Effects and Safety of an Oral Adsorbent on Chronic Kidney Disease Progression: A Systematic Review and Meta-Analysis

Uremic toxins mediate kidney diseases: the role of aryl hydrocarbon receptor

Aryl hydrocarbon receptor (AhR) was originally identified as an environmental sensor that responds to pollutants. Subsequent research has revealed that AhR recognizes multiple exogenous and endogenous molecules, including uremic toxins retained in the body due to the decline in renal function. Therefore, AhR is also considered to be a uremic toxin receptor. As a ligand-activated transcriptional factor, the activation of AhR is involved in cell differentiation and senescence, lipid metabolism and fibrogenesis. The accumulation of uremic toxins in the body is hazardous to all tissues and organs. The identification of the endogenous uremic toxin receptor opens the door to investigating the precise role and molecular mechanism of tissue and organ damage induced by uremic toxins. This review focuses on summarizing recent findings on the role of AhR activation induced by uremic toxins in chronic kidney disease, diabetic nephropathy and acute kidney injury. Furthermore, potential clinical approaches to mitigate the effects of uremic toxins are explored herein, such as enhancing uremic toxin clearance through dialysis, reducing uremic toxin production through dietary interventions or microbial manipulation, and manipulating metabolic pathways induced by uremic toxins through controlling AhR signaling. This information may also shed light on the mechanism of uremic toxin-induced injury to other organs, and provide insights into clinical approaches to manipulate the accumulated uremic toxins.

Attenuation of indoxyl sulfate-induced cell damage by cinchonidine-a Cinchona alkaloid-through the downregulation of p53 signaling pathway by promoting MDM2 cytoplasmic-nuclear shuttling in endothelial cells

Renocardiac syndromes are a critical concern among patients with chronic kidney disease (CKD). High level of indoxyl sulfate (IS), a protein-bound uremic toxin, in plasma is known to promote the pathogenesis of cardiovascular diseases by impairing endothelial function. However, the therapeutic effects of the adsorbent of indole, a precursor of IS, on renocardiac syndromes is still debated. Therefore, novel therapeutic approaches should be developed to treat IS-associated endothelial dysfunction. In the present study, we have found that cinchonidine, a major Cinchona alkaloid, exhibited superior cell-protective effects among the 131 test compounds in IS-stimulated human umbilical vein endothelial cells (HUVECs). IS-induced cell death, cellular senescence, and impairment of tube formation in HUVECs were substantially reversed after treatment with cinchonidine. Despite the cinchonidine did not alter reactive oxygen species formation, cellular uptake of IS and OAT3 activity, RNA-Seq analysis showed that the cinchonidine treatment downregulated p53-modulated gene expression and substantially reversed IS-caused G0/G1 cell cycle arrest. Although the mRNA levels of p53 were not considerably downregulated by cinchonidine in IS-treated HUVECs, the treatment of cinchonidine promoted the degradation of p53 and the cytoplasmic-nuclear shuttling of MDM2. Cinchonidine exhibited cell-protective effects against the IS-induced cell death, cellular senescence, and impairment of vasculogenic activity in HUVECs through the downregulation of p53 signaling pathway. Collectively, cinchonidine may be a potential cell-protective agent to rescue IS-induced endothelial cell damage.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Association between prevalence of laxative use and history of bone fractures and cardiovascular diseases in patients with chronic kidney disease: the Fukuoka Kidney disease Registry (FKR) study

BACKGROUND

Constipation is a common complication in patients with chronic kidney disease (CKD) and is involved in the pathogenesis of dysbiosis and progression of CKD. However, little is known about its association with disorders of the bone-cardiovascular axis in patients with CKD.

METHODS

We performed a cross-sectional analysis of 3878 patients with CKD using the baseline dataset of the Fukuoka Kidney disease Registry study, as a multicenter, prospective cohort study of pre-dialysis CKD patients. The main exposure of interest was constipation defined as use of at least one type of laxative. The main outcomes were the histories of bone fractures and cardiovascular diseases (CVDs) as manifestations of disorders of the bone-cardiovascular axis.

RESULTS

The prevalences of laxative use and histories of bone fractures and CVDs increased as kidney function declined. Among the 3878 patients, 532 (13.7%) patients used laxatives, 235 (6.1%) patients had prior bone fractures, and 1001 (25.8%) patients had prior CVDs. Histories of bone fractures and CVDs were significantly more prevalent among laxative users (P < 0.05). Multivariable-adjusted logistic regression analysis revealed that patients with laxatives had a significantly higher odds ratios for histories of bone fractures and CVDs than those without laxatives [adjusted odds ratios (95% confidence intervals) 1.67 (1.20-2.31) and 1.70 (1.30-2.22), respectively, P < 0.05].

CONCLUSIONS

These results suggest that constipation indicated by laxative use is associated with increased prevalences of historical bone fractures and CVDs in pre-dialysis patients with CKD.

Tissue Factor, Thrombosis, and Chronic Kidney Disease

Coagulation abnormalities are common in chronic kidney disease (CKD). Tissue factor (TF, factor III) is a master regulator of the extrinsic coagulation system, activating downstream coagulation proteases, such as factor Xa and thrombin, and promoting fibrin formation. TF and coagulation proteases also activate protease-activated receptors (PARs) and are implicated in various organ injuries. Recent studies have shown the mechanisms by which thrombotic tendency is increased under CKD-specific conditions. Uremic toxins, such as indoxyl sulfate and kynurenine, are accumulated in CKD and activate TF and coagulation; in addition, the TF-coagulation protease-PAR pathway enhances inflammation and fibrosis, thereby exacerbating renal injury. Herein, we review the recent research studies to understand the role of TF in increasing the thrombotic risk and CKD progression.

Microbial-Derived Tryptophan Catabolites, Kidney Disease and Gut Inflammation

Uremic metabolites, molecules either produced by the host or from the microbiota population existing in the gastrointestinal tract that gets excreted by the kidneys into urine, have significant effects on both health and disease. Tryptophan-derived catabolites are an important group of bacteria-produced metabolites with an extensive contribution to intestinal health and, eventually, chronic kidney disease (CKD) progression. The end-metabolite, indoxyl sulfate, is a key contributor to the exacerbation of CKD via the induction of an inflammatory state and oxidative stress affecting various organ systems. Contrastingly, other tryptophan catabolites positively contribute to maintaining intestinal homeostasis and preventing intestinal inflammation—activities signaled through nuclear receptors in particular—the aryl hydrocarbon receptor (AhR) and the pregnane X receptor (PXR). This review discusses the origins of these catabolites, their effect on organ systems, and how these can be manipulated therapeutically in the future as a strategy to treat CKD progression and gut inflammation management. Furthermore, the use of biotics (prebiotics, probiotics, synbiotics) as a means to increase the presence of beneficial short-chain fatty acids (SCFAs) to achieve intestinal homeostasis is discussed.

POTENTIAL THERAPEUTIC OPTIONS TARGETING THE GUT DYSBIOSIS IN CHRONIC KIDNEY DISEASE

The gut microbiota plays an important physiological role in controlling not only the function of the gastrointestinal tract, but also in maintaining systemic homeostasis. Quantitative and /or qualitative disturbances of the gut microbiota (dysbiosis) are an important element in the complex pathogenesis of many diseases, including chronic kidney disease (CKD). In the disease, the mutual interactions between disturbed gut microbiota and the progression of CKD (pathophysiological "kidney-gut axis") have been demonstrated. The kidney failure causes water and nitrogen waste retention which leads to disturbances of motility, secretion and absorption in the gastrointestinal tract. These abnormalities contribute to the development of gut dysbiosis, accompanied by overproduction of toxic bacterial metabolites, with their translocation to the peripheral blood and development of endotoxemia. As a consequence, chronic kidney "low-grade" inflammation and oxidative stress develop, with further deterioration of kidney function in the mechanism of the "vicious cycle" of the kidney-gut axis. Considering the key role of gut dysbiosis and the kidney-gut axis, the attempts to restore the gut eubiosis seem to have an important role in the treatment of CKD and may be even regarded as a form of causal therapeutic intervention. The paper briefly discusses the basics of the pathophysiological kidney-gut axis in CKD and potential methods of modulating the abnormal gut microbiota in this disease, including the use of probiotic or prebiotic preparations, agents that absorb bacterial-derived toxins in the intestinal lumen, fecal microbiota transplantation and drugs used so far for other indications (acarbose, meclofenamate, lubiprostone).

The Dual Roles of Protein-Bound Solutes as Toxins and Signaling Molecules in Uremia

In patients with severe kidney disease, renal clearance is compromised, resulting in the accumulation of a plethora of endogenous waste molecules that cannot be removed by current dialysis techniques, the most often applied treatment. These uremic retention solutes, also named uremic toxins, are a heterogeneous group of organic compounds of which many are too large to be filtered and/or are protein-bound. Their renal excretion depends largely on renal tubular secretion, by which the binding is shifted towards the free fraction that can be eliminated. To facilitate this process, kidney proximal tubule cells are equipped with a range of transport proteins that cooperate in cellular uptake and urinary excretion. In recent years, innovations in dialysis techniques to advance uremic toxin removal, as well as treatments with drugs and/or dietary supplements that limit uremic toxin production, have provided some clinical improvements or are still in progress. This review gives an overview of these developments. Furthermore, the role protein-bound uremic toxins play in inter-organ communication, in particular between the gut (the side where toxins are produced) and the kidney (the side of their removal), is discussed.

The Microbiome and Uremic Solutes

Uremic retention solutes, especially the protein-bound compounds, are toxic metabolites, difficult to eliminate with progressive renal functional decline. They are of particular interest because these uremic solutes are responsible for the pathogenesis of cardiovascular and chronic kidney diseases. Evidence suggests that the relation between uremic toxins, the microbiome, and its host is altered in patients with chronic kidney disease, with the colon’s motility, epithelial integrity, and absorptive properties also playing an important role. Studies found an alteration of the microbiota composition with differences in species proportion, diversity, and function. Since uremic toxins precursors are generated by the microbiota, multiple therapeutic options are currently being explored to address dysbiosis. While an oral adsorbent can decrease the transport of bacterial metabolites from the intestinal lumen to the blood, dietary measures, supplements (prebiotics, probiotics, and synbiotics), and antibiotics aim to target directly the gut microbiota composition. Innovative approaches, such as the modulation of bacterial enzymes, open new perspectives to decrease the plasma level of uremic toxins.

The Intestinal Microbiota and Metabolites in the Gut-Kidney-Heart Axis of Chronic Kidney Disease

Emerging evidences demonstrate the involvement of gut microbiota in the progression of chronic kidney disease (CKD) and CKD-associated complications including cardiovascular disease (CVD) and intestinal dysfunction. In this review, we discuss the interactions between the gut, kidney and heart in CKD state, and elucidate the significant role of intestinal microbiota in the gut-kidney-heart axis hypothesis for the pathophysiological mechanisms of these diseases, during which process mitochondria may serve as a potential therapeutic target. Dysregulation of this axis will lead to a vicious circle, contributing to CKD progression. Recent studies suggest novel therapies targeting gut microbiota in the gut-kidney-heart axis, including dietary intervention, probiotics, prebiotics, genetically engineered bacteria, fecal microbiota transplantation, bacterial metabolites modulation, antibiotics, conventional drugs and traditional Chinese medicine. Further, the identification of specific microbial communities and their corresponding pathophysiological metabolites and the illumination of the gut-kidney-heart axis may contribute to innovative basic research, clinical trials and therapeutic strategies against CKD progression and uremic complications in CKD patients.

Differences in gut microbiota structure in patients with stages 4-5 chronic kidney disease

The gut microbiota can affect human metabolism, immunity, and other biologic pathways through the complex gut-kidney axis (GKA), and in turn participate in the occurrence and development of kidney disease. In this study, 39 patients with stage 4-5 chronic kidney disease (CKD) and 40 healthy individuals were recruited and 16S rDNA sequencing was performed to analyze the V3-V4 conserved regions of their microbiota. A total of 795 operational taxonomic units (OTUs) shared between groups or specific to each group were obtained, among which 255 OTUs with significant differences between the two groups were identified (P<0.05). Adonis differential analysis showed that the diversity of gut microbiota was highly correlated with CKD stages 4-5. Additionally, 61 genera with differences in the two groups were identified (P<0.05) and 111 species with significant differences in the phyla, classes, orders, families, and genera between the two groups were identified (P<0.05). The differential bacterial genera with the greatest contribution were, in descending order: c_Bacteroidia, o_Bacteroidales, p_Bacteroidetes, c_Clostridia, o_Clostridiales, etc. Those with the greatest contribution in stages 4-5 CKD were, in descending order: p_Proteobacteria, f_Enterobacteriaceae, o_Enterobacteriales, c_Gammaproteobacteria, c_Bacilli, etc. The results suggest that the diversity of the microbiota may affect the occurrence, development, and outcome of the terminal stages of CKD.

The Therapeutic Strategies for Uremic Toxins Control in Chronic Kidney Disease

Uremic toxins (UTs) are mainly produced by protein metabolized by the intestinal microbiota and converted in the liver or by mitochondria or other enzymes. The accumulation of UTs can damage the intestinal barrier integrity and cause vascular damage and progressive kidney damage. Together, these factors lead to metabolic imbalances, which in turn increase oxidative stress and inflammation and then produce uremia that affects many organs and causes diseases including renal fibrosis, vascular disease, and renal osteodystrophy. This article is based on the theory of the intestinal-renal axis, from bench to bedside, and it discusses nonextracorporeal therapies for UTs, which are classified into three categories: medication, diet and supplement therapy, and complementary and alternative medicine (CAM) and other therapies. The effects of medications such as AST-120 and meclofenamate are described. Diet and supplement therapies include plant-based diet, very low-protein diet, probiotics, prebiotics, synbiotics, and nutraceuticals. The research status of Chinese herbal medicine is discussed for CAM and other therapies. This review can provide some treatment recommendations for the reduction of UTs in patients with chronic kidney disease.

Efficacy of AST-120 for Patients With Chronic Kidney Disease: A Network Meta-Analysis of Randomized Controlled Trials

AST-120, an oral spherical activated carbon, may delay the need for kidney dialysis and improve uremia symptoms because it can adsorb acidic and basic organic compounds, especially small-molecule uremic toxins. However, previous studies produced no conclusive evidence regarding the benefits of AST-120 in delaying the progression of chronic kidney disease (CKD). Therefore, this systematic review and network meta-analysis evaluated the effects of AST-120 in patients with CKD. Related keywords of CKD and AST-120 were used to search four databases to obtain potential evidence on this topic, and two authors individually completed evidence selection, data extraction, and quality assessment. Network meta-analysis was performed for mortality, end-stage renal disease, composite renal outcomes, and laboratory outcomes based on a frequentist approach. In total, 15 randomized controlled trials (n = 3,763) were included in the present synthesis, and the pooled results revealed non-significant differences in mortality among the treatment strategies. Low- and high-dose AST-120 were not superior to no AST-120 treatment regarding renal outcomes. However, the event rates of end-stage renal disease (risk ratio [RR] = 0.78, 95% confidence interval [CI] = 0.62–0.99) and composite renal outcomes (RR = 0.78, 95% CI: 0.63–0.97) were significantly lower in the tailored-dose AST-120 group than in no AST-120 group. The results did not reveal a small-study effect on the outcomes. Tailored dosing of AST-120 appeared to represent an optimal treatment strategy because it resulted in lower rates of composite renal outcomes and end-stage renal disease.

Diverse roles of microbial indole compounds in eukaryotic systems

Indole and its derivatives are widespread across different life forms, functioning as signalling molecules in prokaryotes and with more diverse roles in eukaryotes. A majority of indoles found in the environment are attributed to bacterial enzymes converting tryptophan into indole and its derivatives. The involvement of indoles among lower organisms as an interspecies and intraspecies signal is well known, with many reports showing that inter‐kingdom interactions involving microbial indole compounds are equally important as they influence defence systems and even the behaviour of higher organisms. This review summarizes recent advances in our understanding of the functional properties of indole and indole derivatives in diverse eukaryotes. Furthermore, we discuss current perspectives on the role of microbial indoles in human diseases such as diabetes, obesity, atherosclerosis, and cancers. Deciphering the function of indoles as biomarkers of metabolic state will facilitate the formulation of diet‐based treatments and open unique therapeutic opportunities.

Effect of Renamezin upon attenuation of renal function decline in pre-dialysis chronic kidney disease patients: 24-week prospective observational cohort study

Renamezin^® is a modified capsule-type oral spherical adsorptive carbon which lowers indoxyl sulfate levels in patients with advanced chronic kidney disease (CKD). This 24-week prospective observational cohort study was performed to evaluate the effect of Renamezin^® upon attenuation of renal function decline. A total of 1,149 adult patients with baseline serum creatinine 2.0–5.0 mg/dL were enrolled from 22 tertiary hospital in Korea from April 2016 to September 2018. Among them, a total of 686 patients completed the study and were included in the intention-to-treat analysis. A total of 1,061 patients were included in the safety analysis. The mean age was 63.5 years and male patients were predominant (63.6%). Most of the patients (76.8%) demonstrated high compliance with study drug (6g per day). After 24 week of treatment, serum creatinine was increased from 2.86±0.72 mg/dL to 3.06±1.15 mg/dL (p<0.001), but estimated glomerular filtration rate was not changed significantly during observation period (22.3±6.8 mL/min/1.73m² to 22.1±9.1 mL/min/1.73m², p = 0.243). Patients with age over 65 years old and those under good systolic blood pressure control <130 mmHg were most likely to get benefit from Renamezin^® treatment to preserve renal function. A total of 98 (9.2%) patients out of 1,061 safety population experienced 134 adverse events, of which gastrointestinal disorders were the most common. There were no serious treatment-related adverse events. Renamezin^® can be used safely to attenuate renal function decline in moderately advanced CKD patients.

Protein-bound uremic toxin lowering strategies in chronic kidney disease: a systematic review and meta-analysis

INTRODUCTION

Accumulation of protein-bound uremic toxins, including indoxyl sulfate and p-cresyl sulfate, are associated with increased cardiovascular disease and mortality in chronic kidney disease (CKD). We performed a systematic review and meta-analysis to synthesize the available strategies for lowering protein-bound uremic toxin levels in CKD patients.

METHODS

We conducted a meta-analysis by searching the databases of MEDLINE, Scopus, and the Cochrane Central Register of Controlled Trials for observational studies and randomized controlled trials (RCTs) that examined the effect of dietary protein restrictions, biotic supplements (including prebiotics, probiotics, and synbiotics), AST-120, dialysis techniques, and the outcome of preservation of residual renal function (RRF) on indoxyl sulfate and p-cresyl sulfate levels. Random-effect model meta-analyses were used to compute changes in the outcomes of interest.

RESULTS

A total of 38 articles (2,492 patients), comprising 28 RCTs, 8 single-arm or prospective cohort studies, and 2 cross-sectional studies were included in this meta-analysis. When compared with placebo, prebiotics, synbiotics, and AST-120 provided significantly lower levels of both serum indoxyl sulfate and p-cresyl sulfate. There were no significant reductions in serum indoxyl sulfate and p-cresyl sulfate levels in patients receiving probiotics. Preservation of RRF in dialysis patients resulted in lower levels of both of the protein-bound uremic toxins. When compared with conventional hemodialysis, hemodiafiltration significantly decreased serum p-cresyl sulfate alone, whereas a significant change in serum indoxyl sulfate levels was observed only in studies with long-term observation periods. Very low protein diet (VLPD) and other oral medications yielded insignificant differences in protein-bound uremic toxins.

CONCLUSIONS

The present meta-analysis demonstrated that prebiotics, synbiotics, and AST-120 can effectively reduce both serum indoxyl sulfate and p-cresyl sulfate in CKD patients when compared with placebo. Preservation of RRF was associated with lower serum indoxyl sulfate and p-cresyl sulfate levels. The effect of biotic supplements was detected only in dialysis patients. For non-dialysis CKD patients, the results were limited due to the small number of studies. Further studies are needed to determine the efficacy in these populations.

Novel conservative management of chronic kidney disease via dialysis-free interventions

PURPOSE OF REVIEW

In advanced chronic kidney disease (CKD) patients with progressive uremia, dialysis has traditionally been the dominant treatment paradigm. However, there is increasing interest in conservative and preservative management of kidney function as alternative patient-centered treatment approaches in this population.

RECENT FINDINGS

The primary objectives of conservative nondialytic management include optimization of quality of life and treating symptoms of end-stage renal disease (ESRD). Dietetic-nutritional therapy can be a cornerstone in the conservative management of CKD by reducing glomerular hyperfiltration, uremic toxin generation, metabolic acidosis, and phosphorus burden. Given the high symptom burden of advanced CKD patients, routine symptom assessment using validated tools should be an integral component of their treatment. As dialysis has variable effects in ameliorating symptoms, palliative care may be needed to manage symptoms such as pain, fatigue/lethargy, anorexia, and anxiety/depression. There are also emerging treatments that utilize intestinal (e.g., diarrhea induction, colonic dialysis, oral sorbents, gut microbiota modulation) and dermatologic pathways (e.g., perspiration reduction) to reduce uremic toxin burden.

SUMMARY

As dialysis may not confer better survival nor improved patient-centered outcomes in certain patients, conservative management is a viable treatment option in the advanced CKD population.

Targeting Uremic Toxins to Prevent Peripheral Vascular Complications in Chronic Kidney Disease

Chronic kidney disease (CKD) exhibits progressive kidney dysfunction and leads to disturbed homeostasis, including accumulation of uremic toxins, activated renin-angiotensin system, and increased oxidative stress and proinflammatory cytokines. Patients with CKD are prone to developing the peripheral vascular disease (PVD), leading to poorer outcomes than those without CKD. Cumulative evidence has showed that the synergy of uremic milieu and PVD could exaggerate vascular complications such as limb ischemia, amputation, stenosis, or thrombosis of a dialysis vascular access, and increase mortality risk. The role of uremic toxins in the pathogenesis of vascular dysfunction in CKD has been investigated. Moreover, growing evidence has shown the promising role of uremic toxins as a therapeutic target for PVD in CKD. This review focused on uremic toxins in the pathophysiology, in vitro and animal models, and current novel clinical approaches in reducing the uremic toxin to prevent peripheral vascular complications in CKD patients.

The clinical impact of gut microbiota in chronic kidney disease

Gut microorganisms play critical roles in both maintaining host homeostasis and the development of diverse diseases. Gut dysbiosis, an alteration of the composition and function of gut microorganisms, is commonly seen in patients with chronic kidney disease (CKD). CKD itself contributes to a disruption of the symbiotic relationship between the gut microbiota and the host, while the resulting gut dysbiosis may play a part in stage progression of CKD. This bidirectional relationship supports the concept that the gut microbiota is considered a novel focus for the pathogenesis and management of CKD. This article examines the interaction between the gut microbiota and the kidney, the mutual effects of dysbiosis and CKD, and possible treatment options to restore gut eubiosis, and reduce CKD progression and its related complications.

New therapeutic targets in chronic kidney disease progression and renal fibrosis

INTRODUCTION

The current therapeutic armamentarium to prevent chronic kidney disease (CKD) progression is limited to the control of blood pressure and in diabetic patients, the strict control of glucose levels. Current research is primarily focused on the reduction of inflammation and fibrosis at different levels.

AREAS COVERED

This article examines the latest progress in this field and places an emphasis on inflammation, oxidative stress, and fibrosis. New therapeutic targets are described and evidence from experimental and clinical studies is summarized. We performed a search in Medline for articles published over the last 10 years.

EXPERT OPINION

The search for therapeutic targets of renal inflammation is hindered by an incomplete understanding of the pathophysiology. The determination of the specific inducers of inflammation in the kidney is an area of heightened potential. Prevention of the progression of renal fibrosis by blocking TGF-β signaling has been unsuccessful, but the investigation of signaling pathways involved in late stages of fibrosis progression could yield improved results. Preventive strategies such as the modification of microbiota-inducers of uremic toxins involved in CKD progression is a promising field because of the interaction between the gut microbiota and the renal system.