Prospects for Protective Potential of Moringa oleifera against Kidney Diseases

Kidney diseases are regarded as one of the major public health issues in the world. The objectives of this study were: (i) to investigate the causative factors involved in kidney disease and the therapeutic aspects of Moringa oleifera, as well as (ii) the effectiveness of M. oleifera in the anti-inflammation and antioxidant processes of the kidney while minimizing all potential side effects. In addition, we proposed a hypothesis to improve M. oleifera based drug development. This study was updated by searching the key words M. oleifera on kidney diseases and M. oleifera on oxidative stress, inflammation, and fibrosis in online research databases such as PubMed and Google Scholar. The following validation checking and scrutiny analysis of the recently published articles were used to explore this study. The recent existing research has found that M. oleifera has a plethora of health benefits. Individual medicinal properties of M. oleifera leaf extract, seed powder, stem extract, and the whole extract (ethanol/methanol) can up-increase the activity of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH), while decreasing the activity of inflammatory cytokines such as TNF-α, IL-1β, IL-6, and COX-2. In our study, we have investigated the properties of this plant against kidney diseases based on existing knowledge with an updated review of literature. Considering the effectiveness of M. oleifera, this study would be useful for further research into the pharmacological potential and therapeutic insights of M. oleifera, as well as prospects of Moringa-based effective medicine development for human benefits.


Introduction
Kidney diseases are considered among the major health problems worldwide. Acute kidney injury (AKI) is closely connected with chronic kidney diseases (CKD). Since 1990, CKD has been included in the list of non-communicable conditions investigated by the global burden of disease study. As the disease's growth rate accelerates, it has become a global concern. The majority of incidents occur in low and lower-middle income countries [1][2][3]. The kidneys gradually lose their ability to function in CKD patients, and the glomerular filtration rate (GFR) falls below 60 mL/min per 1.73 m 2 [1,2]. Mainly people who have been already suffering from diabetes, heart disease, or high blood pressure are at a high risk of developing CKD. Few drugs, such as prolyl hydroxylase domain inhibitors against anemia in CKD [3], can be used to treat CKD complications. The main pathologies involved in kidney complications are inflammation, oxidative stress, apoptosis, and fibrosis [4]. Unfortunately, no potential drug for treating kidney diseases exists at databases and discussed in this study ( Figure 1). All information compiled in the was obtained from these research articles.

Phytochemical Content and Pharmacological Potential of M. oleifera on Kidney eases
M. oleifera contains several bioactive phytochemicals including flavonoids and i ocyanates [10]; polyphenols, carotenoids, alkaloids, and terpenoids [11]; and tri noids, moringyne, monopalmitic, di-oleic triglyceride, campesterol, stigmasterol, βterol, avenasterol, and vitamin A [12]. These bioactive phytochemicals are found oleifera roots, fruits, and seeds. These phytochemicals have medicinal properties w have been shown to be effective antioxidant, antimicrobial, inflammatory, and an cinogenic agents [28]. More studies are required to explore the role of bioactive p chemicals specially in kidney diseases.
M. oleifera also possesses a variety of pharmacological properties, which are c associated with the presence of its bioactive compounds. Therefore, in the followin tion we highlighted the pharmacological potential of M. oleifera. M. oleifera showed macological potential against some plausible factors such as oxidative stress, infla tion, fibrosis, and other pathologies responsible for kidney diseases. The potential e of M. oleifera against risk factors associated with kidney disease in the following se as shown in Figures 2 and 3.

Phytochemical Content and Pharmacological Potential of M. oleifera on Kidney Diseases
M. oleifera contains several bioactive phytochemicals including flavonoids and isothiocyanates [10]; polyphenols, carotenoids, alkaloids, and terpenoids [11]; and triterpenoids, moringyne, monopalmitic, di-oleic triglyceride, campesterol, stigmasterol, β-sitosterol, avenasterol, and vitamin A [12]. These bioactive phytochemicals are found in M. oleifera roots, fruits, and seeds. These phytochemicals have medicinal properties which have been shown to be effective antioxidant, antimicrobial, inflammatory, and anti-carcinogenic agents [28]. More studies are required to explore the role of bioactive phytochemicals specially in kidney diseases.
M. oleifera also possesses a variety of pharmacological properties, which are closely associated with the presence of its bioactive compounds. Therefore, in the following section we highlighted the pharmacological potential of M. oleifera. M. oleifera showed pharmacological potential against some plausible factors such as oxidative stress, inflammation, fibrosis, and other pathologies responsible for kidney diseases. The potential effects of M. oleifera against risk factors associated with kidney disease in the following sections as shown in Figures 2 and 3.  Renoprotective effects of M. oleifera against oxidative stress. Stress stimuli (streptoz CoCl2, methotrexate, tilmicosin, TiO2NPs, acetaminophen (APAP), glycerol, and Salmone creased malondialdehyde (MDA), lipid peroxidation products (LPP), total protein carbonyl (TPCC), blood urea nitrogen (BUN), creatinine, and nitric oxide (NO) production via trigge active oxygen species (ROS), H2O2, glutathione disulfide (GSSG), and lactoperoxidase (LPO dative stress emerged as a result of these events. MO-induced models, on the other hand, inc the expression of catalase (CAT); superoxide dismutase (SOD); glutathione peroxidase (GP tathione (GSH), total antioxidant capacity (TAC); delta-amino levulinic acid dehydratase (A and G-6-Pase, which then activates glutathione (GSH). These stressors inhibit the expression idative stress suppressive factors. ROS, H2O2, GSSG, and LPO, all related to oxidative stres decreased by GSH. GSH is also capable of reducing oxidative stress. Renoprotective effects of M. oleifera against oxidative stress. Stress stimuli (streptozotocin, CoCl 2 , methotrexate, tilmicosin, TiO 2 NPs, acetaminophen (APAP), glycerol, and Salmonella) increased malondialdehyde (MDA), lipid peroxidation products (LPP), total protein carbonyl content (TPCC), blood urea nitrogen (BUN), creatinine, and nitric oxide (NO) production via triggering reactive oxygen species (ROS), H 2 O 2 , glutathione disulfide (GSSG), and lactoperoxidase (LPO). Oxidative stress emerged as a result of these events. MO-induced models, on the other hand, increased the expression of catalase (CAT); superoxide dismutase (SOD); glutathione peroxidase (GPx); glutathione (GSH), total antioxidant capacity (TAC); delta-amino levulinic acid dehydratase (ALAD), and G-6-Pase, which then activates glutathione (GSH). These stressors inhibit the expression of oxidative stress suppressive factors. ROS, H 2 O 2 , GSSG, and LPO, all related to oxidative stress, were decreased by GSH. GSH is also capable of reducing oxidative stress.  The expression of C-reactive protein (CRP), which activates NF-kB in the cytosol, is linked to stress factors. TNF-, Il-6, Il-1B, iNOS, and COX-2 are all activated when NF-kB enters the nucleus and binds to DNA. All of these elements have been linked to the development of inflammation. NO is activated even more by iNOS. NO is thought to be a pro-inflammatory mediator that causes inflammation. In the cytosol, M. oleifera suppressed the expression of CRP and NF-kB. It also boosted cortisol, adrenaline, NK, and Treg cells, which helped reduce inflammation. Anti-inflammatory hormones Cortisol and Adrenaline Both NK cells and Treg cells are anti-inflammatory regulators.

Oxidative Stress
Oxidative stress is caused by an imbalance between the excessive free radical generation and insufficient antioxidant defense [29,30]. It is frequently observed in CKD [31][32][33], and has become a diagnostic factor [34]. A number of studies documented that M. oleifera has antioxidative properties to protect and/or alleviate cellular damage (Table 1 and Figure 2). M. oleifera extracts and compounds, particularly quercetin, kaempferol, isothiocyanates, rutin, myricetin, ascorbic acid, and β-carotene, showed antioxidant potentials either via direct scavenging of free radicals [35]. The expression of C-reactive protein (CRP), which activates NF-kB in the cytosol, is linked to stress factors. TNF-, Il-6, Il-1B, iNOS, and COX-2 are all activated when NF-kB enters the nucleus and binds to DNA. All of these elements have been linked to the development of inflammation. NO is activated even more by iNOS. NO is thought to be a pro-inflammatory mediator that causes inflammation. In the cytosol, M. oleifera suppressed the expression of CRP and NF-kB. It also boosted cortisol, adrenaline, NK, and Treg cells, which helped reduce inflammation. Anti-inflammatory hormones Cortisol and Adrenaline Both NK cells and Treg cells are anti-inflammatory regulators.

Oxidative Stress
Oxidative stress is caused by an imbalance between the excessive free radical generation and insufficient antioxidant defense [29,30]. It is frequently observed in CKD [31][32][33], and has become a diagnostic factor [34]. A number of studies documented that M. oleifera has antioxidative properties to protect and/or alleviate cellular damage (Table 1 and Figure 2). M. oleifera extracts and compounds, particularly quercetin, kaempferol, isothiocyanates, rutin, myricetin, ascorbic acid, and β-carotene, showed antioxidant potentials either via direct scavenging of free radicals [35]. ↓urea, and ↓creatinine ↑serum levels of protein, ↑albumin, ↑globulin, ↑GPx, and ↑CAT ↓KIM-1, and ↓TNF-α and ↑Bcl-2, ↓TIMP-1 [48]  Methanol extract of M. oleifera reduced the oxidative stress in STZ induced male rats by lowering the production of MDA, ROS, LDL, and CHOL, which increase the risk of CKD [36,54]. Methanol extract also lowered the generation of MDA, AOPP, NO, H 2 O 2 , GPx, and GST, all of which induce oxidative stress in ischemia-induced Wistar rats [29]. Another study showed that metabolic extract reduced the levels of BUN and creatinine, and total protein is increased in CKD patients [42]. Ethanolic extract of M. oleifera inhibits oxidative stress and atherosclerosis in CKD by lowering LDL [20]. 8-OHdG causes oxidative stress to DNA and promotes cancer [56], ameliorated by the ethanolic extract of M. oleifera [56]. Ethanol extracts decrease the plasma creatinine level by enhancing the process of creatinine clearance [30]. Plasma sodium and potassium levels were raised after treating nickelinduced Wistar rats with ethanolic extract of M. oleifera [34]. Ethanolic extract detoxified plasma by reducing the bilirubin levels (indirect/direct), urea levels, etc., in ML-induced male Sprague Dawley rats [48]. HO-1 and Nrf2 expression were stimulated by leaf extract of M. oleifera at dosages of 300 and 400 mg/kg body weight, respectively [25,41]. Leaf extracts up-regulated the level of total thiol TiO 2 NPs induced male albino rats, which play an important role in antioxidant protection [41]. Leaf extract of M. oleifera also downregulated the oxidative stress generating mediators in sodium fluoride (NaF)-induced Oreochromis niloticus, gentamicin-induced rabbit, and APAP-treated mice [23,42,57].
M. oleifera alcoholic extract reduced oxidative stress by lowering the lipid peroxidation, and ROS in iodide injected rabbits [51]. Furthermore, fermented leaf extract of M. oleifera boosts the antioxidant activity in bacteria-induced mice [53]. M. oleifera extract reduced the manifestation of MDA, indicating that the free radicle overproduction was reduced in both Tilmicosin and Hg induced rats. Abarikwu et al. showed that SOD level was increased after treatment with M. oleifera in tilmicosin induced rats [40]. Hydroalcoholic root extract raised blood sugar, antioxidant enzyme activities, and G-6-phase activities, which protect the kidney from nephropathy in Beryllium-induced rats [45]. Seed powder reduced free radical species, TPCC, metal content, and increased ALAD activity in lead-treated rats [57]. In arsenic-treated rats, seed powder of M. oleifera considerably increased antioxidant function including GSH, CAT, and ALAD [46].

Inflammation
The kidney is responsible for maintaining whole-body homeostasis. Kidney disease is characterized by inflammation as a major pathology [58][59][60]. Acute or chronic disease such as ischemia, toxins, or inflammation affects kidney tubules, causing kidney fibrosis that is associated with reduction of GFR in kidneys [61]. Kidney injury is linked to the production of cytokines levels, which prolongs the acute phase of kidney disease [62]. Moreover, chronic inflammation is regarded as a comorbid condition in CKD [63]. Many plants have an anti-inflammatory action through active substances such as hesperidin, diosmin, withaferin, fucoidan, thymoquinone, etc. [64][65][66][67]. Here, the anti-inflammatory effects of M. oleifera has been discussed. M. oleifera has been reported to exhibit strong inflammatory activity (Table 1 and Figure 3). Methanolic extract of M. oleifera reduced inflammation in STZ induced male Wister rats by down-regulating the tumor necrosis factor (TNF-α), IL-6, and MCP-1, an important chemokine [36,54]. Tang et al. investigated the effects of ethanolic extract of M. oleifera in metformin-induced mice and observed that the M. oleifera declines the production of inflammatory markers and the expression of cyclooxygenase-2 (COX-2) and nitric oxide synthase (iNOS) by reducing the phosphorylation of mitogen-activated protein kinase (MAPK) pathway [20]. Ethanolic extract of M. oleifera down-regulates the inflammatory cytokines in CoCl 2 -induced rats, including NO, which is involved in the pathogenesis of inflammation [37]. Leaf extract of M. oleifera inhibits inflammatory cytokines production and regulates the inflammation by inhibiting NF-kB [25]. It was also observed that inflammation in Tilmicosin (Til) induced rats was reduced by M. oleifera extracts [39]. M. oleifera leaf extract protects against interstitial kidney inflammation with fibrosis by down-regulating KIM-1 in TiO 2 NPs induced male albino rats [41]. M. oleifera extract increases the secretion of cortisol, adrenaline, Treg cells, NK, and leptin, promoting anti-inflammatory cytokines and regulating the immune system [47]. M. oleifera treatment reduced the expression of KIM-1, TIMP-1, and TNF-α in ML-induced male Sprague Dawley rats [48]. TNF-α, an inflammatory cytokine that stimulates IL-1; IL-6, downregulated by M. oleifera in Seabream (Sparus aurata); and activated TGF-β, elicits anti-inflammatory effects [49]. M. oleifera also reduced the inflammatory cytokines in APAP-treated mice, where APAP induces AKI [50]. Fermented extract of leaves also reduces the Nrf2 in Salmonella-induced mice [53].
Moringa seed's phytochemicals can reduce the production of nitric oxide (NO) and the gene expression of LPS-inducible iNOS and interleukins 1β and 6 (IL-1β and IL-6) compared to curcumin [68]. Flavonoids have been shown to be effective inhibitors of nitric oxide synthase type 2 (NOS-2) actions, and it also inhibits protein tyrosine kinase action that is involved in the NOS-2 expression at the molecular level [69][70][71]. Flower extract can cause the activation of pro-inflammatory proteins such as toll-like receptors. In the flowers, quercetin and kaempferol can inhibit the signal transducer and activator of transcription 1 (STAT-1) and the NF-κB pathways [72,73]. M. oleifera flowers contain 80% hydroethanolic, a potent agent of anti-inflammation in the NF-κB signaling pathway [74]. Scientists discovered that phenolic glycosides suppress inducible iNOS expression and NO production in mouse macrophage cells, as well as COX-2 and iNOS proteins [75,76]. Moringa extracts eventually down-regulate the inflammatory mediators because its seeds and flowers contain many bioactive compounds. Each of these compounds has its individual effects.

Fibrosis
Kidney fibrosis is defined as a radical harmful connective tissue deposition on the kidney parenchyma, which leads to renal dysfunction. Epithelial to mesenchymal transition (EMT) is the main mechanism of kidney fibrosis, and the TGFβ-1-SMAD pathway and hypoxia are known as the main modulator of EMT [32,77]. TGF-β-induced expression of fibronectin, type I collagen, and PAI-1 rat kidney fibroblast cells is reduced by M. oleifera extract [55]. Furthermore, moringa root extract selectively inhibited TGF-β-induced phosphorylation of SMAD4 and ERK expression. These results suggest that moringa root extract may reduce renal fibrosis by a mechanism related to its antifibrotic activity in rat kidney fibroblast cells. Oral administration of M. oleifera seed extract reduced CCl4-induced liver fibrosis in rats [78].

Other Pathologies Those Are Associated with Kidney Diseases
Autophagy has a critical role in kidney physiology and homeostasis [79], and, thus, its regulation is an important determinant of kidney diseases [61]. AKI or CKD causes mitochondrial damage, but damaged mitochondria begin to accumulate in response to these types of stimuli. Autophagy protects the kidney through the removal of ROS-producing mitochondria [80][81][82]. Apoptosis is a type of programmed cell death in which cells are killed by a controlled system. It is an energy-dependent complex process [83]. It contributes to develop AKI, even organ failure [84]. Ischemia/reperfusion (I/R) induces apoptosis or necrosis in the kidney and loss of tubular cells, leading to decreased GFR [85,86]. Renal tubular cells express cell surface 'death receptors' of TNF-α which is responsible for inducing apoptosis [87]. Also, ROS production in kidney disease is responsible for promoting apoptosis [86].
TNF-α inducer of apoptosis, also increased the expression of apoptosis-related molecules which was down-regulated by ethanol extract of M. oleifera in CoCl 2-treated rats [37,88]. Leaf extract at a dose of 300 mg/kg body weight reduced the expression of caspase-9, the precursor of caspase-3, leading to apoptosis [25,89]. Bcl-2 inhibited apoptosis by blocking cytochrome c release and preventing caspase activation [90] while it was up-regulated by ethanol extract of M. oleifera in ML-induced rats. M. oleifera also reduced the expression of TIMP-1, which is involved in renal fibrosis and apoptosis [48].

Prospects for M. oleifera in Drug Development
Researchers are targeting the development of drugs from natural sources instead of the synthetic drug because natural sources have fewer side effects than synthetic sources. Nigerian scientists proved that M. oleifera is a beneficial herb and causes no harm to the body and kidneys [91]. Another study reported that higher doses of M. oleifera created toxicity in rats, but a moderate level dose of M. oleifera is safe [92]. M. oleifera has been shown to alleviate diabetic nephropathy in alloxan-induced rats [93]. Acetaminophen causes hepato-renal toxicity, which can be cured by M. oleifera treatment at the dosage of 500 mg/kg [94]. M. oleifera reduced necrosis, dilatation of renal tubules in Cd-induced rats, where Saleh et al. suggested that M. oleifera could be used as an herbal drug [95]. M. oleifera leaf extracts reduced oxidative stress, kidney, and liver damage [96]. A randomized placebo-controlled study suggested that M. oleifera leaf capsules can be used to control blood sugar level and blood pressure level [97]. Moreover, aqueous extracts of M. oleifera can reduce metal (As (III), Cd, Ni and Pb) toxicity and showed the protective effects in Saccharomyces cerevisiae [98].
The rich phytochemical profile and advances in biotechnological techniques have made this tree indispensable for opening a new era in medical science. An in vitro propagation technique provides new insights into developing more effective, eco-friendly, and biodegradable products using mass multiplication and production techniques. Though efficiency in in vitro propagation techniques for M. oleifera has been established, there are still gaps in the production of metabolites and those specific metabolites in the human body. The use of biotechnological approaches will help in the commercialization of important plant products. There is no doubt that biotechnological protocols will allow great research to make M. oleifera one of the essential solutions for various health issues including kidney diseases.

Conclusions
Kidney function declines with age, and aging-related kidney complications proportionately increase. Their side effects limit the effectiveness of existing drugs for treating kidney diseases and, therefore, natural compounds with fewer side effects are being evaluated. The literature discussed in this review suggests that M. oleifera alleviates several pathological factors associated with kidney diseases, including inflammation and oxidative stress. However, a mechanism associated with protective potential of M. oleifera against kidney diseases has been provided in this study (Figure 4).  ; superoxide dismutase (SOD); glutathione peroxidase (GPx); glutathione (GSH); total antioxidant capacity (TAC); delta-amino levulinic acid dehydratase (ALAD); and G-6-Pase, which facilitated oxidative stress reduction by activating glutathione (GSH), a non-protein thiol that suppresses free radicals. GSH suppresses the oxidative stress situation. M. oleifera also suppressed oxidative stressors caused by ROS, H2O2, GSSG, and LPO by inhibiting MDA, LPP, TPCC, BUN, Creatinine, and NO. Bcl-2 was similarly produced by stress stimuli and was linked to the suppression of necrosis, induced by M. oleifera. M. oleifera inhibited the expression of Caspase-9, a protein involved in the formation of caspases. Following NF-kB, stress stimuli also increased CRP expression. NF-kB then moved from the cytosol to the nucleus, bound to DNA, and activated inflammation-related proteins. M. oleifera inhibited the mechanism by which inflammation factors were produced, hence, reducing inflammation. M. oleifera has been linked to a reduction in the progression of kidney disease. ; superoxide dismutase (SOD); glutathione peroxidase (GPx); glutathione (GSH); total antioxidant capacity (TAC); delta-amino levulinic acid dehydratase (ALAD); and G-6-Pase, which facilitated oxidative stress reduction by activating glutathione (GSH), a non-protein thiol that suppresses free radicals. GSH suppresses the oxidative stress situation. M. oleifera also suppressed oxidative stressors caused by ROS, H 2 O 2 , GSSG, and LPO by inhibiting MDA, LPP, TPCC, BUN, Creatinine, and NO. Bcl-2 was similarly produced by stress stimuli and was linked to the suppression of necrosis, induced by M. oleifera. M. oleifera inhibited the expression of Caspase-9, a protein involved in the formation of caspases. Following NF-kB, stress stimuli also increased CRP expression. NF-kB then moved from the cytosol to the nucleus, bound to DNA, and activated inflammation-related proteins. M. oleifera inhibited the mechanism by which inflammation factors were produced, hence, reducing inflammation. M. oleifera has been linked to a reduction in the progression of kidney disease.
This study discusses the insights of M. oleifera against kidney diseases including AKI and CKD, which have not been reported previously. In addition, further studies are needed to confirm the effects of the bioactive phytochemicals (vitamins, alkaloids, polyphenols, isothiocyonates, glucosinolates, tannins, and saponins) of M. oleifera against kidney diseases. We anticipate that the points raised in this review will provide a future research direction for understanding how pharmacological interventions based on natural products could modulate kidney disease. In contrast, it would shed light on how M. oleiferabased drugs would potentially be a kidney protective agent in treating aging-associated kidney abnormalities. Considering the harmful effects of synthetic resources and their non-renewable nature, the use of natural resources as a source of medicine has received a lot of attention in recent years. M. oleifera based medicine would be an excellent protective agent against several risk factors associated with kidney diseases.