Effect of vitamins E + C and taurine on the oxidative state of DNA in the liver of growing pigs *

Growing pigs (n=21) at an initial liveweight of 30 kg were divided into three groups of 7 animals each and housed in individual cages for 100 days. The pigs were fed with similar diets (13.5 MJ ME and 178 g crude protein/kg) but with different additions of vitamins C+E and taurine. The antioxidative vitamins E and C supplied to diets with high energy concentrations (containing lard) can act as pro-oxidants on liver DNA in growing pigs. Taurine decreased the concentration of products from nucleotide oxidation, but in the presence of vitamin E and C, promoted hepatocyte lesions.


INTRODUCTION
A high concentration of energy and protein in the diet can enhance the rate of energy metabolism, activity of electron transport in the mitochondrial respiratory chain and cause an increase in the synthesis of Reactive Oxygen Species (ROS) (Weindruch, 2002).ROS enhance the destruction of lipids, proteins, carbohydrates and DNA.Oxidative DNA damage leads to formation of 8-oxo-2deoxyguanosine, an adduct that occurs in DNA and causes mutagenesis (Helbock et al., 1998).Vitamin E prevents lipid peroxidation while vitamin C reduces the tocopheryl radical to its active form, tocopherol.It can be expected that a complex antioxidative system requires an antioxidant affiliated with DNA and therefore taurine, mainly taurine's amino group, which is strongly associated with DNA, can be one of the potential antioxidative agents protecting DNA.However, 52 YITAMINS E+C AND TAURINE-PICS LIYER DNA unlimited supply of antioxidants can activate pro-oxidative processes resulting in an imbalance in redox homeostasis.The objective of this study was to determine the effects of vitamins E and C and taurine on the oxidative state of DNA in relation to antioxidative/oxidative indicators of redox homeostasis in growing pigs as a model for humans.
At the end of the experiment the animals were fasted for 12 h and blood was sampled from the heart.Thiobarbituric acid reactive substances (TBARS) were measured with 1.2.3.3-tetraethoxypropane(TEP) as the standard by a colorimetric method.Activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were analysed by Randox Laboratories Ltd. kits at 37°C in a COBAS FARA II analyser.8-oxo-2'-deoxyguanosine (8-oxo-dG) and 2'-deoxyguanosine were determined using a Dionex HPLC with electrochemical (at 350 mV) and UV (at 254 nm) detectors and a 250x4.6 mm Supelcosil LC-18-S column (5pm grain).The amount of 8-oxo-dG in DNA was calculated as the number of 8-oxo-dG mołecules/10 6 unmodified dG molecules.Albumin, total bilirubin, glucose, asparagine transferase (AST) and alaninę transferase (ALT) were determined using Vitros DT II (Johnson and Johnson, USA).
The results were subjected to statistical analysis by monofactorial ANOVAand Duncan's rangę test, using the Statgraphic 4.1 Plus software package.

RESULTS AND DISCUSION
The addition of antioxidants increased the activity of SOD.This enzyme catalyses the dismutation of the superoxide radical (0~2) which is produced by single electron reduction of oxygen, especially in the mitochondrial respiratory chain (Sohal et al., 1995).Dietary antioxidants support the system of defence against ROS in cells, which could lead to SOD protection.
Serum albumins belong to major antioxidants.The elevated serum albumin concentrations and decreased NO', concentrations in pigs receiving antioxidants may suggest that the degradation of the celi structure was associated with the water phase and thereby protecting a protein fraction.However, feeding diets supplemented with antioxidants E and C (group II) significantly affected the oxidations of 2-deoxyguanosine (dG) at the C-8 position, which led to an increased concentration of 8-oxodG in liver DNA.These results confirm earlier results (Niemiec and Sawosz, 2004) regarding the pro-oxidative function of vitamin C in rats.Vitamin C can increase generation of °OH in a superoxide anion-driven, redox active Fe 2+ catalysed, Fenton reaction.DNA is highly resistant to O 2 or H 2 0 2 , while sensitive to the hydroxyl radical (OH).However, it is likely that reduced transition metal ions, mainly Fe (II) and Cu (II) can inhibit the activities of 8-oxo-2'deoxyguanosine 5'triphosphate pyrophospho-hydrolase (8-oxo-dGTPase), (Kasprzak et al., 1999).This enzyme termed an antimutagenic, "sanitizes" the cellular nucleotide pool (Mo et al., 1992) and prevents incorporation of 8-oxo-dG into DNA.The presence of 8-oxodG in the DNA template was observed in liver disease (Kitada et al., 2001) and may stimulate mutagenesis and cancerogenesis (Shibutani et al., 1991).
The addition of taurine (Group III) could counteract the negative effects of vitamin C because the concentration of 8-oxodG in liver DNA was significantly lower than in Group II, and was similar to Group I.The aminę group of taurine has a high affinity to DNA.Redmond et al. (1998) demonstrated that taurine protected DNA against ROS generated by respiratory bursts in neutrophils.However, the activities of ALT and total bilirubin in the serum of pigs receiving vitamins E+C and taurine (Group III) increased, which may be indicative of hepatocyte lesions.

CONCLUSIONS
Antioxidative vitamins E and C supplied to diets with a high concentration of energy (containing lard) can act as pro-oxidants on DNA in growing pigs.However, taurine decreases the concentration of oxidative stress-related compounds involving products from nucleotide oxidation, but in the presence of vitamins E and C may contribute to liver damage.