The renal tubular Na-Cl co-transporter (NCCT): a potential genetic link between blood pressure and bone density?

Association between metabolic syndrome and osteoporosis among adults aged 50 years and older: using the National Health Information Database in South Korea

This study aimed to examine the association between a history of metabolic syndrome (MetS) and osteoporosis with specific characteristics. The results showed that MetS was inversely associated with osteoporosis. In contrast, MetS was positively associated with osteoporosis in both obese men and postmenopausal obese women.

PURPOSE

Although several previous studies have investigated the association between MetS and osteoporosis, their findings remain controversial. This study aimed to examine the association between a MetS history and osteoporosis using a subset of data from a large, long-term, national database.

METHODS

This nested case-control study used the National Health Information Database (NHID) of the Korea National Health Insurance Service (NHIS) from 2009 to 2017. Osteoporosis (n = 459,771) and control (n = 459,771) participants were matched in a 1:1 ratio by age, gender, income, and region of residence. MetS was defined based on the modified National Cholesterol Education Program-Adult Treatment Panel III criteria. Crude and adjusted odds ratios (ORs) with 95% confidence intervals (CIs) for osteoporosis in patients with MetS and its components were analyzed using logistic regression. Subgroup analyses were performed according to the combination of gender, menopausal status, and obesity status.

RESULTS

The adjusted OR (95% CI) for osteoporosis in patients with MetS was 0.95 (0.94-0.96). This finding was consistent with the subgroup analyses in normal weight men, premenopausal (pre-MP) women with all obesity statuses, and postmenopausal (post-MP) underweight and normal weight women. In contrast, the opposite was observed for obese men (OR = 1.05, 95% CI = 1.01-1.09) and post-MP obese women (OR = 1.05, 95% CI = 1.01-1.08).

CONCLUSION

This study results suggested that MetS was associated with a low occurrence of osteoporosis. In contrast, MetS was associated with a high occurrence of osteoporosis in both obese men and post-MP obese women.

Relationship Between Metabolic Syndrome and Bone Health - An Evaluation of Epidemiological Studies and Mechanisms Involved

Metabolic syndrome (MetS) and osteoporosis are two medical problems plaguing the ageing populations worldwide. Though seemingly distinctive to each other, metabolic derangements are shown to influence bone health. This review summarises the relationship between MetS and bone health derived from epidemiological studies and explains the mechanistic basis of this relationship. The discourse focuses on the link between MetS and bone mineral density, quantitative sonometric indices, geometry and fracture risk in humans. The interesting sex-specific trend in the relationship, probably due to factors related to body composition and hormonal status, is discussed. Mechanistically, each component of MetS affects the bone distinctly, forming a complex interacting network influencing the skeleton. Lastly, the effects of MetS management, such as pharmacotherapies, exercise and bariatric surgery, on bone, are presented. This review aims to highlight the significant relationship between MetS and bone, and proper management of MetS with the skeletal system in mind could prevent cardiovascular and bone complications.

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.

The relationship among hypertension, antihypertensive medications, and osteoporosis: a narrative review

Osteoporosis and hypertension are two frequent diseases among the aging population that share a similar etiopathology and often coexist. Moreover, treatment of hypertension affects bone mineral density and, therefore, can worsen osteoporosis. This narrative review considers the influence of the main etiologic factors that contribute to the development of hypertension and osteoporosis and examines the effect of the most often used antihypertensives on bones. A computerized literature search of relevant English publications regarding the etiology of hypertension and osteoporosis as well as the impact of antihypertensives on osteoporosis from 1996 to 2011 was completed in October 2011. The latest update in the search was performed from May to June 2012. The most relevant nongenetic factors in the etiology of osteoporosis and hypertension are low calcium intake, vitamin D and vitamin K deficiency, high consumption of sodium salt, and the effects of different forms of nitric oxide. Thiazide diuretics are the only antihypertensives that have a positive influence on bone mineral density. For other antihypertensive drugs, the data are conflicting, indicating that they may have a potentially negative or positive influence on bone mineral density and fracture risk reduction. Some studies did not find a correlation between the use of antihypertensives and bone mineral density. Due to the frequent coexistence of hypertension and osteoporosis, when selecting long-term antihypertensive therapy the potential effects of antihypertensive drugs on development, worsening, or improvement of osteoporosis should also be considered.

Blood pressure and bone mineral density in premenopausal and postmenopausal women

INTRODUCTION

Previous studies regarding the associations between blood pressure (BP) and bone mineral density (BMD) have shown conflicting results. However, menopausal status and pharmacotherapy may modify this relationship. The objective of this study was to explore the association between systolic BP (SBP) and diastolic BP (DBP) and BMD in pre- and postmenopausal women, and to assess the extent to which this association is mediated by menopausal status and pharmacotherapy.

METHODS

A cross-sectional study was conducted using a sample of 4,058 pre- and postmenopausal women aged 40 years or older (N = 991 and 3,067, respectively), who participated in NHANES III. BMD measurement of the femur neck was used as the primary outcome measure. Regression models were used to examine the association between SBP or DBP and BMD.

RESULTS

The unadjusted models for systolic and diastolic BP were positively and significantly associated with femoral BMD in premenopausal women (p = 0.0039 and p = 0.0065, respectively) as well as in postmenopausal women (p < 0.0001 for both SBP and DBP). After adjusting for covariates in the multivariate models, the association between BP and BMD in postmenopausal women no longer prevailed. In premenopausal women, the association between SBP or DBP and BMD was modified by hormone therapy (p = 0.0278 and p = 0.0025, respectively). Once the stratum-specific adjusted models by hormone therapy use were examined, the association between SBP or DBP and BMD was no longer significant.

CONCLUSIONS

The study results suggest that there is no link between BP and BMD in pre- and postmenopausal women.

Rare independent mutations in renal salt handling genes contribute to blood pressure variation

The effects of alleles in many genes are believed to contribute to common complex diseases such as hypertension. Whether risk alleles comprise a small number of common variants or many rare independent mutations at trait loci is largely unknown. We screened members of the Framingham Heart Study (FHS) for variation in three genes-SLC12A3 (NCCT), SLC12A1 (NKCC2) and KCNJ1 (ROMK)-causing rare recessive diseases featuring large reductions in blood pressure. Using comparative genomics, genetics and biochemistry, we identified subjects with mutations proven or inferred to be functional. These mutations, all heterozygous and rare, produce clinically significant blood pressure reduction and protect from development of hypertension. Our findings implicate many rare alleles that alter renal salt handling in blood pressure variation in the general population, and identify alleles with health benefit that are nonetheless under purifying selection. These findings have implications for the genetic architecture of hypertension and other common complex traits.

Thiazide diuretics directly induce osteoblast differentiation and mineralized nodule formation by interacting with a sodium chloride co-transporter in bone

Thiazide diuretics are used worldwide as a first-choice drug for patients with uncomplicated hypertension. In addition to their antihypertensive effect, thiazides increase bone mineral density and reduce the prevalence of fractures. Traditionally, these effects have been attributed to increased renal calcium reabsorption that occurs secondary to the inhibition of the thiazide-sensitive sodium chloride cotransporter (NCC) in the distal tubule. The aim of the current study was to determine whether thiazides exert a direct bone-forming effect independent of their renal action. We found that the osteoblasts of human and rat bone also express NCC, suggesting that these bone-forming cells may be an additional target for thiazides. In vitro, NCC protein was virtually absent in proliferating human and fetal rat osteoblasts, whereas its expression dramatically increased during differentiation. Thiazides did not affect osteoblast proliferation, but directly stimulated the production of the osteoblast differentiation markers runt-related transcription factor 2 (runx2) and osteopontin. Using overexpression/knockdown studies in fetal rat calvarial cells, we show that thiazides increase the formation of mineralized nodules, but loop diuretics do not. Overall, our study demonstrates that thiazides directly stimulate osteoblast differentiation and bone mineral formation independent of their effects in the kidney. Therefore, in addition to their use as antihypertensive drugs, our results suggest that thiazides may find a role in the prevention and treatment of osteoporosis.

Calcium-sensing receptor gene A986S polymorphism and bone mass in hypertensive women

BACKGROUND

The function of the calcium-sensing receptor (CaSR) is to maintain serum calcium concentration within a narrow physiological range. Two types of mutations have been described: activating that causes hypocalcemia and inactivating, which leads to hypercalcemia. The objective was to assess the effect of CaSR gene A986S polymorphism on the lumbar spine bone mass, calcium metabolism parameters and markers of bone remodeling in hypertensive women.

METHODS

The study included 48 patients (mean age 59 +/- 10 years) with mild-to-moderate hypertension, according to JNC VI and who did not present any associated diseases. We determined the following in all patients: Ca, P, Mg, PTHi, 25-vitamin D, 1,25-vitamin D, osteocalcin, deoxypyridinoline in urine, 24-h urine calcium. A bone densitometry of the lumbar spine was also performed. CaSR gene A986S polymorphism was also studied in all patients by PCR.

RESULTS

Genotype frequency was 69% for AA, 27% for AS and 4% for SS, with a prevalence of 82% for allele A and 18% for allele S. Patients with a lack of allele S had lower levels of p (3.5 +/- 0.5 vs. 4 +/- 0.4, p = .034). No differences in calcium plasma levels, urinary calcium excretion and bone mass were observed.

CONCLUSIONS

We found no clinical significance in the parameters studied of the CaSR gene A986S polymorphism in hypertensive women.

Hydrochlorothiazide efficacy and polymorphisms in ACE, ADD1 and GNB3 in healthy, male volunteers

OBJECTIVE

The antihypertensive effect of thiazide diuretics has recently been associated with genetic variation in the angiotensin I-converting enzyme (ACE), alpha-adducin (ADD1) and the G protein subunit beta3 (GNB3). Analysis of short-term diuretic effects may provide insight into the mechanisms behind these findings.

METHODS

A total of 103 male volunteers took 25 and 100 mg hydrochlorothiazide (HCT) after a placebo day, each. We measured volume, sodium, chloride, potassium, calcium excretion, blood pressure and heart rate.

RESULTS

Excretion and cardiovascular parameters were highly constant between the 2 placebo days. The resting heart rate was 2-3 beats/minute (bpm) higher per ACE insertion allele on all 4 study days. The HCT-induced excretion of sodium, chloride and volume was independent of the genotypes. The additional potassium excretion induced by 100 mg HCT was 44+/-21, 33+/-27 and 16+/-26 mmol (mean+/-SD, p<0.001) in ACE II, ID and DD carriers and the same trend was observed after 25 mg HCT. As a second finding, the 100 mg HCT-induced calcium retention was 0.2+/-1.2, 0.7+/-0.8 and 1.7+/-2.1 mmol in ADD1 Gly/Gly, Gly/Trp and Trp/Trp carriers (p=0.002) and the same trend existed after 25 mg HCT.

CONCLUSION

The effects of genetic polymorphisms were stronger with the higher diuretic dose. ACE insertion allele carriers appeared to be more prone to hypokalaemia than deletion allele carriers. ADD1 Trp460 carriers may especially benefit from the calcium-sparing effect of thiazides. Both associations should be further studied in long-term treatment with thiazide diuretics.

Polymorphism of the solute carrier family 12 (sodium/chloride transporters) member 3, SLC12A3, gene at exon 23 (+78G/A: Arg913Gln) is associated with elevation of urinary albumin excretion in Japanese patients with type 2 diabetes: a 10-year longitudinal study

AIMS/HYPOTHESIS

We have shown previously that the SLC12A3 +78G/A polymorphism in exon 23 (Arg913Gln) was a new candidate for conferring susceptibility to diabetic nephropathy. The aim of this study was to confirm the effect of this polymorphism on the elevation of urinary albumin excretion in type 2 diabetic patients.

METHODS

We retrospectively studied 264 Japanese patients with type 2 diabetes over a ten-year period. The subjects were classified into two groups: (1) persistent normoalbuminuria or microalbuminuria, or improvement from microalbuminuria to normoalbuminuria (group N); and (2) progression from normoalbuminuria to microalbuminuria or overt proteinuria, or progression from microalbuminuria to overt proteinuria (group P). They were assessed for association with the +78G/A polymorphism.

RESULTS

The frequency of the +78A allele was significantly higher in group N than in group P (10% vs 1%, p=0.021). By logistic regression analysis and discriminant analysis, the substituted allele was shown to be an independent factor correlating negatively to the elevation of albumin excretion (p=0.043 and 0.022, respectively).

CONCLUSIONS/INTERPRETATION

The SLC12A3 +78A(+) genotype may have a protective effect against the development and/or progression of diabetic nephropathy in Japanese type 2 diabetic patients.

Inactivation of the Na-Cl co-transporter (NCC) gene is associated with high BMD through both renal and bone mechanisms: analysis of patients with Gitelman syndrome and Ncc null mice

Chronic thiazide treatment is associated with high BMD. We report that patients and mice with null mutations in the thiazide-sensitive NaCl cotransporter (NCC) have higher renal tubular Ca reabsorption, higher BMD, and lower bone remodeling than controls, as well as abnormalities in Ca metabolism, mainly caused by Mg depletion.

INTRODUCTION

Chronic thiazide treatment decreases urinary Ca excretion (UVCa) and increases BMD. To understand the underlying mechanisms, Ca and bone metabolism were studied in two models of genetic inactivation of the thiazide-sensitive NaCl cotransporter (NCC): patients with Gitelman syndrome (GS) and Ncc knockout (Ncc(-/-)) mice.

MATERIALS AND METHODS

Ca metabolism was analyzed in GS patients and Ncc(-/-) mice under conditions of low dietary Ca. BMD was measured by DXA in patients and mice, and bone histomorphometry was analyzed in mice.

RESULTS

GS patients had low plasma Mg. They exhibited reduced UVCa, but similar serum Ca and GFR as control subjects, suggesting increased renal Ca reabsorption. Blood PTH was lower despite lower serum ionized Ca, and Mg repletion almost corrected both relative hypoparathyroidism and low UVCa. BMD was significantly increased in GS patients at both lumbar (+7%) and femoral (+16%) sites, and osteocalcin was reduced. In Ncc(-/-) mice, serum Ca and GFR were unchanged, but UVCa was reduced and PTH was elevated; Mg repletion largely corrected both abnormalities. Trabecular and cortical BMD were higher than in Ncc(+/+) mice (+4% and +5%, respectively), and despite elevated PTH, were associated with higher cortical thickness and lower endosteal osteoclastic surface.

CONCLUSIONS

Higher BMD is observed in GS patients and Ncc(-/-) mice. Relative hypoparathyroidism (human) and bone resistance to PTH (mice), mainly caused by Mg depletion, can explain the low bone remodeling and normal/low serum Ca despite increased renal Ca reabsorption.

The DASH diet and sodium reduction improve markers of bone turnover and calcium metabolism in adults

Dietary strategies to prevent and treat osteoporosis focus on increased intake of calcium and vitamin D. Modification of whole dietary patterns and sodium reduction may also be effective. We examined the effects of two dietary patterns and three sodium levels on bone and calcium metabolism in a randomized feeding study. A total of 186 adults, aged 23-76 y, participated. After a 2-wk run-in period, participants were assigned randomly to diets containing three levels of sodium (50, 100 and 150 mmol/d) to be consumed for 30 d in random order. Serum osteocalcin (OC), C-terminal telopeptide of type I collagen (CTX), fasting serum parathyroid hormone (PTH), urinary sodium, potassium, calcium and cAMP were measured at baseline and at the end of each sodium period. The Dietary Approaches to Stop Hypertension (DASH) diet reduced serum OC by 8-11% and CTX by 16-18% (both P < 0.001). Urinary calcium excretion did not differ between subjects that consumed the DASH and control diets. Reducing sodium from the high to the low level significantly decreased serum OC 0.6 microg/L in subjects that consumed the DASH diet, fasting serum PTH 2.66 ng/L in control subjects and urinary calcium 0.5 mmol/24 h in both groups. There were no consistent effects of the diets or sodium levels on urinary cAMP. In conclusion, the DASH diet significantly reduced bone turnover, which if sustained may improve bone mineral status. A reduced sodium intake reduced calcium excretion in both diet groups and serum OC in the DASH group. The DASH diet and reduced sodium intake may have complementary, beneficial effects on bone health.

Bone mass and bone modelling markers in hypertensive postmenopausal women

Numerous phosphocalcium alterations associated with bone mineral density in hypertension have been described, but very few studies assess them. This study assesses bone mass in hypertensive postmenopausal women and the hypertension influence determining both calcium homeostasis and bone turnover markers. Blood and urine samples were analysed for calcium metabolism-related parameters. Densitometry studies were conducted in the lumbar spine (L2-L4). Hypertensive osteoporotic women--selected from 82 women, with 22% osteoporosis prevalence, similar to the rate for the same age in the Spanish population--had significantly higher levels of body mass index (29+/-4 vs 26+/-4, P=0.019), calciuria (293+/-146 vs 210+/-116 mg/24 h, P=0.023) and calcium/creatinine ratio (0.33+/-0.2 vs 0.22+/-0.1 P=0.003) vs hypertensive nonosteoporotic women. No relation was found between systolic and diastolic blood pressure with bone mass. However, there was a negative osteocalcin correlation (r=-0.386, P=0.0001, and r=-0.242, P=0.033). Calciuria is associated with bone mass decrease in hypertensive women, and there is no relation between bone mass and blood pressure.