A variety of different organic products can be produced by pyrolysis reactions of biomass at high temperature (Mathew et al., 2015). Therefore, the composition of WV is complex. Many studies have indicated that WV is rich in phenolic compounds (Ma et al., 2011), which endows WV with antioxidant capacity (Yang et al., 2016) as well as scavenging radical capacity (Loo et al., 2007). Free radicals can destroy lipids, proteins and DNA through oxidative damage (Pietta, 2000). Therefore, there is a desire to discover natural compounds that can remove reactive oxygen species and have strong scavenging capacity. The scavenging effects of WV are in the order of superoxide anion radical > diphenyl bitter acyl radicals > hydroxyl radical (Wei et al., 2010). Our previous research showed that WV significantly decreases superoxide radical contents and the IC50 value was 18.306 mg/mL (Wang et al., 2020). WV is therefore more effective at scavenging O2− radicals than DPPH or •OH radicals.
These results indicate that WV could potentially be a natural antioxidant and relieve oxidative stress (Wei et al., 2010; Cai et al., 2012). However, there are no reports on the effect of WV on antioxidant enzyme activities in freshwater organisms. MDA and antioxidant enzymes activities indicate levels of oxidative stress and redox in organisms, and both are impacted by PFOA (Stahl et al., 2011; Yuan, et al., 2017). In this study, lipid peroxidation was alleviated by application or co-application of WV. SOD activities showed a significant change at the same time. H2O2 produced in the process of SOD catalysis can be removed by CAT (Xu et al., 2013). CAT activities decreased with PFOA exposure of 1 to 10 days. These results indicate that PFOA destroyed the antioxidant enzyme system. However, CAT activities were increased in WV and co-application groups, indicating that WV attenuated the inhibition of PFOA and activated enzyme activities.
GPx can increase the content of GSH, and then GSH can inhibit lipid peroxidation and reduce the content of MDA (Feng et al., 2015; Stockwell et al., 2017). However, the activity of GPx was inhibited by PFOA in our study, leading to an increase in MDA content. At the same time, WV activated enzyme activities and attenuated the inhibition of PFOA in WV co-application groups. GST is involved in detoxification in cells. In our study, GST activities were increased in all treatment groups with WV or PFOA. Changes in GST activities may be due to the toxicity of PFOA and complex chemical constituents of WV. Therefore, alteration of GST activities indicates that PFOA and WV affected oxidative stress-related processes in planarians. GR maintains the reduced status of glutathione (GSH) in cells. PFOA treatment resulted in oxidative stress and inhibited GR activities. WV, as a free radical scavenger, may have elevated levels of GSH and improved tolerance to PFOA by activating GR activities in WV co-application groups.
COX, MAO and SDH are localized to the mitochondrial membrane. PFOA induces dysregulation resulting in oxidative stress (Yuan et al., 2016). COX binds to the mitochondrial membrane and participates in electron transfer (Srinivasan and Avadhani, 2012). PFOA and WV increase the activities of COX. These changes in enzymatic activities may be due to mitochondrial dysfunction caused by PFOA (Huang et al., 2013). WV probably increased the activities of COX because it is rich in organic acids and participates in the pumping out of protons. MAO is a key enzyme in the outer mitochondrial membrane and plays a role in amine metabolism (Lisa et al., 2009). In this study, MAO activities were significantly activated at first and then inhibited by PFOA, implying that MAO activities increased due to PFOA stress and then decreased as a result of tolerance to PFOA. Because WV is an acid liquid, it can increase MAO enzyme activity. The activity of SDH is closely related to the function of mitochondria. In this study, increase in SDH activity indicated that mitochondrial function was increased under PFOA tress. By contrast, WV decreased SDH activity. This may have been due to antioxidant activities of WV. In general, the above experimental results show that WV functions in biochemical protection of planarians.
We determined DNA damage using comet assays after exposure of planarians to PFOA or WV. PFOA exerts genotoxic effects on paramecium (Kawamoto et al., 2010), HepG2 cells (Wielsøe et al., 2015) and humans (Franken et al., 2017) through DNA oxidative damage caused by intracellular reactive oxygen species. WV reduced the olive tail moment and DNA in the tail (%), thus alleviating DNA damage caused by PFOA. The alleviating effects of WV may be closely related to its free radical scavenging abilities. The mechanism of free radical scavenging abilities of WV in planarians remains to be further studied. We observed significant effects on gpx, gst and gr gene expression by treatment with PFOA or WV. Changes in gpx expression were consistent with changes in enzyme activities. There was a trend of gene expression being down-regulated by PFOA treatment and then up-regulated. WV stabilized gpx expression to protect planarians against oxidative stress. gst mRNA expression was down-regulated and then up-regulated following co-application of PFOA and WV. These results showed that gst is involved in alleviating stress caused by PFOA through detoxification. Our experimental data showed that GR activities and gr expression levels were inhibited under PFOA stress at the beginning of the experiment. Moreover, gr gene expression was significantly increased in groups administered WV but maintained a similar trend to that in the control group. However, the regulation of gene expression needs further research due to the complex components of WV.