Sahin et al., 2009) and vitamins (i.e., vitamins E, C, and A; Sahin et al., 2001; Sahin and Kucuk, 2003) that act as co-factors and co-enzymes for antioxidant enzymes due to their deceased retentions or increased excretions, or both (Balnave, 2004). Both NF-κB and Nrf2 are redox-sensitive transcription factors (Nair et al., 2007) and play a role in induction of phase II detoxifying-antioxidant defense mechanisms to cope with oxidative stress through enhancing the expression of several enzymes, such as NAD(P)H quinone oxidoreductase 1, glutamate-cysteine ligase, heme oxygenase 1, glutathione S-transferase, and uridine diphosphate-glucuronosyltransferase (Na and
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Surh, 2008). Increased expression of NF-κB (Figure 3A) and deceased expression of Nrf2 (Figure 3B) in heat-stressed quails could be related to their activation (Nelson et al., 2004; Gilmore, 2006) and translocation (Itoh et al., 1999; Yamamoto et al., 2008; Nguyen et al., 2009), respectively, to overcome oxidative stress caused by exposure to HS (Table 2). Similar to supplemental EGCG, melatonin as an antioxidant was shown to increase antioxidant enzyme activities, inhibit NF-κB expression, and enhance Nrf2 expression in the hepatic injury model (Jung et al., 2009). Kim et al. (2001) and Afaq et al. (2003) showed that EGCG treatment reduced NF-κB expression surge triggered by UV radiation-induced skin damage. Supplemental EGCG was also shown to increase heme oxygenase 1 activity in rat neurons to protect from oxidative stress, which was associated with activation of Nrf2 translocation (Romeo et al., 2009). Depressions in feed intake and egg production were associated with increased hepatic MDA, an indicator of lipid peroxidation and decreased hepatic SOD, CAT, and GSH-Px activities, indicators of the antioxidant defense system (Table 2). Significant interactions (Figures 1, 2, and 3) showed that EGCG alleviated the adverse effects on these variables caused by exposure to HS. Our data ascertain that polyphenols act as modifiers of
Figure 2. Effects of environmental temperature [–□– = thermoneutral (22°C for 24 h/d) and –■– = heat stress (34°C for 8 h/d followed by 22°C for 16 h/d)] and dietary epigallocatechin-3-gallate (EGCG) supplementation on hepatic oxidative stress biomarkers. Environmental temperature × supplemental EGCG interaction effect on malondialdehyde (MDA) level (P < 0.0001; pooled SEM = 0.08; panel A) and superoxide dismutase (SOD; P < 0.0001; pooled SEM = 2.1; panel B), catalase (CAT; P < 0.01; pooled SEM = 1.6; panel C), and glutathione peroxidase (GSH-Px; P < 0.04; pooled SEM = 0.5; panel D) activities was significant.
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Figure 3. Effects of environmental temperature [white bars = thermoneutral (TN; 22°C for 24 h/d) and gray bars = heat stress (HS; 34°C for 8 h/d followed by 22°C for 16 h/d)] and dietary epigallocatechin-3-gallate (EGCG) supplementation (without lines = 0 mg/kg; vertical lines = 200 mg/kg; horizontal lines = 400 mg/kg) on hepatic transcription factors. Data are means of quadruplets of assays and expressed as relative to control (%). A representative blot is shown. Environmental temperature × supplemental EGCG interaction effect on nuclear factor κ-light-chainenhancer of activated B cells (NF-κB; P < 0.0001; pooled SEM = 3.8; panel A) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2; P < 0.03; pooled SEM = 5.0; panel B) expressions was significant.
signal transduction pathways to elicit their cytoprotective responses (Surh et al., 2005; Rahman et al., 2006) though suppressing NF-κB activation and enhancing Keap1 dissociation from Nrf2 that occurs in response to stressors, which are accompanied by suppression of lipid peroxidation and elevation of antioxidant enzyme activities (Table 2).
In conclusion, exposure to HS depressed performance variables, induced lipid peroxidation, increased antioxidant enzyme activities, enhanced NF-κB expression, and suppressed Nrf2 expression. The nature of these response variables to supplemental EGCG was opposite to exposure to HS. Alterations in performance, oxidative stress biomarkers, and transcription factors
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Table 2. Correlations among performance variables, hepatic oxidative stress biomarkers, and hepatic nuclear transcription factors1,2 Variable
EP
MDA
SOD
CAT
GSH-Px
NF-κB
Nrf2
FI EP MDA SOD CAT GSH-Px NF-κB
0.91
−0.85 −0.82
0.85 0.76 −0.93
0.82 0.83 −0.90 0.90
0.86 0.84 −0.90 0.92 0.91
−0.86 −0.83 0.95 −0.97 −0.90 −0.93
0.74 0.73 −0.89 0.90 0.79 0.83 −0.92
1P
< 0.01 for all correlation coefficients. = feed intake, g/d; EP = egg production, %; MDA = malondialdehyde, nmol/g; SOD = superoxide dismutase, U/mg of protein; CAT = catalase, U/mg of protein; GSH-Px = glutathione peroxidase, U/mg of protein; NF-κB = nuclear factor κ-light-chain-enhancer of activated B cells; Nrf2 = nuclear factor (erythroid-derived 2)like 2. 2FI
occurred at a greater rate in quails subjected to HS than in those reared under the TN condition. Our data suggest that EGCG elicits antioxidant effects through inhibiting NF-κB expression and activating Nrf2 expression, which were activated and suppressed in the HS environment.
ACKNOWLEDGMENTS We thank the Veterinary Control and Research Institute of Elazig, Turkey, for providing the experimental facility. Thanks are extended to DSM Co. (Istanbul, Turkey) and Insanay Kanatli Hayvan Uretim Paz. Tic. Inc. (Elazig, Turkey) for gifting EGCG and quails.
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