Untargeted plasma and tissue metabolomics in rats with chronic kidney disease given AST-120

The Effect of Renaltec on Serum Uremic Toxins in Cats with Experimentally Induced Chronic Kidney Disease

Serum uremic toxins markedly increase in cats with chronic kidney disease (CKD) and have deleterious consequences. Renaltec is an oral adsorbent that binds uremic toxin precursors in the gut. In this prospective cohort study utilizing 13 purpose-bred cats with remnant kidney model-induced CKD (12 IRIS Stage 2, 1 IRIS Stage 3) eating a standardized renal diet, we aimed to assess the effect of Renaltec administration on serum indoxyl sulfate (IDS) and p-cresol sulfate (pCS) concentrations. Cats were sequentially treated with standard of care for 56 days, 500 mg Renaltec orally once daily for 56 days, and then three months later, 500 mg Renaltec orally twice daily for 56 days. Serum IDS and pCS concentrations were measured 28 and 56 days after the administration of Renaltec. Blood pressure and kidney function were measured before and 56 days after the administration of Renaltec. Significant decreases in serum IDS and pCS concentrations were observed for both once- and twice-daily dosing, particularly during the first 28 days of administration. More cats with BID dosing had clinically significant reductions in serum IDS and pCS concentrations than with SID dosing. Renaltec can reduce the serum concentrations of deleterious gut-derived uremic toxins in cats with CKD.

Metabolomic identification of predictive and early biomarkers of cisplatin-induced acute kidney injury in adult head and neck cancer patients

AIM

Cisplatin causes acute kidney injury (AKI) in approximately one third of patients. Serum creatinine and urinary output are poor markers of cisplatin-induced AKI. Metabolomics was utilized to identify predictive or early diagnostic biomarkers of cisplatin-induced AKI.

METHODS

Thirty-one adult head and neck cancer patients receiving cisplatin (dose ≥70 mg/m2) were recruited for metabolomics analysis. Urine and serum samples were collected prior to cisplatin (pre), 24-48 h after cisplatin (24-48 h) and 5-14 days (post) after cisplatin. Based on serum creatinine concentrations measured at the post timepoint, 11/31 patients were classified with clinical AKI. Untargeted metabolomics was performed using liquid chromatography-mass spectrometry (LC-MS).

RESULTS

Metabolic discrimination was observed between "AKI" patients and "no AKI" patients at all timepoints. Urinary glycine, hippuric acid sulfate, 3-hydroxydecanedioc acid and suberate were significantly different between AKI patients and no AKI patients prior to cisplatin infusion. Urinary glycine and hippuric acid sulfate were lower (-2.22-fold and -8.85-fold), whereas 3-hydroxydecanedioc acid and suberate were higher (3.62-fold and 1.91-fold) in AKI patients relative to no AKI patients. Several urine and serum metabolites were found to be altered 24-48 h following cisplatin infusion, particularly metabolites involved with mitochondrial energetics.

CONCLUSIONS

We propose glycine, hippuric acid sulfate, 3-hydroxydecanedioc acid and suberate as predictive biomarkers of predisposition to cisplatin-induced AKI. Metabolites indicative of mitochondrial dysfunction may serve as early markers of subclinical AKI.

Discovery of the toxicity-related quality markers and mechanisms of Zhi-Zi-Hou-Po decoction based on Chinmedomics combined with differentially absorbed components and network pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Zhi-Zi-Hou-Po decoction (ZZHPD), as a representative traditional Chinese medicine (TCM) formula for the treatment of depression, has frequently triggered hepatorenal toxicity in recent years. However, its toxic effect, material basis, and underlying mechanisms have not been fully elucidated.

AIM OF THE STUDY

To explore the hepatorenal toxicity-material basis-quality markers (Q-markers) and multiple mechanisms of ZZHPD.

MATERIALS AND METHODS

ZZHPD-induced rat model of toxicity was evaluated by behavioral indicators, biochemical parameters, and histopathological sections. Then, UHPLC-Q-Exactive Orbitrap-MS combined with multivariate data analysis was utilized to identify the endogenous differential metabolites and the prototype components of ZZHPD in the plasma. A comprehensive strategy integrating in-house library, diagnostic ions, Compound Discover software, and network databases was constructed to identify the chemical constituents of ZZHPD. Additionally, the differentially absorbed components of ZZHPD were screened out based on the spectrum-effect relationship (toxic state and normal state), feature extraction of exogenous components, and variable influence on projection (VIP). Further, Chinmedomics and network pharmacology oriented by differentially absorbed components were performed to predict toxicity-related Q-markers and core targets, as well as relevant pathways. Finally, the binding ability between components and targets was predicted using molecular docking, and the mRNA expression of core target genes was determined by real-time qPCR experiment.

RESULTS

ZZHPD exerted significant hepatotoxicity and nephrotoxicity in rats accompanied by body weight loss, abnormal biochemical indicators, and pathologic characteristics with mild inflammation and cell damage. The results of plasma metabolomics indicated that 22 differential metabolites interfered by ZZHPD mainly involved in primary bile acid biosynthesis, arginine and proline metabolism, phenylalanine metabolism and biosynthesis, sphingolipid metabolism, pyrimidine and purine metabolism. Firstly, 106 chemical substances of ZZHPD were identified, 44 of them were absorbed into the blood, mainly including 7 iridoid glycosides, 15 flavonoids, 5 lignans, and others. Then, the correlation analysis results suggested that 12 of 19 differentially absorbed constituents were highly correlated with 22 differential metabolites and recognized as potential Q-markers. Finally, 9 toxicity-related Q-markers were predicted and confirmed with better binding ability to 5 core targets (PTGS2, CASP3, TNF, PPARG, HMOX1), including 3 flavonoids (naringin, hesperidin, and neohesperidin), 2 iridoid glycosides (geniposide and genipin-1-β-D-gentiobioside), 2 lignans (honokiol and magnolol), organic acid (chlorogenic acid), and crocin (crocetin). The real-time qPCR results showed that the mRNA levels of CASP3, TNF-α, and PPARG significantly increased in the damaged liver. Combining metabolomics and network pharmacology results, the multiple mechanisms of toxicity might involve in oxidative damage, inflammation, and apoptosis pathways.

CONCLUSION

Taken together, the toxicity-related Q-markers of ZZHPD screened for the first time in this work were reliable, and the holistic intervention for hepatorenal toxicity further revealed the multi-component, multi-target, and multi-pathway features in TCM. The integrated approach provides a novel perspective for the discovery of toxicity/efficacy-related substances and mechanistic studies in TCM.

4-Ethylphenol-fluxes, metabolism and excretion of a gut microbiome derived neuromodulator implicated in autism

Gut-microbiome-derived metabolites, such as 4-Ethylphenol [4EP], have been shown to modulate neurological health and function. Although the source of such metabolites is becoming better understood, knowledge gaps remain as to the mechanisms by which they enter host circulation, how they are transported in the body, how they are metabolised and excreted, and the way they exert their effects. High blood concentrations of host-modified 4EP, 4-ethylphenol sulfate [4EPS], are associated with an anxiety phenotype in autistic individuals. We have reviewed the existing literature and discuss mechanisms that are proposed to contribute influx from the gut microbiome, metabolism, and excretion of 4EP. We note that increased intestinal permeability is common in autistic individuals, potentially explaining increased flux of 4EP and/or 4EPS across the gut epithelium and the Blood Brain Barrier [BBB]. Similarly, kidney dysfunction, another complication observed in autistic individuals, impacts clearance of 4EP and its derivatives from circulation. Evidence indicates that accumulation of 4EPS in the brain of mice affects connectivity between subregions, particularly those linked to anxiety. However, we found no data on the presence or quantity of 4EP and/or 4EPS in human brains, irrespective of neurological status, likely due to challenges sampling this organ. We argue that the penetrative ability of 4EP is dependent on its form at the BBB and its physicochemical similarity to endogenous metabolites with dedicated active transport mechanisms across the BBB. We conclude that future research should focus on physical (e.g., ingestion of sorbents) or metabolic mechanisms (e.g., conversion to 4EP-glucuronide) that are capable of being used as interventions to reduce the flux of 4EP from the gut into the body, increase the efflux of 4EP and/or 4EPS from the brain, or increase excretion from the kidneys as a means of addressing the neurological impacts of 4EP.

Efficacy and mechanism of Baicao Fuyanqing suppository on mixed vaginitis based on 16S rRNA and metabolomics

Background

Mixed vaginitis is the infection of the vagina by at least two different pathogens at the same time, both of which contribute to an abnormal vaginal environment leading to signs and symptoms. Baicao Fuyanqing suppository (BCFYQ) is a Miao ethnomedicine, used to treat various vaginitis. The aim of this study was to investigate the efficacy and possible mechanism of BCFYQ in the treatment of mixed vaginitis based on 16S rRNA high-throughput sequencing and metabonomics.

Methods

Escherichia coli and Candida albicans were used to establish mixed vaginitis model in SD rats. Three groups of low, medium and high doses (0.18/0.36/0.64 g.kg-1) were established, and administered vaginally once a day for 6 consecutive days. After the last administration, vaginal pH and IL-1β, IL-2, IL-13 and IgA levels were measured, and the vaginal tissue was examined pathologically. In addition, the vaginal flora was characterised by 16S rRNA, and endogenous metabolites in the vaginal tissue were detected by UHPLC-Q-Exactive MS.

Results

Compared with the model group, BCFYQ can reduce the vaginal pH of rats, make it close to the normal group and improve the damaged vaginal epithelial tissue. The results of ELISA showed that BCFYQ decreased the levels of IL-1 β and IL-2 and increased the levels of IL-13 and IgA (P<0.05). In addition, BCFYQ may increase the abundance of vaginal flora, especially Lactobacillus. The differential metabolite enrichment pathway suggests that the therapeutic mechanism of BCFYQ is mainly related to lipid metabolism and amino acid metabolism.

Conclusion

Our research shows that BCFYQ has a good therapeutic effect on mixed vaginitis. It repairs the damaged vaginal mucosa by regulating the vaginal flora and lipid metabolism disorders to improve the local immune function of the vagina and inhibit the growth and reproduction of pathogens.

Plasma Metabolomic Profiling after Feeding Dried Distiller's Grains with Solubles in Different Cattle Breeds

Dried distiller's grains with solubles (DDGS) are rich in nutrients and can enhance animals' growth and immunity. However, there are few reports on the effects of a diet of DDGS on plasma metabolism and the related action pathways in domestic animals. In this study, groups of Guanling yellow cattle (GY) and Guanling crossbred cattle (GC) having a basal diet served as the control groups (GY-CG and GC-CG), and DDGS replacing 25% of the diet of GY and GC served as the replacement groups (GY-RG and GC-RG), with three cattle in each group. Plasma samples were prepared for metabolomic analysis. Based on multivariate statistical and univariate analyses, differential metabolites and metabolic pathways were explored. Twenty-nine significantly different metabolites (p < 0.05) were screened in GY-RG compared with those in GY-CG and were found to be enriched in the metabolic pathways, including choline metabolism in cancer, linolenic acid metabolism, and amino acid metabolism. Nine metabolites showed significant differences (p < 0.05) between GC-RG and GC-CG and were mainly distributed in the metabolic pathways of choline metabolism in cancer, glycerophospholipid metabolism, prostate cancer metabolism, and gonadotropin-releasing hormone (GnRH) secretion. These results suggest that a DDGS diet may promote healthy growth and development of experimental cattle by modulating these metabolic pathways. Our findings not only shed light on the nutritional effects of the DDGS diet and its underlying mechanisms related to metabolism but also provide scientific reference for the feed utilization of DDGS.

Innate Immunity System in Patients With Cardiovascular and Kidney Disease

With a global burden of 844 million, chronic kidney disease (CKD) is now considered a public health priority. Cardiovascular risk is pervasive in this population, and low-grade systemic inflammation is an established driver of adverse cardiovascular outcomes in these patients. Accelerated cellular senescence, gut microbiota-dependent immune activation, posttranslational lipoprotein modifications, neuroimmune interactions, osmotic and nonosmotic sodium accumulation, acute kidney injury, and precipitation of crystals in the kidney and the vascular system all concur in determining the unique severity of inflammation in CKD. Cohort studies documented a strong link between various biomarkers of inflammation and the risk of progression to kidney failure and cardiovascular events in patients with CKD. Interventions targeting diverse steps of the innate immune response may reduce the risk of cardiovascular and kidney disease. Among these, inhibition of IL-1β (interleukin-1 beta) signaling by canakinumab reduced the risk for cardiovascular events in patients with coronary heart disease, and this protection was equally strong in patients with and without CKD. Several old (colchicine) and new drugs targeting the innate immune system, like the IL-6 (interleukin 6) antagonist ziltivekimab, are being tested in large randomized clinical trials to thoroughly test the hypothesis that mitigating inflammation may translate into better cardiovascular and kidney outcomes in patients with CKD.

Identifying disease progression in chronic kidney disease using proton magnetic resonance spectroscopy

Chronic kidney disease (CKD) affects approximately 10% of the world population, higher still in some developing countries, and can cause irreversible kidney damage eventually leading to kidney failure requiring dialysis or kidney transplantation. However, not all patients with CKD will progress to this stage, and it is difficult to distinguish between progressors and non-progressors at the time of diagnosis. Current clinical practice involves monitoring estimated glomerular filtration rate and proteinuria to assess CKD trajectory over time; however, there remains a need for novel, validated methods that differentiate CKD progressors and non-progressors. Nuclear magnetic resonance techniques, including magnetic resonance spectroscopy and magnetic resonance imaging, have the potential to improve our understanding of CKD progression. Herein, we review the application of magnetic resonance spectroscopy both in preclinical and clinical settings to improve the diagnosis and surveillance of patients with CKD.

The interaction between intestinal bacterial metabolites and phosphatase and tensin homolog in autism spectrum disorder

Intestinal bacteria-associated para-cresyl sulfate (pCS) and 4-ethylphenyl sulfate (4EPS) are elevated in autism spectrum disorder (ASD). Both metabolites can induce ASD-like behaviors in mice, but the molecular mechanisms are not known. Phosphatase and tensin homolog (PTEN) is a susceptibility gene for ASD. The present study investigated the relation between pCS and 4EPS and PTEN in ASD in a valproic acid (VPA)-induced murine ASD model and an in vitro LPS-activated microglial model. The VPA-induced intestinal inflammation and compromised permeability in the distal ileum was not associated with changes of PTEN expression and phosphorylation. In contrast, VPA reduced PTEN expression in the hippocampus of mice. In vitro results show that pCS and 4EPS reduced PTEN expression and derailed innate immune response of BV2 microglial cells. The PTEN inhibitor VO-OHpic did not affect innate immune response of microglial cells. In conclusion, PTEN does not play a role in intestinal inflammation and compromised permeability in VPA-induced murine model for ASD. Although pCS and 4EPS reduced PTEN expression in microglial cells, PTEN is not involved in the pCS and 4EPS-induced derailed innate immune response of microglial cells. Further studies are needed to investigate the possible involvement of reduced PTEN expression in the ASD brain regarding synapse function and neuronal connectivity.

The Biology of Veganism: Plasma Metabolomics Analysis Reveals Distinct Profiles of Vegans and Non-Vegetarians in the Adventist Health Study-2 Cohort

It is unclear how vegetarian dietary patterns influence plasma metabolites involved in biological processes regulating chronic diseases. We sought to identify plasma metabolic profiles distinguishing vegans (avoiding meat, eggs, dairy) from non-vegetarians (consuming ≥28 g/day red meat) of the Adventist Health Study-2 cohort using global metabolomics profiling with ultra-performance liquid chromatography mass spectrometry (UPLC-MS/MS). Differences in abundance of metabolites or biochemical subclasses were analyzed using linear regression models, adjusting for surrogate and confounding variables, with cross-validation to simulate results from an independent sample. Random forest was used as a learning tool for classification, and principal component analysis was used to identify clusters of related metabolites. Differences in covariate-adjusted metabolite abundance were identified in over 60% of metabolites (586/930), after adjustment for false discovery. The vast majority of differentially abundant metabolites or metabolite subclasses showed lower abundance in vegans, including xanthine, histidine, branched fatty acids, acetylated peptides, ceramides, and long-chain acylcarnitines, among others. Many of these metabolite subclasses have roles in insulin dysregulation, cardiometabolic phenotypes, and inflammation. Analysis of metabolic profiles in vegans and non-vegetarians revealed vast differences in these two dietary groups, reflecting differences in consumption of animal and plant products. These metabolites serve as biomarkers of food intake, many with potential pathophysiological consequences for cardiometabolic diseases.

Anti-obesity natural products and gut microbiota

The link between gut microbiota and obesity or other metabolic syndromes is growing increasingly clear. Natural products are appreciated for their beneficial health effects in humans. Increasing investigations demonstrated that the anti-obesity bioactivities of many natural products are gut microbiota dependent. In this review, we summarized the current knowledge on anti-obesity natural products acting through gut microbiota according to their chemical structures and signaling metabolites. Manipulation of the gut microbiota by natural products may serve as a potential therapeutic strategy to prevent obesity.

Metabolomic and transcriptomic analysis reveals endogenous substrates and metabolic adaptation in rats lacking Abcg2 and Abcb1a transporters

Abcg2/Bcrp and Abcb1a/Pgp are xenobiotic efflux transporters limiting substrate permeability in the gastrointestinal system and brain, and increasing renal and hepatic drug clearance. The systemic impact of Bcrp and Pgp ablation on metabolic homeostasis of endogenous substrates is incompletely understood. We performed untargeted metabolomics of cerebrospinal fluid (CSF) and plasma, transcriptomics of brain, liver and kidney from male Sprague Dawley rats (WT) and Bcrp/Pgp double knock-out (dKO) rats, and integrated metabolomic/transcriptomic analysis to identify putative substrates and perturbations in canonical metabolic pathways. A predictive Bayesian machine learning model was used to predict in silico those metabolites with greater substrate-like features for either transporters. The CSF and plasma levels of 169 metabolites, nutrients, signaling molecules, antioxidants and lipids were significantly altered in dKO rats, compared to WT rats. These metabolite changes suggested alterations in histidine, branched chain amino acid, purine and pyrimidine metabolism in the dKO rats. Levels of methylated and sulfated metabolites and some primary bile acids were increased in dKO CSF or plasma. Elevated uric acid levels appeared to be a primary driver of changes in purine and pyrimidine biosynthesis. Alterations in Bcrp/Pgp dKO CSF levels of antioxidants, precursors of neurotransmitters, and uric acid suggests the transporters may contribute to the regulation of a healthy central nervous system in rats. Microbiome-generated metabolites were found to be elevated in dKO rat plasma and CSF. The altered dKO metabolome appeared to cause compensatory transcriptional change in urate biosynthesis and response to lipopolysaccharide in brain, oxidation-reduction processes and response to oxidative stress and porphyrin biosynthesis in kidney, and circadian rhythm genes in liver. These findings present insight into endogenous functions of Bcrp and Pgp, the impact that transporter substrates, inhibitors or polymorphisms may have on metabolism, how transporter inhibition could rewire drug sensitivity indirectly through metabolic changes, and identify functional Bcrp biomarkers.

Skeletal myopathy in CKD: a comparison of adenine-induced nephropathy and 5/6 nephrectomy models in mice

Preclinical animal models of chronic kidney disease (CKD) are critical to investigate the underlying mechanisms of disease and to evaluate the efficacy of novel therapeutics aimed to treat CKD-associated pathologies. The objective of the present study was to compare the adenine diet and 5/6 nephrectomy (Nx) CKD models in mice. Male and female 10-wk-old C57BL/6J mice (n = 5-9 mice/sex/group) were randomly allocated to CKD groups (0.2-0.15% adenine-supplemented diet or 5/6 Nx surgery) or the corresponding control groups (casein diet or sham surgery). Following the induction of CKD, the glomerular filtration rate was reduced to a similar level in both adenine and 5/6 Nx mice (adenine diet-fed male mice: 81.1 ± 41.9 µL/min vs. 5/6 Nx male mice: 160 ± 80.9 µL/min, P = 0.5875; adenine diet-fed female mice: 112.9 ± 32.4 µL/min vs. 5/6 Nx female mice: 107.0 ± 45.7 µL/min, P = 0.9995). Serum metabolomics analysis indicated that established uremic toxins were robustly elevated in both CKD models, although some differences were observed between CKD models (i.e., p-cresol sulfate). Dysregulated phosphate homeostasis was observed in the adenine model only, whereas Ca2+ homeostasis was disturbed in male mice with both CKD models. Compared with control mice, muscle mass and myofiber cross-sectional areas of the extensor digitorum longus and soleus muscles were ∼18-24% smaller in male CKD mice regardless of the model but were not different in female CKD mice (P > 0.05). Skeletal muscle mitochondrial respiratory function was significantly decreased (19-24%) in CKD mice in both models and sexes. These findings demonstrate that adenine diet and 5/6 Nx models of CKD have similar levels of renal dysfunction and skeletal myopathy. However, the adenine diet model demonstrated superior performance with regard to mortality (∼20-50% mortality for 5/6 Nx vs. 0% mortality for the adenine diet, P < 0.05 for both sexes) compared with the 5/6 Nx surgical model.NEW & NOTEWORTHY Numerous preclinical models of chronic kidney disease have been used to evaluate skeletal muscle pathology; however, direct comparisons of popular models are not available. In this study, we compared adenine-induced nephropathy and 5/6 nephrectomy models. Both models produced equivalent levels of muscle atrophy and mitochondrial impairment, but the adenine model exhibited lower mortality rates, higher consistency in uremic toxin levels, and dysregulated phosphate homeostasis compared with the 5/6 nephrectomy model.

Nuclear receptor PXR targets AKR1B7 to protect mitochondrial metabolism and renal function in AKI

Acute kidney injury (AKI) is a worldwide public health problem with no specific and satisfactory therapies in clinic. The nuclear pregnane X receptor (PXR) is involved in the progression of multiple diseases, including metabolic diseases, atherosclerosis, hypertension, liver injury, etc. However, its role in kidney injury remains to be understood. In this study, we have investigated the role of PXR in AKI and underlying mechanism(s) involved in its function. PXR was robustly down-regulated and negatively correlated with renal dysfunction in human and animal kidneys with AKI. Silencing PXR in rats enhanced cisplatin-induced AKI and induced severe mitochondrial abnormalities, whereas activating PXR protected against AKI. Using luciferase reporter assays, genomic manipulation, and proteomics data analysis on the kidneys of PXR^-/- rats, we determined that PXR targeted Aldo-keto reductase family 1, member B7 (AKR1B7) to improve mitochondrial function, thereby ameliorating AKI. We confirmed the protective role of PXR against kidney injury using genomic and pharmacologic approaches in an ischemia/reperfusion model of AKI. These findings demonstrate that disabling the PXR/AKR1B7/mitochondrial metabolism axis is an important factor that can contribute to AKI, whereas reestablishing this axis can be useful for treating AKI.

Normothermic Ex-vivo Kidney Perfusion in a Porcine Auto-Transplantation Model Preserves the Expression of Key Mitochondrial Proteins: An Unbiased Proteomics Analysis

Normothermic ex-vivo kidney perfusion (NEVKP) results in significantly improved graft function in porcine auto-transplant models of donation after circulatory death injury compared with static cold storage (SCS); however, the molecular mechanisms underlying these beneficial effects remain unclear. We performed an unbiased proteomics analysis of 28 kidney biopsies obtained at three time points from pig kidneys subjected to 30 min of warm ischemia, followed by 8 h of NEVKP or SCS, and auto-transplantation. 70/6593 proteins quantified were differentially expressed between NEVKP and SCS groups (false discovery rate < 0.05). Proteins increased in NEVKP mediated key metabolic processes including fatty acid ß-oxidation, the tricarboxylic acid cycle, and oxidative phosphorylation. Comparison of our findings with external datasets of ischemia-reperfusion and other models of kidney injury confirmed that 47 of our proteins represent a common signature of kidney injury reversed or attenuated by NEVKP. We validated key metabolic proteins (electron transfer flavoprotein subunit beta and carnitine O-palmitoyltransferase 2, mitochondrial) by immunoblotting. Transcription factor databases identified members of the peroxisome proliferator-activated receptors (PPAR) family of transcription factors as the upstream regulators of our dataset, and we confirmed increased expression of PPARA, PPARD, and RXRA in NEVKP with reverse transcription polymerase chain reaction. The proteome-level changes observed in NEVKP mediate critical metabolic pathways. These effects may be coordinated by PPAR-family transcription factors and may represent novel therapeutic targets in ischemia-reperfusion injury.

Challenges of reducing protein-bound uremic toxin levels in chronic kidney disease and end stage renal disease

The prevalence of chronic kidney disease (CKD) in the worldwide population is currently estimated between 11% and 13%. Adequate renal clearance is compromised in these patients and the accumulation of a large number of uremic retention solutes results in an irreversible worsening of renal function which can lead to end stage renal disease (ESRD). Approximately three million ESRD patients currently receive renal replacement therapies (RRTs), such as hemodialysis, which only partially restore kidney function, as they are only efficient in removing mainly small, unbound solutes from the circulation while leaving larger and protein-bound uremic toxins (PBUTs) untouched. The accumulation of PBUTs in patients highly increases the risk of cardiovascular events and is associated with higher mortality and morbidity in CKD and ESRD. In this review, we address several strategies currently being explored toward reducing PBUT concentrations, including clinical and medical approaches, therapeutic techniques, and recent developments in RRT technology. These include preservation of renal function, limitation of colon derived PBUTs, oral sorbents, adsorbent RRT technology, and use of albumin displacers. Despite the promising results of the different approaches to promote enhanced removal of a small percentage of the more than 30 identified PBUTs, on their own, none of them provide a treatment with the required efficiency, safety and cost-effectiveness to prevent CKD-related complications and decrease mortality and morbidity in ESRD.

Uremic Toxins in the Progression of Chronic Kidney Disease and Cardiovascular Disease: Mechanisms and Therapeutic Targets

Chronic kidney disease (CKD) is a progressive loss of renal function. The gradual decline in kidney function leads to an accumulation of toxins normally cleared by the kidneys, resulting in uremia. Uremic toxins are classified into three categories: free water-soluble low-molecular-weight solutes, protein-bound solutes, and middle molecules. CKD patients have increased risk of developing cardiovascular disease (CVD), due to an assortment of CKD-specific risk factors. The accumulation of uremic toxins in the circulation and in tissues is associated with the progression of CKD and its co-morbidities, including CVD. Although numerous uremic toxins have been identified to date and many of them are believed to play a role in the progression of CKD and CVD, very few toxins have been extensively studied. The pathophysiological mechanisms of uremic toxins must be investigated further for a better understanding of their roles in disease progression and to develop therapeutic interventions against uremic toxicity. This review discusses the renal and cardiovascular toxicity of uremic toxins indoxyl sulfate, p-cresyl sulfate, hippuric acid, TMAO, ADMA, TNF-α, and IL-6. A focus is also placed on potential therapeutic targets against uremic toxicity.

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.

Role of gut microbiota in identification of novel TCM-derived active metabolites

Traditional Chinese Medicine (TCM) has been extensively used to ameliorate diseases in Asia for over thousands of years. However, owing to a lack of formal scientific validation, the absence of information regarding the mechanisms underlying TCMs restricts their application. After oral administration, TCM herbal ingredients frequently are not directly absorbed by the host, but rather enter the intestine to be transformed by gut microbiota. The gut microbiota is a microbial community living in animal intestines, and functions to maintain host homeostasis and health. Increasing evidences indicate that TCM herbs closely affect gut microbiota composition, which is associated with the conversion of herbal components into active metabolites. These may significantly affect the therapeutic activity of TCMs. Microbiota analyses, in conjunction with modern multiomics platforms, can together identify novel functional metabolites and form the basis of future TCM research.

Potential Biomarkers for Early Detection of 3-MCPD Dipalmitate Exposure in Sprague-Dawley Rats

3-Chloro-1,2-propandiol (3-MCPD) dipalmitate is one of the major 3-MCPD esters formed during food processing. In this single-dose study, the metabonomic profile changes in the 48 h after orally administrated 3-MCPD dipalmitate at 1600 mg/kg BW to Sprague-Dawley (SD) rats were determined with liquid chromatography (LC) coupled with mass spectrometry (MS) system. The chemical structures of 12 potential biomarkers for 3-MCPD dipalmitate exposures early detection were detected and tentatively identified from the plasma of SD rats, including indoxyl sulfate, phenol sulfate, p-cresol sulfate, 2-phenylethanol glucuronide, p-cresol glucuronide, p-cresol, allantoin, phenylacetylglycine, pyrocatechol sulfate, phenyllactic acid, 5-hydroxyindoleacetic acid, and creatinine. Taking into account the metabolites identified from SD rats' kidney, liver, testes, and spleen samples, 3-MCPD dipalmitate might potentially disturb the phenylalanine, tryptophan, tyrosine, glycine, fatty acid, and purine metabolisms. The results suggested that the 12 plasma metabolites could be potentially applied in detecting the early exposures of 3-MCPD esters.

Protocol for parallel proteomic and metabolomic analysis of mouse intervertebral disc tissues

The comprehensiveness of data collected by "omics" modalities has demonstrated the ability to drastically transform our understanding of the molecular mechanisms of chronic, complex diseases such as musculoskeletal pathologies, how biomarkers are identified, and how therapeutic targets are developed. Standardization of protocols will enable comparisons between findings reported by multiple research groups and move the application of these technologies forward. Herein, we describe a protocol for parallel proteomic and metabolomic analysis of mouse intervertebral disc (IVD) tissues, building from the combined expertise of our collaborative team. This protocol covers dissection of murine IVD tissues, sample isolation, and data analysis for both proteomics and metabolomics applications. The protocol presented below was optimized to maximize the utility of a mouse model for "omics" applications, accounting for the challenges associated with the small starting quantity of sample due to small tissue size as well as the extracellular matrix-rich nature of the tissue.

Urine Metabolomics Study on Potential Hepatoxic Biomarkers Identification in Rats Induced by Aurantio-Obtusin

Previous studies revealed the hepatotoxic effect of aurantio-obtusin on rats. The aim of this study was to identify potential biomarkers of urine caused by aurantio-obtusin. Sprague–Dawley (SD) rats with body weight of 0, 4, 40, and 200 mg/kg were orally given aurantio-obtusin for 28 days, and urine was collected for 24 h after the last administration. The urine metabolites in the aurantio-obtusin group and the control group were analyzed by ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). Twenty-three metabolites were identified as potential biomarkers, and 10 of them were up-regulated, including xanthosine, hippuric acid, 5-L-glutamyl-taurine, etc. The other 13 biomarkers were down-regulated, including thymidine, 3-methyldioxyindole, cholic acid, etc. The significant changes of these biomarkers indicated that purine metabolism, taurine and hypotaurine metabolism, primary bile acid biosynthesis, pyrimidine metabolism, and tryptophan metabolism played an important role in the hepatotoxicity of aurantio-obtusin in rats. In this paper, the safety and potential risk of aurantio-obtusin were studied for the first time by combining the toxicity of aurantio-obtusin with the results of urine metabolomics, which provided information for the mechanism of liver injury induced by aurantio-obtusin.

Uremic Toxic Blood-Brain Barrier Disruption Mediated by AhR Activation Leads to Cognitive Impairment during Experimental Renal Dysfunction

BACKGROUND

Uremic toxicity may play a role in the elevated risk of developing cognitive impairment found among patients with CKD. Some uremic toxins, like indoxyl sulfate, are agonists of the transcription factor aryl hydrocarbon receptor (AhR), which is widely expressed in the central nervous system and which we previously identified as the receptor of indoxyl sulfate in endothelial cells.

METHODS

To characterize involvement of uremic toxins in cerebral and neurobehavioral abnormalities in three rat models of CKD, we induced CKD in rats by an adenine-rich diet or by 5/6 nephrectomy; we also used AhR^-/- knockout mice overloaded with indoxyl sulfate in drinking water. We assessed neurologic deficits by neurobehavioral tests and blood-brain barrier disruption by SPECT/CT imaging after injection of ^99mTc-DTPA, an imaging marker of blood-brain barrier permeability.

RESULTS

In CKD rats, we found cognitive impairment in the novel object recognition test, the object location task, and social memory tests and an increase of blood-brain barrier permeability associated with renal dysfunction. We found a significant correlation between ^99mTc-DTPA content in brain and both the discrimination index in the novel object recognition test and indoxyl sulfate concentrations in serum. When we added indoxyl sulfate to the drinking water of rats fed an adenine-rich diet, we found an increase in indoxyl sulfate concentrations in serum associated with a stronger impairment in cognition and a higher permeability of the blood-brain barrier. In addition, non-CKD AhR^-/- knockout mice were protected against indoxyl sulfate-induced blood-brain barrier disruption and cognitive impairment.

CONCLUSIONS

AhR activation by indoxyl sulfate, a uremic toxin, leads to blood-brain barrier disruption associated with cognitive impairment in animal models of CKD.

Uraemic syndrome of chronic kidney disease: altered remote sensing and signalling

Uraemic syndrome (also known as uremic syndrome) in patients with advanced chronic kidney disease involves the accumulation in plasma of small-molecule uraemic solutes and uraemic toxins (also known as uremic toxins), dysfunction of multiple organs and dysbiosis of the gut microbiota. As such, uraemic syndrome can be viewed as a disease of perturbed inter-organ and inter-organism (host-microbiota) communication. Multiple biological pathways are affected, including those controlled by solute carrier (SLC) and ATP-binding cassette (ABC) transporters and drug-metabolizing enzymes, many of which are also involved in drug absorption, distribution, metabolism and elimination (ADME). The remote sensing and signalling hypothesis identifies SLC and ABC transporter-mediated communication between organs and/or between the host and gut microbiota as key to the homeostasis of metabolites, antioxidants, signalling molecules, microbiota-derived products and dietary components in body tissues and fluid compartments. Thus, this hypothesis provides a useful perspective on the pathobiology of uraemic syndrome. Pathways considered central to drug ADME might be particularly important for the body's attempts to restore homeostasis, including the correction of disturbances due to kidney injury and the accumulation of uraemic solutes and toxins. This Review discusses how the remote sensing and signalling hypothesis helps to provide a systems-level understanding of aspects of uraemia that could lead to novel approaches to its treatment.

Metabolic Activation of Flavin Monooxygenase-mediated Trimethylamine-N-Oxide Formation in Experimental Kidney Disease

Cardiovascular disease (CVD) remains the leading cause of death in chronic kidney disease (CKD) patients despite treatment of traditional risk factors, suggesting that non-traditional CVD risk factors are involved. Trimethylamine-N-oxide (TMAO) correlates with atherosclerosis burden in CKD patients and may be a non-traditional CVD risk factor. Serum TMAO concentrations are significantly increased in CKD patients, which may be due in part to increased hepatic flavin monooxygenase (FMO)-mediated TMAO formation. The objective of this work was to elucidate the mechanism of increased FMO activity in CKD. In this study, FMO enzyme activity experiments were conducted in vitro with liver microsomes isolated from experimental CKD and control rats. Trimethylamine was used as a probe substrate to assess FMO activity. The FMO activator octylamine and human uremic serum were evaluated. FMO gene and protein expression were also determined. FMO-mediated TMAO formation was increased in CKD versus control. Although gene and protein expression of FMO were not changed, metabolic activation elicited by octylamine and human uremic serum increased FMO-mediated TMAO formation. The findings suggest that metabolic activation of FMO-mediated TMAO formation is a novel mechanism that contributes to increased TMAO formation in CKD and represents a therapeutic target to reduce TMAO exposure and CVD.

Uremic metabolites impair skeletal muscle mitochondrial energetics through disruption of the electron transport system and matrix dehydrogenase activity

Chronic kidney disease (CKD) leads to increased skeletal muscle fatigue, weakness, and atrophy. Previous work has implicated mitochondria within the skeletal muscle as a mediator of muscle dysfunction in CKD; however, the mechanisms underlying mitochondrial dysfunction in CKD are not entirely known. The purpose of this study was to define the impact of uremic metabolites on mitochondrial energetics. Skeletal muscle mitochondria were isolated from C57BL/6N mice and exposed to vehicle (DMSO) or varying concentrations of uremic metabolites: indoxyl sulfate, indole-3-acetic-acid, l-kynurenine, and kynurenic acid. A comprehensive mitochondrial phenotyping platform that included assessments of mitochondrial oxidative phosphorylation (OXPHOS) conductance and respiratory capacity, hydrogen peroxide production (JH2O2), matrix dehydrogenase activity, electron transport system enzyme activity, and ATP synthase activity was employed. Uremic metabolite exposure resulted in a ~25-40% decrease in OXPHOS conductance across multiple substrate conditions (P < 0.05, n = 5-6/condition), as well as decreased ADP-stimulated and uncoupled respiratory capacity. ATP synthase activity was not impacted by uremic metabolites; however, a screen of matrix dehydrogenases indicated that malate and glutamate dehydrogenases were impaired by some, but not all, uremic metabolites. Assessments of electron transport system enzymes indicated that uremic metabolites significantly impair complex III and IV. Uremic metabolites resulted in increased JH2O2 under glutamate/malate, pyruvate/malate, and succinate conditions across multiple levels of energy demand (all P < 0.05, n = 4/group). Disruption of mitochondrial OXPHOS was confirmed by decreased respiratory capacity and elevated superoxide production in cultured myotubes. These findings provide direct evidence that uremic metabolites negatively impact skeletal muscle mitochondrial energetics, resulting in decreased energy transfer, impaired complex III and IV enzyme activity, and elevated oxidant production.

Chronic kidney disease: Biomarker diagnosis to therapeutic targets

Chronic kidney disease (CKD), characterized as renal dysfunction, is recognized as a major public health problem with high morbidity and mortality worldwide. Unfortunately, there are no obvious clinical symptoms in early stage disease until severe damage has occurred. Further complicating early diagnosis and treatment is the lack of sensitive and specific biomarkers. As such, novel biomarkers are urgently needed. Metabolomics has shown an increasing potential for identifying underlying disease mechanisms, facilitating clinical diagnosis and developing pharmaceutical treatments for CKD. Recent advances in metabolomics revealed that CKD was closely associated with the dysregulation of numerous metabolites, such as amino acids, lipids, nucleotides and glycoses, that might be exploited as potential biomarkers. In this review, we summarize recent metabolomic applications based on animal model studies and in patients with CKD and highlight several biomarkers that may play important roles in diagnosis, intervention and development of new therapeutic strategies.

Tissue, urine and blood metabolite signatures of chronic kidney disease in the 5/6 nephrectomy rat model

INTRODUCTION

Progressive chronic kidney disease (CKD) is an important cause of morbidity and mortality. It has a long asymptomatic phase, where routine blood tests cannot identify early functional losses, and therefore identifying common mechanisms across the many etiologies is an important goal.

OBJECTIVES

Our aim was to characterize serum, urine and tissue (kidney, lung, heart, spleen and liver) metabolomics changes in a rat model of CKD.

METHODS

A total of 17 male Wistar rats underwent 5/6 nephrectomy, whilst 13 rats underwent sham operation. Urine samples were collected weekly, for 6 weeks; blood was collected at weeks 0, 3 and 6; and tissue samples were collected at week 6. Samples were analyzed on a nuclear magnetic resonance spectroscopy platform with multivariate and univariate data analysis.

RESULTS

Changes in several metabolites were statistically significant. Allantoin was affected in all compartments. Renal asparagine, creatine, hippurate and trimethylamine were significantly different; in other tissues creatine, dimethylamine, dimethylglycine, trigonelline and trimethylamine were significant. Benzoate, citrate, dimethylglycine, fumarate, guanidinoacetate, malate, myo-inositol and oxoglutarate were altered in urine or serum.

CONCLUSION

Although the metabolic picture is complex, we suggest oxidative stress, the gut-kidney axis, acid-base balance, and energy metabolism as promising areas for future investigation.

The effect of chronic kidney disease on CYP2B expression and activity in male Wistar rats

Chronic kidney disease (CKD) is characterized by progressive reduction in kidney function over time. CKD affects greater than 10% of the population and its incidence is on the rise due to the growing prevalence of its risk factors. Previous studies demonstrated CKD alters nonrenal clearance of drugs in addition to reducing renal clearance. We assessed the function and expression of hepatic CYP2B enzymes using a rat model of CKD. CKD was induced in Wistar rats by supplementing their chow with adenine and confirmed through the detection of elevated uremic toxins in plasma. Liver enzymes AST and ALT were unchanged by the adenine diet. Bupropion was used as a probe substrate for hepatic CYP2B function using rat liver microsomes. The resulting metabolite, hydroxy-bupropion, and bupropion were quantified by ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry. Level of mRNA and protein were determined by RT-PCR and Western blot, respectively. The results of our study demonstrate that CYP2B1 is downregulated in a rat model of CKD. CYP2B1 mRNA level was significantly decreased (88%, P < 0.001) in CKD relative to control. Similarly, maximal enzymatic velocity (Vmax) for CYP2B was decreased by 46% in CKD relative to control (P < 0.0001). Previous studies involving patients with CKD demonstrated altered bupropion pharmacokinetics compared to control. Hence, our results suggest that these alterations may be mediated by attenuated CYP2B hepatic metabolism. This finding may partially explain the alterations in pharmacokinetics and nonrenal drug clearance frequently observed in patients with CKD.

Untargeted metabolomics reveals N, N, N-trimethyl-L-alanyl-L-proline betaine (TMAP) as a novel biomarker of kidney function

The diagnosis and prognosis of chronic kidney disease (CKD) currently relies on very few circulating small molecules, which can vary by factors unrelated to kidney function. In end-stage renal disease (ESRD), these same small molecules are used to determine dialysis dose and dialytic clearance. Therefore, we aimed to identify novel plasma biomarkers to estimate kidney function in CKD and dialytic clearance in ESRD. Untargeted metabolomics was performed on plasma samples from patients with a single kidney, non-dialysis CKD, ESRD and healthy controls. For ESRD patients, pre- and post-dialysis plasma samples were obtained from several dialysis modalities. Metabolomics analysis revealed over 400 significantly different features in non-dialysis CKD and ESRD plasma compared to controls while less than 35 features were significantly altered in patients with a single kidney. N,N,N-trimethyl-L-alanyl-L-proline betaine (TMAP, AUROC = 0.815) and pyrocatechol sulfate (AUROC = 0.888) outperformed creatinine (AUROC = 0.745) in accurately identifying patients with a single kidney. Several metabolites accurately predicted ESRD; however, when comparing pre-and post-hemodialysis, TMAP was the most robust biomarker of dialytic clearance for all modalities (AUROC = 0.993). This study describes TMAP as a novel potential biomarker of kidney function and dialytic clearance across several hemodialysis modalities.

An update of urine and blood metabolomics in chronic kidney disease

Chronic kidney disease is considered as a serious obstacle in global health, with increasing incidence and prevalence. In spite of numerous attempts by using recent omics technologies, specially metabolomics, for understanding pathophysiology, molecular mechanism and identification reliable consensus biomarkers for diagnosis and prognosis of this complex disease, the current biomarkers are still insensitive and many questions about its pathomechanism are still to be unanswered. This review is focused on recent findings about urine and serum/plasma metabolite biomarkers and changes in the pathways that occurs in the disease conditions. The urine and blood metabolome content in the normal and disease state is investigated based on the current metabolomics studies and well known metabolite candidate biomarkers for chronic kidney disease are discussed.

NMR and MS urinary metabolic phenotyping in kidney diseases is fit-for-purpose in the presence of a protease inhibitor

When using an appropriate data analysis pipeline, protease inhibitor (PI)-containing urine samples are fit-for-purpose for metabolic phenotyping of patients with nephrotic syndrome and proteinuria.

Effects of housing conditions on behaviors and biochemical parameters in juvenile cynomolgus monkeys (Macaca fascicularis)

To investigate the effects of environmental enrichment on laboratory monkeys, we studied behavioral and physiological differences following changes in housing conditions. Ten male and female juvenile cynomolgus monkeys were first housed in pairs for 8 weeks after quarantine/acclimatization (singly housed) and subsequently housed alone for the next 8 weeks. Monkeys were subjected to evaluations of body weight gain, stereotypic or affiliative behaviors, cortisol, 4-ethylphenyl sulfate (4EPS) and catecholamine concentrations in biological samples, and blood chemistry tests under both housing conditions. Under paired housing, the stereotypic behavioral score decreased in both sexes, and the affiliative behavioral score increased in males and showed an increasing trend in females. Under single housing, the stereotypic score increased in both sexes, and the affiliative score decreased in males. Paired housing decreased serum calcium and urine cortisol concentrations in both sexes and decreased plasma cortisol in males and plasma 4EPS concentrations in females. The stereotypic score was positively correlated with serum calcium, plasma and urine cortisol, and plasma 4EPS concentration and negatively correlated with the affiliative score. The feces painting score, affiliative score, and plasma cortisol and serum calcium concentrations showed sex differences, suggesting differences in responsiveness to environmental changes between males and females. In conclusion, paired housing improved behavioral abnormalities in juvenile cynomolgus monkeys, suggesting that it may be an effective environmental enrichment paradigm. Calcium, cortisol, and 4EPS concentrations in biological samples may be useful indices for evaluating the effects of environmental enrichment.

Tissue metabolomics study to reveal the toxicity of a traditional Tibetan medicine 'Renqing Changjue' in rats

Renqing Changjue (RQCJ), a precious Traditional Tibetan Medicine (TTM), has been widely used in the management of diseases of the digestive system, toxinosis and pyreticosis. However, in the formula, a significant level of heavy metals, which are potential toxic elements, are present. Therefore, it is important to assess the toxicity of RQCJ dynamically and holistically. In the present study, a ¹H NMR metabolomics approach and inductively coupled plasma mass spectrometry (ICP-MS) were implemented to analyze the samples of liver, kidney and spleen from rats treated with RQCJ. The results revealed that 9 metabolites in the liver, 13 metabolites in the kidney and 16 metabolites in the spleen were significantly altered, which suggest that disturbances in TCA cycle, amino acid metabolism, energy metabolism and oxidative stress are produced by successive administration of RQCJ over 15 days. Complemented by histopathology and biochemical assay, the trends of the metabolite levels indicate that RQCJ caused tissue injury to a certain extent, which was evidenced by the high levels of As and Hg in the tissue. The toxic effects of RQCJ were alleviated in liver and kidney during the recovery period, and RQCJ may cause long-term damage in spleen. These findings provide a significant experimental proof on the estimated safety and valuable information about the metabolism of RQCJ, which will be valuable in determining the health risks of the drug.

GC/MS-Based Metabolomics Reveals Biomarkers in Asthma Murine Model Modulated by Opuntia humifusa

GC/MS coupled with multivariate statistical analysis was performed to identify marker metabolites in serum of mice after healing ovalbumin- (OVA-) induced asthma using Opuntia humifusa. Principal component analysis (PCA) score plot showed separation among groups, with metabolite profiles of serum showing differences according to various treatments for the asthma murine model. Levels of stearic acid and arachidic acid were significantly lower in the serum from OVA-induced group than those from the control group. Dexamethasone treatment group was characterized by higher serum levels of urea, myristic acid, and palmitic acid along with lower levels of aspartic acid compared to OVA-induced group. O. humifusa treatment mice groups showed dose-proportional higher levels of urea and glycerol than OVA-induced group. These results highlight that GC/MS-based metabolomics is a powerful technique for identifying molecular markers of asthma.

Metabolomics in chronic kidney disease: Strategies for extended metabolome coverage

Chronic kidney disease (CKD) is becoming a major public health issue as prevalence is increasing worldwide. It also represents a major challenge for the identification of new early biomarkers, understanding of biochemical mechanisms, patient monitoring and prognosis. Each metabolite contained in a biofluid or tissue may play a role as a signal or as a driver in the development or progression of the pathology. Therefore, metabolomics is a highly valuable approach in this clinical context. It aims to provide a representative picture of a biological system, making exhaustive metabolite coverage crucial. Two aspects can be considered: analytical and biological coverage. From an analytical point of view, monitoring all metabolites within one run is currently impossible. Multiple analytical techniques providing orthogonal information should be carried out in parallel for coverage improvement. The biological aspect of metabolome coverage can be enhanced by using multiple biofluids or tissues for in-depth biological investigation, as the analysis of a single sample type is generally insufficient for whole organism extrapolation. Hence, recording of signals from multiple sample types and different analytical platforms generates massive and complex datasets so that chemometric tools, including data fusion approaches and multi-block analysis, are key tools for extracting biological information and for discovery of relevant biomarkers. This review presents the recent developments in the field of metabolomic analysis, from sampling and analytical strategies to chemometric tools, dedicated to the generation and handling of multiple complementary metabolomic datasets enabling extended metabolite coverage to improve our biological knowledge of CKD.

Mediterranean Diet Score: Associations with Metabolic Products of the Intestinal Microbiome, Carotid Plaque Burden, and Renal Function

Metabolic products of the intestinal microbiome such as trimethylamine N-oxide (TMAO) that accumulate in renal failure (gut-derived uremic toxins, GDUTs) affect atherosclerosis and increase cardiovascular risk. We hypothesized that patients on a Mediterranean diet and those consuming lower amounts of dietary precursors would have lower levels of GDUTs. Patients attending vascular prevention clinics completed a Harvard Food Frequency Questionnaire (FFQ) and had plasma levels of TMAO, p-cresylsulfate, hippuric acid, indoxyl sulfate, p-cresyl glucuronide, phenyl acetyl glutamine, and phenyl sulfate measured by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. Carotid plaque burden was measured by ultrasound; CKD-Epi equations were used to estimate the glomerular filtration rate. In total, 276 patients completed the study. Even moderate renal function significantly increased plasma GDUTs, which were significantly associated with higher carotid plaque burden. There was no significant difference in plasma levels of any GDUT associated with a Mediterranean diet score or with intake of dietary precursors. In omnivorous patients with vascular disease, the intake of dietary precursors of intestinal metabolites or adherence to a Mediterranean diet did not change plasma GDUT. Approaches other than diet, such as probiotics and repopulation of the intestinal microbiome, may be required to mitigate the adverse effects of GDUTs.

Untargeted Metabolomics Identifies Novel Potential Biomarkers of Habitual Food Intake in a Cross-Sectional Study of Postmenopausal Women

Background

Recent studies suggest that untargeted metabolomics is a promising tool to identify novel biomarkers of individual foods. However, few large cross-sectional studies with comprehensive data on habitual diet and circulating metabolites have been conducted.

Objective

We aimed to identify potential food biomarkers and evaluate their predictive accuracy.

Methods

We conducted a cross-sectional analysis of consumption of 91 food groups or items, assessed by a 152-item food-frequency questionnaire, in relation to 1186 serum metabolites measured by mass spectrometry-based platforms from 1369 nonsmoking postmenopausal women (mean age = 68.3 y). Diet-metabolite associations were selected by Pearson's partial correlation analysis (P < 4.63 × 10-7, |r| > 0.2). The predictive accuracy of the selected food metabolites was evaluated from the area under the curve (AUC) calculated from receiver operating characteristic analysis conducted among women in the top and bottom quintiles of dietary intake.

Results

We identified 379 diet-metabolite associations. Forty-two food groups or items were correlated with 199 serum metabolites. We replicated 63 metabolites as biomarkers of habitual food intake reported in previous cross-sectional studies. Among those not previously shown to be associated with habitual diet, several are biologically plausible and were reported in acute feeding studies including: banana and dopamine 3-O-sulfate (r = 0.34, AUC = 76%) and dopamine 4-O-sulfate (r = 0.33, AUC = 74%), garlic and alliin (r = 0.24, AUC = 69%), N-acetylalliin (r = 0.27, AUC = 70%), and S-allylcysteine (r = 0.23, AUC = 69). Two unannotated metabolites were the strongest predictors for dark fish (X-02269, r = 0.51, AUC = 94%) and coffee intake (X-21442, r = 0.62, AUC = 98%).

Conclusion

In this comprehensive, cross-sectional analysis of habitual food intake and serum metabolites among postmenopausal women, we identified several potentially novel food biomarkers and replicated others. Our findings contribute to the limited literature on food-based biomarkers and highlight the significant and promising role that large cohort studies with archived blood samples could play in this field. This study was registered at clinicaltrials.gov as NCT03282812.

Metabolic products of the intestinal microbiome and extremes of atherosclerosis

BACKGROUND AND AIMS

There is increasing awareness that the intestinal microbiome plays an important role in human health. We investigated its role in the burden of carotid atherosclerosis, measured by ultrasound as total plaque area.

METHODS

Multiple regression with traditional risk factors was used to identify three phenotypes among 316/3056 patients attending vascular prevention clinics. Residual score (RES; i.e. the distance off the regression line, similar to standard deviation) was used to identify the 5% of patients with much less plaque than predicted by their risk factors (Protected, RES <-2), the 90% with about as much plaque as predicted (Explained, RES -2 to 2), and the 5% with much more plaque than predicted (Unexplained RES >2). Metabolic products of the intestinal microbiome that accumulate in renal failure - gut-derived uremic toxins (GDUT) - were assayed in plasma by ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry.

RESULTS

Plasma levels of trimethylamine n-oxide (TMAO), p-cresyl sulfate, p-cresyl glucuronide, and phenylacetylglutamine were significantly lower among patients with the Protected phenotype, and higher in those with the Unexplained phenotype, despite no significant differences in renal function or in dietary intake of nutrient precursors of GDUT. In linear multiple regression with a broad panel of risk factors, TMAO (p = 0.011) and p-cresyl sulfate (p = 0.011) were significant independent predictors of carotid plaque burden.

CONCLUSIONS

The intestinal microbiome appears to play an important role in atherosclerosis. These findings raise the possibility of novel approaches to treatment of atherosclerosis such as fecal transplantation and probiotics.

Effects of sulfur-fumigation on the pharmacokinetics, metabolites and analgesic activity of Radix Paeoniae Alba

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Paeoniae Alba (Baishao, BS), one of the most commonly used traditional Chinese medicinal herbs, has many pharmacological effects including analgesic activity. Previous studies found that sulfur-fumigation, a post-harvest handling process developed to prevent mold contamination of medicinal herbs, altered the quality of BS. However, whether sulfur-fumigation affects the pharmacokinetics, safety and efficacy of BS warrants further investigation.

AIM OF THE STUDY

To evaluate the feasibility of sulfur-fumigation as a post-harvest handling process of BS from the viewpoints of pharmacokinetics, safety and efficacy.

MATERIALS AND METHODS

The pharmacokinetic behaviors of four active components of BS and one characteristic component of sulfur-fumigated BS (S-BS) were evaluated by high performance liquid chromatography triple quadrupole mass spectrometry (HPLC-TQ-MS/MS). The safety was investigated using ultra high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS) based metabolomics approach after intragastric (i.g.) administration of non-fumigated BS (N-BS) and S-BS in rats. The analgesic efficacy was compared using hot-plate test in mice, after i.g. administration of N-BS and S-BS, at both high and low dosages.

RESULTS

Systemic exposures of paeoniflorin and oxypaeoniflorin, two analgesic components of BS, were significantly decreased in the S-BS treated group compared to the N-BS treated group, while paeoniflorin sulfonate, one of the sulfur-containing derivatives of S-BS, was detected in all time-points of S-BS treated group with the area under the plasma concentration-time curve (AUC_0-t) and the maximum plasma concentration (C_max) as high as 7077.06 ± 2232.97ng/mL*h and 1641.42 ± 634.79ng/mL respectively, which indicated that sulfur-fumigation altered the pharmacokinetic behaviors of BS. Besides, paeoniflorin sulfonate and its four metabolites with ambiguous toxicities, as well as one endogenous metabolite p-cresol glucuronide, the biomarker of disordered homeostasis of intestinal bacteria and bile acid, were identified as the characteristic metabolites in S-BS administered rats, suggesting that sulfur-fumigation reduced the safety of BS. Furthermore, the analgesic effects at both low and high dosages were decreased in different extent when compared to N-BS administered groups, indicating that sulfur-fumigation weakened the efficacy of BS.

CONCLUSION

Sulfur-fumigation altered the pharmacokinetics, as well as reduced the safety and efficacy of BS, suggesting that sulfur-fumigation is not recommended for post-harvest handling of BS.

Microbiota-derived uremic retention solutes: perpetrators of altered nonrenal drug clearance in kidney disease

INTRODUCTION

Scientific interest in the gut microbiota is increasing due to improved understanding of its implications in human health and disease. In patients with kidney disease, gut microbiota-derived uremic toxins directly contribute to altered nonrenal drug clearance. Microbial imbalances, known as dysbiosis, potentially increase formation of microbiota-derived toxins, and diminished renal clearance leads to toxin accumulation. High concentrations of microbiota-derived toxins such as indoxyl sulfate and p-cresol sulfate perpetrate interactions with drug metabolizing enzymes and transporters, which provides a mechanistic link between increases in drug-related adverse events and dysbiosis in kidney disease. Areas covered: This review summarizes the effects of microbiota-derived uremic toxins on hepatic phase I and phase II drug metabolizing enzymes and drug transporters. Research articles that tested individual toxins were included. Therapeutic strategies to target microbial toxins are also discussed. Expert commentary: Large interindividual variability in toxin concentrations may explain some differences in nonrenal clearance of medications. Advances in human microbiome research provide unique opportunities to systematically evaluate the impact of individual and combined microbial toxins on drug metabolism and transport, and to explore microbiota-derived uremic toxins as potential therapeutic targets.

Site-Specific Fucosylation Analysis Identifying Glycoproteins Associated with Aggressive Prostate Cancer Cell Lines Using Tandem Affinity Enrichments of Intact Glycopeptides Followed by Mass Spectrometry

Fucosylation (Fuc) of glycoproteins plays an important role in regulating protein function and has been associated with the development of several cancer types including prostate cancer (Pca). Therefore, the research of Fuc glycoproteins has attracted increasing attention recently in the analytical field. Herein, a strategy based on lectin affinity enrichments of intact glycopeptides followed by mass spectrometry has been established to evaluate the specificities of various Fuc-binding lectins for glycosite-specific Fuc analysis of nonaggressive (NAG) and aggressive (AG) Pca cell lines. The enrichment specificities of Fuc glycopeptides using lectins (LCA, PSA, AAL, LTL, UEA I, and AOL) and MAX extraction cartridges alone, or in tandem, were evaluated. Our results showed that the use of lectin enrichment significantly increased the ratio of fucosylated glycopeptides to total glycopeptides compared to MAX enrichment. Furthermore, tandem use of lectin followed by MAX increased the number of identifications of Fuc glycopeptides compared to using lectin enrichment alone. LCA, PSA, and AOL showed stronger binding capacity than AAL, LTL, and UEA I. Also, LCA and PSA bound specifically to core Fuc, whereas AOL, AAL, and UEA I showed binding to both core Fuc and branch Fuc. The optimized enrichment method with tandem enrichment of LCA followed by MAX (LCA-MAX) was then applied to examine the Fuc glycoproteomes in two NAG and two AG Pca cell lines. In total, 973 intact Fuc glycopeptides were identified and quantified from 252 Fuc proteins by using the tandem-mass-tags (TMT) labeling and nanoliquid chromatography-mass spectrometry (nanoLC-MS/MS) analysis. Further data analysis revealed that 51 Fuc glycopeptides were overexpressed more than 2-fold in AG cell lines compared to NAG cells. The analysis of protein core fucosylation has great potential for aiding our understanding of invasive activity of AG Pca and may lead to the development of diagnostic approaches for AG Pca.

Indoxyl sulfate potentiates endothelial dysfunction via reciprocal role for reactive oxygen species and RhoA/ROCK signaling in 5/6 nephrectomized rats

Accumulative indoxyl sulfate (IS) retained in chronic kidney disease (CKD) can potentiate vascular endothelial dysfunction, and herein, we aim at elucidating the underlying mechanisms from the perspective of possible association between reactive oxygen species (ROS) and RhoA/ROCK pathway. IS-treated nephrectomized rats are administered with antioxidants including NADPH oxidase inhibitor apocynin, SOD analog tempol, and mitochondrion-targeted SOD mimetic mito-TEMPO to scavenge ROS, or ROCK inhibitor fasudil to obstruct RhoA/ROCK pathway. First, we find in response to IS stimulation, antioxidants treatments suppress increased aortic ROCK activity and expression levels. Additionally, ROCK blockade prevent IS-induced increased NADPH oxidase expression (mainly p22phox and p47phox), mitochondrial and intracellular ROS (superoxide and hydrogen peroxide) generation, and decreased Cu/Zn-SOD expression in thoracic aortas. Apocynin, mito-TEMPO, and tempol also reverse these markers of oxidative stress. These results suggest that IS induces excessive ROS production and ROCK activation involving a circuitous relationship in which ROS activate ROCK and ROCK promotes ROS overproduction. Finally, ROS and ROCK depletion attenuate IS-induced decrease in nitric oxide (NO) production and eNOS expression levels, and alleviate impaired vasomotor responses including increased vasocontraction to phenylephrine and decreased vasorelaxation to acetylcholine, thereby preventing cardiovascular complications accompanied by CKD. Taken together, excessive ROS derived from NADPH oxidase and mitochondria coordinate with RhoA/ROCK activation in a form of positive reciprocal relationship to induce endothelial dysfunction through disturbing endothelium-dependent NO signaling upon IS stimulation in CKD status.

p-Cresyl Sulfate

If chronic kidney disease (CKD) is associated with an impairment of kidney function, several uremic solutes are retained. Some of these exert toxic effects, which are called uremic toxins. p-Cresyl sulfate (pCS) is a prototype protein-bound uremic toxin to which many biological and biochemical (toxic) effects have been attributed. In addition, increased levels of pCS have been associated with worsening outcomes in CKD patients. pCS finds its origin in the intestine where gut bacteria metabolize aromatic amino acids, such as tyrosine and phenylalanine, leading to phenolic end products, of which pCS is one of the components. In this review we summarize the biological effects of pCS and its metabolic origin in the intestine. It appears that, according to in vitro studies, the intestinal bacteria generating phenolic compounds mainly belong to the families Bacteroidaceae, Bifidobacteriaceae, Clostridiaceae, Enterobacteriaceae, Enterococcaceae, Eubacteriaceae, Fusobacteriaceae, Lachnospiraceae, Lactobacillaceae, Porphyromonadaceae, Staphylococcaceae, Ruminococcaceae, and Veillonellaceae. Since pCS remains difficult to remove by dialysis, the gut microbiota could be a future target to decrease pCS levels and its toxicity, even at earlier stages of CKD, aiming at slowing down the progression of the disease and decreasing the cardiovascular burden.