The present study found that puerarin was the most abundant isoflavone in kudzu vine extract. In vitro experiments on human liver-derived HepG2 cells showed that kudzu vine extract had cytoprotective and antioxidant properties. In vivo experiments on rats showed that 0 % and 30 % kudzu vine ethanolic extracts significantly reduced hepatic damage (as measured by increase in ALT and AST) and hepatic lipid peroxidation (as measured by increase in MDA), and 30 % kudzu vine extract caused a significant increase in the antioxidant GSH.
Liver disease remains one of the most serious health problems worldwide. The liver is the main organ that metabolizes xenobiotics to help eliminate waste from the body; hence, the liver is exposed to a high concentration of chemicals, drugs, and natural products, which can lead to liver dysfunction, cell injury, and organ failure . More than 100 human diseases, including liver diseases, are related to oxidative stress .
Herbal plants have recently gained attention as potential treatments for cancers, metabolic diseases, allergies, ischemia, and inflammation, and especially for their hepatoprotective activities. Most commonly, these hepatoprotective activities seem to be related to the antioxidant capacity of these plants. Naturally derived antioxidants counteract the oxidative stress induced by many hepatotoxins . The quest to discover such naturally occurring antioxidants has become a major scientific focus over the past few decades. The antioxidant activities of isoflavones have been associated with the hepatoprotective effect of these compounds. Plant-derived isoflavone compounds are thought to contribute to the prevention of diseases associated with oxidative stress .
Kudzu root is a rich source of isoflavone glucosides. Common isoflavones of kudzu root include puerarin (daidzein 8-C-glucoside), daidzin (daidzein 7-O-glucoside), daidzein, genistein and formononetin . These isoflavones have been associated with antioxidant, hepatoprotective and other pharmacological effects [23, 24]. Among the isoflavones in kudzu root, puerarin is the most abundant (approximately 23% w/w) and has attracted considerable attention because of its potent ability to cause various pharmacological effects . A previous study found that puerarin was the most abundant isoflavone contained in the kudzu vine (nearly 50%), followed by daidzin (3.58%), daidzein (0.92%), genistein (0.03%) and other isoflavones (0.5%) ; these results are consistent with the present study. Unlike kudzu root, the beneficial actions of kudzu vine against liver disease have not been extensively investigated.
In the present study, we investigated the antioxidant activity and the hepatoprotective effect of kudzu vine extract. t-BHP was used to induce hepatotoxicity in the HepG2 cell line. The cell viability and inhibition of ROS generation was then examined in vitro. All concentrations of kudzu vine extract significantly protected the cell from dying and inhibited the ROS production in a dose-dependent manner. There was a clear correlation between the ratio of protection and the level of antioxidant activity provided by kudzu treatment. ROS production from cells occurs via multiple mechanisms. Large numbers of oxygen free radicals are produced within the liver during the removal of xenobiotics and toxins, and oxidative stress caused by ROS has been linked to various liver diseases [12, 20, 25]. In comparison with normal cells, malignant cells seem to remain functional under higher levels of endogenous oxidative stress in vitro and in vivo [12, 26, 27].
We also used CCl4 to induce hepatotoxicity in rats. CCl4 is actively converted by cytochrome P-450, especially CYP2E1, in the liver tissues to its highly reactive trichloromethyl free radical CCl3.. The CCl3. radical reacts with cellular macromolecular protein and polyunsaturated fatty acids [12, 13] in the presence of molecular oxygen, it forms more toxic trichloromethylperoxyl radicals CCl3O along with H2O2, O2−, and OH [28, 29]. So, CCl4 is conventionally used to induce liver toxicity, to allow the testing of drugs for their hepatoprotective property. The CCl4 treatment elevates the levels of plasma enzymes ALT and AST, which are indicators of cellular leakage and loss of functional integrity of cell membranes in the liver [30, 31]. The activities of ALT and AST were significantly suppressed after the administration of kudzu vine extracts in the present study. This suggests that kudzu vine extract effectively protected hepatocytes against the toxic effects of CCl4, resulting in a reduction in plasma ALT and AST levels in CCl4-treated rats.
An increase in MDA levels, as seen in our study after CCl4 administration, indicates enhancement of lipid peroxidation, leading to tissue damage and failure of antioxidant defence mechanisms to prevent the formation of excessive free radicals [16, 28, 30]. Significant reductions in hepatic lipid peroxidation were detected only in the water and 30 % kudzu vine ethanolic extract-treated groups. There were no significant changes observed in the 70 % and 95 % kudzu vine ethanolic extract-treated groups. Changes in MDA levels and plasma AST and ALT levels displayed the same trends.
GSH was reduced in the liver of CCl4-treated rats, while an increased GSH level was observed in conjunction with the administration of 30 % ethanol-derived kudzu vine extract. GSH is a highly effective extra- and intra-cellular antioxidant compound that plays a central role in coordinating the body’s antioxidant defence processes . GSH protects cells against electrophilic attack from xenobiotics such as free radicals and peroxides [28, 29, 32].
Our results suggest that the potent radical scavenging activity of kudzu vine extracts ameliorates oxidative stress and terminates the chain reaction involved in lipid peroxidation. Therefore, the hepatoprotective effect of kudzu vine extract is mainly due to its ability to neutralize the increase of free radicals caused by chemicals. The potency of hepatoprotective activity in high concentration ethanolic extracts was lower than that of the low concentration ethanolic extracts in the rat model studied, indicating that the amount and kind of ingredients may vary depending on the extraction conditions. Further study into the underlying cause of these differences is needed.