Aqueous extract of Terminalia arjuna prevents carbon tetrachloride induced hepatic and renal disorders
© Manna et al; licensee BioMed Central Ltd. 2006
Received: 12 June 2006
Accepted: 30 September 2006
Published: 30 September 2006
Carbon tetrachloride (CCl4) is a well-known hepatotoxin and exposure to this chemical is known to induce oxidative stress and causes liver injury by the formation of free radicals. Acute and chronic renal damage are also very common pathophysiologic disturbances caused by CCl4. The present study has been conducted to evaluate the protective role of the aqueous extract of the bark of Termnalia arjuna (TA), an important Indian medicinal plant widely used in the preparation of ayurvedic formulations, on CCl4 induced oxidative stress and resultant dysfunction in the livers and kidneys of mice.
Animals were pretreated with the aqueous extract of TA (50 mg/kg body weight) for one week and then challenged with CCl4 (1 ml/kg body weight) in liquid paraffin (1:1, v/v) for 2 days. Serum marker enzymes, namely, glutamate pyruvate transaminase (GPT) and alkaline phosphatase (ALP) were estimated in the sera of all study groups. Antioxidant status in both the liver and kidney tissues were estimated by determining the activities of the antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST); as well as by determining the levels of thiobarbutaric acid reactive substances (TBARS) and reduced glutathione (GSH). In addition, free radical scavenging activity of the extract was determined from its DPPH radical quenching ability.
Results showed that CCl4 caused a marked rise in serum levels of GPT and ALP. TBARS level was also increased significantly whereas GSH, SOD, CAT and GST levels were decreased in the liver and kidney tissue homogenates of CCl4 treated mice. Aqueous extract of TA successfully prevented the alterations of these effects in the experimental animals. Data also showed that the extract possessed strong free radical scavenging activity comparable to that of vitamin C.
Our study demonstrated that the aqueous extract of the bark of TA could protect the liver and kidney tissues against CCl4-induced oxidative stress probably by increasing antioxidative defense activities.
Exposure to various organic compounds including a number of environmental pollutants and drugs can cause cellular damages through metabolic activation of those compounds to highly reactive substances such as reactive oxygen species (ROS). Free radical induced lipid peroxidation is believed to be one of the major causes of cell membrane damage leading to a number of pathological situations [1–3]. Reports from our laboratory and other investigators have established that the industrial solvent, carbon tetrachloride (CCl4) is a potent environmental hepatotoxin [4–7]. A number of recent reports clearly demonstrated that in addition to hepatic problems, CCl4 also causes disorders in kidneys, lungs, testis and brain as well as in blood by generating free radicals [8–11]. Reports from Perez et al, Ogeturk et al and Churchill et al suggested that exposure to this solvent causes acute and chronic renal injuries [12–14]. In addition, reports on various documented case studies established that CCl4 produces renal diseases in humans [15, 16]. Extensive evidence demonstrated that .CCl3 and .Cl are formed as a result of the metabolic activation of CCl4, which in turn, initiate lipid peroxidation process. A known potent antioxidant, vitamin E, could protect CCl4 induced liver injury indicating that oxidative stress is responsible for CCl4 induced hepatic disorder in this particular model [17, 18]. Studies also showed that various herbal extracts could protect organs against CCl4 induced oxidative stress by altering the levels of increased lipid peroxidation, and enhancing the decreased activities of antioxidant enzymes, like superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) as well as enhanced the decreased level of the hepatic reduced glutathione (GSH) [19, 20]. Knowledge on the protective mechanisms against toxin and drug induced organ-toxicities leads scientists to look for biologically active relevant compounds from herbal plants, which can possess intrinsic antioxidant activity and protect those organs from unwanted oxidative stress. In the modern medicine, plants occupy a significant birth as raw materials for some important drug preparations [21–23]. India is well known for a plethora of medicinal plants. The traditional Indian medicinal plants act as antiradicals and DNA cleavage protectors . These plants have also been considered to protect health, longevity, intelligence, immunosurveillance and body resistance against different infections and diseases. Tephrosia purpurea , Silybum marianum , Picrorhiza kurroa , Cajanus indicus [28, 29], Phyllanthus niruri [30–32], etc. posses hepatoprotective property against different toxins and drugs induced hepatic disorders. Terminalia arjuna (TA) is also an important medicinal plant widely used in the preparation of ayurvedic formulations for over three centuries primarily as a cardiac tonic in India . Clinical evaluation of this plant indicates that it can be of benefit in the treatment of coronary artery diseases, heart failure and possibly hypercholesterolemia [34–36]. It has also been found to be antibacterial and antimutagenic [37–39]. However, most of the beneficial works on this plant have been carried out on the alcoholic extract of its bark and very little is known about its role on toxin-induced either hepatic or renal disorders. In this particular study, protective role of aqueous extract of the bark of TA was evaluated against CCl4-induced toxicity in the liver and kidney. Firstly, the radical scavenging activity of the extract was determined from its 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical quenching ability and the data were compared to those obtained from a known free radical scavenger, vitamin C. Secondly, the dose- and time-dependent effects of the extract against CCl4-induced toxicity were evaluated by measuring the levels of the serum marker enzymes, glutamate pyruvate transaminase (GPT) followed by determining its effect on another serum marker enzyme, alkaline phosphatase (ALP) using optimum dose and time. Finally, hepatic and renal oxidant-antioxidant status was evaluated by measuring the levels of a) antioxidant enzymes SOD, CAT and GST; b) ROS scavenger GSH and c) extent of lipid peroxidation in both the livers as well as the kidneys in mice. In addition, study on the effect of a known antioxidant, vitamin E, was also included against CCl4 induced hepatic and renal oxidative stress.
Terminalia arjuna (TA), belonging to the family Combretaceae, has a long history of medicinal uses in India. It is a shade and ornamental tree. The bark of the tree is useful as an anti-ischemic and cardioprotective agent in hypertension and in ischemic heart disease. The bark was collected from local markets.
Swiss albino mice (male, body weight 20 ± 2 g) were acclimatized under laboratory condition for a fortnight before starting experiments. They were provided with standard diet and water ad libitum. The animals were divided into four groups, each group having six mice.
Bradford reagent, bovine serum albumin (BSA), DPPH, and protein estimation kit were purchased from Sigma-Aldrich Chemical Company, (St. Louis, MO) USA. CCl4, 1-chloro-2,4-dinitrobenzene (CDNB), 5,5'-dithiobis(2-nitrobenzoic acid) [DTNB, (Ellman's reagent)], disodium hydrogen phosphate (Na2HPO4), ethylene diamine tetraacetic acid (EDTA), glacial acetic acid, hydrogen peroxide (H2O2), nicotinamide adenine dinucleotide reduced (NADH), nitro blue tetrazolium (NBT), phenazine methosulphate (PMT), potassium dihydrogen phosphate (KH2PO4), reduced glutathione (GSH), sodium dihydrogen phosphate (NaH2PO4), sodium pyrophosphate, trichloro acetic acid (TCA), thiobarbituric acid (TBA), vitamin C, vitamin E were bought from Sisco research laboratory, India.
Preparation of aqueous extract of TA
The bark of TA was cut into pieces and was homogenized in 50 mM sodium phosphate buffer; pH 7.2, at 4°C and the homogenate was centrifuged at 12,000 g for 30 minutes to get rid of unwanted debris. The supernatant was dialyzed against ice-cold water and centrifuged again under the same condition. The supernatant was collected and lyophilized. The freeze-dried material was weighed, dissolved in the same phosphate buffer and used for this study.
Determination of radical scavenger activity in cell-free system
Quenching of DPPH radical
The radical scavenger activity of the aqueous TA extract was measured spectrophotometrically using the DPPH radical . Aqueous TA extract at various concentrations were added to DPPH in methanol (125 μM, 2 ml) solution. The final volume was adjusted to 4 ml with water. The solution was shaken and incubated at 37°C for 30 minutes in the dark. The decrease in absorbance of DPPH was measured at 517 nm. Percent inhibition was calculated by comparing the absorbance values of the control and the extract. A parallel experiment was carried out under the same conditions in which TA extract was replaced by vitamin C and used as a positive control.
Determination of dose-dependent effect of the extract
To determine the dose of the TA extract necessary for the maximum hepatic and renal protection, six different groups of mice were separately treated with six different doses of the extract – 1 mg, 5 mg, 10 mg, 25 mg, 50 mg and 100 mg/kg body weight for 7 days prior to CCl4 treatment (in liquid paraffin 1:1, v/v) for 2 days at a dose of 1 ml/kg body weight. Twenty-four hours after the final dose of CCl4 administration, all mice were sacrificed. The GPT levels were measured from the blood sera of all the experimental animals.
Determination of time-dependent effect of the extract
To determine the time needed for the TA extract to exhibit maximum hepatic and renal protection, six different groups of mice were separately treated with the extract at a dose of 50 mg/kg body weight for 1, 3, 5, 7 and 10 days prior to CCl4 (1 ml/kg body weight) intoxication. Twenty-four hours after the final dose of CCl4 administration, all experimental mice were sacrificed, blood samples were collected and the GPT levels were measured.
Pre-treatment with the aqueous extract of TA
The pretreatment group was divided into three sub-groups each consisted of six mice. The first group served as normal control. The second group received CCl4 orally (1 ml/kg body weight) for 2 days and treated as toxin control. The third group received the aqueous TA extract for 7 days (50 mg/kg body weight) orally followed by CCl4 treatment at a dose of 1 ml/kg body weight for 2 days. Mice were sacrificed after 24 hours of the final dose of CCl4 administration and blood, livers and kidneys were collected. For the positive control vitamin E (200 mg/kg body weight) was administered orally to a group of 6 mice for 7 days followed by CCl4 administration as described earlier.
Preparation of liver and kidney homogenates
About 200 mg of liver and kidney tissue were homogenized separately in 10 volume of 100 mM KH2PO4 buffer containing 1 mM EDTA, pH 7.4 and centrifuged at 12,000 g for 30 minutes at 4°C. The supernatant was collected and used for following experiments as described below. Protein concentration of the supernatant was measured according to the method of Bradford  using crystalline BSA as standard.
Assessment of serum specific markers enzymes
Blood samples collected from puncturing mice hearts were kept overnight for clotting and then centrifuged at 3,000 g for 10 minutes. GPT and ALP levels in all the sample sera were estimated by the methods of Rietman and Frankel  and Kind and King  respectively.
Assay of antioxidant enzymes in the liver and kidney homogenates
The activity of SOD was measured following the method of Nishikimi  and then modified by Kakkar . About 5 μg total protein from each of the liver and kidney homogenates were mixed with sodium pyrophosphate buffer, PMT and NBT. The reaction was started by the addition of NADH. The reaction mixture was incubated at 30°C for 90 seconds and stopped by the addition of 1 ml of glacial acetic acid. The absorbance of the chromogen formed was measured at 560 nm. One unit of SOD activity is defined as the enzyme concentration required for the inhibition of chromogen production by 50% in one minute under the assay conditions.
The enzyme CAT catalyzes the conversion of H2O2 into water. The CAT activity was measured by the method of Bonaventura . About 5 μg protein from the liver and kidney homogenates were mixed with 2.1 ml of 7.5 mM H2O2 and the reaction was allowed to continue for 10 minutes at 25°C. The disappearance of peroxide was continuously recorded from the absorbance at 240 nm for the specified period of time. One unit of CAT activity is defined as the amount of enzyme necessary for reducing1 μmol of H2O2 per minute.
GST catalyzes the conjugation reaction with glutathione in the first step of mercapturic acid synthesis. GST activity was measured by the method of Habig and Jakoby . The reaction mixture contained suitable amount of the enzyme (25 μg of protein in homogenates), KH2PO4 buffer, EDTA, CDNB and GSH. The reaction was carried out at 37°C and monitored spectrophotometrically by the increase in absorbance of the conjugate of GSH and CDNB at 340 nm. A blank was run in absence of the enzyme. One unit of GST activity is 1 μmol product formation per minute.
Assay of non-enzymatic antioxidant in the liver and kidney homogenates
GSH level was measured by the method of Ellman . The homogenate (720 μl) was double diluted and 5% TCA was added to it to precipitate the protein content of the homogenate. After centrifugation (10,000 g for 5 minutes) the supernatant was taken, DTNB solution (Ellman's reagent) was added to it and the absorbance was measured at 412 nm. A standard graph was drawn using different concentrations of a standard GSH solution (1 mg/ml). With the help of the standard graph, GSH contents in the liver and kidney homogenates of the experimental animals were calculated.
Estimation of lipid peroxidation products
Degree of lipid peroxidation in the liver and kidney tissue homogenates of all the experimental animals was determined in terms of thiobarbituric acid reactive substances (TBARS) formation . The sample containing1 mg protein was mixed with 1 ml TCA (20%), 2 ml TBA (0.67%) and heated for 1 hour at 100°C. After cooling, the precipitate was removed by centrifugation. The absorbance of the sample was measured at 535 nm using a blank containing all the reagents except the tissue homogenate. As 99% of the TBARS is malondialdehyde (MDA), TBARS concentrations of the samples were calculated using the extinction co-efficient of MDA, which is 1.56 × 105 M-1cm-1.
All the values are represented as mean ± S.D. (n = 6). Data on biochemical investigations were analyzed using analysis of variance (ANOVA) and the group means were compared by Duncan's Multiple Range Test (DMRT). A probability of p < 0.05 was considered as significant.
Effect of the aqueous TA extract on radical scavenger activity in cell-free system
Dose-dependent preventive activity of the aqueous TA extract
Time-dependent preventive activity of the aqueous TA extract
Effect of the aqueous TA extract on ALP level
Effect of the aqueous TA extract on SOD activity
Effect of the aqueous TA extract on CAT activity
Effect of the aqueous TA extract on GST activity
Effect of the aqueous TA extract on GSH level
Effect of the aqueous TA extract on lipid peroxidation
Present study was conducted to evaluate the protective effect of the aqueous extract of TA against CCl4 induced hepatic and renal disorders in mice. Results suggest that the extract possesses protective action against both hepatic and renal dysfunctions induced by the potent toxin, CCl4. Data showed that the extract responds in both dose- and time-dependent manner. Maximum protective activity of the extract was obtained when administered once daily at a dose of 50 mg/kg body weight for 7 days before toxin administration as revealed from the figures 2 and 3. This dose and time have been followed for the subsequent studies.
A number of chemicals including various environmental toxicants and clinically useful drugs can cause severe cellular damages in different organs of our body through the metabolic activation to highly reactive substances such as free radicals. CCl4 is one of such extensively studied environmental toxicant. The reactive metabolite trichloromethyl radical (.CCl3) has been formed from the metabolic conversion of CCl4 by cytochrome P-450 . As O2 tension rises, a greater fraction of .CCl3 present in the system reacts very rapidly with O2 and many orders of magnitude more reactive free radical, CCl3OO. has been generated from .CCl3 . These free radicals initiate the peroxidation of membrane poly-unsaturated fatty acids (PUFA) , generates PUFA. and covalently bind to microsomal lipids and proteins . This phenomenon results in the generation of ROS, (like the superoxide anion O2-, H2O2 and the hydroxyl radical, .OH). Evidence suggests that various enzymatic and non-enzymatic systems have been developed by the cell to cope up with the ROS and other free radicals. However, when a condition of oxidative stress establishes, the defense capacities against ROS becomes insufficient . ROS also affects the antioxidant defense mechanisms, reduces the intracellular concentration of GSH and decreases the activity of SOD and CAT. It has also been known to decrease the detoxification system produced by GST . Increasing evidence indicates that oxidative stress causes organ injury and carcinogenesis .
In the present study, it has been observed that CCl4 induced a significant elevation of the levels of serum marker enzymes, GPT and ALP. In addition, this potent toxicant caused significant decrease in SOD, CAT and GST activities, depleted the GSH content and enhanced lipid peroxidation in both liver and kidney. We also determined the levels of the markers related to renal damages. However, under the present experimental conditions (1 ml/kg body weight for 2 days), there was no change in either the urea nitrogen or creatinine (non protein nitrogen) in the serum of CCl4intoxicated animals. Besides, we did not find any change in the creatinine level in the urine of the experimental animals (data not shown) as well. The exact reason for this is not clearly known. One possibility is that, the time of CCl4 exposure to the animals was not enough for the renal damage although oxidative stress could be induced by that exposure. Tirkey et al  have recently conducted experiments to determine the effect of CCl4 on the renal damages in rats and obtained similar results.
It has been reported that SOD, CAT and GST constitute a mutually supportive team of defense against ROS [58, 59]. The decreased activity of SOD in liver and kidney in CCl4 treated mice may be due to the enhanced lipid peroxidation or inactivation of the antioxidative enzymes. This would cause an increased accumulation of superoxide radicals, which could further stimulate lipid peroxidation. GST binds to liophilic compounds and acts as an enzyme for GSH conjugation reactions . Decrease in GSH activity during CCl4 toxicity might be due to the decreased availability of GSH resulted during the enhanced lipid peroxidation. Administration of the aqueous extract of TA prior to CCl4 intoxication could not only prevent the CCl4 induced increased levels of serum marker enzymes GPT and ALP, but also protected the antioxidant machineries of the liver and kidney as revealed from the enhanced levels of SOD, CAT and GST activities, increased level of GSH content and decreased level of lipid peroxidation. Besides, the extract showed radical scavenging activity by reacting with DPPH and this scavenging activity is comparable to that of a potent free radical scavenger, vitamin C in cell free system.
In the liver, CCl4 is metabolized by the cytochrome P450-dependent monooxygenase systems followed by its conversion to more chemically active form, trichloromethyl radical (.CCl3) . The enzymes involved in this process are located in the endoplasmic reticulum of the liver and their activities are dependent on many environmental factors. Some herbal extracts are known to prevent the oxidative damages in different organs by altering the levels of cytochrome P-450 through their antioxidant properties . Our results suggest that the aqueous extract of the bark of TA possesses potent antioxidative activity and protects liver and kidney against CCl4 induced oxidative stress probably via the alteration of cytochrome P-450.
Combining all, we would like to say that the aqueous extract of TA protects liver and kidney tissues against oxidative damages and could be used as an effective protector against CCl4 induced hepatic and renal damages. Further works are needed to fully characterize the responsible active principle(s) present in the plant and elucidate its possible mode of action and that is in progress.
The work has partly been supported by the Department of Atomic Energy (DAE), Government of India (a Grant-In-Aid to PCS, Sanction No. 2002/37/35/BRNS/2065). PM acknowledges the receipt of a UGC ad-hoc fellowship. MS acknowledges the receipt of financial support from DAE. The authors are grateful to the Director of Bose Institute for providing the laboratory facilities and Mr. Prasanta Pal for excellent technical assistance for the study.
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