Thiazide-sensitive NaCl-cotransporter in the Intestine

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.

Seasonal flexibility of the gut structure and physiology in Eremias multiocellata

Although gut seasonal plasticity has been extensively reported, studies on physiological flexibility, such as water-salt transportation and motility in reptiles, are limited. Therefore, this study investigated the intestinal histology and gene expression involved in water-salt transport (AQP1, AQP3, NCC, and NKCC2) and motility regulation (nNOS, CHRM2, and ADRB2) in desert-dwelling Eremias multiocellata during winter (hibernating period) and summer (active period). The results showed that mucosal thickness, the villus width and height, the enterocyte height of the small intestine, and the mucosal and submucosal thicknesses of the large intestine were greater in winter than in summer. However, submucosal thickness of the small intestine and muscularis thickness of the large intestine were lower in winter than in summer. Furthermore, AQP1, AQP3, NCC, nNOS, CHRM2, and ADRB2 expressions in the small intestine were higher in winter than in summer; AQP1, AQP3, and nNOS expressions in the large intestine were lower in winter than in summer, with the upregulation of NCC and CHRM2 expressions; no significant seasonal differences were found in intestinal NKCC2 expression. These results suggest that (i) intestinal water-salt transport activity is flexible during seasonal changes where AQP1, AQP3 and NCC play a vital role, (ii) the intestinal motilities are attenuated through the concerted regulation of nNOS, CHRM2, and ADRB2, and (iii) the physiological flexibility of the small and large intestine may be discrepant due to their functional differences. This study reveals the intestinal regulation and adaptation mechanisms in E. multiocellata in response to the hibernation season.

Arterial Blood Pressure, Neuronal Excitability, Mineral Metabolism and Cell Volume Regulation Mechanisms Revealed by Xenopus laevis oocytes

Xenopus laevis oocytes have been an invaluable tool to discover and explore the molecular mechanisms and characteristics of many proteins, in particular integral membrane proteins. The oocytes were fundamental in many projects designed to identify the cDNA encoding a diversity of membrane proteins including receptors, transporters, channels and pores. In addition to being a powerful tool for cloning, oocytes were later used to experiment with the functional characterization of many of the identified proteins. In this review I present an overview of my personal 30-year experience using Xenopus laevis oocytes and the impact this had on a variety of fields such as arterial blood pressure, neuronal excitability, mineral metabolism and cell volume regulation.

The European and Japanese eel NaCl cotransporter β exhibit chloride currents and are resistant to thiazide type diuretics

The thiazide-sensitive Na⁺-Cl^- cotransporter (NCC) is the major pathway for salt reabsorption in the mammalian distal convoluted tubule, and the inhibition of its function with thiazides is widely used for the treatment of arterial hypertension. In mammals and teleosts, NCC is present as one ortholog that is mainly expressed in the kidney. One exception, however, is the eel, which has two genes encoding NCC. The eNCCa is located in the kidney and eNCCb, which is present in the apical membrane of the rectum. Interestingly, the European eNCCb functions as a NaCl cotransporter that is nevertheless resistant to thiazides and is not activated by low-chloride hypotonic stress. However, in the Japanese eel rectal sac, a thiazide-sensitive NaCl transport mechanism has been described. The protein sequences between eNCCβ and jNCCβ are 98% identical. Here, by site-directed mutagenesis, we transformed eNCCβ into jNCCβ. Our data showed that jNCCβ, similar to eNCCβ, is resistant to thiazides. In addition, both NCCβ proteins have high transport capacity with respect to their renal NCC orthologs, and in contrast to known NCCs, exhibit electrogenic properties that are reduced when residue I172 is substituted by A, G or M. This is considered a key residue for the chloride ion-binding sites of NKCC and KCC. We conclude that NCCb proteins are not sensitive to thiazides and have electrogenic properties dependent on Cl^-, and site I172 is important for the function of NCCβ.

The Effects of Osteoporotic and Non-osteoporotic Medications on Fracture Risk and Bone Mineral Density

Osteoporosis is a highly prevalent bone disease affecting more than 37.5 million individuals in the European Union (EU) and the  United States of America (USA). It is characterized by low bone mineral density (BMD), impaired bone quality, and loss of structural and biomechanical properties, resulting in reduced bone strength. An increase in morbidity and mortality is seen in patients with osteoporosis, caused by the approximately 3.5 million new osteoporotic fractures occurring every year in the EU. Currently, different medications are available for the treatment of osteoporosis, including anti-resorptive and osteoanabolic medications. Bisphosphonates, which belong to the anti-resorptive medications, are the standard treatment for osteoporosis based on their positive effects on bone, long-term experience, and low costs. However, not only medications used for the treatment of osteoporosis can affect bone: several other medications are suggested to have an effect on bone as well, especially on fracture risk and BMD. Knowledge about the positive and negative effects of different medications on both fracture risk and BMD is important, as it can contribute to an improvement in osteoporosis prevention and treatment in general, and, even more importantly, to the individual's health. In this review, we therefore discuss the effects of both osteoporotic and non-osteoporotic medications on fracture risk and BMD. In addition, we discuss the underlying mechanisms of action.

The impact of thiazide diuretics on bone mineral density and the trabecular bone score: the Rotterdam Study

The decreased risk of osteoporotic fractures in thiazide diuretics (TD) users is possibly not only caused by an increase in bone mineral density (BMD), but by an increase in other determinants of bone strength as well, such as the trabecular bone score (TBS). To test this hypothesis, we studied the association between TD use and both lumbar spine BMD (LS-BMD) and lumbar spine TBS (LS-TBS) cross-sectionally in 6096 participants from the Rotterdam Study, as well as the association between TD use and bone turnover estimated by serum osteocalcin levels. We found that past and current use of TD were associated with an increase of LS-BMD (β = 0.021 g/cm² (95% CI: 0.006;0.036) and β = 0.016 g/cm² (95% CI: 0.002;0.031), respectively). Use of ≥1 defined daily dose (DDD) (β = 0.028, 95% CI: 0.010;0.046; p for trend within DDD of use <0.001) and use of >365 days (β = 0.033, 95% CI: 0.014;0.052; p for trend within duration of use <0.001) were positively associated with LS-BMD. No significant association between TD use and LS-TBS was observed. Mean serum osteocalcin levels were significantly different between users and non-users of TD (20.2 ng/ml (SD 8.3) and 22.5 ng/ml (SD 17.0), respectively, p < 0.001). Furthermore, linear regression analysis showed that the use of TD was associated with a 3.2 ng/l (95% CI: -4.4.; -2.0) lower serum osteocalcin level compared to non-use of TD, when adjusted for Rotterdam Study cohort, age, and sex. Our results may implicate that the decreased fracture risk in TD users is explained by increased bone mass rather than by improved bone microarchitecture. Alternatively, changes in bone microarchitecture might not be detected through TBS and more sophisticated techniques are possibly needed to study a potential effect of TD on bone microarchitecture.

A novel distal convoluted tubule-specific Cre-recombinase driven by the NaCl cotransporter gene

Cre-lox technology has revolutionized research in renal physiology by allowing site-specific genetic recombination in individual nephron segments. The distal convoluted tubule (DCT), consisting of distinct early (DCT1) and late (DCT2) segments, plays a central role in Na⁺ and K⁺ homeostasis. The only established Cre line targeting the DCT is Pvalb-Cre, which is limited by noninducibility, activity along DCT1 only, and activity in neurons. Here, we report the characterization of the first Cre line specific to the entire DCT. CRISPR/Cas9 targeting was used to introduce a tamoxifen-inducible IRES-Cre-ERT2 cassette downstream of the coding region of the Slc12a3 gene encoding the NaCl cotransporter (NCC). The resulting Slc12a3-Cre-ERT2 mice were crossed with R26R-YFP reporter mice, which revealed minimal leakiness with 6.3% of NCC-positive cells expressing yellow fluorescent protein (YFP) in the absence of tamoxifen. After tamoxifen injection, YFP expression was observed in 91.2% of NCC-positive cells and only in NCC-positive cells, revealing high recombination efficiency and DCT specificity. Crossing to R26R-TdTomato mice revealed higher leakiness (64.5%), suggesting differential sensitivity of the floxed site. Western blot analysis revealed no differences in abundances of total NCC or the active phosphorylated form of NCC in Slc12a3-Cre-ERT2 mice of either sex compared with controls. Plasma K⁺ and Mg²⁺ concentrations and thiazide-sensitive Na⁺ and K⁺ excretion did not differ in Slc12a3-Cre-ERT2 mice compared with controls when sex matched. These data suggest genetic modification had no obvious effect on NCC function. Slc12a3-Cre-ERT2 mice are the first line generated demonstrating inducible Cre recombinase activity along the entire DCT and will be a useful tool to study DCT function.

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.

Thiazide Treatment in Primary Hyperparathyroidism-A New Indication for an Old Medication?

CONTEXT

There is no therapy for control of hypercalciuria in nonoperable patients with primary hyperparathyroidism (PHPT). Thiazides are used for idiopathic hypercalciuria but are avoided in PHPT to prevent exacerbating hypercalcemia. Nevertheless, several reports suggested that thiazides may be safe in patients with PHPT.

OBJECTIVE

To test the safety and efficacy of thiazides in PHPT.

DESIGN

Retrospective analysis of medical records.

SETTING

Endocrine clinic at a tertiary hospital.

PATIENTS

Fourteen male and 58 female patients with PHPT treated with thiazides.

INTERVENTIONS

Data were compared for each patient before and after thiazide administration.

MAIN OUTCOME MEASURES

Effect of thiazide on urine and serum calcium levels.

RESULTS

Data are given as mean ± standard deviation. Treatment with hydrochlorothiazide 12.5 to 50 mg/d led to a decrease in mean levels of urine calcium (427 ± 174 mg/d to 251 ± 114 mg/d; P < 0.001) and parathyroid hormone (115 ± 57 ng/L to 74 ± 36 ng/L; P < 0.001), with no change in serum calcium level (10.7 ± 0.4 mg/dL off treatment, 10.5 ± 1.2 mg/dL on treatment, P = 0.4). Findings were consistent over all doses, with no difference in the extent of reduction in urine calcium level or change in serum calcium level by thiazide dose.

CONCLUSION

Thiazides may be effective even at a dose of 12.5 mg/d and safe at doses of up to 50 mg/d for controlling hypercalciuria in patients with PHPT and may have an advantage in decreasing serum parathyroid hormone level. However, careful monitoring for hypercalcemia is required.

Thiazide-sensitive Na+ -Cl- cotransporter (NCC) gene inactivation results in increased duodenal Ca2+ absorption, enhanced osteoblast differentiation and elevated bone mineral density

Inactivation of the thiazide-sensitive sodium chloride cotransporter (NCC) due to genetic mutations in Gitelman's syndrome (GS) or pharmacological inhibition with thiazide diuretics causes hypocalciuria and increased bone mineral density (BMD) with unclear extrarenal calcium (Ca(2+) ) regulation. We investigated intestinal Ca(2+) absorption and bone Ca(2+) metabolism in nonsense Ncc Ser707X (S707X) homozygous knockin mice (Ncc(S707X/S707X) mice). Compared to wild-type and heterozygous knockin littermates, Ncc(S707X/S707X) mice had increased intestinal absorption of (45) Ca(2+) and expression of the active Ca(2+) transport machinery (transient receptor potential vanilloid 6, calbindin-D9K , and plasma membrane Ca(2+) ATPase isoform 1b). Ncc(S707X/S707X) mice had also significantly increased Ca(2+) content accompanied by greater mineral apposition rate (MAR) in their femurs and higher trabecular bone volume, cortical bone thickness, and BMD determined by μCT. Their osteoblast differentiation markers, such as bone alkaline phosphatase, procollagen I, osteocalcin, and osterix, were also significantly increased while osteoclast activity was unaffected. Analysis of marrow-derived bone cells, either treated with thiazide or directly cultured from Ncc S707X knockin mice, showed that the differentiation of osteoblasts was associated with increased phosphorylation of mechanical stress-induced focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK). In conclusion, NCC inhibition stimulates duodenal Ca(2+) absorption as well as osteoblast differentiation and bone Ca(2+) storage, possibly through a FAK/ERK dependent mechanism.

Antihypertensive medications, bone mineral density, and fractures: a review of old cardiac drugs that provides new insights into osteoporosis

Osteoporosis is increasing in prevalence and importance as society's age, with the clinical consequence of fractures of the hip, spine, and upper extremity, leading to impaired quality of life, loss of function and independence, and increased morbidity and mortality. A major risk factor for osteoporosis is older age, and cardiovascular diseases also share this risk factor; therefore, osteoporosis and cardiovascular disease often coexist and share risk factors. Medications used for the treatment of cardiovascular diseases, in particular antihypertensive drugs, have been shown in a variety of studies of varying designs to modulate bone health in both a positive or negative manner. In this article, we reviewed the pharmacology, potential mechanisms, and possible effects on bone mineral density and fracture risk of commonly prescribed antihypertensive medications, including thiazide and non-thiazide diuretics, beta-blockers, calcium channel blockers, renin-angiotensin-aldosterone system agents, and nitrates.

Mechanisms of guanylin action on water and ion absorption at different regions of seawater eel intestine

Guanylin (GN) inhibited water absorption and short-circuit current (Isc) in seawater eel intestine. Similar inhibition was observed after bumetanide, and the effect of bumetanide was abolished by GN or vice versa, suggesting that both act on the same target, Na(+)-K(+)-2Cl(-) cotransporter (NKCC), which is a key player for the Na(+)-K(+)-Cl(-) transport system responsible for water absorption in marine teleost intestine. However, effect of GN was always greater than that of bumetanide: 10% greater in middle intestine (MI) and 40% in posterior intestine (PI) for Isc, and 25% greater in MI and 34% in PI for water absorption. After treatment with GN, Isc decreased to zero, but 20-30% water absorption still remained. The remainder may be due to the Cl(-)/HCO3 (-) exchanger and Na(+)-Cl(-) cotransporter (NCC), since inhibitors for these transporters almost nullified the remaining water absorption. Quantitative PCR analysis revealed the presence of major proteins involved in water absorption; the NKCC2β and AQP1 genes whose expression was markedly upregulated after seawater acclimation. The SLC26A6 (anion exchanger) and NCCβ genes were also expressed in small amounts. Consistent with the inhibitors' effect, expression of NKCC2β was MI > PI, and that of NCCβ was MI << PI. The present study showed that GN not only inhibits the bumetanide-sensitive Na(+)-K(+)-Cl(-) transport system governed by NKCC2β, but also regulates unknown ion transporters different from GN-insensitive SLC26A6 and NCC. A candidate is cystic fibrosis transmembrane conductance regulator Cl(-) channel, as demonstrated in mammals, but its expression is low in eel intestine, and its role may be minor, as indicated by the small effect of its inhibitors.

The sodium chloride cotransporter SLC12A3: new roles in sodium, potassium, and blood pressure regulation

SLC12A3 encodes the thiazide-sensitive sodium chloride cotransporter (NCC), which is primarily expressed in the kidney, but also in intestine and bone. In the kidney, NCC is located in the apical plasma membrane of epithelial cells in the distal convoluted tubule. Although NCC reabsorbs only 5 to 10% of filtered sodium, it is important for the fine-tuning of renal sodium excretion in response to various hormonal and non-hormonal stimuli. Several new roles for NCC in the regulation of sodium, potassium, and blood pressure have been unraveled recently. For example, the recent discoveries that NCC is activated by angiotensin II but inhibited by dietary potassium shed light on how the kidney handles sodium during hypovolemia (high angiotensin II) and hyperkalemia. The additive effect of angiotensin II and aldosterone maximizes sodium reabsorption during hypovolemia, whereas the inhibitory effect of potassium on NCC increases delivery of sodium to the potassium-secreting portion of the nephron. In addition, great steps have been made in unraveling the molecular machinery that controls NCC. This complex network consists of kinases and ubiquitinases, including WNKs, SGK1, SPAK, Nedd4-2, Cullin-3, and Kelch-like 3. The pathophysiological significance of this network is illustrated by the fact that modification of each individual protein in the network changes NCC activity and results in salt-dependent hypotension or hypertension. This review aims to summarize these new insights in an integrated manner while identifying unanswered questions.

Electroneutral cation-Cl- cotransporters NKCC2β and NCCβ expressed in the intestinal tract of Japanese eel Anguilla japonica

In the present study, we aimed to elucidate the mechanisms of intestinal Na(+) and Cl(-) absorption in Japanese eel, focusing on electroneutral cation-Cl(-) cotransporters, NKCC2β and NCCβ, expressed in the intestinal tract. First, we cloned cDNAs encoding NKCC2β and NCCβ from the intestinal tract of Japanese eel. In both freshwater- and seawater-acclimated eels, quantitative PCR analysis showed that NKCC2β was predominantly expressed in the anterior and posterior intestines, and that NCCβ expression was specifically high in the rectum. According to immunohistochemistry with anti-eel NKCC2β (reacting with NKCC2β but not with NCCβ) and T4 antibody (reacting with both NKCC2β and NCCβ), NKCC2β was localized in the apical surface of the epithelial cells in the anterior and posterior intestines, whereas NCCβ was likely to be distributed to that in the rectum. Furthermore, a specific NCC inhibitor, hydrochlorothiazide, inhibited of Na(+) and Cl(-) absorption, as well as water absorption, in the rectal sac preparations from seawater eel, indicating the involvement of NCCβ in ion absorption in the rectum. Our findings indicate that NKCC2β expressed in the anterior and posterior intestines and NCCβ in the rectum are importantly involved in ion absorption to reduce osmolality of ingested seawater prior to water absorption in seawater-acclimated eel.

Thiazide-induced severe hypercalcemia: a case report and review of literature

Most common causes of hypercalcemia are hyperparathyroidism, malignancy, vitamin D-mediated conditions such as sarcoidosis, and vitamin D toxicity. Less commonly, hypercalcemia can be caused by drugs such as thiazide diuretics and lithium. Mild hypercalcemia is usually asymptomatic but severe hypercalcemia is associated with nausea, vomiting, abdominal pain, excessive thirst, muscle weakness, lethargy, confusion, and fatigue. We are reporting a case of abdominal pain and altered mental status caused by thiazide-induced severe hypercalcemia of 19.8 mg/dL. This is the most severe case of thiazide-induced hypercalcemia that we have seen reported. Patients on thiazide diuretics should have their electrolytes frequently checked, especially patients on calcium supplements. Management usually includes hydration and discontinuation of drugs causing hypercalcemia.

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.

Lithium fluxes indicate presence of Na-Cl cotransport (NCC) in human lens epithelial cells

During regulatory volume decrease (RVD) of human lens epithelial cells (hLECs) by clotrimazole (CTZ)-sensitive K fluxes, Na-K-2Cl cotransport (NKCC) remains active and K-Cl cotransport (KCC) inactive. To determine whether such an abnormal behavior was caused by RVD-induced cell shrinkage, NKCC was measured in the presence of either CTZ or in high K media to prevent RVD. NKCC transports RbCl + NaCl, and LiCl + KCl; thus ouabain-insensitive, bumetanide-sensitive (BS) or Cl-dependent (ClD) Rb and Li fluxes were determined in hyposmotic high NaCl media with CTZ, or in high KCl media alone, or with sulfamate (Sf) or nitrate as Cl replacement at varying Rb, Li or Cl mol fractions (MF). Unexpectedly, NKCC was inhibited by 80% with CTZ (IC(50) = 31 microM). In isosmotic (300 mOsM) K, Li influx was approximately 1/3 of Rb influx in Na, 50% lower in Sf, and bumetanide-insensitive (BI). In hypotonic (200 mOsM) K, only the ClD but not BS Li fluxes were detected. At Li MFs from 0.1-1, Li fluxes fitted a bell-shaped curve maxing at approximately 0.6 Li MF, with the BS fluxes equaling approximately 1/4 of the ClD-Li influx. The difference, i.e. the BI/ClD Li influx, saturated with increasing Li and Cl MFs, with K(ms) for Li of 11 with, and 7 mM without K, and of approximately 46 mM for Cl. Inhibition of this K-independent Li influx by thiazides was weak whilst furosemide (<100 microM) was ineffective. Reverse transcription polymerase chain reaction and Western blots verified presence of both NKCC1 and Na-Cl cotransport (NCC). In conclusion, in hyposmotic high K media, which prevents CTZ-sensitive K flux-mediated RVD in hLECs, NKCC1, though molecularly expressed, was functionally silent. However, a K-independent and moderately thiazide-sensitive ClD-Li flux, i.e. LiCC, likely occurring through NCC was detected operationally and molecularly.

High prevalence of hypovitaminosis D and secondary hyperparathyroidism in elders living in nonprofit homes in South Brazil

OBJECTIVES

Hypovitaminosis D (HD) and secondary hyperparathyroidism (SHP) are common in elders, and many factors could contribute to them. The objectives of this study were to estimate the prevalence of HD, SHP, and its associated factors, in individuals living in nonprofit homes for elders in south Brazil. Design Cross-sectional study.

METHODS

Serum 25-hydroxyvitamin D 25(OH)D, intact parathyroid hormone (PTH), total calcium, phosphorus, alkaline phosphatase, magnesium, creatinine, and albumin levels were measured in late spring, November, 2005. The presence of factors potentially related with HD and SHP-age, sex, weight, height, skin phototype, sun exposure, exercise, smoking, use of < or = 5 medications or diuretics or alcohol, and daily calcium ingestion.

RESULTS

102 subjects age 77.8 +/- 9.0 were included in the study. HD was found in 85.7% and SHP in 53% of the subjects. The estimated daily calcium ingestion was 720 mg. There was no association between serum 25(OH)D levels and any of the risk factors evaluated. Serum 25(OH)D levels were correlated with serum PTH (r = -0.358, P = 0.000), calcium (r = 0.306, P = 0.002), and albumin (r = 0.253, P = 0.011) levels. In univariate analysis, SHP was positively associated with age (P = 0.006), and female sex (0.007); and negatively associated with sunlight exposure (P = 0.020), GFR (P = 0.000), Ln25(OH)D (P = 0.002), and total serum calcium (P = 0.024). After multivariate model adjustment, age [OR 1.09 (CI 1.01-1.18); P = 0.024], Ln25(OH)D [OR 0.92 (CI 0.08-0.74); P = 0.013], GFR [OR 0.96 (CI 0.92-0.99); P = 0.013], and hydrochlorothiazide treatment [OR 7.63 (CI 1.67-34.9); P = 0.008] were independently associated with SHP.

CONCLUSIONS

HD and SHP are highly prevalent in elders living in old-age homes. No associations were established between common risk factors and low serum levels of 25(OH)D levels; however, SHP was independently related with age, 25(OH)D, GFR, and hydrochlorothiazide use.

Incidence and clinical spectrum of thiazide-associated hypercalcemia

PURPOSE

The study determines the incidence of thiazide-associated hypercalcemia and clarifies its clinical features and natural history.

METHODS

In a population-based descriptive study, Olmsted County, Minn, residents with thiazide-associated hypercalcemia were identified through the Rochester Epidemiology Project and the Mayo Clinic Laboratory Information System. Changes in incidence rates were evaluated by Poisson regression.

RESULTS

Seventy-two Olmsted County residents (68 women and 4 men; mean age, 64 years) with thiazide-associated hypercalcemia first recognized in 1992 to 2001 were identified. The overall annual age- and sex-adjusted (to 2000 US whites) incidence was 7.7 (95% confidence interval [CI], 5.9-9.5) per 100,000. There was an increase in incidence after 1996, peaking at 16.3 (95% CI, 8.3-24.3) per 100,000 in 1998. The highest rate was 55.3 per 100,000 in 70- to 79-year-old women. Hypercalcemia was identified a mean of 6+/-7 years after thiazide initiation, and the average highest serum calcium was 10.7+/-0.3 mg/dL with serum parathyroid hormone (obtained in 53 patients) of 4.8+/-2.7 pmol/L. Of 33 patients who discontinued the thiazide, 21 (64%) had persistent hypercalcemia. Patients subsequently diagnosed with primary hyperparathyroidism had the highest average serum calcium and parathyroid hormone levels of 11.0+/-0.3 mg/dL and 6.3+/-2.4 pmol/L, respectively.

CONCLUSION

The persistence of hypercalcemia in patients discontinuing thiazides, and similarities in the clinical spectrum, suggest that underlying primary hyperparathyroidism is common in patients who develop hypercalcemia while taking thiazide diuretics.

Gitelman syndrome: genetic and expression analysis of the thiazide-sensitive sodium-chloride transporter in blood cells

Gitelman syndrome is caused by mutations of the SLC12A3 gene, which encodes the thiazide-sensitive NaCl transporter NCCT. Although several mutations causing Gitelman syndrome have been described, their molecular consequences have been rarely studied. We report a patient with Gitelman syndrome due to a mutation in the GT donor splicing site of intron 9. The analysis of RNA from peripheral blood cells showed a complete deletion of exon 9. This case report confirms the feasibility of using readily accessible blood cells to study the expression of the SLC12A3 gene, a procedure that may facilitate further studies of the functional genomics of Gitelman syndrome.