Phenotypic and pharmacogenetic evaluation of patients with thiazide-induced hyponatremia

Effects of thiazides and new findings on kidney stones and dysglycemic side effects

Thiazide and thiazide-like diuretics (thiazides) belong to the most frequently prescribed drugs worldwide. By virtue of their natriuretic and vasodilating properties, thiazides effectively lower blood pressure and prevent adverse cardiovascular outcomes. In addition, through their unique characteristic of reducing urine calcium, thiazides are also widely employed for the prevention of kidney stone recurrence and reduction of bone fracture risk. Since their introduction into clinical medicine in the early 1960s, thiazides have been recognized for their association with metabolic side effects, particularly impaired glucose tolerance, and new-onset diabetes mellitus. Numerous hypotheses have been advanced to explain thiazide-induced glucose intolerance, yet underlying mechanisms remain poorly defined. Regrettably, the lack of understanding and unpredictability of these side effects has prompted numerous physicians to refrain from prescribing these effective, inexpensive, and widely accessible drugs. In this review, we outline the pharmacology and mechanism of action of thiazides, highlight recent advances in the understanding of thiazide-induced glucose intolerance, and provide an up-to-date discussion on the role of thiazides in kidney stone prevention.

Cosmic kidney disease: an integrated pan-omic, physiological and morphological study into spaceflight-induced renal dysfunction

Missions into Deep Space are planned this decade. Yet the health consequences of exposure to microgravity and galactic cosmic radiation (GCR) over years-long missions on indispensable visceral organs such as the kidney are largely unexplored. We performed biomolecular (epigenomic, transcriptomic, proteomic, epiproteomic, metabolomic, metagenomic), clinical chemistry (electrolytes, endocrinology, biochemistry) and morphometry (histology, 3D imaging, miRNA-ISH, tissue weights) analyses using samples and datasets available from 11 spaceflight-exposed mouse and 5 human, 1 simulated microgravity rat and 4 simulated GCR-exposed mouse missions. We found that spaceflight induces: 1) renal transporter dephosphorylation which may indicate astronauts' increased risk of nephrolithiasis is in part a primary renal phenomenon rather than solely a secondary consequence of bone loss; 2) remodelling of the nephron that results in expansion of distal convoluted tubule size but loss of overall tubule density; 3) renal damage and dysfunction when exposed to a Mars roundtrip dose-equivalent of simulated GCR.

The Effect of Thiazide Diuretics on Urinary Prostaglandin E2 Excretion and Serum Sodium in the General Population

CONTEXT

Thiazide-induced hyponatremia is one of the most common forms of hyponatremia, but its pathogenesis is incompletely understood. Recent clinical data suggest links with prostaglandin E2 (PGE2) and a single nucleotide polymorphism (SNP) in the prostaglandin transporter gene (SLCO2A1), but it is unknown if these findings also apply to the general population.

OBJECTIVE

To study the associations between serum sodium, thiazide diuretics, urinary excretions of PGE2 and its metabolite (PGEM), and the rs34550074 SNP in SLCO2A1 in the general population.

DESIGN

Prospective population-based cohort study (Rotterdam Study).

SETTING

General population.

PARTICIPANTS

2,178 participants (65% female, age 64 ± 8 years).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Serum sodium levels.

RESULTS

Higher urinary PGE2 excretion was associated with lower serum sodium: difference in serum sodium for each two-fold higher PGE2 -0.19 mmol/l (95%CI -0.31 to -0.06), PGEM -0.29 mmol/l (95%CI -0.41 to -0.17). This association was stronger in thiazide users (per two-fold higher PGE2 -0.73 vs. -0.12 mmol/l and PGEM -0.6 vs. -0.25 mmol/l, p for interaction < 0.05 for both). A propensity score matching analysis of thiazide vs. non-thiazide users yielded similar results. The SNP rs34550074 was not associated with lower serum sodium or higher urinary PGE2 or PGEM excretion in thiazide or non-thiazide users.

CONCLUSIONS

Serum sodium is lower in people with higher urinary PGE2 and PGEM excretion and this association is stronger in thiazide users. This suggests that PGE2-mediated water reabsorption regulates serum sodium, which is relevant for the pathogenesis of hyponatremia in general and thiazide-induced hyponatremia in specific.

Label-free detection of prostaglandin transporter (SLCO2A1) function and inhibition: insights by wound healing and TRACT assays

The prostaglandin transporter (PGT, SLCO2A1) mediates transport of prostanoids (a.o. prostaglandin E2 (PGE2)) into cells and thereby promotes their degradation. Overexpression of PGT leads to low extracellular PGE2 levels and has been linked to impaired wound healing of diabetic foot ulcers. Inhibition of PGT could thus be beneficial, however, no PGT inhibitors are currently on the market and drug discovery efforts are hampered by lack of high-through screening assays for this transporter. Here we report on a label-free impedance-based assay for PGT that measures transport activity through receptor activation (TRACT) utilizing prostaglandin E2 receptor subtype EP3 and EP4 that are activated by PGE2. We found that induction of PGT expression on HEK293-JumpIn-SLCO2A1 cells that also express EP3 and EP4 leads to an over 10-fold reduction in agonistic potency of PGE2. PGE2 potency could be recovered upon inhibition of PGT-mediated PGE2 uptake with PGT inhibitors olmesartan and T26A, the potency of which could be established as well. Moreover, the TRACT assay enabled the assessment of transport function of PGT natural variants. Lastly, HUVEC cells endogenously expressing prostanoid receptors and PGT were exploited to study wound healing properties of PGE2 and T26A in real-time using a novel impedance-based scratch-induced wound healing assay. These novel impedance-based assays will advance PGT drug discovery efforts and pave the way for the development of PGT-based therapies.

Urinary Prostaglandin E2 Excretion and the Risk of Cardiovascular and Kidney Disease

BACKGROUND

Inhibition of prostaglandin synthesis by nonsteroidal anti-inflammatory drugs is associated with cardiovascular mortality and kidney disease. This study hypothesizes that urinary prostaglandin E2 (PGE2) and PGE2 metabolite (PGEM) excretions are markers of cardiovascular and kidney health, because they reflect both systemic and kidney-derived PGE2 production.

METHODS AND RESULTS

PGE2 and PGEM were measured in spot urine samples from 2291 participants (≥55 years old) of the population-based Rotterdam Study. Urinary PGE2 and PGEM excretions were analyzed using linear regression analyses to identify cross-sectional associations with cardiovascular risk factors and baseline estimated glomerular filtration rate (eGFR). Longitudinal associations with cardiovascular mortality and kidney outcomes (eGFR <60 or <45 mL/min per 1.73 m2 and the composite outcome 40% eGFR loss or kidney failure) were assessed with Cox regression. Urinary PGE2 and PGEM excretions were higher with increasing age, lower eGFR, smoking, diabetes, and albuminuria. A 2-fold higher urinary PGE2 and PGEM excretion was associated with a higher risk of cardiovascular mortality (28 825 patient-years; 160 events; PGE2 hazard ratio [HR], 1.27, [95% CI, 1.06-1.54]; PGEM HR, 1.36 [95% CI, 1.10-1.67]). Higher PGE2 excretions were also associated with a higher risk of incident eGFR <60 mL/min per 1.73 m2 (31 530 person-years; 691 events; HR, 1.13 [95% CI, 1.02-1.25]) with similar HRs for the other kidney outcomes.

CONCLUSIONS

Urinary PGE2 and PGEM excretions are novel markers for the presence and progression of cardiovascular and kidney disease. Future studies should address whether these associations are causal and can be targeted to improve cardiovascular and kidney outcomes.

Prostaglandin E2, Osmoregulation, and Disease Progression in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Prostaglandin E2 (PGE2) plays a physiological role in osmoregulation, a process that is affected early in autosomal dominant polycystic kidney disease (ADPKD). PGE2 has also been implicated in the pathogenesis of ADPKD in preclinical models, but human data are limited. Here, we hypothesized that urinary PGE2 excretion is associated with impaired osmoregulation, disease severity, and disease progression in human ADPKD.

METHODS

Urinary excretions of PGE2 and its metabolite (PGEM) were measured in a prospective cohort of patients with ADPKD. The associations between urinary PGE2 and PGEM excretions, markers of osmoregulation, eGFR and height-adjusted total kidney volume were assessed using linear regression models. Cox regression and linear mixed models were used for the longitudinal analysis of the associations between urinary PGE2 and PGEM excretions and disease progression defined as 40% eGFR loss or kidney failure, and change in eGFR over time. In two intervention studies, we quantified the effect of starting tolvaptan and adding hydrochlorothiazide to tolvaptan on urinary PGE2 and PGEM excretions.

RESULTS

In 562 patients with ADPKD (61% female, eGFR 63±28 ml/min per 1.73 m 2 ), higher urinary PGE2 or PGEM excretions were independently associated with higher plasma copeptin, lower urine osmolality, lower eGFR, and greater total kidney volume. Participants with higher baseline urinary PGE2 and PGEM excretions had a higher risk of 40% eGFR loss or kidney failure (hazard ratio, 1.28; 95% confidence interval [CI], 1.13 to 1.46 and hazard ratio, 1.50; 95% CI, 1.26 to 1.80 per two-fold higher urinary PGE2 or PGEM excretions) and a faster change in eGFR over time (-0.39 [95% CI, -0.59 to -0.20] and -0.53 [95% CI, -0.75 to -0.31] ml/min per 1.73 m 2 per year). In the intervention studies, urinary PGEM excretion was higher after starting tolvaptan, while urinary PGE2 excretion was higher after adding hydrochlorothiazide to tolvaptan.

CONCLUSIONS

Higher urinary PGE2 and PGEM excretions in patients with ADPKD are associated with impaired osmoregulation, disease severity, and progression.

Syndrome of Inappropriate Antidiuresis: From Pathophysiology to Management

Hyponatremia is the most common electrolyte disorder, affecting more than 15% of patients in the hospital. Syndrome of inappropriate antidiuresis (SIAD) is the most frequent cause of hypotonic hyponatremia, mediated by nonosmotic release of arginine vasopressin (AVP, previously known as antidiuretic hormone), which acts on the renal V2 receptors to promote water retention. There are a variety of underlying causes of SIAD, including malignancy, pulmonary pathology, and central nervous system pathology. In clinical practice, the etiology of hyponatremia is frequently multifactorial and the management approach may need to evolve during treatment of a single episode. It is therefore important to regularly reassess clinical status and biochemistry, while remaining alert to potential underlying etiological factors that may become more apparent during the course of treatment. In the absence of severe symptoms requiring urgent intervention, fluid restriction (FR) is widely endorsed as the first-line treatment for SIAD in current guidelines, but there is considerable controversy regarding second-line therapy in instances where FR is unsuccessful, which occurs in around half of cases. We review the epidemiology, pathophysiology, and differential diagnosis of SIAD, and summarize recent evidence for therapeutic options beyond FR, with a focus on tolvaptan, urea, and sodium-glucose cotransporter 2 inhibitors.

Hyponatremia Demystified: Integrating Physiology to Shape Clinical Practice

Hyponatremia is one of the most common problems encountered in clinical practice and one of the least-understood because accurate diagnosis and management require some familiarity with water homeostasis physiology, making the topic seemingly complex. The prevalence of hyponatremia depends on the nature of the population studied and the criteria used to define it. Hyponatremia is associated with poor outcomes including increased mortality and morbidity. The pathogenesis of hypotonic hyponatremia involves the accumulation of electrolyte-free water caused by either increased intake and/or decrease in kidney excretion. Plasma osmolality, urine osmolality, and urine sodium can help to differentiate among the different etiologies. Brain adaptation to plasma hypotonicity consisting of solute extrusion to mitigate further water influx into brain cells best explains the clinical manifestations of hyponatremia. Acute hyponatremia has an onset within 48 hours, commonly resulting in severe symptoms, while chronic hyponatremia develops over 48 hours and usually is pauci-symptomatic. However, the latter increases the risk of osmotic demyelination syndrome if hyponatremia is corrected rapidly; therefore, extreme caution must be exercised when correcting plasma sodium. Management strategies depend on the presence of symptoms and the cause of hyponatremia and are discussed in this review.

Exercise-Associated Hyponatremia in Marathon Runners

Exercise-associated hyponatremia (EAH) was first described as water intoxication by Noakes et al. in 1985 and has become an important topic linked to several pathological conditions. However, despite progressive research, neurological disorders and even deaths due to hyponatremic encephalopathy continue to occur. Therefore, and due to the growing popularity of exercise-associated hyponatremia, this topic is of great importance for marathon runners and all professionals involved in runners' training (e.g., coaches, medical staff, nutritionists, and trainers). The present narrative review sought to evaluate the prevalence of EAH among marathon runners and to identify associated etiological and risk factors. Furthermore, the aim was to derive preventive and therapeutic action plans for marathon runners based on current evidence. The search was conducted on PubMed, Scopus and Google Scholar using a predefined search algorithm by aggregating multiple terms (marathon run; exercise; sport; EAH; electrolyte disorder; fluid balance; dehydration; sodium concentration; hyponatremia). By this criterion, 135 articles were considered for the present study. Our results revealed that a complex interaction of different factors could cause EAH, which can be differentiated into event-related (high temperatures) and person-related (female sex) risk factors. There is variation in the reported prevalence of EAH, and two major studies indicated an incidence ranging from 7 to 15% for symptomatic and asymptomatic EAH. Athletes and coaches must be aware of EAH and its related problems and take appropriate measures for both training and competition. Coaches need to educate their athletes about the early symptoms of EAH to intervene at the earliest possible stage. In addition, individual hydration strategies need to be developed for the daily training routine, ideally in regard to sweat rate and salt losses via sweat. Future studies need to investigate the correlation between the risk factors of EAH and specific subgroups of marathon runners.

Pathophysiology of Drug-Induced Hyponatremia

Drug-induced hyponatremia caused by renal water retention is mainly due to syndrome of inappropriate antidiuresis (SIAD). SIAD can be grouped into syndrome of inappropriate antidiuretic hormone secretion (SIADH) and nephrogenic syndrome of inappropriate antidiuresis (NSIAD). The former is characterized by uncontrolled hypersecretion of arginine vasopressin (AVP), and the latter is produced by intrarenal activation for water reabsorption and characterized by suppressed plasma AVP levels. Desmopressin is useful for the treatment of diabetes insipidus because of its selective binding to vasopressin V2 receptor (V2R), but it can induce hyponatremia when prescribed for nocturnal polyuria in older patients. Oxytocin also acts as a V2R agonist and can produce hyponatremia when used to induce labor or abortion. In current clinical practice, psychotropic agents, anticancer chemotherapeutic agents, and thiazide diuretics are the major causes of drug-induced hyponatremia. Among these, vincristine and ifosfamide were associated with sustained plasma AVP levels and are thought to cause SIADH. However, others including antipsychotics, antidepressants, anticonvulsants, cyclophosphamide, and thiazide diuretics may induce hyponatremia by intrarenal mechanisms for aquaporin-2 (AQP2) upregulation, compatible with NSIAD. In these cases, plasma AVP levels are suppressed by negative feedback. In rat inner medullary collecting duct cells, haloperidol, sertraline, carbamazepine, and cyclophosphamide upregulated V2R mRNA and increased cAMP production in the absence of vasopressin. The resultant AQP2 upregulation was blocked by a V2R antagonist tolvaptan or protein kinase A (PKA) inhibitors, suggestive of the activation of V2R-cAMP-PKA signaling. Hydrochlorothiazide can also upregulate AQP2 in the collecting duct without vasopressin, either directly or via the prostaglandin E2 pathway. In brief, nephrogenic antidiuresis, or NSIAD, is the major mechanism for drug-induced hyponatremia. The associations between pharmacogenetic variants and drug-induced hyponatremia is an area of ongoing research.

Diagnosis and Management of Hyponatremia: A Review

IMPORTANCE

Hyponatremia is the most common electrolyte disorder and it affects approximately 5% of adults and 35% of hospitalized patients. Hyponatremia is defined by a serum sodium level of less than 135 mEq/L and most commonly results from water retention. Even mild hyponatremia is associated with increased hospital stay and mortality.

OBSERVATIONS

Symptoms and signs of hyponatremia range from mild and nonspecific (such as weakness or nausea) to severe and life-threatening (such as seizures or coma). Symptom severity depends on the rapidity of development, duration, and severity of hyponatremia. Mild chronic hyponatremia is associated with cognitive impairment, gait disturbances, and increased rates of falls and fractures. In a prospective study, patients with hyponatremia more frequently reported a history of falling compared with people with normal serum sodium levels (23.8% vs 16.4%, respectively; P < .01) and had a higher rate of new fractures over a mean follow-up of 7.4 years (23.3% vs 17.3%; P < .004). Hyponatremia is a secondary cause of osteoporosis. When evaluating patients, clinicians should categorize them according to their fluid volume status (hypovolemic hyponatremia, euvolemic hyponatremia, or hypervolemic hyponatremia). For most patients, the approach to managing hyponatremia should consist of treating the underlying cause. Urea and vaptans can be effective treatments for the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure, but have adverse effects (eg, poor palatability and gastric intolerance with urea; and overly rapid correction of hyponatremia and increased thirst with vaptans). Severely symptomatic hyponatremia (with signs of somnolence, obtundation, coma, seizures, or cardiorespiratory distress) is a medical emergency. US and European guidelines recommend treating severely symptomatic hyponatremia with bolus hypertonic saline to reverse hyponatremic encephalopathy by increasing the serum sodium level by 4 mEq/L to 6 mEq/L within 1 to 2 hours but by no more than 10 mEq/L (correction limit) within the first 24 hours. This treatment approach exceeds the correction limit in about 4.5% to 28% of people. Overly rapid correction of chronic hyponatremia may cause osmotic demyelination, a rare but severe neurological condition, which can result in parkinsonism, quadriparesis, or even death.

CONCLUSIONS AND RELEVANCE

Hyponatremia affects approximately 5% of adults and 35% of patients who are hospitalized. Most patients should be managed by treating their underlying disease and according to whether they have hypovolemic, euvolemic, or hypervolemic hyponatremia. Urea and vaptans can be effective in managing the syndrome of inappropriate antidiuresis and hyponatremia in patients with heart failure; hypertonic saline is reserved for patients with severely symptomatic hyponatremia.

Current and Future Burdens of Heat-Related Hyponatremia: A Nationwide Register-Based Study

CONTEXT

A seasonal variation in hyponatremia, with higher incidence rates during hot summer days, has been demonstrated. Whether this applies to cool temperate regions is currently unknown.

OBJECTIVE

The aim of this study was to investigate the influence of ambient temperature on hyponatremia in the Swedish population under current and future climate scenarios.

METHODS

This nationwide cohort study identified all patients hospitalized with a first-ever principal diagnosis of hyponatremia between October 2005 and December 2014. Incidence rates for hyponatremia were calculated as number of hospitalizations divided by person-days at risk in the adult Swedish population at a given temperature, in increments of 1 °C.

RESULTS

The incidence of hyponatremia was stable at 0.3 per million person-days from -10 to 10 °C, but increased rapidly at 24-hour mean temperatures above 15 °C, with 2.26 hospitalizations per million days at the highest recorded temperature of 25 °C. Women and elderly carried the greatest risk, with an incidence of 35 hospitalizations per million days in individuals ≥ 80 years of age on the hottest days, corresponding to a 15-fold increase in incidence compared with cool days. A future 1 or 2 °C increase in mean temperature is expected to increase the incidence of hyponatremia by 6.3% and 13.9%, respectively.

CONCLUSION

The risk of hospitalization due to hyponatremia increases rapidly at temperatures above 15 °C, indicating a threshold effect. Over the next decades, rising global temperatures are expected to increase the inpatient burden of hyponatremia by approximately 10%. Strategies for protecting vulnerable groups are necessary to reduce this risk.

2022 Guidelines of the Taiwan Society of Cardiology and the Taiwan Hypertension Society for the Management of Hypertension

Hypertension is the most important modifiable cause of cardiovascular (CV) disease and all-cause mortality worldwide. Despite the positive correlations between blood pressure (BP) levels and later CV events since BP levels as low as 100/60 mmHg have been reported in numerous epidemiological studies, the diagnostic criteria of hypertension and BP thresholds and targets of antihypertensive therapy have largely remained at the level of 140/90 mmHg in the past 30 years. The publication of both the SPRINT and STEP trials (comprising > 8,500 Caucasian/African and Chinese participants, respectively) provided evidence to shake this 140/90 mmHg dogma. Another dogma regarding hypertension management is the dependence on office (or clinic) BP measurements. Although standardized office BP measurements have been widely recommended and adopted in large-scale CV outcome trials, the practice of office BP measurements has never been ideal in real-world practice. Home BP monitoring (HBPM) is easy to perform, more likely to be free of environmental and/or emotional stress, feasible to document long-term BP variations, of good reproducibility and reliability, and more correlated with hypertension-mediated organ damage (HMOD) and CV events, compared to routine office BP measurements. In the 2022 Taiwan Hypertension Guidelines of the Taiwan Society of Cardiology (TSOC) and the Taiwan Hypertension Society (THS), we break these two dogmas by recommending the definition of hypertension as ≥ 130/80 mmHg and a universal BP target of < 130/80 mmHg, based on standardized HBPM obtained according to the 722 protocol. The 722 protocol refers to duplicate BP readings taken per occasion ("2"), twice daily ("2"), over seven consecutive days ("7"). To facilitate implementation of the guidelines, a series of flowcharts encompassing assessment, adjustment, and HBPM-guided hypertension management are provided. Other key messages include that: 1) lifestyle modification, summarized as the mnemonic S-ABCDE, should be applied to people with elevated BP and hypertensive patients to reduce life-time BP burden; 2) all 5 major antihypertensive drugs (angiotensin-converting enzyme inhibitors [A], angiotensin receptor blockers [A], β-blockers [B], calcium-channel blockers [C], and thiazide diuretics [D]) are recommended as first-line antihypertensive drugs; 3) initial combination therapy, preferably in a single-pill combination, is recommended for patients with BP ≥ 20/10 mmHg above targets; 4) a target hierarchy (HBPM-HMOD- ambulatory BP monitoring [ABPM]) should be considered to optimize hypertension management, which indicates reaching the HBPM target first and then keeping HMOD stable or regressed, otherwise ABPM can be arranged to guide treatment adjustment; and 5) renal denervation can be considered as an alternative BP-lowering strategy after careful clinical and imaging evaluation.

Thiazide-associated hyponatremia in internal medicine patients: analysis of epidemiological and biochemical profiles

Thiazide-associated hyponatremia (TAH) is a clinically important side effect of the therapy with thiazide and thiazide-like diuretics. This study aims to analyze epidemiological, biochemical, and symptomatological profiles (including volume status) of patients admitted with TAH. A retrospective hospital record study was performed. Epidemiological and biochemical parameters and symptoms were compared between the thiazide (n = 143) and non-thiazide (n = 282) groups. Patients in the thiazide group were classified as hypo-, normo-, or hypervolemic. Furthermore, the comparison of epidemiological, biochemical, partially pharmacotherapeutical, and symptomatological parameters between the hypovolemic and normovolemic groups was performed. The thiazide group showed lower s-Na (p = 0.008), s-K (p <0.001), s-Cl (p <0.001), measured s-osmolality (p = 0.021), and eGFR (p <0.001); higher s-urea (p <0.001), s-creatinine (p = 0.023), s-glucose (p <0.001), u-osmolality (p = 0.012), u-Na (p <0.001), u-K (p = 0.023), and u-Cl (p <0.001). Patients using thiazide were older (p <0.001), more likely to be female (p = 0.011), and with symptoms corresponding more to chronic hyponatremia. Compared to the normovolemic group (n = 93; 65%), the hypovolemic patients (n = 47; 32.9%) showed higher s-urea (p = 0.005), s-creatinine (p = 0.045), and s-UA (p = 0.010); lower eGFR (p = 0.032), u-Na (p = 0.015), u-Cl (p = 0.016), anorexia (p <0.001), and a higher frequency of furosemide use (p <0.001). Thiazide use is a crucial etiological cause of hypotonic hyponatremia among internal medicine inpatients, associated with more severe hyponatremia, but with no difference in the in-hospital mortality. Even in hypo-osmolar conditions of TAH, 32.9% of patients exhibited signs of volume depletion. FE-UA did not differ between the hypovolemic and the normovolemic patients in TAH conditions. Anorexia and the combination of thiazide together with furosemide, rather than thiazide use alone, were risk factors for hypovolemic hyponatremia without affecting FE-UA.

Effects of Hydrochlorothiazide and Metformin on Aquaresis and Nephroprotection by a Vasopressin V2 Receptor Antagonist in ADPKD: A Randomized Crossover Trial

BACKGROUND AND OBJECTIVES

The vasopressin V2 receptor antagonist tolvaptan is the only drug that has been proven to be nephroprotective in autosomal dominant polycystic kidney disease (ADPKD). Tolvaptan also causes polyuria, limiting tolerability. We hypothesized that cotreatment with hydrochlorothiazide or metformin may ameliorate this side effect.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a clinical study and an animal study. In a randomized, controlled, double-blind, crossover trial, we included 13 tolvaptan-treated patients with ADPKD. Patients were treated for three 2-week periods with hydrochlorothiazide, metformin, or placebo in random order. Primary outcome was change in 24-hour urine volume. We also measured GFR and a range of metabolic and kidney injury markers.

RESULTS

Patients (age 45±8 years, 54% women, measured GFR of 55±11 ml/min per 1.73 m2) had a baseline urine volume on tolvaptan of 6.9±1.4 L/24 h. Urine volume decreased to 5.1 L/24 h (P<0.001) with hydrochlorothiazide and to 5.4 L/24 h (P<0.001) on metformin. During hydrochlorothiazide treatment, plasma copeptin (surrogate for vasopressin) decreased, quality of life improved, and several markers of kidney damage and glucose metabolism improved. Metformin did not induce changes in these markers or in quality of life. Given these results, the effect of adding hydrochlorothiazide to tolvaptan was investigated on long-term kidney outcome in an animal experiment. Water intake in tolvaptan-hydrochlorothiazide cotreated mice was 35% lower than in mice treated with tolvaptan only. Combination treatment was superior to "no treatment" on markers of disease progression (kidney weight, P=0.003 and cystic index, P=0.04) and superior or equal to tolvaptan alone.

CONCLUSIONS

Both metformin and hydrochlorothiazide reduced tolvaptan-caused polyuria in a short-term study. Hydrochlorothiazide also reduced polyuria in a long-term animal model without negatively affecting nephroprotection.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2022_03_21_CJN11260821.mp3.

A Vasopressin-Induced Change in Prostaglandin Receptor Subtype Expression Explains the Differential Effect of PGE2 on AQP2 Expression

Arginine vasopressin (AVP) stimulates the concentration of renal urine by increasing the principal cell expression of aquaporin-2 (AQP2) water channels. Prostaglandin E₂ (PGE₂) and prostaglandin_2α (PGF_2α) increase the water absorption of the principal cell without AVP, but PGE₂ decreases it in the presence of AVP. The underlying mechanism of this paradoxical response was investigated here. Mouse cortical collecting duct (mkpCCD_c14) cells mimic principal cells as they endogenously express AQP2 in response to AVP. PGE₂ increased AQP2 abundance without desmopressin (dDAVP), while in the presence of dDAVP, PGE₂, and PGF_2α reduced AQP2 abundance. dDAVP increased the cellular PGD₂ and PGE₂ release and decreased the PGF_2α release. MpkCCD cells expressed mRNAs for the receptors of PGE₂ (EP1/EP4), PGF₂ (FP), and TxB₂ (TP). Incubation with dDAVP increased the expression of EP1 and FP but decreased the expression of EP4. In the absence of dDAVP, incubation of mpkCCD cells with an EP4, but not EP1/3, agonist increased AQP2 abundance, and the PGE₂-induced increase in AQP2 was blocked with an EP4 antagonist. Moreover, in the presence of dDAVP, an EP1/3, but not EP4, agonist decreased the AQP2 abundance, and the addition of EP1 antagonists prevented the PGE₂-mediated downregulation of AQP2. Our study shows that in mpkCCD_c14 cells, reduced EP4 receptor and increased EP1/FP receptor expression by dDAVP explains the differential effects of PGE₂ and PGF_2α on AQP2 abundance with or without dDAVP. As the V2R and EP4 receptor, but not the EP1 and FP receptor, can couple to Gs and stimulate the cyclic adenosine monophosphate (cAMP) pathway, our data support a view that cells can desensitize themselves for receptors activating the same pathway and sensitize themselves for receptors of alternative pathways.

The Role of Vasopressin V2 Receptor in Drug-Induced Hyponatremia

Hyponatremia is frequently encountered in clinical practice and usually induced by renal water retention. Many medications are considered to be among the various causes of hyponatremia, because they either stimulate the release of arginine vasopressin (AVP) or potentiate its action in the kidney. Antidepressants, anticonvulsants, antipsychotics, diuretics, and cytotoxic agents are the major causes of drug-induced hyponatremia. However, studies addressing the potential of these drugs to increase AVP release from the posterior pituitary gland or enhance urine concentration through intrarenal mechanisms are lacking. We previously showed that in the absence of AVP, sertraline, carbamazepine, haloperidol, and cyclophosphamide each increased vasopressin V2 receptor (V2R) mRNA and aquaporin-2 (AQP2) protein and mRNA expression in primary cultured inner medullary collecting duct cells. The upregulation of AQP2 was blocked by the V2R antagonist tolvaptan or protein kinase A (PKA) inhibitors. These findings led us to conclude that the nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is the main mechanism of drug-induced hyponatremia. Previous studies have also shown that the V2R has a role in chlorpropamide-induced hyponatremia. Several other agents, including metformin and statins, have been found to induce antidiuresis and AQP2 upregulation through various V2R-independent pathways in animal experiments but are not associated with hyponatremia despite being frequently used clinically. In brief, drug-induced hyponatremia can be largely explained by AQP2 upregulation from V2R-cAMP-PKA signaling in the absence of AVP stimulation. This paper reviews the central and nephrogenic mechanisms of drug-induced hyponatremia and discusses the importance of the canonical pathway of AQP2 upregulation in drug-induced NSIAD.

Thiazide diuretics and the rate of disease progression in autosomal dominant polycystic kidney disease: an observational study

BACKGROUND

In autosomal dominant polycystic kidney disease (ADPKD), hypertension is prevalent and cardiovascular events are the main cause of death. Thiazide diuretics are often prescribed as second-line antihypertensives, on top of renin-angiotensin-aldosterone system (RAAS) blockade. There is a concern, however, that diuretics may increase vasopressin concentration and RAAS activity, thereby worsening disease progression in ADPKD. We aimed to investigate the validity of these suggestions.

METHODS

We analysed an observational cohort of 533 ADPKD patients. Plasma copeptin (surrogate for vasopressin), aldosterone and renin were measured by enzyme-linked immunosorbent assay and radioimmunoassay, respectively. Linear mixed models were used to assess the association of thiazide use with estimated glomerular filtration rate (eGFR) decline and Cox proportional hazards models for the association with the composite kidney endpoint of incident end-stage kidney disease, 40% eGFR decline or death.

RESULTS

A total of 23% of participants (n = 125) used thiazide diuretics at baseline. Compared with non-users, thiazide users were older, a larger proportion was male, they had lower eGFRs and similar blood pressure under more antihypertensives. Plasma copeptin was higher, but this difference disappeared after adjustment for age and sex. Both renin and aldosterone were higher in thiazide users. There was no difference between thiazide users and non-users in the rate of eGFR decline {difference -0.35 mL/min/1.73 m2 per year [95% confidence interval (CI) -0.83 to -0.14], P = 0.2} during 3.9 years of follow-up (interquartile range 2.5-4.9). This did not change after adjustment for potential confounders [difference final model: 0.08 mL/min/1.73 m2 per year [95% CI -0.46 to -0.62], P = 0.8). In the crude model, thiazide use was associated with a higher incidence of the composite kidney endpoint [hazard ratio (HR) 1.53 (95% CI 1.05-2.23), P = 0.03]. However, this association lost significance after adjustment for age and sex and remained unassociated after adjustment for additional confounders [final model: HR 0.80 (95% CI 0.50-1.29), P = 0.4].

CONCLUSIONS

These data do not show that thiazide diuretics have a detrimental effect on the rate of disease progression in ADPKD and suggest that these drugs can be prescribed as second-line antihypertensives.

Risk of Electrolyte Disorders, Syncope, and Falls in Patients Taking Thiazide Diuretics: Results of a Cross-Sectional Study

BACKGROUND

Thiazide diuretics are a mainstay in the management of hypertension and often associated with dyselectrolytemias. We investigated the prevalence of and risk factors for hyponatremia and hypokalemia in thiazide users, substance-specific differences, and the association of thiazides with syncope and falls.

METHODS

In this cross-sectional analysis all patients admitted to an interdisciplinary emergency department in Switzerland between January 1, 2017, and December 31, 2018, with measurements of serum sodium and potassium were included. Data regarding serum electrolytes and creatinine were analyzed to classify for dysnatremias, dyskalemias, and acute kidney injury. Chart reviews were performed to screen for syncope or falls.

RESULTS

A total of 1604 patients (7.9%) took thiazides. Acute kidney injury was significantly more common in thiazide users (22.1 vs 7%, P < .0001). Hyponatremia (22.1 vs 9.8%, P < .0001) and hypokalemia (19 vs 11%, P < .0001) were more frequent with thiazides. Thiazide use together with higher age and female sex were independent predictors of hyponatremia and hypokalemia. A dose-dependent effect was found for electrolyte disorders, and there was a variance in risk between the investigated substances with chlorthalidone bearing the highest and hydrochlorothiazide the lowest risk. Patients taking thiazide diuretics had significantly more episodes of syncope and falls.

CONCLUSIONS

Thiazide use is a clear risk factor for hyponatremia and hypokalemia. The effect appears to be dose-dependent and highly variable depending on the substance. Syncope and falls seem to be causally related to thiazide use. Especially in patients who are elderly, female, and prone to falls, the use of thiazide diuretics should be thoroughly questioned.

Potential Use of Pharmacogenetics to Reduce Drug-Induced Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Syndrome of inappropriate antidiuretic hormone (SIADH) is a common cause of hyponatremia, and many cases represent adverse reactions to drugs that alter ion channel conductance within the peptidergic nerve terminals of the posterior pituitary. The frequency of drug-induced SIADH increases with age; as many as 20% of patients residing in nursing homes have serum sodium levels below 135 mEq/L. Mild hyponatremia is associated with cognitive changes, gait instability, and falls. Severe hyponatremia is associated with cerebral edema, seizures, permanent disability, and/or death. Although pharmacogenetic tests are now being deployed for some drugs capable of causing SIADH (e.g., antidepressants, antipsychotics, and opioid analgesics), the implementation of these tests has been based upon the prior known association of these drugs with other serious adverse drug reactions (e.g., electrocardiographic abnormalities). Work is needed in large observational cohorts to quantify the strength of association between pharmacogene variants and drug-induced SIADH so that decision support can be developed to identify patients at high risk.

The Combined Use of Fractional Urate and Potassium Excretion in the Diagnosis of Diuretic-Induced Hyponatremia

Introduction Thiazide and loop-diuretics are among the most widely used drugs in the therapy of hypertension and chronic heart failure. Furthermore, hyponatremia is the most prevalent electrolyte imbalance affecting up to 25-30% of hospitalized patients while syndrome of inappropriate antidiuresis (SIAD) is involving approximately 35% of hyponatraemic inpatients. Clinical and laboratoristic algorithms support the differential diagnosis of hypotonic hyponatremia in actual guidelines of SIAD, but a potential bias is represented by the misleading clinical assessment of the extracellular volume status in diuretic-treated patients where the necessity of withdrawal of the therapy is mandatory. We investigated the role of fractional uric acid and potassium excretion (FEUA and FEK) in the differential diagnosis of hypotonic hyponatremia in SIAD and diuretic-treated patients. Methods Thirty-six SIAD, 30 thiazide-induced hyponatremia (TIH), and 32 diuretic-induced hyponatremia (DIH) patients were investigated calculating FEUA and FEK values in receiver operating characteristic (ROC) curve analysis to improve the diagnostic approach of hypotonic hyponatremia. Results The combination of the two investigated markers showed different significative results generating patterns useful to discriminate among the three different hyponatremic groups. Conclusion The fractional uric acid and potassium excretion could be considered as new markers in the diagnostic approach of hyponatremic diuretic-treated patients where classical algorithms could fail.

Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders

We discuss the use of urine electrolytes and urine osmolality in the clinical diagnosis of patients with fluid, electrolytes, and acid-base disorders, emphasizing their physiological basis, their utility, and the caveats and limitations in their use. While our focus is on information obtained from measurements in the urine, clinical diagnosis in these patients must integrate information obtained from the history, the physical examination, and other laboratory data.

Psychotropic drugs upregulate aquaporin-2 via vasopressin-2 receptor/cAMP/protein kinase A signaling in inner medullary collecting duct cells

Psychotropic drugs may be associated with hyponatremia, but an understanding of how they induce water retention in the kidney remains elusive. Previous studies have postulated that they may increase vasopressin production in the hypothalamus without supporting evidence. In this study, we investigated the possibility of drug-induced nephrogenic syndrome of inappropriate antidiuresis using haloperidol, sertraline, and carbamazepine. Haloperidol, sertraline, or carbamazepine were treated in inner medullary collecting duct (IMCD) suspensions and primary cultured IMCD cells prepared from male Sprague-Dawley rats. The responses of intracellular cAMP production, aquaporin-2 (AQP2) protein expression and localization, vasopressin-2 receptor (V2R) and AQP2 mRNA, and cAMP-responsive element-binding protein (CREB) were tested with and without tolvaptan and the protein kinase A (PKA) inhibitors H89 and Rp-cAMPS. In IMCD suspensions, cAMP production was increased by haloperidol, sertraline, or carbamazepine and was relieved by tolvaptan cotreatment. In primary cultured IMCD cells, haloperidol, sertraline, or carbamazepine treatment increased total AQP2 and decreased phosphorylated Ser261-AQP2 protein expression. Notably, these responses were reversed by cotreatment with tolvaptan or a PKA inhibitor. AQP2 membrane trafficking was induced by haloperidol, sertraline, or carbamazepine and was also blocked by cotreatment with tolvaptan or a PKA inhibitor. Furthermore, upregulation of V2R and AQP2 mRNA and phosphorylated CREB was induced by haloperidol, sertraline, or carbamazepine and was blocked by tolvaptan cotreatment. We conclude that, in the rat IMCD, psychotropic drugs upregulate AQP2 via V2R-cAMP-PKA signaling in the absence of vasopressin stimulation. The vasopressin-like action on the kidney appears to accelerate AQP2 transcription and dephosphorylate AQP2 at Ser261.NEW & NOTEWORTHY It is unclear whether antipsychotic drugs can retain water in the kidney in the absence of vasopressin. This study demonstrates that haloperidol, sertraline, and carbamazepine can produce nephrogenic syndrome of inappropriate antidiuresis because they directly upregulate vasopressin-2 receptor and aquaporin-2 (AQP2) via cAMP/PKA signaling. We showed that, in addition to AQP2 trafficking, AQP2 protein abundance was rapidly increased by treatment with antipsychotic drugs in association with dephosphorylation of AQP2 at Ser261 and accelerated AQP2 transcription.

[Hyponatremia - causes, diagnostic evaluation and treatment]

Intact osmoregulation prevents osmotic gradients thereby limiting cell swelling and shrinking. Hyponatremia is a state of an osmole-free water excess compared to the amounts of solutes and clinical management of hyponatremic patients requires pathophysiology-oriented approaches to select appropriate treatments. Clinicians need to assess the patient's volume status to differentiate hyponatremia with volume depletion, expansion or normovolemia, respectively. In addition, work-up includes differentiation between acute and chronic and asymptomatic and symptomatic hyponatremia. Estimation of free water-clearance helps predicting Serum-Na⁺ changes and is important to prevent overcorrection of hyponatremia. Water restriction, hypertonic salt, urea, V2-receptor-blockers and recently sodium glucose cotransporter 2 (SGLT2) inhibitors were employed to treat patients with hyponatremia.

Recent advances in studies of SLCO2A1 as a key regulator of the delivery of prostaglandins to their sites of action

Solute carrier organic anion transporter family member 2A1 (SLCO2A1, also known as PGT, OATP2A1, PHOAR2, or SLC21A2) is a plasma membrane transporter consisting of 12 transmembrane domains. It is ubiquitously expressed in tissues, and mediates the membrane transport of prostaglandins (PGs, mainly PGE₂, PGF_2α, PGD₂) and thromboxanes (e.g., TxB₂). SLCO2A1-mediated transport is electrogenic and is facilitated by an outwardly directed gradient of lactate. PGs imported by SLCO2A1 are rapidly oxidized by cytoplasmic 15-hydroxyprostaglandin dehydrogenase (15-PGDH, encoded by HPGD). Accumulated evidence suggests that SLCO2A1 plays critical roles in many physiological processes in mammals, and it is considered a potential pharmacological target for diabetic foot ulcer treatment, antipyresis, and non-hormonal contraception. Furthermore, whole-exome analyses suggest that recessive inheritance of SLCO2A1 mutations is associated with two refractory diseases, primary hypertrophic osteoarthropathy (PHO) and chronic enteropathy associated with SLCO2A1 (CEAS). Intriguingly, SLCO2A1 is also a key component of the Maxi-Cl channel, which regulates fluxes of inorganic and organic anions, including ATP. Further study of the bimodal function of SLCO2A1 as a transporter and ion channel is expected to throw new light on the complex pathology of human diseases. Here, we review and summarize recent information on the molecular functions of SLCO2A1, and we discuss its pathophysiological significance.

Association between newly initiated thiazide diuretics and hospitalization due to hyponatremia

Purpose

Thiazide diuretics are the most common origin of drug-induced hyponatremia. However, population-based studies on clinical outcomes are lacking. We therefore explored the time course and absolute risk of thiazide-associated hospitalization due to hyponatremia in Sweden.

Methods

Population-based case-control study including patients hospitalized with a principal diagnosis of hyponatremia (n = 11,213) compared with controls (n = 44,801). Linkage of registers was used to acquire data. Multivariable regression was applied to explore time-dependent associations between thiazide diuretics and hospitalization due to hyponatremia. Attributable risks were calculated assessing the disease burden attributable to thiazides.

Results

Individuals initiating thiazide treatment were exposed to an immediate increase in risk for hospitalization with adjusted odds ratio (aOR) (95% CI) of 48 (28–89). The associations gradually declined reaching an aOR of 2.9 (2.7–3.1) for individuals treated for longer than 13 weeks. The attributable risk of hyponatremia-associated hospitalization due to thiazides of any treatment length was 27% (3095/11,213). Among 806 patients initiating treatment < 90 days before hospitalization, hyponatremia could be attributed to thiazides in 754. Based on nationwide data, 616,678 individuals were initiated on thiazides during the 8-year study period suggesting an absolute risk of 0.12% (754/661,678) for subsequent hospitalization with a main diagnosis of hyponatremia.

Conclusions

Thiazide diuretics attributed to more than one in four individuals hospitalized due to hyponatremia. The risk increase was very pronounced during the first month of treatment and then gradually declined, without returning to normal. However, the absolute risk for the development of hyponatremia demanding hospitalization may for most individuals be modest.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00228-020-03086-6.

MicroRNA-132 regulates salt-dependent steady-state renin levels in mice

The body's salt and fluid balance is regulated by the renin-angiotensin-aldosterone system. Generation of prostaglandin-E2 (PGE2) in a cyclo-oxygenase-2 (COX-2)-dependent manner in the macula densa, the salt-sensing cells of the kidney, plays a dominant role in renin regulation. Here we show that miR-132 directly targets Cox-2 and affects subsequent PGE2 and renin levels. MiR-132 is induced and reduced by low- and high salt treatment, respectively, in a p38- and ERK1/2-independent and CREB- and salt inducible kinase-dependent manner. Silencing of miR-132 in mice increases macula densa COX-2 expression and elevates PGE2 and renin levels, which are abrogated by the selective COX-2-inhibitor Celecoxib. Furthermore, a low or high salt diet induces and reduces macula densa miR-132 expression, while low salt diet combined with silencing miR-132 further increases renin levels. Taken together, we demonstrate a posttranscriptional regulatory role for salt-dependent miR-132 in fine-tuning the steady-state levels of renin.

Hypertonic saline, isotonic saline, water restriction, long loops diuretics, urea or vaptans to treat hyponatremia

Introduction: Hyponatremia is the most common fluid and electrolyte abnormality. It is associated with much higher morbidity and mortality rates than found in non hyponatremic patients.Areas covered: When the physician is faced to a hyponatremic patient he first has to confirm that hyponatremia is associated with hypoosmolality. Then he must answer to a series of questions: What is its origin? Is it acute or chronic? Which treatment is the most appropriate? We will discuss the various options for the treatment of hypotonic hyponatremia. For a better comprehensive approach of the treatment we will also discuss some pathophysiological data. The use of urea in euvolemic and hypervolemic hyponatremia will be particularly discussed. Literature was reviewed from Jan 1970 to Dec 2019.Expert opinion: Prospective studies showing the benefit in decreasing morbidity by increasing SNa in patients with chronic hyponatremia should be done. These studies should also compare the efficacy and side effects of urea therapy compare to vaptans.

The Role of Fractional Excretion of Uric Acid in the Differential Diagnosis of Hypotonic Hyponatraemia in Patients with Diuretic Therapy

Hyponatraemia is the most common electrolyte imbalance found in hospital population and worldwide thiazide and loop-diuretics are among the most widely used drugs. Syndrome of inappropriate antidiuresis diagnosis (SIAD) is complicated in the presence of diuretic therapy due to the misleading clinical assessment of the extracellular volume status, and in order to make SIAD diagnosis it is often necessary to withdraw diuretic therapy. Our study aimed to investigate the diagnostic role of these alternative markers of volume status, serum uric acid (sUA) and fractional excretion of uric acid (FEUA), in hyponatraemic patients treated with different diuretic drugs. Eighty-nine patients were enrolled with the diagnosis of SIAD, diuretic-induced hyponatremia (DIH, treated with furosemide and potassium canrenoate) or thiazide-induced hyponatremia (TIH, treated with hydrochlorothiazide, metolazone or indapamide) and investigated with receiver operating characteristic analysis and a sensitivity test. Our results show that FEUA discriminated better than sUA between SIAD and DIH patients (area under curve 0.96, <0.001 vs. 0.88, <0.001) while it was a poor marker to discriminate between SIAD and TIH (0.65, NS vs. 0.67, NS). In conclusions, FEUA is an excellent marker to discriminate SIAD vs. sodium depleted patients treated with furosemide and/or potassium canrenoate while the diuretic withdrawal, beyond obtaining a serum Na normalization, is still mandatory for differential diagnosis of sodium depleted patients affected by thiazide-induced hyponatraemia.

A Randomized Trial of Distal Diuretics versus Dietary Sodium Restriction for Hypertension in Chronic Kidney Disease

BACKGROUND

Distal diuretics are considered less effective than loop diuretics in CKD. However, data to support this perception are limited.

METHODS

To investigate whether distal diuretics are noninferior to dietary sodium restriction in reducing BP in patients with CKD stage G3 or G4 and hypertension, we conducted a 6-week, randomized, open-label crossover trial comparing amiloride/hydrochlorothiazide (5 mg/50 mg daily) with dietary sodium restriction (60 mmol per day). Antihypertension medication was discontinued for a 2-week period before randomization. We analyzed effects on BP, kidney function, and fluid balance and related this to renal clearance of diuretics.

RESULTS

A total of 26 patients (with a mean eGFR of 39 ml/min per 1.73 m²) completed both treatments. Dietary sodium restriction reduced sodium excretion from 160 to 64 mmol per day. Diuretics produced a greater reduction in 24-hour systolic BP (SBP; from 138 to 124 mm Hg) compared with sodium restriction (from 134 to 129 mm Hg), as well as a significantly greater effect on extracellular water, eGFR, plasma renin, and aldosterone. Both interventions resulted in a similar decrease in body weight and NT-proBNP. Neither approaches decreased albuminuria significantly, whereas diuretics did significantly reduce urinary angiotensinogen and β2-microglobulin excretion. Although lower eGFR and higher plasma indoxyl sulfate correlated with lower diuretic clearance, the diuretic effects on body weight and BP at lower eGFR were maintained. During diuretic treatment, higher PGE2 excretion correlated with lower free water clearance, and four patients developed mild hyponatremia.

CONCLUSIONS

Distal diuretics are noninferior to dietary sodium restriction in reducing BP and extracellular volume in CKD. Diuretic sensitivity in CKD is maintained despite lower diuretic clearance.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

DD-study: Diet or Diuretics for Salt-sensitivity in Chronic Kidney Disease (DD), NCT02875886.

Mechanism of Thiazide Diuretic Arterial Pressure Reduction: The Search Continues

Thiazide diuretic (TZD)-mediated chronic reduction of arterial pressure is thought to occur through decreased total peripheral vascular resistance. Further, the decreased peripheral vascular resistance is accomplished through TZD activation of an extrarenal target, resulting in inhibition of vascular constriction. However, despite greater than five decades of investigation, little progress has been made into the identification of the TZD extrarenal target. Proposed mechanisms range from direct inhibition of constrictor and activation of relaxant signaling pathways in the vascular smooth muscle to indirect inhibition through decreased neurogenic and hormonal regulatory pathways. Surprisingly, particularly in view of this lack of progress, comprehensive reviews of the subject are absent. Moreover, even though it is well recognized that 1) several types of hypertension are insensitive to TZD reduction of arterial pressure and, further, TZD fail to reduce arterial pressure in normotensive subjects and animals, and 2) different mechanisms underlie acute and chronic TZD, findings derived from these models and parameters remain largely undifferentiated. This review 1) comprehensively describes findings associated with TZD reduction of arterial pressure; 2) differentiates between observations in TZD-sensitive and TZD-insensitive hypertension, normotensive subjects/animals, and acute and chronic effects of TZD; 3) critically evaluates proposed TZD extrarenal targets; 4) proposes guiding parameters for relevant investigations into extrarenal TZD target identification; and 5) proposes a working model for TZD chronic reduction of arterial pressure through vascular dilation.

Hypertension: a new treatment for an old disease? Targeting the immune system

Arterial hypertension represents a serious public health problem, being a major cause of morbidity and mortality worldwide. The availability of many antihypertensive therapeutic strategies still fails to adequately treat around 20% of hypertensive patients, who are considered resistant to conventional treatment. In the pathogenesis of hypertension, immune system mechanisms are activated and both the innate and adaptive immune responses play a crucial role. However, what, when and how the immune system is triggered during hypertension development is still largely undefined. In this context, this review highlights scientific advances in the manipulation of the immune system in order to attenuate hypertension and end-organ damage. Here, we discuss the potential use of immunosuppressants and immunomodulators as pharmacological tools to control the activation of the immune system, by non-specific and specific mechanisms, to treat hypertension and improve end-organ damage. Nevertheless, more clinical trials should be performed with these drugs to establish their therapeutic efficacy, safety and risk-benefit ratio in hypertensive conditions. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Measurement of prostaglandin metabolites is useful in diagnosis of small bowel ulcerations

BACKGROUND

We recently reported on a hereditary enteropathy associated with a gene encoding a prostaglandin transporter and referred to as chronic enteropathy associated with SLCO2A1 gene (CEAS). Crohn’s disease (CD) is a major differential diagnosis of CEAS, because these diseases share some clinical features. Therefore, there is a need to develop a convenient screening test to distinguish CEAS from CD.

AIM

To examine whether prostaglandin E major urinary metabolites (PGE-MUM) can serve as a biomarker to distinguish CEAS from CD.

METHODS

This was a transactional study of 20 patients with CEAS and 98 patients with CD. CEAS was diagnosed by the confirmation of homozygous or compound heterozygous mutation of SLCO2A1. We measured the concentration of PGE-MUM in spot urine by radioimmunoassay, and the concentration was compared between the two groups of patients. We also determined the optimal cut-off value of PGE-MUM to distinguish CEAS from CD by receiver operating characteristic (ROC) curve analysis.

RESULTS

Twenty Japanese patients with CEAS and 98 patients with CD were enrolled. PGE-MUM concentration in patients with CEAS was significantly higher than that in patients with CD (median 102.7 vs 27.9 μg/g × Cre, P < 0.0001). One log unit increase in PGE-MUM contributed to 7.3 increase in the likelihood for the diagnosis of CEAS [95% confidence interval (CI) 3.2-16.7]. A logistic regression analysis revealed that the association was significant even after adjusting confounding factors (adjusted odds ratio 29.6, 95%CI 4.7-185.7). ROC curve analysis revealed the optimal PGE-MUM cut-off value for the distinction of CEAS from CD to be 48.9 μg/g × Cre with 95.0% sensitivity and 79.6% specificity.

CONCLUSION

PGE-MUM measurement is a convenient, non-invasive and useful test for the distinction of CEAS from CD.

A genome-wide association study of sodium levels and drug metabolism in an epilepsy cohort treated with carbamazepine and oxcarbazepine

OBJECTIVE

To ascertain the clinical and genetic factors contributing to carbamazepine- and oxcarbazepine-induced hyponatremia (COIH), and to carbamazepine (CBZ) metabolism, in a retrospectively collected, cross-sectional cohort of people with epilepsy.

METHODS

We collected data on serum sodium levels and antiepileptic drug levels in people with epilepsy attending a tertiary epilepsy center while on treatment with CBZ or OXC. We defined hyponatremia as Na+ ≤134 mEq/L. We estimated the CBZ metabolic ratio defined as the log transformation of the ratio of metabolite CBZ-diol to unchanged drug precursor substrate as measured in serum.

RESULTS

Clinical and genetic data relating to carbamazepine and oxcarbazepine trials were collected in 1141 patients. We did not observe any genome-wide significant associations with sodium level in a linear trend or hyponatremia as a dichotomous trait. Age, sex, number of comedications, phenytoin use, phenobarbital use, and sodium valproate use were significant predictors of CBZ metabolic ratio. No genome-wide significant associations with CBZ metabolic ratio were found.

SIGNIFICANCE

Although we did not detect a genetic predictor of hyponatremia or CBZ metabolism in our cohort, our findings suggest that the determinants of CBZ metabolism are multifactorial.

Approach to and management of abnormalities in plasma sodium

The differential diagnosis between hypertonic, isotonic and hypotonic hyponatremia are presented. The help of some usual serum (urea, uric acid and TCO₂) and urine parameters (mainly osmolality and sodium concentration) are discussed and help to determine the best treatment. Morbidity associated with untreated hyponatremia and with the different treatment available is also discussed. Who to prevent and treat ODS (osmotic demyelating syndrome) is recalled. The pathophysiology and treatment of hypernatremia are also discussed.

Urinary Extracellular Vesicle Protein Profiling and Endogenous Lithium Clearance Support Excessive Renal Sodium Wasting and Water Reabsorption in Thiazide-Induced Hyponatremia

Introduction

Thiazide diuretics are among the most widely used antihypertensive medications worldwide. Thiazide-induced hyponatremia (TIH) is 1 of their most clinically significant adverse effects. A priori TIH must result from excessive saliuresis and/or water reabsorption. We hypothesized that pathways regulating the thiazide-sensitive sodium-chloride cotransporter NCC and the water channel aquaporin-2 (AQP₂) may be involved. Our aim was to assess whether patients with TIH would show evidence of altered NCC and AQP₂ expression in urinary extracellular vesicles (UEVs), and also whether abnormalities of renal sodium reabsorption would be evident using endogenous lithium clearance (ELC).

Methods

Blood and urine samples were donated by patients admitted to hospital with acute symptomatic TIH, after recovery to normonatremia, and also from normonatremic controls on and off thiazides. Urinary extracellular vesicles were isolated and target proteins evaluated by western blotting and by nanoparticle tracking analysis. Endogenous lithium clearance was assessed by inductively coupled plasma mass spectrometry.

Results

Analysis of UEVs by western blotting showed that patients with acute TIH displayed reduced total NCC and increased phospho-NCC and AQP₂ relative to appropriate control groups; smaller differences in NCC and AQP₂ expression persisted after recovery from TIH. These findings were confirmed by nanoparticle tracking analysis. Renal ELC was lower in acute TIH compared to that in controls and convalescent case patients.

Conclusion

Reduced NCC expression and increased AQP₂ expression would be expected to result in saliuresis and water reabsorption in TIH patients. This study raises the possibility that UEV analysis may be of diagnostic utility in less clear-cut cases of thiazide-associated hyponatremia, and may help to identify patients at risk for TIH before thiazide initiation.

Transplantation of a Gitelman Syndrome Kidney Ameliorates Hypertension: A Case Report

Gitelman syndrome is caused by inactivating mutations of the gene that encodes the renal sodium/chloride cotransporter (NCC; encoded by SLC12A3), resulting in hypokalemia, hypomagnesemia, hypocalciuria, and metabolic alkalosis. Renal salt wasting commonly provokes mild hypotension. The paucity of previous kidney transplants from donors with known tubulopathies suggests that such conditions may be considered contraindications to donation. A 76-year-old man received a live unrelated kidney transplant from a donor with known Gitelman syndrome secondary to a pathogenic mutation of SLC12A3. Immediate graft function preceded the emergence of the Gitelman syndrome biochemical phenotype and blood pressure subsequently improved. The recipient developed unexpected hyponatremia. Potential causes are discussed, including the possibility that it paralleled the physiologic changes seen in the high-volume state of thiazide-induced hyponatremia. Transplanted kidneys are subject to nephrotoxicity from the use of calcineurin inhibitors. Acquired Gitelman syndrome may confer a potential long-term advantage to the recipient through both improved blood pressure control and protection against the calcineurin inhibitor-induced side-effect profile caused by NCC overactivation. Both the donor and recipient remain well. In conclusion, Gitelman syndrome need not preclude kidney donation and transference of the phenotype may have benefits for the recipient.

Hypertension genomics and cardiovascular prevention

Hypertension continues to be a major risk factor for global mortality, and recent genome-wide association studies (GWAS) have expanded in size, leading to the identification of further genetic loci influencing blood pressure. In light of the new knowledge from the largest cardiovascular GWAS to date, we review the potential impact of genomics on discovering potential drug targets, risk stratification with genetic risk scores, drug selection with pharmacogenetics, and exploring insights provided by gene-environment interactions.

Clinical and Molecular Features of Thiazide-Induced Hyponatremia

Purpose of Review

Hypertension affects more than 30% of the world’s adult population and thiazide (and thiazide-like) diuretics are amongst the most widely used, effective, and least costly treatments available, with all-cause mortality benefits equivalent to angiotensin-converting enzyme inhibitors or calcium channel antagonists. A minority of patients develop thiazide-induced hyponatremia (TIH) and this is largely unpredictable at the point of thiazide prescription. In some cases, TIH can cause debilitating symptoms and require hospital admission. Although TIH affects only a minority of patients exposed to thiazides, the high prevalence of hypertension leads to TIH being the most common cause of drug-induced hyponatremia requiring hospital admission in the UK. This review examines current clinical and scientific understanding of TIH. Consideration is given to demographic associations, limitations of current electrolyte monitoring regimens, clinical presentation, the phenotype evident on routine clinical blood and urine tests as well as more extensive analyses of blood and urine in research settings, recent genetic associations with TIH, and thoughts on management of the condition.

Recent Findings

Recent genetic and phenotyping analysis has suggested that prostaglandin E2 pathways in the collecting duct may have a role in the development of TIH in a subgroup of patients. Greater understanding of the molecular pathophysiology of TIH raises the prospect of pre-prescription TIH risk profiling and may offer novel insights into how TIH may be avoided, prevented and treated.

Summary

The rising prevalence of hypertension and the widespread use of thiazides mean that further understanding of TIH will continue to be a pressing issue for patients, physicians, and scientists alike for the foreseeable future.

Renal Considerations in the Treatment of Hypertension

There are renal implications when employing intensive blood pressure control strategies. While this approach provides cardiovascular benefit in patients with and without chronic kidney disease, the impact on renal disease progression differs according to the pattern of underlying renal injury. In the setting of proteinuria, stringent blood pressure control has generally conferred a protective effect on renal disease progression, but in the absence of proteinuria, this benefit tends to be much less impressive. Thiazide diuretics are frequently part of the regimen to achieve intensive blood pressure control. These drugs can cause hyponatremia and present with biochemical evidence mimicking the syndrome of inappropriate antidiuretic hormone secretion. Altered prostaglandin transport may explain the unique susceptibility to this complication observed in some patients. Hyperkalemia is also a complication of intensive blood pressure lowering particularly in the setting of renin-angiotensin-aldosterone blockade. There are strategies and new drugs now available that can allow use of these blockers and at the same time ensure a normal plasma potassium concentration.

Biomarkers of adverse drug reactions

Adverse drug reactions can be caused by a wide range of therapeutics. Adverse drug reactions affect many bodily organ systems and vary widely in severity. Milder adverse drug reactions often resolve quickly following withdrawal of the casual drug or sometimes after dose reduction. Some adverse drug reactions are severe and lead to significant organ/tissue injury which can be fatal. Adverse drug reactions also represent a financial burden to both healthcare providers and the pharmaceutical industry. Thus, a number of stakeholders would benefit from development of new, robust biomarkers for the prediction, diagnosis, and prognostication of adverse drug reactions. There has been significant recent progress in identifying predictive genomic biomarkers with the potential to be used in clinical settings to reduce the burden of adverse drug reactions. These have included biomarkers that can be used to alter drug dose (for example, Thiopurine methyltransferase (TPMT) and azathioprine dose) and drug choice. The latter have in particular included human leukocyte antigen (HLA) biomarkers which identify susceptibility to immune-mediated injuries to major organs such as skin, liver, and bone marrow from a variety of drugs. This review covers both the current state of the art with regard to genomic adverse drug reaction biomarkers. We also review circulating biomarkers that have the potential to be used for both diagnosis and prognosis, and have the added advantage of providing mechanistic information. In the future, we will not be relying on single biomarkers (genomic/non-genomic), but on multiple biomarker panels, integrated through the application of different omics technologies, which will provide information on predisposition, early diagnosis, prognosis, and mechanisms. Impact statement • Genetic and circulating biomarkers present significant opportunities to personalize patient therapy to minimize the risk of adverse drug reactions. ADRs are a significant heath issue and represent a significant burden to patients, healthcare providers, and the pharmaceutical industry. • This review details the current state of the art in biomarkers of ADRs (both genetic and circulating). There is still significant variability in patient response which cannot be explained by current knowledge of genetic risk factors for ADRs; however, we discussed how specific advances in genomics have the potential to yield better and more predictive models. • Many current clinically utilized circulating biomarkers of tissue injury are valid biomarkers for a number of ADRs. However, they often give little insight into the specific cell or tissue subtype which may be affected. Emerging circulating biomarkers with potential to provide greater information on the etiology/pathophysiology of ADRs are described.

Hyponatremia in the elderly: challenges and solutions

Decreased serum sodium concentration is a rather frequent electrolyte disorder in the elderly population because of the presence of factors contributing to increased antidiuretic hormone, the frequent prescription of drugs associated with hyponatremia and also because of other mechanisms such as the “tea and toast” syndrome. The aim of this review is to present certain challenges in the evaluation and treatment of hyponatremia in the elderly population and provide practical solutions. Hyponatremia in elderly subjects is mainly caused by drugs (more frequently thiazides and antidepressants), the syndrome of inappropriate antidiuretic hormone secretion (SIAD) or endocrinopathies; however, hyponatremia is multifactorial in a significant proportion of patients. Special attention is needed in the elderly population to exclude endocrinopathies as a cause of hyponatremia before establishing the diagnosis of SIAD, which then requires a stepped diagnostic approach to reveal its underlying cause. The treatment of hyponatremia depends on the type of hyponatremia. Special attention is also needed to correct serum sodium levels at the appropriate rate, especially in chronic hyponatremia, in order to avoid the osmotic demyelination syndrome. In conclusion, both the evaluation and the treatment of hyponatremia pose many challenges in the elderly population.