Urinary Acid Research Articles

Investigation of renal tubular function with newly diagnosed type 1 diabetes mellitus during diabetic ketoacidosis

BackgroundProximal renal tubular dysfunction occurs during diabetic ketoacidosis (DKA) in type 1 diabetes. However, only a few studies have reported on the multiple proximal renal tubular functions simultaneously. Moreover, to the best of our knowledge, distal renal tubular function has not yet been investigated.MethodsPatients with newly diagnosed type 1 diabetes mellitus were classified into those with DKA and those without DKA, and their proximal and distal renal tubular functions were investigated. The diagnostic criteria for DKA were blood glucose > 200 mg/dL, blood pH < 7.3 or HCO3– < 15 mEq/L, and urine ketone body positivity.ResultsSix patients with DKA and five patients without DKA were included. In patients with DKA, urinary β2-microglobulin levels were significantly higher, while blood pH, HCO3–, and tubular reabsorption of phosphorus were significantly lower than in those without DKA. There were no significant differences in blood glucose, HbA1c, serum phosphorus, urinary N-acetyl-beta-glucosaminidase, and urinary amino acid excretion between patients with and without DKA. Elevated NH3 levels and impaired urinary acidification were not observed in patients with and without DKA.ConclusionsIn patients with newly diagnosed type 1 diabetes mellitus complicated with DKA, multiple proximal renal tubular dysfunctions occur simultaneously, suggesting transient Fanconi syndrome. Distal renal tubular acidosis was unlikely. The diagnostic criteria for DKA are appropriate also in the view of proximal renal tubular dysfunction and are considered suggestive of pathophysiological factors that may cause proximal renal tubular dysfunction.

Carbonic anhydrase, water dissociation and physiology of Kidney.

Carbonic anhydrase (CA) is a zinc metalloenzyme widely distributed throughout the tissues of the body. In the kidney, this enzyme is thought to play a pivotal role in urinary acidification and bicarbonate reabsorption. Two distinct isozymes of carbonic anhydrase have now been identified in the mammalian kidney. A soluble cytoplasmic form, similar if not identical to human erythrocyte carbonic anhydrase C, accounts for the bulk of the renal carbonic anhydrase activity.

Fat Distribution and Urolithiasis Risk Parameters in Uric Acid Stone Formers and Patients with Type 2 Diabetes Mellitus.

Key Points Under a controlled diet, uric acid stone formers (UASFs) and diabetic patients have higher endogenous net acid production.Under a controlled diet, UASFs have lower ammonium-to-net acid excretion ratio.Body fat inversely correlates with urine buffer capacity in normal individuals, but this relationship is lost in diabetic patients and UASFs. Background Uric acid (UA) nephrolithiasis affects approximately 10% of kidney stones, with a greater preponderance among patients with obesity and diabetes mellitus (DM). UA lithogenicity is driven by abnormally acidic urine pH. Distinguishing the contribution of intrinsic (e.g., body adiposity) versus external (e.g., dietary) factors to UA stone propensity is challenging because of uncontrolled diets in outpatients in previously published studies. Methods This compilation of metabolic studies with body composition examined by dual-energy x-ray absorptiometry scan and blood and urine biochemistry collected under a controlled metabolic diet was conducted across three distinct populations: 74 UA stone formers (UASF group), 13 patients with type 2 DM without kidney stones (DM group), and 51 healthy volunteers (HV group). Results Compared with HVs, both UASFs and patients with DM exhibited higher levels of net acid excretion (NAE) and significantly lower urine pH and lower proportion of NAE excreted as ammonium (NH4 +/NAE), all under controlled diets. UASFs exhibited significantly lower NH4 +/NAE compared with patients with DM. UASFs also showed higher total body and truncal fat compared with HVs. Among the HVs, lower NH4 +/NAE ratio correlated with higher truncal and total fat. However, this association was abolished in the UASF and DM groups who exhibit a fixed low NH4 +/NAE ratio across a range of body and truncal fat. Conclusions The findings suggest a dual defect of diet-independent increase in acid production and impaired kidney NH4 + excretion as major contributors to the risk of UA stone formation. There is an inverse physiologic association between body fat content and NH4 +/NAE in HVs, whereas NH4 +/NAE is persistently low in UASFs and patients with DM, regardless of body fat, representing pathophysiology.

Kidney Stones of Type I vs. Type II Diabetic Patients: Are There Any Differences?

Background: This study highlighted the differences between the biochemical compositions of urinary stones from patients with type 1 diabetes versus those with type 2 diabetes. Materials and Methods: This study included patients diagnosed with kidney stones and diabetes who were referred to the Urological Clinic of the Dr. C. I. Parhon Hospital in Iasi from April 2017 to April 2024. We analyzed the spectroscopic stone composition from 128 lithiasis patients treated in our Clinic. In the current study, the distribution of the biochemical composition of stones varied significantly between diabetic patients with type 2 diabetes, who formed primarily mixed uric acid stones, and diabetic patients with type 1 diabetes, who mainly developed pure uric acid stones (p &lt; 0.001). Patients with uric acid stones had significantly higher mean creatinine values than the other stone types (p &lt; 0.001). Urinary pH levels were abnormal for all biochemical subtypes of stones, indicating acidic urine. However, patients with uric acid stones had lower pH values than the group average. From the Kaplan–Mayer analysis, patients with pure uric acid stones had a shorter time to stone recurrence compared to patients with other biochemical types identified. Conclusions: These findings, which highlight the prevalence of pure uric acid stones in patients with type 1 diabetes and the impact of this on the strategy for dissolving pure stones, represent a significant advancement in understanding urinary lithiasis in diabetic patients.

Comparing Holotranscobalamin and Total Vitamin B12 in Diagnosing Vitamin B12 Deficiency in Megaloblastic Anemia Patients.

Background Megaloblastic anemia is characterized by abnormally large red blood cells caused by a deficiency in either vitamin B12 or folic acid, both of which are essential for DNA synthesis. Vitamin B12 insufficiency can lead to severe neurological damage, making early identification of vitamin B12 deficiency crucial to prevent irreversible harm. Vitamin B12 deficiency results in decreased levels of holotranscobalamin (Holo-TC) and increased levels of methylmalonic acid (MMA). Methylmalonic acid is considered the gold standard for diagnosing B12 deficiency because it is a specific marker that rises when B12 is insufficient, even when serum B12 levels appear normal. Elevated MMA levels reflect impaired B12 metabolism, making it a critical tool for early detection and intervention. Previous research indicates that Holo-TC, the active form of vitamin B12 available to cells, is a more specific diagnostic tool for early vitamin B12 deficiency than total B12. This study aims to determine the diagnostic validity of total vitamin B12 and Holo-TC using MMA as the gold standard in patients with megaloblastic anemia. Methods A total of 95 megaloblastic anemia patients were selected from Jinnah Hospital and Lahore General Hospital, Lahore, Pakistan, after receiving approval from the ethical review committees. This was a cross-sectional study. Whole blood, serum, and urine samples were collected in ethylenediamine tetraacetic acid (EDTA) vials, gel vials, and urine containers, respectively. The EDTA samples were used for complete blood count measurements using a hematology analyzer (Sysmex-XT 1800i, Sysmex America, Inc., Mundelein, IL), while serum and urine samples were employed for the detection of serum folic acid, cobalamin, Holo-TC, and MMA levels through manual enzyme-linked immunosorbent assay (ELISA) techniques. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of Holo-TC and cobalamin were calculated. Results The majority of patients fell within the age group of 20-70 years, with 57% of them being females and 43% males; Holo-TC exhibited a sensitivity of 98.9% and specificity of 50.00%, with a PPV of 98.90% and NPV of 50%. Vitamin B12 demonstrated a sensitivity of 63% and specificity of 50%, with a PPV of 98.33% and NPV of 2.85%. The diagnostic accuracy of Holo-TC and vitamin B12 was observed to be 97.8% and 63%, respectively. Conclusions Between the two, Holo-TC displays higher diagnostic accuracy than vitamin B12 and can serve as the primary test for patients suspected of having vitamin B12 deficiency.

Urinary Acidification and Pharmacological Inhibition of OCT/OAT Reduce the Severity of Experimental Vancomycin-Induced AKI

Urinary Acidification and Pharmacological Inhibition of OCT/OAT Reduce the Severity of Experimental Vancomycin-Induced AKI

Acute Effect of High Fat Intake on Urinary Acidification Parameters in Uric Acid Stone Formers and Non-stone Forming Controls

Acute Effect of High Fat Intake on Urinary Acidification Parameters in Uric Acid Stone Formers and Non-stone Forming Controls

Revisiting voltage-coupled H+ secretion in the collecting duct.

Experimental studies have shown that V-type ATPase-driven H+ secretion is dependent on transepithelial voltage. On this basis, the "voltage hypothesis" of urinary acidification by the collecting duct was derived. Accordingly, it has been supposed that the lumen-negative potential created by the reabsorption of Na+ via the epithelial Na+ channel (ENaC) enhances electrogenic H+ secretion via V-type H+-ATPase. This concept continues to be widely used to explain acid/base disorders. Importantly, however, a solid proof of principle for the voltage hypothesis in physiologically relevant situations has not been reached. Rather, it has been challenged by recent in vivo functional studies. In this review, we outline the arguments and experimental observations explaining why voltage-coupled H+ secretion in the collecting duct often appears poorly applicable for rationalizing changes in H+ secretion as a function of more or less ENaC function in the collecting duct.

Effect of D,L methionine and ammonium chloride on urine acidification, urinary fractional excretion of calcium, and blood bicarbonate in clinically healthy goats.

Urinary acidification with ammonium chloride (AC) for urolith dissolution is a common treatment for goats with urolithiasis. Studies have reported increased fractional excretion of calcium (FECa) following AC administration, which could increase calcium-based urolithiasis. D,L methionine (MET) may result in similar acidification with less calcium excretion. To compare the effects of orally administered MET and AC on urine and blood pH, FECa, and blood HCO3- concentrations in male goats. Prospective, randomized, crossover study. 12 healthy, 5-to-6-month-old Boer-cross wethers were administered 200 mg/kg of AC or MET orally for 14 days with a 7-day washout period between trials. Venous blood and urine samples were collected every 2 days. The effects of treatment and treatment day on urine and blood pH, HCO3-, and FECa were assessed using linear mixed models. Ammonium chloride and MET lowered least squares means (LSM) urine pH on day 6 (LSM, 7.49; 95% CI, 6.44 to 8.54), 8 (LSM, 7.78; 95% CI, 6.73 to 8.83), and 10 (LSM, 7.53; 95% CI, 6.49 to 8.58) when compared to day 0 (LSM, 8.23; 95% CI, 7.18 to 9.28). Some goats' urine indicated acidification (pH < 7.0) in the first phase of the trial; however, for the entire trial, a significant treatment effect was not detected on urine pH, blood pH, blood HCO3- or log10 FECa. Ammonium chloride and MET acidified urine of some goats. Dietary cation-anion difference should be considered when treating healthy goats to acidify their urine.

Assessing the Influence of Urine pH on the Efficacy of Ciprofloxacin and Fosfomycin in Immunocompetent and Immunocompromised Murine Models of Escherichia coli and Klebsiella pneumoniae Infection in the Lower Urinary Tract.

In vitro studies have suggested that acidic pH may reduce and increase the efficacy of ciprofloxacin and fosfomycin, respectively, when used to treat Escherichia coli and Klebsiella pneumoniae infections. We assessed the effects of acidic, neutral, and alkaline urine pH on the efficacy of optimized ciprofloxacin and fosfomycin dosages in UTI murine model of E. coli and K. pneumoniae. Immunocompetent and immunocompromised mice with adjusted urine pH were inoculated with E. coli and K. pneumoniae strains, and the efficacy was assessed based on the bacterial concentrations in tissues and fluids at 72 h, with respect to untreated controls. At acidic urine pH, both antimicrobials were effective, achieving similar reductions in E. coli concentrations in the kidneys in immunocompetent and immunocompromised mice and in K. pneumoniae in immunocompetent mice. At a neutral urine pH, both therapies reduced the presence of E. coli in the kidneys of immunocompetent mice. However, in immunocompromised mice, antimicrobials were ineffective at treating E. coli infection in the kidneys at a neutral urine pH and showed reduced efficacy against K. pneumoniae at both acidic and neutral urine pH. The results showed no correlation between urine pH and antimicrobial efficacy, suggesting that the reduced effectiveness is associated with the animals' immunocompetence status.

Urinary D-asparagine level is decreased by the presence of glioblastoma

Gliomas, particularly glioblastomas (GBMs), pose significant challenges due to their aggressiveness and poor prognosis. Early detection through biomarkers is critical for improving outcomes. This study aimed to identify novel biomarkers for gliomas, particularly GBMs, using chiral amino acid profiling. We used chiral amino acid analysis to measure amino acid L- and D-isomer levels in resected tissues (tumor and non-tumor), blood, and urine from 33 patients with primary gliomas and 24 healthy volunteers. The levels of D-amino acid oxidase (DAO), a D-amino acid-degrading enzyme, were evaluated to investigate the D-amino acid metabolism in brain tissue. The GBM mouse model was created by transplanting GBM cells into the brain to confirm whether gliomas affect blood and urine chiral amino acid profiles. We also assessed whether D-amino acids produced by GBM cells are involved in cell proliferation. D-asparagine (D-Asn) levels were higher and DAO expression was lower in glioma than in non-glioma tissues. Blood and urinary D-Asn levels were lower in patients with GBM than in healthy volunteers (p < 0.001), increasing after GBM removal (p < 0.05). Urinary D-Asn levels differentiated between healthy volunteers and patients with GBM (area under the curve: 0.93, sensitivity: 0.88, specificity: 0.92). GBM mouse model validated the decrease of urinary D-Asn in GBM. GBM cells used D-Asn for cell proliferation. Gliomas induce alterations in chiral amino acid profiles, affecting blood and urine levels. Urinary D-Asn emerges as a promising diagnostic biomarker for gliomas, reflecting tumor presence and severity.

Preservation of urine specimens for metabolic evaluation of recurrent urinary stone formers.

Stability of concentrations of urinary stone-related metabolites was analyzed from samples of recurrent urinary stone formers to assess necessity and effectiveness of urine acidification during collection and storage. First-morning urine was collected from 20 adult calcium-stone forming patients at Tomas Bata Hospital in the Czech Republic. Urine samples were analyzed for calcium, magnesium, inorganic phosphate, uric acid, sodium, potassium, chloride, citrate, oxalate, and urine particles. The single-voided specimens were collected without acidification, after which they were divided into three groups for storage: samples without acidification ("NON"), acidification before storage ("PRE"), or acidification after storage ("POST"). The analyses were conducted on the day of arrival (day 0, "baseline"), or after storage for 2 or 7days at room temperature. The maximum permissible difference (MPD) was defined as ±20 % from the baseline. The urine concentrations of all stone-related metabolites remained within the 20 % MPD limits in NON and POST samples after 2days, except for calcium in NON sample of one patient, and oxalate of three patients and citrate of one patient in POST samples. In PRE samples, stability failed in urine samples for oxalate of three patients, and for uric acid of four patients after 2days. Failures in stability often correlated with high baseline concentrations of those metabolites in urine. Detailed procedures are needed to collect urine specimens for analysis of urinary stone-related metabolites, considering both patient safety and stability of those metabolites. We recommend specific preservation steps.

Variant analysis and PGT-M of OTC gene in a Chinese family with ornithine carbamoyltransferase deficiency

BackgroundOrnithine carbamoyltransferase deficiency (OTCD) is a kind of X-linked metabolic disease caused by a deficiency in ornithine transcarbamylase leading to urea cycle disorders. The main reason is that the OTC gene variants lead to the loss or decrease of OTC enzyme function, which hinders the ammonia conversion to urea, resulting in hyperammonemia and severe neurological dysfunction. Here, we studied one Chinese family of three generations who consecutively gave birth to two babies with OTCD. This study aims to explore the pathogenicity of two missense variants in the OTC gene and investigate the application of preimplantation genetic testing for monogenic (PGT-M) for a family troubled by Ornithine carbamoyltransferase deficiency (OTCD).MethodsThe retrospective method was used to classify the pathogenicity of two missense variants in the OTC gene in a family tortured by OTCD. Sanger sequencing was used to validate the variants in the OTC gene, and then the pathogenicity of variants was confirmed through family analysis and bioinformatics software. We used PGT-M to target the OTC gene and select a suitable embryo for transplantation. Prenatal diagnosis was recommended to confirm previous results using Sanger sequencing and karyotyping at an appropriate gestational stage. Tandem mass spectrometry (MS-MS) and gas chromatography-mass spectrometry (GC-MS) were used to detect fetal metabolism after birth. The number of the study cohort is ChiCTR2100053616.ResultsTwo missense variants, c.959G > C (p.Arg320Pro) and c.634G > A (p.Gly212Arg), were validated in the OTC gene in this family. According to the ACMG genetic variation classification criteria, the missense variant c.959G > C can be considered as “pathogenic”, and the missense variant c.634G > A can be regarded as “likely benign.” PGT-M identified a female embryo carrying the heterozygous variant c.959G > C (p.Arg320Pro), which was selected for transplantation. Prenatal diagnosis revealed the same variant in the fetus, and continued pregnancy was recommended. A female baby was born, and her blood amino acid testing and urine organic acid testing were regular. Follow-up was conducted after six months and indicated the girl was healthy.ConclusionOur research first validated the segregation of both c.959G > C and c.634G > A variants in the OTC gene in a Chinese OTCD family. Then, we classified variant c.959G > C as “pathogenic” and variant c.634G > A as “likely benign”, providing corresponding theoretical support for genetic counseling and fertility guidance in this family. PGT-M and prenatal diagnosis were recommended to help the couple receive a female baby successfully with a six-month follow-up.

Effects of pH on the Pathogenicity of Escherichia coli and Klebsiella pneumoniae on the Kidney: In Vitro and In Vivo Studies.

Urine pH reflects the functional integrity of the body and may influence the virulence of uropathogenic Escherichia coli and Klebsiella pneumoniae, the main causes of urinary tract infections (UTIs). This study evaluated the effects of acidic pH on the pathogenicity of uropathogenic E. coli and K. pneumoniae strains, in vitro and in vivo. Four uropathogenic E. coli and four K. pneumoniae strains were used. Biofilm formation, growth competition indices, motility, and adhesion and invasion of human renal cells were analyzed in media with acidic, neutral, and alkaline pH. A murine lower UTI model was used, with urine adjusted to acidic, neutral, or alkaline pH. At acidic pH, E. coli and K. pneumoniae exhibited higher bacterial concentrations in the kidneys and systemic symptoms, including bacteremia. Alkaline urine pH did not affect bacterial concentrations of any strain. In mice with UTIs caused by E. coli Nu14 and K. pneumoniae HUVR42 and acidic urine pH, histopathological studies of the kidneys showed acute inflammation affecting the urothelium and renal parenchyma, which are traits of acute pyelonephritis. These results indicate that acidic pH could increase the pathogenicity of E. coli and K. pneumoniae in murine models of lower UTI, promoting renal infection and acute inflammation.

Investigation of the Effects of N-acetylcysteine and Selenium on Vesicoureteral Reflux Nephropathy: An Experimental Study

IntroductionThis study aimed to investigate the effects of N-acetylcysteine (NAC) and selenium (Se) on vesicoureteral reflux (VUR) nephropathy. MethodsA total of 44 rabbits in 7 groups, namely group 1 (Control), group 2 (VUR + sterile urine), group 3 (VUR + sterile urine + NAC), group 4 (VUR + sterile urine + Se), group 5 (VUR + infected urine), group 6 (VUR + infected urine + NAC) and group 7 (VUR + infected urine + Se), were used. 99mTc Dimercaptosuccinic acid renal scan (DMSA), cystogram and urine culture were performed both at the beginning and end of the study. Left VUR was created surgically, and E. coli was inoculated in infected urine groups. NAC and Se were administered daily for 21 days. Malondialdehyde (MDA) measurement, inflammatory response scores (IRSs), and cicatrization response scores (CRSs) in renal tissues were evaluated. ResultsVUR did not reduce left renal uptake values in neither group 2 nor group 5. MDA levels of the left kidney were significantly higher in group 5 compared to group 1 (p = 0.001). There was no significant difference in MDA levels between group 5 and group 6, and between group 5 and group 7. Left kidney IRSs were found to be higher in all other groups except group 2 compared to the control group (p < 0.001). Left kidney CRSs were significantly higher in group 5 compared to group 2 (p = 0.026), group 6 (p < 0.001) and group 7 (p = 0.006). ConclusionA decrease in renal functions was not observed in VUR, even if there was infection. When CRSs were evaluated, NAC and Se had protective effects in terms of scar formation in VUR nephropathy. Type of StudyExperimental animal study. Levels of EvidenceN/A.

Hypocitraturia as a biomarker of renal tubular acidosis in patients with Sjögren’s disease

IntroductionSjögren’s disease (SD) is an immune-mediated chronic inflammatory disease that affects epithelial tissues, mainly salivary and lacrimal glands. It also presents extraglandular manifestations. The main renal manifestation is tubulointerstitial nephritis (TIN), which can manifest as renal tubular acidosis (RTA). Urinary citrate may be a biomarker of RTA in these patients. The objective of this study was to evaluate whether hypocitraturia is a predictive biomarker of RTA in a sample of patients with SD in a tertiary hospital in southern Brazil.MethodsAll patients with SD who met the inclusion criteria and who participated in the rheumatology outpatient clinic of the Irmandade Santa Casa de Misericórdia de Porto Alegre were included. Demographic, SD, serological and urinary data were obtained. RTA was considered in those patients who persistently presented urinary pH above 5.5 and serum pH below 7.35. Patients who persistently had urinary pH above 5.5 underwent a urinary acidification test with furosemide and fludrocortisone. These patients received 1 mg of fludrocortisone and 40 mg of furosemide and had their urine samples tested 2, 4 and 6 h after taking the medications. The test was stopped at any urine sample with pH 5.5 or less. The variables were expressed as mean and standard deviation or interquartile range. The association between hypocitraturia and RTA was assessed using the chi-square.ResultsForty-two patients were included, 95.2% female with a median age of 61.73 years. The prevalence of complete distal RTA was 4.88%. Twenty-eight patients underwent urine acidification testing. Five patients had hypocitraturia, and two of them had complete distal RTA. The association between hypocitraturia and RTA was statistically significant (p < 0.012), with a sensitivity of 100%, specificity of 91.2% and accuracy of 91.7%. The negative predictive value was 100%. The global renal assessment of the population demonstrated two patients with RTA, one patient with decreased renal function and six patients with proteinuria greater than 0.5 g/24 h.ConclusionThe prevalence of RTA in the studied population was 4.88%. Hypocitraturia had high sensitivity and accuracy for the diagnosis of RTA.

Cannabinoid receptor type 1 activation causes a water diuresis by inducing an acute central diabetes insipidus in mice.

Cannabis and synthetic cannabinoid consumption are increasing worldwide. Cannabis contains numerous phytocannabinoids that act on the G protein-coupled cannabinoid receptor type 1 (CB1R) and cannabinoid receptor type 2 expressed throughout the body, including the kidney. Essentially every organ, including the kidney, produces endocannabinoids, which are endogenous ligands to these receptors. Cannabinoids acutely increase urine output in rodents and humans, thus potentially influencing total body water and electrolyte homeostasis. As the kidney collecting duct (CD) regulates total body water, acid/base, and electrolyte balance through specific functions of principal cells (PCs) and intercalated cells (ICs), we examined the cell-specific immunolocalization of CB1R in the mouse CD. Antibodies against either the C-terminus or N-terminus of CB1R consistently labeled aquaporin 2 (AQP2)-negative cells in the cortical and medullary CD and thus presumably ICs. Given the well-established role of ICs in urinary acidification, we used a clearance approach in mice that were acid loaded with 280 mM NH4Cl for 7 days and nonacid-loaded mice treated with the cannabinoid receptor agonist WIN55,212-2 (WIN) or a vehicle control. Although WIN had no effect on urinary acidification, these WIN-treated mice had less apical + subapical AQP2 expression in PCs compared with controls and developed acute diabetes insipidus associated with the excretion of large volumes of dilute urine. Mice maximally concentrated their urine when WIN and 1-desamino-8-d-arginine vasopressin [desmopressin (DDAVP)] were coadministered, consistent with central rather than nephrogenic diabetes insipidus. Although ICs express CB1R, the physiological role of CB1R in this cell type remains to be determined.NEW & NOTEWORTHY The CB1R agonist WIN55,212-2 induces central diabetes insipidus in mice. This research integrates existing knowledge regarding the diuretic effects of cannabinoids and the influence of CB1R on vasopressin secretion while adding new mechanistic insights about total body water homeostasis. Our findings provide a deeper understanding about the potential clinical impact of cannabinoids on human physiology and may help identify targets for novel therapeutics to treat water and electrolyte disorders such as hyponatremia and volume overload.

#1905 Sex differences in primary distal renal tubular acidosis: a single-centre retrospective study

Abstract Background and Aims The kidney has been described as one of the most estrogen-responsive organs after reproductive ones. Many non-X-linked renal diseases present with sex differences. Although not completely elucidated, an influence of estrogens has been described in several transporters along the renal tubule such as the Na+/phosphate cotransporter (NaPi-IIa) in the proximal tubule, the Na+/K+/2Cl⁻ cotransporter (NKCC) in the thick ascending limb of the loop of Henle, the thiazide-sensitive Na+/Cl⁻ cotransporter (NCC) in the distal convoluted tubule and the epithelial sodium channel (ENaC) expressed by the principal cells of the collecting duct. Our study aimed to investigate possible phenotypic sex differences over the natural history of primary distal renal tubular acidosis (dRTA), a rare genetic condition characterized by impaired urinary acidification in the collecting duct that results in non-anion gap metabolic acidosis, hypokalemia, hypercalciuria, nephrolithiasis and nephrocalcinosis, which can lead to chronic kidney disease (CKD). Method We included a cohort of 31 genetically confirmed dRTA patients (19 women and 12 men) followed at the London Tubular Centre. We retrospectively collected data from 2012 to 2023. Estimated glomerular filtration rate (eGFR) was calculated with the CKD-EPIcr formula. Hypokalemia was defined as serum potassium &amp;lt; 3.5 mmol/L, hypercalciuria was defined as urinary calcium/creatinine (uCa/Cr) &amp;gt; 0.7 mmol/mmol and acidosis was defined as HCO3− ≤ 22 mmol/L. Data were analyzed using non-parametric Mann-Whitney as appropriate (Prism GraphPad 8.0.2). A p value &amp;lt; 0.05 was considered as statistically significant. Results Baseline characteristics and prevalence of different mutations are shown in Table 1. At baseline, both cohorts were young, with preserved kidney function. 60% of women were acidotic compared to 50% of men, and 30% of men were hypokalemic compared to 8% of women. The majority of patients in both cohorts presented with overt hypercalciuria (60% of women vs 90% of men). Prevalence of nephrolithiasis and nephrocalcinosis was similar among women and men. At baseline, no statistically significant difference between sexes was found for serum or urinary parameters. Interestingly, men exhibited a tendency towards higher annual mean slope of eGFR (−3.3 ± 2.5 mL/min/1.73 m2) compared to women (−0.5 ± 1.5 mL/min/1.73 m2) in a statistically significant fashion (Fig. 1a). Although not statically significant, we noticed a tendency towards higher fractional excretion of phosphate (FEPO4) (Fig. 1b) and dyslipidemia in men (Fig. 1c). There was no difference in PTH between the two groups (Fig. 1c). Conclusion Men affected by primary dRTA are at increased risk of CKD progression, tend to have a more severe phenotype at baseline and appear to be more dyslipidemic than women. This is consistent with findings in the literature that report accelerated CKD progression and higher cardiovascular morbidity and mortality in men. To our knowledge, this is the first study reporting sex differences in primary dRTA.

Regulation of renal acid-base balance by Epac isoforms in proximal tubule and collecting duct

Proper regulation of acid-base homeostasis has utmost significance for well-being and survival of the living organisms. Up to 50% of emergency room patients have notable disturbances in pH and associated morbific manifestations, which impedes effective treatment. Kidneys play a central role in regulation of acid-base balance by reabsorbing HCO3− via NHE-3 in the proximal tubule (PT) and secreting H+ via V-ATPase pump by the intercalated cells of collecting duct (CD). Exchange proteins directly activated by cAMP (Epac) are most prominently expressed in the proximal tubule and collecting ducts, the sites critical for acid-base transport in the renal tubule. However, the significance and physiological relevance of Epac isoforms (Epac1 and Epac2) for controlling HCO3− reabsorption and H+ secretion and by extension, the systemic pH regulation is not known. Here, we used transgenic mouse models lacking both or individual Epac1 and Epac2 isoforms to examine the systemic adaptation to acid-base insults and to inquire on the perturbed molecular signaling mechanisms and end-effectors in freshly isolated split-opened PTs and CDs using biochemical and fluorescent imaging tools. Deletion of Epac1&amp;2 caused a dramatic decrease in NHE-3 protein levels in an additive manner. Moreover, we detected a marked redistribution of NHE-3 to the base of brush border in proximal tubule cells rendering its inactivation. Consistently, NHE-3 activity was more than 70% decreased upon Epac1&amp;2 deletion, as was assessed by a rate of recovery after intracellular acidification in freshly isolated split-opened PTs. Furthermore, V-ATPase activity was similarly decreased in A-type of intercalated cells in freshly isolated CDs despite compensatory accumulation on the apical side, as monitored with confocal microscopy in cortical and medullary kidney sections of the knockout. In unstressed conditions, Epac1&amp;2 deletion did not affect arterial pH and HCO3− levels, while urinary pH was significantly reduced. Dietary acid load (280 mM NH4Cl in drinking water for 3 days) unmasked severe hyperchloremic metabolic acidosis with pH 7.17±0.01 and HCO3− 14.5±0.6 mM and impaired urinary acidification. Deletion of Epac2 alone recapitulated the phenotype of double knockout, whereas Epac1−/− mice did not demonstrate notable deficiencies in response to dietary acid load. Overall, we concluded that Epac signaling plays a major role in urinary acidification with the dominant contribution of Epac2 isoform by regulating acid-base transport in both proximal tubule (via NHE-3) and the collecting duct (via V-ATPase). Epac1&amp;2 and Epac2 deletion of impairs renal adaptation to the acid load resulting in severe metabolic acidosis. This research was supported by NIH-NIDDK DK117865, DK119170, AHA EIA35260097 (to O. Pochynyuk) and AHA-23POST1020372 (to K. Pyrshev). 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.

Lithium-Induced Disruption of Intracellular Ca2+ Balance in the Collecting Duct Intercalated Cells Contributes to Metabolic Acidosis in Mice

INTRODUCTION. Lithium (Li+) is an effective mood stabilizer that continues to be widely used in modern psychiatric practice. One of the most common adverse effects of Li+ therapy is nephrogenic diabetes insipidus manifesting in reduced urinary concentrating ability due to impaired vasopressin (AVP) signaling in the collecting duct principal cells. While distal tubular acidosis has also been reported in patients receiving Li+, molecular determinants underlying the pathophysiological effects of Li+ on the collecting duct intercalated cells and renal acid-base transport remain to be fully elucidated. Activation of Gq-coupled vasopressin 1a receptors (V1aR) in A-intercalated cells reportedly induces intracellular Ca2+ ([Ca2+]i) mobilization and stimulates luminal H+ secretion, resulting in urine acidification. OBJECTIVE. The objective of this study was to test if Li+ impaired V1aR-induced [Ca2+]i response in the intercalated cells of murine collecting ducts. HYPOTHESIS. We hypothesized that Li+ markedly impaired V1aR-dependent [Ca2+]i signaling in A-intercalated cells causing the reduction of luminal proton secretion in the collecting duct. METHODS. We combined immunofluorescent imaging in freshly isolated collecting duct segments with metabolic cage studies in C57BL/6NJ (Jackson Labotatory) mice receiving a regular Teklad 2918 chow (control) or a Teklad 2918-based diet containing 0.3% lithium carbonate (Li+-treated) to evaluate how Li+ affects V1aR-mediated [Ca2+]i signal, H+ transport by intercalated cells, as well as urinary pH and ammonia excretion. RESULTS. We found that AVP elicited a transient [Ca2+]i response in the aquaporin-2 (AQP2) negative cells from collecting duct segments isolated from control mice. The response was mediated by Ca2+ release from the endoplasmic reticulum (ER), as it was inhibited by pretreatment of collecting duct segments with thapsigargin, a SERCA pump inhibitor. The amplitude of the AVP-induced calcium transient was 4 times lower in the AQP2-negative cells isolated from Li+-treated mice. Li+ intake remarkably facilitated store-operated calcium entry (SOCE) in the collecting duct cells, indicating chronic ER depletion and stress. At the systemic level Li+-treated mice exhibited urine alkalinization (by 0.8 pH units) and a 6-fold elevation in urinary ammonium excretion, when compared to controls. CONCLUSIONS. Intracellular Ca2+ signaling in the intercalated cells is an essential determinant of acid-base handling in the collecting duct. Our findings reveal that Li+ markedly alters [Ca2+]i signaling in the intercalated cells, causing urine alkalinization and elevated ammonium excretion, likely, to compensate for ensuing metabolic acidosis. NIDDK R01DK125464. 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.