Modeling of hyperoxaluric calcium oxalate nephrolithiasis: experimental induction of hyperoxaluria by hydroxy-L-proline

Hydroxyproline increases inflammation and Uropathogenic E. coli (UPEC) infection in female rats

Calcium oxalate (CaOx) kidney stones may be associated with urinary tract infections (UTIs). However, the mechanisms for this association are not well-established. The objective of this study was to investigate the effect of oxalate on immunity and UTI development in vivo. Female Sprague-Dawley rats were fed a control diet for 3 days before continuing this diet or starting a 5% Hydroxy-L-proline diet (HLP; oxalate precursor) for 7 days. Rats were subsequently infected transurethrally with Uropathogenic E. coli (UPEC, a bacterium that causes UTI) and sacrificed 3 days later. Urine, blood, kidney, and bladder samples were collected. Urinary oxalate levels, renal CaOx crystal deposition, inflammatory markers, and the bacterial load were assessed using ion chromatography-mass spectrometry, immunohistochemistry, qRT-PCR, western blotting, enzyme-linked immunosorbent assays, or colony forming unit assays. Animals fed HLP and infected with UPEC had a significant increase in urinary oxalate levels, renal CaOx deposition, pro-inflammatory macrophages, pro-inflammatory cytokines, and bacterial loads compared to animals fed the control diet with UPEC infection. In addition, HLP-fed animals had significantly reduced anti-inflammatory renal macrophages and anti-inflammatory cytokine levels in their plasma, urine, and kidneys. These findings suggest that oxalate may play a novel role in the propagation of UTI development.

Baicalin attenuated oxidative stress and inflammation in ethylene glycol-induced urolithiasis in adult male SD rats

AIMS

Baicalin is a flavonoid derived from the root of the medicinal plant Scutellaria baicalensis Georgi (S. baicalensis) and is known for its various pharmacological properties. This study aimed to investigate the impact of baicalin (BAI) on the occurrence of kidney calcium oxalate crystal formation induced by ethylene glycol in male SD rats.

MAIN METHODS

A rat model of renal stones was created and various concentrations of baicalin were used for intervention. Samples of urine, blood, and kidney tissue were taken from the rats, and they were euthanized for biochemical and histopathological examinations.

KEY FINDINGS

Our results show that baicalin treatment improved the weight loss induced by ethylene glycol (EG) and ammonium chloride (AC) in rats. Baicalin also reduced the formation of calcium oxalate crystals and protected kidney function in rats with urolithiasis. Furthermore, it lowered the level of malondialdehyde (MDA) and elevated the activity of antioxidant enzymes compared to the stone control group. Additionally, baicalin notably alleviated renal inflammation in rats with urolithiasis.

SIGNIFICANCE

The present study attributed clinical evidence first time that claiming the significant antiurolithic effect of baicalin and could be a cost-effective candidate for the prevention and treatment of urolithiasis.

Establishment of an artificial urine model in vitro and rat or pig model in vivo to evaluate urinary crystal adherence

The current study aimed to establish an experimental model in vitro and in vivo of urinary crystal deposition on the surface of ureteral stents, to evaluate the ability to prevent crystal adhesion. Non-treated ureteral stents were placed in artificial urine under various conditions in vitro. In vivo, ethylene glycol and hydroxyproline were administered orally to rats and pigs, and urinary crystals and urinary Ca were investigated by Inductively Coupled Plasma-Optical Emission Spectrometer. in vitro, during the 3- and 4-week immersion periods, more crystals adhered to the ureteral stent in artificial urine model 1 than the other artificial urine models (p < 0.01). Comparing the presence or absence of urea in the composition of the artificial urine, the artificial urine without urea showed less variability in pH change and more crystal adhesion (p < 0.05). Starting the experiment at pH 6.3 resulted in the highest amount of crystal adhesion to the ureteral stent (p < 0.05). In vivo, urinary crystals and urinary Ca increased in rat and pig experimental models. This experimental model in vitro and in vivo can be used to evaluate the ability to prevent crystal adhesion and deposition in the development of new ureteral stents to reduce ureteral stent-related side effects in patients.

Long-Term Sodium Deficiency Reduces Sodium Excretion but Impairs Renal Function and Increases Stone Formation in Hyperoxaluric Calcium Oxalate Rats

Excessive sodium intake is associated with nephrolithiasis, but the impact of sodium-deficient (SD) diets is unknown. Hence, we investigated the effects of short- and long-term SD diets on the expression of renal aquaporins and sodium transporters, and thus calcium oxalate (CaOx) crystal formation in hyperoxaluria rats. In a short-term sodium balance study, six male rats received drinking water and six received 0.75% ethylene glycol (EG) to induce hyperoxaluria. After a 30-day period of feeding on normal chow, both groups were treated with a normal-sodium diet for 5 days, followed by a sodium-free diet for the next 5 days. In a long-term SD study (42 days), four groups, induced with EG or not, were treated with normal-sodium water and sodium-free drinking water, alternately. Short-term sodium restriction in EG rats reversed the daily positive sodium balance, but progressively caused a negative cumulative water balance. In the long-term study, the abundant levels of of Na/H exchanger, thiazide-sensitive Na-Cl cotransporter, Na-K-ATPase, and aquaporins-1 from SD + EG rats were markedly reduced, corresponding to a decrease in Uosm, as compared to SD rats. Increased urine calcium, AP(CaOx)index, and renal CaOx deposition were also noted in SD + EG rats. Although the SD treatment reduced sodium excretion, it also increased urinary calcium and impaired renal function, ultimately causing the formation of more CaOx crystals.

Identification and validation of the biomarkers related to ferroptosis in calcium oxalate nephrolithiasis

Ferroptosis is a specific type of programmed cell death characterized by iron-dependent lipid peroxidation. Understanding the involvement of ferroptosis in calcium oxalate (CaOx) stone formation may reveal potential targets for this condition. The publicly available dataset GSE73680 was used to identify 61 differentially expressed ferroptosis-related genes (DEFERGs) between normal kidney tissues and Randall's plaques (RPs) from patients with nephrolithiasis through employing weighted gene co-expression network analysis (WGCNA). The findings were validated through in vitro and in vivo experiments using CaOx nephrolithiasis rat models induced by 1% ethylene glycol administration and HK-2 cell models treated with 1 mM oxalate. Through WGCNA and the machine learning algorithm, we identified LAMP2 and MDM4 as the hub DEFERGs. Subsequently, nephrolithiasis samples were classified into cluster 1 and cluster 2 based on the expression of the hub DEFERGs. Validation experiments demonstrated decreased expression of LAMP2 and MDM4 in CaOx nephrolithiasis animal models and cells. Treatment with ferrostatin-1 (Fer-1), a ferroptosis inhibitor, partially reversed oxidative stress and lipid peroxidation in CaOx nephrolithiasis models. Moreover, Fer-1 also reversed the expression changes of LAMP2 and MDM4 in CaOx nephrolithiasis models. Our findings suggest that ferroptosis may be involved in the formation of CaOx kidney stones through the regulation of LAMP2 and MDM4.

Diet-induced nephrocalcinosis in aquarium-raised juvenile spotted wolffish Anarhichas minor

Wolffish are regularly housed in aquaria, but little data on their husbandry and health is available for caretakers. High occurrence rates of nephrocalcinosis and urolithiasis have been observed in Atlantic Anarhichas lupus and spotted A. minor wolffish housed at 2 Canadian zoological institutions. To explore the effect of diet on nephrocalcinosis and urolithiasis development, a 16 mo prospective study was conducted. A total of 32 juvenile spotted wolffish were randomly assigned to one of 4 experimental groups fed exclusively with the following diet: (1) Skretting® Europa 18 pellets; (2) Mazuri® LS Aquatic Carni-Blend Diet Formula; (3) vitamin-supplemented fish-based diet, and (4) vitamin-supplemented invertebrate-based diet. Urinalysis, radiographs, and complete necropsies were performed at the end of the study. None of the wolffish developed uroliths during the study period. All specimens fed with the fish-based and invertebrate-based diets developed nephrocalcinosis, whereas this condition was seen in 12.5 and 0% of the fish in the Skretting® and Mazuri® groups, respectively. Affected wolffish often presented with oxalate crystalluria and increased radiodensity of the posterior kidneys. Urinalysis and radiographic study were considered useful in the antemortem diagnosis of nephrocalcinosis. None of the previously published risk factors for the development of nephrocalcinosis in fish were supported by the results of this study. However, nutritional analyses of the 4 diets suggest that high dietary levels of gelatin or vitamin C or low levels of vitamin E could be potential risk factors for the development of nephrocalcinosis in spotted wolffish and thus warrant further study.

The Protective Role of Dietary Polyphenols in Urolithiasis: Insights into Antioxidant Effects and Mechanisms of Action

Urolithiasis is a common urological disease with increasing prevalence and high recurrence rates around the world. Numerous studies have indicated reactive oxygen species (ROS) and oxidative stress (OS) were crucial pathogenic factors in stone formation. Dietary polyphenols are a large group of natural antioxidant compounds widely distributed in plant-based foods and beverages. Their diverse health benefits have attracted growing scientific attention in recent decades. Many literatures have reported the effectiveness of dietary polyphenols against stone formation. The antiurolithiatic mechanisms of polyphenols have been explained by their antioxidant potential to scavenge free radicals and ROS, modulate the expression and the activity of endogenous antioxidant and prooxidant enzymes, regulate signaling pathways associated with OS, and maintain cell morphology and function. In this review, we first describe OS and its pathogenic effects in urolithiasis and summarize the classification and sources of dietary polyphenols. Then, we focus on the current evidence defining their antioxidant potential against stone formation and put forward challenges and future perspectives of dietary polyphenols. To conclude, dietary polyphenols offer potential applications in the treatment and prevention of urolithiasis.

Proposal for pathogenesis-based treatment options to reduce calcium oxalate stone recurrence

Objective

Prevalence of kidney stone disease continues to increase globally with recurrence rates between 30% and 50% despite technological and scientific advances. Reduction in recurrence would improve patient outcomes and reduce cost and stone morbidities. Our objective was to review results of experimental studies performed to determine the efficacy of readily available compounds that can be used to prevent recurrence.

Methods

All relevant literature up to October 2020, listed in PubMed is reviewed.

Results

Clinical guidelines endorse the use of evidence-based medications, such as alkaline agents and thiazides, to reduce urinary mineral supersaturation and recurrence. However, there may be additional steps during stone pathogenesis where medications could moderate stone risk. Idiopathic calcium oxalate stones grow attached to Randall's plaques or plugs. Results of clinical and experimental studies suggest involvement of reactive oxygen species and oxidative stress in the formation of both the plaques and plugs. The renin-angiotensin-aldosterone system (RAAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, mitochondria, and NOD-like receptor pyrin domain containing-3 (NLRP3) inflammasome have all been implicated at specific steps during stone pathogenesis in animal models.

Conclusion

In addition to supersaturation-reducing therapies, the use of anti-oxidants, free radical scavengers, and inhibitors of NADPH oxidase, NLRP3 inflammasome, and RAAS may prove beneficial for stone prevention. Compounds such as statins and angiotensin converting enzyme inhibitors are already in use as therapeutics for hypertension and cardio-vascular disease and have previously shown to reduce calcium oxalate nephrolithiasis in rats. Although clinical evidence for their use in stone prevention in humans is limited, experimental data support they be considered along with standard evidence-based medications and clinical expertise when patients are being counselled for stone prevention.

Effects of frankincense on experimentally induced renal stones in rats

Objectives

Frankincense (Luban) is a resin obtained from trees of genus Boswellia. The south of Oman hosts Boswellia sacra trees known to have many social, religious and medicinal uses. The anti-inflammatory and therapeutic potential of Luban has recently attracted the interest of the scientific community. The aim is to study the efficacy of Luban water extract and its essential oils on experimentally induced renal stones in rats.

Materials and Methods

A rat model of urolithiasis induced by trans-4-hydroxy-L-proline (HLP) was used. Wistar Kyoto rats (27 males, 27 females) were randomly distributed into nine equal groups. Treatment groups were given Uralyt-U (standard) or Luban (50, 100 and 150 mg/kg/day), starting Day 15 from HLP induction for a duration of 14 days. The prevention groups were given Luban in similar doses, starting Day 1 of HLP induction for 28 days. Several plasma biochemical and histological parameters were recorded. Data were analysed with GraphPad Software. Comparisons were performed by one-way analysis of variance (ANOVA) and the Bonferroni test.

Results

The lithogenic effects of HLP, such as an increase in urine oxalate and cystine, an increase in plasma uric acid and an increase in kidney levels of calcium and oxalate, have all been best significantly reversed by the Luban dose of 150 mg/kg/day. The histological changes of HLP on the kidney tissue including calcium oxalate crystal formation, cystic dilatation, high degree of tubular necrosis, inflammatory changes, atrophy and fibrosis have also been ameliorated by Luban dose of 150 mg/kg/day.

Conclusion

Luban has shown a significant improvement in the treatment and prevention of experimentally induced renal stones, particularly at a dose of 150 mg/kg/day. Further studies on the effect of Luban in other animal models and humans with urolithiasis are warranted.

Untargeted and targeted metabolomics reveal bile acid profile changes in rats with ethylene glycol-induced calcium oxalate nephrolithiasis

Calcium oxalate (CaOx) nephrolithiasis is a prevalent disorder linked to metabolism. Examining metabolic alterations could potentially give an initial understanding of the origins of CaOx nephrolithiasis. This study aims to determine gut metabolic biomarkers differentiating CaOx nephrolithiasis utilizing untargeted and targeted metabolomics. CaOx nephrolithiasis model rats were built by 1% ethylene glycol administration. Histologic staining and renal function measurement revealed the presence of crystals in the lumen of the renal tubules, the renal injury and interstitial fibrosis in CaOx rats, demonstrating that the models of CaOx were established successfully. Hematoxylin & eosin (H&E) staining showed that CaOx group had inflammation and damage in the ileal tissue. Immunofluorescence and PCR results displayed that the tight junction proteins, ZO-1 and Occludin levels were decreased in the ileal tissues of the CaOx group. The untargeted metabolomic analysis revealed that 269 gut metabolites were differentially expressed between the CaOx group and the control group. Meanwhile, bile secretion, the main metabolic pathway in CaOx nephrolithiasis, was identified. Following, five significant bile acid metabolites were selected utilizing the targeted bile acid metabolomics, including Hyodeoxycholic acid (HDCA), Glycohyodeoxycholic acid (GHDCA), Nor-Deoxycholic Acid, omega-muricholic acid, and Taurolithocholic acid. Among these metabolites, HDCA and GHDCA presented the highest predictive accuracy with AUC = 1 to distinguish the CaOx group from the control group. As a result of network pharmacology, target genes of HDCA and GHDCA in CaOx nephrolithiasis were enriched in oxidative stress and apoptosis pathways. Conclusively, our study provides insight into bile acids metabolic changes related to CaOx nephrolithiasis. Although alterations in biochemical pathways indicate a complex pathology in CaOx rats, bile acid changes may serve as biomarkers of CaOx nephrolithiasis.

Hydroxyproline stimulates inflammation and reprograms macrophage signaling in a rat kidney stone model

Meals rich in oxalate are associated with calcium oxalate (CaOx) kidney stone disease. Hydroxy-L-proline (HLP) is an oxalate precursor found in milk and collagen-containing foods. HLP has been shown to induce CaOx crystal formation in rodents. The purpose of this study was to evaluate the effect of HLP induced oxalate levels on inflammation and renal leukocytes during crystal formation. Male Sprague-Dawley rats (6-8 weeks old) were fed a control diet containing no oxalate for 3 days before being randomized to continue the control diet or 5% HLP for up to 28 days. Blood, 24 h urine, and kidneys were collected on Days 0, 7, 14, or 28. Urinary oxalate levels, crystal deposition, and renal macrophage markers were evaluated using ion chromatography-mass spectrometry, immunohistochemistry, and qRT-PCR. Renal leukocytes were assessed using flow cytometry and RNA-sequencing. HLP feeding increased urinary oxalate levels and renal crystal formation in animals within 7 days. HLP also increased renal macrophage populations on Days 14 and 28. Transcriptome analysis revealed that renal macrophages from animals fed HLP for 7 days were involved in inflammatory response and disease, stress response to LPS, oxidative stress, and immune cell trafficking. Renal macrophages isolated on Day 14 were involved in cell-mediated immunological pathways, ion homeostasis, and inflammatory response. Collectively, these findings suggest that HLP-mediated oxalate levels induce markers of inflammation, leukocyte populations, and reprograms signaling pathways in macrophages in a time-dependent manner. Additional studies investigating the significance of oxalate on renal macrophages could aid in our understanding of kidney stone formation.

Drosophila melanogaster: a simple genetic model of kidney structure, function and disease

Although the genetic basis of many kidney diseases is being rapidly elucidated, their experimental study remains problematic owing to the lack of suitable models. The fruitfly Drosophila melanogaster provides a rapid, ethical and cost-effective model system of the kidney. The unique advantages of D. melanogaster include ease and low cost of maintenance, comprehensive availability of genetic mutants and powerful transgenic technologies, and less onerous regulation, as compared with mammalian systems. Renal and excretory functions in D. melanogaster reside in three main tissues - the transporting renal (Malpighian) tubules, the reabsorptive hindgut and the endocytic nephrocytes. Tubules contain multiple cell types and regions and generate a primary urine by transcellular transport rather than filtration, which is then subjected to selective reabsorption in the hindgut. By contrast, the nephrocytes are specialized for uptake of macromolecules and equipped with a filtering slit diaphragm resembling that of podocytes. Many genes with key roles in the human kidney have D. melanogaster orthologues that are enriched and functionally relevant in fly renal tissues. This similarity has allowed investigations of epithelial transport, kidney stone formation and podocyte and proximal tubule function. Furthermore, a range of unique quantitative phenotypes are available to measure function in both wild type and disease-modelling flies.

Atorvastatin Decreases Renal Calcium Oxalate Stone Deposits by Enhancing Renal Osteopontin Expression in Hyperoxaluric Stone-Forming Rats Fed a High-Fat Diet

Calcium oxalate (CaOx) is the major constituent of kidney stones. Growing evidence shows a close connection between hyperlipidemia, cardiovascular disease (CVD), and the formation of kidney stones. Owing to their antioxidant properties, statins control hyperlipidemia and may ameliorate CaOx stone formation. The present study was designed to investigate the suppressive effects of statins on CaOx urolithiasis and their potential mechanism. We used rats fed a high-fat diet (HFD) to achieve hyperlipidemia (HL) and hydroxyproline (HP) water to establish a hyperoxaluric CaOx nephrolithiasis model; the animals were administered statins (A) for 28 days. The rats were divided into eight groups treated or not with A, i.e., Control, HP, HL, HL + HP. HL aggravated urinary calcium crystallization compared to the control. Due to increased expression of renal osteopontin (OPN), a key anti-lithic protein, and reduced free radical production, the calcium crystals in the urinary bladder increased as renal calcium deposition decreased. The levels of the ion activity product of CaOx (AP(CaOx)) decreased after statins administration, and AP(Calcium phosphate) (CaP) increased, which suggested the dominant calcium crystal composition changed from CaOx to CaP after statin administration. In conclusion, atorvastatin decreases renal CaOx stone deposits by restoring OPN expression in hyperoxaluric rats fed a HFD.

Melamine and oxalate coexposure induces early kidney tubular injury through mitochondrial aberrations and oxidative stress

Exposure to melamine, which is ubiquitous in daily life, is linked to adverse kidney outcomes. The melamine tolerable daily intake in humans is based on the no-observed-effect-level (NOEL) established in a single-toxicant murine model. However, humans are often simultaneously exposed to multiple environmental nephrotoxicants. The NOEL of melamine during coexposure with other toxicants needs to be evaluated. Oxalate is a potentially nephrotoxic terminal metabolite, and hyperoxaluria is reportedly associated with chronic kidney disease. We explored whether these two potential nephrotoxicants can interact and enhance kidney injury. We established a Sprague-Dawley rat model of coexposure to the melamine NOEL (63 mg/kg/day) and 2% hydroxy-L-proline (HLP, an oxalate precursor) in drinking water to simulate human environmental melamine exposure. Melamine/oxalate coexposure increased proximal tubular cell mitochondrial reactive oxygen species levels, lipid peroxidation and oxidative DNA damage. The degrees of mitochondrial damage, tubular cell apoptosis, tubular atrophy, and interstitial fibrosis were elevated in coexposed rat kidneys. The evidence indicated that exposure to the melamine NOEL can cause renal tubular injury via oxidative stress and that this effect may be enhanced via interaction of melamine with other environmental factors, such as oxalate. Thus, melamine risk assessment and toxicity prevention should be conducted carefully in different susceptible populations.

Oxalate Alters Cellular Bioenergetics, Redox Homeostasis, Antibacterial Response, and Immune Response in Macrophages

Individuals with calcium oxalate (CaOx) kidney stones can have secondarily infected calculi which may play a role in the development of recurrent urinary tract infection (UTI). Uropathogenic Escherichia coli (UPEC) is the most common causative pathogen of UTIs. Macrophages play a critical role in host immune defense against bacterial infections. Our previous study demonstrated that oxalate, an important component of the most common type of kidney stone, impairs monocyte cellular bioenergetics and redox homeostasis. The objective of this study was to investigate whether oxalate compromises macrophage metabolism, redox status, anti-bacterial response, and immune response. Monocytes (THP-1, a human monocytic cell line) were exposed to sodium oxalate (soluble oxalate; 50 µM) for 48 hours prior to being differentiated into macrophages. Macrophages were subsequently exposed to calcium oxalate crystals (50 µM) for 48 hours followed by UPEC (MOI 1:2 or 1:5) for 2 hours. Peritoneal macrophages and bone marrow-derived macrophages (BMDM) from C57BL/6 mice were also exposed to oxalate. THP-1 macrophages treated with oxalate had decreased cellular bioenergetics, mitochondrial complex I and IV activity, and ATP levels compared to control cells. In addition, these cells had a significant increase in mitochondrial and total reactive oxygen species levels, mitochondrial gene expression, and pro-inflammatory cytokine (i.e. Interleukin-1β, IL-1β and Interleukin-6, IL-6) mRNA levels and secretion. In contrast, oxalate significantly decreased the mRNA levels and secretion of the anti-inflammatory cytokine, Interleukin-10 (IL-10). Further, oxalate increased the bacterial burden of primary macrophages. Our findings demonstrate that oxalate compromises macrophage metabolism, redox homeostasis, and cytokine signaling leading to a reduction in anti-bacterial response and increased infection. These data highlight a novel role of oxalate on macrophage function.

Diminishment of Nrf2 Antioxidative Defense Aggravates Nephrotoxicity of Melamine and Oxalate Coexposure

Chronic kidney disease (CKD) usually causes devastating healthy impacts on patients. However, the causes affecting the decline of kidney function are not fully revealed, especially the involvement of environmental pollutants. We have revealed that exposure to melamine, a ubiquitous chemical in daily life, is linked to adverse kidney outcomes. Hyperoxaluria that results from exposure to excessive oxalate, a potentially nephrotoxic terminal metabolite, is reportedly associated with CKD. Thus, we explored whether interaction of these two potential nephrotoxicants could enhance kidney injury. We established a renal proximal tubular HK-2 cell model and a Sprague-Dawley rat model of coexposure to melamine with sodium oxalate or hydroxy-L-proline to investigate the interacting adverse effects on kidneys. Melamine and oxalate coexposure enhanced the levels of reactive oxygen species, lipid peroxidation and oxidative DNA damage in the HK-2 cells and kidney tissues. The degrees of tubular cell apoptosis, tubular atrophy, and interstitial fibrosis were elevated under the coexposed condition, which may result from the diminishment of Nrf2 antioxidative capacity. To conclude, melamine and oxalate coexposure aggravates renal tubular injury via impairment of antioxidants. Accumulative harmful effects of exposure to multiple environmental nephrotoxicants should be carefully investigated in the etiology of CKD progression.

Effect of Vitamin B2-Deficient Diet on Hydroxyproline- or Obesity-Induced Hyperoxaluria in Mice

SCOPE

Hyperoxaluria is a major cause of kidney stone disease. Around half of the oxalate in mammals is supplied from the diet and the other half is endogenously synthesized from glyoxylate. Reduction of hepatic glycolate oxidase (GO) activity is one approach to reduce endogenous production of oxalate. However, there are currently few effective dietary approaches to reduce hepatic GO activity.

METHODS AND RESULTS

In the present study, it is investigated whether restriction of dietary vitamin B2 (VB2) can reduce hepatic GO activity and oxalate excretion in mice with hyperoxaluria induce by hydroxyproline (Hyp) or obesity. It is found that VB2 restriction significantly reduces hepatic GO activity in both the Hyp- and obesity-induced model of hyperoxaluria in mice. However, VB2 restriction reduces urinary oxalate excretion only in the Hyp-treated mice and not the obese mice. This difference could be due to the contribution of endogenous oxalate production that manifests as increased hepatic GO activity in Hyp-treated mice but not obese mice.

CONCLUSION

Together these results suggest that VB2 restriction could be a new dietary approach to improve hyperoxaluria when endogenous production of oxalate is increased.

Dysregulated oxalate metabolism is a driver and therapeutic target in atherosclerosis

Dysregulated glycine metabolism is emerging as a common denominator in cardiometabolic diseases, but its contribution to atherosclerosis remains unclear. In this study, we demonstrate impaired glycine-oxalate metabolism through alanine-glyoxylate aminotransferase (AGXT) in atherosclerosis. As found in patients with atherosclerosis, the glycine/oxalate ratio is decreased in atherosclerotic mice concomitant with suppression of AGXT. Agxt deletion in apolipoprotein E-deficient (Apoe-/-) mice decreases the glycine/oxalate ratio and increases atherosclerosis with induction of hepatic pro-atherogenic pathways, predominantly cytokine/chemokine signaling and dysregulated redox homeostasis. Consistently, circulating and aortic C-C motif chemokine ligand 5 (CCL5) and superoxide in lesional macrophages are increased. Similar findings are observed following dietary oxalate overload in Apoe-/- mice. In macrophages, oxalate induces mitochondrial dysfunction and superoxide accumulation, leading to increased CCL5. Conversely, AGXT overexpression in Apoe-/- mice increases the glycine/oxalate ratio and decreases aortic superoxide, CCL5, and atherosclerosis. Our findings uncover dysregulated oxalate metabolism via suppressed AGXT as a driver and therapeutic target in atherosclerosis.

The Activation of ROS/NF-κB/MMP-9 Pathway Promotes Calcium-Induced Kidney Crystal Deposition

Idiopathic hypercalciuria is an important risk factor for the formation of calcium-containing kidney stones. Matrix metalloproteinase-9 (MMP-9) is closely related to cell and tissue remodeling and is involved in ectopic tissue calcification. However, little is known about its role in kidney stone formation. In this study, we found that the expression of MMP-9 and that of osteoblastic-related proteins was increased in normal rat kidney epithelial-like (NRK-52E) cells following treatment with a high concentration of calcium, while the knockout or overexpression of MMP-9 could, respectively, significantly inhibit or upregulate the expression of osteoblastic-related proteins and calcium crystal deposition. In addition, apoptosis and calcium crystal deposition were significantly reduced in Sprague-Dawley rats with 1,25(OH)₂D₃-induced hypercalciuria following MMP-9 inhibitor I treatment. Furthermore, inhibiting reactive oxygen species (ROS) production or the nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) pathway significantly reduced calcium-induced MMP-9 expression and calcium crystal deposition. In summary, our results suggested that a high calcium concentration promotes epithelial-osteoblastic transformation and calcium crystal deposition in renal tubule cells by regulating the ROS/NF-κB/MMP-9 axis and identified a novel role for MMP-9 in regulating calcium-induced calcium crystal deposition in renal tubules.

Randall's plaque and calcium oxalate stone formation: role for immunity and inflammation

Idiopathic calcium oxalate (CaOx) stones often develop attached to Randall's plaque present on kidney papillary surfaces. Similar to the plaques formed during vascular calcification, Randall's plaques consist of calcium phosphate crystals mixed with an organic matrix that is rich in proteins, such as inter-α-trypsin inhibitor, as well as lipids, and includes membrane-bound vesicles or exosomes, collagen fibres and other components of the extracellular matrix. Kidney tissue surrounding Randall's plaques is associated with the presence of classically activated, pro-inflammatory macrophages (also termed M1) and downregulation of alternatively activated, anti-inflammatory macrophages (also termed M2). In animal models, crystal deposition in the kidneys has been associated with the production of reactive oxygen species, inflammasome activation and increased expression of molecules implicated in the inflammatory cascade, including osteopontin, matrix Gla protein and fetuin A (also known as α2-HS-glycoprotein). Many of these molecules, including osteopontin and matrix Gla protein, are well known inhibitors of vascular calcification. We propose that conditions of urine supersaturation promote kidney damage by inducing the production of reactive oxygen species and oxidative stress, and that the ensuing inflammatory immune response promotes Randall's plaque initiation and calcium stone formation.

Protective effect of apigenin on ethylene glycol-induced urolithiasis via attenuating oxidative stress and inflammatory parameters in adult male Wistar rats

AIMS

Apigenin (4',5,7-trihydroxyflavone) is one of the subclasses of flavonoids and has various pharmacological effects. The present work was carried out to study the effect of apigenin on ethylene glycol-induced kidney damage in male Wistar rats.

MAIN METHODS

We evaluated the effects of apigenin orally administrated in normal and urolithiatic rats. Animals were assigned to nine groups in random: normal control; apigenin alone (0.005, 0.01, and 0.02 g/kg bw); urolithiatic control (0.75% ethylene glycol and 1.0% ammonium chloride in drinking water); apigenin (0.005, 0.01, and 0.02 g/kg bw) plus ethylene glycol and ammonium chloride; and cystone (0.75 g/kg bw) plus ethylene glycol and ammonium chloride. At the end of 28th day of treatment, animals were sacrificed for biochemical and histopathological assays.

KEY FINDINGS

Our results indicated that the apigenin treatment decreased the formation of urinary stones in urolithiatic rats. Also, apigenin reduced the generation of malondialdehyde and enhanced antioxidant enzymes activities in the kidney homogenate of rats. It also caused a significant decrease in the calcium oxalate crystals numbers in urinary sample of rats with ethylene glycol-induced hyperoxaluria. These findings were supported by histopathological examinations.

SIGNIFICANCE

Based on the results obtained, apigenin attenuate ethylene glycol-related kidney damage in male Wistar rats. Although the underlying mechanism of apigenin effect has not been determined, reduction of urinary levels of stone-producing constituents, antioxidant activities, and inhibition of TGF-β signaling may be involved.

Microbial genetic and transcriptional contributions to oxalate degradation by the gut microbiota in health and disease

Over-accumulation of oxalate in humans may lead to nephrolithiasis and nephrocalcinosis. Humans lack endogenous oxalate degradation pathways (ODP), but intestinal microbes can degrade oxalate using multiple ODPs and protect against its absorption. The exact oxalate-degrading taxa in the human microbiota and their ODP have not been described. We leverage multi-omics data (>3000 samples from >1000 subjects) to show that the human microbiota primarily uses the type II ODP, rather than type I. Furthermore, among the diverse ODP-encoding microbes, an oxalate autotroph, Oxalobacter formigenes, dominates this function transcriptionally. Patients with inflammatory bowel disease (IBD) frequently suffer from disrupted oxalate homeostasis and calcium oxalate nephrolithiasis. We show that the enteric oxalate level is elevated in IBD patients, with highest levels in Crohn's disease (CD) patients with both ileal and colonic involvement consistent with known nephrolithiasis risk. We show that the microbiota ODP expression is reduced in IBD patients, which may contribute to the disrupted oxalate homeostasis. The specific changes in ODP expression by several important taxa suggest that they play distinct roles in IBD-induced nephrolithiasis risk. Lastly, we colonize mice that are maintained in the gnotobiotic facility with O. formigenes, using either a laboratory isolate or an isolate we cultured from human stools, and observed a significant reduction in host fecal and urine oxalate levels, supporting our in silico prediction of the importance of the microbiome, particularly O. formigenes in host oxalate homeostasis.

Antiurolithic effects of medicinal plants: results of in vivo studies in rat models of calcium oxalate nephrolithiasis-a systematic review

Urolithiasis is one of the oldest diseases affecting humans, while plants are one of our oldest companions providing food, shelter, and medicine. In spite of substantial progress in understanding the pathophysiological mechanisms, treatment options are still limited, often expensive for common people in most parts of the world. As a result, there is a great interest in herbal remedies for the treatment of urinary stone disease as an alternative or adjunct therapy. Numerous in vivo and in vitro studies have been carried out to understand the efficacy of herbs in reducing stone formation. We adopted PRISMA guidelines and systematically reviewed PubMed/Medline for the literature, reporting results of various herbal products on in vivo models of nephrolithiasis/urolithiasis. The Medical Subject Heading Terms (Mesh term) "Urolithiasis" was used with Boolean operator "AND" and other related Mesh Unique terms to search all the available records (July 2019). A total of 163 original articles on in vivo experiments were retrieved from PubMed indexed with the (MeshTerm) "Urolithiasis" AND "Complementary Therapies/Alternative Medicine, "Urolithiasis" AND "Plant Extracts" and "Urolithiasis" AND "Traditional Medicine". Most of the studies used ethylene glycol (EG) to induce hyperoxaluria and nephrolithiasis in rats. A variety of extraction methods including aqueous, alcoholic, hydro-alcoholic of various plant parts ranging from root bark to fruits and seeds, or a combination thereof, were utilized. All the investigations did not study all aspects of nephrolithiasis making it difficult to compare the efficacy of various treatments. Changes in the lithogenic factors and a reduction in calcium oxalate (CaOx) crystal deposition in the kidneys were, however, considered favorable outcomes of the various treatments. Less than 10% of the studies examined antioxidant and diuretic activities of the herbal treatments and concluded that their antiurolithic activities were a result of antioxidant, anti-inflammatory, and/or diuretic effects of the treatments.

Nephroprotective Effect of Pleurotus ostreatus and Agaricus bisporus Extracts and Carvedilol on Ethylene Glycol-Induced Urolithiasis: Roles of NF-κB, p53, Bcl-2, Bax and Bak

This study was designed to assess the nephroprotective effects of Pleurotus ostreatus and Agaricus bisporus aqueous extracts and carvedilol on hyperoxaluria-induced urolithiasis and to scrutinize the possible roles of NF-κB, p53, Bcl-2, Bax and Bak. Phytochemical screening and GC-MS analysis of mushrooms’ aqueous extracts were also performed and revealed the presence of multiple antioxidant and anti-inflammatory components. Hyperoxaluria was induced in Wistar rats through the addition of 0.75% (v/v) ethylene glycol in drinking water for nine weeks. The ethylene glycol-administered rats were orally treated with Pleurotus ostreatus and Agaricus bisporus aqueous extracts (100 mg/kg) and carvedilol (30 mg/kg) daily during the last seven weeks. The study showed that Pleurotus ostreatus, Agaricus bisporus and carvedilol all successfully inhibited ethylene glycol-induced histological perturbations and the elevation of serum creatinine, serum urea, serum and urinary uric acid, serum, urinary and kidney oxalate, urine specific gravity, kidney calcium, kidney NF-κB, NF-κB p65, NF-κB p50, p53, Bax and Bak expressions as well as serum TNF-α and IL-1β levels. Moreover, the treatment decreased the reduction in urinary creatinine, urinary urea, ratios of urinary creatinine to serum creatinine and urinary urea to serum urea, Fex Urea and Bcl-2 expression in kidney. In conclusion, although Pleurotus ostreatus and Agaricus bisporus extracts and carvedilol all significantly inhibited the progression of nephrolithiasis and showed nephroprotective effects against ethylene glycol-induced kidney dysfunction, Pleurotus ostreatus and Agaricus bisporus seemed to be more effective than carvedilol. Moreover, the nephroprotective effects may be mediated via affecting NF-κB activation, extrinsic apoptosis and intrinsic apoptosis pathways.

Urinary monocyte chemoattractant protein 1 associated with calcium oxalate crystallization in patients with primary hyperoxaluria

Background

Patients with primary hyperoxaluria (PH) often develop kidney stones and chronic kidney disease. Noninvasive urine markers reflective of active kidney injury could be useful to gauge the effectiveness of ongoing treatments.

Methods

A panel of biomarkers that reflect different nephron sites and potential mechanisms of injury (clusterin, neutrophil gelatinase-associated lipocalin (NGAL), 8-isoprostane (8IP), monocyte-chemoattractant protein 1(MCP-1), liver-type fatty acid binding protein (L-FABP), heart-type fatty acid binding protein (H-FABP), and osteopontin (OPN)) were measured in 114 urine specimens from 30 PH patients over multiple visits. Generalized estimating equations were used to assess associations between biomarkers and 24 h urine excretions, calculated proximal tubular oxalate concentration (PTOx), and eGFR.

Results

Mean (±SD) age at first visit was 19.5 ± 16.6 years with an estimated glomerular filtration rate (eGFR) of 68.4 ± 21.0 ml/min/1.73m². After adjustment for age, sex, and eGFR, a higher urine MCP-1 concentration and MCP-1/creatinine ratio was positively associated with CaOx supersaturation (SS). Higher urine NGAL and NGAL/creatinine as well as OPN and OPN/creatinine were associated with higher eGFR. 8IP was negatively associated with PTOx and urinary Ox, but positively associated with CaOx SS.

Conclusion

In PH patients greater urine MCP-1 and 8IP excretion might reflect ongoing collecting tubule crystallization, while greater NGAL and OPN excretion may reflect preservation of kidney mass and function. CaOx crystals, rather than oxalate ion may mediate oxidative stress in hyperoxaluric conditions. Further studies are warranted to determine whether urine MCP-1 excretion predicts long term outcome or is altered in response to treatment.

The effects of the inactivation of Hydroxyproline dehydrogenase on urinary oxalate and glycolate excretion in mouse models of primary hyperoxaluria

The major clinical manifestation of the Primary Hyperoxalurias (PH) is increased production of oxalate, as a consequence of genetic mutations that lead to aberrant glyoxylate and hydroxyproline metabolism. Hyperoxaluria can lead to the formation of calcium-oxalate kidney stones, nephrocalcinosis and renal failure. Current therapeutic approaches rely on organ transplants and more recently modifying the pathway of oxalate synthesis using siRNA therapy. We have recently reported that the metabolism of trans-4-hydroxy-L-proline (Hyp), an amino acid derived predominantly from collagen metabolism, is a significant source of oxalate production in individuals with PH2 and PH3. Thus, the first enzyme in the Hyp degradation pathway, hydroxyproline dehydrogenase (HYPDH), represents a promising therapeutic target for reducing endogenous oxalate production in these individuals. This is supported by the observation that individuals with inherited mutations in HYPDH (PRODH2 gene) have no pathological consequences. The creation of mouse models that do not express HYPDH will facilitate research evaluating HYPDH as a target. We describe the phenotype of the Prodh2 knock out mouse model and show that the lack of HYPDH in PH mouse models results in lower levels of urinary oxalate excretion, consistent with our previous metabolic tracer and siRNA-based knockdown studies. The double knockout mouse, Grhpr KO (PH2 model) and Prodh2 KO, prevented calcium-oxalate crystal deposition in the kidney, when placed on a 1% Hyp diet. These observations support the use of the Grhpr KO mice to screen HYPDH inhibitors in vivo. Altogether these data support HYPDH as an attractive therapeutic target for PH2 and PH3 patients.

Stiripentol protects against calcium oxalate nephrolithiasis and ethylene glycol poisoning

Increased urinary oxalate excretion (hyperoxaluria) promotes the formation of calcium oxalate crystals. Monogenic diseases due to hepatic enzymes deficiency result in chronic hyperoxaluria, promoting end-stage renal disease in children and young adults. Ethylene glycol poisoning also results in hyperoxaluria promoting acute renal failure and frequently death. Stiripentol is an antiepileptic drug used to treat children affected by Dravet syndrome, possibly by inhibiting neuronal lactate dehydrogenase 5 isoenzyme. As this isoenzyme is also the last step of hepatic oxalate production, we hypothesized that Stiripentol would potentially reduce hepatic oxalate production and urine oxalate excretion. In vitro, Stiripentol decreased in a dose-dependent manner the synthesis of oxalate by hepatocytes. In vivo, Stiripentol oral administration reduced significantly urine oxalate excretion in rats. Stiripentol protected kidneys against calcium oxalate crystal deposits in acute ethylene glycol intoxication and chronic calcium oxalate nephropathy models. In both models, Stiripentol improved significantly renal function. Patients affected by Dravet syndrome and treated with Stiripentol had a lower urine oxalate excretion than control patients. A young girl affected by severe type I hyperoxaluria received Stiripentol for several weeks: urine oxalate excretion decreased by two-thirds. Stiripentol is a promising potential therapy against genetic hyperoxaluria and ethylene glycol poisoning.

Opportunities for future therapeutic interventions for hyperoxaluria: targeting oxidative stress

INTRODUCTION

Oxalate is a toxic byproduct of metabolism and is normally produced in quantities easily removed from the body. However, under specific circumstances oxalate production is increased resulting in deposition of calcium oxalate (CaOx) crystals in the kidneys as well as other organs causing inflammation and injury. Excessive buildup of crystal deposits in the kidneys causes eventual loss of renal function requiring renal transplantation. Areas covered: Cellular exposure to CaOx crystals induces the production of reactive oxygen species (ROS) with the involvement of renin-angiotensin aldosterone system (RAAS), mitochondria, and NADPH oxidase. Inflammasomes are activated and pro-inflammatory cytokines, such as IL-1β and IL-18 are produced. We reviewed results of experimental and clinical studies of crystal renal epithelial cell interactions with emphasis on cellular injury and ROS production. Expert opinion: Treatment should depend upon the level of hyperoxaluria and whether it is associated with CaOx crystal deposition. Persistent low grade or intermittent hyperoxaluria can be treated with antioxidants, free radical scavengers. Hyperoxaluria associated with CaOx crystal deposition will require administration of angiotensin II receptor blockers, and NADPH oxidase or NLRP3 inflammasome inhibitors. DASH-style diet will be beneficial in both cases.

Loss of the androgen receptor suppresses intrarenal calcium oxalate crystals deposition via altering macrophage recruitment/M2 polarization with change of the miR-185-5p/CSF-1 signals

Crystals can trigger a wide range of kidney injuries that may link to the development of kidney stones. Infiltrating macrophages may influence hyperoxaluria-induced intrarenal calcium oxalate (CaOx) crystals deposition, yet their linkage to sex hormones remains unclear. Here we demonstrated that suppressing the androgen receptor (AR) expression in renal tubular epithelial cells increased the macrophage recruitment/M2 polarization that may result in enhancing the phagocytosis of intrarenal CaOx crystals. Mechanism dissection suggested that AR can suppress macrophage colony-stimulating factor 1 (CSF-1) expression via increasing miRNA-185-5p expression to suppress the M2 macrophage polarization-mediated intrarenal CaOx crystals phagocytosis. The preclinical study using glyoxylate-induced intrarenal CaOx crystals deposition mouse model revealed that renal tubule-specific AR knockout mice have less intrarenal CaOx crystals deposition with more recruited M2 macrophages in the kidney compared with the wild-type mice. Results from the in vivo rat model using hydroxy-L-proline-induced CaOx crystals deposition also demonstrated that targeting the AR with ASC-J9® suppressed the intrarenal CaOx crystals deposition via increasing the renal macrophage recruitment/M2 polarization. Together, results from multiple preclinical studies using multiple in vitro cell lines and in vivo mouse/rat models all demonstrated that targeting the AR with a small molecule ASC-J9® may function via altering macrophage recruitment/M2 polarization to decrease the intrarenal CaOx crystals deposition, a key phenotype seen in many kidney stone disease patients with hyperoxaluria.

Oxalate induces type II epithelial to mesenchymal transition (EMT) in inner medullary collecting duct cells (IMCD) in vitro and stimulate the expression of osteogenic and fibrotic markers in kidney medulla in vivo

EMT occurs in response to a number of stresses conditions as mechanical stretch, cancer, hypoxia, oxidative stress (ROS), among others. EMT describes a phenotypical change induced in epithelial cells. It is characterized by increases in motility, extracellular matrix synthesis, proliferation, and invasiveness. The present study analyzed if oxalate ions (Ox) could induce EMT in IMCD cells. Ox (0.5 mM) and transforming growth factor beta (TGF-β1 20 ng/mL) exposition during 48 hours increased migration and invasiveness, increased mesenchymal marker expression (Vimentin, alpha-smooth muscle actin: α-SMA, TGF-β1) and decreased epithelial marker expression (E-cadherin). IMCD stimulated with Ox and TGF-β1 and then exposed to the osteogenic medium during 15 days significantly increased early osteogenic markers (RUNX-2 and Alkaline Phosphatase) expression. Hyperoxaluric mice fed with trans-4-hydroxy-L-proline (HPL) presented calcium oxalate crystal excretion, increased in TGF-β1 expression and collagen fibers deposition and increased early osteogenic markers (RUNX-2 and Alkaline Phosphatase) at 60 days. Our in vitro and in vivo results suggest that oxalate induces EMT in inner medulla collecting duct cells and it may be involved in fibrotic tissue development, osteogenic differentiation and calcium crystal production both implicated in nephrolithiasis.

Drosophila melanogaster as a function-based high-throughput screening model for antinephrolithiasis agents in kidney stone patients

Kidney stone disease involves the aggregation of stone-forming salts consequent to solute supersaturation in urine. The development of novel therapeutic agents for this predominantly metabolic and biochemical disorder have been hampered by the lack of a practical pre-clinical model amenable to drug screening. Here, Drosophila melanogaster, an emerging model for kidney stone disease research, was adapted as a high-throughput functional drug screening platform independent of the multifactorial nature of mammalian nephrolithiasis. Through functional screening, the therapeutic potential of a novel compound commonly known as arbutin that specifically binds to oxalate, a key component of kidney calculi, was identified. Through isothermal titration calorimetry, high-performance liquid chromatography and atomic force microscopy, arbutin was determined to interact with calcium and oxalate in both free and bound states, disrupting crystal lattice structure, growth and crystallization. When used to treat patient urine samples, arbutin significantly abrogated calculus formation in vivo and outperformed potassium citrate in low pH urine conditions, owing to its oxalate-centric mode of action. The discovery of this novel antilithogenic compound via D. melanogaster, independent of a mammalian model, brings greater recognition to this platform, for which metabolic features are primary outcomes, underscoring the power of D. melanogaster as a high-throughput drug screening platform in similar disorders. This is the first description of the use of D. melanogaster as the model system for a high-throughput chemical library screen. This article has an associated First Person interview with the first authors of the paper.

Urothelium proliferation is a trigger for renal crystal deposits in a murine lithogenesis model

Most mouse kidney stone models induce nephrocalcinosis rather than urolithiasis. The aim of our study was to find an accelerated experimental model in order to study the early events of stone formation, that is, at the time of crystal binding to intrarenal urothelium. C57B6 mice exposed to vitamin D supplements and water containing hydroxyl-L-proline, ammonium chloride and calcium chloride were studied for 42 days. A group receiving urothelial cell mitogen Fibroblast Growth Factor 7 (FGF7) was compared to control group receiving saline. Calcium oxalate monohydrate (COM) crystals were detected in urines by day 2 and within urinary spaces in specialized fornix areas in both groups as soon as day 14 with enhanced deposits in FGF7 group compared to controls at day 21. Urothelial cells proliferation, uroplakin III downregulation and de novo expression of osteopontin receptor CD44 detected in FGF7 group, were delayed in the control group (day 42). Crystal aggregates within specialized fornix areas by day 42 were located in urinary spaces but also within and under a multilayered metaplastic urothelium, simultaneous to macrophages influx. Point of note, administration of a normal diet by day 21 was responsible for a spontaneous crystal clearance. Our data show that under supersaturation conditions, urothelial cell proliferation and calcium oxalate crystal retention occur within specialized fornix areas. Enhanced crystal deposits following FGF7 administration suggest that urothelium proliferation would be a relevant trigger for renal stone formation.

Prevalence, pathophysiological mechanisms and factors affecting urolithiasis

The formation of urinary stone, urolithiasis, is one the oldest known disease affecting human throughout different civilizations and times. The exact pathophysiological mechanism of urolithiasis is not yet clear, as these calculi are of various types and too complex for simple understanding. A single theory cannot explain its formation; therefore, different theories are presented in various times for its explanation like free particle, fixed particle, Randall's plaque theory. In addition, various factors and components are identified that play an important role in the formation of these urinary calculi. In this review, composition of kidney stones, its prevalence/incidence, explanation of pathophysiological mechanisms and role of various factors; urinary pH, uric acid, parathyroid hormone, citrate, oxalate, calcium and macromolecules; osteopontin, matrix Gla protein, kidney injury molecules, urinary prothrombin fragment-1, Tamm-Horsfall protein, inter-α-inhibitors, have been discussed in detail.

In vitro and in vivo models for the study of urolithiasis

Preclinical animal research has greatly contributed and will continue to contribute in our understanding of various disease states and provided methods for more understanding of disease states and designs to test novel pharmaco-therapeutic interventions against these diseases. For urolithiasis, scientists have developed numerous in vitro and in vivo models that attempt to replicate human urolithiasis. In this review, I have explained in vitro and in vivo models that are more common, affordable, and easy to replicate. In the in vitro models, I have focused on the CaOx crystallization models and in the in vivo models, hyperoxaluric rat model has been explained along with other available option such as Knockout (KO) mice and fly models. Each model has been explained stepwise along with its pros and cons.

Hydroxyproline Metabolism and Oxalate Synthesis in Primary Hyperoxaluria

Background Endogenous oxalate synthesis contributes to calcium oxalate stone disease and is markedly increased in the inherited primary hyperoxaluria (PH) disorders. The incomplete knowledge regarding oxalate synthesis complicates discovery of new treatments. Hydroxyproline (Hyp) metabolism results in the formation of oxalate and glycolate. However, the relative contribution of Hyp metabolism to endogenous oxalate and glycolate synthesis is not known.Methods To define this contribution, we performed primed, continuous, intravenous infusions of the stable isotope [¹⁵N,¹³C₅]-Hyp in nine healthy subjects and 19 individuals with PH and quantified the levels of urinary ¹³C₂-oxalate and ¹³C₂-glycolate formed using ion chromatography coupled to mass detection.Results The total urinary oxalate-to-creatinine ratio during the infusion was 73.1, 70.8, 47.0, and 10.6 mg oxalate/g creatinine in subjects with PH1, PH2, and PH3 and controls, respectively. Hyp metabolism accounted for 12.8, 32.9, and 14.8 mg oxalate/g creatinine in subjects with PH1, PH2, and PH3, respectively, compared with 1.6 mg oxalate/g creatinine in controls. The contribution of Hyp to urinary oxalate was 15% in controls and 18%, 47%, and 33% in subjects with PH1, PH2, and PH3, respectively. The contribution of Hyp to urinary glycolate was 57% in controls, 30% in subjects with PH1, and <13% in subjects with PH2 or PH3.Conclusions Hyp metabolism differs among PH types and is a major source of oxalate synthesis in individuals with PH2 and PH3. In patients with PH1, who have the highest urinary excretion of oxalate, the major sources of oxalate remain to be identified.

Oxalate-Degrading Enzyme Recombined Lactic Acid Bacteria Strains Reduce Hyperoxaluria

OBJECTIVE

To develop recombinant lactic acid bacteria (LAB) strains that express oxalate-degrading enzymes through biotechnology-based approach for the treatment of hyperoxaluria by oral administration.

MATERIAL AND METHODS

The coding gene of oxalate decarboxylase (ODC) and oxalate oxidase (OxO) was transformed into Lactococcus lactis MG1363. The oxalate degradation ability in vitro was evaluated in media with high concentration of oxalate. Hyperoxaluria rat models through high oxalate diet were given recombinant LAB through oral administration. Twenty-four-hour urinary oxalate was measured, and kidney stone formation was investigated.

RESULTS

LAB recombined with the coding gene of ODC could effectively decrease the amount of oxalate in the media and in the urine of rats. Moreover, the formation of calcium oxalate crystals in kidneys was also inhibited. The acid-induced promoter p170 significantly enhanced the reduction of hyperoxaluria. However, recombinant LAB expressing heterologous OxO showed less efficiency in oxalate degradation even in the presence of p170.

CONCLUSION

LAB expressing ODC is more efficient in degradation of oxalate in vitro and in vivo than that expressing OxO. This present study provided novel recombinant probiotic strains as a potential treatment tool against oxalosis.

Changes of Klotho protein and Klotho mRNA expression in a hydroxy-L-proline induced hyperoxaluric rat model

Klotho protein is recognized as having a renoprotective effect and is used as a biomarker for kidney injury. We investigated the level of Klotho protein in hyperoxaluria-induced kidney injury and the effects of vitamin E (Vit E) and vitamin C (Vit C) supplementation. Hyperoxaluria was induced by feeding 2% (w/v) Hydroxy-L-proline (HLP) in the drinking water for 21 days. Rats were divided into 5 groups; control (Group 1, n=7), HLP treated rats that received nothing else (Group 2, n=7), Vit E (Group 3, n=6), Vit C (Group 4, n=6) and both Vit E and Vit C (Group 5, n=7). Vit E (200 mg/kg) was injected on days 1, 6, 11 and 16, while Vit C (500 mg/kg) was given intravenously on days 1 and 11. The Klotho protein levels and oxidative status were measured. The expression level of kidney Klotho protein expression was significantly reduced by HLP-treatment, while the mRNA expression was higher (P<0.05), the plasma and kidney malondialdehyde and kidney superoxide dismutase activities were increased, and the kidney reduced glutathione and urinary total antioxidant status were decreased (P<0.05). All of these changes were ameliorated by administration of Vit E, Vit C or especially the co-administration of both. In conclusion, HLP-induced hyperoxaluria reduced the kidney Klotho protein level, which could be restored by Vit E and/or Vit C.

Transcriptional study of hyperoxaluria and calcium oxalate nephrolithiasis in male rats: Inflammatory changes are mainly associated with crystal deposition

Hyperoxaluria associated with renal deposition of calcium oxalate (CaOx) crystals causes renal injury and inflammation leading to number of diseases including chronic kidney disease (CKD). It is however, not been possible to separate the renal consequences of hyperoxaluria from that of CaOx crystal deposition. We decided to utilize ethylene glycol (EG) model where hyperoxaluria and CaOx crystal deposition can be separated in time. To test our hypothesis, male rats were made hyperoxaluric by administering EG, rats were euthanized and kidneys were extracted on day 14, when occasional crystal is seen in the kidneys and day 28, when all animals have developed renal CaOx crystal deposits. Total RNA was extracted for microarray analysis and genome wide analysis of differentially expressed genes was performed to investigate differences between hyperoxaluria and crystal induced alterations in the kidneys. Immunohistochemical and Hematoxylin and Eosin (H&E) staining was also done for macromolecules with significant role in stone formation. All EG fed rats became hyperoxaluric by day 7, showed a few crystal deposits on day 14, and had heavy crystal deposition by day 28. There were significant changes in the expression of genes encoding for NADPH Oxidases; macromolecular crystallization modulators; genes involved in inflammasome activation; and osteogenic marker genes. Results demonstrate major differences between hyperoxaluria and CaOx crystal induced changes in the kidneys. Injury and inflammation are mainly associated with crystal deposition indicating significant role played by crystal retention.

Roles of dietary glycine, proline, and hydroxyproline in collagen synthesis and animal growth

Glycine, proline, and hydroxyproline (Hyp) contribute to 57% of total amino acids (AAs) in collagen, which accounts for one-third of proteins in animals. As the most abundant protein in the body, collagen is essential to maintain the normal structure and strength of connective tissue, such as bones, skin, cartilage, and blood vessels. Mammals, birds, and fish can synthesize: (1) glycine from threonine, serine, choline, and Hyp; (2) proline from arginine; and (3) Hyp from proline residues in collagen, in a cell- and tissue-specific manner. In addition, livestock (e.g., pigs, cattle, and sheep) produces proline from glutamine and glutamate in the small intestine, but this pathway is absent from birds and possibly most fish species. Results of the recent studies indicate that endogenous synthesis of glycine, proline, and Hyp is inadequate for maximal growth, collagen production, or feed efficiency in pigs, chickens, and fish. Although glycine, proline and Hyp, and gelatin can be used as feed additives in animal diets, these ingredients except for glycine are relatively expensive, which precludes their inclusion in practical rations. Alternatively, hydrolyzed feather meal (HFM), which contains 9% glycine, 5% Hyp, and 12% proline, holds great promise as a low cost but abundant dietary source of glycine, Hyp, and proline for ruminants and nonruminants. Because HFM is deficient in most AAs, future research efforts should be directed at improving the bioavailability of its AAs and the balance of AAs in HFM-supplemented diets. Finally, HFM may be used as a feed additive to prevent or ameliorate connective tissue disorders in domestic and aquatic animals.

Combination of vitamin E and vitamin C alleviates renal function in hyperoxaluric rats via antioxidant activity

Hyperoxaluria and oxidative stress are risk factors in calcium oxalate (CaOx) stone formation. Supplement with antioxidant could be effective in prevention of recurrent stone formation. The present study aims to evaluate the protective effects of vitamin E and vitamin C in hyperoxaluric rat. The experiment was performed in rats for 21 days. Rats were divided into 5 groups as follows: control (group 1, n=8), hyperoxaluric rats (group 2, n=8), hyperoxaluric rats with vitamin E supplement (group 3, n=7), hyperoxaluric rats with vitamin C supplement (group 4, n=7) and hyperoxaluric rats with vitamin E and C supplement (group 5, n=7). Hyperoxaluria was induced by feeding hydroxyl L-proline (HLP) 2% w/v dissolved in drinking water. Intraperitoneal 200 mg/kg of vitamin E was given in groups 3 and 5 on days 1, 6, 11 and 16, while 500 mg of vitamin C was injected intravenously in groups 4 and 5 on days 1 and 11. Renal functions and oxidative status were measured. The urinary oxalate excretion was increased in HLP supplement rats, while glomerular filtration rate, proximal water and sodium reabsorption were significantly lower in group 2 compared with a control (P<0.05). Giving antioxidants significantly lower urinary calcium oxalate crystals (P<0.05). Hyperoxaluric rats had higher plasma malondialdehyde (PMDA) and lower urinary total antioxidant status (UTAS), which were alleviated by vitamin E and/or vitamin C supplement. In conclusion, giving combination of vitamin E and vitamin C exerts a protective role against HLP-induced oxalate nephropathy.

Calcium oxalate crystals and oxalate induce an epithelial-to-mesenchymal transition in the proximal tubular epithelial cells: Contribution to oxalate kidney injury

TGF-β1 is the main mediator of epithelial-to-mesenchymal transition (EMT). Hyperoxaluria induces crystalluria, interstitial fibrosis, and progressive renal failure. This study analyzed whether hyperoxaluria is associated with TGF-β1 production and kidney fibrosis in mice and if oxalate or calcium oxalate (CaOx) could induce EMT in proximal tubule cells (HK2) and therefore contribute to the fibrotic process. Hyperoxaluria was induced by adding hydroxyproline and ethylene glycol to the mice’s drinking water for up to 60 days. Renal function and oxalate and urinary crystals were evaluated. Kidney collagen production and TGF-β1 expression were assessed. EMT was analyzed in vitro according to TGF-β1 production, phenotypic characterization, invasion, cell migration, gene and protein expression of epithelial and mesenchymal markers. Hyperoxaluric mice showed a decrease in renal function and an increase in CaOx crystals and Ox urinary excretion. The deposition of collagen in the renal interstitium was observed. HK2 cells stimulated with Ox and CaOx exhibited a decreased expression of epithelial as well as increased expression mesenchymal markers; these cells presented mesenchymal phenotypic changes, migration, invasiveness capability and TGF-β1 production, characterizing EMT. Treatment with BMP-7 or its overexpression in HK2 cells was effective at preventing it. This mechanism may contribute to the fibrosis observed in hyperoxaluria.

Studies using a porcine model: what insights into human calcium oxalate stone formation mechanisms has this model facilitated?

Animal models are useful in the study of many human diseases. Our current understanding of the biological, physiological, and biochemical aspects of hyperoxaluria and calcium oxalate urolithiasis has been greatly informed by studies using animals. Recently, limitations in the extrapolation to humans of research results derived from laboratory rodents have been identified. The use in biomedical research of a variety of organisms, including large animals, is increasingly encouraged. The purpose of this article is to review the use of pigs in biomedical and stone research, to provide a rationale for using pigs in metabolic stone research, and to describe our 8-year experience in developing a porcine platform for studying hyperoxaluria and calcium oxalate urolithiasis. In this article, we share and review some of the highlights of our findings. We also report results from a recent feeding swine study that demonstrated oxalate-induced renal nephropathy. Finally, we offer ideas for future directions in urolithiasis research using swine.

Histological aspects of the "fixed-particle" model of stone formation: animal studies

Crystallization by itself is not harmful as long as the crystals are not retained in the kidneys and are allowed to pass freely down the renal tubules to be excreted in the urine. A number of theories have been proposed, and studies performed, to determine the mechanisms involved in crystal retention within the kidneys. It has been suggested that urinary transit through the nephron is too fast for crystals to grow large enough to be retained. Thus, free particle mechanism alone cannot lead to stone formation, and there must be a mechanism for crystal fixation within the kidneys. Animal model studies suggest that crystal retention is possible through both the free- and fixed-particle mechanisms. Crystal-cell interaction leads to pathological changes which promote crystal attachment to either epithelial cells or their basement membrane. Alternatively, crystals aggregate and produce large enough particles to block the tubules particularly at sites, where urinary flow is affected because of changes in the luminal diameter of the tubule. Crystal deposits plugging the openings of the ducts of Bellini may be the result of such a phenomenon. Intratubular crystals translocating to renal interstitium may produce osteogenic changes in the epithelial or endothelial cells resulting in the formation of the Randall's plaques. Thus, fixation appears to be either through the formation of Randall's plugs, crystal plugs clogging the openings of the ducts of Bellini or sub-epithelial crystal deposits, and the Randall's plaques.

Animal models of urinary stone disease

The etiology of stone disease remains unknown despite the major technological advances in the treatment of urinary calculi. Clinically, urologists have relied on 24-h urine collections for the last 30-40 years to help direct medical therapy in hopes of reducing stone recurrence; yet little progress has been made in preventing stone disease. As such, there is an urgent need to develop reliable animal models to study the pathogenesis of stone formation and to assess novel interventions. A variety of vertebrate and invertebrate models have been used to help understand stone pathogenesis. Genetic knockout and exogenous induction models are described. Surrogates for an endpoint of stone formation have been urinary crystals on histologic examination and/or urinalyses. Other models are able to actually develop true stones. It is through these animal models that real breakthroughs in the management of urinary stone disease will become a reality.