## 6 Discussion  
In this study, we showed that both TQ and metformin efficiently alleviated oxidative stress in GM-induced nephrotoxicity in rats. However, only TQ produced reno-protective effects. We also confirmed the effects of GM on kidney function. The accumulation of GM, either intracellularly or in the cell membrane, lead to an increase in the production of ROS that interact with cellular macromolecules (lipids, protein, DNA). ROS increase denaturation of proteins, DNA damage, and production of MDA as a marker of lipid peroxidation (LPO) of the cell membrane's lipids. These events lead to cellular injury and necrosis cascades that are commonly known as gentamicin-mediated nephrotoxicity (Figure 3) [26]. In addition, increases in the production of ROS by GM lead to depletion of antioxidant enzymes activity, such as superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) Figure 1 [27]. The most common markers indicating renal dysfunction and GM-nephrotoxicity are the increase of serum levels of creatinine and blood urea nitrogen [28]. Figure 2: Tubular changes in in the four groups. When compared with the control group, GM induced vacuolar degeneration (thin arrow) and tubular irregularities (dotted arrow). The hyaline droplets seen in the GM-treated group (thick arrow) were reduced in the TQ-treated and MF-treated groups, and the tubular regularity preservation was more pronounced in the TQ-treated group. (**A**): Control group; (**B**): GM-treated group; (**C**): TQ-treated group; (**D**): MF-treated group. H&E staining. In the present study, the daily injection of GM for four weeks resulted in nephrotoxicity as manifested by increased serum urea and creatinine concentrations. In addition, GM injection appeared to generate excess ROS, which resulted in a significant reduction in GLPX-1 and SOD levels, together with a significant increase in the MDA level. Histopathologically, GM affected both the glomerular and tubular structure of the kidney. The glomerular changes manifested as mesangial cell hyperellularity and glomerular endothelial cell proliferation with a resultant reduction in Bowman's space. As reported in another study, GM simultaneously induced the proliferation and apoptosis of mesangial cells in vitro and glomerular mesangial cells in vivo [13]. This study also revealed that, in the renal tubules, GM induced vacuolar degeneration of the tubular epithelium with evidence of tubular necrosis and tubular irregularities. In a study performed by [PERSON] et al. in 2012, tubular alterations caused by GM treatment appeared early in the form of necrosis, degeneration, and vacuolisation, and over time the degeneration progressed to severe necrosis. The degenerated tubules showed swelling, cytolysis, and tubular irregularity [14]. Thus, our results (glomerular and tubular changes) add support to the main pathophysiologic theme in GM-induced nephrotoxicity and are consistent with many previously published data [7; 29; 30; 31]. [PERSON] and his co-workers, attributed GM-induced nephrotoxicity to ROS generation and increased endothelin-1 level, in addition to cellular infiltration  
Figure 3: Gentamicin induction of nephrotoxicity by ROS pathway. TQ protects the proximal tubules by acting as a scavenger of ROS and preventing nephrotoxicity. and apoptosis [7]. Thus, it seems that any animal trial aiming to reduce GM-induced nephrotoxicity should involve a substance with antioxidant activity and ROS scavenger properties [26]. In the current work, we tested the ability of well-known substances (TQ and MF) with antioxidant properties to reduce GM-induced nephrotoxicity. This is the first time that the two drugs (QT and MF) have been compared side-by-side for prevention of nephropathy in the same model (rats) at the same time. MF is widely used in diabetes, and many novel studies recommend TQ in treatment of diabetes [15; 22] and prevention of diabetic complications, especially diabetic nephropathy.