Several xenobiotics promote toxicity in the heart due to its very high energetic metabolic rate and its lowest antioxidant levels when compared to other organs (Costa et al., 2013). The present work reports, for the first time, the harmful impacts induced by maneb exposure on the redox status and fatty acids profile in the heart of mice, and their alleviation by sodium selenite administration via the diet.
Analysis of organ weight in toxicological studies is an important factor in the assessment of the potential harmful effects of xenobiotics (Nirogi et al., 2014). In this regard, our study demonstrated that both absolute and relative heart weights increased significantly in maneb-exposed mice, when compared to those of the control animals. Nevertheless, their body weight was not changed. The heart hypertrophy could be attributed to the structural changes recorded in the cardiac tissue, showing several cytoplasmic vacuolizations of cardiomyocytes, as indicates the microscopic examination of the heart sections of maneb-treated mice (Fig. 4, B). Our findings were consistent with the previous results obtained by Li et al. (2003), who have associated intracytoplasmic vacuolization with an increase in the liver weight of rats euthanized with CO2 gas. On the other hand, we have noted, for the first time, a significant rise in the appetite of Se-treated mice (both MB + Se and Se groups), objectified with a significant rise in their food intake. Our data agreed with a previous report of Soudani et al. (2011), where an increase in food intake has been shown in rats exposed to K2Cr2O7, co-administered with a selenium supplemented diet. The increase of food intake, noticed in the current study, might be due to the ability of selenium to induce hyperphagia, as reported earlier by Bunk and Combs (1980) in selenium deficient chickens, receiving a diet supplemented with this trace element.
Plasma lipid profile was another criterion investigated to evaluate the influence of maneb on the cardiac function. Our results showed that, in comparison with the control group, maneb treatment enhanced the concentration of TC, TG and LDL-C in plasma; and reduced that of HDL-C. Such changes might indicate the ability of this fungicide to alter the lipid metabolism and induce myocardial disorders. Moreover, maneb treatment elevated the AI and the atherosclerotic indexes (TC/HDL-C and LDL-C/HDL-C), which are considered as central indicators of cardiovascular complications, as reported by Chaâbane et al. (2016) in rats exposed to another fungicide, penconazole. Supplementation of Se in the diet of maneb-exposed mice modulated the changes produced in the plamsa lipid profile. This shows the beneficial effect of this essential mineral in regulating lipid metabolism, probably through inducing antioxidant enzymes’ activities and glutathione level, as reported previously by El-Demerdash and Nasr (2014) in diazinon-induced hyperlipidemic rats.
It has been demonstrated that maneb-induced cellular toxicity is mediated through the stimulation of ROS generation leading to oxidative stress in several tissues (Sefi et al., 2019; 2020). Following maneb exposure, we noted an increase in the cardiac levels of hydrogen peroxide (H2O2), probably resulting from a mitochondrial dysfunction. The metal-catalyzed conversion of H2O2, through Fenton or Haber-Weiss reactions, yields the hydroxyl radical (HO.), a powerful oxidant which can alter lipids through initiating the lipid peroxidation process (Lane, 2002). This fact was supported in the current study by a pronounced rise in MDA content following maneb treatment. Similar observations have been noted after imazalil treatment of mice (Jin et al., 2018). Thus, the increase in MDA level could be due to maneb-induced free radicals’ formation and reduced antioxidant defense system resulting in LPO, as reported by our previous studies (Sefi et al., 2019; 2020). The improvement of MDA and H2O2 levels after Se supplementation via the diet of maneb-treated mice could reflect the antioxidant potential of this trace element and its capacity to protect tissues integrity and function.
Lipids are known to be the major biomolecules affected by free radicals or reactive oxygen species (ROS) attacks. In this regard, the LPO process consists in an oxidative degradation of PUFA, the main components of biological membranes (Gutteridge and Halliwell, 2000). Thus, this could alter cell membrane fatty acids composition. So, our study focused on assessing the effects of maneb toxicity on fatty acids profile in the heart of mice. Saturated fatty acid (SFA) levels in control as well as MB-treated groups showed a same profile. Meanwhile, PUFA levels were modified in maneb-treated mice. A decrease in the levels of total PUFA, total n-3 PUFA as well as DHA and EPA was detected in MB-treated group, which might alter cardiomyocytes function resulting probably from their oxidation by the process of lipid peroxidation, as reported by Song and Miyazawa (2001) in patulin-treated mice. Despite a non-significant decrease in the level of total n-6 PUFA was observed in our study, the content of eicosadienoic acid (C20:2 \(\omega 6)\) significantly (P < 0.01) dropped in the heart of maneb-exposed mice, reflecting a higher risk of inflammation. Indeed, this fatty acid is directly connected to the pro-inflammatory cytokines IL-6 and IL-10 (Muralidharan et al., 2019). Eicosadienoic acid is suggested to have the potential to attenuate the pro-inflammatory effects of linoleic acid (LA), which was increased in the current study, lowering thereby the risk of inflammation (Huang et al., 2011). A significant reduction in the ratio of unsaturated to saturated fatty acids (PUFA/SFA ratio) was noted in the heart of maneb-exposed mice as a result of the produced changes in fatty acids profile. This reflects a decrease of membrane fluidity as reported by Komidori et al. (1985) in uremic hemodialyzed patients and by Mills et al. (1995) in human erythrocytes. Furthermore, MB induced a substantial rise in MUFA levels, objectified by a significant rise of cis-vaccenic (C18:1) and palmitoleic (C16:1) acids. Also, the ratio of MUFA to PUFA increased in maneb-treated mice. Such modifications were explained by the activation of the defensive mechanisms in order to preserve the stability of lipid membrane (Assies et al., 2014). The significant decrease of heart MDA and H2O2 levels, as a result of Se supplementation, might explain the improvement of fatty acids alterations in MB + Se group.
Proteins may also be affected by ROS causing the impairment of their structure and the loss of the enzymatic activity. In this regard, the current study showed a significant elevation of protein carbonyl (PCO) content in the cardiac tissue of MB group, which indicated protein oxidation induced by maneb exposure. Interestingly, Se supplementation to the diet of maneb-intoxicated mice exhibited a protective role, as it reduced the PCO levels. According to Reddy et al. (2009), the anti-oxidative effect of this trace element may result from its capacity to counteract the harmful effects caused by ROS, offering thereby a significant protection to the proteins against oxidative modification.
Biochemical parameters in the blood provided important information about cardiotoxicity induced by maneb. In fact, CK and LDH plasma activities are the biomarkers commonly employed to evaluate the extent of myocardial damage as reported by Dugbartey et al. (2016). LDH activity, a good indicator of heart injury, has been estimated for myocardial necrosis (Lee and Goldman, 1986). As for CK, this enzyme is considered as a biomarker of environmental stress (Li et al., 2010). It catalyzes the conversion of creatine and consumes adenosine triphosphate (ATP) to create phosphocreatine and adenosine diphosphate (ADP). The amounts of these enzymes in the blood reflect the modulation in plasma membrane integrity and/or permeability. In the current study, maneb induced a significant rise in the plasma activities of LDH and CK leading to a myocardial injury. The enhanced release of these intracellular enzymes from the cardiac cells into the bloodstream might be ascribed to an excessive generation of ROS following maneb exposure. According to Omole et al. (2018), rats’ treatment with the drug cyclophosphamide, another cardiotoxic agent, compromises the integrity and function of myocardial membranes through triggering LPO. Co-treatment with Se significantly reduced plasma LDH and CK activities. The beneficial effect of Se may be attributed to its ability to counteract the LPO process, which leads to plasma membrane stabilization and prevents the leakage of cardiac enzymes.
The cells have diverse antioxidant defense mechanisms to attenuate oxidative insults and repair the impaired macromolecules. As part of the total antioxidant system, non-enzymatic antioxidants, like GSH and vitamin C, play a crucial role in overcoming oxidative damage. GSH is an important tripeptide with a thiol group. It is a potent free radicals’ scavenger with cardioprotective effects (Manna et al., 2008). Vitamin C is a water-soluble antioxidant which can neutralize directly free radicals (Molyneux et al., 2002). In the present work, the cardiac levels of GSH and vitamin C were significantly decreased as a result of maneb exposure, which could be due to their consumption in fungicide detoxification. Supplementation of Se via the diet was found to increase the levels of these non-enzymatic antioxidants in the heart tissue, which could be attributed to its high antioxidative capacity.
At the same time, enzymatic antioxidants like SOD, CAT and GPx are recognized as first line defense against the toxic effects of ROS. SOD catalyzes the dismutation of superoxide anions to H2O2, which is detoxified to oxygen and water by the combined action of CAT and GPx. In the present study, a significant depletion in SOD and GPx heart activities was observed in maneb-treated mice. The depletion of SOD activity might be attributed to its excessive use in the dismutation of superoxide anions to H2O2. Regarding GPx activity, its inhibition might reflect a defense response against the excessive production of H2O2 by the fungicide. On the other hand, our findings revealed an increase of CAT activity in the heart of maneb-treated mice. The enhancement of CAT activity under oxidative stress conditions could be explained as a compensatory mechanism adopted by the organism (Tchantchou et al., 2004; Douarre et al., 2012). Co-treatment with Se improved SOD, GPx and CAT activities, highlighting its antioxidant properties. Likewise, Ghorbel et al. (2017) have demonstrated the capacity of selenium to ameliorate the activities of these enzymatic antioxidants in the heart tissue of rats intoxicated with aluminium chloride.
The biochemical changes were in line with the histopathological study of the heart tissue, which revealed that maneb exposure provoked the disruption and loss of cardiac myofibers integrity and cytoplasmic vacuolization of cardiomyocytes. Se co-treatment ameliorated the cardiac histoarchitecture.