Oxalate Degradation Research Articles

Enhanced photocatalytic degradation of crystal violet and malachite green oxalate dyes by NiAg2O infused chitosan nanocomposites

The present study investigated the catalysis of Lupeol-loaded chitosan nanoparticles infused with NiAg2O nanoparticles to create a NiAg2O/Lup@CS nanocomposite. Recent advances in nanomaterials with unique architectures and functionalities have successfully treated contaminated soil and industrial wastewaters. Consequently, a lupeol@chitosan nanoparticle loaded with NiAg2O was created, and its catalytic effectiveness in degrading industrial dye pollution was examined. The ionic gelation synthesis route was used to produce the NiAg2O/Lup@CS nanocomposite. After that, the resultant nanocomposite underwent extensive analysis to determine its elemental composition through EDAX, surface bonding, nature, crystallinity using FTIR, FESEM, and XRD, and powdered particle size using HRTEM. Subsequently, the produced nanocomposite's efficacy in photo-catalytically degrading Crystal violet and Malachite green oxalate were evaluated. Moreover, the Crystal violet and Malachite green oxalate degradation kinetics were studied using the Langmuir–Hinshelwood model, which also offered a plausible photocatalytic process. The catalytic mechanism suggested that the addition of Lup@CS nanoparticles would have had the effect of speeding up photocurrent transport by increasing the quantity of electrons and holes produced by the photon's irradiation. This highlights the significance of creating innovative composite photocatalysts. The study also observed the superior photocatalytic activity of NiAg2O/Lup@CS nanocomposite with 86.14 % degradation of Crystal violet and 86.65 % degradation of Malachite green oxalate.

Optimization of Plant Oxalate Quantification and Generation of Low-Oxalate Maize (Zea mays L.) through O7 Overexpression.

Oxalate, the simplest dicarboxylic acid, is a prevalent antinutrient that chelates with various metals and can lead to the formation of kidney stones in humans. The accurate detection of the oxalate concentration in food and the cultivation of low-oxalate crops are important for enhancing public health. In this study, we established a high-throughput and highly sensitive technique for oxalate detection using ultra-high-performance liquid chromatographic-triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS). Additionally, we overexpressed the gene O7, which encodes oxalyl-CoA synthetase in the maize oxalate degradation pathway, resulting in O7-OE lines. By employing the UPLC-QqQ-MS/MS method to measure oxalate levels in these transgenic lines, we observed that the oxalate content in the kernels of O7-OE lines was reduced by approximately 43%, with a concurrent increase in some micronutrients such as zinc. Importantly, the transgenic maize showed normal seed storage compound accumulation or other agronomic characteristics. In summary, we developed a high-throughput detection method that advances oxalate measurement. Furthermore, by generating new maize germplasm with diminished oxalate, our work offers potential health advantages to consumers.

Secondary products and molecular mechanism of calcium oxalate degradation by the strain Azospirillum sp. OX-1

The oxalate-carbonate pathway (OCP) involves degradation of soil oxalate to carbonate. To exploit and manage this natural mineralization of assimilated atmospheric CO2 into stable carbonates, improved understanding of this complex biotransformation process is needed. A strain of oxalate-degrading bacteria, Azospirillum sp. OX-1, was isolated from soil, and its secondary products of calcium oxalate degradation were analyzed and characterized using SEM, XRD, TG/DTG-DTA and FTIR-spectroscopy. The molecular mechanism of calcium oxalate degradation was also analyzed using proteomics. The results showed, for the first time, that OX-1 could not only degrade calcium oxalate to calcium carbonate, but also that the process was accompanied by synthesis of methane. Proteomic analysis demonstrated that OX-1 has a dual enzyme system for calcium oxalate degradation, using formyl-CoA transferase (FRC) and thiamine pyrophosphate (ThDP)-dependent oxalyl-CoA decarboxylase (OXC) to form calcium carbonate. Up-regulated expression of enzymes related to methane synthesis was also detected during calcium oxalate degradation. Since methane is also a potent greenhouse gas, these new results suggest that the utility of exploiting the OCP to reduce atmospheric CO2 must be re-evaluated and that further studies should be conducted to reveal how widespread the methane producing capacity of strain OX-1 is in other bacteria and soil environments.

Water-saving and water-spending strategy: The physiological, proteomic and metabolomic investigation of wheat response to drought and the following recovery

Drought as water deficit in the soil represents the most commonly occurring and the most variable environmental stress factor worldwide. Plants have evolved various strategies to cope with drought stress in relation to their other needs such as the necessity to supply carbon in plants with a C3 type of photosynthetic assimilation. In the present study, two wheat cultivars, Baletka and Tobak, representing two contrasting water management strategies, were studied at physiological, proteomic and metabolomic levels to provide a complex view on their phenotypic responses to drought treatment and subsequent recovery. Physiological characteristics clearly distinguished Baletka and Tobak and, moreover, in water-saving Baletka, both proteomics and metabolomics analyses revealed significant remodelling of cell wall, changes in endocytosis and cell signalling, and, especially, changes in synthesis of other defence proteins and LTI65kDa protein (also known as RD29B protein) which has been detected in wheat for the first time. LEA1 protein was proposed as a component of drought stress memory in Baletka. An amazing finding was the enhanced accumulation of oxalate oxidase implying enhanced oxalate oxidase activity leading to faster degradation of oxalate with the simultaneous gain of two molecules of CO2 which may represent an alternative source of CO2 for C3 plants exposed to drought stress.

Gut and Urinary Microbiota in Cats with Kidney Stones.

Upper urinary tract urolithiasis is an emerging disease in cats, with 98% of kidney stones composed of calcium oxalate. In humans, disturbances in the intestinal and urinary microbiota are suspected to contribute to the formation of calcium oxalate stones. We hypothesized that similar mechanisms may be at play in cats. This study examines the intestinal and urinary microbiota of nine cats with kidney stones compared to nine healthy cats before, during, and after treatment with the antibiotic cefovecin, a cephalosporin. Initially, cats with kidney stones displayed a less diverse intestinal microbiota. Antibiotic treatment reduced microbiota diversity in both groups. The absence of specific intestinal bacteria could lead to a loss of the functions these bacteria perform, such as oxalate degradation, which may contribute to the formation of calcium oxalate stones. This study confirms the presence of a distinct urobiome in cats with kidney stones, characterized by greater richness and diversity compared to healthy cats. These findings highlight the potential of microbiota modulation as a strategy to prevent renal lithiasis in cats.

Deficient butyrate metabolism in the intestinal microbiome is a potential risk factor for recurrent kidney stone disease.

Intestinal microbiome dysbiosis is a known risk factor for recurrent kidney stone disease (KSD) with prior data suggesting a role for dysfunctional metabolic pathways other than those directly utilizing oxalate. To identify alternative mechanisms, the current study analyzed differences in the metabolic potential of intestinal microbiomes of patients (n = 17) and live-in controls (n = 17) and determined their relevance to increased risk for KSD using shotgun metagenomic sequencing. We found no differences in the abundance of genes associated with known oxalate degradation pathways, supporting the notion that dysfunction in other metabolic pathways plays a role in KSD. Further analysis showed decreased abundance of key enzymes involved in butyrate biosynthesis in patient intestinal microbiomes. Furthermore, de novo construction of microbial genomes showed that the majority of genes significantly enriched in non-stone formers are affiliated with Faecalibacterium prausnitzii, a major butyrate producer. Specifically pertaining to butyrate metabolism, the majority of abundant genes mapped back to F. prausnitzii, Alistipes spp., and Akkermansia muciniphila. No differences were observed in ascorbate or glyoxylate metabolic pathways. Collectively, these data suggest that impaired bacterial-associated butyrate metabolismmay be an oxalate-independent mechanism that contributes to an increased risk for recurrent KSD. This indicates that the role of the intestinal microbiome in recurrent KSD is multi-factorial, which is representative of the highly intertwined metabolic nature of this complex environment.Future bacteria-based treatments must not be restricted to targeting only oxalate metabolism.

Therapeutic effects of probiotics and herbal medications on oxalate nephrolithiasis: a mini systematic review.

The majority of all kidney stone cases are oxalate urolithiasis with a high risk of recurrence. Beside its widespread occurrence, kidney stones are characterized by severe complications and high treatment costs. Probiotics and herbal medications could be forthcoming therapeutic interventions in the management of oxalate kidney stones. The PubMed/MEDLINE database was searched for keywords "Oxalobacter formigenes" AND "Oxalate" OR "oxalate degradation" AND "Lactobacillus" OR "Bifidobacterium" OR "recombinant Lactobacillus" OR "Bacillus subtilis", and "urolithiasis" AND "herbal extract". The search returned 253 results, 38 of which were included in the review. Most of the oxalate-degrading probiotics belong to the Oxalobacter formigenes, Lactobacillus, Bifidobacterium, and Bacillus genus with a minimum dosage of 107 CFU in the form of capsules, sachets, and lyophilized powder. Oxalate concentration in media was 5-50mM with an incubation time ranging from 24h to 14 days. The majority of the studies suggested that probiotic supplementation might be useful for reducing urinary excretion of oxalate and urea and alleviation of stone formation. Different herbal extracts were used on murine models of nephrolithiasis (induced by 0.5-3% ethylene glycol) with reduction of renal inflammation and urinary parameters, and calcium oxalate crystals. Several strains of probiotics and herbal extracts confer protective effects against kidney stone/nephrolithiasis, indicating their promising nature for being considered as elements of preventive / adjuvant therapeutic strategies.

Detection of oxalyl-CoA decarboxylase (oxc) and formyl-CoA transferase (frc) genes in novel probiotic isolates capable of oxalate degradation in vitro

Oxalate degradation is one of lactic acid bacteria’s desirable activities. It is achieved by two enzymes, formyl coenzyme A transferase (frc) and oxalyl coenzyme A decarboxylase (oxc). The current study aimed to screen 15 locally isolated lactic acid bacteria to select those with the highest oxalate degradation ability. It also aimed to amplify the genes involved in degradation. MRS broth supplemented with 20 mM sodium oxalate was used to culture the tested isolates for 72 h. This was followed by an enzymatic assay to detect remaining oxalate. All isolates showed oxalate degradation activity to variable degrees. Five isolates demonstrated high oxalate degradation, 78 to 88%. To investigate the oxalate-degradation potential of the selected isolates, they have been further tested for the presence of genes that encode for enzymes involved in oxalate catabolism, formyl coenzyme A transferase (frc) and oxalyl coenzyme A decarboxylase (oxc). Three strains showed bands with the specific OXC and FRC forward and reverse primers designated as (SA-5, 9 and 37). Species-level identification revealed Loigolactobacillus bifermentans, Lacticaseibacillus paracasei, and Lactiplantibacillus plantarum. Preliminary results revealed that the tested probiotic strains harbored both oxc and frc whose products are putatively involved in oxalate catabolism. The probiotic potential of the selected strains was evaluated, and they showed high survival rates to both simulated gastric and intestinal fluids and variable degrees of antagonism against the tested Gram-positive and negative pathogens and were sensitive to clarithromycin but resistant to both metronidazole and ceftazidime. Finally, these strains could be exploited as an innovative approach to establish oxalate homeostasis in humans and prevent kidney stone formation.

Screening of oxalate-degrading probiotics and preventive effect of Lactiplantibacillus plantarum AR1089 on kidney stones.

Calcium oxalate stone is the main type of kidney stone, so far there is no specific drug treatment. Here, we screened for oxalate-degrading probiotics and evaluated the potential preventive effect of lactic acid bacteria in rats with hyperoxaluria-induced kidney stones. The oxalate degradation efficiencies of the probiotics were determined to be 5-20% by in vitro experiments, of which the degradation efficiencies of Lactiplantibacillus plantarum AR342 and L. plantarum AR1089 were 17.32% and 14.15%, respectively. Through animal experiments, we found that L. plantarum AR1089 significantly attenuated kidney injury, as demonstrated by improving renal dysfunction and renal fibrosis, lowering creatinine and urea nitrogen levels. L. plantarum AR1089 was also effective in decreasing the number of calcium oxalate crystals in the urine and kidneys as well as ameliorating oxidative stress as evidenced by lowering the level of MDA and decreasing the level of SOD and CAT. Moreover, supplementation of L. plantarum AR1089 inhibited renal crystalline deposition by down-regulating the expression of KIM-1, OPN and MCP-1, and prevented hyperoxaluria-induced kidney stones by regulating the gut microbiota. Taken together, the present study shows that oral administration of L. plantarum AR1089, by attenuating kidney injury and regulating gut microbiota, is a potential therapy to reduce calcium oxalate crystals and prevent the progression of kidney stones.

Microbial Degradation Of Calcium Oxalate And Its Potential Application

Calcium oxalate is a naturally occurring compound found in various plants and minerals, and its accumulation in the kidney leads to the formation of kidney stones in humans. One of the main causes of kidney stone formation is a decrease in the number of intestinal microbiota which are capable of degrading calcium oxalate. This study focuses on bacterial degradation of calcium oxalate accumulated in humans. Searching for Calcium oxalate degrading strain with high degrading activity has become one of the priorities from the context of research. The study aimed to isolate and characterize microorganisms which are capable of degrading calcium oxalate. Calcium oxalate degrading microorganisms were isolated from faecal samples by using MRS-calcium oxalate medium. Calcium oxalate degrading bacteria were identified on the basis of colour reduction on calcium oxalate medium plate after the incubation period. The morphological and biochemical characterization of isolates were studied. Quantitative determination of degradation was performed by using an indole assay. The activity of isolates was observed by the degradation of kidney stones. Isolates showed better results for degradation of kidney stones after 2 weeks of the incubation period.

Hierarchical MnO2-ZnO functionalized SiO2 nanofibrous membranes with enhanced Fenton-like catalytic performance for dye removal

In this work, flexible and hierarchical structured MnO2-ZnO/SiO2 nanofibrous membranes (NFMs) as easily recyclable Fenton-like catalysts have been developed utilizing the combination of electrospinning and a hydrothermal growth method. By capitalizing the advantages of the high specific surface area and synergism effects of bimetallic oxides, the optimal membranes exhibited prominent catalytic activity in the degradation of malachite green oxalate (MGO). Specifically, within a mere 15 min at an initial pH, 98.1% of MGO was degraded, demonstrating a remarkable degradation rate of 0.2744 min−1. Free radical scavenging experiments and Electron Paramagnetic Resonance studies conclusively identified superoxide radical species (O2•–) as the main reactive species for the degradation of MGO. Furthermore, the resultant flexible membranes displayed excellent stability and could be effortlessly recycled after catalytic process, surpassing the performance of conventional powdery Fenton-like catalysts. Notably, the resultant membranes could be used for dynamic catalyst for MGO removal and could efficiently treat 418 mL MGO with a flux of 5650.5 L m−2 h−1. The successful fabrication of these MnO2-ZnO/SiO2 membranes paves the way for the development of more efficient and applicable Fenton-like catalytic materials for water treatments and offers more inspirations for innovative designs of fiber-based or membrane-based catalysts.

Rhubarb: A novel model plant to study the conundrum of calcium oxalate synthesis

The study investigated calcium oxalate (CaOx) crystal composition, accumulation, synthesis, and degradation in five rhubarb species from the North-Western Indian Himalayas. Techniques like optical and scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), inductively coupled plasma-optical emission spectrometry (ICP-OES), X-ray diffraction spectroscopy (XRD), and real-time (qRT-PCR) expression analysis of strategic genes were used to understand the processes of oxalate synthesis and precipitation. Results showed crystals tend to accumulate around vascular bundles in all species, irrespective of size, indicating a consistent pattern. Crystal synthesis and accumulation were stress-driven, linked to substrate composition, and in planta soluble oxalate and calcium levels, paralleling oxalate precursors. Based on their availability, CaOx crystals precipitated heavy metals mostly associated with its weddellite form. Crystal content correlated positively with mRNA levels of calcium/oxalate/ascorbate-related and stress-responsive genes, and negatively with oxalate oxidation/decarboxylation genes. CaOx crystals were suggested as potential biominerals for addressing heavy metal stress in agriculture.

Probiotic Lactobacillus strains isolated from date waste and wastewater for the kidney stone, intestinal oxalate-degradation and antioxidant activity

Lactic acid bacteria (LAB) are probiotic organisms and are promising alternatives to manage kidney stone problems. Oxalate digesting LAB was screened from date wastes and date wastewater. LAB was isolated using De Man, Rogosa and Sharpe agar (MRS agar) medium and was subjected to oxalate degradation assay in a calcium oxalate plate. The strain was further subjected to assay for its capacity to tolerate acidic pH value and bile salt. Then, anti-urolithiatic activity assay was carried out by in vitro analysis. Based on preliminary characteristics, among 62 oxalate degrading strains, twenty-four strains exhibited a greater than 10 mm zone. The potent bacterial strains were identified as Lactobacillus cassei, L. acidophilus, L. gasseri and L. fermentum. Isolates from date wastes showed better antagonistic properties towards bacterial pathogens. At 50 µg Calcium oxalate concentration, 75.6 ± 0.865 degradation was achieved by L acidophilus. LAB isolated from date waste showed promising anti-urolithiasis activity. Hence, date waste may serve as a potential source for LAB probiotics to treat hyperoxaluria.

3D Carbon Microspheres with a Maze-Like Structure and Large Mesopore Tunnels Built From Rapid Aerosol-Confined Coherent Salt/Surfactant Templating.

Hierarchically porous carbons with tailor-made properties are essential for applications wherein rich active sites and fast mass transfer are required. Herein, a rapid aerosol-confined salt/surfactant templating approach is proposed for synthesizing hierarchically porous carbon microspheres (HPCMs) with a maze-like structure and large mesopore tunnels for high-performance tri-phase catalytic ozonation. The confined assembly in drying microdroplets is crucial for coherent salt (NaCl) and surfactant (F127) dual templating without macroscopic phase separation. The HPCMs possess tunable sizes, a maze-like structure with highly open macropores (0.3-30µm) templated from NaCl crystal arrays, large intrawall mesopore tunnels (10-45nm) templated from F127, and rich micropores (surface area >1000 m2 g-1 ) and oxygen heteroatoms originated from NaCl-confined carbonization of phenolic resin. The structure formation mechanism of the HPCMs and several influencing factors on properties are elaborated. The HPCMs exhibit superior performance in gas-liquid-solid tri-phase catalytic ozonation for oxalate degradation, owing to their hierarchical pore structure for fast mass transfer and rich defects and oxygen-containing groups (especially carbonyl) for efficient O3 activation. The reactive oxygen species responsible for oxalate degradation and the influences of several structure parameters on performance are discussed. This work may provide a platform for producing hierarchically porous materials for various applications.

Revisit the Role of Salinity in Heterogeneous Catalytic Ozonation: The Trade-Off between Reaction Inhibition and Mass Transfer Enhancement.

Heterogeneous catalytic ozonation (HCO) is an effective technology for advanced wastewater treatment, while the influence of coexisting salts remains unclear and controversial. Here, we systematically explored the influence of NaCl salinity on the reaction and mass transfer of HCO through lab experiments, kinetic simulation, and computational fluid dynamics modeling, and proposed that the trade-off between reaction inhibition and mass transfer enhancement would affect the pollutants degradation pattern under varying salinity. The increase of NaCl salinity decreased ozone solubility and accelerated the futile consumption of ozone and hydroxyl radicals (•OH), and the maximum •OH concentration under 50 g/L salinity was only 23% of that without salinity. However, the increase of NaCl salinity also significantly reduced the ozone bubble size and enhanced the interphase and intraliquid mass transfer, with the volumetric mass transfer coefficient being 130% higher than that without salinity. The trade-off between reaction inhibition and mass transfer enhancement shifted under different pH values and aerator pore sizes, and the oxalate degradation pattern would change correspondingly. Besides, the trade-off was also identified for Na2SO4 salinity. These results emphasized the dual influence of salinity and offered a new theoretical perspective on the role of salinity in the HCO process.

A novel Ce-Ni@biochar nanocomposite withenhanced photocatalytic activity towards organicdyesdegradation: impact of process variables and water matrices.

The intent of this research work is to implement a biogenic, affordable, and highly effective Ce-Ni@biochar catalyst in order to study its photoactivity in the removal of crystal violet and malachite green oxalate. The catalyst was synthesized using liquid phase reduction method where cerium and nickel nanoparticles are embedded on the rice husk biochar for photocatalytic degradation of organic dyes in the presence of sunshine. Various characterization techniques were conducted on fabricated catalyst for adequate evaluation of the chemical composition as well as morphological and topographical properties of the formed compound. The nanoparticles embedded on biochar persuade increased charge separation that resulted in a substantial decrease in electron-hole recombination rate. The synergistic actions of the catalyst resulted in a high level of photocatalytic activity. The fabricated nanocatalyst showed excellent photoactivity that caused 96 and 99% degradation of crystal violet and malachite green oxalate, a growing industrial pollutant, within 35 and 25 min, respectively. A persuasive mechanism and kinetics are well presented. A series of investigations were done on other factors, such as contact duration, catalyst dosage, starting concentration, interfering ions, and pH, to know its degradation pursuance. The impacts of different water matrices were also investigated. The removal effectiveness of the synthesized catalyst persisted after five consecutive cycles. Marking the burgeoning industrial effluents as a result of rapid industrialization and also focusing on easy availability and low-cost source as well as high efficiency, reusability of the catalyst imparts its novelty and need of this research work.

#6180 OXALATE NEPHROPATHY SECONDARY TO ENTERIC HYPEROXALURIA: A RARE CAUSE OF END STAGE RENAL FAILURE – A REPORT OF 2 CASES

Abstract Background and Aims Oxalate nephropathy is a rare cause of renal failure which is usually due to primary or secondary hyperoxaluria. Secondary hyperoxaluria results from increased intake or increased intestinal oxalate availability (enteric hyperoxaluria), increased intestinal oxalate degradation, or increased colonic permeability to oxalate [1]. Little is known about the burden of end stage kidney disease in this group of patients as most of the initial literature was from case reports and case series. More recently, prevalence of 1- 4.01% was reported from biopsy studies suggesting that this entity is indeed a cause of kidney failure that needs to be considered [2,3]. Method We present two cases of oxalate nephropathy secondary to enteric hyperoxaluria following small bowel resections. Results CASE ONE 82 year old man with a solitary kidney who was admitted in the ED on account of a decline in renal function on a background of episodes of loose stools. This was his second admission in two months on account of decline in renal function. He had emergency laparotomy and adhesiolysis as a result small bowel obstruction from volvulus 12 months earlier. Other past medical history include left nephroureterectomy for renal cancer, transurethral resection of bladder tumour, hypertension, Barretts and appendectomy. His medications were Omeprazole(which was switched to Famotidine due to hypomagnesaemia 7 months postop), Atenolol and Adcal D3. Renal immunology and myeloma screen were negative. Urine was bland and ultrasound did not show any obstruction. His AKI was initially thought to be pre-renal and there was some improvement in renal function with fluids during his first admission although renal function didn't return to baseline. His renal function progressively worsened in a spate of a few months. He had a baseline creatinine of 130 prior to his laparotomy which worsened to 184 post surgery bur the improved to about 109 few days post op. However, his renal function was noticed to decline 9 months post op and eventually his creatinine peaked at 751, fourteen months post op. He eventually had a renal biopsy 13 months post op that showed oxalosis, acute tubular injury and patchy interstitial fibrosis. His renal function continued to deteriorate and he was eventually commenced on haemodialysis. CASE TWO A 75-year-old man who was referred to the renal clinic on account of a decline in renal function. He had a past medical history of Crohn's disease, previous right hemicolectomy 26 years ago with revision 4 years ago, ileostomy(with subsequent reversal), inguinal herniorrhaphy, hypertension and BPH. He was on Azathioprine for his Crohn's and his initial decline in renal function was thought to be attributable to Azathioprine. Other medications include: Amlodipine 5 mg, Finasteride 5 mg, Loperamide 2 mg bd, Tamsulosin 400mcg od. At referral, his renal function had progressively deteriorated over the previous few months from a baseline creatinine of 145 to 303, 44 months after his last surgery. Urinalysis showed trace of protein and + of blood however, urine ACR was normal. Vasculitis and myeloma screen were also normal. Ultrasound ruled out any obstruction. Despite pausing Azathioprine, renal function continued to deteriorate with creatinine peaking at 561 over the next 2 months. He subsequently had a renal biopsy that showed chronic damage with oxalate casts. He was subsequently commenced on haemodialysis. Conclusion These two cases highlight the need to consider enteric hyperoxaluria in patients presenting with unexplained decline in renal function who have had bowel surgery or have risk factors for fat malabsorption. This is important due to the usual poor prognosis in this group of patients [1].

OXALATE-DEGRADING ACTIVITY IN FECAL MICROBIOTA IS ASSOCIATED WITH OBESITY AND CARDIOVASCULAR EVENTS IN END-STAGE KIDNEY DISEASE PATIENTS

Objective: In contrast to the general population, the obesity paradox observed in end-stage kidney disease (ESKD) patients is associated with a better CVD prognosis. Considering the similar signature of the gut microbiota in oxalate metabolism, obesity, and CVD, we hypothesized that altered oxalate-degrading activity (ODA) in the fecal microbiota, rather than obesity per se, might influence the development of CVD in ESKD patients. Design and method: A total of 32 ESKD patients aged 52.5 (40-62) years were enrolled in this retrospective observational cohort pilot study. CVD events were defined as any new-onset disease of the heart and associated blood vessels during the 3-year follow-up period after completion of evaluation. The fecal total ODA, defined as the total ability of the different strains of oxalate-degrading bacteria to metabolize oxalate, was determined by redoximetric titration with KMnO4; results were expressed as % oxalate degradation per 0.01 g of feces. Data analysis and all graphs were generated using MedCalc software. Results: Total fecal ODA ranged from -16 to 24%/0.01 g feces and was inversely correlated with BMI (Fig. 1). During the 3-year follow-up period, 5/7 (71.4%) obese patients, 2/11 (18.2%) overweight patients, and 2/14 (14.3%) normal-weight patients experienced CVD (⇙2 = 8.4, p = 0.01). The ROC analysis showed that a negative total fecal ODA (<-1%/0.01 g feces) was the most appropriate cut-off point for predicting CVD events in ESKD patients, with a sensitivity of 77.8% and a specificity of 74% (Fig. 2). In univariate Cox regression analysis, both obesity (HR 8.2, 95% CI 1.2; 18.1) and negative fecal total ODA (HR 9.4, 95% CI 2.3; 19.4) were associated with CVD events. In the multivariate model of Cox regression analysis adjusted for age, dialysis vintage, diabetes, and dyslipidemia, negative total fecal ODA, but not obesity, was associated with CVD events in our cohort (Fig. 3). Conclusions: Our findings provide preliminary evidence that a decrease in fecal total ODA is associated with obesity and the development of CVD in ESKD patients. Further studies are needed to determine altered fecal total ODA as a risk factor for the development of CVD in ESKD patients.

New perspectives for bio-technical treatment of oxalate-containing waste streams from bauxite processing

Alumina is typically produced from bauxite ore using the Bayer process, in which the ore is mixed with alkaline liquor under elevated temperatures. Australian bauxite ore contains a wide range of organics, which detrimentally affect the Bayer process. Therefore, the removal of organic compounds from the alkaline Bayer process liquor is critical in maintaining process efficiency and alumina quality. Oxalate (C2O42−) is a key organic impurity in the Bayer process liquors that requires removal as it increases in concentration in the processing circuit as the Bayer liquor is continually recycled. Compared to conventional physiochemical or physical methods (e.g., chemical precipitation, wet-oxidation, liquor burning), microbial bioreactor treatment processes have the potential to be more economical and environmentally sustainable for oxalate removal. Some Australian alumina refineries have implemented full-scale bioreactors such as moving bed biofilm reactors (MBBRs) and aerobic suspended growth bioreactors (ASGB). While these bioreactors are robust and effective in removing oxalate, they have some limitations, such as the need for pre-acidification of influent and the loss of ammonia (nutrient) through volatilization. Therefore, this study aimed to provide an overview of the fundamentals and recent advances in biotechnical processes for the treatment of alkaline oxalate-containing liquor. Laboratory-scale studies on promising new biotreatment concepts, such as the use of bioelectrochemical systems to facilitate concurrent oxalate degradation and caustics recovery, as well as the utilization of nitrogen-fixing microorganisms to obviate the requirement for external nutrient dosage, are discussed. Perspectives for further research on oxalate-containing waste streams are also proposed.

Increased abundance of bacteria of the family Muribaculaceae achieved by fecal microbiome transplantation correlates with the inhibition of kidney calcium oxalate stone deposition in experimental rats.

The incidence of nephrolithiasis is increasing rapidly worldwide. Calcium oxalate is the most common constituent, contributing to approximately 80% of all kidney stones. The gut microbiome, through its oxalate-degrading ability, may play a role in decreasing morbidity due to urinary calculus. Fecal microbiome transplantation (FMT) has been reported to be effective in restoring the gastrointestinal microbial community in different conditions. The transplantation of whole communities that have oxalate-degrading function may be a more effective strategy than the transplantation of isolated strains. FMT was carried out in male guinea pigs and male Sprague-Dawley laboratory rats (SDRs). Fresh feces were collected from guinea pigs housed in metabolic cages. SDRs were divided into four groups: two groups received standard rat chow (SC) (groups SC and SC + FMT), and two groups were fed a 5% potassium oxalate diet (OD) (groups OD + phosphate-buffered saline (PBS) and OD + FMT). On day 14, groups OD + PBS, OD + FMT, and SC + FMT received either PBS or guinea pig feces by esophageal gavage. The composition of the microbiota of guinea pigs and SDRs was analyzed using a 16S rRNA gene sequencing approach. Biochemical analysis of urine samples from SDRs revealed the presence of calcium oxalate (CaOx) crystals, which were presumed to originate from kidney stones. Renal function was examined using real-time PCR analysis and immunohistochemical staining for renin, angiotensin-converting enzyme, and osteopontin (OPN) expression. FMT resulted in a gut microbiota that was a mixture of guinea pig and SDR bacteria. A microbial network involving Muribaculaceae, Lactobacillus, and Bifidobacterium was activated by FMT in group OD + FMT. As a result, urinary oxalate, calcium, uric acid, creatinine and urea in urine samples were reduced significantly. Similarly, significant reduction of uric acid and blood urea nitrogen to creatinine ratio in serum samples was observed (p < 0.05). Microscopic observations revealed a high CaOx crystal score (4+) in the kidneys of rats in group OD + PBS, whereas a lower score (2+) was observed in the rats in group OD + FMT. Up-regulation of OPN and down-regulation of renin were also associated with FMT. A microbial network involving Muribaculaceae and other oxalate-degrading bacteria achieved by FMT was capable of reducing urinary oxalate excretion and CaOx crystal deposition in the kidney through increasing intestinal oxalate degradation. FMT may exert a renoprotective function in oxalate-related kidney stones.