Great strides in the understanding of renal magnesium and calcium reabsorption

Intakes of magnesium, calcium and risk of fatty liver disease and prediabetes

OBJECTIVE

Obesity and insulin resistance play important roles in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Mg intake is linked to a reduced risk of metabolic syndrome and insulin resistance; people with NAFLD or alcoholic liver disease are at high risk of Mg deficiency. The present study aimed to investigate whether Mg and Ca intakes were associated with risk of fatty liver disease and prediabetes by alcohol drinking status.

DESIGN

We analysed the association between Ca or Mg intake and fatty liver disease, prediabetes or both prediabetes and fatty liver disease in cross-sectional analyses.

SETTING

Third National Health and Nutrition Examination Survey (NHANES III) follow-up cohort of US adults.

SUBJECTS

Nationally representative sample of US adults in NHANES (n 13 489).

RESULTS

After adjusting for potential confounders, Mg intake was associated with approximately 30 % reduced odds of fatty liver disease and prediabetes, comparing the highest intake quartile v. the lowest. Mg intake may only be related to reduced odds of fatty liver disease and prediabetes in those whose Ca intake is less than 1200 mg/d. Mg intake may also only be associated with reduced odds of fatty liver disease among alcohol drinkers.

CONCLUSIONS

The study suggests that high intake of Mg may be associated with reduced risks of fatty liver disease and prediabetes. Further large studies, particularly prospective cohort studies, are warranted to confirm the findings.

Calcium/magnesium intake ratio, but not magnesium intake, interacts with genetic polymorphism in relation to colorectal neoplasia in a two-phase study

Some studies suggest that the calcium to magnesium ratio intakes modify the associations of calcium or magnesium with risk of colorectal adenoma, adenoma recurrence, and cancer. Parathyroid hormone (PTH) plays a key role in the regulation of homeostasis for both calcium and magnesium. We hypothesized that polymorphisms in PTH and 13 other genes may modify the association between the calcium/magnesium intake ratio and colorectal neoplasia risk. We conducted a two-phase study including 1336 cases and 2891 controls from the Tennessee Colorectal Polyp Study. In Phase I, we identified 19 SNPs that significantly interacted with the calcium/magnesium intake ratio in adenoma risk. In Phase II, rs11022858 in PTH was replicated. In combined analysis of phases I and II, we found high calcium/magnesium intake ratio tended to be associated with a reduced risk of colorectal adenoma (P for trend, 0.040) among those who carried the TT genotype in rs11022858. In stratified analyses, calcium intake (≥ 1000 mg/d) was significantly associated with 64% reduced adenoma risk (OR = 0.36 (95% CI : 0.18-0.74)) among those homozygous for the minor allele (TT genotype) (P for trend, 0.012), but not associated with risk in other genotypes (CC/TC). Conversely, we found that highest magnesium intake was significantly associated with 27% reduced risk (OR = 0.73 (95% CI : 0.54-0.97)) of colorectal adenoma (P for trend, 0.026) among those who possessed the CC/TC genotypes, particularly among those with the TC genotype, whereas magnesium intake was not linked to risk among those with the TT genotype. These findings, if confirmed, will help for the development of personalized prevention strategies for colorectal cancer. © 2015 Wiley Periodicals, Inc.

Calcium intake and ion transporter genetic polymorphisms interact in human colorectal neoplasia risk in a 2-phase study

BACKGROUND

The kidney-specific sodium-potassium-chloride cotransporter (NKCC2) protein encoded by solute carrier family 12 member 1 (SLC12A1) is the direct downstream effector of the inward-rectifier potassium channel (ROMK) encoded by potassium inwardly-rectifying channel, subfamily J, member 1 (KCNJ1), both of which are critical for calcium reabsorption in the kidney.

OBJECTIVE

We hypothesized that polymorphisms in KCNJ1, SLC12A1, and 7 other genes may modify the association between calcium intake and colorectal neoplasia risk.

METHODS

We conducted a 2-phase study in 1336 cases and 2891 controls from the Tennessee Colorectal Polyp Study.

RESULTS

In phase I, we identified 5 single-nucleotide polymorphisms (SNPs) that significantly interacted with calcium intake in adenoma risk. In phase II, rs2855798 in KCNJ1 was replicated. In combined analysis of phases I and II, the P values for interactions between calcium intake and rs2855798 were 1 × 10(-4) for all adenoma and 5 × 10(-3) for multiple/advanced adenoma. The highest calcium intake was not associated with risk among those with no variant allele but was significantly associated with a 41% reduced adenoma risk among those who carried at least 1 variant allele in KCNJ1. The corresponding reduction in risk of multiple or advanced adenomas was 52% among those with at least 1 variant allele. The P values for interactions between calcium intake and combined SNPs from the KCNJ1 and SLC12A1 genes were 7.5 × 10(-5) for adenoma and 9.9 × 10(-5) for multiple/advanced adenoma. The highest calcium intake was not associated with risk among those with nonvariant alleles in 2 genes but was significantly associated with a 34% reduced adenoma risk among those who carried a variant allele in 1 of the genes. The corresponding reduction in risk of multiple or advanced adenomas was 64% among those with variant alleles in both genes.

CONCLUSION

These findings, if confirmed, will be critical for the development of personalized prevention strategies for colorectal cancer.

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis: phenotype-genotype correlation and outcome in 32 patients with CLDN16 or CLDN19 mutations

BACKGROUND AND OBJECTIVES

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is a rare autosomal recessive renal tubular disease. It is caused by mutations in CLDN16 and CLDN19, encoding claudin-16 and -19, respectively. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is usually complicated by progressive CKD. The objectives of this study were to describe the clinical and genetic features of familial hypomagnesemia with hypercalciuria and nephrocalcinosis and analyze phenotype-genotype associations in patients with CLDN16 or CLDN19 mutations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Data from 32 genetically confirmed patients (9 patients with CLDN16 and 23 patients with CLDN19 mutations) from 26 unrelated families were retrospectively reviewed.

RESULTS

Diagnosis was based on clinical criteria at a median age of 9.5 years and confirmed by genetic testing at a median age of 15.5 years. In total, 13 CLDN16 or CLDN19 mutations were identified, including 8 novel mutations. A founder effect was detected for the recurrent CLDN16 p.Ala139Val mutation in North African families and the CLDN19 p.Gly20Asp mutation in Spanish and French families. CKD was more frequently observed in patients with CLDN19 mutations: survival without CKD or ESRD was 56% at 20 years of age in CLDN19 versus 100% in CLDN16 mutations (log rank P<0.01). Ocular abnormalities were observed in 91% of patients with CLDN19 mutations and none of the patients with CLDN16 mutations (P<0.01). Treatments seem to have no effect on hypercalciuria and CKD progression.

CONCLUSIONS

Patients with CLDN19 mutations may display more severe renal impairment than patients with CLDN16 mutations. Ocular abnormalities were observed only in patients with CLDN19 mutations.

[Inherited monogenic kidney stone diseases: recent diagnostic and therapeutic advances]

Hereditary monogenic kidney stone diseases are rare diseases, since they account for nearly 2% of nephrolithiasis cases in adults and 10% in children. Most of them are severe, because they frequently are associated with nephrocalcinosis and lead to progressive impairment of renal function unless an early and appropriate etiologic treatment is instituted. Unfortunately, treatment is often lacking or started too late since they are often misdiagnosed or overlooked. The present review reports the genotypic and phenotypic characteristics of monogenic nephrolithiases, with special emphasis on the recent advances in the field of diagnosis and therapeutics. Monogenic stone diseases will be classified into three groups according to their mechanism: (1) inborn errors of the metabolism of oxalate (primary hyperoxalurias), uric acid (hereditary hyperuricemias) or other purines (2,8-dihydroxyadeninuria), which, in addition to stone formation, result in crystal deposition in the renal parenchyma; (2) congenital tubulopathies affecting the convoluted proximal tubule (such as Dent's disease, Lowe syndrome or hypophosphatemic rickets), the thick ascending limb of Henlé's loop (such as familial hypomagnesemia and Bartter's syndromes) or the distal past of the nephron (congenital distal tubular acidosis with or without hearing loss), which are frequently associated with nephrocalcinosis, phosphatic stones and extensive tubulointerstitial fibrosis; (3) cystinuria, an isolated defect in tubular reabsorption of cystine and dibasic aminoacids, which results only in the formation of stones but requires a cumbersome treatment. Analysis of stones appears of crucial value for the early diagnosis of these diseases, as in several of them the morphology and composition of stones is specific. In other cases, especially if nephrocalcinosis, phosphatic stones or proteinuria are present, the evaluation of blood and urine chemistry, especially with regard to calcium, phosphate and magnesium, is the key of diagnosis. Search for mutations is now increasingly performed in as much as genetic counselling is important for the detection of heterozygotes in autosomic recessive diseases and of carrier women in X-linked diseases. In conclusion, better awareness to the rare monogenic forms of nephrolithiasis and/or nephrocalcinosis should allow early diagnosis and treatment which are needed to prevent or substantially delay progression of end-stage renal disease. Analysis of every first stone both in children and in adults should never be neglected, in order to early detect unusual forms of nephrolithiasis requiring laboratory evaluation and deep etiologic treatment.

Partial human genetic deficiency in tissue kallikrein activity and renal calcium handling

A loss-of-function polymorphism of the human tissue kallikrein (TK) gene (R53H) induces a major decrease in enzyme activity. Inactivation of the TK gene in mice causes a defect in tubular calcium (Ca) reabsorption. Therefore, this study investigated the Ca phenotype of carriers of the 53H allele. In a crossover study, 30 R53R homozygous and 10 R53H heterozygous young white male individuals were randomly assigned to two 7-d low-Ca diets (10 mmol/d) associated with either a low-sodium (Na)/high-potassium (K) diet or a high-Na/low-K diet to modulate TK synthesis. On the seventh day of each diet, the participants were studied before and during a 2-h infusion of furosemide that functionally excludes the thick ascending limb and increases Ca delivery to distal tubular segments. Urinary kallikrein activity was 50 to 60% lower in R53H participants than in R53R participants. Adaptation of urinary Ca excretion to the contrasted Na/K diets was unaffected in R53H participants. By contrast, R53H participants after furosemide infusion had significantly lower serum ionized Ca concentrations than did R53R participants (P < 0.0001) and tendency toward nonsignificantly higher urinary Ca excretions than did R53R participants (P = 0.14). These effects were more marked under low-Na/high-K diet. Despite nonsignificant differences in urinary Ca excretions between the two groups, these results suggest in R53H individuals an increase in Ca reabsorption in the thick ascending limb under baseline conditions that counteracts a distal tubular defect that is revealed by furosemide infusion. In humans as in mice, TK thus may act as an intrarenal modulator of Ca reabsorption.

Hydrochlorothiazide in CLDN16 mutation

BACKGROUND

Hydrochlorothiazide (HCT) is applied in the therapy of familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC) caused by claudin-16 (CLDN16) mutation. However, the short-term efficacy of HCT to reduce hypercalciuria in FHHNC has not yet been demonstrated in a clinical trial.

METHODS

Four male and four female patients with FHHNC and CLDN16 mutation, under long-standing HCT therapy (0.4-1.2 mg/kg, median 0.9 mg/kg, dose according to calciuria), aged 0.7-22.4 years, were included in a clinical study to investigate the effect of HCT on calciuria. The study design consisted of three periods: continued therapy for 4 weeks, HCT withdrawal for 6 weeks and restart of therapy at the same dose for 4 weeks. Calciuria and magnesiuria were assessed weekly as Ca/creat and Mg/creat ratio, every 2 weeks in 24 h urine, and serum Mg, K and kaliuria (s-Mg, s-K and K/creat) at weeks 0, 6, 10 and 14. The data of each study period were averaged and analysed by Friedman and Wilcoxon test.

RESULTS

Ca/creat was significantly reduced by HCT (median before/at/after withdrawal 0.76/1.24/0.77 mol/mol creat; n = 8, P<0.05). The reduction of Ca/24 h by HCT was not statistically significant (0.13/0.19/0.13 mmol/kg x 24 h; n = 5). Serum Mg (0.51/0.64/0.56 mmol/l; n = 8, P<0.05) and Serum K (3.65/4.35/3.65 mmol/l; n = 8, P<0.05) were significantly higher during withdrawal. However, Mg/creat (0.98/0.90/0.90 mol/mol creat; n = 8), Mg/24 h (0.14/0.12/0.18 mmol/kg x 24h; n = 5) and K/creat (6.3/8.4/6.2 mol/mol creat; n = 8) remained statistically unchanged during withdrawal.

CONCLUSIONS

We demonstrated that HCT is effective in reducing hypercalciuria due to CLDN16 mutation on a short-term basis. However, the efficacy of HCT to attenuate disease progression remains to be elucidated.

Endothelia of term human placentae display diminished expression of tight junction proteins during preeclampsia

This study explores the molecular composition of the tight junction (TJ) in human term placenta from normal women and from patients with preeclampsia, a hypertensive disorder of pregnancy. Maternal endothelial dysfunction is a critical characteristic of preeclampsia; hence, we have analyzed its impact on placental vessels. The study concentrates on the TJ because this structure regulates the sealing of the paracellular route. We have found that, in placental endothelial vessels, TJ components include the peripheral protein ZO-1 and the integral proteins occludin and claudins 1, 3, and 5. During preeclampsia, the amounts of occludin and ZO-1 exhibit no significant variation, whereas those of claudins 1, 3, and 5 diminish, suggesting the presence of leakier TJs in the endothelia of the preeclamptic placenta, possibly in response to the decreased perfusion of this organ during preeclampsia. We have unexpectedly found that, in normal placentae, the multinucleated syncytiotrophoblast layer displays claudin 4 at the basal surface of the plasma membrane, and claudin 16 along the apical and basolateral surfaces. The presence of membrane-lined channels that cross the syncytiotrophoblast constituting a paracellular pathway has been determined by transmission electron microscopy and by the co-immunolocalization of claudin 16 with the plasma membrane proteins Na+K+-ATPase and GP135. Since claudin 16 functions as a paracellular channel for Mg2+, its diffuse pattern in preeclamptic placentae suggests the altered paracellular transport of Mg2+ between the maternal blood and the placental tissue.

Intrauterine programming of urinary calcium and magnesium excretion in children born to mothers with insulin dependent diabetes mellitus

BACKGROUND

Offspring of diabetic rats have reduced urinary calcium and magnesium excretion compared with offspring of controls; these differences persist up to 16 weeks after birth, a time equivalent to young adulthood in humans.

OBJECTIVES

To test the hypothesis that urinary calcium and magnesium excretion would be lower in children born to mothers with insulin dependent diabetes mellitus (ChMIDDM) than those born to non-diabetic mothers.

METHODS

Concentrations of calcium, magnesium, sodium, and creatinine were measured in first void spot urine samples collected from 45 (28 male; median age 9.6 years) ChMIDDM and 127 (58 male; median age 11.3 years) controls. Analysis of covariance was used to test for differences in urinary calcium to creatinine ratios (UCa/Cr), magnesium to creatinine ratios (UMg/Cr), and log sodium to creatinine ratios (logUNa/Cr) between controls and ChMIDDM after allowing for the effects of sex and age.

RESULTS

UCa/Cr (difference -0.10, 95% confidence interval (CI) -0.19 to -0.01; p = 0.03) and UMg/Cr (difference -0.15, 95% CI -0.22 to -0.08; p<0.0001) were lower in ChMIDDM than controls. However, logUNa/Cr did not differ between ChMIDDM and controls (difference -0.14, 95% CI -0.33 to 0.05; p = 0.1). The daily estimated intake of magnesium, sodium, and protein were significantly higher and that of calcium non-significantly higher in ChMIDDM than controls. In ChMIDDM, UCa/Cr and UMg/Cr were not related to diabetic control of mothers.

CONCLUSIONS

Results of this study provide the first evidence that in humans, as in rats, there is modification of renal Ca and Mg handling in ChMIDDM, which persists well into childhood.

[Familial hypomagnesemia with hypercalciuria and nephrocalcinosis. Association with ocular abnormalities]

BACKGROUND

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is an unusual disease that usually leads to end-stage renal failure. There is no specific treatment and, to a variable degree, patients with this disease present ocular abnormalities. The illness is due to a defect in the reabsorption of magnesium and calcium at the thick ascending limb of Henle because of a mutation of the PCLN-1 gene, which encodes a protein, paracellin-1, which intervenes in the reabsorption of both cations.

OBJECTIVE

To review outcome and the incidence of ocular abnormalities in our patients and in cases described in Spain and to compare the incidence found with that in groups from other countries.

METHOD

Retrospective study of a group of patients with familial hypomagnesemia with hypercalciuria and nephrocalcinosis diagnosed at a hospital.

RESULTS

There were six girls and three boys with clinical symptoms of polyuria, polydipsia, and less frequently, urinary tract infections and lithiasis. All had hypomagnesemia, hypercalciuria and nephrocalcinosis. Five of the patients had renal failure at diagnosis and four underwent transplantation without recurrence. Eight patients had diverse ocular abnormalities. Eighty-one percent of Spanish patients had ocular abnormalities compared with 24 % of those from other countries. There was no evidence of successful medical treatment.

CONCLUSIONS

Almost half of the patients presented chronic renal failure at diagnosis and most of the patients reached end-stage renal failure in the second or third decade of life. Normal glomerular filtration rate was found only in patients diagnosed at an early age. The most frequent extra-renal association in Spanish patients (81 %) corresponded to ocular abnormalities. Effective treatment consists of kidney transplantation that completely corrects the tubular disorder.

Association of Paracellin-1 with ZO-1 Augments the Reabsorption of Divalent Cations in Renal Epithelial Cells

Paracellin-1 (PCLN-1) belongs to the claudin family of tight junction proteins and possibly plays a critical role in the reabsorption of magnesium and calcium. So far, the physiological properties of PCLN-1 have not been clarified. In the present study, we investigated whether PCLN-1 is associated with ZO-1. We also investigated whether (45)Ca(2+) transport across the paracellular barrier is affected by this association. In vitro binding analysis using glutathione S-transferase fusion protein showed that the C-terminal TRV sequence, especially Thr and Val residues, of PCLN-1 interacts with ZO-1. Next, PCLN-1 was stably expressed in Madin-Darby canine kidney cells using a FLAG tagging vector. ZO-1 was co-immunoprecipitated with the wild-type PCLN-1 and the alanine substitution (TAV) mutant. However, mutants of the deletion (Delta TRV) and the alanine substitution (ARV and TRA) inhibited the association of PCLN-1 with ZO-1. Confocal immunofluorescence demonstrated that the wild-type PCLN-1 and the TAV mutant localized in the tight junction along with ZO-1, but the Delta TRV, ARV, and TRA mutants were widely distributed in the lateral membrane including the tight junction area. Interestingly, monolayers of cells expressing the wild-type PCLN-1 and the TAV mutant showed higher activities of (45)Ca(2+) transport from apical to basal compartments, compared with those expressing the Delta TRV, ARV, and TRA mutants and the mock cells. (45)Ca(2+) transport was inhibited by increased magnesium concentration suggesting that magnesium and calcium were competitively transported by PCLN-1. It was noted that a positive electrical potential gradient enhanced (45)Ca(2+) transport from apical to basal compartments without affecting the opposite direction of transport. Thus, PCLN-1 localizes to the tight junction followed by association with ZO-1, and the PCLN-1.ZO-1 complex may play an essential role in the reabsorption of divalent cations in renal epithelial cells.

Arachidonic acid-activated Na+-dependent Mg2+ efflux in rat renal epithelial cells

Arachidonic acid (AA), a metabolite of membrane phospholipids, and its metabolites are increased in Mg2+ deficiency. We examined whether the extracellular Mg2+ concentration affects AA production and whether AA regulates a putative Na+-dependent Mg2+ efflux pathway in renal epithelial NRK-52E cells. We used the cells cultured in 5 mM Mg2+-containing medium for 2 days because they enable us to detect Na+-stimulated Mg2+ efflux that was not observed in normal culture medium. Removal of extracellular Mg2+ increased AA release both in the absence and presence of extracellular Na+. This was inhibited by methyl arachidonyl fluorophosphonate (MAFP, 10 microM), an inhibitor of cytosolic phospholipase A) (cPLA2) and Ca2+-independent phospholipase A2 (iPLA2), and bromoenol lactone (BEL, 10 microM), an inhibitor of iPLA2. However, LY-311727 (10 microM), a secretory phospholipase A2 (sPLA2) inhibitor, had no inhibitory effect. Reverse transcriptase-polymerase chain reaction (RT-PCR) showed that NRK-52E cells express cPLA2 and iPLA2 mRNAs, but not sPLA2. In the mag-fura 2 fluorescence measurements, extracellular Mg2+ removal caused slight decrease in the intracellular free Mg2+ concentration ([Mg2+]i) in the Na+-free condition. The addition of Na+ caused a rapid decrease in [Mg2+]i, indicating the presence of a Na+-dependent Mg2+ efflux pathway. The Na+-dependent [Mg2+]i decrease was suppressed by MAFP and BEL. On the other hand, AA metabolite inhibitors, nordihydroguaiaretic acid (NDGA) (50 microM), indomethacin (10 microM) and 17-octadecynoic acid (ODYA) (10 microM), enhanced the Na+-dependent [Mg2+]i decrease. Furthermore, the addition of exogenous AA (30 microM) enhanced the Na+-dependent [Mg2+]i decrease, which was significantly inhibited by imipramine (0.1 mM), a putative Na+/Mg2+-exchanger inhibitor. These results suggest that extracellular Mg2+ removal elevates AA release mediated mainly by iPLA2 and that AA upregulates the Na+-dependent Mg2+ efflux in NRK-52E cells.

Novel paracellin-1 mutations in 25 families with familial hypomagnesemia with hypercalciuria and nephrocalcinosis

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is an autosomal recessive tubular disorder that is frequently associated with progressive renal failure. The primary defect is related to impaired tubular reabsorption of magnesium and calcium in the thick ascending limb of Henle's loop. Mutations in PCLN-1, which encodes the renal tight junction protein paracellin-1 (claudin-16), were identified as the underlying genetic defects. Comprehensive clinical data and the results of PCLN-1 mutation analysis of 25 FHHNC families with 33 affected individuals are presented. Patients presented mainly with urinary tract infections, polyuria, and hematuria at a median age of 3.5 yr. At the time of diagnosis, the GFR was already decreased to <60 ml/min per 1.73 m(2) for 11 patients. Twelve patients exhibited progression to end-stage renal disease, at a median age of 14.5 yr. Treatment with magnesium salts and thiazides seemed to have no effect on the progression of the disease. Genotype analysis revealed PCLN-1 mutations in all except three mutant alleles (94%). Fifteen different mutations were observed, including eight novel mutations. The accumulation of mutations affecting the first extracellular loop was striking, with 48% of all mutant alleles exhibiting a Leu151Phe exchange. Haplotype analysis strongly suggested a founder effect among patients with FHHNC who originated from Germany or eastern European countries. In 13 of 23 families, hypercalciuria and/or nephrolithiasis were observed in otherwise unaffected family members, indicating a possible role of heterozygous PCLN-1 mutations in yielding hypercalciuric stone-forming conditions.