CCl4 when administrated is distributed and deposited to organs such as the liver, brain, kidney, lung and heart . The reactive metabolite trichloromethyl radical (•CCl3) and trichloromethyl peroxide radical (CCl3O2•) 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 more reactive free radicals, like CCl3OO• is generated from •CCl3. These free radicals initiate the peroxidation of membrane poly unsaturated fatty acids (PUFA), cell necrosis, GSH depletion, membrane damage and loss of antioxidant enzyme activity.
In this experimental study we investigated the protective effect of aqueous extract of Podophyllum hexandrum Free radicals e.g. superoxide radical, hydrogen peroxide and hydroxyl radical, from both endogenous and exogenous sources, are implicated in the etiology of several degenerative diseases, such as coronary artery disease, stroke, rheumatoid arthritis, diabetes and cancer . High consumption of fruits and vegetables is associated with low risk for these diseases, which is attributed to the antioxidant vitamins and other phytochemicals [23, 24]. The extent of initial damage caused by free radicals is further amplified by Fenton reaction generated hydroxyl radicals in the presence of superoxide and hydrogen peroxide . Thus, the redox state and concentration of iron ions in the cellular milieu plays a crucial role in amplification of damage  as they interact with membranes to generate alkoxyl and peroxyl radicals, thereby inflicting further damage to the cellular system .
Superoxide is biologically important since it can be decomposed to form stronger oxidative species such as singlet oxygen and hydroxyl radicals, which are very harmful to the cellular components in a biological system . Superoxide radical is generated from O2 by multiple pathways [29, 30]. Using NBT assay system to generate superoxide radical, dose dependent inhibition was observed in the increasing concentration of Podophyllum hexandrum rhizome aqueous extract indicating its potential to possess scavenging properties.
Hydrogen peroxide itself is not very reactive, but it can give highly reactive species •OH radical through Fenton reaction . Earlier reports suggest that H2O2 could induce DNA break in the intact cell and purified DNA . The H2O2-scavenging activity of Podophyllum hexandrum aqueous extract and the standard BHT increased in a dose dependent manner. With comparable results observed at highest concentration. Similar results were reported by Duh  for Chrysanthemum morifolium with high relationship between phenolic content and scavenging activity of the aqueous extracts on hydrogen peroxide. As previously reported by Chaudhary et al., that Podophyllum hexandrum possess strong antioxidant activity against superoxide and hydroxyl radical under in vitro conditions . Chawla et al., have also established the antioxidant potential of different extracts of Podophyllum hexandrum .
The level of kidney and lung MDA in CCl4 treated group was significantly higher than the control group. The increase in MDA level in both the tissues suggests enhanced peroxidation leading to tissue damage and failure of the antioxidant mechanisms to prevent the production of excessive free radicals. Our previous results have shown that ethanolic extract of Podophyllum hexandrum possess strong hepatoprotective activity against CCl4 induced damage in albino rats . Similar results were previously reported in kidney by Ogeturk  and liver tissues by Yang  and Melin , which stated that CCl4 metabolized by cytochrome p-450 generates a highly reactive free radical, and initiates lipid peroxidation of the cell membrane of the endoplasmic reticulum and causes a chain reaction. These reactive oxygen species can cause oxidative damage in DNA, proteins and lipids. However pretreatment of Podophyllum hexandrum extract in this study significantly prevent CCl4-induced lipid peroxidation in kidney and lung tissue. Our results are in conformation to the already published report by Padma and Setty  that administration of aqueous extract of Phyllanthus fraternus significantly decreased the carbon tetrachloride induced lipid peroxidation in different organs of rats under in vivo conditions.
GSH as we know is involved in several defense processes against oxidative damage protects cells against free radicals, peroxides and other toxic compounds . Indeed, glutathione depletion increases the sensitivity of cells to various aggressions and also has several metabolic effects. It is widely known that a deficiency of GSH within living organisms can lead to tissue disorder and injury . In our study, the kidney and lung GSH level in CCl4 treated group was significantly decreased compared with control group. Likewise we  and others, Ohta , reported a significant decrease in the GSH content in different organs of rats, when injected with CCl4. Pretreatment however, with Podophyllum hexandrum aqueous extract increased GSH level as compared with CCl4 groups and thus affording protection. The antioxidant effects are likely to be mediated by the restoration of CCl4 induced decreased SOD, GR, GPx and GST activities in various tissues of rats. Treatment of rats with Podophyllum hexandrum aqueous extract significantly increased rat lung and kidney SOD, GR, GST and GPx activities. Tirkey  have recently conducted experiments to determine the effect of CCl4 on the renal damages in rats and obtained similar results. All these enzymes are major free radical scavenging enzymes that have shown to be reduced in a number of pathophysiological processes and diseases such as diabetes . Thus, activation of these enzymes by the administration of Podophyllum hexandrum aqueous extract clearly shows that Podophyllum through its free radical scavenging activity could exert a beneficial action against pathophysiological alterations caused by the presence of superoxide, hydrogen peroxide and hydroxyl radicals.