Aged garlic extract protects against oxidative stress and renal changes in cisplatin-treated adult male rats

Cisplatin (CP) is an inorganic, divalent, water soluble, platinum-containing compound. CP is a highly efficient anti-neoplastic drug commonly used as a first-line therapy for treatment of various solid tumors such as: stomach cancer, ovarian cancer, lung cancer, bladder cancer and germ cell tumors [1]. The anticancer effect of CP is mediated by apoptosis and DNA-crosslinks with subsequent cytotoxic lesions in malignant cells [2]. However, its clinical use is associated with dose and duration-dependent nephrotoxic side effect [3]. The exact mechanism of CP-induced nephrotoxicity is not well understood. Thus, several hypotheses have been supposed to explain such effect. Generation of reactive oxygen species (ROS), impaired glutathione metabolism, alterations in the mitochondrial antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), reduce glutathione (GSH) and increase lipid peroxidation are the most plausible mechanisms of CP-induced toxicity [4]-[7]. CAT and SOD are enzymes of the intrinsic antioxidant defense system, which are responsible for the dissemination of superoxide free radicals [4]. In addition, stress on endoplasmic reticulum and activation of tumor necrosis factor-α (TNF-α)-mediated apoptotic pathway have been reported as pathophysiological mechanisms in CP-induced nephrotoxicity [2].

Medicinal plants and natural herbal products have potential antioxidant activity and are therefore often administered along with chemotherapeutic agents to provide better protection against their toxic side effects [4],[8],[9]. Therefore, to increase the clinical usefulness of CP, various free radical scavengers have been used to ameliorate CP-induced nephrotoxicity [3],[8]. Recently, much attention has been given to possible role of natural dietary antioxidants in protecting the kidney against CP-induced nephrotoxicity [8]-[11].

Garlic is a commonly worldwide used food and its medical properties have been well recognized for centuries [12]. Garlic and its compounds which have been reported to have diverse biological activities such as anticarcinogenic, anti-artherosclerotic, antidiabetic, renoprotective, antioxidant and immune modulation, antibacterial, antihypertensive and various other biological actions [5],[12]-[14].

Aged garlic extract (AGE) is an odorless product resulting from prolonged extraction of fresh garlic at room temperature. AGE is sold in both dry form and as a liquid containing 10% ethanol. The process of aging gently modifies harsh and irritating compounds from the raw garlic and naturally generates unique and beneficial compounds through both enzymatic and natural chemical reactions. AGE contains various antioxidant organosulfur compounds, mainly S-Allylcysteine and allicin. These compounds play an important role as antioxidants [13]. These organosulfur compounds exert their antioxidant actions by scavenging ROS, enhancing cellular antioxidant enzymes and increasing glutathione in the cells [12],[14].

AGE has been previously used to ameliorate the toxic effect of different therapeutic and toxic agents include CP [15], doxorubicin [16], acrylamide [17] and cadmium [18]. The present study has been designed to investigate the effect of AGE on the oxidative stress, biochemical and histomorphological changes of kidney in adult male Wistar albino rats treated with CP.

No deaths were recorded in the rats of the different groups throughout the period of the study. However, a reduction in the activity and appetite with diarrhea, loss luster and hair fall were observed in the CP-treated rats.

CP exhibits a potent antineoplastic effect against wide variety of solid tumors. However, its uses in the clinical field was markedly limited due to the occurrence of many side effects mainly the nephrotoxicity [1]-[3]. As the exact mechanisms responsible for CP- induced nephrotoxicity were not fully understood; several studies have been performed to explain how CP could induce toxicity [2],[3],[11]. To ameliorate the toxic effects of CP, many strategies have been proposed using various natural and synthetic free radical scavengers and antioxidants [3],[4],[6],[7],[10],[11],[21]. Such substances might provide nephroprotection against CP toxicity [11],[29].

AGE, a natural and dietary substance, was known to have different active antioxidant organosulfur compounds mainly S-Allylcysteine and allicin [12],[13]. These compounds enhanced cellular antioxidant enzymes, increased GSH content in the cells and scavenged the free radicals [12]-[14]. The protective effect of AGE against doxorubicin-induced cardiotoxicity [16], cadmium-induced toxicity [18] and acrylamide - induced oxidative damage in multiple organs [17] have been previously investigated in literatures. Thus, the present study aimed to evaluate the possible protective effect of AGE against CP-induced oxidative stress and renal damage in adult male rats.

In the present study, single injection of CP (7.5 mg/kg i.p.) revealed a significant reduction in the final body weight of the rats compared to that of control group. In agreement with the results of this study, a significant reduction in the body weight of CP-treated rats was observed 3-5 days after single i.p injection (5-7.5 mg/kg) of CP [10],[21],[30]. The reduction of the body weight in CP-treated rats might be in part due to the direct toxic effect of CP on renal tubules that caused reduction in water reabsorbtion and excessive sodium excretion with subsequent polyuria, dehydration and reduction of body weight [7],[20],[29]; or might be due to gastrointestinal toxicity with subsequent decrease in appetite, ingestion and assimilation of food [7],[8]. On the other hand, an obvious gain in the body weight was observed in AGE pre-treated rats. Such effect gave an approval on the possible protective effect of AGE against the toxicity of CP on renal and intestinal tissues.

In this study, a remarkable decrease in the absolute weight and a significant increase in the relative weight of the kidneys were observed in CP-treated rats. These results were in accordance with that of Mansour et al. [6]; Arhoghro et al. [8]; Anusuya et al. [15]; Nasr [21]; Ali and Al-Moundhri [29] who stated that a single CP injection (7.5 mg/kg i.p.) resulted in loss in the absolute and increase in relative weights of the kidneys in rats. The reduction in absolute kidney weight in CP-treated rats could be due to the damage in renal tissues and reduction in their functions [31]. However, the increase in reno-somatic index (kidney weight/body weight ratio) might be due to the edema of renal parenchyma since CP was known to cause renal inflammation [6],[9],[15]. The oral intake of AGE returned the relative kidney weight of CP-treated close to those of control rats. This protective effect of AGE on the kidney weights could be attributed to its anti-inflammatory effect that decreased the renal edema induced by CP [15]. However, the AGE showed no effect on the kidney weight of normal rats. This indicated that, the AGE had no influence on the morphology and functions of the normal kidney.

Serum creatinine, urea, uric acid and BUN levels were considered the main parameters that determine the glomerular filtration rate [20]. In the present study, nephrotoxicity of CP was evident from the elevated levels of serum urea, uric acid, creatinine and BUN levels. The elevation in the serum levels of these renal biomarkers might be due to the impaired renal functions [15], tubular obstruction, and/or the back-leakage of the renal tubules [20]. Such functional disturbance in CP exposed rats could indicate the ability of CP to inhibit protein synthesis in the tubular cells [9] or to initiate lipid peroxidation and generate free radicals in renal tubules [3],[4],[6],[7]. Similar findings were previously reported in different studies [5],[6],[8],[20]. The elevation in the kidney biomarkers was due to the direct toxic effect of CP on the glomerular and tubular structures through the generation of ROS. Contraction of the mesangial cells with subsequent alteration in the filtration surface area resulted from the generation of ROS [32].

However, the serum BUN, urea, uric acid and creatinine levels revealed marked improvement in the combined AGE + CP- treated rats. These results confirmed the ability of AGE to improve or normalize the renal function through its organosulfur compounds that could increase the antioxidant effect and decrease lipid peroxide levels by scavenging the free radicals and increasing intracellular concentration of glutathione [15]. In agree with the results of this study, feeding of AGE provided a protective effect in other experimental studies [5],[15]-[18].

In our study, pre-treatment with AGE produced significant reduction in MDA level and significant elevation of SOD, CAT activities and GSH levels of the renal tissues in CP-treated rats. These findings provide an evidence about the antioxidant effect of AGE against CP-induced oxidative stress and lipid peroxidation. In agree with the results of this study, reduction in the activity of antioxidant enzymes (CAT & SOD), increased lipid peroxidation (MDA) and depletion of GSH in renal tissues were implicated in the pathogenesis of CP nephrotoxicity [4]-[6].

ROS produced by xanthine-xanthine oxidase system, mitochondria and NADPH oxidase in cells directly act on lipid, proteins and DNA of the cell and destroy them [7]. However, animals pre-treated with AGE showed significant improvement in biochemical. histological and ultrastructural changes in renal tissues induced by CP. Many studies have demonstrated that AGE prevents the oxidative stress and exerts a protective effect against different toxic agents through its powerful antioxidant and free radical scavengers [14]-[17].

In our study, the histopathological changes confirmed the biochemical findings, where reduction in the size of the glomerular capillary tufts, dilatation of Bowman's capsule, degeneration, necrosis and detachment of the proximal tubular epithelial cell lining, shedding of the apical microvilli and accumulation of homogenous exudates within the dilated tubular lumina of both proximal and distal convoluted tubules were observed in renal sections at the corticomedullary zone of CP-treated rats. Some of the tubules were totally degenerated and cellular details were completely lost. Distal tubular cells were also affected. Consistent with the results of the present study, Mansour et al. [6]; Abdelmaguid et al. [27], Nasr [18]; Ali and Al-Moundhri, [28]; Chirino et al. [29] reported similar findings in rats exposed to different doses of CP.

Glomerular atrophy, degeneration of the tubular epithelium and interstitial inflammatory cell infiltration were the main histopathological findings of CP-treated renal tissues. Although glomerular pathology was not identified in the majority of CP-treated animals [7]; other studies have reported glomerular damage in CP-induced renal injury [10],[33],[34]. In our study, administration of CP caused not only an extensive degeneration of the tubular epithelium but also glomerular damage as well. The histopathological observations of the present study agreed with those of the previous investigations [18],[26],[27],[33],[34].

In addition to the histopathological findings, prominent ultrastructural changes were observed in the proximal tubular epithelial cells, where marked tubular degeneration with distinct apoptotic changes, loss of apical microvilli, irregularity of basement membrane, rarification of cytoplasm, marginal condensation of nuclear chromatin, vesiculation in the mitochondria and presence of many lysosomes were observed in CP-treated renal tissues. Irregular glomerular basement membrane, fusion of foot processes, increase mesangial matrix with proliferation of mesangial cells were observed in the electron microscopic examination of CP-treated rats as well. The ultrastructure changes in our work were in accordance with the observations of the prior investigations [10],[11],[35], where cytoplasmic vacuolization, dissociation of mitochondria from basal infoldings, loss of basal infoldings, many pinocytotic vesicles and lysosomes in apical region of the proximal tubular epithelial cells were reported in renal sections of CP-treated rats.

Both histopathological and ultrastructural findings of the present study revealed the direct toxic effect of CP on the renal tissues. The histopathological changes obtained in the present study run parallel with the reports documented by Abdelmaguid et al. [10], Nasr [21]; Chirino et al. [30]; Ali and AL-Moundhri [29] who found tubular necrosis and glomerular atrophy in CP-treated animals. Reduction or complete absence of the apical microvilli induced an impairment in amino acids and glucose absorption. In addition, presence of many mitochondria of variable length with dense matrix along basolateral folding was indicative of respiratory impairment. Such mitochondrial changes might be due to the response of mitochondria to overcome the direct stress of CP on renal tissues. The author added that, condensation of nuclear chromatin, presence of necrotic debris in the tubular lumen with tubular damage and appearance of lysosomal bodies in any cell might be indicating the degenerative activity and the onset of necrosis [35].

However, in combined AGE + CP-treated animals, normal foot processes, glomerular mesangium, preserved apical microvilli, restored nuclear structure with no evidence of inflammatory cell infiltration were noticed in the present study.

Inflammation was considered as an important mechanism in CP- induced nephrotoxicity in which TNF-α showed a central role [2]. Thus, absence of infiltration of the inflammatory cells in combined AGE + CP-treated renal tissues, in contrast to CP-treated tissues, could be considered as a prove to the anti-inflammatory effect of AGE [34]. To our knowledge, this study was the first one demonstrating the protective effect of AGE on CP-induced nephrotoxicity at biochemical, histomorphological and ultrastructural levels.

Apoptosis is an important way of cell death in normal and pathological processes. In the present study, different apoptotic changes, in the form of membrane budding, cell shrinkage and chromatin condensation, were observed in CP-treated renal tissue. The process of apoptosis was explained by three different pathways: extrinsic pathway, mitochondrial/intrinsic pathway [2]. The authors added that, the mitochondrial/intrinsic pathway revealed an important role in CP-induced nephrotoxicity. Thus, the protective role of AGE on CP-induced nephrotoxicity might be primarily due to its anti-apoptotic property.

The findings of present study demonstrated that most of biochemical, histological and ultrastructural alterations induced by CP treatment could be ameliorated by the pre-treatment with AGE, where the morphological and biochemical changes in AGE + CP-treated rats were markedly less than those observed in rats treated with CP alone.

From the findings of the present study, we can conclude that, AGE has an ameliorative effect against CP-induced oxidative stress and renal damage through its antioxidant, anti-inflammatory and antiapoptotic properties. However, the protective Effect of AGE against both antineoplastic activity of CP and the effect of CP on the mitochondrial intrinsic pathway did not investigate in this work. Thus, these points need further studies to be fulfilled.