The results of GC-MS identified 39 compounds and the major compounds were 9-Octadecenamide, (Z)- which is belonging to amide compounds, and Eucalyptol which is belonging to monoterpenoid. In this concern, Baj et al. (2013) isolated 37 compounds from the essential oil from sage leaves grown in Poland, most of them belong to monoterpenoids. Moreover, Mohamed and Mustafa (2019) in Sudan identified 42 compounds and the main compound was α-terpineol followed by camphor, α-pinene, camphene, and β-cymen. Additionally, Abu-Darwish et al. (2013) isolated 25 compounds. The major compounds were oxygen-containing monoterpenes including 1,8-cineole and camphor. The HPLC analysis of the water extract of S. Officinalis revealed that this plant is rich in polyphenols and the majorities were coumaric, chlorogenic, coffeic, gallic, and ellagic acids, catechin, vanillin, and rutin. It was reported that the major phytochemicals in S. Officinalis are alkaloids, fatty acids, carbohydrate, glycosidic derivatives such as flavonoid glycosides, saponins, and cardiac glycosides as well as phenolic compounds such as tannins and coumarins, steroids, polyacetylenes, terpenes, and terpenoids such as sesquiterpenoids, terpenoids (mono-, di-, and tri-) and some waxes (Badiee et al. 2012; El Hadri et al. 2010). Moreover, these phytochemicals were mainly isolated from the essential oil, aqueous and methanolic extracts (Ghorbani and Esmaeilizadeh 2017). The differences in the chemical composition between the current results and the previous data may be due to several environmental factors such as water availability, climate, and altitude (Russo et al. 2013).
Cd as an environmental pollutant can enter the food chain via different routes and induces severe adverse health effects to the vital organs in humans (Bernhoft 2013). International organizations such as WHO and ATSDR have grouped Cd as the most hazardous chemicals (Andjelkovic et al. 2019) which harm the liver and kidney (Andjelkovic et al. 2019; Rani et al. 2014). Additionally, S. Officinalis is well-documented in traditional medicine around the globe for its beneficial effects. Its bioactive ingredients have been extensively studied and reviewed by various extraction techniques (Jakovljević et al. 2019). Nowadays, many research studies have been conducted to find new biological effects for this plant. In this study, we evaluated the role and the mechanism (s) of action of SOE against Cd intoxication in a rat model. The selected doses of Cd and the extract were literature-based (El-Kady et al. 2009; Arabi et al. 2014, respectively).
Our results showed that Cd alone administration induced a loss of body weight and a significant elevation in liver and kidney indices, NO, cholesterol, triglycerides, LDL, serum cytokines, hepatic and renal MDA, mRNA expression of Bax accompanied by a significant decrease in HDL, hepatic and renal antioxidant enzymes and their mRNA gene expression. The decrease in body weight and the elevation of ALT and AST in intoxicated rats reported herein is similar to that reported previously and indicated that the reduction of body weight is mainly owing to the detrimental effect on liver function (Padilla et al. 2010). The serum ALT and AST are involving in the catabolism of the amino acids and the production of bile so, these enzymes acting as critical biomarkers of liver function. The increase in these transaminases in the serum indicated the leakage of these enzymes into the bloodstream due to the severe damage of the membrane of the hepatocyte (Hall and Cash 2012; Kang et al. 2013). Moreover, the decrease in Alb and TP indicated the increase in excretion of high molecular mass protein (Genchi et al. 2020). The elevation of creatinine, uric acid, and urea reported in our study agreed with Borges et al. (2008). Although the increase of urea is considered the first marker in kidney dysfunction, creatinine is the most trustable marker and it rises if the kidneys suffer any damaging insult. In this concern, Hussein et al. (2014) reported that the pathological changes in the renal tissue include significant increases in serum urea and creatinine in rats exposed to Cd. The disturbances in lipid profile in Cd-treated rats suggested that this element generates oxidative stress which disturbs the balance between antioxidant and pro-oxidant resulting in the damage of cell function and unfavorable biological reactions leading to dyslipidemia (Olisekodiaka et al. 2012). Similar outcomes were reported by several authors and indicated an increase in cholesterol, triglycerides, and LDL levels in rats exposed to Cd (Badisa et al. 2007; Genchi et al. 2020; Murugavel and Pari 2007).
Several reports indicated that the hepatotoxicity of Cd was attributed mainly ROS generation, protein, lipid peroxidation, and inflammation since the main mode of action of this metal is the generation of ROS and the diminish of the antioxidant defense system (SOD, CAT, GSH, and GPx) (Andjelkovic et al. 2019; Rahimzadeh et al. 2017). The generation of ROS including hydroxyl, hydrogen peroxide, and superoxide radicals modulate different components in the cell components mainly protein, lipids, and carbohydrates leading to the discrepancy of the metabolic dysfunction and cell integrity (Kaur et al. 2020). Moreover, MDA is a well-known player of lipid peroxide, whose malignant activities lead to injury to parenchymal cells (Andjelkovic et al. 2019) and its forms interfere with many biomolecules such as DNA, acetaldehyde, and the advanced glycation end products that comprise cell integrity (Li et al. 2015). Taken together, the elevation of liver and kidney indices and the oxidative markers (NO and MDA) along with the diminution of the hepatic and renal antioxidant enzymes suggesting that Cd exposure promotes the early oxidative damage leading to the development of consequential pathological conditions owing to its prolonged retention in different tissues (Abdel-Aziem et al. 2011; Renugadevi and Milton Prabu 2010; Winiarska-Mieczan 2018).
The elevation of serum cytokine levels in rats treated with Cd in our study is in agreement with previous reports (Bonaventura et al. 2017; Markiewicz-Górka et al. 2019). These results suggested that exposure to Cd stimulates the cytokines production leading to cellular immune response disorders and all of these disturbances are consequences of the oxidative damage of Cd (Bonaventura et al. 2017; Turley et al. 2019). These results also confirmed that Cd affects the macrophages M1-type which is accountable for the inflammatory response via the releasing of the pro-inflammatory cytokines (Saqib et al. 2018). Furthermore, TNF-α is a cytokine produced by activated macrophages in response to pathogens and other harmful stimuli and is a necessary factor for local and systemic inflammation (Kany et al. 2019). In addition, TNF-α amplifies and prolongs the inflammatory reactions by triggering other cells to release cytokines such as IL-1β and media such as NO and ROS, all of which promote further inflammation and tissue damage (Elkhadragy et al. 2017; Alghasham et al. 2013).
Additionally, the disturbances in mRNA expression of the pro-apoptotic gene (Bax), anti-apoptotic gene (Bcl-2), and the antioxidant enzymes (CAT, GPx, and SOD) along with the elevation of DNA fragmentation confirmed the hypothesis that the mechanism of Cd induces its toxicity via oxidative damage as suggested previously (Abdel-Aziem et al. 2011; Zhu et al. 2020; Mężyńska et al. 2018; Genchi et al. 2020). The pathological changes in the liver and kidney reported herein were also in accordance with the previous reports who indicated that Cd exposure induces severe histological alterations in these organs and others and all of these changes resulted from the oxidative damage of this element (El-Kady et al. 2009; Satarug, 2018; Zhu et al. 2020).
In current results, administration of SOE alleviated and/or prevent the hazards of Cd. Animals who received SOE alone did not significantly affect the biochemical parameters, gene expression, or histology of the liver and kidney. The protective role of SOE is primarily due to the antioxidant and radical savaging properties of the bioactive constitutes in the extract. The highest content of these bioactive compounds and polyphenols gave this extract a great advantage in the therapy of several diseases resulted from several environmental toxins which have oxidative damage to living organisms. Natural antioxidants are well known to protect cells against the overproduction of ROS, consequently, counteract oxidative stress-mediated cells and tissue damage.
Previous reports indicated that SOE has a potent antioxidant activity and increases the resistance of the liver against oxidative damage (Horvẚthovẚ et al. 2016; Kolac et al. 2017; Poulios et al. 2020). It protects against oxidative and DNA damage through the elevation of glutathione peroxidase activity (Kozics et al. 2013). In our study, we found that SO essential oil is rich in 9-octadecenamide and other fatty acids which were reported to have strong antioxidant activity (Aktumsek et al. 2013; Olaoluwa et al. 2018; Nengroo and Rauf 2019; Karimi et al. 2015). Moreover, the extract is rich in polyphenols mainly coumaric, chlorogenic, catechin, ellagic, and gallic acids, vanillin, naringenin, and rutin which are well-known antioxidants. Godarzi et al. (2020) reported that coumaric acid protects the kidneys against ischemia-reperfusion (I/R) injury through its antioxidants and anti-inflammatory effects and exhibited hepatoprotective efficiency via the inhibition of lipid peroxidation, the generation of intracellular ROS, and the upregulation of the detoxifying enzymes (Shen et al. 2019). Chlorogenic and coffeic acids also were reported to possess antioxidants and prevent ROS-induced DNA damage (Tomac et al. 2020).
Additionally, it was reported that catechins exert antioxidant activity via different direct and indirect mechanisms including chelating metal ions, scavenging ROS, enhancing the antioxidant enzymes, suppressing the pro-oxidant enzymes, inducing the enzymes of phase II detoxification and the antioxidant enzymes (Ping-Hsiao et al. 2007; Bernatoniene and Kopustinskiene 2018). Vanillin also was reported to exhibit stronger antioxidant effects than Trolox and modulates the intracellular antioxidant activity such as SOD, CAT, and GSH-Px (Zhao et al. 2017). The high concentration of ellagic and gallic acids reported herein in SOE supports the previous findings of Jasicka-Misiak et al. (2018) and Zhang et al. (2014) who reported that SOE possesses a potent antioxidant activity because of its high content of ellagic and gallic acids. In the same concern, naringenin and rutin exert a potential antioxidant effect through the control of the effectors' mechanisms of ROS generation (Nishimura et al. 2013). Taken together, antioxidant and radical scavenging activities of SOE are due to the high content of bioactive compounds and polyphenols which were able to counteract the oxidative damage of Cd and protect DNA, protein, and lipid damage in rats. Moreover, the high dose was more effective against Cd-induced oxidative damage, genotoxicity than the low dose due to the higher content of these bioactive constitutes.