الفهرس 
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Abstract
Renal ischemia is the most common cause of acute renal failure and results from a generalized or localized impairment of oxygen and nutrients delivery to the cells of the kidney. The kidney is very vulnerable to ischemic injury because of the high rate of baseline oxygen use by renal cells, especially the metabolically active proximal tubule cells. This renders the kidney incapable of increasing oxygen transport in response to hypoxia, thus leading to tubular cell injury due to a mismatch of local tissue oxygen supply and demand and accumulation of waste products of metabolism. As a result of this imbalance, many changes occur such as vascular congestion, formation of edema, diminished microvascular blood flow, and adhesion of inflammatory cells to the endothelium with subsequent infiltration into the kidney tissue. A number of potent mediators are generated by the injured epithelial proximal tubular cell, includ¬ing proinflammatory cytokines, such as tumor necrosis factor alpha (TNF-α) and interleukins. The tubular epithelial cells undergo injury and, if it is severe, cell death occurs by apoptosis and necrosis.
Reperfusion injury following a ischemia can be mediated by several mechanisms including the generation of ROS, cellular derangement, microvessel congestion and compression, polymorphonuclear neutrophil (PMN)-mediated damage as well as hypercoagulation. Reperfusion with the resulting inflow of molecular O2 into constricted microvesseles leads to congestion and red cells trapping. Owing to their highly reactive nature, ROS generated upon reperfusion can oxidatively modify virtually every type of biomolecule found in cells including nucleic acids, membrane lipids, enzymes and receptors, thereby paradoxically inducing cell dysfunction (oxygen paradox). The role of free radicals is of particular importance because it can potentially explain each of the other mechanisms of reperfusion injury. Thus, the pathogenesis of renal I/R injury appears to be multifactorial and interdependent involving hypoxia, excessive ROS production with a resultant oxidative stress, cytokine overproduction and inflammatory responses with eventual cell damage.
The damaging effect induced by I/R is not only restricted to the specific tissue undergoing the initial ischemia but also it leads to injury to remote organs such as the liver. This effect is so called remote organ injury (ROI). Examination of the mechanisms underlying ROI has found roles for the same factors implicated in the local organ dysfunction produced by I/R injury: ROS, leukocytes, and inflammatory mediators such as TNF-α. These factors may be directly released from the primary injured tissue or indirectly from activated leukocytes or other inflammatory cells.
Celecoxib (CEB) is a non-steroidal anti-inflammatory drug (NSAID) commonly used as analgesic and anti-inflammatory. Celecoxib selectively inhibits cyclooxygenase-2 (COX-2) enzyme. COX-2 is the inducible/ pathological form of cyclooxygenase enzymes which is activated in damaged and inflamed tissues in response to proinflammatory cytokines (e.g. interleukin (IL)-1, IL-2 and TNF-α), and reactive oxygen intermediates.
Pentoxifylline (PTX) is a trisubstitute xanthine derivative used for the treatment of intermittent claudication and other circulatory disorders. It is an active hemorheological drug that has also an anti-inflammatory effect. Pentoxifylline is a competitive nonselective phosphodiesterase (PDE) inhibitor. The inhibition of this enzyme leads to elevated levels of cAMP, activates protein kinase A (PKA) that leads to the inhibition of (TNF-α) production and leukotrienes synthesis.
The present study was designed to investigate the effects of celecoxib and pentoxifylline, given alone and in combination, on kidney damage induced by bilateral renal I/R. In addition, the effects of these two drugs on the changes induced by renal I/R in the liver, as a remote organ, were evaluated.
Thirty five male albino rats weighing 200-250 g were included in this study and randomly assigned into the following five experimental groups (7 rats per group):
Group 1: Control (sham-operated) group: The rats of this group received 1ml of gum acacia by oral gavage daily for 7 days. Thereafter, the rats of this group were anesthetized and operated but were not subjected to any renal ischemia/reperfusion (I/R).
Group 2: (I/R group): The rats of this group received 1m of gum acacia (prepared as 2% solution) by oral gavage daily for 7 days. Thereafter, the rats in this group were exposed to renal ischemia for 1hour followed by reperfusion for another 1 hour.
Group 3: (CEB+I/R group): The rats of this group were treated with celecoxib (CEB) at a dose of 10 mg/kg given by oral gavage daily for 7 days. Thereafter, all rats of this group were anesthetized and operated as in I/R group.
Group 4: (PTX+I/R group): The rats of this group were treated with pentoxifylline at a dose of 200 mg/kgby oral gavage daily for 7 days. Thereafter, all rats of this group were anesthetized and operated as in I/R group.
Group 5: ((CEB+PTX)+I/R group)): The rats in this group were treated with the two drugs as in groups 3 and 4 for 7 days. Thereafter, all rats of this group were anesthetized and operated as in I/R group.
At the end of experimental period blood was collected for the determination of:
- Urea concentration.
- Creatinine concentration.
- Alanine aminotransferase (ALT) activity.
- Aspartate aminotransferase (AST) activity.
- Tumor necrosis factor-alpha (TNF-α) level.
Then kidneys and livers were excised from the rats immediately after the reperfusion period, and then preserved at 2-8o C for the determination of:
- TNF-α level.
- Myeloperoxidase (MPO) level.
- Reduced glutathione (GSH) level.
- Superoxide dismutase (SOD) activity.
- Malondialdehyde (MDA) level.
- Total protein content.
Portions of excised kidneys and livers were taken and processed for histopathological examination.
The results of this study demonstrated that renal ischemia for 60 minutes followed by 60 minutes reperfusion caused local responses in the kidney and remote effects on the liver as reflected by detrimental changes in kidney and liver histology, function, inflammatory status and oxidant-antioxidant balance. Also, the present study showed that treatment of rats with CEB, PTX or simultaneously with both drugs before renal I/R induction provided protection to the kidney and liver against the consequences of renal I/R as evidenced by the following observations: (1) Drug pretreatment, in the present study, protected the functions of the kidney and liver as shown by the changes in serum levels of creatinine and urea (as indices of kidney function) and serum activities of ALT and AST (as indices of liver function). These parameters, in drug-pretreated I/R groups, were very close to the corresponding values in the sham-operated control group. (2) Drug pretreatment in I/R groups attenuated the I/R-related histopathological changes in both the kidney and liver. (3) Drug pretreatment in I/R groups reversed the changes in kidney and liver tissue levels of TNF-α and MPO (as indices of inflammation and neutrophil tissue infiltration), and MDA and GSH levels and SOD activities (as indices of the oxidant and antioxidant status) as compared to the untreated I/R group.
The results obtained from our research indicated that local and systemic inflammatory responses, lipid peroxidation and oxidative stress are involved in the pathogenesis of I/R-induced local and remote organ injury. In the present study, pretreatment of rats with CEB and/or PTX was found to have an outstanding protective effect on renal I/R-induced injury in the kidney and liver. The present study is the first to evaluate simultaneously the nephroprotective and hepatoprotective effects of the COX-2 inhibitor; celecoxib (CEB) and the methylxanthine phosphodiesterase inhibitor; pentoxifylline (PTX) in a model of acute renal I/R injury in rats.
These protective effects can be attributed, at least in part, to the ability of each drug to suppress the production of TNF-α, inhibit neutrophil tissue infiltration, decrease lipid peroxidation and balance the oxidant-antioxidant status of the affected organs. The extent of improvement in serum and tissue biochemical parameters and histological outcomes was similar in the two groups of rats treated with CEB and PTX before the induction of renal I/R injury. It is worth nothing that combined administration of both drugs before the induction of renal I/R had no additive or synergistic nephroprotective and hepatoprotective effect compared to the results of treatment with each drug alone. Thus, the results of the present study, when combined with the knowledge that CEB and PTX have been used safely in human for some therapeutic indications, may represent a promising therapeutic approach for ameliorating kidney and liver injury following renal I/R in patients who are expected to be exposed to renal I/R as in many clinical settings, such as kidney transplantation, partial nephrectomy or suprarenal procedures of the aorta where it is necessary to perform I/R to control blood loss.