Toxic Effects of Indoxyl Sulfate on Osteoclastogenesis and Osteoblastogenesis

Multiscale effects of the calcimimetic drug, etelcalcetide on bone health of rats with secondary hyperparathyroidism induced by chronic kidney disease

Chronic kidney disease-induced secondary hyperparathyroidism (CKD-SHPT) heightens fracture risk through impaired mineral homeostasis and elevated levels of uremic toxins (UTs), which in turn enhance bone remodeling. Etelcalcetide (Etel), a calcium-sensing receptor (CaSR) agonist, suppresses parathyroid hormone (PTH) in hyperparathyroidism to reduce excessive bone resorption, leading to increased bone mass. However, Etel's effect on bone quality, chemical composition, and strength is not well understood. To address these gaps, we established a CKD-SHPT rat model and administered Etel at a human-equivalent dose concurrently with disease induction. The effects on bone and mineral homeostasis were compared with a CKD-SHPT (vehicle-treated group) and a control group (rats without SHPT). Compared with vehicle-treated CKD-SHPT rats, Etel treatment improved renal function, reduced circulating UT levels, improved mineral homeostasis parameters, decreased PTH levels, and prevented mineralization defects. The upregulation of mineralization-promoting genes by Etel in CKD-SHPT rats might explain its ability to prevent mineralization defects. Etel preserved both trabecular and cortical bones with attendant suppression of osteoclast function, besides increasing mineralization. Etel maintained the number of viable osteocytes to the control level, which could also contribute to its beneficial effects on bone. CKD-SHPT rats displayed increased carbonate substitution of matrix and mineral, decreased crystallinity, mineral-to-matrix ratio, and collagen maturity, and these changes were mitigated by Etel. Further, Etel treatment prevented CKD-SHPT-induced deterioration in bone strength and mechanical behavior. Based on these findings, we conclude that in CKD-SHPT rats, Etel has multiscale beneficial effects on bone that involve remodeling suppression, mineralization gene upregulation, and preservation of osteocytes.

Indoxyl sulfate exacerbates alveolar bone loss in chronic kidney disease through ferroptosis

OBJECTIVES

The purpose of this study was to determine whether indoxyl sulfate (IS) is involved in alveolar bone deterioration and to elucidate the mechanism underlying alveolar bone loss in chronic kidney disease (CKD) patients.

MATERIALS AND METHODS

Mice were divided into the control group, CP group (ligature-induced periodontitis), CKD group (5/6 nephrectomy), and CKD + CP group. The concentration of IS in the gingival crevicular fluid (GCF) was determined by HPLC. The bone microarchitecture was evaluated by micro-CT. MC3T3-E1 cells were stimulated with IS, and changes in mitochondrial morphology and ferroptosis-related factors were detected. RT-PCR, western blotting, alkaline phosphatase activity assays, and alizarin red S staining were utilized to assess how IS affects osteogenic differentiation.

RESULTS

Compared with that in the other groups, alveolar bone destruction in the CKD + CP group was more severe. IS accumulated in the GCF of mice with CKD. IS activated the aryl hydrocarbon receptor (AhR) in vitro, inhibited MC3T3-E1 cell osteogenic differentiation, caused changes in mitochondrial morphology, and activated the SLC7A11/GPX4 signaling pathway. An AhR inhibitor attenuated the aforementioned changes induced by IS.

CONCLUSIONS

IS activated the AhR/SLC7A11/GPX4 signaling pathway, inhibited osteogenesis in MC3T3-E1 cells, and participated in alveolar bone resorption in CKD model mice through ferroptosis.

Current therapeutic approach of chronic kidney disease-mineral and bone disorder

Chronic kidney disease (CKD) has emerged as one of the leading noncommunicable diseases affecting >10% of the population worldwide. Bone and mineral disorders are a common complication among patients with CKD resulting in a poor life quality, high fracture risk, increased morbidity and cardiovascular mortality. According to Kidney Disease: Improving Global Outcomes, renal osteodystrophy refers to changes in bone morphology found in bone biopsy, whereas CKD-mineral and bone disorder (CKD-MBD) defines a complex of disturbances including biochemical and hormonal alterations, disorders of bone and mineral metabolism and extraskeletal calcification. As a result, the management of CKD-MBD should focus on the aforementioned parameters, including the treatment of hyperphosphatemia, hypocalcemia, abnormal PTH and vitamin D levels. Regarding the bone fragility fractures, osteoporosis and renal osteodystrophy, which constitute the bone component of CKD-MBD, anti-osteoporotic agents constitute the mainstay of treatment. However, a thorough elucidation of the CKD-MBD pathogenesis is crucial for the ideal personalized treatment approach. In this paper, we review the pathology and management of CKD-MBD based on the current literature with special attention to recent advances.

Indoxyl Sulfate-Induced Macrophage Toxicity and Therapeutic Strategies in Uremic Atherosclerosis

Cardiovascular disease (CVD) frequently occurs in patients with chronic kidney disease (CKD), particularly those undergoing dialysis. The mechanisms behind this may be related to traditional risk factors and CKD-specific factors that accelerate atherosclerosis and vascular calcification in CKD patients. The accumulation of uremic toxins is a significant factor in CKD-related systemic disorders. Basic research suggests that indoxyl sulfate (IS), a small protein-bound uremic toxin, is associated with macrophage dysfunctions, including increased oxidative stress, exacerbation of chronic inflammation, and abnormalities in lipid metabolism. Strategies to mitigate the toxicity of IS include optimizing gut microbiota, intervening against the abnormality of intracellular signal transduction, and using blood purification therapy with higher efficiency. Further research is needed to examine whether lowering protein-bound uremic toxins through intervention leads to a reduction in CVD in patients with CKD.

The Bone-Vascular Axis in Chronic Kidney Disease: From Pathophysiology to Treatment

PURPOSE OF REVIEW

This review aims to describe the pathogenic factors involved in bone-vessel anomalies in CKD which are the object of numerous experimental and clinical research.

RECENT FINDINGS

Knowledge on the pathophysiological mechanisms involved in the regulation of vascular calcification and mineral-bone disorders is evolving. Specific bone turnover anomalies influence the vascular health while recent studies demonstrate that factors released by the calcified vessels also contribute to bone deterioration in CKD. Current therapies used to control mineral dysregulations will impact both the vessels and bone metabolism. Available anti-osteoporotic treatments used in non-CKD population may negatively or positively affect vascular health in the context of CKD. It is essential to study the bone effects of the new therapeutic options that are currently under investigation to reduce vascular calcification. Our paper highlights the complexity of the bone-vascular axis and discusses how current therapies may affect both organs in CKD.

Potential effects of specific gut microbiota on periodontal disease: a two-sample bidirectional Mendelian randomization study

Introduction

Periodontal disease (PD) presents a substantial global health challenge, encompassing conditions from reversible gingivitis to irreversible periodontitis, often culminating in tooth loss. The gut-oral axis has recently emerged as a focal point, with potential gut microbiota dysbiosis exacerbating PD.

Methods

In this study, we employed a double-sample bidirectional Mendelian randomized (MR) approach to investigate the causal relationship between specific gut microbiota and periodontal disease (PD) and bleeding gum (BG) development, while exploring the interplay between periodontal health and the gut microenvironment. We performed genome-wide association studies (GWAS) with two cohorts, totalling 346,731 (PD and control) and 461,113 (BG and control) participants, along with data from 14,306 participants' intestinal flora GWAS, encompassing 148 traits (31 families and 117 genera). Three MR methods were used to assess causality, with the in-verse-variance-weighted (IVW) measure as the primary outcome. Cochrane's Q test, MR-Egger, and MR-PRESSO global tests were used to detect heterogeneity and pleiotropy. The leave-one-out method was used to test the stability of the MR results. An F-statistic greater than 10 was accepted for instrument exposure association.

Results and conclusion

Specifically, Eubacterium xylanophilum and Lachnoclostridium were associated with reduced gum bleeding risk, whereas Anaerotruncus, Eisenbergiella, and Phascolarctobacterium were linked to reduced PD risk. Conversely, Fusicatenibacter was associated with an elevated risk of PD. No significant heterogeneity or pleiotropy was detected. In conclusion, our MR analysis pinpointed specific gut flora with causal connections to PD, offering potential avenues for oral health interventions.

Chromatin accessibility and epigenetic deoxyribose nucleic acid (DNA) modifications in chronic kidney disease (CKD) osteoblasts: a study of bone and osteoblasts from pediatric patients with CKD

Maturation defects are intrinsic features of osteoblast lineage cells in CKD patients. These defects persist ex vivo, suggesting that CKD induces epigenetic changes in bone cells. To gain insights into which signaling pathways contribute to CKD-mediated, epigenetically driven, impairments in osteoblast maturation, we characterized RNA expression and DNA methylation patterns by RNA-Seq and MethylationEpic in primary osteoblasts from nine adolescent and young adult dialysis patients with end-stage kidney disease and three healthy references. ATAC-Seq was also performed on a subset of osteoblasts. Bone matrix protein expression was extracted from the iliac crest and evaluated by proteomics. Gene set enrichment analysis was used to establish signaling pathways consistently altered in chromatin accessibility, DNA methylation, and RNA expression patterns. Single genes were suppressed in primary osteoblasts using shRNA and mineralization characterized in vitro. The effect of nuclear factor of activated T cells (NFAT) signaling suppression was also assessed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) incorporation. We found that signaling pathways critical for osteoblast differentiation were strongly downregulated in CKD osteoblasts. Gene set enrichment analysis identified highly significant methylation changes, differential chromatin accessibility, and altered RNA expression in NFAT signaling targets. NFAT inhibition reduced osteoblast proliferation. Combined analysis of osteoblast RNA expression and whole bone matrix composition identified 13 potential ligand-receptor pairs. In summary, epigenetic changes in CKD osteoblasts associate with altered expression of multiple osteoblast genes and signaling pathways. An increase in NFAT signaling may play a role in impaired CKD osteoblast maturation. Epigenetic changes also associate with an altered bone matrix, which may contribute to bone fragility. Further studies are necessary to elucidate the pathways affected by these genetic alterations since elucidating these pathways will be vital to correcting the underlying biology of bone disease in the CKD population.

Role and Regulation of Transcription Factors in Osteoclastogenesis

Bones serve mechanical and defensive functions, as well as regulating the balance of calcium ions and housing bone marrow.. The qualities of bones do not remain constant. Instead, they fluctuate throughout life, with functions increasing in some situations while deteriorating in others. The synchronization of osteoblast-mediated bone formation and osteoclast-mediated bone resorption is critical for maintaining bone mass and microstructure integrity in a steady state. This equilibrium, however, can be disrupted by a variety of bone pathologies. Excessive osteoclast differentiation can result in osteoporosis, Paget's disease, osteolytic bone metastases, and rheumatoid arthritis, all of which can adversely affect people's health. Osteoclast differentiation is regulated by transcription factors NFATc1, MITF, C/EBPα, PU.1, NF-κB, and c-Fos. The transcriptional activity of osteoclasts is largely influenced by developmental and environmental signals with the involvement of co-factors, RNAs, epigenetics, systemic factors, and the microenvironment. In this paper, we review these themes in regard to transcriptional regulation in osteoclastogenesis.

Emerging nanotherapeutic strategies targeting gut-X axis against diseases

Gut microbiota can coordinate with different tissues and organs to maintain human health, which derives the concept of the gut-X axis. Conversely, the dysbiosis of gut microbiota leads to the occurrence and development of various diseases, such as neurological diseases, liver diseases, and even cancers. Therefore, the modulation of gut microbiota offers new opportunities in the field of medicines. Antibiotics, probiotics or other treatments might restore unbalanced gut microbiota, which effects do not match what people have expected. Recently, nanomedicines with the high targeting ability and reduced toxicity make them an appreciative choice for relieving disease through targeting gut-X axis. Considering this paradigm-setting trend, the current review summarizes the advancements in gut microbiota and its related nanomedicines. Specifically, this article introduces the immunological effects of gut microbiota, summarizes the gut-X axis-associated diseases, and highlights the nanotherapeutics-mediated treatment via remolding the gut-X axis. Moreover, this review also discusses the challenges in studies related to nanomedicines targeting the gut microbiota and offers the future perspective, thereby aiming at charting a course toward clinic.

Astragaloside IV attenuates indoxyl sulfate-induced injury of renal tubular epithelial cells by inhibiting the aryl hydrocarbon receptor pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus membranaceus Fisch. ex Bunge has long been used to treat chronic kidney disease (CKD) in China. However, the mechanism of action requires further study. Indoxyl sulfate accumulation is the key cause of CKD progression. The aryl hydrocarbon receptor (AhR) plays an essential role in the renal tubular injury induced by indoxyl sulfate (IS).

AIM

We explored the effects of Astragaloside IV (AS-IV), a minor component of the flowering perennial Astragalus membranaceus Fisch. ex Bunge, on AhR activity during IS-induced injury of renal tubular epithelial cells.

METHODS

C57BL/6 mice fed a 0.2% adenine diet (adenine + IS) and intraperitoneally injected with IS were used to study the protective effects of AS-IV, and specifically the effect on the AhR. In addition, apoptosis (annexin/PI), oxidative stress and the AhR pathway were investigated in IS-stimulated HK-2 cells treated with AS-IV. The binding of AS-IV to the AhR was assessed in a molecular docking analysis. AhR knockdown using AhR siRNA allowed determination of the effects of AS-IV in IS-stimulated HK-2 cells.

RESULTS

AS-IV inhibited tubulointerstitial injury in adenine + IS mice. While AS-IV did not reduce serum IS levels, it did inhibit AhR expression in the kidney. In IS-stimulated HK-2 cells, AS-IV also dramatically reduced apoptosis, decreased oxidative stress responses and inhibited the expression of the AhR pathway. The molecular docking analysis showed surface binding of AS-IV to the AhR. Following AhR knockdown in HK-2 cells, IS-induced apoptosis was reduced and could not be further reduced by AS-IV.

CONCLUSION

By targeting the AhR, AS-IV may alleviate IS-induced renal tubular injury, thus offering a novel therapeutic approach to the treatment of chronic renal failure.

Tryptophan intake, not always the more the better

Objectives

To investigate the effects of excessive tryptophan intake on the body and the effects of tryptophan metabolism-related aryl hydrocarbon receptor (AhR) pathway in healthy rats and chronic kidney disease rats, to study the adverse effects of excess tryptophan.

Design

In Part I Experiment, the healthy rats were fed with diet containing 0.6, 1.2 and 1.8% tryptophan for 12 weeks. After the intervention, the blood and kidney tissues were collected. Serum creatinine and blood urea nitrogen were detected. Hematoxylin-eosin (H&E) staining was used to observe renal pathological changes. Enzyme-linked immunosorbent assay was used to detect serum kynurenic acid and AhR levels. The kidney levels of AhR, CyP1A1 and CyP1B1 were detected by western-blot. In Part II Experiment, the chronic kidney disease (CKD) model was induced by intra-gastric gavage with adenine for 4 weeks. Then the CKD rats were given tryptophan at a dose of 100 mg/kg or 500 mg/kg for eight weeks. Rat survival curve, renal function, renal tissue pathology and serum AhR were detected. Tryptophan-targeted ultra-high-performance liquid chromatography coupled with multiple reaction monitoring mass spectrometry (UHPLC-MRM-MS) was employed to quantitatively access the tryptophan-targeted metabolites in two parts experiments.

Results

In part I experiment, high tryptophan diet can increase the level of blood urea nitrogen (BUN) in healthy rats and induce focal renal tubulointerstitial injury. Tryptophan-targeted analyzes showed that high tryptophan diet feeding can significantly increase the concentration of kynurenine and indole metabolites. The serum AhR level and kidney AhR, CyP1A1 and CyP1B1 were also significantly increased in high tryptophan diet rats. In part II experiment, high tryptophan intervention induced a significant increase in mortality, serum creatinine, urea nitrogen levels, and renal pathological damage in CKD rats. The levels of tryptophan-targeted metabolites, kynurenine, xanthurenate, picolinic acid, 5-hydroxyindole-3-acetic acid, indole-3-lactic acid, indoleacetate and indoxyl sulfate, showed an upward trend in the high-dose tryptophan group (Ade + Trp-H) compared with the adenine group. The serum AhR of Ade + Trp-H rats was significantly higher than those of adenine rats.

Conclusion

Moderate tryptophan intake may be beneficial, but excessive tryptophan can lead to accumulation of kynurenine and indole metabolites, activate AhR pathway and induce kidney injury.

Is Adynamic Bone Always a Disease? Lessons from Patients with Chronic Kidney Disease

Renal osteodystrophy (ROD) is a common complication of end-stage kidney disease that often starts early with loss of kidney function, and it is considered an integral part in management of patients with chronic kidney disease (CKD). Adynamic bone (ADB) is characterized by suppressed bone formation, low cellularity, and thin osteoid seams. There is accumulating evidence supporting increasing prevalence of ADB, particularly in early CKD. Contemporarily, it is not very clear whether it represents a true disease, an adaptive mechanism to prevent bone resorption, or just a transitional stage. Several co-players are incriminated in its pathogenesis, such as age, diabetes mellitus, malnutrition, uremic milieu, and iatrogenic factors. In the present review, we will discuss the up-to-date knowledge of the ADB and focus on its impact on bone health, fracture risk, vascular calcification, and long-term survival. Moreover, we will emphasize the proper preventive and management strategies of ADB that are pivotal issues in managing patients with CKD. It is still unclear whether ADB is always a pathologic condition or whether it can represent an adaptive process to suppress bone resorption and further bone loss. In this article, we tried to discuss this hard topic based on the available limited information in patients with CKD. More studies are needed to be able to clearly address this frequent ROD finding.

Indoxyl Sulfate Alters the Humoral Response of the ChAdOx1 COVID-19 Vaccine in Hemodialysis Patients

Background and aims: Vaccination for severe acute respiratory syndrome coronavirus 2(SARS-CoV-2) is strongly recommended. The efficacy of SARS-CoV-2 vaccine for patients with end-stage renal disease is low. Indoxyl sulfate (IS) is a representative protein bound uremic toxin arousing immune dysfunction in CKD patients. It is unknown whether IS impairs the efficacy of vaccines for SARS-CoV-2. Materials and Methods: From 1 June 2021, to 31 December 2021, hemodialysis patients (n = 358) and a control group (n = 59) were eligible to receive the first dose of the ChAdOx1 COVID-19 vaccine. Titer measurements indicative of the humoral response (anti-S1 IgG and surrogate virus neutralization test (sVNT) results) and indoxyl sulfate concentration measurement were performed 4 weeks after ChAdOx1 vaccine injection. Results: The serum concentrations of anti-S1 IgG were 272 ± 1726 AU/mL and 2111 ± 4424 AU/mL in hemodialysis patients and control group (p < 0.05), respectively. The sVNT values were 26.8 ± 21.1% and 54.0 ± 20.2% in the hemodialysis and control groups (p < 0.05), respectively. There was a decreasing trend for the anti-S1 IgG titer from the lowest to highest quartile of IS (p < 0.001). The patients with higher concentrations of IS had lower sVNT (p for trend < 0.001). Conclusion: Hemodialysis patients had weaker humoral immunity after the first dose of the ChAdOx1 vaccine. Higher concentration of IS altered the development of anti-S1 antibodies and sVNT-measured neutralization.