Reabsorption Of Amino Acids Research Articles

Amino acid metabolism in kidney health and disease.

Amino acids form peptides and proteins and are therefore considered the main building blocks of life. The kidney has an important but under-appreciated role in the synthesis, degradation, filtration, reabsorption and excretion of amino acids, acting to retain useful metabolites while excreting potentially harmful and waste products from amino acid metabolism. A complex network of kidney transporters and enzymes guides these processes and moderates the competing concentrations of various metabolites and amino acid products. Kidney amino acid metabolism contributes to gluconeogenesis, nitrogen clearance, acid-base metabolismand provision of fuel for tricarboxylic acid cycle and urea cycle intermediates, and is thus a central hub for homeostasis. Conversely, kidney disease affects the levels and metabolism of a variety of amino acids. Here, we review the metabolic role of the kidney in amino acid metabolism and describe how different diseases of the kidney lead to aberrations in amino acid metabolism. Improved understanding of the metabolic and communication routes that are affected by disease could provide new mechanistic insights into the pathogenesis of kidney diseases and potentially enable targeted dietary or pharmacological interventions.

Proximal tubule hypertrophy and hyperfunction: a novel pathophysiological feature in disease states.

The role of proximal tubules (PTs), a major component of the renal tubular structure in the renal cortex, has been examined extensively. Along with its physiological role in the reabsorption of various molecules, including electrolytes, amino acids and monosaccharides, transcellular transport of different hormones and regulation of homeostasis, pathological events affecting PTs may underlie multiple disease states. PT hypertrophy or a hyperfunctioning state, despite being a compensatory mechanism at first in response to various stimuli or alterations at tubular transport proteins, have been shown to be critical pathophysiological events leading to multiple disorders, including diabetes mellitus, obesity, metabolic syndrome and congestive heart failure. Moreover, pharmacotherapeutic agents have primarily targeted PTs, including sodium-glucose cotransporter 2, urate transporters and carbonic anhydrase enzymes. In this narrative review, we focus on the physiological role of PTs in healthy states and the current understanding of the PT pathologies leading to disease states and potential therapeutic targets.

Arteriovenous metabolomics in pigs reveals CFTR regulation ofmetabolism inmultiple organs.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF), a multiorgan disease that exhibits diverse metabolic defects. However, other than specific CFTR mutations, the factors that influence disease progression and severity remain poorly understood. Aberrant metabolite levels have been reported, but whether CFTR loss itself or secondary abnormalities (infection, inflammation, malnutrition, and various treatments) drive metabolic defects are uncertain. Here, we implemented comprehensive arteriovenous metabolomics in newborn CF pigs, and the results revealed CFTR as a bona fide regulator of metabolism. CFTR loss impaired metabolite exchange across organs, including disrupted lung uptake of fatty acids yet enhanced uptake of arachidonic acid, a precursor of pro-inflammatory cytokines. CFTR loss also impaired kidney reabsorption of amino acids and lactate and abolished renal glucose homeostasis. These and additional unexpected metabolic defects prior to disease manifestations reveal a fundamental role for CFTR in controlling multi-organ metabolism. Such discovery informs a basic understanding of CF, provides a foundation for future investigation, and has implications for developing therapies targeting only a single tissue.

Human Adenovirus Serotype 5 (HAdV-5) Infection of Kidney Fibroblast Cells Disrupts Cysteine, Purine, and Unsaturated Fatty Acid Metabolism in a Dose- and Time-Dependent Manner

Kidneys partake in numerous metabolic responsibilities, notably clearance of insulin from circulation, gluconeogenesis, and reabsorption of amino acids. Viral-induced kidney damage, either acutely or chronically, can occur from direct impact on kidney cells and from systemic and local immunological responses to counter the viral infection. Thus, it is likely that metabolic dysfunction is a consequence of infections. The detriments of viral infection on kidney cell metabolism remains an unelucidated area. We used human adenovirus serotype 5 (HAdV-5) to infect human embryonic kidney cells (HEK293T) in a dose- and time-dependent manner. We hypothesized that optimal metabolic dysfunction results after 24 hours of infection and at the highest viral dose. Cells were exposed to three viral dosages (0.5,1.0,2.0 multiplicity of infection [MOI]) and metabolism assessed by untargeted metabolomics at four time points (6-,12-,24-, 36-hours post infection [HPI]). A total of 182 metabolites were identified in our study. As early as 6 hrs, the metabolic profile of infected cells exhibited downregulation of cystathionine, cysteine, homocysteine, hypoxanthine, linoleic acid, and oleic acid with upregulation of 5'-Deoxy-5'-methylthioadenosine (MTA) and adenine. Peak dysregulation for carbohydrate, cysteine, organic acid, purine, and unsaturated fatty acid-related metabolites was observed at 12 hrs. At 24 hours, tapering of the overall metabolite response was observed with further dysregulation seen at 36 hours. Across all three dosages, responses to infection were similar. Perturbation of the cysteine, purine, and unsaturated fatty acid metabolic pathways has not previously been considered with HAdV-5 infection and a commonly used cell line exhibiting properties of kidney, and historically neuronal components. Although not investigated, uncovering adenoviral impact on enzymatic activity in these pathways could elucidate more understanding of renal impairment. These data altogether suggest that substantial DNA viral infection disrupts cellular metabolic pathways that may impair renal functions but need to be evaluated in an in vivo model. USDA HSI Educational Grant 2021-03397. Bailey-J Sanchez was supported by USDA HSI Educational Grant 2021-03397. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cystinuria: A rare cause of bladder stone

Cystinuria is an inherited metabolic disorder progressing with recurrent kidney stones due to impaired reabsorption of dibasic amino acids and arises from mutations in the SLC3A1 and SLC7A9 on chromosome 2. Here, we present the case of a 1-year 10-month-old male child with recurrent episodes of urinary tract infections. On evaluation, duplex kidneys and a large bladder calculus were found which was surgically managed. Stone analysis and the genetic study were suggestive of cystinuria.

Molecular Insights to the Structure-Interaction Relationships of Human Proton-Coupled Oligopeptide Transporters (PepTs).

Human proton-coupled oligopeptide transporters (PepTs) are important membrane influx transporters that facilitate the cellular uptake of many drugs including ACE inhibitors and antibiotics. PepTs mediate the absorption of di- and tri-peptides from dietary proteins or gastrointestinal secretions, facilitate the reabsorption of peptide-bound amino acids in the kidney, and regulate neuropeptide homeostasis in extracellular fluids. PepT1 and PepT2 have been the most intensively investigated of all PepT isoforms. Modulating the interactions of PepTs and their drug substrates could influence treatment outcomes and adverse effects with certain therapies. In recent studies, topology models and protein structures of PepTs have been developed. The aim of this review was to summarise the current knowledge regarding structure-interaction relationships (SIRs) of PepTs and their substrates as well as the potential applications of this information in therapeutic optimisation and drug development. Such information may provide insights into the efficacy of PepT drug substrates in patients, mechanisms of drug-drug/food interactions and the potential role of PepTs targeting in drug design and development strategies.

Genetic and clinical characterization of familial renal glucosuria.

Familial renal glucosuria (FRG) is a hereditary disorder caused by variants in SLC5A2 encoding sodium-glucose cotransporter 2 (SGLT2). In this study, we aimed to characterize proximal tubule solute transport, glucagon secretion and the genotype-phenotype relationship in FRG patients. We sequenced SLC5A2 and PDZK1IP1 in 21 FRG patients and measured the renal threshold of glucose (RTG) in 15 patients. We built an open-source online calculator of RTG, evaluated the proximal tubule transport of amino acid, uric acid and phosphate, and explored glucagon secretion after glucose ingestion in FRG patients. We identified 12 novel SLC5A2 variants (G484D, R564W, A212S, c.574+1G>C, W649*, S592Cfs*6, Q579*, Y339*, V39F, G491E, A464E and G360D) in our cohort and yielded 111 SLC5A2 variants from literature review. RTG in our cohort ranged from 1.0 to 9.2mmol/L. Patients with two SLC5A2 variants had lower RTG (3.9 vs 6.2mmol/L) and higher 24-h urinary glucose excretion (24hUG) than single-variant carriers (291.0 vs 40.0mmol/1.73 m2). Patients with homozygous missense or in-frame indels had mean 24hUG of 457.2mmol/1.73 m2, comparable to those with homozygous truncating variants (445.0mmol/1.73 m2) and significantly more than those with homozygous splicing variants (196.6mmol/1.73 m2). Patients with homozygous missense variants involving conservative residues (582.0mmol/1.73 m2) had more 24hUG than those with variants at non-conservative residues (257.6mmol/1.73 m2). Four out of 14 tested patients had mild aminoaciduria. The RTG of FRG patients had no significant correlation to phosphate reabsorption but a potential negative correlation to the fractional excretion of uric acid. Postprandial suppression of glucagon secretion was absent in most FRG patients. We built a comprehensive map showing the impact of SLC5A2 variant type and variant location on glucosuria severity. Our results highlighted the role of key residues in maintaining the transport function of SGLT2 and the functional link between glucosuria and reabsorption of amino acid and uric acid in FRG patients.

Excretion of excess nitrogen and increased survival by loss of SLC6A19 in a mouse model of ornithine transcarbamylase deficiency.

Protein catabolism ultimately yields toxic ammonia, which must be converted to urea by the liver for renal excretion. In extrahepatic tissues, ammonia is temporarily converted primarily to glutamine for subsequent hepatic extraction. Urea cycle disorders (UCDs) are inborn errors of metabolism causing impaired ureagenesis, leading to neurotoxic accumulation of ammonia and brain glutamine. Treatment includes dietary protein restriction and oral "ammonia scavengers." These scavengers chemically combine with glutamine and glycine to yield excretable products, creating an alternate pathway of waste nitrogen disposal. The amino acid transporter SLC6A19 is responsible for >95% of absorption and reabsorption of free neutral amino acids in the small intestine and kidney, respectively. Genetic SLC6A19 deficiency causes massive neutral aminoaciduria but is typically benign. We hypothesized that inhibiting SLC6A19 would open a novel and effective alternate pathway of waste nitrogen disposal. To test this, we crossed SLC6A19 knockout (KO) mice with spfash mice, a model of ornithine transcarbamylase (OTC) deficiency. Loss of SLC6A19 in spfash mice normalized plasma ammonia and brain glutamine and increased median survival in response to a high protein diet from 7 to 97 days. While induced excretion of amino acid nitrogen is likely the primary therapeutic mechanism, reduced intestinal absorption of dietary free amino acids, and decreased muscle protein turnover due to loss of SLC6A19 may also play a role. In summary, the results suggest that SLC6A19 inhibition represents a promising approach to treating UCDs and related aminoacidopathies.

Biology of Peptide Transporter 2 in Mammals: New Insights into Its Function, Structure and Regulation.

Peptide transporter 2 (PepT2) in mammals plays essential roles in the reabsorption and conservation of peptide-bound amino acids in the kidney and in maintaining neuropeptide homeostasis in the brain. It is also of significant medical and pharmacological significance in the absorption and disposing of peptide-like drugs, including angiotensin-converting enzyme inhibitors, β-lactam antibiotics and antiviral prodrugs. Understanding the structure, function and regulation of PepT2 is of emerging interest in nutrition, medical and pharmacological research. In this review, we provide a comprehensive overview of the structure, substrate preferences and localization of PepT2 in mammals. As PepT2 is expressed in various organs, its function in the liver, kidney, brain, heart, lung and mammary gland has also been addressed. Finally, the regulatory factors that affect the expression and function of PepT2, such as transcriptional activation and posttranslational modification, are also discussed.

Influence of alimentary factors on the absorption of feed nutrients and poultry productivity

The article is a summary of the literature on the main aspects of the modern bird feeding system. Theoretical aspects and results of experimental research of scientists on the substantiation of parameters of protein and amino acid nutrition are given, which is an important factor that, under appropriate conditions can significantly guarantee the realization of the genetic potential of corresponding breeds and crosses of poultry. It is shown that an important aspect of protein nutrition is the ratio of feed amino acids. Their negative interaction can be caused by a deficiency of one or more amino acids, an imbalance between them, antagonism, and toxicity. This is accompanied by effects on various physiological and biochemical processes, significantly affects appetite, intestinal absorption, renal reabsorption and transport of amino acids, their catabolism, rate of protein decomposition, synthesis, and formation of toxic metabolic products. The data show that the required level of energy for the bird's body is provided by carbohydrates (mainly of plant origin) and lipids (fat supplements of various origins). It is noted that lipids promote the absorption, transport, and deposition of fat-soluble vitamins. The effectiveness of using fat supplements as energy depends on their source. At the same time, among the indispensable nutrients that have a significant impact on growth intensity, reproductive quality, poultry productivity, and biological value of products, an important role is played by macro-and micronutrients. Many researchers emphasize that along with the use of traditional feeds in poultry feeding, the possibilities of non-traditional cereals rich in protein and lipids are not fully used. A limiting factor in their use is the presence in their composition of anti-nutrients contained in many feeds. Once in the digestive tract of animals, they negatively affect the absorption of feed nutrients. In most cases, the consumption of such feed by animals is manifested in growth retardation, increased feed consumption, hormonal effects, and, less frequently, in the dysfunction of certain organs.

Extracorporeal Shockwave Lithotripsy for Cystine Stones in Children: An Observational, Retrospective, Single-Center Analysis.

Purpose: Cystinuria is a genetic disorder characterized by a defective reabsorption of cystine and dibasic amino acids leading to development of urinary tract calculi from childhood onward. Cystine lithiasis is known to be resistant to fragmentation. The aim was to evaluate our long-term experience with extracorporeal shockwave lithotripsy (ESWL) used as first-line urological treatment to treat cystine stones in children.Methods: We retrospectively reviewed the charts of all children who underwent ESWL for cystine stone. We assessed the 3-month stone-free rate, according to age, younger (group 1) or older (group 2) than 2 years old.Results: Between 2003 and 2016, 15 patients with a median (IQR) age at first treatment of 48 (15–108) months underwent ESWL in monotherapy. Median age was, respectively, 15 and 108 months in each group. The median (IQR) stone burden was 2,620 (1,202–8,265) mm3 in group I and 4,588 (2,039–5,427) mm3 in group II (p = 0.96). Eleven patients had bilateral calculi. ESWL was repeated on average 2.4 times, with a maximum of 4 for patients of group I, and 4.8 times, with a maximum of 9 for group II (p > 0.05). ESWL in monotherapy was significantly more efficient to reach stone-free status for children under 2 years of age: 83% vs. 6.2% (p = 0.040). The median (IQR) follow-up of the study was 69 (42–111) months.Conclusion: ESWL appears as a valid urological option for the treatment of cystine stones, in young children. Even if cystine stones are known to be resistant to fragmentation, we report 83% of stone-free status at 3 months with ESWL used in monotherapy in children under 2 years old with cystinuria. In older children, the success rate is too low to recommend ESWL as a first line approach.

Basal renal phenotype and response to induction of aristolochic acid nephropathy in mice lacking the neutral amino acid transporter B0AT1 (SLC6A19)

Background B0AT1 (SLC6A19) mediates the reabsorption of neutral amino acids, including branched-chain amino acids (BCAA), in the intestine and kidney (expressed in early and mid-proximal tubule - S1/S2). Dietary restriction of BCAA has been proposed to improve metabolic health by inhibiting mTOR and inducing autophagy. Here we characterized basal kidney function and determined whether B0AT1 KO protects the kidney from aristolochic acid-induced nephropathy (AAN), a model of proximal tubular injury. Methods In male B0AT1 KO and littermate wild-type mice (WT) mice, we measured fractional renal amino acid excretion and performed renal FITC-sinistrin clearance studies under terminal anesthesia to determine renal creatinine handling. A set of female mice was injected with aristolochic acid (3 mg/kg i.p.) or vehicle every 3 days for 3 weeks, and kidneys were harvested 3 weeks later for RTqPCR analyses (n=7-16 mice per group). Results RTqPCR and Western blotting confirmed absence of renal B0AT1 mRNA in KO, associated with increased fractional renal excretion of neutral amino acids, including BCAA (to 20-40%), whereas plasma levels of BCAA were not changed. In vehicle-treated mice, plasma creatinine was slightly higher in KO vs WT (0.080±0.002 vs 0.074±0.002 mg/dl; *P<0.05). Clearance studies revealed a trend for lesser fractional excretion of creatinine in KO vs WT (P=0.057), suggesting lesser creatinine secretion contributed to higher plasma levels. Urinary albumin/creatinine ratio (UACR) and urinary glucose/creatinine ratio (UGCR) were tripled and doubled in female KO vs WT (180±18 vs 62±5 ng/μg*; 1.35±0.26 vs 0.70±0.06 mg/mg*), respectively, suggesting a modest impairment in proximal tubular albumin and glucose reabsorption. The renal expression of the alternative neutral amino acid transporter B0AT3 (SLC6A18), expressed in S1-S3, was reduced in KO (to 32±5% of WT*). This may be due to KO model generation, as B0AT1 and B0AT3 are co-expressed side-by-side on the same chromosome. Whole kidney CCR2 and KIM-1 mRNA expression were modestly higher in KO vs WT, which may reflect enhanced amino acid and glucose transport in the vulnerable S3 segment in the outer medulla. In the absence of robust effects on plasma creatinine, AAN significantly increased UACR vs vehicle in WT (+164±39 vs +52±14 ng/μg*) but not in KO (-18±30 vs +57±49 ng/μg) when measured after completion of injections. Moreover, increases in CCR2 and TIMP1 expression in response to AAN vs vehicle observed in WT (+206±28%; +203±45%) were attenuated in KO (+54±20%*; +81±39%*). Conclusions Genetic deletion of B0AT1 in male and female mice induces distinct effects on kidney transport beyond amino acids. Follow up studies with higher doses of AA are needed to more fully evaluate the nephroprotective potential of B0AT1 inhibition.

Analysis of SLC7A9 gene mutations among Jordanian patients with cystinuria

BackgroundCystinuria is known as a heritable disorder affecting the cysteine reabsorption by renal system as well as the reabsorption of dibasic amino acids. The main objectives of the present study were to identify genetic mutations in SLC7A9 gene associated with cystinuria. MethodsA cross sectional study design was conducted. A total of 28 patients diagnosed with cystinuria were included. Molecular techniques were applied to identify genetic mutations in SLC7A9 gene. ResultsThe mean age of study participants was 31.57 ± 2.88 years, and slightly more than two thirds of participants were males. Mutations of SLC 7A9 gene showed that the majority of cases (57.1%) were homogeneous, (7.1%) heterogeneous, and slightly more than one third of patients had no mutations. There was no statistically significant relationship between mutations for the SLC7A9 gene and gender (p = 0.249). ConclusionMutations in the SLC7A9 gene are prevalent and can be used as molecular tools to diagnose cystinuria.

Water salinity and postprandial effects on transcription of peptide and amino acid transporters in the kidney of Mozambique tilapia (Oreochromis mossambicus)

Preservation of amino acids is highly important, as these are vital nutrients that support many physiological and biochemical processes. During fish osmoregulation, the kidney reabsorbs amino acids and short peptides that are filtered from the blood into the nephron. However, little is known about reabsorption systems in teleost kidney. To identify transporters involved in this process, we examined by PCR the expression of eight genes, coding to peptide and amino acid transporters, as well as of two ion transport systems, in the kidney of the euryhaline Mozambique tilapia (Oreochromis mossambicus). We found that three amino acid transporters (slc1a5, ASCT2; slc7a9, b0,+AT; slc6a19, B0AT) and one peptide transporter (slc15a2, PepT2) were expressed in the kidney, as were the two ion transporters VHA and NHE3 (coded by atp6v1a and slc9a3, respectively). Next, to investigate transcriptional interactions of these transporters with osmoregulation and nutritional status, we compared by qPCR expression levels in fish acclimated to either fresh or saltwater and at three time points after feeding (6, 24, 72 h). Significant effect of salinity was detected on the expression of ASCT2 and VHA, whereas time after feeding affected PepT2 and VHA transcripts. Interactions between salinity and feeding significantly affected NHE3 transcription. PepT2 expression was an order of magnitude higher than free amino acid transporters, indicating the importance of peptide reabsorption in the kidney of Mozambique tilapia. Immunofluorescence staining of PepT2 showed an apical staining while, b0,+AT antibody stained the basolateral membrane of the nephrons epithelial cells. The two transporters expression were found in separates segment of the nephrons. These results reveal specific transporters involved in kidney reabsorption of amino acids and short peptides and their response to the fish osmotic and nutritional status.

Diagnostic Approach in Cystinuria: A Case Report

Cystinuria is an, inherited metabolic disorder progressing with recurrent kidney stones due to impaired reabsorption of dibasic amino acids and arises from mutations in the SLC3A1 and SLC7A9 on chromosome 2. Cystine crystals were detected in the urinalysis of a 17-year-old male patient who was investigated for recurrent kidney stones. Because of demonstration of cystine excretion in the urinary amino acid analysis and having positive family history, we suspected Cystinuria Type B and initiated supportive therapy. However, based on the results of molecular analyses his diagnosis was changed as Cystinuria Type A. In conclusion, our final diagnosis was changed according to the molecular analyses but our treatment approach did not change. Therefore we would like to emphasize that, prominent physical examination findings and supportive laboratory test results will be sufficient for the diagnosis of cystinuria.

Computational analysis identifies druggable mutations in human rBAT mediated Cystinuria

Culex quinquefasciatus Cqm1 protein acts as the receptor for Lysinibacillus sphaericus mosquito-larvicidal binary (BinAB) toxin that is used worldwide for mosquito control. We found amino acid transporter protein, rBAT, as phylogenetically closest Cqm1 homolog in humans. The present study reveals large evolutionary distance between Cqm1 and rBAT, and rBAT ectodomain lacks the sequence motif which serves as binding-site for the BinAB toxin. Thus, BinAB toxin can be expected to remain safe for humans. rBAT (heavy subunit; SLC3A1) and catalytic b0,+AT (light subunit; SLC7A9), linked by single disulfide bond, mediate renal reabsorption of cystine and dibasic amino acids in Na+ independent manner. Mutations in rBAT cause type I Cystinuria disease which shows global prevalence, and rBAT can be thought as an important pharmacological target. However, 3D structures of rBAT and b0,+AT, the two components of b0,+ heteromeric amino acid transporter systems, are not available. We constructed a reliable homology model of rBAT using Cqm1 coordinates and that of transmembrane b0,+AT subunit using LAT1 coordinates. Mapping of pathogenic mutations onto rBAT ectodomain revealed their scattered distribution throughout the rBAT protein. Further, our computational simulations-based scoring of several known deleterious mutations of rBAT revealed that mutations those do not compromise the protein fold and stability, are localized on the same face of the molecule. These residues are expected to interact with the b0,+AT transporter. The present study thus identifies druggable sites on rBAT that could be targeted for the treatment of type I Cystinuria. Communicated by Ramaswamy H. Sarma

MP43-05 ENZYMATIC LOWERING OF PLASMA CYSTINE PREVENTS FORMATION AND GROWTH OF STONES IN A MOUSE MODEL OF CYSTINURIA UNDER DEHYDRATION CHALLENGE

You have accessJournal of UrologyStone Disease: Medical & Dietary Therapy (MP43)1 Apr 2020MP43-05 ENZYMATIC LOWERING OF PLASMA CYSTINE PREVENTS FORMATION AND GROWTH OF STONES IN A MOUSE MODEL OF CYSTINURIA UNDER DEHYDRATION CHALLENGE Giulia Agnello, Jason Wiggins, Silvia Ferrati, Anthony Quinn, Scott Rowlinson, and J Stuart Wolf* Giulia AgnelloGiulia Agnello More articles by this author , Jason WigginsJason Wiggins More articles by this author , Silvia FerratiSilvia Ferrati More articles by this author , Anthony QuinnAnthony Quinn More articles by this author , Scott RowlinsonScott Rowlinson More articles by this author , and J Stuart Wolf*J Stuart Wolf* More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000898.05AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Cystinuria is an autosomal recessive disease caused by mutations in the SLC3A1 and/or SLC7A9 dibasic amino acid transporter genes. The defective reabsorption of dibasic amino acids filtered by the glomerulus leads to high urine cystine content, subsequent cystine crystallization and the formation of upper tract urinary calculi, with recurrent stone passages and/or need for multiple procedural interventions. Symptomatic stone events include severe abdominal pain, hydronephrosis, hematuria, infective syndromes and chronic pain. Although high fluid intake remains a cornerstone of therapy, this regimen is inadequate at reaching the target cystine urine concentration owing to poor compliance, periods of increased fluid loss (fever, diarrhea/vomiting, high ambient temperature; PMID:16001591, 7996811) or impact on quality of life (e.g. nocturia and increased day time micturition frequency). We are developing a highly novel approach for the treatment of cystinuria patients that works by reducing cystine delivery into the kidney tubules through enzymatic lowering of plasma cystine. Herein, we investigated the therapeutic potential of this approach to prevent cystine stone formation in dehydration prone environments. METHODS: We used a murine model of cystinuria (SLC3A1-/-) that develops cystine stones in the kidneys and bladder (PMID:28165480) and rationed water to 65% to model dehydration conditions. During water rationing, mice were dosed with a human enzyme with novel activity for cystine. Stone burden in the kidneys and bladder was assessed by microcomputed tomography, and plasma and urine cystine concentration was monitored over time. RESULTS: Enzymatic reduction of plasma cystine prevented stone formation and growth in the kidneys and bladder, even under dehydration challenge. Lowering of plasma cystine resulted in reduction of cystine concentration in urine despite temporary dehydration. CONCLUSIONS: This study provides proof of concept that enzymatic lowering of plasma cystine levels is effective at reducing the cystine concentration in the urine in a mouse model of cystinuria in temporary dehydration conditions, and prevents formation and growth of cystine stones. Enzymatic lowering of plasma cystine warrants further investigation as a new potential approach for disease management of cystinuric patients unresponsive or intolerant to current treatment, or facing quality of life factors that impact the ability to comply with current treatment approaches. Source of Funding: This study was funded by Aeglea BioTherapeutics, Inc. © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e648-e649 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Giulia Agnello More articles by this author Jason Wiggins More articles by this author Silvia Ferrati More articles by this author Anthony Quinn More articles by this author Scott Rowlinson More articles by this author J Stuart Wolf* More articles by this author Expand All Advertisement PDF downloadLoading ...

Amino Acid Metabolism in the Kidneys: Nutritional and Physiological Significance.

The kidneys are developed from the intermediate mesoderm of the embryo. They are important for osmoregulation, regulation of acid-base balance, reabsorption of nutrients, and excretion of metabolites. In fish, the kidneys also serve as a hematopoietic, lymphoid and endocrine organ for the generation of red blood cells, the development of lymphocytes, and the production of hormones (e.g., glucocorticoids, catecholamines, and thyroid hormones). In humans and all animals, kidneys play a vital role in the metabolism and reabsorption of amino acids (AAs) and glucose. Specifically, this organ contributes to glucose synthesis from AAs, lactate and pyruvate via the gluconeogenesis pathway; regulates acid-base balance via inter-organ metabolism of glutamine; and synthesizes arginine, tyrosine, and glycine, respectively, from citrulline, phenylalanine, and 4-hydroxyproline. In mammals and birds, kidneys participate in creatine synthesis. Renal dysfunction adversely alters the concentrations of AAs in blood, while promoting muscle protein breakdown, inflammation, mitochondrial abnormalities, defects in the immune response, and cardiovascular diseases. Moderation of dietary AA intake has a protective and therapeutic effect on chronic kidney disease. Understanding the functions and metabolism of AAs in kidneys is essential for maintaining whole-body homeostasis, improving health and well-being, and preventing or treating renalmetabolic diseases in humans and farm animals (including swine, poultry, ruminants, fish and shrimp).

Proximal renal tubular acidosis with and without Fanconi syndrome.

Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO3−) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO3− wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO3− not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO3− reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO3−, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaPi-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.

Morphological Characteristics of the Developing Cecum of Japanese Quail (Coturnix coturnix japonica).

The current investigation was carried out to record the final stages of the development of both middle and distal parts of quail ceca, Coturnix coturnix japonica to understand the role of ceca in digestion, immune system, and absorption. The cellular and subcellular structures, including epithelial cell height, microvillus surface area, the proportion of goblet cells, the thickness of muscle layer, and cecum diameter showed great variations during the development. An undeveloped smooth muscularis mucosa was observed for the first time on the ED5. Primordia of glands were observed on the ED7. On the ED15, the middle part exhibited two shapes of mucosal villi: tongue-shaped villi and U-shaped. The plicae and crypts of Lieberkühn were demonstrated on the hatching day. The lymphatic tissues appeared in the wall of both parts of the ceca at the 4 weeks of age. Scanning electron microscopy revealed a great difference in the mucosal surface between different regions. Telocytes were observed in-between the muscle fibers and formed a network during the post-hatching period. Because of fermentation and other bacterial or chemical processes that have been shown to occur in the ceca, this study supports two hypotheses: the cecal development is related to diet and the cecal epithelium act as a site for primary absorption of nutrients or for re-absorption of electrolytes or amino acids derived from the urine.