Background
Kidney damage or an estimated glomerular filtration rate less than 60 ml/min per 1.73 square metres are both indicators of chronic renal failure (CRF), which is also known as end-stage renal illness [
1]. A progressive decrease of kidney function that eventually necessitates the use of renal replacement therapy is a sign [
2]. CRF occurs more frequently, has a bad prognosis, and costs a lot to treat. This illness not only seriously affects people's health but also poses a serious financial challenge for the worldwide health care industry [
3]. Rising rates of diabetes and hypertension, which are significant causes of the morbidity and mortality associated with CRF [
4,
5], add to the burden of CRF. CRF alone is a significant independent risk factor for the development of cardiovascular illness, including hypertension [
6].
Adenine causes chronic renal failure in rats, which manifests as severe renal insufficiency and metabolic abnormalities that are very similar to those seen in uremic people [
7]. Additionally, mesangial enlargement, endothelial dysfunction, and glomerular fibrosis are caused by cellular oxidative stress associated with CRF [
8].
The NLRP3 inflammasome, which stands for nucleotide-binding and oligomerization domain, leucine-rich repeat, and pyrin domain-containing 3, promotes the development and release of proinflammatory cytokines, which results in excessive inflammatory responses and causes irreparable damage to the body [
9]. The NLRP3 inflammasome is implicated in the pathogenesis and progression of chronic renal failure, according to numerous studies [
10‐
13].
A growing body of evidence clearly suggested that the renal tissues of CR have significantly higher levels of NLRP3 expression and caspase-1. For patients with fibrosis, it may be possible to predict that the NLRP3 inflammasome will be involved in the management of renal failure [
13‐
15]. Additionally, research has shown that 5/6-nephrectomized renal models and unilateral ureteral blockage mice both have higher levels of activated NLRP3 inflammasomes in the renal matrix [
16,
17]. Adenosine triphosphate hydrolysis to adenosine diphosphate is inhibited by the small molecule MCC950 (Phase II clinical trials), which presents NLRP3 in a closed conformation and prevents oligomerization and activation of the NLRP3 inflammasome [
18]. Additionally, it inhibits the processing of cytokines like IL-1 and pyroptosis as a result of NLRP3 activation [
19].
Animal illness models for multiple sclerosis [
20], traumatic brain injury [
21], cryopyrin-associated periodic syndromes [
22], Alzheimer's disease, and Parkinson's disease have all shown promise for MCC950 [
23,
24]. Additionally, it was demonstrated that MCC950 could reduce diabetic kidney injury by inhibiting the NLRP3/caspase-1/IL-1 pathway [
25]. According to a recent study, MCC950 inhibits the NLRP3 inflammasome, which prevents acute renal failure by increasing hypoxia-inducible factor 1 and BCL2/adenovirus E1B interacting protein-mediated mitophagy, which lessens the effects of iohexol-induced apoptosis and renal injury [
26]. However, another study reported that the reduction of the NLRP3 inflammasome by MCC950 resulted in a considerable amount of renal inflammation and injury in the model of diabetic kidney mice [
27].
Based on the previously mentioned information, efforts have been made to identify effective and precise ways to restrict NLRP3 activation in the group of auto-inflammatory diseases, such as obesity, diabetes, and hypertension. The impact of the inflammasome in human disease studies has prompted these efforts. Therefore, the objective of the current investigation was to evaluate any potential renoprotective benefits of the NLRP3 inflammasome inhibitor MCC950 in rats with CRF caused by adenine.
Discussion
A vital prerequisite for improving the prognosis for CRF patients is an efficient treatment or prevention [
38]. The innate immune system's primary components, the inflammasomes, respond to cellular stress by boosting the production of pro-inflammatory cytokines like IL-1 and IL-18 and by promoting pyroptosis, an inflammatory form of cell death [
39]. A number of renal diseases, including acute renal failure [
40], chronic renal failure [
41], diabetic nephropathy [
42], and crystal-related nephropathy have been linked to the NLRP3 inflammasome [
43].
The initial adenine diet paradigm resulted in renal disease with early onset, substantial tubulointerstitial fibrosis, tubular atrophy, crystal formation, and significant vessel calcification. Lower adenine consumption in rats has now been demonstrated to cause gradually escalating renal impairment and cardiovascular disease. These chronic adenine diet models enable the study of relatively constant renal and cardiovascular disease, which is similar to CRF in people. Cardiovascular disease is a major source of increased morbidity and death in CRF patients, however the relationships between CRF and cardiovascular disease are poorly understood [
44]. Renal vascular disease has been defined as a disorder in which the primary renal arteries gradually occlude, causing hypertension and renal hypoperfusion, eventually leading to chronic renal ischemia [
45]. Adenine could elevated serum urea nitrate, serum creatinine concentrations, and uric acid excretion in urine in this model, caused proteinuria, and promoted renal tubulointerstitial nephritis and fibrosis, which mimicked CRF in people [
46].
Furthermore, the model resulted in a significant decrease in free amino acids and calcium concentration, hypoalbuminemia, increased albuminuria, hyperlipidemia, and vascular calcification, all of which are features found in clinical CRF. The kidneys were significantly enlarged, with interstitial inflammatory infiltrates and crystalline tubulointerstitial deposits, as well as oxidative stress, resembling a human CRF mechanistic route [
47]. Also, adenine caused rapid onset kidney damage, increasing blood urea nitrogen and serum creatinine concentrations within 6 days, causing apoptotic lesions in 70–80 percent of kidney tissue within 4 weeks, and causing distended fibrotic kidneys with a granulated attendance [
44].
In the current investigation, therapy with the NLRP3 inflammasome inhibitor MCC950 significantly decreased blood pressure, albumin, glucose, and ketone body levels in the urine, as well as serum levels of urea and creatinine in rats with adenine-induced CRF.
Instead of end-stage renal disease, hypertension is one of the main causes of mortality and morbidity in people with CRF [
48]. Thus, the impact of MCC950 on blood pressure was assessed in this study. The findings demonstrated that long-term adenine feeding was linked to higher systolic and diastolic blood pressure. Long-term adenine therapy increases blood pressure, according to studies by [
7,
49]. Animals received both adenine and the MCC950; the latter successfully prevented the rise in blood pressure.
Previous study looked into the efficacy of MCC950 in lowering blood pressure and preventing renal fibrosis, inflammation, and dysfunction in mice with pre-existing hypertension [
50]. In that study, hypertensive C57BL6/J mice were treated for 11 days with three different doses of MCC950 (2, 5, and 10 mg/kg/day) to determine the best antihypertensive dosage, which was 10 mg/kg/day. Also, Zhang and colleagues investigated the effectiveness of MCC950 on mouse models of type 2 diabetes at a dosage of 20mg/kg and discovered that MCC950 might be used as a tool for primary prevention of diabetic kidney damage [
25]. On the other hand, another study found that MCC950's suppression of the NLRP3 inflammasome led to severe renal inflammation and injury in a model of diabetic kidney mice. In the study of Østergaard and colleagues, MCC950 was administered at a total weekly dose of 15 mg/kg i.p. in non-diabetic and diabetic apolipoprotein E knockout mice with established diabetic kidney disease, resulting in increased renal injury and macrophage infiltration in association with increased cellular oxidative stress, as well as increased mesangial expansion and glomerulosclerosis via upregulation of inflammatory and fibrotic markers [
27]. A plausible reason for these disparate results might be found in the multiple mice models of diabetes studied, which differed from our model, as well as the distinct MCC950 dosing regimen employed.
Due to glomerular and tubular damage brought on by CRF, both protein filtration and reabsorption mechanisms become dysfunctional, resulting in increased levels of albumin and glucose excretion in the urine [
51,
52]. Additionally, the kidney cortex and medulla shared some degree of sustained elevation in free fatty acids and ketone bodies as a result of chronic renal ischemia [
53,
54]. Given that the serum levels of creatinine are influenced by glomerular filtration rate, the rise in creatinine and blood urea nitrogen is regarded as a significant indicator of renal damage [
55]. Furthermore, in the adenine model of CRF, proteinuria might be produced by injury to the glomeruli or renal tubules caused by the precipitation of 2,8-dihydroxyadenine, an adenine metabolite.
When serum creatinine levels double over the usual amount due to renal damage, the ability to filter out creatinine is reduced, increasing creatinine levels, and the glomerular filtration rate is thought to have been reduced by half [
56]. Increased protein catabolism or the conversion of ammonia to urea as a result of increased enzyme production involved in urea assembly are both associated with increased blood urea nitrogen [
57]. In the same way, a study reported a reduction in urinary albumin to creatinine ratio and decreased serum creatinine related to kidney injury improvement by MCC950 treatment in a mice model of diabetic nephropathy [
25]. Another study demonstrated that ozone therapy's modulation of the NLRP3 inflammasome in the 5/6 nephrectomized CRF rat model led to an improvement in renal function and a decrease in serum urea and creatinine [
41].
Reactive oxygen species (ROS) and NLRP3 inflammasome interactions help control immunological reactions during inflammation. According to studies, the activation of the NLRP3 inflammasome has a minor influence on ROS generation [
58,
59]. Additionally, ROS may cause the NLRP3 components that are involved in inducing apoptosis in innate immune cells during inflammation [
60]. When renal proximal tubular epithelial cells are damaged, it is seen that the expression of oxidative stress markers increases and the activity of the antioxidant enzyme superoxide dismutase decreases. This results in the activation of the NLRP3 inflammasome and proinflammatory pathways, including nuclear factor-kB [
61,
62].
The pathophysiology of CRF is significantly influenced by reactive oxygen species. Free oxygen radicals can cause the cell membrane's lipid to oxidize, which can result in renal tubular cell necrosis [
63]. Furthermore, it is well-known that intracellular reduced glutathione, the most effective non-enzymatic antioxidant involved in neutralizing free radicals, regulates the cellular redox environment to control a variety of cellular processes, including gene expression, cell-cycle progression, apoptosis, and metabolism [
64]. Nitric oxide deficit that is less severe than decreased kidney nitric oxide production and/or increased nitric oxide bio-inactivation may have a role in the development of CRF [
65].
In the present work, we discovered that treatment with MCC950 significantly reduced levels of oxidative stress indicators such malondialdehyde, significantly increased levels of the antioxidant enzyme GSH, and significantly increased levels of nitric oxide in the adenine-induced CRF rat model. These findings are consistent with earlier study which suggested that NLRP3 suppression with MCC950 therapy may prevent the development of chronic kidney disease brought on by cisplatin by reducing oxidative stress and inflammation [
62].
The kidneys, trachea, and digestive system all have low levels of NGAL expression when subjected to typical physiological conditions. On the other hand, when there is damage, NGAL secretion increases quickly in the thick ascending limb of the renal tubules [
66]. In addition, NGAL closely reflects the pattern of renal impairment in CRF patients and is a powerful and independent risk factor for CRF development [
67]. A recent study investigated that NGAL has the potential to be an appropriate biomarker for CRF identification in the early stages [
68]. In this investigation, we found that NGAL, which has long been recognized as a sign of CRF, was significantly elevated in rats with adenine-induced CRF. These findings support the findings of [
69] study, which found that NGAL was elevated in adenine-induced CRF. Additionally, it showed that NGAL participates in nephrogenic regeneration and healing during the course of kidney injury [
70]. The current study further shown that prolonged therapy with MCC950 for 28 days dramatically reduced tissue NGAL levels in adenine-induced CRF to levels that were nearly identical to the PBS group. By blocking the NLRP3/caspase-1/IL-1 pathway and lowering urinary NGAL levels in mice with a model of diabetic nephropathy, researchers demonstrated that MCC950 might significantly alleviate diabetic chronic kidney injury [
25]. Additionally, in the remnant kidney rat model of CRF, suppression of the NLRP3 inflammasome lowers the levels of NGAL in the urine [
71].
Microscopical analysis in the adenine rat model demonstrated tubulointerstitial damage with infiltrating leukocytes, interstitial edoema, and widening of the bowman's space, according to previous histological findings in CRF [
72]. These conclusions agree with those of the current investigation on the histological changes in adenine-induced CRF. The larger improvement was evident in the current investigation when MCC950 was administered to adenine-induced rats for 28 days, and this improvement was indicated by histological improvement in renal tissues.
Through inflammatory cytokines, CRF formation and progression are controlled. Additionally, it is well acknowledged that the levels of numerous inflammatory cytokines, including IL-6, IL-1, and tumor necrosis factor-, were higher in CRF patients [
73]. Adenine administration may increase the plasma levels of several inflammatory cytokines, including tumor necrosis factor and IL-1 [
69]. The pathophysiology of CRF is strongly influenced by oxidative stress, which can also lead to mitochondrial apoptosis and worsen renal failure [
74]. The apoptotic protein caspase-3 and the inflammatory mediator IL-1 were therefore examined. Moreover, research suggested that adenine-induced CRF may include caspase-3 [
75].
An earlier investigation revealed that the activation of caspase-3 and -7 resulted in the activation of the NLRP3 inflammasome and the oversecretion of IL-1 [
76]. Additionally, the NLRP3/caspase-3 pathway's effects on the cell cycle and apoptosis may contribute to the formation of myeloid cells [
76]. Through a considerable decrease in the protein expression of both interleukin 1 and caspase-3, the present study demonstrated a significant improvement in the adenine-induced CRF rats treated with MCC950. Not in line with the findings of [
25], who demonstrated that blocking the NLRP3/caspase-1/IL-1 pathway with MCC950 efficiently repaired diabetic kidney damage. In general, the current data strongly indicate the renoprotective action of MCC950 in adenine-induced CRF. These findings are confirmed by the biochemical, histological, and immunohistochemistry outcomes of this investigation.