Sepsis stimulates an immune response, causing activation of a cascade of immune activities resulting in tissue damage, multiple organ failure, and death. Sepsis pathology may be due to several factors, like bacterial or fungus infections. Septic acute kidney injury (S-AKI) is the most common cause of kidney injury in the ICU. In the previous study, Höcherl et al. [20] reported deterioration of kidney functions after induction of severe sepsis using LPS in vivo model.
In the present study, the cecal slurry injection increased oxidative stress markers in kidneys tissue homogenate. The reactive oxygen and nitrogen species and/or free radicals may take apart in sepsis pathogenesis. Nitric oxide, superoxide, hydrogen peroxide, and hydroxyl radical may have a key role in endotoxemia. Nitric oxide is one of the vital parameter affecting sepsis. Cellular depletion of GSH can lead to apoptosis, presumably via activation of mitogen-activated protein kinase (MAPK) cascades in various cell models [21]. These results are in agreement with Andrades et al. [22] who reported that the oxidative stress caused proteins damage. The SOD and CAT found to be critical parameters in sepsis; elevation of SOD and CAT caused accumulation of H2O2 in cells. Meanwhile, Vasanthkumar et al. [23] reported similar increments in LPO and NO after sepsis induction in mice using LPS.
On the other hand, It is well established that proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), and IL-6, contribute to the development of AKI in septic patients [24]. Macrophages were documented to be the primary source of inflammatory (pro-inflammatory and anti-inflammatory) mediators, thus playing a key role in modulating the host immune response [25]. IL-1β was found to be involved in the inflammatory symptoms (fever, lymphocyte responses, and neutrophil migration) and several inflammatory diseases. Besides, IL-1β was indicated to increase recruitment of inflammatory cells including the peritoneal cavit y[25].
Inflammatory cytokines produced by leukocytes activation such as TNF-α, IL-1α, IL-1β, and IL-6 and chemokines such as IL-8, also contribute to sepsis severity. Reactive oxygen species activate the production of pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α. Furthermore, it triggered a downstream NF-κB activation, a pathway by which TNF-α induces apoptosis in a human monocytic cell line.
Moreover, the over release of NO due to inducible iNOS activity has been accompanied by general vasodilatation and consequently hypotension. Expression of iNOS is usually controlled by NF-κB activation in sepsis. The overproduction of NO was found to mediate apoptosis in some diseases including septic shock through the endoplasmic reticulum stress pathway in some cell types as it reacts with proteins and nucleic acids causing cytotoxic effects elicited by DNA or mitochondrial damage [26]. Increased NO and PGs release, vasodilator mediators, and the downregulation of vasoconstrictive receptors were among several mechanisms implicated in the failure of vascular smooth muscle cells proper constriction properly and the mediation of endotoxemia-related vasodilation [27]. Hemodynamics as well as inflammatory changes were suggested to be contributed in the development of renal impairment [28]. The present results showed a marked elevation in inflammatory markers in kidney tissues of sepsis group as well as marked rise in Bax content with a significant depletion in Bcl-2 content that are the key proteins critical for apoptosis.
Pathogenic bacteria and their products trigger the activation of NF-κB, playing a central role in the formation of networks between cytokines and the inflammatory mediators, leading to the pathophysiology of septic shock [5, 29]. The inflammatory process activates a series of receptors and transcription factors such as NF-κB and the receptor for advanced glycation products, which lead to β cell dysfunction and apoptosis.
PGEs are important paracrine regulators of kidney function produced from arachidonic acid and exert their action via the PGE receptors [30]. PEGs affect renal vascular resistance, glomerular filtration rate, tubular reabsorption of salt and water, and renin secretion as indicated by Hao and Breyer [31]. The present study indicated increased renal contents of PGE2 in kidney homogenate of sepsis-induced rats, agreeing with previous studies of Höcherl et al. [32] which indicated huge increments in PGE2 in response to LPS treatment.
Recently, Meurer et al. [33] found increased adrenocortical and medullary tissue contents of PGE2 in response to endotoxemia-related AKI. PEG2 was found to exert a dual effect on renal vascular tone, inducing vasodilatation at lower concentrations and vasoconstriction at higher concentrations. The stimulated vasodilator PGE2 and PGI2 system might be regarded beneficial in sepsis, only within the kidney, thus protecting the kidney against endotoxemia-related injury.
Several of antioxidant and anti-inflammatory markers were performed in the present study to distinguish the potency of both curcumin and propolis on the kidney disorder in the endotoxemic rat. Though both curcumin and propolis, in the present study, were found to modulate the oxidative stress as well as inflammatory markers in kidney tissue of sepsis-induced rats, the therapeutic potential of curcumin is highly considered due to its ability to inhibit NF-kB activation and its downstream genes including IL-1β, TNF-α, and IL-6 expression [34]. As NF-kB regulates the expression of over 500 genes associated with inflammation, tumorigenesis, cellular survival/proliferation, and chemoresistance [35].
Curcumin inhibited NF-κB activation in sepsis-induced muscle protein degradation by preventing the phosphorylation and degradation of IkBα thus resulting in inhibition of inflammation and exert other anti-inflammatory effects, including oxygen radical scavenging [36].
The desirable protective or putative therapeutic properties of curcumin may be regarding its antioxidant and anti-inflammatory properties. Yang et al. [37] reported a reduction in proteinuria and inflammatory markers in diabetic nephropathy treated with curcumin.
Propolis has wide biological and potential therapeutic impacts due to anti-inflammatory and the antioxidant action of CAPE (the major component of propolis), regarding its ability to inhibit the systemic inflammatory response, NF-κB, and apoptosis.
Teles et al. [38] reported the administration of red propolis to 5/6 renal ablation animal model was found to partially reduce kidney hypertension, proteinuria, and serum creatinine, infiltration, and reduced oxidative stress. He attributed its renoprotection property to reduction of both renal inflammation and oxidative stress.
Pinocembrin, is the phenolic compound found in propolis, reduces the content of proinflammatory cytokines (TNF-α, interleukin-1beta (IL-1β)), chemokines, inducible nitric oxide synthase (iNOS), and aquaporin-4 [39]. Another study suggested that pinocembrin appears to suppress the nuclear translocation of NF-κB and decrease TNF-α expression [40].
Curcumin treatment was reported to increase GSH content and the activity of antioxidant enzymes as documented by Mylonas and Kouretas [41]. In vivo study by Qiu et al. [42] demonstrated curability to increase GSH content and to upregulate SOD, CAT activities in the liver of a murine model after glycerol-induction of nephrotoxicity. Curcumin markedly inhibited hemolysis and lipid peroxidation of erythrocytes induced by linoleate by functioning as a scavenger of NO and blocking its synthesizing enzyme [25]. Curcumin also markedly decreased LPO and NO in the kidney of sepsis-induced mice [23]. C66, a novel curcumin derivative, was reported to reduce TNF-α, IL-1β, COX-2, and NF-κB production, in high glucose-stimulated diabetic rats [43].
On the other hand, Sabuncuoglu et al. [11] reported that propolis providing an alternative therapy against resistant strains infections by elevation GSH content and reduced bacterial translocation in the ileum after bile duct ligation by enhancing mucosal barrier function, thus reducing bacterial overgrowth.
Malondialdehyde concentrations are commonly being used as potential oxidative stress biomarkers and indicators of oxidative lipid damage. The chemical structure of the constituent polyphenols enables propolis to eliminate free radicals. The flavonoids in propolis are powerful antioxidants capable of scavenging free radicals and thereby protecting the cell membrane against lipid peroxidation [44]
In the present study, curcumin reduced the production of pro-inflammatory mediators in the sepsis rat model. This reduction could be due to inhibited cyclic AMP signaling in macrophages. Under normal conditions, NF-κB is bound to be an inhibitor and sequester in the cytoplasm [45]. The regulatory pathway triggers the inflammatory processes, which in turn regulate the inflammatory process via activation of the inflammatory cytokines; PGE2 and NO. Moreover, Wang et al. [45] indicated translocation of NF-κB, after LPS treatment, from the cytoplasm to the nucleus initiating the release of various inflammatory mediators: iNOS, COX-2, NO, and PGE2.
The anti-inflammatory activity of propolis appears related to its associated constituents: flavonoids, phenolic acids and their esters, terpenoids, steroids, and amino acids, with CAPE being the most studied compound. The main mechanisms underlying the anti-inflammatory activity of propolis include (1) the inhibition of cyclooxygenase (COX) and consequent inhibition of prostaglandin biosynthesis, (2) free radical scavenging as discussed below; (3) inhibition of nitric oxide synthesis; (4) reduction in the concentration of inflammatory cytokines; and (5) immunosuppressive activity [46].
Bcl-2 (a member of proteins family) maintain cellular homeostasis and regular apoptosis by various cytokines including IL-1β, so Bcl-2 has very critical role in many biological processes and diseases [37]. Bcl-2 family members were considered as key regulators that control the release of cytochrome C and other apoptosis-promoting factors from mitochondria. Therefore, the present work suggests that overexpression of Bcl-2 prevented apoptosis in the kidney of curcumin pre-treated septic rats. In the present study, curcumin pre-treatment markedly inhibited Bax content parallel to elevated Bcl-2 contents in kidney tissues more than the propolis did. Apoptosis could be mediated by NO through the endoplasmic reticulum and the transcriptional factors (stress pathway), taking place by Bax acting as proapoptotic molecules located in the cytosol under non-apoptotic conditions and translocated to the mitochondria in response to apoptotic stimuli. NO-induced apoptosis through a mechanism involving cytochrome C release from mitochondria [47]. Scorrano et al. [48] reported that Bax and Bak were to operate on endoplasmic reticulum as well as mitochondria in maintaining Ca2+ homeostasis.
In addition, histopathological examination revealed that cecal slurry injection caused acute kidney injury represented by capillary congestion, leukocyte infiltration, tubular degeneration, and the formation of casts and luminal debris due to oxidative stress that caused proinflammatory cytokines storm and apoptosis. These results are in agreement with Liu et al. [49] and Wang et al. [50]. Kidneys of septic rats pretreated with curcumin indicated an improvement compared with a kidney of sepsis-induced rats due to the protective effect of curcumin against oxidative stress and inhibition of cytokines release as previously reported by Yang et al. [37] and Moneim et al. [10]. Meanwhile, kidney tissue from rats pre-treated with propolis before sepsis induction showed protective impact against toxic effect of sepsis; these results are in agreement with Sameni et al. [51] although mild cognition and little interstitial hemorrhage of kidney tissue is still seen.
