Reactive oxygen spices play a critical role in the death and survival of diseases. Previous in vivo studies have documented that excessive endogenous Elastase causes pulmonary emphysema through inflammation and oxidative stress (17–19). In this regard, current in vitro study identified the oxidative stress signaling pathway of Elastase to induce cell injuries in pulmonary epithelial cells. The results of the present study showed that Elastase decreased the gene expression of OXR1, P21, Nrf2, HO1, and NQO1 in a concentration-dependent manner which was associated with decreases in antioxidant enzymes activity and content.
Reactive oxygen spices (ROS) and other non-radical oxygen derivatives, as by-products of metabolism, are constantly generated in biological systems and cause damage to DNA, proteins, and lipids (20). The biological antioxidant defense system effectively neutralized oxidative stress by preventing free radicals-mediated organ damage (21).
OXR1 is identifying as a key regulator in resistance against the pathology of diseases which discovered first as an essential factor for inhibition of oxidative stress damage in eukaryotes organs 20 years ago (22). A study by Volkert et al. in 2000 reported that OXR1 depletion in Saccharomyces cerevisiae enhanced sensitivity to H2O2injuries (5).
Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and cyclin-dependent kinase inhibitor 1A (P21) known as crucial factors for regulating ROS levels by controlling downstream antioxidant enzymes. Indeed, subsequently to oxidative stress, Nrf2 activation leads to upregulation of several antioxidant genes, including the Heme oxygenase-1 (HO-1), and NADH quinone oxidoreductase 1 (NQO1) (23). According to a study by Yang et al. in 2014, the OXR1 gene through controlling the gene expression level of P21 (as an activator of Nrf2 protein) has a key role in the antioxidant defense system which supports the hypothesis that OXR1 protect against oxidative stress damage via P21-Nrf2-HO1-NQO1 dependent manner (5). In this context, the results of the current experiment demonstrated that Elastase exposure caused to decreases in the antioxidant defense system which was showed by the lower levels of SOD, CAT, GPx activity, and GSH content. The upstream regulator's genes evaluation also revealed the downregulation of OXR1-related genes which suggested the cytotoxicity effects of Elastase on lung epithelial cells through destruction of the antioxidant protection system.
Oxidative stress process seems to be involved in the pathology of emphysema process (24). As expected, in the current study the data showed a significant increase in oxidative stress biomarkers including reactive oxygen and nitrogen species (ROS/RNS) content and Malondialdehyde in response to Elastase exposure. Accordingly, it seems to antioxidant management can be considered in preventing and controlling of this destructive process. In recent years, there is a growing focus on natural antioxidants, with remarkable cytoprotective properties against cell injuries induced by oxidative stress. Ellagic acid is a polyphenolic compound found in green tea and other natural sources such as pomegranate, strawberry, raspberry, and eucalyptus bark. Ellagic acid has potent antioxidant and anti-apoptotic properties that can inhibit or prevent cellular oxidation. Ellagic acid reduces oxidative stress by scavenging free radicals and increases the antioxidant enzymes (25–27). Treatment with 10 µmol/L Ellagic acid for 24 hours demonstrated the inhibition effects against oxidative stress induced by Elastase which showed by increases in OXR1-P21-Nrf2-HO1-NQO1 genes expression and antioxidant factors including SOD, GPx, GSH and TAC. These data suggest the potent antioxidant properties of this natural antioxidant.
In this regard, Rozentsvit et al. in the experimental study on the antioxidant effects of Ellagic acid, reported that Ellagic acid significantly diminishes free radical levels and attenuates the impairment of oxidative stress induced by high glucose medium (28). Another in vitro study by Te-Mao et al. on human bladder cancer cells showed that Ellagic acid causes to cell cycle arrest and apoptosis through P53/P21 genes expression-depended mechanism (29). These reported data are in line with the results of the current study on the positive antioxidant properties of Ellagic acid against Elastase-induced oxidative damage.
In conclusion, the present findings can highlight the novel mechanism underlying the oxidative stress induces by Elastase through OXR1 and related genes. Moreover, the benefit of Ellagic acid on cytoprotection, resulting from its antioxidant properties was documented. However, further molecular and cellular studies on the cytoprotective activity of Ellagic acid are necessary.