Vaptans for the treatment of hyponatremia

Overcoming Challenges: Doxycycline as an Alternative Treatment for Hyponatremia in Managing Syndrome of Inappropriate Secretion of Anti-diuretic Hormone (SIADH) in Small Cell Lung Cancer (SCLC): A Case Report

Hyponatremia, a common complication in small cell lung cancer (SCLC), can arise from various causes such as cancer itself, its treatment, paraneoplastic syndrome-induced SIADH secretion (syndrome of inappropriate anti-diuretic hormone secretion), and brain metastasis. While fluid restriction is the initial approach, refractory cases require pharmacological intervention in managing hyponatremia secondary to SIADH. This case report presents doxycycline as an alternative treatment option for a patient with refractory hyponatremia and SCLC with brain metastases, resulting in improved serum sodium levels. However, the use of doxycycline was associated with acute pancreatitis, prompting its discontinuation without establishing a definitive causal relationship. This case report highlights the importance of alternative treatments in resource-limited settings and emphasizes personalized care for hyponatremia in SCLC patients. Doxycycline can be an option, but safety and effectiveness require further study.

Transcription factor c-Maf deletion improves streptozotocin-induced diabetic nephropathy by directly regulating Sglt2 and Glut2

The transcription factor c-Maf has been widely studied and has been reported to play a critical role in embryonic kidney development; however, the postnatal functions of c-Maf in adult kidneys remain unknown as c-Maf-null C57BL/6J mice exhibit embryonic lethality. In this study, we investigated the role of c-Maf in adult mouse kidneys by comparing the phenotypes of tamoxifen-inducible (TAM-inducible) c-Maf-knockout mice (c-Maffl/fl; CAG-Cre-ERTM mice named "c-MafΔTAM") with those of c-Maffl/fl control mice, 10 days after TAM injection [TAM(10d)]. In addition, we examined the effects of c-Maf deletion on diabetic conditions by injecting the mice with streptozotocin, 4 weeks before TAM injection. c-MafΔTAM mice displayed primary glycosuria caused by sodium-glucose cotransporter 2 (Sglt2) and glucose transporter 2 (Glut2) downregulation in the kidneys without diabetes, as well as morphological changes and life-threatening injuries in the kidneys on TAM(10d). Under diabetic conditions, c-Maf deletion promoted recovery from hyperglycemia and suppressed albuminuria and diabetic nephropathy by causing similar effects as did Sglt2 knockout and SGLT2 inhibitors. In addition to demonstrating the potentially unique gene regulation of c-Maf, these findings highlight the renoprotective effects of c-Maf deficiency under diabetic conditions and suggest that c-Maf could be a novel therapeutic target gene for treating diabetic nephropathy.

A step-by-step guide for the diagnosis and management of hyponatraemia in patients with stroke

Hyponatraemia is common in patients with stroke and associated with adverse outcomes and increased mortality risk. The present review presents the underlying causes and provides a thorough algorithm for the diagnosis and management of hyponatraemia in stroke patients. Concomitant diseases and therapies, such as diabetes, chronic kidney disease and heart failure, along with diuretics, antidepressants and proton pump inhibitors are the most common causes of hyponatraemia in community. In the setting of acute stroke, the emergence of hyponatraemia might be attributed to the administration of hypotonic solutions and drugs (ie. mannitol and antiepileptics), poor solute intake, infections, as well as stroke-related conditions or complications, such as the syndrome of inappropriate secretion of antidiuretic hormone, cerebral salt wasting syndrome and secondary adrenal insufficiency. Diagnostically, the initial step is to differentiate hypotonic from non-hypotonic hyponatraemia, usually caused by hyperglycaemia or recent mannitol administration in patients with stroke. Determining urine osmolality, urine sodium level and volume status are the following steps in the differentiation of hypotonic hyponatraemia. Of note, specific parameters, such as fractional uric acid and urea excretion, along with plasma copeptin concentration, may further improve the diagnostic yield. Therapeutic options are based on the duration and symptoms of hyponatremia. In the case of acute or symptomatic hyponatraemia, hypertonic saline administration is recommended. Hypovolaemic chronic hyponatremia is treated with isotonic solution administration. Although fluid restriction remains the first-line treatment for the rest forms of chronic hyponatraemia, therapies increasing renal free water excretion may be necessary. Loop diuretics and urea serve this purpose in patients with stroke, whereas sodium-glucose transport protein-2 inhibitors appear to be a promising therapy. Nevertheless, it is yet unclear whether the appropriate restoration of sodium level improves outcomes in such patients. Randomized trials designed to compare therapeutic strategies in managing hyponatraemia in patients with stroke are required.

Ratio Profile: Physiologic Approach to Estimating Appropriate Intravenous Fluid Rate to Manage Hyponatremia in the Syndrome of Inappropriate Antidiuresis

A hyponatremic patient with the syndrome of inappropriate antidiuresis (SIAD) gets normal saline (NS), and the plasma sodium decreases, paradoxically. To explain, desalination is often invoked: if urine is more concentrated than NS, the fluid's salts are excreted while some water is reabsorbed, exacerbating hyponatremia. But comparing concentrations can be deceiving. They should be converted to quantities because mass balance is key to unlocking the paradox. The [sodium] equation can legitimately be used to track all of the sodium, potassium, and water entering and leaving the body. Each input or output "module" can be counterbalanced by a chosen iv fluid so that the plasma sodium stays stable. This equipoise is expressed in terms of the iv fluid's infusion rate, an easy calculation called the ratio profile. Knowing the infusion rate that maintains steady state, we can prescribe the iv fluid at a faster rate in order to raise the plasma sodium. Rates less than the ratio profile may risk a paradox, which essentially is caused by an iv fluid underdosing. Selecting an iv fluid that is more concentrated than urine is not enough to prevent paradoxes; even 3% saline can be underdosed. Drinking water adds to the ratio profile and is underestimated in its ability to provoke a paradox. In conclusion, the quantitative approach demystifies the paradoxical worsening of hyponatremia in SIAD and offers a prescriptive guide to keep the paradox from happening. The ratio profile method is objective and quickly deployable on rounds, where it may change patient management for the better.

Fluid management in hospitalized pediatric patients

The proper use of intravenous fluids has likely been responsible for saving more lives than any other group of substances. Proper use includes prescribing an appropriate electrolyte and carbohydrate solution, at a calculated rate or volume, for the right child, at the right time. Forming intravenous fluid plans for hospitalized children requires an understanding of water and electrolyte physiology in healthy children and how different pathology deviates from the norm. This review highlights fluid management in several disease types, including liver disease, diabetic ketoacidosis, syndrome of inappropriate antidiuretic hormone, diabetes insipidus, kidney disease, and intestinal failure as well as in those with nonphysiologic fluid losses. For each disease, the review discusses specific considerations, evaluations, and management strategies to consider when customizing intravenous fluid plans. Ultimately, all hospitalized children should receive an individualized fluid plan with recurrent evaluations and fluid modifications to provide optimal care.

Endocrine system dysfunction and chronic heart failure: a clinical perspective

Chronic heart failure (CHF) leads to an excess of urgent ambulatory visits, recurrent hospital admissions, morbidity, and mortality regardless of medical and non-medical management of the disease. This excess of risk may be attributable, at least in part, to comorbid conditions influencing the development and progression of CHF. In this perspective, the authors examined and described the most common endocrine disorders observed in patients with CHF, particularly in individuals with reduced ejection fraction, aiming to qualify the risks, quantify the epidemiological burden and discuss about the potential role of endocrine treatment. Thyroid dysfunction is commonly observed in patients with CHF, and sometimes it could be the consequence of certain medications (e.g., amiodarone). Male and female hypogonadism may also coexist in this clinical context, contributing to deteriorating the prognosis of these patients. Furthermore, growth hormone deficiency may affect the development of adult myocardium and predispose to CHF. Limited recommendation suggests to screen endocrine disorders in CHF patients, but it could be interesting to evaluate possible endocrine dysfunction in this setting, especially when a high suspicion coexists. Data referring to long-term safety and effectiveness of endocrine treatments in patients with CHF are limited, and their impact on several "hard" endpoints (such as hospital admission, all-cause, and cardiovascular mortality) are still poorly understood.

Vasopressin-Dependent Disorders: What Is New in Children?

Arginine vasopressin (AVP)-mediated osmoregulatory disorders, such as diabetes insipidus (DI) and syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are common in the differential diagnosis for children with hypo- and hypernatremia and require timely recognition and treatment. DI is caused by a failure to concentrate urine secondary to impaired production of or response to AVP, resulting in hypernatremia. Newer methods of diagnosing DI include measuring copeptin levels; copeptin is AVP's chaperone protein and serves as a surrogate biomarker of AVP secretion. Intraoperative copeptin levels may also help predict the risk for developing DI after neurosurgical procedures. Copeptin levels hold diagnostic promise in other pediatric conditions, too. Recently, expanded genotype and phenotype correlations in inherited DI disorders have been described and may better predict the clinical course in affected children and infants. Similarly, newer formulations of synthetic AVP may improve pediatric DI treatment. In contrast to DI, SIADH, characterized by inappropriate AVP secretion, commonly leads to severe hyponatremia. Contemporary methods aid clinicians in distinguishing SIADH from other hyponatremic conditions, particularly cerebral salt wasting. Further research on the efficacy of therapies for pediatric SIADH is needed, although some adult treatments hold promise for pediatrics. Lastly, expansion of home point-of-care sodium testing may transform management of SIADH and DI in children. In this article, we review recent developments in the understanding of pathophysiology, diagnostic workup, and treatment of better outcomes and quality of life for children with these challenging disorders.

C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates

In this review article, we summarized recent advances in C–H hetero-functionalization of arenes through palladacyclopentane-type intermediates.

Dual Vasopressin Receptor Antagonism to Improve Congestion in Patients With Acute Heart Failure: Design of the AVANTI Trial

BACKGROUND

Loop diuretics are the main treatment for patients with acute heart failure, but are associated with neurohormonal stimulation and worsening renal function and do not improve long-term outcomes. Antagonists to arginine vasopressin may provide an alternative strategy to avoid these effects. The AVANTI study will investigate the efficacy and safety of pecavaptan, a novel, balanced dual-acting V1a/V2 vasopressin antagonist, both as adjunctive therapy to loop diuretics after admission for acute heart failure, and later as monotherapy.

METHODS AND RESULTS

AVANTI is a double-blind, randomized phase II study in 571 patients hospitalized with acute heart failure and signs of persistent congestion before discharge. In part A, patients will receive either pecavaptan 30 mg/d or placebo with standard of care for 30 days. In part B, eligible patients will continue treatment or receive pecavaptan or diuretics as monotherapy for another 30 days. The primary end points for part A are changes in body weight and serum creatinine; for part B, changes in body weight and blood urea nitrogen/creatinine ratio.

CONCLUSIONS

This study will provide the first evidence that a balanced V1a/V2 antagonist may safely enhance decongestion, both as an adjunct to loop diuretics and as an alternative strategy.

TRIAL REGISTRATION NUMBER

NCT03901729.

Hyponatremia in the Neurologically Ill Patient: A Review

Hyponatremia is a well-known disorder commonly faced by clinicians managing neurologically ill patients. Neurological disorders are often associated with hyponatremia during their acute presentation and can be associated with specific neurologic etiologies and symptoms. Patients may present with hyponatremia with traumatic brain injury, develop hyponatremia subacutely following aneurysmal subarachnoid hemorrhage, or may manifest with seizures due to hyponatremia itself. Clinicians caring for the neurologically ill patient should be well versed in identifying these early signs, symptoms, and etiologies of hyponatremia. Early diagnosis and treatment can potentially avoid neurologic and systemic complications in these patients and improve outcomes. This review focuses on the causes and findings of hyponatremia in the neurologically ill patient and discusses the pathophysiology, diagnoses, and treatment strategies for commonly encountered etiologies.

Phosphine-Catalyzed α-Umpolung-Aldol Reaction for the Synthesis of Benzo[ b]azapin-3-ones

A novel phosphine-catalyzed intermolecular cyclization between 2-sulfonamidobenzaldehyes and ynones is reported. This methodology serves as a conduit for the construction of benzo[ b]azepin-3-ones in good to excellent yields under mild conditions. The resulting 2-benzylidene moieties are formed exclusively in the E-configuration. Mechanistically, this unusual annulation occurs through a phosphine-catalyzed α-umpolung addition, followed by an aldol reaction. One of the benzo[ b]azepin-3-one products was converted to the core structure of 3-amino-[ a]benzazepin-2-one-1-alkanoic acids, many of which function as angiotensin-converting enzyme inhibitors.

Correction of Hyponatremia May Be a Treatment Stratification Biomarker: A Two-Stage Systematic Review and Meta-Analysis

Changes in serum sodium concentration ([Na⁺]_serum) can permit evaluation of the treatment effect of vasopressin antagonists (vaptans) in patients with worsening heart failure (HF) or cirrhotic ascites; that is, they may act as a treatment stratification biomarker. A two-stage systematic review and meta-analysis were carried out and contextualized by experts in fluid resuscitation and translational pharmacology (registration ID in the International Prospective Register of Systematic Reviews (PROSPERO): CRD42017051440). Meta-analysis of aggregated dichotomous outcomes was performed. Pooled estimates for correction of hyponatremia (normalization or an increase in [Na⁺]_serum of at least 3–5 mEq/L) under treatment with vaptans (Stage 1) and for clinical outcomes in both worsening HF (rehospitalization and/or death) and cirrhotic ascites (ascites worsening) when correction of hyponatremia is achieved (Stage 2) were calculated. The body of evidence was assessed. Correction of hyponatremia was achieved under vaptans (odds ratio (OR)/95% confidence interval (95% CI)/I²/number of studies (n): 7.48/4.95–11.30/58%/15). Clinical outcomes in both worsening HF and cirrhotic ascites improved when correction of hyponatremia was achieved (OR/95% CI/I²/n: 0.51/0.26–0.99/52%/3). Despite the appropriateness of the study design, however, there are too few trials to consider that correction of hyponatremia is a treatment stratification biomarker. Patients with worsening HF or with cirrhotic ascites needing treatment with vaptans, have better clinical outcomes when correction of hyponatremia is achieved. However, the evidence base needs to be enlarged to propose formally correction of hyponatremia as a new treatment stratification biomarker. Markers for use with drugs are needed to improve outcomes related to the use of medicines.

Effect of tolvaptan on renal water and sodium excretion and blood pressure during nitric oxide inhibition: a dose-response study in healthy subjects

Background

Tolvaptan is a selective vasopressin receptor antagonist. Nitric Oxide (NO) promotes renal water and sodium excretion, but the effect is unknown in the nephron’s principal cells. In a dose-response study, we measured the effect of tolvaptan on renal handling of water and sodium and systemic hemodynamics, during baseline and NO-inhibition with L-NMMA (L-NG-monomethyl-arginine).

Methods

In a randomized, placebo-controlled, double blind, cross over study, 15 healthy subjects received tolvaptan 15, 30 and 45 mg or placebo. L-NMMA was given as a bolus followed by continuous infusion during 60 min. We measured urine output (UO), free water clearance (C_H2O), fractional excretion of sodium (FE_Na), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaCγ), plasma vasopressin (p-AVP) and central blood pressure (cBP).

Results

During baseline, FE_Na was unchanged. Tolvaptan decreased u-ENaC_γ dose-dependently and increased p-AVP threefold, whereas u-AQP2 was unchanged. During tolvaptan with NO-inhibition, UO and C_H2O decreased dose-dependently. FE_Na decreased dose-independently and u-ENaC_γ remained unchanged. Central BP increased equally after all treatments.

Conclusions

During baseline, fractional excretion of sodium was unchanged. During tolvaptan with NO-inhibition, renal water excretion was reduced dose dependently, and renal sodium excretion was reduced unrelated to the dose, partly via an AVP dependent mechanism. Thus, tolvaptan antagonized the reduction in renal water and sodium excretion during NO-inhibition. Most likely, the lack of decrease in AQP2 excretion by tolvaptan could be attributed to a counteracting effect of the high level of p-AVP.

Trial registration

Clinical Trial no: NCT02078973. Registered 1 March 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0501-1) contains supplementary material, which is available to authorized users.

Hyponatremia, all-cause mortality, and risk of cancer diagnoses in the primary care setting: A large population study

BACKGROUND

Hyponatremia has been associated with increased all-cause mortality in hospitalized individuals. In this study we examine the risk of all-cause mortality in primary care subjects with hyponatremia, while also exploring the association with subsequent diagnosis of cancer.

METHODS

Retrospective cohort study on subjects who underwent blood tests, consulting their general practitioner 2000-2012 in Copenhagen, Denmark. Reference range for sodium was 135-145mmol/L, and mild, moderate, and severe hyponatremia were defined as 130-135, 125-129, and <125mmol/L, respectively. Primary outcome was all-cause mortality, and secondary outcomes overall and specific types of cancer diagnoses.

RESULTS

Among 625,114 included subjects (mean age 49.9 [SD±18.4] years; 43.5% males), 90,926 (14.5%) deaths occurred. All-cause mortality was increased in mild, moderate, and severe hyponatremia (age-adjusted mortality rates [IRs, incidence rates] 26, 30, and 36 per 1000 person-years (py), respectively and incidence rate ratios [IRRs] 1.81 [95% CI: 1.76-1.85], 2.11 [2.00-2.21], and 2.52 [2.26-2.82], respectively) compared with individuals with normonatremia (IR 14 per 1000 py). For the secondary endpoint an increased level-dependent risk was found with lower sodium levels in relation to cancer overall, head and neck cancers, and pulmonary cancer, with severe hyponatremia associated with the highest IRRs (1.77 [1.39-2.24], 5.24 [2.17-12.63]), and 4.99 [3.49-7.15], respectively).

CONCLUSIONS

All levels of hyponatremia are associated with all-cause mortality in primary care patients and hyponatremia is linked to an increased risk of being diagnosed with any cancer, particularly pulmonary and head and neck cancers.

Nephrogenic syndrome of inappropriate antidiuresis secondary to an activating mutation in the arginine vasopressin receptor AVPR2

CONTEXT

Nephrogenic syndrome of inappropriate antidiuresis (NSIAD), resulting from activating mutations in the arginine vasopressin receptor type 2 (AVPR2), is a rare cause of hyponatraemia. However, its true prevalence may be underestimated and it should be considered in the investigation of unexplained hyponatraemia, with implications for management and targeted gene testing.

OBJECTIVE

We describe a structured approach to the investigation of hyponatraemia in a young patient, which allowed a diagnosis of NSIAD to be made. We review current knowledge of NSIAD and use a structural modelling approach to further our understanding of the potential mechanisms by which the causative mutation leads to a constitutively active AVPR2.

DESIGN

Clinical and biochemical investigation of hyponatraemia; a formal water load test with measurement of arginine vasopressin levels (AVP); sequencing of AVPR2; and computed structural modelling of the wild-type and constitutively activated mutant receptors.

RESULTS

A 38-year-old man presented with intermittent confusion and nausea associated with hyponatraemia and a biochemical picture consistent with syndrome of inappropriate antidiuretic hormone (SIADH). Adrenocortical and thyroid function and an acute intermittent porphyria screen were normal. Cross-sectional imaging of the head, chest and abdomen did not identify an underlying cause and so we proceeded to a water load test. This demonstrated a marked inability to excrete a free water load (just 15% of a 20 ml/kg oral load by 240 min postingestion), with the onset of hyponatraemia (Na(+) 125 mmol/l, urine osmolality 808 mOsm/kg). However, AVP levels were low throughout the test (0·4-0·9 pmol/l), consistent with a diagnosis of NSIAD. AVPR2 sequencing revealed a previously described hemizygous activating mutation (p.Arg137Cys). Through structural modelling of AVPR2, we suggest that disruption of a hydrogen bond between residues Thr269 and Arg137 may promote stabilization of the receptor in its active conformation. Since diagnosis, the patient has adhered to modest fluid restriction and remained well, with no further episodes of hyponatraemia.

CONCLUSION

NSIAD should be considered in young patients with unexplained hyponatraemia. A water load test with AVP measurement is a potentially informative investigation, while AVPR2 sequencing provides a definitive molecular genetic diagnosis and a rationale for long-term fluid restriction.

Efficacy and Safety of Vasopressin Receptor Antagonists for Euvolemic or Hypervolemic Hyponatremia: A Meta-Analysis

Hyponatremia, defined as a nonartifactual serum sodium level <135 mmol/L, is the most common fluid and electrolyte abnormality in clinical practice. Traditional managements (fluid restriction, hypertonic saline and loop diuretics, etc.) are difficult to maintain or ineffective. Recently, vasopressin receptor antagonists (VRAs) have shown promise for the treatment of hyponatremia. We aimed to conduct a meta-analysis to evaluate the efficacy and safety of VRAs in patients with euvolemic or hypervolemic hyponatremia. We searched Pubmed, Cochrane Library, Web of Science and Springer, etc. (latest search on June 4, 2015) for English publications with randomized controlled trials. Two authors independently screened the citations and extracted data. We calculated pooled relative risk (RR), risk difference (RD), weighted mean difference (WMD) or standard mean difference (SMD), and 95% confidence intervals (CIs) by using random and fixed effect models. We collected data from 18 trials involving 1806 patients. Both random and fixed effect meta-analyses showed that VRAs significantly increased the net change of serum sodium concentration (WMD(random) = 4.89 mEq/L, 95%CIs = 4.35-5.43 and WMD(fixed) = 4.70 mEq/L, 95%CIs = 4.45-4.95), response rate (RR(random )= 2.77, 95%CIs = 2.29-3.36 and RR(fixed) = 2.95, 95%CIs = 2.56-3.41), and 24-hour urine output (SMD(random) = 0.82, 95%CIs = 0.65-1.00 and SMD(fixed) = 0.79, 95%CIs = 0.66-0.93) compared to placebo. Furthermore, VRAs significantly decreased body weight (WMD(random) = -0.87 kg, 95%CIs = -1.24 to -0.49 and WMD(fixed) = -0.91 kg, 95%CIs = -1.22 to -0.59). In terms of safety, rates of drug-related adverse events (AEs), rapid sodium level correction, constipation, dry mouth, thirst, and phlebitis in the VRA-treated group were greater than those in control group. However, there was no difference in the total number of AEs, discontinuations due to AEs, serious AEs, death, headache, hypotension, nausea, anemia, hypernatremia, urinary tract infection, renal failure, pyrexia, upper gastrointestinal bleeding, diarrhea, vomiting, peripheral edema, and dizziness between the 2 groups. Random effect meta-analyses showed that post treatment urine osmolality, supine systolic blood pressure, and diastolic blood pressure were lowered (WMD(random) = -233.07 mOsmol/kg, 95%CIs = -298.20-147.94; WMD(random) = -6.11 mmHg, 95%CIs = -9.810 to -2.41; WMD(random )= -2.59 mmHg, 95%CIs = -4.06 to -1.11, respectively), but serum osmolality was increased (WMD(random) = 9.29 mOsmol/kg, 95%CIs = 5.56-13.03). There was no significant change from baseline in serum potassium concentration between the 2 groups (WMD(fixed) = 0.00 mmHg, 95%CIs = -0.07-0.06). VRAs are relatively effective and safe for the treatment of hypervolemic and euvolemic hyponatremia.

Copeptin in the diagnosis of vasopressin-dependent disorders of fluid homeostasis

Copeptin and arginine vasopressin (AVP) are derived from a common precursor molecule and have equimolar secretion and response to osmotic, haemodynamic and stress-related stimuli. Plasma concentrations of copeptin and AVP in relation to serum osmolality are highly correlated. The physiological functions of AVP with respect to homeostasis of fluid balance, vascular tonus and regulation of the endocrine stress response are well known, but the exact function of copeptin is undetermined. Quantification of AVP can be difficult, but copeptin is stable in plasma and can be easily measured with a sandwich immunoassay. For this reason, copeptin has emerged as a promising marker for the diagnosis of AVP-dependent fluid disorders. Copeptin measurements can enable differentiation between various conditions within the polyuria-polydipsia syndrome. In the absence of prior fluid deprivation, baseline copeptin levels >20 pmol/l identify patients with nephrogenic diabetes insipidus. Conversely, copeptin levels measured upon osmotic stimulation differentiate primary polydipsia from partial central diabetes insipidus. In patients with hyponatraemia, low levels of copeptin together with low urine osmolality identify patients with primary polydipsia, and the ratio of copeptin to urinary sodium can distinguish the syndrome of inappropriate antidiuretic hormone secretion from other AVP-dependent forms of hyponatraemia.

A copeptin-based classification of the osmoregulatory defects in the syndrome of inappropriate antidiuresis

The syndrome of inappropriate antidiuretic hormone secretion (SIADH), also referred to as syndrome of inappropriate antidiuresis (SIAD), is the most common cause of hyponatremia characterized by extracellular hypotonicity and impaired urine dilution in the absence of any recognizable nonosmotic stimuli for the antidiuretic hormone arginine vasopressin (AVP). Hyponatremia in SIADH is primarily the result of excessive water retention caused by a combination of inappropriate antidiuresis and persistent fluid intake in the presence of impaired osmoregulated inhibition of thirst. It is sometimes aggravated by a sodium deficiency caused by a decreased intake or a secondary natriuresis in response to elevated extracellular volume. Inappropriate antidiuresis usually results from endogenous production of AVP that can be either ectopic (from a malignancy) or eutopic (from the hypothalamus/neurohypophysis). Regardless of its origin, different types of osmotic dysregulation of AVP have been reported with possibly fundamental deviations in treatment need and efficacy. A recent quantitative analysis of 50 patients with SIADH, which underwent serial measurements of copeptin during hypertonic saline infusion, revealed five distinct types of osmoregulatory defect ("type A to E") without affiliation to specific underlying diseases. In addition to apparently impaired osmoregulated inhibition of AVP release in the majority of patients, 12% of patients showed an AVP-independent mechanism of inappropriate antidiuresis, whilst 20% of them presented a reverse relation between hormone release and serum osmolality, presumably related to interrupted nonosmotic inhibitory pathways. The interference of these different types of SIAD with clinical presentation and therapy response will be a relevant subject for future research.

Hyponatremia in the intensive care unit: How to avoid a Zugzwang situation?

Hyponatremia is a common electrolyte derangement in the setting of the intensive care unit. Life-threatening neurological complications may arise not only in case of a severe (<120 mmol/L) and acute fall of plasma sodium levels, but may also stem from overly rapid correction of hyponatremia. Additionally, even mild hyponatremia carries a poor short-term and long-term prognosis across a wide range of conditions. Its multifaceted and intricate physiopathology may seem deterring at first glance, yet a careful multi-step diagnostic approach may easily unravel the underlying mechanisms and enable physicians to adopt the adequate measures at the patient’s bedside. Unless hyponatremia is associated with obvious extracellular fluid volume increase such as in heart failure or cirrhosis, hypertonic saline therapy is the cornerstone of the therapeutic of profound or severely symptomatic hyponatremia. When overcorrection of hyponatremia occurs, recent data indicate that re-lowering of plasma sodium levels through the infusion of hypotonic fluids and the cautious use of desmopressin acetate represent a reasonable strategy. New therapeutic options have recently emerged, foremost among these being vaptans, but their use in the setting of the intensive care unit remains to be clarified.

[Hyponatremias: From pathophysiology to treatments. Review for clinicians]

Hyponatremia could be defined as a public health topic: too many patients are concerned in both hospitalized and general populations; hyponatremia induces lots of clinical outcomes and a great economic burden. Its pathophysiology involves thirst regulation (hypotonic water intakes) and losses regulation (through the kidney under vasopressin control). Diagnostic approach should insure that hyponatremia reflects hypo-osmolality and hypotonicity: first, a false hyponatremia should be ruled out, then a non-hypotonic one. Next step is clinic: extracellular status should be evaluated. When increased, any edematous status should be evoked: heart failure, liver cirrhosis or nephrotic syndrome. When decreased, any cause of extracellular dehydration should be evoked: natriuresis could help distinguishing between renal (adrenal insufficiency, diuretics use or salt-losing nephropathy) or extrarenal (digestive mostly) etiologies. When clinically normal, a secretion of inappropriate antidiuretic hormone (SIADH) should be evoked, once hypothyroidism or hypoadrenocorticism have been ruled out. Therapy depends on the severity of the clinical impact. From extracellular rehydration, through fluid restriction, the paraneoplastic and heart failure-induced SIADH benefit from a new class of drug, available among the therapeutic strategies: aquaretics act through antidiuretic hormone receptor antagonism (vaptans). Their long-term benefits still have to be proven but it is a significant step forward in the treatment of hyponatremias.

Clinical characteristics of responders to treatment with tolvaptan in patients with acute decompensated heart failure: Importance of preserved kidney size

BACKGROUND

Recent clinical trials have demonstrated the efficacy of short-term treatment with tolvaptan, an oral vasopressin V2 receptor antagonist, in patients with heart failure. However, the response to tolvaptan varies among patients. The aim of this study was to determine factors associated with response to tolvaptan in patients with acute decompensated heart failure (ADHF).

METHODS

The Tolvaptan Registry, a prospective, observational, multicenter cohort study performed in Japan, aims to determine factors affecting the responsiveness of tolvaptan in patients with ADHF. We enrolled ADHF patients treated with tolvaptan and they were divided into two groups: responders and non-responders. Responders were defined as subjects who met all of the following three conditions: (1) increasing urine volume during a 24-hour period after the start of tolvaptan treatment; (2) improvement in New York Heart Association functional class; and (3) decrease in cardiothoracic ratio assessed by chest X-ray on day 3 of tolvaptan administration.

RESULTS

Among the 114 patients, treatment with tolvaptan improved three conditions of heart failure in more than half of all the cohorts (71 patients, 62%). As for baseline characteristics, estimated glomerular filtration rate, urine osmolality, and kidney size were significantly greater in responders than in non-responders. Multivariate logistic analysis revealed that kidney size was independently associated with responders (odds ratio: 1.083, p=0.001, 95% confidence interval 1.031-1.137).

CONCLUSIONS

The main clinical characteristic of responders to treatment with tolvaptan is that kidney size is preserved.

Syndrome of inappropriate antidiuretic hormone secretion and cerebral/renal salt wasting syndrome: similarities and differences

Hyponatremia (sodium levels of <135 mEq/L) is one of the most common electrolyte imbalances in clinical practice, especially in patients with neurologic diseases. Hyponatremia can cause cerebral edema and brain herniation; therefore, prompt diagnosis and proper treatment is important in preventing morbidity and mortality. Among various causes of hyponatremia, diagnosing syndrome of inappropriate antidiuretic hormone secretion (SIADH) and cerebral/renal salt wasting syndrome (C/RSW) is difficult due to many similarities. SIADH is caused by excess of renal water reabsorption through inappropriate antidiuretic hormone secretion, and fluid restriction is the treatment of choice. On the other hand, C/RSW is caused by natriuresis, which is followed by volume depletion and negative sodium balance and replacement of water and sodium is the mainstay of treatment. Determinating volume status in hyponatremic patients is the key point in differential between SIADH and C/RSW. However, in most situations, differential diagnosis of these two diseases is difficult because they overlap in many clinical and laboratory aspects, especially to assess differences in volume status of these patients. Although distinction between the SIADH and C/RSW is difficult, improvement of hypouricemia and an increased fractional excretion of uric acid after the correction of hyponatremia in SIADH, not in C/RSW, may be one of the helpful points in discriminating the two diseases. In this review, we compare these two diseases regarding the pathophysiologic mechanisms, diagnosis, and therapeutic point of view.

Evaluation and management of hyponatraemia in children

AIM

Paediatric hyponatraemia is usually caused by an excess of antidiuretic hormone and may lead to serious neurological complications. It is challenging for clinicians to differentiate between conditions causing excess water and salt loss. This review analyses individual causes of hyponatraemia and focuses on optimal diagnostic algorithms and treatment strategies.

CONCLUSION

Correct evaluation of hyponatraemia requires proper understanding of the aetiology and appropriate management calls for a detailed history, physical examination and specific laboratory investigations.

Management of hyponatremia in various clinical situations

OPINION STATEMENT

Hyponatremia is the most common electrolyte abnormality in both inpatient and outpatient settings. The condition primarily results from the combination of impaired free water excretion due to elevated vasopressin levels in conjunction with a source of free water intake. Recent studies have revealed that even mild and asymptomatic hyponatremia is associated with deleterious consequences. It is an independent risk factor for mortality and is also associated with increased length of hospitalization and hospital costs. Even mild chronic hyponatremia can result in subtle neurologic impairment and bone demineralization, leading to falls and associated bone fractures in the elderly. Hyponatremia can be a difficult condition to treat, with varying therapeutic strategies based on the etiology, severity, duration, and extent of neurologic symptoms. The ideal magnitude of correction is also controversial, as both inadequate therapy and overly aggressive therapy can result in neurologic injury. Formulas that have been devised to aid in the treatment of hyponatremia can be inaccurate in that they fail to adequately account for the renal response to therapy. Hyponatremic encephalopathy is the most serious complication of hyponatremia, and can result in permanent neurologic impairment or death if left untreated. Individuals most at risk for developing hyponatremic encephalopathy are postmenarchal women, children under 16 years of age, patients with central nervous system disease or hypoxemia, and patients in the postoperative setting. The preferred therapy for hyponatremic encephalopathy is a 100-ml bolus of 3 % sodium chloride (513 mEq/L) administered in repeated doses until symptoms reverse, with the goal of increasing the serum sodium 5-6 mEq/L. Vasopressin (V2) antagonists (vaptans) are not appropriate for the management of acute hyponatremic encephalopathy, as the onset of action is not sufficiently rapid and the increase in sodium is not predictable. Vaptans are primarily indicated for the treatment of asymptomatic hyponatremia due to SIAD that is refractory to conventional measures.

Effect of vasopressin antagonism on renal handling of sodium and water and central and brachial blood pressure during inhibition of the nitric oxide system in healthy subjects

Background

Tolvaptan is a selective vasopressin receptor antagonist (V2R) that increases free water excretion. We wanted to test the hypotheses that tolvaptan changes both renal handling of water and sodium and systemic hemodynamics during basal conditions and during nitric oxide (NO)-inhibition with L-NG-monomethyl-arginine (L-NMMA).

Methods

Nineteen healthy subjects were enrolled in a randomized, placebo-controlled, double-blind, crossover study of two examination days. Tolvaptan 15 mg or placebo was given in the morning. L-NMMA was given as a bolus followed by continuous infusion during 60 minutes. We measured urine output(UO), free water clearance (C_H2O), fractional excretion of sodium (FE_Na), urinary aquaporin-2 channels (u-AQP2) and epithelial sodium channels (u-ENaC_γ), plasma vasopressin (p-AVP), central and brachial blood pressure(cBP, bBP).

Results

During baseline conditions, tolvaptan caused a significant increase in UO, C_H2O and p-AVP, and FE_Na was unchanged. During L-NMMA infusion, UO and C_H2O decreased more pronounced after tolvaptan than after placebo (-54 vs.-42% and -34 vs.-9% respectively). U-AQP2 decreased during both treatments, whereas u-ENaC_γ decreased after placebo and increased after tolvaptan. CBP and bBP were unchanged.

Conclusion

During baseline conditions, tolvaptan increased renal water excretion. During NO-inhibition, the more pronounced reduction in renal water excretion after tolvaptan indicates that NO promotes water excretion in the principal cells, at least partly, via an AVP-dependent mechanism. The lack of decrease in u-AQP2 by tolvaptan could be explained by a counteracting effect of increased plasma vasopressin. The antagonizing effect of NO-inhibition on u-ENaC suggests that NO interferes with the transport via ENaC by an AVP-dependent mechanism.

A copeptin-based classification of the osmoregulatory defects in the syndrome of inappropriate antidiuresis

Hyponatremia, the most frequent electrolyte disorder, is caused predominantly by the syndrome of inappropriate antidiuresis (SIAD). A comprehensive characterization of SIAD subtypes, defined by type of osmotic dysregulation, is lacking, but may aid in predicting therapeutic success. Here, we analyzed serial measurements of serum osmolality and serum sodium, plasma arginine vasopressin (AVP), and plasma copeptin concentrations from 50 patients with hyponatremia who underwent hypertonic saline infusion. A close correlation between copeptin concentrations and serum osmolality existed in 68 healthy controls, with a mean osmotic threshold±SD of 282±4 mOsM/kg H2O. Furthermore, saline-induced changes in copeptin concentrations correlated with changes in AVP concentrations in controls and patients. With use of copeptin concentration as a surrogate measure of AVP concentration, patients with SIAD could be grouped according to osmoregulatory defect: Ten percent of patients had grossly elevated copeptin concentrations independent of serum osmolality (type A); 14% had copeptin concentrations that increased linearly with rising serum osmolality but had abnormally low osmotic thresholds (type B); 44% had normal copeptin concentrations independent of osmolality (type C), and 12% had suppressed copeptin concentrations independent of osmolality (type D). A novel SIAD subtype discovered in 20% of patients was characterized by a linear decrease in copeptin concentrations with increasing serum osmolality (type E or "barostat reset"). In conclusion, a partial or complete loss of AVP osmoregulation occurs in patients with SIAD. Although the mechanisms underlying osmoregulatory defects in individual patients are presumably diverse, we hypothesize that treatment responses and patient outcomes will vary according to SIAD subtype.

Tolvaptan can improve clinical course in responders

We previously defined "responders" as patients with increases in urine volume (UV) on day 1 after the administration of tolvaptan (TLV), and demonstrated that responders to TLV could be predicted with considerable accuracy by urine osmolality (U-OSM) levels. Responders and non-responders to TLV should be associated with different clinical courses after a certain time following TLV administration. Therefore, the aim of the present study was to validate our definition of responders by clinical parameters 1 week after administration of TLV. Data (n = 85) were obtained from in hospital patients with decompensated heart failure (HF) who had received TLV at 3.75-15 mg daily, and clinical data at 1 week after the administration of TLV were compared with those of baseline. Sixty patients (70.6%) were "responders", in whom UV on day 1 increased after the administration of TLV compared with day 0. "Non-responders" were older, and had higher serum creatinine concentration and lower baseline U-OSM than "responders". Serum creatinine concentration increased significantly in "non-responders", but was unchanged in "responders". Body weight, plasma B-type natriuretic peptide concentration, and HF symptom score decreased significantly in "responders", but remained unchanged in "non-responders". Increases in UV after the first administration of TLV were closely correlated with improvement of congestive HF after 1 week of TLV treatment, which verified our definition of "responders" to TLV.

Tolvaptan in the treatment of acute hyponatremia associated with acute kidney injury

Hyponatremia defined as a plasma sodium concentration of less than 135 mmol/L is a very common disorder, occurring in hospitalized patients. Hyponatremia often results from an increase in circulating arginine vasopressin (AVP) levels and/or increased renal sensitivity to AVP, combined with an increased intake of free water. Hyponatremia is subdivided into three groups, depending on clinical history and volume status: hypovolemic, euvolemic, and hypervolemic. Acute symptomatic hyponatremia is usually treated with hypertonic (3%) saline. Syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH) and hypervolemic hyponatremia caused by heart failure or cirrhosis are treated with vasopressin antagonists (vaptans) since they increase plasma sodium (Na²⁺) concentration via their aquaretic effects (augmentation of free-water clearance). The role of tolvaptan in the treatment of acute hyponatremia and conversion of oliguric to nonoliguric phase of acute tubular necrosis has not been previously described.

Convenient synthesis of substituted tetrahydrofuran via Lewis base catalyzed [3 + 2] domino reactions

A DABCO catalyzed domino reaction between 3-oxo-4-(2-oxoindolin-3-ylidene) butanoates and allenoates furnished 2,3,5-substituted tetrahydrofuran furan derivatives bearing oxindole moiety and two exocyclic double bonds in high yield.

Urea transport mediated by aquaporin water channel proteins

Aquaporins (AQPs) are a family of membrane water channels that basically function as regulators of intracellular and intercellular water flow. To date, thirteen aquaporins have been characterized. They are distributed wildly in specific cell types in multiple organs and tissues. Each AQP channel consists of six membrane-spanning alpha-helices that have a central water-transporting pore. Four AQP monomers assemble to form tetramers, which are the functional units in the membrane. Some of AQPs also transport urea, glycerol, ammonia, hydrogen peroxide, and gas molecules. AQP-mediated osmotic water transport across epithelial plasma membranes facilitates transcellular fluid transport and thus water reabsorption. AQP-mediated urea and glycerol transport is involved in energy metabolism and epidermal hydration. AQP-mediated CO2 and NH3 transport across membrane maintains intracellular acid-base homeostasis. AQPs are also involved in the pathophysiology of a wide range of human diseases (including water disbalance in kidney and brain, neuroinflammatory disease, obesity, and cancer). Further work is required to determine whether aquaporins are viable therapeutic targets or reliable diagnostic and prognostic biomarkers.

Tolvaptan as a tool in renal physiology

For decades, the Brattleboro rat has been a useful model in kidney physiology. These animals manifest central diabetes insipidus (lack of circulating vasopressin) due to a mutation in the vasopressin-neurophysin gene. V2 receptor-mediated vasopressin actions in the kidney can be assessed in these animals by infusing the V2-selective vasopressin analog 1-desamino-8-D-arginine vasopressin (dDAVP). However, the major commercial supplier in the United States has ceased production, creating the need for another reliable experimental model of V2 receptor-mediated vasopressin action in rodents. We designed an in vivo protocol to investigate vasopressin responses in the rat kidney using osmotic minipumps loaded with tolvaptan, a nonpeptide competitive inhibitor of the vasopressin V2 receptor. Tolvaptan-infused rats had a mean urinary osmolality of <300 vs. >2,000 mosmol/kgH₂O in vehicle-infused rats. The tolvaptan infusion produced large decreases in the renal abundance of aquaporin-2 (AQP2), aquaporin-3 (AQP3), the β-subunit of the epithelial sodium channel (β-ENaC), and γ-ENaC that were comparable to the differences seen in vehicle-infused vs. vasopressin-infused Brattleboro rats. Thus we conclude that tolvaptan infusion in rats provides an additional model (besides dDAVP-infusion in the Brattleboro rat) for the assessment of V2 receptor-mediated vasopressin actions in the kidney. We also provide ancillary in vitro data in rat inner-medullary-collecting-duct suspensions showing that tolvaptan can block vasopressin's effects on phosphorylation of the water channel AQP2 in vitro. Specifically, tolvaptan almost completely inhibited the ability of vasopressin to increase AQP2 phosphorylation at Ser256, Ser264, and Ser269, while strongly inhibiting a vasopressin-induced decrease in AQP2 phosphorylation at Ser261.

Vasopressin and the regulation of aquaporin-2

Water excretion is regulated in large part through the regulation of osmotic water permeability of the renal collecting duct epithelium. Water permeability is controlled by vasopressin through regulation of the water channel, aquaporin-2 (AQP2). Two processes contribute: (1) regulation of AQP2 trafficking to the apical plasma membrane; and (2) regulation of the total amount of the AQP2 protein in the cells. Regulation of AQP2 abundance is defective in several water-balance disorders, including many polyuric disorders and the syndrome of inappropriate antidiuresis. Here we review vasopressin signaling in the renal collecting duct that is relevant to the two modes of water permeability regulation.

Tolvaptan for the treatment of hyponatremia and hypervolemia in patients with congestive heart failure

Patients with heart failure often show increased arginine vasopressin secretion and enhanced sympathetic and renin-angiotensin-aldosterone activation, which accelerate renal water reabsorption, causing water retention and volume overload. Tolvaptan is an orally active antagonist of arginine vasopressin type 2 receptors in the collecting duct of the kidney that inhibits water reabsorption without substantially affecting the electrolyte balance. Tolvaptan in combination with conventional diuretics improves fluid retention and congestive symptoms in patients with heart failure and volume overload, with minimal effects on hemodynamics and serum potassium. Tolvaptan slightly increases serum sodium concentrations, generally within the normal range. Although it does not seem to affect long-term mortality, tolvaptan does improve short-term water retention and congestive symptoms in heart failure patients with volume overload despite the use of conventional diuretics, and is approved for this indication in Japan.