Engineered microorganisms: A new direction in kidney stone prevention and treatment

Numerous studies have shown that intestinal and urinary tract flora are closely related to the formation of kidney stones. The removal of probiotics represented by lactic acid bacteria and the colonization of pathogenic bacteria can directly or indirectly promote the occurrence of kidney stones. However, currently existing natural probiotics have limitations. Synthetic biology is an emerging discipline in which cells or living organisms are genetically designed and modified to have biological functions that meet human needs, or even create new biological systems, and has now become a research hotspot in various fields. Using synthetic biology approaches of microbial engineering and biological redesign to enable probiotic bacteria to acquire new phenotypes or heterologous protein expression capabilities is an important part of synthetic biology research. Synthetic biology modification of microorganisms in the gut and urinary tract can effectively inhibit the development of kidney stones by a range of means, including direct degradation of metabolites that promote stone production or indirect regulation of flora homeostasis. This article reviews the research status of engineered microorganisms in the prevention and treatment of kidney stones, to provide a new and effective idea for the prevention and treatment of kidney stones.

Beneficial roles of gastrointestinal and urinary microbiomes in kidney stone prevention via their oxalate-degrading ability and beyond

Formation of calcium oxalate (CaOx) crystal, the most common composition in kidney stones, occurs following supersaturation of calcium and oxalate ions in the urine. In addition to endogenous source, another main source of calcium and oxalate ions is dietary intake. In the intestinal lumen, calcium can bind with oxalate to form precipitates to be eliminated with feces. High intake of oxalate-rich foods, inappropriate amount of daily calcium intake, defective intestinal transporters for oxalate secretion and absorption, and gastrointestinal (GI) malabsorption (i.e., from gastric bypass surgery) can enhance intestinal oxalate absorption, thereby increasing urinary oxalate level and risk of kidney stone disease (KSD). The GI microbiome rich with oxalate-degrading bacteria can reduce intestinal oxalate absorption and urinary oxalate level. In addition to the oxalate-degrading ability, the GI microbiome also affects expression of oxalate transporters and net intestinal oxalate transport, cholesterol level, and short-chain fatty acids (SCFAs) production, leading to lower KSD risk. Recent evidence also shows beneficial effects of urinary microbiome in KSD prevention. This review summarizes the current knowledge on the aforementioned aspects. Potential benefits of the GI and urinary microbiomes as probiotics for KSD prevention are emphasized. Finally, challenges and future perspectives of probiotic treatment in KSD are discussed.

Chloride/Multiple Anion Exchanger SLC26A Family: Systemic Roles of SLC26A4 in Various Organs

Solute carrier family 26 member 4 (SLC26A4) is a member of the SLC26A transporter family and is expressed in various tissues, including the airway epithelium, kidney, thyroid, and tumors. It transports various ions, including bicarbonate, chloride, iodine, and oxalate. As a multiple-ion transporter, SLC26A4 is involved in the maintenance of hearing function, renal function, blood pressure, and hormone and pH regulation. In this review, we have summarized the various functions of SLC26A4 in multiple tissues and organs. Moreover, the relationships between SLC26A4 and other channels, such as cystic fibrosis transmembrane conductance regulator, epithelial sodium channel, and sodium chloride cotransporter, are highlighted. Although the modulation of SLC26A4 is critical for recovery from malfunctions of various organs, development of specific inducers or agonists of SLC26A4 remains challenging. This review contributes to providing a better understanding of the role of SLC26A4 and development of therapeutic approaches for the SLC26A4-associated hearing loss and SLC26A4-related dysfunction of various organs.

Personalized Medicine in Urolithiasis: AI Chatbot-Assisted Dietary Management of Oxalate for Kidney Stone Prevention

Accurate information regarding oxalate levels in foods is essential for managing patients with hyperoxaluria, oxalate nephropathy, or those susceptible to calcium oxalate stones. This study aimed to assess the reliability of chatbots in categorizing foods based on their oxalate content. We assessed the accuracy of ChatGPT-3.5, ChatGPT-4, Bard AI, and Bing Chat to classify dietary oxalate content per serving into low (<5 mg), moderate (5-8 mg), and high (>8 mg) oxalate content categories. A total of 539 food items were processed through each chatbot. The accuracy was compared between chatbots and stratified by dietary oxalate content categories. Bard AI had the highest accuracy of 84%, followed by Bing (60%), GPT-4 (52%), and GPT-3.5 (49%) (p < 0.001). There was a significant pairwise difference between chatbots, except between GPT-4 and GPT-3.5 (p = 0.30). The accuracy of all the chatbots decreased with a higher degree of dietary oxalate content categories but Bard remained having the highest accuracy, regardless of dietary oxalate content categories. There was considerable variation in the accuracy of AI chatbots for classifying dietary oxalate content. Bard AI consistently showed the highest accuracy, followed by Bing Chat, GPT-4, and GPT-3.5. These results underline the potential of AI in dietary management for at-risk patient groups and the need for enhancements in chatbot algorithms for clinical accuracy.

Glycolate oxidase-1 gene variants influence the risk of hyperoxaluria and renal stone development

PURPOSE

Oxalate is an excellent calcium ion attractor with great abundance in the human body, and the liver is the major source of oxalate. The Glycolate oxidase-1 (GOX1) gene is solely responsible for the glycolate and glyoxylate metabolism and produces oxalate. This study has been designed to comprehend the association of genetic variants of the GOX1 gene with the risk of hyperoxaluria and renal stone disease in the Indian population.

METHOD

The present study is a candidate gene approach prospective case-control study carried out on 300 participants (150 cases and 150 controls) at Muljibhai Patel Urological Hospital, Gujarat, India. Biochemical parameters, including serum levels of calcium, creatinine, parathyroid hormone, and 24-h urine metabolites, were performed. The genotyping of GOX1 gene variants rs6086287, rs2235250, rs2255183, and rs2294303 was performed using a customized TaqMan assay probe by RT-PCR.

RESULT

Parathyroid hormone, serum creatinine, and urine metabolites were significantly elevated in nephrolithiasis compared to healthy individuals. All mutated homozygous genotypes GG (rs6086287), TT (rs2235250), GG (rs2255183), and CC (rs2294303) were significantly associated with a high risk of renal stone disease. Individuals diagnosed with hyperoxaluria and carrying TG (rs6086287), AG (rs2255183), and TT (rs2294303) genotypes have a significantly high risk of renal stone disease. Moreover, haplotype analysis and correlation analysis also confirmed the strong association between genetic variants and nephrolithiasis.

CONCLUSION

Genetic variants of the GOX1 genes were associated with renal stone disease. In the presence of risk genotype and hyperoxaluria, the susceptibility to develop renal stone disease risk gets modulated.

Diagnostic value of urinary Tamm-Horsfall protein and 24 h urine osmolality for recurrent calcium oxalate stones of the upper urinary tract: Cross-sectional study

We aimed to investigate the diagnostic value of urinary Tamm-Horsfall protein (THP) and 24 h urine osmolality for recurrent calcium oxalate (CaOx) stones. Clinical data of 120 patients with upper urinary tract stones admitted to our hospital between January 2020 and January 2022 were retrospectively reviewed. Patients were divided into recurrence (53 patients) and non-recurrence (67 patients) groups based on postoperative stone recurrence. Meanwhile, 50 healthy patients were selected as the control group. Urinary THP levels, 24 h urine osmolality, and biochemical indices were compared between the three groups; their diagnostic values for stone recurrence were evaluated using receiver operating characteristic (ROC) curves. Urinary THP, 24 h urine osmolality, and biochemical indices were significantly higher in the recurrence group than in the non-recurrence and control groups (P < 0.05). The 24 h urine osmolality was positively correlated with urinary oxalic acid and calcium excretion. ROC curve analysis showed that optimal cutoff values of urinary THP and 24 h urine osmolality for the diagnosis of stone development were ≥27.01 mg/L and ≥577.69 mOsm/(kg H2O), respectively. Furthermore, these indices combined significantly improved the accuracy of diagnosis. Urinary THP and 24 h urine osmolality were higher in patients with recurrent CaOx stones. Detection of both parameters combined can accurately diagnose stone recurrence.

Sanjin Paishi Decoction improves the imbalance of gut microbiota and regulates MAPK signaling pathway to inhibit calcium oxalate stones in rats

INTRODUCTION

Sanjin Paishi Decoction (SJPSD) has positive effects on stone prevention; however, there is a lack of convincing evidence in the prevention of calcium oxalate stones. This study aimed investigates the effect of SJPSD on calcium oxalate stones and to explore its mechanism.

METHODS

The rat model of calcium oxalate stones was established and rats were treated with different doses of SJPSD. The pathological damage of kidney tissues was observed by HE staining, the deposition of calcium oxalate crystals in kidney tissues was examined by Von Kossa staining, and the levels of creatinine (CREA), urea (UREA), calcium (Ca), phosphorus (P), and magnesium (Mg) in serum were analyzed biochemically, the levels of IL-1β, IL-6, and TNF-α in serum were measured by ELISA, and the protein expression of Raf1, MEK1, p-MEK1, ERK1/2, p-ERK1/2, and Cleaved caspase-3 in kidney tissues was analyzed by Western blot. Moreover, the changes in gut microbiota were analyzed by 16S rRNA sequencing.

RESULTS

SJPSD attenuated the pathological damage of renal tissues, reduced the levels of CREA, UREA, Ca, P, and Mg, and inhibited the expression of Raf1, p-MEK1, p-ERK1/2, and Cleaved caspase-3 in renal tissues (P < 0.05). SJPSD treatment affected the composition of intestinal microbiota in rats with calcium oxalate stones.

CONCLUSION

The mechanism of SJPSD inhibition of calcium oxalate stone injury in rats may be related to the inhibition of the MAPK signaling pathway and regulation of gut microbiota imbalance.

Hydroxycitric acid prevents hyperoxaluric-induced nephrolithiasis and oxidative stress via activation of the Nrf2/Keap1 signaling pathway

Nephrolithiasis is a common and frequently-occurring disease in the urinary system with high recurrence. The present study aimed to explore the protective effect and underlying mechanism of hydroxycitric acid (HCA) in hyperoxaluria-induced nephrolithiasis in vitro and in vivo. Crystal deposition and pathophysiological injury in rat models of glyoxylate-induced nephrolithiasis were examined using H&E staining. Cell models of nephrolithiasis were established by oxalate-treated renal tubular epithelial cells. The levels of oxidative stress indexes were determined by ELISA kits. Cell proliferation in vivo and in vitro was evaluated using a cell counting kit-8 (CCK-8) assay and Ki-67 cell proliferation detection kit. Cell apoptosis was measured by flow cytometry and TUNEL staining. The protein levels were examined by western blotting. Our results showed that HCA administration significantly reduced crystal deposition and kidney injury induced by glyoxylate. HCA also alleviated oxidative stress via upregulating the antioxidant enzyme activities of superoxide dismutase (SOD) and catalase (CAT) and reducing the malondialdehyde (MDA) content. Moreover, HCA treatment promoted cell proliferation and inhibited apoptosis of renal tubular epithelial cells exposed to hyperoxaluria. Of note, Nrf2 activator dimethyl fumarate (DMF) exerted the same beneficial effects as HCA in nephrolithiasis. Mechanistically, HCA prevented crystal deposition and oxidative stress induced by hyperoxaluria through targeting the Nrf2/Keap1 antioxidant defense pathway, while knockdown of Nrf2 significantly abrogated these effects. Taken together, HCA exhibited antioxidation and anti-apoptosis activities in nephrolithiasis induced by hyperoxaluria via activating Nrf2/Keap1 pathway, suggesting that it may be an effective therapeutic agent for the prevention and treatment of nephrolithiasis.

Estrogen's Tissue-Specific Regulation of the SLC26A6 Anion Transporter Reveal a Phenotype of Kidney Stone Disease in Estrogen-Deficient Females: A Systematic Review

Kidney stone formation is an intricate process that involves a disruption in the interplay of the multiple organs and systems involved in regulating the concentration of specific ions in the body. Women who have gone through menopause are susceptible to kidney stone disease. This systematic review aims to investigate the potential influence of estrogen on kidney function and oxalate homeostasis, notably through the anion transporter SLC26A6 (also known as putative anion transporter 1 or PAT1) in females. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 checklist, a systematic search of online databases included Pubmed, ScienceDirect Journals, and Ingenta Connect Journals. Predetermined criteria to include and exclude papers, gathering articles published between 2012 and 2022, were determined. After a thorough analysis, eight articles (three cohorts, one case-control, one in vivo, one in vitro, and two cross-sectional studies) were identified for the final quality assessment review.  The eight selected and quality-assessed articles provided evidence of a directly proportional connection between estrogen and kidney function. A correlation between serum estrogen levels and the development of kidney stone disease was confirmed. Administration of β-estradiol was shown to effectively inhibit the function of the anion transporter PAT1 in a tissue-specific manner. In the case of the kidney, estrogen was observed to down-regulate PAT1, which led to a reduction in oxalate transporting activity and, consequently, a decrease in kidney stone formation. Consensus suggests that serum estrogen levels and optimal kidney functioning are interrelated. Furthermore, analysis of the quality-assessed articles and a comprehensive literature review revealed estrogen's tissue-specific regulation of the PAT1 anion transporter aids in maintaining kidney function and anion homeostasis. Additional research is needed to solidify estrogen's role in kidney stone disease to determine its therapeutic value in clinical practice.

Oxalate (dys)Metabolism: Person-to-Person Variability, Kidney and Cardiometabolic Toxicity

Oxalate is a metabolic end-product whose systemic concentrations are highly variable among individuals. Genetic (primary hyperoxaluria) and non-genetic (e.g., diet, microbiota, renal and metabolic disease) reasons underlie elevated plasma concentrations and tissue accumulation of oxalate, which is toxic to the body. A classic example is the triad of primary hyperoxaluria, nephrolithiasis, and kidney injury. Lessons learned from this example suggest further investigation of other putative factors associated with oxalate dysmetabolism, namely the identification of precursors (glyoxylate, aromatic amino acids, glyoxal and vitamin C), the regulation of the endogenous pathways that produce oxalate, or the microbiota's contribution to oxalate systemic availability. The association between secondary nephrolithiasis and cardiovascular and metabolic diseases (hypertension, type 2 diabetes, and obesity) inspired the authors to perform this comprehensive review about oxalate dysmetabolism and its relation to cardiometabolic toxicity. This perspective may offer something substantial that helps advance understanding of effective management and draws attention to the novel class of treatments available in clinical practice.

Oxalate in Foods: Extraction Conditions, Analytical Methods, Occurrence, and Health Implications

Oxalate is an antinutrient present in a wide range of foods, with plant products, especially green leafy vegetables, being the main sources of dietary oxalates. This compound has been largely associated with hyperoxaluria, kidney stone formation, and, in more severe cases, systematic oxalosis. Due to its impact on human health, it is extremely important to control the amount of oxalate present in foods, particularly for patients with kidney stone issues. In this review, a summary and discussion of the current knowledge on oxalate analysis, its extraction conditions, specific features of analytical methods, reported occurrence in foods, and its health implications are presented. In addition, a brief conclusion and further perspectives on whether high-oxalate foods are truly problematic and can be seen as health threats are shown.

OxaBIND: A tool for identifying oxalate-binding domain(s)/motif(s) in protein(s)

High oxalate level in blood and urine may cause oxalate-related disorders, particularly kidney stone disease. To unravel disease mechanisms, investigations of oxalate level and its binding proteins are required. However, the information on oxalate-binding proteins is limited due to a lack of appropriate tool for their investigations. Therefore, we have developed a freely accessible web-based tool, namely OxaBIND (https://www.stonemod.org/oxabind.php), to identify oxalate-binding site(s) in any proteins of interest. The prediction model was generated by recruiting all of the known oxalate-binding proteins with solid experimental evidence (from PubMed and RCSB Protein Data Bank). The potential oxalate-binding domains/motifs were predicted from these oxalate-binding proteins using PRATT tool and used to discriminate these known oxalate-binding proteins from the known non-oxalate-binding proteins. The best one, which provided highest fitness score, sensitivity and specificity, was then implemented to create the OxaBIND tool. After inputting protein identifier or sequence (which can be single or multiple), details of all the identified oxalate-binding site(s), if any, are presented in both textual and graphical formats. OxaBIND also provides theoretical three-dimensional (3D) structure of the protein with oxalate-binding site(s) being highlighted. This tool will be beneficial for future research on the oxalate-binding proteins, which play important roles in the oxalate-related disorders.

Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

Chronic kidney disease (CKD) is a significant global public health concern associated with high morbidity and mortality rates. The maintenance of oxalate homeostasis plays a critical role in preserving kidney health, particularly in the context of CKD. Although the relationship between oxalate and kidney stone formation has been extensively investigated, our understanding of oxalate homeostasis in non-stone-forming CKD remains limited. This review aims to present an updated analysis of the existing literature, focusing on the intricate mechanisms involved in oxalate homeostasis in patients with CKD. Furthermore, it explores the key factors that influence oxalate accumulation and discusses the potential role of oxalate in CKD progression and prognosis. The review also emphasizes the significance of the gut-kidney axis in CKD oxalate homeostasis and provides an overview of current therapeutic strategies, as well as potential future approaches. By consolidating important findings and perspectives, this review offers a comprehensive understanding of the present knowledge in this field and identifies promising avenues for further research.

Dynamics of differentiated-renal epithelial cell monolayer after calcium oxalate injury: The role of cyclooxygenase-2

AIMS

Calcium oxalate (Oxa), constituent of most common kidney stones, damages renal tubular epithelial cells leading to kidney disease. Most in vitro studies designed to evaluate how Oxa exerts its harmful effects were performed in proliferative or confluent non-differentiated renal epithelial cultures; none of them considered physiological hyperosmolarity of renal medullary interstitium. Cyclooxygenase 2 (COX2) has been associated to Oxa deleterious actions; however, up to now, it is not clear how COX2 acts. In this work, we proposed an in vitro experimental system resembling renal differentiated-epithelial cells that compose medullary tubular structures which were grown and maintained in a physiological hyperosmolar environment and evaluated whether COX2 → PGE2 axis (COX2 considered a cytoprotective protein for renal cells) induces Oxa damage or epithelial restitution.

MAIN METHODS

MDCK cells were differentiated with NaCl hyperosmolar medium for 72 h where cells acquired the typical apical and basolateral membrane domains and a primary cilium. Then, cultures were treated with 1.5 mM Oxa for 24, 48, and 72 h to evaluate epithelial monolayer restitution dynamics and COX2-PGE2 effect.

KEY FINDINGS

Oxa completely turned the differentiated phenotype into mesenchymal one (epithelial-mesenchymal transition). Such effect was partially and totally reverted after 48 and 72 h, respectively. Oxa damage was even deeper when COX2 was blocked by NS398. PGE2 addition restituted the differentiated-epithelial phenotype in a time and concentration dependence.

SIGNIFICANCE

This work presents an experimental system that approaches in vitro to in vivo renal epithelial studies and, more important, warns about NSAIDS use in patients suffering from kidney stones.

Analytical Methods for Oxalate Quantification: The Ubiquitous Organic Anion

Oxalate is a divalent organic anion that affects many biological and commercial processes. It is derived from plant sources, such as spinach, rhubarb, tea, cacao, nuts, and beans, and therefore is commonly found in raw or processed food products. Oxalate can also be made endogenously by humans and other mammals as a byproduct of hepatic enzymatic reactions. It is theorized that plants use oxalate to store calcium and protect against herbivory. Clinically, oxalate is best known to be a major component of kidney stones, which commonly contain calcium oxalate crystals. Oxalate can induce an inflammatory response that decreases the immune system's ability to remove renal crystals. When formulated with platinum as oxaliplatin (an anticancer drug), oxalate has been proposed to cause neurotoxicity and nerve pain. There are many sectors of industry that are hampered by oxalate, and others that depend on it. For example, calcium oxalate is troublesome in the pulp industry and the alumina industry as it deposits on machinery. On the other hand, oxalate is a common active component of rust removal and cleaning products. Due to its ubiquity, there is interest in developing efficient methods to quantify oxalate. Over the past four decades, many diverse methods have been reported. These approaches include electrochemical detection, liquid chromatography or gas chromatography coupled with mass spectrometry, enzymatic degradation of oxalate with oxalate oxidase and detection of hydrogen peroxide produced, and indicator displacement-based methods employing fluorescent or UV light-absorbing compounds. Enhancements in sensitivity have been reported for both electrochemical and mass-spectrometry-based methods as recently as this year. Indicator-based methods have realized a surge in interest that continues to date. The diversity of these approaches, in terms of instrumentation, sample preparation, and sensitivity, has made it clear that no single method will work best for every purpose. This review describes the strengths and limitations of each method, and may serve as a reference for investigators to decide which approach is most suitable for their work.

Kidney Stone Prevention

Kidney stone disease (KSD) (alternatively nephrolithiasis or urolithiasis) is a global health care problem that affects almost people in developed and developing countries. Its prevalence has been continuously increasing with a high recurrence rate after stone removal. Although effective therapeutic modalities are available, preventive strategies for both new and recurrent stones are required to reduce physical and financial burdens of KSD. To prevent kidney stone formation, its etiology and risk factors should be first considered. Low urine output and dehydration are the common risks of all stone types, whereas hypercalciuria, hyperoxaluria, and hypocitraturia are the major risks of calcium stones. In this article, up-to-date knowledge on strategies (nutrition-based mainly) to prevent KSD is provided. Important roles of fluid intake (2.5-3.0 L/d), diuresis (>2.0-2.5 L/d), lifestyle and habit modifications (for example, maintain normal body mass index, fluid compensation for working in high-temperature environment, and avoid cigarette smoking), and dietary management [for example, sufficient calcium at 1000-1200 mg/d, limit sodium at 2 or 3-5 g/d of sodium chloride (NaCl), limit oxalate-rich foods, avoid vitamin C and vitamin D supplements, limit animal proteins to 0.8-1.0 g/kg body weight/d but increase plant proteins in patients with calcium and uric acid stone and those with hyperuricosuria, increase proportion of citrus fruits, and consider lime powder supplementation] are summarized. Moreover, uses of natural bioactive products (for example, caffeine, epigallocatechin gallate, and diosmin), medications (for example, thiazides, alkaline citrate, other alkalinizing agents, and allopurinol), bacterial eradication, and probiotics are also discussed. Adv Nutr 2023;x:xx-xx.

Network pharmacology and experimental validation to elucidate the pharmacological mechanisms of Bushen Huashi decoction against kidney stones

INTRODUCTION

Kidney stone disease (KS) is a complicated disease with an increasing global incidence. It was shown that Bushen Huashi decoction (BSHS) is a classic Chinese medicine formula that has therapeutic benefits for patients with KS. However, its pharmacological profile and mechanism of action are yet to be elucidated.

METHODS

The present study used a network pharmacology approach to characterize the mechanism by which BSHS affects KS. Compounds were retrieved from corresponding databases, and active compounds were selected based on their oral bioavailability (≥30) and drug-likeness index (≥0.18). BSHS potential proteins were obtained from the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database, whereas KS potential genes were obtained from GeneCards and OMIM, TTD, and DisGeNET. Gene ontology and pathway enrichment analysis were used to determine potential pathways associated with genes. The ingredients of BSHS extract were identified by the ultra-high-performance liquid chromatography coupled with quadrupole orbitrap mass spectrometry (UHPLC-Q/Orbitrap MS). The network pharmacology analyses predicted the potential underlying action mechanisms of BSHS on KS, which were further validated experimentally in the rat model of calcium oxalate kidney stones.

RESULTS

Our study found that BSHS reduced renal crystal deposition and improved renal function in ethylene glycol(EG)+ammonium chloride(AC)-induced rats, and also reversed oxidative stress levels and inhibited renal tubular epithelial cell apoptosis in rats. BSHS upregulated protein and mRNA expression of E2, ESR1, ESR2, BCL2, NRF2, and HO-1 in EG+AC-induced rat kidney while downregulating BAX protein and mRNA expression, consistent with the network pharmacology results.

DISCUSSION

This study provides evidence that BSHS plays a critical role in anti-KS via regulation of E2/ESR1/2, NRF2/HO-1, and BCL2/BAX signaling pathways, indicating that BSHS is a candidate herbal drug for further investigation in treating KS.

Dietary oxalate-calcium balance and the incidence of hypertension and chronic kidney disease: a prospective study among an Asian population

Background

The potential effects of dietary oxalate (Ox) intake on cardio-renal function have remained unestablished. We evaluated the effect of usual Ox intake and its interaction with dietary calcium (Ca) on incident hypertension (HTN) and chronic kidney disease (CKD).

Methods

Adult men and women, free of HTN and CKD at baseline (2006–2008), were recruited. Dietary intakes were assessed using a validated food frequency questionnaire, and the outcomes were documented up to 2014–2017. Multivariate Cox proportional hazard regression models were used to estimate the development of HTN and CKD in relation to Ox intakes. Repeated-measures generalized estimating equation (GEE) linear regression models were used to assess possible effect of Ox-intake on the estimated glomerular filtration rate (eGFR) and blood pressure levels over eight years.

Results

Dietary Ox intakes were positively associated with incident CKD (HR = 2.59, 95% CI = 1.46–4.64) and HTN (HR = 1.79, 95% CI = 1.05–3.04). Compared to high-Ca consumers, subjects who had lower Ca intakes (< 990 vs. 1580 mg/d) had a higher incidence of CKD and HTN (HR = 2.43, 95% CI = 1.06–5.55, and HR = 1.72, 95% CI = 0.76–3.78). Participants with higher intakes of Ox (> 220 vs. < 150 mg/d) had lower eGFR values (75.3, 95% CI = 75.0–76.5 vs. 77.3, 95% CI = 76.6–78.1 mL/min/1.73m², P_time×group = 0.004) and higher SBP levels (112, 95% CI = 111–113 vs. 109, 95% CI = 108–110 mmHg, P_time×group = 0.007) overtime.

Conclusion

Higher dietary Ox intake may increase the risk of HTN and CKD. The relation between dietary Ox and risk of HTN and CKD seems to be varied by Ca intake, and subjects with lower Ca intakes may be more burdened by excessive amounts of dietary Ox.

Probiotic Oxalate-Degrading Bacteria: New Insight of Environmental Variables and Expression of the oxc and frc Genes on Oxalate Degradation Activity

Oxalate, a compound produced by many edible plants and as a terminal metabolite in the liver of mammals, is a toxin that has a detrimental role to human health. Humans and other mammals do possess enzymatic systems to degrade oxalate. Moreover, numerous oxalate-degrading bacteria reside in the mammalian gut and, thus, provide an important function for hosts. The current review focuses on the environmental factors that influence the efficacy of probiotic oxalate-degrading bacteria, relative to oxalate metabolism. We describe the mechanism of oxalate catabolism and its consumption by obligate and facultative anaerobic oxalate-degrading bacteria, in both in vitro and in vivo environments. We also explore the environmental variables that impact oxalate degradation. Studies on single species degrade oxalate have not shown a strong impact on oxalate metabolism, especially in high oxalate conditions such as consumption of foods high in oxalate (such as coffee and chocolate for humans or halogeton in animal feed). Considering effective variables which enhance oxalate degradation could be used in application of effective probiotic as a therapeutic tool in individuals with hyperoxaluria. This study indicates probiotics can be considered a good source of naturally occurring oxalate degrading agent in human colon.

Increased Rates of Supplement-Associated Oxalate Nephropathy During COVID-19 Pandemic

Introduction

Causes of secondary oxalate nephropathy include enteric dysfunction and excessive intake of oxalate or oxalate precursors. During the COVID-19 pandemic, there has been a dramatic rise in sales of supplements and vitamin C, during which time we observed an apparent increase in the proportion of ingestion-associated oxalate nephropathy.

Methods

We retrospectively reviewed secondary oxalate nephropathy and compared pre-pandemic (2018–2019) and pandemic (2020–early 2022) time periods.

Results

We identified 35 patients with kidney biopsy proven (30 native, 5 allograft) oxalate nephropathy at a single academic institution. Supplement-associated oxalate nephropathy comprised a significantly higher proportion of cases during COVID-19 pandemic compared with the preceding 2 years (44% vs. 0%, P = 0.002), and was associated with use of vitamin C, dietary changes, and supplements. Oxalate nephropathy in the kidney allograft, in contrast, remained associated with enteric hyperoxaluria, antibiotic use, and dehydration. Many patients had diabetes mellitus (57%), hypertension (40%) and/or pre-existing chronic kidney disease (CKD, 49%). Of 9 patients in which the potentially causative ingestion was identified and removed, 8 experienced improvement in kidney function.

Conclusion

There was a shift toward supplements rather than enteric hyperoxaluria as a leading cause of secondary oxalate nephropathy during the COVID-19 pandemic. Kidney outcomes are better than those observed for enteric hyperoxaluria, if the offending agent is identified and removed.

Analysis and Characterization of Lactobacillus paragasseri and Lacticaseibacillus paracasei: Two Probiotic Bacteria that Can Degrade Intestinal Oxalate in Hyperoxaluric Rats

In the present study, we characterized the probiotic properties of two commercially available bacterial strains, Lactobacillus paragasseri UBLG-36 and Lacticaseibacillus paracasei UBLPC-87, and evaluated their ability to degrade oxalate in vitro and in a hyperoxaluria-induced nephrolithiasis rat model. UBLG-36 harboring two oxalate catabolizing genes, oxalyl coenzyme A decarboxylase (oxc) and formyl coenzyme A transferase (frc), was previously shown to degrade oxalate in vitro effectively. Here, we show that UBLPC-87, lacking both oxc and frc, could still degrade oxalate in vitro. Both these strains harbored several potential putative probiotic genes that may have conferred them the ability to survive in low pH and 0.3% bile, resist antibiotic stress, show antagonistic activity against pathogenic bacteria, and adhere to epithelial cell surfaces. We further evaluated if UBLG-36 and UBLPC-87 could degrade oxalate in vivo and prevent hyperoxaluria-induced nephrolithiasis in rats. We observed that rats treated with 4.5% sodium oxalate (NaOx) developed hyperoxaluria and renal stones. However, when pre-treated with UBLG-36 or UBLPC-87 before administering 4.5% NaOx, the rats were protected against several pathophysiological manifestations of hyperoxaluria. Compared to the hyperoxaluric rats, the probiotic pre-treated rats showed reduced urinary excretion of oxalate and urea (p < 0.05), decreased serum blood urea nitrogen and creatinine (p < 0.05), alleviated stone formation and renal histological damage, and an overall decrease in renal tissue oxalate and calcium content (p < 0.05). Taken together, both UBLG-36 and UBLPC-87 are effective oxalate catabolizing probiotics capable of preventing hyperoxaluria and alleviating renal damage associated with nephrolithiasis.

Pilot testing for long-term impact of glycerol-induced acute kidney injury on oxalate homeostasis in rats

Abstract. There is a general lack of research on the long-term effects of acute kidney injury (AKI) on oxalate-degrading bacteria (ODB) and their total oxalate-degrading activity (ODA) in fecal microbiota. In the present pilot study, we separately evaluated the changes in the ODB number and their total ODA in fecal microbiota at 3-time points after glycerol-induced AKI. In addition, we assessed the interactions between AKI-induced renal histopathological changes and ODB, total fecal ODA, and plasma and urine oxalate concentrations in rats. Methods. The male Wistar rats (200-300 g, n = 20) on oxalate-free diet were randomly divided into 2 groups. After 24-h of water deprivation, experimental group 1 (n = 10) received an intramuscular injection of 50% glycerol (10 ml/kg of body weight), and group 2 (n = 10) served as a control. The numbers of ODB (incubated in a highly selective Oxalate Medium and determined using the culture method), total fecal ODA and urinary oxalate (UOx) excretion were measured after injection on days 8, 22 and 70. The method of redoximetric titration with a KMnO4 solution was adopted to evaluate total ODA in fecal microbiota. Renal injury was assessed by histopathology examination, serum creatinine plasma oxalic acid (POx) concentration and daily proteinuria levels after removing the animals from the experiment on day 70. Results. After glycerol injection on days 8 and 22, no differences were found in the numbers of ODB, their total fecal ODA, and UOx excretion level between the experimental and control groups. However, after AKI initiation on day 70, the numbers of ODB, total fecal ODA, and daily UOx excretion were significantly lower in the experimental group as compared with the control group. In addition, in 10 weeks following AKI, the number of ODB had a direct correlation with UOx excretion and an inverse correlation with POx and serum creatinine concentrations and daily proteinuria. Total ODA in fecal microbiota was directly associated with the percentage of renal interstitial fibrosis and the average glomerular volumes in the experimental rats. Conclusions: AKI had long-term negative effects on the quantitative and qualitative characteristics of ODB in fecal microbiota in rats. Moreover, the results of our study confirmed an increasing trend in total fecal ODA according to the aggravation of renal interstitial fibrosis and glomerular volume in rats’ kidneys. Further studies are warranted to gain more insight into the mechanism of oxalate homeostasis impairment in AKI.

Novel Starting Points for Human Glycolate Oxidase Inhibitors, Revealed by Crystallography-Based Fragment Screening

Primary hyperoxaluria type I (PH1) is caused by AGXT gene mutations that decrease the functional activity of alanine:glyoxylate aminotransferase. A build-up of the enzyme’s substrate, glyoxylate, results in excessive deposition of calcium oxalate crystals in the renal tract, leading to debilitating renal failure. Oxidation of glycolate by glycolate oxidase (or hydroxy acid oxidase 1, HAO1) is a major cellular source of glyoxylate, and siRNA studies have shown phenotypic rescue of PH1 by the knockdown of HAO1, representing a promising inhibitor target. Here, we report the discovery and optimization of six low-molecular-weight fragments, identified by crystallography-based fragment screening, that bind to two different sites on the HAO1 structure: at the active site and an allosteric pocket above the active site. The active site fragments expand known scaffolds for substrate-mimetic inhibitors to include more chemically attractive molecules. The allosteric fragments represent the first report of non-orthosteric inhibition of any hydroxy acid oxidase and hold significant promise for improving inhibitor selectivity. The fragment hits were verified to bind and inhibit HAO1 in solution by fluorescence-based activity assay and surface plasmon resonance. Further optimization cycle by crystallography and biophysical assays have generated two hit compounds of micromolar (44 and 158 µM) potency that do not compete with the substrate and provide attractive starting points for the development of potent and selective HAO1 inhibitors.

Dietary oxalate to calcium ratio and incident cardiovascular events: a 10-year follow-up among an Asian population

Background and aim

The potential cardiovascular impact of usual intakes of oxalate (Ox) is uninvestigated. We evaluated the effect of dietary Ox and its interaction with dietary calcium (Ca) on incident cardiovascular disease (CVD).

Methods

We included 2966 adult men and women aged 19–84 y without known CVD during baseline enrollment (2006–2008) of the Tehran Lipid and Glucose Study. Dietary intakes were assessed using a validated FFQ, and incident CVD (i.e., coronary heart disease, stroke, and CVD mortality) were documented through March 2018.

Results

A 7.1% incident of CVD occurred during a median follow-up of 10.6 y. After multivariable adjustment for traditional risk factors and key dietary nutrients, including total fat and fiber, Ox intakes ≥220 mg/d increased incident CVD (HR T3 vs. T1 = 1.47, 95% CI = 1.02–2.12). This association was potentiated (HR T3 vs. T1 = 2.42, 95% CI = 1.19–4.89) in subjects who had a lower intake of Ca (< 981 mg/d); in a low-Ca diet, an even lower amount of dietary Ox (second tertile, 148–220 mg/d) was related to increased CVD events by 92% (HR = 1.92, 95% CI = 1.00–3.70). No association was observed between dietary Ox and CVD events in the presence of medium- and high levels of Ca intakes. The critical cut-off point of Ox-to-Ca for predicting CVD events was 0.14, which was related to an increased risk of CVD by 37% (HR = 1.37, 95% CI = 1.02–1.84).

Conclusion

Higher dietary Ox intake appeared to be associated with a modestly elevated risk of incident CVD, especially in a diet with a lower amount of Ca.

Short-Chain Fatty Acids Reduced Renal Calcium Oxalate Stones by Regulating the Expression of Intestinal Oxalate Transporter SLC26A6

Renal calcium oxalate (CaOx) stone is a common urologic disease with a high prevalence and recurrence rate. However, short-chain fatty acids (SCFAs) are less often reported in the prevention of urolithiasis. This study aimed to explore the effect of SCFAs on the renal CaOx stone formation and the underlying mechanisms. Ethylene glycol was used to induce renal CaOx crystals in rats. SCFAs (acetate, propionate, or butyrate) were added as supplements to the drinking water with or without antibiotics. Because intestinal oxalate transporters SLC26A6 and SLC26A3 regulate the excretion and absorption of oxalate in the intestine, we injected adeno-associated virus 9 (AAV9)-SLC26A6-shRNA (short hairpin RNA) and AAV9-SLC26A3 into the tail vein of rats to suppress SLC26A6 and overexpress SLC26A3 expression in the intestine, respectively, to explore the role of SLC26A3 and SLC26A6 (SLC26A3/6) in the reduction of renal CaOx crystals induced by SCFAs. Results showed that SCFAs reduced renal CaOx crystals and urinary oxalate levels but, however, increased the abundance of SCFA-producing bacteria and cecum SCFA levels. SCFA supplements still reduced renal crystals and urinary oxalate after gut microbiota depletion. Propionate and butyrate downregulated intestinal oxalate transporter SLC26A3 expression, while acetate and propionate upregulated SLC26A6 expression, both in vivo and in vitro. AAV9-SLC26A3 exerted a protective effect against renal crystals, while AAV9-SLC26A6-shRNA contributed to the renal crystal formation even though the SCFAs were supplemented. In conclusion, SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones. IMPORTANCE Some studies found that the relative abundances of short-chain-fatty-acid (SCFA)-producing bacteria were lower in the gut microbiota of renal stone patients than healthy controls. Our previous study demonstrated that SCFAs could reduce the formation of renal calcium oxalate (CaOx) stones, but the mechanism is still unknown. In this study, we found that SCFAs (acetate, propionate, and butyrate) reduced the formation of renal calcium oxalate (CaOx) crystals and the level of urinary oxalate. Depleting gut microbiota increased the amount of renal crystals in model rats, and SCFA supplements reduced renal crystals and urinary oxalate after gut microbiota depletion. Intestinal oxalate transporter SLC26A6 was a direct target of SCFAs. Our findings suggested that SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones.

Pathogenesis of COVID-19 described through the lens of an undersulfated and degraded epithelial and endothelial glycocalyx

The glycocalyx surrounds every eukaryotic cell and is a complex mesh of proteins and carbohydrates. It consists of proteoglycans with glycosaminoglycan side chains, which are highly sulfated under normal physiological conditions. The degree of sulfation and the position of the sulfate groups mainly determine biological function. The intact highly sulfated glycocalyx of the epithelium may repel severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) through electrostatic forces. However, if the glycocalyx is undersulfated and 3-O-sulfotransferase 3B (3OST-3B) is overexpressed, as is the case during chronic inflammatory conditions, SARS-CoV-2 entry may be facilitated by the glycocalyx. The degree of sulfation and position of the sulfate groups will also affect functions such as immune modulation, the inflammatory response, vascular permeability and tone, coagulation, mediation of sheer stress, and protection against oxidative stress. The rate-limiting factor to sulfation is the availability of inorganic sulfate. Various genetic and epigenetic factors will affect sulfur metabolism and inorganic sulfate availability, such as various dietary factors, and exposure to drugs, environmental toxins, and biotoxins, which will deplete inorganic sulfate. The role that undersulfation plays in the various comorbid conditions that predispose to coronavirus disease 2019 (COVID-19), is also considered. The undersulfated glycocalyx may not only increase susceptibility to SARS-CoV-2 infection, but would also result in a hyperinflammatory response, vascular permeability, and shedding of the glycocalyx components, giving rise to a procoagulant and antifibrinolytic state and eventual multiple organ failure. These symptoms relate to a diagnosis of systemic septic shock seen in almost all COVID-19 deaths. The focus of prevention and treatment protocols proposed is the preservation of epithelial and endothelial glycocalyx integrity.

Calyceal Diverticula Disease: Diagnosis and Management Options in the Era of Non-Contrast CT Scan

INTRODUCTION

Calyceal diverticula (CD) are traditionally diagnosed by contrast studies. However, non-contrast CT is the standard imaging modality for kidney stones. Therefore, we aimed to determine if the lack of contrast imaging affected outcomes of the management of symptomatic CD with stone.

MATERIALS AND METHODS

This is a retrospective study of patients diagnosed with CD with intracalyceal stone from 2000 to 2017 analyzing demographics, clinical data, and success of different treatment options. The timing of CD diagnosis is correlated to the success of the first treatment.

RESULTS

Forty-eight patients were found. CD was diagnosed prior to intervention in 20 (42%) cases and intraoperatively during flexible ureteroscopy in 17 (35%) and 11 (23%) cases were diagnosed after failed intervention, mainly ESWL. We found that the success rate of treatment was highly affected by the timing and modality of diagnosis. Preoperative diagnosis of CD was associated with 69% success rate of the first intervention. In contrast, there was a 0% success rate of first treatment if CD was not diagnosed with contrast imaging. Furthermore, univariate analysis showed no significant association between sociodemographics and clinical variables and success treatment (p > 0.05).

CONCLUSIONS

The delay in diagnosing CD with stone contributes significantly to the success rate and the number of treatments.

The Effect of Oxalobacter formigenes Colonization in Patients with Calcium Oxalate Renal Stones in Comparison with Healthy People in Qom: A Case-Control Study

Background: Urinary stones are a major problem world, and their incidence has increased significantly in recent years. Objectives: This study aimed to develop a simple and rapid molecular method based on PCR and qPCR assays to detect Oxalobacter formigenes (which causes oxalate degradation in intestines) in fecal samples of healthy volunteers and patients with calcium oxalate nephrolithiasis, and determine the amount of urinary oxalate in the two groups. Methods: This study was performed on urine and fecal samples of 73 patients with kidney stones and 52 healthy individuals. After DNA extraction, PCR and qPCR assays were performed on two gene regions of O. formigenes, OXC, and FRC. Also, urine oxalate was measured in the study population using biochemical methods. Results: We found that the presence of O. formigenes could reduce the risk of kidney stones and calcium oxalate stones. In fact, both FRC and OXC genes were involved in the diagnosis of O. formigenes; however, the results based on the FRC gene showed higher efficiency. In addition, the presence or absence of stones did not affect the amount of urinary excretion of oxalate, rather it is affected by diet. Conclusions: Molecular identification of O. formigenes by PCR and qPCR assays allows rapid, specific, and reproducible detection in fecal samples, which also allows immediate processing of these samples in clinical conditions.

Dietary Fiber and Prebiotic Compounds in Fruits and Vegetables Food Waste

The fruits and vegetables processing industry is one of the most relevant food by-products, displaying limited commercial exploitation entailing economic and environmental problems. However, these by-products present a considerable amount of dietary fiber and prebiotics with important biological activities, such as gut microbiota modulation, lowering the glycemic load and replacing some unhealthy ingredients with an impact on food texture. Therefore, the international scientific community has considered incorporating their extracts or powders to preserve or fortify food products an area of interest, mainly because nowadays consumers demand the production of safer and health-promoting foods. In the present review, literature, mainly from the last 5 years, is critically analyzed and presented. A particular focus is given to utilizing the extracted dietary fibers in different food products and their impact on their characteristics. Safety issues regarding fruits and vegetables wastes utilization and anti-nutritional compounds impact were also discussed.

The serum metabolome of COVID-19 patients is distinctive and predictive

BACKGROUND

Metabolism is critical for sustaining life, immunity and infection, but its role in COVID-19 is not fully understood.

METHODS

Seventy-nine COVID-19 patients, 78 healthy controls (HCs) and 30 COVID-19-like patients were recruited in a prospective cohort study. Samples were collected from COVID-19 patients with mild or severe symptoms on admission, patients who progressed from mild to severe symptoms, and patients who were followed from hospital admission to discharge. The metabolome was assayed using gas chromatography-mass spectrometry.

RESULTS

Serum butyric acid, 2-hydroxybutyric acid, l-glutamic acid, l-phenylalanine, l-serine, l-lactic acid, and cholesterol were enriched in COVID-19 and COVID-19-like patients versus HCs. Notably, d-fructose and succinic acid were enriched, and citric acid and 2-palmitoyl-glycerol were depleted in COVID-19 patients compared to COVID-19-like patients and HCs, and these four metabolites were not differentially distributed in non-COVID-19 groups. COVID-19 patients had enriched 4-deoxythreonic acid and depleted 1,5-anhydroglucitol compared to HCs and enriched oxalic acid and depleted phosphoric acid compared to COVID-19-like patients. A combination of d-fructose, citric acid and 2-palmitoyl-glycerol distinguished COVID-19 patients from HCs and COVID-19-like patients, with an area under the curve (AUC) > 0.92 after validation. The combination of 2-hydroxy-3-methylbutyric acid, 3-hydroxybutyric acid, cholesterol, succinic acid, L-ornithine, oleic acid and palmitelaidic acid predicted patients who progressed from mild to severe COVID-19, with an AUC of 0.969. After discharge, nearly one-third of metabolites were recovered in COVID-19 patients.

CONCLUSIONS

The serum metabolome of COVID-19 patients is distinctive and has important value in investigating pathogenesis, determining a diagnosis, predicting severe cases, and improving treatment.

Composition of Urine Collected from Non-Stone-Forming Chinese Persons during Different Short-Term Periods of the Day

The purpose of this study in a small group of non-stone-forming Chinese persons was to measure the levels of supersaturation with calcium oxalate and calcium phosphate and pH with the aim of confirming if any of the different short-term urine samples were better for risk evaluation than a 24-h sample. Nine normal men and 1 woman collected urine during 4 periods of the day. Period 1 between 08 and 12 h, Period 2 between 12 and 18 h, Period 3 between 18 and 22 h, and Period 4 between 22 and 08 h. Each sample was analysed for calcium, oxalate, citrate, magnesium and phosphate, and estimates of supersaturation with calcium oxalate (CaOx) and calcium phosphate (CaP) were expressed in terms of AP(CaOx) and AP(CaP) index. An estimate of the solute load of CaOx was also calculated. Urine composition for 24-h urine (Period 24) was obtained mathematically from the analysed variables. Urine composition corresponding to 14-h urine portions 22-12 h (Period 14N) and 08-22 h (Period 14 D) were calculated. The lowest pH levels were recorded in Period 1 urine. The highest level of AP(CaOx) index was recorded during Period 1, and the product AP(CaOx) index × 107 × hydrogen ion concentration was significantly higher in Period 1 urine than in 24-h urine (p = 0.02). Also, the product SL(CaOx) × 107 × hydrogen ion concentration was significantly higher in Period 1 urine (p = 0.02). Low AP (CaP) index levels were recorded in Period 4, but also in all periods following dietary loads of calcium and phosphate. With the important reservation that the analytical results were obtained from non-stone-forming persons, the conclusion is that analysis of urine samples collected between 08 and 12 h might be an alternative to 24-h urine. The risk evaluation might advantageously be expressed either in terms of the product AP(CaOx) index × 107 × hydrogen ion concentration or the product SL(CaOx) × 107 × hydrogen ion concentration.

Novel insights into cytochrome P450 enzyme and solute carrier families in cadmium-induced liver injury of pigs

Cadmium (Cd) is a typical pollutant and carcinogen in environment. Exposure assessment of contaminants is an important component of occupational and environmental epidemiological studies. Early studies of Cd have focused on aquatic animals, chickens and rats. However, toxicological evaluation of Cd in pigs has not been reported. Therefore, twelve pigs were randomly divided into two groups (n = 6): the control group and the Cd group (Cd content: 15 ± 0.242 mg/kg feed) in this study, the experimental period was 30 d, and the toxic effects of Cd on the liver of weanling piglets were examined by antioxidant function, liver function, Cd content, histological examination and transcriptomics. The results showed that the changes of antioxidant function, liver function and Cd content were significant in the liver. Transcriptional profiling results showed that 399 differentially expressed genes (DEGs) were significantly up-regulated while 369 DEGs were remarkably down-regulated in Cd group, and which were concentrated in three ontologies: molecular function, cellular component and biological processes. Interestingly, significant changes in some genes of the cytochrome P450 enzyme (CYP450) and solute carrier (SLC) families have been observed and were consistent with qRT-PCR results. In conclusion, Cd could cause liver injury in weanling piglets and change the transcriptomic characteristics of liver. CYP450 and SLC families play an indispensable role in Cd-mediated hepatotoxicity. Importantly, changes in mRNA levels of CYP2B22, CYP7A1, CYP8B1, SLC26A8, SLC11A1, SLC27A2 and SLC22A7 induced by Cd have been reported for the first time. Our findings will provide a new insight for better assessing the mechanism of Cd toxicity to the liver.

The faecal metabolome in COVID-19 patients is altered and associated with clinical features and gut microbes

Although SARS-CoV-2 can invade the intestine, though its effect on digestion and absorption is not fully understood. In the present study, 56 COVID-19 patients and 47 age- and sex-matched healthy subjects were divided into a discovery cohort and a validation cohort. Blood, faeces and clinical information were collected from the patients in the hospital and at discharge. The faecal metabolome was analysed using gas chromatography-mass spectrometry, and Spearman’s correlation analyses of clinical features, the serum metabolome, and the faecal micro- and mycobiota were conducted. The results showed that, the faeces of COVID-19 patients were enriched with important nutrients that should be metabolized or absorbed, such as sucrose and 2-palmitoyl-glycerol; diet-related components that cannot be synthesized by humans, such as 1,5-anhydroglucitol and D-pinitol; and harmful metabolites, such as oxalate, were also detected. In contrast, purine metabolites such as deoxyinosine and hypoxanthine, low-water-soluble long-chain fatty alcohols/acids such as behenic acid, compounds rarely occurring in nature such as D-allose and D-arabinose, and microbe-related compounds such as 2,4-di-tert-butylphenol were depleted in the faeces of COVID-19 patients. Moreover, these metabolites significantly correlated with altered serum metabolites such as oxalate and gut microbesincluding Ruminococcaceae, Actinomyces, Sphingomonas and Aspergillus. Although levels of several faecal metabolites, such as sucrose, 1,5-anhydroglucitol and D-pinitol, of discharged patients were not different from those of healthy controls (HCs), those of oxalate and 2-palmitoyl-glycerol did differ. Therefore, alterations in the faecal metabolome of COVID-19 patients may reflect malnutrition and intestinal inflammation and warrant greater attention. The results of present study provide new insights into the pathogenesis and treatment of COVID-19.

Differential bound proteins and adhesive capabilities of calcium oxalate monohydrate crystals with various sizes

Adhesion of calcium oxalate (CaOx) crystals onto renal tubular epithelial cells is one of the critical steps in kidney stone formation. However, effects of crystal size on the crystal adhesive capability remained unclear. This study compared the adhesive capabilities of CaOx monohydrate (COM) crystals with various sizes (<10 μm, 20-30 μm, 50-60 μm, and > 80 μm). Crystal-cell adhesion assay showed size-dependent increase of COM crystal adhesion onto epithelial cell surface using the larger crystals. Identification of apical membrane proteins that could bind to COM crystals by tandem mass spectrometry (nanoLC-ESI-ETD MS/MS) demonstrated size-specific sets of the COM crystal-binding proteins. Among these, numbers of known oxalate-binding proteins and COM crystal receptors were greatest in the set of the largest size (>80 μm). Atomic force microscopy (AFM) revealed that adhesive forces between carboxylic-immobilized AFM tip and COM crystal surface and between COM-mounted AFM tip and renal epithelial cell surface were size-dependent (greater for the larger crystals). In summary, the adhesive capability of COM crystals is size-dependent - the larger the greater adhesive capability. These data may help better understanding of the pathogenic mechanisms of kidney stone formation at an initial stage when renal tubular cells are exposed to various sizes of COM crystals.