Different health-related deleterious effects are associated with BPA exposure in living organisms, with BPA showing that endocrine-disrupting chemicals induce oxidative stress (Singh et al. 2016; Meli et al. 2020). BPA induces oxidative stress by generating reactive oxygen species (ROS) through the generation of free radicals, and thereby causes an imbalance between ROS and antioxidant defenses which then results in oxidative damage (Kobroob et al. 2018; Amjad et al. 2020). The hepatotoxic effect of BPA was established in this study as demonstrated with a significant (p < 0.05) increase in the activities of ALP, AST, and ALT, and a concomitant decrease in total protein and albumin in BPA-exposed chicks. This is in line with the study carried out by Oguazu et al. (2015) and Abdel-Gwaad et al. (2020) as they reported an increase in ALT, AST, and AST which indicates hepatotoxicity action of BPA. Naringin is an example of a flavonoid that has been reported to possess several pharmacological effects such as anti-inflammatory, hypolipidemic, antioxidant, antiviral, antimicrobial, anti- apoptotic, hepatoprotective, and immunomodulatory effects (Changxing et al. 2018).
Hepatoprotective activities were observed in the naringin-treated groups as there was a significant decrease in ALT, AST, and ALP and a corresponding increase in total protein. This corroborated the earlier study of Imam et al. (2016) who reported that co-administration of naringin with aluminum ameliorated aluminum-induced liver damage and oxidative stress. Furthermore, the levels of TC, TAG, and LDL-c were significantly (p < 0.05) higher in BPA intoxicated chicks with a concurrent decrease in HDL-c as observed in the present study. This agreed with the findings of Eweda et al. (2020) who reported that BPA induced dyslipidemic state and increased triglycerides (steatosis) and cholesterol accumulation in the liver tissue of rat. Marmugi et al. (2012) also reported that the exposure of rat to BPA resulted in hypertriglyceridemia, hypercholesterolemia, and alterations of fatty acids composition in the liver. More so, there was upregulation of genes which are linked with de novo lipogenesis and cholesterol synthesis in the liver. Kumar et al. (2019) reported that treatment with naringin produced noteworthy developments in altered lipid profiles. The anti-hyperlipidemic effect of naringin was established in this study as naringin reversed the toxicity of BPA by decreasing LDL-c, TC, TG, and increasing HDL-c in chicks treated naringin.
The scavenging and neutralization of free radicals such as superoxide radicals, hydrogen peroxides (H2O2), and hydroperoxides are done by antioxidants, thereby preventing oxidation reactions. During oxidative stress, free radicals increase in the body (Amjad et al. 2020). This study showed an increase in H2O2 contents in the liver of BPA-exposed chicks. This was in concordance with the study of da Silva et al. (2018) who reported an exaggerated increase H2O2 generation in thyrocytes of female Wistar rats intoxicated with BPA. More so, Kabuto et al. (2003) observed that BPA caused the overproduction of H2O2 with resultant oxidative stress. In our study, naringin reduced the level of H2O2 in groups treated BPA-treated chicks and naringin-only treated groups. The antioxidant and free radical scavenging power of naringin was earlier reported by Rashmi et al. (2018) who showed the H2O2 radical scavenging potential of naringin in streptozotocin-induced liver damage. Also, Miles and Calder (2021) reported that naringin increased liver and kidney expression of anti-inflammatory transcription factors.
In this study, the increase in the level of MDA caused lipid peroxidation because of BPA-induced oxidative stress as earlier reported by Kobroob et al. (2018) and Eweda et al. (2020). Lipid peroxidation of biological membranes is known to cause loss of membrane fluidity, increases membrane permeability, alters receptor function, and changes in membrane potential. It can be observed in this study that the MDA level was exaggerated in the liver of BPA intoxicated chickens. However, in this study, the group co-treated with naringin caused a significant (p < 0.05) reduction in the MDA level, as previously reported by Rajadurai and Stanely (2006) & Alam et al. (2014).
Glutathione (GSH) is one of the non-enzymatic antioxidants that is depleted during oxidative stress. In this study, a decreased level of GSH was observed in the liver in the BPA-exposed chicks, which depicts ongoing oxidative stress caused by BPA toxicity. Kobroob et al. (2018) reported a decrease in GSH in rats exposed to BPA. However, the co-treated with naringin showed improvements in the activities of GSH. This supports the study of Kumar et al. (2019) who stated that administration of naringin to diabetic rats raised the concentration of GSH. The GPx, SOD, and GST are known to protect tissues from damage caused by oxidative stress by detoxification of several substrates generated from cellular oxidative processes (Sravani et al. 2016). The GPx activity in the liver increased in the BPA-exposed chicks in this study, and this might be a result of the adaptive response. We proposed that this could be a result of nuclear translocation of nuclear erythroid-related factor 2 (Nrf2). The first step is the modification of the keap1 segment of Nrf2-Keap1 pathway. Nrf2 is usually low when it is not activated by stress factors. In the presence of ROS such as superoxide, hydroxyl, and peroxyl radicals, cysteine residues (such as Cys 151) are oxidized the sulfhydryl groups on the Keap1 segment. This changes the conformity of Keap1 segment and prevents it from attaching to Nrf2. The Nrf2 released within the cytosol enters the nucleus and heterodimerize with small Maf proteins, and further binds to regulatory gene recognized as antioxidant response elements (ARE). Substances that can initiate activity at the ARE include environmental pollutants, hydrogen peroxide and nitric oxide. The Nrf2-Maf-ARE complex then initiates subsequent specific antioxidant and detoxification genes such as that of GST, GPx, GSH and SOD; thereby, increasing antioxidant activities and inactivating ROS (Baird and Dinkova-Kostova 2011; Oyagbemi et al. 2017). The antioxidant effect of naringin was established as naringin restored the levels of GSH, GST, GPX, and SOD in the hepatic tissue of BPA-exposed chicks.
TNF-α is an example of a pro-inflammatory cytokine, which plays a significant role in the host’s defense against injury. It was stated that BPA toxicity exacerbated the proinflammatory cytokines expression along with interleukins such as IL-1β, IL-6, IL-8, and tumor necrosis factor alpha (TNF-α) as previously reported (Wang et al. 2019; Meli et al. 2020). This is in agreement with this present study as there was noticeable higher expression of TNF-α in the liver of the BPA-exposed chicks compared to the control and naringin-treated chicks. Naringin has been reported to possess a hepatoprotective effect by regulating inflammatory cytokines and increasing antioxidant enzymes (Caglayan et al. 2018). This study establishes that naringin reduces the expression of TNF-α in birds co-administered with naringin and BPA. Caspase-3 is a biomarker of cell death. In this study, there was an increase expression of caspase-3 in the liver of BPA intoxicated chicks. This showed that hepatic apoptosis might have resulted from inflammation and oxidative stress following BPA toxicity (Abdel-Rahman et al. 2018; Liu et al. 2022). This is in tandem with the work of Elgawish and Abdelrazek (2014) where increase in expression of caspase-3 in testes of male rats exposed to lead acetate was observed. The anti-apoptotic effect of naringin was exhibited in the BPA group co-treated with naringin and naringin treated groups by cleaving caspase-3 and inhibiting the genes and proteins involved in apoptotic pathways such as P53, P 16INK 49 (Yuan and Yang 2022).