Renal Bicarbonate Research Articles

The Role of the Endocrine System in the Regulation of Acid-Base Balance by the Kidney and the Progression of Chronic Kidney Disease.

Systemic acid-base status is primarily determined by the interplay of net acid production (NEAP) arising from metabolism of ingested food stuffs, buffering of NEAP in tissues, generation of bicarbonate by the kidney, and capture of any bicarbonate filtered by the kidney. In chronic kidney disease (CKD), acid retention may occur when dietary acid production is not balanced by bicarbonate generation by the diseased kidney. Hormones including aldosterone, angiotensin II, endothelin, PTH, glucocorticoids, insulin, thyroid hormone, and growth hormone can affect acid-base balance in different ways. The levels of some hormones such as aldosterone, angiotensin II and endothelin are increased with acid accumulation and contribute to an adaptive increase in renal acid excretion and bicarbonate generation. However, the persistent elevated levels of these hormones can damage the kidney and accelerate progression of CKD. Measures to slow the progression of CKD have included administration of medications which inhibit the production or action of deleterious hormones. However, since metabolic acidosis accompanying CKD stimulates the secretion of several of these hormones, treatment of CKD should also include administration of base to correct the metabolic acidosis.

Loss of the Secretin Receptor Impairs Renal Bicarbonate Excretion and Aggravates Metabolic Alkalosis in Mice during Acute Base-Loading.

During acute base excess, the renal collecting duct β -intercalated cells ( β -ICs) become activated to increase urine base excretion. This process is dependent on pendrin and cystic fibrosis transmembrane regulator (CFTR) expressed in the apical membrane of β -ICs. The signal that leads to activation of this process was unknown. Plasma secretin levels increase during acute alkalosis, and the secretin receptor (SCTR) is functionally expressed in β -ICs. We find that mice with global knockout for the SCTR lose their ability to acutely increase renal base excretion. This forces the mice to lower their ventilation to cope with this challenge. Our findings suggest that secretin is a systemic bicarbonate-regulating hormone, likely being released from the small intestine during alkalosis. The secretin receptor (SCTR) is functionally expressed in the basolateral membrane of the β -intercalated cells of the kidney cortical collecting duct and stimulates urine alkalization by activating the β -intercalated cells. Interestingly, the plasma secretin level increases during acute metabolic alkalosis, but its role in systemic acid-base homeostasis was unclear. We hypothesized that the SCTR system is essential for renal base excretion during acute metabolic alkalosis. We conducted bladder catheterization experiments, metabolic cage studies, blood gas analysis, barometric respirometry, perfusion of isolated cortical collecting ducts, immunoblotting, and immunohistochemistry in SCTR wild-type and knockout (KO) mice. We also perfused isolated rat small intestines to study secretin release. In wild-type mice, secretin acutely increased urine pH and pendrin function in isolated perfused cortical collecting ducts. These effects were absent in KO mice, which also did not sufficiently increase renal base excretion during acute base loading. In line with these findings, KO mice developed prolonged metabolic alkalosis when exposed to acute oral or intraperitoneal base loading. Furthermore, KO mice exhibited transient but marked hypoventilation after acute base loading. In rats, increased blood alkalinity of the perfused upper small intestine increased venous secretin release. Our results suggest that loss of SCTR impairs the appropriate increase of renal base excretion during acute base loading and that SCTR is necessary for acute correction of metabolic alkalosis. In addition, our findings suggest that blood alkalinity increases secretin release from the small intestine and that secretin action is critical for bicarbonate homeostasis.

Utility of 6% hydroxyethyl starch 130/0.4 in oral cancer surgeries with a duration of over 6 hours: A retrospective case-control study.

To evaluate the utility of 6% hydroxyethyl starch (HES) 130/0.4 in oral cancer surgeries with durations over 6 hours. Using a case-control study design, the investigators enrolled patients who underwent oral cancer surgery involving osteotomy or manipulation near the major blood vessels at the Department of Orofacial Surgery in our hospital between 2017 and 2020. The predictor variable was 6% HES130/0.4. Outcomes included in-out balance and other postoperative parameters pertaining to circulatory maintenance (blood loss, urine volume, infusion volume, blood transfusion volume, albumin dose, hemoglobin levels, blood albumin levels, and doses of vasopressors used to maintain blood pressure), as well as pre- and postoperative renal function, pH, bicarbonate levels, and base excess. Changes in renal function were evaluated by assessing blood urea nitrogen and creatinine levels before surgery and at 1 and 7 days postoperatively. The Mann-Whitney U test was used for between-group comparisons, and Student t test was used for intragroup comparisons. The statistical significance was set at P < .05. A total of 65 patients underwent oral cancer surgery with a duration over 6 hours during the study period. The administration of 6% HES130/0.4 at 22.1 ± 7.5 mL/kg/day did not increase blood loss or the blood transfusion volume. Moreover, patients who were administered 6% HES130/0.4 had a significantly larger mean urine volume and infusion volume than those who were not administered 6% HES130/0.4. The infusion therapy could maintain the urine volume and did not worsen renal function. The results of this study showed that administration of 6% HES130/0.4 at a dose lower than 25 mL/kg in patients undergoing oral cancer surgery over 6 hours was effective for circulation maintenance but did not increase the intraoperative blood loss or transfusion volume. This treatment did not cause any dilutional metabolic acidosis or renal dysfunction.

Effect of 5 weeks of oral acetazolamide on patients with pulmonary vascular disease: A randomized, double-blind, cross-over trial

BackgroundThe carbonic anhydrase inhibitor acetazolamide stimulates ventilation through metabolic acidosis mediated by renal bicarbonate excretion. In animal models, acetazolamide attenuates acute hypoxia-induced pulmonary hypertension (PH), but its efficacy in treating patients with PH due to pulmonary vascular disease (PVD) is unknown. Methods28 PVD patients (15 pulmonary arterial hypertension, 13 distal chronic thromboembolic PH), 13 women, mean±SD age 61.6±15.0 years stable on PVD medications, were randomised in a double-blind crossover protocol to 5 weeks acetazolamide (250mg b.i.d) or placebo separated by a ≥2 week washout period. Primary endpoint was the change in 6-minute walk distance (6MWD) at 5 weeks. Additional endpoints included safety, tolerability, WHO functional class, quality of life, arterial blood gases, and hemodynamics (by echocardiography). ResultsAcetazolamide had no effect on 6MWD compared to placebo (treatment effect: mean change [95%CI] -18 [-40 to 4]m, p=0.102) but increased arterial blood oxygenation through hyperventilation induced by metabolic acidosis. Other measures including pulmonary hemodynamics were unchanged. No severe adverse effects occurred, side effects that occurred significantly more frequently with acetazolamide vs. placebo were change in taste (22/0%), paraesthesia (37/4%) and mild dyspnea (26/4%). ConclusionsIn patients with PVD, acetazolamide did not change 6MWD compared to placebo despite improved blood oxygenation. Some patients reported a tolerable increase in dyspnoea during acetazolamide treatment, related to hyperventilation, induced by the mild drug-induced metabolic acidosis. Our findings do not support the use of acetazolamide to improve exercise in patients with PVD at this dosing. ClinicalTrials.gov IdentifierNCT02755298

Renal fluid and acid/base balance during refeeding in restrictive eating disorders.

Fluid shifts have been ascribed to central diabetes insipidus in patients with anorexia nervosa hospitalized for refeeding. Recent data, however, suggest that vasopressin production is not dysregulated in this population. Our objective was to describe the trajectory of fluid imbalances in relationship to kidney function, electrolyte disturbances, and acid/base balance during refeeding. A retrospective review of daily fluid balance and biochemical values was performed in 70 sequential unique patients admitted to University of California at Los Angeles Hospital Medical Stabilization Program for Eating Disorders from December 2018 to November 2020. Participants (2 males/68 females) were between 10 and 24 years of age and with a median body mass index of 16.1 (14.3, 18.1) kg/m2 . A severe negative fluid balance (>-900 ml/day) was observed in 80% of patients at some point during hospitalization. Serum sodium concentrations were normal on admission and remained stable during refeeding. Serum bicarbonate concentrations were 25 ± 1mEq/dl on admission and increased above the normal range in 31% of patients. Metabolic alkalosis was inversely associated with the development of a negative fluid balance. Estimated glomerular filtration rate was impaired in 54% of patients, improved with refeeding, and was not associated with the development of a severe negative fluid balance or metabolic alkalosis. Chronic energy deprivation alters the physiology of renal fluid and bicarbonate handling in ways that are independent of vasopressin and glomerular filtration. Further studies are warranted to understand the renal adaptations that occur during energy restriction and subsequent refeeding. Massive urinary fluid losses occur in patients with restrictive eating disorders hospitalized for refeeding. In addition, many patients have impaired renal bicarbonate excretion. These findings suggest that chronic energy deprivation impairs the kidney's ability to handle the shifts in fluid and acid/base balance that occur when appropriate oral nutrition is re-introduced.

Oxidized alkyl phospholipids stimulate sodium transport in proximal tubules via a nongenomic PPARγ-dependent pathway

Oxidized phospholipids have been shown to exhibit pleiotropic effects in numerous biological contexts. For example, 1-O-hexadecyl-2-azelaoyl-sn-glycero-3-phosphocholine (azPC), an oxidized phospholipid formed from alkyl phosphatidylcholines, is a peroxisome proliferator–activated receptor gamma (PPARγ) nuclear receptor agonist. Although it has been reported that PPARγ agonists including thiazolidinediones can induce plasma volume expansion by enhancing renal sodium and water retention, the role of azPC in renal transport functions is unknown. In the present study, we investigated the effect of azPC on renal proximal tubule (PT) transport using isolated PTs and kidney cortex tissues and also investigated the effect of azPC on renal sodium handling in vivo. We showed using a microperfusion technique that azPC rapidly stimulated Na+/HCO3− cotransporter 1 (NBCe1) and luminal Na+/H+ exchanger (NHE) activities in a dose-dependent manner at submicromolar concentrations in isolated PTs from rats and humans. The rapid effects (within a few minutes) suggest that azPC activates NBCe1 and NHE via nongenomic signaling. The stimulatory effects were completely blocked by specific PPARγ antagonist GW9662, ERK kinase inhibitor PD98059, and CD36 inhibitor sulfosuccinimidyl oleate. Treatment with an siRNA against PPAR gamma completely blocked the stimulation of both NBCe1 and NHE by azPC. Moreover, azPC induced ERK phosphorylation in rat and human kidney cortex tissues, which were completely suppressed by GW9662 and PD98059 treatments. These results suggest that azPC stimulates renal PT sodium-coupled bicarbonate transport via a CD36/PPARγ/mitogen-activated protein/ERK kinase/ERK pathway. We conclude that the stimulatory effects of azPC on PT transport may be partially involved in volume expansion.

Hypertrophic pyloric stenosis masked by kidney failure in a male infant with a contiguous gene deletion syndrome at Xp22.31 involving the steroid sulfatase gene: case report

BackgroundContiguous gene deletion syndrome at Xp22.3 resulting in nullisomy in males or Turner syndrome patients typically encompasses the steroid sulfatase gene (STS) and contiguously located other genes expanding the phenotype. In large deletions, that encompass also the Kallmann syndrome 1 gene (KAL1), occasionally infantile hypertrophic pyloric stenosis (IHPS) and congenital anomalies of the kidney and urinary tract (CAKUT) have been reported.Patient presentationWe report on a male newborn with family history in maternal uncle of renal abnormalities and short stature still without ichthyosiform dermatosis. The baby presented CAKUT with kidney failure and progressive vomiting. Renal bicarbonate loss masked hypochloremic and hypokalemic metabolic alkalosis classically present in IHPS and delayed its diagnosis. Antropyloric ultrasound examination and cystourethrography were diagnostic. After Fredet-Ramstedt extramucosal pyloromyotomy feeding and growing was regular and he was discharged home. Comparative whole-genome hybridization detected a maternal inherited interstitial deletion of 1.56 Mb on Xp22.31(6,552,712_8,115,153) × 0 involving the STS gene, but not the KAL1 gene.ConclusionsAberrant cholesterol sulfate storage due to STS deletion as the underlying pathomechanism is not limited to oculocutaneous phenotypes but could also lead to co-occurrence of both IHPS and kidney abnormalities, as we report. Thus, although these two latter pathologies have a high incidence in the neonatal age, their simultaneous association in our patient is resembling not a chance but a real correlation expanding the clinical spectrum associated with Xp22.31 deletions.

METABOLIC ALKALOSIS DRIVING RESPIRATORY FAILURE IN POST ACUTECOVID-19 SYNDROME

TOPIC: Pulmonary Physiology TYPE: Medical Student/Resident Case Reports INTRODUCTION: Survival of the acute phase of COVID-19 infection can leave patients with multiple long-term sequelae described as Post-acute covid-19 syndrome (PACS). We present a case of a patient with PACS manifested as pulmonary fibrosis, carbon dioxide retention and difficulty weaning from BIPAP that experienced dramatic improvement following treatment with Acetazolamide. CASE PRESENTATION: 66-year-old female presented for 7 days of worsening cough and shortness of breath. She was found to be hypoxic on presentation with COVID-19 test resulting positive and was admitted. Her hospital course was complicated by rapid increase in oxygen requirements with the initiation of BIPAP on hospital day 19. At this time, arterial blood gas (ABG) revealed mixed respiratory acidosis and metabolic alkalosis with pH 7.41, CO2 77 and HCO3 of 43. She was continued on BIPAP for several days before being weaned to high flow nasal cannula. On hospital day 44 she was noted to be increasingly lethargic. ABG obtained at this time showed pH of 7.3, CO2 >110 and HCO3 of 68. She was placed back on BIPAP and serial ABGs were monitored. At about 12 hours after the initiation of BIPAP, she developed a post-hypercapnic alkalosis with ABG demonstrating pH 7.46, CO2 90 and HCO3 50. At this time, BIPAP was stopped and Acetazolamide was administered at 500mg IV daily for 2 days.The patient experienced significant improvement in her mental status and work of breathing. She was weaned to nasal cannula. An ABG obtained the day following the second acetazolamide dose showed improvement in both metabolic alkalosis and respiratory acidosis with pH 7.42, CO2 62 and HCO3 34. DISCUSSION: The role of correcting metabolic alkalosis in hypercapnic respiratory failure has been described over the years. Trials conducted have utilized the carbonic anhydrase inhibitor Acetazolamide to promote renal bicarbonate excretion with goal statistical endpoints of early liberation from mechanical ventilation, reduced hospital stay or mortality but have generally failed to demonstrate statistically significant benefit.In the DIABOLO trial, mechanically ventilated COPD patients with metabolic alkalosis were assigned to either Acetazolamide infusion or placebo. The study concluded without statistically significant benefit in the primary outcome (duration of mechanical ventilation) or important secondary outcomes such as ICU mortality or ICU length of stay. However, the average serum bicarbonate level was only 27 between the two groups. This leads to the question if acetazolamide may have benefits in specific patients with a more severe alkalosis in the right clinical context as shown in this case study. CONCLUSIONS: Alkalosis may surpass compensation and perpetuate hypercapnic respiratory failure. This may be especially common ARDS patients managed with a fluid restricted approach. Administration of acetazolamide may benefit appropriately selected patients. REFERENCE #1: Nalbandian A, Sehgal K, Gupta A, et al. Post-acute COVID-19 syndrome. Nat Med. Published online March 22, 2021. doi:10.1038/s41591-021-01283-z REFERENCE #2: Faisy C, Meziani F, Planquette B, et al. Effect of Acetazolamide vs Placebo on Duration of Invasive Mechanical Ventilation Among Patients With Chronic Obstructive Pulmonary Disease: A Randomized Clinical Trial. JAMA. 2016;315(5):480-488. doi:10.1001/jama.2016.0019 REFERENCE #3: Adamson R, Swenson ER. Acetazolamide Use in Severe Chronic Obstructive Pulmonary Disease. Pros and Cons. Ann Am Thorac Soc. 2017;14(7):1086-1093. doi:10.1513/AnnalsATS.201701-016FR DISCLOSURES: No relevant relationships by Jackson Heilbronn, source=Web Response no disclosure on file for Christina Kwon;No relevant relationships by Michael Ulrich, source=Web Response

A role for tubular Na+/H+ exchanger NHE3 in the natriuretic effect of the SGLT2 inhibitor empagliflozin.

Inhibitors of proximal tubular Na+-glucose cotransporter 2 (SGLT2) are natriuretic, and they lower blood pressure. There are reports that the activities of SGLT2 and Na+-H+ exchanger 3 (NHE3) are coordinated. If so, then part of the natriuretic response to an SGLT2 inhibitor is mediated by suppressing NHE3. To examine this further, we compared the effects of an SGLT2 inhibitor, empagliflozin, on urine composition and systolic blood pressure (SBP) in nondiabetic mice with tubule-specific NHE3 knockdown (NHE3-ko) and wild-type (WT) littermates. A single dose of empagliflozin, titrated to cause minimal glucosuria, increased urinary excretion of Na+ and bicarbonate and raised urine pH in WT mice but not in NHE3-ko mice. Chronic empagliflozin treatment tended to lower SBP despite higher renal renin mRNA expression and lowered the ratio of SBP to renin mRNA, indicating volume loss. This effect of empagliflozin depended on tubular NHE3. In diabetic Akita mice, chronic empagliflozin enhanced phosphorylation of NHE3 (S552/S605), changes previously linked to lesser NHE3-mediated reabsorption. Chronic empagliflozin also increased expression of genes involved with renal gluconeogenesis, bicarbonate regeneration, and ammonium formation. While this could reflect compensatory responses to acidification of proximal tubular cells resulting from reduced NHE3 activity, these effects were at least in part independent of tubular NHE3 and potentially indicated metabolic adaptations to urinary glucose loss. Moreover, empagliflozin increased luminal α-ketoglutarate, which may serve to stimulate compensatory distal NaCl reabsorption, while cogenerated and excreted ammonium balances urine losses of this "potential bicarbonate." The data implicate NHE3 as a determinant of the natriuretic effect of empagliflozin.

Proteomic analysis in lupus mice identifies Coronin-1A as a potential biomarker for lupus nephritis

BackgroundApproximately 50% of systemic lupus erythematosus (SLE) patients develop nephritis, which is among the most severe and frequent complications of the disease and a leading cause of morbidity and mortality. Despite intensive research, there are still no reliable lupus nephritis (LN) markers in clinical use that can assess renal damage and activity with a high sensitivity and specificity. To this end, the aim of this study was to identify new clinically relevant tissue-specific protein biomarkers and possible underlying molecular mechanisms associated with renal involvement in SLE, using mass spectrometry (MS)-based proteomics.MethodsKidneys were harvested from female triple congenic B6.NZMsle1/sle2/sle3 lupus mice model, and the respective sex- and age-matched C57BL/6 control mice at 12, 24 and 36 weeks of age, representing pre-symptomatic, established and end-stage LN, respectively. Proteins were extracted from kidneys, purified, reduced, alkylated and digested by trypsin. Purified peptides were separated by liquid chromatography and analysed by high-resolution MS. Data were processed by the Progenesis QIp software, and functional annotation analysis was performed using DAVID bioinformatics resources. Immunofluorescence and multiple reaction monitoring (MRM) MS methods were used to confirm prospective biomarkers in SLE mouse strains as well as human serum samples.ResultsProteomic profiling of kidney tissues from SLE and control mice resulted in the identification of more than 3800 unique proteins. Pathway analysis revealed a number of dysregulated molecular pathways that may be mechanistically involved in renal pathology, including phagosome and proximal tubule bicarbonate reclamation pathways. Proteomic analysis supported by human transcriptomic data and pathway analysis revealed Coronin-1A, Ubiquitin-like protein ISG15, and Rho GDP-dissociation inhibitor 2, as potential LN biomarkers. These results were further validated in other SLE mouse strains using MRM-MS. Most importantly, experiments in humans showed that measurement of Coronin-1A in human sera using MRM-MS can segregate LN patients from SLE patients without nephritis with a high sensitivity (100%) and specificity (100%).ConclusionsThese preliminary findings suggest that serum Coronin-1A may serve as a promising non-invasive biomarker for LN and, upon validation in larger cohorts, may be employed in the future as a screening test for renal disease in SLE patients.

Carbonic anhydrase inhibition and chemoreflex control of breathing: A litmus test for methazolamide as a viable alternative to acetazolamide.

Carbonic anhydrase inhibition and chemoreflex control of breathing: A litmus test for methazolamide as a viable alternative to acetazolamide.

Abstract P2038: A Nobel I551F Mutant of Sodium Handling Transporter NBCe1 Has Cytosolic Retention and Diminishes Transport Activity

The electrogenic Na + /HCO 3 - cotransporter NBCe1 is expressed in many organs and controls sodium handling. NBCe1 homozygous mutation causes not only severe hypotension but also proximal renal tubular acidosis in human and rodents. Here we shows the functional significance of the mutations reported from NCBI database on NBCe1 function. We identified 14 mutations in NBCe1 variant A(kidney type), resulting in the single amino acid substitutions, A425T, F461L, A465S, L494F, N503H, A518T, A518G, I523V, V533D, Y535H, I551F, Y554H, M753V, and L785I. Immunocytological analysis with confocal microscopy revealed only I551F mutant was expressed predominantly in the cytoplasm of HEK 293 cells and MDCK cells. Functional analysis using Xenopus oocytes revealed that I551F mutant had a significantly reduced activity corresponding to 52% of that of wild-type (p&lt;0.01). Whole and biotinylated western blotting in HEK293 cells confirmed that the surface expression of I551F mutant was significantly reduced. Deglycosylation study revealed that I551F has impaired N-glycosylation. To examine the role of I551 in more detail, we also examined the properties of artificial mutants I551A, I551P, I551K, I551R, I551D and I551E in HEK293 and MDCK cells. All of artificial mutants were properly expressed in the plasma membrane. By contrast, only I551F mutant was predominantly expressed in cytoplasmic regions. These results indicate that I551F mutation inactivates the NBCe1 function with cytoplasmic retention. Because NBCe1 plays a major role in renal proximal sodium and bicarbonate reabsorption, I551F mutation may be associated with the disturbance in systemic acid-base balance or the changes in blood pressure.

Carbonic anhydrase inhibitors in patients with respiratory failure and metabolic alkalosis: a systematic review and meta-analysis of randomized controlled trials

BackgroundMetabolic alkalosis is common in patients with respiratory failure and may delay weaning in mechanically ventilated patients. Carbonic anhydrase inhibitors block renal bicarbonate reabsorption, and thus reverse metabolic alkalosis. The objective of this systematic review is to assess the benefits and harms of carbonic anhydrase inhibitor therapy in patients with respiratory failure and metabolic alkalosis.MethodsWe searched the following electronic sources from inception to August 2017: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and SCOPUS. Randomized clinical trials were included if they assessed at least one of the following outcomes: mortality, duration of hospital stay, duration of mechanical ventilation, adverse events, and blood gas parameters. Teams of two review authors worked in an independent and duplicate manner to select eligible trials, extract data, and assess risk of bias of the included trials. We used meta-analysis to synthesize statistical data and then assessed the certainty of evidence using the GRADE methodology.ResultsSix eligible studies were identified with a total of 564 participants. The synthesized data did not exclude a reduction or an increase in mortality (risk ratio (RR) 0.94, 95% confidence interval (CI) 0.57 to 1.56) or in duration of hospital stay (mean difference (MD) 0.42 days, 95% CI −4.82 to 5.66) with the use of carbonic anhydrase inhibitors. Carbonic anhydrase inhibitor therapy resulted in a decrease in the duration of mechanical ventilation of 27 h (95% CI −50 to −4). Also, it resulted in an increase in PaO2 (MD 11.37 mmHg, 95% CI 4.18 to 18.56) and a decrease in PaCO2 (MD −4.98 mmHg, 95% CI −9.66, −0.3), serum bicarbonate (MD −5.03 meq/L, 95% CI −6.52 to −3.54), and pH (MD −0.04, 95% CI −0.07 to −0.01). There was an increased risk of adverse events in the carbonic anhydrase inhibitor group (RR 1.71, 95% CI 0.98 to 2.99). Certainty of evidence was judged to be low for most outcomes.ConclusionIn patients with respiratory failure and metabolic alkalosis, carbonic anhydrase inhibitor therapy may have favorable effects on blood gas parameters. In mechanically ventilated patients, carbonic anhydrase inhibitor therapy may decrease the duration of mechanical ventilation. A major limitation of this finding was that only two trials assessed this clinically important outcome.

A mouse model of pseudohypoaldosteronism type II reveals a novel mechanism of renal tubular acidosis

Pseudohypoaldosteronism type II (PHAII) is a genetic disease characterized by association of hyperkalemia, hyperchloremic metabolic acidosis, hypertension, low renin, and high sensitivity to thiazide diuretics. It is caused by mutations in the WNK1, WNK4, KLHL3 or CUL3 gene. There is strong evidence that excessive sodium chloride reabsorption by the sodium chloride cotransporter NCC in the distal convoluted tubule is involved. WNK4 is expressed not only in distal convoluted tubule cells but also in β-intercalated cells of the cortical collecting duct. These latter cells exchange intracellular bicarbonate for external chloride through pendrin, and therefore, account for renal base excretion. However, these cells can also mediate thiazide-sensitive sodium chloride absorption when the pendrin-dependent apical chloride influx is coupled to apical sodium influx by the sodium-driven chloride/bicarbonate exchanger. Here we determine whether this system is involved in the pathogenesis of PHAII. Renal pendrin activity was markedly increased in a mouse model carrying a WNK4 missense mutation (Q562E) previously identified in patients with PHAII. The upregulation of pendrin led to an increase in thiazide-sensitive sodium chloride absorption by the cortical collecting duct, and it caused metabolic acidosis. The function of apical potassium channels was altered in this model, and hyperkalemia was fully corrected by pendrin genetic ablation. Thus, we demonstrate an important contribution of pendrin in renal regulation of sodium chloride, potassium and acid-base homeostasis and in the pathophysiology of PHAII. Furthermore, we identify renal distal bicarbonate secretion as a novel mechanism of renal tubular acidosis.

Sodium bicarbonate cotransporter NBCe2 gene variants increase sodium and bicarbonate transport in human renal proximal tubule cells.

RationaleSalt sensitivity of blood pressure affects >30% of the hypertensive and >15% of the normotensive population. Variants of the electrogenic sodium bicarbonate cotransporter NBCe2 gene, SLC4A5, are associated with increased blood pressure in several ethnic groups. SLC4A5 variants are also highly associated with salt sensitivity, independent of hypertension. However, little is known about how NBCe2 contributes to salt sensitivity, although NBCe2 regulates renal tubular sodium bicarbonate transport. We hypothesized that SLC4A5 rs10177833 and rs7571842 increase NBCe2 expression and human renal proximal tubule cell (hRPTC) sodium transport and may be a cause of salt sensitivity of blood pressure.ObjectiveTo characterize the hRPTC ion transport of wild-type (WT) and homozygous variants (HV) of SLC4A5.Methods and resultsThe expressions of NBCe2 mRNA and protein were not different between hRPTCs carrying WT or HV SLC4A5 before or after dopaminergic or angiotensin (II and III) stimulation. However, luminal to basolateral sodium transport, NHE3 protein, and Cl-/HCO3- exchanger activity in hRPTCs were higher in HV than WT SLC4A5. Increasing intracellular sodium enhanced the apical location of NBCe2 in HV hRPTCs (4.24±0.35% to 11.06±1.72% (P<0.05, N = 3, 2-way ANOVA, Holm-Sidak test)) as determined by Total Internal Reflection Fluorescence Microscopy (TIRFM). In hRPTCs isolated from kidney tissue, increasing intracellular sodium enhanced bicarbonate-dependent pH recovery rate and increased NBCe2 mRNA and protein expressions to a greater extent in HV than WT SLC4A5 (+38.00±6.23% vs HV normal salt (P<0.01, N = 4, 2-way ANOVA, Holm-Sidak test)). In hRPTCs isolated from freshly voided urine, bicarbonate-dependent pH recovery was also faster in those from salt-sensitive and carriers of HV SLC4A5 than from salt-resistant and carriers of WT SLC4A5. The faster NBCe2-specific bicarbonate-dependent pH recovery rate in HV SCL4A5 was normalized by SLC4A5- but not SLC4A4-shRNA. The binding of purified hepatocyte nuclear factor type 4A (HNF4A) to DNA was increased in hRPTCs carrying HV SLC4A5 rs7571842 but not rs10177833. The faster NBCe2-specific bicarbonate-dependent pH recovery rate in HV SCL4A5 was abolished by HNF4A antagonists.ConclusionNBCe2 activity is stimulated by an increase in intracellular sodium and is hyper-responsive in hRPTCs carrying HV SLC4A5 rs7571842 through an aberrant HNF4A-mediated mechanism.

Chemoreactomic analysis of citrulline malate molecules

Citrulline malate that is essential for the biosynthesis of arginine promotes dehydration of ammonium endotoxins, by participating in the urea cycle. The indications for the use of citrulline malate are functional asthenia, asthenic syndrome, overfatigue, increased fatigue, and rehabilitation during recovery following diseases. Objective: to simulate the biological properties of citrulline malate. Material and methods. Reliable estimates of more than 2,500 biological activities were obtained for this molecule, which were compared with those of the reference molecules of acetylcarnitine and meldonium. Results and discussion. The data obtained from chemoreactome simulation may suggest that there are substantial differences between the pharmacological effects of citrulline malate and the reference molecules. Malate anion as a component of citrulline malate significantly enhances the absorption of citrulline molecules in the gastrointestinal tract regardless of gastric acidity. Citrulline malate improves renal bicarbonate anion absorption, which contributes to the overcoming of acidosis. The results of chemoreactome simulation indicate that citrulline malate has antidepressant, anxiolytic, and anti-inflammatory properties, which can make a substantial contribution to the development of anti-asthenic and detoxifying effects of the drug. Citrulline malate can also show anticoagulant, antivasopressor, hypoglycemic, antihypercholesterolemic, and antimicrobial effects. These properties of citrulline malate can contribute to the earliest recovery of patients after asthenia or intensive strenuous exercises as compared to those of the reference molecules (meldonium, acetylcarnitine). Conclusion. The findings are consistent with the available experimental and clinical data and are indicative of promising clinical applications of citrulline malate.

Gene Variants in Sodium Bicarbonate Cotransporter NBCe2 Increase Sodium and Bicarbonate Transport in Human Renal Proximal Tubule

RationaleThe sodium bicarbonate cotransporter NBCe2 (encoded by SLC4A5) is involved in the regulation of renal tubular sodium bicarbonate transport. We hypothesized that human SLC4A5 single nucleotide polymorphisms (SNPs, rs10177833 and rs7571842) increase NBCe2 expression and renal proximal tubule (RPT) sodium transport and may be a cause of salt sensitivity of blood pressure.ObjectiveTo characterize the function of wild‐type (WT) and homozygous variants (HV) of SLC4A5.Methods and ResultsThe expressions of NBCe2 mRNA and protein were not different between RPT cells (RPTCs) carrying WT (n=4) or HV SLC4A5 (n=6) before or after dopaminergic or angiotensin (II and III) stimulation. However, total transcellular (luminal to basolateral) RPTC sodium transport, NHE3 protein expression, and Cl−/HCO3− exchanger activity were higher in HV than WT SLC4A5. Bicarbonate‐dependent pH recovery after an intracellular acid load, as well as NBCe2 mRNA and protein, was increased when intracellular sodium was elevated (5.2±1.1 mM) in HV SLC4A5 compared with WT SLC4A5 (pH recovery Vmax 0.22±0.02 and Km 6.39±0.81 in HV vs Vmax 0.28±0.02 and Km 4.30±0.53 in WT, P&lt;0.05, P&lt;0.05, n=3). The increased NBCe2‐specific bicarbonate‐dependent pH recovery in HV was verified in stable SLC4A5 shRNA cell lines (n=8/12/group). RPTCs carrying HV SLC4A5 had increased binding of HNF4A to SLC4A5 DNA (1.52±0.10‐fold, N=3, P&lt;0.05, t‐test), using purified HNF4A and ChIP and oligo binding assays. Additionally, the difference between HV and WT in bicarbonate‐dependent pH recovery was abolished by two HNF4A antagonists. RPTCs isolated from human urine of salt‐sensitive subjects who are HV for SLC4A5 had increased bicarbonate dependent pH recovery, relative to salt‐resistant subjects who are WT for SLC4A5 (n=4/group).ConclusionsNBCe2 activity is stimulated by an increase in intracellular sodium and is hyper‐responsive in RPTCs carrying HV SLC4A5 through an aberrant HNF4A‐mediated mechanism, which may be a key mechanism in the etiology of human salt sensitivity.

Effect of increased protein intake on renal acid load and renal hemodynamic responses

Increased protein intake versus maltodextrin intake for 4 weeks lowers blood pressure. Concerns exist that high‐protein diets reduce renal function. Effects of acute and 4‐week protein intake versus maltodextrin intake on renal acid load, glomerular filtration rate and related parameters were compared in this study. Seventy‐nine overweight individuals with untreated elevated blood pressure and normal kidney function were randomized to consume a mix of protein isolates (60 g/day) or maltodextrin (60 g/day) for 4 weeks in energy balance. Twenty‐four‐hour urinary potential renal acid load (uPRAL) was compared between groups. A subgroup (maltodextrin N = 27, protein mix N = 25) participated in extra test days investigating fasting levels and postprandial effects of meals supplemented with a moderate protein‐ or maltodextrin‐load on glomerular filtration rate, effective renal plasma flow, plasma renin, aldosterone, pH, and bicarbonate. uPRAL was significantly higher in the protein group after 4 weeks (P ≤ 0.001). Postprandial filtration fraction decreased further after the protein‐supplemented breakfast than after the maltodextrin‐supplemented breakfast after 4 weeks of supplementation (P ≤ 0.001). Fasting and postprandial levels of glomerular filtration rate, effective renal plasma flow, renin, aldosterone, angiotensin‐converting enzyme, pH and bicarbonate did not differ between groups. In conclusion, 4 weeks on an increased protein diet (25% of energy intake) increased renal acid load, but did not affect renal function. Postprandial changes, except for filtration fraction, also did not differ between groups. These data suggest that a moderate increase in protein intake by consumption of a protein mix for 4 weeks causes no (undesirable) effects on kidney function in overweight and obese individuals with normal kidney function.

Renal tubular acidosis is highly prevalent in critically ill patients.

IntroductionHyperchloremic acidosis is frequent in critically ill patients. Renal tubular acidosis (RTA) may contribute to acidemia in the state of hyperchloremic acidosis, but the prevalence of RTA has never been studied in critically ill patients. Therefore, we aimed to investigate the prevalence, type, and possible risk factors of RTA in critically ill patients using a physical-chemical approach.MethodsThis prospective, observational trial was conducted in a medical ICU of a university hospital. One hundred consecutive critically ill patients at the age ≥18, expected to stay in the ICU for ≥24 h, with the clinical necessity for a urinary catheter and the absence of anuria were included.Base excess (BE) subset calculation based on a physical-chemical approach on the first 7 days after ICU admission was used to compare the effects of free water, chloride, albumin, and unmeasured anions on the standard base excess. Calculation of the urine osmolal gap (UOG) - as an approximate measure of the unmeasured urine cation NH4+ - served as determinate between renal and extrarenal bicarbonate loss in the state of hyperchloremic acidosis.ResultsDuring the first week of ICU stay 43 of the patients presented with hyperchloremic acidosis on one or more days represented as pronounced negative BEChloride. In 31 patients hyperchloremic acidosis was associated with RTA characterized by a UOG ≤150 mosmol/kg in combination with preserved renal function. However, in 26 of the 31 patients with RTA metabolic acidosis was neutralized by other acid-base disturbances leading to a normal arterial pH.ConclusionsRTA is highly prevalent in critically ill patients with hyperchloremic acidosis, whereas it is often neutralized by the simultaneous occurrence of other acid-base disturbances.Trial registrationClinicaltrials.gov NCT02392091. Registered 17 March 2015

Structural Differences in Respiratory System and Airway of Parturients

Oxygen consumption increases with increased alveolar ventilation and respiratory alkalosis occurs. Thus, PaCO2 becomes 28-32 mmHg in pregnant women, and this amount is compensated with renal bicarbonate absorption. Preoxygenation can be made slower by inhalation of 100% oxygen for 2-5 minutes. Denitrogenation of the lungs occurs after three minutes [11. Baraka AS, Taha SK, Aouad MT, El-Khatib MF, Kawkabani NI (1999) Preoxygenation: comparison of maximal breathing and tidal volume breathing techniques. Anesthesiology 91: 612-616.]. Another method can be applied quickly with 4-8 deep breaths of 100% oxygen [22. Benumof JL (1999) Preoxygenation: best method for both efficacy and efficiency. Anesthesiology 91: 603-605.]. However, for pregnant women who will have a cesarean section under general anesthesia, an oxygen fraction of 1 has been shown to increase fetal oxygenation more compared with the 0.3 or 0.5 FiO2 [33. Khaw KS, Ngan Kee WD, Chu CY, Ng FF, Tam WH, et al. (2010) Effects of different inspired oxygen fractions on lipid peroxidation during general anaesthesia for elective Caesarean section. Br J Anaesth 105: 355-360. ]. As this may lead to free oxygen radicals and apsorbtion atalectesia, 80 % oxygen is recommended.