Ionizing radiations are recognized to stimulate oxidative stress by the production of reactive oxygen species (ROS) such as superoxide (O2·‾), (OH·) and hydrogen peroxide (H2O2) (Jameel and Mohammed, 2021) causing a lopsidedness in the prooxidants and antioxidants in the cells (Nasret al., 2020). Numerous mechanisms may cause cellular injury after radiation exposure but the formation of oxygen free radicals followed by LPO which may be one of the main reasons in the sequential of events (Wanget al., 2019). Radiation generates ROS that combined with cellular molecules, including DNA, lipids, and proteins (Jiaet al., 2021).
The current data registered a pronounced decline in the antioxidant defense system concomitant with the growing lipid and hydrogen peroxides levels in liver tissues following γ-radiation exposure. In compatible with the present study of Zakaria2017; Sarhan and Naoum 2020 who registered a decline in the activities of SOD, GST and GSH content which may be due to the formation of ROS that reacst with the enzymes molecules causing denaturation and limited inactivation of enzymes. Under ordinary situations, lipid peroxidation occurs in narrow range in body tissues while, the exaggerated formation of free radicals forming peroxidative modifications that at the end promotes LPO (Sacket al., 2017; Akhigbe and Ajayi, 2021), which is ascribed to the oxidation of the polyunsaturated fatty acids by generation of free radical causing structure and function modifications to molecules cellular membrane by direct way, through transporting energy or by indirect way, through formation of dominant oxygen derived free radical (OH·), superoxide (O2·‾) and nitric oxide (NO-) (Abd-Ellatefet al., 2017 and Iuchiet al., 2019) or to the deficiency in antioxidants levels which have the ability to hunt peroxy radicals after radiation exposure (Forman and Zhang, 2021).
Also, Sun et al.(2018) and Olivareset al.(2020) reported that radiation exposure exhibited decline in GSH content through minimizing the efficacy of GSH-Rx or reducing the activity of G-6-PD leading to scarcity of NADPH which is essential to modify oxidized glutathione (GSSG) to its reduced form GSH (Xionget al., 2020) or through oxidative stress which caused a decrease in glutamate levels, which has been estimated to be in relation with decline intracellular GSH levels, as GSH vied with glutamate for the glutamate binding site of the gamma glutamyl cysteine synthetase, the primary and controlling step of GSH synthesis or caused malfunction of cellular membranes uncontrolling GSH mobilization (Formanet al., 2009) or elevated the usage of GSH (acts a reductant for peroxides and free radicals) to neutralize the excess of free radicals (Olivareset al., 2020).
Besides, the current work showed that irradiated rats exhibited a pronounced reduction in the efficacy of hepatic antioxidant enzymes such as SOD and CAT. The reported decline in SOD efficiency is probably due to rise of O2·‾ generation or suppression by the H2O2, which results in the reduction in the CAT efficacy, which is responsible for degeneration of H2O2 (Wang et al., 2018). While, decline in CAT efficiency may be a result of excessive usage to face off LPO formation, besides detoxifying H2O2 into H2O and O2 (Rajputet al., 2021). Another related finding, the present study showed that RAPD-PCR analysis succeeded in demonstration of the genetic damages induced by irradiation (IRR) by using of both primers OP-B10 and OP-B14 in one and three weeks periods. RAPD-PCR pattern with OP-B10 primer of whole body γ-irradiated rats at 4 Gy after one week produced differences represented in disappearing of half of the marker bands. While, additional new bands beside the control marker bands are appeared in the irradiated group after three weeks of treatment. This goes in agreement with Ahmed et al. 2020 who suggested that the vanishing or emrging of an amplified RAPD segment is most likely due to DNA damage and mutations at the primer-template interaction point, as well as unfair mitotic recombination or other structural effects that have sped up primer hybridization.
Also, γ-radiation can induce cellular DNA damage by both straight and vicarious ways. Straight way inducing by destruction of chemical bonds in DNA molecules, while vicarious way resulting by the formation of ROS such as OH· and O2·‾ radical leading to DNA fragmentation by causing single- and double-stranded DNA breaks, mutations and LPO leading to cellular injury causing cellular death (Ahmedet al. 2020).
On other hand, the present results showed that, MSCs/BM extract; markedly inhibited the harmful effect of γ-radiation on antioxidant defense system. As it reduced LPO in parallel with elevated the efficacy of CAT, SOD and GSH-Px in liver tissue. The in vivo protection and particular replies of MSCs to oxidative stress may act an important role in adjusting tissue homeostasis as well as renewal of tissues after oxidative damage (Sagaradzeet al., 2020 and Yanet al., 2021) through a straight hunting and deactivation of the free radical or production of the endogenous antioxidant enzymes such as CAT and SOD. Angeloniet al. 2020 Showed that MSCs implantation could restore the imbalance between ROS and the antioxidant defense system by elevating the antioxidant capacity as well as modifying LPO.
Also, In other researches human MSCs transplantation markedly reduced oxidative stress following radiation exposure (Huet al., 2019) by inducing a transcription factor, nuclear related factor 2 (Nrf2) which is essentially adjusted the main and inducible level of cytoprotective genes. Its activation is a type of protection against oxidative stress through SOD production leading to ROS reduction in liver (Zhouet al., 2020).
In addition, the current results showed that MSCs usage is highly succeeded in healing the decomposition of cells DNA of the irradiated rats (STR) when it used alone or with silymarin supplement (SSR). The results reflects the greet efficiency of the MSCs when it used alone or combined with silymarin supplement in repairing the genetic changes due to irradiation. In agreement with this Vazet al. 2021 who showed that BM/MSCs pretreatment were markedly reduced the number of cells with chromosomal mutations and exhibited the perfect outcomes by reducing chromosomal mutations towards the normal, but still markedly elevated when compared to healthy control group. This explained as MSCs can restore alterations in DNA genome and keep the liver tissues safe from apoptosis following γ-radiation exposure (Ezqueret al., 2017). This defense is multifactorial including modifying the oxidative stress reaction, organ injury and renovation.
Moreover, Natural antioxidants have a constantly and essential role for inhibition of ROS, with keeping little amount important to adjust normal cell function (Aziz et al., 2019). Along with this, the present study showed that silymarin administration prior to exposure of rats to ionizing radiation greatly normalized all the hepatic antioxidant parameters such as SOD, CAT, and GST as well as LPO and H2O2 levels. The present results are in line with previous studies of Abdelazim 2017; Al-Hazmi 2020 and Ghonaimet al.,(2021) who showed the very antioxidant capacity of silymarin which is eligible for catching ROS.
This could be through silymarin elevation of the antioxidant potential of cells by improving the harmful effects of free radical reactions (El-Maddawy & Gad, 2012 and Farajiet al., 2019), protect hepatocytes (and other cells in the body and brain) from free radical reactions by catching of free radicals such as OH- type (Gillessen and Schmidt, 2020) with an effect on DNA-expression through inhibition of nuclear factor NF- B & inhibiting LPO (Li et al., 2012), stimulates hepatocytes protein production and reduces the oxidation of GSH (Kwon et al., 2013). Moreover, silymarin has metabolic and cell adjusting effects, called carrier mediated regulation of the fluidity of hepatocytes microsomes and the liver mitochondrial membrane (Vahabzadehet al., 2018).
Additionally, the present results showed that silymarin supplementation (SI) itself succeeded in producing a banding profile identical to the control after one week only, but it produced a negative effect by damaging the DNA when the period prolonged to three weeks. While, it produced a profile near to the control groups in silymarin treated irradiated rats after one week only. This goes in agreement with El Mesallamyet al. 2011 and Adhikariet al. 2013 who showed that silymarin administered 1 hr before irradiation (moderated radiation) and for 7 and 14 days following γ-irradiation induced changes in nucleic acids in its target organs; liver, spleen and bone marrow through producing modifications in RNA and DNA concentrations and inhibit nuclear DNA injury in male rats.
Moreover, silymarin regulates lopsidedness between cell regeneration and cell death through interfering with the expressions of cell cycle controllers and proteins implicated in cell death (Kimet al., 2021). Silymarin reacts with the estradiol receptor and activate it in the hepatocytes cells, and the activated receptor could elevate the liver endonuclear RNA polymerase I efficacy and the number of ribosomes in intracytoplasm, activate the transcription of ribosome RNA and the production of enzyme, structure protein and cellular DNA indirectly, which are useful to hepatic cytothesis (Karimiet al., 2011; and Hajiaghamohammadiet al., 2012).