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Abstract With carps as the object of study， the effects of benzo[a]pyrene concentration on SOD and CAT in carp kidneys were studied. There were three treatment groups and one control group. The exposure method was the static method. The superoxide dismutase （SOD） and catalase （CAT） activity was determined 30 d later. The results showed that after exposing to different concentrations of benzo[a]pyrene （0， 0.1， 0.5 and 1.0 ??g /L） for 30 d， the SOD activity was higher in the low concentration group （0.1 ??g/L） than in the control group； the 0.5 ??g/L benzo[a]pyrene group had no significant difference from the control group； and under the concentration of 1.0 ??g/L， the SOD activity decreased remarkably. The CAT activity was higher in the 0.1 ??g/L group than in the control group， and decreased significantly in the 1.0 ??g/L benzo[a]pyrene group compared with the control group. The results showed that benzo[a]pyrene had certain effects on the antioxidant enzymes in carp kidneys. This study provides a theoretical basis for water environmental pollution.
Key words Benzo[a]pyrene； Carp； Kidney； SOD； CAT
Polycyclic aromatic hydrocarbons （PAHs） are a class of common pollutants， which mainly come from the smoke and tail gas produced during the combustion of coal and petroleum and the industrial wastewater of coking and refining， having the carcinogenic， teratogenic and mutagenic characteristics. Through the monitoring of water environment， it could be known that PAHs produce a large quantity of reactive oxygen radicals through oxidation or the oxidation of their intermediate metabolites[1]， thereby causing toxic reactions such as DNA breaking， lipid peroxidation and enzyme inactivation[2]. Benzo[a]pyrene is a typical example of PAHs due to its stable property and strong carcinogenicity[3]. Some studies show that benzo[a]pyrene is a highly active carcinogen， which is not a direct cancerogen， but can acquire carcinogenicity by interacting with the mixed??function oxidase in cytomicrosome. With the increase of benzo[a]pyrene concentration， the occurrence rate of cancer would also be proved， and the incubation period of tumors would also be remarkably shortened. Benzo[a]pyrene not only would induce cancer in animals， but also would result in cancerous tumors in the filial generation， as well as deformity or even death of embryos[4-9].
The antioxidant enzymes in fish mainly include superoxide dismutase （SOD） and catalase （CAT）. SOD is a kind of superoxide radical??scavenging factor naturally existing in organisms， which could convert the hazardous superoxide radical into hydrogen peroxide through above reaction[10]. CAT catalyzes in??vivo waste， hydrogen peroxide， which is decomposed into completely harmless water， thereby reducing the damage to organisms[11]. Kidney is an important organ of organisms， which takes charge of the excretory function in organisms. It could eliminate the final products of protein metabolism and toxins and waste harmful to organisms， so as to regulate body fluid equilibrium and electrolyte acid??base equilibrium. Kidney secretes bioactive substances， and retains water and other useful substances through reabsorption function[12]. The kidneys from fish contain rich antioxidant enzymes， and therefore， the pollution level of water body was described by studying the effects of different concentrations of benzo[a]pyrene on SOD and CAT content in fish kidneys. Currently， there have been many studies on marine fishes[13-14]， while there were few studies on freshwater fish. Carp is a kind of representative freshwater fish. This study was conducted to provide a theoretical basis for the improvement of water environment through the investigation on the effects of benzo[a]pyrene on antioxidant enzymes in carps. Materials and Methods
The experiment was carried out in June 2016， in the Jiangsu Provincial Key Laboratory of Veterinary Bio??pharmaceutical High??tech Research.
Experimental animals
The tested fish was purchased from a fishery free of pollution. The purchased carps were from the same fishpond with an average body mass of （25.16 ??2.15） g. They were sterilized with 5% saline solution and then delivered to the laboratory[15].
Instruments and reagents
Ultraviolet spectrophotometer UV 2000 （Unocal）； refiner ART and benzo[a]pyrene （BaP）， purchased from AccuStandard， America； cosolvent dimethyl sulfoxide （DMSO）， purchased from Amreccr， America； superoxide dismutase （SOD） and catalase （CAT） kit， purchased from Nanjing Jiancheng Bioengineering Institute； other reagents， analytically pure.
Experimental methods
Exposure All the experiment fish was cultured in dechlorinated tap water， which was analyzed for components in it. The results showed that the heavy metals in the water could hardly be monitored， so the water quality could satisfy the survival of carps. After being domesticated for two weeks， the carps were randomly grouped， and each treatment group included four carps. The carps were cultured in a plastic cylinders （100 cm ?? 70 cm ?? 50 cm）， each of which was filled with water according to 200 L/cylinder. The water was exchanged by one half every day， to keep the concentration basically the same. Air was introduced during the experimental period with an air pump. Fodder was input timely every day. The water temperature was basically controlled at about 23 ??. The experiment lasted for 30 d under natural illumination， and the water was exchanged once every 5 d to thoroughly clean the water tanks. Benzo[a]pyrene was dissolved in water， with the addition of cosolvent DMSO as the solubility of benzo[a]pyrene is small. The four treatments were set with the benzo[a]pyrene according to the concentrations of 0， 0.1， 0.5 and 1.0 ??g/L， respectively. Each of the concentration had two replicates， and the control group was only input with DMSO[16].
Sampling and sample treatment The fish was taken out and cut， obtaining the kidneys which were cleaned with pre??cooled 0.9% normal saline. The residual liquid was removed with filter paper， and the kidneys were preserved at -4 ??. During the treatment， the kidneys were added with 0.9% normal saline at a ratio of 1 g?? 10 ml and homogenized. The homogenate was then centrifuged at 4 ?? under 5 000 r/min for about 10 min. The supernatant was removed， and enzyme activity analysis and protein content determination were performed. Each fish served as one independent sample. Determination of enzyme activity
Determination of （SOD） activity The SOD activity was determined by xanthine oxidase[17-18]. The activity of SOD： For 1 mg of the protein in 1 ml of reaction liquid， when the inhibiting rate reaches 50%， the corresponding SOD amount is a nitrite unit （NU）. The SOD activity of carp kidneys was determined with the SOD kit.
The determination principle： Kidney SOD activity A （SOD）/（NU?¤mg） = 2{ （Dcontrol tube-Ddetermination tube）/Dcontrol tube} ?? （Total volume of reaction liquid/Sample amount）/Protein content.
Determination of CAT activity[19] The activity of CAT： The relative amount of hydrogen peroxide as the substrate decomposed by 1 mg of protein in 1 min is one activity unit.
The determination principle： The decomposition of H2O2 by CAT is terminated by adding ammonium molybdate， which reacts with the residual H2O2， producing a kind of flaxen complex， the amount of which was determined at 405 nm， for the calculation of CAT activity.
Determination of protein content
The protein content in each sample was determined by Lowry method， with bovine serum albumin as reference[18].
Data processing
The experimental data was subjected to one??way analysis of variance with SPSS 13.0， and correlation analysis was performed with CORREL.
Results and Analysis
Effect of benzo[a]pyrene on SOD activity in kidneys from carps
The effect of benzo[a]pyrene on SOD activity in kidneys from carps after 30 d is shown in Fig. 1. It could be seen from Fig. 1 that after 30 d of exposure to different concentrations of benzo[a]pyrene， the SOD activity of 0.1， 0.5 and 1.0 ??g/L groups was 6.355 U/mg higher than， 0.415 U/mg lower than and 2.985 U/mg lower than that of the control group， respectively. The CORREL correlation analysis in Excel showed that after exposing carps in water containing different concentrations of benzo[a]pyrene for 30 d， the SOD activity was in negative correlation the concentration of benzo[a]pyrene （r =-0.81）. There was a very significant difference between the 0.1 ??g/L benzo[a]pyrene treatment and the control group （P??0.01）； and there was a significant difference between the 1.0 ??g/L benzo[a]pyrene treatment and the control group （P??0.05）.
Effect of benzo[a]pyrene on CAT activity in kidneys from carps
It could be seen from Fig. 2 that after 30 d of exposure to different concentrations of benzo[a]pyrene， the CAT activity of 0.1， 0.5 and 1.0 ??g/L groups was 1.155 U/mg higher than， 0.993 U/mg lower than and 1.678 U/mg lower than that of the control group， respectively. The CORREL correlation analysis in Excel showed that after exposing carps in water containing different concentrations of benzo[a]pyrene for 30 d， the CAT activity was in negative correlation with the concentration of benzo[a]pyrene （r =-0.92）. There were a significant difference between the 1.0 ??g/L benzo[a]pyrene treatment and the control group （P??0.05）. Discussion
Benzo[a]pyrene belongs to PAH pollutants. It is widely distributed in nature with strong carcinogenicity， and generally serves as a representative environmental carcinogen， as well as a main environmental pollution detection object[1，3].
In the oxidation??reduction process in organisms， a large quantity of reactive oxygen would be produced， and the normal metabolic process of organisms also would produce reactive oxygen， which includes superoxide anion free radical （O-2?¤）， hydroxyl radical （?¤OH） and hydrogen peroxide （H2O2）. Free radical is an important factor for the production of reactive oxygen， but only a few free radicals are necessary for organisms. These free radicals generally serve as the second messenger， which plays an important role in the signal transduction， and is capable of affecting the expression of gene. However， free radicals are very lively， and if they accumulate in vivo excessively and are not scavenged timely， they would attack various biomacromolecules in vivo and induce various physiological disease changes in living body[19]. In the long??term evolutionary process of living organisms， a set of self??protection system capable of defensing outside invasions is formed， i.e.， the antioxidant system， which could scavenge excessive free radicals in living body. The antioxidant enzymes include SOD and CAT[20].
SOD is a kind of very important antioxidant defensive functional enzyme existing in living body. Among the antioxidant enzymes， SOD belongs to primary enzymes， playing an important role in scavenging reactive oxygen[21-22]. Reactive oxygen radicals are normal metabolites in living body. When microorganisms enter organisms， they would be regarded as foreign matters and devoured by phagocytes， resulting in the production of large quantities of superoxide anion radical （O-2?¤）， H2O2， ?¤OH and various derivates. These derivates have very strong oxidability， and could attack most surrounding biomolecules， resulting in the phenomena including protein denaturation， lipid peroxidation and DNA breaking[23]. If they could not be scavenged immediately， they would cause aging， immunity reduction and even death of organisms. However， in??vivo SOD could reacted with hazardous substances to produce H2O2， which as a kind of reactive oxygen in organisms could react with CAT， thereby decomposing the hazardous substances in organism into water[11]. SOD and CAT both could protect organisms from the damage by external substances. Their activity is closely related to the immune level in living body， playing an important role in the improvement of the immunologic function of organisms and the enhancement of immunity function[24]. Under normal conditions， antioxidant protective enzymes constitute a protection system for scavenging reactive oxygen to keep the production and scavenging of reactive oxygen in a dynamic equilibrium， so as to protect organisms from damage[20]. The pollutants in water body are mainly PAHs， and benzo[a]pyrene is a typical one of PAHs[3]. Therefore， in this study， the effects of different concentrations of benzo[a]pyrene on SOD and CAT contents in kidneys from carps were investigated， so as to provide some data for water quality monitoring. According to related researches， in the antioxidant defense system， for the infection against low??concentration pollutants， the activity of enzymes or the content of active substances increase； and when the pollution level increases continuously and damage has been caused to organisms， the activity of antioxidant enzymes and the content of active substances would decrease[25]. The data and conclusions obtained in this study are the same as above. When the benzo[a]pyrene concentration was lower （0.1 ??g/L）， the SOD and CAT activity was higher than that of the control group， and with the increase of the benzo[a]pyrene concentration， the SOD and CAT activity was lower than that of the control group. And the correlation coefficients were -0.81 and -0.92， respectively， indicating that the variation showed a decreasing trend overall， which might be due to that when the foreign matters infect organisms， the antioxidant defense mechanism of organisms is stimulated， resulting in the production of antioxidant enzymes SOD and CAT in large quantities， which scavenge free radicals in vivo， thereby playing the role of protecting organisms. With the infection concentration increases， the antioxidant defense effect of organisms is limited， and the accumulation of reactive oxygen free radicals and the damage to cytomembrane might be caused， and further reduce the healthy level of organisms[19].
Agricultural Biotechnology 2018References
[1] REY??SALGUEIROL R， MARTINEZ??CARBALLOE M， GARCIA??FALCON MS， et al. Survey of polycyclic aromatic hydrocarbons in canned bivalves and investigation of their potential sources[J]. Food Research International， 2009， 42（8）： 983-988.
[2] WINSTON GW. Oxidants and antioxidants in aquatic animal[J]. Comp Biochem Physiol， 1991， 100： 173-176.
[3] HUANG CJ， HU XR， DONG QX. Effects of benzo[a]pyrene antioxidant defense system in tilapia liver[J]. Journal of Shantou University： Natural Science Edition， 2006（4）： 51-56. （in Chinese）
[4] LIU N， SHEN MH. Food toxicology[M]. Beijing： China Light Industry Press， 2007. （in Chinese）
[5] ZHENG RH， WANG CG. Effects of polycyclic aromatic hydrocarbon contaminants on fish??s reproduction function[J]. Taiwan Strait， 2004， 23（2）： 245-252. （in Chinese） [6] DUAN XL， WEI FS. The Environmental pollution caused by benzo （a） pyrene，its harm to health and the research focuses on it[J]. World Sci??Tech R & D， 2002， 24（1）： 11-16. （in Chinese）
[7] WANG GF. Benzopyrene??s harm to human body and its production and control in foods[J]. Journal of Heze University， 2014， 36（2）： 66-70. （in Chinese）
[8] YE M， LIU BC， DU HJ， et al. Benzo（a）pyrene induced changes of cyclin D1， CDK4 and E2F??1/4 expression in human embryo lung fibroblasts[J]. Journal of Hygiene Research， 2006（2）： 135-138. （in Chinese）
[9] WANG JJ， MU Y， SONG GN， et al. Observation and study on the carcinogenic and teratogenic effects of benzopyrene[J]. Chinese Journal of Reproductive Health， 1997（4）： 159-161. （in Chinese）
[10] XU FC. Basic biochemistry[M]. Guangzhou： South China University of Technology Press， 1999： 202-203. （in Chinese）
[11] ZHUANG HS， YANG G. Study on the acute and subacute toxicities of bisphenol a on the carp[J]. Environmental Chemistry， 2005， 24（6） ： 682-684. （in Chinese）
[12] YANG HM， LIU JL. Zoonomy[M]. Beijing： Higher Education Press， 2011. （in Chinese）
[13] WANG CG， CHEN YX， ZHENG WY， et al. Effects of the mixture of benzo[a]pyrene and pyrene exposure on spleen antioxidant defend system in Liza haematocheila[J]. Acta Oceanologica Sinica， 2003， 25 （2）： 135-139. （in Chinese）
[14] PACHECO M， SANTOS MA. Induction of liver EROD and erythrocytic nuclear abnormalities by cyclophosphamide and PAHs in Anguilla anguilla L.[J]. Ecotoxicology and Environmental Safety， 1998， 40（1/2）： 71-76.
[15] SHEN Y， ZHEN FF， REN HQ， et al. The acute toxicity effect of P??NCB to brocarded carp （Cyprinus carpio）[J]. Ecologyand Environmental Sciences， 2007， 16（2）： 407-409. （in Chinese）
[16] BI YJ. Ecological risk assessment of white mud desulfurization wastewater discharging into the sea[D]. Qingdao： Ocean University of China， 2012. （in Chinese）
[17] JI JP. Micro rapid determination method of superoxide dismutase[J]. Journal of Southeast University， 1991， 10（1）： 27-30. （in Chinese）
[18] LI K， ZHOU ZL， CHEN LQ， et al. Assessment of various biomarkers in Carassius auratus exposed to benzo[a]pyrene[J]. Research of Environmental Sciences， 2006（1）： 91-95. （in Chinese）
[19] JIN LH， BAHN JH， EUM WS， et al. Transduction of human catalase mediated by an HIV??1 TAT protein basic domain and arginine??rich peptides into mammalian cells[J]. Free Radical Biology ?? Medicine， 2001， 31（11）： 1509-1519. （in Chinese） [20] ZHANG KF， ZHANG ZP， CHEN Y， et al. Antioxidant defense system in animals[J]. Chinese Journal of Zoology， 2007， 42（2） ： 153-160. （in Chinese）
[21] CHEN JJ， CAO JL， LUO YJ， et al. Effects of fluoride on the activity of immune??related enzymes and IL??1 protein expression in gill of carp （Cyprinus carpio）[J]. Acta Agriculturae Nucleatae Sinica， 2014， 28（6）： 1092-1098. （in Chinese）
[22] HAN ZP， YANG ZH， WU X， et al. Effects of lead stress on antioxidant enzymes activities in Arundo donax Linn.[J]. Acta Agriculturae Nucleatae Sinica， 2010， 24（4）： 846-850. （in Chinese）
[23] IIALL IB， GUTTERID GJMC. Free radicals in biology and mcdicine[M]. Oxford： Clarendon Press， 1989.
[24] WANG Y， HU YB， JIANG NC. Effects of ammonia??N and nitrite??N on immune enzymes of Macrobrachium rosenbergii[J]. Journal of Zhejiang University： Science edition， 2005， 32 （6） ： 698-705. （in Chinese）
[25] LIU J， LIN ZY， WANG KJ. Effects of different concentrations of benzo（a）pyrene on antioxidant enzymes in gastropod abalone， Haliotis diversicolor[J]. Journal of Applied of Oceanography， 2014（4）： 486-491. （in Chinese）
Key words Benzo[a]pyrene； Carp； Kidney； SOD； CAT
Polycyclic aromatic hydrocarbons （PAHs） are a class of common pollutants， which mainly come from the smoke and tail gas produced during the combustion of coal and petroleum and the industrial wastewater of coking and refining， having the carcinogenic， teratogenic and mutagenic characteristics. Through the monitoring of water environment， it could be known that PAHs produce a large quantity of reactive oxygen radicals through oxidation or the oxidation of their intermediate metabolites[1]， thereby causing toxic reactions such as DNA breaking， lipid peroxidation and enzyme inactivation[2]. Benzo[a]pyrene is a typical example of PAHs due to its stable property and strong carcinogenicity[3]. Some studies show that benzo[a]pyrene is a highly active carcinogen， which is not a direct cancerogen， but can acquire carcinogenicity by interacting with the mixed??function oxidase in cytomicrosome. With the increase of benzo[a]pyrene concentration， the occurrence rate of cancer would also be proved， and the incubation period of tumors would also be remarkably shortened. Benzo[a]pyrene not only would induce cancer in animals， but also would result in cancerous tumors in the filial generation， as well as deformity or even death of embryos[4-9].
The antioxidant enzymes in fish mainly include superoxide dismutase （SOD） and catalase （CAT）. SOD is a kind of superoxide radical??scavenging factor naturally existing in organisms， which could convert the hazardous superoxide radical into hydrogen peroxide through above reaction[10]. CAT catalyzes in??vivo waste， hydrogen peroxide， which is decomposed into completely harmless water， thereby reducing the damage to organisms[11]. Kidney is an important organ of organisms， which takes charge of the excretory function in organisms. It could eliminate the final products of protein metabolism and toxins and waste harmful to organisms， so as to regulate body fluid equilibrium and electrolyte acid??base equilibrium. Kidney secretes bioactive substances， and retains water and other useful substances through reabsorption function[12]. The kidneys from fish contain rich antioxidant enzymes， and therefore， the pollution level of water body was described by studying the effects of different concentrations of benzo[a]pyrene on SOD and CAT content in fish kidneys. Currently， there have been many studies on marine fishes[13-14]， while there were few studies on freshwater fish. Carp is a kind of representative freshwater fish. This study was conducted to provide a theoretical basis for the improvement of water environment through the investigation on the effects of benzo[a]pyrene on antioxidant enzymes in carps. Materials and Methods
The experiment was carried out in June 2016， in the Jiangsu Provincial Key Laboratory of Veterinary Bio??pharmaceutical High??tech Research.
Experimental animals
The tested fish was purchased from a fishery free of pollution. The purchased carps were from the same fishpond with an average body mass of （25.16 ??2.15） g. They were sterilized with 5% saline solution and then delivered to the laboratory[15].
Instruments and reagents
Ultraviolet spectrophotometer UV 2000 （Unocal）； refiner ART and benzo[a]pyrene （BaP）， purchased from AccuStandard， America； cosolvent dimethyl sulfoxide （DMSO）， purchased from Amreccr， America； superoxide dismutase （SOD） and catalase （CAT） kit， purchased from Nanjing Jiancheng Bioengineering Institute； other reagents， analytically pure.
Experimental methods
Exposure All the experiment fish was cultured in dechlorinated tap water， which was analyzed for components in it. The results showed that the heavy metals in the water could hardly be monitored， so the water quality could satisfy the survival of carps. After being domesticated for two weeks， the carps were randomly grouped， and each treatment group included four carps. The carps were cultured in a plastic cylinders （100 cm ?? 70 cm ?? 50 cm）， each of which was filled with water according to 200 L/cylinder. The water was exchanged by one half every day， to keep the concentration basically the same. Air was introduced during the experimental period with an air pump. Fodder was input timely every day. The water temperature was basically controlled at about 23 ??. The experiment lasted for 30 d under natural illumination， and the water was exchanged once every 5 d to thoroughly clean the water tanks. Benzo[a]pyrene was dissolved in water， with the addition of cosolvent DMSO as the solubility of benzo[a]pyrene is small. The four treatments were set with the benzo[a]pyrene according to the concentrations of 0， 0.1， 0.5 and 1.0 ??g/L， respectively. Each of the concentration had two replicates， and the control group was only input with DMSO[16].
Sampling and sample treatment The fish was taken out and cut， obtaining the kidneys which were cleaned with pre??cooled 0.9% normal saline. The residual liquid was removed with filter paper， and the kidneys were preserved at -4 ??. During the treatment， the kidneys were added with 0.9% normal saline at a ratio of 1 g?? 10 ml and homogenized. The homogenate was then centrifuged at 4 ?? under 5 000 r/min for about 10 min. The supernatant was removed， and enzyme activity analysis and protein content determination were performed. Each fish served as one independent sample. Determination of enzyme activity
Determination of （SOD） activity The SOD activity was determined by xanthine oxidase[17-18]. The activity of SOD： For 1 mg of the protein in 1 ml of reaction liquid， when the inhibiting rate reaches 50%， the corresponding SOD amount is a nitrite unit （NU）. The SOD activity of carp kidneys was determined with the SOD kit.
The determination principle： Kidney SOD activity A （SOD）/（NU?¤mg） = 2{ （Dcontrol tube-Ddetermination tube）/Dcontrol tube} ?? （Total volume of reaction liquid/Sample amount）/Protein content.
Determination of CAT activity[19] The activity of CAT： The relative amount of hydrogen peroxide as the substrate decomposed by 1 mg of protein in 1 min is one activity unit.
The determination principle： The decomposition of H2O2 by CAT is terminated by adding ammonium molybdate， which reacts with the residual H2O2， producing a kind of flaxen complex， the amount of which was determined at 405 nm， for the calculation of CAT activity.
Determination of protein content
The protein content in each sample was determined by Lowry method， with bovine serum albumin as reference[18].
Data processing
The experimental data was subjected to one??way analysis of variance with SPSS 13.0， and correlation analysis was performed with CORREL.
Results and Analysis
Effect of benzo[a]pyrene on SOD activity in kidneys from carps
The effect of benzo[a]pyrene on SOD activity in kidneys from carps after 30 d is shown in Fig. 1. It could be seen from Fig. 1 that after 30 d of exposure to different concentrations of benzo[a]pyrene， the SOD activity of 0.1， 0.5 and 1.0 ??g/L groups was 6.355 U/mg higher than， 0.415 U/mg lower than and 2.985 U/mg lower than that of the control group， respectively. The CORREL correlation analysis in Excel showed that after exposing carps in water containing different concentrations of benzo[a]pyrene for 30 d， the SOD activity was in negative correlation the concentration of benzo[a]pyrene （r =-0.81）. There was a very significant difference between the 0.1 ??g/L benzo[a]pyrene treatment and the control group （P??0.01）； and there was a significant difference between the 1.0 ??g/L benzo[a]pyrene treatment and the control group （P??0.05）.
Effect of benzo[a]pyrene on CAT activity in kidneys from carps
It could be seen from Fig. 2 that after 30 d of exposure to different concentrations of benzo[a]pyrene， the CAT activity of 0.1， 0.5 and 1.0 ??g/L groups was 1.155 U/mg higher than， 0.993 U/mg lower than and 1.678 U/mg lower than that of the control group， respectively. The CORREL correlation analysis in Excel showed that after exposing carps in water containing different concentrations of benzo[a]pyrene for 30 d， the CAT activity was in negative correlation with the concentration of benzo[a]pyrene （r =-0.92）. There were a significant difference between the 1.0 ??g/L benzo[a]pyrene treatment and the control group （P??0.05）. Discussion
Benzo[a]pyrene belongs to PAH pollutants. It is widely distributed in nature with strong carcinogenicity， and generally serves as a representative environmental carcinogen， as well as a main environmental pollution detection object[1，3].
In the oxidation??reduction process in organisms， a large quantity of reactive oxygen would be produced， and the normal metabolic process of organisms also would produce reactive oxygen， which includes superoxide anion free radical （O-2?¤）， hydroxyl radical （?¤OH） and hydrogen peroxide （H2O2）. Free radical is an important factor for the production of reactive oxygen， but only a few free radicals are necessary for organisms. These free radicals generally serve as the second messenger， which plays an important role in the signal transduction， and is capable of affecting the expression of gene. However， free radicals are very lively， and if they accumulate in vivo excessively and are not scavenged timely， they would attack various biomacromolecules in vivo and induce various physiological disease changes in living body[19]. In the long??term evolutionary process of living organisms， a set of self??protection system capable of defensing outside invasions is formed， i.e.， the antioxidant system， which could scavenge excessive free radicals in living body. The antioxidant enzymes include SOD and CAT[20].
SOD is a kind of very important antioxidant defensive functional enzyme existing in living body. Among the antioxidant enzymes， SOD belongs to primary enzymes， playing an important role in scavenging reactive oxygen[21-22]. Reactive oxygen radicals are normal metabolites in living body. When microorganisms enter organisms， they would be regarded as foreign matters and devoured by phagocytes， resulting in the production of large quantities of superoxide anion radical （O-2?¤）， H2O2， ?¤OH and various derivates. These derivates have very strong oxidability， and could attack most surrounding biomolecules， resulting in the phenomena including protein denaturation， lipid peroxidation and DNA breaking[23]. If they could not be scavenged immediately， they would cause aging， immunity reduction and even death of organisms. However， in??vivo SOD could reacted with hazardous substances to produce H2O2， which as a kind of reactive oxygen in organisms could react with CAT， thereby decomposing the hazardous substances in organism into water[11]. SOD and CAT both could protect organisms from the damage by external substances. Their activity is closely related to the immune level in living body， playing an important role in the improvement of the immunologic function of organisms and the enhancement of immunity function[24]. Under normal conditions， antioxidant protective enzymes constitute a protection system for scavenging reactive oxygen to keep the production and scavenging of reactive oxygen in a dynamic equilibrium， so as to protect organisms from damage[20]. The pollutants in water body are mainly PAHs， and benzo[a]pyrene is a typical one of PAHs[3]. Therefore， in this study， the effects of different concentrations of benzo[a]pyrene on SOD and CAT contents in kidneys from carps were investigated， so as to provide some data for water quality monitoring. According to related researches， in the antioxidant defense system， for the infection against low??concentration pollutants， the activity of enzymes or the content of active substances increase； and when the pollution level increases continuously and damage has been caused to organisms， the activity of antioxidant enzymes and the content of active substances would decrease[25]. The data and conclusions obtained in this study are the same as above. When the benzo[a]pyrene concentration was lower （0.1 ??g/L）， the SOD and CAT activity was higher than that of the control group， and with the increase of the benzo[a]pyrene concentration， the SOD and CAT activity was lower than that of the control group. And the correlation coefficients were -0.81 and -0.92， respectively， indicating that the variation showed a decreasing trend overall， which might be due to that when the foreign matters infect organisms， the antioxidant defense mechanism of organisms is stimulated， resulting in the production of antioxidant enzymes SOD and CAT in large quantities， which scavenge free radicals in vivo， thereby playing the role of protecting organisms. With the infection concentration increases， the antioxidant defense effect of organisms is limited， and the accumulation of reactive oxygen free radicals and the damage to cytomembrane might be caused， and further reduce the healthy level of organisms[19].
Agricultural Biotechnology 2018References
[1] REY??SALGUEIROL R， MARTINEZ??CARBALLOE M， GARCIA??FALCON MS， et al. Survey of polycyclic aromatic hydrocarbons in canned bivalves and investigation of their potential sources[J]. Food Research International， 2009， 42（8）： 983-988.
[2] WINSTON GW. Oxidants and antioxidants in aquatic animal[J]. Comp Biochem Physiol， 1991， 100： 173-176.
[3] HUANG CJ， HU XR， DONG QX. Effects of benzo[a]pyrene antioxidant defense system in tilapia liver[J]. Journal of Shantou University： Natural Science Edition， 2006（4）： 51-56. （in Chinese）
[4] LIU N， SHEN MH. Food toxicology[M]. Beijing： China Light Industry Press， 2007. （in Chinese）
[5] ZHENG RH， WANG CG. Effects of polycyclic aromatic hydrocarbon contaminants on fish??s reproduction function[J]. Taiwan Strait， 2004， 23（2）： 245-252. （in Chinese） [6] DUAN XL， WEI FS. The Environmental pollution caused by benzo （a） pyrene，its harm to health and the research focuses on it[J]. World Sci??Tech R & D， 2002， 24（1）： 11-16. （in Chinese）
[7] WANG GF. Benzopyrene??s harm to human body and its production and control in foods[J]. Journal of Heze University， 2014， 36（2）： 66-70. （in Chinese）
[8] YE M， LIU BC， DU HJ， et al. Benzo（a）pyrene induced changes of cyclin D1， CDK4 and E2F??1/4 expression in human embryo lung fibroblasts[J]. Journal of Hygiene Research， 2006（2）： 135-138. （in Chinese）
[9] WANG JJ， MU Y， SONG GN， et al. Observation and study on the carcinogenic and teratogenic effects of benzopyrene[J]. Chinese Journal of Reproductive Health， 1997（4）： 159-161. （in Chinese）
[10] XU FC. Basic biochemistry[M]. Guangzhou： South China University of Technology Press， 1999： 202-203. （in Chinese）
[11] ZHUANG HS， YANG G. Study on the acute and subacute toxicities of bisphenol a on the carp[J]. Environmental Chemistry， 2005， 24（6） ： 682-684. （in Chinese）
[12] YANG HM， LIU JL. Zoonomy[M]. Beijing： Higher Education Press， 2011. （in Chinese）
[13] WANG CG， CHEN YX， ZHENG WY， et al. Effects of the mixture of benzo[a]pyrene and pyrene exposure on spleen antioxidant defend system in Liza haematocheila[J]. Acta Oceanologica Sinica， 2003， 25 （2）： 135-139. （in Chinese）
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