Genetic Variation in the Renal Sodium Transporters NKCC2, NCC, and ENaC in Relation to the Effects of Loop Diuretic Drugs

Navigating the multifaceted intricacies of the Na+-Cl- cotransporter, a highly regulated key effector in the control of hydromineral homeostasis

The Na+-Cl- cotransporter (NCC; SLC12A3) is a highly regulated integral membrane protein that is known to exist as three splice variants in primates. Its primary role in the kidney is to mediate the cosymport of Na+ and Cl- across the apical membrane of the distal convoluted tubule. Through this role and the involvement of other ion transport systems, NCC allows the systemic circulation to reclaim a fraction of the ultrafiltered Na+, K+, Cl-, and Mg+ loads in exchange for Ca2+ and [Formula: see text]. The physiological relevance of the Na+-Cl- cotransport mechanism in humans is illustrated by several abnormalities that result from NCC inactivation through the administration of thiazides or in the setting of hereditary disorders. The purpose of the present review is to discuss the molecular mechanisms and overall roles of Na+-Cl- cotransport as the main topics of interest. On reading the narrative proposed, one will realize that the knowledge gained in regard to these themes will continue to progress unrelentingly no matter how refined it has now become.

Structure-function relationships in the sodium chloride cotransporter

The thiazide sensitive Na+:Cl− cotransporter (NCC) is the principal via for salt reabsorption in the apical membrane of the distal convoluted tubule (DCT) in mammals and plays a fundamental role in managing blood pressure. The cotransporter is targeted by thiazide diuretics, a highly prescribed medication that is effective in treating arterial hypertension and edema. NCC was the first member of the electroneutral cation-coupled chloride cotransporter family to be identified at a molecular level. It was cloned from the urinary bladder of the Pseudopleuronectes americanus (winter flounder) 30 years ago. The structural topology, kinetic and pharmacology properties of NCC have been extensively studied, determining that the transmembrane domain (TM) coordinates ion and thiazide binding. Functional and mutational studies have discovered residues involved in the phosphorylation and glycosylation of NCC, particularly on the N-terminal domain, as well as the extracellular loop connected to TM7-8 (EL7-8). In the last decade, single-particle cryogenic electron microscopy (cryo-EM) has permitted the visualization of structures at high atomic resolution for six members of the SLC12 family (NCC, NKCC1, KCC1-KCC4). Cryo-EM insights of NCC confirm an inverted conformation of the TM1-5 and TM6-10 regions, a characteristic also found in the amino acid-polyamine-organocation (APC) superfamily, in which TM1 and TM6 clearly coordinate ion binding. The high-resolution structure also displays two glycosylation sites (N-406 and N-426) in EL7-8 that are essential for NCC expression and function. In this review, we briefly describe the studies related to the structure-function relationship of NCC, beginning with the first biochemical/functional studies up to the recent cryo-EM structure obtained, to acquire an overall view enriched with the structural and functional aspects of the cotransporter.

Polymorphisms in common antihypertensive targets: Pharmacogenomic implications for the treatment of cardiovascular disease

The idea of personalized medicine came to fruition with sequencing the human genome; however, aside from a few cases, the genetic revolution has yet to materialize. Cardiovascular diseases are the leading cause of death globally, and hypertension is a common prelude to nearly all cardiovascular diseases. Thus, hypertension is an ideal candidate disease to apply tenants of personalized medicine to lessen cardiovascular disease. Herein is a survey that visually depicts the polymorphisms in the top eight antihypertensive targets. Although there are numerous genome-wide association studies regarding cardiovascular disease, few studies look at the effects of receptor polymorphisms on drug treatment. With 17,000+ polymorphisms in the combined target proteins examined, it is expected that some of the clinical variability in the treatment of hypertension is due to polymorphisms in the drug targets. Recent advances in techniques and technology, such as high throughput examination of single mutations, structure prediction, computational power for modeling, and CRISPR models of point mutations, allow for a relatively rapid and comprehensive examination of the effects of known and future polymorphisms on drug affinity and effects. As hypertension is easy to measure and has a plethora of clinically viable ligands, hypertension makes an excellent disease to study pharmacogenomics in the lab and the clinic. If the promises of personalized medicine are to materialize, a concerted effort to examine the effects polymorphisms have on drugs is required. A clinician with the knowledge of a patient's genotype can then prescribe drugs that are optimal for treating that specific patient.

The Expanding Role of Pyridine and Dihydropyridine Scaffolds in Drug Design

Pyridine-based ring systems are one of the most extensively used heterocycles in the field of drug design, primarily due to their profound effect on pharmacological activity, which has led to the discovery of numerous broad-spectrum therapeutic agents. In the US FDA database, there are 95 approved pharmaceuticals that stem from pyridine or dihydropyridine, including isoniazid and ethionamide (tuberculosis), delavirdine (HIV/AIDS), abiraterone acetate (prostate cancer), tacrine (Alzheimer's), ciclopirox (ringworm and athlete's foot), crizotinib (cancer), nifedipine (Raynaud's syndrome and premature birth), piroxicam (NSAID for arthritis), nilvadipine (hypertension), roflumilast (COPD), pyridostigmine (myasthenia gravis), and many more. Their remarkable therapeutic applications have encouraged researchers to prepare a larger number of biologically active compounds decorated with pyridine or dihydropyridine, expandeing the scope of finding a cure for other ailments. It is thus anticipated that myriad new pharmaceuticals containing the two heterocycles will be available in the forthcoming decade. This review examines the prospects of highly potent bioactive molecules to emphasize the advantages of using pyridine and dihydropyridine in drug design. We cover the most recent developments from 2010 to date, highlighting the ever-expanding role of both scaffolds in the field of medicinal chemistry and drug development.

The genetic landscape of the human solute carrier (SLC) transporter superfamily

The human solute carrier (SLC) superfamily of transporters is comprised of over 400 membrane-bound proteins, and plays essential roles in a multitude of physiological and pharmacological processes. In addition, perturbation of SLC transporter function underlies numerous human diseases, which renders SLC transporters attractive drug targets. Common genetic polymorphisms in SLC genes have been associated with inter-individual differences in drug efficacy and toxicity. However, despite their tremendous clinical relevance, epidemiological data of these variants are mostly derived from heterogeneous cohorts of small sample size and the genetic SLC landscape beyond these common variants has not been comprehensively assessed. In this study, we analyzed Next-Generation Sequencing data from 141,456 individuals from seven major human populations to evaluate genetic variability, its functional consequences, and ethnogeographic patterns across the entire SLC superfamily of transporters. Importantly, of the 204,287 exonic single-nucleotide variants (SNVs) which we identified, 99.8% were present in less than 1% of analyzed alleles. Comprehensive computational analyses using 13 partially orthogonal algorithms that predict the functional impact of genetic variations based on sequence information, evolutionary conservation, structural considerations, and functional genomics data revealed that each individual genome harbors 29.7 variants with putative functional effects, of which rare variants account for 18%. Inter-ethnic variability was found to be extensive, and 83% of deleterious SLC variants were only identified in a single population. Interestingly, population-specific carrier frequencies of loss-of-function variants in SLC genes associated with recessive Mendelian disease recapitulated the ethnogeographic variation of the corresponding disorders, including cystinuria in Jewish individuals, type II citrullinemia in East Asians, and lysinuric protein intolerance in Finns, thus providing a powerful resource for clinical geneticists to inform about population-specific prevalence and allelic composition of Mendelian SLC diseases. In summary, we present the most comprehensive data set of SLC variability published to date, which can provide insights into inter-individual differences in SLC transporter function and guide the optimization of population-specific genotyping strategies in the bourgeoning fields of personalized medicine and precision public health.

Furosemide Exposure and Prevention of Bronchopulmonary Dysplasia in Premature Infants

OBJECTIVE

To evaluate the association between furosemide exposure and risk of bronchopulmonary dysplasia (BPD).

STUDY DESIGN

This retrospective cohort study included infants (2004-2015) born at 23-29 weeks gestational age and 501-1249 g birth weight. We compared the demographic and clinical characteristics of infants exposed and not exposed to furosemide between postnatal day 7 and 36 weeks postmenstrual age. We examined the association between furosemide exposure and 2 outcomes: BPD and BPD or death. We performed multivariable probit regression models that included demographic and clinical variables in addition to 2 instrumental variables: furosemide exposure by discharge year, and furosemide exposure by site.

RESULTS

Of 37 693 included infants, 19 235 (51%) were exposed to furosemide; these infants were more premature and had higher respiratory support. Of 33 760 infants who survived to BPD evaluation, 15 954 (47%) had BPD. An increase in the proportion of furosemide exposure days by 10 percentage points was associated with a decrease in both the incidence of BPD (4.6 percentage points; P = .001), and BPD or death (3.7 percentage points; P = .01).

CONCLUSIONS

More days of furosemide exposure between postnatal day 7 and 36 weeks was associated with decreased risk of BPD and a combined outcome of BPD or death.

Diuretic Resistance in Heart Failure

PURPOSE OF REVIEW

Diuretic resistance (DR) occurs along a spectrum of relative severity and contributes to worsening of acute heart failure (AHF) during an inpatient stay. This review gives an overview of mechanisms of DR with a focus on loop diuretics and summarizes the current literature regarding the prognostic value of diuretic efficiency and predictors of natriuretic response in AHF.

RECENT FINDINGS

The pharmacokinetics of diuretics are impaired in chronic heart failure, but little is known about mechanisms of DR in AHF. Almost all diuresis after administration of a loop diuretic dose occurs in the first few hours after administration and within-dose DR can develop. Recent studies suggest that DR at the level of the nephron may be more important than defects in diuretic delivery to the tubule. Because loop diuretics induce natriuresis, urine sodium (UNa) concentration may serve as a functional, physiological, and direct measure for diuretic responsiveness to a given loop diuretic dose. Identifying and targeting individuals with DR for more aggressive, tailored therapy represents an important opportunity to improve outcomes. A better understanding of the mechanistic underpinnings of DR in AHF is needed to identify additional biomarkers and guide future trials and therapies.

Structure-function relationships in the renal NaCl cotransporter (NCC)

The thiazide-sensitive Na⁺-Cl^- cotransporter (NCC) is the major pathway for salt reabsorption in the distal convoluted tubule, serves as a receptor for thiazide-type diuretics, and is involved in inherited diseases associated with abnormal blood pressure. The functional and structural characterization of NCC from different species has led us to gain insights into the structure-function relationships of the cotransporter. Here we present an overview of different studies that had described these properties. Additionally, we report the cloning and characterization of the NCC from the spiny dogfish (Squalus acanthias) kidney (sNCC). The purpose of the present study was to determine the main functional, pharmacological and regulatory properties of sNCC to make a direct comparison with other NCC orthologous. The sNCC cRNA encodes a 1033 amino acid membrane protein, when expressed in Xenopus oocytes, functions as a thiazide-sensitive Na-Cl cotransporter with NCC regulation and thiazide-inhibition properties similar to mammals, rather than to teleosts. However, the K_m values for ion transport kinetics are significantly higher than those observed in the mammal species. In summary, we present a review on NCC structure-function relationships with the addition of the sNCC information in order to enrich the NCC cotransporter knowledge.

Association of Genetic Variation in the Epithelial Sodium Channel Gene with Urinary Sodium Excretion and Blood Pressure

This study was performed to investigate whether genetic variation in the epithelial sodium channel (ENaC) is associated with 24-h urinary sodium excretion and blood pressure. A total of 3345 participants of the KoGES_Ansan and Ansung study were eligible for this study. Genomic DNA samples were isolated from peripheral blood and genotyped on the Affymetrix Genome-Wide Human SNP Array 5.0. Thirty-four single nucleotide polymorphisms (SNPs) were extracted for gene regions (SCNN1A, SCNN1B, and SCNN1G) as additive components by using Plink. Twenty-four-hour sodium excretions were estimated from spot urine samples using the Tanaka formula. The general linear model (GLM) was applied to assess the association between SNPs and urinary sodium excretion or blood pressure. In the SCNN1G gene, six SNPs (rs4073291, rs12934362, rs7404408, rs4494543, rs5735, and rs6497657) were significantly different in 24-h urinary sodium excretion according to gene variants. However, no difference was found in blood pressure among participants with gene variants of ENaC. Our finding indicated that 24-h urinary sodium excretions were different according to variants of the SCNN1G gene in large samples. Further studies to replicate these findings are warranted.

Practical Pharmacogenomic Approaches to Heart Failure Therapeutics

OPINION STATEMENT

The major challenge in applying pharmacogenomics to everyday clinical practice in heart failure (HF) is based on (1) a lack of robust clinical evidence for the differential utilization of neurohormonal antagonists in the management of HF in different subgroups, (2) inconsistent results regarding appropriate subgroups that may potentially benefit from an alternative strategy based on pharmacogenomic analyses, and (3) a lack of clinical trials that focused on testing gene-guided treatment in HF. To date, all pharmacogenomic analyses in HF have been conducted as post hoc retrospective analyses of clinical trial data or of observational patient series studies. This is in direct contrast with the guideline-directed HF therapies that have demonstrated their safety and efficacy in the absence of pharmacogenomic guidance. Therefore, the future of clinical applications of pharmacogenomic testing will largely depend on our ability to incorporate gene-drug interactions into the prescribing process, requiring that preemptive and cost-effective testing be paired with decision-support tools in a value-based care approach.

A pharmacogenetic investigation of intravenous furosemide in decompensated heart failure: a meta-analysis of three clinical trials

We conducted a meta-analysis of pharmacogenomic substudies of three randomized trials conducted in patients with decompensated heart failure (HF) that were led by National Heart Lung and Blood Institute (NHLBI)-funded HF Network to test the hypothesis that candidate genes modulate net fluid loss and weight change in patients with decompensated HF treated with a furosemide-based diuretic regimen. Although none of the genetic variants previously shown to modulate the effects of loop diuretics in healthy individuals were associated with net fluid loss after 72 h of treatment, a set of rare variants in the APOL1 gene, which codes for apolipoprotein L1 (P=0.0005 in the random effects model), was associated with this end point. Moreover, a common variant in the multidrug resistance protein-4 coding gene (ABCC4, rs17268282) was associated with weight loss with furosemide use (P=0.0001). Our results suggest that both common and rare genetic variants modulate the response to a furosemide-based diuretic regimen in patients with decompensated HF.

The future of pharmacogenetics in the treatment of heart failure

Heart failure is a common disease with high levels of morbidity and mortality. Current treatment comprises β-blockers, ACE inhibitors, aldosterone antagonists and diuretics. Variation in clinical response seen in patients begs the question of whether there is a pharmacogenetic component yet to be identified. To date, the genes most studied involve the β-1, β-2, α-2 adrenergic receptors and the renin-angiotensin-aldosterone pathway, mainly focusing on SNPs. However results have been inconsistent. Genome-wide association studies and next-generation sequencing are seen as alternative approaches to discovering genetic variations influencing drug response. Hopefully future research will lay the foundations for genotype-led drug management in these patients with the ultimate aim of improving their clinical outcome.

Impact of mineralocorticoid receptor polymorphisms on urinary electrolyte excretion with and without diuretic drugs

Aim: Polymorphisms in the mineralocorticoid receptor may affect urinary sodium and potassium excretion. We investigated polymorphisms in the MR gene in relation to urinary electrolyte excretion in two separate studies. Patients & methods: The genotype–phenotype association was studied in healthy volunteers after single doses of bumetanide, furosemide, torsemide, hydrochlorothiazide, triamterene and after NaCl restriction. Results: High potassium excretion under all conditions except torsemide, and high NaCl excretion after bumetanide and furosemide were associated with the A allele of the intron-3 polymorphism (rs3857080). This polymorphism explained 5–10% of the functional variation and in vitro, rs3857080 affected DNA binding of the transcription factor LHX4. Conclusion: rs3857080 may be a promising new candidate for research in cardiac and renal disorders and on antialdosteronergic drugs like spironolactone.

Original submitted 23 June 2014; Revision submitted 5 November 2014

Extracellular water and blood pressure in adults with growth hormone (GH) deficiency: a genotype-phenotype association study

Objectives

Growth hormone deficiency (GHD) in adults is associated with decreased extracellular water volume (ECW). In response to GH replacement therapy (GHRT), ECW increases and blood pressure (BP) reduces or remains unchanged. Our primary aim was to study the association between polymorphisms in genes related to renal tubular function with ECW and BP before and 1 year after GHRT. The ECW measures using bioimpedance analysis (BIA) and bioimpedance spectroscopy (BIS) were validated against a reference method, the sodium bromide dilution method (Br⁻).

Design and Methods

Using a candidate gene approach, fifteen single-nucleotide polymorphisms (SNPs) in nine genes with known impact on renal tubular function (AGT, SCNN1A, SCNN1G, SLC12A1, SLC12A3, KCNJ1, STK39, WNK1 and CASR) were genotyped and analyzed for associations with ECW and BP at baseline and with their changes after 1 year of GHRT in 311 adult GHD patients. ECW was measured with the Br⁻, BIA, and BIS.

Results

Both BIA and BIS measurements demonstrated similar ECW results as the reference method. At baseline, after adjustment for sex and BMI, SNP rs2291340 in the SLC12A1 gene was associated with ECW volume in GHD patients (p = 0.039). None of the SNPs influenced the ECW response to GHRT. One SNP in the SLC12A3 gene (rs11643718; p = 0.024) and three SNPs in the SCNN1G gene [rs5723 (p = 0.02), rs5729 (p = 0.016) and rs13331086 (p = 0.035)] were associated with the inter-individual differences in BP levels at baseline. A polymorphism in the calcium-sensing receptor (CASR) gene (rs1965357) was associated with changes in systolic BP after GHRT (p = 0.036). None of these associations remained statistically significant when corrected for multiple testing.

Conclusion

The BIA and BIS are as accurate as Br⁻ to measure ECW in GHD adults before and during GHRT. Our study provides the first evidence that individual polymorphisms may have clinically relevant effects on ECW and BP in GHD adults.

Blood pressure regulation via the epithelial sodium channel: from gene to kidney and beyond

The epithelial sodium channel (ENaC) has long been recognized as playing a vital role in blood pressure (BP) regulation due to its involvement in fluid balance. The genes encoding the three ENaC subunits are likewise important contributors to hypertension, both in rare monogenic diseases and in the general population. The unusually high numbers of genetic variants associated with complex traits, including BP, that are located in non-coding areas suggest an involvement of these variants in regulatory functions. This may involve differential regulation of expression in different tissues. Emerging evidence indicates that the ENaC plays an important role in BP determination not only via its actions in the kidney, but also in other tissues commonly involved in BP regulation. The ENaC in the central nervous system is proposed to regulate BP via sympathetic nervous system activity. Recent evidence suggests that the ENaC contributes to vascular function and the myogenic response. Additional roles potentially include initiation of the baroreceptor reflex via ENaC in the baroreceptors and driving high salt intake with a 'taste for salt' via ENaC in the tongue. The present review describes the involvement of the ENaC in the determination of BP at a genetic and physiological level, detailing recent evidence for its role in the kidney and in other pertinent tissues.

Pharmacogenomics and heart failure in congenital heart disease

Congenital heart disease (CHD) constitutes a lifelong challenge in heart failure management. Current therapy is based mainly on physiologic principles extrapolated from the management of left ventricular failure in adult populations with either ischemic or nonischemic cardiomyopathy. However, there is good evidence of genomic variability in the origin and progression of CHD that suggests the need for a individualized approach to treatment. The developing science of pharmacogenomics presents an opportunity for CHD management broadly, and especially in the context of heart failure. There is growing evidence that individualizing drug therapy for these patients might be beneficial, and that prediction of response to therapy might be possible by incorporating genomic data into the treatment algorithm for individual patients.

Genetic predisposition and nongenetic risk factors of thiazolidinedione-related edema in patients with type 2 diabetes

OBJECTIVE

This study aimed to analyze the association of thiazolidinedione (TZD)-related edema with genetic and clinical variables and develop a simple points system to predict the risk of developing TZD-related edema.

METHODS

Fifty-eight (21.6%) of 268 individuals who received TZD for type 2 diabetes developed peripheral edema. Twenty-eight tag single nucleotide polymorphisms (SNPs) from candidate genes involved in sodium and water reabsorption were genotyped. Cox regression and logistic regression models were used to analyze the associations of different genotypes and weighted genotypic scores with TZD-related edema risk.

RESULTS

Individuals with edema were older, predominantly female, and had greater weight gain. The AQP2 rs296766 T allele was associated with TZD-related edema [allelic P=0.0059; odds ratio (OR), 2.89; 95% confidence interval (CI), 1.61-5.17]. The SLC12A rs12904216 G allele had borderline significance (allelic P=0.049), which disappeared after correction for multiple testing. Patients with two SNP-based (AQP2 rs296766 and SLC12A1 rs12904216), who weighted genotypic scores within the top quartile, had a higher risk of developing TZD-related edema (OR, 16.45; 95% CI, 3.05-88.76). Combining the weighted genetic scores of two SNPs or all SNPs with age and sex information significantly improved the predictive power for TZD-related edema. We also developed a simple risk factor-based points system to predict an individual's risk of developing TZD-related edema.

CONCLUSION

A clinically applicable prediction model including age, sex, and genetic information from AQP2 rs296766 and/or SLC12A rs12904216 SNPs can be developed to estimate the risk of TZD-related edema in type 2 diabetes patients.

Pharmacogenetics in chronic heart failure: new developments and current challenges

The individual patient responses to chronic heart failure (HF) pharmacotherapies are highly variable. This variability cannot be entirely explained by clinical characteristics, and genetic variation may play a role. Therefore, this review will summarize the background pharmacogenetic literature for major HF pharmacotherapy classes (ie, β-blockers, angiotensin-converting enzyme inhibitors, digoxin, and loop diuretics), evaluate recent advances in the HF pharmacogenetic literature in the context of previous findings, and discuss the challenges and conclusions for HF pharmacogenetic data and its clinical application.

Identification of diuretic non-responders with poor long-term clinical outcomes: a 1-year follow-up of 176 non-azotaemic cirrhotic patients with moderate ascites

In cirrhosis, the development of ascites and the response to diuretics are determined by the RAAS (renin-angiotensin-aldosterone system) and renal sodium handling system. We hypothesized that SNPs (single nucleotide polymorphisms) affecting candidate genes in the RAAS and renal sodium handling pathway may influence initial diuretic responsiveness and affect clinical outcome in non-azotaemic cirrhotic patients with moderate ascites. We prospectively recruited 176 patients and 245 controls and determined their genetic polymorphisms for 24 SNPs of ten genes involved in the RAAS and renal sodium handling pathway. In cirrhotic patients with moderate ascites, multivariate analysis showed that diuretic unresponsiveness was predicted by a high basal plasma aldosterone level, by a high aldosterone/renin ratio and by specific risk genotypes of ACE (gene encoding angiotensin-converting enzyme), CYP11B2 (gene encoding aldosterone synthase) and ADDA (gene encoding α-adducin). This association between genetic polymorphisms and diuretic unresponsiveness was confirmed by an independent validation cohort. Notably, additive effects in relation to diuretic unresponsiveness were observed in cases where there was the simultaneous presence of the three risk genotypes. Among patients carrying any of the risk genotypes, more episodes of paracentesis and ascites-related readmission after 3 months of treatment, as well as a reduced 1-year survival rate, were observed. In addition to traditional predictors, our present study provides additional genetic and neurohormonal predictors that will help to identify diuretic non-responders among cirrhotic patients with moderate ascites. Among those carrying unfavourable risk genotypes, additional therapies, including paracentesis and albumin infusion, should be started as early as possible.

The genetics of loop diuretic effects

Little is known about the genetic impact on loop diuretic effects. We newly investigated five genetic polymorphisms in 95 healthy volunteers, who had ingested bumetanide, frusemide and torsemide. The subjects excreted means of 20.2 g sodium chloride, 2.87 g potassium and 261 mg calcium over 24 h. Concerning sodium chloride, the subjects excreted 2.2 g less per two T-alleles of C825T in the G nucleotide β-subunit 3 (GNB3), 3.2 g less per two Met32-alleles of Val32Met in the atrial natriuretic peptide precursor (ANP) and 2.8 g more per two Arg152-alleles of Ter152Arg in ANP (P=0.007, 0.05 and 0.007). Concerning potassium, the subjects excreted 0.42 g more per two ANP Arg152-alleles (P=0.023). Concerning calcium, the subjects excreted 32 mg more per two deletion-alleles of the insertion/deletion polymorphism in the angiotensin-converting enzyme, 44 mg more per two Trp460-alleles of Gly460Trp in α-adducin (ADD1) and 42 mg less per two GNB3 T-alleles (P=0.006, 0.023 and 0.008). The common genetic impact together with three polymorphisms in the sodium chloride cotransporter and the epithelial sodium channel was 20, 15, 10 and 23% of the variation in the urinary excretion of sodium chloride, volume, potassium and calcium. This exceeded the fraction of variation explained by differences in the pharmacokinetics: 13, 10, 11 and 6%. Thus, genetic variation seems to be a stronger predictor of the loop diuretic drug response than pharmacokinetic variation.

Genetic profiling of human cell lines used as in vitro model to study cardiovascular pathophysiology and pharmacotoxicology

BACKGROUND

Cell lines are widely used to monitor drug pharmacokinetics and pharmacodynamics and to investigate a number of biochemical mechanisms. However, little is known about the genetic profile of these in vitro models.

OBJECTIVES

To analyze genetic profile of Thp1, U937, HL60, K562, HepG2, Kyn2, and Caco2 human cell lines with a focus on genetic variations within genes involved in the development of cardiovascular pathologies and drug treatment response.

METHODS

Multiplex polymerase chain reaction (PCR), PCR-restriction fragment length polymorphism and TaqMan assays were used to genotype 120 polymorphisms within 68 genes previously shown to be involved in various processes such as inflammation, lipid metabolism, and blood pressure.

RESULTS

We provide here a list of potential polymorphisms known to be associated with cardiovascular disease. Our results show that the seven cell lines examined carry several of these mutations within genes of interest. Due to the abundance of these variations, only two examples will be given in this abstract. For instance, U937 cells are homozygous for APOE varepsilon4, a mutant associated with higher susceptibility to cardiovascular diseases and lower response to statins. Our study also showed that deletion in intron 16 of the ACE gene, which is associated with susceptibility to hypertension and variation of response to ACE inhibitors, can be found in all considered cells but Kyn2 cells.

CONCLUSION

We provide here a data bank of different cell lines genetic profile. In our opinion, this useful information may bring insights into the design and choice of an adequate in vitro model and may help to explain mysterious discrepancies in data from different laboratories.

The thiazide-sensitive Na+-Cl- cotransporter: molecular biology, functional properties, and regulation by WNKs

The thiazide-sensitive Na+-Cl(-) cotransporter is the major salt reabsorption pathway in the distal convoluted tubule, which is located just after the macula densa at the beginning of the aldosterone-sensitive nephron. This cotransporter was identified at the molecular level in the early 1990s by the pioneering work of Steven C. Hebert and coworkers, opening the molecular area, not only for the Na+-Cl(-) cotransporter but also for the family of electroneutral cation-coupled chloride cotransporters that includes the loop diuretic-sensitive Na+-K+-2Cl(-) cotransporter of the thick ascending limb of Henle's loop. This work honoring the memory of Steve Hebert presents a brief review of our current knowledge about salt and water homeostasis generated as a consequence of cloning the cotransporter, with particular emphasis on the molecular biology, physiological properties, human disease due to decreased or increased activity of the cotransporter, and regulation of the cotransporter by a family of serine/threonine kinases known as WNK. Thus one of the legacies of Steve Hebert is a better understanding of salt and water homeostasis.